U.S. patent application number 16/473087 was filed with the patent office on 2019-11-14 for lithium metal anode, fabrication method thererof, and lithium secondary battery comprising same anode.
The applicant listed for this patent is POSCO, RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE & TECHNOLOGY. Invention is credited to Hong-Youl BAE, Weon-Soo BAE, Mun Kyu CHO, Nam Soon CHOI, Jin Hong KIM, Sang-Lag LEE, Yong Won LEE, Ji-Woong MOON.
Application Number | 20190348668 16/473087 |
Document ID | / |
Family ID | 62626690 |
Filed Date | 2019-11-14 |
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United States Patent
Application |
20190348668 |
Kind Code |
A1 |
KIM; Jin Hong ; et
al. |
November 14, 2019 |
LITHIUM METAL ANODE, FABRICATION METHOD THEREROF, AND LITHIUM
SECONDARY BATTERY COMPRISING SAME ANODE
Abstract
One embodiment of the present invention relates to a lithium
metal anode. Wherein the lithium metal anode comprises a current
collector and a lithium metal thin film layer disposed on at least
one surface of the current collector and having a thickness in a
range of 0.1 to 200 .mu.m and a coating layer disposed on a surface
of the lithium metal thin film layer, wherein, the coating layer
comprising a Li--N--C--H--O based ionic compound.
Inventors: |
KIM; Jin Hong; (Pohang-si,
Gyeongsangbuk-do, KR) ; BAE; Hong-Youl; (Pohang-si,
Gyeongsangbuk-do, KR) ; CHO; Mun Kyu; (Pohang-si,
Gyeongsangbuk-do, KR) ; CHOI; Nam Soon; (Ulsan,
KR) ; LEE; Sang-Lag; (Pohang-si, Gyeongsangbuk-do,
KR) ; BAE; Weon-Soo; (Pohang-si, Gyeongsangbuk-do,
KR) ; LEE; Yong Won; (Ulsan, KR) ; MOON;
Ji-Woong; (Pohang-si, Gyeongsangbuk-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSCO
RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE & TECHNOLOGY |
Pohang-si, Gyeongsangbuk-do
Pohang-si, Gyeongsangbuk-do |
|
KR
KR |
|
|
Family ID: |
62626690 |
Appl. No.: |
16/473087 |
Filed: |
December 15, 2017 |
PCT Filed: |
December 15, 2017 |
PCT NO: |
PCT/KR2017/014870 |
371 Date: |
June 24, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/366 20130101;
C25D 7/00 20130101; H01M 4/382 20130101; H01M 2004/021 20130101;
H01M 4/66 20130101; H01M 10/052 20130101; H01M 4/667 20130101; H01M
4/134 20130101; H01M 4/0452 20130101; H01M 2004/027 20130101; C25D
9/08 20130101; H01M 4/0423 20130101; C25D 3/42 20130101; H01M
4/1395 20130101; H01M 10/0525 20130101 |
International
Class: |
H01M 4/134 20060101
H01M004/134; H01M 10/0525 20060101 H01M010/0525; H01M 4/66 20060101
H01M004/66; H01M 4/1395 20060101 H01M004/1395; H01M 4/04 20060101
H01M004/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2016 |
KR |
10-2016-0178149 |
Oct 31, 2017 |
KR |
10-2017-0143551 |
Claims
1. A lithium metal anode comprising: a current collector; a lithium
metal thin film layer disposed on at least one surface of the
current collector and having a thickness in a range of 0.1 .mu.m to
200 .mu.m; and a coating layer disposed on a surface of the lithium
metal thin film layer, wherein, the coating layer comprising a
Li--N--C--H--O based ionic compound.
2. The lithium metal anode of claim 1, wherein the coating layer
further comprises LiF.
3. The lithium metal anode of claim 1, The Li--N--C--H--O based
ionic compound comprises Li--O, C--N, C--O, and C--H bonds.
4. The lithium metal anode of claim 1, The Li--N--C--H--O based
ionic compound is at least one of the compounds represented by
formulas (1) and (2). Li.sup.+-[O--R.sub.1--R.sub.2
.sub.n.sub.1A.sub.1.sup.-+Li [Formula 1] (wherein in the formula 1,
R.sub.1 and, R.sub.2 are each CH.sub.mF.sub.2-m (m is one of 0, 1,
or 2), A.sub.1 is ##STR00015## and n1 is an integer of 1 to 10)
##STR00016## (wherein in the formula 2, R.sub.3, and R.sub.4 are
each CH.sub.mF.sub.2-m (m is one of 0, 1, or 2), A.sub.2 is
##STR00017## and n2 is an integer of 1 to 10.)
5. The lithium metal anode of claim 4, the compound represented by
the formula (1) is at least one of the compounds represented by the
following formulas (1-1) and (1-2), and the compound represented by
the formula (2) is at least one of the compounds represented by the
following formulas (2-1) and (2-2). ##STR00018## (wherein in the
formula 1-1, n3 is an integer of 1 to 5.) ##STR00019## (wherein in
the formula 1-2, R.sub.5 and R.sub.6 are each CH.sub.mF.sub.2-m (m
is one of 0, 1, or 2), and n4 is an integer of 1 to 5.)
##STR00020## (wherein in the formula 2-1, n5 is and integer of 1 to
5.) ##STR00021## (wherein in the formula 2-2, R.sub.7 and R.sub.8
are each CH.sub.mF.sub.2-m (m is one of 0, 1, and 2), and n6 is an
integer of 1 to 5.)
6. The lithium metal anode of claim 1, wherein a thickness of the
coating layer is in a range of 2 nm to 2 .mu.m.
7. The lithium metal anode of claim 1, wherein a thickness of the
coating layer is in a range of 10 nm to 500 nm.
8. The lithium metal anode of claim 1, the lithium metal thin film
layer has a flat surface microstructure without dendrite, and the
lithium metal thin film layer comprises a columnar structure
extending upward from the current collector.
9. The lithium metal anode of claim 8, wherein an average diameter
of the columnar structure is in the range of 0.1 .mu.m to 100
.mu.m.
10. The lithium metal anode of claim 1, wherein an average pore
fraction of the lithium metal thin film layer is 10% or less.
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. A lithium secondary battery comprising: an anode; a cathode;
and electrolyte, the anode is a lithium metal anode according to
claim 1.
19. A lithium metal anode comprising: a current collector; a
lithium metal thin film disposed on at least one surface of the
current collector; and, a protective layer disposed on the surface
of the lithium metal thin film.
20. The lithium metal anode of claim 19, a thickness of the lithium
metal thin film is from 5 .mu.m to 100 .mu.m.
21. The lithium metal anode of claim 19, a thickness of the
protective layer is from 10 nm to 100 nm.
22. The lithium metal anode of claim 19, wherein the protective
layer comprises at least one selected from the group consisting of
F, P, C, O and S.
23. (canceled)
24. (canceled)
25. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention is in related to a lithium metal
anode, method for manufacturing the same, and lithium secondary
battery including the same.
BACKGROUND
[0002] Lithium metal has a high theoretical capacity of about 3,860
mAh/g and a density as low as 0.53 g/cm.sup.3. Therefore, when
lithium metal is used as the anode material of the secondary
battery, the energy density of the battery can be greatly
improved.
[0003] Graphite having a theoretical capacity of about 372 mAh/g is
mainly used as an anode material of a commercially available
lithium secondary battery. The energy density of a lithium
secondary battery using such graphite as an anode material is about
150 to 250 Wh/kg.
[0004] However, in recent years, the use of lithium secondary
batteries has expanded from portable electronic devices to electric
power tools, automobiles, and the like, so that demand for lithium
secondary batteries having high energy density is increasing.
[0005] In order to develop such a lithium secondary battery having
high energy density, researches for applying lithium metal as an
anode material of a lithium secondary battery are actively
conducted.
[0006] However, when the lithium metal is used as an anode of a
lithium secondary battery, the lithium metal anode includes a
surface reaction layer which is difficult to control composition
and characteristics due to the high reactivity of lithium.
Accordingly, the surface reaction layer is a major cause of
deteriorating reproducibility and characteristics of battery.
[0007] Therefore, it is urgent to develop a technique which
improves the energy density, excellent charge/discharge
characteristics, and reproducibility of the battery by applying a
lithium metal anode.
DESCRIPTION
Technical Problem
[0008] These embodiments are intended to provide a lithium metal
anode including a surface film (coating layer) whose composition
and characteristics are controlled and a lithium secondary battery
comprising the lithium metal anode.
[0009] The present embodiments provide a method of manufacturing a
lithium metal anode capable of simultaneous manufacturing a lithium
metal thin film layer and a coating layer on the surface of the
lithium metal thin film layer in one process.
Technical Solution
[0010] A lithium metal anode according to an embodiment of the
present invention includes a current collector; a lithium metal
thin film layer disposed on at least one surface of the current
collector and having a thickness in a range of 0.1 .mu.m to 200
.mu.m; and a coating layer disposed on a surface of the lithium
metal thin film layer, wherein, the coating layer comprising a
Li--N--C--H--O based ionic compound.
[0011] The coating layer can further comprises LiF.
[0012] The Li--N--C--H--O based ionic compound can include Li--O,
C--N, C--O, and C--H bonds.
[0013] The Li--N--C--H--O based ionic compound is at least one of
the compounds represented by formulas (1) and (2).
Li.sup.+-[O--R.sub.1--R.sub.2 .sub.n.sub.1A.sub.1.sup.-+Li [Formula
1]
[0014] (wherein in the formula 1, R.sub.1 and, R.sub.2 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, or 2),
[0015] A.sub.1 is
##STR00001##
and
[0016] n1 is an integer of 1 to 10)
##STR00002##
[0017] (wherein in the formula 2, R.sub.3, and R.sub.4 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, or 2),
[0018] A.sub.2 is
##STR00003##
and
[0019] n2 is an integer of 1 to 10.)
[0020] the compound represented by the formula (1) is at least one
of the compounds represented by the following formulas (1-1) and
(1-2), and the compound represented by the formula (2) is at least
one of the compounds represented by the following formulas (2-1)
and (2-2).
##STR00004##
[0021] (wherein in the formula 1-1, n3 is an integer of 1 to
5.)
##STR00005##
[0022] (wherein in the formula 1-2, R.sub.5 and R.sub.6 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, or 2), and
[0023] n4 is an integer of 1 to 5.)
##STR00006##
[0024] (wherein in the formula 2-1, n5 is and integer of 1 to
5.)
##STR00007##
[0025] (wherein in the formula 2-2, R.sub.7 and R.sub.8 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, and 2), and
[0026] n6 is an integer of 1 to 5.)
[0027] A thickness of the coating layer may be in a range of 2 nm
to 2 .mu.m, and a thickness of the coating layer may be in a range
of 10 nm to 500 nm.
[0028] A lithium metal thin film layer has a flat surface
microstructure without dendrite, and the lithium metal thin film
layer includes a columnar structure extending upward from the
current collector.
[0029] An average diameter of the columnar structure may be in the
range of 0.1 .mu.m to 100 .mu.m.
[0030] An average pore fraction of the lithium metal thin film
layer may be 10% or less.
[0031] A method for manufacturing a lithium metal anode according
to an embodiment of the present invention includes the steps of:
restraining a current collector and a lithium source in both
directions and laminating them after electrically insulating the
current collector and the lithium source in a plating solution; and
forming simultaneously a metal thin film layer and a coating layer
on at least one surface of the current collector by applying a
current between the current collector and the lithium source;
wherein the plating solution comprises a nitrogen-based
compound.
[0032] The nitrogen-based compound may be at least one selected
from the group consisting of lithium nitrate, lithium bis
fluorosulfonyl imide, lithium bis trifluoromethane sulfonimide,
e-Caprolactam, N-methyl-e-caprolactam, triethylamine, and
tributylamine.
[0033] The plating solution includes the nitrogen-based compound in
an amount of 1 wt % to 100 wt % based on 100 wt % of the plating
solution.
[0034] The plating solution can further include a fluorine-based
compound.
[0035] The fluorine compound may be at least one selected from the
group consisting of Lithium difluoro phosphate, Lithium hexafluoro
phosphate, Lithium difluoro bisoxalato phosphate, Lithium
tetrafluoro oxalato phosphate, Lithium difluoro oxalate borate,
Lithium difluoro oxalato borate, Lithium tetrafluoro oxalato
borate, Fluoroethylene carbonate, Difluoroethylene carbonate, and
1,1,2,2-Tetrafluoroethyl 2,2,3,3-Tetrafluoropropyl ether.
[0036] The plating solution includes the fluorine compound in an
amount of 0.1 wt % to 30 wt % based on 100 wt % by weight of the
plating solution.
[0037] A lithium metal anode according to another embodiment of the
present invention includes a current collector, a lithium metal
thin film disposed on at least one surface of the current
collector; and, a protective layer disposed on the surface of the
lithium metal thin film.
[0038] A thickness of the lithium metal thin film is from 5 .mu.m
to 100 .mu.m.
[0039] A thickness of the protective layer is from 10 nm to 100
nm.
[0040] The protective layer comprises at least one selected from
the group consisting of F, P, C, O and S.
[0041] According to another embodiment of the present invention,
there is provided a method of manufacturing a lithium metal anode,
comprising: restraining a current collector and a lithium source in
up and down direction and laminating them after electrically
insulating the current collector and the lithium source in a
electrolyte; and forming a lithium metal thin film on a surface of
the current collector by applying a current to the current
collector and the lithium source, wherein, a protective layer is
formed on a surface of the lithium metal thin film at the step of
forming a lithium metal thin film on a surface of the current
collector, and the protective layer comprises at least one selected
from the group consisting of F, P, C, O and S.
[0042] The step of forming simultaneously a metal thin film layer
and a coating layer is carried out by applying a current between
the current collector and the lithium source so that the average
current density is in the range of 0.1 mA/cm.sup.2 to 100
mA/cm.sup.2 based on the current collector area.
[0043] A lithium secondary battery according to an embodiment of
the present invention includes an anode, a cathode, and an
electrolyte, and the anode may be a lithium metal anode according
to the embodiment of the present invention.
Effect
[0044] The lithium metal anode according to the embodiments can
provide a lithium metal anode having a homogeneous interface since
a lithium metal thin film layer and a coating layer located on at
least one side of the lithium metal thin film layer are
simultaneously formed during the manufacturing process.
[0045] Further, according to the embodiments, it is possible to
provide a lithium secondary battery in which electrochemical
characteristics such as charge/discharge characteristics are
remarkably improved by applying a lithium metal anode including a
coating layer whose composition and characteristics are controlled
on at least one surface of the lithium metal thin film layer.
BRIEF DESCRIPTION OF DRAWINGS
[0046] FIGS. 1 and 2 schematically illustrate a lithium metal anode
according to one embodiment, respectively.
[0047] FIGS. 3 and 4 schematically show a manufacturing process of
a lithium metal anode according to an embodiment.
[0048] FIG. 5 is a schematic view of a lithium secondary battery
according to an embodiment.
[0049] FIGS. 6a and 6b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Example 1.
[0050] FIGS. 7a and 7b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Example 6.
[0051] FIGS. 8a and 8b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Comparative Example 1.
[0052] FIGS. 9a and 9b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Comparative Example 2.
[0053] FIGS. 10a and 10b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Comparative Example 3.
[0054] FIGS. 11a and 11b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Comparative Example 4.
[0055] FIGS. 12a to 12d show the results of surface component
analysis of the lithium metal anode produced according to Example
11.
[0056] FIGS. 13a to 13d show the results of analyzing the surface
components of the lithium metal anode produced according to
Examples 2 to 4.
[0057] FIGS. 14a to 14d show the results of surface component
analysis of the lithium metal anode prepared according to
Comparative Examples 1 to 4.
[0058] FIG. 15a is a graph showing a charge/discharge performance
evaluation result of a lithium secondary battery to which a lithium
metal anode manufactured according to Examples 1 to 6 is
applied.
[0059] FIG. 15B shows the results of analyzing the surface
components of the lithium metal anode prepared according to Example
1 and Comparative Examples 1 to 4.
[0060] FIG. 16 (a) shows the microstructure of a lithium metal
anode produced according to Experimental Example 4 of the present
invention, and FIG. 16 (b) shows the microstructure of a lithium
metal anode manufactured by a conventional electrodeposition
method.
[0061] FIG. 17 shows the surface composition of the lithium metal
anode produced according to Experimental Example 4 of the present
invention, and
[0062] FIG. 18 shows the surface composition of a lithium metal
anode manufactured by a conventional method.
[0063] FIG. 19 shows the results of repetition of charging and
discharging of a battery made of a lithium metal anode manufactured
by the method of Experimental Example 4.
[0064] FIG. 20 shows the results of repetition of charging and
discharging of a battery made of a lithium metal anode manufactured
by a deposition method (PVD).
[0065] FIG. 21 shows charge-discharge characteristics and results
of Experimental Example 4 and Comparative Examples 5 and 6.
DETAILED DESCRIPTION OF THE INVENTION
[0066] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying drawings.
The present invention may be embodied in many different forms and
is not limited to the embodiments described herein.
[0067] In order to clearly illustrate the present invention, parts
not related to the description are omitted, and the same or similar
components are denoted by the same reference numerals throughout
the specification.
[0068] In addition, since the sizes and thicknesses of the
respective components shown in the drawings are arbitrarily shown
for convenience of explanation, the present invention is not
necessarily limited to those shown in the drawings.
[0069] Also, throughout the specification, when an element is
referred to as "comprise" an element, it is understood that the
element may include other elements as well, without departing from
the other elements unless specifically stated otherwise.
[0070] Hereinafter, a lithium metal anode according to the present
invention will be described in detail with reference to the
drawings.
[0071] FIG. 1 schematically shows a lithium metal anode according
to an embodiment.
[0072] In FIG. 1, a lithium metal anode 10 according to an
embodiment includes a current collector 11, a lithium metal thin
film layer 12, and a coating layer 13.
[0073] More specifically, in the lithium metal anode 10 according
to the present embodiment, the lithium metal thin film layer 12 is
positioned on both sides of the current collector 11, and the
coating layer 13 is located on the surface of the lithium metal
thin film layer 12.
[0074] The current collector 11 is for electrical connection in the
cell.
[0075] The current collector 11 may have a shape of a foil but is
not limited thereto. For example, the current collector 11 may be a
mesh, a foam, a rod, a wire, or may be in the form of a sheet of
woven wire or fiber.
[0076] As the material of the current collector 11, a material
having electrical conductivity and having a limited reaction with
lithium can be used. As the material of the current collector 11,
for example, any one of a conductive material such as copper,
nickel, titanium, stainless steel, gold, platinum, silver,
tantalum, ruthenium and alloys thereof, carbon, conductive polymer,
or a composite fiber coated with a conductive layer on a
non-conductive polymer; or a combinations thereof may be used.
[0077] If the collector 11 is thick, the weight of the battery
increases and the energy density of the battery decrease. If the
thickness of the current collector 11 is reduced, there is a danger
of overheat damage during high current operation and may be damaged
by the tension during the battery manufacturing process. Therefore,
the thickness of the current collector 11 may range from 1 .mu.m to
50 .mu.m.
[0078] The lithium metal thin film layer 12 may be located on at
least one surface of the current collector 11.
[0079] The lithium metal thin film layer 12 is characterized in
that it has a smooth and dense surface microstructure without
dendrite and includes a columnar structure extending upward from
the current collector 11.
[0080] In the present invention, the columnar structure included in
the lithium metal thin film layer 12 can be prepared by forming the
lithium metal thin film layer 12 using an electrochemical plating
method using a plating solution containing an appropriate
component.
[0081] The average diameter of the columnar structure may be in the
range of 0.1 .mu.m to 100 .mu.m, more specifically in the range of
5 .mu.m to 40 .mu.m.
[0082] When the average diameter of the columnar structure is not
less than 0.1 .mu.m, the surface uniformity of the lithium metal
thin film layer 12 is excellent. Therefore, when the lithium metal
anode according to the embodiment is applied to a battery, a
lithium secondary battery has excellent electrochemical
characteristics.
[0083] In addition, when the average diameter of the columnar
structure is 100 .mu.m or less, the time required for forming the
lithium metal thin film layer 12 can be shortened, thereby
improving the productivity.
[0084] This is because the average diameter of the columnar
structure can be controlled by controlling the conditions of the
electrodeposition process. For example, lowering the current
density during the electrodeposition process increases the average
diameter of the columnar structure, and increasing the current
density decreases the average diameter of the columnar structure.
That is, if the current density is lowered to increase the average
diameter of the columnar structure, the time required for forming
the lithium metal thin film layer 12 becomes long.
[0085] In the present specification, the average diameter of the
columnar structure can be measured using the method of ASTM E 112
for the surface microstructure of the lithium metal anode 10.
[0086] On the other hand, the average pore fraction of the lithium
metal thin film layer 12 may be 0.1% to 10%, more specifically 1%
to 5%.
[0087] When the lithium metal thin film layer 12 has an average
pore fraction of more than 10%, the lithium metal thin film layer
12 has a porous microstructure. In this case, when the lithium
metal anode according to the embodiment is applied to a lithium
secondary battery, desorption and adhesion of lithium are unevenly
generated in the lithium metal anode 10 during charging and
discharging to promote dendritic growth, and as dead lithium or the
like, the battery capacity and charge/discharge life are
deteriorated. In addition, when the lithium metal thin film layer
12 is manufactured with a low average pore fraction of 0.1% or
less, the time required for forming the lithium metal thin film
layer 12 according to the embodiment is increased, and productivity
is reduced.
[0088] Next, the thickness of the lithium metal thin film layer 12
may be in the range of 0.1 .mu.m to 200 .mu.m, more specifically
0.1 .mu.m to 30 .mu.m.
[0089] When the thickness of the lithium metal thin film layer 12
is large, when the lithium metal anode according to the embodiment
is applied to a lithium secondary battery, the weight of the
battery increases and energy density becomes low. Further, since
the production time and cost are increased in proportion to the
thickness of the lithium metal thin film layer 12, the thickness of
the lithium metal thin film layer 12 is preferably 200 .mu.m or
less.
[0090] When the thickness of the lithium metal thin film layer 12
is too thin, the charge/discharge life of the battery is
deteriorated when the lithium metal anode according to the
embodiment is applied to a lithium secondary battery. Specifically,
during charging/discharging of the battery, lithium in the battery
is gradually consumed due to side reaction between lithium
contained in the active material and electrolyte, and the capacity
of the battery is reduced. If the thickness of the lithium metal
thin film layer 12 is thin, the amount of lithium that can
replenish the lithium consumed during charging and discharging is
reduced, so that the charge and discharge life of the battery is
lowered. Therefore, the thickness of the lithium metal thin film
layer 12 is preferably 0.1 .mu.m or more
[0091] The thickness of the lithium metal thin film layer 12 can be
easily controlled by controlling electrodeposition process
conditions such as current density and electrodeposition time in
the step of forming the lithium metal thin film layer 12 using the
electrochemical plating method.
[0092] Meanwhile, the lithium metal anode 10 according to the
embodiment of the present invention includes a coating layer 13
positioned on the surface of the lithium metal thin film layer
12.
[0093] The coating layer 13 is formed by a reaction between the
electrodeposited lithium metal and a plating solution in the
process of manufacturing the lithium metal thin film layer 12. The
thickness, composition and characteristics of the coating layer 13
can be controlled by adjusting the composition of the plating
solution and the conditions of the electrodeposition process.
[0094] The thickness of the coating layer 13 may be in the range
of, 2 nm to 2 .mu.m, more specifically, 10 nm to 500 nm.
[0095] If the thickness of the coating layer 13 located on the
surface of the lithium metal thin film layer 12 is too thick, the
lithium ion conductivity may be lowered and the interfacial
resistance may increase, so that the charge/discharge
characteristics may be deteriorated when the that is applied to
battery. If the thickness of the coating layer 13 is too small, the
coating layer 13 may be easily lost in the process of applying the
lithium metal anode according to the embodiment to the battery.
[0096] Therefore, it is preferable that the coating layer 13 is
formed uniformly and densely on the entire surface of the lithium
metal thin film layer 12 with a thin thickness within the range of
the thickness.
[0097] On the other hand, the coating layer 13 contains a
Li--N--C--H--O based ionic compound.
[0098] In the present embodiment, the coating layer 13 containing
the Li--N--C--H--O based ionic compound is formed by controlling
the composition and content of the plating solution during the
process of manufacturing the lithium metal thin film layer 12 by an
electroplating process.
[0099] The Li--N--C--H--O based ionic compound may include Li--O,
C--N, C--O, and C--H bonds.
[0100] More specifically, the Li--N--C--H--O based ionic compound
may include a compound represented by any one of the following
formulas (1) and (2)
Li.sup.+-[O--R.sub.1--R.sub.2 .sub.n.sub.1A.sub.1.sup.-+Li [Formula
1]
(wherein in the formula 1, R.sub.1 and, R.sub.2 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, or 2),
[0101] A.sub.1 is
##STR00008##
and
[0102] n1 is an integer of 1 to 10)
##STR00009##
[0103] (wherein in the formula 2, R.sub.3, and R.sub.4 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, or 2),
[0104] A.sub.2 is
##STR00010##
and
[0105] n2 is an integer of 1 to 10.)
[0106] More specifically, the compound represented by Formula 1 may
be at least one compound represented by Formula 1-1 or Formula
1-2.
[0107] The compound represented by Formula 2 may be at least one
compound represented by Formula 2-1 or Formula 2-2.
##STR00011##
[0108] (wherein in the formula 1-1, n3 is an integer of 1 to
5.)
[0109] More specifically, for example, lithium nitrate (LiNO.sub.3)
is used as a nitrogen-based compound, and a plating solution in
which an appropriate amount of the lithium nitrate is added to an
ether solvent is used. In the case of forming the lithium metal
thin film layer 12, the coating layer 13 containing the compound
represented by the formula 1-1 may be formed on the surface of the
lithium metal thin film layer 12.
##STR00012##
[0110] (wherein in the formula 1-2, R.sub.5 and R.sub.6 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, or 2), and
[0111] n4 is an integer of 1 to 5.)
[0112] More specifically, for example, by using a plating solution
prepared by using lithium bisfluorosulfonyl imide
(LiN(FSO.sub.2).sub.2) as a nitrogen-based compound and adding it
in an appropriate amount to an ether solvent. When the lithium
metal thin film layer 12 is formed through the electrodeposition
process, the coating film 13 containing the compound represented by
the general formula 1-2 may be formed on the surface of the lithium
metal thin film layer 12.
[0113] When lithium bisfluorosulfonylimide (LiN(FSO.sub.2).sub.2)
is used as the nitrogen-based compound contained in the plating
solution, the Li--N--C--H--O based ionic compound may have a
structure in which some of the C--H bonds of the --CH.sub.2--
structure is substituted with a C--F bond to form
--CH.sub.mF.sub.2-m-- (m is one of 0, 1, and 2).
##STR00013##
[0114] (wherein in the formula 2-1, n5 is and integer of 1 to
5.)
[0115] More specifically, for example, when the lithium metal thin
film layer 12 is formed through electrodeposition using a plating
solution in which lithium nitrate is used as a nitrogen-based
compound and is added in a proper amount to a carbonate-based
solvent. The coating layer 13 containing the compound represented
by the general formula 2-1 may be formed on the surface of the
lithium metal thin film layer 12.
##STR00014##
[0116] (wherein in the formula 2-2, R.sub.7 and R.sub.8 are each
CH.sub.mF.sub.2-m (m is one of 0, 1, and 2), and
[0117] n6 is an integer of 1 to 5.)
[0118] More specifically, for example, a lithium metal thin film
layer 12 is formed through an electrodeposition process using a
plating solution obtained by using lithium bisfluorosulfonylimide
as a nitrogen-based compound and adding the lithium
bisfluorosulfonylimide to a carbonate-based solvent in an
appropriate amount. The coating layer 13 containing the compound
represented by the general formula 2-2 can be formed on the surface
of the lithium metal thin film layer 12.
[0119] When lithium bisfluorosulfonylimide (LiN(FSO.sub.2).sub.2)
is used as the nitrogen-based compound contained in the plating
solution, the Li--N--C--H--O based ionic compound may have a
structure in which a part of the C--H bonds of the --CH.sub.2-- may
be substituted with a C--F bond to have a structure of
--CH.sub.mF.sub.2-m-- (m is one of 0, 1, and 2).
[0120] That is, in this embodiment, in the step of forming the
lithium metal thin film layer 12, the nitrogen compound contained
in the plating solution and the kind of the solvent and the content
thereof are controlled, so that the coating layer 13 containing at
least one compound selected from the compounds represented by the
formulas 1 and 2 may be disposed on the surface of the lithium
metal thin film layer 12.
[0121] On the other hand, the coating layer 13 may further include
LiF in addition to a Li--N--C--H--O based ionic compound.
[0122] More specifically, for example, when lithium
bisfluorosulfonylimide (LiN(FSO.sub.2).sub.2) is used as the
nitrogen-based compound contained in the plating solution, the
coating layer 13 may further contain LiF in addition to the
Li--N--C--H--O based ionic compound.
[0123] Also, when the plating solution further contains a
fluorine-based compound such as fluoroethylene carbonate (FEC), the
coating layer 13 may contain LiF together with a Li--N--C--H--O
based ionic compound.
[0124] Thus, when the coating layer 13 further contains LiF, the
electrochemical performance of the coating layer 13 can be further
improved by interaction with a Li--N--C--H--O based ionic
compound.
[0125] When the lithium metal anode 10 including the coating layer
13 containing a Li--N--C--H--O based ionic compound is applied to a
lithium secondary battery as in the present embodiment, side
reactions between the electrolyte and the lithium metal thin film
layer 12 are blocked. In addition, it is possible to improve the
charge/discharge life of the lithium secondary battery by
suppressing the growth of dendrite by making the desorption and
attachment of lithium uniform on the surface of the lithium metal
thin film layer 12.
[0126] In addition, defects can be prevented from occurring in
subsequent processes such as packaging, transportation, storage,
and battery application of the lithium metal anode 10 of this
embodiment. Since the lithium metal anode 10 according to the
present embodiment includes the coating layer 13 positioned on the
surface of the lithium metal thin film layer 12, the reaction of
the lithium metal thin film layer 12 with water and/or oxygen can
be blocked in the subsequent process,
[0127] the reaction of the lithium metal thin film layer 12 with
moisture and/It is possible to effectively prevent the formation of
a non-uniform surface reaction layer on the surface of the lithium
metal thin film layer 12. It is very effectively prevented that a
non-uniform surface reaction layer (Native surface film) is formed
on the surface of the lithium metal thin film layer 12.
[0128] FIG. 2 schematically shows a lithium metal anode for a
secondary battery according to another embodiment.
[0129] Referring to FIG. 2, the lithium metal anode 10 according to
the present embodiment includes a current collector 11, a lithium
metal thin film layer 12 disposed on one surface of the current
collector 11, and a coating layer 13 positioned on the lithium
metal thin film layer 12.
[0130] The current collector 11, the lithium metal thin film layer
12, and the coating layer 13 of this embodiment are the same as
those described in the embodiment with reference to FIG. 1.
Therefore, detailed description of the same or similar components
will be omitted.
[0131] Next, a method of manufacturing a lithium metal anode
according to an embodiment of the present invention will be
described.
[0132] A method of manufacturing a lithium metal anode according to
an embodiment includes: restraining a current collector and a
lithium source in both directions and laminating them after
electrically insulating the current collector and the lithium
source in a plating solution; and forming simultaneously a metal
thin film layer and a coating layer on at least one surface of the
current collector by applying a current between the current
collector and the lithium source.
[0133] FIG. 3 schematically shows a manufacturing process of a
lithium metal anode 10 for a secondary battery according to an
embodiment of the present invention.
[0134] Referring to FIG. 3, a current collector 11 and a lithium
source 20 to be laminated with a lithium metal thin film layer are
supported in a plating solution 30.
[0135] The lithium source 20 can be, for example, a lithium metal,
a lithium alloy, a foil obtained by pressing the lithium metal or
lithium alloy on a current collector, or the like.
[0136] The current collector 11 is the same as that described
above, and will not be described here.
[0137] The plating solution 30 may be prepared by dissolving a
lithium salt in a non-aqueous solvent.
[0138] In this embodiment, the plating solution 30 is characterized
in that it contains a nitrogen-based compound as at least one of
the lithium salt and the non-aqueous solvent.
[0139] The nitrogen-based compound includes at least one selected
from the group consisting of lithium nitrate, lithium bis
fluorosulfonyl imide, lithium bis trifluoromethane sulfonimide,
e-Caprolactam, N-methyl-e-caprolactam, triethylamine, and
tributylamine.
[0140] At least one of lithium nitrate, lithium bis fluorosulfonyl
imide and lithium bis trifluoromethane sulfonamide of the
nitrogen-based compounds, can be used as a lithium salt.
[0141] At least one of e-Caprolactam, N-methyl-e-caprolactam,
triethylamine and tributylamine of the nitrogen-based compounds can
be used as a non-aqueous solvent.
[0142] The plating solution 30 may include the nitrogen-based
compounds in an amount ranging from 1% by weight to 100% by weight,
more specifically from 5% by weight to 90% by weight, more
specifically from 5% by weight to 70% by weight, more specifically
5% by weight to 60% by weight based on 100 wt % of the plating
solution.
[0143] When the content of the nitrogen-based compound is less than
1% by weight, there is a problem that the Li--N--C--H--O based
ionic compound in the coating layer 13 is not formed properly.
[0144] Meanwhile, the plating solution 30 may be prepared using
only the nitrogen-based compound, but a general non-aqueous solvent
may be added as an auxiliary solvent in consideration of the
viscosity of the plating solution. If the viscosity of the plating
solution is too high, the mobility of lithium ions is lowered and
the ion conductivity of the plating solution is lowered, so that
the time required for forming the lithium metal thin film layer 12
is increased and productivity is reduced.
[0145] The auxiliary solvent may include, for example, at least one
of ethylene carbonate, propylene carbonate, dimethyl carbonate,
ethyl methyl carbonate, diethyl carbonate, 1,2-dimethoxyethane,
diethylene glycol dimethyl ether, tetraethylene glycol dimethyl
ether, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane or
1,3,5-trioxane.
[0146] The auxiliary solvent for controlling the viscosity of the
plating solution may be included in an amount ranging from 5% by
weight to 70% by weight, more specifically from 10% by weight to
60% by weight, based on 100% by weight of the plating solution.
[0147] Further, the plating solution 30 may further include a
fluorine-based compound.
[0148] The fluorine-based compound, for example, includes at least
one of Lithium difluoro phosphate, Lithium hexafluoro phosphate,
Lithium difluoro bisoxalato phosphate, Lithium tetrafluoro oxalato
phosphate, Lithium difluoro oxalate borate, Lithium difluoro
oxalato borate, Lithium tetrafluoro oxalato borate, Fluoroethylene
carbonate, Difluoroethylene carbonate, and 1,1,2,2-Tetrafluoroethyl
2,2,3,3-Tetrafluoropropyl ether.
[0149] The plating solution 30 may contain the fluorine-based
compound in an amount ranging from 0.1% by weight to 30% by weight,
more specifically from 1% by weight to 10% by weight, based on 100%
by weight of the plating solution.
[0150] When the content of the fluorine-based compound is less than
0.1% by weight, the interaction between the nitrogen compound and
the fluorine-based compound does not occur smoothly in the plating
solution, and the effect of improving the properties of the coating
layer 13 of the lithium metal anode 10 is not exhibited. When the
content of the fluorine compound exceeds 30% by weight, LiF
formation due to the direct reaction between the fluorine-based
compound and lithium is excessively generated, and the
electrochemical characteristics of the coating layer 13 is
deteriorated.
[0151] Next, after the insulating film 40 is positioned between the
current collector 11 and the lithium source 20, the current
collector 11, the lithium source 20, and the insulating film 40 are
laminated and restrained in both directions by using the restraint
device 50.
[0152] At this time, the restraint device 50 can use a method
generally used in the related art such as a manual clamping method,
a uniaxial pressing method using a hydraulic pressure, a pneumatic
pressure, or the like, and is not particularly limited.
[0153] The insulating film 40 may be a separator material used for
a lithium secondary battery, and is not particularly limited.
[0154] After the electrodeposition equipment is constructed as
described above, a current is applied to the current collector 11
and the lithium source 20 using the power supply 60 to form the
coating layer 13 and the lithium metal thin film layer 12 on the
current collector 11. At this time, the current collector 11 is
connected to the (-) electrode and the lithium source 20 is
connected to the (+) electrode.
[0155] The step of forming the lithium metal thin film layer and
the coating layer on at least one surface of the current collector
11 is performed by applying a current between the current collector
11 and the lithium source 20.
[0156] The applied current may range from an average current
density of 0.1 mA/cm.sup.2 to 100 mA/cm.sup.2, more specifically,
0.5 mA/cm.sup.2 to 20 mA/cm.sup.2, based on the collector surface
area. When the current density is increased, the deposition rate of
the lithium metal thin film layer is increased, so that the
productivity is increased. However, the characteristics of the
coating layer are deteriorated and then the performance of the
produced lithium metal anode is lowered. Therefore, the current
density is preferably in the above range.
[0157] Lithium moved from the lithium source 20 through the
application of the electric current is electrodeposited on the
surface of the current collector 11 to form the lithium metal thin
film layer 12. At this time, the thickness of the lithium metal
thin film can be easily controlled by controlling current density,
electrodeposition time, and electrodeposition process
conditions.
[0158] The coating layer 13 can be formed by a reduction
decomposition reaction of the plating solution 30 on the surface of
the current collector 11 and a reaction between the
electrodeposited lithium metal thin film layer and the plating
solution 30. The thickness, composition, and characteristics of the
coated layer can be controlled by adjusting the composition of the
plating solution 30 and the electrodeposition process
conditions.
[0159] That is, the method for manufacturing a lithium metal anode
according to the embodiments is characterized in that a metallic
thin film layer and a coating layer are simultaneously formed using
an electroplating process which is an electrochemical plating
method.
[0160] More specifically, the electrodeposition process is
performed in condition of normal temperature and atmospheric
pressure (for example, 25.degree. C., 1 atm), so that lithium ions
are supplied from a lithium source, and lithium thin film layer 12
is laminated on the current collector 11 by electrochemically
method.
[0161] When the electrochemical plating method is used, the lithium
metal anode can be economically produced, the large area stacking
can be easily achieved, and the thickness of the lithium metal thin
film layer can be easily controlled. In addition, it is possible to
control so that the coating layer having a specific component as
described above is uniformly and densely formed on the surface of
the lithium metal thin film layer during the manufacturing process.
Therefore, when a lithium metal anode manufactured by the method
according to this embodiment is applied to a lithium secondary
battery, a lithium secondary battery having excellent
electrochemical performance can be realized.
[0162] FIG. 3 shows a manufacturing process in which only one
current collector 11 and one lithium source 20 are located, but a
plurality of current collectors 11 may exist.
[0163] FIG. 4 schematically shows a process of manufacturing a
lithium metal anode according to another embodiment.
[0164] Referring to FIG. 4, the current collector 11 may be
positioned on both sides of the lithium source 20 with the
insulating film 40 interposed therebetween, according to another
embodiment of the process for producing a lithium metal anode. The
current collector 11 and the lithium source 20 are connected to the
power supply unit 60 to receive a current and a lithium metal thin
film layer is formed on the surface of the current collector
11.
[0165] Likewise, by controlling the reduction decomposition
reaction of the plating solution 30 on the surface of the current
collector 11 and the reaction between the electrodeposited lithium
metal thin film layer and the plating solution 30, a coating layer
having a desired composition and characteristics is formed on the
surface of the lithium metal thin film layer.
[0166] The lithium metal anode manufactured by the method according
to the embodiments can be usefully used as a anode of a lithium
secondary battery. That is, the lithium secondary battery according
to one embodiment includes the cathode, the electrolyte, and the
separator together with the lithium metal anode described
above.
[0167] FIG. 5 schematically shows a structure of a lithium
secondary battery according to an embodiment.
[0168] Referring to FIG. 5, the lithium secondary battery 100
includes an electrode assembly including a cathode 70, an anode 10,
and a separator 90 disposed between the cathode 70 and the anode
10.
[0169] The electrode assembly is wound or folded and housed in the
battery container 95.
[0170] Thereafter, the electrolyte 80 is injected into the battery
container 95 and sealed to complete the lithium secondary battery
100. At this time, the battery container 95 may have a cylindrical
shape, a square shape, a pouch shape, a coin shape, or the
like.
[0171] The anode 10 uses the lithium metal anode 10 according to
the above-described embodiments.
[0172] The cathode 70 may include a cathode active material layer
and a cathode current collector.
[0173] The cathode active material layer can comprise lithium
compound including at least one metal selected from Ni, Co, Mn, Al,
Cr, Fe, Mg, Sr, V, La and Ce; and at least one non-metallic element
selected from the group consisting of O, F, S, and P. The cathode
active material layer may include active material particles having
a size of about 0.01 to 200 .mu.m, and may be appropriately
selected depending on the required characteristics of the
battery.
[0174] Optionally, a conductive material may be added to the
cathode active material layer.
[0175] The conductive material may be, for example, carbon black
and ultrafine graphite particles, fine carbon such as acetylene
black, nano metal particle paste, and the like, but not limited
thereto.
[0176] The cathode collector serves to support the cathode active
material layer. As the cathode collector, for example, an aluminum
foil, a nickel foil or a combination thereof may be used, but the
present invention is not limited thereto.
[0177] As the electrolyte 80 to be filled in the lithium secondary
battery 100, a non-aqueous electrolyte or a solid electrolyte may
be used.
[0178] The non-aqueous liquid electrolyte may include, for example,
a lithium salt such as lithium hexafluorophosphate and lithium
perchlorate, and a solvent such as ethylene carbonate, propylene
carbonate, and butylene carbonate. As the solid electrolyte, a gel
polymer electrolyte obtained by impregnating a polymer electrolyte
such as polyethylene oxide or polyacrylonitrile with an
electrolytic solution, or an inorganic solid electrolyte such as
LiI or Li.sub.3N can be used.
[0179] The separator 90 separates the cathode and the anode and
provides a passage for lithium ions. Any separator 90 may be used
as long as it is commonly used in a lithium secondary battery. That
is, it is possible to use the separator having a low resistance to
ion movement of an electrolyte and an excellent ability to
impregnate an electrolyte. The separator may be selected from, for
example, glass fiber, polyester, polyethylene, polypropylene,
polytetrafluoroethylene, or a combination thereof, and may be in
the form of a nonwoven fabric or a woven fabric. Meanwhile, when
the solid electrolyte is used as the electrolyte 80, the solid
electrolyte may also serve as the separator 90.
[0180] Next, a lithium metal anode for a secondary battery and a
method of manufacturing the same according to another embodiment of
the present invention will be described.
[0181] The lithium metal anode for a secondary battery according to
another embodiment of the present invention may include a current
collector, a lithium metal thin film positioned on at least one
surface of the current collector, and a protective layer disposed
on a surface of the lithium metal thin film.
[0182] First, the current collector is located at the center of the
lithium metal anode. The current collector is for electrical
connection within the cell. The current collector may have the form
of a thin foil and may include Cu.
[0183] If the thickness of the current collector is increased, the
weight of the battery is increased and the energy density of the
battery is lowered. If the thickness of the current collector is
reduced, there is a risk of overheating during high current
operation and being damaged by the tension during the battery
manufacturing process. In this embodiment, the thickness of the
current collector may preferably be 6 to 100 .mu.m.
[0184] The lithium metal thin film may be positioned on both sides
of the current collector. As will be described later, the lithium
metal thin film can be manufactured by an electroplating process.
At this time, the thickness of the lithium metal thin film can be
easily controlled by controlling current density, electrodeposition
time, electrodeposition process conditions, and the like.
[0185] The thickness of the lithium metal thin film may be 5 .mu.m
to 100 .mu.m.
[0186] A protective layer is placed on the surface of the lithium
metal thin film. The protective layer is formed by the reaction
between the electrodeposited lithium and the plating solution in
the process of manufacturing the lithium metal thin film, and the
composition of the plating solution and electrodeposition process
conditions are controlled to control the thickness, composition,
characteristics of the protective layer.
[0187] The thickness of the protective layer is preferably from 10
nm to 100 nm. If the thickness of the protective layer is too
thick, the lithium ion conductivity is lowered and the high rate
charge/discharge characteristics may be lowered when that is
applied to the battery. If the thickness of the protective layer is
too small, the characteristics are unstable and the protective
layer may be lost during application of the battery. The protective
layer is preferably thin and uniformly and densely formed over the
entire lithium surface.
[0188] The protective layer improves the charge/discharge
efficiency (coulombic efficiency) by lowering the polarization
voltage when the secondary battery is applied, and can improve the
charge/discharge life by suppressing the side reaction with the
electrolyte.
[0189] The protective layer may comprise F, P, C, O, S, and the
like. More specifically, the protective layer may comprise a
material such as CF.sub.3, SO.sub.2, ROCO.sub.2Li(R=alkyl group),
Li.sub.2CO.sub.3, LiF, and the like.
[0190] In this embodiment, the lithium metal thin film is
positioned on both sides of the current collector and the
protective layer may be located on the lithium metal thin film.
Alternatively, the lithium metal anode for a secondary battery may
include a lithium metal thin film and a protective layer only on
one surface of the current collector.
[0191] Hereinafter, a method for manufacturing a lithium metal
anode for a secondary battery according to another embodiment of
the present invention will be described.
[0192] According to another embodiment of the present invention,
there is provided a method of manufacturing a lithium metal anode,
comprising:
[0193] restraining a current collector and a lithium source in up
and down direction and laminating them after electrically
insulating the current collector and the lithium source in a
electrolyte; and forming a lithium metal thin film on a surface of
the current collector by applying a current to the current
collector and the lithium source, wherein, a protective layer is
formed on a surface of the lithium metal thin film at the step of
forming a lithium metal thin film on a surface of the current
collector, and the protective layer comprises at least one selected
from the group consisting of F, P, C, O and S.
[0194] Specifically, a current collector to which lithium is to be
deposited and a lithium source are supported in an electrolyte for
electrodeposition. The lithium source may be a lithium metal having
a purity of 95 to 99.99%, a foil in which a lithium metal is
laminated thinly on a current collector, lithium carbonate, lithium
chloride, lithium nitride, or the like. As an electrolyte for
electrodeposition, a conventional electrolytic solution in which a
lithium salt such as LiPF.sub.6, LiTFSI, or LiFSI used in a lithium
ion battery is dissolved in a solvent can be used.
[0195] Next, after the insulating film is positioned between the
current collector and the lithium source, a current collector, a
lithium source and an insulating film are stacked and restrained in
up and down direction by using a restraint device. The restraint
device can use a method generally used in the related art such as a
manual clamping method, a uniaxial pressing method using a
hydraulic pressure, a pneumatic pressure, or the like, and is not
particularly limited. The insulating film may be a separator
material used for a lead acid battery, a nickel battery, a lithium
ion battery or the like, and is not particularly limited. After the
electrodeposition equipment is constructed, a current is applied to
the current collector and the lithium source using a power supply.
At this time, the current collector is connected to the (-)
electrode and the lithium source is connected to the (+)
electrode.
[0196] Through this voltage application, lithium moved from the
lithium source is electrodeposited on the surface of the current
collector to form a lithium metal thin film. At this time, the
thickness of the lithium metal thin film can be easily controlled
by controlling current density, electrodeposition time,
electrodeposition process conditions, and the like. Further, a
protective layer may be formed on the surface of the lithium metal
thin film by a reaction between the lithium electrodeposited on the
current collector and the electrodeposition solution. The
thickness, composition, and characteristics of the protective layer
can be controlled by adjusting the composition of the
electrodeposition solution and the electrodeposition process
conditions.
DETAILED EXAMPLE OF THE INVENTION
[0197] Hereinafter, the present invention will be described in more
detail with reference to experimental examples. These experimental
examples are only for illustrating the present invention, and the
present invention is not limited thereto.
Example 1--Electrodeposition Process (Using a Plating Solution
Containing a Nitrogen-Based and Fluorine-Based Compound)
[0198] A lithium metal anode was prepared by the same process as
shown in FIG. 3.
[0199] The plating solution 30 is prepared by adding a lithium bis
(fluorosulfonyl) imide and a lithium nitrate as a nitrogen based
compounds to a 1,2-dimethoxyethane solvent, in amounts of 40% by
weight and 10% by weight based on 100% by weight of the plating
solution, respectively. Then 10% by weight of fluoroethylene
carbonate, which is a fluorine based compound, was added based on
100% by weight of the plating solution.
[0200] As the lithium source 20, a lithium metal plate having a
purity of 99.9% or more and having a thickness of 500 .mu.m was
pressed on a copper plate, and the current collector 11 was made of
a copper foil having a thickness of about 15 .mu.m.
[0201] The lithium source 20 and the current collector 11 are
laminated in an electrically insulated state in the plating
solution 30 and then the lithium source 20 and the current
collector 11 are connected to each other through (+) and (-)
electrode. Accordingly, a lithium metal thin film layer 12 was
formed on the surface of the current collector 11. At this time, a
lithium metal thin film layer 12 having a thickness of about 20
.mu.m was prepared with an average current density of 0.7
mA/cm.sup.2 and a process time of about 6 hours. At this time, the
reduction decomposition reaction of the plating solution 30 on the
surface of the current collector 11 and the reaction between the
electrodeposited lithium metal thin film layer 12 and the plating
solution 30 are controlled to form a coating layer 13 on the
surface of the lithium metal thin film layer 12.
Example 2--Electrodeposition Process (Change in Composition of
Plating Solution)
[0202] A lithium metal anode was prepared in the same manner as an
Example 1, except that lithium nitrate, which is a nitrogen
compound, and fluoroethylene carbonate, which is a fluorine
compound, were not added during the preparation of the plating
solution.
Example 3--Electrodeposition Process (Change in Plating Solution
Composition)
[0203] A lithium metal anode was prepared in the same manner as an
Example 1, except that lithium nitrate, which is a nitrogen-based
compound, was not added during the preparation of the plating
solution and fluoroethylene carbonate as a fluorine compound was
added in an amount of 10% by weight based on 100% by weight of the
plating solution.
Example 4--Electrodeposition Process (Change in Composition of
Plating Solution)
[0204] A lithium metal anode was prepared in the same manner as an
Example 1, except that lithium nitrate, which is a nitrogen-based
compound, was not added during the preparation of the plating
solution and fluoroethylene carbonate as a fluorine compound was
added in an amount of 20% by weight based on 100% by weight of the
plating solution.
Example 5--Electrodeposition Process (Change in Composition of
Plating Solution)
[0205] A lithium metal anode was prepared in the same manner as an
Example 1, except that fluoroethylene carbonate, which is a
fluorine compound, was not added during the preparation of the
plating solution.
Example 6--Electrodeposition Process (Change in Composition of
Plating Solution)
[0206] A lithium metal anode was prepared in the same manner as an
Example 1, except that, lithium nitrate, which is a nitrogen
compound, was added in an amount of 20% by weight based on 100% by
weight of the plating solution, and lithium bis (fluorosulfonyl)
imide as a nitrogen compound and fluoroethylene carbonate as a
fluorine compound were not added.
Comparative Example 1--Electrodeposition Process (Using a Plating
Solution Containing Only a Fluorine-Based Compound)
[0207] A lithium metal anode was prepared in the same manner as an
Example 1, except that the plating solution was prepared as
follows.
[0208] Lithium hexafluorophosphate (LiPF.sub.6) was added to a
solvent in which ethylene carbonate and ethyl methyl carbonate were
mixed in a volume ratio of 3:7 in an amount of 30 wt % based on 100
wt % of the plating solution.
Comparative Example 2--Electrodeposition Process (Using a Plating
Solution Containing No Nitrogen-Based and Fluorine-Based
Compounds)
[0209] A lithium metal anode was prepared in the same manner as an
Example 1, except that the plating solution was prepared as
follows.
[0210] Lithium perchlorate (LiClO.sub.4) was added to a solvent in
which ethylene carbonate and ethyl methyl carbonate were mixed in a
volume ratio of 3:7 in an amount of 20 wt % based on 100 wt % of
the plating solution.
Comparative Example 3--Physical Vapor Deposition Process
[0211] In order to compare the microstructural characteristics and
the electrochemical performance of the lithium metal anode
manufactured by the conventional physical vapor deposition (PVD)
method with the lithium metal anode produced according to the
embodiments, a lithium metal thin film layer (Li--Cu foil) having a
thickness of about 20 .mu.m was prepared.
[0212] The lithium metal anode is prepared by a method of vacuum
thermal evaporation. The method is that a lithium metal ingot
having a purity of 99.9% or higher in a high vacuum chamber of
10.sup.-5 torr or less is heated to 700.degree. C. or higher and
laminated on the surface of a Cu foil.
Comparative Example 4--Rolling Process
[0213] In order to compare the microstructure characteristics and
the electrochemical performance of the lithium metal anode prepared
by the rolling method with the lithium metal anode prepared
according to the embodiments, a lithium metal anode having a
thickness of about 20 .mu.m (Li--Cu foil) was prepared.
[0214] The lithium metal anode was prepared by rolling a lithium
metal foil having a purity of 99.9% or more and a thickness of
about 100 .mu.m together with a copper foil in an inert gas
atmosphere.
Experimental Example 1--Microstructure Analysis of Lithium Metal
Anode
[0215] The surface and cross section of the lithium metal anode
prepared according to Example 1, Example 6 and Comparative Examples
1 to 4 were measured at a magnification of .times.2,000 using a
scanning electron microscope.
[0216] FIGS. 6a and 6b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode prepared
according to Example 1. FIGS. 7a and 7b are SEM photographs showing
the surface and cross-sectional micrographs of the lithium metal
anode prepared according to Example 6.
[0217] FIGS. 8a and 8b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Comparative Example 1. FIGS. 9a and 9b are SEM
photographs of the surface and cross-sectional microstructure of
the lithium metal anode produced according to Comparative Example
2. FIGS. 10a and 10b are SEM photographs of the surface and
cross-sectional microstructure of the lithium metal anode produced
according to Comparative Example 3. FIGS. 11a and 11b are SEM
photographs of the surface and cross-sectional microstructure of
the lithium metal anode produced according to Comparative Example
4.
[0218] Referring to FIGS. 6a and 6b, a lithium metal anode
manufactured using a plating solution containing both a nitrogen
compound and a fluorine compound according to Example 1 has a
smooth and dense surface microstructure without a dendrite. In
addition, a cross section of the lithium metal thin film layer of
the lithium metal anode manufactured according to Example 1 has a
columnar structure extending upward from the current collector.
[0219] Next, referring to FIGS. 7a and 7b, it can be confirmed that
the lithium metal anode manufactured using the plating solution
containing only the nitrogen-based compound according to Example 6
has a smooth and dense surface microstructure without the dendrite.
It can also be confirmed that the lithium metal thin film layer of
the lithium metal anode produced according to Example 6 has a
columnar structure stretched upward from the collector as an
Example 1.
[0220] Referring to FIGS. 8a and 8b, a lithium metal anode
manufactured using a plating solution containing only a
fluorine-based compound according to Comparative Example 1 has a
large number of dendrite protrusions and a non-uniform
microstructure with high porosity.
[0221] Referring to FIGS. 9a and 9b, according to Comparative
Example 2, a lithium metal anode made using a plating solution
containing neither a fluorine-containing compound nor a
nitrogen-based compound was formed in many dendrites and a
non-uniform microstructure having a high porosity.
[0222] That is, referring to the surface and cross-sectional
photographs of the lithium metal anode produced according to
Comparative Examples 1 and 2, even when the electrodeposition
process is used, when the plating solution does not contain a
nitrogen compound as in the present invention, it can be seen that
the columnar structure of the lithium metal thin film layer is not
densely and uniformly grown and the resin dendrites are easily
formed and the pores and surface roughness of the lithium metal
thin film layer are increased.
[0223] On the other hand, referring to FIGS. 10a and 10b and FIGS.
11a and 11b, it can be seen that lithium metal anode of Comparative
Examples 3 and 4 prepared by the physical vapor deposition method
or the rolling method as in the prior art have a polycrystalline or
microcrystalline structure of amorphous form.
[0224] That is, it is confirmed that the lithium metal anode
according to the embodiments has a microstructural characteristic
that the lithium metal thin film layer has a columnar structure,
unlike the lithium metal anode (Li--Cu foil) manufactured by the
existing commercialized method.
Experimental Example 2--Analysis of Film Components of a Lithium
Metal Anode
[0225] Surface components of the lithium metal anode prepared
according to Examples 1 to 4 and Comparative Examples 1 to 4 were
analyzed by the following method.
[0226] The analysis was carried out by using X-ray photoelectron
spectroscopy (XPS). The lithium metal anode of each of Examples to
4 and Comparative Examples 1 to 4 was subjected to surface analysis
using peak intensity corresponding to Li 1s, C 1s, N 1s, and F 1s
to analyze the constituents of the surface portion.
[0227] FIGS. 12a and 12d show the results of analyzing the surface
components of the lithium metal anode prepared in Example 1, and
FIGS. 13a and 13d show the results of analyzing the surface
components of the lithium metal anode prepared in Examples 2 to 4.
FIGS. 14a and 14d show the results of analyzing the surface
components of the lithium metal anode prepared according to
Comparative Examples 1 to 4.
[0228] Referring to FIGS. 12a and 12d and FIGS. 13a and 13d, on the
surface of the lithium metal thin film layer of the lithium metal
anode manufactured according to the examples 1 to 4, it can be
confirmed that a coating layer containing a Li--N--C--H--O based
ionic compound having all of Li--O, C--N, C--O and C--H bonds is
formed by the nitrogenous compound contained in the plating
solution. Further, it can be confirmed that the coating contains
LiF by the fluorine-based compound contained in the plating
solution.
[0229] In addition, no lithium was observed on the surface of the
lithium metal anode, and it was confirmed that the coating layer
prepared according to Examples 1 to 4 was uniformly formed on the
surface of the lithium metal thin film layer.
[0230] In addition, lithium hydroxide (LiOH), lithium carbonate
(Li.sub.2CO.sub.3), lithium oxide (Li.sub.2O), and the like, which
are components of a surface reaction layer (Native surface film)
observed on a conventional lithium metal surface, were not observed
at all. Thus, it can be seen that when the lithium metal anode is
manufactured by the method of the present invention, the formation
of the lithium metal thin film layer and the coating layer are
simultaneously formed, and the generation of the nonuniform surface
reaction layer can be effectively suppressed.
[0231] On the other hand, in Examples 2 to 4, the content of
fluoroethylene carbonate as the fluorine compound was changed from
0% to 10% based on 100% by weight of the plating solution in the
production of the plating solution. FIGS. 13a and 13d, it can be
confirmed that as the content of the additive increases, the
intensity of the peak corresponding to each component and bond
changes. It can be seen that the composition and properties of the
coating layer formed on the surface of the lithium metal thin film
layer can be controlled by controlling the composition of the
plating solution.
[0232] On the other hand, referring to FIGS. 14a and 14d, peaks
corresponding to the C--N bond were not observed in the case of
Comparative Example 1 and Comparative Example 2 in which the
nitrogen compound was not contained in the plating solution, and
this confirms that the coating layer formed on the surface of the
lithium metal thin film layer does not contain a Li--N--C--H--O
based ionic compound.
[0233] In addition, according to Comparative Example 3, no peak
corresponding to the C--N bond was observed on the surface of the
lithium metal anode produced by the conventional physical vapor
deposition method and on the surface of the lithium metal thin film
of the lithium metal anode produced by rolling according to
Comparative Example 4. It can be confirmed that the Li--N--C--H--O
based ionic compound is not present on the surface. Therefore, in
the case of a lithium metal anode manufactured by a physical vapor
deposition and rolling method, a surface reaction layer (Native
surface film) composed of lithium hydroxide (LiOH), lithium
carbonate (Li.sub.2CO.sub.3), lithium oxide (Li.sub.2O) can be
confirmed.
[0234] Since lithium hydroxide, lithium carbonate, lithium oxide,
and the like, have very low lithium ion conductivity, so that the
surface reaction layer composed of these components can prevent
smooth movement of lithium ions during charging and discharging.
Further, the surface reaction layer composed of the above
components is fragile and has low applicability caused by volume
change, so that it can be easily broken when a repeated volume
change of the lithium metal anode during charging and discharging.
Such breakage of the reaction layer may lead to abrupt and
non-uniform reaction between the lithium metal and the electrolytic
solution, resulting in deterioration of the charge-discharge
performance of the battery.
Experimental Example 3--Evaluation of Charge/Discharge Performance
of a Battery Using a Lithium Metal Anode
[0235] A lithium secondary battery (2032 type coin full cell)
having a structure as shown in FIG. 6 was manufactured using the
lithium metal anode prepared according to Examples 1 to 6 and
Comparative Examples 1 to 4, and the charging/discharging
performance was evaluated respectively.
[0236] The cathode was prepared such that the cathode active
material layer was laminated on one surface of the current
collector (Al foil) using a cathode active material slurry
containing LiCoO.sub.2 (99 wt %) active material, a conductive
material and a binder. At this time, the capacity per unit area of
the cathode was made to be 3.1 mAh/cm.sup.2, which is the cathode
capacity level of the currently commercialized lithium secondary
battery (using a graphite anode).
[0237] A mixed solvent of ethylene carbonate and ethyl methyl
carbonate (3:7 by volume) in which 1 M of LiPF.sub.6 was dissolved
was used as an electrolyte solution.
[0238] The separator used was a model 2400 of Celgard, a
polypropylene material, and a 2032 type coin cell of Hohsen Co.,
Ltd. was used as a battery container.
[0239] The charge/discharge performance of the lithium secondary
battery manufactured by the above method was evaluated as
follows.
[0240] The charging step was charged with a constant current up to
4.25V at 0.2 C and then charged up to 4.25V to 0.05 C. The
discharging step was discharged at a constant current of 0.5 C to
3.0V.
[0241] FIGS. 15a and 15b show the results of evaluating the
charge/discharge performance of the lithium secondary battery
manufactured by the above method by applying the lithium metal
anode prepared according to Examples 1 to 6 and Comparative
Examples 1 to 4.
[0242] FIG. 15a is a graph showing a charge/discharge performance
evaluation result of a lithium secondary battery to which a lithium
metal anode manufactured according to Examples 1 to 6 is applied.
FIG. 15B shows the results of analyzing the surface components of
the lithium metal anode prepared according to Example 1 and
Comparative Examples 1 to 4.
[0243] Table 1 also shows the results of evaluating the
charge-discharge lifetime based on 80% of the initial discharge
capacity.
TABLE-US-00001 TABLE 1 division Charge/discharge life (times)
Example 1 40 Example 2 21 Example 3 32 Example 4 19 Example 5 30
Example 6 32 Comparative Example 1 2 Comparative Example 2 2
Comparative Example 3 7 Compare to 4 4
[0244] Referring to FIGS. 15a and 15b and Table 1, it can be seen
that the lithium secondary battery to which the lithium metal anode
manufactured according to Examples 1 to 6 is applied is remarkably
superior compared to Comparative Examples 1 to 4.
[0245] Therefore, the results of Experimental Examples 1 to 3
indicate that the lithium metal anode manufactured by the method of
the present invention contains a coating layer containing a
Li--N--C--H--O based compound through control of plating solution
composition and process conditions. Also, it can be confirmed that
the lithium metal thin film layer is formed by uniformly stacking
lithium through the coating layer to suppress the growth of
dendrite and to have a dense microstructure.
[0246] Accordingly, when the lithium metal anode according to the
embodiments is applied to a lithium secondary battery, it can be
confirmed that the charge/discharge performance of the battery is
improved.
Experimental Example 4
[0247] Lithium metal foil with a purity of 99% and a thickness of
200 .mu.m was used as a lithium source, and a Cu foil with a
thickness of 10 .mu.m was used as a current collector, which is a
base material on which lithium is electrodeposited. The
electrolytic solution was prepared by dissolving LiFSI lithium salt
in 1,2-dimethoxyethane at a concentration of 1M and adding 5 wt %
of fluoroethylene carbonate based on the lithium salt. As the
insulating film, a cell guard 2400 used in a lithium ion battery
was used to laminate a current collector, an insulating film, and a
lithium source in this order, to carry it on the electrolytic
solution to be charged, and press both sides to the restraint plate
to apply pressure. Lithium was deposited on the surface of the
current collector by applying a current to the current collector
and the lithium source as the (-) and (+) electrodes, respectively,
using a power supply unit. The current density was in the range of
0.1 to 100 mA/cm.sup.2. The electrodeposition time was 2 minutes to
120 hours to prepare a lithium metal thin film having a thickness
of 5 .mu.m to 50 .mu.m.
[0248] FIG. 16 (a) shows the microstructure of the lithium metal
anode produced according to this Experimental Example. FIG. 6 (b)
shows the microstructure of a lithium metal anode produced by a
conventional electrodeposition method.
[0249] Referring to FIG. 16, it can be seen that the lithium metal
anode manufactured according to the present experimental example
has a dense microstructure without a dendrite. However, in the case
of a lithium metal anode manufactured by a conventional
electrodeposition method (FIG. 16b), lithium was found to have a
porous microstructure while growing in the form of a dendrite. That
is, the lithium metal anode manufactured by the method of
manufacturing a lithium metal anode according to this embodiment
can have a dense fine structure without a dendrite on its
surface.
[0250] FIG. 17 shows the surface composition of the lithium metal
anode prepared according to Experimental Example 4. In addition,
the surface composition of a lithium metal anode produced by a
conventional method such as laminating or PVD is shown in FIG. 18.
Referring to FIG. 18, in the case of a lithium metal anode
manufactured by a conventional method, it is produced by a method
of rolling or vapor deposition, and only oxygen and carbon
components are present on the surface.
[0251] However, with reference to FIG. 17, in the case of a lithium
metal electrode manufactured by the method according to an
embodiment of the present invention, a components of F, P, S, and
like, which originated from an in-situ generated surface protective
layer during a lithium electrodeposition process.
Experimental Example 5: Evaluation of Electrochemical
Characteristics
[0252] FIG. 19 shows the result of repeating the Li stripping/Li
plating by preparing a lithium metal anode prepared by the method
of Experimental Example 4 and a cell made of a combination of a Li
foil and a coin cell. FIG. 20 shows a result of repeating charge
and discharge by fabricating a coin cell in which a lithium metal
anode and a Li foil were combined by a conventional PVD method.
Comparing to FIGS. 19 and 20, it can be seen that the overvoltage
of the lithium metal anode manufactured by the conventional PVD
method takes a large from the beginning of the cell operation, and
the overvoltage tends to increase significantly with the lapse of
the cycle. However, it has been confirmed that the lithium metal
anode manufactured by the method according to an embodiment of the
present invention has a relatively low overvoltage and a stable
cycle characteristic.
Experimental Example 6: Evaluation of Charge/Discharge
Characteristics
[0253] A battery (coin full cell) was manufactured using the
lithium metal anode manufactured by the method of Experimental
Example 4 to evaluate charge-discharge characteristics. LCO
materials were used for the cathode material and the charge and
discharge characteristics of the lithium metal cathode manufactured
by the rolling (Comparative Example 5) and the deposition
(Comparative Example 6) processes were evaluated.
[0254] The charge-discharge characteristics and the results of
Experimental Example 4 and Comparative Examples 5 and 6 are shown
in FIG. 21. Referring to FIG. 21, it was confirmed that the lithium
metal anode manufactured by the method of the present invention had
excellent charge/discharge life characteristics as compared with
the comparative example.
[0255] As described above, in the method of manufacturing a lithium
metal anode according to an embodiment of the present invention, a
lithium metal anode (Li--Cu foil) can be formed by applying an
electroplating process which can use low-cost process equipment at
normal temperature and pressure. It has excellent economical
efficiency and commerciality compared with the conventional vacuum
deposition process. In addition, the method of manufacturing a
lithium metal anode according to an embodiment of the present
invention can easily control the thickness of a lithium film to a
range of several to several hundreds .mu.m through a change in an
electrodeposition process condition. Therefore, as the lithium
thickness becomes thinner, problems of the conventional rolling
process in which surface defects are increased can be solved.
[0256] The lithium metal anode manufactured in this manner can have
a dense microstructure without a dendrite on its surface, and the
protective layer is positioned to lower the polarization voltage,
thereby improving the charge-discharge efficiency (coulombic
efficiency) and suppressing the side reaction with the electrolyte.
Accordingly, the charge and discharge life can be improved.
[0257] It will be understood by those skilled in the art that
various changes in form and details may be made therein without
departing from the spirit and scope of the present invention as
defined by the following claims. It is therefore to be understood
that the above-described embodiments are illustrative in all
aspects and not restrictive.
DESCRIPTION OF SYMBOLS
[0258] 10: Lithium metal anode [0259] 11: Current collector [0260]
12: Lithium metal thin film layer [0261] 13: Coating layer [0262]
20: Lithium source [0263] 30: plating solution [0264] 40:
Insulating film [0265] 50: Restraint device [0266] 60: Power supply
[0267] 70: Cathode [0268] 80: Electrolyte [0269] 90: Separate
[0270] 95: Battery container [0271] 100: Lithium secondary
battery
* * * * *