U.S. patent application number 13/822383 was filed with the patent office on 2013-07-11 for negative active material, lithium secondary battery comprising the negative active material and manufacturing method thereof.
This patent application is currently assigned to KOREA ELECTRONICS TECHNOLOGY INSTITUTE. The applicant listed for this patent is Yong Nam Jo, Young Jun Kim, Min Sik Park. Invention is credited to Yong Nam Jo, Young Jun Kim, Min Sik Park.
Application Number | 20130177815 13/822383 |
Document ID | / |
Family ID | 46133839 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130177815 |
Kind Code |
A1 |
Kim; Young Jun ; et
al. |
July 11, 2013 |
NEGATIVE ACTIVE MATERIAL, LITHIUM SECONDARY BATTERY COMPRISING THE
NEGATIVE ACTIVE MATERIAL AND MANUFACTURING METHOD THEREOF
Abstract
Disclosed are an anode active material, a non-aqueous lithium
secondary battery, and a preparation method thereof. The surface of
a carbonaceous material is modified without using an electrolyte
additive, and the reactivity and structural stability of the
surface is improved, thereby obtaining long lifetime
characteristics without deteriorating charge/discharge efficiency
and rate characteristics when applied as an anode active material
of a non-aqueous lithium secondary battery. The anode active
material comprises a carbonaceous material, and a coating layer
formed on the surface of the carbonaceous material through hetero
atom substitution, wherein the hetero atom can be phosphorus (P) or
sulfur (S). A side reaction with an electrolyte on the surface of
the carbonaceous material is inhibited and the structural stability
of the surface is enhanced by forming a coating layer on the
surface of the carbonaceous material with a hetero atom such as
phosphorus (P) or sulfur (S).
Inventors: |
Kim; Young Jun; (Yongin-si,
KR) ; Jo; Yong Nam; (Seoul, KR) ; Park; Min
Sik; (Suwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Young Jun
Jo; Yong Nam
Park; Min Sik |
Yongin-si
Seoul
Suwon-si |
|
KR
KR
KR |
|
|
Assignee: |
KOREA ELECTRONICS TECHNOLOGY
INSTITUTE
Seongnam-si, Gyeonggi-do
KR
|
Family ID: |
46133839 |
Appl. No.: |
13/822383 |
Filed: |
August 19, 2011 |
PCT Filed: |
August 19, 2011 |
PCT NO: |
PCT/KR11/06110 |
371 Date: |
March 12, 2013 |
Current U.S.
Class: |
429/231.8 ;
427/113 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 4/133 20130101; H01M 4/366 20130101; H01M 4/0471 20130101 |
Class at
Publication: |
429/231.8 ;
427/113 |
International
Class: |
H01M 4/133 20060101
H01M004/133 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2010 |
KR |
10-2010-0091296 |
Aug 3, 2011 |
KR |
10-2011-0077357 |
Claims
1. An anode active material for use in a non-aqueous lithium
secondary battery, comprising: a carbonaceous material; and a
coating layer of hetero elements formed on the surface of the
carbonaceous material, wherein the hetero elements include
phosphorus (P).
2. The anode active material of claim 1, wherein the hetero
elements include sulfur (S).
3. The anode active material of claim 1, wherein the carbonaceous
material includes at least one of artificial graphite, natural
graphite, graphitized carbon fiber, graphitized mesocarbon
microbeads, petroleum coke, plastic resins, carbon fiber and
pyrocarbon.
4. The anode active material of claim 3, wherein the carbonaceous
material has L.sub.a(110)>10 nm and L.sub.c(002)>10 nm L,
wherein L.sub.a(110)=0.89.lamda./[B.sub.110cos(.theta..sub.110)]
and L.sub.s(002)=0.89.lamda./[B.sub.002cos(.theta..sub.002)],
wherein .lamda. is the wavelength of Cu K.alpha.(.lamda.=0.15418
nm) and B is a full width at half-maximum (FWHM) value with respect
to (110) or (002) peak according to Bragg diffraction angle.
5. The anode active material of claim 4, wherein the carbonaceous
material has 0.344 nm or less as d.sub.002 with respect to (002)
peak.
6. The anode active material of claim 3, wherein the carbonaceous
material has a specific surface area of less than 10 m.sup.2/g.
7. The anode active material of claim 3, wherein the carbonaceous
material has a degree of graphitization in the range of 0.4 to 1.0,
and the degree of graphitization is calculated according to (degree
of graphitization)=(3.44-d.sub.002)/(0.086).
8. The anode active material of claim 1, wherein the content of the
coating layer is less than 10 wt % with respect to the carbonaceous
material.
9. The anode active material of claim 8, wherein the coating layer
is formed uniformly on the overall surface of the carbonaceous
material or formed on part of the surface of the carbonaceous
material.
10. A lithium secondary battery including an anode formed of an
anode active material that includes a carbonaceous material and a
coating layer of hetero elements formed on the surface of the
carbonaceous material, wherein the hetero elements include
phosphorus (P) or sulfur (S).
11. A method for fabricating an anode active material for use in a
non-aqueous lithium secondary battery, the method comprising:
preparing a carbonaceous material and a hetero element material;
and forming a coating layer of hetero elements on the surface of
the carbonaceous material using the hetero element material,
wherein the hetero elements include phosphorus (P).
12. The method of claim 11, wherein the hetero elements further
include sulfur (S).
13. The method of claim 12, wherein the hetero element material
includes at least one of NH.sub.4PF.sub.6,
(NH.sub.4).sub.2PO.sub.4, NH.sub.4PO.sub.3,
(NH.sub.4).sub.2SO.sub.3, (NH.sub.4).sub.2SO.sub.4,
NH.sub.4SO.sub.4, and (NH.sub.4).sub.2S.sub.2O.sub.8.
14. The method of claim 13, wherein the forming of the coating
layer comprises: dissolving the hetero element material in a
solvent to form a solution; uniformly mixing the carbonaceous
material with the solution to form a mixture; vacuum-drying the
mixture; and performing heat treatment on the dried material
through thermal decomposition to form the coating layer based on
the hetero elements on the surface of the carbonaceous material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a non-aqueous lithium
secondary battery and a fabricating method thereof, and more
particularly, to an anode active material, a non-aqueous lithium
secondary battery including the anode active material, and a method
for fabricating the anode active material in which the surface of a
carbonaceous material used as the anode active material of the
lithium secondary battery is treated using hetero elements in order
to suppress side reaction of the carbonaceous material with an
electrolyte at the surface thereof and to enhance structural
stability, thereby improving lifespan characteristics and rate
characteristics of the non-aqueous lithium secondary battery.
BACKGROUND ART
[0002] As portable small electric/electronic devices are widely
propagated, new secondary batteries such as a nickel metal hydride
battery and a lithium secondary battery are actively being
developed.
[0003] The lithium secondary battery uses metal lithium as an anode
active material and a non-aqueous solvent as an electrolyte.
Lithium can generate a high voltage because it has considerable
ionization tendency, and thus a battery having a high energy
density using lithium is under development. The lithium secondary
battery using metal lithium as an anode active material has been
used as a next-generation battery for a long time.
[0004] However, the lithium secondary battery has a short life
cycle because lithium dendrites grow from the anode and penetrate
an insulating membrane as charging and discharging of the lithium
secondary battery are repeated, resulting in short-circuit with the
cathode, causing battery failure.
[0005] To solve the problem that the life cycle of the lithium
secondary battery is reduced due to anode deterioration, a method
of using a carbon-based material capable of
intercalating/deintercalating lithium ions instead of metal lithium
as an anode active material was proposed.
[0006] In a lithium secondary battery having an anode formed using
a carbonaceous material, the lithium ions are intercalated into
carbon according to reaction at the cathode during
charging/discharging. Electrons are transferred to a carbonaceous
material of the anode and thus carbon is negatively charged to
deintercalate the lithium ions from the cathode and intercalate the
lithium ions into the carbonaceous material of the anode during
charging, whereas the lithium ions are deintercalated from the
carbonaceous material of the anode and intercalated into the
cathode during discharging. Using this mechanism, precipitation of
metal lithium at the anode can be prevented to achieve a lithium
secondary battery having a considerably long life cycle.
[0007] The lithium secondary battery using a carbonaceous material
as an anode active material is called a lithium ion secondary
battery and has been widely propagated as a battery of portable
electronic/communication devices. However, when a carbonaceous
material is used as an anode active material, the charge/discharge
potential of lithium is lower than the stable range of a
conventional non-aqueous electrolyte, and thus decomposition of
electrolyte occurs during charging/discharging, causing low initial
charging/discharging efficiency of the current lithium secondary
battery using a carbonaceous material as an anode material, short
battery lifespan, and deterioration of rate characteristics.
Accordingly, methods for stabilizing the surface of a carbonaceous
anode active material using an electrolyte additive having a
decomposition potential higher than that of a carbonaceous
electrolyte, such as VC, FEC, etc. are proposed in order to
increase the lifespan of a non-aqueous lithium secondary battery
using a carbonaceous material.
[0008] However, the electrolyte additive cannot solve the problems
of rate characteristics and charging/discharging efficiency
deterioration although it increases the lifespan of the lithium
secondary battery.
DETAILED DESCRIPTION OF THE INVENTION
Technical Problems
[0009] An object of the present invention is to provide an anode
active material surface-treated using hetero elements, a
non-aqueous lithium secondary battery including the anode active
material, and a method for fabricating the anode active material by
reforming the surface of a carbonaceous material without using an
electrolyte additive so as to improve reactivity and structural
stability of the surface, thus improving battery lifespan without
deteriorating charging/discharging efficiency and rate
characteristics when the carbonaceous material is used as an anode
active material of the non-aqueous lithium secondary battery.
Technical Solutions
[0010] The objects of the present invention can be achieved by
providing an anode active material for use in a non-aqueous lithium
secondary battery, which includes a carbonaceous material, and a
coating layer of hetero elements formed on the surface of the
carbonaceous material, wherein the hetero elements include
phosphorus (P).
[0011] The hetero elements may include sulfur (S).
[0012] The carbonaceous material may include at least one of
artificial graphite, natural graphite, graphitized carbon fiber,
graphitized mesocarbon microbeads, petroleum coke, plastic resins,
carbon fiber and pyrocarbon.
[0013] The carbonaceous material may have L.sub.a(110)>10 nm and
L.sub.c(002)>10 nm L, wherein
L.sub.a(110)=0.89.lamda./[B.sub.110cos(.theta..sub.110)] and
L.sub.s(002)=0.89.lamda./[B.sub.002cos(.theta..sub.002)], wherein
.lamda. is the wavelength of Cu K.alpha.(.lamda.=0.15418 nm) and B
is a full width at half-maximum (FWHM) value with respect to (110)
or (002) peak according to Bragg diffraction angle.
[0014] The carbonaceous material may have 0.344 nm or less as
d.sub.002 with respect to (002) peak.
[0015] The carbonaceous material may have a specific surface area
of less than 10 m.sup.2/g.
[0016] The carbonaceous material may have a degree of
graphitization in the range of 0.4 to 1.0, and the degree of
graphitization is calculated according to (degree of
graphitization)=(3.44-d.sub.002)/(0.086).
[0017] The content of the coating layer may be less than 10 wt %
with respect to the carbonaceous material.
[0018] The coating layer may be formed uniformly on the overall
surface of the carbonaceous material or formed on part of the
surface of the carbonaceous material.
[0019] The present invention provides a lithium secondary battery
including an anode formed of the anode active material.
[0020] The present invention provides a method for fabricating an
anode active material for use in a non-aqueous lithium secondary
battery, the method includes preparing a carbonaceous material and
a hetero element material, and forming a coating layer of hetero
elements on the surface of the carbonaceous material using the
hetero element material, wherein the hetero elements include
phosphorus (P).
[0021] The hetero elements may further include sulfur (S).
[0022] The hetero element material may include at least one of
NH.sub.4PF.sub.6, (NH.sub.4).sub.2PO.sub.4, NH.sub.4PO.sub.3,
(NH.sub.4).sub.2SO.sub.3, (NH.sub.4).sub.2SO.sub.4,
NH.sub.4SO.sub.4, and (NH.sub.4).sub.2S.sub.2O.sub.8.
[0023] The forming of the coating layer may include dissolving the
hetero element material in a solvent to form a solution; uniformly
mixing the carbonaceous material with the solution to form a
mixture; vacuum-drying the mixture; and performing heat treatment
on the dried material through thermal decomposition to form the
coating layer based on the hetero elements on the surface of the
carbonaceous material.
Advantageous Effects
[0024] According to the present invention, a coating layer can be
formed on the surface of a carbonaceous material used as an anode
active material of a non-aqueous lithium secondary battery by using
hetero elements such as phosphorus (P) or sulfur (S), thereby
suppressing a side reaction of the carbonaceous material at the
surface thereof according to the coating layer formed on the
carbonaceous material and enhancing structural stability.
[0025] Furthermore, affinity of the anode active material with the
electrolyte can be improved so as to enhance battery lifespan and
rate characteristics of the non-aqueous lithium secondary
battery.
[0026] In addition, fabricating efficiency of the anode active
material can be improved according to a simple surface treatment
process.
DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is a flowchart illustrating a method for fabricating
an anode active material surface-treated with hetero elements for a
non-aqueous lithium secondary battery according to an embodiment of
the present invention.
[0028] FIG. 2 shows pictures of anode active materials according to
embodiments of the present invention and a comparative example.
[0029] FIG. 3 shows EDS (Energy Dispersive Spectroscopy) analysis
results regarding an anode active material according to a first
embodiment of the present invention.
[0030] FIG. 4 shows EDS analysis results regarding an anode active
material according to a second embodiment of the present
invention.
[0031] FIG. 5 shows an XPS (X-ray Photoelectron Spectroscopy)
analysis result regarding the anode active material according to
the first embodiment of the present invention.
[0032] FIG. 6 shows an XPS analysis result regarding the anode
active material according to the second embodiment of the present
invention.
[0033] FIG. 7 shows XRD (X-ray diffraction) analysis results
regarding the anode active materials according to the embodiments
of the present invention and the comparative example.
[0034] FIG. 8 is a graph showing lifespan characteristics of a
non-aqueous lithium secondary battery according to surface
treatment temperatures of the anode active materials according to
the embodiments of the present invention and the comparative
example.
[0035] FIG. 9 is a graph showing rate characteristics of
non-aqueous lithium secondary batteries according to the
embodiments of the present invention and the comparative
example.
MODE FOR CARRYING OUT THE INVENTION
[0036] In describing embodiments of the present invention, detailed
descriptions of constructions or processes known in the art may be
omitted to avoid obscuring appreciation of the invention by a
person of ordinary skill in the art with unnecessary detail
regarding such known constructions and functions.
[0037] Accordingly, the meaning of specific terms or words used in
the specification and claims should not be limited to the literal
or commonly employed sense, but should be construed or may be
different in accordance with the intention of a user or an operator
and customary usages. Therefore, the definition of the specific
terms or words should be based on the contents across the
specification. It should be understood, however, that there is no
intent to limit the invention to the particular forms disclosed,
but on the contrary, the invention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope
of the invention as defined by the claims.
[0038] Embodiments of the present invention will be described in
detail with reference to the attached drawings.
[0039] An anode active material of a non-aqueous lithium secondary
battery according to an embodiment of the present invention
includes a carbonaceous material and a coating layer of hetero
elements formed on the surface of the carbonaceous material. The
hetero elements include phosphorus (P) or sulfur (S).
[0040] The carbonaceous material may use at least one of amorphous
carbon materials such as artificial graphite, natural graphite,
graphitized carbon fiber, graphitized mesocarbon microbeads,
petroleum coke, plastic resins, carbon fiber, pyrocarbon, etc.
[0041] The following carbonaceous materials are preferably used in
order to stably form the coating layer of hetero elements on the
surface of the carbonaceous material and also to improve lifespan
characteristics and rate characteristics of the non-aqueous lithium
secondary battery employing the anode active material.
[0042] A carbonaceous material having L.sub.a(110)>10 nm and
L.sub.c(002)>10 nm L is preferably used. L.sub.a(110) and
L.sub.c(002) can be represented as
L.sub.a(110)=0.89.lamda./[B.sub.110cos(.theta..sub.110)] and
L.sub.c(002)=0.89.lamda./[B.sub.002cos(.theta..sub.002)]. Here,
.lamda. is the wavelength of Cu K.alpha.(.lamda.=0.15418 nm) and B
denotes a full width at half-maximum (FWHM) value with respect to
(110) or (002) peak according to Bragg diffraction angle. A
carbonaceous material having 0.344 nm or less as d.sub.002 with
respect to (002) peak is preferably used.
[0043] Furthermore, a carbonaceous material having a degree of
graphitization in the range of 0.4 to 1.0 is preferably used. Here,
the degree of graphitization can be calculated according to (degree
of graphitization)=(3.44-d.sub.002)/(0.086).
[0044] In addition, a carbonaceous material having a specific
surface area of 10 m.sup.2/g or less is preferably used.
[0045] The coating layer may be formed by heat-treating the surface
of the carbonaceous material through thermal decomposition using
10% or less by weight of a hetero element material respect to the
carbonaceous material. That is, components other than the hetero
elements are removed from the hetero element material during heat
treatment of the hetero element material through thermal
decomposition and the hetero elements forms the coating layer on
the surface of the carbonaceous material. The coating layer may be
formed uniformly on the overall surface of the carbonaceous
material or on only part of the surface of the carbonaceous
material according to the quantity of the heat-treated hetero
element material. The hetero element material may be present in
forms of various compounds including hetero elements. For example,
the hetero element material includes NH.sub.4PF.sub.6,
(NH.sub.4).sub.2PO.sub.4, NH.sub.4PO.sub.3,
(NH.sub.4).sub.2SO.sub.3, (NH.sub.4).sub.2SO.sub.4,
NH.sub.4SO.sub.4, (NH.sub.4).sub.2S.sub.2O.sub.8, etc. However, the
hetero element material is not limited thereto.
[0046] In this manner, the coating layer of hetero elements such as
phosphorus or sulfur is formed on the surface of the carbonaceous
material used as the anode active material of the non-aqueous
lithium secondary battery, and thus side reaction of the
carbonaceous material at the surface thereof can be suppressed and
structural stability can be enhanced. Furthermore, affinity of the
anode active material with the electrolyte can be improved so as to
enhance battery lifespan and rate characteristics of the
non-aqueous lithium secondary battery. In addition, production
efficiency of the anode active material can be improved through the
simple surface treatment process.
[0047] A method of forming the anode active material of the
non-aqueous lithium secondary battery, which is surface-treated
with the hetero element material, according to the present
invention will now be described with reference to FIG. 1. FIG. 1 is
a flowchart illustrating a method for fabricating an anode active
material surface-treated with hetero elements for a non-aqueous
lithium secondary battery according to an embodiment of the present
invention.
[0048] Referring to FIG. 1, the method of fabricating the anode
active material according to the present invention includes a step
(S11) of preparing the carbonaceous material and the hetero element
material and steps (S13 to S19) of forming the coating layer on the
surface of the carbonaceous material using the hetero element
material.
[0049] Specifically, the carbonaceous material and the hetero
element material are prepared in step S11. Here, a carbonaceous
material having a mean particle size of less than 15 .mu.m may be
used as the carbonaceous material. NH.sub.4PF.sub.6,
(NH.sub.4).sub.2PO.sub.4, NH.sub.4PO.sub.3,
(NH.sub.4).sub.2SO.sub.3, (NH.sub.4).sub.2SO.sub.4,
NH.sub.4SO.sub.4, (NH.sub.4).sub.2S.sub.2O.sub.8, etc. may be used
as the hetero element material.
[0050] The hetero element material is dissolved in deionized (DI)
water to form an aqueous solution in step S13. Here, while ID water
is used as a solvent in the present embodiment, an organic solvent
such as alcohol can be used.
[0051] The carbonaceous material is mixed with the aqueous solution
to form a mixture in step S15. Step S15 may be performed for about
15 minutes to uniformly mix the carbonaceous material with the
aqueous solution.
[0052] The mixture is vacuum-dried in step S17. Vacuum drying may
be performed at a temperature in the range of 80 to 150.degree. C.
for 1 to 5 hours.
[0053] The material dried in step S17 is heat-treated through
thermal decomposition in step S19 to form the anode active material
corresponding to the carbonaceous material surface-treaded with the
hetero element material according to the present invention. That
is, during the process of thermally treating the hetero element
material through thermal decomposition, components other than the
hetero elements are removed from the hetero element material and
the hetero elements forms the coating layer on the surface of the
carbonaceous material. Heat treatment in step S19 may be performed
in an inert gas atmosphere at a temperature in the range of 200 to
3000.degree. C. for 1 hour or longer. For example, heat treatment
can be performed in an Ar or N.sub.2 atmosphere at a heating rate
of 10.degree. C./min.
[0054] While the aqueous solution of the carbonaceous material and
the hetero element material is formed, vacuum-dried and
heat-treated to form the coating layer of the surface of the
carbonaceous material through steps S13 to S19 in the present
embodiment of the invention, the present invention is not limited
thereto. For example, it is possible to dissolve the hetero element
material in a solvent to form a solution, inject the solution into
the carbonaceous material, and then heat-treat the carbonaceous
material into which the solution has been injected to form the
coating layer on the surface of the carbonaceous material.
Otherwise, it is possible to mix powders of the carbonaceous
material and the hetero element material and heat-treat the mixed
powders to form the coating layer on the surface of the
carbonaceous material. That is, the coating layer is formed on the
surface of the carbonaceous material through a dry method. While
heat treatment is performed in an inert gas atmosphere in the
present embodiment, heat treatment may be carried out in a vacuum
or oxidizing atmosphere.
[0055] To evaluate the lifespan and rate characteristics of the
non-aqueous lithium secondary battery using the anode active
material according to the present invention, non-aqueous lithium
secondary batteries according to embodiments and a comparative
example were manufactured as follows. In the embodiments, a
carbonaceous material surface-treated with a hetero element
material is used as the anode active material. In the comparative
example, a carbonaceous material that is not surface-treated with a
hetero element material is used as the anode active material. The
non-aqueous lithium secondary batteries according to the
embodiments and the comparative example are manufactured in the
same manner, excepting the anode active materials, and thus
description is focused on the method of fabricating the non-aqueous
lithium secondary battery according to the embodiments.
[0056] A slurry is formed using 96 wt % of an anode active
material, 2 wt % of binding agent SBR and a thickener CMC, and
water as a solvent. This slurry is coated on Cu foil having a
thickness of 20 .mu.m, dried, consolidated using a press, and then
dried in vacuum at 120.degree. C. for 16 hours, to manufacture an
electrode in the form of a circular plate having a diameter of 12
mm. Punched lithium metal foil having a diameter of 14 mm is used
as a counter electrode, and a PE film is used as a membrane. A
mixed solution of LiPF.sub.6 of 1M and EC/DMC mixed in a ratio of
3:7 is used as an electrolyte. The electrolyte is impregnated into
the membrane, and the membrane is interposed between the electrode
and the counter electrode and then is set in a SUS case, achieving
a test cell for electrode evaluation, that is, the non-aqueous
lithium secondary battery.
[0057] The carbonaceous material can be at least one of amorphous
carbon materials such as artificial graphite, natural graphite,
graphitized carbon fiber, graphitized mesocarbon microbeads,
petroleum coke, plastic resins, carbon fiber, pyrocarbon, etc.
[0058] The hetero element material can be NH.sub.4PF.sub.6,
(NH.sub.4).sub.2PO.sub.4, NH.sub.4PO.sub.3,
(NH.sub.4).sub.2SO.sub.3, (NH.sub.4).sub.2SO.sub.4,
NH.sub.4SO.sub.4, or (NH.sub.4).sub.2S.sub.2O.sub.8. However, the
hetero element material is not limited thereto.
[0059] The carbonaceous material surface-treated with the hetero
element material can be used as an anode active material of a
non-aqueous lithium secondary battery using a carbonate
electrolyte. Furthermore, the carbonaceous anode active material
surface-treated with the hetero element material can be applied to
a lithium secondary battery having a non-aqueous electrolyte
operating in a voltage range of 0V to 5V.
[0060] An anode plate is manufactured by adding a conducting
material, a binding agent, a filler, a dispersing agent, an ion
conducting material, a pressure increasing agent, and one or more
generally used additive components to powder of the anode active
material surface-treated with the hetero element material as
necessary, to form a slurry or paste. The slurry or paste is coated
on an electrode support plate using doctor blade method, for
example, dried, and then pressed with a rolling roll, to
manufacture the anode plate.
[0061] Here, graphite, carbon black, acetylene black, Ketjen black,
carbon fiber, metal powder, etc. may be used as the conductive
material. PVdF, polyethylene, etc. may be used as the binding
agent. The anode plate (also referred to as a current collector)
may be formed of copper, nickel, stainless steel or aluminum foil
or sheet, or carbon fiber, etc.
[0062] The lithium secondary battery is manufactured using the
anode formed as above. The lithium secondary battery may have any
of coin, button, sheet, cylindrical, and rectangular shapes. The
anode, electrolyte and membrane of the lithium secondary battery
use those of conventional lithium secondary batteries.
[0063] A cathode active material includes a material reversibly
capable of intercalating and deintercalating lithium ions. A
lithium-transition metal oxide such as LiCoO.sub.2, LiNiO.sub.2,
LiMnO.sub.2, LiMn.sub.2O.sub.4, or
LiNi.sub.1-x-yCo.sub.xM.sub.yO.sub.2 (0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1, 0.ltoreq.x+y.ltoreq.1, M being metal such as
Al, Sr, Mg, La, etc.) may be used as the cathode active material.
Otherwise, one or more of the above cathode active materials can be
used. The above-mentioned cathode active material is exemplary and
the present invention is not limited thereto.
[0064] The electrolyte may use a non-aqueous electrolyte containing
lithium carbonate dissolved in an organic solvent, an inorganic
solid electrolyte, an inorganic solid electrolyte compound, etc.
However, the present invention is not limited thereto.
[0065] Here, carbonate, ester, ether or ketone may be used as a
solvent of the non-aqueous electrolyte. Dimethyl carbonate (DMC),
diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl
carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate
(EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene
carbonate (BC), etc. may be used as the carbonate. Butyrolactone
(BL), decanolide, valerolactone, mevalonolactone, caprolactone,
n-methyl acetate, n-ethyl acetate, n-propyl acetate, etc. may be
used as the ester. Dibutyl ether may be used as the ether.
Polymethylvinyl ketone may be used as the ketone. The non-aqueous
electrolyte according to the present invention is not limited to
non-aqueous organic solvents.
[0066] Examples of the lithium carbonate of the non-aqueous
electrolyte include one or more of LiPF.sub.6, LiBF.sub.4,
LiSbF.sub.6, LiAsF.sub.6, LiClO.sub.4, LiCF.sub.3SO.sub.3,
LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2,
LiAlO.sub.4, LiAlCl.sub.4,
LiN(C.sub.xF.sub.2x+1SO.sub.2)(C.sub.yF.sub.2x+1SO.sub.2) (x and y
being natural numbers) and LiSO.sub.3CF.sub.3, or a mixture
thereof.
[0067] A porous film formed from polyolefin such as PP or PE or a
porous material such as non-woven fabric may be used as the
membrane.
EMBODIMENTS AND COMPARATIVE EXAMPLE
[0068] In the comparative example, natural graphite having a mean
particle size of less than 15 .mu.m was used as the carbonaceous
material that is not surface-treated with the hetero element
material for the anode active material.
[0069] In the first embodiment, natural graphite having a mean
particle size of less than 15 .mu.m, which has been surface-treated
using NH.sub.4PF.sub.6 as the hetero element material in order to
use phosphorus (P) as the hetero elements, was used as the anode
active material.
[0070] In the embodiment, natural graphite having a mean particle
size of less than 15 .mu.m, which has been surface-treated using
(NH.sub.4).sub.2SO.sub.4 as the hetero element material in order to
use sulfur (S) as the hetero elements, was used as the anode active
material.
[0071] The anode active materials according to the first and second
embodiments were fabricated as follows. To introduce P and S to the
surface of natural graphite as a carbonaceous material, 3 wt % of
NH.sub.4PF.sub.6 and 3 wt % of (NH.sub.4).sub.2SO.sub.4 were
respectively dissolved in DI water, uniformly coated on the surface
of the natural graphite, and heat-treated at 800.degree. C., to
form anode active materials having P or S contained in the surface
thereof, which are used for a non-aqueous lithium secondary
battery.
[0072] Comparing morphologies of the anode active materials
according to the first and second embodiments and the comparative
example, no surface structure variation and no impurity generation
in the natural graphite were observed, as shown in FIG. 2.
[0073] It can be confirmed that P and S are uniformly distributed
on the surfaces of the natural graphite from EDS and XPS analysis
results regarding the anode active materials according to the first
and second embodiments, which are shown in FIGS. 3 and 4. FIGS. 3
and 4 show element mapping results of the surfaces of the natural
graphite, to which P and S have been introduced, which are obtained
through EDS analysis.
[0074] Referring to FIG. 3, 0.59 wt % of P was detected from the
natural graphite in the case of the anode active material according
to the first embodiment. Referring to FIG. 4, 0.28 wt % of S was
detected from the surface of the natural graphite in the case of
the anode active material according to the second embodiment.
[0075] Results of XPS analysis for analyzing the surface structures
of the anode active materials according to the first and second
embodiments are shown in FIGS. 5 and 6. Referring to FIG. 5, it can
be confirmed that P 2 p peak (131 to 135 eV) is formed on the
surface of the anode active material according to the first
embodiment. Referring to FIG. 6, it can be confirmed that S 2 p
peak (161 to 168 eV) is formed on the surface of the anode active
material according to the second embodiment. This means that P and
S existing on the surface of the natural graphite form specific
combinations with carbon of the natural graphite.
[0076] Results of XRD analysis for analyzing the anode active
materials according to the comparative example and the first and
second embodiments are shown in FIG. 7. Referring to FIG. 7,
impurities or second phases are not generated after introduction of
the hetero elements. L.sub.a(110) and L.sub.c(002) calculated on
the basis of the XRD results are listed in Table 1. It can be
confirmed from Table 1 that L.sub.a(110) is hardly varied and
L.sub.c(002) is reduced after the hetero elements is
introduced.
TABLE-US-00001 TABLE 1 L.sub.c(002) [nm] L.sub.a(aa0) [nm]
Comparative example 35.854 71.413 First embodiment 31.512 71.402
Second embodiment 32.268 71.422
[0077] Values of d.sub.002 and FWHM values of the anode active
materials according to the comparative example and the first and
second embodiments, obtained through the XRD data, are shown in
Table 2. Referring to Table 2, d.sub.002 hardly varies and FWHM
values increase after the hetero elements is introduced. This is
regarded as a result of substitution or doping of some of P or S
introduced to the surface of the natural graphite for the surface
of the natural graphite. Specific surface areas of the anode active
materials according to the comparative example and the first and
second embodiments were measured as 2.7845 m.sup.2/g, 2.7461
m.sup.2/g and 2.7199 m.sup.2/g, respectively.
TABLE-US-00002 TABLE 2 2.theta.(.degree.) FWHM*(.degree.) d**(nm)
Comparative example 26.474 0.225 0.3366(8) First embodiment 26.453
0.256 0.3369(5) Second embodiment 26.458 0.250 0.3368(4) *Full
Width at half maximum for (002) peak **Interlayer spacing for (002)
peak
[0078] The lifespan and rate characteristics of non-aqueous lithium
secondary batteries including the anode active materials according
to the comparative example and the first and second embodiments
were checked through the following test.
[0079] To check the influence of the type of the hetero element
material on the lifespan of the non-aqueous lithium secondary
battery, the following test was performed using non-aqueous lithium
secondary batteries to which the anode active materials according
to the comparative example and first and second embodiments are
applied. 3 cycles of charging/discharging of the non-aqueous
lithium secondary batteries to which the anode active materials
according to the comparative example and first and second
embodiments are applied were performed using current of 0.2 C (72
mA/g), and then 50 cycles of charging/discharging were carried out
using current of 0.5 C (180 mA/g). The test results are shown in
FIG. 8. As can be confirmed from FIG. 8, the non-aqueous lithium
secondary batteries having the anode active materials
surface-treated with the hetero element material according to the
first and second embodiments have a longer lifespan than that of
the comparative example.
[0080] To check the influence of the type of the hetero element
material on rate characteristics of the non-aqueous lithium
secondary batteries, the following test was performed using the
non-aqueous lithium secondary batteries to which the anode active
materials according to the comparative example of first and second
embodiments were applied. 1-cycle charging/discharging of the
non-aqueous lithium secondary batteries to which the anode active
materials according to the comparative example and first and second
embodiments were applied was performed using current of 0.2 C (72
mA/g). Then, charging is performed with fixed current of 0.5 C (180
mA/g) and discharging cycles are respectively performed for 3
seconds using 0.2 C (72 mA/g), 0.5 C (180 mA/g), 1 C (360 mA/g), 2
C (720 mA/g), 3 C (1080 mA/g) and 5 C (1800 mA/g). Subsequently, 2
cycles of charging/discharging are performed using 0.2 C (72 mA/g).
The test results are shown in FIG. 9. As can be confirmed from FIG.
9, rate characteristics are improved after surface treatment.
[0081] The above-described test results show that the coating layer
formed on the natural graphite by treating the surface of the
natural graphite using the hetero element material effectively
suppresses side reaction due to direct contact with the electrolyte
and enhance structural stability of the surface of the natural
graphite, thereby improving battery lifespan and output
characteristic of the non-aqueous lithium secondary battery to
which the anode active material surface-treated with the hetero
element material is applied.
[0082] The detailed description of the preferred embodiments of the
present invention has been given to enable those skilled in the art
to implement and practice the invention. Although the invention has
been described with reference to the preferred embodiments, those
skilled in the art will appreciate that various modifications and
variations can be made in the present invention without departing
from the spirit or scope of the invention described in the appended
claims.
* * * * *