U.S. patent application number 16/650743 was filed with the patent office on 2020-10-01 for negative electrode active material, negative electrode including the negative electrode active material, and secondary battery including the negative electrode.
This patent application is currently assigned to LG CHEM, LTD.. The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Jung Hyun CHOI, Rae Hwan JO, Dong Hyuk KIM, Eun Kyung KIM, Su Min LEE, Yong Ju LEE, Il Geun OH, Se Mi PARK.
Application Number | 20200313173 16/650743 |
Document ID | / |
Family ID | 1000004927181 |
Filed Date | 2020-10-01 |
United States Patent
Application |
20200313173 |
Kind Code |
A1 |
OH; Il Geun ; et
al. |
October 1, 2020 |
NEGATIVE ELECTRODE ACTIVE MATERIAL, NEGATIVE ELECTRODE INCLUDING
THE NEGATIVE ELECTRODE ACTIVE MATERIAL, AND SECONDARY BATTERY
INCLUDING THE NEGATIVE ELECTRODE
Abstract
A negative electrode active material which includes a core
including SiO.sub.x (0<x<2), a shell disposed on the core and
includes lithium silicate, and a coating layer disposed on the
shell and includes carbon nanotubes. Also, a method of preparing a
negative electrode active material as well as a negative electrode
and a battery including the same.
Inventors: |
OH; Il Geun; (Daejeon,
KR) ; KIM; Eun Kyung; (Daejeon, KR) ; LEE;
Yong Ju; (Daejeon, KR) ; JO; Rae Hwan;
(Daejeon, KR) ; LEE; Su Min; (Daejeon, KR)
; CHOI; Jung Hyun; (Daejeon, KR) ; KIM; Dong
Hyuk; (Daejeon, KR) ; PARK; Se Mi; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Assignee: |
LG CHEM, LTD.
Seoul
KR
|
Family ID: |
1000004927181 |
Appl. No.: |
16/650743 |
Filed: |
October 19, 2018 |
PCT Filed: |
October 19, 2018 |
PCT NO: |
PCT/KR2018/012455 |
371 Date: |
March 25, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/0525 20130101;
H01M 4/485 20130101; H01M 4/366 20130101; H01M 2004/027 20130101;
H01M 4/483 20130101; H01M 4/587 20130101; H01M 4/625 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 4/485 20060101 H01M004/485; H01M 4/48 20060101
H01M004/48; H01M 4/62 20060101 H01M004/62; H01M 4/587 20060101
H01M004/587; H01M 10/0525 20060101 H01M010/0525 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2017 |
KR |
10-2017-0135882 |
Claims
1. A negative electrode active material, comprising: a core
comprising SiO.sub.x, wherein 0<x<2; a shell disposed on the
core, wherein the shell comprises lithium silicate; and a coating
layer disposed on the shell, wherein the coating layer comprises
carbon nanotubes.
2. The negative electrode active material of claim 1, wherein the
shell has a thickness of 10 nm to 1 .mu.m.
3. The negative electrode active material of claim 1, wherein the
lithium silicate comprises at least one of Li.sub.2SiO.sub.3 and
Li.sub.2Si.sub.2O.sub.5.
4. The negative electrode active material of claim 1, wherein the
lithium silicate is present in an amount of 1 wt % to 45 wt % based
on a total weight of the negative electrode active material.
5. The negative electrode active material of claim 1, wherein the
coating layer has a thickness of 10 nm to 1 .mu.m.
6. The negative electrode active material of claim 1, wherein the
carbon nanotubes have a diameter of 1 nm to 150 nm, and the carbon
nanotubes have a length of 100 nm to 5 .mu.m.
7. The negative electrode active material of claim 1, wherein the
carbon nanotubes are present in an amount of 0.1 wt % to 20 wt %
based on a total weight of the negative electrode active
material.
8. A method of preparing a negative electrode active material, the
method comprising: mixing SiO.sub.x particles and Li.sub.2CO.sub.3,
wherein 0<x<2; and performing a heat treatment on the mixed
SiO.sub.x particles and Li.sub.2CO.sub.3 with a catalyst in a
H.sub.2 gas atmosphere.
9. The method of claim 8, wherein a weight ratio of the SiO.sub.x
particles to the Li.sub.2CO.sub.3 is in a range of 1:0.111 to
1:0.667.
10. The method of claim 8, wherein the heat treatment is performed
at a temperature range of 800.degree. C. to 1,200.degree. C.
11. The method of claim 8, wherein the catalyst comprises at least
one oxide selected from the group consisting of iron (Fe) and
calcium (Ca).
12. The method of claim 8, wherein the H.sub.2 gas atmosphere is
formed by introducing H.sub.2 into the mixed SiO.sub.x particles
and Li.sub.2CO.sub.3 at a flow rate of 500 sccm to 1,000 sccm for a
time period of 30 minutes to 2 hours.
13. The method of claim 8, further comprising: performing an acid
treatment on the heat-treated SiO.sub.x particles and
Li.sub.2CO.sub.3 after of performing the heat treatment.
14. A negative electrode comprising the negative electrode active
material of claim 1.
15. The negative electrode of claim 14, further comprising
graphite-based active material particles.
16. A secondary battery comprising: the negative electrode of claim
15; a positive electrode; a separator disposed between the positive
electrode and the negative electrode; and an electrolyte.
Description
TECHNICAL FIELD
Cross-Reference to Related Applications
[0001] This application claims the benefit of Korean Patent
Application No. 10-2017-0135882, filed on Oct. 19, 2017, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
TECHNICAL FIELD
[0002] The present invention relates to a negative electrode active
material, a negative electrode including the negative electrode
active material, and a secondary battery including the negative
electrode, wherein, specifically, the negative electrode active
material includes a core including SiO.sub.x(0<x<2); a shell
which is disposed on the core and includes lithium silicate; and a
coating layer which is disposed on the shell and includes carbon
nanotubes.
BACKGROUND ART
[0003] Requirements for the use of alternative energy or clean
energy have increased due to the rapid increase in the use of
fossil fuels, and, as a part of this trend, power generation and
electricity storage using an electrochemical reaction are the most
actively researched areas.
[0004] Currently, a typical example of an electrochemical device
using the electrochemical energy may be a secondary battery and
there is a trend that its usage area is expanding more and more. In
recent years, demand for secondary batteries as an energy source
has been significantly increased as technology development and
demand with respect to portable devices, such as portable
computers, mobile phones, and cameras, have increased. Among these
secondary batteries, lithium secondary batteries having high energy
density, i.e., high capacity, have been subjected to considerable
research and have been commercialized and widely used.
[0005] In general, a secondary battery is composed of a positive
electrode, a negative electrode, an electrolyte, and a separator.
The negative electrode includes a negative electrode active
material in which lithium ions from the positive electrode are
intercalated and deintercalated, and silicon-based particles having
high discharge capacity may be used as the negative electrode
active material. However, the silicon-based particle, such as
SiO.sub.x (0.ltoreq.x<2), has limitations in that it has low
initial efficiency, life characteristics are not excellent, and its
volume is excessively changed during charge and discharge.
[0006] Typically, techniques for forming a coating layer on a
surface of a silicon-based particle have been used to address this
limitation. For example, a technique of forming a carbon coating
layer including amorphous carbon on the surface of the
silicon-based particle is being used (Korean Patent Application
Laid-open Publication No. 10-2015-0112746). However, since it is
insufficient to secure a conductive path only by the carbon coating
layer including amorphous carbon, an effect of improving initial
efficiency and life characteristics is not significant. Also, since
a separate process for forming the carbon coating layer is
required, there is a limitation in that a preparation process may
not be simplified.
[0007] Thus, there is a need for a negative electrode active
material capable of further improving the initial efficiency and
life characteristics and a method of preparing a negative electrode
active material by which the preparation process may be
simplified.
PRIOR ART DOCUMENT
Patent Document
[0008] Korean Patent Application Laid-open Publication No.
10-2015-0112746
DISCLOSURE OF THE INVENTION
Technical Problem
[0009] An aspect of the present invention provides a negative
electrode active material capable of improving initial efficiency
and life characteristics, a negative electrode including the same,
a secondary battery including the negative electrode, and a method
of preparing a negative electrode active material by which a
preparation process may be simplified.
Technical Solution
[0010] According to an aspect of the present invention, there is
provided a negative electrode active material which includes: a
core including SiO.sub.x(0<x<2); a shell which is disposed on
the core and includes lithium silicate; and a coating layer which
is disposed on the shell and includes carbon nanotubes.
[0011] According to another aspect of the present invention, there
is provided a negative electrode including the negative electrode
active material and a secondary battery including the negative
electrode.
[0012] According to another aspect of the present invention, there
is provided a method of preparing a negative electrode active
material which includes: mixing SiO.sub.x(0<x<2) and
Li.sub.2CO.sub.3; and performing a heat treatment on the mixed
SiO.sub.x(0<x<2) and Li.sub.2CO.sub.3 with a catalyst in a
H.sub.2 gas atmosphere.
Advantageous Effects
[0013] According to the present invention, since a negative
electrode active material includes lithium silicate, initial
efficiency and capacity of a battery may be improved. Also, since
the negative electrode active material includes carbon nanotubes,
the initial efficiency and life characteristics of the battery may
be improved and excessive volume expansion of a core during charge
and discharge of the battery may be controlled. Since both of the
lithium silicate and the carbon nanotubes may be formed in the
negative electrode active material during the preparation of the
negative electrode active material, a process of preparing the
negative electrode active material may be simplified.
MODE FOR CARRYING OUT THE INVENTION
[0014] Hereinafter, the present invention will be described in more
detail to allow for a clearer understanding of the present
invention.
[0015] It will be understood that words or terms used in the
specification and claims shall not be interpreted as the meaning
defined in commonly used dictionaries. It will be further
understood that the words or terms should be interpreted as having
a meaning that is consistent with their meaning in the context of
the relevant art and the technical idea of the invention, based on
the principle that an inventor may properly define the meaning of
the words or terms to best explain the invention.
[0016] The terminology used herein is for the purpose of describing
particular example embodiments only and is not intended to be
limiting of the present invention. In the specification, the terms
of a singular form may include plural forms unless referred to the
contrary.
[0017] It will be further understood that the terms "include,"
"comprise," or "have" when used in this specification, specify the
presence of stated features, numbers, steps, elements, or
combinations thereof, but do not preclude the presence or addition
of one or more other features, numbers, steps, elements, or
combinations thereof.
[0018] A negative electrode active material according to an
embodiment of the present invention may include a core including
SiO.sub.x(0<x<2); a shell which is disposed on the core and
includes lithium silicate; and a coating layer which is disposed on
the shell and includes carbon nanotubes.
[0019] The core may include SiO.sub.x(0<x<2), and,
specifically, may include SiO.sub.x(0<x.ltoreq.1). Since the
core includes SiO.sub.x(0<x<2), discharge capacity of a
secondary battery may be increased.
[0020] The core may have an average particle diameter (D.sub.50) of
1 .mu.m to 30 .mu.m, particularly 3 .mu.m to 20 .mu.m, and more
particularly 4 .mu.m to 7 .mu.m. In a case in which the average
particle diameter satisfies the above range, since a path necessary
for diffusion of lithium ions is secured, electrode resistance is
reduced and volume expansion of the electrode may be controlled. In
the present specification, the average particle diameter (D.sub.50)
may be defined as a particle diameter at 50% in the cumulative
particle diameter distribution. The average particle diameter
(D.sub.50), for example, may be measured by using a laser
diffraction method. The laser diffraction method may generally
measure a particle diameter ranging from a submicron level to a few
mm and may obtain highly repeatable and high-resolution
results.
[0021] The shell may be disposed on the core. Specifically, the
shell may cover at least a portion of a surface of the core. More
specifically, the shell may cover the entire surface of the
core.
[0022] The shell may include lithium silicate, and, specifically,
the shell may include lithium silicate and SiO.sub.x(0<x<2).
The SiO.sub.x(0<x<2) of the shell may be the same as the
SiO.sub.x(0<x<2) of the core, and may specifically be
SiO.sub.x(0<x.ltoreq.1), for example, SiO.
[0023] The lithium silicate may include at least one of
Li.sub.2SiO.sub.3 and Li.sub.2Si.sub.2O.sub.5. The lithium silicate
may be formed by reaction of Li.sub.2CO.sub.3 with the
SiO.sub.x(0<x<2) of the core or the shell. Since an amount of
SiO.sub.2 initially acting irreversibly may be reduced while the
lithium silicate is formed, initial efficiency and capacity of the
battery may be improved.
[0024] The lithium silicate may be included in an amount of 1 wt %
to 45 wt %, particularly 1 wt % to 20 wt %, and more particularly 1
wt % to 12 wt % based on a total weight of the negative electrode
active material. In a case in which the amount of the lithium
silicate satisfies the above range, the initial efficiency and
capacity of the battery may be improved.
[0025] The shell may have a thickness of 10 nm to 1 .mu.m,
particularly 10 nm to 400 nm, and more particularly 50 nm to 350
nm. In a case in which the thickness satisfies the above range,
since the path necessary for the diffusion of lithium ions is
secured, the electrode resistance is reduced and the volume
expansion of the electrode may be controlled.
[0026] The coating layer may be disposed on the shell.
Specifically, the coating layer may cover at least a portion of a
surface of the shell. More specifically, the coating layer may
cover the entire surface of the shell.
[0027] The coating layer may include carbon nanotubes.
[0028] Since a conductive path of the negative electrode active
material may be secured by the carbon nanotubes, life
characteristics of the secondary battery may be improved. The
carbon nanotubes may be formed by reaction of H.sub.2 gas with
CO.sub.2 generated during the formation of the lithium
silicate.
[0029] The carbon nanotubes may have a diameter of 1 nm to 150 nm,
particularly 1 nm to 100 nm, and more particularly 1 nm to 50 nm.
The carbon nanotubes may have a length of 100 nm to 5 .mu.m,
particularly 100 nm to 3 .mu.m, and more particularly 100 nm to 1
.mu.m. In a case in which the diameter or length of the carbon
nanotubes is satisfied, since the conductive path may be secured,
the initial efficiency and life characteristics may be improved.
The carbon nanotubes are formed by reaction of Li.sub.2CO.sub.3 and
the core through a heat treatment in the presence of a catalyst
during the preparation of the negative electrode active material,
wherein the carbon nanotubes formed by such a method may have the
above-described diameter and length.
[0030] The carbon nanotubes may be included in an amount of 0.1 wt
% to 20 wt %, particularly 0.1 wt % to 15 wt %, and more
particularly 0.1 wt % to 13 wt % based on the total weight of the
negative electrode active material. In a case in which the amount
of the carbon nanotubes satisfies the above range, since the
conductive path may be sufficiently secured, the initial efficiency
and life characteristics may be improved and excessive volume
expansion of the core during charge and discharge may be
controlled.
[0031] The coating layer may have a thickness of 10 nm to 1 .mu.m,
particularly 10 nm to 500 nm, and more particularly 10 nm to 300
nm. In a case in which the thickness satisfies the above range, a
reduction in capacity due to the carbon nanotubes may be minimized
while electrical conductivity is improved.
[0032] A negative electrode according to another embodiment of the
present invention may include a negative electrode active material,
and, herein, the negative electrode active material is the same as
the negative electrode active material of the above-described
embodiments. Specifically, the negative electrode may include a
current collector and a negative electrode active material layer
disposed on the current collector. The negative electrode active
material layer may include the negative electrode active material.
Furthermore, the negative electrode active material layer may
further include a binder and/or a conductive agent.
[0033] The current collector is not particularly limited as long as
it has conductivity without causing adverse chemical changes in the
battery. For example, copper, stainless steel, aluminum, nickel,
titanium, fired carbon, or aluminum or stainless steel that is
surface-treated with one of carbon, nickel, titanium, silver, or
the like may be used as the current collector. Specifically, a
transition metal that adsorbs carbon well, such as copper or
nickel, may be used as the current collector. The current collector
may have a thickness of 6 .mu.m to 20 .mu.m, but the thickness of
the current collector is not limited thereto.
[0034] The binder may include at least one selected from the group
consisting of a polyvinylidene fluoride-hexafluoropropylene
copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF),
polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol,
carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose,
regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,
polyethylene, polypropylene, polyacrylate, an
ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, a
styrene-butadiene rubber (SBR), a fluorine rubber, polyacrylic
acid, and polymers in which hydrogen thereof is substituted with
lithium (Li), sodium (Na), or calcium (Ca), and may also include
various copolymers thereof.
[0035] The conductive agent is not particularly limited as long as
it has conductivity without causing adverse chemical changes in the
battery, and, conductive materials, for example, graphite such as
natural graphite and artificial graphite; carbon black such as
acetylene black, Ketjen black, channel black, furnace black, lamp
black, and thermal black; conductive fibers such as carbon fibers
or metal fibers; conductive tubes such as carbon nanotubes; metal
powder such as fluorocarbon powder, aluminum powder, and nickel
powder; conductive whiskers such as zinc oxide whiskers and
potassium titanate whiskers; conductive metal oxide such as
titanium oxide; or polyphenylene derivatives, may be used.
[0036] A secondary battery according to another embodiment of the
present invention may include a negative electrode, a positive
electrode, a separator disposed between the positive electrode and
the negative electrode, and an electrolyte, and the negative
electrode is the same as the above-described negative electrode.
Since the negative electrode has been described above, detailed
descriptions thereof will be omitted.
[0037] The positive electrode may include a positive electrode
collector and a positive electrode active material layer which is
formed on the positive electrode collector and includes a positive
electrode active material.
[0038] In the positive electrode, the positive electrode collector
is not particularly limited as long as it has conductivity without
causing adverse chemical changes in the batteries, and, for
example, stainless steel, aluminum, nickel, titanium, fired carbon,
or aluminum or stainless steel that is surface-treated with one of
carbon, nickel, titanium, or silver may be used. Also, the positive
electrode collector may typically have a thickness of 3 .mu.m to
500 .mu.m and may have a surface with fine roughness to improve
adhesion to the positive electrode active material. The positive
electrode collector may be used in various shapes, for example, a
film, a sheet, a foil, a net, a porous body, a foam body, a
non-woven fabric body, and the like.
[0039] The positive electrode active material may be a typically
used positive electrode active material. Specifically, the positive
electrode active material may include a layered compound, such as
lithium cobalt oxide (LiCoO.sub.2) or lithium nickel oxide
(LiNiO.sub.2), or a compound substituted with one or more
transition metals; lithium iron oxides such as LiFe.sub.3O.sub.4;
lithium manganese oxides such as Li.sub.1+c1Mn.sub.2-c1O.sub.4
(0.ltoreq.c1.ltoreq.0.33), LiMnO.sub.3, LiMn.sub.2O.sub.3, and
LiMnO.sub.2; lithium copper oxide (Li.sub.2CuO.sub.2); vanadium
oxides such as LiV.sub.3O.sub.8, V.sub.2O.sub.5, and
Cu.sub.2V.sub.2O.sub.7; nickel (Ni)-site type lithium nickel oxide
expressed by a chemical formula of LiNi.sub.1-c2M.sub.c2O.sub.2
(where M is at least one selected from the group consisting of
cobalt (Co), manganese (Mn), aluminum (Al), copper (Cu), iron (Fe),
magnesium (Mg), boron (B), and gallium (Ga), and c2 satisfies
0.01.ltoreq.c.ltoreq.20.3); lithium manganese composite oxide
expressed by a chemical formula of LiMn.sub.2-c3M.sub.c3O.sub.2
(where M is at least one selected from the group consisting of Co,
Ni, Fe, chromium (Cr), zinc (Zn), and tantalum (Ta), and c3
satisfies 0.01.ltoreq.c.ltoreq.30.1) or Li.sub.2Mn.sub.3MO.sub.8
(where M is at least one selected from the group consisting of Fe,
Co, Ni, Cu, and Zn); and LiMn.sub.2O.sub.4 having a part of Li
being substituted with alkaline earth metal ions, but the positive
electrode active material is not limited thereto. The positive
electrode may be Li-metal.
[0040] The positive electrode active material layer may include a
positive electrode conductive agent and a positive electrode binder
as well as the above-described positive electrode active
material.
[0041] In this case, the positive electrode conductive agent is
used for providing conductivity to the electrode, wherein any
conductive agent may be used without particular limitation as long
as it has electronic conductivity without causing adverse chemical
changes in the battery. Specific examples of the positive electrode
conductive agent may be graphite such as natural graphite and
artificial graphite; a carbon-based material such as carbon black,
acetylene black, Ketjen black, channel black, furnace black, lamp
black, thermal black, and carbon fibers; metal powder or metal
fiber of such as copper, nickel, aluminum, and silver; conductive
whiskers such as zinc oxide whiskers and potassium titanate
whiskers; conductive metal oxide such as titanium oxide; or
conductive polymers such as polyphenylene derivatives, and one
alone or a mixture of two or more thereof may be used.
[0042] Also, the positive electrode binder functions to improve
binding between positive electrode active material particles and
adhesion between the positive electrode active material and the
positive electrode collector. Specific examples of the positive
electrode binder may be polyvinylidene fluoride (PVDF), a
polyvinylidene fluoride-hexafluoropropylene copolymer
(PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl
cellulose (CMC), starch, hydroxypropyl cellulose, regenerated
cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene,
polypropylene, an ethylene-propylene-diene polymer (EPDM), a
sulfonated EPDM, a styrene-butadiene rubber (SBR), a fluoro rubber,
or various copolymers thereof, and one alone or a mixture of two or
more thereof may be used.
[0043] The separator separates the negative electrode and the
positive electrode and provides a movement path of lithium ions,
wherein any separator may be used as the separator without
particular limitation as long as it is typically used in a
secondary battery, and particularly, a separator having high
moisture-retention ability for an electrolyte as well as low
resistance to the transfer of electrolyte ions may be used.
Specifically, a porous polymer film, for example, a porous polymer
film prepared from a polyolefin-based polymer, such as an ethylene
homopolymer, a propylene homopolymer, an ethylene/butene copolymer,
an ethylene/hexene copolymer, and an ethylene/methacrylate
copolymer, or a laminated structure having two or more layers
thereof may be used. Also, a typical porous nonwoven fabric, for
example, a nonwoven fabric formed of high melting point glass
fibers or polyethylene terephthalate fibers may be used.
Furthermore, a coated separator including a ceramic component or a
polymer component may be used to secure heat resistance or
mechanical strength, and the separator having a single layer or
multilayer structure may be selectively used.
[0044] The electrolyte may include an organic liquid electrolyte,
an inorganic liquid electrolyte, a solid polymer electrolyte, a
gel-type polymer electrolyte, a solid inorganic electrolyte, or a
molten-type inorganic electrolyte which may be used in the
preparation of the lithium secondary battery, but the present
invention is not limited thereto.
[0045] Specifically, the electrolyte may include a non-aqueous
organic solvent and a metal salt.
[0046] Examples of the non-aqueous organic solvent may be aprotic
organic solvents, such as N-methyl-2-pyrrolidone, propylene
carbonate, ethylene carbonate, butylene carbonate, dimethyl
carbonate, diethyl carbonate, .gamma.-butyrolactone, 1,2-dimethoxy
ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl
sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane,
acetonitrile, nitromethane, methyl formate, methyl acetate,
phosphate triester, trimethoxy methane, a dioxolane derivative,
sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, a
propylene carbonate derivative, a tetrahydrofuran derivative,
ether, methyl propionate, and ethyl propionate.
[0047] In particular, ethylene carbonate and propylene carbonate,
ring-type carbonates among the carbonate-based organic solvents,
well dissociate a lithium salt in the electrolyte solution due to
high dielectric constants as high-viscosity organic solvents, and
thus, the ring-type carbonate may be preferably used. Since an
electrolyte solution having high electrical conductivity may be
prepared when the ring-type carbonate is mixed with low-viscosity,
low-dielectric constant linear carbonate, such as dimethyl
carbonate and diethyl carbonate, in an appropriate ratio, such a
combined use may be more preferably used.
[0048] A lithium salt may be used as the metal salt, and the
lithium salt is material that is readily soluble in the non aqueous
electrolyte solution, wherein, for example, any one selected from
the group consisting of F.sup.-, Cl.sup.-, I.sup.-, NO.sub.3.sup.-,
N(CN).sub.2.sup.-, BF.sub.4.sup.-, ClO.sub.4.sup.-, PF.sub.6.sup.-,
(CF.sub.3).sub.2PF.sub.4.sup.-, (CF.sub.3).sub.3PF.sub.3.sup.-,
(CF.sub.3).sub.4PF.sub.2.sup.-, (CF.sub.3).sub.5PF.sup.-,
(CF.sub.3).sub.6P.sup.-, CF.sub.3SO.sub.3.sup.-,
CF.sub.3CF.sub.2SO.sub.3.sup.-, (CF.sub.3SO.sub.2).sub.2N.sup.-,
(FSO.sub.2).sub.2N.sup.-, CF.sub.3CF.sub.2(CF.sub.3).sub.2CO.sup.-,
(CF.sub.3SO.sub.2).sub.2CH.sup.-, (SF.sub.5).sub.3C.sup.-,
(CF.sub.3SO.sub.2).sub.3C.sup.-,
CF.sub.3(CF.sub.2).sub.7SO.sub.3.sup.-, CF.sub.3CO.sub.2.sup.-,
CH.sub.3CO.sub.2.sup.-, SCN.sup.-, and
(CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.- may be used as an anion of
the lithium salt.
[0049] At least one additive, for example, a haloalkylene
carbonate-based compound such as difluoroethylene carbonate,
pyridine, triethylphosphite, triethanolamine, cyclic ether,
ethylenediamine, n-glyme, hexaphosphoric triamide, a nitrobenzene
derivative, sulfur, a quinone imine dye, N-substituted
oxazolidinone, N,N-substituted imidazolidine, ethylene glycol
dialkyl ether, an ammonium salt, pyrrole, 2-methoxy ethanol, or
aluminum trichloride, may be further included in the electrolyte in
addition to the above-described electrolyte components for the
purpose of improving life characteristics of the battery,
preventing a decrease in battery capacity, and improving discharge
capacity of the battery.
[0050] A negative electrode according to another embodiment of the
present invention is similar to the negative electrode of the
above-described embodiment, but there is a difference in that the
negative electrode further includes graphite-based active material
particles. The graphite-based active material particles may be used
by being mixed with the active material particles of the
above-described embodiment which are composed of the core, the
shell, and the coating layer. As a result, charge/discharge
characteristics of the battery may be improved. The graphite-based
active material particles may include at least one selected from
the group consisting of artificial graphite, natural graphite,
graphitized carbon fibers, and graphitized mesocarbon
microbeads.
[0051] According to another embodiment of the present invention, a
battery module including the secondary battery as a unit cell and a
battery pack including the battery module are provided. Since the
battery module and the battery pack include the secondary battery
having high capacity, high rate capability, and high cycle
characteristics, the battery module and the battery pack may be
used as a power source of a medium and large sized device selected
from the group consisting of an electric vehicle, a hybrid electric
vehicle, a plug-in hybrid electric vehicle, and a power storage
system.
[0052] A method of preparing a negative electrode active material
according to another embodiment of the present invention may
include: mixing SiO.sub.x(0<x<2) particles and
Li.sub.2CO.sub.3; and performing a heat treatment on the mixed
SiO.sub.x(0<x<2) particles and Li.sub.2CO.sub.3 with a
catalyst in a H.sub.2 gas atmosphere.
[0053] In the mixing, the SiO.sub.x(0<x<2) particles may have
an average particle diameter (D.sub.50) of 3 .mu.m to 20 .mu.m, for
example, 4 .mu.m to 7 .mu.m.
[0054] The Li.sub.2CO.sub.3 may have an average particle diameter
(D.sub.50) of 100 nm to 5 .mu.m, for example, 100 nm to 1 .mu.m. In
a case in which the average particle diameter satisfies the above
range, since reactivity of Li.sub.2CO.sub.3 may be improved, an
amount of unreacted Li.sub.2CO.sub.3 may be minimized, and thus,
the desired amount of carbon nanotubes may be obtained.
[0055] A weight ratio of the SiO.sub.x(0<x<2) particles to
the Li.sub.2CO.sub.3 may be in a range of 1:0.111 to 1:0.667,
particularly 1:0.25 to 1:0.667, and more particularly 1:0.429 to
1:0.667. In a case in which the weight ratio satisfies the above
range, since SiO.sub.2 of the SiO.sub.x(0<x<2) particles may
be sufficiently reduced, the initial efficiency of the battery may
be improved, and the life characteristics of the secondary battery
may be improved because the amount of the carbon nanotubes formed
from the Li.sub.2CO.sub.3 is sufficient.
[0056] The performing of the heat treatment may include applying
heat under specific conditions after the mixed
SiO.sub.x(0<x<2) particles and Li.sub.2CO.sub.3 are
introduced into a reaction furnace.
[0057] The performing of the heat treatment may be performed in a
state in which the catalyst is mixed with the mixed
SiO.sub.x(0<x<2) particles and Li.sub.2CO.sub.3. The catalyst
plays a role in forming a deposit for forming carbon nanotubes from
Li.sub.2CO.sub.3. The catalyst may include at least one oxide
selected from the group consisting of Fe and Ca. Since both of the
lithium silicate and the carbon nanotubes may be formed in the
negative electrode active material by the heat treatment, the
process of preparing the negative electrode active material may be
simplified.
[0058] The H.sub.2 gas plays a role in supplying hydrogen
constituting the carbon nanotubes. The H.sub.2 gas may be
introduced into the reaction furnace. For the H.sub.2 gas
atmosphere, H.sub.2 may be introduced into the mixed
SiO.sub.x(0<x<2) and Li.sub.2CO.sub.3 at a flow rate of 500
sccm to 1,000 sccm for a time period of 30 minutes to 2 hours.
[0059] A temperature of the heat treatment may be in a range of
800.degree. C. to 1,200.degree. C., particularly 850.degree. C. to
1,000.degree. C., and more particularly 850.degree. C. to
950.degree. C. In a case in which the heat treatment temperature
satisfies the above range, a phenomenon, in which the carbon
nanotubes include side chain branches, may be suppressed.
[0060] The method of preparing a negative electrode active material
may further include performing an acid treatment on the
heat-treated SiO.sub.x(0<x<2) particles and Li.sub.2CO.sub.3
after the heat treatment. Specifically, the acid treatment may
include stirring of the heat-treated SiO.sub.x(0<x<2)
particles in 10 M to 12 M HCl for 10 minutes to 1 hour, but the
present invention is not limited thereto. At least a portion of the
lithium silicate and unreacted Li.sub.2CO.sub.3 may be removed by
the acid treatment. Specifically, at least a portion of
Li.sub.4SiO.sub.4, particularly, the entire Li.sub.4SiO.sub.4 of
the lithium silicate may be removed.
[0061] Hereinafter, preferred examples will be provided for better
understanding of the present invention. It will be apparent to
those skilled in the art that these examples are only provided to
illustrate the present invention and various modifications and
alterations are possible within the scope and technical spirit of
the present invention. Such modifications and alterations fall
within the scope of claims included herein.
EXAMPLE AND COMPARATIVE EXAMPLES
Example 1: Preparation of Battery
[0062] (1) Preparation of Negative Electrode Active Material
[0063] 1) Preparation of Mixture of SiO.sub.x(0<x<2)
Particles and Li.sub.2CO.sub.3
[0064] 6 g of SiO particles having an average particle diameter
(D.sub.50) of 5 .mu.m and 4 g of Li.sub.2CO.sub.3 having an average
particle diameter (D.sub.50) of 1 .mu.m were stirred for 10 minutes
by using a ball mill to prepare a mixture.
[0065] 2) Heat Treatment Process
[0066] 3 g of the mixture and 0.3 g of Fe/CaO (iron oxide and
calcium oxide), as a catalyst, were mixed and then introduced into
a reaction furnace, a temperature of the reaction furnace was set
to 900.degree. C. while H.sub.2 gas was introduced into the
reaction furnace at a flow rate of 500 sccm, and the mixture was
heat-treated for 3 hours. A material obtained after the heat
treatment was stirred in 10 M HCl for 30 minutes and then filtered
to prepare a negative electrode active material of Example 1. The
results of checking the prepared negative electrode active material
by a particle size analyzer, a transmission electron microscope
(TEM), inductively coupled plasma-emission spectrometry (ICP), and
thermogravimetric analysis are presented in Table 1.
[0067] (2) Preparation of Negative Electrode
[0068] The prepared negative electrode active material, graphite,
carbon black as a conductive agent, and carboxylmethyl cellulose
(CMC) and styrene butadiene rubber (SBR), as a binder, were mixed
in a weight ratio of 4.8:91:1:1.7:1.5 to prepare 5 g of a mixture.
A negative electrode slurry was prepared by adding 28.9 g of
distilled water to the mixture. A 20 .mu.m thick copper (Cu) thin
film, as a negative electrode collector, was coated with the
negative electrode slurry and dried. In this case, a temperature of
circulating air was 60.degree. C. Subsequently, the coated negative
electrode collector was roll-pressed, dried in a vacuum oven at
130.degree. C. for 12 hours, and then punched into a circle having
an area of 1.4875 cm.sup.2 to prepare a negative electrode.
[0069] (3) Preparation of Secondary Battery
[0070] The prepared negative electrode was used and a lithium
(Li)-metal thin film cut into a circle of area 1.7671 cm.sup.2 was
used as a positive electrode. A porous polyethylene separator was
disposed between the positive electrode and the negative electrode,
and a lithium coin half-cell was prepared by injecting an
electrolyte solution in which 0.5 wt % vinylene carbonate was
dissolved and 1 M LiPF.sub.6 was dissolved in a mixed solution in
which a mixing volume ratio of ethyl methyl carbonate (EMC) to
ethylene carbonate (EC) was 7:3.
Example 2: Preparation of Battery
[0071] A secondary battery was prepared in the same manner as in
Example 1 except that 5 g of the SiO particles and 5 g of
Li.sub.2CO.sub.3 were used in the preparing of the mixture of the
SiO.sub.x(0<x<2) particles and Li.sub.2CO.sub.3 of Example
1.
Comparative Example 1: Preparation of Battery
[0072] 3 g of SiO particles having an average particle diameter
(D.sub.50) of 5 .mu.m and 0.3 g of Fe/CaO (iron oxide and calcium
oxide), as a catalyst, were mixed and then disposed in a chamber,
and a heat of 900.degree. C. was applied for 3 hours while CO.sub.2
was introduced into the chamber at a flow rate of 100 sccm.
Thereafter, the heat-treated material was stirred in a 10 M HCl
aqueous solution for 30 minutes and then filtered to dispose carbon
nanotubes on the SiO particles. Thereafter, a negative electrode
and a secondary battery were prepared by the same method as the
method of preparing the negative electrode and secondary battery of
Example 1.
TABLE-US-00001 TABLE 1 Negative electrode Comparative active
material Example 1 Example 2 Example 1 X value of SiOx 0.6 0.3 1
excluding lithium silicate Average particle 5 5 5 diameter
(D.sub.50) of core (.mu.m) Thickness of shell (nm) 325 420 0 Amount
of lithium 10.4 40.4 0 silicate based on total weight of negative
electrode active material (wt %) Thickness of coating 200 350 250
layer (nm) Amount of carbon 10.2 13.2 12.1 nanotubes based on total
weight of negative electrode active material (wt %)
Experimental Example 1: Evaluation of Discharge Capacity, Initial
Efficiency, and Capacity Retention
[0073] The batteries of Examples 1 and 2 and Comparative Example 1
were charged and discharged to evaluate discharge capacity, initial
efficiency, and capacity retention, and the results thereof are
listed in Table 2 below.
[0074] In 1.sup.st cycle and 2.sup.nd cycle, the batteries were
charged and discharged at 0.1 C, and charging and discharging were
performed at 0.5 C from a 3.sup.rd cycle to a 49th cycle. A 50th
cycle was terminated in a charged state (state in which lithium was
included in the negative electrode).
[0075] Charge condition: CC (constant current)/CV (constant
voltage) (5 mV/0.005 C current cut-off)
[0076] Discharge condition: CC (constant current) condition 1.5
V
[0077] The discharge capacity (mAh/g) and the initial efficiency
(%) were derived from the results during the first charge and
discharge cycle. Specifically, the initial efficiency (%) was
derived by the following calculation.
Initial efficiency (%)=(discharge capacity after the 1st
discharge/1st charge capacity).times.100
[0078] The capacity retention was derived by the following
calculation.
Capacity retention (%)=(discharge capacity in the 49th
cycle/discharge capacity in the first cycle).times.100
TABLE-US-00002 TABLE 2 Discharge Initial Capacity Battery capacity
(mAh/g) efficiency (%) retention (%) Example 1 408.2 90.2 74.2
Example 2 405.1 90.5 72.6 Comparative 401.6 87.5 71.3 Example 1
[0079] Referring to Table 2, it may be understood that discharge
capacity, initial efficiencies, and capacity retentions of Examples
1 and 2 were better than those of Comparative Example 1. The reason
for this is that the lithium silicate was simultaneously formed
while the carbon nanotubes were formed from Li.sub.2CO.sub.3.
* * * * *