KR20190057950A - Electrode assembly and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrode assembly and a lithium secondary battery comprising the same. The electrode assembly comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The positive electrode comprises a positive electrode active material of a lithium composite transition metal oxide comprising at least one selected from a group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). In the lithium composite transition metal oxide, the content of nickel (Ni) in the total element is 80 mol% or more. The positive electrode active material has a particle size distribution of a unimodal distribution. The separator comprises an aramid coating layer on at least one surface of a porous polymer membrane. According to the present invention, the lithium secondary battery can exhibit excellent stability while satisfying high capacity and high output.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode assembly and a lithium secondary battery including the electrode assembly.

The present invention relates to an electrode assembly and a lithium secondary battery including the electrode assembly.

2. Description of the Related Art In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, electric vehicles, and the like, the demand for secondary batteries of small size and light weight and relatively high capacity has been rapidly increasing. Particularly, the lithium secondary battery is light in weight and has a high energy density, and is attracting attention as a driving power source for portable devices. Accordingly, research and development efforts for improving the performance of the lithium secondary battery have been actively conducted.

The lithium secondary battery has a structure in which an organic electrolyte or a polymer electrolyte is filled between a positive electrode and a negative electrode, which are made of an active material capable of intercalating and deintercalating lithium ions, and oxidized when lithium ions are inserted / And electrical energy is produced by the reduction reaction.

Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O _4, etc.) and lithium iron phosphate compound (LiFePO ₄ ) were used as the cathode active material of the lithium secondary battery . As a method for improving the low thermal stability while maintaining the excellent reversible capacity of LiNiO ₂ , there has been proposed a lithium composite metal oxide (Li) in which a part of nickel is replaced with cobalt (Co), manganese (Mn) Hereinafter, simply referred to as "NCM-based lithium complex transition metal oxide" or "NCA-based lithium complex transition metal oxide"). As the anode active material, a carbonaceous material or a metal or non-metal oxide having a low average potential is used. As the separation membrane, a porous membrane produced by using a polyolefin-based polymer (PE, PP, etc.) is mainly used.

However, NCM-based / NCA-based lithium composite transition metal oxide, which has been conventionally developed as a cathode active material, has insufficient capacitance characteristics and thus has a limitation in application of a high capacity and high voltage battery. In order to overcome such a problem, studies for increasing the content of Ni in NCM-based / NCA-based lithium composite transition metal oxides have been conducted. However, when a high-nickel nickel cathode active material having a high nickel content is used, the structural stability and chemical stability of the cathode active material are deteriorated, side reactions with the electrolyte are increased, and thermal stability is rapidly deteriorated. Therefore, there is still a need to develop a lithium secondary battery that satisfies both high capacity and high output and excellent stability.

Korean Patent Publication No. 2016-0032311

Disclosure of Invention Technical Problem [8] The present invention provides an electrode assembly and a lithium secondary battery including the electrode assembly, which exhibit excellent stability while satisfying high capacity and high output, and exhibit excellent thermal stability even in a high voltage range of 4.5 V or higher, and can suppress electrolyte side reactions.

The present invention relates to a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode contains nickel (Ni) and cobalt (Co), and is selected from the group consisting of manganese (Mn) Wherein the lithium complex transition metal oxide has a nickel content of at least 80 mol% in the total transition metal element, and the cathode active material has a single-rod distribution unimodal distribution, wherein the separator comprises an aramid coating layer formed on at least one surface of the porous polymer membrane.

The present invention also provides a lithium secondary battery including the electrode assembly.

According to the present invention, a lithium-transition metal composite oxide having a high content of nickel (High-Ni) having a nickel (Ni) content of 80 mol% or more and a cathode active material exhibiting a unimodal distribution of particle size distribution curves, By using a separator having an aramid coating layer formed thereon, it is possible to exhibit excellent stability while satisfying high capacity and high output.

In particular, it exhibits excellent thermal stability even in a high voltage range of 4.5 V or higher, suppresses side reaction of electrolyte, improves lifetime characteristics, and secures safety in overcharging.

Fig. 1 shows a particle size distribution curve of the positive electrode active material of Example 1. Fig.
Fig. 2 shows the particle size distribution curve of the cathode active material of Example 2. Fig.
3 shows the particle size distribution curve of the cathode active material of Comparative Example 3. Fig.
4 shows the particle size distribution curve of the cathode active material of Comparative Example 4. Fig.
5 is a graph showing the results of an overcharge test of the lithium secondary batteries of Example 1 and Comparative Example 1. Fig.
FIGS. 6A and 6B are graphs showing gas production amount and leakage current at high voltage in Comparative Example 1 (FIG. 6A) and Example 2 (FIG. 6B).

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention. Herein, terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of the term to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

The electrode assembly of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode includes nickel (Ni) and cobalt (Co) Wherein the content of nickel (Ni) in the total transition metal element is at least 80 mol%, and the cathode active material is at least one selected from the group consisting of The separator having a particle size distribution of a unimodal distribution, wherein the separator comprises an aramid coating layer formed on at least one surface of the porous polymer membrane.

The present invention includes a high-content nickel-based lithium transition metal oxide having a nickel (Ni) content of 80 mol% or more in the total transition metal element as a cathode active material in order to secure a high capacity. However, a high-Ni-based lithium complex transition metal oxide having a nickel (Ni) content of 80 mol% or more is inferior in structural stability and chemical stability, has an increased side reaction with an electrolyte, . In order to overcome such a problem, a high-Ni-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is used and an aramid coating layer is formed on at least one surface of the porous polymer film. The stability was improved by using the formed separator.

However, if a separator having an aramid coating layer formed on at least one surface of the porous polymer membrane is used, there arises a problem that capacity and output characteristics are deteriorated due to an increase in cell resistance due to the aramid coating layer. In the present invention, when a separator having an aramid coating layer is used, by using a high-Ni-based positive electrode active material having an unimodal distribution with a single particle size distribution curve, So that high capacity and high power can be realized. In general, when the cathode active material and the cathode active material are mixed, the filling density of the anode is improved and the capacity is improved. However, when a high-Ni (Ni-Ni) When using a lithium-composite transition metal oxide and a separator having an aramid coating layer formed thereon, the cell resistance is reduced when a cathode active material having a unimodal distribution having a peak particle size distribution curve is used And thus it was possible to secure an improved high capacity and high output. Further, the present invention reduces the BET specific surface area of the cathode active material by using a separator having an aramid coating layer formed thereon, and simultaneously using a unimodal distribution cathode active material having a peak of the particle size distribution curve, And the stability problem in a high voltage region of 4.5 V or more is solved.

The positive electrode, the negative electrode and the separator constituting the electrode assembly of the present invention will be described concretely by structure.

<Anode>

The positive electrode includes a positive electrode collector, and a positive electrode active material layer formed on the positive electrode collector and including a positive electrode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium, , Silver or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the cathode current collector to increase the adhesive force of the cathode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The positive electrode active material layer may include a positive electrode active material. The positive electrode active material may be typically contained in an amount of 70 to 98% by weight based on the total weight of the positive electrode active material layer.

The cathode active material according to an embodiment of the present invention includes at least one selected from the group consisting of nickel (Ni) and cobalt (Co), manganese (Mn), and aluminum (Al) to be. For example, the cathode active material may be an NCM-based lithium composite transition metal oxide including nickel (Ni), cobalt (Co), and manganese (Mn), or nickel (Ni), cobalt Based transition metal oxide. In addition, the cathode active material may be a four-component lithium composite transition metal oxide including four components of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). The positive electrode active material includes four components of manganese (Mn) and aluminum (Al) together with nickel (Ni) and cobalt (Co), thereby greatly improving the structural stability and ensuring sufficient stability even in a high voltage region of 4.5 V or more . Particularly, according to an embodiment of the present invention, a cathode active material containing four components of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) is used and an aramid coating layer is formed By using a separator, stability can be sufficiently ensured even under a high voltage, and stability in overcharging can be remarkably improved.

In the cathode active material according to an embodiment of the present invention, the content of nickel (Ni) in the total transition metal elements contained in the lithium composite transition metal oxide is 80 mol% or more. More preferably, in the cathode active material, the content of nickel (Ni) in the total transition metal elements contained in the lithium composite transition metal oxide may be 88 mol% or more. As described above, by using a high-content nickel-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more, a high capacity can be secured.

Specifically, the cathode active material may be a lithium complex transition metal oxide represented by the following general formula (1).

[Chemical Formula 1]

Li _p Ni _{1 - (x 1 + y 1 + z 1 )} Co _{x 1} M ^a _{y 1} M ^b _{z 1} M ^c _{q 1} O ₂

Wherein M ^a is at least one element selected from the group consisting of Mn and Al and M ^b is at least one element selected from the group consisting of Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, and at least one or more elements selected from the group consisting of Cr, ^c M is Al, Zr, Ti, Mg, Ta, Nb, and at least one element selected from the group consisting of Mo and Cr, 0.9≤p≤1.5, 0 < x1? 0.2, 0 <y1? 0.2, 0? z1? 0.1, 0? q1? 0.1, and 0 <x1 + y1 + z1? 0.2.

In the lithium complex transition metal oxide of Formula 1, Li may be contained in an amount corresponding to p, that is, 0.9? P? 1.5. If p is less than 0.9, there is a possibility that the capacity is lowered. If p is more than 1.5, particles are sintered in the firing step, and thus the production of the cathode active material may be difficult. Considering the remarkable effect of improving the capacity characteristics of the cathode active material according to the Li content control and the sintering property at the time of manufacturing the active material, Li is more preferably in the range of 1.0? P? 1.15.

In the lithium composite transition metal oxide of Formula 1, Ni may be included in an amount corresponding to 1- (x1 + y1 + z1), for example, 0.8? 1- (x1 + y1 + z1) <1. When the content of Ni in the lithium composite transition metal oxide of Formula 1 is 0.8 or more, sufficient amount of Ni is sufficient to contribute to charge and discharge, and high capacity can be achieved. More preferably, Ni can be included in the range of 0.88? 1- (x1 + y1 + z1)? 0.99.

In the lithium complex transition metal oxide of Formula 1, Co may be included in an amount corresponding to x1, that is, 0 < x1 0.2. If the content of Co in the lithium complex transition metal oxide of Formula 1 exceeds 0.2, there is a fear of an increase in cost. Considering the remarkable effect of improving the capacity characteristics according to the presence of Co, the Co may be more specifically included in an amount of 0.05? X1? 0.2.

In the lithium composite transition metal oxide of Formula 1, M ^a may be Mn or Al, or Mn and Al. Such a metal element may improve the stability of the active material and, as a result, improve the stability of the battery. Considering the effect of improving lifetime characteristics, the M ^a may be included in the content corresponding to y 1, that is, 0 <y 1? 0.2. If y1 in the lithium complex transition metal oxide of Formula 1 is more than 0.2, the output characteristics and the capacity characteristics of the battery may be deteriorated. The M ^a may be more specifically contained in an amount of 0.05? Y1? 0.2.

In the lithium complex transition metal oxide represented by Formula 1, M ^b may be a doping element contained in the crystal structure of the lithium complex transition metal oxide, and M ^b may be included in the content corresponding to z 1, that is, 0? Z 1? have.

In the lithium complex transition metal oxide of Formula 1, the metal element of M ^c may not be contained in the lithium complex transition metal oxide structure, and when the precursor and the lithium source are mixed and fired, M ^c sources are mixed together and fired , A lithium complex transition metal oxide may be prepared by doping the M ^c on the surface of the lithium composite transition metal oxide through a method of adding an M ^c source separately after forming a lithium complex transition metal oxide and firing the mixture. The M ^c may be included in a content corresponding to q 1, that is, a content not lowering the characteristics of the cathode active material within a range of 0? Q 1? 0.1.

The cathode active material according to an embodiment of the present invention has a particle size distribution of a unimodal distribution in which the particle size distribution curve has one peak.

In general, when the cathode active material and the cathode active material, which are major particles, are mixed, the filling density of the anode is improved and the capacity is improved. However, as in the present invention, a high nickel content of 80 mol% When a separator having a high-Ni-based lithium composite transition metal oxide and an aramid coating layer formed thereon is used, the cell resistance is reduced by using a cathode active material having a particle size distribution of unimodal distribution Rather, capacity and output characteristics can be improved.

The cathode active material may have a particle size distribution of a unimodal distribution having an average particle diameter (D ₅₀ ) of 9 to 15 μm. More preferably, the cathode active material may have an average particle diameter (D ₅₀ ) of 9 to 13 μm, and more preferably an average particle diameter (D ₅₀ ) of 10 to 12 μm. By using the cathode active material having the average particle diameter (D ₅₀ ) within the above range, the cell resistance can be reduced, a high capacity and high output can be secured, and side reactions with the electrolyte can be reduced and stability can be ensured.

More specifically, the cathode active material may have a particle size distribution of a unimodal distribution having a particle diameter ratio of D ₁₀ / D ₉₀ of not less than 0.3. More preferably, the positive active material than may be a D ₁₀ / D ₉₀ particle size ratio of 0.3 to 0.6, more preferably the D ₁₀ / D ₉₀ particle size ratio of 0.3 to 0.4. By using the cathode active material having the D ₁₀ / D ₉₀ particle size ratio within the above range, it is possible to reduce the cell resistance, secure a high capacity and high output even though the particle size distribution of the unimodal distribution can be secured, and reduce the BET specific surface area of the cathode active material Thereby reducing the side reaction with the electrolytic solution and securing excellent stability.

The cathode active material may have a BET specific surface area of 1.0 m ² / g or less, more preferably a BET specific surface area of 0.3 to 0.9 m ² / g, and more preferably a BET specific surface area of 0.7 to 0.9 m ² / g . By using a cathode active material having a BET specific surface area within the above range, side reactions with the electrolyte can be reduced and stability can be improved. In particular, excellent stability can be ensured even in a high voltage range of 4.5 V or more.

In the present invention, the average particle diameter (D ₅₀ ), D ₁₀ , and D ₉₀ can be defined as particle diameters corresponding to 50%, 10%, and 90% of the volume accumulation amount in the particle diameter distribution curve, respectively. The average particle diameter (D ₅₀ ), D ₁₀ , and D ₉₀ can be measured using, for example, a laser diffraction method. For example, the average particle size (D ₅₀ ) of the cathode active material is measured by dispersing the particles of the cathode active material in a dispersion medium and introducing the particles into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000) (D ₅₀ ) corresponding to 50% of the volume accumulation amount in the measuring apparatus can be calculated.

The cathode active material layer may optionally include a conductive material and a binder together with the cathode active material.

The conductive material is used for imparting conductivity to the electrode. The conductive material is not particularly limited as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. These may be used alone or in admixture of two or more. The conductive material may be typically contained in an amount of 1 to 30% by weight based on the total weight of the cathode active material layer.

In addition, the binder serves to improve adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose ), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof. One kind or a mixture of two or more kinds of them may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the cathode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the cathode active material may be prepared by coating the cathode active material and a composition for forming a cathode active material layer formed by mixing a binder and a conductive material in a solvent, onto the cathode current collector, followed by drying and rolling. At this time, the types and contents of the cathode active material, the binder, and the conductive material are as described above.

Examples of the solvent include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and the like. Water and the like, and one kind or a mixture of two or more kinds can be used. The amount of the solvent to be used is sufficient to dissolve or disperse the cathode active material, the conductive material and the binder in consideration of the coating thickness of the slurry and the yield of the slurry, and then to have a viscosity capable of exhibiting excellent thickness uniformity Do.

Alternatively, the positive electrode may be produced by casting the composition for forming the positive electrode active material layer on a separate support, then peeling off the support from the support, and laminating the obtained film on the positive electrode current collector.

< Separator >

The separator includes an aramid coating layer formed on at least one surface of the porous polymer membrane.

The present invention uses a high-content nickel-lithium composite transition metal oxide having a nickel content of 80 mol% or more and uses a separator having an aramid coating layer formed on at least one surface of the porous polymer membrane Thereby improving stability. However, if a separator having an aramid coating layer is used, there arises a problem that the capacity and output characteristics are deteriorated due to an increase in cell resistance due to the aramid coating layer. Accordingly, in the present invention, by using the separator having an aramid coating layer and using the above-mentioned positive electrode active material, it is possible to suppress an increase in cell resistance due to the use of a separator having an aramid coating layer and to realize a high capacity and high output .

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions. The separator according to an embodiment of the present invention is not particularly limited as long as the porous polymer membrane of the separator has a low resistance to ion movement of the electrolyte, And preferably at least one selected from the group consisting of a polyolefin-based polymer, a polyvinylidene fluoride-based polymer, a polyvinyl chloride-based polymer, polyacrylonitrile, cellulose and nylon. The thickness of the porous polymer membrane may be 9 to 22 탆.

An aramid coating layer is formed on at least one surface of the porous polymer membrane. The aramid coating layer comprises at least one selected from the group consisting of para-aramid (e.g., poly (para-phenylene terephthalamide)) and meta-aramid (e.g., poly (meta-phenylene isophtalamide) But is not limited thereto. The thickness of the aramid coating layer may be 1.0 to 3.0 탆, and more preferably 1.5 to 2.0 탆. If the thickness of the aramid coating layer is less than 1.0 占 퐉, it is difficult to ensure uniformity of the coating, and it is difficult to suppress the thermal deformation of the separator, so that it may be difficult to ensure stability. When the thickness exceeds 3.0 占 퐉, So that the energy density may be lowered due to an increase in the thickness of the cell.

The total thickness of the separator having the aramid coating layer formed on at least one surface of the porous polymer membrane may be 12 to 25 탆, and more preferably 13 to 22 탆.

It is preferable that the separator having the aramid coating layer formed therein has a reduced air permeability as compared with a separator composed of a porous polymer membrane having no aramid coating layer but is not reduced to a certain level or more. Accordingly, the separator according to an embodiment of the present invention in which the aramid coating layer is formed may have an air permeability of 150 to 350 sec / 100 ml, and more preferably 160 to 300 sec / 100 ml. By using a separator in which an aramid coating layer having air permeability within the above range is formed, high output can be realized without deteriorating battery performance while improving stability.

On the other hand, the separator according to one embodiment of the present invention in which the aramid coating layer is formed can satisfy 15% or less of longitudinal shrinkage after storage at 150 ° C for 1 hour, and 15% or less of shrinkage percentage of transverse shrinkage. It is possible to secure the safety in overcharging.

<Cathode>

The negative electrode includes a negative electrode collector, and a negative electrode active material layer formed on the negative electrode collector and including a negative electrode active material.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to enhance the binding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. The negative electrode active material layer may be formed by applying and drying a composition for forming a negative electrode including a negative electrode active material on the negative electrode collector and, optionally, a binder and a conductive material, or by casting the composition for forming a negative electrode on a separate support , And a film obtained by peeling from the support may be laminated on the negative electrode collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; _{SiO β (0 <β <2} ), SnO 2, vanadium oxide, which can dope and de-dope a lithium metal oxide such as lithium vanadium oxide; Or a composite containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, and any one or a mixture of two or more thereof may be used. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar coke derived cokes).

In addition, the binder and the conductive material may be the same as those described above for the anode.

<Lithium secondary battery>

According to another embodiment of the present invention, there is provided an electrochemical device including the electrode assembly. The electrochemical device may be specifically a lithium secondary battery.

The lithium secondary battery may further include a battery container that houses the positive electrode, the negative electrode, and the electrode assembly of the separator, and a sealing member that seals the battery container.

Examples of the electrolyte used in the present invention include an organic-based liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. no.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is a straight, branched or cyclic hydrocarbon group of C2 to C20, which may contain a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN (C2F5SO3) 2, LiN (C2F5SO2) 2, LiN (CF3SO2) 2. LiCl, LiI, or LiB (C 2 O 4) 2 may be used. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

In addition to the electrolyte components, the electrolyte may contain, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate or the like, pyridine, triethanolamine, or the like for the purpose of improving lifetime characteristics of the battery, Ethyl phosphite, triethanol amine, cyclic ether, ethylenediamine, glyme, hexametriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, At least one additive such as benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, The additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it can be used in portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles hybrid electric vehicle (HEV)).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example  One

As a cathode active material, LiNi _{0 . 83} Co _{0 . 11} Mn _{0 . 06} O ₂ particles (D ₅₀ = 11.23 μm, D ₁₀ / D ₉₀ = 0.325, BET specific surface area = 0.8 m ² / g) were used. The cathode active material, the carbon black conductive material, and the PVdF binder were mixed in a N-methylpyrrolidone solvent in a weight ratio of 95: 2.5: 2.5 to prepare a composition for forming a cathode active material layer, Dried at 130 캜, and rolled to prepare a positive electrode.

A composition for forming an anode active material layer was prepared by mixing natural graphite, a carbon black conductive material and a PVdF binder in a N-methylpyrrolidone solvent in a weight ratio of 85: 10: 5 as a negative electrode active material, To prepare a negative electrode.

A composition for forming an aramid coating layer containing meta-aramid was prepared and coated on both surfaces of a polyethylene porous polymer membrane (thickness: 9 mu m) to a thickness of 2 mu m to prepare a separator having a total thickness of 13 mu m .

The electrode assembly was manufactured through a separator having an aramid coating layer formed between the positive electrode and the negative electrode prepared as described above. After the electrode assembly was positioned inside the case, an electrolyte was injected into the case to manufacture a lithium secondary battery Respectively. The electrolyte solution was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent composed of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3/4/3) Respectively.

Example  2

As a cathode active material, LiNi _{0 . 86} Co _{0 . 1} Mn _{0 . 02} A1 _{0 . A} lithium secondary battery was produced in the same manner as in Example 1 except that particles of ₀₂ O ₂ (D ₅₀ = 10.58 μm, D ₁₀ / D ₉₀ = 0.38, BET specific surface area = 0.85 m ² / g) .

Comparative Example  One

A lithium secondary battery was produced in the same manner as in Example 1 except that a polyethylene porous polymer membrane (thickness: 9 mu m) having no aramid coating layer was used as a separator.

Comparative Example  2

As a cathode active material, LiNi _{0 . 5} Co _{0 . 2} Mn _{0 . 3} O ₂ particles (D ₅₀ = 6.94 탆) was used as a negative electrode active material, thereby preparing a lithium secondary battery.

Comparative Example  3

As a cathode active material, LiNi _{0 . 83} Co _{0 . 11} Mn _{0 .} Particles of ₀₆ O ₂ (D ₅₀ = 18 μm) and LiNi ₀ of the fine particles _{. 83} Co _{0 . 11} Mn _{0 . 6} O ₂ particles (D ₅₀ = 5 μm) were mixed at a weight ratio of 8: 2, to prepare a lithium secondary battery.

Comparative Example  4

As a cathode active material, LiNi _{0 . 83} Co _{0 . 11} Mn _{0 .} Particles of ₀₆ O ₂ (D ₅₀ = 20 μm) and LiNi ₀ of the fine particles _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ particles (D ₅₀ = 5 μm) were mixed at a weight ratio of 8: 2, to prepare a lithium secondary battery.

[ Experimental Example  1: Particle size distribution of cathode active material and BET Specific surface area  Measure]

The cathode active materials in Examples 1 and 2 and Comparative Examples 1 to 4 were irradiated with an ultrasound of about 28 kHz at an output of 60 W using a laser diffraction particle size analyzer (Microtrac MT 3000) to measure the particle size distribution. The results are shown in Table 1 and Figs.

In addition, the BET surface area was measured using a BELSORP-mini, and the results are shown in Table 1.

Average particle diameter (D ₅₀ ) (탆) D ₁₀ (占 퐉) D ₉₀ (占 퐉) D ₁₀ / D ₉₀ BET specific surface area (m ² / g) Example 1 11.23 7.15 22 0.325 0.8 Example 2 10.58 6.57 16.99 0.38 0.85 Comparative Example 1 11.23 7.15 22 0.325 0.8 Comparative Example 2 6.94 3.52 12.64 0.278 0.51 Comparative Example 3 Majority 18 /
Particle 5 4.53 21.7 0.209 1.12 Comparative Example 4 Majority 20 /
Particle 5 3.6 29.1 0.124 1.136

Referring to Table 1 and FIGS. 1 to 4, Example 1 (FIG. 1) and Example 2 (FIG. 2) showed a unimodal distribution in which the particle size distribution of the cathode active material had one peak, The particle size ratio of D ₁₀ / D ₉₀ was 0.3 or more, and the BET specific surface area was reduced to 1.0 m ² / g or less.

On the other hand, Comparative Example 3 (Fig. 3) and Comparative Example 4 (Fig. 4) showed a bimodal distribution (Bimodal distribution) The particle size distribution of the cathode active material having two peaks, D ₁₀ / D less than ₉₀ particle size ratio of 0.3 And the BET specific surface area was increased to about 1.0 m ² / g or more.

[ Experimental Example  2: Separator  Ten Contraction ratio  And air permeability evaluation]

The separators in Example 1 and Comparative Example 1 were stored at 120 ° C for 1 hour and at 150 ° C for 1 hour, respectively, and then the heat shrinkage was evaluated. The results are shown in Table 2.

The air permeability of the separator in Example 1 and Comparative Example 1 was measured, and the results are shown in Table 2.

Example 1 Comparative Example 1 120 C, 1H
Longitudinal axis contraction ratio (%) 4 9 Abaxial shrinkage (%) 0 4 150 ° C, 1 Hr
Longitudinal axis contraction ratio (%) 12 73 Abaxial shrinkage (%) 10 73 Air permeability (sec / 100ml) 281 165

Referring to Table 2, the separator of Example 1 in which an aramid coating layer was formed had a significantly reduced heat shrinkage after storage at 120 ° C and 150 ° C, as compared with the separator of Comparative Example 1 in which no aramid coating layer was formed Respectively. In particular, the difference in heat shrinkage between Comparative Example 1 and Comparative Example 1 was remarkably large at 150 ° C.

In addition, the air permeability of the separator of Example 1 in which the aramid coating layer was formed was slightly higher than that of the separator of Comparative Example 1 in which the aramid coating layer was not formed at the air permeability of 281 sec / ml, 350 sec / ml or less.

[ Experimental Example  3: Performance evaluation of lithium secondary battery]

Charging and discharging tests were carried out on the lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 4 under the conditions of a charging end voltage of 4.55 V and a discharge end voltage of 2.5 V and a discharge end voltage of 0.3 C / , Output and cell resistance were measured. The results are shown in Table 3.

Cell Resistance (ohm) Charging capacity (mAh / g) Discharge capacity (mAh / g) Example 1 21.3 225.5 207.7 Example 2 23.2 229.1 208.2 Comparative Example 1 20.8 225.4 207.9 Comparative Example 2 22.5 201.1 171.4 Comparative Example 3 28 224 204 Comparative Example 4 32 224 203

Referring to Table 3, in Example 1 and Example 2, cell resistance was low, and excellent capacity and output characteristics were shown. Specifically, the capacities of Examples 1 and 2 were significantly increased as compared with Comparative Example 2 using a cathode active material having a nickel (Ni) content of less than 80 mol%. Compared with Comparative Example 3 and Comparative Example 4 using a cathode active material mixed with an opposite particle and a small particle, the cell resistance was significantly reduced in Example 1 and Example 2, and capacity and output characteristics were improved.

[ Experimental Example  4: Stability evaluation]

In order to evaluate the stability of the lithium secondary battery produced in Example 1 and Comparative Example 1, a charging test was performed at a maximum of 10 V by applying a current of 1.0 C at 25 캜. The voltage (solid line) and the temperature ). The results are shown in Fig.

A lithium secondary battery coin half cell manufactured by using lithium metal as a negative electrode was fabricated as in Example 2 and Comparative Example 1, The results are shown in FIG. 6A (Comparative Example 1) and FIG. 6B (Example 2).

The lithium secondary battery Coin Half Cell, which was produced as in Example 2 and Comparative Example 1 using lithium metal as the negative electrode, was subjected to a current of 0.25 C proportional to the mass of the cathode active material, And then discharged at the same current of 0.2 C up to 2.5 V for formation. Thereafter, when the voltage is maintained at 4.7V at a constant current of 0.1C and then maintained at 4.7V for 120 hours, a method of measuring the amount of current generated without maintaining a constant current, The results are shown in FIG. 6A (Comparative Example 1) and FIG. 6B (Example 2).

Referring to FIG. 5, in the case of Comparative Example 1, it is observed that the voltage temporarily drops after 900 seconds, which is considered to be the voltage drop caused by the vent. After that, the temperature of the cell rises sharply and eventually explosion occurs. On the other hand, in Example 1, the vent timing at which the voltage temporarily drops is faster than that in Comparative Example 1, and subsequently the cell temperature is continuously increased, but after reaching the upper limit voltage (10 V), i.e., after 1,400 seconds, It can be confirmed that the temperature drops.

Referring to FIG. 6A (Comparative Example 1) and FIG. 6B (Example 2), in Comparative Example 1, the amount of gas generated at a high voltage was about 0.108 bar, whereas in Example 2, the amount of gas generated at a high voltage was 0.0262 bar It can be confirmed that it is remarkably decreased. In addition, in the case of Comparative Example 1, a side reaction at a high voltage can be confirmed through a large leakage current at a high voltage, but it can be confirmed that a leak current is remarkably reduced in Example 2 . As a result, it can be seen that the stability under high voltage was further improved in Example 2 using a four-component cathode active material of nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al).

Claims (12)

A positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
Wherein the positive electrode comprises a positive electrode active material of a lithium-transition metal oxide including at least one selected from the group consisting of manganese (Mn) and aluminum (Al) including nickel (Ni) and cobalt (Co) The composite transition metal oxide has a nickel (Ni) content of 80 mol% or more in the total transition metal elements,
The cathode active material has a particle size distribution of a unimodal distribution,
Wherein the separator comprises an aramid coating layer formed on at least one side of the porous polymer membrane.
The method according to claim 1,
Wherein the cathode active material is a four component lithium composite transition metal oxide including nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al).
The method according to claim 1,
Wherein the cathode active material is a lithium complex transition metal oxide represented by the following formula (1).
[Chemical Formula 1]
Li _p Ni _{1 - (x 1 + y 1 + z 1 )} Co _{x 1} M ^a _{y 1} M ^b _{z 1} M ^c _{q 1} O ₂
Wherein M ^a is at least one element selected from the group consisting of Mn and Al and M ^b is at least one element selected from the group consisting of Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, and at least one or more elements selected from the group consisting of Cr, ^c M is Al, Zr, Ti, Mg, Ta, Nb, and at least one element selected from the group consisting of Mo and Cr, 0.9≤p≤1.5, 0 < x1? 0.2, 0 <y1? 0.2, 0? z1? 0.1, 0? q1? 0.1, and 0 <x1 + y1 + z1? 0.2.
The method according to claim 1,
Wherein the cathode active material has an average particle diameter (D ₅₀ ) of 9 to 15 μm.
The method according to claim 1,
The positive electrode active material is the electrode assembly more than 0.3 diameter ratio of D ₁₀ / D _90.
The method according to claim 1,
Wherein the cathode active material has a BET specific surface area of 1.0 m ² / g or less.
The method according to claim 1,
Wherein the separator comprises at least one porous polymer membrane selected from the group consisting of a polyolefin-based polymer, a polyvinylidene fluoride-based polymer, a polyvinyl chloride-based polymer, polyacrylonitrile, cellulose and nylon.
The method according to claim 1,
Wherein the thickness of the aramid coating layer is 1.0 to 3.0 占 퐉.
The method according to claim 1,
Wherein the separator has a thickness of 12 to 25 占 퐉.
The method according to claim 1,
And the air permeability of the separator is 150 to 350 sec / 100 ml.
The method according to claim 1,
Wherein the separator has a longitudinal shrinkage after storage at 150 DEG C for one hour of 15% or less and a transverse shrinkage ratio of 15% or less.
A lithium secondary battery comprising an electrode assembly according to any one of claims 1 to 11.

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