KR102331305B1 - Electrode assembly and lithium secondary battery comprising the same - Google Patents

Abstract

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 contains nickel (Ni) and cobalt (Co), and is selected from the group consisting of manganese (Mn) and aluminum (Al) A positive electrode active material of a lithium composite transition metal oxide comprising at least one, wherein the lithium composite transition metal oxide has a nickel (Ni) content of 80 mol% or more among all metal elements, and the positive electrode active material is unimodal distribution), wherein the separator is an electrode assembly including an aramid coating layer formed on at least one surface of a porous polymer membrane, and a lithium secondary battery including the same.

Description

Electrode assembly and lithium secondary battery including the same

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

Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight and relatively high-capacity secondary batteries is rapidly increasing. In particular, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.

In a lithium secondary battery, an organic electrolyte or a polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions, and lithium ions are intercalated/deintercalated from the positive electrode and the negative electrode. Electric energy is produced by a reduction reaction with

As a cathode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O _{4 ,} etc.), lithium iron phosphate compound (LiFePO ₄ ), etc. were used. . In addition, _{as a method for improving low thermal stability while maintaining the excellent reversible capacity of LiNiO 2} , a lithium composite metal oxide in which a part of nickel (Ni) is substituted with cobalt (Co) or manganese (Mn)/aluminum (Al) ( Hereinafter, simply referred to as 'NCM-based lithium composite transition metal oxide' or 'NCA-based lithium composite transition metal oxide') has been developed. A carbon material or a metal or non-metal oxide having a low average potential is used as the anode active material, and a porous membrane manufactured using a polyolefin-based polymer (PE, PP, etc.) is mainly used as the separator.

However, the conventionally developed NCM-based/NCA-based lithium composite transition metal oxide as a positive electrode active material does not have sufficient capacity characteristics, so there is a limit to the application of high-capacity and high-voltage batteries. In order to improve this problem, recently, research to increase the content of Ni in the NCM-based/NCA-based lithium composite transition metal oxide has been conducted. However, when a high-concentration nickel positive active material having a high nickel content is used, structural stability and chemical stability of the positive active material are deteriorated, a side reaction with an electrolyte is increased, and thermal stability is rapidly reduced. Accordingly, there is still a need to develop a lithium secondary battery that satisfies both high capacity and high output and excellent stability at the same time.

Korean Patent Publication No. 2016-0032311

An object of the present invention is to provide an electrode assembly capable of satisfying high capacity and high output and exhibiting excellent stability, in particular, excellent thermal stability even in a high voltage region of 4.5V or higher, and suppressing electrolyte side reactions, and a lithium secondary battery including the same.

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 contains nickel (Ni) and cobalt (Co), and is selected from the group consisting of manganese (Mn) and aluminum (Al) A positive electrode active material of a lithium composite transition metal oxide including at least one, wherein the lithium composite transition metal oxide has a nickel (Ni) content of 80 mol% or more among all transition metal elements, and the positive electrode active material has a unimodal distribution ( It has a particle size distribution of unimodal distribution, and the separator provides an electrode assembly including an aramid coating layer formed on at least one surface of the porous polymer membrane.

In addition, the present invention provides a lithium secondary battery including the electrode assembly.

According to the present invention, a lithium composite transition metal oxide with a high content of nickel (Ni) having a nickel (Ni) content of 80 mol% or more, and a positive electrode active material having a particle size distribution curve showing a unimodal distribution is used, By using the separator having an aramid coating layer, it can exhibit excellent stability while satisfying high capacity and high output.

In particular, it exhibits excellent thermal stability even in a high voltage region of 4.5V or more, can suppress side reactions of the electrolyte, improve lifespan characteristics, and secure safety during overcharge.

1 shows a particle size distribution curve of the positive active material of Example 1. FIG.
2 shows a particle size distribution curve of the positive active material of Example 2.
3 shows a particle size distribution curve of the positive active material of Comparative Example 3.
4 shows a particle size distribution curve of the positive active material of Comparative Example 4.
5 is a graph showing the results of overcharging the lithium secondary batteries of Example 1 and Comparative Example 1;
6A and 6B are graphs measuring the amount of gas generated 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 more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to best describe his invention. Based on the principle that it can be done, it should be interpreted 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 contains nickel (Ni), cobalt (Co), and manganese (Mn) and aluminum (Al) A positive electrode active material of a lithium composite transition metal oxide comprising at least one selected from the group, wherein the lithium composite transition metal oxide has a nickel (Ni) content of 80 mol% or more among all transition metal elements, and the positive electrode active material includes It has a particle size distribution of unimodal distribution, and the separator includes an aramid coating layer formed on at least one surface of the porous polymer membrane.

In order to secure a high capacity, the present invention includes a high-content nickel (High-Ni)-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more among all transition metal elements as a positive electrode active material. However, in the case of a high nickel (Ni)-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more, structural stability and chemical stability are deteriorated, side reactions with the electrolyte are increased, and thermal stability is rapidly reduced. There is a problem being In order to overcome this 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 membrane. Stability was improved by using the formed separator.

However, when a separator having an aramid coating layer formed on at least one surface of the porous polymer membrane is used, cell resistance is increased due to the aramid coating layer, thereby causing a problem in that capacity and output characteristics are lowered. Accordingly, in the present invention, when a separator having an aramid coating layer is used, a high content nickel (High-Ni)-based positive electrode active material having a unimodal distribution having a particle size distribution curve having one peak is used, thereby increasing cell resistance was suppressed and high capacity and high output could be realized. In general, when a positive electrode active material, which is the opposite side, and a positive electrode active material, which are small particles, are mixed and used, the filling density of the positive electrode is improved and the capacity is improved. When a separator with an aramid coating layer is used while using a lithium-based composite transition metal oxide, the cell resistance is reduced when using a unimodal distribution cathode active material with a single peak in the particle size distribution curve. Rather, it was possible to secure improved high capacity and high output. Furthermore, the present invention reduces the BET specific surface area of a positive electrode active material by using a separator having an aramid coating layer and at the same time using a positive electrode active material having a unimodal distribution having a particle size distribution curve having one peak, and electrolyte solution It was possible to secure excellent stability by reducing the side reaction with the reaction, and also solved the stability problem in the high voltage region of 4.5V or more.

The positive electrode, the negative electrode, and the separator constituting the electrode assembly of the present invention will be described in detail for each configuration.

<Anode>

The positive electrode includes a positive electrode current collector, and a positive electrode active material layer formed on the positive electrode current 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 change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , silver or the like surface-treated may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the positive electrode current collector. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, and the like.

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

The positive active material according to an embodiment of the present invention includes nickel (Ni) and cobalt (Co), and lithium composite transition metal oxide including at least one selected from the group consisting of manganese (Mn) and aluminum (Al). am. For example, the positive active material may be an NCM-based lithium composite transition metal oxide including nickel (Ni), cobalt (Co) and manganese (Mn), or nickel (Ni), cobalt (Co) and aluminum (Al) ) may be an NCA-based lithium composite transition metal oxide containing. In addition, the positive active material may be a quaternary lithium composite transition metal oxide essentially including four components of nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al). Since the positive active material includes four components of manganese (Mn) and aluminum (Al) along with nickel (Ni) and cobalt (Co), structural stability is greatly improved, and stability can be sufficiently secured even in a high voltage region of 4.5V or higher. . In particular, according to an embodiment of the present invention, a cathode active material including four components of nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al) is used, and an aramid coating layer is formed. By using the separator, stability can be sufficiently secured even under a high voltage, and stability can also be remarkably improved during overcharge.

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

Specifically, the positive electrode active material may be a lithium composite transition metal oxide represented by the following formula (1).

[Formula 1]

Li _p Ni _{1 -(x1+y1+z1)} Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ₂

In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and At least one element selected from the group consisting of Cr, M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, 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 composite transition metal oxide of Formula 1, Li may be included in an amount corresponding to p, that is, 0.9≤p≤1.5. If p is less than 0.9, there is a fear that the capacity may decrease, and if it exceeds 1.5, the particles are sintered in the sintering process, so it may be difficult to manufacture the positive electrode active material. Considering the remarkable effect of improving the capacity characteristics of the positive electrode active material according to the control of the Li content and the balance of sinterability during the preparation of the active material, Li may be more preferably included in an amount of 1.0≤p≤1.15.

In the lithium composite transition metal oxide of Formula 1, Ni may be included in a content 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, an amount of Ni sufficient to contribute to charging and discharging is secured, thereby increasing the capacity. More preferably, Ni may be included as 0.88≤1-(x1+y1+z1)≤0.99.

In the lithium composite transition metal oxide of Formula 1, Co may be included in an amount corresponding to x1, that is, 0<x1≤0.2. When the content of Co in the lithium composite transition metal oxide of Formula 1 exceeds 0.2, there is a risk of cost increase. Considering the significant effect of improving capacity characteristics according to the inclusion of Co, Co may be included in a content of 0.05≤x1≤0.2 more specifically.

In the lithium composite transition metal oxide of Formula 1, M ^a may be Mn or Al, or Mn and Al, and these metal elements may improve the stability of the active material and, as a result, may improve the stability of the battery. Considering the life property improving effect, the M ^a may be included in an amount corresponding to y1, i.e., 0 <y1≤0.2 content. If the lithium in the composite transition metal oxide of the formula (1) y1 exceeds 0.2 and is more fear that the output characteristics and capacity characteristics of the battery decreases, the M ^a may be included in an amount of 0.05≤y1≤0.2 in detail.

In the lithium composite transition metal oxide of Formula 1, M ^b may be a doping element included in the crystal structure of the lithium composite transition metal oxide, and M ^b may be included in a content corresponding to z1, that is, 0≤z1≤0.1. have.

In the lithium composite transition metal oxide of Formula 1, ^{the metal element of M c} may not be included in the structure of the lithium composite transition metal oxide, and when the precursor and the lithium source are mixed and fired, the M ^c source is mixed and fired or , it is possible to prepare a lithium composite transition metal oxide in which ^{M c} is doped on the surface of the lithium composite transition metal oxide through a method of ^{separately adding a source of M c} and sintering after forming the lithium composite transition metal oxide. The M ^c may be included in an amount corresponding to q1, that is, a content that does not deteriorate the characteristics of the positive electrode active material within the range of 0≤q1≤0.1.

The positive 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 a positive electrode active material, which is the opposite side, and a positive electrode active material, which are small particles, are mixed and used, the filling density of the positive electrode is improved and the capacity is improved. In the case of using a high-Ni-based lithium composite transition metal oxide and a separator having an aramid coating layer at the same time, the cell resistance is reduced by using a positive electrode active material having a unimodal distribution of particle size distribution. Rather, capacity and output characteristics can be improved.

The positive active material may have a particle size distribution of a unimodal distribution having an _{average particle diameter (D 50 ) of 9 to 15 μm.} Even more preferably, the positive electrode 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 positive electrode active material having an average particle diameter (D ₅₀ ) within the above range, cell resistance can be reduced, high capacity and high output can be secured, and stability can be secured by reducing side reactions with the electrolyte.

In addition, more specifically, the positive active material may have a particle size distribution of a unimodal distribution with a particle diameter ratio _{of D 10} /D _{90 of 0.3 or more.} Even more preferably, the positive active material may have _{a particle diameter ratio of D 10} /D ₉₀ of 0.3 to 0.6, and more preferably, _{a particle diameter ratio of D 10} /D ₉₀ of 0.3 to 0.4. _{By using a positive active material having a particle size ratio of D 10} /D ₉₀ within the above range, cell resistance is reduced, high capacity and high output can be secured despite the particle size distribution of unimodal distribution, and the BET specific surface area of the positive electrode active material is reduced It is possible to reduce side reactions with the electrolyte and secure excellent stability.

The positive 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 still more preferably a BET specific surface area of 0.7 to 0.9 m ² /g. can By using a positive electrode 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, and in particular, excellent stability can be secured even in a high voltage region of 4.5V or more.

In the present invention, the average particle diameter (D ₅₀ ), D ₁₀ , and D ₉₀ may be defined as particle diameters corresponding to 50%, 10%, and 90% of the volume accumulation in the particle size distribution curve, respectively. The average particle diameter (D ₅₀ ), D ₁₀ , and D ₉₀ may be measured using, for example, a laser diffraction method. For example, in the method for measuring the average particle diameter (D ₅₀ ) of the positive active material, the particles of the positive active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (eg, Microtrac MT 3000) to about 28 kHz After irradiating the ultrasonic waves with an output of 60 W, the average particle diameter D ₅₀ corresponding to 50% of the volume accumulation amount in the measuring device can be calculated.

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

The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive active material layer.

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

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above positive electrode active material. Specifically, the cathode active material and, optionally, a composition for forming a cathode active material layer formed by mixing a binder and a conductive material in a solvent may be coated on a cathode current collector, and then dried and rolled. In this case, the type and content of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent commonly used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during application for the production of the positive electrode thereafter. do.

Alternatively, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling it from the support 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-Ni-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more, and a separator in which an aramid coating layer is formed on at least one surface of a porous polymer membrane. This improved the stability. However, when a separator having an aramid coating layer is used, cell resistance increases due to the aramid coating layer, thereby causing a problem in that capacity and output characteristics are deteriorated. Therefore, in the present invention, by using the above-described positive active material at the same time as using the separator having the aramid coating layer, the increase in cell resistance caused by the use of the separator having the aramid coating layer is used, and high capacity and high output are realized. made it possible

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. The porous polymer membrane of the separator according to an embodiment of the present invention has low resistance to ion movement of the electrolyte and is excellent in electrolyte moisture content, without particular limitation. It may be used, and preferably may include at least one selected from the group consisting of polyolefin-based polymers, polyvinylidene fluoride-based polymers, polyvinyl chloride-based polymers, polyacrylonitrile, cellulose and nylon. The thickness of the porous polymer film may be 9 to 22㎛.

An aramid coating layer is formed on at least one surface of the porous polymer membrane. The aramid coating layer includes at least one selected from the group consisting of para-aramid (eg, poly(para-phenylene terephthalamide)) and meta-aramid (eg, poly(meta-phenylene isophtalamide)). However, it is not particularly limited thereto. The thickness of the aramid coating layer may be 1.0 to 3.0 μm, more preferably 1.5 to 2.0 μm. If the thickness of the aramid coating layer is less than 1.0 μm, it is difficult to ensure uniformity of the coating, and it is difficult to suppress thermal deformation of the separator, so it may be difficult to secure stability, and if it exceeds 3.0 μm, the thickness of the entire separator increases This may lead to a decrease in energy density due to an increase in the thickness of the cell.

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

The separator having an aramid coating layer has a reduced air permeability compared to a separator made of only a porous polymer film without an aramid coating layer, but preferably does not decrease above a certain level. Therefore, the separator according to an embodiment of the present invention in which the aramid coating layer is formed may have air permeability of 150 to 350 sec/100ml, and more preferably 160 to 300sec/100ml. By using the separator having an aramid coating layer having air permeability within the above range, it is possible to realize high output without degrading battery performance while improving stability.

On the other hand, the separator according to an embodiment of the present invention in which the aramid coating layer is formed has a vertical shrinkage ratio of 15% or less and a horizontal shrinkage ratio of 15% or less after storage at 150° C. for 1 hour. Accordingly, high temperature It is possible to secure safety in the battery, and safety in case of overcharging.

<Cathode>

The negative electrode includes a negative electrode current collector, and a negative electrode active material layer formed on the negative electrode current 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 change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

The anode active material layer may optionally include a binder and a conductive material together with the anode active material. The anode active material layer may be formed by applying a composition for forming an anode including an anode active material, and optionally a binder and a conductive material on an anode current collector and drying, or casting the composition for forming a cathode on a separate support, and then , may also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the negative active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples 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 alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0 < β < 2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the above-mentioned metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, flaky, spherical or fibrous shape, and Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

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

<Lithium secondary battery>

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

Specifically, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

Examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries. no.

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

The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolanes and the like may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of 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 electrolyte may exhibit excellent performance.

The lithium salt may 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 is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2 or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, 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 positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle, HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Example One

_{LiNi 0} as a positive electrode active material _{. 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 positive active material, the carbon black conductive material, and the PVdF binder are mixed in an N-methylpyrrolidone solvent in a weight ratio of 95:2.5:2.5 to prepare a composition for forming a positive electrode active material layer, which is applied to one surface of an aluminum current collector and dried at 130° C., and then 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 as an anode active material in an N-methylpyrrolidone solvent in a weight ratio of 85:10:5, and this was used on one side of a copper current collector. was applied to prepare a negative electrode.

Prepare a composition for forming an aramid coating layer containing meta-aramid, and coat it on both sides of a polyethylene porous polymer membrane (thickness 9㎛) to a thickness of 2㎛ to prepare a separator with a total thickness of 13㎛ prepared.

An electrode assembly is prepared by interposing a separator having an aramid coating layer formed between the positive electrode and the negative electrode prepared as described above, the electrode assembly is placed inside the case, and the electrolyte is injected into the case to manufacture a lithium secondary battery did. At this time, the electrolyte is prepared by dissolving _{lithium hexafluorophosphate (LiPF 6} ) at a concentration of 1.0 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3 / 4 / 3) did.

Example 2

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

comparative example One

A lithium secondary battery was manufactured in the same manner as in Example 1 except that a polyethylene porous polymer membrane (thickness 9 μm) without an aramid coating layer was used as a separator.

comparative example 2

_{LiNi 0} as a positive electrode active material _{. 5} Co _{0 . 2} Mn _{0 . 3} O ₂ A lithium secondary battery was manufactured in the same manner as in Example 1, except that particles (D _{50 = 6.94 μm) were used.}

comparative example 3

_{LiNi 0} of the opposite side as the positive electrode active material _{. 83} Co _{0 . 11} Mn _{0 . 06} O ₂ particles (D ₅₀ = 18 μm) and small LiNi _{0 . 83} Co _{0 . 11} Mn _{0 . 06} O ₂ A lithium secondary battery was prepared in the same manner as in Example 1, except that the particles (D ₅₀ = 5 μm) were mixed in a weight ratio of 8:2 and used.

comparative example 4

_{LiNi 0} of the opposite side as the positive electrode active material _{. 83} Co _{0 . 11} Mn _{0 . 06} O ₂ particles (D ₅₀ = 20 μm) and small LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . A} lithium secondary battery was prepared in the same manner as in Example 1, except that 1 O ₂ particles (D _{50 = 5 μm) were mixed in a weight ratio of 8:2.}

[ Experimental example 1: Particle size distribution and BET of positive active material specific surface area measurement]

The positive active material in Examples 1 and 2 and Comparative Examples 1 to 4 was irradiated with an ultrasonic wave of about 28 kHz with an output of 60 W using a laser diffraction particle size measuring device (Microtrac MT 3000) to measure the particle size distribution, The results are shown in Table 1 and FIGS. 1 to 4 .

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

Average particle diameter (D ₅₀ ) (㎛) D ₁₀ (μm) D ₉₀ (μm) 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 Opposition 18/
elementary particle 5 4.53 21.7 0.209 1.12 Comparative Example 4 Opposition 20/
elementary particle 5 3.6 29.1 0.124 1.136

Referring to Table 1 and FIGS. 1 to 4, in Example 1 (FIG. 1) and Example 2 (FIG. 2), the particle size distribution of the positive active material showed a unimodal distribution having 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 in which the particle size distribution of the positive active material had two peaks, and the particle size ratio of _{D 10} /D _{90 was less than 0.3.} , and the BET specific surface area ^{was increased to about 1.0 m 2} /g or more.

[ Experimental example 2: of separator Heat shrinkage and air permeability evaluation]

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

In addition, the air permeability of the separators in Example 1 and Comparative Example 1 was measured, and the results are shown in Table 2.

Example 1 Comparative Example 1 120℃, 1Hr
Vertical axis shrinkage (%) 4 9 Transverse shrinkage (%) 0 4 150℃, 1Hr
Vertical axis shrinkage (%) 12 73 Transverse shrinkage (%) 10 73 Air permeability (sec/100ml) 281 165

Referring to Table 2, the separator of Example 1 having an aramid coating layer had a significantly reduced thermal shrinkage after storage at 120° C. and 150° C. compared to the separator of Comparative Example 1 without forming an aramid coating layer. did. In particular, in the case of 150 ° C., the difference in heat shrinkage from Comparative Example 1 was significantly larger.

In addition, the air permeability of the separator of Example 1 in which an aramid coating layer was formed was 281 sec/ml, and the air permeability was slightly increased compared to the separator of Comparative Example 1 in which an aramid coating layer was not formed, but the air permeability of Example 1 350 sec/ml or less was satisfied.

[ Experimental example 3: Lithium secondary battery performance evaluation]

The lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were charged and discharged under the conditions of a final charge voltage of 4.55V, a final discharge voltage of 2.5V, and 0.3C/0.3C, and the initial capacity , output and cell resistance were measured, and 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, Examples 1 and 2 showed low cell resistance, and excellent capacity and output characteristics. Specifically, the capacity of Examples 1 and 2 was significantly increased compared to Comparative Example 2 using a cathode active material having a nickel (Ni) content of less than 80 mol%. In addition, compared to Comparative Examples 3 and 4 using the positive active material in which the large and small particles were mixed, the cell resistance of Examples 1 and 2 was significantly reduced, and it could be confirmed that the capacity and output characteristics were improved.

[ Experimental example 4: Stability evaluation]

In order to evaluate the stability of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 during overcharging, a current of 1.0 C was applied at 25° C. to carry out a charging experiment up to 10 V, and the voltage (solid line) and temperature (dotted line) over time (dotted line) ) was measured, and the results are shown in FIG. 5 .

In addition, as in Example 2 and Comparative Example 1, except that the lithium secondary battery prepared using lithium metal as the negative electrode was charged to 0.1C and 5.0V in CC mode while charging in CC mode. The amount of gas generated was measured, and the results are shown in FIGS. 6A (Comparative Example 1) and 6B (Example 2).

In addition, as in Example 2 and Comparative Example 1, except for the lithium secondary battery coin half cell prepared using lithium metal as the negative electrode, 4.25V at a current of 0.2C proportional to the mass of the positive electrode active material After charging to 2.5V, the formation was carried out by discharging at the same current of 0.2C. After that, after charging to 4.7V with a constant current of 0.1C, when the voltage is maintained at 4.7V for 120 hours, it is a method of measuring the amount of current generated without maintaining a constant current. was measured, and the results are shown in FIGS. 6A (Comparative Example 1) and 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 a voltage drop due to the vent. After that, the temperature of the cell rises rapidly and finally an explosion occurs. On the other hand, in Example 1, the vent point at which the voltage temporarily drops is faster than in Comparative Example 1, followed by a continuous increase in the cell temperature, but gradually after reaching the upper limit voltage (10V), that is, after 1,400 seconds You can see the temperature drop.

6A (Comparative Example 1) and 6B (Example 2), in the case of Comparative Example 1, the gas generation amount at high voltage is about 0.108 bar, whereas in the case of Example 2, the gas generation amount at the high voltage is 0.0262 bar. It can be seen that there is a significant decrease. In addition, in the case of Comparative Example 1, the side reaction at high voltage can be confirmed through the occurrence of a large amount of leakage current at high voltage, but in the case of Example 2, it can be confirmed that the leakage current is significantly reduced. . Through this, it can be seen that in the case of Example 2 using a quaternary positive electrode active material of nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al), stability under high voltage was further improved.

Claims (12)

A positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
The positive electrode includes a positive active material of a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and at least one selected from the group consisting of manganese (Mn) and aluminum (Al), the lithium In the composite transition metal oxide, the content of nickel (Ni) in the total transition metal element is 80 mol% or more,
The positive active material has a particle size distribution of unimodal distribution,
The separator is an electrode assembly including an aramid (aramid) coating layer formed on at least one surface of the porous polymer membrane.
According to claim 1,
The cathode active material is an electrode assembly of a quaternary lithium composite transition metal oxide including nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al).
According to claim 1,
The cathode active material is an electrode assembly of a lithium composite transition metal oxide represented by the following formula (1).
[Formula 1]
Li _p Ni _{1 -(x1+y1+z1)} Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ₂
In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, and M ^b is Zr, W, Mg, Al, Ce, Hf, Ta, La, Ti, Sr, Ba, Nb, Mo, and At least one element selected from the group consisting of Cr, M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, 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.
According to claim 1,
The positive active material has an average particle diameter (D ₅₀ ) of 9 to 15 μm in an electrode assembly.
According to claim 1,
The positive active material is an electrode assembly having a particle size ratio _{of D 10} /D _{90 of 0.3 or more.}
According to claim 1,
The positive active material is an electrode assembly having a BET specific surface area of 1.0 m ² /g or less.
According to claim 1,
The separator is an electrode assembly comprising at least one porous polymer membrane selected from the group consisting of polyolefin-based polymers, polyvinylidene fluoride-based polymers, polyvinyl chloride-based polymers, polyacrylonitrile, cellulose and nylon.
According to claim 1,
The thickness of the aramid coating layer is 1.0 to 3.0㎛ electrode assembly.
According to claim 1,
The thickness of the separator is 12 to 25㎛ electrode assembly.
According to claim 1,
The air permeability of the separator is 150 to 350 sec/100ml of the electrode assembly.
According to claim 1,
The separator has an electrode assembly having a vertical shrinkage ratio of 15% or less and a horizontal shrinkage ratio of 15% or less after storage at 150° C. for 1 hour.
A lithium secondary battery comprising the electrode assembly according to any one of claims 1 to 11.

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