KR20200044703A - Negative electrode and secondary battery comprising the negative electrode - Google Patents

Abstract

The present invention relates to a negative electrode which includes a negative electrode active material layer, wherein the negative electrode active material layer includes negative electrode active material particles, and the negative electrode active material particles include a core including graphite particles; and a carbon coating layer disposed on the core. The negative electrode active material particles satisfy the following conditions regarding the particle size distribution, 6.7 μm <= D_min <= 12 μm, 1.2 <= D_90/D_10 <= 2.3, and 23.2 μm <= D_50 <= 26 μm.

Description

A negative electrode and a secondary battery comprising the negative electrode {NEGATIVE ELECTRODE AND SECONDARY BATTERY COMPRISING THE NEGATIVE ELECTRODE}

The present invention includes a negative electrode active material layer, the negative electrode active material layer includes negative electrode active material particles, and the negative electrode active material particles include a core including graphite particles; And a carbon coating layer disposed on the core, wherein the negative electrode active material particles satisfy the following conditions in particle size distribution.

6.7㎛ ≤ D _min ≤ 12㎛

1.2 ≤ D ₉₀ / D ₁₀ ≤ 2.3

23.2㎛ ≤ D ₅₀ ≤ 26㎛

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing, and as a part, the most actively researched fields are power generation and power storage using electrochemical reactions.

At present, a representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually expanding. Recently, as technology development and demand for portable devices such as portable computers, portable telephones, and cameras have increased, the demand for secondary batteries as an energy source has rapidly increased. In general, a secondary battery is composed of an anode, a cathode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions from the positive electrode, and silicon-based particles having a large discharge capacity may be used as the negative electrode active material.

On the other hand, in recent years, research is being conducted to improve the charging speed of the secondary battery. Among them, attempts are being made to improve the rapid charging performance of the secondary battery by developing a negative electrode material.

For example, conventionally, a method of improving the rapid charging performance of a secondary battery by forming a carbon coating layer on the surface of a negative electrode active material has been used. However, it is difficult to achieve rapid charging performance only with the carbon coating layer, and there are limitations in the content of the carbon coating layer when considering capacity.

Therefore, a new method for improving the rapid charging performance of the secondary battery is required.

One problem to be solved by the present invention is to provide a negative electrode and a secondary battery capable of improving the rapid charging performance of the secondary battery and improving processability in manufacturing.

According to an embodiment of the present invention, a negative electrode active material layer, the negative electrode active material layer includes negative electrode active material particles, and the negative electrode active material particles include a core including graphite-based particles; And a carbon coating layer disposed on the core, wherein the negative electrode active material particles are provided with a negative electrode satisfying the following conditions in the particle size distribution.

6.7㎛ ≤ D _min ≤ 12㎛

1.2≤ D ₉₀ / D ₁₀ ≤ 2.3

23.2㎛ ≤ D ₅₀ ≤ 26㎛

According to another embodiment of the present invention, a secondary battery including the negative electrode is provided.

According to the present invention, by removing the relatively small negative active material particles among the negative active material particles, the particle size distribution of the negative active material particles is 6.7㎛ ≤ D _min ≤ 12㎛, 1.2 ≤ D ₉₀ / D ₁₀ ≤ 2.3, 23.2㎛ ≤ D ₅₀ ≤ 26 μm may be satisfied. Accordingly, pores are secured between the anode active material particles in the anode active material layer, the pore resistance of the anode active material layer may be lowered, and the diffusion distance of lithium ions may be shortened. Therefore, since lithium ions can rapidly move into the negative electrode active material particles, the rapid charging performance of the battery can be improved. In addition, the tap density of the negative electrode active material particles whose particle size distribution is adjusted to the above level is improved, so that the processability in manufacturing the negative electrode can be improved.

1 is a particle size distribution chart of the negative electrode active material particles of Comparative Example 1 and Examples 1 and 2.
2 is a graph showing a voltage change during charging of batteries using the negative active material particles of Comparative Example 1 and Examples 1 and 2.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The terminology used herein is only used to describe exemplary embodiments, and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this specification, the terms "include", "have" or "have" are intended to indicate the presence of implemented features, numbers, steps, elements or combinations thereof, one or more other features or It should be understood that the existence or addition possibilities of numbers, steps, elements, or combinations thereof are not excluded in advance.

In the present specification, D ₅₀ and D ₉₀ may be defined as particle sizes corresponding to 50% and 90% of the volume accumulation amount in a particle size distribution curve (graph curve of particle size distribution), respectively, and D _max is the particle size distribution curve It can be defined as the largest particle diameter among the particle diameters shown in, D _min can be defined as the smallest particle diameter among the particle diameters shown in the particle size distribution curve. The D ₅₀ , D ₉₀ , D _max and D _min can be measured, for example, by using a laser diffraction method. The laser diffraction method can generally measure a particle diameter of several mm from a submicron region, and can obtain results of high reproducibility and high resolution.

In this specification, the tap density corresponds to a value obtained by measuring the final density obtained by filling the container with 40 g of the negative electrode active material and vibrating up and down about 1000 times.

In this specification, the pore resistance is punched out to a size of 1.4875 cm ² of the negative electrode of the present invention, and then a separation membrane is interposed between the negatively punched negative electrodes. After this, the coin cell is poured with an electrolyte solution, and then left for about 24 hours, and then the frequency range is set from 106 Hz to 0.05 Hz with an electrochemical impedance analysis equipment, and the impedance is measured. It may be a pore resistance measured by separating the pore resistance.

<Cathode>

The negative electrode according to an embodiment of the present invention includes a negative electrode active material layer, the negative electrode active material layer includes negative electrode active material particles, and the negative electrode active material particles include a core including graphite particles; And a carbon coating layer disposed on the core, wherein the negative electrode active material particles may satisfy the following conditions in the particle size distribution.

6.7㎛ ≤ D _min ≤ 12㎛

1.2 ≤ D ₉₀ / D ₁₀ ≤ 2.3

23.2㎛ ≤ D ₅₀ ≤ 26㎛

The negative electrode may include a current collector and a negative electrode active material layer disposed on the current collector. The negative active material layer may include the negative active material particles. Furthermore, the negative electrode active material layer may further include a binder and / or a conductive material.

The current collector may be any one that has conductivity without causing a chemical change in the battery, and is not particularly limited. For example, the current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel. Specifically, a transition metal that adsorbs carbon well, such as copper and nickel, can be used as the current collector. The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

The negative active material particles may include the core and the carbon coating layer.

The core may include graphite-based particles. The graphite-based particles may include at least one of natural graphite and artificial graphite. Most preferably, the graphite-based particles may include artificial graphite. The artificial graphite has an advantage in that it suppresses the volume expansion of the negative electrode and can significantly improve the life of the battery. In addition, when the artificial graphite is used, the particle size distribution can be easily adjusted by adjusting the size of the sieve during the sieve process.

The carbon coating layer may be disposed on the core. The carbon coating layer may cover at least a part of the surface of the core. The conductivity of the negative electrode active material particles may be improved by the carbon coating layer, and initial efficiency, lifespan characteristics, and battery capacity characteristics of the secondary battery including the negative electrode active material particles may be improved. In addition, the diffusion degree of lithium ions is improved by the carbon coating layer, so that the rapid charging performance of the battery may be improved.

The carbon coating layer may include at least one of amorphous carbon and crystalline carbon.

The crystalline carbon can further improve the conductivity of the core. The crystalline carbon may include at least one selected from the group consisting of florene, carbon nanotubes, and graphene.

The amorphous carbon can appropriately maintain the strength of the carbon coating layer to suppress expansion of the core. The amorphous carbon may be a carbon-based material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic materials, or a hydrocarbon as a source of chemical vapor deposition.

The other organic material carbide may be a sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or a carbide of edohexose and a combination of organic substances selected from combinations thereof.

The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be metherin, etherin, ethylene, acetylene, propane, butane, butene, pentane, isobutane or hexane. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon is benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, And anthracene or phenanthrene.

In the negative electrode active material particles, the carbon coating layer may be included in 0.5 to 10 parts by weight relative to 100 parts by weight of the core, specifically 1 to 5 parts by weight, and more specifically 2 to 4 parts by weight You can. When the above range is satisfied, the rapid charging performance by the carbon coating layer may be further improved.

D _min of the negative electrode active material particles may be in the following range.

6.7㎛ ≤ D _min ≤ 12㎛

The above range means that a peak of a negative electrode active material particle having a particle diameter of less than 6.7 μm (hereinafter referred to as fine powder) and a peak of a negative electrode active material particle having a particle diameter of greater than 12 μm are not detected when measuring particle size distribution. When the negative electrode active material particles contain the fine powder, since the fine powder is present between the relatively large negative electrode active material particles in the prepared negative electrode, the lithium ion diffusion path becomes too long, and the pore resistance of the negative electrode active material layer increases. Is done. Accordingly, the diffusion resistance is excessively increased, such that lithium ions cannot rapidly enter the negative electrode active material particles when the battery is rapidly charged. In addition, while lithium precipitation easily occurs, the reversible capacity of the negative electrode decreases, deterioration of the battery occurs, and at the same time, rapid charging performance of the secondary battery deteriorates. On the other hand, when the D _min of the negative electrode active material particles exceeds 12 μm, the size of the negative electrode active material particles generally increases as the particle size distribution curve of the negative electrode active material particles moves to the right. Accordingly, the specific surface area of the negative electrode active material particle is reduced, and when charging at a high rate, lithium ions are difficult to sufficiently contact the negative electrode active material particle. Therefore, the rapid charging performance may be deteriorated. Alternatively, in this embodiment, since the D _min of the negative electrode active material particle satisfies the above range, that is, the negative electrode active material particle does not contain the fine powder, the diffusion distance of lithium within the negative electrode active material particle may be reduced. At the same time, since the particle size distribution curve does not move excessively to the right, lithium precipitation may be delayed, and a decrease in the reversible capacity of the negative electrode may be suppressed. In addition, the degeneration of the battery can be controlled, which can lead to an improvement in the rapid charging performance of the secondary battery. Also, since D _min is not too high, the tap density can be increased.

More specifically, the D _min may be in the following range.

9㎛ ≤ D _min ≤ 12㎛

When the specific range is satisfied, the particle distribution becomes more uniform, and the pore resistance of the cathode can be further reduced, so that the rapid charging performance can be further improved.

D ₅₀ of the negative electrode active material particle may be in the following range.

23.2㎛ ≤ D ₅₀ ≤ 26㎛

When the D ₅₀ is less than 23.2 μm, relatively small particles increase, and the specific surface area of the negative electrode active material particles increases, so that the high temperature storage performance of the battery may be poor. On the other hand, when the D ₅₀ is more than 26 μm, the excessively large particles are increased, and the cathode resistance increases, so that the rapid charging performance may be deteriorated. The D ₅₀ can be controlled together with the control of the D _min as described above, the negative electrode active material particles in 6.7㎛ ≤ D _min ≤ 12㎛.

Specifically, D ₅₀ of the negative electrode active material particles may satisfy the following range.

24㎛ ≤ D ₅₀ ≤ 26㎛

D ₉₀ / D ₁₀ of the negative electrode active material particles may be in the following range.

1.2 ≤ D ₉₀ / D ₁₀ ≤ 2.3

The negative electrode active material particles having a D ₉₀ / D ₁₀ of less than 1.2 are excessively expensive and time consuming in the manufacturing process, and thus a process problem occurs. Conversely, when the D ₉₀ / D ₁₀ is _greater than 2.3, the size of the negative electrode active material particles becomes non-uniform, and both small and large particles are increased. Therefore, the density of the negative electrode active material layer is not uniform, so battery stability and rapid charging performance may be deteriorated.

More specifically, D ₉₀ / D ₁₀ of the negative electrode active material particles may be in the following range.

1.4 ≤ D ₉₀ / D ₁₀ <2.0

D _max of the negative electrode active material particles may be in the following range.

D _max ≤ 76㎛

When the above range is satisfied, the relatively large-sized particles are reduced, and the specific surface area of the negative electrode active material particles increases, so that lithium ions can sufficiently contact the negative electrode active material particles during high rate charging, so that the rapid charging performance can be improved. .

More specifically, D _max of the negative electrode active material particles may be in the following range.

50㎛ ≤ D _max ≤ 60㎛

When the specific range is satisfied, particles of a relatively large size are further reduced, and the rapid charging performance may be further improved.

The tab density of the negative electrode active material particles may be 0.88 g / cc to 1.2 g / cc, specifically 0.9 g / cc to 1.1 g / cc, and more specifically 0.92 g / cc to 1.0 g / cc. have. When the above range is satisfied, since the contact area between the current collector and the negative electrode active material particles is increased, the negative electrode adhesion can be improved and the life of the battery can be improved. In addition, when manufacturing the negative electrode, aggregation phenomenon between the negative electrode active material particles may be suppressed. Accordingly, in a filtering process for removing particles formed by agglomeration of components in the negative electrode slurry, filter clogging may be minimized. Therefore, processability may be improved when manufacturing the cathode.

The negative active material particles may be prepared in the following way. Specifically, the method includes a core comprising graphite-based particles; And a carbon coating layer disposed on the core; may include the step of removing the pre-particles of less than a certain size, to obtain a negative electrode active material particles. In addition, the core and the carbon coating layer are the same as the core and carbon coating layers described in the above-described embodiment.

The pre-particles before the pre-particles of less than the specified size are removed correspond to the negative electrode active material particles in which fine powder is not removed. That is, the particle size distribution curve for the pre-particles before the pre-particles of less than the specified size are removed is biased toward the lower particle diameter, and the peak width of the particle size distribution curve is wide.

In the step of obtaining the anode active material particles by removing the pre-particles of less than the specific size, removing the pre-particles of less than the specific size may be performed through a mechanical classification facility.

The binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride), polyacrylonitrile (polyacrylonitrile), polymethyl methacrylate (polymethylmethacrylate), poly Vinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), alcohol It may include at least one selected from the group consisting of sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and materials substituted with hydrogen, Li, Na, or Ca, etc., It may also include various copolymers of these.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powders; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The negative active material layer may have a pore resistance of 7.1 Ω to 7.85 Ω, specifically 7.3 Ω to 7.8 Ω, and more specifically 7.5 Ω to 7.6 Ω. The above range can be derived by using the negative electrode active material particles of the above-described embodiment. When the above range is satisfied, since lithium ions can be smoothly diffused in the negative electrode active material layer, the rapid charging performance of the battery may be improved. Specifically, when the pore resistance is more than 7.9 Ω, since the diffusion path of lithium ions becomes too long, lithium ions are likely to diffuse in the horizontal direction (in parallel with the current collector surface) of the negative electrode active material layer, and lithium ions are negative electrode active material layers It is difficult to diffuse in the vertical direction (direction perpendicular to the current collector surface). Therefore, when the battery is rapidly charged, a problem may occur in that the capacity of the battery decreases and lithium precipitates. Conversely, when the pore resistance is too small to be less than 7.1 Ω, there are too many pores in the anode active material layer or the size of the pores is too large, thereby reducing the contact between the anode active materials. Accordingly, a problem occurs in that the conductivity of the cathode is lowered.

<Secondary battery>

The secondary battery according to another embodiment of the present invention may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, a detailed description is omitted.

The positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and may include a positive electrode active material layer including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on aluminum or stainless steel surfaces , Surface treatment with nickel, titanium, silver, or the like can be used. In addition, the positive electrode current collector may have a thickness of usually 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium iron oxide such as LiFe ₃ O ₄ ; Lithium manganese oxides such as the formula Li _{1 + c1} Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Represented by the formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3) Ni-site lithium nickel oxide; Formula LiMn _2-c3 M _c3 O ₂ (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO ₈ (here, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn.) Lithium manganese composite oxide represented by; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions, and the like, are not limited thereto. The anode may be Li-metal.

The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery configured, it can be used without particular limitation as long as it has electronic conductivity without causing a chemical change. 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 whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers, such as polyphenylene derivatives, etc. are mentioned, and 1 type of these or a mixture of 2 or more types can be used.

In addition, the positive electrode 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, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and one of them, or a mixture of two or more thereof may be used.

As a separator, a negative electrode and a positive electrode are separated and a passage for lithium ions is provided. As a separator, it can be used without particular limitation as long as it is used as a separator in a secondary battery. It is preferred. Specifically, porous polymer films such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. A laminate structure of two or more layers of may be used. In addition, a conventional porous non-woven fabric, for example, a high-melting point glass fiber, non-woven fabric made of polyethylene terephthalate fiber or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be used in a single-layer or multi-layer structure.

Examples of the electrolyte include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the manufacture of a lithium secondary battery, but are not limited thereto.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dime Methoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxorun, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid triester, trimethoxy methane, dioxone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyropion Aprotic organic solvents such as methyl acid and ethyl propionate can be used.

Particularly, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and can be preferably used because they have high dielectric constant and dissociate lithium salts well, and these cyclic carbonates include dimethyl carbonate and diethyl carbonate. When the same low-viscosity and low-permittivity linear carbonate is mixed and used in an appropriate ratio, an electrolyte having a high electrical conductivity can be produced, and thus it can be more preferably used.

The metal salt may be a lithium salt, the lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, is in the lithium salt anion ^{F -, Cl -, I -} , NO 3 -, N (CN _{^{) 2 -, BF 4 -,}} ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF - ^{_{, (CF 3) 6 P -}} , CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 _{^{CO -, (CF 3 SO 2}} ) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO ₂ ^-, SCN ^- can be used at least one member selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N.

In addition to the components of the electrolyte, the electrolyte includes haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, and tree for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substitutedoxazolidinone, N, N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may also be included.

According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics, and a cycling characteristic, a medium-to-large device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system It can be used as a power source.

Hereinafter, a preferred embodiment is provided to help understanding of the present invention, but the above embodiment is merely illustrative of the present description, and it is apparent to those skilled in the art that various changes and modifications are possible within the scope and technical thought scope of the present description, It is natural that such variations and modifications fall within the scope of the appended claims.

Examples and comparative examples

Comparative Example 1: Preparation of cathode

D _max is 74 μm, D ₉₀ is 34 μm, D ₅₀ is 22 μm, D ₁₀ is 13 μm, D _min is 5 μm, D ₉₀ from the particle size distribution (measurement equipment: Microtrac S3500) derived by laser diffraction. A negative active material particle having a D ₁₀ of 2.6 was prepared. The negative active material particles include artificial graphite and a carbon coating layer formed on the artificial graphite, and the carbon coating layer was formed by coating and heat treating the pitch. The carbon coating layer was 3.5 parts by weight based on 100 parts by weight of the core.

The negative electrode active material particles, Super C65 as a conductive material, styrene butadiene rubber (SBR) as a binder, and a thickener, carboxymethylcellulose (CMC), were mixed in a weight ratio of 95.6: 1: 2.3: 1.1, respectively, and water was added to add the negative electrode. A slurry was prepared. Subsequently, the negative electrode slurry was applied to a copper foil, and after rolling, vacuum dried at about 130 ° C. for 8 hours to prepare a negative electrode for a lithium secondary battery, respectively. At this time, the loading of the negative electrode was prepared to be 3.6mAh / cm ² . At this time, the porosity of the electrode was 28%.

Comparative Examples 2 to 5 and Examples 1 and 2: Preparation of cathode

The negative electrodes of Comparative Examples 2 to 5 and Examples 1 and 2 were prepared in the same manner as in Comparative Example 1, except that the negative electrode active material particles having different physical properties as shown in Table 1 below were used.

Particle size properties of negative electrode active material particles (㎛) D _min D ₁₀ D ₅₀ D ₉₀ D ₉₀ / D ₁₀ D _max Comparative Example 1 5 13 22 34 2.6 74 Comparative Example 2 7.1 15 22 35 2.3 104 Comparative Example 3 8.5 18 27 45 2.5 104 Comparative Example 4 6 14.3 24 39 2.7 88 Comparative Example 5 5 13.4 23.8 41.3 3.1 124 Example 1 8 17 24 36 2.1 74 Example 2 10 17 24 32 1.9 52

The particle size distribution curves for the negative electrode active material particles used in Comparative Example 1 and Examples 1 and 2, respectively, are shown in FIG. 1.

Experimental Example 1: Evaluation of tap density

It is shown in Table 2 by measuring the powder filling density after tapping 1000 times after adding 40 g of each of the negative electrode active material particles used in Comparative Examples 1 to 5 and Examples 1 and 2 into a 100 ml cylinder.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Example 1 Example 2 Tap density (g / cc) 0.85 0.89 0.90 0.78 0.83 0.90 0.93

According to Table 2, it can be seen that, compared to the tap density of the negative electrode active material particles used in Comparative Examples 1, 2, 4 and 5, the tap density of the negative electrode active material particles used in Examples 1 and 2, respectively, is high. Therefore, when the negative electrode active material particles used in Examples 1 and 2 are used, aggregation between the negative electrode active material particles is reduced. Accordingly, in a filtering process for removing particles formed by agglomeration of components in the negative electrode slurry, filter clogging may be minimized. Therefore, processability may be improved when manufacturing the cathode.

Experimental Example 2: Evaluation of pore resistance

The pore resistance was evaluated for each of the negative electrode of Comparative Example 1 and Examples 1 and 2. The cathode was used as a working electrode and a counter electrode, and an electrode assembly was prepared by interposing a polyethylene separator between the working electrode and the counter electrode. A symmetric cell was prepared by injecting 0.5 wt% of vinylidene carbonate and 1 M LiPF6 into a solvent in which ethylene carbonate (EC) and diethylene carbonate (EMC) were mixed at a volume ratio of 1: 4 to the electrode assembly.

The symmetric cell was set with an electrochemical impedance analysis equipment to set the frequency range from 106 Hz to 0.05 Hz, the impedance was measured, and the electrolyte resistance and pore resistance were separated to measure the pore resistance. The results are shown in Table 3 below.

Comparative Example 1 Example 1 Example 2 Pore resistance (Ω) 8.0 7.8 7.6

Referring to Table 3, it can be seen that the pore resistances of Examples 1 and 2 were lower than those of Comparative Example 1. This seems to be because a negative electrode active material in which the particle size distribution was adjusted to a desired level by removing the fine powder was used.

Experimental Example 3: Rapid charging performance evaluation of the battery

Secondary batteries were prepared by the following methods using the negative electrodes of Comparative Examples 1 to 5 and Examples 1 and 2, respectively.

A lithium (Li) metal thin film cut into a circle of 1.7671 cm 2 was used as an anode. A porous polyethylene separator is interposed between the positive electrode and the negative electrode (comparative examples 1 to 5 and negative electrodes of Examples 1 and 2), and the mixed volume ratio of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) is 7: 3. Lithium coin half-cell was prepared by dissolving vinylene carbonate dissolved in 0.5% by weight in a mixed solution and injecting an electrolyte in which LiPF ₆ with a concentration of 1M was dissolved.

After charging the prepared half cells at a current rate of 2.9C for 12 minutes to evaluate the rapid charging performance by deriving the SOC (Li plating SOC) in which lithium is precipitated, it is shown in FIGS. 2 and 4.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Example 1 Example 2 Li plating SOC (%) 36 33 24 29 36 39 43

Referring to Figure 2 and Table 4, compared to the battery using the negative electrode of Comparative Examples 1 to 5, in the case of the battery using the negative electrode of Example 1 or Example 2, lithium precipitation occurs, the point at which the potential of the battery starts to rise It can be seen that the SOC is high. That is, in the case of the embodiments, it can be confirmed that the charging of the battery is more efficiently performed during rapid charging.

Claims (10)

It includes a negative electrode active material layer,
The negative active material layer includes negative active material particles,
The negative active material particles include a core including graphite-based particles; And a carbon coating layer disposed on the core.
The negative electrode active material particles satisfy the following conditions in the particle size distribution.
6.7㎛ ≤ D _min ≤ 12㎛
1.2 ≤ D ₉₀ / D ₁₀ ≤ 2.3
23.2㎛ ≤ D ₅₀ ≤ 26㎛
The method according to claim 1,
The negative electrode active material particles satisfy the following conditions.
9㎛ ≤ D _min ≤ 12㎛
The method according to claim 1,
The negative electrode active material particles satisfy the following conditions.
D _max ≤ 76㎛
The method according to claim 1,
The negative electrode active material particles satisfy the following conditions.
50㎛ ≤ D _max ≤ 60㎛
The method according to claim 1,
The graphite-based particle is a negative electrode comprising at least one of natural graphite and artificial graphite.
The method according to claim 1,
A negative electrode in which the carbon coating layer is included in 0.5 to 10 parts by weight based on 100 parts by weight of the core.
The method according to claim 1,
The carbon coating layer is an anode comprising at least one of amorphous carbon and crystalline carbon.
The method according to claim 1,
Cathode having a tap density of 0.88 g / cc to 1.2 g / cc.
The method according to claim 1,
Cathode having pore resistance of 7.1 Ω to 7.85 Ω.
The negative electrode of claim 1;
anode;
A separator interposed between the anode and the cathode; And
Secondary battery comprising an electrolyte.

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