KR20220076640A - Negative electrode and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the same, wherein the negative electrode of the present invention includes a negative electrode material comprising a core containing graphite and a shell containing amorphous carbon disposed on the core, The content of amorphous carbon is 1 to 10% by weight based on the total weight of the negative electrode material, and is a prelithiated negative electrode.

Description

Anode for lithium secondary battery and lithium secondary battery including same

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery, and more particularly, to an anode for a lithium secondary battery and a lithium secondary battery having excellent fast charging performance and initial efficiency.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used.

The secondary battery has conventionally used lithium metal as the negative electrode, but as the battery short-circuit due to the formation of dendrites and the risk of explosion due to this become a problem, reversible intercalation and desorption of lithium ions are possible, The use of carbon-based active materials that maintain structural and electrical properties is emerging.

As the carbon-based active material, various types of carbon-based materials such as artificial graphite, natural graphite, and hard carbon have been applied. have. Since the graphite-based active material has a low cost, structural stability, and a discharge voltage as low as -0.2V compared to lithium, a battery using the graphite-based active material can exhibit a high discharge voltage of 3.6V, so it is a lot in terms of energy density of lithium batteries. provides advantages.

However, graphite has problems due to the formation of complex solid electrolyte interphase (SEI) and volume expansion. The SEI layer, which represents a physical barrier between the lithium ionized carbon electrode, the electrolyte, and the binder, not only causes irreversible charge loss, but can also affect the long-term cycle stability of the lithium secondary battery.

이상으로 열처리하여 제조되는 인조흑연이 있다. 천연흑연은 인조흑연에 비해 흑연화도가 높고 저가이며, 높은 리튬이온 저장용량을 나타낸다. 반면 인조흑연은, 장기 수명과 고출력 특성이 요구되는 제품에 여전히 사용되고 있다. Graphite is produced in nature and mined from natural graphite, coal-based and petroleum-based pitch, etc.

There is artificial graphite manufactured by heat treatment as described above. Compared to artificial graphite, natural graphite has a high degree of graphitization, is low cost, and exhibits high lithium ion storage capacity. On the other hand, artificial graphite is still used in products requiring long life and high output characteristics.

On the other hand, in this graphite-based negative electrode material, in order to improve the fast charging performance, a graphite-based negative electrode material coated with amorphous carbon on the graphite surface is being studied, and such a negative electrode material is initially irreversible due to the surface amorphous carbon layer There may be a problem that the initial efficiency is lowered due to a large capacity loss.

Korean Patent Application Laid-Open No. 10-2019-0117633 discloses a technique for reducing initial irreversibility by performing prelithiation before manufacturing a lithium secondary battery in order to minimize the initial irreversible capacity loss of the negative electrode. However, the said document does not relate to the negative electrode material which has graphite as a core, and does not mention the effect of improving rapid charging performance.

Accordingly, there is a need to develop a technology for improving the fast charging performance and preventing a decrease in initial efficiency.

Korean Patent Publication No. 10-2019-0117633

An object of the present invention is to provide an anode having excellent lifespan characteristics and rolling performance while improving fast charging performance, and a lithium secondary battery including the same.

The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode material consisting of a core containing graphite and a shell containing amorphous carbon disposed on the core, and the content of the amorphous carbon is based on the total weight of the negative electrode material 1 to 10% by weight, and it is a pre-lithiated negative electrode.

In an embodiment of the present invention, the amorphous carbon is included in an amount of 1.5 to 7% by weight based on the total weight of the negative electrode material.

In one embodiment of the present invention, the negative electrode material includes secondary particles formed by agglomeration of one or more primary particles.

In an embodiment of the present invention, the graphite of the negative electrode material may be natural graphite.

In an embodiment of the present invention, the graphite of the negative electrode material may be artificial graphite.

In an embodiment of the present invention, the negative electrode material is a spherical or similar spherical particle having an average particle diameter (D ₅₀ ) of 7 to 20 μm.

In one embodiment of the present invention, the negative electrode of the present invention further comprises uncoated graphite in addition to the negative electrode material, and the first negative active material of the first negative active material layer disposed on the current collector is composed of uncoated graphite and the second anode active material of the second anode active material layer disposed on the first anode active material layer may be composed of the anode material.

In one embodiment of the present invention, the weight ratio of the uncoated graphite to the negative electrode material is 4:6 to 6:4 based on the total weight of the negative electrode active material.

In one embodiment of the present invention, the average particle diameter (D ₅₀ ) of the uncoated graphite is 10㎛ to 22㎛.

In one embodiment of the present invention, the uncoated graphite is artificial graphite.

In one embodiment of the present invention, the negative electrode includes 0.5 to 5% by weight of the binder.

In addition, the lithium secondary battery according to the present invention includes the negative electrode.

The negative electrode for a lithium secondary battery according to the present invention improves rapid charging performance by adopting a negative electrode material consisting of a core containing graphite as an anode active material and a shell containing amorphous carbon disposed on the core, and applying pre-lithiation technology This improves the initial efficiency and optimizes the content of amorphous carbon contained in the anode material to exhibit excellent lifespan characteristics.

Hereinafter, the present invention will be described in detail. Prior to this, 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 should properly understand the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined in

In the present application, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It is to be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. Also, when a part of a layer, film, region, plate, etc. is said to be “on” another part, it includes not only the case where the other part is “directly on” but also the case where there is another part in between. Conversely, when a part of a layer, film, region, plate, etc. is said to be “under” another part, it includes not only cases where it is “directly under” another part, but also cases where another part is in between.

Hereinafter, the present invention will be described in detail.

The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode material consisting of a core containing graphite and a shell containing amorphous carbon disposed on the core, and the content of the amorphous carbon is based on the total weight of the negative electrode material 1 to 10% by weight, and is an anode for a lithium secondary battery that has been pre-lithiated.

The inventors of the present invention, the loss of initial irreversible capacity due to the amorphous carbon contained in the negative electrode material of the present invention can be compensated for by prelithiation, but when the content of the amorphous carbon is above a certain level, the rolling performance is negatively affected Therefore, an anode having excellent electrode density was developed by optimizing the content of amorphous carbon included in the anode material of the present invention.

The negative electrode material of the present invention consists of a core containing graphite and a shell containing amorphous carbon disposed on the core, and the content of the amorphous carbon constituting the shell is 1 to 10% by weight based on the total weight of the negative electrode material, Preferably it is 1.5 to 7 weight%, More preferably, it is 2 to 5 weight%. When the content of the amorphous carbon is within the above numerical range, there is an excellent effect of rolling performance and rapid charging performance.

The negative electrode material of the present invention is a carbon material in which an amorphous carbon material is disposed on a graphite core to constitute a shell, and “disposed” herein includes attaching one component to (or placing it on) another component ) is used to indicate any method of placing next to or adjacent to. The negative electrode material may be a composite or a single body. Here, the composite means that one element and another element are complexed, and the single element is made up of a single element, and the single element is made of the same component, but changes in mechanical properties or chemical properties in one part through a treatment such as surface modification indicates that there is

The graphite constituting the core of the anode material of the present invention may include natural graphite, artificial graphite, or a mixture thereof.

The natural graphite may be spherical or near-spherical natural graphite formed by modifying flaky natural graphite particles. Specifically, the natural graphite may be formed by agglomeration of the flaky natural graphite particles. More specifically, the natural graphite may be formed by drying or abrading natural graphite particles in the form of scales through a mechanical process.

The artificial graphite may be block graphitized artificial graphite, powder graphitized artificial graphite, or a mixture thereof.

The block graphitized artificial graphite means that a plurality of primary particles made of graphite are aggregated or combined to have a spherical secondary particle structure. In this case, the secondary particle structure may be one in which the plurality of primary particles are aggregated, combined, or assembled non-parallel to each other.

The primary particles of the block graphitized artificial graphite may be artificial graphite crystallized by calcining one or more carbon raw materials selected from the group consisting of needle cokes, mosaic cokes and coal tar pitch. and specifically, may have an isotropic or anisotropic crystal structure synthesized using non-acicular petroleum/coal-based pitch coke or resin-based pitch as a raw material.

When the block graphitized artificial graphite is applied to the negative active material of a lithium secondary battery, the irreversible capacity at the time of activation is small, the rapid discharge characteristic is excellent, and the cycle characteristic is excellent. The block graphitized artificial graphite may have voids in the secondary particle structure.

The powder (powder) graphitized artificial graphite is a plurality of primary particles made of graphite are aggregated, combined, or granulated, and may form a mass. The primary particles of the powder graphitized artificial graphite may be artificial graphite crystallized by calcining at least one carbon raw material selected from the group consisting of needle cokes, mosaic cokes, and coal tar pitch. and specifically, may have an isotropic or anisotropic crystal structure synthesized using non-acicular petroleum/coal-based pitch coke or resin-based pitch as a raw material, and may have high crystallinity. The powder graphitized artificial graphite may have micropores therein, and may have excellent rollability and electrolyte impregnation property due to the micropores.

As used herein, the term “primary particle” refers to an original particle when a different type of particle is formed from a certain particle, and a plurality of primary particles are aggregated, combined, or granulated to form secondary particles. can do.

As used herein, the term “secondary particles” refers to physically separable large particles formed by aggregation, bonding, or granulation of individual primary particles.

In a preferred embodiment of the present invention, the negative electrode material may be an amorphous carbon material coated on uncoated artificial graphite. Carbon coating on artificial graphite serves to prevent uniform SEI layer formation and volume expansion, and is known to be effective in improving charge and discharge performance in lithium secondary batteries, but the amorphous carbon coating layer of the present invention is artificial graphite It can facilitate the entry and exit of lithium ions in the particles, can have the effect of lowering the charge transfer resistance of lithium ions, can improve structural stability compared to other carbon-based particles such as natural graphite, and further improve the fast charging performance of the battery. can be improved

The amorphous carbon coating layer may include amorphous carbon, specifically, may include at least one selected from the group consisting of soft carbon and hard carbon, and may preferably include soft carbon.

The amorphous carbon coating layer may be formed by providing one or more materials selected from the group consisting of pitch, rayon, and polyacrylonitrile-based resins or a precursor of the materials to the surface of the artificial graphite particles, and then pyrolyzing them. The heat treatment process for forming the amorphous carbon coating layer may be performed in a temperature range of 1000°C to 4000°C. At this time, when the heat treatment process is carried out at less than 1000°C, it may be difficult to form a uniform carbon coating layer, and when it is carried out at a temperature exceeding 4000°C, there is a problem in that the carbon coating layer is excessively formed during the process.

The negative electrode material of the present invention is a spherical or similar spherical particle, and may have an average particle diameter (D ₁₀ ) of 1 μm to 20 μm, specifically 5 μm to 15 μm, more specifically 8 μm to 12 μm, and the average particle diameter ( D ₅₀ ) may be 7 µm to 30 µm, specifically 10 µm to 25 µm, more specifically 15 µm to 22 µm, and the average particle diameter (D ₉₀ ) is 20 µm to 45 µm, specifically 25 µm to 40 µm , more specifically, may be 30 μm to 36 μm, and the maximum particle diameter (D _max ) may be 75 μm or less.

When the negative electrode material satisfies the average particle diameter (D ₁₀ ), average particle diameter (D ₅₀ ) and average particle diameter (D ₉₀ ) in the above ranges, excellent output and initial efficiency can be properly balanced, and excellent tap density is exhibited, and the electrode An excellent loading amount can be exhibited at the time of coating.

If the particle diameter of the negative electrode material is too small, a problem of a decrease in initial efficiency may occur due to an increase in specific surface area, and if the particle diameter of the artificial graphite is excessively large, the initial efficiency may increase, but output characteristics and dispersion stability may be impaired. Accordingly, the artificial graphite satisfies the average particle diameter (D ₁₀ ), the average particle diameter (D ₅₀ ), and the average particle diameter (D ₉₀ ) in the above ranges, so that the output characteristics and the initial efficiency can be appropriately harmonized.

In the present invention, the average particle diameter (D ₁₀ ) may be defined as a particle size based on 10% of the particle size distribution, and the average particle size (D ₅₀ ) may be defined as a particle size based on 50% of the particle size distribution, The average particle size (D ₉₀ ) may be defined as a particle size based on 90% of the particle size distribution, and the maximum particle size (D _max ) may be defined as a particle size based on the maximum value of the particle size distribution. The average particle diameter is not particularly limited, but may be measured using, for example, a laser diffraction method or a scanning electron microscope (SEM) photograph. In general, the laser diffraction method can measure a particle diameter of several mm from a submicron region, and can obtain a result having high reproducibility and high resolution.

The theoretical capacity of the negative electrode material of the present invention as described above may be 340 mAh/g or more, preferably 345 to 360 mAh/g, and more preferably 348 to 355 mAh/g.

In one specific example, the negative electrode of the present invention may have a multilayer structure of two layers, and may further include uncoated graphite in addition to the negative electrode material as an anode active material. The anode of the two-layer structure has a structure including a first anode active material layer disposed on a current collector and a second anode active material layer disposed on the second anode active material layer, and the first anode of the first anode active material layer The active material is composed of uncoated graphite, and the second negative active material of the second negative electrode active material layer is composed of graphite coated with amorphous carbon, which is the above-described negative electrode material.

Lithium ions emitted from the positive electrode by composing the first negative electrode active material layer with uncoated graphite to facilitate the manufacture of the high-loading electrode, and by configuring the second negative electrode active material layer close to the positive electrode with graphite coated with amorphous carbon It is quickly occluded in the second anode active material layer of the anode to improve the fast charging performance, and lithium ions stored in the second anode active material layer are transferred to the first anode active material layer to form the first anode active material layer and the second anode active material layer. The effect of allowing lithium ions to be evenly distributed can be expected.

In one specific example, the weight ratio of the negative electrode material to the uncoated graphite may be 4:6 to 6:4 based on the total weight of the negative electrode active material, preferably 45:55 to 55:45. When satisfying the above numerical range, it is preferable that the rapid charging performance and the rolling performance can be harmoniously improved.

The average particle diameter (D ₅₀ ) of the uncoated graphite may be 10 μm to 22 μm, preferably 12 to 18 μm. In addition, the graphite is more preferably artificial graphite.

The negative electrode of the present invention may be prepared by coating the negative electrode slurry including the negative electrode material on the negative electrode current collector, drying and rolling.

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

The negative electrode slurry may include 77.5 wt% to 99 wt%, specifically 80 wt% to 98.5 wt%, of the negative electrode active material based on the total solids weight of the negative electrode slurry.

The negative electrode slurry may further include a conductive material and a binder in addition to the negative electrode material described above.

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 black, such as carbon black, acetylene black, Ketjen black, channel black, Farness 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 powder; 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 conductive material may be used in an amount of 0.1 wt% to 9 wt% based on the total solids weight of the negative electrode active material slurry.

The binder is not particularly limited as long as it is a conventional binder used in preparing the negative electrode slurry, but for example, any one or two of the water-based binders selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber, and acrylic rubber. A mixture of the above may be used. The binder may be included in an amount of 10% by weight or less based on the total solids content of the negative electrode active material slurry, and specifically 0.1 to 10% by weight, more specifically 0.5 to 5% by weight. If the content of the binder is less than 0.1% by weight, the effect of the use of the binder is insignificant, which is not preferable. Not desirable.

The negative electrode slurry may additionally include a thickener.

The negative electrode slurry may include 0.1% to 3% by weight of the thickener based on the total weight of the solid content of the negative electrode slurry, specifically 0.2% to 2% by weight, more specifically 0.5% to 1.5% by weight may include

When the negative electrode slurry contains the thickener in the above range, storage stability of the slurry can be ensured by exhibiting an appropriate thickening effect, and the thickener is included within a certain amount in the negative electrode active material slurry, so that the performance of the battery is not reduced. .

The thickener may be at least one selected from the group consisting of carboxymethyl cellulose (CMC), hydroxypropyl cellulose, and regenerated cellulose, and specifically carboxymethyl cellulose (CMC).

The present invention also provides an electrochemical device including the negative electrode. The electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

Specifically, the lithium secondary battery includes a positive electrode positioned to face the negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the negative electrode is as described above.

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

In addition, the positive electrode of the present invention may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and 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 change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the 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.

The cathode active material may include a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; lithium manganese oxides such as Formula Li _1+y Mn _2-y O ₄ (where y is 0 - 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and 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 ; Ni site-type lithium nickel oxide represented by the formula LiNi _1-y M _y O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and y = 0.01 - 0.3); Formula LiMn _2-y M _y O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 - 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, ternary lithium-manganese composite oxide represented by Ni, Cu, or Zn; LiMn ₂ O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; Ternary lithium with Fe ₂ (MoO ₄ ) ₃ , Li(Ni _a Co _b Mn _c )O ₂ (0<a<1, 0<b<1, 0<c<1, a+b+c=1) Transition metal composite oxide, etc. are mentioned. Since the negative electrode of the present invention is for improving the rapid charging performance of a high-output battery, the effect of the present invention will be further maximized when lithium cobalt oxide advantageous for high output is selected in the positive electrode active material.

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

In this case, the positive electrode 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 has electronic conductivity without causing 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 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 or a mixture of two or more thereof may 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), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and as long as it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to respect and an excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. 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 optionally be used in a single-layer or multi-layer structure.

In addition, 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, and the like, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it is not going to be

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 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 C ₂ to C ₂₀ 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 sulfolane may be used. Among them, 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 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 LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ , etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

The electrolyte may include, in addition to the electrolyte components, haloalkylene carbonate-based compounds such as difluoroethylene carbonate for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity; or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N One or more additives such as -substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, the lithium secondary battery including the negative electrode according to the present invention has excellent fast charging performance and improved rolling performance, so that it is easy to manufacture a high-loading electrode, and since it shows a stable capacity retention rate, a mobile phone, a notebook computer , a portable device such as a digital camera, and an electric vehicle field such as a 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-to-large 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 several different forms and is not limited to the embodiments described herein.

Comparative Example 1

The average particle diameter (D ₅₀ ) was 16 μm to 17 μm, and uncoated artificial graphite was prepared. The artificial graphite, carbon black as a conductive material, and styrene butadiene rubber (SBR) as a binder were mixed in a weight ratio of 98.7:0.5:0.8 to prepare a negative electrode slurry.

The negative electrode slurry was applied to a 10 μm-thick copper (Cu) metal thin film, which is a negative electrode current collector, and rolled and dried to prepare a negative electrode.

Comparative Example 2

Artificial graphite to be a core and pitch were heat-treated at 1100° C. under N ₂ atmosphere to carbonize the pitch, thereby preparing artificial graphite coated with amorphous carbon. In this case, the average particle diameter (D ₅₀ ) of the artificial graphite coated with the amorphous carbon is 16 μm to 17 μm, and the content of the amorphous carbon is 0.3 wt %.

An anode was prepared in the same manner as in Comparative Example 1, except that the coated artificial graphite was used instead of the uncoated artificial graphite used in Comparative Example 1 when preparing the negative electrode slurry.

Comparative Example 3

As in Comparative Example 2, artificial graphite having an average particle diameter (D ₅₀ ) of 16 μm to 17 μm and an amorphous carbon content of 3 wt % was prepared through the carbonization process of the pitch.

An anode was prepared in the same manner as in Comparative Example 1, except that the coated artificial graphite was used instead of the uncoated artificial graphite used in Comparative Example 1 when preparing the negative electrode slurry.

Comparative Example 4

As in Comparative Example 2, artificial graphite having an average particle diameter (D ₅₀ ) of 16 μm to 17 μm and an amorphous carbon content of 20 wt % was prepared through the carbonization process of the pitch.

An anode was prepared in the same manner as in Comparative Example 1, except that the coated artificial graphite was used instead of the uncoated artificial graphite used in Comparative Example 1 when preparing the negative electrode slurry.

Experimental Example 1: Lithium-plated SOC by rapid charging

In order to confirm the rapid charging characteristics of the negative electrode for a lithium secondary battery of Comparative Example 1-4, a liplating experiment was performed.

First, after punching the prepared negative electrode for a lithium secondary battery to the size of a coin cell, a polyolefin separator was interposed between the lithium foil as a counter electrode, and then ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed in a volume ratio of 50:50 A coin-type half cell was prepared by injecting an electrolyte in which 1M LiPF ₆ was dissolved in one solvent.

Thereafter, the activation process was performed by charging and discharging each of the coin-type half cells including the negative electrode of the comparative examples in 3 cycles at a current density of 0.1 C-rate in a voltage range of 1.5 V to 0.005 V, respectively. In this way, the half-cell that has completed the activation process is CC (constant current) charged up to SOC 60% with a current density of 3C-Rate, and the inflection point of dQ/dV is checked in the voltage (SOC)-capacity profile graph. Table 1 shows the results of quantifying Li-plating SOC (%), which is the SOC at the point in time when lithium precipitation occurs on the surface of the anode. As the SOC of the inflection point increases, it can be evaluated that the rapid charging performance is excellent.

Experimental Example 2: Electrode thickness change rate

In order to evaluate the rolling performance of the negative electrode for lithium secondary batteries of Comparative Example 1-4, the thickness of the negative electrode before and after rolling was measured, and the ratio of the thickness decrease compared to the thickness before rolling was substituted into the following formula (1), and the result is shown in Table 1.

Equation (1) Thickness change rate (%) = (thickness before rolling - thickness after rolling)*100/(thickness before rolling)

Lithium plating SOC(%) Thickness change rate (%) Comparative Example 1 31.6 41.7 Comparative Example 2 33.5 39.8 Comparative Example 3 49.4 37.1 Comparative Example 4 52.4 11.9

Referring to Table 1, the higher the amorphous carbon content of the negative electrode material, the greater the lithium plating SOC. Through this, it was confirmed that the negative electrode material having a high amorphous carbon content was excellent in fast charging performance. However, as the content of the amorphous carbon in the negative electrode material increases, the thickness change rate is small, which means that it is disadvantageous for manufacturing a high-loading electrode.

Example 1

Artificial graphite coated with the same amorphous carbon as in Comparative Example 2 was prepared (the content of amorphous carbon was 0.3% by weight). The artificial graphite, carbon black as a conductive material, and styrene butadiene rubber (SBR) as a binder were mixed in a weight ratio of 98.7:0.5:0.8 to prepare a negative electrode slurry.

The negative electrode slurry was applied to a 10 μm-thick copper (Cu) metal thin film, which is a negative electrode current collector, and rolled and dried to prepare a negative electrode. After immersing the prepared negative electrode in an electrolyte solution in which 1M LiPF ₆ is dissolved in a solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 30:70 for 2 hours, lithium metal in the electrolyte solution A thin film was laminated on the negative electrode and pressurized for 6 hours to complete lithiation to complete the preparation of the negative electrode.

Example 2

In the same manner as in Example 1, except that the artificial graphite coated with the amorphous carbon of Comparative Example 3 (the content of amorphous carbon was 3 wt%) was used as the negative electrode active material in the preparation of the negative electrode slurry in Example 1 Preparation of the negative electrode was completed.

Example 3

In the preparation of the negative electrode slurry in Example 1, the amorphous carbon is coated on the artificial graphite core as the negative electrode active material, and the negative electrode material having an amorphous carbon content of 5 wt% was used, except for the same method as in Example 1 to complete the preparation of the negative electrode.

Comparative Example 5

In the preparation of the negative electrode slurry in Example 1, the amorphous carbon is coated on the artificial graphite core as the negative electrode active material, and the negative electrode material having an amorphous carbon content of 13% by weight was used, except for the same method as in Example 1 to complete the preparation of the negative electrode.

Comparative Example 6

In the same manner as in Example 1, except that the artificial graphite coated with the amorphous carbon of Comparative Example 4 (amorphous carbon content of 20% by weight) was used as the negative electrode active material in the preparation of the negative electrode slurry in Example 1 Preparation of the negative electrode was completed.

Experimental Example 3: Initial Efficiency

A coin-type half cell including the negative electrode of Examples 1-3 and Comparative Examples 1-6 was prepared. The coin-type half cell manufactured in the same manner as in Experimental Example 1 was tested for charging/discharging reversibility using an electrochemical charging/discharging device. During charging, a current was applied at a current density of 0.2 C-rate up to a voltage of 0.005 V (vs. Li/Li+), and during discharging, a voltage of 1.5 V was performed with the same current density. The initial efficiency was calculated by substituting the formula (2) below, and the results are shown in Table 2.

Equation (2) Initial efficiency (%) = Discharge capacity at 1 ^ST cycle * 100/1 Charge capacity at ^ST cycle

Experimental Example 4: Capacity retention rate

A positive electrode slurry was prepared by mixing LiCoO ₂ positive electrode active material, carbon black as a conductive material, and PVDF as binder in N-methyl-2 pyrrolidone solvent in a weight ratio of 97:1.5:1.5. The prepared positive electrode slurry was applied to an aluminum metal thin film having a thickness of 10 μm, dried and rolled.

After interposing a polyolefin separator between the negative electrode and the positive electrode prepared in Examples 1 to 3 and Comparative Examples 1 to 6, ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed in a volume ratio of 50:50 A full cell was prepared by injecting an electrolyte in which 1M LiPF ₆ was dissolved in one solvent. Lifespan characteristics were measured for the full cell. Specifically, at 25°C, 0.5C/4.2V constant current/constant voltage (CC/CV) 4.2V/0.05C conditions and discharges at 0.33C/3V constant current, PNE-0506 charger/discharger (Manufacturer: PNE Solution) , 5V, 6A) was used to measure the discharge capacity.

As 1 cycle, 100 cycles and 500 cycles were repeated, and the capacity retention rate was calculated according to the following formula (3), and the results are shown in Table 2.

Equation (3) Capacity retention rate (%) = {(discharge capacity in the corresponding cycle)/(discharge capacity in the first cycle)} Х 100

Content of amorphous carbon (wt%) Initial efficiency (%) Capacity retention rate (%) 100 cycles 500 cycles Comparative Example 1 0 93.6 97.22 91.38 Comparative Example 2 0.3 93. 96.90 90.87 Comparative Example 3 3 91.2 95.64 89.56 Comparative Example 4 20 86 89.97 84.00 Example 1 0.3 99.7 97.30 92.04 Example 2 3 100.5 99.01 97.41 Example 3 5 100.5 98.80 97.03 Comparative Example 5 13 100.4 95.9 92.3 Comparative Example 6 20 100.2 91.15 86.41

Referring to Table 2, the half cells to which the negative electrode of Comparative Examples 1 to 4 are applied, the higher the content of amorphous carbon in the negative electrode material, the greater the irreversible capacity is, so the initial efficiency tends to be lowered. The half cell to which the negative electrode of 3 is applied is shown to have excellent initial efficiency regardless of the content of amorphous carbon because the initial irreversible capacity decrease is compensated for by all-lithiation.

In addition, the battery to which the pre-lithiated negative electrode of Example 2 was applied showed much better capacity retention after a long cycle compared to the battery to which the negative electrode of Comparative Example 3 was not subjected to pre-lithiation, which was This is the effect of the initial irreversible compensation.

In addition, in Comparative Examples 5 to 6 to which graphite having a relatively high content of amorphous carbon was applied, even though the irreversible capacity was compensated by prelithiation, the capacity retention rate was lower than that of Examples 1 to 3. Therefore, in introducing graphite coated with amorphous carbon to the negative electrode to improve fast charging performance, it is preferable to select graphite having an amorphous carbon content of 10 wt% or less in order to prevent deterioration of lifespan characteristics.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the drawings disclosed in the present invention are for explanation rather than limiting the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these drawings. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (12)

A negative electrode material comprising a core including graphite and a shell including amorphous carbon disposed on the core,
The content of the amorphous carbon is 1 to 10% by weight based on the total weight of the negative electrode material,
Anode for pre-lithiated lithium secondary batteries.
The negative electrode for a lithium secondary battery according to claim 1, wherein the amorphous carbon is included in an amount of 1.5 to 7% by weight based on the total weight of the negative electrode material.
The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode material comprises secondary particles formed by agglomeration of one or more primary particles.
The negative electrode for a lithium secondary battery according to claim 1, wherein the graphite is natural graphite.
The negative electrode for a lithium secondary battery according to claim 1, wherein the graphite is artificial graphite.
The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode material is a spherical or similar spherical particle having an average particle diameter (D ₅₀ ) of 7 to 20 μm.
According to claim 1, further comprising uncoated graphite in the negative electrode material,
The first negative electrode active material of the first negative electrode active material layer disposed on the current collector is composed of uncoated graphite,
The second negative electrode active material of the second negative electrode active material layer disposed on the first negative electrode active material layer is a negative electrode for a lithium secondary battery, characterized in that composed of the negative electrode material.
The negative electrode for a lithium secondary battery according to claim 7, wherein a weight ratio of the uncoated graphite to the negative electrode material is 4:6 to 6:4 based on the total weight of the negative electrode active material.
The negative electrode for a lithium secondary battery according to claim 7, wherein the average particle diameter (D ₅₀ ) of the uncoated graphite is 10 μm to 22 μm.
The negative electrode for a lithium secondary battery according to claim 7, wherein the uncoated graphite is artificial graphite.
The negative electrode for a lithium secondary battery according to claim 1, wherein the binder is contained in an amount of 0.5 to 5% by weight.
A lithium secondary battery comprising the negative electrode of claim 1.