KR20210101540A - Negative electrode, and secondary battery comprising the same - Google Patents

Abstract

The present invention provides a negative electrode which comprises: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and comprising a negative electrode active material, wherein the negative electrode active material comprises at least one selected from silicon and silicon-based oxide, satisfies a specific formula, and D_90 is 3 to 10 ㎛.

Description

Anode, and a secondary battery comprising the same

The present invention relates to an anode and a 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 general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. In addition, the positive electrode and the negative electrode may have an active material layer including a positive active material or a negative active material on a current collector. Lithium-containing metal oxides such as LiCoO ₂ and LiMn ₂ O ₄ are generally used for the positive electrode as a positive electrode active material. Accordingly, a carbon-based active material and a silicon-based active material that do not contain lithium are used as the negative electrode active material for the negative electrode.

In particular, among the negative active materials, silicon-based active materials are attracting attention in that they have a capacity that is about 10 times higher than that of carbon-based active materials, and due to their high capacity, a high energy density can be realized even with a thin electrode. However, the silicon-based active material has a problem in that it is easy to break particles due to volume expansion due to insertion/desorption of lithium, and the electrical contact between particles is broken due to this volume expansion/contraction, and thus lifespan characteristics are deteriorated. have.

Accordingly, there is a need to develop a secondary battery capable of improving the lifespan characteristics while implementing high capacity and energy density of the silicon-based active material.

Korean Patent Application Laid-Open No. 10-2017-0074030 relates to a negative active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same, and discloses a negative active material including a porous silicon-carbon composite, but solves the above problems There are limits to solving it.

Korean Patent Publication No. 10-2017-0074030

One object of the present invention is to provide an anode active material for improving lifespan characteristics and preventing an increase in electrode thickness in an anode including a silicon-based material.

The present invention is a negative electrode current collector; and an anode active material layer formed on the anode current collector and including an anode active material, wherein the anode active material includes at least one selected from silicon and silicon-based oxide, and satisfies Equation 1 below, D ₉₀ A negative electrode having this thickness of 3 µm to 10 µm is provided.

[Equation 1]

1.0 ≤ (D ₉₀ -D ₁₀ )/D ₅₀ ≤ 2.5

In addition, the present invention is the above-described negative electrode; an anode opposite to the cathode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte; provides a secondary battery comprising.

The negative electrode of the present invention includes an anode active material, wherein the negative active material includes a silicon-based material (silicon and/or silicon-based oxide), satisfies a specific equation regarding particle size distribution, and D ₉₀ is characterized in that it is in a specific range . By controlling the particle diameter and particle size distribution of the negative electrode active material, the negative electrode of the present invention minimizes side reactions with the electrolyte and improves the pore structure of the electrode by adjusting the packing degree of the active material to an appropriate level, thereby lowering the resistance, the negative electrode active material It is possible to improve the cycle life characteristics by preventing the distortion of the negative electrode due to the volume expansion/contraction of

1 is a graph showing the particle size distribution of a negative active material according to Preparation Examples 1 to 9.
2 is a graph showing the thickness change rate of the negative electrode according to the charging SOC of Examples and Comparative Examples.
3 is a graph showing the cycle capacity retention rate of Examples and Comparative Examples.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define 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 there is.

The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.

In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the presence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, elements, or combinations thereof.

In the present specification, D ₁₀ , D ₅₀ , D ₉₀ , and D ₉₉ are defined as particle diameters corresponding to 10%, 50%, 90%, and 99% of the cumulative volume, respectively, in the particle size distribution curve of the particles. The D ₁₀ , D ₅₀ , D ₉₀ , and D ₉₉ may be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of several mm from a submicron region, and can obtain high reproducibility and high resolution results.

Hereinafter, the present invention will be described in detail.

<Cathode>

The present invention relates to a negative electrode, and specifically to a negative electrode for a lithium secondary battery.

Specifically, the negative electrode of the present invention is a negative electrode current collector; and an anode active material layer formed on the anode current collector and including an anode active material, wherein the anode active material includes at least one selected from silicon and silicon-based oxide, and satisfies Equation 1 below, D ₉₀ This is 3 µm to 10 µm.

[Equation 1]

1.0 ≤ (D ₉₀ -D ₁₀ )/D ₅₀ ≤ 2.5.

In general, silicon-based active materials (for example, silicon or silicon-based oxide) are known to have a capacity about 10 times higher than that of carbon-based active materials. It is expected that it will be possible to realize a thin film electrode having an energy density. However, the silicon-based active material has a large degree of volume expansion/contraction according to the insertion/desorption of lithium according to charging and discharging, and accordingly, an electrical short circuit between the active materials is a problem, thereby deteriorating the lifespan characteristics.

In addition, in order to prevent excessive volume expansion/contraction of the conventional silicon-based active material, a method of adjusting the size of the active material to a nanometer (nm) level has been studied. There is a problem in that the side reaction of the electrode is deepened and the lifespan characteristics deteriorate rapidly, and it is difficult to secure a pore in the electrode, so that the charge transfer resistance is increased. In addition, when the size of the silicon-based active material is adjusted to the nanometer (nm) level, the dispersibility of the negative electrode active material is not good during the preparation of the negative electrode slurry, and accordingly, it is difficult to uniformly form the negative electrode active material layer. And it is not easy to apply to the actual industrial field.

In order to solve this problem, the negative active material included in the negative electrode of the present invention includes at least one selected from silicon and silicon-based oxide, satisfies Equation 1, and D ₉₀ is adjusted to a specific range. Accordingly, the negative electrode according to the present invention can not only minimize side reactions with the electrolyte, but also improve the pore structure in the electrode by adjusting the packing degree of the particles to an appropriate level, thereby lowering the charge transfer resistance, silicon and/or It is possible to prevent the anode from being distorted due to volume expansion/contraction due to charging and discharging of the silicon-based oxide. In particular, in the negative electrode of the present invention, since the size of the negative active material included therein is at the micrometer (㎛) level, it is easy to prepare and disperse the slurry, and it is possible to uniformly form the negative electrode active material layer, which is preferable for mass production of the negative electrode. Accordingly, in the negative electrode of the present invention and the secondary battery including the same, the pore structure of the electrode is improved, thereby lowering the charge transfer resistance, minimizing the change in electrode thickness due to charging and discharging, and improving lifespan characteristics to a remarkable level.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. Specifically, the negative electrode current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, one in which the surface of copper or stainless steel is surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. have.

The negative electrode current collector may typically have a thickness of 3 to 500 μm.

The negative electrode current collector may form fine irregularities on the surface to strengthen the bonding strength of the negative electrode active material. For example, the negative electrode current collector 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 negative electrode includes a negative active material layer formed on the negative electrode current collector, and the negative active material layer includes a negative electrode active material.

The negative active material includes at least one selected from silicon (Si) and a silicon-based oxide.

The silicon-based oxide _{may be a compound represented by SiO x} (0<x<2). Since SiO ₂ does not react with lithium ions and cannot store lithium, x is preferably within the above range.

Specifically, the negative active material may include silicon. Conventionally, Si is advantageous in that its capacity is about 2.5 to 3 times higher than that of silicon oxide (for example, SiO _x (0<x<2)), but the degree of volume expansion/contraction due to charging and discharging of Si is in the case of silicon-based oxide. However, in the present invention, by adjusting the particle diameter of the negative active material containing silicon to a specific range, the problem of deterioration of lifespan characteristics caused by volume expansion of silicon can be effectively solved, and silicon The advantages of high capacity and energy density can be more preferably realized.

The silicon may be polycrystalline silicon (poly-Si). The polycrystalline silicon may be defined as an aggregate of monocrystal silicon. When the polycrystalline silicon is used as silicon, it is preferable because high capacity and high energy density can be achieved, and it is preferable in terms of low cost.

The purity of the polycrystalline silicon is preferably 99.0% or more, preferably 99.5% or more, and in the above range, it is preferable in terms of realization of high capacity and high energy density of polycrystalline silicon.

The negative active material may further include a carbon coating layer formed on the silicon and/or silicon-based oxide. The carbon coating layer may function as a protective layer that suppresses volume expansion of silicon and/or silicon-based oxide and prevents a side reaction with an electrolyte.

The carbon coating layer may be included in an amount of 0.1 wt% to 10 wt%, preferably 1 wt% to 6 wt%, in the negative active material, and when the carbon coating layer is in the above range, the volume expansion of silicon and/or silicon-based oxide is excellent. It is preferable in terms of being able to prevent side reactions with the electrolyte while controlling the level.

The weight of the carbon coating layer may be measured by thermogravimetric analysis (TGA).

The carbon coating layer may be an amorphous carbon coating layer. Specifically, the carbon coating layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

The negative active material satisfies Equation 1 below.

[Equation 1]

1.0 ≤ (D ₉₀ -D ₁₀ )/D ₅₀ ≤ 2.5

_{When (D 90} -D ₁₀ )/D ₅₀ of the negative active material exceeds 2.5, it may be understood that the particle size distribution is too wide, in this case, charging and discharging in the negative electrode including silicon and/or silicon-based oxide, specifically silicon There is a problem in that the non-uniformity and thickness increase of the active material layer are increased according to the current state, and the electrical contact between the active materials is cut according to the change in the volume of the active material, so that the lifespan characteristics are rapidly deteriorated. _{When (D 90} -D ₁₀ )/D ₅₀ of the negative active material is less than 1.0, the particle size distribution is narrow and uniform, but the packing density between the active materials is low, so the thickness of the negative electrode is large, and thus the contact between the active materials is lowered. Deterioration of lifespan characteristics may be exacerbated.

The (D ₉₀ -D ₁₀ )/D ₅₀ may be 1.0 to 2.5, preferably 1.3 to 2.4, and more preferably 1.6 to 2.0, and when the range is in the range, the particle size distribution is adjusted to a desired level to the degree of packing of the active material can be adjusted to a desirable level, electrode thickness change can be minimized, and electrical contact between active materials can be improved, which is more advantageous in improving lifespan characteristics.

_{D 90} of the negative active material is 3 μm to 10 μm. The anode active material according to the present invention satisfies Equation 1 _{and adjusts D 90} to a specific range, thereby controlling the specific surface area of the anode active material to a desired level and minimizing side reactions with the electrolyte, as well as packing particles By adjusting the degree to an appropriate level, it is possible to prevent volume expansion/contraction due to charging and discharging of the silicon-based active material, and thus reduction in electrical contact between the particles.

_{When D 90} of the negative active material is less than 3 μm, since the particle size of the active materials is too small, the specific surface area of the active material increases, which may intensify side reactions with the electrolyte, and the electrode pore is small, so the charge transfer resistance increases and the lifespan performance decreases. There is a risk of becoming an anode, it is difficult to uniformly disperse the anode active material during the manufacture of the anode, non-uniform formation of the anode active material layer is caused, and mass production of the anode may be difficult. _{In addition, when D 90} of the anode active material is greater than 10 μm, the distance between particles between the active materials increases due to charging and discharging of the active material, so that electrical contact is very deteriorated, and thus the life performance of the anode may deteriorate.

_{D 90} of the negative active material may be preferably 3.5 μm to 9.0 μm, more preferably 4.0 to 7.5 μm, and more preferably 5.5 μm to 6.2 μm, and when it is in the range, electrical contact between active materials can be improved. In addition, it is possible to minimize the change in electrode thickness, which is more advantageous in improving the lifespan characteristics, and it is possible to minimize the generation of excessive fine powder during the particle size control process, thereby providing excellent dispersibility and reducing gas generation due to side reactions with the electrolyte.

_{D 99} of the negative active material may be 20 μm or less, preferably 7 μm to 17 μm, more preferably 9 μm to 12 μm, and uniform formation of the negative electrode active material layer, the silicon-based active material during charging and discharging in the above range. It is preferable in terms of improving electrical contact.

_{D 50} of the negative active material may be 1 μm to 5 μm, preferably 2 μm to 4 μm, and D ₁₀ of the silicon-based active material may be 0.1 μm to 1.5 μm, preferably 0.3 μm to 1.0 μm. In the above range, it is possible to prevent a side reaction problem of the electrolyte due to excessively small particle size, uniform coating of the negative electrode, and lower charge transfer resistance by properly securing the pore structure, and silicon-based due to excessively large particle size Problems such as an increase in the degree of volume expansion of the active material and an increase in electrode thickness change can be prevented. In addition, when satisfying the ranges of Equations 1 and D _{90 while satisfying the ranges of D 50} and/or D ₁₀ , the packing degree of the active material can be adjusted to a desired level, the electrode thickness change can be minimized, and the electrical contact between the active materials can be improved, which is more preferable for improving lifespan characteristics.

D ₁₀ , D ₅₀ , D ₉₀ , and D ₉₉ of the negative active material are sieving, milling, classification, etc. to an appropriate level for the negative active material including at least one selected from silicon and silicon-based oxide. It can be implemented by the method

The BET specific surface area of the negative active material may be 1 m ² /g to 5 m ² /g, preferably 1.5 m ² /g to 3.5 m ² /g, and side reaction with the electrolyte may be prevented when it is within the above range preferred in The BET specific surface area of the negative active material may be measured by, for example, a Brunauer-Emmett-Teller (BET) measurement method using BELSORP (BET equipment) manufactured by BEL JAPAN using an adsorbed gas such as nitrogen.

The anode active material may be included in the anode active material layer in an amount of 60 wt% or more, preferably 60 wt% to 90 wt%, more preferably 65 wt% to 80 wt%.

The negative active material layer may further include a binder.

In the aspect that the binder further improves electrode adhesion and provides sufficient resistance to volume expansion/contraction of the active material, styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber (acrylic rubber), butyl rubber, fluoro rubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA: polyvinyl alcohol), At least one selected from the group consisting of polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN: polyacrylonitrile), and polyacryl amide (PAM: polyacryl amide) or a copolymer thereof may include.

Specifically, the binder may include at least one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyacrylamide, and polyacrylonitrile. More specifically, the binder has high strength, has excellent resistance to volume expansion/contraction of the silicon-based negative active material, and provides excellent flexibility to the binder to prevent distortion and warpage of the electrode. and at least one selected from polyacrylic acid, and more specifically, a copolymer of polyvinyl alcohol and polyacrylic acid. The copolymer of polyvinyl alcohol and polyacrylic acid may be a copolymer of a vinyl alcohol monomer and an acrylic acid monomer.

The binder may be included in an amount of 5 wt% to 30 wt%, preferably 15 wt% to 25 wt%, in the anode active material layer, and it is preferable in terms of being able to more effectively control the volume expansion of the active material when it is in the range .

The negative active material layer may further include a conductive material. The conductive material may be used to improve the conductivity of the negative electrode, and it is preferable to have conductivity without causing a chemical change.

The conductive material may include graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives; conductive fibers such as carbon fibers, carbon nanofibers (CNF) and metal fibers; conductive tubes such as carbon nanotubes (CNTs); and at least one selected from the group consisting of conductive whiskers such as zinc oxide and potassium titanate, preferably carbon black.

The conductive material may be included in the anode active material layer in an amount of 5 wt% to 20 wt%, more preferably 7 wt% to 15 wt%.

The thickness of the negative active material layer may be 10 μm to 100 μm, preferably 20 μm to 60 μm.

The negative electrode is prepared by dispersing the negative electrode active material, the binder and the conductive material in a solvent for forming the negative electrode slurry on the negative electrode current collector, and coating the negative electrode slurry on the negative electrode current collector, followed by drying and rolling. can be manufactured.

The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, preferably distilled water, in terms of facilitating dispersion of the components.

<Secondary battery>

The present invention provides a secondary battery including the above-described negative electrode, specifically, a lithium secondary battery.

Specifically, the secondary battery according to the present invention includes the above-described negative electrode; an anode opposite to the cathode; a separator interposed between the negative electrode and the positive electrode; and electrolyte;

The positive electrode is a positive electrode current collector; A positive electrode active material layer formed on the positive electrode current collector may be included.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. Specifically, the negative electrode current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, one in which the surface of copper or stainless steel is surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. have.

The positive electrode current collector may typically have a thickness of 3 to 500 μm.

The positive electrode current collector may form fine concavities and convexities on the surface to strengthen the bonding force of the negative electrode active material. For example, the negative electrode current collector 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 positive active material layer may include a positive active material.

The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, a lithium transition metal composite oxide containing lithium and at least one transition metal consisting of nickel, cobalt, manganese, and aluminum; Preferably, it may include a transition metal including nickel, cobalt and manganese and a lithium transition metal composite oxide including lithium.

More specifically, as the lithium transition metal composite oxide, lithium-manganese oxides (eg, LiMnO ₂ , LiMn ₂ O _{4 ,} etc.), lithium-cobalt-based oxides (eg, LiCoO _{2 ,} etc.), lithium-nickel oxide-based oxide (eg, LiNiO _{2 ,} etc.), lithium-nickel-manganese oxide (eg, LiNi _1-Y Mn _Y O ₂ (here, 0<Y<1), LiMn _2-z Ni _z O ₄ (here, 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (eg, LiNi _1-Y1 Co _Y1 O ₂ (here, 0<Y1<1), etc.), lithium-manganese -Cobalt-based oxides (eg, LiCo _1-Y2 Mn _Y2 O ₂ (here, 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (here, 0<Z1<2), etc.), lithium -nickel-manganese-cobalt oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (here, 0<p<1, 0<q<1, 0<r1<1, p+q+ r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or Lithium-nickel-cobalt-transition metal (M) oxide (eg, Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ , wherein M is Al, Fe, V, Cr, Ti, Ta, Mg and is selected from the group consisting of Mo, and p2, q2, r3 and s2 are atomic fractions of each independent element, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2 +q2+r3+s2=1) and the like), and any one or two or more compounds may be included. Among them, the lithium transition metal composite oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel-manganese-cobalt oxide (for example, Li (Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or Li(Ni _0.8 Mn _0.1 Co _0.1 )O _{2 ,} etc.), or lithium nickel cobalt aluminum oxide (eg For example, it may be Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ etc.), and the lithium transition metal in consideration of the significant improvement effect according to the control of the type and content ratio of the element forming the lithium transition metal composite oxide. The composite oxide is Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ and the like, and any one or a mixture of two or more thereof may be used.

The positive active material may be included in an amount of 80 wt% to 99 wt%, preferably 92 wt% to 98.5 wt%, in the cathode active material layer in consideration of the sufficient capacity of the cathode active material.

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

The binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, specifically polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose from the group consisting of woods, recycled cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber and fluororubber. It may include at least one selected, preferably polyvinylidene fluoride.

The binder may be included in an amount of 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, in the cathode active material layer in terms of sufficiently securing binding force between components such as the cathode active material.

The conductive material may be used to assist and improve conductivity in the secondary battery, and is not particularly limited as long as it has conductivity without causing chemical change. Specifically, the conductive material may include 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; and at least one selected from the group consisting of polyphenylene derivatives, and preferably carbon black in view of improving conductivity.

The conductive material may be included in an amount of 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, in the cathode active material layer in terms of sufficiently securing electrical conductivity.

The thickness of the positive active material layer may be 30 μm to 400 μm, preferably 50 μm to 110 μm.

The positive electrode may be prepared by coating a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming the positive electrode slurry on the positive electrode current collector, followed by drying and rolling.

The solvent for forming the cathode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount having a desirable viscosity when the cathode active material and, optionally, a binder and a conductive material are included. can For example, the solvent for forming the positive electrode slurry is the positive electrode slurry such that the concentration of the solids including the positive electrode active material, and optionally the binder and the conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt% can be included in

The separator separates the anode and the anode and provides a passage for lithium ions to move, and can be used without any particular limitation as long as it is normally used as a separator in a lithium secondary battery. Excellent is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or 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, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, 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, etc. that can be used in the manufacture of secondary batteries, and are limited to these it is not

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

The organic solvent may be used without 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, gamma-butyrolactone, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (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 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 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 LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO 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 0.1 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.

The secondary battery may be manufactured by inserting an electrolyte solution after interposing a separator between the above-described negative electrode and positive electrode according to a conventional secondary battery manufacturing method.

The secondary battery according to the present invention is useful for portable devices such as mobile phones, notebook computers, digital cameras, and the like, and electric vehicles such as hybrid electric vehicles (HEVs). can be used Accordingly, the present invention also provides a medium and large-sized battery module including the secondary battery as described above as a unit cell.

These medium and large-sized battery modules can be preferably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

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.

manufacturing example

Preparation Example 1: Preparation of negative active material

A carbon coating layer was formed by chemical vapor deposition (CVD) of methane as a hydrocarbon gas on Si (purity of 99.5% or more), which is polycrystalline silicon, at 950°C. Next, by sieving, milling, and classifying the Si having the carbon coating layer formed, D ₁₀ , D ₅₀ , D ₉₀ , and D ₉₉ were adjusted to 0.7 μm, 2.5 μm, 6.5 μm, and 15 μm, respectively, to prepare the negative active material of Preparation Example 1 (specific surface area 1.7 m ² /g). 1 and Table 1 show the particle size distribution of Preparation Example 1.

The carbon coating layer was included in the negative active material of Preparation Example 1 in an amount of 3% by weight. The weight of the carbon coating layer was measured by thermogravimetric analysis (TGA).

Preparation Examples 2 to 9: Preparation of negative active material

Anode active materials of Preparation Examples 2 to 9 were prepared in the same manner as in Preparation Example 1, except that the particle size distribution was adjusted to Table 1 and FIG. 1 below.

In addition, the BET specific surface area of Preparation Examples 1 to 9 is shown in Table 1 below. In Table 1 below, the BET specific surface area of the negative active material was measured by pretreating the negative active material at 130° C. and BET (Brunauer-Emmett-Teller) measurement method using BELSORP (BET equipment) manufactured by BEL JAPAN using nitrogen gas.

Carbon coating layer content (based on the total weight of the negative electrode active material, weight %) D ₁₀ (μm) D ₅₀ (μm) D ₉₀ (μm) D ₉₉ (μm) (D ₉₀ -D ₁₀ )/D ₅₀ BET specific surface area (m ² /g) Preparation Example 1 3 0.7 2.5 6.5 15 2.32 1.7 Preparation 2 3 0.5 3.0 5.8 9.5 1.77 2.2 Preparation 3 3 0.7 3.0 5.2 8.5 1.50 2.5 Preparation 4 3 0.7 2.4 3.7 6.9 1.25 2.9 Preparation 5 3 1.0 4.5 17.5 29.9 3.67 1.0 Preparation 6 3 0.5 4.0 10.8 13 2.58 1.9 Preparation 7 3 2.0 5.0 6.8 10 0.96 1.4 Preparation 8 3 0.03 1.3 2.3 4.8 1.74 6.4 Preparation 9 3 1.0 7.2 12.7 18.9 1.78 1.3

Example

Example 1: Preparation of negative electrode

A negative active material prepared in Preparation Example 1 as an anode active material, a copolymer of polyvinyl alcohol and polyacrylic acid (product name: Aquacharge, manufacturer: Sumitomo) as the binder and carbon black (Super C65) as a conductive material in a ratio of 70:20:10 The mixture was mixed in a weight ratio, and this was added to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry.

As a negative electrode current collector, the negative electrode slurry was coated on one side of a copper current collector (thickness: 15 μm) with ^{a loading amount of 10 mAh/cm 2} , rolled, and dried in a vacuum oven at 130° C. for 10 hours to dry the negative electrode. An active material layer (thickness: 29 μm) was formed, and this was used as the negative electrode according to Example 1 (thickness of the negative electrode: 44 μm).

Example 2: Preparation of negative electrode

A negative electrode of Example 2 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 2 was used instead of the negative active material of Preparation Example 1.

Example 3: Preparation of negative electrode

A negative electrode of Example 3 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 3 was used instead of the negative active material of Preparation Example 1.

Example 4: Preparation of negative electrode

A negative electrode of Example 4 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 4 was used instead of the negative active material of Preparation Example 1.

Comparative Example 1: Preparation of negative electrode

A negative electrode of Comparative Example 1 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 5 was used instead of the negative active material of Preparation Example 1.

Comparative Example 2: Preparation of negative electrode

A negative electrode of Comparative Example 2 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 6 was used instead of the negative active material of Preparation Example 1.

Comparative Example 3: Preparation of negative electrode

A negative electrode of Comparative Example 3 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 7 was used instead of the negative active material of Preparation Example 1.

Comparative Example 4: Preparation of negative electrode

A negative electrode of Comparative Example 4 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 8 was used instead of the negative active material of Preparation Example 1.

Comparative Example 5: Preparation of negative electrode

A negative electrode of Comparative Example 5 was prepared in the same manner as in Example 1, except that the negative active material of Preparation Example 9 was used instead of the negative active material of Preparation Example 1.

Experimental example

Experimental Example 1: Measurement of electrode thickness change according to charging SOC

<Manufacture of secondary battery>

A lithium metal counter electrode was prepared as the positive electrode.

Each negative electrode according to Examples 1 to 4 and Comparative Examples 1 to 5, a polypropylene separator was interposed between the positive electrode prepared above, and electrolyte was injected to form a coin-shaped half-cell Example 1 to 4, the secondary batteries of Comparative Examples 1 to 5 were prepared, respectively. The electrolyte is an organic solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) are mixed in a volume ratio of 30:70, LiPF6 as a lithium salt is added at a concentration of 1M, and fluoroethylene carbonate (FEC) is prelithiated as an additive. What was added in an amount of 2% by weight based on the total weight of the solution was used.

<Evaluation of changes in electrode thickness according to charging SOC>

The electrode thickness change rate according to the SOC of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5 prepared above was measured.

Specifically, the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5 were charged and discharged at 0.1C to measure the discharge capacity of each of the negative electrodes of Examples 1 to 4 and Comparative Examples 1 to 5.

After preparing four secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5, respectively, based on the discharge capacity of the four secondary batteries, SOC (State of Charge) 10%, 30%, 50%, 80%, respectively was charged, and the secondary battery was disassembled to recover the negative electrode, washed and dried.

The rate of change (%) in the thickness of the anode compared to the thickness of the anode before charging of the recovered anode was measured by the following formula, and is shown in Table 2 and FIG. 2 .

Anode thickness change rate (%) according to charging SOC SOC 10% SOC 30% SOC 50% SOC 80% Example 1 85 132 158 203 Example 2 78 126 143 186 Example 3 66 118 136 164 Example 4 60 113 130 148 Comparative Example 1 148 218 277 357 Comparative Example 2 110 170 216 282 Comparative Example 3 127 179 233 307 Comparative Example 4 64 116 133 146 Comparative Example 5 88 152 202 286

Referring to Table 2 and FIG. 2, in the case of the negative electrode including the negative active material of the Examples, by adjusting the particle size distribution and the packing degree of the active material to an appropriate level, the negative electrode thickness change according to charging and discharging compared to Comparative Examples 1 to 3 and 5 It can be seen that there is less

Comparative Example 4 exhibits a similar level of negative electrode thickness change rate as in Examples due to its small particle size, but exhibits very poor performance in cycle capacity retention due to severe electrolyte side reactions due to charging and discharging, as will be described later.

Experimental Example 2: Capacity retention rate evaluation according to cycle

For the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5 prepared above, discharge capacity evaluation and capacity retention rate evaluation were performed using an electrochemical charger/discharger. At the time of charging, a current was applied at a current density of 0.5C-rate up to a voltage of 4.2V, and at the time of discharging, a voltage of 2.5V was performed with the same current density.

The capacity retention ratio was measured by measuring the discharge capacity according to the cycle of the lithium secondary batteries of Examples and Comparative Examples, and the capacity retention ratio was evaluated by the following formula. The change in the capacity retention rate according to the cycle is shown in FIG. 3, and the capacity retention rate at 30 cycles is shown in Table 3 below.

Capacity retention rate (%) = (discharge capacity in the Nth cycle)/(discharge capacity in the first cycle) × 100

(Wherein, N is an integer from 1 to 30)

Capacity retention (%) @ 30cycle Example 1 60.3 Example 2 64.3 Example 3 59.4 Example 4 56.7 Comparative Example 1 37.9 Comparative Example 2 39.2 Comparative Example 3 39.2 Comparative Example 4 31.3 Comparative Example 5 38.5

Referring to Table 3 and FIG. 3, the secondary battery including the negative active material of the embodiments minimizes side reactions with the electrolyte and adjusts the packing degree of the active material to an appropriate level, thereby causing an electrical short circuit between the active materials due to volume expansion/contraction of the silicon-based active material. problems can be avoided. Accordingly, it can be confirmed that the secondary batteries of the Examples exhibit a superior capacity retention rate compared to the case of Comparative Examples.

Claims (12)

negative electrode current collector; and
A negative electrode active material layer formed on the negative electrode current collector, the negative electrode active material comprising a;
The negative active material includes at least one selected from silicon and silicon-based oxide, satisfies Equation 1 below, and a negative electrode having a _{D 90 of 3 μm to 10 μm:}
[Equation 1]
1.0 ≤ (D ₉₀ -D ₁₀ )/D ₅₀ ≤ 2.5.
The method according to claim 1,
The negative active material is a negative electrode comprising silicon.
The method according to claim 1,
wherein the silicon is polycrystalline silicon.
The method according to claim 1,
_{D 99} of the negative active material is 20㎛ or less.
The method according to claim 1,
_{D 50} of the negative active material is 1㎛ to 5㎛ the negative electrode.
The method according to claim 1,
_{D 10} of the negative active material is 0.1 μm to 1.5 μm.
The method according to claim 1,
The negative electrode active material has a BET specific surface area of 1 m ² /g to 5 m ² /g.
The method according to claim 1,
The anode active material further includes a carbon coating layer formed on at least one selected from the group consisting of silicon and silicon-based oxide.
9. The method of claim 8,
The carbon coating layer is an anode comprising 0.1 wt% to 10 wt% in the anode active material.
The method according to claim 1,
The anode active material layer is an anode comprising 60% by weight or more of the anode active material.
The method according to claim 1,
The negative electrode active material layer has a thickness of 10 μm to 100 μm.
a negative electrode according to claim 1;
an anode opposite to the cathode;
a separator interposed between the negative electrode and the positive electrode; and
A secondary battery comprising; an electrolyte.

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