KR20150014329A - Anode Active Material with Improved Wetting Properties and Lithium Secondary Battery Having the Same - Google Patents

Abstract

The present invention relates to a negative electrode active material with improved wetting properties and a secondary battery comprising the same. More specifically, provided are a negative electrode active material including carbon particles and a nano-structured silicon (Si) layer formed on the carbon particle, and the secondary battery comprising the same.

Description

[0001] The present invention relates to an anode active material for a secondary battery having improved wettability and a lithium secondary battery comprising the anode active material.

The present invention relates to a negative active material for a secondary battery having improved wettability and a secondary battery including the same.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It has been commercialized and widely used.

Lithium composite metal oxide is used as a cathode active material of such a lithium secondary battery, and graphite which is capable of inserting / desorbing lithium has been typically used as an anode active material of such a lithium secondary battery. However, since such an electrode using graphite has a low charge capacity, there is a limit in providing a lithium secondary battery exhibiting excellent capacity characteristics.

Accordingly, inorganic active materials such as silicon (Si), germanium (Ge), and antimony (Sb) have been studied. Such a inorganic active material has a very large lithium bonding amount particularly in the case of a silicon anode active material, and can exhibit a high theoretical capacity of 3580 mAh / g.

However, the inorganic anode active material such as silicon exhibits pulverization due to insertion / desorption of lithium, that is, a large volume change during charging / discharging of the battery, and as the anode active material is separated from the current collector, A contact loss occurred. Accordingly, in the battery using the conventional inorganic negative electrode active material, loss of the reversible capacity occurred in accordance with the charge-discharge cycle.

Therefore, the previously known inorganic negative electrode active material, for example, the silicon negative active material and the lithium secondary battery including the lithium negative electrode active material have disadvantages in that they exhibit low cycle life characteristics and capacity retention ratio despite their advantages according to their high charge capacities.

In addition, when silicon having a low conductivity is coated on the negative electrode active material to produce such a silicon-based negative active material, the reaction does not sufficiently take place in the outermost silicon layer, so that the internal reaction of the negative active material is limited, There was a problem that the capacity was reduced.

Therefore, a need exists for a technique capable of solving such a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have confirmed that a desired effect can be achieved when a silicon (Si) layer having a nanostructure formed on carbon particles is included as described later And completed the present invention.

Accordingly, the negative active material for a secondary battery according to the present invention comprises carbon particles and a nanostructured silicon (Si) layer formed on the carbon particles.

When the negative electrode active material is manufactured using the nanostructured silicon, the absolute volume expansion of the negative electrode active material due to charging and discharging of the battery is reduced, thereby improving the cycle characteristics of the battery.

In one specific example, the carbon particles are composed of crystalline graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, Ketjenblack, super P, graphene, Lt; / RTI > More specifically, the carbon particles may be crystalline artificial graphite, and / or crystalline natural graphite.

The diameter of such carbon particles may be from 1 micrometer or greater to 20 micrometer or less. The smaller the diameter of the carbon particles, the wider the specific surface area of the active material. In one specific example, the specific surface area of the carbon particles may be 2 m ² / g or more to 7 m ² / g or less.

In one specific example, the nanostructured silicon may be in the form of nanoparticles, and such silicon nanoparticles may have a size of 1 nanometer or more to 100 nanometers or less.

In one specific example, the silicon may be in the form of nanowires, which may be 10 nanometers or more to 500 nanometers or less in diameter and 20 nanometers or more to 1000 nanometers or less in length.

In one specific example, the silicon layer may be grown based on carbon particles, and the thickness of the silicon layer may be greater than or equal to 20 nanometers and less than or equal to 1500 nanometers.

The present invention provides a negative electrode comprising the negative active material.

At this time, the negative electrode may have a loading density of 1.5 mAh / cm ² or more to 8.5 mAh / cm ² or less.

The present invention also provides a secondary battery in which an electrolyte solution is impregnated in an electrode assembly including the negative electrode, the positive electrode, and the separator interposed between the negative electrode and the positive electrode.

In one specific example, the positive electrode may include a lithium transition metal oxide represented by the following formula (1) or (2) as a positive electrode active material.

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

In this formula,

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more anions of -1 or -2;

0.9? X? 1.2, 0 <y <2, 0? Z <0.2.

(1-x) LiM'O _2-y A _y -xLi ₂ MnO _{3 -y '} A _y' (2)

In this formula,

M 'is Mn _a M _b ;

M is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and two period transition metals;

A is at least one selected from the group consisting of anions of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ ;

0 <x <1, 0 <y? 0.02, 0 <y? 0.02, 0.5? A? 1.0, 0 b? 0.5, a + b =

In one specific example, the secondary battery may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.

The present invention provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source.

At this time, the device may be an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

As described above, the negative electrode active material for a secondary battery according to the present invention improves the wettability of the negative electrode active material by forming a nanostructured silicon layer as thin as possible on the finer carbon particles, thereby providing a high capacity secondary battery There is an effect that can be.

As described above, the negative active material for a secondary battery according to the present invention includes carbon particles and a nanostructured silicon (Si) layer formed on the carbon particles.

The present invention also relates to a secondary battery including an anode including the anode active material, a cathode including at least one of lithium metal oxide and lithium metal phosphate, and a separator interposed between the cathode and the anode, Thereby providing a battery.

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

The lithium metal oxide of the anode may be LiMO ₂ (M = Co, Ni, Mn), Li _{1 + x} Mn _{2 -x} O ₄₊ (0? _X ? 0.3) and LiNi _1-x M _x O ₂ Li, Mn, Al, Cu, Fe, Mg, B or Ga and 0.01? X? 0.3), and the lithium metal phosphorus is LiMPO ₄ (M = Fe, Co, Ni, Mn) , the lithium metal oxide of the anode is _{LiCoO 2, LiNiO 2, LiMn 2} O 4, Li (Ni a Mn b Co c) O 2 (a + b + c = 1), LiNi 0.5 Mn 1.5 O 4 and LiNi _0.5 Mn _0.5 O ₂ , and the lithium metal phosphates include LiFePO ₄ , LiMnPO ₄ and Li ₃ V ₂ (PO ₄ ) ₃ , but are not limited thereto. Among them, LiNi _0.5 Mn _1.5 O _4, LiCoPO ₄ , y Li ₂ MnO ₃ (1-y) LiNi _a Mn _b Co _c O ₂ (0.2 ≤ y ≤ 0.8, a + b + c = 1) and Li ₃ V ₂ (PO ₄ ) ₃ .

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes 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, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component for suppressing expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The positive electrode according to the present invention can be prepared by applying a slurry prepared by mixing a positive electrode mixture containing the above-described compounds to a solvent such as NMP, coating the positive electrode collector, followed by drying and rolling.

The cathode current collector is generally made to have a thickness of not less than 3 micrometers and not more than 500 micrometers. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Carbon, nickel, titanium, silver, or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The present invention also provides a lithium secondary battery comprising the positive electrode, the negative electrode, the separator, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode is prepared, for example, by applying a negative electrode mixture containing the negative electrode active material on a negative electrode collector and then drying the same. The negative electrode mixture may contain the components as described above, if necessary. Further, the negative electrode may be operated in a voltage range of 0V to 3.5V with respect to lithium.

The anode current collector is generally made to have a thickness of not less than 3 micrometers and not more than 500 micrometers. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally not less than 0.01 micrometer to 10 micrometers, and the thickness is generally not less than 5 micrometers and not more than 300 micrometers. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

The present invention provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source.

At this time, specific examples of the device include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (20)

Carbon particles; And
A nanostructured silicon (Si) layer formed on the carbon particles;
And a negative electrode active material for a secondary battery. 2. The method of claim 1, wherein the carbon particles are composed of crystalline graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, Ketjen black, super P, graphene, Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt; The negative electrode active material for a secondary battery according to claim 2, wherein the carbon particles are crystalline graphite and / or crystalline natural graphite. The negative electrode active material for a secondary battery according to claim 1, wherein the carbon particles have a diameter ranging from 1 micrometer to 20 micrometers. The negative electrode active material for a secondary battery according to claim 1, wherein the carbon particles have a specific surface area of 2 m ² / g or more to 7 m ² / g or less. The negative electrode active material for a secondary battery according to claim 1, wherein the silicon is in the form of nanoparticles. The negative electrode active material for a secondary battery according to claim 6, wherein the silicon nanoparticles have a size of 1 nanometer or more to 100 nanometers or less. The negative electrode active material for a secondary battery according to claim 1, wherein the silicon is in the form of nanowires. The negative electrode active material for a secondary battery according to claim 8, wherein the silicon nanowire has a diameter of 10 nanometers or more to 500 nanometers or less and a length of 20 nanometers or more to 1000 nanometers or less. The negative electrode active material for a secondary battery according to claim 1, wherein the thickness of the silicon layer is 20 nanometers or more to 1500 nanometers or less. The negative electrode active material for a secondary battery according to claim 1, wherein the silicon layer is grown on the basis of carbon particles. An anode comprising the anode active material according to any one of claims 1 to 11. The cathode according to claim 12, wherein the cathode has a loading density of 1.5 mAh / cm ² or more to 8.5 mAh / cm ² or less. An electrode assembly comprising a cathode, an anode, and a separator interposed between the cathode and the anode according to claim 9, wherein the electrolyte assembly is impregnated with the electrolyte. 15. The secondary battery according to claim 14, wherein the positive electrode comprises a lithium transition metal oxide represented by the following general formula (1) or (2) as a positive electrode active material:
Li _x M _y Mn _{2 - y} O _{4 - z z} (1)
In this formula,
M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;
A is one or more anions of -1 or -2;
0.9? X? 1.2, 0 <y <2, 0? Z <0.2.


(1-x) LiM'O _2-y A _y -xLi ₂ MnO _{3 -y '} A _y' (2)
In this formula,
M 'is Mn _a M _b ;
M is one or more selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and two period transition metals;
A is at least one selected from the group consisting of anions of PO ₄ , BO ₃ , CO ₃ , F and NO ₃ ;
0 <x <1, 0 <y? 0.02, 0 <y? 0.02, 0.5? A? 1.0, 0 b? 0.5, a + b = 15. The secondary battery according to claim 14, wherein the secondary battery is a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery. 15. A battery module comprising a secondary battery according to claim 14 as a unit cell. A battery pack comprising the battery module according to claim 17. The device according to claim 18, comprising the battery pack as a power source. 20. The device of claim 19, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.