KR100719716B1 - Negative electrode for lithium rechargeable battery and lithium rechargeable 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 including the same. In the negative electrode for a lithium secondary battery including a negative electrode plate and a negative electrode active material layer formed on at least one surface of the negative electrode plate, the negative electrode active material layer is lithium ion Provided is a negative electrode for a lithium secondary battery comprising a styrene-butadiene rubber binder containing a negative electrode active material and a metal carbide filler capable of inserting and detaching.

Description

A negative electrode for a lithium secondary battery and a lithium secondary battery including the same TECHNICAL FIELD

1 is a cross-sectional view of a lithium secondary battery shown as an embodiment of the present invention.

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a negative electrode for a lithium secondary battery capable of suppressing a swelling phenomenon in which the thickness of a battery is expanded, and a lithium secondary battery including the same. .

With the recent rapid development of the electronics, telecommunications, and computer industries, the use of portable electronic products such as camcorders, mobile phones, notebook PCs, etc., as well as the compactness, light weight, and high functionality of the devices are becoming common. The demand for it is increasing. In particular, the rechargeable lithium secondary battery has a high energy density per unit weight of about 3 times as compared with the conventional lead acid battery, nickel-cadmium battery, nickel-hydrogen battery, and nickel-zinc battery, and can be rapidly charged. Development is underway.

Conventionally, it has been proposed to use lithium metal having a very high energy density as a negative electrode active material of a lithium secondary battery. However, dendrite is formed on the negative electrode during charging, and the electrode penetrates through the separator during subsequent charge / discharge. There is a danger of reaching the anode and causing an internal short circuit. In addition, the precipitated dendrite rapidly increases the reactivity according to the increase in the specific surface area of the lithium electrode and reacts with the electrolyte at the electrode surface to form a polymer film lacking electron conductivity. For this reason, the battery resistance rapidly increases or there are particles isolated from the network of electron conduction, which acts as a factor that inhibits charging and discharging.

Due to this problem, a method of using a graphite material capable of intercalation / deintercalation of lithium ions as a negative electrode active material has recently been proposed. In general, since the graphite negative electrode active material does not precipitate metal lithium, internal short circuits due to dendrites do not occur and thus additional disadvantages do not occur.

In the case of a lithium secondary battery including a graphite-based negative electrode active material, a water-based system in which a styrene-butadiene rubber (SBR) binder is dispersed in water together with a cellulose methyl cellulose (CMC) thickener instead of a polyvinylidene fluoride (PVdF) binder in manufacturing a negative electrode Binder system is used. PVdF has excellent binding ability but lacks flexibility, and thus, when natural graphite having high expansion shrinkage rate due to charge / discharge is used as the active material, the bond between the active material and the binder is broken and the cycle characteristics of the battery are easily deteriorated. The SBR is known to improve battery capacity and charge and discharge efficiency because of its high elasticity. However, SBR has a problem in that the binding property between the metal current collector and the active material is lower than that of PVdF, thereby shortening cycle characteristics. In addition, SBR has a problem of causing agglomeration (agglomerization), etc., which is high in swelling property and inhibits dispersibility in slurry production.

In particular, graphite used as a negative electrode active material increases the interlayer distance (theoretical value 3.354 kPa) to 3.7 kPa with the insertion of lithium ions (diameter of 0.61 kPa), thereby causing a problem regarding the shape stability of the battery.

Accordingly, the present invention has been made to solve the above problems, an object of the present invention is to provide a lithium secondary battery negative electrode and a lithium secondary battery comprising the same that can suppress the swelling of the negative electrode during charging.

In the negative electrode for a lithium secondary battery comprising a negative electrode plate and a negative electrode active material layer formed on at least one surface of the negative electrode plate in order to achieve the above object, the negative electrode active material layer is a negative electrode active material and metal carbide that can insert and detach lithium ions The negative electrode for lithium secondary batteries which contains the styrene-butadiene rubber binder which mix | blended the filler is provided.

The present invention also provides a lithium secondary battery comprising the negative electrode.

Hereinafter, the present invention will be described in more detail.

The present invention provides a negative electrode for a lithium secondary battery capable of suppressing swelling of a plate through reinforcement of styrene butadiene rubber (SBR) used as a binder of a negative electrode active material layer forming a negative electrode, and a lithium secondary battery comprising the same. Can be.

By mixing a metal carbide filler in the SBR to improve the tensile strength characteristics of the SBR, it is possible to suppress the electrode plate swelling by using as a binder for the negative electrode active material. The metal carbide filler preferably has an elastic modulus greater than 10 × 10 ⁶ psi. Conventionally, oxides such as ZnO, SiO _2, etc. have been used as fillers, but in the present invention, metal carbides having a modulus of elasticity larger than those of oxides may be used as fillers to enhance tensile strength of SBR binders. When metal carbide is blended into the SBR, compressive stress occurs due to the difference in tensile force between the interface of the metal carbide and the SBR rubber, thereby obtaining a high tensile strength.

As the metal carbide, at least one carbide selected from tungsten carbide (W ₂ C) and titanium carbide (TiC) may be used. The tungsten carbide has an elastic modulus of 90 × 10 ⁶ psi, and the titanium carbide has an elastic modulus of 45.7 × 10 ⁶ psi. The content of the metal carbide may be 0.5 to 5% by weight based on the SBR.

The content of the SBR binder incorporating the metal carbide filler according to the present invention is 0.1 to 20% by weight, preferably 0.1 to 10% by weight based on the negative electrode active material. If the content of the binder is too small, the adhesion between the negative electrode active material and the negative electrode active material, between the negative electrode active material and the current collector is insufficient, and if the content is too high, the adhesion becomes good, but the content of the negative electrode active material decreases by that amount, which is disadvantageous in increasing the battery capacity. .

As the negative electrode active material capable of inserting and detaching lithium ions, carbon materials such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, and lithium alloy may be used. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or lower, mesophase pitch-based carbon fibers (MPCF), and the like. The crystalline carbon includes a graphite material, and specific examples thereof include natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. The carbonaceous material is preferably a material having an d002 interplanar distance of 3.35 to 3.38 kPa and an Lc (crystallite size) of at least 20 nm by X-ray diffraction. As the lithium alloy, an alloy of lithium with aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium may be used.

The negative electrode active material layer may further include a conductive material to improve electronic conductivity. The conductive material is not particularly limited, but may be graphite based on artificial graphite or natural graphite, carbon black based on acetylene black, Ketjen black, denka black, thermal black, channel black, conductive fibers such as carbon fiber, metal fiber, Metal powders such as copper, nickel, aluminum and silver, conductive metal oxides such as titanium oxide, or conductive polymers such as polyaniline, polythiophene, polyacetylene and polypyrrole may be used alone or in combination thereof. 0.1-10 weight% is preferable with respect to a negative electrode active material, and, as for the addition amount of a electrically conductive material, it is more preferable that it is 1-5 weight%. When the content of the conductive material is less than 0.1% by weight, the electrochemical properties are lowered, and when the content of the conductive material is more than 10% by weight, the energy density per weight is reduced.

The said negative electrode active material layer is formed by apply | coating the negative electrode active material slurry obtained by mixing and disperse | distributing a negative electrode active material, a binder, etc. to a solvent, to a negative electrode plate, and drying and rolling it. As the solvent, a nonaqueous solvent or water is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

The lithium secondary battery according to the present invention includes the negative electrode, the positive electrode, and the nonaqueous electrolyte solution. The positive electrode includes a positive electrode plate and a positive electrode active material layer formed on at least one surface of the positive electrode plate, and the positive electrode active material layer includes a positive electrode active material capable of inserting and detaching lithium ions. The positive electrode is formed by applying a positive electrode active material slurry obtained by mixing and dispersing a positive electrode active material, a binder, and the like in a solvent, onto the positive electrode plate, and drying and rolling it.

As the positive electrode active material, at least one selected from cobalt, manganese, nickel and at least one of a composite oxide with lithium is preferable, and a lithium-containing compound described below may be preferably used.

Li _x Mn _{1 - y} M _y A ₂ (1)

Li _x Mn _{1 - y} MyO _{2 - z} X _z (2)

Li _x Mn ₂ O _{4 - z} X _z (3)

Li _x Mn _{2 - y} M _y M ' _z A ₄ (4)

Li _x Co _{1 - y} M _y A ₂ (5)

Li _x Co _{1 - y} M _y O _{2 - z} X _z (6)

Li _x Ni _{1 - y} M _y A ₂ (7)

Li _x Ni _{1 - y} M _y O _{2 - z} X _z (8)

Li _x Ni _{1 - y} Co _y O _{2 - z} X _z (9)

Li _x Ni _{1 -y- z} Co _y M _z A _α (10)

Li _x Ni _{1 -y- z} Co _y M _z O _{2 -α} X _α (11)

Li _x Ni _{1 -y- z} Mn _y M _z A _α (12)

Li _x Ni _{1 -y- z} Mn _y M _z O _{2 -α} X _α (13)

(Wherein 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M 'are the same or different, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements, A is selected from the group consisting of O, F, S and P And X is selected from the group consisting of F, S and P.)

As the positive electrode plate and the negative electrode plate, metals such as aluminum, copper, nickel, silver, stainless steel, alloys of these metals, and the like can be used. Usually, aluminum or an aluminum alloy is used as a positive electrode plate, and copper or a copper alloy is used as a negative electrode plate.

The non-aqueous electrolyte may include a lithium salt and a non-aqueous organic solvent, and may further include additives for improving charge and discharge characteristics, preventing overcharge, and the like. The lithium salt acts as a source of lithium ions in the battery to enable operation of the basic lithium battery, and the non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) ₂ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ It may be used in combination of one or two or more selected from the group consisting of. The concentration of the lithium salt is preferably used in the range of 0.6 to 2.0M, more preferably in the range of 0.7 to 1.6M. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, and if it exceeds 2.0M, the viscosity of the electrolyte is increased, there is a problem that the mobility of lithium ions decreases.

As the non-aqueous organic solvent, carbonate, ester, ether or ketone may be used alone or in combination. The carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), Propylene carbonate (PC), butylene carbonate (BC), and the like may be used, and as the ester, γ-butyrolactone (GBL), n-methyl acetate, n-ethyl acetate, n-propyl acetate, and the like may be used. As the ether, dibutyl ether may be used, but is not limited thereto.

In the case of the carbonate-based solvent in the non-aqueous organic solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, it is preferable to use the cyclic carbonate and the chain carbonate by mixing in a volume ratio of 1: 1 to 1: 9. The performance of the electrolyte is preferable when mixed in the above volume ratio.

The non-aqueous organic solvent may also further comprise an aromatic hydrocarbon-based organic solvent. Specific examples of the aromatic hydrocarbon organic solvent may include benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, mesitylene, and the like. It may be used alone or in combination. It is preferable that the volume ratio of the carbonate solvent / aromatic hydrocarbon-based organic solvent in the electrolyte solution containing the aromatic hydrocarbon-based organic solvent is 1: 1 to 30: 1. The performance of the electrolyte solution may be desirable to be mixed in the volume ratio.

The lithium secondary battery may include a separator that prevents a short circuit between the positive electrode and the negative electrode and provides a movement path of lithium ions, and the separator may include a polyolefin-based polymer film such as polypropylene or polyethylene, or a multi-film or microporous film thereof. , Woven and nonwoven fabrics can be used. In addition, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

1 is a cross-sectional view of a rectangular type lithium secondary battery shown as one embodiment of the present invention.

Referring to FIG. 1, a lithium secondary battery stores an electrode assembly 12 including a positive electrode 13, a negative electrode 15, and a separator 14 in a can 10 together with an electrolyte, It is formed by sealing the upper end with the cap assembly 20. The cap assembly 20 includes a cap plate 40, an insulating plate 50, a terminal plate 60, and an electrode terminal 30. The cap assembly 20 is combined with the insulating case 70 to seal the can 10.

The electrode terminal 30 is inserted into the terminal through-hole 41 formed in the center of the cap plate 40. When the electrode terminal 30 is inserted into the terminal through-hole 41, the tubular gasket 46 is coupled to the outer surface of the electrode terminal 30 and inserted together to insulate the electrode terminal 30 and the cap plate 40. . After the cap assembly 20 is assembled to the upper end of the can 10, the electrolyte is injected through the electrolyte injection hole 42 and the electrolyte injection hole 42 is closed by a stopper 43.

The electrode terminal 30 is connected to the negative electrode tab 17 of the negative electrode 15 or the positive electrode tab 16 of the positive electrode 13 to act as a negative electrode terminal or a positive electrode terminal.

The lithium secondary battery of the present invention is not limited to the above shape, and any shape including a cylindrical shape, a pouch, etc., including the negative electrode of the present invention and capable of operating as a battery, is possible.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

Comparative example  One

A positive electrode active material slurry was prepared by dispersing a LiCoO ₂ positive electrode active material, a polyvinylidene fluoride binder, and a carbon conductive agent (Super P) in an N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 92: 4: 4. . The positive electrode active material slurry was coated on an aluminum foil current collector having a thickness of 15 μm, dried, and rolled to prepare a positive electrode. Artificial graphite as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96: 2: 2, and then dispersed in water to prepare a slurry. The negative electrode was prepared by coating the copper foil current collector having a thickness of about μm, followed by drying and rolling.

The prepared electrodes were wound and compressed using a polyethylene separator, placed in a rectangular can, and then injected with an electrolyte to prepare a lithium secondary battery. At this time, an ethylene carbonate and diethyl carbonate mixed solution (1: 1 volume ratio) in which LiPF ₆ was dissolved in 1.0 M was used.

Example  One

A tungsten carbide (W ₂ C) as a binder for the negative electrode active material 2 was conducted in the same manner as the comparative example 1, except that the styrene-butadiene rubber by weight% formulation.

Example  2

It carried out similarly to the comparative example 1 except using styrene butadiene rubber which mix | blended 2 weight% of titanium carbide (TiC) as a binder for negative electrode active materials.

<Swelling characteristics>

The lithium secondary batteries of Comparative Examples 1 and 2 were charged at a charging voltage of 0.5 C and 4.2 V at 25 ° C. under constant current-constant voltage (CC-CV) conditions, and then 4 hours in a high temperature chamber at 90 ° C. After leaving, the cell thickness change was measured and the results are shown in Table 1. The thickness change rate in Table 1 shows the change rate at the time of the battery thickness before high temperature standing.

Thickness change rate after 4 hours at 90 ℃ Comparative Example 1 16.5% Example 1 14.0% Example 2 14.0%

As shown in Table 1, it can be seen that an excellent swelling inhibiting effect is obtained by using the SBR binder in which the metal carbide filler is blended as the binder for the negative electrode active material.

The present invention can suppress the electrode plate swelling through the strengthening of the SBR by using a metal carbide filler in combination with the SBR binder used as the binder for the negative electrode active material.

Although the present invention has been described with reference to the above embodiments, it is merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (19)

In the negative electrode for a lithium secondary battery comprising a negative electrode plate and a negative electrode active material layer formed on at least one surface of the negative electrode plate, The negative electrode active material layer is a negative electrode for a lithium secondary battery comprising a styrene butadiene rubber binder containing a negative electrode active material and a metal carbide filler capable of inserting and detaching lithium ions. delete The negative electrode for a rechargeable lithium battery of claim 1, wherein the metal carbide is at least one carbide selected from tungsten carbide and titanium carbide. The negative electrode for a rechargeable lithium battery of claim 1, wherein the content of the metal carbide is 0.5 to 5 wt% based on the styrene butadiene rubber binder. The negative electrode for a lithium secondary battery according to claim 1, wherein the content of the styrene butadiene rubber in which the metal carbide filler is blended is 0.1 to 20 wt% based on the negative electrode active material. The negative electrode of claim 5, wherein the content of the styrene-butadiene rubber is 0.1 to 10 wt% based on the negative electrode active material. The negative electrode of claim 1, wherein the negative electrode active material is selected from the group consisting of crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, and lithium alloy. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer further comprises a conductive material. The method of claim 8, wherein the conductive material is artificial graphite, natural graphite, acetylene black, Ketjen black, denka black, thermal black, channel black, carbon fiber, metal fiber, copper powder, nickel powder, aluminum powder, silver powder, titanium oxide , Polyaniline, polythiophene, polyacetyl and polypyrrole negative electrode for a lithium secondary battery, characterized in that used alone or in combination. A positive electrode including a positive electrode plate and a positive electrode active material layer formed on at least one surface of the positive electrode plate; And a negative electrode active material layer formed on at least one surface of the negative electrode plate and the negative electrode plate, wherein the negative electrode active material layer comprises a styrene-butadiene rubber binder containing a negative electrode active material capable of inserting and desorbing lithium ions and a metal carbide filler. cathode; And A lithium secondary battery comprising a nonaqueous electrolyte. delete The lithium secondary battery of claim 10, wherein the metal carbide is at least one carbide selected from tungsten carbide and titanium carbide. The lithium secondary battery according to claim 10, wherein the content of the metal carbide is 0.5 to 5% by weight based on the styrene-butadiene rubber binder. The lithium secondary battery according to claim 10, wherein the content of the styrene butadiene rubber in which the metal carbide filler is blended is 0.1 to 20 wt% based on the negative electrode active material. The method of claim 14, wherein the content of the styrene butadiene rubber lithium secondary battery, characterized in that 0.1 to 10% by weight based on the negative electrode active material. The lithium secondary battery according to claim 10, wherein the negative electrode active material is selected from the group consisting of crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, and lithium alloy. The lithium secondary battery according to claim 10, wherein the negative electrode active material layer further comprises a conductive material. 18. The method of claim 17, wherein the conductive material is artificial graphite, natural graphite, acetylene black, Ketjen black, denka black, thermal black, channel black, carbon fiber, metal fiber, copper powder, nickel powder, aluminum powder, silver powder, titanium oxide , Polyaniline, polythiophene, polyacetyl and polypyrrole lithium secondary battery, characterized in that used alone or in combination. The method of claim 10, wherein the positive electrode active material layer comprises a positive electrode active material capable of inserting and detaching lithium ions, wherein the positive electrode active material is a lithium compound selected from the group consisting of (1) to (13) A lithium secondary battery characterized by the above. Li _x Mn _{1 - y} M _y A ₂ (1) Li _x Mn _{1 - y} MyO _{2 - z} X _z (2) Li _x Mn ₂ O _{4 - z} X _z (3) Li _x Mn _{2 - y} M _y M ' _z A ₄ (4) Li _x Co _{1 - y} M _y A ₂ (5) Li _x Co _{1 - y} M _y O _{2 - z} X _z (6) Li _x Ni _{1 - y} M _y A ₂ (7) Li _x Ni _{1 - y} M _y O _{2 - z} X _z (8) Li _x Ni _{1 - y} Co _y O _{2 - z} X _z (9) Li _x Ni _{1 -y- z} Co _y M _z A _α (10) Li _x Ni _{1 -y- z} Co _y M _z O _{2 -α} X _α (11) Li _x Ni _{1 -y- z} Mn _y M _z A _α (12) Li _x Ni _{1 -y- z} Mn _y M _z O _{2 -α} X _α (13) (Wherein 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M 'are the same or different, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements, A is selected from the group consisting of O, F, S and P And X is selected from the group consisting of F, S and P.)

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