KR20070059389A - Anode active material for secondary battery with high capacity - Google Patents

Abstract

A negative electrode active material for a secondary battery is provided to inhibit a volumetric change in a core layer causable during charging and discharging of lithium and have high charge and discharge capacity and excellent cycle life characteristics. The negative electrode active material for a secondary battery comprises: a core layer including a metal or metalloid component capable of being repetitively charged and discharged with lithium, and an iron(Fe) component; and a crystalline carbon layer. The negative electrode active material is prepared by the steps of: (1) mixing iron(Fe)-containing metal or metalloid with crystalline carbon; and (2) mechanically alloying the mixture in a mechano fusion apparatus.

Description

High capacity negative electrode active material for secondary battery {ANODE ACTIVE MATERIAL FOR SECONDARY BATTERY WITH HIGH CAPACITY}

1 is a cross-sectional view of a negative electrode active material prepared according to an embodiment of the present invention.

2 is a SEM photograph of the negative electrode active material prepared in Comparative Example 2.

The present invention relates to a negative electrode active material for a secondary battery and a secondary battery using the negative electrode active material.

Lithium secondary batteries are manufactured by using a material capable of inserting and desorbing lithium ions as a negative electrode and a positive electrode, and filling an organic or polymer electrolyte between a positive electrode and a negative electrode, and when lithium ions are inserted and desorbed from a positive electrode and a negative electrode. Electrical energy is generated by oxidation and reduction.

Currently, carbonaceous materials are mainly used as a negative electrode active material constituting the negative electrode of a lithium secondary battery. However, in order to further improve the capacity of the lithium secondary battery, it is necessary to use a high capacity negative electrode active material.

In order to satisfy this demand, there is an example of using a Si, Al, etc., a metal having a higher charge / discharge capacity than the carbonaceous material, and a metal capable of being electrochemically alloyed with lithium. However, the metal-based negative electrode active material is cracked and micronized due to a large volume change associated with charging and discharging of lithium. Therefore, the capacity of the secondary battery using the metal-based negative electrode active material decreases rapidly as the charge and discharge cycle progresses, and the cycle Life is shortened.

Japanese Patent Application Laid-Open No. 2001-297757 proposes an electrode active material having a structure mainly composed of an α phase (for example, Si) composed of lithium and a chargeable and dischargeable element, and a β phase, which is an intermetallic compound or solid solution of this element with another element b. It was.

However, there is a problem in that the conventional method described above cannot obtain sufficient and good cycle life characteristics and thus cannot be used as a practical negative electrode active material for lithium secondary batteries.

The present invention uses a negative electrode active material that sequentially includes an amorphous carbon layer and a crystalline carbon layer on the surface of a core layer including lithium, a metal or metalloid capable of repeatedly charging and discharging, and an iron (Fe) component. , The negative electrode active material for secondary battery having a high charge and discharge capacity and excellent cycle life characteristics by suppressing the volume change of the core layer that can occur during charging and discharging of lithium, and maintaining the high conductivity and conduction path between the particles of the negative electrode active material and the secondary battery using the same To provide. In addition, to provide a method for producing the negative electrode active material.

The present invention includes a core layer comprising a lithium or a metal or metalloid capable of repeatedly charging and discharging and an iron (Fe) component; And it provides a negative electrode active material comprising a crystalline carbon layer sequentially and a secondary battery using the same.

Optionally, an amorphous carbon layer may be interposed between the core layer and the crystalline carbon layer.

In addition, the present invention comprises a first step of mixing crystalline carbon with a metal or metalloid containing iron (Fe); And a second step of mechanically alloying the mixture in a Mechano Fusion apparatus.

Hereinafter, the present invention will be described in detail.

Since iron (Fe) is a component having a small charge / discharge capacity with lithium, since iron is included in the core layer, it is possible to suppress a volume change of the core layer that may occur during charge / discharge of lithium.

In the present invention, the metal or metalloid component may include at least one metal or metalloid or an alloy thereof selected from Si, Al, Sn, Sb, Bi, As, Ge, and Pb. If it can charge and discharge, it will not limit in particular.

The iron (Fe) component contained in the core layer is preferably 20 ppm or more and 10000 ppm or less. Core material containing less than 20ppm of iron (Fe) component has to be very high-purity, so the raw material price of the material is expensive. If it exceeds 10000ppm, iron (Fe) component is exposed to the surface of the active material to catalyze the decomposition of electrolyte solution. Can cause.

Crystalline carbon includes natural graphite and artificial graphite having a high degree of graphitization. Examples of the graphite-based material include MCMB (MesoCarbon MicroBead), carbon fiber, and natural graphite.

Examples of amorphous carbon include a coal tar pitch, a petroleum pitch, and a carbon-based material made by heat treatment using various organic materials as raw materials.

In the negative electrode active material sequentially comprising a core layer and a crystalline carbon layer, it is preferable to use a core layer: crystalline carbon layer = 90 to 10 parts by weight: 10 to 90 parts by weight.

In addition, in the negative electrode active material including a core layer, an amorphous carbon layer and a crystalline carbon layer sequentially, the core layer: amorphous carbon layer: crystalline carbon layer = 90 to 10 parts by weight: 0.1 to 50 parts by weight: 9 to 90 parts by weight It is desirable to.

If the core layer containing the metal or metalloid component and the iron (Fe) component is less than 10 parts by weight, the reversible capacity is small, meaning as a high capacity negative electrode active material, and if the crystalline carbon layer is less than 9 parts by weight, it is difficult to secure sufficient conductivity. If the amorphous carbon layer is less than 0.1 part by weight, it may not play a sufficient role in inhibiting expansion, and if it is more than 50 parts by weight, there is a fear of capacity loss and conductivity deterioration.

The crystalline carbon layer preferably has an interlayer distance d002 of carbon of 0.3354 nm or more and 0.35 nm or less. The lower limit is theoretically the lowest possible interlayer distance of graphite, and less than that, and carbon having an interlayer distance exceeding the upper limit is poor in conductivity, thereby lowering the conductivity of the coating layer, thereby preventing smooth lithium charge and discharge characteristics.

The thickness of the crystalline carbon layer is not particularly limited but is preferably 1 micron or more and 10 microns or less. If the thickness of the layer is less than 1 micron, it is difficult to secure sufficient conductivity between the particles. If the thickness is more than 15 microns, the proportion of carbonaceous contained in the negative electrode active material becomes high, and thus high charge and discharge capacity cannot be obtained.

The amorphous carbon layer preferably has an interlayer distance d002 of carbon of 0.34 nm or more and a thickness of 5 nm or more. If the thickness is less than 5 nm, the effect of suppressing volume change is not sufficient. If the distance between the layers is less than 0.34nm, the volume change of the coating layer itself due to the charge and discharge is severe, the effect of suppressing the volume change of the core layer is lowered and the cycle performance is lowered.

The negative electrode active material of the present invention, the first step of mixing a metal or metalloid containing iron (Fe) and crystalline carbon; And a second step of mechanical alloying the mixture in a Mechano Fusion device. Mechanical alloying (Mechanical Alloying) is to create an alloy of uniform composition by applying a mechanical force.

The metal or metalloid containing iron (Fe) of the first step may be mixed with metal or metalloid and iron such that the iron content is 20-10000ppm.

The metal or metalloid containing iron (Fe) of the first step and the crystalline carbon may be mixed in a ratio of metal or metalloid: crystalline carbon = 90 to 10 parts by weight: 10 to 90 parts by weight.

The negative electrode in the present invention can be prepared by conventional methods known in the art. For example, a slurry may be prepared by mixing and stirring a binder and a solvent, a conducting agent, and a dispersant in the negative electrode active material of the present invention, and then applying the same to a current collector of a metal material, compressing it, and drying to prepare a negative electrode. have.

The binder may be suitably used in a 1 to 10 weight ratio and the conductive agent in a 1 to 30 weight ratio with respect to the negative electrode active material.

Examples of binders that can be used include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and the like.

Generally, carbon black may be used as the conductive agent, and acetylene black series (such as a Chevron Chemical Company or Gulf Oil Company) may be used as a commercially available product. Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (MMM) There is this.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the slurry of the negative electrode active material can easily adhere to the metal. Representative examples include meshes, foils, and the like, which are manufactured by aluminum, copper, gold, nickel or an aluminum alloy or a combination thereof.

The method of applying the slurry to the current collector is also not particularly limited. For example, it can be applied by a method such as doctor blade, dipping, brushing, and the like, but the coating amount is not particularly limited, but the thickness of the active material layer formed after removing the solvent or the dispersion medium is usually 0.005-5 mm, preferably 0.05-2 mm. The amount of the range which becomes a range is preferable.

The method of removing the solvent or the dispersion medium is not particularly limited, but the solvent or the dispersion medium may be used as quickly as possible within the speed range in which stress concentration occurs and cracks occur in the active material layer or the active material layer does not peel off from the current collector. It is preferable to use a method of adjusting to remove to volatilize. As a non-limiting example it may be dried for 0.5 to 3 days in a vacuum oven at 50 ~ 200 ℃.

The secondary battery of the present invention can be prepared by conventional methods known in the art, including a negative electrode prepared using the negative electrode active material of the present invention. For example, a porous separator may be inserted between the positive electrode and the negative electrode to add an electrolyte solution. Secondary batteries include lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries.

The positive electrode active material which can be used for the positive electrode of the secondary battery according to the present invention includes a lithium-containing transition metal oxide, specifically, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-Y Co _Y O ₂ , LiCo _1-Y Mn _Y O ₂ , LiNi _1-Y Mn _Y O ₂ (where 0 ≦ Y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn _2-z Ni _z O ₄ , LiMn _2-Z Co _Z O ₄ (here, 0 <Z <2), LiCoPO ₄ , and at least one selected from the group consisting of LiFePO ₄ may be used. have.

The electrolyte may include a nonaqueous solvent and an electrolyte salt.

The nonaqueous solvent is not particularly limited as long as it is normally used as a nonaqueous solvent for nonaqueous electrolyte, and cyclic carbonate, linear carbonate, lactone, ether, ester or ketone can be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Examples of the linear carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC) and dipropyl carbonate. (DPC), ethylmethyl carbonate (EMC), methyl propyl carbonate (MPC), and the like. Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, and the like. There is this. In addition, examples of the ester include n-methyl acetate, n-ethyl acetate, methyl propionate, methyl pivalate, and the like. The ketone includes polymethylvinyl ketone. These nonaqueous solvents can be used individually or in mixture of 2 or more types.

The electrolyte salt is not particularly limited as long as it is usually used as an electrolyte salt for nonaqueous electrolyte. Electrolytic salt, non-limiting example, A ⁺ B ^- A salt of the structure, such as, A ⁺ comprises a Li ^+, Na ^+, an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ B ^- is PF ₆ ^{- _{, BF 4 -, Cl -,}} Br -, I -, ClO 4 -, ASF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2 ) ₃ ^- and a salt containing the same anion ion or a combination thereof. In particular, lithium salts are preferred. These electrolyte salts can be used individually or in mixture of 2 or more types.

The secondary battery of the present invention may include a separator. The separator can be used is not particularly limited, it is preferable to use a porous separator, non-limiting examples include a polypropylene-based, polyethylene, or polyolefin-based porous separator.

The secondary battery of the present invention is not limited in appearance, but may be cylindrical, square, pouch type, or coin type using a can.

Hereinafter, the present invention will be described in detail with reference to the following Examples. However, the following examples are merely to illustrate the present invention and the present invention is not limited by the following examples.

(Example 1)

Si and Fe were mixed at 99 parts by weight: 1 part by weight and ball milled to prepare Si containing 10000 ppm of iron.

After mixing 10000ppm of iron containing Si and natural graphite at 50 parts by weight: 50 parts by weight, a negative electrode active material was prepared by performing mechanical alloying for 30 minutes at a rotation speed of 600 times per minute using a Mechano Fusion device manufactured by Hosokawa Micron. ICP analysis of the prepared negative electrode active material contained 4000ppm of Fe.

10 parts by weight of PVDF as a binder and 10 parts by weight of acetylene black as a conductive agent were mixed to 100 parts by weight of the prepared negative electrode active material powder, and NMP was added as a solvent to prepare a uniform slurry. The slurry was coated on 20 micron copper foil, dried and rolled, and then punched to a required size to prepare a negative electrode.

The electrolyte was prepared by dissolving LiPF ₆ in a non-aqueous solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 2 (v: v) to a concentration of 1 M.

Metal lithium was used as the negative electrode and the counter electrode, and a coin-type battery of the present invention was prepared by injecting the electrolyte after interposing a polyolefin-based separator between both electrodes.

(Comparative Example 1)

A negative electrode active material and a battery were manufactured in the same manner as in Example 1, except that high purity Si containing 10 ppm of iron (Fe) was used. ICP analysis of the prepared negative electrode active material contained 7ppm of Fe.

(Comparative Example 2)

A negative electrode active material and a battery were manufactured in the same manner as in Example 1, except that Si containing 18000 ppm of iron (Fe) was used. ICP analysis of the prepared negative electrode active material contained 11000ppm Fe.

(Battery performance experiment)

Looking at the volume change according to the charge and discharge after the three charge and discharge of the batteries prepared in Example 1, Comparative Example 1 and Comparative Example 2, in the case of Example 1, as shown in Table 1, about 51% (33㎛ → 50 Thickness change of the electrode was observed, but in the case of Comparative Example 1, a thickness change of about 150% (30 μm → 74 μm) was observed, indicating that the negative electrode active material of the present invention had a volume expansion inhibiting effect. there was.

In addition, in the battery manufactured using the negative electrode active material obtained in Example 1, there was almost no volume change of the core layer before and after charging and discharging, so that the initial capacity was maintained at about 99.3% until 50 cycles as shown in Table 1 below. On the other hand, in the battery manufactured using the negative electrode active material obtained in Comparative Example 2, Fe exposed to the surface of the active material, the cycle life characteristics were significantly reduced. 2 is a SEM photograph of the negative electrode active material prepared in Comparative Example 2, it can be seen that Fe is exposed on the surface.

Remaining discharge capacity after 50 cycles Initial electrode thickness (μm) Electrode thickness after 3 charge / discharge cycles (㎛) Electrode Expansion Rate (%) (Δt / t _i ) Example 1 99.3% 33 50 51 Comparative Example 1 90.5% 30 74 150 Comparative Example 2 12.7% 26 98 276

The negative electrode active material of the present invention can suppress the volume change of the core layer generated during charge and discharge of lithium by the amorphous carbon layer and the crystalline carbon layer while maintaining a high charge and discharge capacity which is an advantage of the metal or metalloid negative electrode active material. In addition, since iron (Fe) is included in the core layer, volume change of the core layer that may occur during charging and discharging of lithium may be suppressed, thereby improving cycle life characteristics of the battery.

Claims (12)

A core layer comprising lithium, a metal or metalloid component which can be repeatedly charged and discharged, and an iron (Fe) component; And An anode active material sequentially comprising a crystalline carbon layer. The negative electrode active material of claim 1, further comprising an amorphous carbon layer between the core layer and the crystalline carbon layer. The metal or metalloid component of claim 1 or 2, wherein the metal or metalloid component is at least one metal or metalloid or alloy thereof selected from the group consisting of Si, Al, Sn, Sb, Bi, As, Ge, and Pb. Phosphorus cathode active material. The cathode active material according to claim 1 or 2, wherein the iron (Fe) component included in the core layer is 20 to 10000 ppm. According to claim 1, wherein the core layer: crystalline carbon layer = 90 ~ 10 parts by weight: negative electrode active material, characterized in that 10 to 90 parts by weight. The negative electrode active material according to claim 2, wherein the core layer: amorphous carbon layer: crystalline carbon layer = 90 to 10 parts by weight: 0.1 to 50 parts by weight: 9 to 90 parts by weight. The anode active material according to claim 1 or 2, wherein the crystalline carbon layer has an interlayer distance d002 of carbon of 0.3354 nm or more and 0.35 nm or less and a thickness of 1 micron or more and 10 microns or less. The anode active material according to claim 2, wherein the amorphous carbon layer has an interlayer distance d002 of carbon of 0.34 nm or more and a thickness of 5 nm or more. A secondary battery using the negative electrode active material of claim 1 or 2. A first step of mixing crystalline carbon with a metal or metalloid containing iron (Fe); And a second step of mechanically alloying the mixture in a Mechano Fusion apparatus. The method of claim 10, wherein the metal or metalloid containing iron (Fe) of the first step is a metal or metalloid and iron mixed so that the iron content of 20 ~ 10000ppm. 11. The method of claim 10, wherein the metal or metalloid containing iron (Fe) of the first step and the crystalline carbon mixture is a metal or metalloid: crystalline carbon = 90 to 10 parts by weight: 10 to 90 parts by weight Method for producing phosphorous anode active material.

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