Electrode for nonaqueous electrolyte secondary battery and its manufacturing method

【0001】

[Technical field to which the invention belongs]

The present invention relates to an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery using a silicon material having a low resistivity as an active material, and a method for manufacturing the same.

【0002】

[Conventional technology]

In recent years, with the remarkable development of portable electronic devices, communication devices, etc., there is a strong demand for a secondary battery having a high energy density from the viewpoint of economy, miniaturization, and weight reduction of the device. Conventionally, as a measure for increasing the capacity of this type of secondary battery, for example, a method of using oxides such as V, Si, B, Zr, Sn, and a composite oxide thereof as a negative electrode material (Patent Document 1: JP-A-5). -174818, Patent Document 2: Japanese Patent Application Laid-Open No. 6-60867, etc.), Method of applying melt-quenched metal oxide as negative electrode material (Patent Document 3: Japanese Patent Application Laid-Open No. 10-294112), Oxidation to negative electrode material Method using silicon (Patent Document 4: Japanese Patent No. 2997741), Si as negative electrode material₂N₂O and Ge₂N₂A method using O (Patent Document 5: Japanese Patent Application Laid-Open No. 11-102705) and the like are known. Further, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO after mechanical arranging with graphite (Patent Document 6: Japanese Patent Application Laid-Open No. 2000-243396) and a carbon layer on the surface of Si particles by a chemical vapor deposition method. (Patent Document 7: Japanese Patent Application Laid-Open No. 2000-215887), a method of coating a carbon layer on the surface of silicon oxide particles by a chemical vapor deposition method (Patent Document 8: Japanese Patent Application Laid-Open No. 2002-42806), in a silicon material (Patent Document 9: Japanese Patent Application Laid-Open No. 2000-149951) and a method using a silicon thin film by the RF sputtering method (Patent Document 10: Japanese Patent Application Laid-Open No. 2002-83594).

【0003】

[Patent Document 1]

Japanese Unexamined Patent Publication No. 5-17418 [Patent Document 2]

Japanese Patent Application Laid-Open No. 6-60867 [Patent Document 3]

Japanese Unexamined Patent Publication No. 10-294112 [Patent Document 4]

Japanese Patent No. 2997471 [Patent Document 5]

Japanese Unexamined Patent Publication No. 11-102705 [Patent Document 6]

Japanese Unexamined Patent Publication No. 2000-243396 [Patent Document 7]

Japanese Unexamined Patent Publication No. 2000-215887 [Patent Document 8]

Japanese Unexamined Patent Publication No. 2002-42806 [Patent Document 9]

Japanese Unexamined Patent Publication No. 2000-149951 [Patent Document 10]

JP-A-2002-83594 [0004]

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional method, although the charge / discharge capacity is increased and the energy density is increased, the cycleability is insufficient and the characteristics required by the market are still insufficient, so that it is not always satisfactory. However, further improvement in energy density was desired.

【0005】

In particular, in the method of Japanese Patent Application Laid-Open No. 2000-215887, although a uniform carbon film can be formed, since Si itself is used as a negative electrode material in a state of low conductivity, when lithium ions are attached and detached. As a result, the expansion / contraction of the silicon is too large to withstand practical use, and the cycleability is deteriorated. Therefore, a limit on the amount of charge must be provided to prevent this. In the method of, boron is doped in silicon, and Si and SiB are used.₄Although the cycleability has been improved by coexisting with the above, it is still insufficient. In the method of JP-A-2002-83594, a silicon thin film produced by the RF sputtering method is used, which is disadvantageous for industrial production.

【0006】

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery having higher cycle performance, and a method for manufacturing the same.

【0007】

[Means for Solving Problems and Embodiments of the Invention]

As a result of diligent studies to achieve the above object, the present inventor has found a silicon material having a low resistivity, which is effective as an active agent for a negative electrode of a non-aqueous electrolyte secondary battery having a higher cycle property.

【0008】

That is, the development of an electrode material having a large charge / discharge capacity is extremely important, and research and development are being carried out in various places. Under these circumstances, silicon has been of great interest as a negative electrode active material for lithium ion secondary batteries because of its large capacity, but it deteriorates significantly when repeatedly charged and discharged, that is, it is inferior in cycleability. In addition, since the silicon powder itself has low conductivity, it has not been put into practical use except for a small part. From this point of view, as a result of studying with the goal of improving the cycleability and initial efficiency, after reducing the specific resistance of silicon itself, an electrode formed with a thin film on a metal foil by a physical thin film forming method and a chemical thin film forming method was obtained. It has been found that by using it, its performance is significantly improved as compared with the conventional one.

【0009】

More specifically, when silicon was used as the active material for the negative electrode of a lithium-ion secondary battery, the cause of the rapid decrease in charge / discharge capacity after several charges / discharges was examined from the structure itself and analyzed. A large volume change occurs due to the storage and release of a large amount of lithium ions, which causes the destruction of particles, and the volume expansion of silicon, which originally has low conductivity due to the storage of lithium ions, causes the conductivity of the electrode itself. As a result, it was found that the cause was that the movement of the lithium ion in the electrode was hindered by the decrease in the current collecting property, and the cycle property and the efficiency were decreased.

【0010】

Therefore, based on these facts, as a result of diligent studies on reducing the electrical resistance of silicon itself as well as the conductivity of the surface, the silicon itself contains boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium or indium. To reduce the electrical resistance by doping with one or more of the above, and to use an electrode formed on a metal foil by a physical thin film forming method and a chemical thin film forming method, in this case, preferably at least a part of the surface thereof is conductive. By coating with a conductive agent for imparting properties, the above-mentioned problems as a negative electrode active material of a lithium ion secondary battery can be solved, a stable large-capacity charge / discharge capacity can be obtained, and charge / discharge cycleability and charge / discharge cycleability can be obtained. We have found that the efficiency can be significantly improved, and have come to the present invention.

【0011】

Therefore, the present invention provides an electrode for a non-aqueous electrolyte secondary battery having the following thin film of a silicon material having a small resistivity, and a method for manufacturing the same. (1) Silicon is doped with one or more of boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium or indium, and a thin film of silicon material having a specific resistivity of 10 Ωcm or less on a wafer or ingot is formed. An electrode for a non-aqueous electrolyte secondary battery formed on a metal foil by a physical thin film forming method or a chemical thin film forming method. In this case, it is preferable to evaporate the dissimilar conductive agent in the thin film of the silicon material or to cover the thin film of the silicon material to form the dissimilar conductive agent film. (2) Silicon is doped with one or more of boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium or indium, and a silicon material having a low resistivity of 10 Ωcm or less on a wafer or ingot is used. A method for manufacturing an electrode for a non-aqueous electrolyte secondary battery, which comprises forming a thin film of the silicon material on a metal foil by a physical thin film forming method. (3) Use a mixed gas in which a gas containing one or more of boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium or indium is added to the gas of a silane compound containing a silicon atom and a hydrogen atom or a derivative thereof. It is characterized by forming a thin film having a specific resistance of 10 Ωcm or less, which is doped with one or more kinds of boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium or indium on a metal foil by a chemical thin film forming method. A method for manufacturing an electrode for a non-aqueous electrolyte secondary battery.

【0012】

Hereinafter, the present invention will be described in more detail. The present invention is expected to have a charge / discharge capacity several times that of the currently mainstream graphite-based material, particularly when used as a negative electrode active material for a lithium ion secondary battery. The cycle property and efficiency of a silicon-based material, which suffers from performance deterioration due to repeated charging and discharging, have been improved. The silicon material having a low resistivity according to the present invention has boron, phosphorus, and nitrogen in silicon. , Antimon, arsenic, aluminum, gallium or indium is doped with one or more kinds, and silicon itself has low electrical resistance.

【0013】

In the silicon material having a small specific resistance of the present invention, the growth of a silicon single crystal is carried out by using any of the magnetic field pulling (MCZ) method, the chokralsky (CZ) method, and the floating zone melting (FZ) method. Single crystal silicon doped with one or more of nitrogen, antimony, arsenic, aluminum, gallium or indium and having a specific resistance of 10 Ωcm or less on a wafer or ingot, boron produced by the Bridgeman method, phosphorus, To increase the purity of polycrystalline silicon, which is doped with one or more of nitrogen, antimony, arsenic, aluminum, gallium or indium and has a specific resistance of 10 Ωcm or less on a wafer or ingot, and metallic silicon by the melting method. When oxygen gas or the like is blown into slag and discharged, the concentration of boron or phosphorus is increased by blowing a compound containing phosphorus or boron and a salt at the same time as the gas is blown, and the specific resistance is formed to 10 Ωcm or less. Boron, phosphorus, nitrogen, antimony, arsenic, on a silicon thin film formed on a metal foil by using a silicon compound composed of metallic silicon, a silane compound composed of silicon and hydrogen, or a derivative thereof. The method for producing silicon is not particularly limited as long as it is silicon formed by doping one or more kinds of aluminum, gallium or indium and having a specific resistance of 10 Ωcm or less.

【0014】

In the present invention, the silicon material having a low resistivity is doped with one or more of boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium, and indium, and the resistivity value on the wafer or ingot is 10 Ωcm or less. It is silicon having a small specific resistance formed in, more preferably 1 Ωcm or less, still more preferably 0.1 Ωcm or less. The lower limit of the resistance value is not particularly limited, but it is usually 1 × 10.^-5Ωcm or more, especially 1 × 10^-3It is Ω cm or more. In this case, the doping amount of the above element is an amount having the specific resistance of silicon as the above value, but is usually 1 × 10.¹⁴~1×10²⁰atoms / cm³Is.

【0015】

In the electrode for a non-aqueous electrolyte secondary battery of the present invention, a thin film made of a silicon material having a small specific resistance is formed on a metal foil as a conductive substrate by a physical thin film forming method such as a physical vapor deposition method or a chemical thin film forming by a chemical vapor deposition method. It is a thin film electrode formed by the method.

【0016】

In this case, in the former physical thin film forming method, the above-mentioned silicon material having a small specific resistance may be used and vapor-deposited on a metal foil. It is not particularly limited as long as it can be linearly passed through the through hole of the mask and vapor-deposited on the film-forming surface of the substrate, and a known type of physical vapor deposition can be used. For example, known vapor deposition methods such as a vacuum vapor deposition method, a Langmuir brojet vapor deposition method, an organic molecular beam epitaxy method, and a sputtering method can be used. Further, as for the physical vapor deposition apparatus, the vapor phase raw material is applied to the surface of the substrate from a plurality of directions including the direction diagonally intersecting the penetration direction of the through hole of the mask by using the vapor deposition apparatus having a vapor deposition source fixed at a predetermined location. A vapor deposition apparatus having a movable vapor deposition source that can be freely moved or can be vapor-deposited on top can be used.

【0017】

Regarding chemical thin film formation methods such as chemical vapor deposition, the gas of a silane compound containing a silicon atom and a hydrogen atom or a derivative thereof contains one or more of boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium or indium. Silicon is doped with one or more of boron, phosphorus, nitrogen, antimony, arsenic, aluminum, gallium or indium by a chemical thin film formation method using a mixed gas with gas added, and the specific resistance is 10 Ωcm or less. It suffices to form a thin film of SiH as a raw material gas, although it is not particularly limited.₄, Si₂H₆, SiH₂Cl₂Using a silane compound composed of silicon and hydrogen, or a silicon compound composed of a derivative thereof, H₂, N₂Alternatively, when a silicon thin film is obtained by supplying a carrier gas such as an inert gas for a certain period of time and using a combination of gases that use conditions such as temperature and pressure by the reduced pressure CVD method and changing the temperature from low temperature to high temperature, in the gas. Gas containing phosphorus and boron (PH₃, B₂H₆The production method is not particularly limited as long as a silicon thin film doped with phosphorus or boron having a specific resistance of 10 Ωcm or less can be formed by adding a certain amount of (such as). In addition, after forming a thin film in a polycrystalline state, ion-implanting phosphorus and boron, or applying a paste containing phosphorus and boron, a thermal diffusion phenomenon is used to obtain phosphorus and boron having a specific resistance of 10 Ωcm or less. A doped silicon thin film can be formed, and in this case, the manufacturing method is not particularly limited.

【0018】

Here, the thickness of the thin film of the silicon material is appropriately selected, but from the viewpoint of the capacity as an assembled battery combined with the positive electrode and the strength as a thin film, it is 300 Å or more, usually 300 Å to 100 μm, particularly 500 Å to 100 μm, especially. It is preferably about 500 Å to 30 μm. If the film thickness is too thin, sufficient charge / discharge capacity as an assembled battery may not be obtained, and if the film thickness is too thick, the film structure may collapse due to repeated charge / discharge cycles and the cycle performance may deteriorate. is there. It is known that silicon constituting a thin film changes from crystalline to amorphous by doping and dedoping of lithium ions, and is preferably amorphous from the viewpoint of little structural change.

【0019】

When forming the thin film of the silicon material, these conductive agents are co-deposited on the thin film of the silicon material by the physical thin film forming method or the chemical thin film forming method using conductive agents such as silver, copper, iron and nickel at the same time. It is also possible to form the conductive agent film on the thin film of the silicon material. In this case, the thin film of the silicon material and the conductive film can alternately form a plurality of layers.

【0020】

Further, the metal foil is not particularly limited, and a foil made of a metal such as copper, nickel, iron, titanium, cobalt, or an alloy made of a combination thereof, a roughened surface thereof, an expanded metal, or the like can be used. However, metals capable of forming alloys with silicon, such as copper, nickel, and titanium, are preferably used.

【0021】

By using the thin-film electrode obtained in the present invention as a negative electrode material (negative electrode active material), a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics, particularly a lithium ion secondary battery, can be manufactured. can do.

【0022】

In the lithium ion secondary battery obtained by using the above negative electrode material, other materials such as the positive electrode, the negative electrode, the electrolyte and the separator, and the battery shape are not limited. Examples of the positive electrode active material include LiCoO.₂, LiNiO₂, LiMn₂O₄, V₂O₅, MnO₂, TiS₂, MoS₂Oxides of transition metals such as and chalcogen compounds are used. As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium perchlorate or lithium hexafluorofluoride is used, and as the non-aqueous solvent, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, vinylene carbonate, dimethoxy Ethan, γ-butyrolactone, 2-methyltetrahydrofurate, etc. are used alone or in combination of two or more. In addition, various non-aqueous electrolytes and solid electrolytes other than these can also be used.

【0023】

[Example]

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following example,% indicating the composition indicates weight%.

【0024】

[Example 1]<u style="single">Preparation of Si thin film</u>[Pretreatment of metal substrate]

Niraco Co., Ltd.'s 0.03 mm thick, 99.7% pure Ni foil is cut into 4 cm squares, soaked in first-class trichloroethylene manufactured by Tokichi Takahashi Shoten, and used for 15 minutes at ULTRASONIC CLEANER SU-3-T manufactured by Shibata Chemical Co., Ltd. Ultrasonic cleaning was performed. The trichloroethylene in the beaker was replaced with a new one, and ultrasonic cleaning was performed for another 15 minutes for pretreatment.

【0025】

[Evaporation]

ULVAC's VPC-260 vapor deposition equipment is used for vapor deposition, and silicon for semiconductors (resistivity 0.1 Ωcm, boron dope 1.2 x 10) is used as the vapor deposition raw material.¹⁵atoms / cm³, Lynn Dope 1.1 × 10¹⁵atoms / cm³), And this was crushed to a size of about 100 to 1000 μm using a magnetic mortar. A tungsten boat (SF-207) manufactured by Nirako Co., Ltd. was set in the vapor deposition apparatus, and the vapor deposition raw materials were evenly placed in the recessed portion for placing the sample. The pretreated Ni foil, which is a metal substrate, was sandwiched between eyeball clips with a pinch size of 65 mm (sandwich width of about 5 mm), and set at a place about 10 cm directly above the vapor deposition raw material placed on a tungsten boat. Inside the vapor deposition chamber, a rotary pump and a diffusion pump are used, and the degree of vacuum is 4.0 x 10.^-5The vapor deposition was carried out using Torr at a vapor deposition rate of about 0 to 2 Å / s. The X-ray diffraction of the obtained thin-film film is shown in FIG. In FIG. 1, (a) shows bulk Si and Ni, (b) shows a Si thin film deposited on a Ni foil, and (c) shows a Ni foil. From FIG. 1, it can be seen that the vapor-deposited Si thin film is amorphous without the peak of Si (111). The film thickness of the thin-film film was 770 Å as measured by a crystal vibration film thickness meter (CRTM-5000, oscillator SENSOR CRYSTALS GOLD PKG5 5 MHz) manufactured by ULVAC.

【0026】

[Battery characteristic test]

Here, in order to evaluate the battery characteristics of the obtained negative electrode, the test negative electrode was cut out into a 1 cm square, spot welded using a Ni wire of φ0.3 mm, and the electrode lead was attached as the working electrode to separate oxygen and moisture. A three-electrode cell using a glass cell was assembled in a glove box having a sufficiently removed argon gas atmosphere. Metallic lithium was used for the counter electrode and the reference electrode of this 3-electrode cell. Also, as an electrolytic solution, LiClO should be adjusted to a concentration of 1 mol / liter.₄Was dissolved in a 1: 1 mixed solvent of ethylene carbonate and dimethyl carbonate, and a solution obtained was used. Cyclic voltammetry measurement (CV measurement) is performed by connecting each of the three electrodes to a potentiostat and reciprocating the potential of the working electrode (WE) with respect to the reference electrode from 2000 mV to 0 mV at a sweep rate of 1 mV / min. went. The above CV measurement was repeated for 1000 cycles, and the maximum discharge capacity and the retention rate of the discharge capacity at the 1000th cycle were determined. The results are shown in Table 1.

【0027】

[Comparative example 1]

Silicon for semiconductors as a raw material for vapor deposition (resistor 200Ωcm, boron dope 2.3 × 10)¹³atoms / cm³, Lynn Dope 2.3 × 10¹³atoms / cm³) Was used, and the battery characteristics test was performed in the same manner as in Example 1. The results are shown in Table 1.

【0028】

[table 1]<img file="JP2004288564A_D0001.tif" /> 【0029】

[Effect of the invention]

The electrode for a non-aqueous electrolyte secondary battery of the present invention provides good cycleability.

[Simple explanation of drawings]

FIG. 1 is an X-ray diffraction pattern of the vapor-deposited film obtained in Example 1.