WO2005008809A1

WO2005008809A1 - Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery

Info

Publication number: WO2005008809A1
Application number: PCT/JP2004/010453
Authority: WO
Inventors: Takayuki Nakamoto; Yasuhiko Bito
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2003-07-23
Filing date: 2004-07-15
Publication date: 2005-01-27
Also published as: JPWO2005008809A1

Abstract

A negative electrode for nonaqueous electrolyte secondary batteries is disclosed which is capable of absorbing/desorbing lithium. The negative electrode is composed of a deposited film formed on a collector, and the deposited film contains a phase composed of Si as a simple substance and a phase composed of an alloy containing Si. The Si-containing alloy is an alloy of Si and at least one element selected from the group consisting of group IIA elements and transition metal elements, and the content of the Si-containing alloy in the deposited film is not less than 5 volume% but not more than 90 volume%.

Description

Description Negative electrode for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries

The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery comprising a deposited film, and more particularly, to a negative electrode having a high electric capacity and providing a non-aqueous electrolyte secondary battery having excellent high-rate discharge characteristics. Background art

Non-aqueous electrolyte secondary batteries, especially lithium secondary batteries using lithium metal or graphite powder as the negative electrode material, have higher electromotive force and higher energy density than alkaline storage batteries such as nickel-cadmium storage batteries and nickel-hydrogen storage batteries. Therefore, it is used as the main power source for mobile communication devices and portable electronic devices.

In general, a negative electrode of a lithium secondary battery is manufactured by supporting an electrode material mixture containing at least a negative electrode active material and a binder on a current collector. The theoretical capacity of the negative electrode active material is 3 7 2

Graphite powder with mAh / g, gayenium (theoretical capacity: 199 mAhZg), and tin (theoretical capacity: 993 mAh / g), which have a much larger theoretical capacity than graphite powder, are being studied. .

In addition, alloys containing silicon or tin, such as alloys represented by M-xSix (M is at least one selected from the group consisting of Ni, FeCo, and Mn, 50≤x) A study is also underway (Japanese Patent Application Laid-Open No. 10-29411). However, regardless of which active material is used, as long as the negative electrode is made from a material mixture containing a binder, etc. There are limits to meeting demands. The electrode mixture disclosed in Japanese Patent Application Laid-Open No. H10-29494 also includes graphite as a conductive agent and polyvinylidene fluoride as a binder in addition to the alloy powder. This is because the occupied volume does not contribute to the capacity.

On the other hand, studies have been made to use an active material having a large theoretical capacity as a raw material to form a deposited film by a method such as vapor deposition, and to use this as a negative electrode. An electrode composed of a deposited film does not contain a binder or a conductive agent, so that an extremely high capacity can be obtained. However, the electrode composition, the form of the active material, the manufacturing method, and the like are completely different between the conventional mixture layer and the deposited film. Therefore, the conventional mixture

In the field of electrodes consisting of (material mixture), even if the material has excellent characteristics, it is not known what kind of electrode can be obtained by using this as a deposited film. It costs. At present, silicon-based thin-film electrodes such as amorphous silicon thin-film electrodes and microcrystalline silicon thin-film electrodes (Japanese Unexamined Patent Publication No. 2002-83594, Japanese Patent Publication No. Publication No. 295).

As a result of studies by the inventors, the thin-film electrodes described in Japanese Patent Application Laid-Open No. 2002-83594 and Japanese Patent Application Laid-Open No. 2003-72995 have a high capacity but a high efficiency. It has been found that the discharge characteristics are inadequate.

Specifically, a thin-film electrode was manufactured according to the description in JP-A-2002-83594. A test cell was fabricated using this thin film electrode, a counter electrode, and lithium metal as a reference electrode. The battery was charged at a constant current of 0.5 mA at 25 ° C. until the potential of the thin-film electrode reached 0 V with respect to the reference electrode, and then discharged until the potential reached 2 V. As a result, it was confirmed that the thin-film electrode had a high capacity of 380 mAhZg.

However, actually assembled battery as described in JP 2 0 0 2 8 3 5 9 4 No. of Example A, releasing when discharged at a current density of 0. 2mAZc m ² For capacitance, the ratio of the discharge capacity when discharged at a current density of 2. O mAZc m ² (high-rate discharge characteristic) is about 50%, it was not possible to obtain sufficient high rate discharge characteristics.

The electrode area of the battery studied was 8 cm ² on both sides, and the capacity was 25 mAh. Therefore, a current density of 0.2 mA / cm ² corresponds to a current value of 1.6 mA, and the discharge time is about 15.5 hours. On the other hand, the current density of 2. O mAZ cm ² corresponds to a current value of 16 mA, and the discharge time is about 1.5 hours.

In mobile communication devices and portable electronic devices, batteries are often used at a current density equivalent to a discharge time of about 2 hours. However, when a battery using the above-described negative electrode is used under such conditions, there is a problem that the discharge capacity is reduced.

As described above, the reason why the high-rate discharge characteristics of a battery formed of a deposited film is insufficient is that silicon has a low electronic conductivity. According to the semiconductor Handbook 2nd Edition (Ohm-sha), the resistivity of silicon is 2.4 since X 1 is 0 ⁵ Ω · cm, the electronic conductivity of 4. 2 X 1 0- ⁶ SZ cm and low become. Since the above-mentioned thin film electrode is made of silicon, it is considered that the electron conductivity is low and the high-rate discharge characteristics are insufficient.

Further, in a thin film mainly composed of silicon disclosed in Japanese Patent Application Laid-Open No. 2003-72995, a metal element and silicon form a solid solution. Since the solid solution tends to reflect the intrinsic properties of silicon, the electronic conductivity is considered to be close to the intrinsic value of silicon. Therefore, it is considered that the thin-film electrode disclosed in Japanese Patent Application Laid-Open No. 2003-72995 does not have sufficiently high-rate discharge characteristics. Disclosure of the invention The present invention has been made in view of the above circumstances, and comprises a negative electrode for a non-aqueous electrolyte secondary battery having a high electric capacity, which is made of a deposited film having high electron conductivity, and a high capacity and high efficiency including the same. An object is to provide a non-aqueous electrolyte secondary battery having excellent discharge characteristics.

The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery capable of inserting and extracting lithium, wherein the negative electrode comprises a deposited film formed on a current collector, and the deposited film comprises Si alone. And a phase consisting of an alloy containing Si, wherein the alloy containing Si contains at least one element selected from the group consisting of a group 2A element and a transition metal element. The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery, wherein the content of the alloy containing Si in the deposited film is 5% by volume or more and 90% by volume or less.

The deposited film does not contain a binder. Therefore, it is distinguished from a mixture layer formed by applying a slurry in which a mixture comprising an active material and a binder is dispersed in a liquid component onto a current collector and drying the slurry.

Alloy containing the S i is preferably a T i S i _2.

The electron conductivity of the deposited film is preferably 1 SZcm or more. The present invention also relates to a nonaqueous electrolyte secondary battery including a positive electrode capable of inserting and extracting lithium, the above negative electrode, and a nonaqueous electrolyte interposed between the positive electrode and the negative electrode.

ADVANTAGE OF THE INVENTION According to this invention, the negative electrode which consists of a deposited film with a high electronic conductivity and has a high electric capacity is obtained. Further, by using such a negative electrode, a nonaqueous electrolyte secondary battery having high electric capacity and excellent high-rate discharge characteristics can be obtained. Brief Description of Drawings

FIG. 1 is a longitudinal sectional view of a cylindrical battery for evaluating characteristics of the negative electrode of the present invention. It is.

FIG. 2 is a view for explaining a method for preparing a sample for evaluating the electron conductivity of a deposited film constituting the negative electrode of the present invention.

FIG. 3 is a plan view of a sample for evaluating the electron conductivity of the deposited film constituting the negative electrode of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

According to the semiconductor Handbook 2nd Edition (Ohm-sha), because the resistivity of the S i alone 2. a ^{4 X 1 0 5 Ω · cm} , the electronic conductivity is low,

4. a 2 X 1 0- ⁶ SZc m. Meanwhile, PROPERTIES of Metal

Si 1 icides (INSPEC) by Karen Maex, and Marc van Rossum, The

According to Institution of Electrical Engineers, 1 9 9 5 years) resistivity that is described in the electronic conductivity of the alloy containing S i is high, on the order of about 1 0 ⁴ SZc m. For example the electronic conductivity of the T i S i ₂ is ^{l X 1 0 5 S / cm} . Therefore, by mixing a phase composed of Si having a low electron conductivity and a phase composed of an alloy containing Si having a high electron conductivity in the deposited film as described above, It can be expected that the electron conductivity of the film will be higher than that of a deposited film.

In fact, since the deposited film constituting the negative electrode for a non-aqueous electrolyte secondary battery of the present invention contains a phase composed of an alloy containing Si in addition to a phase composed of Si alone, the deposited film consists of only Si. It has much better electron conductivity than a deposited film made of a solid solution mainly composed of Si or a solid solution composed mainly of Si. Note that an alloy containing Si means an intermetallic compound, not a solid solution. The phase composed of a simple substance of Si may be substantially a simple substance, and the phase composed of a simple substance of Si may be doped with impurities such as phosphorus, antimony, and boron. Here, the alloy containing S i comprises S i and at least one element selected from the group consisting of group 2A elements and transition metal elements. 2 Group A elements include Mg, Ca, Sr and Ba. The transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, 〇s, Ir, Pt and Au.

Among the above elements, in particular, Ti, V, Mn, Co, Ni, Cu, Y, Zr, Nb, Mo, Pd, La, Hf, Ta, W, P It is preferable to use at least one selected from the group consisting of t and M. This is because such an alloy can form a deposited film having particularly high electron conductivity, and gives a battery with particularly excellent high-rate discharge characteristics.

The content of the alloy containing Si in the deposited film is 5% by volume to 90% by volume. When the content of the alloy containing Si increases by 90% by volume of the deposited film, the volume ratio of the phase composed of Si alone, which has a high correlation with the discharge capacity, decreases, and the negative electrode capacity becomes insufficient. It becomes. On the other hand, when the content of the alloy containing Si is less than 5% by volume of the deposited film, the proportion of the phase having high electron conductivity is too small, and the proportion of the phase having low electron conductivity is too large. The degree drops rapidly. As a result, only batteries with high capacity but insufficient high-rate discharge characteristics can be obtained.

The content of Si in the alloy containing Si is preferably 33 to 67 atomic%. When the content of Si is smaller than the above, the diffusion of Si from the phase consisting of Si alone into the phase consisting of the alloy containing Si proceeds, and the discharge capacity tends to decrease. On the other hand, when the content of Si is higher than the above, the electronic conductivity of the phase composed of the alloy containing Si decreases, and the Electronic conductivity tends to be low.

Alloys containing Si include Ti Si ₂ , VS i ₂ , M ni, Si ₁₉ ,

C o S Ϊ 2, N i S i ₂ , C u ₃ S i, Y ₃ S ", Z r S", N b S, Mo S, P d S i, La S ", H f S i ₂ , T a S i ₂ , WS i ₂ , P t S i, and M g 2 S i.

It is preferable to use the T i S i _2. This is because Ti Si ₂ has the highest electron conductivity among alloys containing Si, and can provide a battery having the highest high-rate discharge characteristics.

The electron conductivity of the deposited film is preferably 1 S / cm or more, more preferably 300 S / cm or more. If the electron conductivity of the deposited film is less than 1 S / cm, only batteries with insufficient high-rate discharge characteristics can be obtained.

As a method for producing a deposited film, any method can be employed without particular limitation as long as a method capable of obtaining a thin film can be employed. Examples include, but are not limited to, vacuum deposition, chemical vapor deposition (CVD), sputtering, thermal spraying, and plating.

A method for mixing a phase composed of Si alone and an alloy phase containing Si in the deposited film is not particularly limited, and examples thereof include the following. For example, when the CVD method is adopted, a raw material gas containing a predetermined element is mixed with the raw material gas of Si, and the obtained mixed gas is decomposed, and the decomposition product is formed on the current collector from the decomposition product. A deposited film is formed. In the case of employing sputtering, a target of Si and a target of a predetermined element are arranged at predetermined positions, and a deposited film is formed on the current collector by sputtering. In the case of the vacuum evaporation method, a source of Si and a source of a predetermined element are arranged at predetermined positions, and a deposition film is formed on the current collector by evaporation.

From the viewpoint of increasing the content of the phase composed of the alloy containing Si in the deposited film, the temperature of the current collector at the time of forming the deposited film should be set to 600 ° C or less. It is preferable to control the temperature to 200 ° C. (: up to 600 ° C.) From the same viewpoint, the formed deposited film is reduced to 600 ° C. or less, and more preferably to 200 ° C. to 600 ° C. The heat treatment may be performed at 0 ° C. The heating time at that time is preferably 0.5 to 3 hours, and the atmosphere of the heat treatment is an inert gas atmosphere made of Ar gas or the like. If the current collector temperature or the heating temperature exceeds 600 ° C., the temperature is too high, so that the current collector component diffuses into the deposited film, and the non-reactive metal which does not react with lithium. The capacity of the compound tends to decrease due to the formation of the compound, and excessive diffusion reduces the current collector portion, lowers the mechanical strength of the electrode itself, and makes the electrode more susceptible to breakage.

In the present invention, for example, a current collector made of copper, nickel, stainless steel, titanium, or the like can be used. The current collector is preferably electrochemically stable at the negative electrode potential, thin and durable, and preferably has a thickness of 8 to 35 / m. The shape of the current collector is not particularly limited. For example, the surface of the current collector may not be smooth but may have irregularities. As the current collector, it is particularly preferable to use a metal foil such as an electrolytic copper foil, and the surface thereof may be roughened.

When the deposited films are formed on both surfaces of the current collector, the total thickness of the deposited films on both surfaces is preferably 10% or more and 60% or less of the thickness of the current collector. If the total thickness is less than 10% of the thickness of the current collector, the capacity of the negative electrode becomes insufficient, and the battery capacity tends to decrease. On the other hand, if the total thickness exceeds 60% of the thickness of the current collector, the current collector may be damaged when the deposited film expands, and it is difficult to obtain good cycle life characteristics. . When the total thickness is not more than 40% of the thickness of the current collector, the current collector is less likely to be deformed when the deposited film expands, and further excellent cycle life characteristics can be obtained. Is more preferable in that

The crystalline state of the phase composed of Si alone is amorphous or microcrystalline. preferable. Although the reason is not clear, better cycle life characteristics can be obtained if the crystalline state of the phase composed of Si alone is amorphous or microcrystalline.

The non-aqueous solvent of the non-aqueous electrolyte used when producing the non-aqueous electrolyte secondary battery using the above-mentioned negative electrode is not particularly limited, but ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and the like. A mixed solvent of a cyclic carbonate such as dimethyl carbonate, a methyl carbonate, a methyl carbonate, and a chain force carbonate such as getyl carbonate is preferred. Non-aqueous solvents include ether solvents such as 1,2-dimethoxyethane and 1,2-jetoxene, cyclic carboxylate esters such as τ-butyrolactone and avalerolactone, sulfolane, and methyl acetate. A chain ester or the like can also be used.

The solute dissolved in the non-aqueous _{solvent, L i PF 6, L i} BF 4,

L i CF ₃ S 0 ₃ , L i N (CF ₃ S 0 ₂ ) L i N (C ₂ F ₅ S 0 ₂ ) ₂ ,

L i N (CF sS 0 ₂ ) (C ₄ F ₉ S 0 ₂ ), L i C (CF ₃ S O2) ₃ ,

_{_{L i C (C 2 F 5}} S O2) 3, L i A s F 6, L i C 1 〇 _{_{_{4, L i 2 B 10 C}}} , and the like L i ₂ B ₁₂ C 1.

Further, as the non-aqueous electrolyte, an inorganic solid electrolyte, an organic solid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte in which an electrolyte is held in a polymer material, and the like can be used.

The positive electrode to be combined with the above-mentioned negative electrode is not particularly limited. However, as the positive electrode active material, Li Co ₂ , Li Ni 0 ₂ , Li M n ₂ 4, Li M n _{2, and} Li Co ₂ 0.5N i o. ₅ 0 _2, are preferably used those containing L i n i 0.7C o 0.2M n ( lithium-containing transition metal oxides such as uC.

Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to these examples. Example 1

(A) Preparation of negative electrode

Electrodeposited copper foil (31 li thick, manufactured by Furukawa Circuit Oil Co., Ltd.) was used as the current collector. Massive S i (Pure Chemical Co., Ltd., purity 9 9.9 9 9%) and bulk T i S i ₂ (Pure Chemical Co., Ltd., purity 9 9.9 9 9%) and a. 2 Co-evaporation was performed simultaneously by the original evaporation method to form a deposited film.

Specifically, about 0. 0 0 0 0 3 T in vacuum orr, the bulk T i S i ₂ - accelerating voltage of 8 k V, evaporated with an electron beam conditions of current 2 5 0 m A, At the same time, the massive Si was evaporated with an electron beam with an accelerating voltage of 18 kV and a current of 150 mA. And on both sides of the room temperature electrolytic copper foil, the thickness is about

A thin film of 5 m was deposited to obtain a negative electrode A1. At this time, the conditions were appropriately controlled so that the composition of the deposited film was TiSi3.

When the qualitative and quantitative determinations of the phases contained in the obtained deposited film were performed by the methods described below, the presence of two or more phases was confirmed. The deposited film contains a phase composed of Si alone and a phase composed of an alloy containing Si (T i Si ₂ ). The content of the alloy containing Si in the film is as follows. , 11% by volume.

(Mouth) Preparation of positive electrode

Lithium cobaltate (L i C O_〇 ₂₎ powder 8 5 parts by weight of the positive electrode active material, a carbon powder 1 0 part by weight as a conductive agent, and a PV d F 5 parts by weight of a binder were mixed The resulting mixture was dispersed in dehydrated N-methyl-2-pyrrolidone (NMP) to prepare a slurry. This slurry was applied to an aluminum foil as a positive electrode current collector, dried, and rolled to produce a positive electrode.

(8) Preparation of non-aqueous electrolyte

Volume ratio of ethylene carbonate to ethyl methyl carbonate 1: 1 In a mixed solvent, and the L i PF ₆ was prepared a non-aqueous electrolyte solution at a concentration 1 Morunori' Torr.

(8) Assembly of non-aqueous electrolyte secondary battery

FIG. 1 is a longitudinal sectional view of the assembled nonaqueous electrolyte secondary battery. This battery was assembled as follows. The positive electrode 1 and the negative electrode 2 were stacked with Separation Layer 3 interposed therebetween, and spirally wound to produce an electrode body. The positive electrode lead 4 and the negative electrode lead 5 were connected to the positive electrode and the negative electrode in advance. An upper insulating ring 9a and a lower insulating ring 9b were arranged above and below the electrode body, and were housed inside a stainless steel battery case 7. The positive electrode lead 4 was connected to the sealing plate 6, and the negative electrode lead 5 was connected to the bottom of the battery case 7. Thereafter, a non-aqueous electrolyte was injected into the battery case 7. Next, the opening of the battery case 7 is closed with a sealing plate 6 provided with a safety valve via an insulating packing 8, and the sealing process is performed to form a cylindrical hermetic type having a diameter of 18 mm and a height of 65 mm. The rechargeable battery A1 was assembled. The assembly of the nonaqueous electrolyte secondary battery was performed in an atmosphere of dry air whose dew point was adjusted to 150 ° C or less. Example 2

The deposited film obtained in Example 1 was deposited in an inert gas (Ar) atmosphere.

Heat treatment was performed at 300 ° C. for 1 hour to obtain a negative electrode A2. The qualitative and quantitative analysis of the phases contained in the deposited film after the heat treatment was carried out by the methods described below. The deposited film contained a phase consisting of Si alone and a phase consisting of an alloy containing Si (T i Si ₂ ). Was contained, and the content of the alloy containing Si in the film was 69% by volume. Next, a non-aqueous electrolyte secondary battery A2 was produced in the same manner as in Example 1, except that the negative electrode A2 was used. Example 3 ' When depositing thin films on both sides of electrolytic copper foil (made by Furukawa Circuit Oil Co., Ltd., thickness 31 m), except that the electrolytic copper foil was heated to 300 ° C. Using the same deposition conditions, a negative electrode A3 having a deposited film with a thickness of about 5 xm was obtained.

In this case, the composition of the deposited film, such that T i S i _3, were appropriately controlled conditions of vacuum deposition. The qualitative and quantitative analysis of the phases contained in the obtained deposited film was performed by the methods described below.

A phase composed of (T i Si ₂ ) was contained, and the content of the alloy containing Si in the film was 65% by volume. Next, a non-aqueous electrolyte secondary battery A3 was produced in the same manner as in Example 1, except that the negative electrode A3 was used. Comparative Example 1

The same electrodeposited copper foil used in Example 1 was applied on both sides of the same electrodeposited copper foil as used in Example 1 by two-pole RF sputtering using Si Yuichi Get (manufactured by Kojundo Chemical Co., Ltd., purity: 99.99.99%). Then, an Si thin film having a thickness of about 5 was deposited to obtain a negative electrode X1. Here, Ar was used as the sputtering gas, and the above sputtering was performed under the conditions of high-frequency power of 200 W, vacuum degree of 0.1 lT rr, Ar flow rate of 150 sccm, and substrate temperature of room temperature.

Next, a non-aqueous electrolyte secondary battery X1 was produced in the same manner as in Example 1, except that the negative electrode X1 was used. Comparative Example 2

Using S i H 4 and PH ₃ each diluted with H ₂ as the source gas. By C VD method, on both sides of the same electrolytic copper foil as used in Example 1, a thickness of about 5 m A P-doped Si thin film was deposited to form a negative electrode X2.

Here, a mixed gas of H ₂ and S i H ₄ (S i H ₄ content: 10%, A mixed gas of hydrogen, Ltd., a purity 9 9.9 9 9 9%), H ₂ and PH ₃

(PH ₃ content: 10%, manufactured by Nippon Sanso Co., Ltd., purity: 99.99.99%) at a flow rate of lOOsccm and 2sccm, respectively, and CVD under a pressure of 2 Torr. A thin film was deposited on both sides of the electrolytic copper foil heated to 200 ° C. by a heater.

Next, a nonaqueous electrolyte secondary battery X2 was produced in the same manner as in Example 1 except that the negative electrode X2 was used. Comparative Example 3

Electrodeposited copper foil (thickness 14 / im) was used for the current collector. Graphite powder and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 95: 5, and the resulting mixture was dispersed in dehydrated NMP to prepare a slurry. This slurry was applied on both sides of an electrolytic copper foil, dried, and then rolled to obtain a negative electrode X3. Next, a non-aqueous electrolyte secondary battery X3 was produced in the same manner as in Example 1 except that the negative electrode X3 was used.

[Evaluation]

[A] Qualitative properties of deposited film phase

Wide-angle X-ray diffraction was used to qualify the phases contained in each deposited film. Diffraction angle using a wide-angle X-ray diffractometer (product code "RINT-2500", manufactured by Rigaku Denki Co., Ltd.) using a Cu K line at a wavelength of 1.5405 angstroms as a source. The diffraction pattern in the range of 20 = 10 ° to 80 ° was measured to determine the phase.

[B] Content of phase composed of alloy containing Si (volume%)

From the PMA analysis of the cross section (S) of each deposited film, the phase composed of the alloy containing Si was confirmed, and the cross section (s) of the confirmed phase was compared with the entire cross section (S). The area ratio was calculated, and the value was defined as volume%.

[C] Electronic conductivity of deposited film

The electron conductivity of each deposited film was measured by the four probe method.

As shown in FIG. 2, a 5 cm × 5 cm electrolytic copper foil 10 having a 1 cm × 1 cm hole in the center was superimposed on a 5 cm × 5 cm electrolytic copper foil 11. On top of this, a 5 m-thick thin film was prepared under the same conditions as those described for the preparation of the negative electrode.

Next, as shown in FIG. 3, the electrodeposited copper foil 11 having no hole was cut into a size of lcmx2cm including a region 12 where a thin film was formed. The current terminal and the voltage terminal were brought into contact with the region 12 where the thin film was formed and the copper foil region 13 where the thin film did not exist, respectively. The distance between the current and voltage terminals was fixed at 5 mm, and the distance between the voltage terminals was fixed at 5 mm.

[D] High-rate discharge characteristics of batteries

Each battery was charged to 4.2 V with a current of 0.6 A at a charge / discharge temperature of 20 ° C, and then discharged to 2.5 V with a current of 0.4 A to reduce the discharge capacity C 1 I did.

Next, after charging to 4.2 V with a current of 0.6 A, the battery was discharged to 2.5 V with a current of 4 A, and a discharge capacity C 2 was obtained.

The ratio P () of the discharge capacity C2 to the discharge capacity C1 was calculated based on the following equation, and the high-rate discharge characteristics of each battery were evaluated. A battery with a higher P value has a higher high-rate discharge characteristic. If the value of P is 85% or more, it can be said that good high-rate discharge characteristics are obtained.

P (%) = (C 2 ZC 1) X 1 0 0

Table 1 shows the configurations of Examples 1 to 3 and Comparative Examples 1 to 3 and the results of each test. table 1

* P dough. S i

In Table 1, the batteries A1 to A3 of the examples of the present invention have higher capacities than the battery X3 of the comparative example including the negative electrode made of the graphite mixture. Batteries A1 to A3 also have superior high-rate discharge characteristics as compared with batteries X1 and X2 of Comparative Examples each having a negative electrode composed of a Si single phase or a P-doped Si phase. Also, batteries A2 and A3, in which the content of the alloy containing Si in the deposited film is particularly large, are superior to the battery A1, in which the content is small, in the high-rate discharge characteristics.

Since the content of the alloy containing Si in the deposited film was 11% by volume and 69% by volume in the negative electrodes A1 and A2, respectively, the heat treatment of the deposited film reduced the Si. It can be seen that the content of the contained alloy increases. This is because, in a deposited film that is not subjected to heat treatment, the proportion of Ti dissolved in the crystal structure of Si, that is, the proportion of solid solution of Si and Ti becomes large, and the intermetallic compound Ti S It is considered that the content of i ₂ is reduced. Also, in the deposited film formed on the electrolytic copper foil heated to 300 ° C, the ratio of the solid solution of Si and Ti decreased, and the content of the alloy containing Si was 65% by volume. This was almost equivalent to the case where the heat treatment of the deposited film was performed.

S i is the electron conductivity of four. 2, but X 1 0- ⁶ SZ cm and lower, T i S i ₂ electron conductivity of the deposited film containing about 1 1% by ^{volume, 7. 5 X 1 0 2} SZ cm (Example 1), and the electron conductivity is dramatically improved. Electronic conductivity of the T i S i 2 is ^{1 X 1 0 5 S / cm} . This indicates that the inclusion of an alloy with high electron conductivity in the deposited film can provide a dramatic improvement in electron conductivity even when the volume ratio of the alloy is relatively small. The electronic conductivity of the deposited film containing about 69% by volume and 65% by volume of T i Si ₂ was 3.5 × 10 ³ S / cm (Example 2) and

3. It is ^{3 X 1 0 3 S / cm} ( Example 3), towards the content of high electron conductivity alloy is large, it can be seen that the more electron conductivity is improved. It can also be seen that the higher the content of the alloy having high electron conductivity in the deposited film, the more excellent the battery with high rate discharge characteristics can be obtained.

In the negative electrode X 1 deposited film composed only of S i alone, since the electronic conductivity of the deposited film 8 X 1 0- ⁵ S / cm and less, high rate discharge characteristics of the battery X 1 is

34.1% was insufficient. On the other hand, in the negative electrode X2 in which the deposited film was composed of only Si doped with P, the electron conductivity of the deposited film was 5 × 10— ^] SZcm, which was higher than that in Comparative Example 1. However, it was considerably lower than the example of the present invention, and the high-rate discharge characteristic was insufficient at 70.9%. Example 4

In this example, the type of alloy containing Si was examined.

Instead of the massive _{T i S i 2, VS i} 2, Mn S i 2, C o S i 2,

_{N i S, C u 3 S} i, Y 3 S is, Z r S, N b S, Mo S i 2, P d S i, L a S i 2, H f S i 2, T a S i 2 , also WS i _2, P t S i except for using M g ₂ S i, in the same manner as in example 1, to prepare a deposited film. However, in the negative electrode A 20, the massive Si, the massive Co Si ₂ and the massive Ni Si 2 were evaporated by three electron beams, respectively.

At this time, vacuum deposition was performed so that the composition of the deposited film shown in Table 2 was obtained. The matter was appropriately controlled. In addition, the temperature of the deposited film after vacuum

Negative electrode A4A20 was obtained by performing a heat treatment for 1 hour in a vacuum at an optimum heating temperature in a range of 600 ° C.

Heat treatment at a temperature exceeding 600 ° C was also attempted, but Cu, a current collector, was excessively diffused into the deposited film, and at least a part of the negative electrode was broken. .

The qualitative and quantitative analysis of the phases contained in the deposited film was performed by the above-mentioned method, and it was confirmed that two or more types of phases were present. The deposited film contained a phase composed of Si alone and a phase composed of an alloy containing Si as shown in Table 2. The content of the alloy containing Si in the deposited film was as shown in Table 2. <Next, the non-aqueous electrolyte was prepared in the same manner as in Example 1 except that the negative electrodes A4 to A20 were used. Secondary batteries A4 to A20 were produced. The same evaluation as above was performed. Table 2 shows the results. Table 2 Discharge Discharge

Processing alloy electrons

Negative electrode deposited film Capacity Capacity ratio P phase 'Dish' content Content Conductivity

Battery composition (° c) C1 C2 (¾)

(Volume ¾) (S / cm)

(mAh) (mAh)

A4 VSi ₃ Si + VSi ₂ 400 64.1 8.9X10 ² 2776 2600 93.7

A5 MnSi ₃ Si + Hn „Si ₁₉ 300 56.7 9.0X10 ² 2777 2605 93.8

A6 CoSi ₃ Si + Co i ₂ 300 65.9 ■ 2.0X10 ³ 2785 2617 94.0

A7 NiSi ₃ Si + NiSi ₂ 250 66.2 8.9X10 ² 2776 2602 93.7

A8 CuSi Si + CUjSi 250 54.0 5.7X10 ² 2771 2599 93.8

A9 YSi ₃ Si + Y ₃ Si ₅ 300 .65.2 6.0X10 ² 2768 2600 93.9

A10 ZrSi ₃ Si + ZrSi ₂ 400 71.4 8.6X10 ² 2775 2600 93.7

All NbSi ₃ Si + NbSi ₂ 500 68.6 1.4X10 ³ 2779 2611 94.0

A12 MoSi, Si + HoSij 550 66.8 2.5X10 ³ 2783 2620 94.1

A13 PdSi ₂ Si + PdSi 450 59.3 1.0X10 ³ 2774 2601 93.8

A14 LaSij Si + LaSi ₂ 300 76.4 9.0X10 ² 2771 2601 93.9

A15 HfSi ₃ Si + HfSi ₂ 350 71.0 4.3X10 ² 2766 2593 93.7

A16 TaSi, Si + TaSi ,, 450 68.4 1.5X10 ³ 2780 2608 93.8

A17 Si ₃ Si + WSi ₂ 600 66.8 2.5X10 ³ 2782 2621 94.2

A18 PtSi ₂ Si + PtSi 400 59.6 1.1X10 ³ 2778 2607 93.8

A19 gSi Si + Mg ₂ Si 200 76.1 1.1X10 ³ 2778 2606 93.8

AZ0 ^Co o.sNi. _{_{_{. S Si 3 Si + CoSi 2}}} + NiSi 2 300 66.1 1.6X10 3 2780 2605 93.7 In Table 2, the batteries A4 to A20 of the examples of the present invention have higher capacities than the battery X3 of Comparative Example 3 including a negative electrode made of a mixture containing graphite. Batteries A4 to A20 have higher discharge rates than batteries X1 and X2 of Comparative Examples 1 and 2 each having a negative electrode composed of a Si single phase or a P-doped Si phase. Excellent characteristics. All of the alloys containing Si contained in the deposited film have high electron conductivity, which contributes to the improvement of the electron conductivity of the deposited film.As a result, it is possible to obtain a battery with excellent high rate discharge characteristics. Conceivable. When the alloy containing Si is TiSi ₂ , the high-rate discharge characteristics are the most excellent. Example 5

In this example, the content of the alloy containing Si in the deposited film was examined.-By changing the composition of the deposited film, the content of the alloy containing Si was changed to 5% by volume, as shown in Table 3. Negative electrodes A21 to A24 were produced in the same manner as in Example 2, except that the volume was controlled to 10% by volume, 75% by volume and 90% by volume. Next, non-aqueous electrolyte secondary batteries A 21 to A 24 were produced in the same manner as in Example 1 except that negative electrodes A 21 to A 24 were used. The same evaluation as above was performed. Table 3 shows the results. Comparative Example 4

Except that the content of the alloy containing Si was controlled to 3% by volume and 95% by volume as shown in Table 3 by changing the composition of the deposited film, the negative electrode X was produced in the same manner as in Example 2. 4 and X5 were made. Next, nonaqueous electrolyte secondary batteries X4 and X5 were produced in the same manner as in Example 1, except that negative electrodes X4 and X5 were used. The same evaluation as above was performed. Table 3 shows the results. Table 3

In Table 3, the batteries A 21 to A 24 of the examples of the present invention have higher capacities than the battery X 3 of Comparative Example 3 including a negative electrode made of a mixture containing graphite. 21 to A24 have excellent high-rate discharge characteristics compared to the batteries X1 and X2 of Comparative Examples 1 and 2 each having a negative electrode composed of a Si single phase or a P-doped Si phase. I have. From Table 2 and 3, high-rate discharge characteristics is most excellent when alloy containing S i is T i S i _2. This is considered to have the highest electron conductivity T i S i _2.

Battery X4, which contained 3% by volume of the alloy containing Si, had a high capacity, but the high-rate discharge characteristics were insufficient at 75.1%. This is because the volume fraction of T i Si ₂ having high electron conductivity is small, and the volume fraction of Si having low electron conductivity is too large, so that the electron conductivity of the thin film is low.

This is probably due to the low value of 0.55 S / cm. On the other hand, battery A21, which contains 5% by volume of alloy containing Si, has a high-rate discharge characteristic compared to battery X4, although the electronic conductivity of the thin film is 1.05 S / cm. It has improved dramatically. The results show that the use of the negative electrode of the present invention, which satisfies at least 1 S / cm or more of the electron conductivity, can provide the required high-rate discharge characteristics.

Battery X5, which contains 95% by volume of an alloy containing Si, has an excellent high-rate discharge characteristic of 96.0%, but has an insufficient capacity C1 of 125 mAh. I got it. This is probably because the volume ratio of Si, which greatly correlates with the discharge capacity, became too small. Example 6

Here, a negative electrode was prepared by sputtering in the following manner.

S i (manufactured by Kojundo Chemical Co., Ltd., purity 99.99.99%) and

Example 1 was performed under the same conditions as in Comparative Example 1 by two-electrode simultaneous RF sputtering using TiSi 2 (manufactured by Kojundo Chemical Co., Ltd., purity 99.9999%) as an overnight getter. Approximately 5 m thick on both sides of the same electrolytic copper foil used in

A thin film having a composition of TiSi3 was deposited. Next, the heat treatment of the deposited film was performed at 300 ° C. in a vacuum for 3 hours to obtain a negative electrode B1.

The qualitative and quantitative analysis of the phase contained in the deposited film of the negative electrode B1 was performed by the above-described method. As a result, it was observed that the Ti Si ₂ phase and the Si phase were present. The content of T i Si ₂ ) was 68% by volume.

Further, instead of the T i S i ₂ a target, N i S i _2,

Thin films were deposited on both sides of the electrolytic copper foil under the same conditions as above except that Co Si ₂ and Mg Si ₂ were used, respectively. Here, the composition of the deposited film to be the _{N i S i 3, C o} S i 3 and M g S i, respectively, to control the conditions of the sputtering evening ring.

Next, the heat treatment of the obtained deposited films was performed at 250 ° C., 300 ° C., and 200 ° C. for 3 hours in a vacuum, so that the negative electrodes B 2, B 3 and B Got four.

Qualitative and quantitative of the negative electrode B 2, B 3 and B 4 of the deposited film phase contained in Operation was performed by the method described below, during the deposition film of the negative electrode B 2 N i S i ₂ phase and S i phase there was, during the deposition film of the negative electrode B 3 exists C o S i ₂ phase and S i phase. during deposition film of the negative electrode B 4 exist M g ₂ S i ne th and S i phase Observe that The content of the alloy containing Si in each of the deposited films was 63% by volume, 65% by volume, and 71% by volume.

Next, nonaqueous electrolyte secondary batteries B1 to B4 were produced in the same manner as in Example 1, except that the negative electrodes B1 to B4 were used. Example 7

Here, a negative electrode was manufactured by the CVD method in the following manner.

Using S i H ₄ , T i H _4, and PH ₃ each diluted with H ₂ as a source gas, the same electrodeposited copper foil as used in Example 1 was formed on both surfaces by the CVD method. A P-doped Si thin film having a thickness of about 5 xm was deposited to form a negative electrode B5.

Here, a mixed gas of H ₂ and _{S i H 4 (S i H} 4 content 1 0%, Nippon oxygen Corp., purity 9 9.9 9 9 9%) and, H ₂ and T i mixed gas of H ₄

(T i H ₄ content 1 0%, Nippon Sanso Corp., purity 9-9.9 9 9 9%) and. Eta ₂ and a mixed gas of ΡΗ _₃ (ΡΗ ₃ content 1 0%, Nippon Oxygen Co., Ltd., purity 99.99.99%) were supplied at a flow rate of 300 sccm, 100 sccm and 5 sccm, respectively, and the CVD method was performed under a pressure of 3 Torr. A thin film having a composition of TiSi 3 was deposited on both sides of the electrolytic copper foil heated to 300 ° C. by a heater.

Where a qualitative and quantitative determination of phase contained in the deposited film of the negative electrode B 5 rows one by the method described above, during the deposition film, T i S i ₂ phase and S i-phase is present, T i S i ₂ phases Was 68% by volume.

Next, a non-aqueous electrolyte secondary battery B5 was produced in the same manner as in Example 1, except that the negative electrode B5 was used.

The same evaluation as above was performed on the negative electrodes and the batteries prepared in Examples 6 and 7. Table 4 shows the results. Table 4

In Table 4, the batteries B1 to B5 of the examples of the present invention have higher capacities than the battery X3 using graphite as a negative electrode, which is a comparative example. Batteries Bl to B5 also have superior high-rate discharge characteristics compared to comparative batteries X1 and X2, each of which has a negative electrode composed of a single Si phase or a P-doped Si phase. ing. Among them, the batteries B1 and B5 of the examples of the present invention have very good high-rate discharge characteristics. This is because, as in Example 2 described above, the electronic conductivity of the TiSi ₂ phase contained in the deposited film was lower than that of the alloy phase containing Si contained in the other negative electrodes B2 to B4. This is probably because the electron conductivity of the entire deposited film improved. Industrial applicability

The negative electrode for a non-aqueous electrolyte secondary battery of the present invention is composed of a deposited film having a high electron conductivity and has a high electric capacity, and thus has a high electric capacity and a high rate discharge characteristic. It gives the battery. INDUSTRIAL APPLICABILITY The present invention is applicable to all forms of non-aqueous electrolyte secondary batteries, and has, for example, a cylindrical, coin, square, flat or other shape, and a wound or stacked electrode. It is applicable to batteries having a body structure. INDUSTRIAL APPLICABILITY The nonaqueous electrolyte secondary battery of the present invention is useful as a main power supply for mobile communication devices, portable electronic devices, and the like.

Claims

The scope of the claims

1. A negative electrode for a non-aqueous electrolyte secondary battery capable of inserting and extracting lithium, wherein the negative electrode comprises a deposited film formed on a current collector,

The deposited film includes a phase composed of Si alone and a phase composed of an alloy containing Si.

The alloy containing S i is an alloy of S i and at least one element selected from the group consisting of group 2A elements and transition metal elements,

A negative electrode for a non-aqueous electrolyte secondary battery, wherein the content of the Si-containing alloy in the deposited film is 5% by volume to 90% by volume. -

2. The S i alloy containing the, T i S i ₂ a is claims for a non-aqueous electrolyte secondary battery negative electrode of claim 1 wherein.

3. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electron conductivity of the deposited film is 1 S / cm or more.

4. A non-aqueous electrolyte secondary battery comprising a positive electrode capable of inserting and extracting lithium, the negative electrode according to claim 1, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode.