JP2002260669A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery, having a high charge and discharge capacity and high energy density. SOLUTION: This nonaqueous electrolyte secondary battery is provided with an amorphous silicon vapor-deposited film on the collector surface of an negative electrode material, in a nonaqueous electrolyte secondary battery composed of a positive electrode material, the negative electrode material, electrolyte containing lithium salt, and a separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte having lithium ion conductivity as a positive / negative electrode active material, and particularly to a portable electronic device. The present invention relates to a non-aqueous electrolyte secondary battery suitable as a secondary battery used for communication equipment and the like.

[0002]

2. Description of the Related Art In recent years, with the remarkable development of portable electronic devices, communication devices, and the like, a secondary battery having a high energy density has been strongly demanded from the viewpoint of economy and reduction in size and weight of the devices. Conventionally, as a measure to increase the capacity of this type of secondary battery,
A method using an oxide such as V, Si, B, Zr, Sn or a composite oxide thereof as a negative electrode material (JP-A-5-1748
No. 18, JP-A-6-60867, etc.) or a method in which a metal oxide melt-quenched and quenched is used as a negative electrode material (JP-A-10-294112). There are known techniques for making doping and undoping possible.

[0003]

However, in the above-mentioned conventional method, although the charge / discharge capacity is certainly increased and the energy density is improved, the required characteristics in the market are still insufficient, and the charge / discharge capacity is further increased. In addition, improvement in energy density is desired.

The present invention has been made in view of such circumstances, and has as its object to provide a nonaqueous electrolyte secondary battery having a high charge / discharge capacity and high energy density.

[0005]

Means for Solving the Problems and Embodiments of the Invention The present inventors have conducted intensive studies to achieve the above object, and as a result, by adding amorphous silicon to the negative electrode material, the charge / discharge capacity was reduced. The present inventors have found that it is surprisingly improved, and in this case, it is effective to deposit an amorphous silicon film on a current collector of a negative electrode material, and completed the present invention.

Hereinafter, the present invention will be described in more detail. A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode material, a negative electrode material, a non-aqueous electrolyte containing a lithium salt, and a separator. Wherein an amorphous silicon film is deposited on the surface of the current collector of the negative electrode material.

Here, the negative electrode material includes at least a current collector, a binder, and a negative electrode active material. The present invention relates to a negative electrode material obtained by depositing an amorphous silicon film on the current collector surface. use.

[0008] In this case, the current collector on which the amorphous silicon film is deposited is not particularly limited as long as it is an electron conductor that does not adversely affect the constructed battery.
Copper, stainless steel, nickel, titanium, calcined carbon, and the like can be used. The method for depositing an amorphous silicon film on the current collector surface is also not particularly limited.
Monosilane (SiH ₄ ) gas or the like is glow discharge-decomposed and deposited, so-called plasma CVD method. A silicon target is sputtered and deposited in a mixed gas atmosphere of argon and hydrogen. Is heated and evaporated, and ionized and deposited,
Although a so-called ion plating method or the like can be adopted, it is preferable to use a plasma CVD method using an apparatus described later.

[0009] The thickness of the amorphous silicon film is
It is preferably 0.5 to 10 μm, particularly preferably 1 to 5 μm. If the thickness is too small, it is difficult to achieve the object of the present invention. If the thickness is too large, the amorphous silicon film becomes an insulating layer and has no function as a battery.

The negative electrode active material is not particularly limited as long as it is conductive and has resistance to the non-aqueous electrolyte used. For example, (1) a conductive carbonaceous material such as graphite, acetylene black, carbon, etc. Timber,
(2) Metallic materials such as gold, silver and copper, and (3) conductive composite materials such as gold-plated silica fine particles, silver-plated silica fine particles, and copper-coated alumina fine particles can be used. In consideration of characteristics, economy, and the like, it is preferable to use a carbonaceous material among them.

In this case, in order to increase the occlusion capacity (capacity) of the light metal in the electrode, the carbonaceous material or the like is made of a general formula
It is preferable to add a silicon oxide represented by _x (0.8 <x <1.9). Here, when the value of x is 0.8 or less, the amount of metallic silicon is substantially excessive, so that the metallic silicon becomes crystalline and / or block-like, and the content of active silicon may decrease. On the other hand, when the value of x is 1.9 or more,
Since it is substantially silicon dioxide, the content of active silicon is reduced, which may cause a problem. More preferably 0.8 <x <1.6, even more preferably 0.9 <x <1.
3.

The amount of the silicon oxide added is not particularly limited. However, in order to sufficiently exhibit the effect of the addition of the silicon oxide, the amount of the silicon oxide is preferably 20 to 80 wt% in the negative electrode active material.
In particular, the content is preferably set to 40 to 70 wt%. 20wt
%, The effect of adding silicon oxide may be insufficient. On the other hand, when the content exceeds 80 wt%, the proportion of the conductive material added is reduced, and the electron conductivity is reduced, so that the capacity may be reduced.

The binder has a binding action,
The nonaqueous electrolyte to be used, the positive electrode, as long as it has resistance to the potential at the negative electrode, there is no particular limitation,
Polyethylene, polypropylene, polyvinylidene fluoride, or the like can be used.

As the electrolyte used in the nonaqueous electrolyte secondary battery according to the present invention, γ-butyrolactone, propylene carbonate, ethylene carbonate, dimethyl carbonate, methyl formate, 1,2-dimethoxyethane, tetrahydrofuran, dioxolan, dimethylform LiClO ₄ , LiPF ₆ , LiB as a supporting electrolyte in a single or mixed non-aqueous organic solvent such as amide
F ₄ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ), LiN
An organic non-aqueous electrolyte in which a lithium ion dissociable salt such as (SO ₂ CF ₃ ) is dissolved, a polymer solid electrolyte in which a lithium salt is dissolved in a polymer such as polyethylene oxide or a crosslinked polyphospholazene, or Li ₃ A lithium ion conductive non-aqueous electrolyte such as an inorganic solid electrolyte such as N or LiN can be used.

The material of the separator used in the non-aqueous electrolyte secondary battery of the present invention is not limited as long as it has a function of preventing contact of the electrodes, holding the non-aqueous electrolyte, and passing lithium ions. There is no particular limitation, and for example, a porous film, a nonwoven fabric, a woven fabric, or the like can be used. The thickness of the separator is not particularly limited and can be set arbitrarily.
Is preferred, and particularly preferably 20 to 50 μm.

Next, an apparatus and method for depositing an amorphous silicon film on the surface of the current collector of the negative electrode material in the nonaqueous electrolyte secondary battery of the present invention will be described. FIG. 1 shows a vapor deposition apparatus 1 according to one embodiment of the present invention. This vapor deposition apparatus 1 is for vapor-depositing an amorphous silicon film on a current collector by a plasma CVD method, and includes a reaction chamber 10 and a pair of electrodes 11 inside the reaction chamber 10.
A and 11B are provided. A pair of electrodes 11A, 11
B is connected to a discharge power supply 12 so that glow discharge can be performed between the electrodes 11A and 11B. Here, a DC or AC power source can be arbitrarily selected as the discharge power source 12.

A deposition receiver 13 for depositing an amorphous silicon film is mounted on one surface of one electrode 11B, and the deposition receiver 13 is heated to a predetermined temperature on the other surface. A heater 14 is provided.

Further, the gas supply valve 1 is provided in the reaction chamber 10.
A gas supply source 17 for supplying a SiH ₄ -based gas is connected via a gas introduction pipe 16 provided with a gas supply 5, and an exhaust pipe 19 provided with an exhaust valve 18 on the side opposite to the gas supply source 17. The vacuum pump 20 is connected via the.
Further, the reaction chamber 10 is provided with a vacuum gauge 21 for measuring the degree of reduced pressure in the system.

A method for depositing an amorphous silicon film by a plasma CVD method using the above-described deposition apparatus 1 is as follows.
The procedure is as follows. First, a deposition receiver 13 made of a copper foil or the like having a predetermined thickness is placed on one electrode 11B, and then heated by a heater 14 to a predetermined temperature in a range of 100 to 850 ° C. Subsequently, the exhaust valve 18 is fully opened, and the inside of the reaction chamber 10 is set to 1 × 10 ⁻⁵
After reducing the pressure to r or less, the exhaust valve 18 is fully closed.

Thereafter, the gas supply valve 15 is adjusted so that the pressure of the vacuum gauge 21 becomes a predetermined pressure.
To supply SiH ₄ gas into the reaction chamber 10. After the pressure is stabilized, a voltage of about 500 to 5000 V is applied to the electrodes 11A and 11B to start glow discharge. After a lapse of a predetermined time from the start of the discharge, the discharge is stopped to stop the deposition of the amorphous silicon, and an amorphous silicon film having a predetermined thickness is formed on the deposition receiver 13.

The silicon oxide used as the negative electrode active material is, for example, a mixed raw material powder containing at least silicon dioxide powder, which is prepared by mixing 1100 to 1100 in an inert gas atmosphere or under reduced pressure.
After heating in a temperature range of 1600 ° C., preferably 1200 to 1500 ° C. to generate SiO gas, oxygen gas is continuously or intermittently supplied into the SiO gas to form a mixed gas, and the mixed gas is cooled. It can be obtained by precipitating on the surface of a substrate that has been made.

Here, a mixture of silicon dioxide and a powder for reducing the same is used as the mixed raw material powder containing the silicon dioxide powder. Specific examples of the reduced powder include metal silicon and carbon-containing powder. Among these, it is preferable to use metallic silicon in consideration of improvement in reactivity and improvement in yield. The metal silicon is not particularly limited, but it is preferable to use a high-purity metal such as semiconductor grade Si, ceramic grade Si, and chemical grade Si in consideration of improving the purity of the generated silicon oxide powder. It is. The mixing ratio of the silicon dioxide and the powder for reducing the silicon dioxide is appropriately selected,
It is preferable that the preparation is performed so that the reduction is completely performed.

S generated by heating the raw material powder
The iO gas is supplied to the deposition chamber for depositing the silicon oxide powder through the transfer pipe.
000-1300 ° C, more preferably 1100-120
It is desirable to keep the temperature at 0 ° C. That is, when the temperature of the transfer pipe is lower than 1000 ° C., SiO gas is deposited and adhered to the inner wall of the transfer pipe, which may hinder the operation and may make stable continuous operation impossible. On the other hand, even when heating to a temperature exceeding 1300 ° C., not only no further effect can be obtained, but also an increase in power cost may occur.

The oxygen gas supplied to the SiO gas transported to the deposition chamber may be supplied as oxygen gas itself or may be supplied as an inert gas containing oxygen gas. The _x in the obtained silicon oxide powder (SiO _x ) depends on the gas flow rate and the gas supply time when the oxygen gas is supplied.
The value can be adjusted. The method for supplying oxygen gas or the like is not particularly limited, and a method such as a continuous or intermittent method can be appropriately selected depending on the purpose. In addition, SiO
The temperature at which oxygen gas is supplied to and mixed with the gas is 800 to 1
The temperature is preferably 200 ° C, particularly 900 to 1100 ° C.

The mixed gas obtained by supplying the oxygen gas to the SiO gas as described above is placed in the above-mentioned deposition chamber,
To precipitate onto the cooled substrate surface by the refrigerant, it is possible to obtain a silicon oxide powder having a predetermined x values (SiO _x). At this time, the temperature of the substrate surface is not particularly limited, but is preferably 200 to 400 ° C.

The silicon oxide powder deposited on the substrate as described above is collected by an appropriate means such as scraping. The recovered silicon oxide powder can be pulverized by a suitable means such as a ball mill, if necessary, to obtain a desired particle size.

[0027]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 [1] Amorphous Silicon Film Deposition In the vapor deposition apparatus 1 shown in FIG. 1, a copper foil having a thickness of 0.25 mm was used as a deposition receiver 13 and this copper foil was used as an electrode 11B.
After being placed on the top, it was heated to 280 ° C. by the heater 14.
Next, the exhaust valve 18 was fully opened, the pressure inside the reaction chamber 10 was reduced to 1 × 10 ⁻⁶ Torr by suction with the vacuum pump 20, and then the exhaust valve 18 was closed. Subsequently, the gas supply valve 15 was adjusted so that the pressure of the vacuum gauge 21 became 0.5 Torr, and SiH ₄ gas was supplied from the gas supply source 17 into the reaction chamber 10. After the pressure is stabilized, the electrodes 11A, 11B
Was applied, and glow discharge was started.
After a lapse of 15 minutes from the start of discharge, the discharge was stopped to stop the deposition of amorphous silicon. The thickness of the amorphous silicon in the obtained amorphous silicon vapor-deposited copper foil is 1.2 μm.
Met.

[2] Preparation of Battery 100 parts by weight of graphite, SiO _x (x = 1.05)
A kneaded product obtained by kneading 100 parts by weight of a powder and 20 parts by weight of polyvinylidene fluoride (N-methylpyrrolidone solvent) as a binder is applied to an amorphous silicon vapor-deposited copper foil produced by the above-described method, followed by press bonding. 12 with vacuum dryer
It dried at 0 degreeC and 12 hours, and produced the negative electrode.

A lithium foil having a thickness of 20 μm was arranged on the counter electrode of the negative electrode as a positive electrode, and lithium phosphate hexafluoride was used as a nonaqueous electrolyte at a concentration of 1 mol / L in a 1/1 mixed solution of ethylene carbonate and 1,2-dimethoxyethane. A lithium ion secondary battery for evaluation was prepared using a non-aqueous electrolyte solution dissolved at a concentration of 0.1 μm and a polyethylene microporous film having a thickness of 30 μm as a separator.

[3] Evaluation of Charge / Discharge Characteristics (Capacity) After the lithium ion secondary battery obtained as described above was allowed to stand overnight at room temperature, a secondary battery charge / discharge tester (Co., Ltd.)
The following charge / discharge test was carried out using Nagano Corporation. The open circuit voltage before the test was 4.0V. Next, lithium is inserted (charged) into the electrode at a constant current of 0.1 mA until the voltage becomes 0.0 V, and then lithium ions are charged from the electrode until the voltage becomes 3.0 V at a constant current of 0.1 mA. Was released (discharged). The value obtained by dividing the obtained result by the sample weight was determined as the discharge capacity, and was 2700 mAh.
/ G and a very high capacity.

Example 2 When a battery was manufactured using the amorphous silicon vapor-deposited copper foil obtained in Example 1, no SiO _x (x = 1.05) powder was used as a constituent material of the negative electrode material. Except for the above, a lithium ion secondary battery was manufactured in the same manner as in Example 1. When the discharge capacity of the obtained secondary battery was determined in the same manner as in Example 1, it was 1700 mAh / g.
And high capacity.

Example 3 When a battery was manufactured using the amorphous silicon vapor-deposited copper foil obtained in Example 1, SiO _x (x = 1.55) powder was used as a constituent material of the negative electrode material.
A lithium ion secondary battery was produced in the same manner as in Example 1, except that 0 parts by weight was used. When the discharge capacity of the obtained secondary battery was determined in the same manner as in Example 1, it was 2250 mA.
h / g and high capacity.

Example 4 When a battery was produced using the amorphous silicon vapor-deposited copper foil obtained in Example 1, 20 parts of SiO _x (x = 1.05) powder,
A lithium ion secondary battery was produced in the same manner as in Example 1, except that 0 parts by weight was used. When the discharge capacity of the obtained secondary battery was determined in the same manner as in Example 1, it was 1900 mA.
h / g and high capacity.

Example 5 A battery was produced using the amorphous silicon vapor-deposited copper foil obtained in Example 1, except that 200 parts by weight of graphite, which was a constituent material of the negative electrode material, was used. In the same manner as in the above, a lithium ion secondary battery was produced. When the discharge capacity of the obtained secondary battery was determined in the same manner as in Example 1, the discharge capacity was as high as 2000 mAh / g.

Comparative Example 1 A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that a normal copper foil on which an amorphous silicon film was not deposited was used. The discharge capacity of the obtained secondary battery was determined in the same manner as in Example 1.
It was 00 mAh / g.

[Comparative Example 2] When a secondary battery was manufactured using a normal copper foil on which an amorphous silicon film was not deposited, no SiO _x (x = 1.05) powder was used as a constituent material of the negative electrode material. Except for the above, a lithium ion secondary battery was manufactured in the same manner as in Example 1. When the discharge capacity of the obtained secondary battery was determined in the same manner as in Example 1, it was 360 mAh / g.
Met.

Table 1 summarizes the presence or absence of an amorphous silicon vapor-deposited film, the constituent materials of the negative electrode material, and the discharge capacity test results in each of the examples and comparative examples.

[0039]

[Table 1]

[0040] As Reference Example material, silicon dioxide powder: a (BET specific surface area 200m ² / g), a ceramic grade metal silicon powder (BET specific surface area: 4m ² /
g) was mixed at an equimolar ratio to obtain a silicon oxide SiO _x powder.

First, 200 g of the mixed raw material powder was charged into a reactor having a muffle volume of 6000 cm ³ . Subsequently, the pressure inside the reaction furnace was reduced to 0.1 Torr or less by a vacuum pump, and then the heater was energized to raise the temperature to 1350 ° C. and maintained at this temperature. On the other hand, the transport tube was heated to 1100 ° C. by a heater and kept at this temperature. Thereafter, the heater in the deposition chamber is energized, and the temperature in the deposition chamber is set to 9
At the same time as the temperature was set to 00 ° C., a SUS substrate (surface area 200 c
5.0 NL / min of water was passed through the m ² ) refrigerant passage.

Further, an argon gas containing 20% of oxygen gas was continuously supplied into the deposition chamber at 50 cc / min. The surface temperature of the substrate under these conditions is about 280 ° C. After operating for 5 hours under the above conditions, 160 _g of black massive SiO _x was found on the surface of the substrate.
g. After collecting this massive precipitate, it was pulverized with a ball mill for 5 hours to obtain a silicon oxide powder. The obtained silicon oxide powder was an amorphous powder having a BET specific surface area of 210 m ² / g and represented by the general formula SiO _x (x = 1.22).

The oxidation represented by the general formula SiO _x was performed in the same manner as described above except that the temperature in the deposition chamber, the amount of water flowing into the substrate, and the amount of 20% oxygen-containing argon gas were changed as shown in Table 2. Silicon powder was produced.

[0044]

[Table 2]

[0045]

As described above, according to the present invention,
Since the amorphous silicon film is deposited on the current collector surface of the negative electrode material, a high-capacity lithium-ion secondary battery with excellent charge / discharge characteristics can be provided. As a result, a lithium-ion secondary battery is used. Device can be reduced in size and weight.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an apparatus for depositing an amorphous silicon film according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Deposition apparatus 10 Reaction chamber 11A, 11B electrode 12 Power supply for discharge 13 Deposition receiver 14 Heater 15 Gas supply valve 16 Gas introduction pipe 17 Gas supply source 18 Exhaust valve 19 Exhaust pipe 20 Vacuum pump 21 Vacuum gauge

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoru Miyawaki 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Industry Co., Ltd. Gunma Office (72) Inventor Susumu Ueno 2-chome, Isobe, Annaka-shi, Gunma 13-1 Shin-Etsu Kagaku Kogyo Co., Ltd. Gunma Plant F-term (reference) 5H017 BB00 CC01 EE06 HH00 5H029 AJ03 AL06 AL18 AM03 AM04 AM05 AM07 CJ24 HJ02 5H050 AA08 BA17 CB07 DA03 DA09 EA10 EA12 EA24 GA24 HA02

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode material, a negative electrode material, a non-aqueous electrolyte containing a lithium salt, and a separator, wherein an amorphous silicon film is deposited on a current collector surface of the negative electrode material. A non-aqueous electrolyte secondary battery characterized in that: 2. The negative electrode material includes at least a current collector, a binder, and a negative electrode active material. The negative electrode active material may be a carbonaceous material or a general formula SiO.
The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is a carbonaceous material containing a silicon oxide represented by _x (0.8 <x <1.9).