JP2000299108A - Non-aqueous electrolyte battery - Google Patents

Abstract

(57) [Problem] To improve the cycle characteristics by suppressing a volume change at the time of doping and undoping of lithium. A positive electrode provided with a positive electrode active material containing lithium, and a negative electrode active material layer in which a mixture of a silicon compound capable of doping / dedoping lithium and a carbon material are dispersed in a binder are provided. And a nonaqueous electrolyte interposed between the positive electrode and the negative electrode, and the binder has a glass transition temperature of -40 ° C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte battery using a mixture of a silicon compound and a carbon material as a negative electrode material. More specifically, the present invention relates to a non-aqueous electrolyte battery in which cycle characteristics are improved by defining a glass transition temperature of a binder in which the negative electrode material is dispersed.

[0002]

2. Description of the Related Art In recent years, many portable electronic devices such as a camera-integrated video tape recorder, a mobile phone, and a laptop computer have appeared, and their size and weight have been reduced. Research and development for improving the energy density of batteries, particularly secondary batteries, as portable power sources for these electronic devices are being actively promoted. Among them, lithium ion secondary batteries have a higher energy density than conventional non-aqueous electrolyte secondary batteries, such as lead batteries and nickel cadmium batteries, and thus have high expectations.

As a negative electrode material used in a lithium ion battery, carbon materials such as non-graphitizable carbon and graphite are widely used because they exhibit a relatively high capacity and exhibit good cycle characteristics. .

[0004]

However, with the increase in capacity in recent years, the above-mentioned carbon materials are not satisfactory in charge / discharge capacity, and there is a need for higher performance. Therefore, research on non-carbon-based negative electrode materials such as silicon materials showing higher capacity in place of carbon materials has been actively conducted.

However, the non-carbon-based negative electrode material has a large change in volume of the active material itself during doping and undoping of lithium, and the remarkably large cycle deterioration has been a barrier when applied to an actual battery. .

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned conventional circumstances, and a non-aqueous electrolyte battery having improved cycle characteristics by suppressing a volume change at the time of doping and undoping of lithium. The purpose is to provide.

[0007]

According to the present invention, there is provided a non-aqueous electrolyte battery comprising: a positive electrode provided with a positive electrode active material layer containing lithium;
A negative electrode provided with a negative electrode active material layer in which a mixture of a silicon compound and a carbon material capable of doping / dedoping lithium is dispersed in a binder, and the positive electrode and the positive electrode are disposed so as to face the positive electrode. And a non-aqueous electrolyte interposed between the negative electrode and the binder, wherein the binder has a glass transition temperature of −40 ° C. or lower.

In the non-aqueous electrolyte battery according to the present invention as described above, since a binder having a glass transition temperature of -40 ° C. or lower is used as the binder in the negative electrode active material, the lithium The binder absorbs the volume change of the silicon compound negative electrode, and the volume change of the entire negative electrode active material layer is suppressed, so that the cycle deterioration is suppressed.

[0009]

Embodiments of the present invention will be described below.

FIG. 1 shows a configuration example of the nonaqueous electrolyte battery according to the present embodiment. This non-aqueous electrolyte battery 1 includes a negative electrode 2
A negative electrode can 3 containing the negative electrode 2, a positive electrode 4, a positive electrode can 5 containing the positive electrode 4, a separator 6 disposed between the positive electrode 4 and the negative electrode 2, and an insulating gasket 7. Can 3
The positive electrode can 5 is filled with a non-aqueous electrolyte.

The negative electrode 2 is formed by forming a negative electrode active material layer containing the above negative electrode active material and a binder on a negative electrode current collector. For the negative electrode current collector, for example, a metal foil such as a copper foil is used. Further, a known additive or the like may be added to the negative electrode mixture.

In the nonaqueous electrolyte battery 1 according to the present embodiment, a mixture of a silicon compound and a carbon material is used as the negative electrode active material.

As the silicon compound, a compound represented by the general formula M _x Si can be used. Here, M in the above formula is an element other than Li and Si, and specifically, B, C, N, O, Na, Mg, Al, P, S, K, C
a, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
Zn, Rb, Y, Mo, Rh, Pd, In, Sn, C
s, Ba, Ce or Ta.

In the above formula, x is preferably 0.01 or more, more preferably 0.1 or more.

Further, as the carbon material, for example, (00
2) It is possible to widely use a non-graphitizable carbon material having a plane spacing of 0.37 nm or more, a graphite material having a (002) plane spacing of 0.340 nm or less, or a graphitizable carbon material. it can.

Specific examples of the above-mentioned carbon materials include pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon and the like. The cokes include pitch coke, needle coke, petroleum coke, and the like. The fired organic polymer compound is obtained by firing a phenol resin, a furan resin or the like at an appropriate temperature and carbonizing the same.

One of the above-mentioned carbon materials may be used alone, or a plurality thereof may be used as a mixture. Among them, it is particularly preferable to use at least graphitizable carbon, and a mixture of graphitizable carbon and graphitizable carbon or a graphite-based material at an arbitrary ratio can be used.

In the nonaqueous electrolyte battery 1 according to the present embodiment, a resin having a glass transition temperature (Tg) of −40 ° C. or lower is used as a binder for dispersing the above-described negative electrode active material.

Examples of such a resin having a glass transition temperature of -40 ° C. or lower include polyether, polyester, polysiloxane and the like.

By using a relatively soft resin having a glass transition temperature of −40 ° C. or less as a binder for the negative electrode active material layer, the volume change due to expansion and contraction of the silicon compound during doping and undoping of lithium can be prevented. Even if it appears, the binder can absorb the volume change of the silicon compound and suppress the volume change of the entire negative electrode active material layer. Then, by suppressing the change in volume of the negative electrode active material layer at the time of doping / dedoping lithium, the cycle characteristics of the nonaqueous electrolyte battery 1 can be significantly improved.

Further, in this nonaqueous electrolyte battery 1, when the average particle diameter of the silicon compound in the negative electrode active material is R _Si and the average particle diameter of the carbon material is R _c , the silicon compound and the carbon material It is preferable that the particle size ratio R _Si / R _c is 1 or less. That is, the average particle size of the silicon compound in the negative electrode active material is made smaller than the average particle size of the carbon material. By making the average particle size of the silicon compound smaller than the average particle size of the carbon material, the silicon compound enters pores formed by the carbon material having the larger particle size.

That is, in the non-aqueous electrolyte battery 1, the void formed by the carbon material having a larger particle size is used as a field for doping / dedoping a silicon compound having a smaller particle size with lithium. By doping and undoping lithium in the silicon compound in the voids formed by the carbon material, even if a volume change due to expansion and contraction of the silicon compound occurs during the doping and undoping of lithium, the carbon material remains intact. The voids formed absorb the volume change of the silicon compound, and can suppress the volume change of the entire negative electrode active material. Then, by suppressing the volume change of the negative electrode active material at the time of doping and undoping of lithium, the cycle characteristics of the nonaqueous electrolyte battery 1 can be drastically improved.

R _Si / R _c is greater than 1;
When the average particle size of the silicon compound is larger than the average particle size of the carbon material, the carbon material cannot absorb the volume change of the silicon compound due to doping / dedoping of lithium. By setting R _Si / R _c to 1 or less, the volume change of the negative electrode active material at the time of doping or undoping of lithium can be suppressed,
The cycle characteristics of the non-aqueous electrolyte battery 1 can be improved.

[0024] Incidentally, the average particle diameter R _c of the carbon material contained in the negative electrode active material as described above, 10Myuemu～7
About 0 μm is preferable. Further, the shape of the carbon material is not particularly limited, and various shapes of carbon material such as a granular shape and a flake shape can be used.

The average particle size R _Si of the silicon compound contained in the negative electrode active material as described above is 10 μm
Or less, more preferably about 1 μm or less.

Here, the particle size and average particle size of the above-mentioned carbon material and silicon compound will be described. There are various methods for expressing the size of the particles having an irregular shape. In the present embodiment, it is _sufficient that R _Si / R _c is 1 or less. Is not particularly limited.

Specifically, the particle size may be measured, for example, by sieving the particles and determining the size of the particles according to the size of the sieve through which the particles do not pass, or by setting the particles to settle in a liquid, A method of measuring the sedimentation velocity and obtaining the particle diameter (Stokes diameter) using the Stokes equation is exemplified. This Stokes diameter indicates the diameter of spherical particles of the same density that settle at the same speed as the sample particles under the same conditions.

The powder usually comprises a group of particles having a distribution in size.
If the effect on a certain phenomenon is the same as the uniform particle diameter R, it is more convenient to use R as the representative diameter. The diameter R having such a function is defined as the average particle diameter of the powder.
Therefore, the method of obtaining the average particle size also differs depending on the intended purpose. As a method of obtaining the average particle diameter, specifically, for example, a length average diameter (ΣnR / Σn) can be cited, but it is not limited thereto. Here, R is the particle size of each particle, and n is the number of particles.

The negative electrode can 3 houses the negative electrode 2 and serves as an external negative electrode of the nonaqueous electrolyte battery 1.

The positive electrode 4 is formed by forming a positive electrode active material layer containing a positive electrode active material and a binder on a positive electrode current collector. As the positive electrode current collector, for example, an aluminum foil or the like is used. In the case of forming a lithium ion battery, a lithium metal foil can be used as the positive electrode 4.

As the positive electrode active material, a metal oxide, a metal sulfide or a specific polymer can be used depending on the type of the intended battery.

For example, when constituting a lithium primary battery, TiS ₂ , MnO ₂ , graphite, F
eS ₂ or the like can be used. When a lithium secondary battery is configured, TiS ₂ ,
Metal sulfides or oxides such as MoS ₂ , NbSe ₂ , and V ₂ O ₅ can be used.

When a lithium secondary battery is constructed,
The positive electrode active material is mainly composed of Li _x MnO ₂ (wherein, M represents one or more transition metals, and x varies depending on the charge / discharge state of the battery, and is generally 0.05 ≦ x ≦ 1.10.). A lithium composite oxide or the like can be used. The transition metal M constituting the lithium composite oxide is C
o, Ni, Mn and the like are preferable. Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ ,
Li _x Ni _y Co _1-y O ₂ (where x and y vary depending on the charge / discharge state of the battery and are usually 0 <x <1, 0.7 <y <
1.02. ) LiMn ₂ O _{4 and the} like.

The above-mentioned lithium composite oxide can generate a high voltage and is a positive electrode active material excellent in energy density. The positive electrode 2 may use a plurality of these positive electrode active materials in combination.

As the binder for the above-mentioned positive electrode mixture, a well-known binder usually used for a positive electrode mixture of this type of battery can be used. Agents and the like can be added.

The positive electrode can 5 accommodates the positive electrode 4 and serves as an external positive electrode of the lithium battery 1.

The separator 6 separates the positive electrode 4 and the negative electrode 2 from each other, and can be made of a known material generally used as a separator of this type of non-aqueous electrolyte battery. A polymer film is used.

The insulating gasket 7 is incorporated in the negative electrode can 3 and integrated. The insulating gasket 7 is for preventing the leakage of the nonaqueous electrolyte filled in the negative electrode can 3 and the positive electrode can 5.

The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.

As the electrolyte, there can be used a known electrolyte which is usually used for an electrolytic solution of this type of battery. Specifically, LiClO ₄ , LiAsF ₆ , LiPF
₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li,
Lithium salts such as CF ₃ SO ₃ Li, LiCl and LiBr can be mentioned.

As the non-aqueous solvent, various non-aqueous solvents conventionally used for non-aqueous electrolytes can be used. Specifically, for example, propylene carbonate,
Ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-
Diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, acetate, Butyrate, propionate and the like can be used. These non-aqueous solvents may be used alone or in combination of two or more.

The nonaqueous electrolyte battery 1 as described above has a glass transition temperature of -40 ° C. as a binder in the negative electrode active material layer.
Since the following resin is used, a change in volume of the negative electrode active material layer during doping / dedoping of lithium is suppressed, and the cycle characteristics are dramatically improved.

The non-aqueous electrolyte battery 1 as described above
Is manufactured as follows.

The negative electrode 2 is prepared by dispersing a pulverized silicon compound and a carbon material and a binder in a solvent to prepare a negative electrode mixture of a slurry. Next, the obtained negative electrode mixture is uniformly applied on a current collector, and then dried to form a negative electrode active material layer. Known additives and the like can be added to the negative electrode mixture.

Here, in the nonaqueous electrolyte battery 1, a mixture of a silicon compound and a carbon material is used as a negative electrode active material, and a glass transition temperature of -40 is used as a binder.
The temperature is below ℃.

The positive electrode 4 is manufactured by uniformly applying a positive electrode mixture containing a positive electrode active material and a binder on a metal foil serving as a current collector and drying to form a positive electrode active material layer. You.
Known binders can be used as the binder of the positive electrode mixture, and known additives and the like can be added to the positive electrode mixture. In the case of forming a lithium ion battery, a lithium metal foil can be used as the positive electrode 4.

The non-aqueous electrolyte is prepared by dissolving an electrolyte salt in a non-aqueous solvent.

Then, the negative electrode 2 is accommodated in the negative electrode can 3, the positive electrode 4 is accommodated in the positive electrode can 5, and a separator 6 made of a porous polypropylene film or the like is disposed between the negative electrode 2 and the positive electrode 4. The non-aqueous electrolyte is injected into the negative electrode can 3 and the positive electrode can 5, and the negative electrode can 3 and the positive electrode can 5 are caulked and fixed via the insulating gasket 7, thereby completing the non-aqueous electrolyte battery 1.

In the above-described embodiment, the particle size ratio between the silicon compound and the carbon material in the negative electrode active material in the nonaqueous electrolyte battery 1 is specified. It can also be specified.

That is, when the weight of the silicon compound contained in the negative electrode active material of the nonaqueous electrolyte battery 1 is W _Si and the weight of the carbon material is W _C , the weight composition ratio of the silicon compound to the carbon material is W _Si / W _C is set to 1 or less.

That is, the weight composition of the carbon material is made larger than the weight composition of the silicon compound. By making the weight composition of the carbon material larger than the weight composition of the silicon compound, even if a volume change due to expansion and contraction of the silicon compound occurs during doping / dedoping of lithium, a carbon material having a larger weight composition can be obtained. By absorbing the volume change of the silicon compound, the volume change of the entire negative electrode active material can be suppressed. Then, by suppressing the change in the volume of the negative electrode active material during doping and undoping of lithium, the cycle characteristics of the nonaqueous electrolyte battery 1 can be significantly improved.

W _Si / W _C is greater than 1, ie,
When the weight composition of the silicon compound is larger than the weight composition of the carbon material, the carbon material cannot absorb the volume change of the silicon compound due to doping / dedoping of lithium. By setting W _Si / W _C to 1 or less, the volume change of the negative electrode active material at the time of doping and undoping of lithium can be suppressed,
The cycle characteristics of the non-aqueous electrolyte battery 1 can be improved.

In the above embodiment, the non-aqueous electrolyte battery 1 using a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent has been described as an example of the non-aqueous electrolyte battery. The present invention is also applicable to a battery using a solid electrolyte in which an electrolyte is dispersed in a matrix polymer and a battery using a gel solid electrolyte containing a swelling solvent.

The shape of the battery of the present invention is not particularly limited, such as a cylindrical shape, a square shape, a coin shape, a button shape, and the like, and may be formed in various sizes such as a thin shape and a large size. Can be.

[0055]

EXAMPLES In order to confirm the effects of the present invention, a non-aqueous electrolyte battery as described above was manufactured and its characteristics were evaluated.

<Example 1> First, a negative electrode was manufactured as follows.

First, oxygen cross-linking is carried out by using petroleum pitch as a starting material and introducing 10 to 20% of a functional group containing oxygen into it, and then calcining at 1000 ° C. in an inert gas stream to form glassy carbon. A non-graphitizable carbon material with similar properties was obtained. X-ray diffraction measurement of the obtained material revealed that the (002) plane spacing was 3.76 Å and the true specific gravity was 1.58 g / cm ³ .

Next, the obtained non-graphitizable carbon material was pulverized to obtain a carbon material powder having an average particle size of 50 μm, and 60 parts by weight of the carbon material powder and a silicon compound (Mg ₂₎ having an average particle size of 5 μm. Si) 30 parts by weight of powder and 10 parts by weight of polyether (glass transition temperature: -63 ° C) as a binder were mixed to prepare a negative electrode mixture.

Next, the negative electrode mixture was dispersed in acetonitrile to form a slurry, and a small amount of a crosslinking agent was added to the slurry. Then, this slurry is uniformly applied to both surfaces of a copper foil having a thickness of 10 μm, which is a negative electrode current collector, and dried to form a negative electrode active material layer. To produce a negative electrode.

On the other hand, a metal lithium foil having a thickness of 1.85 mm was punched out into a disk shape having substantially the same diameter as the above-mentioned negative electrode to obtain a positive electrode.

In a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate, LiPF ₆
Was dissolved at a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.

The positive electrode obtained as described above is accommodated in a positive electrode can, the negative electrode is accommodated in a negative electrode can, and a space between the positive electrode and the negative electrode is provided.
A separator made of a microporous polypropylene film having a thickness of 25 μm was provided. A non-aqueous electrolyte solution was injected into the positive and negative electrode cans, and the positive and negative electrode cans were caulked and fixed to produce a coin-type non-aqueous electrolyte battery.

Example 2 A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that an equal weight mixture of a pitch-derived non-graphitizable carbon material and natural graphite was used as the carbon material in the negative electrode mixture. A battery was manufactured.

Comparative Example A non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 except that polyvinylidene fluoride (glass transition temperature: -30 ° C.) was used as a binder in the negative electrode mixture. .

The cycle characteristics of the battery manufactured as described above were evaluated.

The cycle characteristic evaluation test was performed in an environment of 23 ° C. First, each battery was charged at a constant current of 1 mA and a low voltage to a lithium potential. Next, a constant current discharge of 1 mA was performed to a final voltage of 1.5 V (potential with respect to lithium). The above process is defined as one cycle, and this cycle is
The cycle was repeated. Then, the discharge capacity retention ratio (%) at the 10th cycle was determined from the ratio of the discharge capacity at the 10th cycle to the discharge capacity at the 1st cycle.

Table 1 shows the discharge capacity retention rates of the batteries of Example 1, Example 2 and Comparative Example. In each of the batteries of Example 1, Example 2, and Comparative Example, almost the same initial capacity was obtained.

[0068]

[Table 1]

As is clear from Table 1, in the batteries of Examples 1 and 2 using a resin having a glass transition temperature lower than −30 ° C. as the binder in the negative electrode active material layer, the binder was used. It can be seen that the discharge capacity retention ratio is dramatically improved as compared with the battery of the comparative example using a resin having a glass transition temperature higher than −30 ° C.

This is because the relatively soft binder absorbs the volume change of the silicon compound even when the volume change of the silicon compound appears during the doping and undoping of lithium, and the volume of the entire negative electrode active material layer is reduced. It is considered that the change was suppressed.

Accordingly, as a binder in the negative electrode active material layer,
It was found that by using a resin having a glass transition temperature lower than −30 ° C., a change in volume of the negative electrode active material layer was suppressed, and good cycle characteristics were obtained.

[0072]

According to the present invention, by defining the particle size ratio between the silicon compound and the carbon material, it is possible to realize a negative electrode material capable of suppressing a change in volume during lithium doping and undoping.

In the present invention, by using this negative electrode material, the cycle characteristics are remarkably improved, and an excellent nonaqueous electrolyte battery can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a nonaqueous electrolyte battery according to the present invention.

[Explanation of symbols]

1 non-aqueous electrolyte battery, 2 negative electrode, 3 negative electrode can, 4
Positive electrode, 5 Positive electrode can, 6 Separator, 7 Insulating gasket

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Imoto 1 in Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture Inside Sony Energy Tech Co., Ltd. (72) Inventor Takeshi Horie Kita Shinagawa, Shinagawa-ku, Tokyo 6-7-35 Inside Sony Corporation (72) Inventor Kazuhiro Noda 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo (72) Inventor Koichiro Moezuka 6-Chome Kita-Shinagawa, Shinagawa-ku, Tokyo No.7-35 Sony Corporation F-term (reference) 5H003 AA04 BA03 BB01 BB04 BB11 BC01 BD00 BD01 BD03 5H014 AA02 BB06 EE08 EE10 HH00 HH01 HH08 5H029 AJ05 AK03 AL01 AL06 AL18 AM03 AM04 AM05 AM07 BJ03 HJ12 DJ08

Claims (5)

[Claims] 1. A binder comprising: a positive electrode provided with a positive electrode active material containing lithium; and a mixture of a silicon compound and a carbon material, which are disposed opposite to the positive electrode and capable of doping and undoping lithium, are contained in a binder. A negative electrode having a negative electrode active material layer dispersed therein, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode, wherein the binder has a glass transition temperature of −40 ° C. or less. Non-aqueous electrolyte battery characterized by the above-mentioned. The average particle diameter of claim 1, wherein said silicon compound and R _Si, when the average particle size of the carbon material and R _C, the ratio R _Si / R _C of the R _Si and R _C is, is 1 or less The non-aqueous electrolyte battery according to claim 1, wherein: 3. The method of claim 1, wherein the silicon compound has a general formula of M _x Si
(Where M is an element excluding Li and Si, and x ≧ 0.0
It is one. The non-aqueous electrolyte battery according to claim 1, wherein 4. The non-aqueous electrolyte battery according to claim 1, wherein the carbon material contains non-graphitizable carbon, graphitizable carbon, or graphite. 5. The non-aqueous electrolyte battery according to claim 1, wherein the carbon material contains at least any two selected from non-graphitizable carbon, graphitizable carbon and graphite.