JP3008269B2 - Rechargeable battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lithium secondary battery.

[0002]

At present, carbonaceous materials are mainly used as negative electrode active materials for lithium secondary batteries. However, the charge / discharge capacity of the carbonaceous material is only about 372 mAh / g, which is the theoretical capacity. Also, fast charging
Discharge is not possible. Furthermore, since the carbonaceous material has a low density, the capacity per volume is inferior.

Also, Proceeding of the Symposium on Rechargeable Lithium and Lithium Ion Batteries (p. 158, 1995)
And solid state ionics (Vol. 74, p.
249, 1994) proposes to add a small amount of silicon to the carbon material as an improvement of the carbon material. That is, an electrode formed by firing a polymer containing silicon has been proposed.

However, even in this case, the charge / discharge capacity is 500
It is only around mAh / g. Therefore, an object of the present invention is to provide a secondary battery that has a large charge / discharge capacity and can withstand a large current density.

[0005]

Means for Solving the Problems The object of the present invention, S
i powder, a conductive agent and a binder, and the Si powder
Powder is used at a rate of 20-70% by volume
(However, Si fine particles are dispersed in graphite particles
Excluding those composed of graphite composites. ) Negative electrode
, A positive electrode, and an electrolyte material.
Solved by the battery below .

In the above secondary battery, it is preferable that the positive electrode is made of a material containing lithium. or,
The electrolyte substance is preferably a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent.

[0007] A secondary battery provided with an electrode composed of the Si powder has a large charge / discharge capacity.
In addition, it can withstand a large current density.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The negative electrode of the secondary battery of the present invention is Si
It is constituted by using a powder, a conductive agent and a binder, and
Si powder is used in a ratio of 20 to 70% (preferably the lower limit is 30%) per volume .

[0009] The secondary battery according to the present invention comprises a Si powder and a conductive agent.
A binder is used, and the Si powder is used per volume.
It is configured to be used at a ratio of 20 to 70% (however,
And a graphite composite in which Si fine particles are dispersed in graphite particles
Excluding those consisting of ) Negative electrode, positive electrode, and electrolysis
Material . In this secondary battery, the positive electrode is formed using a substance containing lithium. The electrolyte substance is a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent. Hereinafter, this will be described in more detail.

[Negative Electrode Active Material (Si)] The material represented by Si may have a crystalline structure, an amorphous structure, or a mixture thereof.

In the present invention, as the negative electrode active material, S
The material represented by i is used at a rate of 20 to 70% per electrode volume. A preferred ratio is 50% of the upper limit per electrode volume. The lower limit is 30%.

[0012]

[Negative Electrode] An electrode (negative electrode) is formed using a negative electrode active material represented by Si. In particular, a conductive agent and a binder are used in addition to the above-mentioned negative electrode active material. Further, a filler is used as needed. These are used within a range where the substance represented by Si satisfies the above conditions.

The conductive agent may be an electronically conductive material which does not cause decomposition or deterioration in the constructed battery. Specifically, it is selected from graphite such as natural graphite or synthetic graphite, carbon black, acetylene black, carbon fiber, metal powder, metal fiber, or polyphenylene derivative as described in JP-A-59-20971. One kind or a mixture of two or more kinds, and other conductive polymers are used. Among them, it is preferable to use acetylene black.

Examples of the binder include polysaccharides such as starch, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, polyvinyl chloride, polyvinylpyrrolidone, tetrafluoroethylene, polyvinylidene fluoride,
One or a mixture of two or more selected from thermoplastic resins such as polyethylene, polypropylene, styrene-butadiene rubber, fluororubber, and polyethylene oxide, and polymers having rubber elasticity are used. In addition, when using what has a functional group which reacts with lithium like a polysaccharide, it is preferable to add the compound which has an isocyanate group, for example, and to deactivate the functional group.

The filler may be any fibrous material that does not cause a chemical change in the battery constructed. Specifically, olefin polymers such as polypropylene and polyethylene, or glass fibers are used. And
The electrode (negative electrode) is obtained by kneading the above constituent materials and molding the mixture into a predetermined shape.

[Electrolyte] An electrolyte is used as the electrolyte. As a solvent constituting the electrolytic solution, an organic solvent such as propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, tetrahydrofuran, dimethyl sulfoxide, and acetonitrile, particularly an aprotic solvent is used. As the solute, a lithium salt is used. As lithium salts,
For example, LiClO ₄ , LiBF ₆ , LiPF ₆ , LiC
One or two or more selected from the group of F ₃ SO ₃ , LiCl, LiBr, LiI and the like are used.

A solid electrolyte can be used in addition to the above electrolyte. The solid electrolyte includes an inorganic solid electrolyte and an organic solid electrolyte. You may use together an inorganic solid electrolyte and an organic solid electrolyte. Examples of the inorganic solid electrolyte include oxides, sulfides, nitrides, and halides of lithium. Examples of the organic solid electrolyte include a polyethylene oxide derivative, a polymer containing a polyethylene oxide derivative, a polypropylene oxide derivative, and a polymer containing a polypropylene oxide derivative.

In addition, polyacrylonitrile may be added to the electrolytic solution. [Positive electrode] The positive electrode is made of a substance containing lithium. Alternatively, it is configured in the same manner as the negative electrode using the positive electrode active material. In particular, it is configured in the same manner as the negative electrode using a lithium-containing transition metal oxide. As the lithium-containing transition metal oxide, a transition metal containing lithium (Ti, V, C
(r, Mn, Fe, Co, Ni, Cu, Mo, W, etc.). Also, alkali metals other than lithium,
Alkaline earth metals, semimetals Al, Ga, In, Ge,
Sn, Pb, Sb, Bi, B, etc. may be mixed. The mixing ratio of these substances is preferably 0 to 40 mol%.

Hereinafter, a specific embodiment will be described.

[0021]

Example 1 [Negative electrode] 55 parts by weight of Si powder (negative electrode active material;
04 mm), 40 parts by weight of acetylene black (conductive agent), and 5 parts by weight of tetrafluoroethylene (binder)
After kneading the mixture, the mixture was rolled into a film and punched out into a circular shape to obtain an electrode pellet. This electrode pellet is
Vacuum dried at 10 ° C. for 12 hours.

The percentage of Si in the negative electrode of this example was 45% (per electrode volume). [Positive electrode] 75 parts by weight of LiMn _11/6 Cr _1/12 B _1/12 O ₄
After kneading a mixture of (positive electrode active material), 20 parts by weight of acetylene black (conductive agent) and 5 parts by weight of tetrafluoroethylene (binder), the mixture was rolled into a film,
It was punched out in a circular shape to obtain an electrode pellet. The electrode pellet was vacuum dried at 110 ° C. for 12 hours.

[Electrolyte] Using a mixed solution of equal amounts of ethylene carbonate and diethylene carbonate as a solvent,
LiClO ₄ was dissolved at a rate of 1 mol / liter. [Lithium Secondary Battery] A lithium secondary battery having the structure shown in FIG. 1 was produced. In addition, in FIG. 1, 1 is a conducting wire and 2 is a diameter of 8 mm.
3 is a quartz glass tube having an outer diameter of 10 mm and an inner diameter of 8 mm, 4 is an o-ring, 5 is a positive electrode having the above structure, 6 is a separator, and 7 is a negative electrode having the above structure. The inside of 3 is filled with the electrolytic solution. In this example, the positive electrode was used in excess of the negative electrode.

[0024]

Comparative Example 3 In Example 1, L, which is an example of Li _x Si (0 <x ≦ 4), was used instead of the Si powder used for the negative electrode.
A lithium secondary battery was manufactured in the same manner except that iSi powder was used. The LiSi in the negative electrode of this comparative example
Was 45% (per electrode volume).

[0025]

Comparative Example 1 A lithium secondary battery was produced in the same manner as in Example 1, except that a negative electrode made of natural graphite having high crystallinity was used instead of the negative electrode made of Si.

[0026]

Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a negative electrode made of low-crystalline low-temperature fired carbon was used instead of the negative electrode made of Si.

[0027]

[Characteristics] A charge / discharge test was performed on the lithium secondary batteries of the above examples. The test was started from the current direction (charging) in which lithium was inserted into the negative electrode side. The results of this charge / discharge test are shown in Table 1 and FIGS. Table 1 Negative electrode active material Current density Capacity density per weight Capacity density per volume mA / cm ² Ah / kg Ah / L Example 1 Si 0.1 3415 7957 0.5 2740 6384 1.0 2133 4970 Comparative Example 3 LiSi 0 0.13241 7549 Comparative Example 1 Natural graphite 0.1 305 687 0.2 245 552 0.4 177 397 0.6 115 259 1.0 38 85 Comparative Example 2 Low-temperature calcined carbon 0.1 232 417 0.2 213 384 0.4 196 354 0.6 175 316 1.0 152 273 As can be seen from the above, the present invention has a large capacity and can perform charge / discharge at a high current density.

[0028]

According to the present invention, a lithium secondary battery having a large capacity and capable of charging and discharging at a high current density can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a lithium secondary battery.

FIG. 2 is a graph showing charge / discharge characteristics of a lithium secondary battery of Example 1.

FIG. 3 is a graph showing a relationship between a current density and a change in capacity during charge / discharge.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-10-208740 (JP, A) JP-A-5-74463 (JP, A) JP-A-7-296798 (JP, A) JP-A-7-296 315822 (JP, A) JP 9-249407 (JP, A) JP 10-223220 (JP, A) JP 10-125317 (JP, A) JP 10-199524 (JP, A) JP-A-7-240201 (JP, A) JP-A-7-249410 (JP, A) Proceedings of the Electrochemical Society, 87-1, p. 356-364 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 4/02 H01M 4/38 H01M 10/40

Claims (3)

(57) [Claims] 1. A method comprising using Si powder, a conductive agent and a binder.
And the Si powder has a ratio of 20 to 70% by volume.
(However, the Si fine particles are black
Consists of graphite composites dispersed in lead particles
Except for 2.) A secondary battery comprising a negative electrode, a positive electrode, and an electrolyte material. 2. The positive electrode is made of a material containing lithium.
The secondary battery according to claim 1, wherein the secondary battery is formed. 3. An electrolyte material comprising a lithium salt dissolved in an organic solvent.
2. The non-aqueous electrolyte solution according to claim 1,
Rechargeable battery.