JPH1125973A - Negative electrode mateal for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery having negative electrode using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a large discharging capacity and a good cycle characteristic even at high-rate discharging by solid-fusing any one or both of CoSi2 and NiSi2 indicating high electric conductivity in Fe of FeSi2 as a negative electrode material. SOLUTION: FeSi2 and CoSi2 for storing discharging lithium are mixed at a mol. ratio of 99:1, baking is performed in an argon atmosphere at a temperature of 1200 deg.C for 24 hours, and thereby a negative electrode active material Fe0.99 Co0.01 Si2 is obtained. The composition of this compound is identified by atomic absorption analysis, and its single phase is identified by X-ray diffraction. This compound is broken to 100 mesh under. For the obtained negative electrode active material powder 85 pts.wt., a binder of 10 pts.wt. and an acetylene black of 5 pts.wt. are kneaded, and dried by reduced pressure. A secondary coin battery thereby manufactured shows a good characteristic even at high-rate discharging. The same holds true for NiSi2 . If both are contained, a ratio is set to a mol. ratio of 99:1 of total or lower.

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, particularly to a negative electrode material.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries are small and lightweight.
In addition, because of the high energy density, portable devices and cordless devices are expected to have high expectations.

Conventionally, lithium-containing metal oxides such as LiCoO ₂ and LiNiO ₂ have been known as a positive electrode active material of a non-aqueous electrolyte secondary battery. On the other hand, as a negative electrode, metal lithium or lithium such as a lithium alloy has been used. Graphite materials and the like that can be occluded and released are known and some have been put to practical use. As disclosed in JP-A-5-159780 as a material having a larger discharge capacity, Fe
It has been proposed that a compound represented by Si ₂ be used for a negative electrode material.

[0004]

However, FeS
i ₂ current density for discharge is charged in the low rate of 3.2 mA / cm ² or less, and when a discharge is low rate, the larger discharge capacity than graphite, and cycle life provides a longer lithium ion secondary battery It can be charged at a low rate and has a current density of 3.2 mA / cm ²
When the battery is discharged at the above high rate, there is a problem that the discharge capacity is reduced to graphite or less.

An object of the present invention is to solve such a problem and to provide a non-aqueous electrolyte secondary battery having excellent characteristics at high rate discharge.

[0006]

In order to solve these problems, a negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention uses CoSi ₂ or Ni as a material capable of inserting and extracting lithium.
Containing either one of Si ₂ compounds or CoS
Fe _{1-(x + y)} Co _x Ni _y Si ₂ using FeSi ₂ containing both i ₂ and NiSi ₂ compounds,
It satisfies the condition of 0 ≦ x <1, 0 ≦ y <1, 0 <x + y <1.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION When charging at a low rate, the overvoltage of FeSi ₂ is not so large, and a discharge capacity larger than graphite can be obtained. However, when charging at a low rate and discharging at a high rate, the electric conductivity of FeSi ₂ is as low as 4 × 10 ³ S / cm, so that the overvoltage at the time of discharging increases and the discharge capacity becomes less than graphite. However, the negative electrode material of the present invention is obtained by partially replacing Fe of FeSi ₂ with Ni or Co, and is 8 × 10 ⁴ S /
CoSi ₂ showing a high electric conductivity of cm and, 3 × 1
0 ⁴ NiSi exhibits a high electrical conductivity as S / cm ₂ The by solid solution in FeSi _2, it is obtained by suppressing the overvoltage of the raised rate discharge electrical conductivity of the FeSi _2. Accordingly, a large discharge capacity can be obtained even at the time of high-rate discharge, and the cycle characteristics can be improved.

As described above, the compound of the present invention is a negative electrode material for providing a nonaqueous electrolyte secondary battery exhibiting excellent high-rate discharge characteristics with respect to the above problems.

For the above reasons, the present invention can be implemented by the embodiments described in the claims. That is, claim 1
As described, either one of CoSi ₂ or NiSi ₂ and a compound of FeSi ₂ , or CoSi ₂ and NiSi _{2
By using} both FeSi ₂ and FeSi ₂ as a negative electrode material, a negative electrode material having high electric conductivity can be obtained.

According to a second aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte, a positive electrode, and a negative electrode capable of inserting and extracting lithium. , CoSi ₂ or NiSi ₂ Or a compound of FeSi ₂ or CoSi ₂ and N ₂
iSi ₂ By using both of these and a compound of FeSi _2, a large discharge capacity can be obtained even during high-rate discharge, and a nonaqueous electrolyte lithium secondary battery having excellent cycle characteristics can be realized.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a longitudinal sectional view of a coin-type nonaqueous electrolyte secondary battery of the present invention. In the figure, reference numeral 1 denotes a battery case processed from an organic electrolytic solution-resistant stainless steel sheet;
Is a sealing plate made of a stainless steel plate, and 3 is a current collector made of a stainless steel plate, which is spot-welded to the inner surface of the battery case 1.
Reference numeral 4 denotes metallic lithium, which is pressed inside the sealing plate 2. Reference numeral 5 denotes a negative electrode according to an example of the present invention.

In preparing the negative electrode 5, first, FeSi ₂ and CoSi ₂ , which are commercially available products, are mixed at a molar ratio of 99: 1, and calcined in an argon atmosphere at 1200 ° C. for 24 hours to obtain a negative electrode active material Fe. _0.99 Co _0.01 Si ₂
I got The composition was confirmed by atomic absorption spectroscopy.
The single phase was confirmed by line diffraction. This composite was ground in an agate mortar to 100 mesh under to obtain a negative electrode active material.

A predetermined amount of a mixture obtained by mixing 10 parts by weight of polyvinylidene fluoride as a binder and 5 parts by weight of acetylene black as a conductive agent with respect to 85 parts by weight of the negative electrode active material is charged on the current collector 3. It is molded into. After drying these current collectors under reduced pressure at 80 ° C., they were used for battery assembly. 6 is a microporous polypropylene separator, 7
Is an insulating gasket made of polypropylene. The electrolytic solution was prepared by dissolving lithium hexafluorophosphate at a concentration of 1 mol / liter as a solute in a mixed solvent of equal volumes of ethylene carbonate and diethyl carbonate. Using the respective samples and reference materials as described above, a battery having a size of 20 mm in diameter and a total height of 1.6 mm was constructed, and electrochemical evaluation was performed. The evaluation method was as follows: charging was performed at a current density of 0.5 mA / cm ^2.
(Low rate) and discharge is 0.5 mA / cm ²
(Low rate) and 5 mA / cm ² (high rate). The electric capacity calculation is performed in the voltage range of 1.5V to 0V,
It was represented by the electric capacity per active material volume. The results are shown in Table 1.

(Example 2) As a negative electrode active material, FeSi ₂ and NiSi ₂ , which are commercially available products, were mixed at a molar ratio of 99: 1, and calcined in an argon atmosphere at 1200 ° C. for 24 hours to obtain Fe _{0.9 9} Ni _0.01 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

Example 3 FeSi ₂ , CoSi ₂ , and NiSi ₂ , which are commercially available products, are used as a negative electrode active material at a molar ratio of 9
By mixing at a ratio of 9: 0.5: 0.5 and firing at 1250 ° C. for 24 hours in an argon atmosphere, Fe
_0.99 Co _0.005 Ni _0.005 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. Table 1 shows the results.
It was shown to.

Example 4 FeSi ₂ and CoSi ₂ , which are commercially available products, were mixed as a negative electrode active material at a molar ratio of 90:10, and calcined in an argon atmosphere at 1200 ° C. for 24 hours to obtain Fe _0.9. Co _0.1 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

Example 5 As a negative electrode active material, FeSi ₂ and NiSi ₂ , which are commercially available products, were mixed at a molar ratio of 90:10, and calcined at 1200 ° C. for 24 hours in an argon atmosphere to obtain Fe _0.9. Ni _0.1 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

[0019] (Example 6) FeSi ₂ is generally commercially available as an anode active material, CoSi _2, a NiSi ₂ molar ratio 9
Mix at a ratio of 0: 5: 5, and add 125 under argon atmosphere.
By firing at 0 ° C. for 24 hours, Fe _0.9 Co _0.05
Ni _0.05 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

Example 7 A commercially available negative electrode active material, FeSi ₂ and CoSi ₂ , was mixed at a molar ratio of 80:20 and calcined in an argon atmosphere at 1200 ° C. for 24 hours to obtain Fe _0.8 Co _0.2 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

Example 8 As a negative electrode active material, FeSi ₂ and NiSi ₂ , which are commercially available products, were mixed at a molar ratio of 80:20, and calcined at 1200 ° C. for 24 hours in an argon atmosphere to obtain Fe _0.8 Ni _0.2 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

(Example 9) As a negative electrode active material, FeSi ₂ , CoSi ₂ , and NiSi ₂ which are commercially available products have a molar ratio of 8
Mix at a ratio of 0:10:10, and add 1 in an argon atmosphere.
By firing at 250 ° C. for 24 hours, Fe _0.8 Co
_0.1 Ni _0.1 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed that the composition was a single phase by X-ray diffraction. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

Example 10 A commercially available negative electrode active material, FeSi ₂ and CoSi ₂ , was mixed at a molar ratio of 70:30 and calcined at 1200 ° C. for 24 hours in an argon atmosphere to obtain Fe _0.7 Co _0.3 Si ₂ was obtained, the synthesized composition was confirmed by atomic absorption analysis, and it was confirmed by X-ray diffraction that it was a single phase. Using this, a coin-type non-aqueous electrolyte secondary battery was manufactured according to Example 1. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

Comparative Example 1 As a comparative example, a coin-type non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that FeSi _2, which was a commercially available product, was used as the negative electrode active material. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

Comparative Example 2 As a comparative example, a coin-type non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a commercially available graphite was used as the negative electrode active material. Then, a charge / discharge test was performed under the same evaluation conditions, and a charge / discharge capacity was calculated. The results are shown in Table 1.

[0026]

[Table 1]

As described above, Table 1 shows that the embodiment of the present invention
The compound of _{1- (x + y)} Co _x Ni _y Si ₂ and FeSi ₂ of Comparative Example 1 has a higher discharge capacity at a low rate (0.5 mA / cm ² ) than the graphite of Comparative Example 2. But high rate (5m
The discharge at A / cm ^2), although the discharge capacity of the FeSi ₂ is reduced below the graphite, the discharge capacity of _{Fe 1- (x + y) Co} x Ni y Si 2 about compared with the graphite or FeSi ₂ 150 mAh / cm
³ or more. This factor is considered to be due to the fact that the electric conductivity of all of the negative electrode active materials prepared in Examples 1 to 10 was higher than the electric conductivity of FeSi ₂ , thereby suppressing the overvoltage.

As described above, the Fe _{1- (x + y)} Co _x Ni _{y of the} present invention is used.
It can be seen that the compound represented by Si ₂ is a negative electrode material that provides a nonaqueous electrolyte secondary battery exhibiting excellent high-rate discharge characteristics.

Further, the negative electrode material of the present invention is
When used for secondary batteries, the positive electrode active material contains lithium
Ti, Mo, W, Nb, V, Mn, Fe, Cr, N
composite oxides or sulfurs of at least one transition metal such as i, Co, etc.
And the like. Especially high voltage and high energy
-Density can be expected and the conventionally known LiCo
O _Two, LiNiO_Two, LiMn_TwoO_FourAnd other positive electrode active materials
It is suitable.

Further, the negative electrode material of the present invention is
When used in secondary batteries, solvents for the non-aqueous electrolyte
Lencarbonate, propylene carbonate, dimethyl
Carbonate, ethyl methyl carbonate, diethyl carbonate
Chain esters such as carbonate, γ-butyrolactone, etc.
Γ-lactones, 1,2-dimethoxyethane, 1,2
-Chain forms such as diethoxyethane, ethoxymethoxyethane, etc.
Ethers, cyclic ethers such as tetrahydrofuran,
Solvent selected from nitriles such as acetonitrile
Alternatively, two or more kinds of mixed solvents can be used. Especially d
Use a mixed solvent containing titanium carbonate as an essential component.
It is preferred to use And as a non-aqueous electrolyte solute
And LiAsF₆ , LiPF₆ , LiAlCl_Four , L
iCLO _Four , LiCF_ThreeSO_Three , LiSbF₆ , LiS
CN, LiCl, LiC₆HSO_Three, Li (CF_ThreeSO_Two)
_Two , LiC (CF_ThreeSO_Two)_Three , C_FourF₆SO_ThreeLi and others
Titanium salts and mixtures thereof can be used.

In the present embodiment, the shape of the battery is a coin type. However, a battery having a cylindrical shape, a square shape, or any other shape can be used.

[0032]

According to the present invention, FeSi is used as a negative electrode material for a non-aqueous electrolyte secondary battery capable of inserting and extracting lithium.
₂ contains either CoSi ₂ or NiSi ₂ ,
Both of them are included and Fe _{1- (x + y)} Co _x Ni _y S
i ₂ (x and y are x ≧ 0, y ≧ 0, and 1> x + y
&Gt; 0), and a non-aqueous electrolyte secondary battery having excellent high rate discharge characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a coin-type battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Current collector 4 Metal lithium 5 Negative electrode 6 Separator 7 Insulating gasket

Claims (2)

[Claims] 1. The chemical formula represented by Fe _{1-(x + y)} Co _x Ni _y Si ₂ , wherein 0 ≦ x <1, 0 ≦ y <1,
A negative electrode material for a non-aqueous electrolyte secondary battery, which is a compound satisfying the following condition: 0 <x + y <1. 2. A non-aqueous electrolyte secondary battery having a non-aqueous electrolyte, a positive electrode, and a negative electrode capable of inserting and extracting lithium, wherein Fe _{1-(x + y)} Co _x Ni _y Si ₂ is used. And 0 ≦ x <1, 0 ≦ y <1,
A non-aqueous electrolyte secondary battery comprising a negative electrode using a compound satisfying the following condition: 0 <x + y <1.