JP2003272614A - Negative electrode active material for nonaqueous electrolyte solution secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode active material for a nonaqueous electrolyte solution secondary battery capable of obtaining a nonaqueous electrolyte solution secondary battery having high capacity, and excellent charge/ discharge characteristics and cycle life characteristics, and a nonaqueous electrolyte solution secondary battery using the negative electrode active material. <P>SOLUTION: The negative electrode active material for the nonaqueous electrolyte solution secondary battery consists either of an intermetallic compound with a constituent ratio expressed in Li<SB>a</SB>X<SB>b</SB>Sn (provided; X is a rare-earth element, 0.2≤a≤3.5, 0.1≤b≤0.5) or an intermetallic compound with a constituent ratio expressed in Li<SB>a</SB>Y<SB>b</SB>Sn (provided; Y is an alkaline-earth metal, 0.2≤a≤3.5, 0.1≤b≤0.5). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode active material for a non-aqueous electrolyte secondary battery capable of inserting and extracting a large amount of an alkali metal such as lithium, and more specifically, by using a specific intermetallic compound. , A high capacity, negative electrode active material for a non-aqueous electrolyte secondary battery capable of producing a non-aqueous electrolyte secondary battery excellent in charge / discharge characteristics and cycle life characteristics, and non-aqueous electrolysis using the negative electrode active material A liquid secondary battery.

[0002]

2. Description of the Related Art With the spread of small portable electric and electronic devices, a small-sized and high-capacity non-aqueous electrolyte (electrolyte) secondary battery has been actively developed. . This non-aqueous electrolyte secondary battery uses a carbonaceous material, lithium metal, a lithium alloy, and a lithium compound as a negative electrode active material.

Conventionally, such a non-aqueous electrolyte secondary battery has a positive electrode active material such as lithium manganate, lithium cobalt oxide, and lithium nickel oxide, and carbon that reversibly absorbs and discharges lithium as a negative electrode active material. A lithium ion secondary battery using a high quality material is used.

On the other hand, when lithium metal is used as the negative electrode active material, it is expected that the capacity will be higher than when a carbonaceous material is used. However, when lithium metal is used, lithium metal grows in a dendrite form from the negative electrode due to repeated deterioration and charging / discharging of lithium due to the reaction between the non-aqueous electrolyte and the lithium metal, and penetrates the separator that is the insulator to form the positive electrode. There are problems that short circuit occurs and cycle life characteristics are short. This has prevented the practical use of lithium metal as a negative electrode active material.

In order to solve such a problem, it is possible to store and release Li reversibly by utilizing the formation of an intermetallic compound, and to store and release Li in the lattice space of Si or another intermetallic compound.
Various proposals have been made for releasing (Japanese Patent Laid-Open No. 7-24
No. 0201 and Japanese Patent Application Laid-Open No. 9-63651), the cycle life characteristics were not sufficient. The negative electrode material made of Si has a high theoretical capacity of 9800 mAh / cc, but in most cases, the compound has a eutectic structure of a metal compound and a solid solution, so that the Li occlusion phase expands in volume during charging and discharging, and unreacted. Since the phase does not change, a large stress strain is generated between the phase grain boundaries, resulting in pulverization, which is not preferable.

Further, Japanese Patent Application Laid-Open No. 2001-297757 proposes that Si having Li storage capacity is simultaneously alloyed with an element having no Li storage capacity to suppress cracking and pulverization and improve cycle life characteristics. Has been done. This is S
A second phase having no Li storage capacity is arranged in contact with the i phase, and L
Although it is intended to restrain the volume change at the time of occlusion and release of i to suppress cracking and pulverization to improve the cycle life, the examples do not mention the charge / discharge efficiency. Further, the presence of the second phase having no Li storage capacity is not preferable because the unit volume or the volume per unit weight is impaired.

As described above, in the prior art, there is a problem of irreversible capacity in that the amount of electricity charged for the first time does not come out at the time of discharging, and furthermore, since the charge / discharge efficiency for each cycle is low, it has a high capacity and excellent charge. A negative electrode active material for a non-aqueous electrolyte secondary battery capable of obtaining a non-aqueous electrolyte secondary battery having discharge characteristics and cycle life characteristics has not yet been obtained.

Therefore, an object of the present invention is to provide a negative electrode active material for a non-aqueous electrolyte secondary battery, which is capable of obtaining a non-aqueous electrolyte secondary battery having high capacity, charge / discharge characteristics and cycle life characteristics, and the negative electrode. It is to provide a non-aqueous electrolyte secondary battery using an active material.

[0009]

The present inventors have found that tin 5
Focusing on the fact that it has a high capacity of 700 mAh / cc and is a metal element, and as a result of repeated studies aimed at reducing its irreversible capacity and improving cycle life characteristics, an alloy of tin and a rare earth element or an alkaline earth metal element. When lithium is previously solid-dissolved in the structure, lithium is not trapped by the trace amount of oxygen present in the alloy, and the irreversible capacity can be almost eliminated. It was found that the cycle life characteristics are improved because the element suppresses volume expansion and contraction during charge and discharge. Further, the structure of the present invention may be a single phase or a multiphase, but each phase contributes to lithium occlusion / release, so that the capacity per unit volume or unit mass is larger than that of the conventional material. I found out that.

The present invention has been made on the basis of these findings and has _a composition ratio of Li _a X _b Sn (where X is a rare earth element, 0.2 ≦ a ≦ 3.5, 0.1 ≦ b ≦ 0). .5) or an intermetallic compound having a composition ratio of Li _a Y _b Sn (provided that Y
Is an alkaline earth metal element, 0.2 ≦ a ≦ 3.5, 0.1
The present invention provides a negative electrode active material for a non-aqueous electrolyte secondary battery, which comprises an intermetallic compound represented by ≦ b ≦ 0.5).

The present invention also provides a non-aqueous electrolyte secondary battery using the above negative electrode active material.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

In the present invention, an intermetallic compound having _a composition ratio of Li _a X _b Sn is used as the negative electrode active material for a non-aqueous electrolyte secondary battery. Here, X is a rare earth element, and Mm
(Misch metal: rare earth mixed metal), scandium,
Examples thereof include yttrium, lanthanum, cerium, praseodymium, neodymium, and lanthanum and cerium are particularly preferable. Moreover, a shows 0.2-3.5 and b shows 0.1-0.5, respectively. If a is less than 0.2 or exceeds 3.5, cycle life characteristics are impaired, and if b is less than 0.1, there is no effect of improving cycle life characteristics.
When it exceeds 0.5, the capacity is impaired, which is not preferable.

Further, according to the present invention, a non-aqueous electrolyte secondary battery is used.
As the negative electrode active material, the composition ratio is Li _aY_bGold represented by Sn
Use intergeneric compounds. Where Y is an alkaline earth metal element
Elementary, beryllium, magnesium, calcium, su
Examples include trontium, magnesium, calci
Um is particularly preferably used. Also, a is 0.2 to
3.5 and b represent 0.1 to 0.5, respectively. a is 0.
If it is less than 2 or exceeds 3.5, the cycle life characteristics are impaired.
When b is less than 0.1, the cycle life characteristics are improved.
There is no end, and if it exceeds 0.5, the capacity will be lost.
Not good.

An example of a method for producing such an intermetallic compound
Is a specific composition formula Li_1.25Ce_{0. 33}Explanation with Sn
To do. First, the composition ratio is Ce_0.33Weigh it to be Sn
Mechanical alloying of cerium chips and tin powder
By doing Ce_0.33Prepare Sn. Then
Prepared Ce_0.33Sn and lithium chips with a specified composition
And mechanical alloying
The composition ratio is Li_1.25Ce_0.33Prepare Sn. Also,
Roll quenching or atomization instead of mechanical alloying
It may be prepared by casting such as shavings.

Next, the non-aqueous electrolyte secondary battery of the present invention will be described. The non-aqueous electrolyte secondary battery of the present invention has, as a basic structure, a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, and the negative electrode uses the negative electrode active material of the present invention as described above, but other The positive electrode, the separator, and the nonaqueous electrolytic solution are not particularly limited, and conventionally known materials for nonaqueous electrolytic solution secondary batteries such as lithium secondary batteries are used.

The negative electrode is prepared by suspending the negative electrode active material of the present invention and, if necessary, a conductive agent and a binder in a suitable solvent to prepare a negative electrode mixture, coating this on a current collector, drying and rolling. ,
It is obtained by pressing, cutting and punching.

In the case of this material, a conductive agent is not always necessary, but carbon black or the like may be used.

Current collectors include copper, stainless steel, nickel,
Examples thereof include titanium, copper, stainless steel whose surface is coated with nickel, carbon, titanium and the like. The form of the current collector is arbitrary, and examples thereof include foil, mesh, film or sheet.

The positive electrode is prepared by suspending a positive electrode active material, and if necessary, a conductive agent and a binder in a suitable solvent to prepare a positive electrode mixture, applying this to a current collector, drying it, rolling it and pressing it. It is obtained by further cutting and punching.

As the positive electrode active material, conventionally known positive electrode active materials such as lithium nickel composite oxide, lithium manganese composite oxide and lithium cobalt composite oxide are used.

Further, as the conductive agent used for the positive electrode,
Carbon black, acetylene black, graphite and the like are used. As the binder, styrene-butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, fluoropolymer, carboxymethyl cellulose, polyvinyl alcohol, etc. are used. Moreover, N-methylpyrrolidone, dimethylformamide, etc. are used as a solvent. Aluminum or aluminum alloy is preferably used as the current collector.

As the separator, a synthetic resin non-woven fabric, polyethylene or polypropylene porous film is preferably used.

In the case of a lithium secondary battery, the non-aqueous electrolyte is
A general non-aqueous electrolytic solution is a solution in which a lithium salt, which is a supporting electrolyte, is dissolved in an organic solvent. Examples of the lithium salt include LiC1O ₄ , LiA1Cl ₄ , and LiP.
_{F 6, LiAsF 6, LiSbF 6} , LiSCN, LiC
1, LiBr, LiI, LiCF ₃ SO ₃ , LiC ₄ F ₉ S
O _{3 and the} like are exemplified, and an electrolyte containing LiPF ₆ is particularly preferable.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; fats such as methyl formate, ethyl acetate and methyl propionate. Group carboxylic acid esters; γ-lactones such as γ-butyrolactone; chain ethers such as 1,2-dimethoxyethane; cyclic ethers such as tetrahydrofuran; other dimethyl sulfoxides, dioxolanes, amides, nitriles, sulfolane It is preferable to use various aprotic solvents such as the class. In particular, a mixed system of cyclic carbonate and chain carbonate, and a system in which an aliphatic carboxylic acid ester is further mixed are preferably used, and a mixed solvent of ethylene carbonate and ethylmethyl carbonate is particularly preferable.

The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may be any of a cylindrical type, a prismatic type, a coin type, a button type and the like. INDUSTRIAL APPLICABILITY The non-aqueous electrolyte secondary battery of the present invention can be suitably used in applications such as mobile information terminals, mobile electronic devices, and automobiles.

[0027]

EXAMPLES The present invention will be specifically described below based on Examples and the like.

Comparative Example 1 A cerium chip (about 1 mm) and tin powder (about 50 μm), which were weighed and mixed so that the composition ratio was Ce _0.33 Sn, and mechanically alloyed with tin powder (about 50 μm) for 20 hours in an argon atmosphere. Due to the composition ratio Ce
_An intermetallic compound consisting of _0.33 Sn was prepared. The mechanical alloying conditions are a weight ratio of the sample to the ball of 1:15, a rotation speed of 300 rpm, and room temperature. The crystal phase of the obtained sample was identified by X-ray diffraction.

Comparative Example 2 An intermetallic compound having a composition ratio of Ce _0.33 Sn was prepared in the same manner as in Comparative Example 1 except that the mechanical alloying time was 80 hours. The crystal phase of the obtained sample was identified by X-ray diffraction.

[Comparative Examples 3 and 4] In the same manner as in Comparative Example 1 except that lanthanum chips and calcium chips were used in place of the cerium chips, the composition ratios were respectively La _0.33 S.
An intermetallic compound consisting of n and Ca _0.33 Sn was prepared. The crystal phase of the obtained sample was identified by X-ray diffraction.

[Examples 1 to 5] As shown in Table 1, an intermetallic compound having a composition ratio of Ce _0.33 Sn and Ce _0.5 Sn and a lithium chip (about 1 mm) were placed under an argon atmosphere for 20 minutes. By mechanical mechanical alloying for a time, an intermetallic compound having the composition ratio shown in Table 1 was prepared. The mechanical alloying conditions are the same as in Comparative Example 1. The crystal phase of the obtained sample was identified by X-ray diffraction.

Examples 6 to 17 In the same manner as in Examples 1 to 5 except that a misch metal chip, a lanthanum chip, and a calcium chip were used in place of the cerium chip, the intermetallic compounds having the composition ratios shown in Table 1 were used. The compound was prepared. The crystal phase of the obtained sample was identified by X-ray diffraction.

[Experimental Example 1] The negative electrode (test electrode) 1 is an example.
1 to 17 and sample powders obtained in Comparative Examples 1 to 4 (intermetallic
Compound) copper mesh (0.25m²) And press it
It was created by doing. The charge / discharge test is the above test pole
1. Lithium plate for counter electrode 2 and reference electrode 3 and non-aqueous electrolyte 4
1 mol LiClO_Four/ PC (polycarbonate) is used
The triode cell shown in FIG. 1 was used. Measurement temperature is 3
0 ° C, measured current density is 0.4 mAcm ^-2, Lithium reference
The electrode potential was 0.0 to 2.0V. The above sample powder
All the series of operations from powder preparation to charge / discharge test
I went in a gon atmosphere.

Table 1 shows Examples 1 to 17 and Comparative Examples 1 to 4.
The first time in a triode cell using the sample powder of
Cycle number) shows charging efficiency and discharge capacity. As shown in Table 1, when the sample powders of Examples 1 to 17 are used for the electrodes, the initial charging efficiency is higher than when the sample powders of Comparative Examples 1 to 4 are used for the electrodes.

Further, FIG. 2 shows Example 2 and Comparative Examples 1-2.
3 shows a charge / discharge curve at the first cycle in a three-electrode cell using the sample powder of 1. as an electrode. As shown in FIG. 2, when the sample powders of Example 2 and Comparative Examples 1 and 2 were used for the electrodes, there was almost no difference in the electrode performance. However, the discharge capacity per volume was about 2000 mAhcm ^-3 , which greatly exceeded the value of the carbon electrode (about 800 mAhcm ^-3 ).

Table 1 shows Examples 1 to 17 and Comparative Examples 1 to 4.
2 shows the capacity retention ratio at the 100th cycle in a three-electrode cell using the sample powder of No. 3 as an electrode. As is clear from Table 1, when the sample powders of Examples 1 to 15 were used for the electrodes, the capacity retention ratio at the 100th cycle was higher than that when the sample powders of Comparative Examples 1 to 4 were used for the electrodes. Greatly superior.

Further, FIG. 3 shows Example 2 and Comparative Examples 1-2.
3 shows the cycle life characteristics of a triode type cell using the sample powder of 1. As shown in FIG. 3, Comparative Examples 1-2
When the sample powder of 1. was used for the electrode, the cycle life characteristics were extremely inferior. This is because there is a drastic volume change accompanying lithium insertion-desorption and an irreversible capacity for each cycle.

On the other hand, when the sample powder of Example 2 was used for the electrode, the cycle life characteristics were remarkably improved.
This is because the rare earth element existing in the alloy is suppressed from reacting with the charged lithium with a small amount of oxygen existing in the alloy or on the surface of the alloy to generate Li ₂ O, and the charging / discharging efficiency is practically 100%. %, And at the same time, the presence of a rare earth element having a large atomic radius suppressed the volume expansion / contraction during charge / discharge. This electrode showed excellent performance not only in cycle life characteristics but also in capacity reversibility in the first cycle. This is because lithium is already CeSn _3.0
It is considered that the volume expansion due to further lithiation was alleviated due to the insertion inside.

[0039]

[Table 1]

[0040]

EFFECTS OF THE INVENTION The negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention can provide a non-aqueous electrolyte secondary battery having high capacity and excellent charge / discharge characteristics and cycle life characteristics.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a triode cell used in Experimental Example 1.

FIG. 2 is a graph showing a charge / discharge curve at the first cycle in a three-electrode cell using the sample powders of Example 2 and Comparative Examples 1 and 2 as electrodes.

FIG. 3 is a graph showing cycle life characteristics in a triode cell using the sample powders of Example 2 and Comparative Examples 1 and 2 as electrodes.

[Explanation of symbols]

1: test pole 2: Counter electrode 3: Reference pole 4: Non-aqueous electrolyte

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichi Numata             1-5-1 Shiomachi, Takehara City, Hiroshima Prefecture Mitsui Metal Ore             Industry Co., Ltd. Battery Materials Division F-term (reference) 5H029 AJ02 AJ03 AJ05 AK03 AL12                       AM03 AM04 AM05 AM07 CJ08                       HJ02                 5H050 AA02 AA07 AA08 BA17 CA08                       CA09 CB12 GA10 HA02

Claims (3)

[Claims] 1. A non-metallic compound having _a composition ratio of Li _a X _b Sn (where X is a rare earth element, 0.2 ≦ a ≦ 3.5, and 0.1 ≦ b ≦ 0.5). Aqueous electrolyte negative electrode active material for secondary batteries. 2. A composition ratio of Li _a Y _b Sn (where Y is an alkaline earth metal element, 0.2 ≦ a ≦ 3.5, 0.1 ≦ b ≦
0.5) A negative electrode active material for a non-aqueous electrolyte secondary battery, which comprises an intermetallic compound represented by 0.5). 3. A non-aqueous electrolyte secondary battery using the negative electrode active material according to claim 1.