JP2012238399A - Electrode material for nonaqueous electrolyte secondary battery, electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode alloy material for nonaqueous electrolyte secondary battery which exhibits excellent volume energy density when charge and discharge are repeated.SOLUTION: An alloy containing the TiFeSi alloy phase or TiFeSialloy phase is used. The alloy contains Ti, Fe and Si, and when the atomic ratio is Ti:Fe:Si=a:b:c(a+b+c=100), c≤69 is satisfied. An alloy having a composition of TiFeSi has the discharge capacity and cycle capacity retention rate both superior to those of an alloy having a composition of TiFeSi.

Description

  The present invention relates to an electrode material for a non-aqueous electrolyte secondary battery, an electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

  Currently, a carbonaceous material capable of occluding and releasing lithium is widely used for the negative electrode of a non-aqueous electrolyte battery typified by a lithium ion secondary battery. However, since a non-aqueous electrolyte battery having a high volumetric energy density is required, research using an alloy as a negative electrode material capable of occluding and releasing lithium has recently attracted attention again.

  Patent Document 1 describes that an alloy having a TiNiSi type crystal structure is used for a negative electrode of a non-aqueous electrolyte secondary battery, and specifically describes a La—Ni—Sn alloy and the like. Patent Document 2 describes a Si—Ti alloy, Si—Zr alloy, Si—Ni alloy, Si—Cu alloy, or Si—Fe alloy containing Si of about 90 weight ratio (about 95% in terms of atomic ratio). Has been. Patent Document 3 describes an alloy containing 95.5 wt% or more of Si and containing Fe as an essential element. Non-Patent Document 1 describes a phase diagram of a Si—Fe—Ti alloy.

JP 2004-335439 A JP 2006-164960 A JP 2010-165508 A

F. Weitzer et al. Intermetallics, page 273-282, vol.16, 2008.

  The alloys described in Patent Documents 1 to 3 containing Si in an atomic ratio of 95% by mass or more have a problem that the discharge capacity retention rate is small when the charge / discharge cycle is repeated.

  The present inventor formed an alloy containing Ti, Ni and Si at an atomic ratio of 1: 1: 1, and performed performance evaluation using it as an electrode material for a nonaqueous electrolyte secondary battery. The results showed excellent discharge capacity retention when the charge / discharge cycle was repeated. However, Ni is a rare metal, which increases the material cost and is difficult to adopt.

  In view of the above problems, an object of the present invention is to provide an electrode material for a non-aqueous electrolyte secondary battery that has an excellent discharge capacity retention rate when a charge / discharge cycle is repeated and that does not increase the cost of raw materials. .

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment or experimental example is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the scope of claims, and is not restricted to the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The present invention includes a non-aqueous electrolyte containing an alloy containing Ti, Fe and Si, and having an elemental composition of Ti: Fe: Si = a: b: c (a + b + c = 100) and c ≦ 69. It is an electrode material for a secondary battery. The alloy is characterized by containing a TiFeSi alloy phase or a TiFeSi ₂ alloy phase. Moreover, this invention is an electrode for nonaqueous electrolyte secondary batteries containing the said electrode material for nonaqueous electrolyte secondary batteries. Moreover, this invention is a nonaqueous electrolyte secondary battery provided with the said electrode for nonaqueous electrolyte secondary batteries.

  The reason why the alloy according to the present invention exhibits excellent performance is not necessarily clear. However, the present inventors infer as follows. Since Si is an element having a high affinity with Li, the presence of Si is considered to be important in order to advance the insertion and release of Li. However, the atomic radius of Si is about 1.1Å, which is very small compared to the atomic radius of Ti (1.46Å) and the atomic radius of Fe (1.27Å). For this reason, if the proportion of Si is too high, the lattice volume is small and the gaps between the lattices are also small, so the amount of Li that can be inserted and removed is considered to be small. In addition, if the proportion of Si is too high, it is considered that the swelling of the electrode accompanying charge / discharge is large and it is difficult to maintain the crystal structure. Therefore, by increasing the ratio of elements other than Si, the lattice volume is increased and the gap between the lattices is also increased. Therefore, the amount of Li that can be inserted and removed increases, and the capacity increases. It is done. In addition, since the swelling of the electrode accompanying charge / discharge can be reduced, it is considered that it is easy to maintain the crystal structure even if the charge / discharge cycle is repeated.

As will be described later, the electrode material for a nonaqueous electrolyte secondary battery according to the example is a TiFeSi alloy phase having a TiFeSi type crystal structure or a TiFeSi ₂ alloy phase having a ZeCrSi ₂ type crystal structure as a result of X-ray diffraction measurement. Existence was confirmed. The phase diagram of the Si—Fe—Ti alloy shown in FIG. 5 in Non-Patent Document 1 is cited here and described as FIG. As can be seen from FIG. 1, in the Si—Fe—Ti alloy, when the Si atomic ratio is 69% or less, a TiFeSi alloy phase or a TiFeSi ₂ alloy phase is formed. Therefore, the electrode material for a non-aqueous electrolyte secondary battery of the present invention has an atomic ratio c of Si in Ti, Fe and Si of 69% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode material for nonaqueous electrolyte secondary batteries which is excellent in the discharge capacity maintenance factor at the time of repeating charging / discharging cycle, and does not increase the cost of a raw material can be provided. Moreover, the electrode for nonaqueous electrolyte secondary batteries which can be used as the nonaqueous electrolyte secondary battery which is excellent in the discharge capacity maintenance rate at the time of repeating a charge / discharge cycle and does not increase the cost of raw materials can be provided. In addition, it is possible to provide a non-aqueous electrolyte secondary battery that has an excellent discharge capacity retention rate when the charge / discharge cycle is repeated and that does not increase the cost of raw materials.

  In the present invention, when the electrode material for a non-aqueous electrolyte secondary battery contains Ti, Fe, and Si, and each elemental composition is Ti: Fe: Si = a: b: c (a + b + c = 100), c It is characterized by including an alloy of ≦ 69. As long as the alloy exhibits the effects of the present invention, it does not prevent the alloy from containing elements other than Ti, Fe, and Si. Even when the alloy phase contains an element other than Ti, Fe, and Si, it is interpreted that the element composed of Ti, Fe, and Si contained in the alloy satisfies the above relational expression.

In addition, the electrode material for a nonaqueous electrolyte secondary battery according to the present invention is characterized by containing a TiFeSi alloy phase or a TiFeSi ₂ alloy phase. Does not interfere with the existence of a foreign phase.

  The electrode for a nonaqueous electrolyte secondary battery according to the present invention contains a metal powder, an alloy, a carbonaceous material, a conductive polymer, a binder, etc. as a material other than the electrode material for the nonaqueous electrolyte secondary battery. May be.

  The electrode for a nonaqueous electrolyte secondary battery according to the present invention is preferably used as a negative electrode for a nonaqueous electrolyte secondary battery.

  The method for producing the electrode material for a non-aqueous electrolyte secondary battery according to the present invention is not limited, and a general method for producing an alloy known as a technology for producing a hydrogen storage alloy can be employed. For example, a high frequency melting method, an arc melting method, a sintering method, a rapid quenching method, a strip casting method, an atomizing method, a plating method, a CVD method, a sputtering method, a rolling method and the like can be mentioned.

  As the atmosphere of the synthesis formation step, it is preferable to employ an inert gas atmosphere, a reduced pressure atmosphere or a vacuum. The temperature is preferably 1000 to 3000 ° C. The cooling rate is preferably 1 ° C./min or more.

    In general, in order to produce an alloy material, it is often necessary to rapidly cool the cooling step in which the temperature is lowered from the melted state and solidified. For example, in order to form the alloy material described in Patent Document 1, a rapid cooling process is required in which the mixture is melted and then cooled and solidified to a temperature below the freezing point at a cooling rate of 100 ° C./second or more. However, when manufacturing the electrode material for nonaqueous electrolyte secondary batteries according to the present invention, the cooling step can be greatly simplified. That is, in order to obtain the alloy phase according to the present invention satisfactorily, the rapid cooling process is not always necessary. Therefore, a special control device for rapid cooling is not particularly required in the production process of the electrode material for a non-aqueous electrolyte secondary battery according to the present invention. For example, in the examples described later, the molten alloy is cooled on copper hearth. That is, such a slow cooling condition can be adopted in the solidifying step of the electrode material for a non-aqueous electrolyte secondary battery according to the present invention.

  In general, after forming an alloy powder having a desired composition, a heat treatment step is often required before use. For example, in order to form the alloy material described in Patent Document 1, after forming the alloy powder, it is necessary to further perform a heat treatment step of maintaining the temperature in a temperature range of 250 to 700 ° C. for about 10 hours. However, when the electrode material for a non-aqueous electrolyte secondary battery according to the present invention is manufactured, it is not always necessary to go through a special heat treatment step after forming the alloy. Therefore, the heat treatment step can be omitted in the production process of the electrode material for a nonaqueous electrolyte secondary battery according to the present invention. Rather, according to the knowledge of the present inventor, there is a knowledge that an electrode material for a non-aqueous electrolyte secondary battery with better charge / discharge cycle performance can be obtained by not providing a heat treatment step after forming the alloy.

  The electrode material for a non-aqueous electrolyte secondary battery according to the present invention can be used after pulverization after forming an alloy. The average particle size of the pulverized powder is preferably 100 μm or less. In particular, the average particle size of the powder after pulverization is preferably 10 μm or less in order to improve the high output characteristics of the nonaqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which an organic solvent such as hexane or water coexists can be used. The classification method is not particularly limited. In both dry and wet classification, a sieve, an air classifier, or the like is used as necessary. The pulverization method is not limited, and for example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, and a sieve are used. At the time of pulverization, wet pulverization in which an organic solvent such as water or ethanol coexists may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The nonaqueous electrolyte used for the lithium secondary battery according to the present invention is not limited. As this electrolyte, those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, and NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ (SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, Examples thereof include organic ionic salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture of two or more. For example, a mixture of LiPF ₆ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ may be used.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to obtain a non-aqueous electrolyte battery having excellent battery characteristics. 2.5 mol / l.

  Hereinafter, the case where the electrode material for a nonaqueous electrolyte secondary battery is used in the negative electrode will be described as an example.

The positive electrode material used for the positive electrode of the counter electrode is not limited, and lithium transition metal composite oxide, lithium transition metal lithium compound, conductive polymer, activated carbon and the like can be used alone or in combination. Examples of the lithium transition metal composite oxide include α-NaFeO such as LiCoO ₂ , LiNi _0.4 Mn _0.4 Co _0.2 O ₂ , Li _1.2 Co _0.1 Ni _0.15 Mn _0.55 O _2. Examples thereof include a layered compound having a type ₂ crystal structure and a compound having a spinel type crystal structure typified by LiMn ₂ O ₄ and LiNi _1.5 Mn _0.5 O ₄ . Examples of the lithium transition metal lithium compound include LiFePO ₄ , LiMn _0.8 Fe _0.2 PO ₄ , and Li ₃ V ₂ (PO ₄ ) ₃ . Examples of the conductive polymer include polypyrrole and polyaniline. Disulfide compounds may be used.

  The average particle size of the positive electrode active material powder is preferably 100 μm or less. In particular, the size of the positive electrode active material powder is preferably 10 μm or less in order to improve the high output characteristics of the nonaqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which an organic solvent such as hexane or water coexists can be used. The classification method is not particularly limited. In both dry and wet classification, a sieve, an air classifier, or the like is used as necessary.

  In the positive electrode and the negative electrode, in addition to the main constituent components, a conductive agent, a binder, a thickener, a filler, and the like may be contained as other constituent components.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. For example, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) One kind of powder, metal fiber, conductive ceramic material, or a mixture thereof can be included as a conductive agent.

  In these, it is preferable to use acetylene black as a electrically conductive agent from a viewpoint of electronic conductivity and coating property. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is preferable to use acetylene black by pulverizing it into ultrafine particles of 0.1 to 0.5 μm because the necessary carbon amount can be reduced. The mixing by these mixing methods is physical mixing, and the ideal is uniform mixing. Therefore, it is possible to mix by a dry type or a wet type using a powder mixer such as a V-type mixer, an S-type mixer, a grinding machine, a ball mill, or a planetary ball mill.

  As the binder, thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene are usually used. One of polymers having rubber elasticity such as butadiene rubber (SBR) or fluoro rubber, or a mixture thereof can be used. The addition amount of the binder is preferably 1 to 50% by weight, particularly 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

  The filler is not particularly limited as long as it does not adversely affect the battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The added amount of the filler is preferably 30% by weight or less based on the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode contain a positive electrode active material or negative electrode material and other materials, and form a mixture using N-methylpyrrolidone, toluene or the like as a solvent, and apply the mixture on the current collector described in detail below. It is preferably produced by, for example, removing the solvent component by heat treatment at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. About the application method, for example, it is preferable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include polyolefin resins typified by polyethylene, polypropylene, etc., polyester resins typified by polyethylene terephthalate, polybutylene terephthalate, etc., polyvinylidene fluoride, vinylidene fluoride- Hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride Down - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. From the viewpoint of charge / discharge characteristics, the porosity is preferably 20% by volume or more.

  As the separator, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and polyvinylidene fluoride and an electrolyte may be used. The use of the nonaqueous electrolyte in the gel state as described above is preferable because it has an effect of preventing leakage.

  Furthermore, it is preferable to use a polymer gel in combination with the above-described porous film, nonwoven fabric or the like as the separator because the liquid retention of the electrolyte is improved. That is, a film is formed by coating the surface of the polyethylene microporous membrane and the microporous wall with a solvophilic polymer having a thickness of several μm or less, and the electrolyte is retained in the micropores of the film. Solvent polymer gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. It is possible to crosslink the monomer by heating a material obtained by adding a radical initiator to such a monomer, or by irradiating an active ray such as an ultraviolet ray (UV) or an electron beam (EB). .

  The structure of the lithium secondary battery is not particularly limited. Examples of this structure include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, a flat battery, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
(Production of TiFeSi)
As the alloy material, each metal was cut out from each ingot of Ti, Fe, and Si. Each metal is weighed so that the atomic ratio is Ti: Fe: Si = 1: 1: 1, and water-cooled copper in the melting chamber of a micro vacuum arc melting apparatus (manufactured by Nisshin Giken Co., Ltd., model number: NEV-AD03). The mixture was placed on Hearth. The melting chamber was evacuated and the operation of introducing argon gas to -0.005 MPa was repeated twice. After evacuating again, argon gas was introduced to -0.04 MPa. In this way, the atmosphere in the dissolution chamber was replaced with argon gas. Next, the placed alloy raw material was arc-melted by the following procedure. First, the alloy raw material was uniformly applied with an arc to dissolve the metal components so that they were uniformly mixed, and then cooled and solidified on a water-cooled copper hearth. The solidified melted lump was turned over, and the back surface was melted by applying an arc again and then cooled on a water-cooled copper hearth to solidify. Such an operation of dissolving the front surface and an operation of dissolving the back surface were taken as one set, and this was repeated 5 sets. The arc current value was 50 A for the first set and 100 A for the second to fifth sets. In the process of cooling and solidifying on a water-cooled copper hearth, it takes about 15 minutes to solidify. That is, this cooling process is slow cooling.

  The alloy ingot thus obtained was pulverized using a stainless steel mortar and then sieved to less than 125 μm using a sieve. Next, this was further pulverized using a planetary ball mill apparatus. That is, after putting 10 stainless steel balls with a diameter of 10 mm into a stainless steel ball mill pot with an internal volume of 80 ml, 3 g of the alloy powder was added together with 0.1 ml of isopropanol as a dispersant, the rotation speed was 150 rpm, and the set time was Ball milling was performed under the condition of 12 hours. In order to prevent the oxidation of the alloy, all the operations for charging and removing the alloy powder from the ball mill pot were performed in a glove box substituted with argon. After ball milling, in order to further remove coarse powder, it was screened to less than 25 μm using a sieve. In this way, an electrode material for a nonaqueous electrolyte secondary battery according to Example 1 was produced.

[Example 2]
(Preparation of TiFeSi ₂ )
For a nonaqueous electrolyte secondary battery according to Example 2, except that each metal was weighed so that the atomic ratio was Ti: Fe: Si = 1: 1: 2. An electrode material was prepared.

[Comparative example]
(Production of TiNiSi)
Example 1 except that Ni alloy was used instead of Fe ingot as an alloy raw material and each metal was weighed so that the atomic ratio was La: Ni: Sn = 1: 1: 1. Similarly, an electrode material for a non-aqueous electrolyte secondary battery according to a comparative example was produced.

  With respect to the electrode materials for non-aqueous electrolyte secondary batteries according to the above Examples and Comparative Examples, X-ray diffraction measurement was performed using an X-ray diffraction measurement apparatus (Miniflex II, manufactured by Rigaku Corporation). The measurement conditions were a Cu tube, 30 kV, 15 mA, a step scan with an interval of 0.02 ° and an integration time of 2 s.

As a result, it was confirmed that the electrode material for a nonaqueous electrolyte secondary battery according to Example 1 had a TiFeSi alloy phase having a TiFeSi type crystal structure. In addition, it was confirmed that the electrode material for a nonaqueous electrolyte secondary battery according to Example 2 had a TiFeSi ₂ alloy phase having a ZeCrSi ₂ type crystal structure. In addition, it was confirmed that the electrode material for a non-aqueous electrolyte secondary battery according to the comparative example had a TiNiSi alloy phase having a TiNiSi type crystal structure.

  The electrode materials for nonaqueous electrolyte secondary batteries according to the above examples and comparative examples are each used as a negative electrode active material, and the negative electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) are contained at a mass ratio of 80:10:10 A negative electrode paste using N-methylpyrrolidone as a solvent was prepared. The negative electrode paste was applied to foamed nickel as an electrode substrate, and then dried at 150 ° C. under reduced pressure. Thus, the electrode for nonaqueous electrolyte secondary batteries was produced.

In order to evaluate the performance as a negative electrode of each of the electrodes for non-aqueous electrolyte secondary batteries produced in this manner, the electrode was used as a working electrode, metal Li was used as a counter electrode and a reference electrode, and ethylene carbonate (EC) and diethyl carbonate. A tripolar glass cell was assembled in a glove box under an argon atmosphere by using an electrolyte obtained by dissolving LiClO ₄ at a concentration of 1 mol / l in a solvent in which (DEC) was mixed at a volume ratio of 1: 1. In this way, a non-aqueous electrolyte secondary battery for negative electrode evaluation was produced.

For each non-aqueous electrolyte secondary battery produced in this manner, a charge / discharge test was repeatedly performed under the condition of 25 ° C., and the discharge capacities (Ah) of the first cycle and the tenth cycle were measured. The capacity density (Ah / cm ³ ) per volume of the negative electrode active material determined from the weight and true density was determined. Here, since the evaluation is performed as a negative electrode, in the following description, an operation of energizing the working electrode in the reduction direction is referred to as “charging”, and an operation of energizing in the oxidation direction is referred to as “discharging”. Charging was performed at a constant current and constant voltage with a current of 41.7 mA / g and 0.02 V (vs. Li / Li ⁺ ), and the constant voltage charging time was 8 hours. The discharge was a constant current discharge with a current of 41.7 mA / g and a discharge end potential of 3.5 V (vs. Li / Li ⁺ ). After the end of charging and after the end of discharging, a 60-minute rest period was provided.

The above results are shown in Table 1 together with the alloy composition.

Comparative Example 1 using TiNiSi as an electrode material for a non-aqueous electrolyte secondary battery showed excellent performance. Examples 1 and 2 using Fe, which is an inexpensive raw material instead of rare metal Ni, also showed excellent performance. When Example 1 using TiFeSi and TiFeSi ₂ Example 2 were compared, Example 1 having a lower Si content resulted in superior discharge capacity and charge / discharge cycle performance. Therefore, the atomic ratio c of Si is preferably 50% or less. Of the alloys containing the TiFeSi alloy phase or the TiFeSi ₂ alloy phase, an alloy containing the TiFeSi alloy phase is preferable.

1 is a phase diagram of a Ti—Fe—Si alloy described in Non-Patent Document 1. FIG.

Claims (4)

Nonaqueous electrolyte secondary battery electrode containing Ti, Fe and Si, and containing an alloy in which c ≦ 69 when these atomic ratios are Ti: Fe: Si = a: b: c (a + b + c = 100) material. The electrode material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the alloy contains a TiFeSi alloy phase or a TiFeSi ₂ alloy phase. The electrode for nonaqueous electrolyte secondary batteries containing the electrode material for nonaqueous electrolyte secondary batteries of Claim 1 or 2. A nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery according to claim 3.