JPH117979A - Non-aqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give high voltage, high capacity, high energy density, an excellent charge and discharge cycle characteristic and high safety to a non-aqueous electrolyte battery by using silicon alloy as the main structural material for negative electrode active material, and using a salt, which contains carbon, as the main structural solute for electrolyte. SOLUTION: As the main structural material for negative electrode active material, silicon alloy expressed with a formula SiMx is used. In the formula, M means one or more kinds of elements, which can form the alloy with silicon, and (x) satisfies a relation that (x)>0. A salt, which contains carbon, is used as the main structural solute for electrolyte. As a salt, which contains carbon, a Li salt expressed with a formula (R1Y1)(R2Y2)NLi is used. In the formula, R1, R2 mean Cn F2n+1 , (n) is 1-4, R1=R2 or R1≠R2, and Y1, Y2 mean CO, SO, SO2 , and Y1=Y2, or Y1≠Y2. A salt as a solute, which includes carbon, is hard to be decomposed, and at the time of reaction with water, the salt as a solute hardly release hydrogen fluoride.

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 battery, and more particularly to a negative electrode active material and an electrolyte used in the battery.

[0002]

2. Description of the Related Art Conventionally, lithium has been typically used as a negative electrode active material for a nonaqueous electrolyte battery. However, dendritic deposition of lithium generated during charging (dendrite)
Therefore, there was a problem in terms of cycle life. In addition, the dendrite penetrates through the separator, causing an internal short circuit and causing ignition.

Further, lithium alloys have been used for the purpose of preventing dendrite generated at the time of charging as described above. However, when the charge amount is increased, there are problems such as fine powdering of the negative electrode and falling off of the negative electrode active material. .

At present, batteries using a carbon material for the negative electrode have been attracting attention for their long life and safety, and some of them have been put to practical use. However, the carbon material used for the negative electrode is
There were problems such as an internal short circuit and a decrease in charging efficiency during rapid charging. These carbon materials generally have a lithium doping potential of the carbon material close to 0 V. Therefore, when rapid charging is performed, the potential becomes 0 V or less, and lithium may be deposited on the electrode. As a result, this may cause an internal short circuit of the cell or lower the discharge efficiency. Although such carbon materials have been considerably improved in terms of cycle life, their relatively low density results in low capacity per volume. That is, this carbon material is still insufficient in terms of high energy density. In addition, in the case where a film needs to be formed on carbon, the initial charge / discharge efficiency decreases, and the amount of electricity used for forming the film is irreversible, which leads to a reduction in capacity corresponding to the amount of electricity. With even higher capacity and higher energy density,
There is a demand for the development of a safe negative electrode material for nonaqueous electrolyte batteries having a long cycle life.

[0005] Binar has already been used as a silicon alloy.
y Alloy Phase Diagrams (p2
465), alloying with a composition up to Li ₂₂ Si ₅ is known. Also, Japanese Patent Application Laid-Open No.
No. 3 reports that a single crystal of silicon is used for the negative electrode. However, when trying to dope lithium into silicon as a negative electrode material of a nonaqueous electrolyte battery for rapid charge / discharge, it was found that lithium was deposited with almost no doping. Then, the present inventor studied an extrinsic semiconductor already having an impurity (dopant), and found that the occlusion and release of lithium proceeded. It was found that this occlusion reaction proceeded at a potential very close to the lithium potential of about 0.1 V, occlusion of lithium near the theoretical capacity occurred, and there was also reversibility. On the other hand, US Pat. No. 5,294,503 discloses Li _x Mg ₂ Si
JP-A-5-159780 discloses FeSi, JP-A-7-29602 discloses Li _x Si, JP-A-8-138.
No. 744 reports that SiB _n is used as a negative electrode material, and JP-A-8-153517 reports that nickel silicide is used as a negative electrode material. However, as a solute of the electrolyte, LiP
It was found that when an electrolyte using F ₆ or LiBF ₄ was used, the charge / discharge efficiency of each cycle was low, and cycle deterioration occurred.

[0006]

In other words, when lithium metal or an alloy of lithium and a metal is used as the negative electrode, there are advantages of high voltage, high capacity, and high energy density, but in terms of cycleability and safety. There is a problem, and when a carbon material is used, it is advantageous in terms of high voltage and safety, but insufficient in terms of high capacity and high energy density. In addition, when a silicon alloy expected to have a high capacity and a high energy density is used as a negative electrode active material, the charge / discharge efficiency of each cycle is low, which leads to a problem that cycle deterioration is caused.

For this reason, high voltage, high energy density,
In order to obtain a secondary battery with excellent charge / discharge cycle characteristics and high safety, lithium can be inserted and released reversibly, and the charge / discharge efficiency in the insertion and extraction of lithium is excellent and the operation is as close to the lithium potential as possible. A compound that operates in the field is desired.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is directed to a non-aqueous electrolyte battery in which the main constituent material of the negative electrode active material used in the non-aqueous electrolyte battery is a silicon alloy. In addition, a salt containing carbon is used as a main constituent solute of the electrolyte.

Further, the above-mentioned carbon-containing salts may be any one of the compounds represented by the following general formula (2): (R1Y1) (R2Y2) NLi... General formula (2) _{Represented by} C _n F _{2n + 1} ,
n is a number from 1 to 4, and R1 = R2 or R1
≠ R2, and Y1 and Y2 are CO, SO, SO ₂
Y1 = Y2 or Y1 ≠ Y2. ) Is used. Further, the salt containing carbon is represented by the general formula (2) wherein R1 =
Characterized by being represented by the non-R2 = CF _3.

That is, in a non-aqueous electrolyte battery, when LiBF ₄ or LiPF ₆ which has been generally used in the past is used as an electrolyte, the ionic conductivity of the electrolyte using the same as a solute is excellent, but once it is decomposed, It has been found that Lewis acids are produced and that reaction with water produces hydrogen fluoride and the like. When a silicon alloy is used as a negative electrode active material using these solutes, impurities generated from the solute react with a film existing on the surface of the silicon alloy, and the surface film changes into a film having high electric resistance and poor ion conductivity. I understood that. Therefore, it is conceivable that the electrode resistance increases each time charging / discharging is performed, which lowers the charging / discharging efficiency, thereby leading to cycle deterioration.

On the other hand, it has been found that the salt containing carbon, which is the solute of the present invention, hardly decomposes as described above, and hardly releases hydrogen fluoride or the like even in the reaction with water. Therefore, when a silicon alloy is used as the negative electrode active material, it is conceivable that an increase in the electrical resistance of the surface film and a decrease in ionic conductivity are suppressed, the charge / discharge efficiency is improved, and the cycle characteristics are improved.

Further, the element which can be alloyed with silicon as referred to herein includes Binary Alloy Phase
All of the elements listed in Diagrams, but preferably Li, Ni, Fe, Co, Mn,
Ca, Mg, P, Al, As, W, B, Ti, V, P
t, Zr, Sr and the like. However, it is not limited to these. The crystal system of the silicon alloy mentioned here includes single crystal, polycrystal, amorphous and the like.

The silicon alloy used in the present invention is preferably a powder having an average particle size of 0.1 to 100 μm. A pulverizer or a classifier is used to obtain a predetermined powder. When obtaining powder, for example, mortar, ball mill, sand mill,
A vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air jet mill, a sieve, and the like are used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed in both dry and wet methods.

The negative electrode material which can be used in conjunction with the present invention includes lithium metal, lithium alloy, etc., calcined carbonaceous compounds capable of inserting and extracting lithium ions or lithium metal, chalcogen compounds, and lithium such as methyllithium. Organic compounds and the like can be mentioned. Further, by using lithium metal, a lithium alloy, and an organic compound containing lithium in combination, lithium can be inserted into the silicon alloy used in the present invention inside the battery.

When the silicon alloy of the present invention is used as a powder, a conductive agent, a binder, a filler or the like can be added as an electrode mixture. Any conductive material may be used as long as it does not adversely affect battery performance. Usually, natural graphite (flaky graphite, flaky graphite, earthy graphite, etc.), artificial graphite, carbon black, acetylene black, Ketjen black, carbon whiskers, carbon fibers and metals (copper, nickel, aluminum, silver, gold, etc.)
A conductive material such as powder, metal fiber, metal deposition, and conductive ceramic material can be included as one type or a mixture thereof. Among these, the combined use of graphite, acetylene black and Ketjen black is desirable. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight.

As the binder, usually, tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, carboxymethyl cellulose, etc. Such as a thermoplastic resin, a polymer having rubber elasticity, a polysaccharide and the like can be used alone or as a mixture of two or more. Further, it is desirable that a binder having a functional group that reacts with lithium, such as a polysaccharide, be deactivated by, for example, methylation. The addition amount is preferably 1 to 50% by weight, particularly 2 to 50% by weight.
30% by weight is preferred.

As the filler, any material may be used as long as it does not adversely affect battery performance. Usually, olefin polymers such as polypropylene and polyethylene, aerosil, zeolite, glass, carbon and the like are used. The added amount of the filler is preferably 30% by weight or less.

The current collector of the electrode active material may be any current collector that does not adversely affect the battery. For example, as a current collector material used for the positive electrode, aluminum, titanium, stainless steel, nickel, fired carbon, conductive polymer, conductive glass and the like, for the purpose of improving adhesiveness, conductivity, oxidation resistance, A material obtained by treating the surface of aluminum, copper, or the like with carbon, nickel, titanium, silver, or the like can be used. As the negative electrode material, copper, stainless steel, nickel, aluminum, titanium, calcined carbon,
In addition to conductive polymers, conductive glasses, and Al-Cd alloys, for the purpose of improving adhesion, conductivity, and oxidation resistance, copper and other surfaces treated with carbon, nickel, titanium, silver, etc. Can be used. These materials can be oxidized on the surface. With respect to these shapes, foil, film, sheet, net, or punched metal, expanded, lath, porous, foamed, and formed fibers are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

On the other hand, MnO ₂ , M
oO ₃ , V ₂ O ₅ , Li _x CoO ₂ , Li _x NiO ₂ ,
Metal oxides such as Li _x Mn ₂ O ₄ , TiS ₂ , Mo
Utilize metal chalcogenides such as S ₂ and NbSe ₃ , graphite intercalation compounds such as polyacene, polyparaphenylene, polypyrrole, and polyaniline, and alkali metal ions such as conductive polymers and various substances capable of absorbing and releasing anions. be able to.

In particular, when the silicon alloy of the present invention is used as a negative electrode active material, V
₂ O ₅ , MnO ₂ , Li _x CoO ₂ , Li _x NiO ₂ ,
Those having an electrode potential of 3 to ₄ V, such as Li _x Mn ₂ O _4, are desirable. In particular, Li _x CoO ₂ , Li _x NiO ₂ , L
i _x Mn lithium-containing transition metal oxides such as ₂ O ₄ are preferred.

Further, as the electrolyte, for example, an organic electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt and the like can be used, and among them, the organic electrolyte is preferable. As the organic solvent of the organic electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, esters such as γ-butyrolactone, tetrahydrofuran, substituted tetrahydrofuran such as 2-methyltetrahydrofuran, dioxolane, Ethers such as diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, dimethylsulfoxide, sulfolane, methylsulfolane,
Acetonitrile, methyl formate, methyl acetate, N-methylpyrrolidone, dimethylformamide and the like can be mentioned, and these can be used alone or as a mixed solvent.

The main constituent solute of the electrolyte used in the present invention may be a salt containing carbon. For example, the formula used in JP-A-58-225045: (C _n X
_{2n + 1} Y) ₂ N ⁻ , M ⁺ , and the following general formulas (3) and (4): (RSO ₂ ) ₃ C ⁻ , M ⁺ ... General formula (3) (RSO ₂ ) O ⁻ , M ⁺ ... A compound represented by the general formula (4) is preferable. More preferably, general formula (2) (R1Y1) (R2Y2) NLi General formula (2) (R1 and R2 in general formula (2) are represented by C _n F _{2n + 1} ,
n is a number from 1 to 4, and R1 = R2 or R1
≠ R2, and Y1 and Y2 are CO, SO, SO ₂
Y1 = Y2 or Y1 ≠ Y2. ) Is used. Still more preferably, R1 = R2 = C ₂ F ₅ or R1 = CF
_3, R2 = is C ₄ to use those represented by F _9. Here, when a lithium-containing transition metal oxide was used as the positive electrode active material, it was found that when R1 = R2 = CF ₃ in the general formula (2) was used, the cycle deterioration was large. That is, when a lithium-containing transition metal oxide is used as the main constituent material of the positive electrode active material, R1 = R2 = CF in the general formula (2).
It is preferable to use a salt represented by other than ₃ . On the other hand, as the solid electrolyte, for example, an inorganic solid electrolyte, an organic solid electrolyte, an inorganic organic solid electrolyte, a molten salt, or the like can be used. Well known inorganic solid electrolytes include lithium nitrides, halides, oxyacid salts, phosphorus sulfide compounds, and the like, and one or more of these can be used in combination. Among them, Li ₃ N, LiI, Li ₅ N
I ₂ , Li ₃ N—LiI—LiOH, Li ₄ SiO ₄ ,
Li ₄ SiO ₄ -LiI-LiOH, xLi ₃ PO
_{4- (1-x)} Li ₄ SiO ₄ , Li ₂ SiS _{3 and the} like are effective. On the other hand, in an organic solid electrolyte, a polyethylene oxide derivative or a polymer containing at least the derivative, a polypropylene oxide derivative or a polymer containing at least the derivative, polyphosphazene or the derivative, a polymer containing an ion dissociating group, a phosphate ester polymer derivative, and a polyvinyl ester A pyridine derivative, a bisphenol A derivative, polyacrylonitrile, polyvinylidene fluoride, a polymer matrix material (gel electrolyte) containing a non-aqueous electrolyte solution in fluororubber, or the like is effective.

As the separator, an insulating thin film having excellent ion permeability and mechanical strength can be used. Olefin polymers such as polypropylene and polyethylene, glass fiber, and organic solvent resistant and hydrophobic
Sheets, microporous membranes, and nonwoven fabrics made of polyvinylidene fluoride, polytetrafluoroethylene, or the like are used.
The pore size of the separator is in a range generally used for a battery, and is, for example, 0.01 to 10 μm. The same applies to the thickness, which is in the range generally used for batteries, for example, 5 to 300 μm.

As described above, the present invention provides a non-aqueous electrolyte battery in which the main constituent material of the negative electrode active material is a silicon alloy, by using a salt containing carbon as the main constituent solute of the electrolyte, thereby reducing the use of lithium metal. Lithium ions can be inserted and extracted at least in the range of 0 to 2 V, and fine powdering during charge and discharge and partial isolation of the negative electrode active material, which are observed in ordinary alloys, can be suppressed. By using as a water electrolyte, it can be used as a negative electrode of a secondary battery having excellent charge / discharge efficiency, excellent cycle characteristics, and excellent charge / discharge characteristics.

[0025]

Embodiments of the present invention will be described below.

(Example 1) As a silicon alloy, Li ₁₂
Si ₇ (a), Ni ₂ Si (b), FeSi (c), C
oSi (d), MnSi (e), CaSi (f), Mg
_{2 Si (g), PSi (} h), AlSi (i), AsS
i (j), WSi (k), B ₃ Si (l), TiSi
(M), SiV ₃ (n) and PtSi (o), each of which was pulverized in a mortar, and using this negative electrode active material, a coin-type non-aqueous electrolyte battery was prototyped as follows. The active material, acetylene black and polytetrafluoroethylene powder were mixed at a weight ratio of 85: 10: 5, and toluene was added and kneaded sufficiently. This is roll-pressed to a thickness of 0.1
mm. Next, this was punched out into a circle having a diameter of 16 mm and dried at 200 ° C. under reduced pressure for 15 hours to obtain a negative electrode 2. The negative electrode 2 was used by being pressed against a negative electrode can 5 provided with a negative electrode current collector 7. The positive electrode 1 is made of LiCoO as a positive electrode active material.
₂ and acetylene black and polytetrafluoroethylene powder were mixed at a weight ratio of 85: 10: 5, and toluene was added and kneaded sufficiently. This was formed into a 0.8 mm thick sheet by a roller press. Next, this is
A positive electrode 1 was obtained by punching out into a circular shape of mm and drying under reduced pressure at 200 ° C. for 15 hours. Positive electrode 1 is a positive electrode can 4 with a positive electrode current collector 6
To be used. (C ₂ F ₅₎ was added to a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1.
An electrolytic solution in which 1 mol / l of SO ₂ ) ₂ NLi was dissolved was used, and a polypropylene microporous film was used for the separator 3. A coin-type lithium battery having a diameter of 20 mm and a thickness of 1.6 mm was manufactured using the above-mentioned positive electrode, negative electrode, electrolyte and separator. Batteries using the respective silicon alloys (a) to (o) are referred to as batteries (A1) to (O1), respectively.

Comparative Example 1 As a solute of the electrolytic solution, (C ₂
A battery was fabricated in the same manner as in Example 1, except that LiBF ₄ was used instead of F ₅ SO ₂ ) ₂ NLi. The obtained batteries are referred to as comparative batteries (A2) to (O2).

(Example 2) As a solute of the electrolytic solution, (C ₂
(CF ₃ SO ₂ ) ₂ N instead of F ₅ SO ₂ ) ₂ NLi
A battery was fabricated in the same manner as in Example 1 except for using Li. The obtained batteries are referred to as batteries (A3) to (O3).

The battery of the present invention (A
1) to (O1), comparative batteries (A2) to (O2), and batteries of the present invention (A3) to (O3) were subjected to charge / discharge cycle tests. The test conditions were a charge current of 3 mA, a charge end voltage of 4.1 V, a discharge current of 3 mA, and a discharge end voltage of 3.0 V. Tables 1 to 3 show the results of the charge / discharge test of these batteries.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

As can be seen from Tables 1, 2 and 3, the batteries (A1) to (O1) and (A3) to (O3) of the present invention using a salt containing carbon as the solute of the electrolytic solution according to the present invention are: And LiBF instead of a salt containing carbon as a solute of the electrolyte
_The charge / discharge characteristics were superior to the comparative batteries (A2) to (O2) using No. _4, and the decrease after 10 cycles was small. Also, from the comparison between the batteries (A1) to (O1) of the present invention and the batteries (A3) to (O3) of the present invention, (C)
_The present invention battery (A1) using ₂ F ₅ SO ₂ ) ₂ NLi
(O1) is, (CF ₃ SO ₂₎ is excellent in charge and discharge characteristics as compared with the present invention battery using _{2 NLi (A3) ~ (O3} ), was small loss after 10 cycles. In the case of using a silicon alloy, although the reason for these phenomena is not clear, it is considered that the state of the interface which occurs between the electrolyte, particularly the solute and the material surface is involved.

In the above embodiment, (C ₂ F ₅ SO ₂ ) ₂ NLi and (CF ₃ SO ₂ ) ₂ N are used as solutes of the electrolytic solution.
Although described for Li, the same effect was confirmed for other carbon-containing salts. The present invention is not limited to the starting materials, the production method, the positive electrode, the negative electrode, the electrolyte, the separator, the shape of the battery, and the like of the active material described in the above-described embodiment.

[0035]

Since the present invention is configured as described above, it is possible to provide a non-aqueous electrolyte battery having high voltage, high capacity, high energy density, excellent charge / discharge cycle characteristics, and high safety.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte battery of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode 2 negative electrode 3 separator 4 positive electrode can 5 negative electrode can 6 positive electrode current collector 7 negative electrode current collector 8 insulating packing

Claims (5)

[Claims] The main constituent material of the negative electrode active material is a general formula (1) SiM _x ... General formula (1) (wherein M in the general formula (1) is at least one element that can be alloyed with silicon; a non-aqueous electrolyte battery characterized by being a silicon alloy represented by x> 0), and wherein a main constituent solute of the electrolyte is a salt containing carbon. 2. The method according to claim 1, wherein the salt containing carbon is at least C
The non-aqueous electrolyte battery according to claim 1, wherein the battery has a bond of -F. 3. A salt containing the carbon, at least the general formula (2) (R1Y1) (R2Y2 ) NLi ···· formula (2) (formula (2) R1 in, R2 is C _n F _{2n + 1}
n is a number from 1 to 4, and R1 = R2 or R1
≠ R2, and Y1 and Y2 are CO, SO, SO ₂
Y1 = Y2 or Y1 ≠ Y2. 2. A salt represented by the formula:
Or the non-aqueous electrolyte battery according to 2. 4. The carbon-containing salt according to the general formula (2)
The nonaqueous electrolyte battery according to claim 3, characterized by being represented by other than R1 = R2 = CF ₃ in. 5. The method according to claim 1, wherein the element M capable of alloying with silicon is L
i, Ni, Fe, Co, Mn, Ca, Mg, P, Al,
2. The non-aqueous electrolyte battery according to claim 1, wherein the non-aqueous electrolyte battery is at least one of As, W, B, Ti, V, Pt, Zr, and Sr.