JPH10270018A - Non-aqueous electrolytic battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery displaying charging/discharging cycle characteristics excellent in high voltage and high energy density by making the main composite substance of the negative electrode active substance out of minute porous aluminum-silicate (zeolite) having fine porous with a specific porous diameter. SOLUTION: Main composite substance of a negative electrode used in a non-aqueous electrolytic battery is designated to minute porous alumino silicate (zeolite) having fine porous with porous diameter 0.4 and 2.0 nm. This zeolite is represented by chemical equation Mx O.aAl2 O3 .bSiO2 .Ly, and M is at least one kind out of alkaline metal or alkaline earth metal. L stands for a metal or carbon, and it is preferable that x stays between 1 and 2, y is more than zero, (a) stays between 0.7 and 1.3 and b stays between 1.5 and 6.0. In addition, M is preferably a lithium salt type by independent Li, and as the material quality of this metal on which a porous metal or a carbon thin layer is arranged on its particle surface, iron, copper and nickel are desirable and its crystal configuration is preferably a cubic crystal. Accordingly, a secondary battery with high safety can be obtained.

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 thereof.

[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. .

[0004] On the other hand, batteries using a carbon material for the negative electrode and the like have attracted attention and have been partially put into practical use for the purpose of prolonging the service life and safety.

However, since the carbon material used for the negative electrode has a lithium doping potential close to 0 V, the potential sometimes drops to 0 V or less when rapid charging is performed, and lithium is deposited on the electrode in some cases. Therefore, an internal short circuit of the cell may be caused or the discharge efficiency may be reduced. Furthermore, this carbon material is still insufficient in terms of high energy density. It is desired to develop a safe negative electrode material for a non-aqueous electrolyte battery having a higher capacity, a higher energy density, a longer cycle life, and a higher safety.

Although the negative electrode active material using the above-described carbon material has been considerably improved in terms of cycle life, the capacity per volume is low due to its relatively small density. In addition, at the time of quick charging, there is a problem that an internal short circuit or a reduction in charging efficiency occurs.

Further, as a negative electrode active material other than lithium metal, a lithium alloy or a carbon material, a composite oxide Li _x Si _{1 -y My} O _z containing silicon and lithium (Japanese Patent Laid-Open No. 7-230800), It has been proposed to use an amorphous chalcogen compound M ¹ M ² _p M ⁴ _q (Japanese Patent Laid-Open No. 7-288123), which is improved in terms of high capacity and high energy density.

[0008] However, the above-mentioned composite oxide has a slow charge of lithium ions in the active material itself and a large resistance of the reaction at the solid-liquid interface.
And high load characteristics are inferior. For the purpose of solving this problem, attempts have been made to add a conductive material to reduce the size of the active material particles and further improve the conductivity. However, a satisfactory effect has not yet been obtained, and the use of a low-density carbon material as the conductive material results in a reduction in capacity per volume. Furthermore, by adding a conductive material, when rapid charging was performed, current concentration partially occurred, and precipitation of lithium from the conductive agent was observed. For this reason, an internal short circuit of the cell may be caused or the charge / discharge efficiency may be reduced.

[0009] Further, in the above-mentioned conventionally proposed complex oxides, it is considered that the reaction with lithium proceeds through the reduction of the oxides. Therefore, irreversible reduction occurs at the initial stage, and the initial charge / discharge efficiency is reduced. There was a drawback that it became lower.

[0010]

As described above, when lithium metal or lithium alloy is used as the negative electrode, there are advantages in terms of high voltage, high capacity, and high energy density, but there are problems in terms of cycleability and safety. When a carbon material is used, it is advantageous in terms of high voltage and safety, but is insufficient in terms of high capacity and high energy density. Furthermore, when an oxide negative electrode is used, high capacity and high energy density have been improved, but those which can be satisfied in terms of rapid charge, high load discharge characteristics, charge / discharge efficiency characteristics, cycle life and safety are obtained. Not been.

For this reason, at a high voltage and a high energy density,
In order to obtain a secondary battery with excellent charge-discharge cycle characteristics and high safety, there is little change in the crystal system or volume change during insertion and extraction of lithium during charging and discharging, and in an operating region as close to the lithium potential as possible. A conductive compound capable of reversibly inserting and extracting lithium has been desired.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a main constituent material of a negative electrode used in a non-aqueous electrolyte battery is a fine electrode having a pore size of 0.4 to 2.0 nm. It is a microporous aluminosilicate (zeolite) having pores.

The zeolites mentioned above have the chemical formula M _x O
· AAl represented by _{2 O 3 · bSiO 2 · L} y, M is at least one among alkali metals or alkaline earth metals, L is a metal or carbon, x is 1 to 2, y is 0 or more, a is desirably 0.7 to 1.3, and b is desirably 1.5 to 6.0. Further, M is preferably a lithium salt type in which Li is solely Li. Further, it is preferable that a porous metal or carbon thin layer is disposed on the particle surface. As the material of the metal, iron, nickel, and copper are preferable. Further, it is desirable that the crystal form belongs to a cubic crystal.

Zeolite is a crystalline aluminosilicate, which has attracted attention as a compound having a relatively large space in its structure and having the potential to occlude a large amount of lithium. When the characteristics as a negative electrode were evaluated using various zeolites, it was found that those having a composition satisfying the above-mentioned contents had a large discharge capacity and were excellent. In addition, although the capacity per unit weight of the active material (mAh / g) is large in general Na salts and Ca salts, the coulomb efficiency in the first cycle was low. The reason for this is not clear, but in these general types of zeolites, in an attempt to act as the negative electrode of a lithium battery, lithium doped in the zeolite by charging and cations such as sodium that the zeolite had had, etc. It was presumed that ion exchange was performed and lithium was trapped.

Therefore, the zeolite was treated in advance with an aqueous solution of a lithium salt, and was changed to a lithium salt type by ion exchange. It was confirmed that the zeolite converted to the lithium salt type had a high coulomb efficiency in the first cycle and had excellent characteristics when used as a negative electrode of a lithium battery.

In the classification of crystal forms, zeolites are classified into several types. Typical examples are cubic, hexagonal, orthorhombic, and monoclinic. As a result of evaluating these typical zeolites having different crystal forms as the negative electrode,
In terms of capacity per unit volume, those having cubic crystals were the best.

Further, the particle size of the zeolite affects the rapid charging performance and the high-load discharge characteristics. The particle size is preferably from 5 to 90 μm. It is presumed that when the particle size is small, electron conductivity is poor, and when the particle size is large, diffusion of lithium ions in the particles is poor. It is considered that a good range between electron conductivity and diffusion of lithium ions in the solid phase is 5 to 90 μm. Zeolite itself is a nonconductor, and as such, has low electron conductivity. In order to function as a negative electrode, it is necessary to mix a conductive material such as carbon powder. We have found that by arranging a porous metal coating on the surface of zeolite particles, it is possible to improve the electron conductivity, and further to improve the rapid charge characteristics and the high load discharge characteristics. Iron, nickel, and copper are suitable for the metal forming the film because they have high conductivity and do not form an alloy with lithium. The thickness of the coating is preferably from 0.3 to 2 μm. It is presumed that if the thickness of the coating is small, sufficient electron conductivity cannot be obtained, and if it is large, the diffusion of lithium ions will be hindered.

Suitable methods for forming the coating include vapor deposition, electroless plating, and mechanochemical methods.

As described above, focusing on the fact that the lithium salt type zeolite has a high capacity, and by adding an improvement in the electronic conductivity to this, it is expected that the zeolite has excellent characteristics as a negative electrode of a lithium secondary battery. Have found the present invention.

It is effective to mix and use lithium and a substance capable of inserting and extracting lithium into the zeolite. Examples of the material that can be used in combination with the negative electrode constituent material of the present invention include lithium metal, a lithium alloy, and a fired carbonaceous compound or a chalcogen compound capable of inserting and extracting lithium ions or lithium metal, and lithium such as n-butyllithium. Organic compounds and the like. In addition, by using lithium metal, a lithium alloy, and an organic compound containing lithium in combination, lithium can be inserted into the zeolite used in the present invention inside the battery.

In the case of the zeolite of the present invention, 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, earthy graphite, etc.), artificial graphite, carbon black, acetylene black, Ketjen black, carbon whiskers, carbon fibers and metals (copper, nickel, iron,
Silver, gold, etc.), a conductive material such as powder, metal fiber, metal vapor 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 2 to 50% by weight.
30% by weight is preferred.

As the binder, usually, tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, carbomethoxy cellulose And the like, a thermoplastic resin, a polymer having rubber elasticity, a polysaccharide and the like can be used as one kind or as a mixture of two or more kinds. Further, it is desirable that a binder having a functional unit 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 30% by weight.
% 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, alumina, carbon and the like are used. The addition amount of the filler is preferably 0 to 30% by weight.

The thus obtained zeolite is used as a negative electrode active material. On the other hand, as the positive electrode active material, MnO
₂ , MoO ₃ , V ₂ O ₅ , Li _x CoO ₂ , Li _x Ni
Metal oxides such as O ₂ , Li _x Mn ₂ O ₄ , Ti
Metal chalcogenides such as S ₂ , MoS ₂ , 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 can be used.

In particular, when the zeolite of the present invention is used as a negative electrode active material, V ₂ O is preferably used from the viewpoint of high energy density.
₅ , MnO ₂ , Li _x CoO ₂ , Li _x NiO ₂ , Li
having an electrode potential of 3~4V such _x Mn ₂ O ₄ is preferred. In particular, Li _x CoO ₂ , Li _x NiO ₂ , Li _x
Lithium-containing transition metal oxides such as Mn ₂ O ₄ are preferred.

As the electrolyte, for example, an organic electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like can be used, and among them, an 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 supporting electrolyte salt includes LiClO ₄ , LiPF
₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , L
iN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ S
O ₂ ) ₂ and LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ). On the other hand, as the polymer solid electrolyte, those obtained by dissolving the above-described supporting electrolyte salt in a polymer such as polyethylene oxide or a crosslinked product thereof, or polyphosphazene or a crosslinked product thereof can be used. Further, inorganic solid electrolytes such as Li ₃ N and LiI can be used. That is, any non-aqueous electrolyte having lithium ion conductivity may be used.

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.

The reason why such excellent charge / discharge characteristics are obtained is not necessarily clear, but is considered as follows. That is, the number of sites that can be occupied by lithium ions in the zeolite crystal is large. Also,
Lithium can be stored and released reversibly in the pores of zeolite. For these reasons, it is estimated that the capacity when using zeolite is large. Lithium ions can be easily occluded as zero-valent lithium to give electrons, and the occluded zero-valent lithium emits electrons and is released as lithium ions. In other words, following the expansion and contraction associated with the insertion and extraction of lithium, the active material itself is not miniaturized or dropped, and the reversibility of charge and discharge is considered to be improved.

[0029]

The negative electrode active material of the present invention mainly comprising a lithium salt type zeolite can absorb and release lithium ions in a non-aqueous electrolyte in a range of at least 0 to 2 V with respect to metallic lithium. Since there is a space inside the structure, a negative electrode having a large lithium storage capacity and a large discharge capacity can be realized.

Further, by regulating the particle size of the zeolite, it is possible to realize a negative electrode having excellent quick charge characteristics and high load discharge characteristics. Furthermore, by coating the zeolite particles with a metal porous film, the electron conductivity is improved, and a negative electrode having excellent rapid charge receiving characteristics and high load discharge characteristics can be realized as described above.

By using such a negative electrode active material as an electrode material, it can be used as a negative electrode of a secondary battery having excellent cyclable charge / discharge characteristics. Further, since the negative electrode potential is low, the voltage of the battery becomes high,
In addition, high energy density is achieved because of its large capacity.

[0032]

DETAILED DESCRIPTION OF THE INVENTION Zeolite particles are ground to a powder having an average particle size of about 10 μm and a particle size range of 1 to 90 μm. More preferably, it is converted to a lithium salt type by ion exchange before being ground. Specifically, it is immersed in an aqueous solution of lithium hydroxide. In this immersion, it is converted to a lithium salt by cation exchange. After immersion, washing with water is carried out to remove the alkali, followed by drying. The conductivity is imparted by mixing a conductive material such as a carbon powder with the dried zeolite powder. A more desirable method for imparting conductivity is to form a conductive porous film on the particle surface. Specifically, there are electroless plating, vapor deposition, mechanochemical and the like. As a material for forming the coating, carbon, in addition to metals such as iron, nickel, and copper, is also suitable. A mixture of a zeolite provided with conductivity and a solution of a binder resin such as polyfukkavinylidene (PVDF) in n-methylpyrrolidone (NMP) is applied on a negative electrode current collector such as a copper foil. After application, the coating is dried and roll-pressed to form a negative electrode.

[0033]

Embodiments of the present invention will be described below.

(Example 1) A porous material having an average particle size of 10 µm, a cubic crystal system, a pore size of 0.5 nm, and a formula of Na ₂ O · A
zeolite represented by l ₂ O ₃ · 2SiO ₂
Dried at 00 ° C. 90 g of dried zeolite as well as 10 g of dried acetylene black mixed powder,
A paste obtained by kneading 50 g of a 10% NMP solution of PVDF was coated on a copper foil by a doctor blade.
The coating thickness was 150 μm. This was dried to remove NMP to obtain a negative electrode. To a mixed powder of 90 g of lithium cobaltate and 10 g of acetylene black, 10% N of PVDF was added.
50 g of the MP solution was kneaded and coated on an Al foil. The coating thickness was 150 μm. This was dried to obtain a positive electrode.
Microporous polypropylene (PP) was used as the separator. The electrolytic solution contains 1 mol of lithium perchlorate (LiClO ₄ ).
A 1 / liter propylene carbonate solution was used. The coin-shaped cell shown in FIG. 1 was prototyped, and a charge / discharge test was performed using this cell. The charge / discharge test was performed at room temperature. The charging was performed at a constant current of 3 mA, and the final voltage was set to 4.1 V. Discharge was performed at a constant current of 3 mA, and the final voltage was set to 2.5 V.

Comparative Example 1 A cell having the same contents as in Example 1 was used except that artificial graphite powder having an average particle size of about 10 μm was used for the negative electrode. The evaluation test was performed under the same conditions as in Example 1.

Comparative Example 2 The negative electrode had an average particle size of about 10 μm,
A cell having the same contents as in Example 1 was used except that SiO ₂ powder was used. The evaluation test was performed under the same conditions as in Example 1.

Example 2 The negative electrode had an average particle size of about 10 μm,
Example 1 was the same as Example 1 except that the chemical formula Na ₂ O.0.5Al ₂ O ₃ .2SiO ₂ was used.

Example 3 The negative electrode had an average particle size of about 10 μm,
Example 1 was the same as Example 1 except that the chemical formula Na ₂ O.1.5Al ₂ O ₃ .2SiO ₂ was used.

Example 4 The negative electrode had an average particle size of about 10 μm,
Example 1 was the same as Example 1 except that the chemical formula Na ₂ O.Al ₂ O ₃ .SiO ₂ was used.

Example 5 The negative electrode had an average particle size of about 10 μm,
Example 1 was the same as Example 1 except that the chemical formula Na ₂ O.Al ₂ O ₃ .8SiO ₂ was used.

[0041] (Example 6) the average particle size of about 10 [mu] m, the immersion treatment in an aqueous solution of the chemical formula _{Na 2 O · Al 2 O 3} · 2SiO lithium hydroxide cubic zeolite represented by ₂ (LiOH) subjected, lithium Change to salt type, Li ₂ O ・ A
l ₂ O ₃ · 2SiO ₂ . The immersion-treated product was washed with water and dried. Using this treated product, a negative electrode having the same composition as in Example 1 was constructed and subjected to a test under the same conditions. Table 1 shows the results of trial production tests performed on the above Examples and Comparative Examples.
Shown in The test was performed at room temperature as described above. The charging was constant current charging, the current was 3 mA, and the end voltage was 4.1 V. Discharge is a constant current discharge with a current of 3 mA and a cutoff voltage of 2.5.
V.

[0042]

[Table 1]

As shown in Table 1, the discharge capacity of the battery according to the present invention is larger than that of the comparative example.
This is because the capacity of the negative electrode is large.

As can be seen from the comparison between the results of Example 1 and Examples 2 to 5, the chemical formula of Na ₂ O.aAl ₂ O ₃ .bSi
It is desirable that a of O _{2 be} approximately 1, 0.7 to 1.3. Further, it is desirable that b is in the range of 1.5 to 6. As can be seen from the results of Example 6, the cell in which zeolite was used as the negative electrode, which was previously converted to the lithium salt type, had 1
High coulomb efficiency at cycle (discharge capacity / charge capacity) and excellent characteristics.

Example 7 The lithium salt type zeolite used in Example 6 was electrolessly plated with nickel. The amount of nickel deposited per gram of zeolite was 200
and mg, Formula _{Na 2 O · Al 2 O 3} · 2SiO 2 ·
0.968Ni was obtained. 100 g of this zeolite and PVD
A paste consisting of 30 g of a 10% NMP solution of F was coated on a copper foil in the same manner as in Example 1. The coating thickness was 150 μm, as in Example 1. This was dried to obtain a negative electrode.
A coin-shaped cell having the same configuration and size as in Example 6 was prototyped and subjected to a test under the same conditions.

Example 8 95 g of the zeolite used in Example 6 was mixed with 5 g of graphite powder, and a graphite layer was formed on the surface of the zeolite particles by mechanofusion.
The same evaluations as in Example 7 were performed using this zeolite.

Example 9 Chemical formula Na ₂ O.Al ₂ O ₃
• 4.4 SiO ₂ , the crystal system is orthorhombic and the chemical formula is Na ₂
A negative electrode having the same composition as in Example 3 was prepared and subjected to the same test, except that zeolite having O.Al ₂ O ₃ .5SiO ₂ and a monoclinic crystal system was used.

Table 2 shows the results of the same evaluation as described above for Examples 7 to 9. In addition, (1) of Example 9 of Table 2 is a test result of a cell in which a zeolite crystal system is orthorhombic, and (2) is a test result of a cell in which monoclinic zeolite is used as a negative electrode.

[0049]

[Table 2]

As can be seen by comparing the results shown in Examples 7 and 8 in Table 2 with the results of Example 6, a porous metal or carbon layer was formed on the surface of the zeolite particles by a mechanochemical method. The discharged battery shows a large capacity. This is because a small amount of the negative electrode conductive agent exhibits an excellent current collecting effect. From the results of Example 8 or 9, the capacity of a battery using a zeolite having a crystal system of orthorhombic or monoclinic as a negative electrode is smaller than the capacity of a battery using a cubic zeolite as a negative electrode. For this reason, cubic zeolite is desirable. Moreover, the battery according to the present invention using zeolite as a negative electrode does not have a capacity decrease after 10 cycles.

The present invention is not limited to the starting materials, production methods, positive electrodes, negative electrodes, electrolytes, separators, battery shapes, etc. of the active materials described in the above embodiments. In addition, the coin type cell is only for describing the present invention, and the shape of the battery is not limited to the coin type.

[0052]

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

[Brief description of the drawings]

FIG. 1 is a sectional view of a coin-type lithium secondary battery for explaining 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] 1. A non-aqueous electrolyte battery, wherein the main constituent material of the negative electrode active material contains at least zeolite. 2. The method according to claim 1, wherein the zeolite has a chemical formula of M _x O.aA.
l ₂ O ₃ .bSiO ₂ .L _y (where M: at least one kind of alkali metal or alkaline earth metal, L is metal or carbon, x = 1 to 2, y ≧ 0, a is 0.7 ~
The non-aqueous electrolyte battery according to claim 1, wherein 1.3 and b are represented by 1.5 to 6.0). 3. The non-aqueous electrolyte battery according to claim 1, wherein a porous film of metal or carbon is provided on the surface of the zeolite particles. 4. The non-aqueous electrolyte battery according to claim 2, wherein M in the chemical formula is Li. 5. A cubic crystal system of the aluminosilicate constituting the zeolite.
The nonaqueous electrolyte battery according to any one of the preceding claims.