JP2819027B2 - All-solid secondary battery - Google Patents

Description

The present invention relates to a novel all-solid-state secondary battery,
The present invention relates to an all-solid secondary battery that does not contain a solvent and has excellent charge / discharge characteristics that can be used safely in a wide temperature range from high to low.

(Prior Art) In recent years, lithium batteries have been actively used as high energy density, high voltage batteries. This uses manganese dioxide or fluorinated graphite for the positive electrode and lithium for the negative electrode, and a high voltage of 3 V or more can be obtained. However, these are primary batteries and cannot be charged.

On the other hand, rechargeable lithium secondary batteries have high energy density, high voltage, and can be discharged many times, so their advantages are many, and they are actively studied in various fields, but they can still withstand sufficient use No batteries have been obtained. These secondary batteries under development use transition metal chalcogen compounds such as MoS ₂ and TiS _{2 and} oxides such as MnO ₂ , Cr ₃ O ₈ and V ₂ O ₅ as the positive electrode active material, and are used as the negative electrode active material. Used lithium, lithium-aluminum alloy, etc., and dissolved an electrolyte such as LiClO ₄ and LiBF ₄ in an aprotic organic solvent such as propylene carbonate and 1,2-dimethoxyethane as an electrolytic solution. Things have been proposed. The following problems can be cited as causes for the insufficient development of these secondary batteries.

The first problem is caused by the organic solvent used for the electrolytic solution. In other words, aprotic solvents that are frequently used at present have a low boiling point and many flammable ones, and stains, ignites, ignites and misuses peripheral members due to liquid leakage or breakage,
There is a risk of explosion due to overcurrent. Further, there is a problem in that the metal lithium deposited on the negative electrode becomes dendritic by repetition of charge and discharge, grows gradually, and finally reaches the positive electrode and is short-circuited.

The second problem is a problem based on the use of the above-described crystalline materials such as chalcogen compounds and oxides as the positive electrode active material. That is, generally, the crystalline substance is Li
The crystal structure collapses due to the penetration of ions into the crystal lattice,
The characteristics as the original crystal cannot be maintained. This is particularly remarkable when the depth of discharge is large, where the amount of infiltration of Li ions is large, and the problem is that if deep discharge is repeated, the battery capacity will be significantly reduced in several times and will not be practical.

Among them, to solve the first problem, Seceria [Extended Abstracts, 163 Meetings, Electrochemical Society (Sequli)
r et al, Extended Abstratis, 163rd Meeting, E
Electrochemical Society), 1983, 83,751 Abstract, No. 493] describes a novel battery using a thin-film polymer electrolyte containing no solvent, and the test results of the electrolyte show that the medium has a medium temperature of about 100 ° C. There is only a statement that it can be used at a temperature, but it cannot be achieved at room temperature. PM Bronski et al., Journal of the American Chemical Society, Vol. 106, p. 6854
1984 (PMBlonsky et al, J. Am. Chem. Soc., 106, 685
4, 1984) describes that polyphosphazenes are useful as electrolytes for electrochemical cells. However, they only show AC conductivity data in the range of 30 ° C. to 97 ° C., and charging / discharging with DC cannot be achieved.

In order to solve the second problem, V _{2 is} used as a positive electrode active material.
O ₅ in the P ₂ O ₅ addition, the melt, the use of the quenched amorphous material is proposed in JP-A-61-116758. But,
The battery proposed here cannot be said to completely solve the above problem, and the first problem has not been solved yet.

(Problems to be Solved by the Invention) An object of the present invention is to substantially eliminate dendride generation and liquid leakage, and in addition, it is not flammable due to its flame retardancy and low vapor pressure, and is safe against explosion. An object of the present invention is to provide an all-solid secondary battery having excellent charge-discharge cycle life and excellent over-discharge resistance.

(Means for Solving the Problems) The present invention relates to the general formula (V ₂ O ₅ ) x · (A) y · zH ₂ O (where x + y = 1,0 <y ≦ 0.5, z = 0.1 to 1.6, A Are GeO ₂ , SiO ₂ , B ₂ O ₃ , MoO ₃ , WO ₃ , Nb ₂ O ₅ , Te
One or more oxides selected from O ₂ , Bi ₂ O ₃ , Cr ₃ O ₈ and ZrO ₂ are shown. ) Is used as a positive electrode active material, lithium or a lithium alloy is used as a negative electrode active material, and a fluoroalkyl sulfone group in which segments represented by the following formulas (I), (II) and (III) are arbitrarily arranged: The present invention relates to an all-solid secondary battery using, as an electrolyte, an oligoalkyleneoxypolyphosphazene having the following formula:

(Where R represents hydrogen or a methyl group, R ′ represents a methyl, ethyl or propyl group, h and k represent the average number of repeating alkyleneoxy units, and 0 ≦ h ≦ 18,0, respectively)
≤k≤20, and l, m, n are integers in the range of 3≤l + m + n≤200000, and l +
n ≠ 0. The positive electrode active material used in the present invention is represented by the general formula (V ₂ O ₅ ) x · (A) y · zH ₂ O (where x + y = 1,0 <y ≦ 0.5, z = 0.1 to 1.6, and A is GeO). _{2, SiO 2, B 2 O} 3, MoO 3, WO 3, Nb 2 O 5, Te
One or more oxides selected from O ₂ , Bi ₂ O ₃ , Cr ₃ O ₈ and ZrO ₂ are shown. ) Is a layered oxide represented by the following formula: here
The compounding ratio of the oxide compounded in V ₂ O ₅ is 0.5 or less, desirably 0.001 to 0.3. Exceeding 0.5 is not preferable because the discharge capacity decreases. Also, z crystallizes at the 0.1 end,
Exceeding 1.6 is not preferable because excess moisture reacts with Li and deteriorates battery characteristics. The layered structure oxide in the present invention means an oxide having a X-ray diffraction pattern as shown in FIG. 1 when a film is formed on a flat substrate by a method to be described later. Say the structure of

Such a layered structure oxide can be prepared by applying a conventional method. That is, V ₂ O ₅ and other oxides to be added are mixed at a predetermined ratio, the resulting mixture is melted, and the melt is brought into contact with a cooled steel plate or copper roll and quenched to obtain water. Dissolve in Alternatively, the melt may be directly poured into water to be quenched and melted. Further, depending on the oxide to be added, a method in which only V ₂ O ₅ is dissolved in water by the above-described method, and then the oxide to be added can be added directly or as an aqueous solution and dissolved. And even V ₂
It can also be prepared by mixing the alkoxide VO (OR) _{3 of} O _{5 and} the alkoxide of the oxide to be added in a predetermined ratio, and then hydrolyzing the mixture. Alternatively, a method of treating an ammonium vanadate aqueous solution or the like with an ion exchange resin to remove ammonium ions is also possible. The intended layered oxide can be obtained by drying the aqueous solution of the oxide prepared in this manner. In this drying step, powders by spray drying, thin films by spin coating, etc.
Various methods can be adopted according to the purpose. For this reason,
When a positive electrode is formed using such a layered structure oxide, the above-described aqueous solution is directly applied to a conductive support such as nickel or stainless steel, and dried to form a positive electrode. A conductive powder such as acetylene black, ketjen black, graphite is added to further impart conductivity to the material powder, and a binder powder such as polytetrafluoroethylene, polyethylene, or polystyrene is further added as necessary. In addition, the mixture can be kneaded and molded to form a pellet or sheet having a predetermined thickness, and attached to a wire net made of stainless steel, nickel, or the like to form a positive electrode.

At this time, the phosphazene polymer used in the present invention may be mixed in an appropriate amount instead of the binder or together with the binder, and molded in the same manner, or the phosphazene polymer may be added to the aqueous solution of the layered structure oxide. A method of dissolving a suitable amount of polymer and then drying and forming a film, or drying and mixing into a powder and then mixing and molding with a conductive powder, etc. promotes lithium ion conduction and has a low internal resistance. This is a useful method because it can form

On the other hand, the negative electrode active material used in the present invention is lithium or a lithium alloy. When these are used as the negative electrode, they can be formed into a sheet as generally used, and the sheet can be used by being pressed against a conductive net such as nickel or stainless steel.

Further, as the electrolyte, the above-mentioned formulas (I), (II) and (II)
An oligoalkyleneoxy polyphosphazene having a fluoroalkyl sulfone group in which the segments shown in I) are arranged arbitrarily is used. This polymer has a basic structure of polyphosphazene, in which an oligoalkyleneoxy side chain with high ionic affinity is arranged on an inorganic polymer skeleton whose main chain is phosphonitrile, which has excellent flexibility and low-temperature characteristics, and has a high degree of ionic dissociation on this side chain. By introducing a fluoroalkylsulfonic acid group having the above formula, high conductivity is achieved by the movement of only lithium ions. This is a high molecular weight polymer, and is suitable for solving the above-mentioned problem of the lithium secondary battery together with high conductivity of lithium ions.

Such a phosphazene polymer is, for example, a lithium salt of oligoalkyleneoxytrifluorobutylsulfonic acid and an alcoholate of oligoethyleneoxymonoalkyl ether, and a dichlorophosphonitrile polymer reacted in a solvent, desalting and purification, and a rubbery substance is obtained. Can be obtained as

When this phosphazene polymer is used as an electrolyte, it can be easily formed into a film by dissolving it in an ether-based solvent such as dimethoxyethane or tetrahydrofuran and applying the same. It is convenient to form a film by using a solvent, or to stack a film formed in advance and formed between the positive electrode and the negative electrode. or,
Due to the battery configuration, the above-mentioned polymer electrolyte can be impregnated into a microporous separator membrane as required.

FIG. 2 shows an example in which the above-described members are used to prepare an all-solid secondary battery of the present invention. This battery is an example of a sheet type battery, and the application form is not limited to this, and it is needless to say that the battery can be applied to a button type, a cylindrical type, and the like.

(Examples) Hereinafter, the present invention will be described in detail with reference to examples. Note that all the batteries were prepared in an argon atmosphere.

Example 1 (1) Production of Positive Electrode Body After a predetermined amount of various oxides was mixed with V ₂ O ₅ , the mixture was heated and melted in a platinum nozzle. The melt was blown onto a high-speed rotating copper rotor and quenched to obtain a ribbon-shaped amorphous material. The thus-obtained amorphous material is dissolved in water and uniformly applied to a central portion 36 cm ² of a 5.5 cm × 9 cm, 20 μm thick stainless steel foil. This was dried at about 80 ° C. to form a film, and then dried at 180 ° C. for 5 hours to obtain a positive electrode body. The above general formula (V ₂ O ₅ ) · (A) y · zH ₂ O
Z in each case was 0.3.

For comparison, the crystalline V ₂ O ₅ powder and the conductive agent acetylene black and polytetrafluoroethylene for molding were 70: 2
A sheet cut to 4.5 cm × 8 cm from a sheet prepared by mixing at 5: 5 was similarly placed on a stainless steel foil and used in Comparative Example 1.

(2) Preparation of Negative Electrode Body A 5.5 cm × 9 cm, 20 μm thick stainless steel foil having a central portion pressed with 40 mg of lithium foil was pressed into a negative electrode body.

(3) Preparation of electrolyte [NP ｛O (CH ₂ CH ₂ O) ₇ CH ₂ CH ₂ CFHCF ₂ SO ₃ Li｝ _0.29 ｛0
(CH ₂ CH ₂ O) ₇ CH ₃ ｝ _1.71 ] Average molecular weight of about 170
Ten thousand phosphazene polymers in dimethoxyethane were prepared.

As a comparative example, a polypropylene nonwoven fabric impregnated with a mixture of propylene carbonate and 1,2-dimethoxyethane in which LiClO ₄ was dissolved at 1 mol / l was used.

(4) Assembly of Battery FIG. 2 is a schematic cross-sectional view of a sheet-type battery which is a specific example of the battery according to the present invention. The external dimensions are adapted to a business card size of 5.5 cm × 9 cm, and the thickness is It is about 0.2 mm. In the figure, 1 is a layered structure oxide film, 2 is lithium metal,
3 is a phosphazene polymer film, 4 is a stainless steel foil, and 5 is a seal. In assembling the battery, a solution of a phosphazene polymer was applied on the positive electrode body, and dimethoxyethane was removed to form an electrolyte membrane. Subsequently, the negative electrode was bonded to a peripheral part having a width of about 5 mm to which a sealing material was applied, and was vacuum-sealed to complete the battery.

(5) Measurement of battery charge / discharge characteristics For these batteries, a constant current charge / discharge of 0.5 mA was performed between 4 V and 2 V, and the capacity retention rate of each battery at this time (discharge capacity of the battery was 100 %).
Table 1 shows the results. However, No. 1 is a comparative example because y = 0, although layered V ₂ O ₅ is used.

Example 2 The mixing ratio of the layered oxide of the positive electrode was changed, and the phosphazene polymer was changed to an [NP ｛O (CH ₂ CH ₂ O) having an average molecular weight of about 1.5 million.
₇ CH ₂ CH ₂ CFHCF ₂ SO ₃ Li｝ _0.41 ｛0 (CH ₂ CH ₂ O) ₇ C
H ₃ ｝ _1.59 ] n, and a battery was assembled in the same manner as in Example 1 except that the negative electrode was made of a lithium-aluminum alloy. However, drying of the layered structure oxide is 20
5 hours at 0 ° C. These batteries were charged / discharged (constant current of 0.5 mA) between 4 V and 2 V, and the average discharge amount up to 100 cycles was measured. The results are shown in Table 2. However, No. 14 uses a layered V ₂ O ₅ but is a comparative example because y = 0.

Example 3 The layered structure oxide of the positive electrode was (V ₂ O ₅ ) _0.9 · (MoO ₃ ) _0.1 ·
A battery was prepared in the same manner as in Example 1 except that the Hofsazene polymer was changed to 0.3H ₂ O and that shown in Table 3 and the capacity retention ratio of each battery was measured. The results are shown in Table 3.

[Brief description of the drawings]

FIG. 1 is an example showing an X-ray diffraction pattern when a layered oxide used in the present invention is formed in a film shape on a flat substrate. FIG. 2 is a schematic sectional view of a sheet-type battery which is a specific example of the battery according to the present invention. 1 is a layered structure oxide film, 2 is metallic lithium, 3 is a phosphazene polymer film, 4 is a stainless steel foil, and 5 is a sealing material.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-162724 (JP, A) WO 88/5064 (WO, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 10/40 H01M 4/48 H01M 4/58

Claims (1)

(57) [Claims] A general formula (V ₂ O ₅ ) x · (A) y · zH ₂ O (where x + y = 1,0 <y ≦ 0.5, z = 0.1-1.6, A is GeO ₂ , SiO ₂ , B ₂ O ₃ , MoO ₃ , WO ₃ , Nb ₂ O ₅ , Te
One or more oxides selected from O ₂ , Bi ₂ O ₃ , Cr ₃ O ₈ and ZrO ₂ are shown. ) Is used as a positive electrode active material, lithium or a lithium alloy is used as a negative electrode active material, and a fluoroalkyl sulfone group in which segments represented by the following formulas (I), (II) and (III) are arbitrarily arranged: An all-solid-state secondary battery comprising, as an electrolyte, an oligoalkyleneoxy polyphosphazene or a mixture thereof. (Where R represents hydrogen or a methyl group, R ′ represents a methyl, ethyl or propyl group, h and k represent the average number of repeating alkyleneoxy units, and 0 ≦ h ≦ 18,0, respectively)
≤k≤20, and l, m, n are integers in the range of 3≤l + m + n≤200000, and l +
n ≠ 0. )