JPH0430148B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a solid electrolyte battery comprising a positive electrode, a negative electrode containing lithium as an active material, and a lithium ion conductive solid electrolyte, and in particular, This is related to the improvement of

(b) Conventional technology As a conventional solid electrolyte for this type of battery, LiI
Generally, the main component was Cal ₂ , Al ₂ O ₃ , Li ₂ S, etc. added thereto. This solid electrolyte has a relatively high conductivity (1 to 2 × 10 ^-5 Ω ^-1
cm ^-1 ) or have a low decomposition voltage of about 2.8 V, so when combined with a lithium negative electrode, such as manganese dioxide, molybdenum trioxide, and vanadium pentoxide as positive electrode active materials, the battery voltage can reach 3.0 V or more. When using this method, there is a problem that the solid electrolyte decomposes and highly corrosive iodine is generated, which corrodes the battery can and packing material. This solid electrolyte also has the disadvantage of being easily decomposed by trace amounts of moisture, resulting in relatively large deterioration during storage.

Therefore, various solid electrolytes have been intensively studied, and in recent years, an electrolyte material having a γ''-lithium phosphate type crystal structure has been proposed _.
Li ₄ in groups such as PO ₄ Li ₃ VO ₄ , Li ₂ MoO ₄
It is thought to be a solid solution of SiO ₄ , Li ₄ GeO ₄ , etc.
It exhibits a conductivity of approximately 1×10 ^-5 Ω ^-1 ·cm ^-1 at room temperature, and has a high decomposition voltage of 3.0 V or more.

When creating a solid electrolyte using an electrolyte material having this γ''-lithium phosphate crystal structure, a solid electrolyte with sufficient strength was obtained by molding the electrolyte material using a powder molding method. conductivity is 10 ^-7 to 10 ^-6 considering contact resistance.
It rose only to about Ω ^-1 cm ^-1 .

Therefore, the applicant has already proposed the use of a solid electrolyte obtained by sintering an electrolyte material having a γ''-lithium phosphate type crystal structure (see Japanese Patent Application No. 179493/1987 for details).

(c) Purpose of the Invention The present invention aims to improve battery performance by further improving the properties of the solid electrolyte in a solid electrolyte obtained by sintering an electrolyte material having a γ″-lithium phosphate type crystal structure. This is the purpose.

(D) Structure of the Invention The present invention has been made to achieve the above object, and its gist is to provide a positive electrode, a negative electrode containing lithium as an active material, and a γ″-lithium phosphate type crystal structure. A solid electrolyte battery includes a solid electrolyte obtained by sintering a mixture of an electrolyte material and an additive having a lower melting point than the electrolyte material.

According to the present invention, when the electrolyte material is sintered, the sinterability of the electrolyte material is improved by the low melting point additive added to the electrolyte material, the contact area between the electrolyte materials is increased, and as a result, the interfacial resistance is reduced. This results in improved conductivity.

(E) Example [Example 1] As an example of an electrolyte material, a Li ₄ SiO ₄ -Li ₃ VO ₄ system was prepared as follows.

That is, lithium carbonate Li ₂ CO ₃ , silica SiO ₂ , and vanadium pentoxide V ₂ O ₅ were weighed out in a molar ratio of 1.7:0.4:0.3, thoroughly pulverized and mixed, and then placed in air at 700°C for 50 hours. React, cool and then crush. For convenience of explanation, the electrolyte material at this point will be referred to as the primary electrolyte material.

Lithium sulfate Li ₂ is used as the primary electrolyte material.
Add 5% by weight of SO ₄ and mix. The electrolyte material at this point is called the secondary electrolyte material.

A mixture of niobium pentoxide, Nb ₂ O ₅ and 20% by weight of the primary electrolyte material was used as a positive electrode mixture.

When creating a battery, the secondary electrolyte material and the positive electrode mixture are sequentially filled into a mold and pressurized to form a 10.0 mm
The molded body was then sintered in air at 900°C for 1 hour, and then cooled. Thereafter, a negative electrode made of a lithium plate was pressure-bonded to the back surface of the solid electrolyte to obtain a button-type battery.
The battery dimensions were 11.5 mm in diameter and 2.0 mm in height.
This battery is called A.

[Example 2] The same method as in Example 1 was carried out except that 5% by weight of sodium chloride NaCl was added as an additive to the primary electrolyte material in Example 1 as the secondary electrolyte material. Battery B was created.

[Example 3] The secondary electrolyte material was obtained by adding 5% by weight of lithium chloride LiCl as an additive to the primary electrolyte material in Example 1, and the above-mentioned first electrolyte material was added to molybdenum trioxide MoO ₃ as a positive electrode mixture. Using a mixture of 20% by weight of the following electrolyte material, and at 650℃ in air.
Battery C was produced in the same manner as in Example 1 except that the battery was sintered for 1 hour.

[Example 4] Battery D was prepared in the same manner as in Example 3, except that a mixture of vanadium pentoxide V ₂ O ₅ and 20% by weight of the primary solid electrolyte material was used as the positive electrode mixture.

[Comparative Example 1] Comparative battery E was prepared in the same manner as in Example 1, except that a sintered primary electrolyte material was used as the solid electrolyte.

[Comparative Example 2] Comparative battery F was created in the same manner as in Example 1 except that the secondary electrolyte material was simply molded without sintering and used as the solid electrolyte. did.

1 and 2 are comparison diagrams of battery characteristics of batteries A to D of the present invention and comparative batteries E and F. FIG. 1 shows the voltage-current characteristics at room temperature, and FIG. 2 shows the discharge characteristics at room temperature with a load of 270 kΩ.

(c) Effects of the invention As is clear from FIGS. 1 and 2, batteries A to D of the present invention have improved battery characteristics compared to comparative batteries E and F. Considering the reason for this, the solid electrolyte used in the battery of the present invention is made of a sintered mixture of an electrolyte material having a γ''-lithium phosphate type crystal structure and an additive having a lower melting point than the electrolyte material. The low melting point additive added to the electrolyte material during sintering of the material improves the sinterability of the electrolyte material and increases the contact area between the electrolyte materials, resulting in reduced interfacial resistance and improved conductivity. This is thought to be due to.

Note that the additives are not limited to lithium sulfate, sodium chloride, and lithium chloride shown in the examples, but lithium hydroxide LiOH and lithium nitrate LiNO ₃ can also be applied, and the electrolyte materials include Li ₄ SiO ₄ shown in the examples. − Not limited to Li ₃ VO ₄ system, Li ₄ SiO ₄ −
Li ₃ PO ₄ system, Li ₄ GeO ₄ −Li ₃ VO ₄ system, Li ₄ GO ₄ −Li ₃
PO ₄ type or LiSiCON can also be applied.

Furthermore, when producing a solid electrolyte, it is advantageous to integrally mold the electrolyte material and the positive electrode mixture and then sinter them, as shown in the examples, because the contact resistance between the two can be reduced.

[Brief explanation of drawings]

Each of the drawings is a comparison diagram of battery characteristics between a battery of the present invention and a comparative battery, with FIG. 1 showing voltage-current characteristics and FIG. 2 showing discharge characteristics, respectively. A, B, C, D...battery of the present invention, E, F...comparison battery.

Claims (1)

[Claims] 1. A positive electrode, a negative electrode containing lithium as an active material,
A solid electrolyte battery comprising a solid electrolyte obtained by sintering a mixture of an electrolyte material having a γ″-lithium phosphate type crystal structure and an additive having a lower melting point than the electrolyte material. 2. The additive is a chloride or a hydroxide. The solid electrolyte battery according to claim 1, which is a sulfate or a nitrate.