JPS63266764A - Negative electrode for secondary battery - Google Patents

Abstract

PURPOSE:To obtain an electrode which is lightweight and has large specific surface area and good workability as the negative electrode of a secondary battery which takes in and out lithium ions by heat-bonding aluminum-low melting point metal alloy powder to a thin film-like electrode substrate with a binder. CONSTITUTION:Aluminum-low melting point metal alloy powder comprising 80-99% aluminum and 1-20% at least one of Mg, Pb, Sn, Bi and In in an atomic ratio is heat-bonded the mesh like substrate of expanded metal or punched metal with a binder comprising olefin base thermoplastic polymer such as polyethylene and polypropylene which is less reactive with alkali metal to form a negative electrode. The aluminum-low melting point metal alloy powder is bonded to the thin electrode substrate plate with electrochemical activity retained, and the electrode having high mechanical strength and large specific surface area can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary battery, and more particularly to a non-aqueous electrolyte secondary battery using an aluminum alloy as an electrode for taking in and taking out lithium ions.

BACKGROUND OF THE INVENTION Secondary batteries using lithium metal as a negative electrode active material are characterized by the ability to achieve high energy density, and several batteries have been proposed to date. For example, titanium disulfide,
There is a method of using an interlayer compound such as graphite or molybdenum disulfide as a positive electrode active material. Furthermore, in recent years, there has been progress in the development of devices that utilize doping and doping of conductive polymers such as polyacetylene. However, in any of these battery systems, the lithium metal used in the negative electrode precipitates in a dendritic structure, resulting in a decrease in charge/discharge efficiency or short circuits.

As countermeasures against this problem, several proposals have been made in the past. For example, there is a method of adding a substance that suppresses dendritic precipitates of lithium to the electrolyte, or a method of alloying lithium to form a negative electrode. Typical alloys include those alloyed with aluminum, lead, tin,
It is known that it is alloyed with a low melting point metal that can absorb lithium, such as bismuth. For alloys of aluminum and lithium, see Japanese Patent Application Laid-Open No. 48-33811 and Japanese Patent Publication No. 4
5 to 30 ffi as described in Japanese Patent No. 8-33812
% of aluminum is added. In this method, the alloy is melted and deposited onto the electrode substrate.

Further, in the method described in Japanese Patent Application Laid-Open No. 52-54)3, a method is used in which alloy powder is sintered and molded into an electrode.

On the other hand, as for the method of alloying lithium with lead, tin, bismuth, etc., as described in JP-A-60-131776, the powder of the above alloy is kneaded with ethylene tetra7ide resin and applied to the electrode base material. There is a way to do it.

Furthermore, as a method for manufacturing electrodes using aluminum alloy powder, Japanese Patent Application Laid-Open No. 59-217%5 discloses a method in which aluminum alloy powder is filled and held in a porous body such as a foamed metal.

Problems to be Solved by the Invention Among the conventional methods mentioned above, in the case of alloy powders of lithium and low-melting point metals such as lead, tin, and bismuth, the powder is kneaded with a binder and applied, so there is no reaction activity during cross-talk. There was a problem in that the strong lithium reacts with the solvent, binder, etc., and the electrode after molding tends to become electrochemically inactive. Furthermore, Li reacts with ethylene tetrachloride during charging and discharging, reducing efficiency.

Means to solve problems The purpose of the present invention is to introduce and extract lithium ions.

In order to solve the above problems, we investigated a method for manufacturing electrodes using an aluminum-low melting point metal alloy.

In order to suppress the formation of dendritic precipitates of lithium, it is effective to use an alloy with a high aluminum content as the electrode for 1ζ. Journal of the Electrochemical Society, Volume 124, 1490 by B. M. L. Rao, R. D. Francis, and H. A. Christopher, 1977 (B, M.
,L.R.Q.O.

R, W, Francis, H, A, Chris
tophen, J, Electochem, So
c.

Vol, 124 (1977), pp, 1490)
As described in , in alloys containing 20% or more aluminum in atomic ratio, the potential of lithium dissolution and precipitation is 0.3 to 0.4 V higher than that of pure lithium metal, and the lithium ions in the electrolyte are The formation of dendritic precipitates is difficult because lithium does not precipitate as lithium metal, but forms a solid solution and alloys in aluminum.

However, when the aluminum content increases in a lithium-aluminum alloy, the alloy becomes brittle and loses its ductility.

In addition, the efficiency of dissolving and depositing lithium in a lithium-aluminum alloy is about 90%, and since the reaction is not completely reversible, there is a problem that the charge-discharge cycle characteristics are poor.

As a solution to these problems, we came up with a method of thermocompression bonding an aluminum-low melting point metal alloy powder to a thin film electrode base material using a suitable binder. Since powder electrodes have a large surface area, they have the effect of lowering the actual current density. In addition, in order to bind the lithium-free aluminum-low melting point alloy powder to the electrode base material due to the binding effect of the halogen-free olefin compound, lithium and binder, solvent, etc. It is possible to prevent reactions with the material and also prevent it from falling off during winding.

1ζ when thermocompression molding aluminum-low melting point alloy powder
The issues are the selection of the binder and the conditions of the manufacturing process. As a base material for thermocompression molding, a mesh metal such as expanded metal or punched metal, which is commonly used in 6ζ, may be used.

On the other hand, with regard to the binder, care must be taken in selecting the binder because the lithium ions taken in during charging after battery installation are highly reactive.

Alcohol-based binders are used to producing lithium hydroxide. It is also believed that halide-based binders also generate lithium halides. Most desirable are olefin-based thermoplastic polymers. Examples include polyethylene, polypropylene, etc. These polymers are softened into a molten state by heat treatment, and have the function of binding aluminum, a low melting point metal, to the electrode base material. The temperature at that time is preferably slightly lower than the softening point.

Function The above polymer powder, aluminum-low melting point metal, carbon powder, and carbon fiber are mixed. The electrode is produced by thermocompression molding the mixture onto an electrode base material such as an expanded band, and the binding effect of the binder is exerted. The temperature at that time is preferably lower than the softening point of the polymer, and the pressure is also preferably about the compression molding pressure of the polymer. In addition, aluminum-low melting point alloys tend to form an oxide film in the air, so
It is necessary to process in an inert gas atmosphere or vacuum.

After cooling, the electrode produced in this manner can be combined with a suitable positive electrode in an inert gas atmosphere to form a radio wave.

Example Next, examples and comparative examples of the present invention will be described.

Example 1 87 parts by weight of powder (100 mesh or less) of aluminum-magnesium alloy (atomic ratio 97; 3), 10 parts by weight of polyethylene powder, carbon 7 eyeper (φ6 μm x 2
-) Add 3 parts by weight (mix and place on a 9φ punched expanded metal made of 5US316 at
Thermocompression molding was carried out at 10° C. and a pressure of 200 kof/−. This was incorporated into a cell as shown in FIG. 1, with an excess lithium aluminum alloy (atomic ratio 50:50) as a counter electrode and a working electrode. The electrolyte is purified 1 mol//
A charge/discharge test was conducted using a propylene carbonate-dimethoxyethane mixed solvent (volume ratio 1:1) containing LtBF+. The charging and discharging conditions were a current density of 0.5 mA/cd and an electrode utilization rate of 10%. Figure 2 shows the change in the number of cycles and coulombic efficiency at that time. From FIG. 2, after maintaining the Coulombic efficiency close to 100% in the initial stage, the efficiency stabilized at around 95%, and even after 100 cycles, the efficiency was still over 90%.

Example 2 Aluminum-magnesium alloy powder (atomic ratio 97:3
．． 10 parts by weight of polypropylene powder, 3 parts by weight of carbon powder, and carbon fiber were added to 87 parts by weight (100 mesh or less) and mixed. The mixture was thermocompression molded on an extract υ band metal (SYS 316.9φ) at a temperature of 180° C. and a pressure of 200 kg/−, and a charge/discharge test was conducted in the same manner as in Example 1.

The relationship between the charge/discharge cycle and the coulombic efficiency at that time is shown in FIG. The coulombic efficiency was maintained at nearly 100% at the beginning of the charge/discharge cycle, and thereafter the efficiency stabilized at around 95%, and even after 100 cycles, the efficiency was still over 90%.

Comparative Example 1 Aluminum-magnesium alloy powder (atomic ratio 97:3
．． (100 meshes or less) 10 parts by weight of polyethylene powder was added to 90 overlapping parts and mixed. The mixture was heated to a temperature of 110°C.
℃ and a pressure of 200 kgf/aJ, and a charge/discharge test was conducted under the same conditions as in Example 2.

The relationship between the charge/discharge cycle and the coulombic efficiency at that time is shown in FIG. At the beginning of the charge/discharge cycle, the coulombic efficiency remained close to 100%, but after that, the coulombic efficiency stabilized at about 95%, and after 100 cycles, the coulombic efficiency decreased to 60%.

In Fig. 1, 1 is a Teflon cell, 2 is lithium, 3 is a separator, 4 is a sample, 5.5' is a current collector, and 6
is a Teflon lid.

Effects of the Invention As described above, according to the present invention, it is possible to process aluminum-low melting point alloy powder while retaining electrochemical activity in the thin electrode base material, so that it has a high strength and a substantially large specific gravity area. It has great industrial value, as electrodes can be produced, and it can therefore be applied to batteries of various shapes, enabling batteries with high current density.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the battery used in the present invention, and FIG. 2 is a curve diagram showing the relationship between charge/discharge cycles and coulombic efficiency.

Claims (1)

[Claims] 1. In a secondary battery using a non-aqueous solvent, a base material, an alloy powder made of aluminum and one or more types of low melting point metal, carbon powder, or carbon fiber, or both, and A negative electrode for a secondary battery, characterized in that it is composed of a binding organic compound. 2. The negative electrode for a secondary battery according to claim 1, wherein the organic compound is an olefinic polymer having low reactivity with alkali metals. 3. A patent claim in which the alloy of aluminum and a low melting point metal is an alloy powder consisting of 1 to 20% of any one or more of magnesium, lead, tin, bismuth, and indium and 80 to 99% of aluminum in terms of atomic ratio. A negative electrode for a secondary battery as described in Scope 1.