JPH0423381B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a zinc electrode that can be applied to alkaline storage batteries that use silver oxide, nickel oxide, etc. as a positive electrode active material and an alkaline solution as an electrolyte. By controlling the particle size of the substances metal zinc and zinc oxide and adding a wetting agent, it is possible to prevent the crystal size of the negative electrode active material from becoming coarser due to charge/discharge cycles, suppress deformation of the zinc electrode plate, and reduce the zinc The purpose is to compensate for insufficient diffusion of the electrolyte within the electrode, minimize the decrease in battery capacity, and improve the cycle life of the battery.

[Background technology]

Conventionally, zinc storage batteries that use metal zinc as an active material in the negative electrode have a high energy density and are free from pollution because zinc is cheap and has a lower potential in alkaline electrolyte than a cadmium electrode. Because of its small size, many studies have been made to put it into practical use.

However, there are drawbacks such as a lack of reliability due to a short circuit phenomenon between the positive and negative electrodes caused by zinc dendrites during the charge/discharge cycle, and difficulty in obtaining a long cycle life due to significant deformation of the zinc electrode during the charge/discharge cycle. be. This is due to the fact that zinc is an electrode that is soluble in an alkaline electrolyte.

Thus, it is known to use a mixture of metallic zinc and zinc oxide as a zinc active material. However, conventionally used metallic zinc has a particle size of several tens of microns to several hundred microns, while zinc oxide has a particle diameter of several tenths of a micron, which is two to three orders of magnitude smaller than that of metallic zinc. be. As described above, the particle size of conventional metal zinc is particularly large compared to the particle size of zinc oxide, resulting in the following drawbacks. First, since the difference in particle size is as large as two or three orders of magnitude, metallic zinc and zinc oxide are not mixed uniformly. Second, because the particle size is large, even if the same amount of metallic zinc is mixed, the number of particles is small and the number that becomes the nucleus for electrodeposition is small, so the zincate ions that are discharge products are returned to their original state during the next charge. It becomes difficult to electrodeposit on the position. Thirdly, since the particle size of the original metal zinc is large, it quickly grows into coarse zinc particles that become the core of dendrite generation.

In order to deal with this problem, we proposed in Japanese Patent Application No. 41843/1983 that the particle diameters of the active materials, metal zinc powder and zinc oxide powder, should be regulated. That is, the particle size of the metal zinc powder is 1 to 6μ, and the particle size of the zinc oxide powder is 0.1 to 0.5μ. By regulating the particle size in this way, it is possible to prevent the crystal size of the active material from becoming coarser due to charging and discharging cycles, suppress deformation of the electrode plate, minimize capacity loss, and improve the cycle life of the battery. can.

However, as charge-discharge cycles are repeated over a longer period of time, the regulated zinc particles gradually become coarser and denser, reducing the number of zinc particles that should form the nucleus of zinc electrodeposition. . As a result, non-uniform electrodeposition occurs, the effective area of the zinc electrode is reduced, and the porosity is reduced, which impedes internal diffusion of the electrolyte and reduces electrical conductivity. That is, a passivation phenomenon occurs, leading to an accelerated deterioration in the utilization rate of the active material as charging and discharging are repeated.

[Disclosure of the invention]

The present invention has been devised in view of these points, and is intended to alleviate the above-mentioned problems and improve the cycle life of a storage battery when applied to a storage battery. That is, the present invention provides a zinc active material consisting of a zinc oxide powder having a particle size of 0.1 to 0.5μ and a metal zinc powder having a particle size of 1 to 6μ, an organic or inorganic wetting agent, and a hydrogen gas generating material. The zinc electrode is made up of an additive that suppresses oxidation and a binder. As is clear from this configuration, the present invention suppresses the deformation of the zinc electrode and improves the cycle life of the battery by regulating the particle size of the active materials, metal zinc powder and zinc oxide powder. Its presence compensates for insufficient diffusion of the electrolyte within the zinc electrode, thereby further improving cycle life.

〔Example〕

Examples of the present invention will be described below, as well as comparative examples.

Example 1 100 parts by weight of zinc oxide powder with a particle size of 0.1 to 0.5μ, 10 parts by weight of metal zinc powder with a particle size of 1 to 6μ, as an additive that increases the hydrogen overvoltage of the zinc electrode and suppresses hydrogen generation. A mixed powder of 2 parts by weight of mercury oxide and 2 parts by weight of polyvinyl alcohol as a wetting agent was mixed with a dispersion of polytetrafluoroethylene (concentration 60%) as a binder.
Add parts by weight and 50 parts by weight of water, and knead while applying shearing force. The obtained kneaded material is rolled using a rolling roller.
Paste sheets rolled to a thickness of 1.0 mm are brought into contact with both sides of the cathode current collector and rolled and crimped to obtain a zinc electrode with a thickness of 1.5 mm.

These 5 zinc negative electrodes and 4 well-known sintered nickel electrodes
Nickel-zinc storage battery A with a capacity of 2AH using
It was created.

Note that conventional metallic zinc powder with a size of several tens of microns to several hundred microns is produced by melting metallic zinc once in a reducing atmosphere and blowing it out in a spray form from a nozzle, whereas the powder used in the present invention The metal zinc powder with a size of 1 to 6μ is obtained by melting metal zinc in a reducing atmosphere, evaporating it, and condensing it.

FIG. 1 is a sectional view of this storage battery A. In this drawing, 1 is a zinc electrode, 2 is a nickel electrode, 3 is a separator, 4 is a liquid retaining layer, 5 is a battery case, 6 is a battery cover, and 7 and 8 are positive and negative electrode terminals.

Example 2 The battery A was the same as the storage battery A in Example 1, except that titanium oxide powder, which was an inorganic wetting agent, was used instead of polyvinyl alcohol, which was used as an organic wetting agent in Example 1. Storage battery B was created.

Comparative Example For comparison, a storage battery C was prepared which was the same as the storage battery A in Example 1 except that polyvinyl alcohol as a wetting agent was not used.

Figure 2 shows a storage battery A using zinc electrodes according to the present invention.
2 is a charge/discharge cycle characteristic chart of B and comparative battery C. FIG. The charging and discharging conditions were to charge at 400 mA for 5 hours and then discharge at 500 mA until the battery voltage reached 1.0V. FIG. 2 shows the initial capacity as 100 as discharge capacity.

It can be seen from FIG. 2 that the cycle characteristics of storage batteries A and B using the zinc electrode according to the present invention are improved compared to the cycle characteristics of comparative battery C.

The reason for this improvement is thought to be that polyvinyl alcohol and titanium oxide are wetting agents and therefore effectively compensate for the lack of electrolyte diffusion caused by the reduced porosity of the zinc electrode. Although polyvinyl alcohol and titanium oxide are used as examples in the examples, other wetting materials such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, sodium alginate, and glucon may be used as long as they have wettability and do not adversely affect battery performance. Organic substances such as acids, and inorganic substances such as oxides, hydroxides, or acid salts (for example, sodium silicate) of zirconium magnesium, calcium aluminum, silicon, etc. can be used. The content ratio of wetting material is 0.1
If it is less than 0.1 parts by weight, it has almost no effect, and if it exceeds 25 parts by weight, it reduces the amount of zinc active material and increases the internal resistance of the zinc electrode.
~25 parts by weight is good, preferably 0.3 to 10 parts by weight.

〔effect〕

As described above, the present invention prevents coarsening of the crystal size of the negative electrode active material due to charge/discharge cycles by controlling the particle size of the metal zinc powder and zinc oxide powder that are the active materials of the zinc electrode and adding a wetting agent. It has great industrial value, as it can prevent deformation of the zinc electrode, compensate for insufficient diffusion of the electrolyte in the zinc electrode, and extend the cycle life of storage batteries using this zinc electrode. It is.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an alkaline zinc storage battery using the zinc electrode according to the present invention, and FIG. 2 is a cycle characteristic diagram of an alkaline zinc storage battery using the zinc electrode according to the invention and a comparative battery.

Claims (1)

[Claims] 1. A zinc active material consisting of zinc oxide powder having a particle size of 0.1 to 0.5μ and metal zinc powder having a particle size of 1 to 6μ, an organic or inorganic wetting agent,
A zinc electrode consisting of an additive that suppresses the generation of hydrogen gas and a binder.