HK1005964B - Cathode additive for alkaline primary cells - Google Patents

Description

Cathode additive for primary alkaline batteries

Technical Field

The invention relates to a primary alkaline battery comprising zinc gel as anode material, an aqueous alkaline electrolyte, a separator and a cathode material comprising manganese dioxide.

Background

The cathode for a primary alkaline cell typically comprises manganese dioxide, graphite, and a binder.

Electrolytes, surfactants and other additives may also be present.

Manganese dioxide, particularly in electrochemically deposited form (EMD), is suitable for the cathode active material.

High-purity synthetic graphite or expanded graphite prepared from natural graphite can be added as a conductive material to the cathode material, and in this case, it is usually used in the form of, for example, 10 to 50 m-diameter powder in the case of synthetic graphite, and 1 to 20 m-diameter powder in the case of expanded graphite. When graphite is uniformly dispersed as a primary matrix of a conductive skeleton in a cathode molded electrode, the graphite functions to ensure charge transfer within the cathode. When synthetic graphite is used, the weight of the graphite is usually 7 to 10%. If expanded graphite is used, specialized mixing techniques can be applied to reduce the weight of the graphite to about 5% while improving the discharge characteristics of the cathode.

In many cases, the cathode consists of a number of cathode rings inserted into the cell casing. The mechanical strength required for these cathode compacts may be provided by a binder. Modern manufacturing plants producing primary alkaline cells operate at very high production speeds. For example, a production rate of 1000 LR6 size batteries per minute can be achieved. These so-called "high speed production lines" impose certain minimum requirements on the mechanical strength of the cathode rings at the feed conveyor line and the clamping plates.

One disadvantage of most adhesives is that they require a large volume which is difficult to achieve with active materials. Also, many binders are hydrophobic, and thus, they hinder the absorption of electrolyte by the cathode during the process of manufacturing the battery. This may adversely affect the performance of the battery.

Typical binders are powdered plastics made from polymers such as Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), Polytetrafluoroethylene (PTFE), Polyacrylates (PA), Polybutadiene (PB) and block polymers or copolymers of the above. It is also known to add the binder in the form of an aqueous dispersion (for example a PTFE or PE dispersion), the water added also having certain properties of the binder for the cathode compact.

The cathode material also comprises an added alkaline electrolyte, preferably a 10-55% potassium hydroxide aqueous solution. Binary electrolytes, such as KOH/NaOH or KOH/LiOH, and ternary electrolytes, such as KOH/NaOH/LiOH, may also be used.

The electrolyte is a substance that fills the voids of the cathode and can impart ionic conductivity to the cathode. In this way, a number of defined properties can be obtained. In this way, the amount of binder can be dispensed with in whole or in part, since these alkaline solutions likewise have certain properties of the binder for the cathode compacts. The choice of the appropriate amount of electrolyte allows the use of a cathode having the greatest porosity, with the result that the membrane resistance of the cathode compact is reduced to a minimum. The reduction in membrane resistance in turn can significantly improve the performance of the overall cell. Cathodes containing, for example, 6% by weight of a strongly basic electrolyte of 50% KOH can improve the discharge characteristics of cells made with such cathodes, as compared to those containing little or no electrolyte. Also, post-storage contact resistance from the battery case to the cathode ring can be significantly reduced by means of a high concentration of the electrolyte.

However, the manufacturing methods using cathodes with high electrolyte content in the cathode material have some disadvantages compared to those with dry cathode mixtures. These cathode compacts are generally manufactured using a so-called rotary disk type press die. These rotating disk type dies are typically made of special steel alloys that are resistant to significantly increased corrosion when the electrolyte content in the cathode formulation is increased.

The addition of a surfactant to the cathode material can improve the absorption of the electrolyte by the cathode. The surfactant is typically added at a very low concentration, for example 1 to 100ppm based on the weight of the cathode, and may be added either uniformly to the cathode mixture or in a preliminary step to the graphite component to reduce the hydrophobicity of the graphite.

In general, surface-active substances may be liquid or solid and may be nonionic, anionic or cationic. For example, aliphatic fluorocompounds, aromatic and aliphatic phosphoric acids or polyethylene glycols are suitable for use.

However, such surfactants sometimes also expose a disadvantage, in which case, owing to their high molecular mobility, they can reach the zinc electrode as counter electrode and thus lead to certain discharge phenomena (for example pulsed discharges), which cause a voltage drop.

Other additives suitable for use include mainly titanium compounds.

U.S. Pat. No. 5,342,712 proposes converting anatase TiO to anatase TiO₂As an additive to the cathode. In order to increase the service life of the alkaline galvanic cells by 15% at higher currents (3.9 discharge), it is necessary to add 0.1 to 2% by weight of titanium dioxide-modified anatase to the cathode material of the alkaline galvanic cells.

However, it is still desirable to use a dry composition cathode, i.e., no or little electrolyte, despite the advantages of a paste cathode in the assembled cell, and to extend the working life of the rotating disk mold used to prepare the cathode, which results in a cost savings in the manufacturing process.

Disclosure of Invention

It is an object of the present invention to provide a solution to the above problems.

According to the invention, this object is achieved in that the cathode material of the primary alkaline battery contains 0.1 to 5 wt.% of an alkali metal titanate and/or an alkaline earth metal titanate.

Preferably, the cathode material of the primary alkaline battery contains magnesium titanate (MgTiO)₃) And/or calcium titanate (CaTiO)₃) And/or lithium titanate (Li)₂TiO₃)。

Mixing magnesium titanate (MgTiO)₃) And/or calcium titanate (CaTiO)₃) And/or lithium titanate (Li)₂TiO₃) The addition of the cathode material can improve the discharge performance of the battery and reduce the amount of exhaust gas in the battery.

The method of the invention for producing a primary alkaline battery comprises adding an alkali metal titanate and/or an alkaline earth metal titanate in powder form to a cathode material containing 4 to 5 wt.% of an electrolyte.

It is preferred that the alkali metal titanate and/or alkaline earth metal titanate added to the cathode material has a particle size of 0.1m to 200m and a BET surface areaIs 0.5 to 500m²/g。

The purity of the alkali metal titanate and/or alkaline earth metal titanate added to the cathode material is preferably 95% or more.

Drawings

FIG. 1 shows a CaTiO-containing compound₃The LR20 battery (1) and the reference battery (2) were compared by discharging continuously through a 2-resistor. It can be seen as an advantage that the battery (1) has a much longer operating time at an open circuit voltage below 0.95V.

Detailed Description

The invention will now be described with reference to the following examples.

Examples

Comprises the following components:

EMD of 86.0%

9.0% of graphite

A 4.5% cathode mixture of electrolyte (50% KOH strong base) was mixed with 0.2%, 0.5%, or 2% by weight of the following titanates:

MgTiO₃magnesium titanate

CaTiO₃Calcium titanate or

Li₂TiO₃And mixing lithium titanate.

For comparison purposes, a cell without titanate addition (reference cell) and a cell containing 0.5% by weight of anatase TiO in the cathode material thereof were prepared₂The battery of (1).

The mixture is granulated and then densified to produce an annular compact. The rings are connected by a connecting ringThe compact is pushed into the battery case and then a separator, which may be in the form of a honeycomb or a coil, is inserted therein. And then metered into a gel-type zinc electrode. The zinc anode contains 68% by weight of zinc powder, which typically has a particle size distribution in the range of 50 to 500m, and about 32% by weight of alkaline electrolyte (e.g., 40% KOH strong base). The anode may additionally be admixed with a small amount of gassing inhibitor (e.g., In)₂O₃Or in (OH)₃) A gelling agent (e.g., Carbopol 940), a surfactant (e.g., ethylene glycol, polyethylene glycol, or a fluorosurfactant).

Table 1 shows the results of experiments conducted using various titanium compounds with respect to the cell performance and the exhaust gas condition. These results show that MgTiO₃、CaTiO₃Or Li₂TiO₃Not only can improve the continuous and intermittent discharge characteristics of the battery, but also can reduce the exhaust gas quantity of the battery.

TABLE 1

Model LR6	Titanium compound	3.9 Ω capacity, hr → 0.75V	Pulse cycle → 0.9V15s/m, 7d/w-1.8 omega	Rapid cycle → 1V15s/m, 1h/d, 7 d/w-2. omega	Exhaust gas volume (ml) without initial discharge 7d at 70 deg.C	The gas displacement (ml) at the initial discharge was 7d at 70 deg.C
							Mignon	0.5％MgTiO30.5％Li2TiO30.5％TiO2Anatase 0.2% MgTiO3Reference to	1.811.801.781.841.731	604555519578525	505495393485471	0.30.30.40.30.4	0.30.30.40.30.4

Model LR20	Titanium compound	2 Ω capacity, hr → 0.9V	Exhaust gas volume (ml) without initial discharge 7d at 70 deg.C	The gas displacement (ml) at the initial discharge was 7d at 70 deg.C
					Mono	0.5％CaTiO30.5％Li2TiO30.5％TiO2Anatase 0.2% MgTiO32％CaTiO3Reference to	9.29.48.89.19.18.6	3.33.73.83.92.93.9	5.56.36.35.867.7

Claims (4)

1. An alkaline primary battery comprising a zinc gel as an anode material, an aqueous alkaline electrolyte, a separator and a cathode material comprising manganese dioxide, characterized in that the cathode material comprises 0.1 to 5% by weight of lithium titanate (Li)₂TiO₃)。

2. The primary alkaline cell of claim 1, wherein said lithium titanate (Li)₂TiO₃) The electrolyte is added into a cathode material containing 4-5 wt% of electrolyte in the form of powder.

3. The primary alkaline battery of claim 2, wherein the lithium titanate (Li) incorporated into the cathode material₂TiO₃) Has a particle diameter of 0.1 to 200 μm and a BET surface area of 0.5 to 500m²/g。

4. The primary alkaline cell of claim 3, wherein the added lithium titanate (Li)₂TiO₃) Is higher than 95%.