DE2451017A1 - ACCUMULATOR - Google Patents

Description

BASF Aktiengesellschaft

Our reference: O.Z. 30 933 Ki / Yes 67OO Ludwigshafen, October 24, 1974

accumulator

The present invention relates to an accumulator (galvanic secondary battery) with two base electrodes applied electrodes of the first type, the anode containing manganese dioxide as the active material.

The goal of today's battery research is to find accumulators that can be used to power electric vehicles suitable »In addition to the problem-free and frequent cyclability, a favorable ratio of performance or Energy content and weight required.

To achieve this goal is next to further improvement of the so-called lead sulfate accumulator, the use of solution accumulators has been proposed (US-PS 1 425 163, GB-PS 449 893). In these accumulators are the active masses in the discharged state dissolved in the aqueous electrolyte. The advantage is compared to the lead sulfate accumulator in the improved energy / weight ratio, since lightweight base electrodes and leads are used can. Furthermore, the quantitative utilization of the active masses is guaranteed, since there is no containment of the active masses There are oxide or metal particles with non-conductive discharge products, as is the case with lead sulfate accumulators is. PbOp and MnOp are particularly suitable as active positive masses, and Pb, Cd and Zn as active negative masses. In comparison for the lead sulphate accumulator, the following results for the usual acid concentrations in some examples Energy values per unit of weight:

609820/0419

System electrolytic acid

2451017 o.z. 30 933 Conc. Wt.% Wh / kg 30th 30th 50 50 34 93 50 84 72 102 18th 35

Pb / PbO ₂

Pb / PbO "

2 η

Zn / MnO "H ₀ SiF. 2 2 ο

Zn / MnO ₂ HBF ₄ Zn / MnO ₂ HClO ₄ Zn / MnO ₂ NH ₃ SO ₃ H

The table takes into account the weight of power supply lines, base electrodes and vessel material with approx. 25 % of the total weight of a battery as well as 90 % utilization of the capacity. This results in energy values that are improved by a factor of three compared to the lead sulphate accumulator.

The disadvantage of the previously known solution accumulators is essentially their poor cyclability. Farther In the case of the MnOp accumulator, the MnOp is only deposited with low current yields. As the current yields when charging are also different on the cathode and anode side, there is an asymmetrical deposition of the active masses, and the performance of the accumulator is limited by the deposited in poor current yield active mass.

Finally, from DT-OS 1 496 192 there is also an accumulator has become known, which has a base electrode made of titanium on the anode side (positive side), on which a pyrolytically produced coating made of a metal oxide, namely manganese dioxide or lead dioxide, is applied. The base electrode is made of titanium and is expediently porous. A zinc electrode is arranged on the cathode side (negative side), while an acidic, zinc-ion-containing aqueous solution, e.g. zinc sulfate with a pH value of 4.5, serves as the electrolyte. In In this accumulator system, the anode represents an electrode of the second kind, since the manganese dioxide increases during discharge Manganese (III) oxide is reduced on the base electrode

609820/0419

- 3 - O.Z. 50

remains. In contrast, zinc dissolves at the cathode, so that this is an electrode of the first type. During charging, zinc is deposited again on the cathode and the Mn ₂ O is oxidized _{to MnO 2.} This accumulator is therefore not a solution accumulator.

The present invention was based on the object of providing an accumulator with two electrodes attached to the base Electrodes of the first type, the anode being a manganese dioxide electrode, in which the active masses be deposited evenly on both base electrodes with a high current yield.

It has now been found that this object can be achieved in that the base electrode on the negative side consists of graphite powder embedded in a binding agent resistant to the electrolyte and the base electrode on the positive side has a coarsely porous structure and made of graphite or with titanium nitride or titanium carbide Coated titanium has mean pore diameters of 0.1 to 2 mm and a pore volume of 20 to 70 %.

When using the base electrodes according to the invention on the negative side, the one opposite to the electrolyte Resistant binder embedded graphite powder exist, a significant increase in the current efficiency of the Achieve metal deposition even at low current densities. The following table shows some current yields, which have been achieved with pure graphite base electrodes or with the base electrodes according to the invention:

Table 1: current efficiency of the zinc deposition from 1 m ₁ and 1 m ZnZSiFg7 solution (pH = 2) of graphite, and graphite-filled plastic electrode at different current densities (80% by weight of graphite grain size 0.2 mm, 20% by weight polypropylene..). T = 25 ° C. (SA = current yield)

609820/0418

ο.ζ. 30th

Base material Electrolytic acid SA (i = 10 mA / cm ² ) SA (i = 50 mA / cm ² ) graphite HBP ₁₁ 50 % 66 % graphite
fuller H ₂ SiF ₆ 76 % $ 80? plastic HBF ₁₁ 84% 89 % H ₂ SiF ₆ 90 % 94%

Graphite-filled plastic electrodes have a density of 1.6-1.8 g / cm3 and are therefore in the range of the usual types of graphite (1.6-1.9 g / cm3). In contrast to graphite electrodes, however, due to their good mechanical stability, they can be manufactured in very small thicknesses down to the thickness of the film and thus bring about a significant improvement in the energy weight of accumulators. In this way, bipolar electrodes can also be easily produced. The condition is that the plastic used does not react with the electrolyte in the battery or that it is attacked by the products produced during cycling. Polypropylene, polyethylene and polyvinyl chloride have proven particularly successful in long-term cycling tests. The graphite powder can have a grain size of 1 to 500 μ. The purity of the graphite depends on the requirements that are made of the cyclability of the battery. Thus, the graphite mainly in the deposition of Zn, Cd or Mn should be very pure and have an ash content of 0.1 to 0.5 wt.%, Which means that it is free from impurities such as Fe, Co, Ni, Cu, etc. is. Such traces of metal can hinder the cathodic deposition of the metal or promote its corrosion.

609820/0419

The base electrodes can either be pressed at temperatures at which the binder is thermoplastic e.g. temperatures of about 250 ° C, or by injection molding.

Another advantage of the graphite-filled plastic electrodes consists in the lack of porosity of the material. While all types of graphite have a certain porosity, at Mixing and pressing of graphite with plastics to obtain a pore-tight electrode, which ensures that no Electrolyte can penetrate the electrode and destroy it. The life of the base electrodes according to the invention is therefore considerably increased compared to conventional base electrodes made of graphite.

The degree of filling of the binder is 50 to 80 wt.% Of graphite and depends on the desired conductivity of the electrode. Electrodes% graphite and 40 to 20 wt.% Binder are preferably 60 to 80 wt. Used which have a specific conductivity cm 1-3 S /. For problem-free contact, the electrodes can be pressed in a sandwich construction from two graphite-filled plates which enclose a metal plate or mesh between them.

The deposition of the metals Cd, Pe, Zn and Mn from corresponding aqueous salt solutions on the electrodes according to the invention takes place in a uniform layer thickness and free of dendrites.

However, the base electrode on the positive side is also essential. Manganese dioxide can only be deposited with a low current yield on the previously known smooth electrodes. For example, the Ah yield when manganese dioxide is deposited on a smooth and less porous graphite electrode, regardless of the active material on the negative side, is only 5.5 % when fully charged (Wh yield 1.1 %) . When using Pormkodies made of binders in which graphite is embedded, their favorable properties on the negative side

609820/0419 - 6 -

- 6 - O.Z. 30th

have been described above, but as base electrodes on the positive side, Ah yields of only 4.0 % and Wh yields of 1.5 % are achieved.

These yields are significantly increased in the case of the base electrodes according to the invention, which have a coarse-pored structure. Suitable materials for the production of these base electrodes are those that are not passivated, for example titanium that is coated with titanium carbide or titanium nitride or, preferably, graphite. The purity of the graphite depends on the requirements that are placed on the battery, in particular its cyclability. It is expedient to use a graphite with an ash content of 0.1 to 0.5% by weight, which is practically free of impurities such as iron, cobalt and nickel. Preferably, the base electrodes of the invention have an mm average pore diameter of 0.5 to 1 and a pore volume of at least 20% _t preferably from 40 to 60%.

The positive base electrodes are advantageously flowed through by the electrolyte.

Table 2: AH and Wh yield a LÖsungsakkumulators with differently structured positive base electrode Negative base electrode: graphite filled polypropylene (. 80% by weight of graphite) Electrolyte: 1 m 1 m ZnZBF ^ _2. Full and deep discharge

i = 0.5 A / dm ² . T = 25 ° C

609820/0419

Base material Positive Ah-Yield Wh-Yield

smooth graphite 5.5 % 1.1 % graphite-filled polypropylene
80 wt.% Of graphite, smooth surface 4.0 % 1.5 % Graphite, waffle iron structure
Area enlargement 1.8 20 % 10 %

Coarse-pored graphite electrode,
Pore volume 30 % ₉ pore diameter 0.2-0.5 mm, not 55-60 % 30-40 % flow through

Coarse-pored graphite electrode,

Pore diameter 0.5-1 mm, 8Ο-9Ο % 6Ο-7Ο % pore volume 40 % _y flows through

Zinc in particular, but also cadmium, iron (in diaphragm cells) are suitable as active substances on the negative side. Manganese and lead.

All acids that form soluble salts with the metals mentioned and anions that are stable to oxidation are suitable as electrolytes have, such as sulfuric acid, tetrafluoroboric acid, hexafluorosilicic acid, perchloric acid and sulfamic acid, wherein Naturally, when using lead, sulfuric acid is not required. These acids are used in such concentrations and amounts used so that the pH of the electrolyte is below 1 after charging and does not rise above 3 after discharging.

The accumulator according to the invention has compared to that from the DT-OS 1 496 192 known accumulator in addition to the above already The advantages to be derived from the further advantage that it has a higher cell voltage and is more resilient. Even the capacity of the battery according to the invention, based on

609820 / 0A19

- * - ο.ζ. 30 933

• f.

the manganese dioxide deposited during charging is in accordance with the invention Accumulator higher, because here the manganese dioxide as the active mass when discharging into the divalent and not like in the known accumulator is only converted into the three-valued stage.

example 1

20 wt.% Polypropylene and 80 wt.% Iron free graphite of particle size 1 to 4, u is processed in Zweischneckenknetmaschinen. The product is at 25O ° C for 10 minutes with

100 kp / cm pressed. The spec. Conductivity of the base electrodes produced in this way (size: 220 220 χ 2 mm) is 1.5 to 2 S / cm. Before being used in an accumulator, the plates are cut to the required size and the surface cleaned of residues of the polypropylene. This can be done by simply scraping or sandblasting happen.

The plastic plates produced above are used as a negative base electrode in a solution accumulator cell. The contact is made via the plates themselves or via a metallic lead which is pressed between two graphite-filled polypropylene plates. A coarse-pored graphite electrode with a pore volume of 40 % (pore diameter 0.5 to 1 mm) and now 5 in thickness, which is arranged between two negatives, serves as the positive. The volume of the cell is 120 ml. The electrolyte is introduced into one chamber of the cell with a small pump that uses little power and is sucked off in the other chamber on the cell bottom. In this way, the electrolyte slowly flows through the positive. The electrolyte contains 1 m CdZBF ₁ ^ ₂ / Im ₁ ^ solution (pH = 1). The cell is charged and discharged at 1 A / dm. Charging time: 5.8 h (turnover 90 JS). When cycled 200 times, the cell has an average Ah yield of 82 % and an average Wh yield of 65 % . Deep discharge of the cell up to 0.7 V cell voltage.

609820/0419 '

- 9 - ο.ζ. 50 933-

Example 2

In a solution accumulator cell as described in Example 1, 1 m Zn / ClO ^ / Im Mn / ClO ^ is used as the electrolyte. At a current density of 0.5 A / dm, 11.6 h (conversion: 90 %) is charged (i _discharge = ° »5 A / dm ² ). During 170 cycles, the cell delivers an average of 80 % Ah yield and 60 % Wh-yield with deep discharge up to 0.7 V cell voltage.

- 10 -

609826/0419

Claims (6)

Claims 1. Accumulator with two electrodes of the first type applied to base electrodes, the active material containing manganese dioxide on the positive side and acidic electrolyte, characterized in that the base electrode on the negative side consists of graphite powder embedded in a binding agent resistant to the electrolyte and the base electrode has a coarsely porous structure on the positive side and consists of graphite or titanium coated with titanium nitride or titanium carbide, with mean pore diameters of 0.1 to 2 mm and a pore volume of 20 to 70 %. 2 «Accumulator according to claim 1, characterized in that the binding agent is polyethylene, polypropylene or polyvinyl chloride. 3. Accumulator according to Claims 1 to 2, characterized in that the graphite powder has a grain size of 1 to 500-U. 4. Accumulator according to Claims 1 to 3, characterized in that the active material on the negative side is lead, iron, cadmium, manganese or, in particular, zinc. 5. Accumulator according to claims 1 to 4, characterized in that the base electrode on the positive side has a pore diameter of 0.5 to 1 mm and a pore volume of at least 20 % _t, preferably 40 to 60 % _t . 6. Accumulator according to Claims 1 to 5, characterized in that the electrolyte flows through the base electrode on the positive side. BASF Aktiengesellschaft. , / Ppi s 609820/0419