CS248152B1 - Negative iron accumulator mass and method of its production - Google Patents

Abstract

The negative iron battery mass is intended primarily for the production of nickel-iron batteries. It contains iron, usually in the form of its oxides, carbon in a conductive form, for example in the form of carbon black or modified graphite, an alkali metal hydroxide and an activator, which is lithium, usually in the form of lithium hydroxide monohydrate and sulphide sulphur, for example in the form of sodium sulphide, in a total amount of 0.4 to 0.7% by weight and in a mutual mass ratio of 1:1 to 1.5.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative iron storage mass, in particular for the production of nickel-iron accumulators comprising: as a rule, iron in the form of its oxides, carbon in a conductive form, for example in the form of carbon black or optionally treated graphite, an alkali metal hydroxide and an activator, and a process for producing the composition.

For the production of the iron electrode mass of nickel-iron accumulators mainly natural iron ores are used, which are treated by various technological operations before being used in the electrode system of the iron electrode. These operations include, in particular, removal of the admixtures by flotation or gravity and subsequent reduction at elevated temperature with hydrogen, optionally methane, iron powder or soot to the final composition of the iron electrode mass, which is a mixture of iron powder and ferrous iron oxide with ferrous sulphide.

To improve the electrochemical properties, various dopants are added to the iron electrode materials. Of these, the use of sulfide ions in the form of sodium sulfide appears to be most effective, either in the electrolyte or by activating the iron electrode mass with a sodium sulfide solution.

In addition, it is also possible to use sulfur in elemental form or in the form of ferrous sulphide, which is most often used as an additive to the ferrous material itself. The presence of sulphide ions positively affects the mechanism of function of the iron electrode in terms of both capacity and charging process and self-discharge of the iron electrode.

Nickel, copper and mercury also have a beneficial effect on the function of the iron electrode.

The lithium salts used as additives in the electrolyte of both nickel-iron and nickel-cadmium cells, as mentioned in a number of applications, primarily affect the capacity of the nickel electrode and thus the life of the cells.

The influence of lithium salt on the function of the iron electrode of the nickel-iron accumulators is only modest in the literature, which in addition explains the influence of this additive on the function of the nickel-iron cell in various ways. One of these works (Falk SM, Salkind AJ, Alkaline Storage Batteries, John Wiley and Sons, Volume I, p. 616, 1969) reports the negative influence of iron on the nickel electrode function, which is eliminated by the presence of lithium in nickel-iron electrolyte. articles. This elimination effect is explained by the formation of lithium-iron alloys. However, the misguided mechanism has not been confirmed.

Another work (Hills S., J. Electrochem. Soc. 112, 1048, 1965) describes the positive effect of lithium on the function of both nickel and iron electrodes, while others (Crenell, JT and Lea FM, Alkaline Accumulators, Longmaus, Green and Co., London, pp. 103, 1928), it is only stated that the influence of lithium on the function of the iron electrode cannot be excluded.

The fact is that lithium is not yet used in ferrous electrode materials. When lithium hydroxide is added to the electrolyte of nickel-iron cells, this is done solely to prolong the life of the nickel electrodes, which limit the overall life of the nickel-iron and nickel-cadmium cells.

Published papers from this field document that chemical activation of iron electrode mass remains an open problem and at the same time one of significant ways of further improvement of functional properties of iron electrode in accumulator as electrochemical system. This is also confirmed by the results of experimental work carried out by the author, focused on the study of the effect of known activating additives on the function of the iron electrode, both individually and in various combinations, the aim of which was to achieve better utilization of the theoretical iron capacity.

These drawbacks are eliminated by a negative iron storage mass, in particular for the production of nickel-iron accumulators, comprising iron in the form of its oxides, carbon in conductive form, for example in the form of carbon black or optionally treated graphite, alkali metal hydroxide and an activator according to the invention. in which the negative iron accumulator thus determined contains lithium and sulphide sulfur as activator in a total amount of 0.4 to

0.7% by weight and in a weight ratio of 1: 1 to 1.5: 1.

The most suitable form in which lithium may be applied is lithium hydroxide as the monohydrate - LiOH. H ₂ 0. sulphide suits soluble alkali metal sulfides, sodium sulfide, namely potassium sulphide. The negative iron storage mass according to the invention in this composition preferably contains 1.2 to 2% by weight of LiOH. H ₂ O and 0.5 to 0.7% by weight of sodium sulfide Na ₂ S.

The process according to the invention consists in adding the two activator components together in a sodium hydroxide solution at a temperature in the range of 50 to 90 [deg.] C. and with stirring to the basic iron component.

The negative iron storage mass prepared by the process of the invention is preferably applicable to existing types of nickel-cadmium accumulators, in which it replaces cadmium in its entirety. The physico-chemical properties of this material allow its processing by the battery manufacturer on existing types of equipment.

The synergistic effect of both activator components, ie lithium and sulphide sulfur, is very well evidenced by the results of measuring the practical utilization of the theoretical iron capacity in the 1st to 5th discharge-charge cycles of a total of 8 types of ferrous material carried out by the stripping test for nickel-cadmium electrodes and arranged in Table 1.

Table 1

Utilization of theoretical iron capacity in% (Cj, denotes theoretical capacity of 1 g Fe = 0,96 Ah)

Sample g Fe in 1 g wt. C _T .g ^ wt. Ah 1. 2. With recovery 3. C _T At 4. cycle 5. Activator 20483 0.610 0.5856 9.37 24.90 20.75 19.85 18.35 - 20483/1 0.610 0.5856 46.92 32.15 29.16 28.33 27.51 If 20483/2 0.610 0.5856 22.47 27.56 29.78 28.35 28.31 Na ₂ N 20483 / A2 0.601 0.5770 30.40 37.53 37.47 35.36 35.30 Li + Na ₂ S 10183 0,600 0.5760 28.40 ’26.31 36.60 36.60 36.60 dtto 80583 0.565 0.5424 38.66 32.49 30.11 30.08 30.05 Li + K ₂ S 80583 / A2 0.556 0.5338 34.08 33.97 33.85 33.86 33.82 dtto 90583 0,622 0.5971 39.01 38.03 37.95 37.92 37.94 Li + Na ₂ S

The chemical compositions of the negative ferrous materials that have been subjected to the above measurements are listed in Table 2.

Table 2

Chemical composition of samples in% by weight

Sample Fe C «2 ° LiOH.HjO Na ₂ N x ₂ sec Li + S Press 20483 61,00 5.02 3.15 - - - - - 20483/1 59.30 4.98 3.00 1.57 - - - - 20483/2 60.07 5.01 3.10 - 0.60 - - - 20483 / A2 60.09 5.18 2.71 1.75 0.66 - 0.56 1.07 10183 60.01 4.80 5.41 1.87 0.62 - 0.56 1.24 80583 56.46 4.72 10.01 1.93 - 0.90 0.58 1,23 80583 / A2 55.64 3.72 9.78 1.51 - 0.82 0.49 1.04 90583 62.17 3.10 6.06 1.81 0.60 - 0.55 1.20

Note: For sample 90583, ferric iron Ί * 2 +3 was used as the basic iron component

Fe-O případech, in all other cases of iron oxides Fe-O ^ having a different Fe: Fe ratio obtained after the reduction of nitrobenzene with iron according to the author's certificate No. 218 931.

Examples

Example 1

5,000 g of Fe _x Oy, obtained after the reduction of nitrobenzene with iron, are introduced into the homogenization mixer and activated with stirring with a sodium hydroxide solution of a specific weight of 1200 kg. m ³ in an amount of 450 ml with the addition of 100 g LiOH. H 2 O and 40 g Na 2 S. The activation solution is heated to 85 ° C before activation and then added dropwise to the stirred contents of the mixer. After 40 minutes of homogenization from the end of the activation, 260% carbon black is added as a conductive component and the mixture is again homogenized.

A mass of composition and parameters corresponding to sample 20483 / A2 and a bulk density of 940 kg is obtained. m ³ .

Example 2

The procedure is analogous to Example 1 except that 100 g of LiOH is used as activator. H ₂ O and 55 g K ₂ S, the activation solution is heated to 60 ° C before being added to the iron component, and 220 g of graphite are added as a conductive component after the homogenization.

A mass of composition and parameters corresponding to sample 80583 / A2 and a bulk density of 960 kg is obtained. m ³ .

Claims (3)

SUBJECT OF THE INVENTION Negative iron accumulator mass, intended in particular for the production of nickel-iron accumulators, containing iron generally in the form of its oxides, carbon in conductive form, for example in the form of carbon black or modified graphite, alkali metal hydroxide and activator, characterized in that it comprises lithium and sulphide sulfur in a total amount of 0.4 to 0.7% by weight and in a weight ratio of 1: 1 to 1.5: 1 to each other. 2. A negative iron storage mass according to claim 1, characterized in that it contains 1.2 to 2.0% by weight of LiOH. And 0.5 to 0.7% by weight of Na2SO4. 3. A method for producing a negative iron storage mass, wherein the two components of the activator are added together in a sodium hydroxide solution at a temperature in the range of 50 to 90 ° C and with stirring to the basic iron component.