RU2020656C1 - Method of forming of metal hydride cell - Google Patents

Abstract

FIELD: alkaline metal-hydride cells. SUBSTANCE: method of forming comes to combining operations of charging and filling the can with hydrogen whose amount is found from formula given in description of invention. EFFECT: enhanced quality.

Description

 The invention relates to the electrical industry, in particular to the production of metal-gas batteries, and can be implemented in the manufacture of metal hydride batteries.

Known metal-hydrogen electrochemical systems, the negative electrode of which, activated by platinum or platinum-palladium, operates in the electrochemical oxidation of hydrogen [1]. Metal hydride batteries (MGA) are second-generation metal-gas systems. Their feature is the use of hydrogen-absorbing intermetallic compounds operating in the regime of reversible electrochemical absorption of hydrogen [2]. Mostly these are compounds based on LaNi ₅ or amorphous alloys of Ti, Ni, V and Cr. In this case, the hydride electrode operates in a bifunctional mode, i.e., gas diffusion (by analogy with a platinum electrode) and capacitive (adsorption - desorption of hydrogen in the electrode volume), which is associated with certain operating features and, in particular, the charge of batteries of this type.

_..The rate of degradation of hydrogen-absorbing intermetallic compounds is determined by the amount of hydrogen contained in the lattice of the compound. During a fast discharge and, therefore, rapid desorption, hydrogen does not have time to diffuse to the grain surface, exposing a clean metal surface prone to poisoning. In this regard, it is advisable to maintain the concentration of hydrogen in the intermetallic during the discharge at the maximum possible level, which can be achieved by significantly exceeding the electrochemical capacity of the hydride electrode over the capacity of the positive electrode. The specified imbalance in the capacitance of the electrode is achieved in various ways. So, in [3] it is proposed to introduce alloys of the Ni – Penes (Ni – Al) type into the active mass composition, which decompose in alkali with the evolution of hydrogen by the reaction
2Al + 2KOH + 2H ₂ O _ → 2KALO ₂ + 3H

_. .

 The hydrogen released in this case is absorbed by the hydride electrode, increasing its activity and capacity. The specified method is technically difficult to implement, since it is impossible to control the completeness of decomposition and, in addition, the mechanical strength of such an electrode is negligible.

, тем самым обеспечивается превышение электрической емкости гидридного электрода (подбором необходимого количества цинка) над емкостью ОНЭ.Closest to the proposed method in technical essence and the achieved result is the method [4], according to which in the electrochemical system consisting of a hydride and nickel oxide electrode (ONE), a third electrode is provided that has a more negative potential than a hydride electrode, for example zinc . When this system is placed in an electrolyte, the hydride electrode is charged due to the dissolution of zinc by reaction
Zn + 4OH ^- _ → Zn (OH) $\genfrac{}{}{0ex}{}{\text{-}}{\text{4}}$ ² +2

This ensures that the electric capacity of the hydride electrode is exceeded (by selecting the required amount of zinc) over the capacity of the ONE.

 The disadvantage of this method is the complexity of the electrical circuit of the battery due to the presence of the third electrode, as well as the formation of zincate in the electrolyte, which in the conditions of long-term operation will inevitably lead to internal circuits, especially in the conditions of a matrix electrolyte. The presence of zincates leads to short circuits after 10-15 cycles.

In this regard, it is proposed a method of charging MGA by simultaneously conducting a forming cycle and filling the housing with hydrogen, while the amount of hydrogen is determined from the formula
M = (C _g.e. - C _po.e ) ˙ q, where M is the mass of hydrogen, g;
_C. - the capacity of the hydride electrode, A ˙ h .;
With _po - the capacity of the positive electrode, A ˙ h .;
q is the electrochemical equivalent of hydrogen, g / A ˙ h.

_→ [H]+OH^- , так и за счет газодиффузионного поглощения водорода интерметаллидом 1/2 H₂_→ H_адс._→ [H]. Количество подаваемого водорода рассчитывается исходя из необходимого превышения емкости гидридного электрода над емкостью положительного электрода. После окончания формировочного цикла аккумулятор от источника газообразного водорода отсоединяется и в дальнейшем эксплуатируется совершенно автономно.The difference of the proposed method is the combination of the formation cycle with filling the body with hydrogen, and the amount of hydrogen is determined by the above formula. The proposed method is technically simple and cost effective. It is based on the use of the gas diffusion properties of the hydride electrode and consists in carrying out an electrochemical charge with the simultaneous supply of gaseous hydrogen into the battery case during the formation cycle. In this case, the absorption of hydrogen occurs, as due to the electrochemical decomposition of water H ₂ O +

_ → [H] + OH ^- , as well as due to the gas diffusion absorption of hydrogen by the intermetallic compound 1/2 H ₂ _ → H _ads. _ → [H]. The amount of hydrogen supplied is calculated based on the required excess of the capacity of the hydride electrode over the capacity of the positive electrode. After the end of the forming cycle, the battery is disconnected from the source of gaseous hydrogen and subsequently operated completely autonomously.

 The tests of the MGA of two options (hydrogen-free formation and the proposed method) showed that in the first case, the stability of the hydride electrode did not exceed 100 cycles with a 50% loss in capacity, and in the second case it reached 1250 cycles under conditions of 80% discharge depth with round-the-clock cycling.

8,5 нл Н₂. При окончании формировочного цикла и полном насыщении гидридного электрода на ОНЭ может происходить выделение кислорода (перезаряд), что однако совершенно безопасно, ввиду его "дожигания" на гидридном электроде по реакции H₂+1/2 O₂_→ H₂O+Q с выделением тепла и образованием воды.PRI me R. The proposed method is implemented in relation to the MGA with a capacity of 10 Ah. (NG-10). The battery consists of 10 positive and 10 negative electrodes. The mass of ONE is 100 g, which, taking into account the specific capacity of 0.1 A˙h / g, corresponds to 10 A˙h. The formation is carried out by a current of 0.1 ... 0.15 C. The capacity of hydride electrodes with the same mass is 2 times higher. Thus, an additional capacity of 10 Ah. is provided by supplying gaseous hydrogen during the forming cycle, based on the indicated ratio, where q is 0.076 g / Ah; M = (20-10) ˙ 0.076 = 0.76 g or in terms of volume

8.5 nl H ₂ . At the end of the forming cycle and complete saturation of the hydride electrode on the ONE, oxygen evolution (recharge) can occur, which is however completely safe, due to its “afterburning” on the hydride electrode by the reaction H ₂ +1/2 O ₂ _ → H ₂ O + Q s heat and water.

 The course of this process means that the battery is fully charged and after disconnecting from an external hydrogen source is ready for further use. The battery was discharged in the mode 0.2 ... 1.0 C with a fluctuation of the capacitance within 10% and a pressure change of 0 ... 10 atm. At 80% discharge depth, the stability of the battery was 1250 cycles.

Claims (1)

METHOD FOR FORMING A METAL HYDRIDE BATTERY by conducting a charge and filling the battery case with hydrogen, characterized in that the case is filled with hydrogen at the same time as the forming charge, and the amount of hydrogen supplied is determined from the formula
M = (C _g.- C _{pol. E} ) q,
where M is the mass of hydrogen, g;
C _ge is the capacity of the hydride electrode, A · g;
C _pol.e - the capacity of the positive electrode, And · g;
q is the electrochemical equivalent of hydrogen, g / A · g