An electrically rechargeable zinc-air cell was developed and demonstrated using a bi-electrode on the cathode side and a 3D zinc electrode. About 200 cycles corresponding to 5000h of operation was achieved with this configuration. An innovating hybrid bi-electrode was evaluated which significantly increase the energy efficiency of our system to about 70% with an energy density close to 110 wh/kg and also improves the power response of the zinc air battery for punctual power demand application.
Specific energies greater than 70 Wh-kg/sup -1/ can only be achieved for a 24 V Ni-Cd battery by reducing the weight of the bipolar collecting support. SORAPEC-NITECH has developed a lightweight foam substrate with which it is now possible to obtain bipolar electrodes with a collector thinner than 0.1 mm. These high volumetric energy density structures are well adapted for sealed battery applications. The performances of these batteries were studied as well as the optimization measures necessary to regulate the gas evolution in the cell during end of charge. The characteristic curves obtained with such cells during these tests are given.< >
This project is related to the study of an alkaline fuel cell with matrix and no precious catalysts. Advantages of an immobilized electrolyte in a matrix are: high compactness of the cell, few electrical linkage when a serial assembly of the elements is realized, ligthening of the auxiliaries. New electrodes structure have been developed. Sponge metal permits good electrical contact between the catalyst and the nickel and no loss of the catalyst from the conductive structure is observed. Fibrous matrices which have been tried offers good electrolyte absorption capacity and for some of them, high bubble point. The fuel cell so realized has good performances, related to the lack of precious catalyst.
The behavior of fibrous nickel electrodes working in Ni-H/sub 2/ batteries has been studied in order to lighten these cells. The characteristics of the electrodes have been chosen taking into account the fact that a compromise between the swelling of electrodes and their capacity had to be defined. Cycling tests in accelerated geostationary mode are reported with this type of cell; 900 cycles have already been obtained without any decrease in performance. The end of discharge cell voltage is practically constant and a capacity equal to approximately 90% of the nominal capacity is recovered.< >
Zinc air batteries use very cheap raw materials (Zinc, Carbon, Potassium Hydroxide) with material costs less than 10€/kWh. The fact that they are water based batteries also makes them much safer and they use environmentally benign and recyclable materials. There is no possibility of thermal runaway or fire either. Zinc-air batteries are therefore an interesting option for the electric vehicle, but also for lower cost stationary storage. High energy density zinc-air batteries are already on the market with energy densities above 400 Wh/kg but they are not rechargeable. The technology to make zinc-air batteries on an industrial scale therefore already exists. The challenge now is to be able to make zinc-air batteries rechargeable. Attempts to develop such a battery have failed due to the poor reversibility of the air electrode and due to the formation of zinc dendrites during charge. By using 3D electrode structures and a protected air electrode, an electrically rechargeable zinc-air battery has been developed which has solved these problems and which has high cycle efficiencies. One of the disadvantages of metal-air batteries is their poor discharge power performance compared to Lithium-ion batteries. The culprit is the air electrode, the zinc electrode is not limited on discharge. Oxygen reduction is a multi-electron reaction with slow kinetics. The reaction is further impaired by the low concentration of the active material (oxygen from the air) and the low molar density of a gaseous reactant. The addition of a second high power cathode has solved this problem and has brought very interesting power and energy performances to our zinc-air battery. High energy densities have also been achieved using zinc electrodes with very high loadings, up to 630 mAh/cm². These zinc-air cells are tested under standard cycling conditions, but also using normalised electric vehicle driving cycles.
