The development trend of molten salt battery technology
Common molten salt batteries are mainly sodium-sulfur batteries and Zebra batteries. After about 30 years of development, sodium-sulfur batteries have developed into the most mature technology and the most practical products in the field of large-capacity chemical energy storage. There are more than 100 application cases above the MW level in the world. In terms of technology, Zebra batteries and sodium-sulfur batteries have more in common, and the technical problems and future development trends faced by the two batteries are relatively similar.
At present, sodium-sulfur batteries are facing some technical challenges, and solving these technical problems has become the future research direction and development trend of sodium-sulfur batteries. First, prepare the Na-p-Al2O3 ion conductive ceramic tube, and use the sodium ion conductivity, strength, density and durability of the ceramic tube to improve the life, efficiency and power characteristics of the sodium-sulfur battery is one of the main development trends. Because of the difficulty in its preparation, the research on the preparation of Na-P-Al203 ceramic powder, the molding, degreasing, firing, ceramic microstructure control, ceramic tube surface degradation, and the influence of metal impurities will be gradually carried out.
Secondly, because the sodium-sulfur battery uses molten sodium and sulfur as active materials, its working temperature is 300-350°C. Therefore, on the one hand, an auxiliary heating and heat preservation system is required when the battery is working, and on the other hand, it is also necessary to strictly manage the temperature of various internal points during the operation of the battery. Solving the heat control and management problems of sodium-sulfur batteries, strictly controlling their operating temperature, and taking structural safety measures to improve the safety of operation is another research and development trend.
The last development trend of sodium-sulfur batteries is the study of integrated module coordination and power management. Because in the application of large-scale energy storage, it is necessary to combine multiple single batteries to form a module (each module of NGK company is 50kW), and then combine multiple modules into a system. There are certain differences in the individual cells within the module, and there are also differences between different modules. Therefore, it is necessary to strictly control the charging and discharging time, voltage, current and other conditions of each single battery and module, otherwise the life of the battery system will be affected, and in severe cases, safety problems will also arise.
Generally speaking, in addition to improving the consistency of sodium-sulfur battery cells, the development of a charge-discharge management system is also one of the keys to improving the life and safety of sodium-sulfur batteries.
The development trend of nickel-hydrogen battery technology
At present, the energy-type Ni-MH battery used in pure electric vehicles (EV) has a mass specific energy of 65~85Wh/kg, and the mass specific energy of high-capacity AA Ni-MH batteries can reach 110Wh/kg, and the volume specific energy is as high as 435Wh/L. In the future, the specific energy of nickel-hydrogen batteries will continue to increase as one of the development trends. Similarly, the specific power of nickel-metal hydride batteries will also be widely developed and applied with the development of HEV. Cobayses Corporation of the United States proposed that the specific power of next-generation power nickel-metal hydride batteries will reach 2000W/kg.
With the improvement of the performance of the cathode material, on the one hand, the charging performance of Ni-MH batteries at high temperatures and high rates is significantly improved, and the charge and discharge rate is closely related to the battery input and output power. In the future, the charge and discharge rate of nickel-metal hydride batteries will gradually increase with the improvement of materials. On the other hand, because the cycle performance of nickel-hydrogen batteries mainly depends on the negative electrode alloy, the reason for the capacity decline of the negative electrode alloy is more due to alloy powdering and surface corrosion inactivation during the electrochemical hydrogen absorption and desorption process. The development of basic research such as composition adjustment and improvement of the cycle performance of the negative electrode has made the cycle life of nickel-hydrogen batteries more than 8000 times and the capacity loss less than 20% is the trend of future research and development.
For nickel-based batteries (nickel-metal hydride, nickel-cadmium, nickel-zinc and other batteries), when the temperature is high, the potential of the oxygen evolution reaction will approach the positive electrode reaction, and the competition between the two will cause the positive electrode charge acceptance ability to deteriorate sharply. Specifically for nickel-hydrogen batteries, when the temperature is low, the electrocatalytic ability and hydrogen diffusion rate of the negative electrode alloy will also decrease significantly, so the kinetic performance cannot be compared with that at room temperature. At present, the specific output power of Panasonic’s nickel-hydrogen battery at -30 feet is only 150W/kg, which is about 10% of that at room temperature. From this point of view, maintaining the working environment temperature will be one of the main trends in the development of nickel-metal hydride batteries in the future.
