Among the various components of electric vehicles, the power battery seems to be the most important part for consumers. Its performance and safety will have a direct impact on the range and experience. Compared with the mainstream lithium-ion batteries on the market, all-solid-state batteries have the advantages of high energy density and high safety, which can enhance the endurance while better ensuring safety. As an emerging technology, it is still immature, but it is about to usher in a breakthrough.
Written by Huang Xinwei
According to the classification of the electrolyte containing liquid electrolyte content, lithium batteries can be divided into four categories: liquid, semi-solid, quasi-solid and all-solid. The electrolytes inside both semi-solid and sub-solid-state batteries are mixed with solid and liquid, and are used as a transitional form when the technology is not mature. As its name suggests, the all-solid-state battery has no liquid electrolyte inside it, and it is all solid-state, which is a mature form of solid-state battery. Among them, the theoretical limit of the energy density of liquid lithium batteries is 300Wh kg, while the energy density of all-solid-state batteries is the highest, which can exceed 600Wh kg, which greatly enhances the endurance. 
All-solid-state batteries have obvious advantages in terms of energy density and safety. At present, the electrolyte inside the mainstream lithium-ion battery is liquid, and the negative electrode is embedded with lithium graphite material. However, the electrolyte of the all-solid-state battery is all solid, and there is no need to consider the possibility of lithium and liquid electrolyte reacting, and the negative electrode can directly use lithium metal as the material, which can reduce the weight of the battery and reduce the volume, so the energy density is higher. Secondly, the solid electrolyte inside the battery has the characteristics of non-flammable, high-temperature resistance, non-volatile and non-corrosive, which replaces the flammable and explosive organic electrolyte, and can ensure high safety under the condition of high energy density. 
All-solid-state batteries are superior to other batteries in terms of energy density and safety, but they also have their own drawbacks. The effective contact between the solid electrolyte and the electrode material is weak, the ionic conductivity is low, and the interface impedance is large, which can have a negative impact on battery performance. In addition, the cost of all-solid-state batteries remains high and cannot be compared with semi-solid-state batteries in terms of price-performance ratio. Therefore, at present, all-solid-state batteries are only in the small-scale production stage, and efforts are still needed to carry out technical research to move towards the mass production stage. In the future, the industry will conduct research in multiple directions to achieve the popularization of all-solid-state batteries as soon as possible. First, the electrode and solid-state electrolyte are kept in close proximity, improving the performance of the battery. Second, it inhibits the growth of lithium metal dendrites, prevents the rapid decay of battery capacity, and reduces the potential danger of accidents. Thirdly, the physicochemical model of all-solid-state batteries is studied in depth to reveal the failure and runaway mechanism of batteries under multi-field coupling. Fourth, research and development of new cheap and reliable solid-state electrolytes, lithium anodes and other supporting key materials, and make breakthroughs in manufacturing processes to reduce costs. 
Despite the diverse and complex technical hurdles, the dawn of the industry seems to be coming. GAC, Changan, Toyota, Nissan and other OEMs plan to mass-produce all-solid-state batteries in the next 3-7 years. In this way, it is likely that many of the above research directions will usher in breakthroughs in the near future. With the blessing of all-solid-state batteries, electric vehicles will have better range and more safety. 