At present, the energy used by human society mainly comes from the transformation of fossil energy, such as oil, coal and natural gas. However, the two major problems of insufficient reserves and environmental pollution have made human society spare no effort in developing and using new energy. Energy such as solar energy, wind energy, geothermal energy, and tidal energy are favored because of their abundant reserves, green and pollution-free nature. To overcome the challenges brought by their intermittent characteristics and store them correctly on a large scale, various physical energy storage and chemical energy storage methods have been developed. Among them, the battery in chemical energy storage is a small, portable, and highly efficient device, so it is widely favored by people and has been widely used in life, especially lithium-ion batteries (LIBs). Although the cost of batteries has dropped significantly in recent years due to the expansion of electric vehicle production, market chaos and competition among electric vehicle manufacturers have led to an increase in the cost of key minerals (especially lithium) used in battery production. Secondly, with the development of LIBs, their energy density has also approached the limit.
To overcome the theoretical capacity limit of LIBs, research on lithium-metal batteries (LMBs) with higher energy density has been re-proposed. However, due to the high reactivity of lithium, the use of excessive lithium increases safety risks and reduces the energy density of LMBs. This contradiction has prompted the proposal of an anode-free lithium-metal battery configuration. Anode-free lithium-metal batteries (AFLMBs) have become promising candidates for solving the safety issues of LMBs due to their safer manufacturing process. However, the limited active materials and unfavorable interfacial reactions on the anode surface lead to the formation of an unstable solid electrolyte interface (SEI) and limited cycle life, which hinders their practical application. Therefore, finding a suitable strategy to improve the cycle stability of AFLMBs is of great significance for promoting the practical application of high energy density systems.
Regulating the composition of electrolytes, such as electrolyte additives, inert co-solvents, etc., is an effective and economical strategy to optimize the battery performance. The cycle stability of AFLMBs is thus improved by in-situ adjustment of the interface composition and the formation of a stable SEI layer. In the second chapter of this paper, the functional electrolyte chemistry of LMBs and AFLMBs is designed and studied. The synergistic effect of two additives is used to improve the cycle stability of ether-based electrolytes for AFLMBs.
In addition to LMBs and AFLMBs, sodium-metal batteries (SMBs) have also been studied due to the abundant reservoirs, low cost of sodium resources, similar working principle, and high compatibility with current LIB production equipment. To overcome the limitations of current commercial sodium salts (such as high cost and water sensitivity etc.), two electrochemically stable novel Na salts were developed, one of which even showed ultra-high stability to water. Ether electrolytes based on those two salts showed excellent cycling stability with organic cathode materials.
In addition, rechargeable magnesium batteries (RMBs) have also been studied. One of the main obstacles to the development of RMBs is the passivation film formed on the surface of the magnesium anode when using common magnesium salts (such as Mg(TFSI) and Mg(ClO)) with aprotic solvents, which hinders the reversible deposition of Mg ions. Chapter 4 proposed a synthesis strategy to obtain high- fluorine magnesium salts for magnesium batteries. The two magnesium salts obtained according to this strategy exhibit a reversible Mg deposition/stripping efficiency of about 99%.