Electrolyte Additives for Interfacial Modification of Cathodes in Lithium-Ion Battery

Increasing the voltage is one of the important ways to improve the energy density of lithium ion batteries. For example, LiNi0.5Mn1.5O4 (4. 7 V), LiNiPO4 ( 5. 1 V) and lithium-rich manganese-based materials exhibit high energy density and low cost at high charge cut-off voltage, showing good application prospects. In addition, increasing the charge cut-off voltage of LiCoO(2 )and NMC battery systems is a simple and effective approach to increase the energy density. However, when the charge cut-off voltage is increased, not only the electrolyte will be oxidatively decomposed at the cathode /electrolyte interface, but also the dissolution of the metal cation from the cathode materials will be accelerated. These are the main causes for the decreased cycle stability and safety. The electrolyte additives can be used for modifying positive electrode interfaces, thus passivating the cathode/electrolyte interface and inhibiting the decomposition of the electrolyte. Moreover, the modified electrolyte can effectively suppress the destruction of the cathode structure. Based on the molecular structure of the additives, the related research results of additives such as sulfonate ester, boric acid ester, phosphate ester, fluorocarbonate, nitrite, anhydride and lithium salt at the positive electrode interface are introduced in this paper. The action mechanisms of different additives are explained and generalized. Furthermore, the combination technology of additives for different batteries are introduced. At last, the development of new electrolyte additives for cathode/electrolyte interface modification are discussed.