Interfaces and Electrolyte Additives for Long-Life Sodium-Ion and Lithium-Ion Batteries

Abstract

Sodium-ion batteries (NIBs) are attracting considerable attention as post lithium-ion batteries (LIBs) as they are a likely ‘drop-in’ technology which can be produced using existing manufacturing lines. One of the processes in manufacturing which is least understood is the formation and conditioning step; both battery technologies require a formation of the surface electrolyte interface (SEI) and cathode electrolyte interface (CEI) for long life cells. Here we discuss the formation, conditioning and electrolyte additives for the creation of the stable interfaces for high cycle life.In particular we highlight the similarities of the formation step in the manufacturing process for a NIB layered oxide-hard carbon chemistry and LIB NMC-graphite, and the subsequent differences in the SEI observed1. Methods for faster formation protocols for NIB and LIB where targeted voltage windows in active formation methods produce more stable interfaces are introduced2,3 and we show the effect upon the composition of the SEI layer using these different protocols.In all cases full cells were made with in a coin-cell figuration, these cells were subjected to different formation protocols and electrolytes additives such as FEC, VC and a new inorganic solid state additive. After formation the impedance of the cells were measured, and then cycled for 500 cycles at a higher rate to accelerate the ageing process. The resistance and the capacity of the cells were monitored during cycling. We show that even in a coin cell configuration significant differences in the cycle life are observed with different formation protocols and electrolyte additives. In addition we show the difference in the stability of the SEI in carbonate-based electrolytes between NIBs and LIBs. The effect upon the stability of the SEI and the performance of a NIB with a sodium metal oxide cathode and a hard carbon anode is discussed in detail and the role of the formation protocols and the inorganic additive. We also suggest the role of the additives for NIB and suggest the mechanism for which the stability is enhanced. Roberts, S. & Kendrick, E. The re-emergence of sodium ion batteries: testing, processing, and manufacturability. Nanotechnol. Sci. Appl. Volume 11, 23–33 (2018).Pathan, T. S., Rashid, M., Walker, M., Widanage, W. D. & Kendrick, E. Active formation of Li-ion batteries and its effect on cycle life. J. Phys. Energy 1, 044003 (2019).Kendrick, E. Optimisation Of Formation And Cell Ageing Protocols For Lithium Ion EV Batteries. Batter. Supercaps (2020). doi:10.1002/batt.202000048