Project R-6895

Improving the performance of rock salt type cathodes for Li-ion batteries through control of the transition metal cation migration using redox reactions of the oxygen sublattice and Li-conductive coatings (Research)

The performance of Li-ion batteries is still far below the threshold for automotive and grid applications. This largely depends on the cathode. The commercially most developed cathode is LiCoO2, but there is a better alternative in LiNixMnxCo1-2xO2(NMC). However, even the best NMC still suffers poor electrode kinetics and large voltage decays on cycling, due to structural rearrangements upon charge-discharge. 1)When Li leaves the structure upon charge, the transition metal (TM) cations can migrate into the vacant Li sites. This reduces the size of these voids making them inaccessible for the Li cations upon their return. 2)At the surface of the cathode, a disordered Li-poor layer without diffusion channels is formed. If the oxygen sublattice plays only a passive role as rigid framework for the cation movements this layer blocks the Li extraction/insertion. 3)There is a loss of cations and oxygen through interaction with the electrolyte. However, for specific compounds with the same structure as NMC there is redox activity of the oxygen sublattice, accompanied by reversible TM cation migration. We propose to engineer the reversibility of the structural transformation also in NMC by coupling the TM cation migration with redox changes at the oxygen sublattice through dedicated TM cation replacement. We also propose to develop a Li-ion conducting coating to prevent contact between electrolyte and cathode to stop oxygen and cation loss and improve the capacity retention.

01 January 2016 - 31 December 2019