Fig. 1: Potential approaches for improving lifetime of LiMO₂ positive electrodes.

Core-shell and gradient materials utilise more stable compositions (often lower Ni-content) near the electrode surface to minimise electrode-electrolyte reactivity and a nickel-rich core stoichiometry to increase energy density. Electrolyte additives are compounds added to the electrolyte solution on the order of a few weight per cent to improve cell lifetime and safety, for example by reacting with the electrode surface to form a protective ‘barrier’ layer. Surface coatings (applied via a variety of methods) on the electrode material can improve cycling stability and lifetime by scavenging corrosive HF, physical blockage of electrolyte components from reaching the electrode surface, slowing RSL growth by blocking oxygen loss from the active material, and via other chemical reactions with the electrolyte components. Heat treatments of surface-coated materials can be used to prepare surface-doped materials with improved chemical stability and that inhibit the growth of surface rock-salt layers. One trend in particle morphology research is to increase primary particle sizes (i.e., transition from polycrystalline to ‘single crystal’ materials), while future prospects include the synthesis of finely tuned particle shapes and sizes. (TEM of RSL adapted from Lin et al.¹⁴).