Recent progress in Co-free, Ni-rich cathode materials for lithium-ion batteries

Cobalt (Co) has played an important role in nickel (Ni)-rich cathode materials in terms of improving electrochemical performance, boosting energy density, and improving cycling life for lithium-ion batteries (LIBs). While Co resources are becoming more cost-effective, they pose environmental challenges that can lead to limitations in production and indicate the need for alternative Co-free, Ni-rich cathodes. This review aims to compile some of the concepts established in recent years to overcome the electrochemical disadvantages of Ni-rich cathodes without Co. With the development of strategies involving single-crystals, core-shell structures, and substitution of Co by other metal ions, problems associated with capacity reduction and the underlying structure degradation mechanism have been resolved. Therefore, structural transformation strategies focusing on potential cathodes with improved energy density and lifetime have been pursued for safe LIBs. We also address possible issues and some new insights to improve the performance of Co-free, Ni-rich cathodes for practical applications.