Core-shell and concentration-gradient cathodes prepared via co-precipitation reaction for advanced lithium-ion batteries

The core-shell structure has been extensively utilized to develop new functional materials and become a research focus in materials science recently. Over the past decades, the requirements of high-capacity, high-rate, long cycle-life and superior safety have been the main driving force for the advance of cathode materials for lithium-ion batteries (LIBs). Correspondingly, the concept of the core-shell structure is introduced to prepare the above desired cathodes. After that, the concentration-gradient structure is further exploited to overcome the drawbacks of the core-shell structure. The co-precipitation route is more suitable for synthesizing core-shell and concentration-gradient structures compared with other methods, such as sol-gel and spray-drying. More importantly, it is capable of producing large-scale cathodes in the domain of LIBs. In this review, we first illustrate the design principles and formation mechanism of core-shell and concentration-gradient cathode materials; then the recent advances in co-precipitation preparation core-shell and concentration-gradient cathodes for high-energy, high-power, long-life and safe LIBs are summarized. Moreover the structural evolution during cycles to uncover the origin of these improved performances is also analysed. Based on these achievements thus gained, we propose a new strategy to enhance the performances of cathodes. Finally, the remaining challenges including fundamental investigation, commercialized application and present possible solutions are also discussed. In this review, the design principles, formation mechanism and recent advances in co-precipitation preparation core-shell and concentration-gradient cathodes for advanced LIBs are summarized. The remaining challenges and possible solutions are also discussed.