Research advances on cobalt-free cathodes for Li-ion batteries - The high voltage LiMn_1.5Ni_0.5O₄ as an example

LiMn_1.5Ni_0.5O₄ is one of the most promising cathode materials for use in either next generation lithium-ion batteries or all solid-state batteries. However, despite the significant Research and Development (R&D) carried out throughout the last two decades the material has not made serious inroads into market. One of the major reasons is the lack of consistency in the reported intrinsic properties and electrochemical performance owing to major controversies in synthesis, crystal structure and bulk and interfacial properties of LiMn_1.5Ni_0.5O₄, notably in contact with electrolytes. This paper is a compelling review providing an assessment on the mainstream R&D dealing with the various crystal structures of LiMn_1.5Ni_0.5O₄ and their evolutions observed during synthesis and cycling in correlation with their electrochemical performance. Influence of electrolytes and additives along with modifications through doping and surface treatments are interrelated, and the electronic and ionic transport properties of the ordered and disordered LiMn_1.5Ni_0.5O₄ phases are discussed. Overall, this review provides a detailed assessment on LiMn_1.5Ni_0.5O₄ and the underlying mechanisms governing its electrochemical performance broadly providing a focused framework for further advancement towards commercialization.