Manganese phosphate coated Li[Ni0.6Co0.2Mn0.2]O2 cathode material: Towards superior cycling stability at elevated temperature and high voltage

Nickel-rich Li[Ni0.6Co0.2Mn0.2]O2 is considered to be the next step forward towards the realization of high-energy lithium-ion batteries and has, thus, attracted intensive attention recently. However, achieving long-term cycling stability at elevated temperatures and voltages still remains a formidable challenge for practical applications. In this work, we successfully synthesized MnPO4-coated Li[Ni0.6Co0.2Mn0.2]O2 (MP-NCM) with an advantageously low coating content of only 1 wt% while providing substantially enhanced electrochemical performance and outstanding cycling stability. This improvement is ascribed to the MnPO4 coating, acting as an ideal protective layer to dramatically reduce the occurring side reactions with the electrolyte, especially at higher temperatures and cut-off voltages. By preventing the direct contact between the cathode active material and the electrolyte, the presence of the coating layer reduces the transition metal dissolution, thus, yielding good structural integrity upon cycling, while its amorphous nature allows for an enhanced apparent lithium ion diffusion, i.e., lithium de-/insertion kinetics. Additionally, the strong covalent bonding of the PO4-group contributes to an increased thermal stability and the high voltage performance of MP-NCM. On the basis of our work, the coating design strategy delivers valuable materials for the practical realization of lithium-ion batteries with superior long-term cycling stability at higher operation temperature and voltage.