Synthesis and Electrochemical Properties of the Li3PO4-Coated LiNi0.5Mn1.5O4 Cathode Materials for High-Voltage Lithium-Ion Batteries

High-voltage spinel (LiNi0.5Mn1.5O4; LNMO) has been a prospective cathode material that may exploit the maximal voltage of 5 V for lithium-ion batteries. However, the practical application has been hindered by the severe electrochemical instability of the Ni2+/Ni4+ redox couple at such a high voltage. Herein, we coated lithium phosphate (Li3PO4) on the surface of the LNMO by a wet-coating method to improve the electrochemical stability. The coating layer provided an effective cathode–electrolyte interphase, which prevented the excessive decomposition of the electrolyte on the surface of LNMO cathode. The Li3PO4-coated LNMO exhibited enhanced rate capability in accordance with the lowered solid-electrolyte interphase (SEI) and charge-transfer resistance values from electrochemical impedance spectroscopy.