Facile synthesis of ZrO2 coated Li2CoPO4F cathode materials for lithium secondary batteries with improved electrochemical properties

A facile synthesis of a metal oxide (ZrO2) coating on the surface of high voltage type Li2CoPO4F cathode material using the conventional solution method is reported in this study. The Li2CoPO4F is prepared by a two step solid state method, followed by the application of wet coating containing various amounts of ZrO2. Among the samples, the 5 wt% ZrO2 coated Li2CoPO4F material shows the best performance with an initial discharge capacity of up to 144 mA h g−1 within the voltage range of 2–5.2 V vs Li at 10 mA g−1. Moreover, this ZrO2 coated cell demonstrates an enhanced capacity retention which is two times higher than that of the uncoated sample. The reversible extraction–insertion of one lithium unit from Li2CoPO4F is successfully carried out in a controlled environment, where the electrolyte decomposition is reduced using a highly durable ZrO2 coating. The nanosized coating over the Li2CoPO4F surface helps to attain a higher discharge capacity even at high current rates. As a consequence, the cell delivers a capacity of 104 mA h g−1 at a high current rate of 100 mA g−1.

► A highly durable ZrO2 coating was applied to 5 V class cathode material Li2CoPO4F.
► The 5 wt% ZrO2 coated sample exhibited highest discharge capacity of 144 mA h g−1.
► 5 wt% samples exhibited higher capacities at 10–500 mA g−1 current rates.
► The durability of Li2CoPO4F increased to 70% after coating even at 100 mA g−1 rate.