7‐Hydroxycoumarin as a Novel Film‐Forming Additive for LiNi 0.5 Mn 1.5 O 4 Cathode at Elevated Temperature

A novel additive, 7‐hydroxycoumarin (7‐HC), is employed to construct a stable interface film on the LiNi 0.5 Mn 1.5 O 4 cathode to improve the cyclic stability of Li/LiNi 0.5 Mn 1.5 O 4 cells at elevated temperature (ca. 55 °C). In the 0.01 wt% 7‐hydroxycoumarin‐containing electrolyte, the capacity retention of Li/LiNi 0.5 Mn 1.5 O 4 cell increases from 78.15 % to 95.64 % at elevated temperature after 100 cycles at 1 C rate. Through theoretical calculations and ex‐situ analysis, it suggests that 7‐HC is susceptible to oxidation than other components of the electrolyte to form a thin and stable film on the surface of LiNi 0.5 Mn 1.5 O 4 cathode. The thin and stable film can effectively reduce the interface oxidation reaction and the “cross‐talk” between the positive electrode and negative electrode and effectively inhibit the structural changes of LiNi 0.5 Mn 1.5 O 4 caused by dissolved transition metals in subsequent cycles, thereby improving the cyclic stability of the cell at elevated temperature.