Enhanced energy density of LiNi0.5Mn0.3Co0.2O2 batteries with negative-electronic-compressibility thin film coating

In this work, we study and compare the electrochemical performance of Li-ion battery (LIB) with and without a BiFe0.95Cu0.05O3 thin film coating. The BiFe0.95Cu0.05O3 thin film is deposited on both LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode and graphite anode electrodes using radio frequency magnetron sputtering. By using galvanostatic charge–discharge measurements, we observe that, in contrast to LIB without BiFe0.95Cu0.05O3 coating, the charging curve of LIB with BiFe0.95Cu0.05O3 coating exhibits a counterintuitive negative slope of the negative electron compressibility (NEC) with a rate of NEC equal to −16.36 × 10−11 meV per electron per cm2. Importantly, we find that the NEC effect has the potential to enhance the energy density in LIB with BiFe0.95Cu0.05O3 coating. The energy density of the first discharge cycle is dramatically increased from 190 Wh/kg for pristine LIB to 255 Wh/kg for LIB coated with the BiFe0.95Cu0.05O3 film. We suggest the origin of this with the change in Mott gap and a concept to apply the NEC effect for enhancing energy density LIB batteries.