On the Durability of Protective Titania Coatings on High-Voltage Spinel Cathodes

TiO2-coating of LiNi0.5-xMn1.5+xO4 (LNMO) by atomic layer deposition (ALD) has been studied as a strategy to stabilize the cathode/electrolyte interface and mitigate transition metal (TM) ion dissolution. The TiO2 coatings were found to be uniform, with thicknesses estimated to 0.2, 0.3, and 0.6 nm for the LNMO powders exposed to 5, 10, and 20 ALD cycles, respectively. While electrochemical characterization in half-cells revealed little to no improvement in the capacity retention neither at 20 nor at 50 degrees C, improved capacity retention and coulombic efficiencies were demonstrated for the TiO2-coated LNMO in LNMO||graphite full-cells at 20 degrees C. This improvement in cycling stability could partly be attributed to thinner cathode electrolyte interphase on the TiO2-coated samples. Additionally, energy-dispersive X-ray spectroscopy revealed a thinner solid electrolyte interphase on the graphite electrode cycled against TiO2-coated LNMO, indicating retardation of TM dissolution by the TiO2-coating.