Effects of Al2O3 coating on electrochemical performance of MCMB material and LiNi0.5Mn1.5O4/MCMB full cells

High-voltage LiNi0.5Mn1.5O4 spinel material is plagued by severe capacity fading in full cells paired with carbon anode, presumably due to the consumption of active Li+ ions induced by the decomposition of electrolyte, as well as the dissolution of transition metal ions form LNMO cathode and the following deposition on carbon anode. Surface coating is considered as an effective means to alleviate the capacity fading of LNMO/carbon full cell. Mesocarbon microbeans (MCMB) particles are coated with different amounts of Al2O3 via a double hydrolysis reaction between Al(NO3)3 and NaAlO2 followed by post-annealing process. It is found that MCMB sample coated with 1 mol% Al2O3 shows better overall electrochemical performance in MCMB/Li half cell. LNMO cathode is also coated with Al2O3 via the same method. It is found that LNMO/MCMB full cell consisting of Al2O3 coated LNMO and MCMB exhibits the best cycling performance. On the cathode side, Al2O3 coating alleviates the interfacial reaction between cathode and electrolyte and the dissolution of transition metal ions from LNMO. On the anode side, Al2O3 coating with proper thickness acts as an artificial SEI to suppress electrolyte decomposition and stabilize SEI during cycling, thus reducing the consumption of active Li+ ions. Furthermore, Al2O3 coating can scavenge HF from the electrolyte, and then form a stable and effective protective layer on electrode surface.