Layered Cathode Materials with Controlled Particle Assembly for High Energy Lithium-Ion Batteries
The as-prepared LiNi1-x-yMnxCoyO2 materials assemble into spherical structures that consist of nanosized primary particles. Revealed by transmission electron microscopy, these primary particles are “fused” together to form atomically disordered interfaces that may allow for lithium and electron diffusion. LiNi1-x-yMnxCoyO2 materials with different ratios of transition metals were synthesized, i.e., LiNi1/3Mn1/3Co1/3O2, LiNi0.4Mn0.4Co0.2O2, LiNi0.5Mn0.3Co0.2O2, LiNi0.6Mn0.2Co0.2O2, most of which show improved electrochemical performance (i.e., discharge capacity, capacity retention) compared to the counterparts synthesized by the conventional co-precipitation method, although different thermal treatment protocols are needed after the spray pyrolysis process. Surface reconstruction was quantified by soft X-ray absorption spectroscopy to investigate the surface phase transition of the LiNi1-x-yMnxCoyO2 materials after electrochemical cycling, and it is found that the materials prepared by spray pyrolysis have thinner surface passivation layers (a rock-salt/spinel mixed structure), which accounts for better capacity retention. This study suggests that morphological engineering by spray pyrolysis may offer an efficient pathway towards stable high-energy layered cathode materials.