Structure Integrity Endowed by a Ti-Containing Surface Layer towards Ultrastable LiNi_0.8Co_0.15Al_0.05O₂for All-Solid-State Lithium Batteries

LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) is regarded as a promising high capacity cathode for rechargeable lithium batteries used in electric vehicles and energy storage devices. However, NCA is structurally unstable under the high voltage operation (>4.3 V) as cracks may develop on the surface and finally lead to capacity fading. To address this problem, we succeed in achieving a nanoscale solid solution surface layer containing Ti on the NCA second particles based on a one step pre-coating method. NCA with a novel functional surface layer shows an obvious enhancement of electrochemical performances in all-solid-state lithium batteries. In particular, NCA-Ti2 exhibits an ultrastable reversible capacity of 115 mAh g −1 with capacity retentions 94% after 100 cycles for all-solid-state lithium batteries. The cracks are directly observed on the surface of the pristine sample while the surface of the Ti-doped sample is intact under high cutoff voltage. These results clearly indicate that the cracks during cycles play an important role in the capacity fading for the NCA cathode materials and Ti-containg solid solution surface layer could effectively improve capacity retention.