Highly  Stable Surface and Structural Origin for Lithium-Rich Layered Oxide Cathode Materials

Abstract

Surface/interfacial engineering is critical for preventing the particle degradation of Li-rich layered oxide (LLOs), especially facet degradation to improve the electrochemical performance. Here, we probe surface structure and performed surface engineering on a LLO. Scanning transmission electron microscopy (STEM) and soft X-ray absorption spectroscopy (sXAS) were performed to analyze the surface structure, and the electrochemical performance was evaluated. The results revealed that the integrated spinel/rock salt (ISR) surface structure formed in situ on the surface, more exactly, spinel phase was formed from C2/m surface, and rock salt phase origin from the R3m surface, which layer enhanced dramatically the cycle stability and suppressed voltage decay. The surface-modified LLO cathode exhibited extremely high capacity retention of 69.6% and a low discharge medium voltage with a decay rate of 0.44 mV cycle -1 after 2,000 cycles. The stability of the surface layer was confirmed from the structural and morphological changes after prolonged cycling. The excellent performance is attributed to the ultra-stable ISR surface layer and multiple ion conductivities (LiPO 3 and Li 2 SO 4 ) and the significant prevention of electrochemical facet degradation. We believe that the concept of ISR surface and the surface modification method will help accelerate the commercialization of LLOs for battery applications.

Keywords: spinel/rock-salt, long-term life, low voltage decay, C2/m surface, facet protection