Probing degradation of Cobalt-free LiNi0.5Mn1.5O4 ceramic cathode in lithium-ion batteries

Abstract High-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode is a promising option for transition to sustainable and cost-effective cobalt-free cathodes, and ceramic cathodes can substantially increase energy density by enabling higher active material loading. However, there need to better apprehend fundamental aspects about the sintering modification and degradation mechanism of LNMO ceramic based lithium-ion batteries (LIBs). Here, by modulating sintering atmosphere and temperature, we reveal the influence of densification degree and chemical environment on the conductivity of LNMO ceramics. Meticulous post-mortem analyses illustrate that unusual prolongation of the charging curves and rapid capacity fading stem from the lower electrochemical potential of Au (~4.53 V) than the ultra-high operating voltage (~4.7 V) of LNMO, leading to evident dissolution of the Au collector and interface disruptions between cathode and collector. Furthermore, Au could migrate across the cathode and separator, ultimately reach and deposit on anode surface. We also find that O 2 -sintered samples could restrain the initial mixed oxidation state of Mn and oxygen vacancies, which alleviates Mn dissolution, oxygen release, irreversible structural evolution of ceramic cathode, and contributes to enhanced conductivity and electrochemical performance. Our findings reveal the collector dissolution and structural degradation mechanisms of LNMO during cycling, and provide a guideline for the design and synthesis of LNMO ceramic cathodes as well as high-voltage LIBs.