Suppression of Voltage-Decay in Li2MnO3 Cathode via Re-construction of Layered-Spinel Coexist Phases

Voltage decay, i.e., voltage decrease during electrochemical cycling is a decade-long challenge for lithium-ion battery. This issue not only leads to a substantial loss of the energy density, but also raises challenge for the battery management system, hindering the commercial application of high capacity lithium-rich oxide. Here, we show that through a combined electrochemical conditioning and thermal treatment, Li2MnO3, the parent compound of lithium-rich oxide that typically displays severe voltage and capacity decay, could be converted into a new phase that essentially suppresses the voltage decay with improved capacity retention and rate performance. By combining atomic-sensitive nuclear magnetic resonance, differential electrochemical mass spectrometry and synchrotron-based resonant inelastic X-ray scattering, we disclose that treatment triggers the formation of three-coexisting phases, i.e., lithium-rich layered, spinel and defect spinel phase, which enables improved reversibility of the oxygen redox activity and enhanced manganese redox reactions in the initial cycle. Our findings suggest the key role of local structure on the voltage decay problem and provide insights for material optimizations towards lithium- and manganese-rich cathodes without voltage decay.