Influence of Carbonate Electrolyte Solvents on Voltage and Capacity Degradation in Li-Rich Cathodes for Li-ion Batteries

Lithium-rich cobalt-free cathodes, such as Li1.2Mn0.6Ni0.2O2 (LMR), are promising next-generation cathode materials because of their high energy density, cost efficiency, and sustainability. Nevertheless, LMRs suffer from degradation problems such as voltage decay during cycling. Different LMR surface doping and coating strategies are proposed to suppress LMR voltage decay with varying extents of success. Here, the role played by different electrolyte solvents in oxygen loss from the LMR surface is instead investigated. X-ray absorption spectroscopy (XAS), electron energy loss spectroscopy (EELS), synchrotron XRD, and online electrochemical mass spectrometry (OEMS) results show that ethylene carbonate (EC) leads to accelerated oxygen loss from the LMR surface. As a result, cycling LMR cathodes in EC-free electrolytes such as pure EMC, improves the capacity retention and reduces voltage decay. This approach provides a new strategy to increase the cycling stability of LMR cathodes, which is important for the development of more sustainable high-performance batteries. The focus lies in comprehending the reaction mechanisms that occur between different electrolyte components and LMR cathodes. The commonly used electrolyte LP57 exhibits significant side reactions with LMR cathode materials during cycling, resulting in severe voltage decay and structural degradation for LMR cathode. By employing an EC-free electrolyte, a remarkable reduction in LMR capacity, and voltage decay is demonstrated, which complements ongoing research on LMR surface modification to prolong its lifespan. image