Inhibiting Oxygen Release from Li-rich, Mn-rich Layered Oxides at the Surface with a Solution Processable Oxygen Scavenger Polymer

摘要

Li-rich Mn-rich layered oxides (LRLO) are considered promising cathode materials for high energy density storage because of their very high capacities that owe to the reversible redox of oxide anions. However, LRLO cathodes also evolve reactive oxygen species on charge, especially in the first formation cycles, which leads to reactivity with the electrolyte at the surface, reconstruction of surface layers, and deleterious impedance growth. Here, a strategy to enhance the cycle performance of a Li-rich Mn-rich layered cathode is demonstrated by scavenging the evolved oxygen species with a polydopamine (PDA) surface coating. PDA, a well-known oxygen radical scavenger, provides a chemically protective layer that diminishes not only the growth of the undesirable cathode electrolyte interphase but also results in less oxygen gas release compared to an unprotected surface, and significantly suppressed phase transformation at the surface. These factors lead to improved rate capability and diminished capacity fading on cycling; namely a capacity fade of 82% over 200 cycles at a C rate for the PDA-coated LRLO, compared to 70% for the bare LRLO material.