Cobalt-Free High-Capacity Ni-Rich Layered Li[Ni0.9Mn0.1]O-2 Cathode

Abstract

Li[Ni0.9Co0.1]O2 (NC90), Li[Ni0.9Co0.05Mn0.05]O2 (NCM90), and Li[Ni0.9Mn0.1]O2 (NM90) cathodes are synthesized for the development of a Co-free high-energy-density cathode. NM90 maintains better cycling stability than the two Co-containing cathodes, particularly under harsh cycling conditions (a discharge capacity of 236 mAh g−1 with a capacity retention of 88% when cycled at 4.4 V under 30 °C and 93% retention when cycled at 4.3 V under 60 °C after 100 cycles). The reason for the enhanced stability is mainly the ability of NM90 to absorb the strain associated with the abrupt anisotropic lattice contraction/extraction and to suppress the formation of microcracks, in addition to enhanced chemical stability from the increased presence of stable Mn4+. Although the absence of Co deteriorates the rate capability, this can be overcome as the rate capability of the NM90 approaches that of the NCM90 when cycled at 60 °C. The long-term cycling stability of NM90 is confirmed in a full cell, demonstrating that it is one of the most promising Co-free cathodes for high-energy-density applications. This study not only provides insight into redefining the role of Mn in a Ni-rich cathode, it also represents a clear breakthrough in achieving a commercially viable Co-free Ni-rich layered cathode.