Hetero-Phase MoO₂/Cu_2–<i>x</i>Se Nanocomposites Distributed in Porous Octahedral Carbon Networks for High-Performance Lithium Storage

Owing to the mixed insertion and multielectron conversion reaction mechanisms, nonstoichiometric copper selenide (Cu2–xSe) has been known as a potential anode for lithium-ion batteries. However, huge volume changes during discharge and charge limit its ability for lithium-ion storage. Constructing heterophase nanocomposite uniformly distributed in the carbon network has been recognized as an effective approach to address the above issue. In this work, polyoxometalate-based metal–organic frameworks were used as the self-template to derive octahedral mesoporous carbon-coated heterophase copper selenide and molybdenum dioxide (MoO2/Cu2–xSe@C) nanocomposites, and the phase transformation of copper selenides from CuSe to Cu2–xSe can be achieved by tuning the pyrolysis temperature, thus optimizing the electrochemical performance. As a result, the optimized electrode delivers a high reversible specific capacity of 864.8 mAh g–1 at 0.2 A g–1 after 100 cycles, an excellent rate capability with a capacity of 480.9 mAh g–1 at 2.0 A g–1, and a long-term stability up to 500 cycles with a capacity decay rate per cycle of only 0.003%. Also, the reaction mechanism and structural stability after cycling were analyzed in detail