Preparation of N-doped porous carbon coated MnO nanospheres through solvent-free in-situ growth of ZIF-8 on ZnMn2O4 for high-performance lithium-ion battery anodes

We present a novel and facile strategy to prepare porous N-doped carbon coated MnO (MnO@NC-Z) nanospheres through solvent-free in-situ growth of ZIF-8 on ZnMn2O4 followed by carbonization. The obtained MnO@NC-Z nanospheres are composed of numerous MnO nanoparticles that are uniformly coated by an ultrathin (∼5 nm) and nitrogen-rich (∼3.7 wt%) carbon layer derived from the in-situ grown ZIF-8 layer, which could not only restrict the volume expansion of MnO during the charge-discharge process but also substantially improve the electrical conductivity. Meanwhile, the synthesized MnO@NC-Z also possesses a high porosity and large specific surface area due to the porous structure of the ZIF-8 precursor and the evaporation of nano-sized Zn reduced from the ZIF-8 during the carbonization process, which could facilitate the fast transport of Li ions. As the anode in lithium-ion batteries (LIBs), the prepared MnO@NC-Z nanospheres deliver excellent performance with a high reversible capacity of 1261 mA h g−1 at 0.2 A g−1, brilliant rate performance of 305 mA h g−1 at a high rate of 5 A g−1, and excellent cycling stability for 1000 cycles at 1 A g−1 with a 96.5% capacity retention. Importantly, this solvent-free strategy of in-situ growth of ZIF-8 can also be extended to synthesize various metal oxides@carbon composites (e.g., FeOx@NC and CoOx@NC) for different applications such as energy storage and conversion.