Expired Milk Powder-Derived N,P-co-Doped Carbon/MnO Composite as the Enhanced Anode for Li Ion Batteries

MnO is regarded as a highly promising anode material for lithium-ion batteries because of its high theoretical specific capacity and abundant resources. Nevertheless, its intrinsic low electrical conductivity and significant volume expansion during cycling lead to poor rate capability and cycling performance, hindering its practical applications. Herein, N,P-co-doped carbon/MnO composite was designed and synthesized using expired milk powder as the nitrogen and phosphorus-codoped carbon source and manganese acetate tetrahydrate as the manganese source by freeze-drying and annealing strategies. In this composite, MnO nanoparticles (average size of 60 nm) are uniformly embedded within a three-dimensional interconnected N,P-co-doped foam-like carbon framework. The 3D carbon skeleton has a reversible wrinkling deformation, effectively mitigating the volume expansion of MnO during charge/discharge cycles and preventing particle aggregation. Additionally, N-doping introduces abundant surface active sites to enhance Li⁺ adsorption and improves electronic conductivity for efficient charge transfer, while P-doping generates defects in the carbon matrix, accelerating the kinetics of Li⁺. Therefore, the synergy between highly dispersed MnO nanoparticles and N,P-co-doped carbon matrices endows exceptional electrochemical performance, including high reversible capacity of 966 mAh g^-1 at 0.2 A g^-1 with 190 cycles, superior rate capability of 318 mAh g^-1 at 4.0 A g^-1, and long cycle performance (retaining 526 mAh g^-1 at 1.0 A g^-1 after 600 cycles). Furthermore, Li full cell assembled with LiFePO₄ as the cathode and this composite as the anode also presents outstanding cycling stability, maintaining a capacity of 111 mAh g^-1 after 250 cycles at 0.1 A g^-1.