Defect-Rich Ni–Co–Se–O Quaternary Heterojunction Nanocomposites for High-Rate Magnesium–Lithium Hybrid Batteries

Magnesium/lithium hybrid-ion batteries (MLHBs) are promising energy storage systems; however, the inherently low conductivities of transition metal oxides (TMOs) lead to redox reactions predominantly occurring on their surfaces, thereby diminishing the active material’s utilization efficiency. To address this, the defect-rich Ni–Co–Se–O quaternary heterojunction nanocomposites were developed in this study. The urchin-like precursor was synthesized via a hydrothermal method, and subsequently, defect-rich Ni 1/3 Co 2/3 Se 2 /Ni 1/3 Co 2/3 O heterogeneous nanocomposites with rhizobium-like mechanism were constructed under high-temperature liquid-phase conditions to serve as the cathode material for MLHBs. This material features multiple heterojunctions and abundant defects, which significantly enhance its charge transfer efficiency. The nanospine surfaces are adorned with nanoparticles, creating a morphological structure reminiscent of rhizobia. This design emulates the symbiotic interaction between rhizobia and legumes, where TMOs provide a high theoretical capacity, and transition metal selenides (TMSs) enhance the conductivity. The Ni 1/3 Co 2/3 Se 2 /Ni 1/3 Co 2/3 O electrode exhibited a high storage capacity (435.7 mAh g –1 ) and a high energy density (288.8 Wh kg –1 ) at 0.5 A g –1, along with a superior rate performance of 269.9 mAh g –1 at 2 A g –1 . After 500 cycles at 1 A g –1, the capacity retention and Coulombic efficiency were 79.4 and >99.2%, respectively. This work provides an effective means to explore the application of symbiotic mechanisms of defect-rich heterogeneous nanocomposites in MLHBs.