Gradient design for Si-based microspheres as ultra-stable Li-storage anode

High-capacity Si-based microspheres are being spotlighted as a promising substitute for commercial spherical graphite anodes in the development of high-energy lithium-ion batteries. Nevertheless, the formidable challenge of their severe mechanochemical degradation during the (de)lithiation process remains unaddressed currently. Herein, we present a Si-based microsphere prepared by the oxygen pumping mechanism under a cost-efficiently low-temperature (250 °C) molten salt reduction environment. By optimally controlling oxygen gradient distribution, the resulted Si-based microspheres exhibit the unique coherent architecture ranging from ordered crystalline Si core to disordered SiO₂^(v) shell. Their structural coherence but regional difference in function achieves a perfect combination of structural compatibility and optimized chemo-mechanical effect, endowing the obtained Si-based microspheres with a nearly intact morphology after 1500 cycles and a 97 % capacity retention after 1000 cycles at 2 A g^-1. Our design broadens research directions for Si anode material design, which will accelerate the practical application of micro-sized Si anode materials.