Interface Engineering of Silicon and Carbon by Forming a Graded Protective Sheath for High-Capacity and Long-Durable Lithium-Ion Batteries

Silicon is one of the most promising anode materials for lithium-ion batteries, whereas its low electronic conductivity and huge volumetric expansion upon lithiation strongly influence its prospective applications. Herein, we develop a facile method to introduce a graded protective sheath onto the surface of Si nanoparticles by utilizing lignin as the carbon source and Ni(NO₃)₂ as the auxiliary agent. Interestingly, the protective sheath is composed of NiSi₂, SiC, and C from the interior to the exterior, thereby guaranteeing excellent compatibility between the neighboring components. Thanks to this unique coating layer, the obtained nanocomposite delivers a large reversible specific capacity (1586.3 mAh g^-1 at 0.2 A g^-1), excellent rate capability (879.4 mAh g^-1 at 5 A g^-1), and superior cyclability (88.2% capacity retention after 500 cycles at 1 A g^-1). Such great performances are found to derive from a slight volumetric expansion, high Li⁺ ion diffusion coefficients, good interface stability, and fast electrochemical kinetics. These properties are obviously superior to those of their counterparts, benefiting from the interface engineering. This study offers new insights into constructing high-capacity and long-durable electrode materials for energy storage.