Two-dimensional nitrogen-doped carbon nanosheets-coated porous SiO composites sponges for durable anode materials of high-energy lithium-ion batteries

Carbon coating has been widely used to improve electronic conductivity of silicon monoxide (SiO) anodes and lower their volume expansion; however, the electrochemical stabilization of carbon layer is still low and large-scale synthesis of SiO@C nanocomposites is still an urgent challenge. Here we develop a facile dry ball milling process for the mass production of sponge-like SiO composites decorated with carbon nanosheets, featuring a simple preparation process, high compaction density, high electronic conductivity, high ionic diffusion capacity and excellent structure stability. 2D nitrogen-doped carbon nanosheets (2D-NC) by simply mixing SiO particles with melamine and polyvinyl pyrrolidone (PVP) as the dual sources of N and C. Upon calcination, the pyrolysis product of melamine, g-C₃N₄, acts as a sacrificial template to effectively direct a novel stacked 2D nanostructure. The formation of uniform 2D-NC coating on SiO enhances both the electronic conductivity and the Li⁺ ions diffusion coefficient, leading to outstanding electrochemical performances of SiO@2D-NC anode. Specifically, the as-prepared SiO@2D-NC anode exhibits a reversible capacity of 954.6 mAh g⁻¹ at 1.0 A g⁻¹ after 200 cycles, along with impressive high-rate performance of 840.6 mAh g⁻¹ at 5.0 A g⁻¹. Additionally, the SiO@2D-NC anode exhibits excellent storage performance with a capacity retention ratio of 91.5 % at 50 ℃ after 16 days. The full cell utilizing the commercial LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode achieves a reversible capacity of 174.1 mAh g⁻¹ and an impressive initial coulombic efficiency of 82 % at 0.2C, while maintaining a high ratio of capacity retention ≈ 82.4 % at 0.5C after 100 cycles and providing a high energy density of 497.8 Wh kg⁻¹.