Si nanoparticles confined in N, P- doped double carbon as efficient anode materials for lithium ion batteries

To tackle mechanical structure instability and low conductivity of silicon-based anode materials, Si nanoparticles enclosed in N, P doped double carbon (N, P-Si/CNTs/C) are designed and manufactured by simple mechanical ball milling and high-temperature carbonization methods. The mechanical action makes carbon nanotubes (CNTs) and silicon particles evenly and tightly intertwined, and a uniform and stable pitch-derived carbon layer is formed on the surfaces of Si particles and CNTs. The N, P-Si/CNTs/C composites have strong oxidation resistance, excellent electrical conductivity and more defects. N, P-Si/CNTs/C composites exhibit positive lithium storage performance as anode materials for lithium-ion batteries. The initial discharge/charge specific capacities of N, P-Si/CNTs/C electrodes are 1494.0/1243.6 mA h g−1 at 0.2 A g−1 with an initial coulombic efficiency of 83.24 %, yet it maintains 603.9 mA h g−1 after 100 cycles with the initial coulombic efficiency of 83.24 %. The specific discharge capacity is 1153.6 mA h g−1 even at 0.5 A g−1. The efficient lithium storage performance is due to the three-dimensional double-carbon network to effectively protect Si nanoparticles from oxidation, increase cycle stability and rate capability, and buffer volume expansion of Si nanoparticles. Doping with N and P can provide a lot of active sites and help the electrolyte penetrate.