Core/Shell Si-Ni/C Anodes for High-Energy-Density Li-Ion Batteries

The goal of this research was the development of low-cost, high-capacity, long-cycle-life and safer anode materials to replace the graphite anode of the common lithium-ion battery. Silicon offers the highest gravimetric capacity as an anode material (e.g. Li₂₂Si₅: nearly 4,200mAh/g). However, Si-based electrodes typically suffer from large volume changes (up to 420%) during insertion and extraction of lithium. This is followed by cracking and pulverization of silicon, which in turn, leads to the loss of electrical contact, an unstable SEI and eventual capacity fading.

Our strategy for reducing the deterioration of silicon involve attaching silicon and silicon-nickel nanoparticles to multiwall carbon nanotubes (MWCNT) in order to create a silicon-based active anode material supported by a strong, rigid and high-electrically-conducting network. The method is based on the pyrolysis of the mixture of nanoparticles and nanotubes with carbon precursor. Silicon-nickel alloying is achieved by electroless or grinding process followed by pyrolysis. Nickel was chosen since, when alloyed with silicon, this metal is expected to stabilize the structure of lithiated silicon nanoparticles, increase electron conductivity and possibly induce graphitization of the carbon shell.

Li/SiNi-MWCNT-C (1.6mg/cm² loading) cells exhibited a de-intercalation capacity of 900mAh/g_anode at C/7, 600mAh/g_anode at C/3.4 and 400mAh/g_anode at C/1.7. Irreversible capacity of 22% and high faradaic efficiency (FE) of 99.5% were obtained. Very highly loaded anodes, weighing 5.5mg/cm², with de-intercalation capacities of 1000mAh/g_anode, demonstrated stable cycle life three times greater than that of graphite.