Amorphous Silicon Nitride - an Anode Material for the Next Generation Li-Ion Batteries

Despite a decade of extensive research, silicon, as material for anodes of lithium ion batteries, still has not become a practical solution. Suffering from enormous expansion/contraction during lithiation/delithiation cycles, silicon undergoes rapid self-destruction resulting in battery failure. To counteract the degradation several options has been explored over the years. Those include downsizing of the material to nanoparticles, doping and coating with organic or inorganic shells. An alternative approach was proposed to mitigate the structural destruction of silicon, which is preparation of the alloyed materials. In the present work we demonstrate the use of nanostructured amorphous substoichiometric silicon nitride as such alternative anode material. We demonstrate that upon lithiation, silicon nitride forms lithiated subunits of silicon and ternary phase of lithium silicon nitride, which serves as a matrix material. Such phase separation leads to remarkable stability: the nanostructured thin films of SiNx allowed fabrication of electrodes exhibiting capacities above 1500 mAh/g for 2000 cycles. To achieve sufficient capacities for the practical applications, we demonstrate the application of this principle to particle-based composite electrodes, using SiNx nanoparticles fabricated through a CVD process. Such amorphous substoichiometric nanoparticles demonstrated reversible capacities above 1000 mAh/g and excellent cycling stability over several hundred cycles. We also demonstrate the effects of chemical composition on initial and long-term cycling stability of nanostructured silicon nitride.