First Principles Study of Aluminum Doped Polycrystalline Silicon as a Potential Anode Candidate in Li-ion Batteries

Addressing sustainable energy storage remains crucial for transitioning to renewable sources. While Li-ion batteries have made significant contributions, enhancing their capacity through alternative materials remains a key challenge. Micro-crystalline silicon is a promising anode material due to its tenfold higher theoretical capacity compared to conventional graphite. However, its substantial volumetric expansion during cycling impedes practical application due to mechanical failure and rapid capacity fading. We propose a novel approach to mitigate this issue by incorporating trace amounts of aluminum into the micro-crystalline silicon electrode using ball milling. We employ density functional theory (DFT) to establish a theoretical framework elucidating how grain boundary sliding, a key mechanism involved in preventing mechanical failure, is facilitated by the presence of trace aluminum at grain boundaries. This, in turn, reduces stress accumulation within the material, reducing the likelihood of failure. To validate our theoretical predictions, we conducted capacity retention experiments on undoped and Al-doped micro-crystalline silicon samples. The results demonstrate significantly reduced capacity fading in the doped sample, corroborating the theoretical framework and showcasing the potential of aluminum doping for improved Li-ion battery performance.