Nickel Silicate Hydroxides/Expanded Graphite as a Stable and Fast-Charging Anode for the Next-Generation Li-ion...

Materials with high specific capacity, ultrahigh stability, and fast-charging capability are essential for the next-generation Li-ion batteries. To meet these demands, it is important to find alternative anode materials beyond graphite as it suffers from multiple challenges, such as low specific capacity, poor rate capability, and unstable behavior at high current densities. Nickel silicate hydroxides (NiSi) are a class of layered materials with high theoretical capacity, low cost, and high mechanical strength. However, they suffer from poor electronic conductivity, which hampers their cyclic stability at high current densities and limits their usage for fast-charging applications. Herein, NiSi grown over expanded graphite (EG) under in situ conditions (NiSi/EG composites) show superior electrochemical performance with ultrahigh stability of 3000 cycles at 1 A g^-1. In addition, it delivered a specific capacity of 231 mAh g^-1 when tested at a current density of 5 A g^-1. Calculations based on density functional theory (DFT) provide insights into the interaction of the Li ion/atom with NiSi and NiSi/EG composites. The DFT results show that NiSi forms an n-type Ohmic contact with graphene, enhancing the electrical conductivity. Ab initio molecular dynamics simulations further show accelerated redox reaction due to the built-in electric field in the NiSi/graphene composites. The significant lowering of the energy barrier of Li-migration upon EG incorporation along with the metallicity of the system plays a pivotal role in enabling the fast-charging capabilities of NiSi.