Research Projects

Sodium-ion batteries (SIBs) are currently under intense research focus for their possible application in developing commercial batteries to address the green energy challenge in India. SIBs, as opposed to lithium-ion batteries (LIBs), use amorphous hard carbon (HC) particles as the anode material for storing Na ions during charging. The narrower interlayer spacing in graphite-based LIB anode particles leaves it unable to intercalate Na ions due to a greater ionic radius of Na+. Nonetheless, the HC particles with randomly oriented graphite layers with greater interlayer spacing and nanopores are found to be suitable anode materials to store Na during charging. Several experiments reveal that the Na storage in HC particles occurs via the 'adsorption-intercalation-pore filling' mechanism, as opposed to the ‘adsorption-intercalation’ of Li ions in the graphite particle-based LIB anodes. The choice of binder materials is also crucial in enhancing the anode’s capacity. The HC particles with passive or active binder materials constitute the HC anode for SIBs. The binder materials ensure the HC particles are mechanically held together during the charge/discharge cycles. The passive binders are made of Na+ conducting polymers (e.g., PVDF) and carbon black particles. Recently, layered materials belonging to the MXene family are being investigated for binding materials of SIB anodes. The MXene materials - a good conductor of electrons - can also intercalate Na ions into its structure, enhancing the specific capacity of the active binder-based anodes. The proposed research aims to develop computational models for the sodiation/desodiation of HC-based anodes at different length scales. First, a single-particle anode model will be proposed considering spherical HC anode particles. The diffusion-based intercalation models for LIB particles cannot be employed directly to model the Na intercalation in HC particles due to a fundamentally different 'adsorption-intercalation-pore filling' mechanism of sodiation. Once the single particle model (SPM) is established, it will be used to propose a pseudo 2D (P2D) model for the SIB half cells, considering the electrochemical kinetics of Na ions in the electrode and electrolyte. The P2D model provides more accurate predictions than the SPM in the faster charging/discharging regime. Next, the computationally expensive two-scale model will be implemented, where the electro-chemo-mechanical response of a representative volume element (RVE) of the anode microstructure will be computed. The effects of active and passive binders in the voltage-capacity response of the HC anode-based SIB half cells will be investigated via RVE computations. Next, the computational model will be employed to propose optimal proportions of the HC particles and active binders to achieve an intended specific capacity. The sodiation-driven mechanical deformation of passive and active anodes will also be investigated computationally.