Sodium-ion batteries constitute a potential alternative to lithium-ion batteries, due to the low cost of Na and raw material abundance. NASICON-framework based NaTi2(PO4)3 for active electrode material are the focus, as a next-generation material because of its high ionic conductivity and large channel for Na-ion insertion and exertion. The diffusion coefficient of Na-ions in these materials is reported in a wide range in works of literature. The transport properties of Na-ion enabling its high ionic conductivities need to be enhanced. Improvement of alkali-ion transport through various experimental techniques have been done like nano sizing, carbonaceous material binding, lattice mismatch, material doping of the battery materials, etc. One of the computational techniques to improve the diffusivity of ions in polyanionic, layer oxide, perovskite materials, etc. is the lattice strain effect reported in some literature. However, depending on the complexities of structure and coordination of other atoms present in the materials, ionic transport could show positive or negative effects on strain in the lattice either compressive (&lt; 0 %) or tensile (&gt; 0 %) strain. Here, we have introduced strain effect uniaxial (x, y, and z-direction) as well as in biaxial direction in xy, xz and yz plane of the NaTi2(PO4)3 crystalline material, from 1% to 3% strain effect, using molecular dynamic (MD) simulation techniques. Interatomic-based partial charge pair potential models using NVE ensemble were used for all strain and MD calculations. Interestingly, the initial results of lattice strain effect with respect to Na-ion self-diffusion coefficient along x, y, and xy, shows positive effect i.e the diffusion coefficient increasing with tensile strain in comparison with unstrained crystal, and it is showing negative effect by compressive strain. The order of magnitude of self-diffusion coefficient of Na-ion in NaTi2(PO4)3 has changed from ~10-10 cm2/s in unstrained to increasing values of ~10-9 cm2/s in a strained structure having a similar vacancy configuration, in case of tensile strain along x, y, and xy. However, reverse phenomena were seen in the case of compressive strain. Since there were not any experimental data of strain effect for this material available for comparison, but the trends in our results using MD simulation might be realistic and could provide a useful point of discussion. Also, further investigation needs to be entertained, to compare with other planes.

Lattice strain effect in NaTi2(PO4)3 battery material on Na-ion transport: A MD simulations study

ACS Spring 2022

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