Kinetic Monte Carlo Simulations of Sodium Ion Transport in NaSICON Electrodes

• Published in: arXiv.org 2023-08
• Main Authors: Wang, Ziliang, Mishra, Tara P, Xie, Weihang, Deng, Zeyu, Gopalakrishnan Sai Gautam, Cheetham, Anthony K, Canepa, Pieremanuele
• Format: Article
• Language: English
• Subjects: Competition; Electrode materials; Electrodes; Energy storage; First principles; Ion transport; Ionic mobility; Ions; Sodium; Titanium; Transition metals
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2308.04772

The development of high-performance sodium (Na) ion batteries requires improved electrode materials. The energy and power densities of Na superionic conductor (NaSICON) electrode materials are promising for large-scale energy storage applications. However, several practical issues limit the full utilization of the theoretical energy densities of NaSICON electrodes. A pressing challenge lies in the limited sodium extraction in low Na content NaSICONs, e.g., \(\rm Na_1V^{IV}V^{IV}(PO_4)_3 \leftrightarrow V^{V}V^{IV}(PO_4)_3 + 1e^- + 1Na^+\). Hence, it is important to quantify the Na-ion mobility in a broad range of NaSICON electrodes. Using a kinetic Monte Carlo approach bearing the accuracy of first-principles calculations, we elucidate the variability of Na-ion transport vs. Na content in three important NaSICON electrodes, Na\(_{\rm x}\)Ti\(_{2}\)(PO\(_{4}\))\(_{3}\), Na\(_{\rm x}\)V\(_{2}\)(PO\(_{4}\))\(_{3}\), and Na\(_{\rm x}\)Cr\(_{2}\)(PO\(_{4}\))\(_{3}\). Our study suggests that Na\(^+\) transport in NaSICON electrodes is almost entirely determined by the local electrostatic and chemical environment set by the transition metal and the polyanionic scaffold. The competition with the ordering-disordering phenomena of Na-vacancies also plays a role in influencing Na-transport. We link the variations in the Na\(^+\) kinetic properties by analyzing the competition of ligand field stabilization transition metal ions and their ionic radii. We interpret the limited Na-extraction at \(x = 1\) observed experimentally by gaining insights into the local Na-vacancy interplay. We propose that targeted chemical substitutions of transition metals disrupting local charge arrangements will be critical to reducing the occurrence of strong Na\(^+\)-vacancy orderings at low Na concentrations, thus, expanding the accessible capacities of these electrode materials.