Abstract
A novel approach based on analyzing the forces and velocities of solvents and anions to compute ligand-exchange rates is here presented and applied to lithium-ion battery (LIB) and sodium-ion battery (SIB) electrolytes. By using ab initio molecular dynamics generated data, we find the ligand-exchange rates to increase as functions of electrolyte salt concentration and to be higher in SIB electrolytes as compared to LIB electrolytes. This indicates both that Na+ transport will be more non-vehicular in nature and have improved kinetics vs Li+, and that increasing the salt concentration is beneficial. The systems studied were basically the first cation solvation shells of Li/NaPF6 in propylene carbonate and acetonitrile using three solvent to salt ratios. Overall, the solvation shells are solvent rich at low salt concentrations, and as functions of concentration, the solvents are replaced by anions. As the SIB electrolytes display higher cation coordination and solvation numbers, we also expect an earlier onset of highly concentrated electrolyte behavior for SIB than LIB electrolytes. These observations should all have an impact on the design of electrolytes for optimal bulk properties, but also be useful with respect to interfacial dynamics.
Highlights
Lithium-ion batteries (LIBs) are the leading energy storage technology for portable electronics and electric vehicles (EVs).1,2 The EV market is currently expanding rapidly, and as the world transitions from fossil fuel power to renewable energy sources, such as wind and solar power, the need for large-scale energy storage increases
By the different radial distribution function (RDF), we find that the LIB electrolytes show smaller solvation shells than the sodium-ion battery (SIB) electrolytes (∼2.4 Å), both with only small shifts as functions of salt concentration (Fig. 1)
The shifts as functions of salt concentration seen in both RDFs originating in the anion, M+–P/F, show how the anions in the cation solvation shell get closer
Summary
Lithium-ion batteries (LIBs) are the leading energy storage technology for portable electronics and electric vehicles (EVs). The EV market is currently expanding rapidly, and as the world transitions from fossil fuel power to renewable energy sources, such as wind and solar power, the need for large-scale energy storage increases. Lithium-ion batteries (LIBs) are the leading energy storage technology for portable electronics and electric vehicles (EVs).. The EV market is currently expanding rapidly, and as the world transitions from fossil fuel power to renewable energy sources, such as wind and solar power, the need for large-scale energy storage increases. Advances in LIB safety, energy and power density, cost, cyclability, and reliable long-term raw material supply are all highly needed. Sodium-ion batteries (SIBs) show promises of decreased cost, improved power performance, and similar energy densities to LIBs.. SIBs generally make use of abundant raw materials, securing the long-term availability of resources.. SIBs generally make use of abundant raw materials, securing the long-term availability of resources.5 With these features, SIBs have been suggested as a possible candidate for large-scale energy storage solutions, and there are already some SIBs commercialized aiming toward the market of E-bikes. Sodium-ion batteries (SIBs) show promises of decreased cost, improved power performance, and similar energy densities to LIBs. SIBs generally make use of abundant raw materials, securing the long-term availability of resources. With these features, SIBs have been suggested as a possible candidate for large-scale energy storage solutions, and there are already some SIBs commercialized aiming toward the market of E-bikes.
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