In Silico Based Rank-Order Determination and Experiments on Nonaqueous Electrolytes for Sodium Ion Battery Applications

Abstract

Electrolytes are an important component of electrochemical energy storage systems and their optimization is critical for emerging beyond lithium ion technologies. Here, an integrated computational-experimental approach is used to rank-order and aid the selection of suitable electrolytes for a Na-ion battery. We present an in silico strategy based on both thermodynamic and kinetic descriptors derived from molecular dynamics simulations to rationally arrive at optimal electrolytes for Na-ion batteries. We benchmarked various electrolytes (pure and binary mixtures of cyclic and acyclic carbonates with NaClO4 salt) to identify appropriate formulations with the overarching goal of simultaneously enhancing cell performance while meeting safety norms. Fundamental insights from computationally derived thermodynamic and kinetic data considerations coupled with atomistic-level description of the solvation dynamics is used to rank order the various electrolytes. Thermodynamic considerations based on free energy evaluation indicate EC:PC as a top electrolyte formulation under equilibrium conditions. However, kinetic descriptors which are important factors dictating the rate capability and power performance suggest EC:DMC and EC:EMC to be among the best formulations. Experimental verification of these optimized formulations was carried out by examining the electrochemical performance of various electrolytes in Na/TiO2nanotubes half cells with NaClO4 salt. Our rate capability studies confirm that EC:DMC and EC:EMC to be the best formulations. These optimized formulations have low-rate specific capacities 120–140 mAh/g whereas the lower ranked electrolytes (EC: DEC) have capacities 95 mAh/g. The various electrolytes are also evaluated from a safety perspective. Such results suggest encouraging prospects for this approach in the a priori prediction of optimal sodium ion systems with possible screening implications for novel battery formulations

Electrolytes, SEI Formation, and Binders: A Review of Nonelectrode Factors for Sodium‐Ion Battery Anodes

“…To further pursue their claims, the authors also performed a study comparing the electrochemical performance of TiO 2 nanotubes in a NaClO 4 electrolyte with various electrolyte solvents. The experimental study supported the findings of the theoretical study, showing that the EC:EMC, and EC:DMC based electrolyte had better capacity retention at higher current rates than the EC:DEC electrolyte …”

“…Summarizing the quantitative analysis of the electrolyte solvents, evidence from the literature would suggest that EC:DMC, and ether‐based solvents are among the most advantageous for a high CE@1 st , while the type of solvent seems to have minimal effect on the total IC. The first conclusion echoes what was reported in the paper by Sankaranarayanan and co‐workers while the latter conclusion is still unclear: it is possible that solvents affect long‐term cycling, but there is not enough data to support the claim, or at the very least, reject it. Furthermore, the promise of IL electrolytes, along with new work, such as water‐based electrolytes, gel‐electrolytes, and solid‐state electrolytes, and polymers, bear more consideration.…”

“…Sankaranarayanan and co‐workers uses a combination of potential mean force (PMF) calculations and molecular dynamics (MD) calculations, to estimate free energies of solvation, ionic conductivity, and activation barriers of various organic solutions with regards to Na‐ion . The simulations go on to suggest that maximum solvation energy occurs in EC, EC:PC, and EC:EMC solvents, while minimum solvation energies occur in PC and EMC solvents.…”

Electronic Structure Insights into the Solvation of Magnesium Ions with Cyclic and Acyclic Carbonates

“…Further information on the ABF algorithm and methodology and simulation details including initial setup, description of the reaction coordinate and data collection can be found in various previously published articles. [16][17][18] Af ully atomistic force field based on the CHARMM general force field (CGENFF) [19] was used to model the cyclic and acyclic carbonates and salt interactions.…”

“…[16] In designing new electrolytes, it is generally desired that the solubility of the salt in nonaqueous solvents are high. Our basic hypothesis is that for as uccessful ione lectrolyte system the ion should have af avorable DG (sol) in ap articulare lectrolyte.…”