Researchers at Tohoku University have devised a means to stabilize lithium or sodium depositions in rechargeable batteries, helping keep their metallic structure intact. The discovery prevents potential battery degradation and short circuiting, and paves the way for higher energy-density metal-anode batteries. An open-access paper on the work appears in the journal Cell Reports Physical Science.
Multivalent cation additives modify the solvation structure of lithium or sodium cations in electrolytes and contribute to flat electrodeposition morphology. Li et al.
Scientists are ever-seeking to develop safer, higher-capacity, and faster charging rechargeable batteries to meet energy needs sustainably. Metal anodes currently show the highest promise to achieve that goal. However, the use of alkali metals poses several problems.
In a rechargeable battery, ions pass from the cathode to the anode when charging, and in the opposite direction when generating power. Repeated deposition and dissolution of metal deforms the structures of lithium and sodium. Additionally, fluctuations in diffusion and electric fields in the electrolytes close to the electrode surface leads to the formation of needle-like microstructures called dendrites. The dendrites are weakly bonded and peel away from the electrodes, resulting in short circuiting and decreases in cycle capacity.
To solve this problem, a research team led by Hongyi Li and Tetsu Ichitsubo from Tohoku University\’s Institute for Materials Research added multivalent cations, such as calcium ions, that altered and strengthened the solvation structure of lithium or sodium ions in the electrolyte.
… focusing on CaTFSA2 as an exemplary additive, we reveal that dendrite-free morphology upon alkali metal electrodeposition can be attained by modifying the solvation structures in dual-cation electrolytes. Addition of Ca2+ promotes alkali cation (Li+ or Na+) to form the contact ion pairs (CIPs) with the counter anions, which replaces the solvent-separated ion pairs that commonly exist in single-cation electrolytes. The strong binding of the CIPs slows the desolvation kinetics of alkali cations and, consequently, realizes a severely constrained alkali metal electrodeposition in a reaction-limited process that is required for the dendrite-free morphology.
—Li et al.
For their next steps, Li and Ichitsubo are hoping to improve the metal anodes’ interfacial design to further enhance the cycle life and power density of the batteries.
Hongyi Li, Masaki Murayama, Tetsu Ichitsubo (2022) “Dendrite-free alkali metal electrodeposition from contact-ion-pair state induced by mixing alkaline earth cation,” Cell Reports Physical Science, doi: 10.1016/j.xcrp.2022.100907