Solvated ions in solid electrodes: alternative routes toward rechargeable batteries based on abundant elements
Storing large amounts of electrical energy is a major challenge for the forthcoming decades. Today, lithium-ion batteries (LIBs) are considered the best option for electric vehicles and grid storage but these rising markets put severe pressure on resource and supply chains. The principle of LIBs is based on solid electrodes separated by a liquid electrolyte between which Li ions are reversibly exchanged during charge and discharge. The efficient Li+ transport in the different phases and across the interfaces is essential for achieving a good performance. A fundamental difference between ion transport in solid phases and ion transport in solutions is that the ions are “naked” in the solid phase but solvated in the liquid phase. Recently major efforts have been initiated to adopt the successful LIB concept to other working ions such as Na+, K+, Mg2+, Ca2+ or Al3+. This is motivated by the promise of lower cost thanks to their abundance as well as in some cases higher energy density. The progress, however, is limited mainly due to an unfavourable mismatch between the solid electrode host structures and the ion radii or too large charge/radius ratios. Especially multivalent ions lead to severe lattice polarization frustrating ion mobility in solid electrodes.
This project aims at a radically different concept, i.e. instead of “naked” ions, solvated ions will be intercalated into the electrodes. Solvent co-intercalation is traditionally considered as highly detrimental. Latest results, however, question the generality of this argument. The SEED project will explore the concept of using solvated ions in solid electrodes for the reversible storage of a variety of ions. As the solvation shell acts as electrostatic shield and can be tuned in its composition, lattice polarization can be minimized. Using this effect, the SEED project finally aims at enabling reversible charge storage of multivalent ions in host structures with properties far beyond current state-of-the art.