The increasing demand for lithium may eventually generate an unstable market for the lithium-ion batteries, which are ubiquitous in portable electronics. The higher availability and lower cost of sodium make it an interesting alternative, especially since the similarity in their chemistry means that some design principles of lithium materials can be borrowed for sodium-ion batteries.
Pedro Lavela and colleagues, University of Córdoba, Spain, have been working on cathode materials for sodium-ion batteries. They studied the effects of non-stoichiometry in sodium vanadium phosphates with a view to improving the electronic conductivity. This was prompted by similar studies into off-stoichiometry in LiFePO4 for lithium-ion battery cathodes.
The addition of excess sodium produced an impurity phase of Na4P2O7 and also resulted in enhanced battery performance. The researchers propose that the impurity phase boosts ion diffusion in the cathode. A full cell assembled from Na3.15V1.95(PO4)3 and graphite showed an energy density of 244 Wh kg–1 at 2.7 volts, which demonstrates the feasibility of the concept.
- Induced Rate Performance Enhancement in Off-Stoichiometric Na3+3xV2–x(PO4)3 with Potential Applicability as the Cathode for Sodium-Ion Batteries,
María J. Aragón, Pedro Lavela, Gregorio F. Ortiz, Ricardo Alcántara, José L. Tirado,
Chem. Eur. J. 2017.