These are preliminary reports that have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information. For more information, please see our FAQs.
Preprints are manuscripts made publicly available before they have been submitted for formal peer review and publication. They might contain new research findings or data. Preprints can be a draft or final version of an author's research but must not have been accepted for publication at the time of submission.
submitted on 10.03.2020, 16:24 and posted on 11.03.2020, 11:40by Ronnie Mogensen, Simon Colbin, Ashok Menon, Erik Björklund, Reza Younesi
Sodium-ion batteries based on all-naturally-abundant elements, in which no cobalt, nickel, copper, and fluorine is used, can lead to a major breakthrough in making batteries more sustainable. Safety aspects -in particular flammability of electrolytes- in the state-of-theart battery technology is another important concern, especially for applications in which large numbers of cells are employed. Non-flammable battery electrolytes studied so far are based on highly fluorinated compounds or high salt concentrations, which suffer from high cost and toxicity. We here propose an electrolyte based on a single solvent and lowcost and fluorine-free salt at the lower range of “standard” concentrations. Our results show -for the first time- that sodium bis(oxalato)borate (NaBOB) is soluble in the nonflammable solvent trimethyl phosphate (TMP). This finding enables a non-flammable electrolyte with high ionic conductivity and promising electrochemical performance in fullcell sodium-ion batteries. An electrolyte of 0.5 M NaBOB in TMP provides ionic conductivity of 5 mS cm-1 at room temperature, which is comparable to commonly used electrolytes based on sodium hexafluorophosphate (NaPF6) and organic carbonate solvents. The proposed electrolyte shows the Coulombic efficiency of above 80% in the first cycle, which increased to about 97% from the second cycle in sodium-ion battery fullcells consisting of a hard carbon anode and Prussian white cathode. This work opens up new opportunities to design safe electrolytes which can further be optimized with electrolyte additives such as vinylene carbonate for industrial applications.