B. Fenelon, J.P. Trigueiro, R.L. Lavall, G.G. Silva
Universidade Federal de Minas Gerais,
Brazil
Keywords: polymer electrolyte, lithium-sulfur battery, lithium bis(oxalate) borate
Summary:
Despite interest due to the sustainable and electrochemical potential presented, the commercialization of Li-S batteries still depends on solutions to operational problems that limit their practical application. A relevant problem is related to the formation of intermediate polysulfides. Dissolved polysulfides tend to migrate from the cathode to the anode, resulting in a shuttle effect, which leads to the deposition of insoluble species on the anode surface. A novel poly(ionic liquid), PILBOB, was synthesized from the commercial ionic liquid poly(diallyldimethylammonium chloride) (PILCl) and lithium bis(oxalate) borate salt (LiBOB), with the aim of designing a suitable electrolyte for Li-S batteries. The synthesized material was characterized by all relevant techniques, which demonstrated that the synthesis was successful, and the material obtained presented satisfactory thermal stability for the desired electrochemical application. PILBOB was used in the production of polymeric solid electrolytes with a mixture of the LiBOB salt and the ionic liquid 1-methyl-1-propyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide (MPPyTFSI) as additional ionic conductors and with the presence of polyacrylonitrile (PAN) in some samples. The use of PAN aimed to improve the performance of lithium‒sulfur batteries through the retention of polysulfides. Four different compositions were investigated with varying contents of ionic liquid. The thermal, morphological and electrical properties of the electrolytes were evaluated. The ionic conductivity values found at 25 °C are between the order of 10-4 and 10-5 S/cm and reach 10-3 S/cm at 100 °C. Linear sweep voltammetry measurements were used to evaluate the electrochemical stability window (ESW) of PIL electrolytes. Ered and Eox were defined as the potentials where the limiting current density reached 0.5 mA/cm2. The electrochemical window between Ered and Eox was 6 V. The results obtained revealed the high purity of the PIL-based electrolytes. The battery tests are in progress.