Three-component solid polymer electrolytes based on li-ion exchanged microporous silicates and an ionic liquid for solid-state batteries

Lithium ion-batteries (LIBs) are the most widely used devices in the area of electrical energy storage. However, several limitations regarding durability and safety are holding them back when it comes to larger applications, such as electric mobility. In this context, solid polymer electrolytes (SPEs) represent one of the most suitable options to overcome these issues. In this work, three-component SPEs based on poly(vinylidene fluoride-co-hexafluoropropylene) as polymer binder, the 1-butyl-3-methylimidazolium thiocyanate ionic liquid as ionic conductive component, and zeolites, to improve SPE ionic conductivity and electrochemical stability, were prepared and characterized. Different zeolite and zeolite-like structures (clinoptilolite, ETS-4 and ETS-10) were used, and the effect of lithium-ion exchange in their structures was evaluated. A clear influence of the ion exchange process on the crystallinity of the prepared samples is observed, which plays a key role in the conduction mechanisms. The ionic conductivity of the samples at room temperature is of the order of 10-5 S.cm-1 , making them suitable for battery applications. The assembled batteries show promising results at room temperature, proving that the ion exchange has a positive effect on battery performance. The ion-exchanged clinoptilolite sample presents the best performance at a prolonged number of cycles, with an initial discharge capacity of about 130 mAh.g-1 at C/10, and a capacity retention of 70% after 50 cycles. Thus, it is proven that the ion exchange process in microporous silicates represents a suitable strategy to develop high performance solid-state LIBs.The authors thank FCT (Fundação para a Ciência e Tecnologia) for financial support under the Strategic Funding UIDB/04650/2020, UID/CTM/50025/2021, UID/FIS/04650/2021, UID/EEA/04436/2021 and UID/QUI/0686/2021 and projects PTDC/FIS-MAC/28157/2017, MIT-EXPL/TDI/0033/2021, POCI-01-0145-FEDER-007688 and POCI-01-0247-FEDER-046985, financed by national funds through the Operational Program, through the Norte Operation Program. Grants SFRH/BD/140842/2018 (J.C.B.) and SFRH/BPD/121526/2016 (D.M.C) and contracts CEECIND/00833/2017 (R.G.) and 2020.04028 CEECIND (C.M.C.) are also acknowledged. Financial support is also acknowledged by the Basque Government (ELKARTEK program), Basque University System Research Groups (IT-1290-19), and University of the Basque Country (GIU18/197)