Single-ion conducting electrolytes are an interesting alternative to liquid binary salt electrolytes, which are currently used in most batteries due to their high ion conductivity. However, the mobility of both cations and anions in these electrolytes results in an ion concentration gradient, and consequent polarisation losses. The ion concentration gradient is especially detrimental for alkali metal batteries. It causes inhomogeneous metal deposition leading to uncontrolled dendrite growth at the alkali metal electrode.¹ Thus, it is necessary to eliminate the free movement of anions. One way to achieve that is by covalently tethering the anions to a polymer backbone. So called ionomers have achieved considerable success toward stabilising lithium metal deposition and preventing dendritic structure.^2,3 By exchanging the counter ion these ionomers can be used in a wide range of different types of batteries. Here, we report on the synthesis and development of novel ionomers derived from inexpensive and chemically robust polymers. The microporous ionomer membranes infused with liquid achieve cation transference numbers close to unity, high ion conductivity (> 10^-5 Scm^-1 at room temperature) over wide temperature ranges, and good thermal and mechanical stabilities, see Fig. 1. Stable Na/Li plating stripping performance is achieved using the ionomer membrane.

1. Lin, D. et al., Nanotechnol. 2017, 12, 194–206.
2. Lu, Y. et al., Adv. Energy Mater. 2015, 5, 1402073.
3. Oh, H. et al., Mater., 2016, 28, 188-196.

Caption Fig.:
Fig 1: (a) Photograph and SEM image of the microporous ionomer membrane. (b) Arrhenius plot of the Na⁺ ion conductivity of the microporous ionomer membrane infused with EC/DEC (vol. 1:1).