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Shi et al. Energy Mater 2023;3:300036 https://dx.doi.org/10.20517/energymater.2023.27 Page 3 of 14

conductor, however, also requires preventing polymeric chain reptation, which requires crosslinking. This
can be done via classical chemical (covalent) crosslinking, but other strategies have been proposed for
obtaining "physical’ crosslinking, for instance, using biphasic systems [20-22] . In this case, one "rigid" phase
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(i.e., crystalline or high Tg) is responsible for the mechanical properties, and the other phase ensures Li
transport. This allows decorrelating Li mobility and mechanical properties, both usually linked to polymer
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chain mobility in monophasic systems. Recently, this approach has been extended to single-ion "dry"
SPEs [23,24] . However, one issue arises for phase-separated systems that include a "dry" SPE phase, which is the
need, in principle, to include solvating and ionic functions onto the same block while maintaining high
chain segmental mobility, similar to "dry" single-ion monophasic SPEs. Thus, in general, polyether chains
are used for ensuring solvation and Li mobility, which results in many of the same limitations as for
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conventional SPEs in terms of electrochemical stability window and operational temperature range. We
recently reported on plasticized ionomeric block copolymers with nano-phase separation based on
polyaromatic backbones able to operate a Li||LiNi Mn Co O (NMC ) battery at 40 °C . Here, we
[25]
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0.33
0.33
111
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propose a plasticized single-ion SPE for fast-charging and low-temperature Li||NMC and Li||NMC
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high-energy LMPBs. Keeping large-scale production in mind, the electrolyte is obtained here via mechanical
processing of the polymer powder incorporating a high dielectric constant liquid phase, which opens the
route for high-volume production via extrusion and rapid implementation of the technology.
EXPERIMENTAL SECTION
Synthesis of polyanionic copolymers
The polyanionic copolymers noted as PTFSI-A/B are aromatic polyethersulfone multi-block copolymers
with ionic blocks bearing lithium trifluoromethane sulfonimide (TFSI), abbreviated as LiTFSI, and
hydrophobic blocks with high glass transition temperatures, i.e., partially fluorinated polysulfone. The A
and B are related to the lengths of ionic and hydrophobic block backbones, respectively. In a typical
example, i.e., a copolymer named PTFSI-10/5 [Scheme 1], the hydrophobic block with a glass transition
-1
temperature (Tg) of 220 °C and a molecular weight of 5,000 g mol alternates with the ionic block. The
-1
ionic block has a molecular weight of 10, 000 g mol in the block backbone and two LiTFSI functions per
structural unit. The synthesis of these copolymers, carried out in three steps, i.e., (i) backbone copolymer
synthesis by a polycondensation reaction; (ii) bromination of an ionic block; and (iii) grafting of TFSI
lithium salt by coupling reaction, was described previously [25-27] . Copolymers with high molecular
weight (Mw) are obtained [Supplementary Table 1]. For PTFSI-10/5, the Mw and polydispersity index (Ip)
of PTFSI-10/5 are 362, 000 g mol-1 and 2.2, respectively, hence in copolymer chains, the repetition of ionic
and hydrophobic blocks (x) ranges between 4 and 10. The lithium concentration in dried membranes,
determined from nuclear magnetic resonance (NMR) spectra and acid-base titration (following the
protocols described in [25,27] ), is presented in Supplementary Table 1. For PTFSI-10/5, the average value is
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1.15 10 mol Li g .
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Polymer electrolyte processing
The copolymer powder was dried under vacuum at 100 °C for 24 h before use. Propylene carbonate (PC,
BASF, Selectipur ) was dried and kept on 4 Å molecular sieves. The polymer electrolytes were prepared in
(TM)
a dry room with a dew point of -65 °C (i.e., H O < 5.4 ppm). The copolymers and PC were mixed in various
2
PTFSI/PC weight ratios, and the mixtures were sealed in a laminated "pouch bag” under vacuum and stored
at 70 °C for 24 h to ensure good uptake of the liquid phase. The mixture was then sandwiched between two
Mylar foils. After pressing at 10 bar for 5 min at room temperature (using another 100-µm Mylar foil as a
spacer), self-standing polymer electrolyte membranes were obtained. In the following, the electrolytes are
named according to the polymer name, followed by the PC weight fraction in the membranes (e.g., PTFSI-
10/5-70 for a SPE containing 70 wt.% of PC).