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Oligoether branched-and-spaced “acid-in-chain” polymers, with variable length side chains attached to the acidic borons have been prepared by a simple two-step reaction sequence. These may be used as anion-retarding hosts for “salt-in-polymer” electrolytes or, alternatively, may be converted to polyanionic electrolytes by reacting with strong Lewis base anions. High ionic conductivities, reaching 7.6×10−5 S cm−1 at 25 °C have been obtained for the former case, using LiTFSI:B proportions of 1:1, and optimized side chain and spacer lengths. The electrochemical windows are wide enough (>4.5 V) for most applications. [Copyright &y& Elsevier]

Lithium polyMOB has been investigated as the polymer in a polymer-in-salt type electrolyte incorporating the salts lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium tetrafluoroborate (LiBF4). While all salts give rubbery solids at high salt contents, only LiClO4 provides high conductivity because only in the case of LiClO4 is the lithium cation motion highly decoupled from the structural relaxation. The crystallization of the salt at high salt contents prevents a favorable combination of mechanical and electrical properties, but the system provides an excellent example of the principle of the polymer-in-salt ionic rubber electrolyte and the factors determining its performance. [Copyright &y& Elsevier]

Plasticized and crosslinked versions of poly(lithium oligoetherato mono-oxalato borate), called lithium polyMOBs, have been studied. In heavily plasticized forms of both polyMOB, and a LiBH4-crosslinked polyMOB, the ionic conductivity reaches 10−3 S cm−1 at room temperature while single ion conductivity is automatically retained. The electrochemical stability window is up to 5 V, for both stainless steel (SS) electrodes. The plasticized forms are fluid, not a gel, due to the low molecular weight of the polyanions. Freestanding gel electrolytes with high single ionic conductivity of 10−4 S cm−1 at ambient can be obtained by incorporation of high molecular weight poly(methyl methacrylate) (PMMA) into the solution. Electrochemical cells using these electrolytes will not suffer from concentration polarization. [Copyright &y& Elsevier]