Polysiloxanes with oligo‐oxyethylene side chains of the type —O(CH2CH2O)7CH3 and —(CH2)3O(CH2CH2O)nCH3 (average n ≈ 7 and 11) were synthesized from poly(hydrogenmethylsiloxane) and characterized by 1H n.m.r., 29Si n.m.r., i.r. and g.p.c. Cyclic analogues were used as model compounds and synthesized from tetramethylcyclotetrasiloxane. Polymer electrolyte complexes were made from the comb polymers and LiClO4 by solvent‐casting from THF, and their conductivities measured as a function of temperature and studied by differential scanning calorimetry and correlated with their conductivity behaviour. Maximum conductivities close to 10−4S cm−1 were achieved at room temperature and at ethylene oxide units to Li+ ratios of about 25. Cross‐linking or blending with high molecular weight poly(oxyethylene) lowers the conductance somewhat but vastly improves the mechanical properties of the complexes, and the blends with PEO can be cast into thin, flexible and tough films with good conducting properties.
A novel water-borne fluorinated binder is synthesized via copolymerizing 2-(perfluorohexyl) ethyl methacrylate (PFHEMA) and poly(ethylene glycol) methacrylate (PEGMA) to improve the performance of lithium ion battery with LiFePO 4 -based cathode materials. The resulting copolymer binders can self-assemble into 150−220 nm particles stably dispersed in aqueous solution. Self-dispersed fluorinated binders (SF binders) with the PFHEMA to PEGMA ratio of 3:1 effectively reduce the overpotential during the highdischarge current density compared with the conventional PVDF cathode binder. Further increasing the PEGMA amount yet decreases the electrochemical performance of SF binders, inconsistent with the expected Li + conduction of the PEO moiety. Molecular dynamics simulations show that the PEO segments reduce the Li + and PF6 − interaction and increase the amount of unpaired Li + . In contrast, the PEO moiety wrapping around Li + can decrease its mobility. These competing effects lead to the observed optimum ratio of PEO to fluorinated moieties. The novel SF binders are fully compatible with LiFePO 4 -based cathode materials and feature small impedance after charging and discharging. Coin cells assembled with the SF cathode binder demonstrated excellent cyclic performance after 150 cycles with negligible decay and near-100% column efficiency. The superior performance of the novel water-borne SF binders makes them excellent candidates for the environmentally friendly production of high-power lithium ion batteries.
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