Lithium Single-Ion Copolymer Nanoparticle Design for Salt-Free Quasi-Solid-State Electrolytes

This work studied the influence of copolymer chemistry on the properties of lithium single-ion quasi-solid-state polymer electrolytes (SIPEs) for lithium batteries. For this purpose, a series of functionalized lithium bis(trifluoromethanesulfonyl)imide poly(methyl methacrylate) copolymer nanoparticles NPs were synthesized by emulsion polymerization with very small particle sizes of around 30 nm. Thus, lithium bis(trifluoromethanesulfonyl)imide methacrylate and methyl methacrylate were copolymerized with an additional comonomer, either styrene (Sty) or poly(ethylene glycol) methacrylate (PEGMA). Then, lithium single-ion conducting quasi-solid-state polymer electrolytes were prepared by mixing the nanoparticles with sulfolane without any additional lithium salt. A deep electrochemical study of the polymer electrolytes was performed measuring ionic conductivity, lithium diffusion coefficient, lithium transference number (t Li+ ), and Li|Li symmetric cells, comparing always the copolymer nature. Interestingly, adding the comonomers to the Poly(LiMTFSI-co-MMA) single-ion polymer nanoparticles showed a significant improvement in the electrochemical SIPEs performance. Poly(LiMTFSI-co-MMA-co-Sty)Np/sulfolane electrolyte showed the most stable and promising electrochemical performance on Li|Li symmetric cells with a low overvoltage of around 0.3 V with an applied current of 0.1 mA cm-2. NMC-based full cells also showed great stability with a high specific capacity of 160 mAh g-1 at 45 degrees C.