Innovative Polymer Hosts for Solid Lithium-ion Battery Electrolytes

• Current electrolytes used in lithium ion batteries are flammable and volatile organic liquids that are fundamentally unstable at the operational voltage of the cells, posing a significant safety risk. A practical approach to get over this obstacle is to substitute the liquid electrolyte solution with a solid (solvent-free) polymer electrolyte (SPE), which is a solution of a lithium salt in a solid polymer matrix. In the past few decades, polyethers, particularly those based on poly(ethylene oxide) (PEO) have been the subject of extensive research as SPEs. However, numerous researchers have noted inherent limits in the overall performance of PEO and other polyether-based electrolytes, driving the search for electrolytes based on alternative types of polymers. A few of those polymers that can be utilized as prospective polymer hosts for future lithium-ion batteries are introduced in this thesis.Organic carbonates are commonly used as liquid electrolytes, therefore their polymeric counterparts, polycarbonates, are suitable as host materials in SPEs. In contrast to PEO, carbonates show weaker coordination with the lithium ion, which consequently results in faster cation transport. In Paper I, we utilize a metal-free catalyst, diphenylammonium triflate (DPAT), to facilitate the ring-opening polymerization of trimethylene carbonate (TMC). This results in a copolymer, poly(trimethylene carbonate)-poly(trimethylene ether) (PTMC-co-PTME), which has a polymer backbone that possesses both carbonate and ether functionalities.In Papers II and III, we evaluate a new family of SPEs based on poly(β-amino ester)s (PBAEs) by employing aza-Michael addition in the presence of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We use off-stoichiometric multifunctional short chain acrylates and amines as monomers to synthesize crosslinked polymer electrolyte films through a one-step, dual-curing, metal catalyst and solvent free method. We establish that structural changes in the polymer backbone can be easily introduced by varying the monomers and their concentrations, resulting in enhanced ionic conductivities. This methodology generates zero side products, is highly atom efficient and produces free-standing electrolyte films in a single step.The use of additives in electrolytes is one of the most convenient and affordable ways to improve lithium-ion battery performance without requiring significant modifications. In Paper IV, we use the procedure described in Paper II to explore the effects of different measured concentrations of dimethyl sulfoxide (DMSO) as an additive in PBAE-based SPEs. DMSO has a high donor and acceptor number, making it an effective solvating agent for both the anions and cations in the electrolyte.

Ämnesord

NATURVETENSKAP  -- Kemi -- Polymerkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Polymer Chemistry (hsv//eng)

Nyckelord

Kemi med inriktning mot polymerkemi

Chemistry with specialization in Polymer Chemistry

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