| Solid polymer electrolytes（SPEs）are considered ideal for the next-generation lithium batteries,due to their excellent mechanical stability,thermal stability and safety.So far,researchers have studied extensively on the preparation and performance evalution of SPEs.In general,however,current study on SPEs is still in the tranfromation from its infancy to rapid-developing stage.The trade-offs between key properties of ionic conductivity,mechanical strength and lithium transference number(t Li+),result in unsatisfactory overall performances of SPEs for practical applications.Therefore,exploring polymers with new chemical component,topology and aggregation structure,and studying their performances working as SPEs,discovering new methods and new mechanisms for the fabrication of high-performance SPEs,are of great significance to promote the development of lithium batteries.In this thesis,we prepared novel SPEs based on alternating and hyperbranched polymers.Multifunctionally synergistic capability was endowed to the polymers by introducing ionic liquid,poly（ethylene glycol）or single-ion conducting moieties.Meanwhile,the transportation of lithium ions was modulated by controlling the aggregation structure,especially microphase separation,of SPEs.As a result,an optimization was achieved among properties such as ionic conductivity,mechanical strength,t Li+,et al.,and high-performance SPEs were obtained.Furthermore,we disclosed in details the structure-property relationship of the resulting SPEs,especially the correlation between performance and degree of branching in hyperbranched polymer electrolytes,providing new insights into the design of next-generation SPEs.The thesis is divided into three parts.1.Preparation and property characterization of high-performance solid polymer electrolytes based on alternating poly（ionic liquid）s（PILs）.In order to improve the ionic conductivity of PIL-based SPEs and achieve SPEs with both high ionic conductivity and high mechanical strength,a novel PIL PPa B-MT with an alternating structure was synthesized through thiol-epoxy click reaction and subsequent post-modifications.The alternating structure can separate the PEG segments and thus suppress their crystallization effectively,leading to an amorphous polymer with a very low glass transition temperature（Tg<-40°C）.Blending with PVDF-HFP and lithium salts,PPa B-MT can form solid polymer electrolytes.The alternating structure of PPa B-MT facilitated the formation of a nanoscale phase separation in the SPEs,in which PPa B-MT phase was highly conductive and PVDF-HFP phase had a high mechanical strength.As a result,the SPEs possessed both high ionic conductivity and high mechanical strength:the ionic conductivity of SPE with 50 wt%PPa B-MT reached 1.4×10-5 S cm-1 at 25°C and 10-4 S cm-1at 85°C;meanwhile,its Young’s modulus exceeded 200 MPa at 25°C.The ionic conductivity was comparable with the record in PIL-based SPEs reported in the literature,while the mechanical strength was dramatically improved.Li stripping and deposition experiments revealed that the SPE could effectively suppress the growth of Li dendrites due to its high mechanical strength.2.Preparation and property characterization of single-ion solid polymer electrolytes based on hyperbranched polymers.In order to simultaneously improve the ionic conductivity and the t Li+of polymer electrolytes,we synthesized and prepared the first hyperbranched sing-ion polymer electrolyte.A novel hyperbranched polymer HPCPEG with-COO-/Li+ion pairs was obtained through a one-pot synthesis,in which an A2-type monomer（Poly（ethylene glycol）diglycidyl ether）reacted with a B3-type monomer（DL-cysteine）via click reactions catalyzed by lithium hydroxide（Li OH）.In HPCPEG,the-COO-moieties are covalently bonded to the polymer backbone and lithium cations are the only moving species.Therefore,HPCPEG is a single lithium ion conductor.The hyperbranched topology suppressed the crystallization of PEG segments completely,and the polymer showed a very low glass transition temperature（Tg<-30°C）.SPEs were obtained by blending HPCPEG with PVDF-HFP.The SPE with 60 wt%HPCPEG showed excellent electrochemical properties:high ionic conductivity up to 2.3×10-5 S cm-1 at 25°C,1.2×10-4 S cm-1 at 85°C;a high t Li+of 0.86;and a stable potential window up to 4.8 V（vs.Li+/Li）.The ionic conductivity was two to three orders of magnitude higher than that of carboxylate-type single-ion conductors reported in literature.The high free volume and non-crystallinity of hyperbranched HPCPEG,together with the synergistic effects of conducting Li cations by the alternating-COO-groups and PEG9 pseudo crown-ethers,endowed high ionic conductivity of the single-ion polymer electrolytes.3.The effects of degree of branching on the performance of solid hyperbranched polymer electrolytes.We prepared SPEs based on hyperbranched polymers with different degree of branching（DB）,and elucidated the impact of hyperbanched structure on the performance of SPEs.Hyperbranched polyether HBPOs with different DBs were synthesized by controlling the reaction temperature during the cationic ring-opening polymerization of an AB2-type monomer（3-ethyl-3-hydroxymethyl-butylene oxide）.After the reaction,the second monomer ethylene oxide was added to the solution,resulting in a series of hyperbranched-star polymer HBPO-star-PEO,in which HBPOs with different DBs act as the core and PEOs are the arms.SPEs were obtained by blending HBPO or HBPO-star-PEO with PVDF-HFP and Li TFSI.As to the HBPO/PVDF-HFP/Li TFSI SPEs,their ionic conductivity were in the range of 10-8to 10-6 S cm-1 at different temperatures（25°C to85°C）,and raised one to two times with the increase of DB of HBPOs from 8%to 47%.While for HBPO-star-PEO/PVDF-HFP/Li TFSI SPEs,their ionic conductivity were in the range of 10-7to 10-4 S cm-1 at different temperatures（25°C to 85°C）,and raised seven to nine times with the increase of DB of HBPO cores from 8%to 47%.Adding 40 wt%ionic liquid EMITFSI into the HBPO-star-PEO/PVDF-HFP/Li TFSI SPEs could further increase their ionic conductivity to 10-6-10-3 S cm-1 at different temperatures（25°C to 85°C）,and the increase in ionic conductivity was more pronounced（～20 times）with the increase of DB of HBPO cores from 8%to 47%.Therefore,ionic conductivity of polymer electrolytes increased with the increase of DB,indicating that the topology of hyperbranched polymers with higer DBs facilitates better ion transportation in polymer matrix. |
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