New progress in research and development of polymer electrolyte materials for power batteries

　　The biggest potential safety hazard of power batteries is battery thermal runaway. Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences Qingdao Institute of Energy Storage Industry Technology has achieved a stage in developing a high-safety polymer electrolyte material system for power batteries to solve this safety problem. Progress, and is rapidly advancing its industrialization process.

　　The biggest potential safety hazard for power batteries is battery thermal runaway. Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences Qingdao Institute of Energy Storage Industry Technology has achieved a stage in developing a high-safety polymer electrolyte material system for power batteries to solve this safety problem. Progress, and is rapidly advancing its industrialization process.　　 With the global energy shortage and environmental pollution increasing, vigorously developing new near-zero emission vehicles represented by pure electric vehicles is one of the development strategies determined by the country. Efficient, safe, and reliable power batteries are the bottleneck restricting the new near-zero emission automobile industry, and it is also one of the "shortcomings" of new energy vehicles. The biggest potential safety hazard of power batteries is battery thermal runaway. Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences Qingdao Institute of Energy Storage Industry Technology has achieved a stage in developing a high-safety polymer electrolyte material system for power batteries to solve this safety problem. Progress, and is rapidly advancing its industrialization process.　　 The existing liquid electrolyte system for lithium-ion batteries cannot meet the requirements of power batteries for high energy, high power, and safety. The R&D team of Qingdao Energy Storage Industry Technology Research Institute put forward the R&D idea of "Rigid and Flexible" and developed a series of new polymer electrolyte systems, which solved the above-mentioned bottleneck problems and greatly improved the safety performance. "Rigid and flexible" is the use of "rigid" framework materials, such as polyimide, aramid, polyaramide, glass fiber and cellulose (NanoEnergy, 2014, 10, 277-287; SolidStateIonics, 2013, 245- 246,49-55; 232,44-48; Journal of the Electrochemical Society, 2013, 161, A1032-A1038; Progress in Polymer Science, 2015, 43, 136-164) non-woven materials to improve the mechanical properties and dimensional thermal stability of the battery; use "soft" Ion transport materials, such as polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polymethyl methacrylate (PMMA), cyanoacrylate and polypropylene carbonate (PPC) ), etc., endows excellent ion conductivity and interface stability, and achieves a win-win effect through the "combination", that is, the combination of two or more materials, and achieves a substantial increase in overall performance, thereby meeting the requirements of power batteries. Respect the nature and cherish the material, and adopt the natural method. This research explores the "rigid and flexible" composite polymer electrolyte system to realize the unity of opposites between rigid and flexible to achieve mechanical strength, heat resistance, potential window, interface stability and ionic conductivity, etc. Comprehensive performance improvement. Figure 1 is the design concept of "Rigid and Flexible" Gel Polymer Electrolyte. Although the traditional vinylidene fluoride system has the advantages of high stability and higher potential window, its ionic conductivity is low, and its mechanical strength and thermal stability in the wet state are very poor. In order to improve the traditional vinylidene fluoride system The properties of the gel polymer electrolyte, the research team used it and polyimide and polysulfone amide and other non-woven materials nano-scale composite, rigid and flexible, integrated, improve the dimensional thermal stability and mechanical strength, to achieve its Comprehensive performance improvement (Journal of the Electrochemical Society, 2013, 160, A769-A774; Macromolecular Materials and Engineering, 2013, 298, 806-813; ACSAppl.Mater.Interfaces, 2013, 5, 128-134); in response to the problem of low lithium ion migration coefficient, a new type of Mono-ion polymer lithium borate as a surface enhancement material (CoordinationChemistryReviews,2015,292,56-73; JournalofMaterialsChemistryA,2015,3,7773-7779) to improve its ion migration number and compatibility, "hardness and flexibility, complement each other" Improve the overall performance of the battery system. The traditional polyacrylonitrile polymer electrolyte has the advantage of higher ionic conductivity, but the physical properties are relatively brittle and the processing performance is not good. The R&D team uses a new type of polymer electrolyte matrix (ACSAppl.Mater.Interfaces, 2015, 7, 4720- 4727; Electrochim.Acta2015,157,191-198; Electrochem.Comm.DOI:10.1016/j.elecom.2015.10.009), combined with the "rigid and flexible" design concept, to achieve comprehensive performance such as processing performance of nitrile polymer electrolyte The promotion. Gel polymer batteries play an important role in improving the safety of power batteries, but still use a small amount of volatile and combustible carbonate solvents. There are still certain safety hazards when used under high temperature or extreme conditions. It fully meets the demanding requirements of electric vehicles for power lithium batteries in terms of high energy and safety performance. Therefore, the development of a new high-safety all-solid-state electrolyte system is of great significance for improving the comprehensive performance of high-energy-density power lithium batteries. In view of the lower potential window and poor dimensional thermal stability and mechanical strength of the traditional PEO system, the researchers used high-potential cyanoacrylate as the material to increase the potential window; at the same time, the thermosetting cellulose non-woven film was used as the material Rigid framework, providing dimensional thermal stability and partially improved mechanical strength, developed a high-safety all-solid polymer electrolyte with high mechanical strength, wide electrochemical window and good dimensional thermal stability. Related research results have been published in international journals ( ScientificReports, 2014, 4, 6272). Aiming at the bottleneck problem of PEO’s low room temperature ionic conductivity, researchers based on the scientific problem itself, starting from the molecular structure that affects ion conductivity, combined with the multi-scale mechanism of ion transmission mechanism and kinetic transmission, designed an amorphous Polycarbonate-based room temperature all-solid polymer electrolyte. After characterization, it is found that the room temperature conductivity of this all-solid polymer electrolyte can reach the order of 10-4S/cm, the electrochemical window is 4.6V, the rate performance is better, and the room temperature long cycle is 1000 The loop capacity retention rate is 90%. Related research results were published in international journals (AdvancedEnergy Materials, DOI: 10.1002/aenm.201501082).　　 The all-solid-state polymer lithium battery prepared by the research team verified its safety performance by acupuncture test (Figure 3). Through testing, it was found that the assembled 6Ah large-capacity ternary system all-solid-state polymer lithium battery showed excellent safety performance. After four times of acupuncture, the all-solid-state lithium battery did not catch fire or explode. This is a traditional liquid lithium battery. Unmatched. This once again proves the advantages of the "rigid and flexible" electrolyte system in improving the safety performance of high energy density lithium batteries. Qingdao Energy Storage Research Institute has adopted the electrolyte design concept of "rigid and flexible" to achieve a series of progress in the development of key materials for high-energy-density polymer electrolyte batteries, and cooperated with Zhongtian Technology to develop large-capacity and high-safety power or storage The industrialization technology of single battery (energy density up to 300Wh/kg) can be used to jointly promote the industrialization of high-energy, high-safety all-solid-state power batteries. At the same time, the R&D team has applied this design concept to actively explore the development of a new generation of ultra-high energy density lithium-air secondary batteries, and gratifying progress has been made.