With the rapid development of electric vehicles and mobile electronic devices, the energy density of lithium-ion batteries that provide power energy is higher. The energy density of lithium-ion batteries based on the plug-in principle is close to its upper limit energy density, and the space is increased. In comparison, lithium metal batteries with lithium as the negative electrode have an unparalleled advantage in increasing energy density. However, lithium metal batteries based on traditional liquid electrolytes have repeated SEI cracking and generation, and lithium negative volume expansion , Lithium dendrite growth, dead crystals and other coulombic efficiency, battery resistance and safety issues, all of which limit the rapid development of high-performance lithium metal batteries.
Recently, relying on the Qingdao Institute of Bioenergy and Process Technology, a team of scientists of the Chinese Academy of Sciences, Qingdao Institute of Bioenergy and Process Technology (hereinafter referred to as 'Qingdao Energy Storage Institute') to solve the above-mentioned key bottleneck problems of lithium metal batteries, with polymers Electrolyte as a core breakthrough point, systematically explore solutions from three aspects: (1) protection of lithium anion by large anion lithium salt; (2) construction of artificial organic/inorganic composite interface film (SEI); (3) consideration of high voltage resistance The development of multi-functional polymer electrolytes protected by lithium negative electrodes, a series of innovative research work has played a significant role in promoting the development of high-performance lithium metal batteries.
In order to solve the problem of lithium dendrites from the perspective of lithium salt, researchers at Qingdao Energy Storage Institute designed and synthesized a new type of perfluoro-t-butoxytrifluoroborate (LiTFPFB) with a large anion structure, which retains the lithium salt. The main structure of LiBF4 anion can improve its stability to aluminum current collector on the one hand; on the other hand, the presence of large anion can form lithium negative electrode protective film in situ to improve the electrochemical performance of lithium metal battery. The ionic conductivity is significantly higher than that of LiBF4, and has good stability to the aluminum current collector. A protective film can be formed on the lithium metal anode to effectively inhibit the further reaction of the lithium metal with the electrolyte, thereby effectively protecting the lithium anode. The results were published as Back Cover in the international journal Chem. Sci. (Chem. Sci., 2018, 9, 3451-3458).
In view of the fact that lithium metal is used as a negative electrode, there are SEI instability, serious side reactions leading to low coulombic efficiency, short cycle life and other unfavorable factors. From the perspective of polymer interface modification, the researchers designed artificial SEI film to effectively protect the metal lithium negative electrode. (Fig. 1a), the SEI film consists of polycyanoacrylate and a lithium oxide derivative dispersed therein (Chem. Mater., 2017, 29, 4682-4689). It was found that the synergy of the organic/inorganic layer makes The interface is fast in conducting lithium ions while ensuring that SEI is not easily detached, and also significantly inhibits side reactions occurring in the interface region (Chem. Mater., 2016, 28, 3578-3606), thereby giving excellent lithium metal batteries. Interface stability and long cycle stability (Chem. Mater., 2018, 30, 4039-4047).
In order to solve the instability of the positive solid electrolyte interface (CEI) in the high voltage (4.45 V) lithium cobaltate/lithium metal battery, electrochemical oxidation side reactions are likely to occur at the interface at high potential, and lithium negative electrodes exist at high current and large capacity. Lithium dendrites and other issues, Qingdao Energy Storage Institute under the guidance of the 'rigid and flexible' polymer electrolyte design concept (Small, 2018. DOI: 10.1002/smll.201800821; Adv. Sci., 2018, 5, 700503) Polyvinyl methyl ether-maleic anhydride multifunctional polymer electrolyte was prepared using bacterial cellulose as a rigid skeleton support material (Energ. Environ. Sci., 2018, 11: 1197-1203). The experimental results show that: the polymerization The electrolyte can have a versatile effect of stabilizing the positive electrode interface and protecting the lithium negative electrode, thereby synergistically improving the long cycle stability of the 4.45 V lithium cobalt oxide/lithium metal battery. At the same time, the article clarifies the polyvinyl methyl ether in detail. - Multifunctional mechanism of action of maleic anhydride polymer electrolytes (Fig. 1b). Due to a series of work on high voltage lithium cobalt oxide/lithium metal batteries, the researchers were invited to write Reviving lithium cobalt oxide for Chem. Soc. Rev. Based lithium s A review of econdary batteries-toward higher energy density (Chem. Soc. Rev., 2018, DOI:10.1039/C8CS00322J), details the research progress of high energy density lithium cobalt oxide batteries, challenges, future opportunities and development directions.
The related series of research has won the National Natural Science Foundation Outstanding Youth Science Fund, the National Key Research and Development Program, the Chinese Academy of Sciences Nano Pilot Project, the Shandong Natural Science Foundation, the Qingdao Energy Storage Industry Scientific Research Think Tank Joint Fund and the Qingdao Energy Institute '13th Five-Year Project. Such a strong funding.
Figure 1 (a) artificially constructed organic/inorganic composite electrolyte membrane (SEI) modified high performance lithium metal anode; (b) polyvinyl methyl ether-maleic anhydride multifunctional polymer electrolyte