Low-cost, long-life, and high-power secondary batteries are one of the effective ways to realize grid-scale energy storage to utilize intermittent renewable energy for power generation. Graphite cathode has the characteristics of low cost and environmental friendliness, while zinc anode has the advantages of high volumetric energy density, abundant reserves, and low zinc deposition/dissolution overpotential. Therefore, zinc/graphite dual-ion battery combines the advantages of zinc anode and graphite anode It has good application prospects in grid-scale energy storage.
Researcher Cui Guanglei and Associate Researcher Zhao Jingwen of the Biomimetic and Solid State Energy System Research Group of Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences. The preliminary research is based on the rapid kinetics of zinc deposition/dissolution and bis(trifluoromethylsulfonic acid) imine anion (TFSI- ) Pseudocapacitance behavior of inserting/extracting graphite to construct a zinc/graphite dual-ion battery based on zinc negative electrode and graphite positive electrode. The battery can achieve 200C charge and discharge with a power density of 16.3 kW/kg (J. Power Sources 2020, 457, 227994). However, due to the high potential of anion insertion/extraction of graphite, partial oxidative decomposition of the electrolyte occurs, which limits the coulombic efficiency and cycle life of the battery.
Recently, the research group took advantage of the feature that divalent zinc ions easily form associative ion pairs with anions. In the Zn(TFSI)2/EMC (methyl ethyl carbonate) electrolyte, the group introduced trimethyl phosphate with strong electron donating ability. Ester (TMP) solvents "bind" TFSI-anions in the solvation region of TMP in the form of associated ion pairs, realizing the "decoupling" separation of EMC solvent molecules and anions, and reducing EMC-TFSI, which has poor oxidation stability -concentration. Electrochemical test results show that this anion solvation structure regulation strategy can increase the electrochemical window of Zn(TFSI)2/EMC electrolyte by 0.45 V, and enable the zinc/graphite dual-ion battery to be charged at a high cut-off voltage of 2.80 V Discharge cycle 1000 times (capacity retention rate reaches 92%). In addition, the Zn(TFSI)2/EMC electrolyte added with TMP still maintains high ionic conductivity and has flame retardant properties, which ensures that the zinc/graphite dual-ion battery has good rate performance and safety performance. This research provides constructive ideas for the development of high-voltage carbonate electrolytes.
Related research results were published on Angew. Chem. Int. Ed., the first author of the paper is Chen Zheng, a postdoctoral fellow from Qingdao Energy Institute. The research work is supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the Dalian Institute of Chemical Technology-Qingdao Institute of Energy Convergence Fund.
Schematic diagram of adjusting the solvation structure of anions to improve electrolyte oxidation stability
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