Research And Application Of Poly(vinylene Carbonate) In High Performance Secondary Batteries

Nowadays,the utilizations of rechargeable lithium-ion batteries?LIBs?are spreading from small-sized portable electronic devices to large-scale electric transportation tools and renewable energy storage systems.The ever-growing demands to increase the energy/power density of LIBs facilitate the development of advanced high-voltage prototype cells containing novel high-voltage cathode materials.Despite attractive properties such as high operating voltages and considerable rate capabilities,the commercialization of LiNi_0.5Mn_1.5O₄ cathodes is plagued by rapid capacity fade that stems from the severe parasitic side reactions with conventional liquid carbonate based electrolytes at a high voltage exceeding 4.5 V?vs.Li⁺/Li?.What's more,the scarcity and high cost of lithium impeding the further commercialization of LIBs.Efforts towards addressing this issue have been mainly focused on the development of sodium batteries.Poly?vinylene carbonate??PVCA?based gel polymer electrolyte,which possesses a merit of good interfacial compatibility with both cathodes and anodes.In this paper,the PVCA was further designed,modified and applied successfully to LiNi_0.5Mn_1.5O₄ based LIBs and sodium batteries.The specific contents are as follows:1)A poly?vinylene carbonate-acrylonitrile?based gel polymer electrolyte?PVN-GPE?is delicately designed by copolymerizing acrylonitrile with vinylene carbonate.The delicately-designed PVN-GPE can exhibit superior compatibility with LiNi_0.5Mn_1.5O₄ cathodes,in order to address the above-mentioned severe parasitic side reactions.When evaluating the electrochemical properties of LiNi_0.5Mn_1.5O₄/graphite full cells assembled with the PVN-GPE,an outstanding cycling stability?with a capacity retention of 93.2%after 200 cycles?has been achieved,which is far more superior than that of conventional liquid electrolytes.It is noted that,the introduction of vinylene carbonate endows PVN-GPE with improved interfacial compatibility towards lithium anodes,which can efficiently suppress the formation of lithium dendrites and enables excellent cycling performance?with a capacity retention of 90%after 200 cycles?of LiNi_0.5Mn_1.5O₄/Li metal batteries.2)A novel polymeric sodium tartaric acid borate is synthesized and blended with poly?vinylene carbonate?to prepare a single-ion conducting gel polymer electrolyte?PSP-GPE?.The PSP-GPE possesses a superior ionic conductivity of 1×10^-4 S cm^-1at ambient temperature and a high sodium ion transference number of 0.88.Compared to the NaClO₄ based liquid electrolyte,the Na₃V₂?PO₄?₃/Na battery assembled with the PSP-GPE exhibits improved cycling performance,especially at elevated temperatures,and effective suppression of sodium dendrites.This work demonstrates a promising method to design single-ion conducting gel polymer electrolytes for elevated-temperature sodium metal batteries.