Electrolyte And Electrode Interfacial Regulation And Their Influences In Alkaline Metal Battery Performance

In the alkali metal ion battery systems,the solid electrolyte interphase layer(SEI)formed by the electrolyte decomposition on the electrode surface due to the side reactions can mitigate the electrolyte decomposition further,then improving the compatibility of the electrolyte/electrode interface,in turn stabilizing the electrode and also improving the battery performance.Thus,it has become a criterion for electrolyte design to form a specific SEI layer by adjusting electrolyte components(such as salts,solvents,and additives)to optimize battery performance.However,compared with the SEI layer,recently many studies have found that the solvation structure of the electrolyte can also affect the performance of electrodes and batteries significantly.But,the reason for the final performance improvement is still attributed to the SEI film derived from a specific solvation structure.How to analyze and clarify these two viewpoints is directly related to the design of the electrolyte and its understanding of the mechanism underlying the battery performance.Therefore,how to construct a relationship between the influences of the SEI layer,solvation structure,interfacial desolvation behaviors,and battery performance is an urgent scientific problem to be solved.Based on this research background,the main research contents and results of this thesis are as follows:A new strategy of switching electrolytes to tune SEI properties was presented,by which a unique and thinner SEI can be pre-formed on the graphite electrode first in an ether-based electrolyte,and then the as-designed graphite electrode can demonstrate extremely high-rate capabilities in a carbonate-based electrolyte,enabling the design of fast-charging and wide-temperature lithium-ion batteries.A molecular interfacial model involving the conformations and electrochemical stabilities of the Li+-solventanion complex was presented to elucidate the differences in SEI formation between ether-based and carbonate-based electrolytes,then interpreting the reason for the obtained higher rate performances.A strategy for adjusting the solvation structure of the electrolyte by solvent and anion was proposed,by which the relationship between the microscopic electrolyte solvation structure and the macroscopic lithium deposition morphology and Coulombic efficiency is explored and constructed.The study found that by weakening the Li+solvent coordination,the de-solvation energy of the electrolyte/electrode interface can be reduced,thereby reducing the polarization of the battery,which can effectively alleviate the lithium dendrites growth and then improve the Coulombic efficiency of the battery.Based on the varied kinetics and electrochemical stability on the electrode surface by varying the electrolyte components,we clarify the influence of each component of the electrolyte on the Li+solvation structure,then build an interfacial model to interpret the relationship between the lithium deposition/stripping process and the electrolyte components.A new method of using additives to modify the solvation structure of the electrolyte is proposed to make the flame-retardant electrolyte of potassium-ion batteries compatible with graphite without increasing the concentration of potassium salts.It is proposed that the basic unit of the electrolyte microstructure(i.e.,K+solvation structure)can be adjusted by the additive vinyl sulfate(DTD)to well control the compatibilities of graphite(i.e.,K+deintercalation or K+-solvent intercalation).On this basis,a graphite-compatible nonflammable electrolyte(1.0 M potassium bis(fluorosulfonyl)imide(KFSI)dissolved in trimethyl phosphate(TMP)with 6 wt%DTD added)was designed.Based on this electrolyte,a safer and high-performance potassium-ion full battery was designed.A new perspective of employing diluent to modify the electrolyte through intermolecular interactions was proposed,by which a novel ultra-low concentration non-flammable electrolyte(i.e.,1.0 M potassium bis(fluorosulfonyl)imide(KFSI)dissolved in trimethyl phosphate in potassium-ion batteries(TMP)and 1,1,2,2tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(HFE)molar ratio of 1:1 mixed solvent)can stabilize the graphite electrode well.We found that there is a dipole-dipole intermolecular interaction between the negatively charged fluorine(δ-F)of HFE and the positively charged hydrogen(δ+H)of TMP,which can effectively adjust the solvation structure of K+,enabling the easier de-solvation of K+at the electrode interface,then realizing the reversible(de-)intercalation of K+within the graphite electrode.Based on this electrolyte,a safer and high-performance potassium-sulfur full battery was designed.