Polymer-Assisted Regulation Of Solid Electrolyte Interface And Its Electrochemical Properties

Given that traditional lithium-ion battery cannot satisfy the future energy storage requirements due to the limitation of utilized material,herein more powerful energy storing devices are urgent to develop.From the perspective of material design,Li mental anode and high Ni ecathode with high electrode capacity and large gap in redox potential between positive and negative electrodes can be selected for matching to improve the energy density.In addition,due to the highly flammable and volatile nature of liquid electrolytes,serious safety issues such as explosions or fires continue to plague the commercialization of lithium-metal batteries.For the cathode,high voltage cathode materials require higher voltage to play more capacity.Traditional liquid electrolyte cannot provide reliable solution to the above issues.Due to the excellent properties of solids electrolyte,such as non-flammable,non-leakage and slower reactivity,it has been expected to develop solid-state batteries with longer life and higher energy density,and simultaneously provides the possibility for lithium metal to be used as the anode of lithium batteries.Therefore,solid-state lithium batteries(SSLBs)have emerged as the most promising candidate for the next generation of energy storage devices.However,solid-state battery applications still suffer from low ion transport efficiency caused by incomplete interface contact or incompatibility between electrolyte and electrode Thus,in this study,we first understand the failure mechanism of solid electrolyte,and then the functional polymer was designed to improve the matching between electrolyte and electrode materials,and was successfully applied in high-voltage lithium metal batteries,showing excellent electrochemical performance.The specific details are as follows:1.In order to understand the mechanism of battery failure and the possible interface evolution at the atomic scale,first-principles calculations were used to build Li and LAGP,as well as LAGP and LCO interface models,and then two different conditions were used for processing after contact and after charging.Finally,the corresponding transfer of lithium ions and electrons across the interface under different conditions is predicted.At situation of contact,the vacancy formation energy(E_v)of lithium in bulk materials is calculated to evaluate the standard chemical potential of lithium and the corresponding charge transfer driving force.Then,cation exchange at the LAGP/LCO interface,including P/Co,Ge/Co and Al/Co,which has been experimentally confirmed,is also considered.Regarding the state of charging,we compared the E_v of Li in the bulk structure and the interface structure to assess where the lithium ions will mainly be stripped.With the construction of our interface model and DFT calculation,ion and electron transfer at the NASICON-type LAGP interface under different conditions in ASSB can be predicted.2.For the interface problem,the targeted functional carbonate layer was used to modify the LAGP based solid electrolyte to achieve the successful operation of the high voltage lithium metal battery.Two functional carbonates,CUMA and MMA,were used for in situ free radical polymerization reaction to form a gel,and the homogeneous organic layer was formed on the surface of LAGP.By controlling the heating time and temperature,the surface phase composition can be precisely adjusted.The electrochemical performance of LAGP solid electrolyte with different modification layers was tested to explore the reasons for the difference of their performance.The NMC811 cell has shown good cycle performance(up to 89%after200 cycles),high coulomb efficiency(over 99.8%per cycle)and good rate performance.3.The synthesis of a cage-type flame-retardant phosphate ester,PUMA:with(1-oxo-2,6,7-trioxa-1,5-phosphabicyclo[2.2.2]octan-4-yl)methanol and methyl acrylic acid ethyl cyanide as raw material,through one step reaction,the PUMA monomer was achieved.Then the monomer mixed with two fluorine boric acid lithium oxalate(Li DFOB)/ethylene carbonate(EC)/dimethyl carbonate(DMC)to obtain a proper matching of the flame retardant of semi-solid gel,with a wide electrochemical window(0～5.4 V vs Li/Li~+)and good electrochemical performance.The high-loading Si C450/NCM811 cell was assembled with a stable cycle of 150cycles and maintained a higher capacity retention rate(84.9%)and an average coulombic efficiency(99.55%),showing higher cycle stability than the liquid electrolyte cell.At the same time,the electrolyte can effectively inhibit the side reaction of the cathode/electrolyte interface and maintain the integrity of the cathode structure.This work provides a new horizon for the development of high voltage and safe lithium-ion batteries,and has a guiding significance for the application of high voltage polymer electrolyte in high voltage batteries.