Research On The Flexible Interface Of Solid Electrolyte Lithium-ion Battery

Solid-state electrolyte lithium batteries have received more and more attention.They use metallic lithium as the negative electrode to obtain high energy density(theoretical specific capacity is about 3800 m Ah g^-1),and can also solve the safety problems caused by flammable liquid electrolytes.Solid electrolyte is the core component of lithium battery,which directly affects battery performance and battery safety.Among them,the interface between the electrolyte and the battery is the key to the dendrite growth and charge-discharge performance of the battery.This thesis conducts research from the perspective of flexible electrolyte/electrode material interface.By optimizing the flexibility and conductivity of the electrolyte membrane,constructing a matching Li/electrolyte flexible interface,the following two aspects are carried out:（1）Construction of flexible lithium ion electrolyte membrane:This paper uses poly（vinylidene fluoride-hexafluoropropylene）（PVDF-HFP）as the polymer flexible matrix,and adds lithium bistrifluoromethanesulfonimide（Li TFSI）,which increases the amorphous area and accelerates the movement of polymer segments,thereby increasing the conductivity of lithium ions.Studies have shown that when the mass ratio of PVDF-HFP:Li TFSI is 6:4,the ionic conductivity of the electrolyte membrane reaches3.17×10^-4 S cm^-1（30℃）,which is the current high level.The assembled lithium symmetrical battery can be cycled stably for 1000 h at a current density of 0.5 m A cm^-2,and there is no dendrite.The button battery was assembled with lithium iron phosphate as the positive electrode.After 200 cycles at 0.1 C,the specific capacity was 127.8 m Ah g^-1,and the capacity retention rate was 85.62%.After 100 cycles at 0.5 C,the capacity retention rate was 63.82%.（2）Li/electrolyte flexible interface construction:Based on the better compatibility between the uniform nucleation of lithium and the flexible electrolyte membrane,in this paper,a metal organic framework material（MOF）is grown on the 3D current collector foam nickel to increase the specific surface area,so that the lithium is deposited uniformly,and the interface compatibility between the electrolyte and the electrode is improved.The test results show that the lithium symmetric battery can be cycled stably for 1000 h at a current density of 1 m A cm^-2.Using polymer electrolyte membrane to match the modified negative electrode lithium,the discharge specific capacity after 100cycles at 0.2 C is 142.4 m Ah g^-1,and the corresponding capacity retention rate is91.49%.After 100 cycles at 0.5 C,the capacity retention rate is 76.93%.