A High-performance Lithium Metal Negative Electrode Is Constructed Based On A Composite Polymer Coating

In recent years,lithium metal has attracted much attention as the most ideal anode material for high energy density batteries.However,the low coulomb efficiency,volume expansion,poor safety and cycle life of lithium metal batteries caused by lithium dendrite are the bottleneck problems that make it difficult to commercialize.At present,many researchers have proposed various modification methods,such as designing new electrode structures,modifying separators,devising and constructing new solid electrolytes.In this paper,in order to solve the problems of the above lithium metal batteries,a high elastic modulus of polymer coating is used as an artificial SEI film?solid electrolyte interface?to regulate the stability of the electrode interface and suppress the growth of lithium dendrites.The research content of the thesis mainly includes three aspects,and the specific results have been concluded as follows:?1?Based on previous experiments,the four kinds of polyurethane monomers selected include hexamethylene diisocyanate?HDI?,4,4-dicycloethylmethane diisocyanate?HMDI?,and toluene-2,4-diisocyanate?TDI?,polymethylene polyphenyl polyisocyanate?PAPI?and polypropylene glycol(HO-PPO₂₀₀₀-OH)were aimed to super-crosslinked polymerize and prepared polymer coatings,meanwhile their properties were tested.The results indicate that the addition of rigid groups such as benzene rings in the molecular segment of the polymer TDI coating can make the chain elongation reach to 500%.At same time,it has excellent thermal stability,lower glass transition temperature after polymerization,and the favourable ionic conductivity.In the meantime,the polymer TDI can adjust the interface due to its flexibility and lithium-friendly sites?-OH?,so that its AC impedance value reaches 140?,and the cyclic stability exceeds 650 h and 300 h cycle stability at 1 mA/cm² and 2 mA/cm²current densities,respectively.At a rate of 0.5 C,a lithium iron phosphate?LiFePO₄,LFP?battery composed of a polymer TDI@Li electrode exhibits excellent cycle performance,and the coulomb efficiency of polymer TDI coating@Cu electrode reaches 93%.?2?Using the TDI-PPO as a functional monomer,the prepared TDI-PPO-TDI triblock molecular chain was crosslinked with SiO₂ nanoparticles to compound a nano-polymer electrolyte CNPE?Cross-linked nanoparticls polymer electrolyte?with a three-dimensional network structure,and a new composite coating LHCNP?Lithium halloysite cross-linked nanoparticls polymer?was obtained by compounding CNPE with nano-tubular lithium-based halloysite.The three-dimensional network structure of CNPE membrane and the halloysite tubular structure can effectively homogenize the lithium ion flux and uniformly deposit the ion beam on the lithium surface,thereby reducing local current and lithium dendrite.The research results show that the chain elongation of LMCNP is as high as 700%and the shear modulus is 0.25 GPa.At 1 mA/cm²,2 mA/cm² current densities,and 5 mA/cm²,the polarization cycles exceed 1000 h,550 h,and 120 h,respectively;At a rate of 2 C,the capacity of the LFP full battery is maintained at 120 mAh/g after 800 cycles;LHCNP coating can achieve uniform lithium ion deposition and peeling behavior,at 0.5 mA/cm² and1 mA/cm².The coulomb efficiency of the LHCNP@Cu/Li electrode reached over 99%.?3?In order to obtain a polymer coating with better performance,a new composite polymer coating LMCNP?Lithium montmorillonoid cross-linked nanoparticls polymer?was synthesized by combining CNPE with layered lithium-based montmorillonite.The three-dimensional space structure of polymer coating can prevent the larger anions from passing through,and the artificial lithium ion channels provided by lithium-based montmorillonite can uniformly deposit lithium ions on the electrode surface.The research results show that the elastic modulus of LMCNP reaches 650%and the shear modulus is0.25 Gpa;At 1 mA/cm²,2 mA/cm²,and 5 mA/cm² current densities,the LMCNP@Li electrode cycle exceeds 2000 h,700 h,and 500 h,respectively;compared with the pure copper electrode,the coulomb efficiency and cycle performance of the LMCNP@Cu electrode have been significantly improved at 0.5 mA/cm² and 1 mA/cm² current densities;At a rate of 2 C,the LFP full cells cycle after 1400 cycles,and the capacity is maintained at120 mAh/g,the coulomb efficiency remains above 99%.