Preparation And Intensive Study Of Molten-Li-Derived High-Capacity Li-Containing Anodes For Lithium Batteries

Existing Li-ion batteries techniques with limited energy density achieved,cannot meet the ever-increasing high-capacity requirements from electrical vehicles,developing high-capcity electrode materials is therefore highly desired.Silicon with very high theoretical specific capacity,low Li⁺-insertion potential and high abundance,is proposed as one of the most promising anode candidates.Nonetheless,the huge volumetric variation up to 300%during cycling usually causes severe particle pulverization and structural fracture of Si anodes,leading to rapid capacity fading and battery failure.Nanostructuring has been proven effective to accommodate the volume change of Si anodes;however,the sharply increased specific surface area accelerates the side reactions with liquid electrolytes,leading to very low initial Coulombic efficiency(ICE)and thereby lowering the energy density.Prelithiation of Si anodes can effectively improve the ICE by compensating the irreversible Li consumption.The resultant Li-rich Li_xSi can be used to match Li-free high-capacity cathodes such as sulfur and oxygen;while huge challenges of intrinsic large volume change,poor electrical conductivity and high reactivity remain to be addressed.Therefore,rationally designing and building of advanced Li_xSi alloy anodes is of great significance to improve its poor cycling.Among the various Li-containing anodes,metallic Li has been regarded as the ultimate choice due to its highest theoretical specific capacity and the lowest redox potential.Whereas Li anodes face huge safety hazards by the uneven Li deposition and severe dendrites growth in liquid organic electrolytes,due to the lack of efficient three-dimensional(3D)current collector hosts and nucleation media.Rationally constructing3D hosts with lithiophilic modification is necessary to regulate uniform Li deposition.While traditional electrochemical deposition for Li anodes production is not appropriate for practical applications due to complex processing procedures;developing scalable and reliable production technique is urgently required.Moreover,to minimize the dendrite-induced safety risks,replacing the liquid organic electrolyte by solid-state electrolytes is a promising and effective strategy.Bare ceramic and solid polymer electrolytes afford their own advantages and shortcomings,neither of them can simultaneously achieve high ionic conductivity,mechanical strength,and processing flexibility.Meanwhile,typical nanoparticles(NPs)-type composite polymer electrolyte(CPE)can only deliver limited performance enhancement;developing reliable 3D filler reinforcement is essential to realize the above requirements.In this thesis,advanced molten-lithium-derived Li_xSi and Li metal anodes,and reliable 3D CPE have been developed to improve the cycling stability of high-energy Li batteries through precise micro/nanostructuring engineering,mainly including:(1)the building of core-shell Li_xSi-Li₂O/Ti_yO_z NPs through a facile coating-then-lithiation strategy to achieve sufficient tolerance of volume change,high electrical conductivity and also high dry-air stability;(2)the gram-scale production of microsized Li_xSi/Cu composites using low-cost microsized Si material with Cu NPs coated to improve the electrical conductivity and buffer the volume change;(3)the scalable thermal preparation of 3D Cu host-reinforced Li metal electrode through hierarchical lithiophilic engineering by facile air annealing and spray coating to achieve stabilized cycling;(4)the low-cost preparation of 3D network-reinforced PEO-based CPE through 3D percolation of ceramic NPs along self-assembled cellulose scaffold to achieve both high Li⁺conductivity and mechanical strength.Details are shown as follows:1.A facile coating-then-lithiation strategy has been first proposed to prepare core-shell Li_xSi-Li₂O/Ti_yO_z NPs material,addressing the intrinsic large volume evolution,poor electrical conductivity,and inferior dry-air compatibility issues of Li_xSi.Of which,the elastic Ti O₂ layer coated on Si NPs can effectively tolerate Si volume expansion during lithiation;and resultant lithiated-Ti O₂ layer can improve the electrical contact among Li_xSi domains,suppress most of solid electrolyte interphase formation on the Si-based core,and protect the inner Li_xSi from ambient corrosion.2.Gram-scale production of microsized Li_xSi/Cu composites has been realized using low-cost Si microparticles via the coating-then-lithiation route,relieving the large volume evolution and poor electrical conductivity challenges of Li_xSi,and getting rid of dependance on costly nanostructured Si.Numerous Cu NPs introduced by electroless deposition,homogeneously dispersed in the Li_xSi-based composites,act as both effective conductive additives and volume buffer phases,maintaining the structural integrity and thereby achieving stable cycling.3.A scalable hierarchical lithiophilic approach has been developed to produce stable Li metal anodes through modifying the lithiophobic metal foam matrix with dual lithiophilic media.The hierarchical lithiophilic decoration,especially the dense surface oxidiation layer by air annealing,enables molten Li infusion by effectively lowering the nucleation barrier;and the sufficient long silver nanowires by spray coating,serve as“Li⁺pump”during cycling to regulate uniform Li deposition,suppressing the growth of lithium dendrites and thus delivering good cycling stability.4.A ceramic NPs network self-assembly strategy has been proposed to realize ordered arrangement of ceramic NPs confined by self-assembled cellulose scaffold,overcoming the dilemma of simultaneously achieving high Li⁺conductivity,mechanical strength,and processing flexibility by CPEs.The 3D reinforcement provides fast and continuous Li⁺pathways along the interfaces for high Li⁺conductivity(1.1×10^-4 S cm^-1at 60°C),and firmly supports the whole CPE enabling good mechanical properties.