Structure Design And Fabrication Of Anode Materials And Electrodes For High-Energy Rechargeable Lithium Batteries

The rapid development of consumer electronics and electric vehicles in recent years makes it imperative to develop high-energy rechargeable lithium batteries.Although silicon?Si?and lithium?Li?metal possess extremely high theoretical specific capacities,the drawbacks of these anode materials severely hinder their practical application.The large volume change of Si during lithiation/delithiation and its poor electrical conductivity lead to the rapid capacity fading during cycling.For the Li metal anodes,the formation of Li dendrites not only causes capacity fading,but also results in short circuiting of the battery and safety hazards.In this dissertation,spherical silicon/carbon hybridswith hierarchical structure design were synthesized to improve the cycling stability of Si-based materials.Meanwhile,a Si-carbon/graphene electrode and a three-dimensional?3D?porous copper current collector for Li metal anodes were also fabricated to boost the practical application of Si and Li metal.Firstly,micron-sized spherical carbon coated graphene wrapped Si/carbon black hybridsassembled by nano-sized structures were synthesized via the water-in-oilemulsion system.In these hybrids,Si nanoparticles?NPs?and carbon black are embedded in graphene spheres,which are further coated by amorphous carbon.The nano-sized structure design greatly improved the electrical conductivity of the hybrids,thus,these hybrids exhibited much improved cycling stability and excellent rate performance(728 mAh g^-1 at 2 A g^-1)compared with Si NPs and Si NPs/graphene hybrids.Secondly,a “concrete-like” Si-carbon/graphene electrode was prepared to improve the stability of the whole electrode structure.In this electrode,Si NPs are embedded in an interlinked graphene network,while the voids between them are filled with amorphous carbon.The graphene network penetrating the electrode greatly enhances the strength,flexibility and electrical conductivity of the electrode,and the elastic carbon scaffold composed of amorphous carbon and graphene can accommodate the volume expansion of Si during lithiation and maintain the integrity of the electrode.As a result,this electrode showed a high reversible capacity of 1711 mAh g^-1 with a high initial Coulombic efficiency of 78%,also displayed good rate capability.Lastly,a 3D porous copper current collector for Li metal anodes was fabricated via chemical dealloying of a commercial available copper-zinc alloy tape.The 3D interconnectedpore structure of this current collector can accommodate the deposition of Li metal,inhibit the formation of Li dendrites and alleviate the huge volume change of Li metal anode during cycling.A Li metal anode withsuch a 3D porous current collector demonstratedapparentlyreduced polarization,excellent cyclingwith a very high CE?>97%?even after 250 cycles,and a long lifespan up to 1000 h in asymmetric Li|Li@Cu cell.When assembled into a full cell against a LiFePO₄ cathode,it exhibited a high capacity retention of 89.7% after 300 cycles,showing great potential to practical application.