Electrochemical Properities Of Porous Graphene/Silicon Composite Materials

With the rapid development of economy and society,people’s demand for high energy density electrical equipment is very urgent,so the development of high energy density lithium-ion batteries is of great significance.The theoretical capacity of graphite anode is little lower than 375 mA h g-1,which cannot meet people’s demand for high-energy compactness,while silicon(Si)anode material has the advantages of high theoretical capacity of 3580 mA h g-1,rich resources,environmental protection and non-toxicity,so the research of Si anode is of great significance to improve the energy density of batteries.However,there is a huge volume expansion of Si materials during the charging and discharging process,which leads to Si anode pulverization,the destruction of the solid electrolyte membrane(SEI)film,and the active material falling off from the current collector.Moreover,its conductivity is poor,which is not conducive to lithium-ion(Li+)transport,hindering the commercialization of lithium-ion battery Si anodes.Based on the research on Si anode at home and abroad,the progress of application technology methods and existing problems,and thus leading to the research content of this paper,this paper is studied from the following aspects:(1)The electrochemical properties of porous graphene(P-rGO)and Si composite anode materials(Si@P-rGO)were studied.P-rGO is a new material with sp2 hybridly linked carbon atoms tightly packed into a single-layer two-dimensional honeycomb lattice structure,and the effects of different binders on the electrochemical performance of Si and P-rGO composite anodes are explored.Four different binders were selected from polyacrylamide(PAM),polyvinylidene fluoride(PVDF),carboxymethylcellulose(CMC),and polyacrylic acid(PAA)to prepare four composite electrodes of Si@P-rGO.The experimental results show that PAM as a binder can make the porous graphene/silicon(Si@P-rGO-PAM)composites compact in structure,form a better conductive network,and improve the electrochemical performance of the composites,P-rGO has a porous structure that is conducive to the embedding and extraction of Li+,and the Si@P-rGO-PAM electrode still has high reversible capacity of 1274 mA h g-1 after 100 cycles at 1000 mA g-1.(2)Study on the electrochemical performance of Si@C/P-rGO composite anode,On the basis of the binder with the best screening performance,the carbon-coated Si particles are Si@C obtained by pyrolysis of glucose as a carbon source for nano Si,and after glucose is carbonized as a carbon source,it can maintain an egg yolk-core-shell structure with Si to prevent Si particles from aggregating,inhibit the volume expansion of Si,and avoid direct contact between Si and electrolyte.The Si@C is mixed with PrGO to obtain a composite anode material Si@C/P-rGO.The porous P-rGO layer is conducive to the insertion and removal of Li+to improve its electrochemical performance,Si particles are fixed on the P-rGO sheet,and the Si distribution on each layer of P-rGO is uniform.P-rGO has superconductivity,which can increase the conductivity of Si-carbon composite anode materials,and has good mechanical properties,which can well inhibit the volume expansion caused by Si during the charging and discharging process.P-rGO has a good mechanical flexibility structure and the carbon layer plays a double-layer protection role on Si,keeping the interface between the electrode and the electrolyte stable,thereby maintaining good electrochemical performance.(3)Polyvinyl alcohol(PVA)is added to nano-Si and P-GO solutions as a surfactant,and then flexible self-supporting composite electrode(Si@P-rGO/PVA)is obtained by chemical reduction and freeze-drying technology.The presence of this electrode without current collector greatly reduces the weight of the negative electrode,and Si and P-rGO can form a uniform conductive network,because P-rGO is one of the strongest materials known,while also having good toughness and can be bent,which can play a good inhibition role when Si volume expands.At the same time,the external P-rGO protects the internal Si away from the electrolyte,prevents the destruction of the SEI film,and improves the electrochemical performance of the electrode.