Structural Design And Electrochemical Performance Of Multi-Interface Graphene/Carbon/Silicon Anode Materials

Along with the large-scale application of lithium-ion batteries,the traditional graphite anode can not fully meet the requirements of the energy storage market.Pitch consists of a large number of polycyclic aromatic hydrocarbons and is a high-quality carbon precursor material.Form pitch,it is easy to design and prepare carbon-based composites with numerous surfaces and interfacial structures,which will enhance the ionic/electronic conductivity and greatly improve the electrochemical performance of composites.However,the exposed surface undoubtedly increases the specific surface area of the materials,resulting in a higher first irreversible capacity loss.Therefore,the purpose of this work is to construct a multi-interface structure within the pitch-based carbon matrix and investigate the effects of interlayer structure on the morphology,structure and Li-storage properties of composites.The main research contents are as follows:We chose pitch as the carbon precursor and used three different synthesis routes to compound with graphene oxide(GO).Comparing the composites obtained from the three different routes(Grinding method G-GP,Melting method M-GP,Solvent dispersion method D-GP)through SEM,TEM and XRD tests,it was found that a more randomly distributed graphene nanosheets are embedded in the D-GP carbon matrix,and a large number of interfaces are formed between graphene and pitch-based carbon matrix.These random graphene sheets hinder the orderly rearrangement of pitch-based carbon layers during carbonization,reducing the overall crystallinity of the material.Due to the fast ion/electron transport channels and additional interfacial energy storage sites provided by the multi-interface structures inside the carbon matrix,D-GP shows the best lithium storage performance:a first reversible capacity of 504 m Ah/g at 0.05 A/g and a specific capacity of 286 m Ah/g even at high currents density of 2 A/g.Further investigation of the preparation conditions shows that D-GP prepared by adding 10 wt.%GO and carbonizing at 800 ~oC possesses better multi-interface structures as well as higher electrochemical properties.A silicon/graphene/carbon composite(Si/G/P)with the multi-interface conductive network structure was prepared by doping silicon nanoparticles into graphene/pitch-based carbon via the D-GP synthesis route.The Si/G/P-10electrode exhibits high rate performance and cycling stability with the reversible specific capacities of 820 m Ah/g and 495 m Ah/g at 0.05 A/g and 2A/g respectively.Even at high current density of 10 A/g the reversible specific capacity of 208 m Ah/g still remains.After 300 cycles at 0.5 A/g,a capacity retention of 95%is still achieved.These multi-interface conductive networks embedded within the pitch-based carbon matrix provide fast ion/electron transport channels and reduce direct contact with electrolyte,meanwhile also greatly improve the structural stability of the Si/G/P-10 electrode and alleviate the breakage of the composite structure caused by repeated volume expansion and shrinkage of the silicon nanoparticles during charging and discharging processes.As a result,The Si/G/P-10 electrode therefore exhibits excellent lithium storage properties.