Study On Hybrid Li Storage Of Amorphous Carbon Anode

Lithium metal anode（LMA）has a high theoretical specific capacity(3860m Ah g^–1)and the lowest potential（–3.04 V vs.SHE）.However,LMA suffers from irreversible side reactions,uncontrolled Li dendrites growth and large volume changes,which hinder the application of LMA.Although 3D current collectors and interface engineering based on carbon materials can enhance the stability of LMA,the low Coulombic efficiency（CE）still limits its industrialization.Nowadays,Hybrid anodes based on graphite intercalation and Li metal plating have been extensively studied,while metallic Li still inevitably reacts with electrolyte when plating on graphite,resulting in CE degradation and dendrite growth.Therefore,this thesis proposes a strategy to use sub-nanopores in hard carbon（HC）storing quasi-metallic Li（QM-Li）to reduce the direct contact between Li and electrolyte.Increasing QM-Li capacity on the basis of intercalation capacity to form HC/QM-Li hybrid anode can improve the energy density of HC.The QM-Li can be stored in sub-nanopores,enabling the HC/QM-Li hybrid anode to cycle stably.The main research contents and results are listed as follows:（1）We studied strategies for the preparation of high-capacity HC materials that are beneficial to industrialization.First,we used charcoal and anthracite as precursors to prepare HC materials by pyrolysis at 1000°C and 1200°C.Then the differences in the internal structures of HC materials were compared via characterizations.In further electrochemical tests we found that anthracite-based HC（AHC）had high carbon production rate,less impurities and stable amorphous structure.It could maintain an average specific capacity of 216.8m Ah g^–1.While charcoal-based HC（CHC）had more internal defects and contains more impurities,so the structure of CHC was unstable and the capacity was lower.In the cycle test to explore the overdischarging cycling performance of HC,the AHC could maintain a high stable CE over 100 cycles with capacity of 500 m Ah g^–1.（2）We exploited the confinement effect of sub-nanopores to encapsulate QM-Li in commercial HC.The cycling stability of the HC/QM-Li hybrid anode was greatly improved compared with the traditional AG/Li hybrid anode.First,the structural differences between AG and HC were compared through characterizations.We found that unique sub-nanopores of HC provided a large pore volume for the storage of QM-Li,effectively preventing the contact between the electrolyte and QM-Li,and avoiding side reactions.In electrochemical tests,the HC/QM-Li hybrid anode could be stably cycled for250 cycles in a half-cell with an ester electrolyte,achieving an extremely high CE of 99.7%.When combined with Li Ni_0.8Co_0.1Mn_0.1O₂（NCM811）cathode and assembled into a full cell for testing,the HC/QM-Li||NCM811 could maintain a capacity retention rate higher than 80%after 200 cycles.The confinement effect of the sub-nanopore structure provided a new idea for the commercial application of LMA.