| With the rapid development of the global economy,the rapid reduction of fossil fuels and the increasing environmental pollution,the construction of high-efficiency,green,and renewable new chemical power sources has received extensive attention.Lithium-ion capacitors have higher power density and cycle life than batteries,and higher energy density than electric double-layer capacitors.In recent years,the development of high-performance Lithium ion capacitors has become the focus of research.However,the traditional lithium-ion capacitors have the safety problem of electrolyte leakage.The development of solid-state lithium-ion capacitors to improve the safety of energy storage equipment has become the focus of future energy storage equipment research.Electrode materials,especially anode materials and solid electrolytes,play a decisive role in the performance of capacitors.The main research contents and results of this paper are as follows:1.The surfactant was used as a soft template to Nb2O5 nanocomposites by hydrothermal synthesis.The composite material has the modification of graphene and nano-amorphous carbon,and has a good pore structure.As a negative electrode material,it exhibits excellent cycle stability and rate performance.A quasi solid-state lithium-ion capacitor was constructed using the ionic liquid gel electrolyte.The performance of the device under different conditions was studied.The device has the best performance at 60 ?:maximum energy density 101.8 Wh kg-1 maximum power density 2 kW kg-1.The effect of electrolyte composition on the energy storage mechanism was studied.It was found that the ionic liquid electrolyte has the largest capacitor contribution while the gel electrolyte has the smallest capacitive contribution.The effect of temperature on the proportion of energy storage is discussed.As the temperature increases,the proportion of capacitor contribution increases gradually.Molecular simulation results show that lithium ions and ionic liquid anions form clusters,thereby inhibiting the migration rate of lithium ions,resulting in a relatively low lithium-ion battery type mechanism of the ionic liquid system.2.Ti2Nb2O9 composite porous graphene nanocomposites(TNO/HrGO)were prepared by co-flocculation.SEM and TEM results show that the TNO nanosheets and the graphene sheets are highly hybridized to form a tight and crisscross nanocomposite.The nanocomposite was found to exhibit excellent cycle stability in the half-cell,and after 2000 cycles,the electrode material still maintained a discharge capacity of 207.1 mA h g'1.The maximum energy density in commercial organic electrolyte lithium ion capacitors is 55.8 Wh kg-1.Finally,a lithium ion capacitor with negative electrode as TNO/HrGO,positive electrode as activated carbon and PVDF-HFP-LiTFSI/[EMIM][BF4]as solid electrolyte was constructed.By comparison,it can be found that the capacitor has the best performance at 60 ?.The maximum energy density is 108.5 Wh kg-1,and the energy density can reach 75.4Wh kg-1 at maximum power density of 11.2 kW kg-1.In summary,this paper studies the high-performance metal oxide composite electrode for the anode material suitable for ionic liquid gel electrolyte and builds an ionic liquid based solid-state lithium ion capacitor.Quasi-solid capacitors have a wider voltage window and a higher temperature window.The energy storage mechanism of ionic liquid electrolytes compared with other electrolytes was studied,and the effect of temperature on ions transport in ionic liquids was discussed.It is found that the ionic liquid electrolyte reduces the lithium ion migration rate due to the lithium ion cluster,resulting in its capacitor contribution being relatively low,but the capacitor contribution gradually increases with the increase of temperature.The structural regulation of high-performance anode materials and the study of ionic liquid electrolyte energy storage mechanism provide research ideas for constructing new quasi solid-state lithium-ion capacitors with broad application prospects. |
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