Construction And Dynamic Mechanism Promotion Research For Lithium Ion Capacitors Based On Silicon And Carbon Materials

The expanding market of portable electronic devices and,especially,the emergence of electric vehicles（EV）and hybrid electric vehicles（HEV）have created increasing demand for advanced energy storage techniques that can provide high energy and power densities and long cycling life.The lithium ion capacitors（LICs）hybrid energy storage systems have been proposed as a way to incorporate the advantages of both lithium ion batteries（LIBs）and Supercapacitors（SCs）into one system.However,due to the limitation of the cathode and anode materials and the mismatch of kinetics,significant progress has not been made in improving the performance of LICs.In view of the existing problems of both positive and negative electrodes,we prepared a variety of cathode materials with high capacity and anode materials with high rate performance in this paper.The main contents are listed as follow:（1）Spherical hard carbon material（GHC）was prepared from glucose by hydrothermal method.The reversible capacity of as-prepared GHC can be maintained at 100 m Ah g^-1under high current density of 10 A g^-1as well as good cycling stability over 3000 cycles with 87.8%capacity retention.The GHC-based LIC device can deliver a high energy density of 138.5 Wh kg^-1at 325 W kg^-1.Even at a high power density of 33250 W kg^-1(10 A g^-1),the device can still provide an energy density of 76.1 Wh kg^-1.（2）The desired microstructure of carbon cathode that suitable for Li PF₆-contained electrolyte is calculated by using density functional theory.Results suggest that only the pore sizes more than 2.18 nm can accommodate the solvatedPF₆^-ions.Experimental results confirm that the capacitive performance of the synthesized activated polyaniline-derived carbon（APDC）can be significantly promoted as the pore size was more than 2 nm.Especially,the APDC-700-based cathode demonstrates outstanding electrochemical performance with high capacitance(171.5 m Ah g^-1at 0.1 A g^-1).In addition,the APDC-700-based anode delivers a reversible capacity of 232 m Ah g^-1at 10 A g^-1.The APDC-700-based symmetrical LIC device can deliver a high energy density of 254.3 Wh kg^-1at 225 W kg^-1,as well as good cycling stability over 10000 cycles.This well-designed work will be conducive to deeply understand the performance improvement of capacitive carbon cathode in Li PF₆electrolyte and provides guidelines for designing advanced LIC devices.（3）The core-shell composites were fabricated by carbon coating and CNT mixture process.Benefiting from the carbon layer and CNT double conductive network,the as-prepared composite materials(B-Si@C_RF-CNT)demonstrates a high reversible capacity of1084 m Ah g^-1at 8 A g^-1as well as good cycling stability over 200 cycles with 83.34%capacity retention at 1 A g^-1.The optimized mass ratio of positive/negative active material was set as 4.5:1 based on the charging and discharging curves of the LIC device.The optimized device（Li C4.5）device can deliver an ultra-high energy density of 300.3 Wh kg^-1at318 W kg^-1,as well as good cycling stability over 10000 cycles.This well-designed work will be conducive to deeply understand the performance improvement of capacitive carbon cathode in Li PF₆electrolyte and provides guidelines for designing advanced LIC devices.（4）The surface modification of APDC-800 was carried out by secondary nitrogen doping via heat treatment process with NH₃.The nitrogen content of as-prepared materials（NAPDC-800）was significant promoted to 4.58 wt%.Attributing to the appreciate pore size and narrow PSD as well as high nitrogen content,the reversible capacity of NAPDC-800cathode can be maintained at 100 m Ah g^-1under ultra-high current density of 20 A g^-1,which is much higher than that of APDC-800.In addition,the electrical conductivity of disordered rock salt Li₃V₂O₅has also promoted by introducing CNT.The as-prepared anode material（Li₃V₂O₅-CNT）demonstrates a high reversible capacity of 100 m Ah g^-1at 20 A g^-1as well as good cycling stability.The optimized device（Li₃V₂O₅-CNT||NAPDC-800）device can deliver an high energy density of 158.6 Wh kg^-1at an ultra-high power density of 65 k W kg^-1as well as good cycling stability over 10000 cycles.