| The use of renewable energy can not be separated from the stable and reliable energy storage technology,lithium-ion battery is the most stable and reliable energy storage devices,which has high energy density characteristics,but there are problems in the charge and discharge rate;the contrary,super capacitor With ultra-fast charge and discharge rate,but there are still defects in the energy density.The ideal energy storage technology should have a fast charge and discharge rate and high energy density.Lithium-ion capacitor is a dual-layer capacitor with high power characteristics and lithium-ion battery high energy density characteristics of the electrochemical energy storage devices.In lithium ion capacitors,the performance of cathode materials on the electrochemical performance of lithium-ion capacitors play a vital role.The synthesis of lithium-ion battery cathode material and activated carbon/carbon nanotube/graphene and other carbon material is a high-performance lithium-ion capacitor cathode material is an important method.In order to obtain lithium ion capacitors with high energy density and high power density,a lithium ion capacitor device was fabricated by a flexible packaging method with simple preparation,low cost and high yield.Lithium iron phosphate/active carbon(LFP/AC),lithium nickel cobalt aluminate/activated carbon(NCA/AC),lithium iron phosphate/graphene(LFP/graphene)were prepared by mixing the positive electrode active materials by mixing electrode materials.Lithium iron phosphate/carbon nanotube(LFP-CNTs)or lithium iron phosphate-carbon nanotubes-Super P(LFP-CNTs-SP),lithium iron phosphate-lithium carbon nanotubes(LFP-CNTs)as the cathode material,graphite as the anode material,lithium iron phosphate battery electrolyte or ordinary lithium-ion battery electrolyte as the electrolyte,were prepared LFP/AC‖graphite,NCA/AC‖graphite flexible packaging lithium-ion capacitors and LFP-graphene‖Graphite,LFP-graphene-CNTs‖graphite,LFP-CNTs‖graphite and LFP-CNTs-SP‖graphite-type flexible packaging lithium-ion capacitors.The morphology of the electrode materials of different types of lithium ion capacitors and lithium ion batteries was measured by SEM.X-ray diffraction(XRD)was used to analyze the electrode materials.Electrochemical evaluation of lithium ion batteries,supercapacitors and lithium ion capacitor electrode materials is carried out by electrochemical methods such as cyclic voltammetry,charge and discharge,magnification,and electrochemical impedance spectroscopy(EIS).Use the LAND battery test system to test the battery for rate and cycle performance.The effects of different electrode materials and the morphology of different electrode materials on the electrochemical performance of lithium ion capacitors and lithium ion batteries were investigated.The main findings are as follows:(1)Lithium iron phosphate and activated carbon were mixed in different proportions as the positive electrode composite material.The graphite was used as the negative electrode material,and the lithium iron phosphate battery electrolyte was used as the electrolyte to be assembled into the wound flexible packaging LFP/ACway graphite type lithium Ion capacitors.93.5%LFP and 80%AC slurry were mixed at 95:5 and 90:10 and 85:15,respectively.At 0.1C and 5 C,the discharge specific capacity of 93.5%LFP electrode material was 122 mAh/g And 91 mAh/g,5 C specific capacity of 0.1 C initial specific capacity of 72%.The discharge capacity of the 93.5%LFP electrode was 102 mAh/g after 94 cycles at 100℃,which was 94%of the initial capacity.The discharge specific capacities of the LFP electrode materials doped with 5%AC at 0.1C and 5C were 126 mAh/g and 98 mAh/g,respectively,and the 5 C specific capacity was 78%of the initial specific capacity of 0.1 C.The LFP electrode material doped with 5%AC at 1C magnification exerts a discharge capacity of 110 mAh/g after 500 cycles,which is 97%of the initial capacity.It is shown that the LFP electrode material doped with 5%AC has better reaction reversibility and cyclic performance than 93.5%LFP.In addition,with the increase of the amount of activated carbon,it can be seen from the magnification performance diagram and the AC impedance diagram The performance gradually strengthened and the internal resistance decreased accordingly.Its energy density at 1 C magnification is 126 Wh/Kg(relative device)with a power density of 200 W/Kg(relative device).(2)The nickel cobalt cobalt aluminate and the activated carbon were mixed in different proportions as the positive electrode composite material,graphite as the anode material,the ordinary lithium ion battery electrolyte as the electrolyte,assembled into the winding flexible packaging NCA/ACustain graphite Type lithium ion capacitors.93.5%NCA and 80%AC slurry were mixed at 95:5 and 90:10 and 85:15,respectively.At 5C,when the NCA electrode material doped with 5%AC was at 0.1C and 5C,The discharge specific capacities were 165 mAh/g and 127 mAh/g,respectively,and the 5 C specific capacity was 77%of the initial specific capacity of 0.1 C.At 1000 ℃,the NCA electrode doped with 5%AC can still exhibit a specific capacity of 116 mAh/g after about 300 cycles,which is about 77%of the initial discharge specific capacity.93.5%NCA electrode materials 0.1C and 5C,the discharge specific capacity is 164 mAh/g and 120 mAh/g,respectively,and the 5 C specific capacity is 0.1%of the initial specific capacity of 0.1%.After a 300°cycle at 93℃,the 93.5%NCA electrode exhibited a discharge specific capacity of 110 mAh/g after about 300 cycles,approximately 75%of the initial discharge specific capacity.The results show that the addition of a small amount of AC can effectively promote the capacity of the cathode material,has a high capacity retention rate,and maintain good cycle stability.In addition,the NCA electrode material doped with 5%AC is better than the pure nickel cobalt aluminate.With the increase of the amount of activated carbon,it can be seen that the magnification performance is gradually enhanced by the magnification performance diagram and the AC impedance diagram And the internal resistance is reduced accordingly.Its energy density at 1C magnification is 218 Wh/Kg(relative device)with a power density of 468 W/Kg(relative device).(3)In the lithium iron phosphate to add a certain amount of three-dimensional self-supporting graphene,(CNTs)or Super-P as the cathode material,graphite as the anode material,lithium iron phosphate battery electrolyte as the electrolyte,assembled into a lithium iron phosphate,Rolling-type flexible packaging LFP-graphene‖graphite,LFP-graphene-CNTs‖graphite,LFP-CNTs‖graphite and LFP-CNTs-SP‖graphite-type flexible packaging lithium-ion capacitors.When PVDF 3%,the LFP as the active material,changing the graphene ratio of 0.5%,1%and 1.5%,the results show that 1%graphene performance after 1.5%graphene,and the difference is not much,but far In the 0.5%graphene performance,from the consideration of expensive graphene,the choice of 1%graphene is the best.Among them,1%graphene LFP electrode at 0.1,5 C magnification when the discharge specific capacity of 125,94 mAh/g,5 C specific capacity of 0.1 C initial specific capacity of 75%,at 1C ratio of the battery in the cycle The discharge capacity after 500 turns is 105 mAh/g,which is 91%of the initial specific capacity.When the graphene is 0.5%,the ratio of PVDF is 2.5%,3%and 3.5%.The results show that the performance of 2.5%PVDF electrode is the best,and the discharge specific capacity is 122,94 mAh/g,5 C specific capacity of 0.1%of the initial specific capacity of 77%,at 1C rate of the battery after the cycle of 500 cycles of discharge capacity of 108 mAh/g,is the initial specific capacity of 91%.When the PVDF is 3.5%and the CNTs is 0.2%,the specific capacity of the LFP electrode with 3%SP is 0.1,96 mAh/g at the rate of 0.1 and 5 C,respectively,and the 5 C specific capacity is 0.1 C.%Of the battery at a rate of 1C after the cycle of 500 cycles after the discharge capacity of 111 mAh/g,is the initial specific capacity of 96%.While the CNTs were 0.2%and PVDF 3.5%LFP electrodes had a specific discharge capacity of 122,87 mAh/g at 0.1 and 5 C,respectively,and a 5 C specific capacity of 0.1 C was 71%of the initial specific capacity,The discharge capacity of the battery after 500 cycles is 105 mAh/g,which is 91%of the initial specific capacity.PVDF of 3.5%,SP 3%of the LFP electrode discharge capacity of 122 mAh/g,5 C times the rate of 91 mAh/g,5 C discharge capacity of 0.1 C of 74%.The discharge capacity of the battery after cycling 500 cycles is 102 mAh/g,which is 94%of the initial specific capacity at 1C.When the PVDF is 2.5%,the specific capacity of the LFP electrode with 1%graphene is 128,94 mAh/g at the rate of 0.1 and 5 C,respectively,and the 5 C specific capacity is 0.1 C,the initial specific capacity is 73%Of the battery under the cycle of 500 cycles after the discharge capacity of 106 mAh/g,is the initial specific capacity of 90%.When the graphene is 1%and the PVDF is 2.5%,the specific capacity of the LFP electrode doped with 0.2%CNTs is 129,104 mAh/g at 0.1 and 5 C,respectively,and the 5 C specific capacity is 0.1C 80%of the capacity,the rate of 1C in the battery after the cycle of 500 cycles after the discharge capacity of 116 mAh/g,96%of the initial specific capacity.Its energy density at 1 C magnification is 133 Wh/kg(relative device)with a power density of 222 W/Kg(relative device). |
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