Structure Design Of New Carbon Materials And Its Electrochemical Charge Storage Mechanism

New carbon materials generally have advantages of adjustable surface and pore structure,superior electrical conductivity and good physical and chemical stability.Thus can be used as electrode material in lithium/sodium/potassium secondary ion batteries?LIBs/NIBs/KIBs?and supercapaciators?SCs?.Currently,new carbon materials becomes the most forefront,attractive and market potential direction of new material industry.However,how to prepare carbon materials with high electrochemical activity by simple and inexpensive methods remains a huge challenge.In this paper,the structure design and construction strategy,preparation method,structure characterization,electrochemical performance test,electrochemical energy storage mechanism and structure-activity relationship of carbon electrode materials are analyzed in depth and systematically.The energy storage mechanism of carbon materials is also revealed from the atomic/electronic point of view by first-principles calculation.In electrochemical applications,the principles of improving its dynamic characteristics,high capacity characteristics and long cycle stability provide novel methods and ideas for the development and application of high performance lithium/sodium/potassium ion batteries and supercapacitors.The main research contents are as follows:?1?A hard carbon nanospherical shell with N-doped and defect-rich nano-graphitized microcrystalline domain is prepared by pre-chelating Ni²⁺with carbon source and limiting the catalytic action of graphitization catalyst at relatively low temperature.The hard carbon nanoshell prepared by this method exhibits a reversible capacity of 1253 mAh/g in lithium-ion batteries.The reversible capacity can be maintained at 1236 mAh/g after 100cycles at the current density of 100 mA/g.For sodium-ion batteries,the reversible capacity can be reachedc at 325 mAh/g and maintained at 174 mAh/g after 200 cycles at the current density of 100 mA/g.It was found that the introduction of N-doped and defect-rich nano-graphitized microcrystalline domain could synergistically increase the lithium storage performance of carbon materials.In addition,in-situ Raman measurements show that the energy storage mechanism of the synthesized hard carbon in lithium-ion batteries is"adsorption-embedding"and that in sodium-ion batteries is"adsorption"mechanism.Finally,the assembly test of LiNi_0.33Co_0.33Mn_0.33O₂?NCM111?/Li₄Ti₅O₁₂?LTO?+hard carbon?HC?battery shows that the introduction of 10wt%hard carbon material in LTO improves the power density and energy density of the battery most effectively.?2?Oxygen rich N-P co-doped open hollow carbon microspheres?N-P-HCMs?are synthesized through phenol/formaldehyde polycondensation reaction on the first obtained colloidal SiO₂ microspheres templates which derived from St?ber method unprecedentedly.As the electrode material of sodium ion batteries,the specific capacity of N-P-HCMs during the second cycle discharge process can be reached at 345.6 mAh/g at current density of 0.05 A/g,and it can still maintain 55 mAh/g sodium storage capacity at a high current density of 10 A/g.At the same time,the high specific capacity of 297 mAh/g can still be maintained after 140 cycles,the retention rate is 85.9%,and the reversible capacity can still be maintained at 53.3 mAh/g after 5000 charges and discharges even at a high current density of 3 A/g.Density functional theory?DFT?calculations and electrochemical measurements show that the introduction of heteroatoms can effectively improve the binding capacity of carbon materials to sodium.It is also proved that phosphorus-containing functional groups will contribute a little more than 2.0 V in the process of sodium storage in carbon materials,while C=O and COOH will contribute more than 1.0-2.0 V and less than 1.0 V in the process of sodium storage in carbon materials.At low potential,C-OH,NQ,N5 and N6 will produce larger capacity contribution.?3?A three-dimensional nitrogen-phosphorus co-doped hard carbon anode material?NPHC?with high rate performance and cyclic stability is obtained by screening biomass with three-dimensional connected pore structure as precursor,constructing reasonable pore structure and introducing heteroatoms to control carbon layer spacing.This three-dimensional pore structure and the introduction of nano-pore and heteroatom not only greatly shorten the transport channel of electrolyte ions,but also provide more active sites for the storage of electrolyte ions,which is also conducive to the increase of specific capacity of materials.The maximum discharge specific capacities of NPHC for sodium and potassium storage reached 335.6 and 338.9 mAh/g respectively in the second cycle at the current density of 25 mA/g.The specific capacities of NPHC for sodium and potassium storage were 52.3 mAh/g the current density of 3000 mA/g and 97.9 mAh/g at the current density of 2000 mA/g.The specific capacity of sodium electrolyte is almost not attenuated after 140 cycles at 100 mA/g current density,while the reversible capacity of potassium electrolyte can still be maintained at 207.2 mAh/g after 200 cycles of discharge.The ion diffusion coefficients in sodium and potassium electrons are also D?NPHC?>D?NHC?>D?HC-Commercial?by constant current batch titration.In addition,the in-situ Raman and Non-in-situ synchrotron radiation XRD demonstrated that the synthesized hard carbon had four different reaction mechanisms:“adsorption-adsorption/embedding-embedding/filling-underpotential deposition”during sodium and potassium storage.?4?We report a universal and readily scalable strategy to produce an N-P-O co-doped free standing 3D graphene through a one-pot red phosphorus-assisted“cutting-thin”technique.The as-produced graphene exhibits continuously 3D hierarchical porous?3D-HPG?structure with good quality(ID/IG=0.4,I_2D/I_G=0.65),but also larger specific surface area?1406 m²/g?.The results of electrochemical tests show that the mass specific capacity of3D-HPG reaches 432 F/g(volume specific capacity reaches 430 F/cm³?material bulk density:0.996 g/cm³?and 416 F/g respectively when the current density is 0.5 A/g in 1M H₂SO₄ and 6M KOH electrolytes.The assembled all-solid-state cell exhibits both high gravimetric and volumetric energy density of 25.3 Wh/kg and 25.2 Wh/L,respectively.Density functional theory?DFT?calculations indicate the N-P-O co-doping could significantly enhance the charge delocalization with benefited electrochemical activity.