Preparation/Modification Of Integrated Carbon Network Self-supporting Film And Its Electrochemical Performance

The limited and uneven distribution of lithium resources on the earth limits the further development and large-scale application of lithium-ion batteries(LIBs).Different from lithium,sodium and potassium have the advantages of extensive resources and low cost.Therefore,sodium ion batteries(SIBs)and potassium ion batteries(PIBs)are considered to be new secondary batteries that are expected to replace lithium ion batteries in the field of large-scale energy storage.Among the two types of batteries,carbon materials are the most promising negative electrode materials because of their stable structure,simple preparation process,and environmental friendliness.In this article,by controlling the plasma power,a carbon-based integrated hard carbon anode material for sodium ion batteries with high sodium storage capacity and high cycle stability is prepared;the advantage of the hollow structure in the buffer of volume expansion is used to obtain the graphite anode material of potassium ion battery which have a high potassium storage capacity and excellent cycle stability.(1)Research on the preparation and modification of integrated hard carbon network and its sodium storage performance.Using phenolic resin as the precursor,plasma treatment is carried out at 900?while carbonizing treatment to prepare hard carbon materials.The graphite microcrystalline structure and surface element content are adjusted by changing the plasma power.The sample prepared by 200 W plasma modification(PRC-200 W)has an integrated carbon network similar to neurons.The fiber diameter in the network is about 10nanometers.The surface has abundant oxygen-containing groups,a short-range ordered carbon structure,and the interlayer spacing is 0.39 nm,the specific surface area is 739.06 m²g^-1.When used as a anode material for sodium ion batteries,it has excellent high rate performance and high cycle stability.The sodium storage capacity is 334.5 m Ah g^-1at a current density of 50 m A g^-1.In addition,the PRC-200 W electrode also exhibits excellent cycle performance.After 10,000 cycles at a current density of 2000 m A g^-1,the sodium storage capacity can still maintain 179.44 m Ah g^-1,which is 72.09%of the initial reversible capacity.The high sodium storage capacity of PRC-200 W is due to its large interlayer spacing,numerous of defects on the surface and abundant oxygen-containing groups;the integrated carbon network and ultra-fine fibers increase the ion electron diffusion rate,which made a huge contribution to its rate performance;the graphite layer on the surface provides protection for the stable cycle of the battery.All of these indicate that the integrated hard carbon network is a promising anode material for sodium ion batteries.(2)Preparation and regulation of integrated graphitized carbon network with defect-rich/sulfur-doped and its potassium storage performance.Using phenolic resin as the oxygen-containing carbon precursor,a novel defect-rich/sulfur-doped integrated graphitized carbon network(ED-IGCN)is constructed through high temperature graphitization and plasma etching/doping.IGCN-1800 prepared by carbonization at 1800?and it has unique structural advantages:(1)a binder-free integrated network interconnected by sp²bonds,which greatly accelerates the electron/ion transmission process;(2)hollow fiber(fiber diameter is about 10 nm)and the thickness of the shell wall is about 1 nm,which provides an ultra-short ion transmission path to further strengthens the diffusion/transmission process and helps to alleviate the volume change during charging and discharging;(3)Defects on the surface of ordered carbon provide more potassium insertion entrances and S doping sites by plasma etching;(4)Plasma-enhanced S doping causes an increase in the interlayer spacing(0.352?0.371 nm),which can effectively reduce the diffusion barrier and ensure that potassium ions can be easily inserted/extracted and the high stability of the material structure.As expected,at a current density of 50 m A g^-1,its potassium storage specific capacity reached 341.1 m Ah g^-1.After 300 cycles,the capacity was 298.3 m Ah g^-1,and the retention rate was 87.4%.In addition,after 10,000 cycles at a current density of 5 A g^-1,it still has a reversible storage capacity of 55.6%.This is the best result of graphitic carbon which have high rate and cycle stability.Kinetic analysis proves that the enhanced Faraday pseudocapacitive K storage mechanism has the greatest effect on the excellent electrochemical performance of graphitic carbon.This research result provides a new idea for the structure design of graphite carbon anode materials for fast charging batteries that can provide stable working voltage,and provides a new idea for the diffusion acceleration mechanism in graphite carbon materials.