Design,Preparation And Electrochemical Performances Of Novel Carbon-based Energy Storage Materials

Secondary batteries are not only the important devices for energy conversion and storage systems,but also the key power for the mobile electronic equipment.Especially for now,as the electric vehicle technology getting mature,the development of battery technology is the top priority.Lithium-ion batteries have been successfully commercialized and occupied the dominant position in the battery market.Although the electric vehicles possess many advantages over fuel vehicles,their safety performance,cruising mileage,and charging rate are still difficult to meet market demands.The improvement of performances in these aspects could be started from two aspects:1.Further optimizing the commercial lithium-ion battery in the commercial market;2.Exploring new secondary battery systems.The energy density,power density,cycle life and safety performan ce of secondary batteries are several factors that constrain their development.Here,series of new carbon-based nanomaterials with different compositions and structures were prepared by doping,modification and compounding methods,which were applied to new secondary batteries,electrochemical supercapacitors,and aqueous Fe-ion battery systems.Series of innovative research results have achieved in such energy storage systems with improved energy density,power density or cycle stability.Details are as follows:?1?Design and prepare a new lithium ion battery anode material to achieve its fast charging performance.MnO inlaid multi-walled carbon nanotubes?MnO@CHNTs?composites were prepared by combining molecular beam precursor template method and subsequent high temperature heat treatment.The characterization results show that the carbon nanotubes can reach several micrometers in length,with diameter about 100 nm and wall thickness about 30 nm,and a large number of 2-3 nm MnO quantum dots are uniformly embedded in the graphite carbon of carbon nanotube walls.The MnO@CHNTs composite forms a stable MnO-graphite heterostructure,increasing the layer spacing of the graphite carbon material to 0.41nm,which is much larger than that of pure graphite?0.34 nm?.Therefore,when MnO@CHNTs composite material served as lithium-ion battery anode,it can be fully charged within 28.3 s,and the specific capacity of anode material is up to 392.8 mAh g^-1 at current density of 50 A g^-1 after 100 cycles?higher than commercial graphite anode?.?2?Construction of a new fast rechargeable sodium/potassium ion battery with prepared MnO@CHNTs composites as anodes.It was found that the MnO quantum dots not only reduced the migration energy barrier of sodium/potassium ions b etween the graphite layers,but also enhanced the adsorption energy towards sodium/potassium ions.Therefore,it delivers excellent capacity and rate performance in the sodium ion battery,demonstrating a capacity of 348.8 mAh g^-1 for the first circle at the current 2 A g^-1,and remains 223.0 mA h g^-1 after 1000 cycles?much higher than the capacity of pure graphite carbon and MnO itself as anodes for sodium ion batteries?.Meanwhile,in potassium ion battery,its capacity can be stably maintained at 220.6 mAh g^-1 after 500 cycles at a current density of 20 A g^-1,meaning a 39.6 seconds charging rate,and the coulomb efficiency is close to 100%,which demonstrates that Fe₃C-MC can significantly improve the capacity,rate and cycle performances of lithium-sulfur batteries.?3?Design and preparation of novel graphene-p-phenyl-graphene?GPG?nanomaterials,and investigation of their applications as potassium and aluminum ion battery electrode materials.The diazotization reaction is carried out to chemically bond the p-phenyl group to the graphene oxide layer,and then completely reducing it by high-temperature heat treatment to obtain a novel GPG nanomaterial.Since the p-phenyl group is chemically bonded between the graphene layers,the interlayer spacing of the graphene is significantly expanded to⁰.56 nm,which facilitates rapid migration of ions between the layers.By constructing potassium ion and aluminum ion batteries,the migration of cation?K⁺?and?AlCl₄^-?anions in GPG was investigated respectively.The results show that the anion and cation can migrate faster between GPG layers after the interlayer spacing is widened.Therefore,the constructed potassium ion battery and aluminum ion battery can be fully charged in43.7 and 28.1 seconds,respectively.?4?Design and preparation of novel graphene-biphenyl-graphene?GBG?and its capacitance properties.The reduced graphene oxides are often stacked in multiple layers,resulting in a decrease in the specific surface area,and thus the electric double layer capacitance is always much lower than the theoretical value.However,the graphene layers are integrated together in the biphenyl bridged GBG,and the interlayers would not be stacked due to the introduction of biphenyl.When the GBG used as a supercapacitor electrode material,ions could be access to the interlayers of graphene,forming electrical double-layer on both two sides of grapheme.Thus,the GBG shows excellent capacity and rate performance.The specific capacity of GBG can reach 446.8 F g^-1 in 6 M KOH aqueous electrolyte at a current density of 1 A g^-1;while in the organic electrolyte system,the specific capacity is 233.6 F g^-1 under two-electrode system.At the same time,GBG achieves fast charging rate when charging it at a high current density of 10 A g^-1?56.8 s full charge?,and discharging at a current density of 0.5 A g^-1,the coulomb efficiency reaches 99.9%and an energy density is up to 118.2 Wh Kg^-1?very close to the energy density of general lithium-ion batteries?.After 5,000 cycles of charge and discharge cycles,the capacity retention rate remains 98.1%,which makes it a promising fast rechargeable energy storage device.?5?Investigation on the kinetic conversion mechanism and electrochemical performance of active sulfur in Fe₃C-MC composites as cathode host for lithium-sulfur batteries.The kinetic conversion mechanism of sulfur reduction in lithium-sulfur battery cathode was systematically analyzed,and the key factors limiting its rapid conversion were discussed.Based on the analysis results,and combined with theoretical calculation,an ultra-thin Fe₃C nanosheets uniformly growing on the surface of porous carbon?Fe₃C-MC?was designed and fabricated for the sulfur host in lithium-sulfur battery.Among them,porous carbon?MC?contributes to the dispersion of high-loading active sulfur species,and Fe₃C nanosheets can not only efficiently adsorb soluble lithium polysulfide produced during the reduction process,but also achieve rapid catalytic conversion process for lithium polysulfide.The results show that the lithium-sulfur battery with Fe₃C-MC as the sulfur positive electrode maintains the capacity of 920 mA h g^-1 after 1000 cycles at a current density of 0.5C,and even at the high current density of 5C,it still remain s a capacity of 727 mA h g^-1.Therefore,Fe₃C-MC accelerates the kinetic conversion process of sulfur reduction,which significantly improves the capacity,rate performances and cycle stability of lithium-sulfur batteries.?6?Construction of novel aqueous Fe-ion battery systems.Here,for the first time,an aqueous rechargeable Fe-ion battery is realized.Fe³⁺/Fe²⁺and Fe²⁺/Fe are used as the redox couples with gold and iron sheets as the electrodes for the cathode and anode electrodes,respectively,and the anion exchange membrane is selected as the battery separator.Since the electrolyte is aqueous,ions can rapidly migrate in the electrolyte,so the Fe-ion battery can achieve rapid charging and discharging rates.In addition,by using graphite as electrodes and a polyethyl methacrylate oxyethyl trimethyl ammonium chloride?METAC?gel as electrolyte instead of the aqueous solution,a rechargeable whole-Fe-ion battery was realized.The new Fe ion battery is non-toxic,environmental friendlyness,and low-cost system,which exhibits promising application prospect in large-scale energy storage systems.