Preparation Of Two-dimensional Metal Oxides/Sulfide And Application In Electrochemical Energy Storage

With the depletion of fossil energy,the demand for renewable energy has become increasingly strong,but due to its regional and intermittent characteristics,the demand for electrical energy storage systems has continued to increase.In addition,the demands from portable electronic devices and electric vehicles have set higher demands on the performance of energy storage systems.At present,two most advanced energy storage technologies:electrochemical capacitors and secondary batteries have been used for large-scale energy storage.The main problem restricting its further development is the exploitation of advanced electrode materials.Obviously,in the past decades,the development of nanoscience and technology has provided tremendous help to improve the electrochemical energy storage performance of advanced electrode materials.Compared with bulk materials,tens to thousands of angstrom nanomaterials provide huge specific surface area for ion adsorption and storage,convenient ion transmission channels,and fast surface redox reactions.The unique properties of these nanomaterials are conducive to improving the energy power density and high current performance of energy storage devices.Two-dimensional materials with few nanometers thickness,due to their unique two-dimensional structure,anisotropy and so on,exhibit a high specific surface area,which can provide excellent storage performance for electrochemical energy storage systems.In particular,compared to the adsorption or insertion mechanism of carbon materials in electrochemical capacitors or secondary batteries,two-dimensional metal oxides and sulfides have a redox storage mechanism that can be bring higher energy density.The metal oxides and sulfides have become a promising energy material for electrochemical energy storage.Although two-dimensional metal oxides and sulfides have many advantages,they still have many problems that limit their application in electrochemical energy storage.Firstly,their complex synthesis conditions and high synthesis cost are not conducive to the large-scale applications of electrochemical energy storage devices.Secondly,the two-dimensional metal oxides and sulfides generally have poor electrical conductivity and unstable material structure to affect performance of energy storage equipment.Therefore,in response to the above two problems,first,we developed a generalized synthesis strategy to prepare twodimensional metal oxide and sulfide nanosheets.Second,we took full advantage of the structural advantages of two-dimensional nanomaterials.Engineer the composition and structure of relevant electrode materials to improve the performance of electrochemical energy storage equipment.1.We have developed a generalized preparation strategy to achieve the controllable preparation of two-dimensional metal oxide nanosheets through the self-assembly mechanism based on the thermoregulated phase transition of P123 surfactant lamellar micelles.After changing the reaction condition parameters(without adding P23,P123 concentration changed from 20 wt%to 10 wt%,standing temperature changed from 50℃ to 40℃,and standing time changed from 2 hours to 1 hour),the change of morphology and analysis of the morphology of the intermediate product determined the self-assembly mechanism based on the thermoregulated phase transition of lamellar micelles.It was clear that temperature and P123 concentration were the key to the formation of lamellar micelles.Based on such a mechanism,eight two-dimensional metal oxide nanosheets of transition metals and main group metals have been successfully synthesized,including Mn3O4,Fe2O3,Co3O4,NiO,CuO,ZnO,SnO2 and Sb2O3.The synthesized metal oxides exhibit good crystal structure and high specific surface area.Due to the universality of this two-dimensional metal oxide synthesis strategy and the advantages of materials,other metal oxides and even other types of two-dimensional materials can also be developed using this strategy.for electrochemical energy storage devices.This is foundation for the performance of electrochemical energy storage devices and cost control.2.SCs have the advantages of pollution-free,high power density,long cycle life,etc.,and have already occupied a certain position in the energy storage of the new era.However,due to its limited energy density,there is a high demand for new electrode materials with superior performance.Manganese-based materials are considered to be the most promising pseudo-capacitor electrode materials due to their low cost,high capacity,and high electrochemical activity.Therefore,we applied the two-dimensional Mn3O4 nanosheets based on the mechanism of P123 lamellar micelle thermoregulated phase transition to supercapacitors.As a potential electrode material for supercapacitors,the two-dimensional Mn3O4 nanosheets compared to their bulk materials have a specific capacity of 126.9 F g-1 at 0.5 A g-1,and have a specific capacity of 78.8 F g-1 at 10 A g1,showing excellent rate performance.After 10,000 cycles,it can still maintain high cycle stability of 96%.This excellent performance of two-dimensional Mn3O4 nanosheets provides a basis for the application of other two-dimensional materials in electrochemical energy storage.3.With the development of the lithium ion battery in the past 30 years,its energy density,power density,safety,low cost and cycle life have been improved.So,it has become the first choice for energy storage equipment of various fields.However,the low theoretical specific capacity of commercial negative electrodes(graphite 372 mAh g-1)has become one of the leading factors limiting the upgrade of lithium-ion batteries.Electrode materials based on conversion reactions and alloy reactions are favored because of their far higher lithium storage capacity than intercalation reactions.CoO is popular because of its actual specific capacity exceeding 1000 mAh g-1.However,CoO anode materials often have low rate performance and weak cycle stability due to their poor conductivity and severe volume expansion.Here,we prepared a two-dimensional porous CoO nanosheet-reduced graphene oxide(rGO)composite based on two steps of P123 layered micelle induction and electrostatic adsorption,and applied it to the anode material of lithium ion batteries.Reversible specific capacity of 1067.7 mAh g-1 at 100 mA g-1,increased to 8.5 A g-1,it has a 60%rate performance.The retention rate is 77%after 400 cycles at 500 mA g-1.It has good cycle performance.We also compared the performance of lithium ion batteries with different ratios of CoO-rGO and pure CoO,and the results showed that the porous structure facilitates the transport of lithium ions and addition of graphene and its three-dimensional graphene cross-links provide electron transport can comprehensively improve the electrochemical performance of lithium ion batteries.4.In lithium-ion batteries,lithium alloy materials have a higher theoretical specific capacity than graphite’s 372 mAh g-1,.For example,silicon anode(3,579 mAh g-1),tin anode(994 mAh g-1).However,the rapid capacity decay and safety problems caused by the violent volume expansion of the alloy have always restricted its development.Unlike alloy reactions,Li2O and Li2S introduced by the conversion reaction can be reversibly formed and decomposed,and a buffer layer can be provided to reduce volume expansion and keep stable capacity.Therefore,the combination of alloy reaction and transformation reaction can effectively alleviate problems such as rapid capacity decay.SnS,with a theoretical specific capacity of 1137 mAh g-1,its weak M-S bond brings higher reversibility and first cycle coulombic efficiency.Its unique interlayer gap facilitates the diffusion of ions.It is an ideal anode material for lithium ion batteries.However,the problems of poor conductivity and volume expansion still need to be solved.Here,we designed a two-dimensional porous rGO-SnS/C sandwich structure based on the two-step method of on the growth of graphene induced by P123 lamellar micelles and the coating of polydopamine,and applied it to the anode materials.At 0.1 A g-1,the first discharge specific capacity can reach 1227 mAh g-1,and the first cycle coulombic efficiency can reach 80%.It has a retention rate of 52%at 5 A g-1 and shows good rate performance.In addition,it still retains 62%of capacity during 200 cycles at 0.5 A g-1 cycle,and has good cycle stability.Compare to rGO-SnS2/C for lithium storage performance,the results show that the larger volume expansion of SnS2 leads to rapid capacity decay.Compared with rGO-SnS2/C and rGO-SnS2,the relatively better cycling performance of rGO-SnS2/C indicates that carbon coating suppresses the volume expansion of SnS2 and exhibits better conductivity.5.Due to the shortage of lithium resources and high cost,sodium elements with lithium in the same main group have become a promising candidate.Sodium and lithium have very similar alkaline-earth metal properties,and sodium has a rich content and a wide distribution on the earth.So,sodium ion batteries follow the pace of lithium ion batteries into the scientists’ vision.The alloy reaction of the sodium ion battery has a relatively low reaction potential,but due to the larger radius of the sodium ion,it will cause more severe volume expansion.The conversion reaction of sodium ion introduces Na2O and Na2S.They can reversibly form and decompose,and can provide a buffer layer to reduce volume expansion.But the conversion reaction has high reaction potential and slow kinetic problems caused by voltage hysteresis effect.Therefore,combining the advantages of alloy reaction and transformation reaction can just make up for their shortcomings.Here,we apply the two-dimensional Sb2O3 nanosheets prepared based on the mechanism of P123 lamellar micelle thermoregulated phase transition to sodium ion battery.After 150 cycles at 100 mA g-1 showed 99%high capacity retention,indicating that the two-dimensional Sb2O3 nanosheets have good structural stability.Its coulombic efficiency has been maintained above 97%,which shows that the two-dimensional structure provides it with fast sodium insertion and sodium removal capabilities.In contrast,the Sb2O3 polyhedron exhibits extremely poor performance as anode for sodium ion batteries.Further verify the applicability of twodimensional materials in sodium ion batteries.It provides support for the expansion of two-dimensional materials in electrochemical energy storage.