Ordered Nanostrctural Electrodes:Design,Preparation And Applications For Advanced Batteries

Although the storage capacity of lithium-ion batteries(LIBs)is close to their theoretical capacity,they still cannot meet the requirement of increasingly developed electronic devices.In addition,the manufacturing cost of LIBs remains high due to the low content of Li resources,uneven distribution in the earth's crust and difficulty in recycling.The development of new alternative batteries,such as metal batteries with high energy density or inexpensive and resource-rich beyond LIBs,is of great significance to the development of the energy storage field in the future.For example,lithium-sulfur(Li-S)battery with ultra-high theoretical specific capacity(1675 mAh g-1)has received extensive attention and research intrest.Benefit from widely distributed and low-cost raw materials,sodium-ion battery(SIB)is aslo considered to be one of the most promising battery systems to replace LIBs.However,due to the unique electrode reaction processes and the characteristics of guest ions in new alternative batteries,how to design new energy storage materials with excellent performance to meet future practical applications is still facing challenges:(1)Complex multiphase reactions and multi-electron transfers always result a low conversion efficiency of active materials,which seriously affects the specific capacity and coulombic efficiency of the battery.How to improve the utilization efficiency of of active materials and increase the reversible capacity of the battery is still a challenge;(2)The per unit area of active material loading in the electrode is relatively low.When the loading is increased,the thick membrane electrode would hinder the transmission of ions and electrons,which leads to a significant degradation of battery performance and affects the energy density of the battery.How to construct the electrodes with high active material loading and high energy density is still a challenge;(3)For beyond LIBs,new alternative ion batteries often face problems such as difficulty in ion deintercalation,slow kinetics,and serious electrode structure collapse due to the large size of guest ions,which would seriously affect the energy output and cycle life of the battery.It is of great significance to obtain new electrode materials with high capacity and high stability.Therefore,how to improve the conversion efficiency of active materials and construct a new electrode material with high energy density and high stability is very important in the field of new alternative batteries.This dissertation focuses on the key issues in new alternative battery systems,such as complex electrode reactions,lower energy density and poor cycle life.We choos new types cathode materials(e.g.,Li-S batteries and SIBs)as research models,and carries out innovative research work in three aspects,including the rational design,controlled preparation and applications in advanced battries.First,the design of nanostructural electrode can promote the reaction kinetics process of the energy storage electrode and achieve a high utilization rate of active materials,which significantly improves the specific capacity and coulombic efficiency of the material;Secondly,the active material loading and energy density on the electrodes have been improved obviously via the construction of hierarchical structure self-supporting electrodes and the fine adjustment of the micro-energy storage interface;Finally,based on this type of cathode material,the performance of new alternative battery systems such as Li-S batteries,SIBs and water-based batteries have been enhanced.The main research contents and results of this thesis are as follows:1.Nanostructural porous carbon nanosheets for Li-S batteriesThe high loading and the easy aggregation of sulfur are hard to be balanced,since sulfur are getting easier to migrate and aggregate at surface of carbon supports,which lead to the low concentration loading or limited sulfur utilization.Thus,how to achieve sulfur confinement and simultaneous highly efficient conversion of intermediate polysulfides(LiPSs)is a challenge for the next-generation Li-S batteries.In this part,the ordered carbon nanosheets with hierarchical structure were obtained through a confinement synthesis strategy.Benefit to the high specific surface area,abundant mesoporous structure and highly dispersed catalytic sites,the as-prepared material as efficient host can simultaneously achieve confinement and efficient conversion of LiPSs,which delivered a significantly improvement in the specific capacity and cycle stability for Li-S batteries.First,the metal organic framework material(ZIF-67)were confined growth on the surface of ZnAl-LDH,followed by a subsequent pyrolysis to obtain a mesoporous carbon nanosheets with high specific surface area(MC-NS),which can be used as a sulfur cathode carrier for Li-S batteries.According to systematic experiments and density functional theory(DFT)calculation results,MC-NS with a rich defect structure and highly dispersed Co-NC catalytic sites achieves a high sulfur loading of 86%(most of the literature report<75%),and the shuttle effect of LiPSs is effectively suppressed.Meanwhile,Co-N-C structure,as a highly active site,could not only help to convert long-chain LiPSs to Li2S2/Li2S but also can catalyze Li2S2/Li2S back to soluble long-chain LiPSs.Therefore,compared with the carbon particles obtained by directly carbonizing ZIF-67,the MC-NS/S as a sulfur cathode delivered a higher specific capacity(1172 mAh g-1)at a current density of 0.2 C,better rate performance and cycle stability(specific capacity can be maintained at 512 mAh g-1 after 1000 cycles at 2 C).In this work,the confinement and the catalytic conversion of LiPSs by two-dimensional mesoporous carbon nanosheets with hierarchical structure provides a new materials platform for the design of high-performance Li-S batteries battery cathodes.2.Self-supported nanostructural electrode for flexible Li-S batteriesIn the traditional assembly process of powder electrodes,the use of conductive agents and binder would cause the low per unit area loading of active material.When the loading increased,too thick membrane electrodes would hinder the transport of ions and electrons,which seriously reduces the energy density of the battery.Based on above,a hierarchical nitrogen-doped carbon nanotube(NCNT)@Co-Co3O4 nanowire array(NWA)integrated electrode was designed and constructed via an in-situ catalytic growth process.The LiPSs adsorption experiment and in-situ Raman spectroscopy systematically verified that NCNT@Co-Co3O4 NWA can effectively promote LiPSs adsorption and catalytic conversion,making the electrode exhibited the desirable specific capacity and excellent cyclic stability at high sulfur loadings(the areal capacity is as high as 8.5 mAh cm-2 at 0.2 C with the sulfur loading of 10 mg cm-2).In addition,the performance of the assembled pouch cells with the NCNT@Co-Co3O4@S cathode also showed a higher capacity and longer cycle stability than that of the reported results.Meanwhile,DFT calculations further proved the effective adsorption and high-efficiency catalytic conversion ability of LiPSs on the Co-Co3O4 heterojunction interface.In order to ensure the advantage of higher energy density of Li-S batteries,the NCNT@Co-CoP nanowire array self-supporting electrode was further constructed.Meanwhile,as verified both experimentally and theoretically,the Co-CoP heterojunction can effectively chemically trap and fast catalyze the LiPSs as well as endow Li+a moderate diffusion barrier,leading a fast-interfacial charge transfer and improved the reaction kinetics.As a sulfur cathode,the NCNT@Co-CoP@S can still maintain a high specific capacity of 603.9 mAh g-1 after 900 cycles at 5 C with a high sulfur loading of 4 mg cm-2.This work provides a new strategy and a certain guideline for the design and development of flexible Li-S batteries with high energy density and high rate performance towards future wearable electronic products.3.Nanostructural transition metal hydroxide nanoarrays for sodium ion batteriesCompared with Li-S batteries that use Li resources,SIBs have similar energy storage mechanisms to LIBs.Meanwhile,due to the abundant,low-cost and widely distributed of raw materials,SIBs are expected to become the next generation of high-performance new alternative ion batteries.However,the host material suffered severe deformation and volume expansion during the repeated(de)intercalation process of Na+,resulting in the structural collapse of the electrode material and the rapid decay of capacity.Therefore,designing a stable and long-life new cathode material for SIBs is the key to push its practical application.In this work,a structured ultra-thin cobalt-based layered double hydroxide(LDH)nanosheet array was synthesized.After electrochemical activation,the obtained material(E-CoFe-LDH)was first used as the cathode material of SIBs,which achieved a significance improvement in cycling life.The results of XRD,FTIR,EXAFS and XPS proved that the activated material benefit to enhance the storage ability of Na+.Thus,the prepared E-CoFe-LDH nanosheet array showed a high reversible specific capacity and cycle stability of?40 mAh g-1 at 2 A g-1 after 32000 cycles(capacity retention rate is?80%),which is much higher than the current reported SIBs cathode.According to the tracking test of the charge and discharge process,the main structure of the material does not change during the Na+ de-intercalation process,and the valence state of Co on the layer and the content of active oxygen(O2-)change reversibly.Meanwhile,O2-is the main the site of reversible adsorption of Na+.Based on this storage mechanism,the reversible and efficient storage of Na+ is realized and the high cycle stability of the material is ensured.This work provides a new material basis for the development of a new type of high-stability,long-life SIBs cathode material.4.Mechanism of metal cations storage in nanostructural transition metal hydroxide cathodesBased on above,the electrochemical activation can significantly improve the Na storage capacity of transition metal hydroxides.In order to reveal the relationship between multi-ion storage and the crystal structure of transition metal hydroxides,we further present 2D cobalt hydroxides with similar morphologies but different crystal phase structures(?-and ?-Co(OH)2)as models to explore their metal ion storage mechanism.First,the prepared samples underwent an electrochemical activation treatment for surface reconstruction(denoted as E-?-and E-?-Co(OH)2).Subsequently,systematic test results show that activated Co(OH)2 has the ability to store multiple metal ions under neutral conditions.Among them,E-?-Co(OH)2 with an intercalated structure exhibits more excellent metal ion storage capacity and long cycle life.Besides,the ion storage capacity of E-?-Co(OH)2 performance of storing ions can be improved by more than 2 times than that of powder sample by the structure design array,which is far better than most of the literature report.Based on the results of ex situ XRD,EXAFS,XANES and XPS analysis,we found that the a-Co(OH)2 with an intercalation structure is more prone to generating the Co-OOH phase,which is beneficial to improve ion storage performance.This work reveals the relationship between cation intercalation and the crystal structure,which will be beneficial to design and enrich advanced multi-ion storage materials for future energy storage systems.