| Nowadays,in gradually progressive modern society of science and technology,the society’s demand for energy capacity is increasing.However,along with the gradual consumption of traditional fossil energy（coal,oil,etc.）reserves and the serious environmental pollution occurred during the using process,people have to turn their attention to renewable energy（water energy,tidal energy,solar energy,etc.）.Nevertheless,the distribution of the above-mentioned renewable energy is sporadic,and the continuous supply capacity is poor.Moreover,most of them are located in remote locations.Therefore,how to store renewable energy in the form of electricity and apply it on a large scale is particularly important.In this regard,there is an urgent need for the promotion and application of new electrical energy storage and conversion technologies.In addition,some current smart terminals（such as electric vehicles,smart devices,etc.）also urgently need the development and innovation of new energy storage system technologies to meet the needs of their increasing usage scenarios.At present,the existing commercial energy storage systems are mainly lithium-ion batteries,but the existing lithium resources also have some disadvantages,such as low reserves,uneven distribution,and high prices.Therefore,developing the next generation of new alkali metal ion batteries,including Sodium-ion battery（SIBs）and potassium-ion battery（PIBs）,has far-reaching significance.In the research of SIBs and PIBs,the capacity and cyclic life of the anode material are related to the energy density performance of the total battery system.However,to explore an ideal anode material with long cycle life and high specific capacity is still an important challenge in current research.In addition,we need to study of the kinetic reaction mechanism,and exploring the interrelationship between electrode morphology evolution and the electrochemical performance during the reaction process.These above research contents can provide important experimental support and theoretical basis to design the ideal next generation energy storage system.In this work,we firstly designed a series of anode materials for sodium-ion and potassium-ion batteries by nano-structure design or composite preparation methods.Subsequently,the kinetic reaction mechanism with the evolution of the chemical composition and physical structure of the electrode structure was explored during the charge-discharge cycles.Novel phenomena such as carbon-sulfur hetero-bonding and selenium-copper hetero-bonding generated in the electrodes were discovered during dynamic cycling,and the relationship between the electrochemical performance of the electrode and its kinetic reaction mechanism was understood and explored in detail.The main research contents and results are as follows:（1）The nitrogen-doped reduced graphene oxide and bismuth sulfide composite（NGBS）was designed and applied NGBS as anode material for PIBs with an excellent performance.Firstly,reducing graphene oxide not only buffers the volume expansion of bismuth sulfide in the composite,but also improves the electron and ion transport capacity of the electrode.Secondly,more defect active sites were introduced on the graphene surface by nitrogen doping,which not only enhanced the adsorption and desorption storage capacity of K-ions,but also further improved the electrical conductivity of the electrode.Finally,through electrochemical tests,the C-S dynamic heterogeneous bonding phenomenon was found during dynamic charge-diacharge process.This heterostructure suppresses the shuttle effect of polysulfur by fixing the intermediate product polysulfur during the charge-discharge process and maintains the stability of the electrode interface reaction during cycling process,which ultimately enables the NGBS electrode to obtain excellent electrochemical performance(427 m A h g-1after 100 cycles at 5 A g-1).（2）Ultrathin bismuth selenide nanosheets with uniform morphology and stable properties were designed and fabricated as anode materials for Na-ion batteries to study their electrochemical performance and energy storage mechanism.In electrochemical tests,the ultrathin bismuth selenide nanosheets electrode can exhibit high specific capacity(538 m A h g-1after 100 cycles at 0.1 A g-1),stable cycle life(1400 cycles at 10 A g-1with 430 m A h g-1)and excellent rate performance(specific capacity of 454 m A h g-1at 5 A g-1and 361 m A h g-1at 20 A g-1).At the same time,by systematically exploring the electrode evolution during cycling,it was found that the initial two-dimensional bismuth selenide nanosheets spontaneously cross-linked with the assistance of the current collector copper to form a three-dimensional network sheet-like electrode structure.The occurrence of this synchronous electrochemical reconstructure phenomenon（in the process of electrochemical charge-discharge cycle,the electrode undergoes the secondary structure or composition evolution to improve the electrochemical cyclic stabilization）resulted in a great change in the chemical composition and physical structure.In addition,in terms of chemical composition evolution,this change inhibits the side reactions such as the shuttle effect of polyselenium by utilizing the hetero-bonding of selenium and copper,and maintains the cycling stability of the electrode.Ultimately,the electrode could achieve significant improvement on the cycle life and rate performance.（3）In order to further explore the synchronous electrochemical reconstructure strategy,pure selenium powder was used to prepare slurry and coated on the the treated copper foil surface.Then,the interrelationships between electrochemical reconstructure process and electrochemical performance were exploring through a series of characterization methods.In terms of electrochemical performance,the pure Se electrode could achieve an ultra-long cycle life(the specific capacity is 529 m A h g-1after 16,000 cycles at 20 A g-1),high specific capacity(100 cycles at 0.1 A g-1with790 m A h g-1)and excellent rate performance(the specific capacity is 636 m A h g-1at10 A g-1,and the specific capacity is 441 m A h g-1at 50 A g-1).During the charging and discharging process,a bond formation reaction occurs between metal selenium and copper,which inhibits the shuttle effect of polyselenium.In addition,the electrode structure is rapidly self-assembled into a three-dimensional cross-linked network structure from pure selenium powder particles after electrochemical cycling,which can greatly improve the ions and electrons transport ability and buffer the electrode volume expansion effect during charging and discharging process.Finally,the electrode could achieve excellent rate performance and cycle performance.（4）In order to improve the deterioration of bismuth electrode performance caused by the pulverizing and stripping of active materials from the electrode in the alloying reaction,the ultrathin bismuth nanosheets（FBNs）were prepared by ultrasonic-assisted electrochemical exfoliation.Meanwhile,FBNs were applied as PIBs anode to investigate the electrochemical performance and kinetic reaction process in detail.The ultra-thin two-dimensional nanostructure of FBNs can effectively alleviate the volume expansion effect on the electrode during the repeatedly K-ion intercalation and extraction process.More contact area between electrode and electrolyte can provide more reactive active sites for K-ion storage,and shorten ion and electron transfer path.Therefore,the FBNs electrode could deliver excellent electrochemical performance(specific capacity is 200 m A h g-1after 2500cycles at 20 A g-1). |
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