| Since the first-generation lithium-ion batteries(LIBs)commercialized by Sony in 1991,related technologies have developed rapidly in the past few decades.Nowadays,LIBs have been widely used in portable electronic devices and electric vehicles.However,because of the ever-growing demands of electric vehicles,the drawbacks of low reserves and uneven distribution of lithium in the earth’s crust led to a rise in the price of lithium resources.And the high cost feature causes LIBs lack of competitiveness in large-scale electric energy storage systems.Consequently,it is imperative to develop metal-ion batteries beyond LIBs in the long run.Sodium ion batteries(SIBs)and potassium ion batteries(KIBs)have emerged due to the abundant reserves of Na and K on earth.Searching for suitable electrode materials is the key to develop KIBs technologies.Unfortunately,the diffusion process of large-size K+in traditional electrode materials(such as layered transition metal oxides)becomes difficult,and the volume change along with the de-intercalation of K+ in the electrode material is also larger,which ultimately lead to the significant decline of the performance.Hence,it’s urgently to design the structures and morphologies for the electrode materials.In this thesis,we focus on the modification of polyanionic compounds,hard carbon and antimony-based electrode materials.Moreover,we have realized high-performance potassium ion full cells based on carbonate and ether electrolytes respectively.In Chapter 1,a general introduction of electrochemical energy storage secondary batteries and the working mechanism along with the key components of KIBs are given firstly.Afterwards,we reviewed the recent progress and prospective of the typical electrode materials and electrolyte for KIBs.Finally,a brief introduction of the background and research details of this thesis are expounded.In Chapter 2,the reagents,material synthesis and material characterization techniques used in this thesis,as well as coin-cell fabrication and electrochemical testing methods are presented in detail.In Chapter 3,a highly disordered hard carbon derived from a skimmed cotton is investigated as KIB’s anode material.The study show that a simple soaking treatment in hydrochloric acid for the skimmed cotton before its high-temperature carbonization can critically impact the microstructure and the diffusion kinetics of the obtained hard carbon significantly.This optimized hard carbon anode exhibits a superior rate performance(165 mA h g-1 at 4 A g-1)and excellent cycling stability.In Chapter 4,a novel three-dimensional macroporous antimony@carbon composite(Sb@C-3DP)is fabricated by a simple KCl template method with a single bi-functional precursor potassium antimony tartrate.The Sb@C-3DP electrode delivers a remarkable reversible capacity(516 mA h g-1 at 0.05 A g-1)and outstanding long-term cycling stability(97%capacity retention after 260 cycles).In Chapter 5,a series of three-dimensional sandwich cheese-like SbxBi1-x@C composites are fabricated by a modified Pechini sol-gel method.As an anode for KIBs,the Sb0.5Bi0.5@C composite exhibits the optimal performance(382 mA h g-1 at 0.05 A g-1 and 83%capacity retention after 400 cycles).More importantly,we further characterized the mechanism of the synergistic effects in the binary alloy to improve the potassium storage performance of Sb0.5Bi0.5@C.In Chapter 6,a carbon-matrixed KVP2O7 powder with a wrinkled pea-shaped particle morphology is fabricated via a spray-drying process.The carbon matrix obtained by in-situ pyrolysis of polyvinyl pyrolidone(PVP)can provide a good electron transport channel for KVP2O7.By optimizing carbon content,the KVP2O7-C cathode can deliver a high energy density of 250.3 W h kg-1.Moreover,various characterization methods were applied to investigate the potassium storage mechanism of KVP2O7.In Chapter 7,we design and synthesize a multi-component coated KVPO4F cathode(KVPF-MC2).The multi-component coating strategy effectively reduces the side reactions at the interface between electrolyte and cathode materials.Furthermore,a full cell constructed by coupling this KVPF-MC2 cathode with a hard carbon anode delivers a high energy density up to 337 W h kg-1 with operating voltage of 3.5 V.The mechanism of multi-component coating strategy to improve the electrochemical performance of KVPO4F cathode is characterized carefully.In Chapter 8,we introduce full cells constructing by the modified cathode and anode materials in chapter 3-7,and by exploring the applicability of the electrode material with the electrolyte,two typical full cell systems based on carbonate electrolyte and high concentration ether electrolyte are optimized.We hope this research work can highlight the design of high-performance potassium ion full cells.In Chapter 9,a brief summary of the main innovative works and deficiencies of this thesis are presented.Some expectation and suggestions for the further research are also given. |
