Construction Of Novel Sodium/Potassium-based Energy Storage Devices And Investigation Of High-Performance Bismuth-Based Anode

Energy is a matter of the national economy and people’s livelihood.The development of high-performance electrochemical energy storage devices plays a pivotal role in achieving the goal of"peak carbon dioxide emissions and carbon neutrality".Currently,lithium-based devices dominate the mainstream energy storage market However,the development of high-performance energy storage devices is severely limited due to the scarcity and uneven di stribution of lithium resources.Based on this,it is one of the essential initiatives to ensure energy security in China by developing high-performance energy storage devices based on non-lithium elements.Sodium/potassium is located in the same main grou p as lithium with similar physical and chemical properties.They also offer the advantages of being abundant and low cost.Consequently,the development of high-performance sodium/potassium-based energy storage devices is of considerable interest.Moreover,the urgent development of high-performance energy storage devices capable of operating under extreme low-temperature conditions has also become a pressing issue.Recently,bismuth-based anodes have been widely concerned due to their lower operating poten tial and higher theoretical capacity.Nonetheless,several challenges persist in the sodium/potassium storage process,including large volume varation,unstable solid electrolyte interphase（SEI）and slow ion transport.These issues significantly impede th e development of high-performance bismuth-based sodium/potassium storage devices.This study employs a combination of theoretical and experimental approaches and focuss on structural design and in-depth study of its internal mechanism to address the aforementioned issues.Furthermore,a bismuth-based high performance sodium/potassium energy storage device is constructed from two aspects:（1）The sodium/potassium ion hybrid capacitors are constructed that exhibits high energy/power density.Furthermore,the high-performance potassium ion hybrid capacitors are designed at low temperatures.（2）The"sodium ion/sodium metal dual mechanism"synergistic energy storage model is proposed firstly constructed,aiming to develop a novel anode that combines high capacity with dendrite-free growth.The specifics of our research are as follows:（1）Self-assembled three-dimensional crosslinking bismuth@carbon anode electrode for high-performance sodium-ion hybrid capacitors.This chapter focuses on the problems of poor interfacial reaction kinetics,huge volume strain and low power density of the traditional bismuth electrode.In this work,three-dimensional crosslinking bismuth@carbon（3DCB@C）anode is constructed by in-situ electrochemical annealing strategy,and the interfacial component differences between different electrolytes and anode is systematically investigated.The results show that the uniform,thin and polyether-rich SEI film is obtained based on DME-based electrolyte.Meanwhile,the electrode can be induced to form the three-dimensional crosslinking structure due to the strong adsorption between DME molecules and bismuth atoms,which promotes the rapid Na⁺transmission and reaction kinetics.Based on these advantages,the 3DCB@C as ano de exhibits the super long cyclic stability(a reversible capacity of～370.9 m Ah g^-1 is received after 8000 cycles at 15 A g^-1)and outstanding rate performance(a reversible capacity of 283.2 m Ah g^-1is obtained at 55 A g^-1)for SIBs.Moreover,3DCB@C and AC are employed as anode and cathode,respectively.The 3DCB@C/AC SIHCs is firstly constructed.It shows a high power density(up to 35280 W kg^-1)and excellent cyclic stability(with a reversible energy density of 75 Wh kg^-1 after 12000 cycles at 2 A g^-1).（2）“Inner-surface”controlled mechanism enhancing the high performance of bismuth-based potassium-ion hybrid capacitors.This chapter focuses on the feature of high capacitance contribution in alloyed bismuth-based anodes.Combining the theory,experiments and diffusion equation,it can be confirmed that CBN（Conjunct Bismuth Nanoparticles）owns the synergy effect with high diffusion and high reaction activity,named as“inner-surface”control.That is,the electrochemical reaction rate in“inner-space”for CBN electrode is equivalent to that of the surface of pseudocapacitor material s,and the electrochemical reaction rate in the bulk phase is equivalent to that of the surface for CBN.Benefited by“inner-space”mechanism,CBN anode delivers an outstanding cycle performance and excellent rate performace as expected in both room temperature and low temperature（-20℃）.Especially,a higher reversible capacity of～212.9 m Ah g^-1 can be received after 5000 cycles at 30 A g^-1.Meanwhile,the first constructed CBN/AC PIHCs exhibits an outstanding energy density(111.8 Wh kg^-1)and power density(14312.6 W kg^-1).（3）Synergistic strategy between electrode and electrolyte facilitating low-temperature potassium-ion hybrid capacitors.This section aims to solve the slow transport of K⁺at low temperature（<-30℃）.The bismuth oxide anode is designed with fast K⁺transport at low temperature through synergistic strategy between electrode and electrolyte.In the preferred electrolyte,the SEI film is formed with an inner layer rich in inorganic components and an outer layer rich in organic components.It can increase the mechanical strength,flexibility and interface stability of electrode.Moreover,MD and DFT calculations indicate that 1 M KPF₆ DME has a greater desolvation energy at low temperature,providing sufficient ion migration pathways and thereby increasing the migration rate of K⁺.Based on above advtanges,the designed anode exhibits a reversible capacity of 222.4 m Ah g^-1after 1000 cycles at 2 A g^-1 under-40℃.In addition,the constructed Bi₂O₃/AC PIHCs achieves a high energy density(105.8 Wh kg^-1)and power density(5440 W kg^-1)at-20℃.（4）Sodium ion/sodium metal dual mechanism mode for enhanced sodium storage performanceThis section aims at addressing the inherent problems of SIB（slow reaction kinetics and huge electrode strain）,as well as the issues of SMB（the severe dendrite growth and volume expansion）.The novel“sodium-ion/sodium-metal dual mechanism”sodium storage mode is firstly proposed to construct the devices with higher capacity and long-time lifespan.Based on dual mechanism,the optimized three-dimensional bismuth anode receives a higher capacity than traditional anodes with single energy storage mechanism,while achieving dendrite-free Na growth.Thus,a high fixed capacity of 2000 m Ah g^-1 can be achieved for 800 h at 1 A g^-1.This result demonstrates that the innovative dual-mechanism energy storage mode can overcome the limited capacity of SIBs.Meanwihile,it is able to construct the sodium-based device with higher capacity and dendrite-free Na growth.