Bulk And Interface Regulation Enabling High-performance Anode Materials For Alkali Metal Ion Batteries

Alkali metal ion batteries(AIBs),including lithium-ion batteries(LIBs),sodium-ion batteries(SIBs),and potassium-ion batteries(PIBs),show high energy and powder density,owing to low standard electrode potential and fast kinetics of the monovalent alkali metal ions.LIBs have many advantages like large energy density,high powder density,desirable stability,and no memory effect,whereas the deficiency and uneven distribution of lithium resources in the earth’s crust limit its further development.In spite of the relatively lower energy density of SIBs and PIBs,their abundant resources provide them a certain market in special application fields like large-scale grids.Meanwhile,the Li,Na and K element are in the same group in periodic table,and therefore,experience from LIBs,including electrode materials,electrolytes and separators,can be used for the exploration of SIBs and PIBs.Energy density is the key index to assess a battery’s performance,which is mainly related to its cathode and anode material.In this thesis,we focus on developing various kinds of anode materials with high energy density and desirable stability for AIBs.Advanced characterization tools and density functional theory(DFT)calculations are also used for elucidating core mechanisms including alkali metal ion storage and property decay.Finally,we evaluate the practical application potential of some special materials according to active material loading,rate and cycling performance,energy density and efficiency.The first part of this thesis is about how to eliminate graphite exfoliation with an artificial solid electrolyte interphase(SEI)for stable LIBs.Although graphite negative material with gentle comprehensive performance has dominated the anode market of commercial LIBs,its relatively low capacity and poor fast-charging property limit further development.In this work,graphite(G)is reported to suffer from low capacity during fast charging,and poor cycling performance since a strange charge failure phenomenon after 200 cycles.By using various characterization techniques like XRD,SEM,TEM and XPS,severe graphite exfoliation and unstable SEI are demonstrated as reasons for the failure of G anode.A newly ultra-thin artificial SEI is proposed,solving these challenges effectively and ensuring extremely stable cycling of G@C anode,with a capacity retention of about 97.5%after 400 cycles at 1 C.Such an artificial SEI modification strategy provides a universal method to design better electrode materials for high-energy LIBs.The second part of this thesis explores advanced red phosphorus/carbon composites for practical application in SIBs.Although SIBs are one of the most promising nextgeneration battery technologies,their relatively low energy density limit further development.This work presents the feasibility of high-capacity P anode using in practical SIBs.Various modification strategies are firstly implemented,including ball milling time,binders,conductive and electrolyte additives,and the corresponding functional mechanisms are also explored.In situ TEM and electrochemical characterization demonstrate that the further hybridization of commercial hard carbon(HC)and prepared phosphorus/carbon(PC)is a desirable method to construct P-based full SIBs.The corresponding energy density is obviously increased compared with HC-based full SIBs.Of note,despite various challenges still faced by P anodes,the exploration in this study is also crucial for enabling the practical application of P anodes beyond laboratory research.The third part of this thesis is about accelerating the transfer and alloying reactions of Sn-based anodes via coordination atom regulation and carbon hybridization for stable LIBs.Although anodes based on Sn alloys like SnO2,SnS,and Sn4P3 show large capacity since their both conversion and alloy reaction,further development is limited by their sluggish conversion reaction,large volume expansion and unstable SEI.Here,we firstly demonstrated the irreversible reaction mechanism of SnO2 and SnS using in situ XRD,and then improved their performance by coordination atom regulation and carbon coating.The optimized SnS/C composite shows superior cyclability for over 500 cycles,contributing to its reinforced conversion and alloy reaction,enhanced bulk structure,higher SEI stability,and accelerated kinetics.This study provides guidance for developing other high-capacity electrode materials for high-energy LIBs.The forth part of this thesis investigates the various electrochemical behaviors of Sn4P3 binary alloy anodes in AIBs.Sn4P3 binary alloy anode has attracted much attention in AIBs,owing to the synergistic effect of P and Sn alloy.However,the alkali metal ion(A+)storage and capacity fading mechanism of Sn4P3 anodes are not well understood.Here,various characterization reveal that the Sn4P3 anode firstly experience segregation of Sn and P,followed by the intercalation of A+in P and then finally in Sn.Meanwhile,differential electrochemical curves indicate that the deep intercalation of A+in P and Sn,contributing to the capacity decay of AIBs.Serious sodium metal dendrite growth and unstable SEI also cause the capacity fading of SIBs and PIBs respectively.The exploration in this work provides theoretical guidance for the development of other alloy-based anode materials in AIBs.The fifth part of this thesis focuses on dual-salt electrolyte additives enabled stable lithium metal anode/lithium-manganese-rich cathode batteries.Although lithium metal anode/lithium-manganese-rich(LMR)cathode batteries have ultra-high energy density,the unstable Li metal and structural deterioration of LMR make the use of these batteries difficult.In this work,we designed a novel electrolyte containing LiBF4 and LiFSI dualsalt additives,which enables the superior cyclability of Li/LMR battery with capacity retentions of about 83.4%,80.4%,and 76.6%after 400 cycles at 0.5 C,1 C,and 2 C,respectively.Various characterization indicate that the dual-salt electrolytes can not only help form a thin,and inorganic species-rich SEI and cathode electrolyte interphase(CEI),but also improve the sustainability of Li metal and LMR cathode.Our electrolyte design strategy provides insights for developing other high-voltage lithium metal batteries.