Structural Optimization And Performance Improvement Of Dual Ion Batteries

With the development of portable electronic devices and electric vehicles,as well as the requirement for high integration of renewable energy sources such as solar energy,wind energy,tidal energy in different applications,cost-effective,large-scale intelligent energy storage equipments are highly demanded.Different from storing and releasing energy through metal ions shuttling between the positive and negative electrodes in the charging and discharging process of traditional metal ion batteries,dual ion batteries store and release energy through the insertion/extraction of anions and cations in the electrolyte.Therefore,dual ion batteries have higher working voltage and energy density.The graphite positive materials can significantly reduce the material cost and exhibit good environmental friendliness.In this paper,based on the systematic investigation of related literature,the key factors affecting the comprehensive performance of the battery are carefully understood.The comprehensive electrochemical performance of dual carbon-based potassium dual ion battery is boosted by optimizing the anode and cathode materials,and by matching the electrodes.And through developing aqueous electrolyte,investigation on the safety performance of dual ion batteries is carried out.The main contents of this thesis are as follows:（1）The research background and status of dual ion batteries are introduced.The working mechanism,electrode materials and electrolytes are summarized.The research significance of this thesis is presented.（2）Preparation of electrodes,electrolytes and the assembling methods of dual ion batteries,and material characterizations and electrochemical measurements used in our work are briefly introduced.（3）Dual carbon-based potassium dual ion batteries are assembled using KS6 as the positive electrode material,6250 mesh natural graphite as the negative electrode material,0.8 M KPF₆ solution in ethylene carbonate and diethyl carbonate（The volume ratio:1:1）solvent as electrolyte.The morphology and structure of the positive and negative materials are characterized by SEM and XRD.The medium voltage up to 4.35 V is obtained in a wide voltage window of 2.4–5.4 V and at the current density of 1.0 C(100 mA g^?1).A reversible discharge capacity up to 54.6 mAh g^?1 for the first cycle is delivered,meanwhile retaining 92.5%of the initial capacity after 400 cycles,i.e.,0.019%capacity fading per cycle.The working mechanism is understood by element distribution,XRD and Raman tests at different working states.（4）A hybrid aqueous/non-aqueous electrolyte is prepared by introducing non-flammable solvent water into Dimethyl Carbonate（an organic solvent commonly used in dual ion batteries）.Combustion experiments show that the electrolyte is non-flammable.First-principle calculations based on the density functional theory and Raman measurement show that the electrolyte does not contain free water.A dual ion battery is assembled using the prepared electrolyte.The electrochemical performance shows that the safe hybrid aqueous/non-aqueous dual ion battery with a wide voltage window of 0-3.2 V is obtained.A reversible discharge capacity up to47.6 mAh g^?1 for the first cycle at the current density of 2.0 C(200 mA g^?1)can be delievered,and the capacity of about 29.6 mAh g^?1 is achieved after 300 cycles.It is noteworthy that the coulomb efficiency of the hybrid aqueous/non-aqueous dual ion battery is as high as 93.9%,which is comparable to that of organic electrolytes dual ion batteries.（5）The main research contents and related results are summarized,and the future development of dual ion battery is prospected.