Construction Of Metal-free Dual-ion Batteries Based On Ionic Liquid Electrolyte And Study Of Anode Materials

The development and utilization of energy sources is an eternal theme for the development of human society.As an energy storage device,batteries have played a pivotal role in social development.It is of great practical significance to develop a battery structure with excellent performance,simple structure,low cost,safety,reliability,and environmental friendliness and easy recycling.As an electrochemical energy storage device,because of its unique working mechanism,the advantages of dual-ion batteries that can meet these requirements have received more and more attention and research.This paper aims to build dual-ion secondary batteries with excellent performance,simple structure,safety,and easy recycling by using pure ionic liquid as the electrolyte and active ion source,and with electrode materials rich in renewable resources and good in environmental compatibility.And its working mechanism is also explored.The specific research contents and conclusions are as follows:?1?A dual graphite battery based on pure 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid electrolyte was constructed.The performance difference between KS6 synthetic graphite and natural graphite in batteries was compared and the results are as follows.The EMImTfO ionic liquid electrolyte has a wide electrochemical window of4.1 V.Under a voltage range of 1.0-3.9 V and a current rate of 1 C,the KS6 synthetic graphite and natural graphite EMImTfO ionic liquid dual graphite batteries exhibit discharge plateau higher than 3.0 V with discharge capacities of 28.5 and 25.8 m Ah g^-1(m_cathode:m_anode=1:1),respectively.Compared with KS6 graphite,EMImTfO dual-ion batteries with natural graphite as electrode material have a better discharge plateau.Because of the higher crystallinity and smaller defect density of natural graphite,the natural graphite EMImTfO ionic liquid dual-ion battery has a smaller charge-discharge voltage hysteresis,higher coulombic efficiency,better cycling performance and less self-discharge.Since theTfO^—anion has a larger third dimension than the EMIm⁺cation?EMIm⁺:5.30?,Tf O:5.69??,graphite on one electrode used in excess?3:1,m/m?has shown that the graphite capacity of EMIm⁺higher than thatTfO^—,which are46.2 and 38.8m Ah g^-1,respectively.Combined with SEM tests,partial peeling of the positive graphite surface occurred after 100 cycles,demonstratingTfO^—has a decisive effect on discharge capacity and cycling perfzormance.Cyclic voltammetry and ex-situ XRD and Raman tests have shown that the processes for the EMIm⁺andTfO^—intercalating/deintercalating from graphite are reversible.?2?To explore electrode materials with a more stable structure and better performance,and inhibit the self-discharge reaction of dual-ion batteries,perylene-3,4,9,10-tetracarboxylic dianhydride?PTCDA?and 1,4,5,8-Naphthalenetetracarboxylic dianhydride?NTCDA?were selected as negative electrode materials.Combined with natural graphite as the positive electrode material,the dual-ion batteries were constructed with EMIm TFSI,PP₁₄TFSI,and Pyr₁₄TFSI ionic liquid electrolytes.Under a voltage range of 1.0-3.5 V and a current rate of 0.1C,Pyr₁₄TFSI-NTCDA dual-ion battery shows the most stable two discharge plateau at 2.5,1.7V and the highest discharge capacity of 114 m Ah g^-1.Cyclic voltammetry tests show that both organic materials can reversibly undergo multi-electron reactions with Pyr⁺₁₄,but the symmetry of the redox peak of NTCDA is better than that of PTCDA.The battery composed of NTCDA and Pyr₁₄TFSI has a weak self-discharge reaction:after 4 hours of standing,the discharge capacity of the battery is 86.1 m Ah g^-1,and the self-discharge rate is only 6.12%h^-1.Ex-situ XRD,FT-IR,and XPS tests show that the crystal structure of NTCDA and graphite changes periodically and reversibly during charging and discharging;the Pyr⁺₁₄ cation and TFSI^—anion synchronously react with NTCDA and graphite during charging and discharging and Pyr⁺₁₄cations combine with C=O on NTCDA to produce a strong chemical interaction,which demonstrates the working mechanism of NTCDA|Pyr₁₄TFSI|NG dual-ion battery.The SEM test results confirmed that the dissolution of NTCDA on the negative electrode during the cycling caused the capacity of battery to decay.Further work to improve the cycling performance of NTCDA|Pyr₁₄TFSI|NG dual-ion battery is still in progress.