Preparation And High Voltage Electrochemical Properties Of Composite Solid Electrolytes Based On Sulfone Additives

The traditional"rigid and flexible"organic-inorganic composite solid electrolyte（CSE）has the advantages of good flexibility of organic polymers and high ionic conductivity and high mechanical strength of inorganic ceramic oxides,but it still faces many challenges to realize its industrial application.It mainly includes the high grain boundary impedance between inorganic particles,the phase separation between polymer and polymer,and the high interface impedance caused by the non-close contact between electrolyte and electrode.In this work,polyacrylonitrile（PAN）,a polymer coating with high oxidation resistance,was coated on the surface of inorganic ceramic oxide particles to improve the contact between ceramic particles.Flame retardant and high pressure resistant additives were further introduced to construct solid-liquid composite electrolytes to solve the electrode/electrolyte interface compatibility.For solid-liquid composite electrolyte,the selection of electrolyte is very important,and the good chemical compatibility between electrolyte and solid electrolyte is of great significance to realize the application of solid-liquid composite electrolyte high voltage system.The main contents are as follows:（1）The strategy of"coating first,then mixing"was first proposed in this chapter.PAN@LLZTO nanoparticles were prepared by mechanical ball milling to build an efficient and stable bridging channel.Casting method was used to introduce highly flexible copolymer matrix PVDF-HFP to prepare CSE with high ionic conductivity,high oxidation stability and good lithium ion migration.Under the current density of 0.1m A cm^-2,the Li//CSE//Li symmetrical battery cycled stably at the overpotential of smaller 180m V for more than 1200h,indicating the excellent interfacial compatibility of Li/CSE.The assembled NCM622//CSE//Li battery with high voltage of 2.8V and 4.3V can cycle stably at different rates,and its discharge specific capacity can reach 132.17m Ah g^-1 after 250cycles at 0.2C rate,and the average Coulomb efficiency（CE）is always greater than 99%.（2）In this chapter,the solid-liquid composite electrolyte CLSE was prepared by introducing flame-retardant high-pressure sulfone additive（SL+Li NO₃+Li TFSI）with good chemical compatibility with CSE.CLSE has a wide electrochemical window（4.75V）,high ionic conductivity(7.6x10^-4S cm^-1)and significantly reduced activation energy(Ea=29.159k J mol^-1).The assembled Li//CLSE//Li symmetrical battery can cycle stably for more than 1000h under 0.1m A cm^-2.NCM622/CLSE//Li also has excellent cycle reversibility,no capacity loss after more than 100 stable cycles,and the Coulomb efficiency is close to 100.0%.（3）In this chapter,a series of characterization of the interface properties between CLSE and electrode after cycling were carried out.By comparing the fitting results of the interface impedance of NCM622//CLSE//NCM622 and NCM622//CSE//NCM622 symmetrical cells at different temperatures,it is found that with the introduction of sulfone-based additives,the value of Ea decreases from 29.15k J mol^-1 to 19.80k J mol^-1,and the lower activation energy is more conducive to the rapid migration of Li⁺at the NCM622/CLSE interface.In addition,through a series of morphology characterization such as SEM,AFM,TEM,it is proved that the compactness of CLSE film does not change after cycling;the surface of Li anode is smooth and complete,there is no obvious dendrite formation,and the thickness of SEI protective layer on the surface is 5～6μm;the structure of NCM622 positive particles is intact and there is a uniform CEI film with 12～15nm thickness on the surface,which protects the stability of positive layered structure and restrains the dissolution of transition metal elements.Finally,the SEI and CEI components were analyzed in detail by XPS characterization technology.The results show that sulfone-based additives effectively regulate the interface components,which has a great impact on the electrochemical performance of the battery.