Design And Development Of High Performance(quasi-)solid Electrolyte And Regulation Research

Solid-state lithium batteries are considered candidates for the next generation of lithium batteries because of their higher energy density and safer characteristics.Solid-state electrolyte is the key part of solid-state lithium battery,which is used to separate the positive and negative electrodes,and provide Li-ion transport channel to achieve the ion conduction between electrodes.However,at present,the ionic conductivity of solid-state electrolyte at room temperature is much lower than liquid electrolytes.And there exits another problem of large interface impedance between solid-state electrolyte and electrodes.Therefore,regulating the ion transport channels and improving the interface contact are crucial for the development of high-performance（quasi-）solid electrolytes.Based on the organic,inorganic and composite solid-state electrolyte systems,unique fast Li-ion conduction channels are designed to make the electrolyte with high ionic conductivity,high mechanical strength and good interface compatibility,while effectively inhibiting the growth of lithium dendrites.The main research contents and results are as follows:（1）According to the characteristics of the semi-open structure of Li-O₂ batteries,a quasi-solid electrolyte（Si O₂-SO₃Li/PVDF-HFP）with high ionic conductivity and high electrolyte retention rate was prepared by combining modified nano-silica particles Si O₂-SO₃Li with polymer PVDF-HFP.The quasi-solid electrolyte has shear-thinning and shear-thickening non-Newtonian fluid characteristics.Among them,the component interaction between sulphonated silica nanoparticles,liquid electrolyte and polymer network is conducive to obtaining good ionic conductivity(5.4×10^-3 S cm^-1 at room temperature)and high liquid electrolyte retention.In addition,the theoretical mechanical simulation and nano-indentation test show that the shear thinning characteristics of Si O₂-SO₃Li/PVDF-HFP can effectively eliminate the stress caused by the electrode volume change during the battery cycling.At the same time,when the external force is suddenly increased（such as high rate）,Si O₂-SO₃Li/PVDF-HFP will dynamically turn to shear thickening and mechanical harden to inhibit the growth of lithium dendrites and puncture.Applying it to batteries,lithium-symmetric batteries with Si O₂-SO₃Li/PVDF-HFP can run for more than 2000 h at room temperature under 1 m A cm^-2,and Li-O₂ batteries can achieve ultra-long life over 5000 h.（2）A garnet-type LLZO-Te-Al solid-state electrolyte was prepared by double-doping Te and Al.The doped elements were used to broaden the bottleneck of LLZO’s ion transport channel,effectively improving the ion conduction of garnet solid electrolyte.The ionic conductivity of LLZO-Te-Al reaches 1.46×10^-4 S cm^-1 at room temperature,and 1.58×10^-5 S cm^-1 at 0℃.Combined with the LLZO-Te-Al and added little liquid electrolyte,the assembled lithium symmetric battery can maintain continuous and stable cycling at the temperature gradient of 25℃-10℃-0℃-10℃with a current density of 2 m A cm^-2.When the positive electrode NCM111 is matched,it can run more than 580 cycles at 0℃and 0.12 C,the capacity retention rate is 81%,and the coulomb efficiency is 100%.（3）A new type all-solid-state electrolyte base on polyether thermoplastic polyurethane（TPU）with high ionic conductivity was obtained by regulating lithium salt and Li Br.The assembled all-solid lithium symmetric battery could cycle stablely for more than 800 h at room temperature with a current density of 0.1 m A cm^-2.Matching the cathode material lithium iron phosphate（LFP）,the capacity retention rate is 76%after 400 cycles at room temperature and 0.5 C.Matching the positive electrode of NCM811,the capacity still has148.5 m Ah g^-1 after 100 cycles under the same conditions,and the capacity retention rate is94%.In addition,the all-solid-state electrolyte has high flexibility,which can improve the interface contact between the electrolyte and electrodes.The experimental and theoretical simulation results show that the prepared electrolyte can adapt to the volume changes of lithium anode and prevent the penetration of lithium dendrites to a certain extent.