Preparation And Electrochemical Performances Of Bacterial Cellulose-based Composite Solid Electrolyte

Lithium-ion batteries have emerged as a viable choice for clean energy due to their high theoretical energy density,lighter weight,smaller size,reduced environmental impact,and good cycling performance.However,the limitations in performance and safety of traditional commercial lithium batteries,such as low energy density and flammable electrolytes,have been gradually recognized.Solid lithium batteries with their high energy density and improved safety have gained increasing attention as a promising development in the field of lithium batteries.As an important component of solid lithium batteries,solid electrolytes have become a research hot-spot due to their balanced performance.Therefore,this study selected bacterial cellulose（BC）as the polymer matrix material and investigated the modification of BC electrolytes using cubic garnet Li₇La₃Zr₂O₁₂（LLZO）,metal-organic framework UIO-66,and I₂ to optimize the performance of bacterial cellulose polymer electrolytes.The main research results of this paper are as follows:（1）The modification of BC electrolytes was studied by incorporating cubic garnet electrolyte LLZO as an active filler.The addition of LLZO can significantly improve the ionic conductivity of the electrolyte,enhance the chemical stability between the electrolyte and lithium metal,and lead to a significant improvement in the performance of the assembled full battery.The room temperature ionic conductivity of the composite electrolyte BC/LLZO（BL）was 2.23×10^-4 S cm^-1,which was 2.12 times higher than that of the BC electrolyte,and the electrochemical window could reach 4.72 V.In addition,the tensile strength of the pure BC electrolyte without LLZO was 5.76 MPa,while the tensile strength of the composite electrolyte BL reached 20.02 MPa.Under the condition of a current density of 0.2 m A cm^-2 at room temperature,the polarization voltage of BL lithium symmetrical cells after 100 hours of cycling was approximately±0.16 V.（2）In-situ growth of UIO-66 on the BL electrolyte membrane was achieved using a hydrothermal solvent method,resulting in a composite electrolyte BC/LLZO/UIO-66（BLU）.The in-situ growth of UIO-66 improved the ionic conductivity of the electrolyte and further enhanced the chemical stability between the electrolyte and lithium metal.The electrochemical performances of the assembled full battery were greatly improved.The cooperative modification mechanism of LLZO and UIO-66 was analyzed in-depth using Raman,infrared,and adsorption energy simulation calculations.The ionic conductivity of prepared BLU electrolyte was 3.76×10^-3 S cm^-1,which was more than 30 times higher than that of the BC electrolyte.The electrochemical window of BLU electrolyte could reach 4.92 V.Under the condition of a current density of 0.2 m A cm^-2 at room temperature,the polarization voltage of Li/BLU/Li battery after 1000 hours of stable cycling was only±0.13 V.However,the polarization voltage of Li/BLU/Li battery after stable cycling for 1000 hours was±0.08 V at a current density of 0.1m A cm^-2 at room temperature.In addition,the average discharge specific capacities of the full BLU battery at 0.1,0.2,0.5,1,and 2 C rates were 165.13,164.05,148.28,119.66,and 78.11 m Ah g^-1,respectively.It showed a significant improvement compared to the full batteries assembled with BC,BL,and BU at 1 C and 2 C rates.After 50 cycles at a rate of 1 C at 28^oC,the bulk impedance and interfacial impedance of the Li/BLU/LFP full battery were smaller than those of the BC full battery,and the interfacial impedance decreased by 63%compared to before cycling.（3）Using LLZO as an active inorganic filler,2 g/L of iodine solution was added to obtain the BC-based composite electrolyte BC/LLZO/I₂（BLI）through stirring,filtration,and freeze-drying.The ionic conductivity of BLI was 5.49×10^-4 S cm^-1,and the electrochemical window was 4.81 V.Under the condition of a current density of 0.1 m A cm^-2 at room temperature,the polarization voltage of Li/BLI/Li battery after 500 hours of stable cycling was±0.06 V.At 28^oC,the average discharge specific capacities of the Li/BLI/LFP battery at 0.1,0.2,0.5,and 1 C rates were 164.10,162.99,147.36,and 125.97 m Ah g^-1,respectively.It showed a significant improvement compared to the full batteries assembled with BC,BL,and BU at 1C rate.After 50 cycles at a rate of 1 C at 28^oC,the interfacial impedance of the full BLI battery was only 48%of that of the full BC battery.The modification mechanism of LLZO and I₂ was analyzed through ultraviolet spectroscopy,Raman spectroscopy,and energy level simulation calculations,suggesting that I₂ effectively inhibits BC crystallization.Additionally,LLZO exhibits adsorption characteristics towards iodine,greatly improving the electrochemical performance of the composite electrolyte BC/LLZO/I₂.