Design And Application Of Bacterial Cellulose-Based Composite Materials In Supercapacitor Electrodes And Lithium Metal Battery Electrolytes

Cellulose,regarded as one of the most abundant renewable resources on the earth,can be fabricated into nanocellulose via chemical modification or mechanical pulverization.Nanocellulose possess numerous strengths such as the excellent mechanical properties,high visible-light transparency,good biocompatibility,and high specific surface area,which has been widely applied to various practical areas.Among these nanocellulose,bacterial cellulose(BC)which is synthesis by various bacteria such as acetobacter into the ultrafine nanofiber(30-80 nm),presents the high crystalline degree(?95%),high polymerization degree(DP:2000-8000),ultrafine nanofibrous structure,high water uptake,and high elastic modulus and tensile strength.Due to these unique properties,bacterial cellulose exhibits the huge potential and application value on flexible and nano energy engineering area.However,trapped by limited nanofibrous structure and chemical composition,the performances of bacterial cellulose fail to satisfy the demand of nano energy engineering area,especially that of high-performance electrode and electrolyte for multifunctional and practical applications.Herein,benefiting the unique nanofibrous structure and natural polysaccharide constituent,BC as the precursor is designed and fabricated into various composite materials,including BC derived activated carbon materials,three-dimensional porous carbon aerogel,composite materials by BC and ceramic.This work widens the application of BC in the field of nano-energy engineering and simultaneously provides a theoretical fundament for the further development and comprehensive utilization of biomass resources.(1)Design and fabrication of nitrogen/sulfur co-doped bacterial cellulose derived porous carbon for cellulose-based supercapacitorsAn ultra-microporous carbon(u-MPC)with ultrahigh integrated capacitance fabricated via one-step carbonization/activation of dense bacterial cellulose(BC)precursor followed by nitrogen/sulfur dual doping is reported.The microporous carbon possesses highly concentrated micropores(?2 nm)and a considerable amount of sub-micropores(<1 nm).The unique porous structure provides high specific surface area(1554 m2/g)and packing density(1.18 g/cm3).The synergistic effects from the particular porous structure and optimal doping effectively enhance ion storage and ion/electron transport.As a result,the remarkable specific capacitances,including ultrahigh gravimetric and volumetric capacitances(430 F/g and 507 F/cm3 at 0.5 A/g),and excellent cycling and rate stability even at a high current density of 10 A/g(327 F/g and 385 F/cm3)are realized.Via compositing the porous carbon and BC skeleton,a robust all-solid-state cellulose supercapacitor presents super high areal energy density(?0.77 mW h/cm2),volumetric energy density(?17.8 W/L)and excellent cyclic stability.(2)Design and fabrication of super-elastic hard carbon aerogels for flexible supercapacitorsAn ultralight and super-elastic hard carbon aerogel with in-situ ultrafine carbon crystals is reported.Based on a novel precursor prepared from self-assembling bacterial cellulose and thiourea molecules,the resulting aerogel possesses a unique cellular structure and simultaneously exhibits remarkable compressive strength(0.32 MPa)and electrical consuctivity(23 S/m)with ultra-low density(1.67 mg/cm3)in addition to excellent compressive cyclability.Armed with the compressed aerogel electrodes,the supercapacitor exhibits excellent electrochemical performance in areal capacitance(0.97 F/cm2)and rate capability.Even at a current density of 20 A/g,it still exhibits a high capacity retention rate(86%)and excellent long-cycle stability.Furthermore,the supercapacitor displays distinguished pressure-response capacitive signal and excellent signal cyclicality.This study provides a unique carbon aerogel for advanced wearable monitoring and energy storage systems.(3)Design and fabrication of bacterial cellulose/Li0.33La0.557TiO3 nanowires(Li0.33La0.557TiO3,LLTO NWs)composite gel electrolyte for lithium metal batteriesAn ultra-robust composite gel electrolyte(CGE)that can effectively stabilize ion deposition for LMBs is designed via fabricating a specially structured aerogel as the matrix.The gel electrolyte matrix with a 3D interconnected highly porous structures and good affinity with liquid electrolytes is fabricated via compositing bacterial cellulose(BC)and Li0.33La0.557TiO3 nanowires(LLTO NWs)into an aerogel.The composite aerogel matrix demonstrates excellent wettability and liquid electrolyte uptake(586±5%),and the resulting CGE presents exceptional Young's modulus of 1.15 GPa and extremely high lithium-ion transference number of 0.88.More significantly,the synergistic effect from robust BC skeleton and LLTO NWs enabling stable ion deposition effectively suppresses the growth of lithium dendrites.Armed with the CGE,ultra-stable symmetric Li/Li cells demonstrate a long cycle life of 1200 hours and highly stable performance even at a high current density of 5 mA/cm2.Furthermore,galf cells with the CGE exhibit remarkable enhancement in capacity,cycling stability,and rate performance.(4)Design and fabrication of bacterial cellulose/Li6.4La3Zr1.4Ta0.6O12(LLZTO)ceramic separator for high-voltage lithium metal batteriesA composite ceramic separator is fabricated via compositing LLZTO nanoparticles into the three-dimensional network structure of bacterial cellulose.The composite ceramic separator possesses the unique porous structure and good affinity with liquid electrolytes.Simultaneously,the separator presents both excellent Young's modulus(0.7 GPa)and high-temperature resistance(up to 1000?).More importantly,benefiting from the unique Li-ion channels,the resulting ceramic separator exhibits high ionic conductivity(1.5 × 10-3 S/m)and Li-ion transfer number(-0.92).The symmetrical Li/Li battery with a ceramic separator also exhibit the remarkable cyclic stability lasting for 870 hours.Even at a high current density of 5 mA/cm2,symmetrical Li/Li batteries still maintain good cyclic stability.In addition,high-voltage lithium metal batteries with ceramic separators displays the significant enhancements in capacity,cycle stability,and rate performance.