The Relationship Between Preparation,Structure And Performance Of Cellulose-Based Membranes For Liquid And Semi-Solid Lithium Batteries

Lithium batteries(LBs)with the lithium metal anode have attracted considerable concentration due to its superior specific energy density of 3860 Ah/kg.While the application of lithium anodes brings more challenges to the design of other components inside LIBs.Especially for the liquid lithium batteries(LLBs)with separators wetted by liquid electrolytes(LEs),the uneven deposition of Li~+on the anode surface can lead to severer.interfacial problems.In order to meet the requirements of the interface stability and safety,herein,two methods were proposed.On the one hand,the interface deposition behavior of LLBs is regulated by designing separators with the optimized micro structures.On the other hand,introducing gel polymer electrolyte membranes(GPEMs)in semi-solid lithium batteries(SLBs)to substitute for LLBs..Cellulose,with degradable and renewable properties,is one of the most abundant natural polymer materials.Meanwhile,the cellulose chains also exhibit the good affinity with organic liquid electrolytes and good thermal stability.Given the aforementioned merits,the cellulose was used as the raw material to prepare porous separators and GPEMs.Significantly,the micro structures of the cellulose membranes were controlled via different manufacturing methods to improve the performances,especially for the interface compatibility.The main content of this dissertation can be divided into the following parts:(1)The structure design and performance optimization of the different sized cellulose-based separators for LLIBsThe Micro-cellulose(MCC)and nano-cellulose(NCC)were mixed in different weight ratios to prepare cellulose separators with tunable pore structures.Results show that the higher content of the NCC can lead to the denser pore structure of the separator,thereby leading to the higher ionic conductivity and lower tensile strength.As a result,the balance of the mechanical and electrochemical performance can be achieved by adjusting the NCC content.(2)The nanocellulose separator with the multi-scale pore structures designed for LLIBsThe cellulose separator based on the mixed cellulose exhibited unfavorable interfacial compatibility due to the uneven Li~+flux on the anode surface,which was resulted from the uneven distribution of pore structures.To address the problem,the separators based on the nanocellulose was prepared.The solvent displacement method and templating method were combined to fabricate the cellulose separators with the multi-scale pore structures(MEPS).Thanks to the high porosity and low tortuosity of the porous networks,the electrochemical performances of MEPS were greatly improved.(3)The relationship between the interface performance and microstructure of the cellulose separator of LLBsThe porous features of the cellulose separators were controlled according to the the“size effect”of cellulose fibrils and the application of the templating method.The regulating effect of the pore size on the propagation of the anode surface was explained by experimental and numerical methods.Besides,the mechanical performance and polarization profiles of the separators with various porosities were compared.It was concluded that the separator with well-designed pore size and porosity can withstand the puncturing of lithium dendrites,correspondingly improving the safety of LLIBs.(4)The preparation of the cellulose-based GPEM for SLBsIn LLBs,Li~+can only transfer through the electrolyte-anode interface via the pore volume of the separator,thus leading to uneven Li deposition.Besides,the flammable organic liquid electrolyte still faces the risk of leakage,which may result in the fire hazards.The GPEM designed for SLBs has been proposed to overcome the safety problems.At first,a self-standing cellulose host was prepared.Based on the experimental results,a 3D amorphous cell of the GPEM was established at the atom level to further study the dependence of the Li~+conductivity on the swelling ratio.(5)The structure and performance optimization of the cellulose-based GPEMs for SLBsFirstly,the reasons for the poor interfacial compatibility of the GPEMs based on the ether cellulose and cellulose were explained based on the swelling test and XRD pattern,respectively.To handle the problems,two kinds of GPEMs,namely the nanocellulose reinforced composite GPEMs and double network-based GPEMs,were proposed.The introduction of nanocellulose can improve the structural stability of the composite host in liquid electrolytes,thus rendering the obvious enhancement of the interfacial compatibility.As for the gel membranes based on the double networks,the interfacial resistance was greatly reduced thanks to the synergistic effect of the two polymer networks.