Modification And Application Of Natural Polysaccharide Alginate To PEO-based Solid Electrolytes

Lithium battery with high energy density has a long life due to lack of memory effect.So it has become a kind of efficient and clean energy,which has received widespread attention.However,the organic electrolyte used in commercial lithium batteries has many safety defects,which seriously hinder the development of lithium batteries.Therefore,solid electrolyte has become the key strategy to solve this problem.Polyethylene oxide(PEO)is one of the earliest and most mature solid electrolyte materials.At present,researchers mainly focus on the enhancement of ionic conductivity and electrochemical window at room temperature for the modification of PEO-based solid electrolyte,but the safety of PEO-based solid electrolyte at high temperature is not well studied.With the improvement of solid electrolyte technology,the focus of research will shift from daily application to scientific exploration,aerospace and other fields.Therefore,it is very necessary to pay attention to the high temperature safety performance of PEO-based solid electrolyte as soon as possible.Alginate has been widely studied in many fields due to its excellent film forming property and stability.And alginate has also been applied in energy storage devices as binder in recent years.At the same time,alginate also has excellent flame retardant properties,which perfectly meet the requirements of improving the safety performance of PEO-based solid electrolyte.Therefore,alginate was applied to modification research of PEO-based solid electrolyte through physical blending,chemical modification and other methods in this paper:(1)Inspired by the three-dimensional support framework,sodium alginate(SA)was fabricated into nanofiber membrane by electrospinning and cross-linked with calcium ions,which was used as the skeleton of PEO-based solid electrolyte to provide flame retardant performance(LOI=28.6)and improve its mechanical strength.The stability of the fiber membrane at high temperature also ensures the structural integrity of the solid electrolyte.At the same time,a small amount of SA was added to the PEO matrix,and the electrochemical stability(>4.6V)and ionic conductivity of PEO were improved through the cross-linking network formed between the two molecular chains.(2)The effects of alginate content and lithium content on the performance of the above composite electrolyte system were investigated in detail.The performance of the composite electrolyte was further improved by changing the types of alginate and oriented design of the nanofiber membrane.(3)The chemical modification of PEO by SA was realized through the grafting polymerization of SA and PEO polymers in the organic phase by esterification reaction.Compared with the crosslinking network formed by physical blending,the formation of chemical bonds has a better effect on the improvement of ionic conductivity.