In a paper published in NANO, researchers from Guizhou Meiling Power Sources Co., Ltd., China have reviewed the recent progress in biopolymer-based electrolyte.
The biopolymer materials with unique characteristics including water solubility, film-forming capability and adhesive property played a key role in the design of zero pollution lithium battery. The biopolymers mentioned in this review were polysaccharide, protein, natural rubber and other polymers.
For polysaccharide, cellulose with good wettability, low cost and good mechanical properties can enhance the mechanical strength of membranes and improve interfacial stability between electrolyte and electrode. However, the porosity control of cellulose-based membranes was still a challenge. Therefore, cellulose derivatives has been studied as electrolyte materials including alkyl cellulose, hydroxyalkyl cellulose, carboxyalkyl cellulose, cellulose esters and bacterial cellulose. In addition, chitin acted as filler of polymeric matrix to increase ionic conductivity.
Anionic structure of pectin resulted in the interaction between lithium ions and polymer matrix, which favored the dissolution of lithium salts in electrolyte. Starch can improve the thermal stability of electrolyte. Chitosan contained -NH2 and -OH groups, which favored the formation of complexes with other components and promoted ionic migration. Tamarind seed polysaccharide was a highly branched polymer, which possessed film-forming nature and film transparency.
For protein, soy protein isolate (SPI) and gelatin were emphasized due to their strong interactions with electrodes. Various different functional groups of SPI facilitated the fast transport of lithium ions and effective immobilization of sulfur species. Gelatin possessed electrochemical stability and it can react with the degradation products of the liquid electrolyte to stabilize the interfaces. Epoxidized natural rubber possessed the glass transition temperature of -20 °C, high flexibility and good elasticity for contacting well with electrodes. Some other biopolymers such as agar, iota-carrageenan and eggshell membranes have also been mentioned for the electrolyte fabrication.
In summary, the starting point of choosing biopolymer as battery material is still limited to the physico-chemical consideration such as their functional groups, chain structures and intermolecular interactions. The real biological effects and ideas are still rejected or ignored during the design of lithium battery.
This work is supported by S&T Planning Project of Guizhou Province (nos. 1411). Corresponding author for this study is Jiayuan Shi ([email protected]). Additional co-authors of the NANO paper is Bin Shi ([email protected]).
For more insight into the research described, readers are invited to access the paper on NANO.
The paper can be found in NANO journal.