Book Description
The energy density of lithium ion batteries (LIBs) is limited by the capacities of the electrode materials. Lithium metal is a promising anode material for future LIBs due to its high theoretical specific capacity (3,860 mAh/g) and low redox potential (-3.04 V vs. standard hydrogen electrode). However, lithium plating in liquid electrolyte will form Li dendritic structure and subsequently penetrate the porous polymeric separator, resulting in battery short circuiting. A straightforward method to suppress the growth of lithium dendrites is to replace the liquid phase electrolyte with a solid-state one. Among different solid-state electrolyte candidates, solid polymer electrolyte (SPE) is advantageous due to its flexible nature and low-cost raw material. However, SPE typically exhibits low ionic conductivity compared to its liquid electrolyte counterpart, which thus could result in restricted use in battery applications. In this work, a rational approach to achieve highly ionic conductive and electrochemically stable SPEs will be discussed. A phase-diagram was firstly mapped out to provide guidance in designing a composite electrolyte with high ionic conductivity at room temperature. The thermal and electrochemical stability of SPE were then characterized. A dual-salt base electrolyte with lithium bis(oxalate)borate (LiBOB) and bis(trifluoromethanesulphonyl)imide (LiTFSI) exhibited excellent electrochemical stability from the passivation layer formed between the electrode/electrolyte interface. In addition, SPEs based on crosslinked fluoropolymer and poly(ethylene glycol) diacrylate (PEGDA) were investigated. Those properties of SPE enable the fabrication of solid-state batteries with lithium metal as an anode. Lithium plating/striping experiments and battery tests were conducted, and the results indicated that the dual-salt SPE could be a promising candidate electrolyte for next generation solid-state rechargeable battery. Sodium ion batteries display good performance yet with limited protection for the inevitable sodium dendrite growth if coupled with metallic sodium electrode, which is an adverse phenomenon that would eventually result in the deterioration of the battery. SPEs with superior ionic conductivity and outstanding electrochemical stability are promising for the all solid-state sodium batteries in grid-storage applications. In this study, a transparent free-standing SPE membrane comprising sodium perchlorate (NaClO4), PEGDA and plastic crystal molecules was fabricated. This sodium based SPE exhibits high sodium-ion conductive property (over 0.925 mS/cm at 30 oC) while being electrochemically stable. A rational approach has also been designed and achieved by using the phase diagram. The NaClO4-based SPE can not only exhibit excellent electrochemical stability with metallic sodium electrode, but also provide remarkable current rate and long-term cycling performance for the solid-state sodium metal batteries (SMB).