Transient Rechargeable Battery with a High Lithium Transport Number Cellulosic Separator

Abstract Transient batteries play a pivotal role in the development of fully autonomous transient devices, which are designed to degrade after a period of stable operation. Here, a new transient separator‐electrolyte pair is introduced for lithium ion batteries. Cellulose nanocrystals (CNCs) are selectively located onto the nanopores of polyvinyl alcohol membranes, providing mobile ions to interact with the liquid electrolyte. After lithiation of CNCs, membranes with electrolyte uptake of 510 wt%, ionic conductivities of 3.077 mS·cm –1 , electrochemical stability of 5.5 V versus Li/Li + , and high Li + transport numbers are achieved. Using an organic electrolyte, the separators enable stable Li metal deposition with no dendrite growth, delivering 94 mAh·g –1 in Li/LiFePO 4 cells at 100 mA·g –1 after 200 cycles. To make the separator‐electrolyte pair transient and non‐toxic, the organic electrolyte is replaced by a biocompatible ionic liquid. As a proof of concept, a fully transient Li/V 2 O 5 cell is assembled, delivering 55 mAh·g –1 after 200 cycles at 100 mA·g –1 . Thanks to the reversible Li plating/stripping, dendrite growth suppression, capacity retention, and degradability, these materials hold a bright future in the uptake of circular economy concepts applied to the energy storage field.