Flexible nanocellulose enhanced Li+ conducting membrane for solid polymer electrolyte

Owing to its flexible, non-leaking, and nonflammable characteristics, solid polymer electrolytes (SPE) has long been considered as a promising replacement of the liquid electrolyte in lithium ion battery. Recently, one dimensional nanofiber/nanowire has been added into SPE, and the continuous network structure can not only improve its mechanical properties but also enhance the ionic conductivity. Although cellulose nanofibrils (CNFs) have been long sought in polymer reinforcement, its effect in SPE has never been investigated. In this study, we show that CNF can be used in fabrication of polyethylene oxide (PEO) SPE. The ionic conductivity of the CNF reinforced SPE increases due to enlarged surface charge density and can reach 3.1 ​× ​10−5 ​S ​cm−1 (25 ​°C) at surface charge density of 1.7 ​mmol/g. Furthermore, the high surface charge density can lower the activation energy for Li+ conduction by enhancing solvation and shortening ion transfer pathway. In essence, CNF can simultaneously improve the thermal, mechanical, and electrochemical properties of the PEO based SPE. The newly designed SPE maintains high electrochemical stability at high temperature of 60 ​°C after over 280 ​h of Li stripping/plating at current density of 0.2 ​mA ​cm−2, and is promising as replacement of liquid electrolyte in lithium ion batteries.