An Improved Thermochemical Energy Storage Material Using Nanocellulose to Stabilize Calcium Chloride Salt

One promising thermochemical reaction for energy storage is the hydration of hygroscopic salts. However, pure salts have poor cycle stability. The present work investigates a new composite material by impregnating a framework of crystalline nanocellulose (CNC) with calcium chloride (CaCl₂). A key aspect of this material is the potential for a nanoscale, stabilizing framework provided by the CNC. Various weight ratios of CNC:CaCl₂ were synthesized. The attachment of the salt to the CNC was determined by TEM and FTIR analyses. The weight loss and enthalpy of dehydration were measured after hydration at prescribed relative humidity and a fixed hydration time. The stability was determined by conducting multiple cycles. The results show that CNC can be successfully impregnated with salt. The nanocellulose binds to submicron salt particles and provides a stabilizing, nanoscale architecture. The composite material shows improved energy storage characteristics and stability. For the given hydration conditions, the CNC improves the hydration rates and allows more water to be absorbed within the hydration timeframe. This improved reaction rate can improve the enthalpy of dehydration for the fixed hydration time. Insufficient CNC (i.e., 1:10) allowed the salt particles to more easily deliquesce. With sufficient CNC framework, the CNC–salt material demonstrated improved stability by retaining structural integrity and specific enthalpy over the course of multiple cycles while pure CaCl₂ deliquesced.