Thermogravimetric study of water-based LiFePO4 composite electrode powders

► In situ humidity-TG device enables water absorption/desorption studies of LiFePO4. ► Pure LiFePO4 is highly water-sensitive. ► Binders used in composite electrode manufacturing protect LiFePO4 against water absorption. ► Even water-based binders such as acryle and polyvinyl alcohol provide substantial protection. Here we demonstrate the powerfulness of in situ thermogravimetric measurements under varied humidity conditions for understanding the water absorption/desorption characteristics of the hygroscopic Li-ion battery positive electrode material, LiFePO4. Both plain LiFePO4 powder and different composite electrodes made with the water-based binders, acryle, polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) are investigated. Out of these binder materials, acryle and PVA are found to protect the electrode to some extent against water absorption. On the contrary, the CMC binder rather enhances the water absorption. Investigation of thermal stabilities of the composite electrodes reveals that they all start to decompose between 200 and 300°C when heated in air.