Thermal stability studies of binder materials in anodes for lithium-ion batteries

The negative electrode (NE) for lithium-ion batteries is conventionally made by casting a mixture of various carbon materials with polyvinylidene difluoride (PVDF) onto copper foil. Differential scanning calorimetry and accelerating rate calorimetry were used to evaluate the thermal stability of several lithiated NE materials: synthetic graphite (SFG-44), mesocarbon microbeads (MCMB), lignin-based hard carbon (HC), and mixtures of these materials. The exothermic heat generation of lithiated NEs, in the absence of the electrolyte, is attributed to the reaction of PVDF with lithiated carbon (LixC6). For all samples here, the total exothermic heat generation increases with an increase in lithiation content. The onset temperature for the thermal reaction of PVDF: with SFG-44 or MCMB does not depend on the lithiation content. However. this onset temperature decreases as lithiation increases in HC electrodes. These differences are attributed to structural differences between highly graphitic SFG-44 and MCMB compared with the far less graphitic HC. Total heat generation increases with PVDF binder content. An alternative resin-based binder. phenol-formaldehyde phenolic-resin (C7H6O)(n), is proposed. Full or partial substitution of this material for PVDF lowers the exothermic heat of reaction of the binder agent with lithiated NE materials. (C) 2000 The Electrochemical Society. S0013-4651(00)02-059-0. All rights reserved.