Robust Free-standing Electrodes for Flexible Lithium-ion Batteries Prepared by a Conventional Electrode Fabrication Process

Highly flexible free-standing electrodes for flexible lithium-ion batteries (LIBs) are prepared by casting slurry on a glass substrate and detaching the film after drying. The slurry is composed of lithium cobalt oxide (LiCoO2) as a cathode material and Super-P as a conductive agent. These are currently used in conventional electrode fabricating. The flexible electrode contains the similar constituents and composition to the electrodes in commercial LIBs, but does not include metal foil as a current collector as that limits the flexibility of the LIB. Polyvinylidene fluoride (PVDF) with hexafluoropropylene (HFP) is used as a binder instead of PVDF alone due to its better mechanical properties (tensile stress, strain, and peel-off strength). In order to compensate for the low electronic conductivity of flexible electrodes without metal foil, a carbon nanotube (CNT) is incorporated into the electrode. The flexible electrodes offer great flexibility with the ability to be bent and folded without deforming. The flexible electrode exhibits high overpotential during charging/discharging process and inferior electrochemical performance (rate capability, energy density and cycling stability) to conventional electrodes with metal foil due to the low electronic conductivity but it delivers reasonable performance in a punch cell with an aluminum-deposited PET substrate as a current collector. Using CNT enhances the electrochemical properties of flexible electrodes, but weakens its mechanical strength at the same time. Therefore, the optimum amount of CNT needs to be determined.