Insight into Superior Electrochemical Performance of 4.5 V High-Voltage LiCoO₂ Using a Robust Polyacrylonitrile Binder

The polyvinylidene fluoride (PVdF) binder is the classic binder for cathodes because of its excellent electrochemical stability and superior adhesion property. However, PVdF is very expensive and sensitive to moisture. Therefore, pursuit of a cost-effective binder is highly desirable, especially for high-voltage cathode application. Polyacrylonitrile (PAN) possesses strong polar C≡N groups, endowing it with oxidation resistance and strong binding properties. Herein, the PAN binder was systematically investigated for the electrochemical performance of the 4.5 V high-voltage LiCoO2 (HV-LCO) electrode. The results showed that the HV-LCO-PAN electrode delivered superior rate capability and cycling stability to the corresponding HV-LCO-PVdF. The PAN binder was highly tolerant of moisture and was capable of forming uniform coating on the cathode materials. Moreover, the PAN binder had ultrahigh mechanical modulus (8.01 GPa) and hardness (381.45 MPa) in a liquid electrolyte, thereby improving cycling stability and rate capability. X-ray photoelectron spectroscopy analysis further demonstrated that PAN formed uniform coating on the surface of LiCoO2 and played a role of an artificial cathode–electrolyte interphase layer, suppressing decomposition of the liquid electrolyte under high cutoff voltage.