On the Challenges to Develop Hybrid Faradaic-Capacitive Electrodes Incorporating a Sacrificial Salt for Lithium-ion Capacitors: The Case of Li3V1.95Ni0.05(PO4)3-AC-Li2C4O4

Abstract

The low capacity of activated carbon (AC) electrodes remains as one of the major limiting factors for the development of high energy density lithium-ion capacitors (LICs). Hybridization of capacitive AC electrodes by incorporating faradaic materials into the electrode formulation could be performed to enhance the capacity of the overall device. However, this strategy requires an accurate electrode design to maximize the performance. In this work, Li₃V_1.95Ni_0.05(PO₄)₃ (LVNP) was selected as faradaic material due to its compatibility with AC, showing high capacity, fast ionic diffusion, and relatively high conductivity. Various formulations and mass loadings have been studied to analyze the impact of incorporating LVNP into the positive electrode on the performance of the hybrid electrode. Moreover, for practical LIC applications, a sacrificial salt -dilithium squarate, Li₂C₄O₄- was included in the hybrid electrode as a pre-lithiation additive, developing a ternary electrode. The sacrificial salt oxidized releasing lithium ions, while the electrochemical performance of the hybrid positive electrode remained almost unaltered. Finally, a cycle life test combined with a post-mortem analysis allows understanding the failure mechanisms of the electrode, suggesting the need of further improvements of the electrolyte and electrode-electrolyte interface to develop long lifetime hybrid faradaic-capacitive electrodes based on LVNP-AC active materials.