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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, Li3V1.95Ni0.05(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. [ABSTRACT FROM AUTHOR]

Prelithiation is a critical step in dual carbon lithium-ion capacitors (LICs) due to the lack of Li + in the system, which needs to be incorporated externally to avoid electrolyte depletion. Several prelithiation techniques have been developed over the years, and recently, dilithium squarate (Li 2 C 4 O 4 ) has been reported as an air-stable, easy to synthesize, safe, and cost-effective prelithiation reagent for LICs. Li 2 C 4 O 4 has successfully been used in a wide range of chemistries, and its integration into positive electrodes has been scaled up to roll-to-roll processing and demonstrated in multilayer pouch cells. However, its influence in the solid electrolyte interphase (SEI) has not yet been studied. In this work, the SEI formed on the hard carbon (HC) negative electrode when using Li 2 C 4 O 4 as a prelithiation agent has been studied by X-ray photoelectron spectroscopy (XPS). The electrode surface has been analyzed in the lithiated and delithiated states along the first lithiation cycle, as well as at the end of the prelithiation protocol, to gain insight into the SEI formation and evolution during the prelithiation process. In addition, an aging test has been carried out to study the long-term SEI stability. We have observed that the use of Li 2 C 4 O 4 induces a chemical modification in the composition of the SEI with respect to the SEI that forms by using a standard electrochemical prelithiation process, resulting in a less soluble interface. Therefore, the chemical composition of the SEI is stable over cycling. Those findings confer to Li 2 C 4 O 4 the ability to tune the SEI of the devices, enabling its use in LICs and LIBs not only as a prelithiation agent but also as a film-forming additive.