Unlocking the Kinetic Potential of Ultra-Thick Electrodes via Mechanism-Guided Phase-Inversion Optimization

• The fundamental mechanism by which solid additives influence phase inversion has been explored and applied for the first time to optimize phase-inversion electrodes (PIEs). • Predictive numerical simulations guide the determination of the critical threshold for phase-inversion extent with minimized polarization. • Transmission line model (TLM) simulations of impedance successfully decouple ionic and electronic processes in PIEs. • Optimizing the phase-inversion process enables ultra-thick electrodes (1.1 mm, 100 mg cm -2 ) with exceptional areal capacity (16 mAh cm -2 ) and fast-charging capability. Bridging the gap between practical and theoretical energy density requires thick electrodes with high areal mass loading, yet these are inherently limited by sluggish kinetics. The phase-inversion method offers a scalable route to low-tortuosity architectures; however, its optimization has been hindered by limited understanding of how solid additives affect the fundamental NMP-H 2 O exchange that governs pore formation. Here, using LiFePO 4 (LFP) as a model system, we show that regulating phase separation dynamics via solid additives enables optimized electrode-level performance. Contrary to the convention that thick electrodes require high carbon content, phase-inversion electrodes (PIEs) follow a distinct moderate-carbon optimization strategy. A critical threshold at 6 wt% carbon yields a hybrid microstructure that preserves ion-transport channels while establishing electronic percolation. Specifically, at this moderate content, the binder is not excessively consumed by the carbon surface, allowing phase-inversion to proceed effectively to form macro-channels, yet enough carbon is present to bridge the active particles within the polymer matrix. This design avoids structural collapse caused by excessive carbon (disordered pores) and the kinetic isolation of low-carbon formulations (insufficient conductivity). The optimized PIEs (22 mg cm -2 ) deliver 75% of electrode-level capacity at 1 C and enable an ultra-thick electrode (1.1 mm, 100 mg cm -2 ) with an exceptional areal capacity of 16 mAh cm -2 . These findings establish a mechanism-informed design principle for practical thick electrodes and provide a scalable strategy extendable to other chemistries.