Thick electrodes for high-energy rechargeable lithium batteries: degradation mechanisms, architectural strategies, and capacity-utilization metrics

Thick electrodes can increase the cell-level energy density of rechargeable lithium (Li) batteries, including liquid-electrolyte Li-ion batteries (LIBs) and all-solid-state Li batteries, by increasing active material loading and reducing the relative fraction of inactive components. However, increased electrode thickness does not guarantee a proportional increase in achievable areal capacity because ion/electron transport, electrolyte accessibility, reaction distribution, and interfacial stability become increasingly limiting under high-loading conditions. This review summarizes the degradation mechanisms that govern thick-electrode performance, focusing on tortuosity-driven ionic transport and electrolyte infiltration limitations, through-thickness concentration polarization, reaction heterogeneity, and resistance buildup. We then discuss how these limitations manifest as electrode-level degradation, including cathode-side active-material underutilization, interfacial byproduct accumulation, particle/contact deterioration, anode-side Li trapping, localized Li plating, and excessive solid electrolyte interphase growth. Recent mitigation strategies are reviewed in terms of low-tortuosity architectures, multilayer and gradient electrodes, conductive network engineering, and model- and diagnostics-guided design. Finally, we argue that designed areal capacity alone is insufficient for evaluating practical thick electrodes. Achievable areal capacity, operating current density, and capacity utilization should be reported together to distinguish nominally high-loading electrodes from electrodes that deliver accessible capacity under relevant operating conditions. This review provides mechanistic and design perspectives for translating high active material loading into practical areal capacity in high-energy rechargeable Li batteries.