Probing the Effect of Electrode Thermodynamics on Reaction Heterogeneity in Thick Battery Electrodes

(NMC) thick electrodes with matched porosity and tortuosity are compared. LFP electrodes develop pronounced depth-oriented state-of-charge (SOC) gradients that worsen with increasing discharge rates, whereas NMC maintains much more uniform SOC distributions under such conditions. This difference originates from their distinct SOC dependence of equilibrium potentials and is quantifiable through a dimensionless "reaction uniformity" number. Intriguingly, LFP thick electrodes also exhibit lateral SOC variations that strengthen during slow discharge. The enhanced reaction uniformity in NMC correlates with better active material utilization and slower capacity fade than LFP, highlighting electrode thermodynamics as a key design consideration for thick electrodes.