Unveiling Coexisting Battery‐Type and Pseudocapacitive Intercalation Mechanisms in Lithium Titanate
Lingping Kong, Paul J. Williams, Fikile R. Brushett, Jennifer L. M. Rupp
Abstract
Abstract Conventional lithium‐ion (Li‐ion) batteries and supercapacitors face inherent trade‐offs between power and energy densities, restricting their adaptability in applications requiring dynamic performance across both regimes. Here, a “zero‐strain” lithium titanate (Li 4 Ti 5 O 12 ) as a new class of battery‐capacitive material exhibiting dual lithiation mechanisms, combining diffusion‐controlled battery‐type redox reactions and surface‐controlled pseudocapacitive intercalation, depending on the operating potential, is revealed. At ≈1.55 V (vs Li/Li + ), lithium titanate undergoes a two‐phase transition reaction between Li 4 Ti 5 O 12 and Li 7 Ti 5 O 12 , involving Li migration between 8a and 16c Wyckoff sites. Upon deeper lithiation to potentials near 0 V, Li ions reoccupy the 8a sites, triggering a reversible pseudocapacitive response with fast kinetics. Leveraging these dual lithiation mechanisms, lithium titanate delivers a high reversible capacity of ≈215 mAh g −1 at 20 mA g −1 , retaining 148 mAh g −1 at 2000 mA g −1 . The high‐rate capability and cycling stability are attributed to a unique structure with minimal lattice strain during Li‐site occupation. This work presents the first clear demonstration of a unique dual‐mode charge storage mechanism in lithium titanate, which can reversibly operate in either battery‐type or pseudocapacitive regimes.