Ex Situ Activation of Li-Excess Layered Cathode Materials for High-Capacity Lithium Ion Batteries

Ex situ activation of Li-excess layered cathode material (Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂) has been carried out via proton exchange in hydrochloric acid (HCl), followed by chemical exfoliation in tetrabutylammonium hydroxide (TBA·OH) solution and post-heat treatment, in which morphologic and structural reconstructions of pristine cathode material simultaneously take place. Exquisite nanoflower-shaped derivative is achieved with significant increased surface area and uniform pore size distribution after protonation and TBA·OH exfoliation. Sintering nanoflower-structured derivative contributes to hierarchical mesoporous structure and cubic spinel phase within final converted cathode material. The chemical activation of Li-excess layered cathode material results in phase transition from original layered to refactored spinel structure. The activated cathode material in spinel phase and hierarchical porous structure shows significantly improved electrochemical performance, which reveals Coulombic efficiency of 99.93% in the initial cycle at 1C (1C=250 mA/g) and retains high specific capacity of 200.8 mAh/g after 100 cycles, in comparison with 59.16% and 58.1 mAh/g of pristine Li-excess layered cathode materials, respectively. Remarkable enhanced rate capability has also been accomplished in activated cathode, delivering initial discharge capacities of 313.6, 267.2, and 126.3 mAh/g at 0.1, 0.5, and 5C, respectively. Such considerably enhanced cycleabilitiy and rate capability can be attributed to ex situ activation of Li₂MnO₃ component, phase transition, and/or morphologic and structural reconstructions of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. This work opens up various routes to achieve excellent electrochemical performance from high-capacity Li-excess layered cathode materials.