An ion-exchange promoted phase transition in a li-excess layered cathode material for high-performance lithium ion batteries

A new approach to intentionally induce phase transition of Li-excess layered cathode materials for high-performance lithium ion batteries is reported. In high contrast to the limited layered-to-spinel phase transformation that occurred during in situ electrochemical cycles, a Li-excess layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ is completely converted to a Li₄Mn₅O₁₂-type spinel product via ex situ ion-exchanges and a post-annealing process. Such a layered-to-spinel phase conversion is examined using in situ X-ray diffraction and in situ high-resolution transmission electron microscopy. It is found that generation of sufficient lithium ion vacancies within the Li-excess layered oxide plays a critical role for realizing a complete phase transition. The newly formed spinel material exhibits initial discharge capacities of 313.6, 267.2, 204.0, and 126.3 mAh g^-1 when cycled at 0.1, 0.5, 1, and 5 C (1 C = 250 mA g^-1), respectively, and can retain a specific capacity of 197.5 mAh g^-1 at 1 C after 100 electrochemical cycles, demonstrating remarkably improved rate capability and cycling stability in comparison with the original Li-excess layered cathode materials. This work sheds light on fundamental understanding of phase transitions within Li-excess layered oxides. It also provides a novel route for tailoring electrochemical performance of Li-excess layered cathode materials for high-capacity lithium ion batteries. A Li-excess layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ is completely converted to a Li₄Mn₅O₁₂-type spinel product via ex situ ion exchanges and a post-annealing process. This sheds light on the fundamental understanding of phase transitions within Li-excess layered oxides and provides a novel route for tailoring electrochemical performance of Li-excess layered cathode materials for high-capacity lithium ion batteries.