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[Li0.2Mn0.54Ni0.13Co0.13]O-2 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.