Novel Low-Strain Layered/Rocksalt Intergrown Cathode for High-Energy Li-Ion Batteries

Both layered- and rocksalt-type Li-rich cathode materials are drawing great attention due to their enormous capacity, while the individual phases have their own drawbacks, such as great volume change for the layered phase and low electronic and ionic conductivities for the rocksalt phase. Previously, we have reported the layered/rocksalt intergrown cathodes with nearly zero-strain operation, while the use of precious elements hinders their industrial applications. Herein, low-cost 3d Mn⁴⁺ ions are utilized to partially replace the expensive Ru⁵⁺ ions, to develop novel ternary Li-rich cathode material Li_1+x[RuMnNi]_1-O₂. The as-designed Li_1.15Ru_0.25Mn_0.2Ni_0.4O₂ is revealed to have a layered/rock salt intergrown structure by neutron diffraction and transmission electron microscopy. The as-designed cathode exhibits ultrahigh lithium-ion reversibility, with 0.86 (231.1 mAh g^-1) out of a total Li⁺ inventory of 1.15 (309.1 mAh g^-1). The X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectra further demonstrate that the high Li⁺ storage of the intergrown cathode is enabled by leveraging cationic and anionic redox activities in charge compensation. Surprisingly, in situ X-ray diffraction shows that the intergrown cathode undergoes extremely low-strain structural evolution during the charge-discharge process. Finally, the Mn content in the intergrown cathodes is found to be tunable, providing new insights into the design of advanced cathode materials for high-energy Li-ion batteries.