High-rate single-crystalline Li-rich layered oxide with diversified surface-phase cation ordering for Li-ion batteries.

Abstract

Advanced lithium-ion batteries require fast-charging high-energy-density electrodes. Li- and Mn-rich layered positive electrodes can offer higher capacity (>280 mAh g^-1) and higher specific energy (>1000 Wh kg^-1) than Ni-rich chemistries, yet it is challenging to produce volumetric-energy-dense Li-rich single crystals. Another concern is the rate performance. Li-rich layered oxides have long been considered to have poor rate capability, not to mention their single-crystal version. Here we report high-rate single-crystal Li-rich layered oxides with fast rechargeability. 0.2 C-discharge capacity of 248 mAh g^-1at 5 C fast-charging as well as 5 C fast-discharging capacity of 179 mAh g^-1 are demonstrated. We prove that the fast rechargeability can be resolved by a complex cation ordering of coherent layered-, cation mixed-, rock salt-, and spinel-type structure. The highly conductive and electrochemically active surface phases can buffer Li⁺ concentration gradients and enable deeper bulk lithiation. The single-crystal morphology and redesigned surface phase ensure mechanical and structural stability over cycling, improving capacity retention to 94.5% over 150 cycles at 0.5 C-rate. This work uncovers the intrinsic high-rate performance of single-crystal Li-rich layered oxides and calls attention to think about the fast-charging potential of positive electrodes with coarse microstructure.