Nickel-rich layered oxides (LiNi_xCo_yMn_1-x-yO₂, x ≥ 0.8, NCM) are the most promising cathode material for next-generation high-energy batteries owing to their low production cost, high specific capacity and high operating voltage. However, the practical deployment of high-voltage NCM cathodes is still plagued by mechanical failure of NCM secondary particles due to the internal strain accumulation and particle crack during (de)lithiation. Herein, we report a convenient coprecipitation strategy to introduce gradient porous structure into the polycrystalline NCM secondary particles. Through multistage micro- and nanostructural tailoring from hydroxide precursor in coprecipitation process to the lithiated oxide during the lithiation stage, which refers to optimal engineering of the precursor micro- and nano-structure by introducing extra organic polymer (polystyrene-acrylonitrile copolymer) as heterogeneous nucleation seeds and alkyl diphenyl ether disulfonate disodium as dispersants, we optimize the primary particle morphology containing nano-voids and secondary particle containing gradient porous structure of the cathode. Through high-resolution aberration-corrected scanning transmission electron microscopy and scanning electron microscopy, the detailed gradient porous structure of the as-obtained nickel-rich layered oxide cathode is clarified, and the formation of gradient porous structure is attributed to the rapid diffusion of the carbonized organic matter by the calcination treatment under oxygen atmosphere during the lithiation stage. This gradient-porous-structured nickel-rich layered oxide cathode can mitigate the anisotropic volume change of the primary particles, suppress intergranular/intragranular cracks and limit impedance growth effectively. The as-obtained cathode exhibits high specific capacity of 180.1 mAh g^-1 (1 C, 25 ^oC) and capacity retention of 87.6 % after 300 cycles even charged to a high cut-off voltage of 4.5 V. Moreover, this cathode presents enhanced high reversible capacity and cycling stability in a wide temperature range of -20~60 ^oC. This study suggests the gradient porous structure design can homogenize stress distribution and mitigate volumetric change, representing a promising pathway to tackle the structural instability upon high-voltage cycling.

Key words: Nickel-rich layered oxides, high voltage, mechanical failure, gradient porous structure, wide temperature range