Oxidation-reconstructed Li$^+$ transport enables high-tap-density single-crystal regeneration of spent LiNi$_{0.5}$Co$_{0.2}$Mn$_{0.3}$O$_2$ positive electrodes

Direct regeneration offers a shortcut to close the material supply loop of lithium-ion batteries and is a promising recycling strategy. However, in spent LiNi$_{0.5}$Co$_{0.2}$Mn$_{0.3}$O$_2$ positive electrode, severe bulk cation disorder and surface rock salt phase hinder Li$^+$ reinsertion. Moreover, the coexistence of single and poly-crystal particles in commercial batteries further complicates uniform re-lithiation and morphological regeneration. Herein, we propose an oxidation strategy to simultaneously regulate the structural reconstruction and morphological evolution of spent material. During oxidation, surface NiO transforms into NiOOH, while targeted oxidation of the anti-site Ni$^{2+}$ to Ni$^{3+}$ in the bulk reduces Li$^+$/Ni$^{2+}$ mixing. This reconstructs Li$^+$ diffusion channels from surface to bulk, facilitating re-lithiation. Meanwhile, structural changes induce lattice expansion in secondary particles, causing their decomposition into primary particles and forming uniform precursor particles. These particles, with continuous Li$^+$ transport channels and NiOOH surface, agglomerate into large single-crystal during calcination. The regenerated LiNi$_{0.5}$Co$_{0.2}$Mn$_{0.3}$O$_2$ achieves a high tap density of 2.57 g/cm$^3$ and retains 80.2% capacity after 600 cycles. This work presents a concept for the direct regeneration of degradable positive materials.