The spinel Mn-based cathodes with 3D Li⁺ diffusion channels, high voltage, and low-cost show promise for developing high-power lithium-ion batteries (LIBs). But the disproportionation and Jahn–Teller distortion lead to structural degeneration and capacity decay, especially at high working temperatures. Herein, considering the merits of single crystals and orientation of exposed crystal planes, single-crystal truncated octahedral LiMn₂O₄ (TO-LMO) with exposed {111}, {100} and {110} facets is rationally designed, in which the mainly exposed {111} facets are truncated by a small portion of {100} and {110} facets. The Li-deficient intermediate phase is innovatively proposed to prepare the single-crystal TO-LMO. The synergistic effects of single crystals and the orientation of exposed crystal planes significantly reduce the disproportionation of Mn³⁺ ions and thereby improve their structural stability. Consequently, the cycling stability of the single-crystal TO-LMO is remarkably enhanced, obtaining outstanding capacity retention of 84.3% after 2000 cycles, much better than that of 61.2% for octahedral LiMn₂O₄. The feasibility of preparing single-crystal truncated octahedral LiNi_0.5Mn_1.5O₄ with exposed {111}, {100}, and {110} facets via the Li-deficient intermediate phase is further demonstrated. These findings offer new insight into regulating the orientation of exposed crystal planes and improving the reversibility of Mn-based redox couples in LIBs.