LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode material is widely used due to its high capacity and low cost but it shows poor cycle stability. It is well established that B³⁺ plays an active role in the charge–discharge cycle of high-Ni ternary cathodes. However, the role of B³⁺ in the cathode structure is rarely discussed. In this work, a simple and efficient solid-state method was used to prepare B-doped NCM811 samples. The results indicate that after 100 cycles at 1C, B-NCM811 exhibited excellent cycling stability with cycle retention rates of 90.7% and 81.3% over 2.7–4.3 V and 2.7–4.5 V, respectively. CV and EIS results indicate that B-doping effectively reduced charge transfer impedance and polarization, which was confirmed by DOS calculation results. Combined with DFT calculations, it was found that B³⁺ in the transition metal (TM) gap tends to bond with oxygen to form BO₄ tetrahedra, and strong B–O bonds can improve structural stability. Moreover, B-doping increased the length of the Li–O bond, reducing the Li⁺ migration barrier. This study demonstrates that B-doping effectively enhances the structural stability of Ni-rich layered cathodes.