<p>This study successfully prepared high-density LiFePO₄/C composite materials using a ternary co-doping strategy of Nb₂O₅, TiO₂, and V₂O₅, combined with particle size optimization and control techniques. The substitution of Nb⁵⁺ for Li⁺ positions can widen the diffusion channels for Li⁺ and enhance its diffusion kinetics. The replacement of Fe²⁺ by Ti⁴⁺ can stabilize the crystal structure, reduce volume changes during charge-discharge processes, and improve cycling stability. The substitution of Fe²⁺ by V^4⁺ and the introduction of electron defects can increase electronic conductivity. The synergistic co-doping of Nb⁵⁺, Ti⁴⁺, and V^4⁺ increased the electrical conductivity of the LFP material from 2.0 × 10^− 1 to 2.6 × 10^− 1 S cm^− 1 and the Li⁺ diffusion coefficient from 7.65 × 10^− 13 to 2.39 × 10^− 12 cm²s^− 1. Moreover, by optimizing the particle size distribution and adopting a non-uniform particle grading strategy, small particles can efficiently fill the gaps between large particles, reducing porosity and further increasing the compaction density. The final Li₀.₉₉₀Nb₀.₀₁₀Fe₀.₉₉₀Ti₀.₀₀₅V₀.₀₀₅PO₄ material achieved an industry-leading compaction density of 2.72&#xa0;g cm^− 3 under a pressure of 226&#xa0;MPa. Electrochemical tests showed that the discharge capacities at 0.2&#xa0;C and 5&#xa0;C rates were 166.2 mAh g^− 1 and 142.4 mAh g^− 1, respectively, and the capacity retention rate after 1000 cycles at 5&#xa0;C was 91.34%. The assembled 14,500 cylindrical battery exhibited excellent volumetric energy density (0.2&#xa0;C: 1166.27 Wh L^− 1, 1&#xa0;C: 1109.62 Wh L^− 1). This research provides an effective material design strategy for the development of high-energy-density lithium iron phosphate batteries.</p>