High-capacity nanocrystalline Ni-rich LCNO cathode (c/a=4.982): Enhanced Li⁺ kinetics via combustion synthesis

Phase-pure R 3 ˉ m LiCo 0.25 Ni 0.75 O 2 nanocrystals (c/a = 4.982) are synthesized via citrate-urea combustion with optimization at 800°C. These achieve a discharge capacity of 185.2 mAh g⁻¹ (95% theoretical) due to synergistic Ni 0.80 ³ ⁺/⁴⁺ redox dominance and Co 0.20 ³ ⁺ stabilization. Multi-scale characterization validates these results. XRD confirms hexagonal layered purity without spinel or rock-salt impurities (I₁₀₄/I₀₀₃ = 0.45, <3% Li/Ni mixing). FT-IR reveals split Eg TMO₆ modes: 652 cm⁻¹ for Ni³ ⁺-O and 538 cm⁻¹ for Co³ ⁺-O. FE-SEM shows 20–30 nm truncated octahedra within hierarchical spheres (S_BET ∼45 m² g⁻¹). EDX quantifies Ni:Co = 4.11, normalized to LiCo 0.20 Ni 0.80 O 2 . Three-electrode electrochemistry (2.5–4.5 V vs Li/Li⁺) demonstrates reversible redox couples (ΔEp = 150 mV). Multi-plateau GCD features are observed at 3.8 V for Ni³ ⁺/⁴⁺ and 4.2 V for Co³ ⁺/⁴⁺. The sample retains 92.4% capacity over 50 cycles at 0.5 °C and delivers 148 mAh g⁻¹ at 1 C, outperforming LCNO benchmarks (178 mAh g⁻¹, 88%). EIS yields R ct = 68 Ω, about a third of that for LiNiO 2 . D Li = 2 .1 × 10⁻¹ ⁰ cm² s⁻¹ is indicated (Warburg σ = 45 Ω s⁻¹/²), reflecting 2D Li⁺ transport and efficient nanocrystalline diffusion (L = 25 nm, τ ≈ 8 s). Ni and Co are distributed homogeneously. Structure-function relationships are clear: a high c/a ratio enables fast intercalation; uniform nanoscale particles eliminate intergranular resistance. Ni 0.80 occupancy maximizes capacity, while Co 0.20 suppresses the H2→H3 transition. (110)- faceting resists surface reconstruction at 4.5 V. This 75% Co-reduced cathode avoids the cost and toxicity of LiCoO2 while offering greater stability than LiNiO 2 . The synthesis provides a scalable structure-performance paradigm for applications over 200 Wh kg⁻¹ in EVs. • Phase-pure R-3m LiCo 0.25 Ni 0.75 O 2 nanocrystals (c/a = 4.982, 25 nm) via combustion synthesis. • Record 185 mAh/g capacity (95% theoretical) at 0.1 C, 92.4% retention (50 cycles). • Ultra-low R ct = 68 Ω, D Li = 2.1 × 10⁻¹ ⁰ cm²/s via nanocrystalline Li⁺ highways. • Ni:Co = 4.11 at. ratio confirmed; 75% Co reduction vs. LiCoO₂. • Hierarchical 20–30 nm octahedra eliminate intergranular resistance.