Crystallographic engineering enables fast low‑temperature ion transport of TiNb2O7 for cold‑region lithium‑ion batteries

As fast-charging lithium-ion batteries race toward sub-zero markets, the anode bottleneck—graphite plating risk and Li₄Ti₅O₁₂ capacity ceiling—intensifies. Now, researchers from Harbin Institute of Technology, led by Prof. Yan Zhang and Prof. Shuaifeng Lou, unveil an Sb/Nb co-doped TiNb₂O₇ (TNO) anode that unlocks 140 mAh g^-1 at 20 C and 500 stable cycles at −30 °C. Published in Nano-Micro Letters, the work delivers a practical pouch cell delivering 1.14 Ah at 17 C with 93.8 % retention after 700 cycles.

Why Crystallographic Engineering Matters

• Band-Gap Narrowing: Sb⁵⁺ substitution lowers the gap from 1.83 → 1.64 eV, doubling intrinsic electronic conductivity.
• Li⁺ Highway Expansion: Nb⁵⁺ enlarges lattice parameters a & c, cutting diffusion barrier from 0.96 → 0.74 eV along the b-axis.
• Low-T Robustness: Stronger Sb–O bonds (6.51 vs 6.13 eV ICOHP) suppress lattice distortion, holding volume swing to 9 % versus 9.5 % in pristine TNO.

Innovative Design & Features

• Single-Step Solid-State Route: Commercial Sb₂O₃ + Nb₂O₅ co-dope at 1100 °C yields 500 nm–2 µm rod crystals without secondary phases.
• Multi-Scale Verification: In-situ XRD tracks solid-solution → two-phase → solid-solution pathway; synchrotron 3D nano-CT shows crack-free grains after 500 cycles at −30 °C.
• Pseudocapacitive Boost: 92 % capacitive contribution at 1 mV s^-1 enables 102 mAh g^-1 at −30 °C with 99.96 % CE.

Applications & Future Outlook

• Pouch-Cell Validation: TNO-Sb/Nb || NCM (N/P 1.05) delivers 94 Wh kg^-1, 243 Wh L^-1 and 0.0089 % fade per cycle at 3 C.
• Extreme Climate Suitability: Stable from −40 °C (101 mAh g^-1, 0.2 C) to high-rate 20 C, outperforming 14 reported TNO variants.

Scalable Pathway: Earth-abundant dopants and ambient-air synthesis position the material for gigafactory adoption in cold-region EVs and aviation.