Dual-Structural-Unit-Designed Bismuth Titanium Oxides: -70 to 80°C Ultra-Wide Temperature Adaptability and 24 000-Cycle Stability for High-Rate Sodium-Ion Storage.

Abstract

Sodium-ion batteries are naturally suitable for large-scale energy storage due to the low cost, yet the high-performance anode material remains a key challenge. Alloy-type bismuth (Bi)-based anodes have high theoretical capacity and an appropriate operating voltage plateau, but the main obstacles are cycle life, rate, and wide operating temperature. This work proposes an innovative design of Bi-based anode materials, where Bi serves as the sodium storage unit and is integrated with a robust Ti-O framework of excellent Na⁺ diffusion ability. Different compounds and synthesis/modified methods are systematically investigated to optimize crystal structure, size, morphology, and conductivity. The optimal Bi₄Ti₃O₁₂ _-x delivers a reversible capacity of 330 mAh g^-1 at 0.5 C, 132 mAh g^-1 at 150 C, and 70 mAh g^-1 even at 250 C. Besides, it can operate under an ultra-wide temperature range from -70°C to 80°C. A reversible charge/discharge capacity of 151 mAh g^-1 at -55°C is achieved. The capacity retention is 97% (25°C, 20 C) and 61% (-40°C, 5 C) over 24 000 cycles. The proposed design of incorporating alloy materials as sodium storage units into the stable host framework unit is expected to complement the effective strategy of practical low-temperature fast-charging electrodes.