Extending the Cycling Potential Window of Li ₄ Ti ₅ O ₁₂ for High Capacity and Silicon Anode Stabilization in Lithium-Ion Batteries

Li 4 Ti 5 O 12 (LTO) is a well-known anode material for long-life and high-rate lithium-ion batteries, typically cycled between 1.0–2.0 V vs. Li/Li + , corresponding to the Li 4 Ti 5 O 12 –Li 7 Ti 5 O 12 two-phase reaction with 175 mAh g −1 capacity. Here, we show that LTO can be reversibly lithiated down to 0.005 V in Li/LTO half-cells, delivering ∼220 mAh g −1 at 0.1 C. Paired with LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LTO full cells exhibit remarkable tolerance to negative-to-positive (N/P) capacity ratios below unity, with an N/P = 0.61 cell achieving an initial capacity of 330 mAh g −1 and stable performance over extended cycling. This behavior is attributed to a spontaneous galvanic reaction between delithiated LTO and plated Li (Li 4 Ti 5 O 12 + Li → Li 7 Ti 5 O 12 ), which converts otherwise inactive Li into reversible capacity. In Si–LTO/NCM811 hybrid cells, LTO stabilizes the Si anode via a similar internal galvanic reaction with isolated Li–Si alloys (δLi 4 Ti 5 O 12 + Li x Si → δLi 7 Ti 5 O 12 + Li x–3δ Si), significantly improving capacity retention and coulombic efficiency. These findings reveal that LTO can simultaneously support deep lithiation and the galvanic reactivation of inactive Li and Li–Si alloys in the anode, offering a practical route to enhance both LTO and Si-based anodes in next-generation lithium-ion batteries.