Probing Capacity Trends in MLi 2 Ti 6 O 14 Lithium-Ion Battery Anodes Using Calorimetric Studies.

Due to higher packing density, lower working potential, and area specific impedance, the MLi 2 Ti 6 O 14 (M = 2Na, Sr, Ba, and Pb) titanate family is a potential alternative to zero-strain Li 4 Ti 5 O 12 anodes used commercially in Li-ion batteries. However, the exact lithiation mechanism in these compounds remains unclear. Despite its structural similarity, MLi 2 Ti 6 O 14 behaves differently depending on charge and size of the metal ion, hosting 1.3, 2.7, 2.9, and 4.4 Li per formula unit, giving charge capacity values from 60 to 160 mAh/g in contrast to the theoretical capacity trend. However, high-temperature oxide melt solution calorimetry measurements confirm strong correlation between thermodynamic stability and the observed capacity. The main factors controlling energetics are strong acid-base interactions between basic oxides MO, Li 2 O and acidic TiO 2 , size of the cation, and compressive strain. Accordingly, the energetic stability diminishes in the order Na 2 Li 2 Ti 6 O 14 > BaLi 2 Ti 6 O 14 > SrLi 2 Ti 6 O 14 > PbLi 2 Ti 6 O 14 . This sequence is similar to that in many other oxide systems. This work exhibits that thermodynamic systematics can serve as guidelines for the choice of composition for building better batteries.