Probing Capacity Trends in MLi₂Ti₆O₁₄ Lithium-Ion Battery Anodes Using Calorimetric Studies

Abstract

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

Calorimetric Study of Mixed Phosphates Na4M3(PO4)2P2O7 (M = Mn2+, Fe2+, Co2+, Ni2+) to Evaluate the Electrochemical Trends

“…The calorimeter was calibrated using the heat content of 5 mg pellets of α-Al 2 O 3 (99.997%). The details of the calorimeter and procedures have been described previously. , …”

“…The details of the calorimeter and procedures have been described previously. 17 S1−S4). The powders were well crystallized with particle size in the nanometric range with porous agglomerates formed in the micrometric range (Figure 1e−h).…”

“…Previous calorimetric studies from our group have provided insights into thermodynamic influence on the structure–property relationships in suites of battery materials. The observed energetics and electrochemical behavior were attributed to their structure, the difference in their ionic radii, and the corresponding effect on bonding, acid–base interactions, enhanced stability owing to hydration, and polymorphic phase selection. − In this paper, we have employed high-temperature oxide melt solution calorimetry to measure enthalpies of formation to elucidate the observed electrochemical behavior in the Na 4 M 3 (PO 4 ) 2 P 2 O 7 family. We found a strong correlation between the energetic stability and ionic radii of the transition metal (M = Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ ), which provides insights into the observed trend in capacity.…”