MLi<sub>2</sub>Ti<sub>6</sub>O<sub>14</sub> (M = 2Na, Sr, Ba, Pb) Titanate Anodes for Lithium-Ion Capacitors (LICs)
Bibliographic record
Abstract
Presence of shared edge, particularly of shared face, decreases the stability of ionic structures, for e.g., the least number of [TiO₆] shared edges (two) makes rutile (hcp) the most stable TiO₂ polymorph (Pauling’s IIIrd rule) [1]. Further, on insertion of (one or three) Li into spinel LiTi₂O₄ (ccp) or Li-substituted defect-spinel Li₄Ti₅O₁₂ (LTO), Li in 8a [LiO₄] sites migrate along with incoming Li to vacant 16c [LiO₆] sites, effectively avoiding face sharing of [TiO₆]-[TiO₆], [LiO₆]-[TiO₆] or [LiO₄]-[TiO₆] polyhedra in the intermediate states. This is unlike the face shared polyhedra that form mid-way during lithium insertion in case of rutile (hcp), brookite (hcp/ccp) or anatase (ccp) [2]. A unique zero-strain two-phase separation occurs favourably at a 1.5 V flat Ti(IV)/Ti(III) redox voltage vs Li, which is far above the deposition potential of lithium. This makes LTO a safe, dendrite-free, high-power, and long-life anode that is widely used commercially (Altair Nano, Toshiba SCiB, Yinlong) as an alternative to graphite. LTO is also reported (Hydro Quebec) to cycle over 30000 times vs LiFePO₄ while retaining 90% capacity. Along these lines, orthorhombic Cmca MLi₂Ti₆O₁₄ (MLTO) (M = 2Na, Sr, Ba, Pb) [3-5] prepared by rapid combustion-synthesis exhibit similar voltage (1.3-1.45 V) and capacity (100-160 mAh/g, upto 4 Li uptake). The first reported compound in this family, BaLi₂Ti₆O₁₄, had a high ionic conductivity (10-3 S/cm, 300ᵒC) and was found by serendipity during attempts to stabilize - a high-temperature type-III superionic Ramsdellite phase (MnO₂) of Li₂Ti₃O₇ - by addition of Ba [6]. Ramsdellite crystallizes in a rutile-type arrangement of 2X1 [TiO₆] polyhedras and reversibly inserts 2.24 Li [7]. Lithium diffusivity - migration pathways, their temperature dependent activation energies and diffusion coefficient - in MLTO was probed using a combination of methods involving bond valence site energy (BVSE) analysis, AC bulk-conductivity analysis, and electrochemistry versus Li was demonstrated. Further, motivated by Amatucci’s pioneering work on high power LTO/Activated Carbon (AC) asymmetric lithium-ion capacitors (LIC) showing electrochemical performance between high-energy battery and high-power capacitors, we employed MLTO electrodes in LICs for the first time. MLTOs were first loaded with lithium (pre-discharged) before assembling them in MLTOs/AC LIC hybrids. AC cathode adsorbs PF6 - ions rapidly in a capacitor-like sloped profile (40 mAh/g) at a higher voltage, while MLTOs (de)intercalate Li (100 mAh/g, 1-2 V) at Ti-redox potential. References: [1] L. Pauling, J. Am. Chem. Soc., 1929, 51, 1010-1026 [2] D.W. Murphy et. al., Solid State Ionics, 1983, 9, 413-417 [3] A. Chaupatnaik, P. Barpanda, J. Mater. Res., 2018, 34, 158-168 [4] A. Dayamani, G. Shinde, A. Chaupatnaik, et.al., J. Power Sources, 2018, 385, 122-129 [5] A. Chaupatnaik, P. Barpanda, J. Electrochem. Soc., 2019, 166, A5122-A5130 [6] W.J. Zheng et. al., Solid State Ionics, 1989, 35, 235-239 [7] M.E. Arroyo y de Dompablo et. al., Mater. Res. Bull., 1997, 32, 993-1001
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".