Solid-Solution Vs. Two-Phase Li-Ion Storage in Nanograined Orthosilicate Cathode Materials
Bibliographic record
Abstract
Lithium metal orthosilicate cathode materials (Li2(Fe,Mn)SiO4 denoted as LMS) have been the subject of significant research interest for the past 10 years because of the high theoretical capacity nearly two times higher than that of the analogous polyanion cathode LiFePO4 (165 mAh/g), if the two lithium ions could be fully extracted and re-inserted in multiple charge/discharge cycles. Despite significant progress, a series of critical issues-questions relating to this strategically important family of cathode materials remain open hampering their full development. One such critical issue is the mechanism of Li ion storage namely, solid-solution behavior (single-phase) vs. two-phase reaction. In analogy with the well understood two-phase separation Li storage mechanism of LiFePO4 cathode the dominant view among those investigating the orthosilicate system is that we have also a two-phase mechanism between monoclinic (P21/n) Li2FeIISiO4 and orthorhombic (Pmn21) one-Li delithiated LiFeIIISiO4. However, in many of these studies the generated discharge curves are not flat but are slanted. Such behavior has been attributed to polarization effects without further characterization leaving an important gap in our understanding. With the view of clarifying this issue we have conducted first principle calculations (1) and in situ (unpublished) and ex situ (submitted) synchrotron XRD and XANES (Fe K-edge and L-edge; Si K-edge and Oxygen K-edge) characterizations of nanostructured LFS cathode in terms of structure evolution and charge compensation at different states of charge (Li(2-x)FeSiO4, x=0, 0.25, 0.50, 0.75, 1.0). This is done by charging/discharging LFS at low current (C/50) to allow for structure relaxation hence unequivocal (quasi-equilibrium condition) probing of the Li storage mechanism: solid solution vs. two-phase reaction. Furthermore, cycling is not limited to the first cycle but is extended to several cycles. For the study we employ a mixed phase (monoclinic/orthorhombic) nanograined Li2FeSiO4 material synthesized via organic-assisted hydrothermal precipitation and annealing at 400 °C (2,3). The data clearly point out towards solid solution mechanism- a finding that should bring new perspective in our pursuit of unlocking the full capacity advantage of the orthosilicate Li-ion host structure. Acknowledgments This work is supported through a Hydro-Québec/Natural Sciences & Engineering Research Council of Canada (NSERC) Collaborative R&D research grant. DTJ acknowledges NSERC support for the work done at the University of Guelph. Synchrotron radiation measurements were performed at the Canadian Light Source, which is supported by CFI, NSERC, University of Saskatchewan, Province of Saskatchewan, Western Economic Diversification Canada, NRC Canada, and CIHR. References 1. Lu, X.; Chiu, H.-C.; Bevan, H. K.; Jiang, D.-T.; Zaghib, K.; Demopoulos, P. G., Density functional theory insights into the structural stability and Li diffusion properties of monoclinic and orthorhombic Li2FeSiO4 cathodes, Journal of Power Sources, 2016, 318, 136-145. 2. Lu, X.; Wei, H. J.; Chiu, H. C.; Gauvin, R.; Hovington, P.; Guerfi, A.; Zaghib, K.; Demopoulos, G. P. Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals, Scientific Reports, 2015, 5, 8599. 3. Arthur, Z.; Chiu, H.-C.; Lu, X.; Chen, N.; Emond, V.; Zaghib, K.; Jiang, D.-T.; Demopoulos, G. P. Spontaneous reaction between uncharged lithium iron silicate cathode and LiPF6-based electrolyte, ChemComm, 52 (2015) 190-193.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".