A Comparative Study of Sulfate-Based Neutral pH Polymer Electrolytes for Low Temperature Applications
Bibliographic record
Abstract
Polymer electrolytes are key enablers for solid-state electrical double layer capacitors (EDLCs) that have thin and flexible form factors. Aqueous-based polymer electrolytes with neutral pH are interesting for their non-corrosiveness, intrinsically safe, and wider voltage window from high overpotential on water decomposition [1-3]. Previously, two neutral pH polymer electrolytes based on polyacrylamide (PAM) host and Li2SO4 [4] or Na2SO4 [5] as ion conductor were developed. These two systems demonstrated good chemical stability (shelf-life >30 days) and wide voltage window (1.9 V with activated carbon). Na2SO4-PAM showed higher ionic conductivity than Li2SO4-PAM under ambient conditions. Nonetheless, the effects of temperature and change in structure (e.g. freezing) to the electrochemical performance are still unclear. In this study, the performances of Li2SO4-PAM and Na2SO4-PAM at different temperatures were compared. The objectives were to (i) understand the ion conduction mechanisms within the polymeric structure, (ii) investigate the working temperature range of these electrolytes, and (iii) correlate the ion-conducting behaviour to their respective thermal properties, especially at the temperature below 0 °C. Metallic cells were constructed to study the electrochemical characteristics of the polymer electrolytes, while differential scanning calorimetry (DSC) was employed to characterize the thermal properties. From the activation energy of conduction above ambient temperatures, ion hopping was considered as the primary mechanism for ion movement in both electrolytes. Interestingly, although Li2SO4-PAM was able to maintain capacitive behaviour <0 ˚C, Na2SO4-PAM underwent severe loss in capacitive behaviour and significant loss in ionic conductivity. By comparing the DSC curves against the respective ionic conductivity at low temperatures (Fig. 1), the amount of crystallized water involved during freezing/melting was deduced as the source of this behaviour. This study elucidated the structure-performance relationship of polymer electrolytes at the low temperature conditions. References: [1] K. Fic, G. Lota, M. Meller, and E. Frackowiak, “Novel insight into neutral medium as electrolyte for high-voltage supercapacitors,” Energy & Env. Sci., 2, 2012 [2] C. Zhong, et al., “A review of electrolyte materials and compositions for electrochemical supercapacitors,” Chem. Soc. Rev., 44, 2015 [3] H.Y. Jin, Z.H. Peng, W.M. Tang, and H.L.W. Chan, “Controllable functionalized carbon fabric for high-performance all-carbon-based supercapacitors”, RSC Advances, 4, 2014 [4] A. Virya and K. Lian, “Li2SO4-polyacrylamide polymer electrolytes for 2.0 V solid symmetric supercapacitors,” Electrochem. Comm., 81, 2017 [5] A. Virya, J. Abella, A. Grindal, and K. Lian, “Na2SO4‐polyacrylamide electrolytes and enabled solid‐state electrochemical capacitors,” Batteries & Supercaps, 2019 Figure 1: Ionic conductivities at various low temperature overlaid with DSC curve for (a) Li2SO4-PAM and (b) Na2SO4-PAM Figure 1
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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 | 0.001 |
| 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".