Quasi-equilibrium voltammetric curves of polaron-conducting polymer films

Anishchenko, Dmitrii V.; Levin, Oleg V.; Malev, V. V.

doi:10.1016/j.electacta.2015.11.044

Cited by 9 publications

(13 citation statements)

References 23 publications

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“…The structural changes were detected in the anode and the cathode of the overcharged cells, indicating migration of the transition metals to the anode, loss of electrodes integrity, and irreversible Li loss from the cathode [22][23][24][25]. As a result, the market share of the low-voltage cathode material LiFePO 4 (LFP) is currently growing [11,[26][27][28]. Low cost, high thermal stability, non-toxicity, and the safety of this material makes it promising for various types of LIB [18,29].…”

Section: Introductionmentioning

confidence: 99%

Overcharge Cycling Effect on the Surface Layers and Crystalline Structure of LiFePO4 Cathodes of Li-Ion Batteries

et al. 2019

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Electrochemical cells using LiFePO4 cathode material are considered one of the safest and most resistant to overcharging among Li-ion batteries. However, if LiFePO4-based electrodes are exposed to high potentials, surface and structural changes may occur in the electrode material. In this study Li/LiFePO4 half-cells were overcharged under different modes with variable cut-off voltages and charge currents. The change in voltage profile, discharge capacity, surface layers composition, and crystalline structure were characterized after overcharge cycles. It was demonstrated that the cathode material is resistant to short-term overcharging up to 5 V, but undergoes irreversible changes with increasing overcharge time or potential. Thus, despite the well-known tolerance of LiFePO4-based batteries to overcharge, a long overcharge time or high cut-off voltage leads to destructive changes in the cathode and should be avoided.

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Section: Introductionmentioning

confidence: 99%

Overcharge Cycling Effect on the Surface Layers and Crystalline Structure of LiFePO4 Cathodes of Li-Ion Batteries

et al. 2019

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“…It is obvious from Figure that the differential form of the isotherm dθ/d E versus E is more convenient for detecting small changes in the intercalation process (compare Figure b to a). Additionally, differential forms of isotherms are often used as the quasiequilibrium voltammetric characteristic of electroactive materials, − as d E ′/d t = v ( t stays for time, in s; v stays for the potential scan rate, in V/s) is a constant in the case of linear sweep voltammetry. Therefore, the expression for quasiequilibrium charging current I = NFAL dθ/d t can be rewritten in a convenient way where I , A , and L are current, redox-active material geometric area, and thickness, respectively.…”

Section: Results and Discussionmentioning

confidence: 99%

New Variant of Electrochemical Intercalation Isotherm: Analysis of Instability Region Dependence on Electrolyte Concentration

et al. 2022

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Electroactive redox materials, encompassing redox polymers, metal−organic frameworks, and intercalation materials, play an important role in a wide range of emerging applications. However, many theoretical issues concerning quantitative thermodynamic description of such materials remain unclear so far. Existing variants of electrochemical intercalation isotherms (namely, the Langmuir−Frumkin isotherm, which often applies to redox polymers and electroactive solid materials, and the reformulated isotherm, accounting for the phase character of the potential distribution within the material) do not explain the dependence of redox materials' voltammetric responses on the electrolyte concentration. In addition to that, studies show that the reformulated isotherm has a higher value of the so-called shortrange interaction parameter at which phase separation starts and asymmetric single-phase regions in comparison to the Langmuir− Frumkin isotherm. A simple modification, accounting for the possibility of both positive and negative ions of the electrolyte solution to intercalate the electroactive redox material, leads to a new variant of electrochemical intercalation isotherm, which includes Langmuir−Frumkin and reformulated isotherms as limiting cases. The new model explains the dependence of redox materials' voltammetric responses on the electrolyte concentration. Theory predicts the dependence of short-range interaction parameters at which phase separation starts on the electrolyte composition. Thus, the new electrochemical intercalation isotherm shows the dependence of its unstable, metastable, and stable regions on the electrolyte concentration and ion distribution coefficients. It opens up a possibility to tune material characteristics such as sizes of single-phase/two-phase regions. In some particular cases, it is possible to induce or eliminate the phase transition by changing the concentration of the electrolyte. We believe that studying such properties may help in future realization of new smart materials with superior characteristics for electrochemical energy storage, use in chemical sensors, medical applications, and so forth.

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“…However, Malev et al demonstrated in the series of works 34,35 that accounting for step-by-step movement of delocalized cation-radicals (which we would refer to as polarons, in accordance with works 74,75 ) leads to a change in the flux equations and in expressions for electrochemical potentials of those charge carriers; this resulted in a difference between mathematical descriptions for p-conjugated organic polymers and redox polymers. 75 In short, differences in model descriptions of those two types of electroactive polymer materials are depicted in Scheme 1 and discussed below. The polaron, delocalized over several repeating units of the p-conjugated polymer chain is depicted in Scheme 1a using polypyrrole as an example.…”

Section: Introductionmentioning

confidence: 95%

“…Eqn (1) is the expression for electrochemical potential of polarons in a conducting p-conjugated polymer, while eqn (2) is the expression for electrochemical potential of oxidized redox centers of a redox polymer. 70,75…”

Section: Introductionmentioning

confidence: 99%

“…This new approach 75 allowed a more precise description of conducting p-conjugated polymers: it explains qualitatively the observed long tails in their CVs, it also explains the broader CV-peaks of CPs in comparison to redox polymer CV-peaks, and additionally gives reasonable explanation concerning the correlation between the doping level of the conducting polymer and its voltammetric peak mid-width. 75 Despite qualitative and sometimes quantitative agreement with experiment, the existing theoretical description concerns main types of electroactive polymers only (namely, conducting polymers and redox polymers). Thus, existing theoretical description is not easily applicable to the hybrid types of electroactive polymers, which possess both types of charge carriers and both charge transfer mechanisms.…”

Section: Introductionmentioning

confidence: 99%

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