Elucidating cycling rate-dependent electrochemical strains in sodium iron phosphate cathodes for Na-ion batteries

Ozdogru, Bertan; Dykes, Hannah; Gregory, Darrell; Saurel, Damien; Vijayakumar, M.; Casas‐Cabañas, Montse; Çapraz, Ömer Özgür

doi:10.1016/j.jpowsour.2021.230297

Cited by 20 publications

(15 citation statements)

References 74 publications

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“…During the insertion/removal of charge carriers, the electrode structures often undergo a phase transformation, associated with the volume mismatch between the new phase and the existing phase in the electrode particle. Depending on the phase transformation pathway and volume mismatch, insertion of an alkali ion into the host structure can cause plastic deformation, mechanical fracturing, and even amorphization in the electrode. − Insertion of Li ions into silicon can cause up to 300% volumetric expansion, and the extraordinarily high transformation strain causes amorphization, which provides a desirable platform for hosting Li ions in the electrode . The high transformation strains during Na intercalation into FePO 4 (17% volume expansion) also cause the formation of amorphous phases between the primary phases, which is beneficial to alleviate the misfit strain energy …”

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confidence: 99%

In Situ Probing Potassium-Ion Intercalation-Induced Amorphization in Crystalline Iron Phosphate Cathode Materials

et al. 2021

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Na-ion and K-ion batteries are promising alternatives for large-scale energy storage due to their abundance and low cost. Intercalation of these large ions could cause irreversible structural deformation and partial to complete amorphization in the crystalline electrodes. A lack of understanding of the dynamic changes in the amorphous nanostructure during battery operation is the bottleneck for further developments. Here, we report the utilization of in-operando digital image correlation and XRD techniques to probe dynamic changes in the amorphous phase of iron phosphate during potassium ion intercalation. In-operando XRD demonstrates amorphization in the electrode’s nanostructure during the first charge and discharge cycle. Additionally, ex situ HR-TEM further confirms the amorphization after potassium-ion intercalation. An in situ strain analysis detects reversible deformations associated with redox reactions in the amorphous phases. Our approach offers new insights into the mechanism of ion intercalation in the amorphous nanostructure which are highly potent for the development of next-generation batteries.

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confidence: 99%

In Situ Probing Potassium-Ion Intercalation-Induced Amorphization in Crystalline Iron Phosphate Cathode Materials

et al. 2021

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“…Previous studies showed a direct correlation between the evolution of potential‐dependent strain derivatives and nanoscale structural changes in the electrode due to the phase transformations. [ 37–39 ] The evolution of strain derivatives closely mimicked the current evolution in cyclic voltammetry and capacity derivative in the galvanostatic cycle. In both cases, the location of the strain derivatives aligned well with the location of either current peaks or peaks of capacity derivative within 0.03 V margin.…”

Section: Resultsmentioning

confidence: 90%

The Role of Transition Metals on Chemo‐Mechanical Instabilities in Prussian Blue Analogues For K‐Ion Batteries: The Case Study on KNHCF Versus KMHCF

Ozdogru

Bal

et al. 2023

Advanced Energy Materials

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Prussian blue analogues (PBAs) cathodes can host diverse monovalent and multivalent metal ions due to their tunable structure. However, their electrochemical performance suffers from poor cycle life associated with chemo‐mechanical instabilities. This study investigates the driving forces behind chemo‐mechanical instabilities in Ni‐ and Mn‐based PBAs cathodes for K‐ion batteries by combining electrochemical analysis, digital image correlation, and spectroscopy techniques. Capacity retention in Ni‐based PBA is 96% whereas it is 91.5% for Mn‐based PBA after 100 cycles at C/5 rate. During charge, the potassium nickel hexacyanoferrate (KNHCF) electrode experiences a positive strain generation whereas the potassium manganese hexacyanoferrate (KMHCF) electrode undergoes initially positive strain generation followed by a reduction in strains at a higher state of charge. Overall, both cathodes undergo similar reversible electrochemical strains in each charge–discharge cycle. There is ~0.80% irreversible strain generation in both cathodes after 5 cycles. XPS studies indicated richer organic layer compounds in the cathode‐electrolyte interface (CEI) layer formed on KMHCF cathodes compared to the KNHCF ones. Faster capacity fades in Mn‐based PBA, compared to Ni‐based ones, is attributed to the formation of richer organic compounds in CEI layers, rather than mechanical deformations. Understanding the driving forces behind instabilities provides a guideline to develop material‐based strategies for better electrochemical performance.

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“…55,59,60 Our previous studies also demonstrated that the formation of the SEI/CEI layers could contribute to the irreversible strain generation in the electrode. 40,43,61 These studies also pointed out a time-dependent irreversible deformation in electrodes associated with the SEI/CEI layer formation.…”

Section: Probing Mechanical Deformations In Lifepo4 Cathodes In Diffe...mentioning

confidence: 96%

Probing the Formation of Cathode-Electrolyte Interface on Lithium Iron Phosphate Cathodes via In Operando Mechanical Measurements

Bal

Ozdogru

Nguyen

et al. 2023

Preprint

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Interfacial instabilities in electrodes control the performance and lifetime of Li-ion batteries. While the formation of solid-electrolyte interface (SEI) on anodes has received much attention, there is still lack of understanding about the formation of cathode-electrolyte interface (CEI) on the cathodes. To fill this gap, we report on dynamic deformations on lithium iron phosphate, LiFePO4 cathodes during charge / discharge by utilizing in-operando digital image correlation, impedance spectroscopy and Cryo X-ray photoelectron spectroscopy. LiFePO4 cathodes were cycled in either LiPF6, LiClO4 or LiTFSI- containing organic liquid electrolytes. Beyond the first cycle, Li-ion intercalation results in a nearly linear correlation between electrochemical strains and the state of (dis)-charge, regardless of the electrolyte chemistry. However, during the first charge in LiPF6 - containing electrolyte, there is a distinct irreversible positive strain evolution at the onset of anodic current rise as well as current decay at around 4.0V. Impedance studies show the increase in surface resistance in the same potential window, suggesting the formation of CEI layers on the cathode. The chemistry of the CEI layer was characterized by X-ray photoelectron spectroscopy. LiF is detected in CEI layer starting as early as 3.4 V and LixPOyFz appeared at voltages higher than 4.0 V during the first charge. Our approach offers new insights into the formation mechanism of CEI layers on the cathode electrodes, which is crucial for the development of robust cathode and electrolyte chemistries for higher performance batteries.

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Elucidating cycling rate-dependent electrochemical strains in sodium iron phosphate cathodes for Na-ion batteries

Cited by 20 publications

References 74 publications

In Situ Probing Potassium-Ion Intercalation-Induced Amorphization in Crystalline Iron Phosphate Cathode Materials

In Situ Probing Potassium-Ion Intercalation-Induced Amorphization in Crystalline Iron Phosphate Cathode Materials

The Role of Transition Metals on Chemo‐Mechanical Instabilities in Prussian Blue Analogues For K‐Ion Batteries: The Case Study on KNHCF Versus KMHCF

Probing the Formation of Cathode-Electrolyte Interface on Lithium Iron Phosphate Cathodes via In Operando Mechanical Measurements

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