Microstructural Evolution Of Iron Oxyfluoride/Carbon Nanocomposites Upon Electrochemical Cycling

Sina, Mahsa; Pereira, Nathalie; Amatucci, Glenn G.; Cosandey, F.

doi:10.1021/acs.jpcc.6b03485

Cited by 17 publications

(25 citation statements)

References 45 publications

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“…This result may be due to the instability of Mn 3+ or Mn 4+ ions in tetrahedral sites compared with octahedral sites considering the oxidized environment of the surface region by F − ion incorporation 27,28 . This face-centred cubic to body-centred tetragonal phase transition is known for the diffusionless transformation 29 , which indicates that the transformation kinetics could be sufficiently fast to accommodate the high current density during the electrochemical cycling ( Supplementary Fig. 7).…”

Section: Surface-concentrated Chemical and Structural Changesmentioning

confidence: 94%

Lithium-free transition metal monoxides for positive electrodes in lithium-ion batteries

et al. 2017

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Lithium-ion batteries based on intercalation compounds have dominated the advanced portable energy storage market. The positive electrode materials in these batteries belong to a material group of lithium-conducting crystals that contain redoxactive transition metal and lithium. Materials without lithium-conducting paths or lithium-free compounds could be rarely used as positive electrodes due to the incapability of reversible lithium intercalation or the necessity of using metallic lithium as negative electrodes. These constraints have significantly limited the choice of materials and retarded the development of new positive electrodes in lithium-ion batteries. Here, we demonstrate that lithium-free transition metal monoxides that do not contain lithium-conducting paths in their crystal structure can be converted into high-capacity positive electrodes in the electrochemical cell by initially decorating the monoxide surface with nanosized lithium fluoride. This unusual electrochemical behaviour is attributed to a surface conversion reaction mechanism in contrast with the classic lithium intercalation reaction. Our findings will o er a potential new path in the design of positive electrode materials in lithium-ion batteries.

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Section: Surface-concentrated Chemical and Structural Changesmentioning

confidence: 94%

Lithium-free transition metal monoxides for positive electrodes in lithium-ion batteries

et al. 2017

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“…The authors assume that the capacity degradation is caused by the gradually decreased amount of amorphous rutile phase and the corresponding increase of less active rock salt phase during further cycling. 44 As far as Na storage is concerned, the more conductive oxyfluoride displayed a much better storability than pure FeF x , especially when resorting to tailored nanostructures, as they are often obtained by wet-chemical methods. 45 Zhou et al 46 investigated the Na-storage phase transformation behavior in ballmilled FeO 0.7 F 1.3 /C nanocomposites with active particle sizes as small as 12 nm.…”

Section: Phase Transformation In Iron Oxyfluoridesmentioning

confidence: 99%

“…The SEI consists of LiF, Fe 0 , trapped Fe 2+ , and likely FeO on the outer surface. 44,83 The SEI layer would grow and become thicker, and cause increased dissolution of Fe and accumulation of insulating LiF, connected with the loss of active species and larger Fe interparticle distance. Therefore, the reconversion step is seriously impeded on progressing cycling, resulting in capacity fading of fluoride materials as observed.…”

Section: Conversion Systems With Prior Lif Splittingmentioning

confidence: 99%

Electrochemically driven conversion reaction in fluoride electrodes for energy storage devices

et al. 2018

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Exploring electrochemically driven conversion reactions for the development of novel energy storage materials is an important topic as they can deliver higher energy densities than current Li-ion battery electrodes. Conversion-type fluorides promise particularly high energy densities by involving the light and small fluoride anion, and bond breaking can occur at relatively low Li activity (i.e., high cell voltage). Cells based on such electrodes may become competitors to other envisaged alternatives such as Lisulfur or Li-air systems with their many unsolved thermodynamic and kinetic problems. Relevant conversion reactions are typically multiphase redox reactions characterized by nucleation and growth processes along with pronounced interfacial and mass transport phenomena. Hence significant overpotentials and nonequilibrium reaction pathways are involved. In this review, we summarize recent findings in terms of phase evolution phenomena and mechanistic features of (oxy)fluorides at different redox stages during the conversion process, enabled by advanced characterization technologies and simulation methods. It can be concluded that well-designed nanostructured architectures are helpful in mitigating kinetic problems such as the usually pronounced voltage hysteresis. In this context, doping and open-framework strategies are useful. By these tools, simple materials that are unable to allow for substantial Li nonstoichiometry (e.g., by Li-insertable channels) may be turned into electroactive materials.

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“…This region is ascribed to the presence of the SEI, which is mostly composed of organic compounds (with lower atomic number). [ 16,27 ] Based on the STEM images (Figure 4 ), the electrode cycled with EC/DEC/FEC has an SEI that uniformly coats the entire Si NP in a dense thick fi lm, whereas the electrode cycled with EC/DEC has an inhomogeneous porous SEI. Furthermore, EELS scanning profi le was performed from the outer surface toward the bulk of these samples (along the indicated line in the Figure 4 a,b) to study the chemical changes from the bulk of the particle to SEI.…”

Section: Surface Characterizationmentioning

confidence: 99%

Direct Visualization of the Solid Electrolyte Interphase and Its Effects on Silicon Electrochemical Performance

Sina

Alvarado

Shobukawa

et al. 2016

Adv Materials Inter

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Fluoroethylene carbonate (FEC) as an electrolyte additive can considerably improve the cycling performance of silicon (Si) electrodes in Li-ion batteries. However, the fundamental mechanism for how FEC contributes to solid electrolyte interphase (SEI) morphological changes and chemical composition is not well understood. Here, scanning transmission electron microscopy coupled with electron energy loss spectroscopy gives a comprehensive insight as to how FEC affects the SEI evolution in terms of composition and morphology throughout electrochemical cycling. In the fi rst lithiation cycle, the electrode cycled in ethylene carbonate (EC): diethylene carbonate (DEC) forms a porous uneven SEI composed of mostly Li 2 CO 3 . However, the electrode cycled in EC/DEC/FEC is covered in a dense and uniform SEI containing mostly LiF. Interestingly, the intrinsic oxide layer (Li x SiO y ) is not observed at the interface of electrode cycled in EC/DEC/FEC after 1 cycle. This is consistent with fl uoride anion formation from the reduction of FEC, which leads to the chemical attack of any silicon-oxide surface passivation layer. Furthermore, surface sensitive helium ion microscopy and X-ray photoelectron spectroscopy techniques give further insights to the SEI composition and morphology in both electrodes cycled with different electrolytes.

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Microstructural Evolution Of Iron Oxyfluoride/Carbon Nanocomposites Upon Electrochemical Cycling

Cited by 17 publications

References 45 publications

Lithium-free transition metal monoxides for positive electrodes in lithium-ion batteries

Lithium-free transition metal monoxides for positive electrodes in lithium-ion batteries

Electrochemically driven conversion reaction in fluoride electrodes for energy storage devices

Direct Visualization of the Solid Electrolyte Interphase and Its Effects on Silicon Electrochemical Performance

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