Electrochemical Delithiation/Relithiation of LiCoPO4: A Two-Step Reaction Mechanism Investigated by in Situ X-ray Diffraction, in Situ X-ray Absorption Spectroscopy, and ex Situ 7Li/31P NMR Spectroscopy

Kaus, Maximilian; Issac, Ibrahim; Heinzmann, Ralf; Doyle, Stephen; Mangold, Stefan; Hahn, Horst; Chakravadhanula, Venkata Sai Kiran; Kübel, Christian; Ehrenberg, Helmut; Indris, Sylvio

doi:10.1021/jp503306v

Cited by 54 publications

(73 citation statements)

References 57 publications

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“…Otherwise no obvious difference between LiFePO 4 , LiCoPO 4 or LiNiPO 4 is observed, although for LiCoPO 4 , the volume change between the different co-existing phases is significantly smaller for a delithiation/lithiation process via the intermediate phase. 21,23 For LiNiPO 4 , the volume change upon delithiation corresponds to LiFePO 4 , and consistently indications of a similar two-phase mechanism have been suggested. 64 The volume change in mixed compositions is clearly smaller, 2-5%, and the influence of substitution appears especially as an increasing volume of the delithiated (x = 0) phase.…”

Section: Partially Delithiated Electrodes-the Effects Of Co and Ni Smentioning

confidence: 74%

“…21,23 Due to slow kinetics, the three phases, although subsequently formed, show broad co-existence ranges. 21,23 Compared to its counterpart FePO 4 phase, formation of CoPO 4 is suggested to be energetically more unfavorable. 23,37 However, no clear explanation for the intermediate Li x CoPO 4 phase appearance has been presented, and the phase is suggested to be at least metastable.…”

Section: 5mentioning

confidence: 99%

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Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe_1-_yM_yPO₄(M= Co, Ni) Electrode Materials

Jalkanen

Karppinen

2015

J. Electrochem. Soc.

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Solid solutions of LiFe 1-y M y PO 4 /C (M = Co, Ni) within the whole substitution range (0 ≤ y ≤ 1) are systematically investigated as safe high-voltage positive electrode materials for Li-ion battery. Especially the similarities and differences between the Co-and Ni-substitution schemes are highlighted. With increasing substitution level y, the orthorhombic unit cell shrinks and the Li + -ion diffusion channel area decreases, more rapidly for the smaller-sized Ni substituent. While the Co 2+ /Co 3+ redox couple shows reversible electrochemical activity, only an initial, partial delithiation is achieved for the Ni 2+ /Ni 3+ couple at all y. However, both substitution schemes similarly affect the Fe 2+ /Fe 3+ redox couple by increasing its potential and enhancing the kinetics. Particularly, a mutual influence of Fe and Co/Ni on the delithation/lithiation characteristics is proposed: ex situ XRD analysis shows signs of a phase-composition change in the Fe 2+ /Fe 3+ region for higher y, and correspondingly, a changed Co 2+ /Co 3+ redox mechanism for lower y is indicated by cyclic voltammetry. We suggest that this behavior is related to a substitution-induced decrease in the volume change between the lithiated and delithiated phases. For the Co-substitution scheme, a composition around y ≈ 0.5 seems optimal for combining a high energy density and a kinetically beneficial, diffusional single-phase delithiation/lithiation mechanism. Li-ion batteries have been traditionally used for small, portable consumer electronics, but their utilization in large-scale applications is rapidly growing. As the size of the battery packs is increasing, the matters of safety, cost, and cycle-life become more crucial. In addition, for applications in transportation, high energy and power densities are demanded. Olivine-structured metal phosphates LiMPO 4 (M = Fe, Mn, Co, Ni) are an interesting material family to replace the layered metal oxides LiMO 2 as the positive electrode.1-4 Their safety owing to their intrinsic structural stability is very tempting for large-scale batteries. The orthorhombic olivine structure (space group Pnma) is composed of LiO 6 and MO 6 octahedra and PO 4 tetrahedra, such that Li + -ion diffusion during lithiation/delithiation takes place only in one dimension, along the b axis. 3,5The iron-based olivine LiFePO 4 is already commercially used in Li-ion batteries; it shows a theoretical capacity of 170 mAh g −1 , high safety and cycle stability, and is in addition cheap and environmentally friendly.1 The delithiation/lithiation (charge/discharge) reaction proceeds as a two-phase reaction with a varying LiFePO 4 /FePO 4 ratio, which brings about a kinetic limitation due to the single Fe valence (Fe 2+ or Fe 3+ ) in the two end-phases, resulting in low carrier density. 1,6 Additionally, the two-phase reaction pathway is restricted by nucleation and growth, when compared to a diffusional single-phase solidsolution mechanism. 7 However, narrow single-phase solid-solution regions are suggested to exist at room-tem...

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Section: Partially Delithiated Electrodes-the Effects Of Co and Ni Smentioning

confidence: 74%

Section: 5mentioning

confidence: 99%

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe_1-_yM_yPO₄(M= Co, Ni) Electrode Materials

Jalkanen

Karppinen

2015

J. Electrochem. Soc.

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“…52 On the other hand, the spectrum of Li 2 CoPO 4 F is similar to that of LiCoPO 4 , although the local structures around cobalt are significantly different. 16,19 From this, it is evident that the spectral features for phosphate-based compounds are dominated by the strong covalent character between the P 3sp and O 2p orbitals rather than their structural coordination.…”

Section: Methodsmentioning

confidence: 98%

Structural Changes in Li₂CoPO₄F during Lithium-Ion Battery Reactions

et al. 2015

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The cobalt-based fluorophosphate Li 2 CoPO 4 F positive electrode has the potential to obtain high energy density in a lithium ion battery since its theoretical capacity is 287 mAh·g −1 when two electrons can react reversibly. This material promises to charge/discharge with an extremely high redox-couple voltage of over 4.8 V vs Li/Li + . Bulk structural analyses including X-ray diffraction, Co K-edge X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) reveal that an orthorhombic Li β CoPO 4 F phase is produced from pristine Li 2 CoPO 4 F by a combination of solid-solution and two-phase reaction manners during the first charging process, and these phases reversibly transform during charge−discharge cycling. The results of 7 Li MAS NMR and classical molecular dynamics simulations suggest that Li ions located at Li(1) sites intercalate/deintercalate through a 1D diffusion path along the b axis, whereas those located at Li(2) and Li(3) sites are fixed. The aforementioned analyses were successfully performed with the enhancement of electrochemical properties by use of a fluoroethylene carbonatebased electrolyte instead of an ethylene carbonate-based one and reducing its volume. Further enhancement was achieved by adding SiO 2 nanoparticles into the electrode slurry. The electrochemical results encourage the possibility of the intercalation/ deintercalation of more than one Li ion from/into Li 2 CoPO 4 F during electrochemical cycling.

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“…S15). [49][50] To confirm the increase in valency, X-ray photoelectron spectroscopy (XPS) was performed on the catalysts before and after delithiation (Fig. 48 Moreover, it is believed that the transition metals M (2+) in LiMPO4 were oxidized for charge compensation when lithium ions were extracted upon electrochemical tuning.…”

mentioning

confidence: 99%

Electrochemical tuning of olivine-type lithium transition-metal phosphates as efficient water oxidation catalysts

Liu

Wang

Lin

et al. 2015

Energy Environ. Sci.

172

131

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Electrochemical Delithiation/Relithiation of LiCoPO₄: A Two-Step Reaction Mechanism Investigated by in Situ X-ray Diffraction, in Situ X-ray Absorption Spectroscopy, and ex Situ ⁷Li/³¹P NMR Spectroscopy

Cited by 54 publications

References 57 publications

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe_1-_yM_yPO₄(M= Co, Ni) Electrode Materials

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe_1-_yM_yPO₄(M= Co, Ni) Electrode Materials

Structural Changes in Li₂CoPO₄F during Lithium-Ion Battery Reactions

Electrochemical tuning of olivine-type lithium transition-metal phosphates as efficient water oxidation catalysts

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Electrochemical Delithiation/Relithiation of LiCoPO4: A Two-Step Reaction Mechanism Investigated by in Situ X-ray Diffraction, in Situ X-ray Absorption Spectroscopy, and ex Situ 7Li/31P NMR Spectroscopy

Cited by 54 publications

References 57 publications

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe1-yMyPO4(M= Co, Ni) Electrode Materials

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe1-yMyPO4(M= Co, Ni) Electrode Materials

Structural Changes in Li2CoPO4F during Lithium-Ion Battery Reactions

Electrochemical tuning of olivine-type lithium transition-metal phosphates as efficient water oxidation catalysts

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Electrochemical Delithiation/Relithiation of LiCoPO₄: A Two-Step Reaction Mechanism Investigated by in Situ X-ray Diffraction, in Situ X-ray Absorption Spectroscopy, and ex Situ ⁷Li/³¹P NMR Spectroscopy

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe_1-_yM_yPO₄(M= Co, Ni) Electrode Materials

Electrochemical Performance and Delithiation/Lithiation Characteristics of Mixed LiFe_1-_yM_yPO₄(M= Co, Ni) Electrode Materials

Structural Changes in Li₂CoPO₄F during Lithium-Ion Battery Reactions