Why Substitution Enhances the Reactivity of LiFePO<sub>4</sub>

Omenya, Fredrick; Chernova, Natasha A.; Zhang, Ruibo; Fang, J. H.; Huang, Yiqing; Cohen, Fred E.; Dobrzynski, Nathaniel; Senanayake, Sanjaya D.; Xu, Wenqian; Whittingham, M. Stanley

doi:10.1021/cm303259j

Cited by 63 publications

(58 citation statements)

References 23 publications

(32 reference statements)

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“…Through cationic substitution, the lattice mismatch can be reduced, accompanied by an increased Li solubility range. Omenya et al reported that vanadium substitution on the iron site in LiFePO 4 increases the rate of Li removal and insertion [43,44]. As shown in Fig.…”

Section: Strain Accommodationmentioning

confidence: 93%

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Two-phase transition of Li-intercalation compounds in Li-ion batteries

2014

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Among all electrode materials, olivine LiFePO 4 and spinel Li 4 Ti 5 O 12 are well-known for their two-phase structure, characterized by a flat voltage plateau. The phase transition in olivine LiFePO 4 may be modeled in single particle and many-particle systems at room temperature, based on the thermodynamic phase diagram which is easily affected by coherency strain and the size effect. Some metastable and transient phases in the phase diagram can also be detected during non-equilibrium electrochemical processes. In comparison to olivine LiFePO 4 , spinel Li 4 Ti 5 O 12 possesses a 'zero strain' property and performs Li-site switching during the phase transition, which lead to a different phase structure. Here, the phase transitions of olivine LiFePO 4 and spinel Li 4 Ti 5 O 12 are systematically reviewed, and the concepts discussed may be extended to other two-phase Li-intercalation compounds in Li-ion batteries.

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Section: Strain Accommodationmentioning

confidence: 93%

“…(c) Diffraction patterns of Li 0.5 FePO 4 (black) and Li 0.5 Fe 0.85 V 0.1 PO 4 (red), insert shows magnified (2 0 0) diffraction peaks of triphylite and heterosite phases. Reproduced from[44] with permission from the American Chemical Society.…”

mentioning

confidence: 99%

Two-phase transition of Li-intercalation compounds in Li-ion batteries

2014

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“…For instance, the nucleation barrier in a phase-separating material was shown to be inversely proportional to the surface area to volume ratio of the nanoparticles 34 . Additionally, Nb doping 46 and V substitution 47 in LFP reduce the lattice mismatch and increase the solubility limits, both strong indicators of decreased transformation barrier. Mn substitution in LiFePO 4 , on the other hand, has been shown to eliminate the nucleation barrier and result in extensive solid solubility upon lithiation 48 .…”

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confidence: 99%

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes

et al. 2014

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Many battery electrodes contain ensembles of nanoparticles that phase-separate upon (de)intercalation. In such electrodes, the fraction of actively-intercalating particles directly impacts cycle life: a vanishing population concentrates the current in a small number of particles, leading to current hotspots. Reports on the active particle population in the phase-separating electrode lithium iron phosphate (LFP) vary widely, ranging from around 0% (particle-byparticle) to 100% (concurrent intercalation). Using synchrotron-based X-ray microscopy, we probed the individual state-of-charge for over 3,000 LFP particles. We observed that the active population depends strongly on the cycling current, exhibiting particle-by-particle-like behaviour at low rates and increasingly concurrent behaviour at high rates, consistent with our phase-field porous electrode simulations. Contrary to intuition, the current density, or current per active internal surface area, is nearly invariant with the global electrode cycling rate. Rather, the electrode accommodates higher current by increasing the active particle population. This behaviour results from thermodynamic transformation barriers in LFP, and such a phenomenon likely extends to other phase-separating battery materials. We propose that modifying the transformation barrier and exchange current density can increase the active population and thus the current homogeneity. This could introduce new paradigms to enhance the cycle life of phaseseparating battery electrodes. 3Electrochemical systems can provide clean and efficient routes for energy conversion and storage. Many electrochemical devices such as batteries, fuel cells, and supercapacitors consist of porous electrodes containing ensembles of nanoparticles 1 . For typical microstructures, the particle density can reach as high as 10 15 cm -3 . To further increase complexity, many intercalation battery electrodes, such as graphite 2 , lithium iron phosphate 3,4 , lithium titanate 5 , and spinel lithium nickel manganese oxide 6 , phase-separate upon (de)intercalation. Such electrodes are physically and chemically heterogeneous on the nanoscale, and likely exhibit inhomogeneous current distributions.In phase-separating electrodes, the active particle population is a crucial factor in determining the overall electrode current and the degree of current homogeneity. The electrode current is given by:where is the reaction area of the th actively-intercalating particle, and is the current density of that particle. Under the approximation of similar particle size, we obtain the final expression in equation 1, where ̅ is the average current density of all actively-intercalating particles, is the total internal surface area of all particles (rather than the projected electrode area), and is the so-called active population. When approaches 0%, the electrode intercalates particle-by-particle with a heterogeneous current distribution; when approaches 100%, the electrode intercalates concurrently with a more homogeneous current ...

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“…The magnetic properties are widely used to determine magnetic interactions, sample purity, transition metal oxidation states, and structural ordering [29,35,36,41]. The magnetic susceptibility, χ, of Li 2 Fe 1-3x/2 V x P 2 O 7 (x = 0, 0.025, 0.05) from 2 to 300 K is shown in Figure 4(a).…”

Section: Resultsmentioning

confidence: 99%

Study on Vanadium Substitution to Iron in Li2FeP2O7 as Cathode Material for Lithium-ion Batteries

Xu¹,

Chou²,

Gu³

et al. 2014

Electrochimica Acta

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Dou, S. (2014). Study on vanadium substitution to iron in Li2FeP 2O7 as cathode material for lithium-ion batteries. Electrochimica Acta, Study on vanadium substitution to iron in Li2FeP 2O7 as cathode material for lithium-ion batteries AbstractA series of Li2Fe1-3x/2VxP 2O7 (x = 0, 0.025, 0.05, 0.075, and 0.1) cathode materials for LIBs were prepared by the sol-gel method. Structural characterization of Li2Fe1-3x/2VxP2O7 (x = 0, 0.025, 0.05, 0.075, and 0.1) samples was conducted by synchrotron X-ray diffraction. The morphology and oxidation states of Fe2+ and V 3+ in the Li2Fe1-3x/2VxP 2O7 samples were confirmed by scanning electron microscopy and magnetic susceptibility measurements, respectively. The electrochemical measurements indicated that Li2Fe1-3x/2VxP 2O7 (x = 0.025) delivered the higher reversible capacity of 79.9 mAh g-1 at 1 C in the voltage range of 2.0 -4.5 V with higher 77.9% capacity retention after 300 cycles than those of Li 2FeP2O7 (48.9 mAh g-1 and 72.6%). Moreover, the rate capability of Li2Fe1-3x/2V xP2O7 (x = 0.025) were also significantly enhanced through vanadium substitution to iron of Li2Fe 1-3x/2VxP2O7. The vanadium substituted to Fe2 site of Li2FeP2O7 decreases Li occupying the Li5 position in the FeO5 unit, leading to a low degree exchange between Li and Fe in the MO5 (M = Li and Fe). The low degree cation disorder was beneficial to lithium-ion extraction/insertion during the charge-discharge process and hence enhances the capacity and rate capability. The low degree cation disorder was beneficial to lithium-ion extraction/insertion during the charge-discharge process and hence enhances the capacity and rate capability.1

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Why Substitution Enhances the Reactivity of LiFePO₄

Cited by 63 publications

References 23 publications

Two-phase transition of Li-intercalation compounds in Li-ion batteries

Two-phase transition of Li-intercalation compounds in Li-ion batteries

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes

Study on Vanadium Substitution to Iron in Li2FeP2O7 as Cathode Material for Lithium-ion Batteries

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Why Substitution Enhances the Reactivity of LiFePO4

Cited by 63 publications

References 23 publications

Two-phase transition of Li-intercalation compounds in Li-ion batteries

Two-phase transition of Li-intercalation compounds in Li-ion batteries

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes

Study on Vanadium Substitution to Iron in Li2FeP2O7 as Cathode Material for Lithium-ion Batteries

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Why Substitution Enhances the Reactivity of LiFePO₄