Study of the LiFePO<sub>4</sub>/FePO<sub>4</sub> Two-Phase System by High-Resolution Electron Energy Loss Spectroscopy

Laffont, Lydia; Delacourt, Charles; Gibot, Pierre; Wu, Minghao; Kooyman, Patricia J.; Masquelier, and C.; Tarascon, J. M.

doi:10.1021/cm0617182

Cited by 508 publications

(578 citation statements)

References 37 publications

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“…structure restricts the flexibility for solid solution phase formation 37 . Instead, two end-member phases, LiFePO 4 and FePO 4 , dominate the crystalline at the beginning.…”

Section: Discussionmentioning

confidence: 99%

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

2014

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The delithiation reaction in lithium ion batteries is often accompanied by an electrochemically driven phase transformation process. Tracking the phase transformation process at nanoscale resolution during battery operation provides invaluable information for tailoring the kinetic barrier to optimize the physical and electrochemical properties of battery materials. Here, using hard X-ray microscopy-which offers nanoscale resolution and deep penetration of the material, and takes advantage of the elemental and chemical sensitivity-we develop an in operando approach to track the dynamic phase transformation process in olivine-type lithium iron phosphate at two size scales: a multiple-particle scale to reveal a rate-dependent intercalation pathway through the entire electrode and a single-particle scale to disclose the intraparticle two-phase coexistence mechanism. These findings uncover the underlying twophase mechanism on the intraparticle scale and the inhomogeneous charge distribution on the multiple-particle scale. This in operando approach opens up unique opportunities for advancing high-performance energy materials.

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“…structure restricts the flexibility for solid solution phase formation 37 . Instead, two end-member phases, LiFePO 4 and FePO 4 , dominate the crystalline at the beginning.…”

Section: Discussionmentioning

confidence: 99%

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

2014

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“…Understanding the Li insertion/extraction mechanism at this interphase boundary is essential to understanding the electrochemical behavior of LFP. [36][37][38][39] Figure 2 HAADF-STEM images of Li-excess layered materials (a) at the pristine state and (b) after 10 cycles. 27 (c, d) EELS comparison of the particle surface and bulk for the pristine and cycled materials.…”

Section: Electrode Materialsmentioning

confidence: 99%

“…Thus, several models, such as the core-shell, 37 spinodal, 38 domino cascade models 39 and so on, were developed to describe the Li insertion at the LiFePO 4 -FePO 4 boundaries.…”

Section: Advanced Aem For Lithium-ion Batteries D Qian Et Almentioning

confidence: 99%

Advanced analytical electron microscopy for lithium-ion batteries

Qian

et al. 2015

NPG Asia Mater

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Lithium-ion batteries are a leading candidate for electric vehicle and smart grid applications. However, further optimizations of the energy/power density, coulombic efficiency and cycle life are still needed, and this requires a thorough understanding of the dynamic evolution of each component and their synergistic behaviors during battery operation. With the capability of resolving the structure and chemistry at an atomic resolution, advanced analytical transmission electron microscopy (AEM) is an ideal technique for this task. The present review paper focuses on recent contributions of this important technique to the fundamental understanding of the electrochemical processes of battery materials. A detailed review of both static (ex situ) and real-time (in situ) studies will be given, and issues that still need to be addressed will be discussed. NPG Asia Materials (2015) 7, e193; doi:10.1038/am.2015.50; published online 26 June 2015 INTRODUCTIONTo implement the commercialization of lithium-ion batteries in electric vehicles and smart grid systems, further improvements are required, especially with respect to the energy/power density, coulombic efficiency and cycle life. These parameters primarily depend on the diffusion of lithium-metal ions, electron transport, structure and chemical dynamics of the electrode/electrolyte materials, among others. During electrochemical cycling, significant changes in the material structure and elemental distributions occur, including ion relocation, lattice expansion/contraction, phase transition and structure/surface reconstruction. These changes could substantially influence ion and electron transport and affect the performance of the entire battery system. Understanding the structure-property relationships for each component and their synergistic behaviors during electrochemical processes is, therefore, essential for the design of new battery materials and the optimization of existing systems.Although many analysis techniques (for example, X-ray diffraction, X-ray absorption spectroscopy, neutron diffraction, nuclear magnetic resonance and so on) have been employed for such studies, most of them can acquire only spatially averaged information. Nevertheless, the structural and chemical evolution of battery materials upon electrochemical cycling can often be linked to specific nanofeatures, such as defects, interfaces and surfaces. As a result, techniques based on analytical transmission electron microscopy (AEM) are ideal tools to study these issues. The capability of AEM to precisely probe the structural/chemical evolutions at an ultrahigh spatial resolution frequently provides insight that cannot be obtained directly using macroscopic characterization methods.

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“…Dreyer et al proposed that the thermodynamic origin of this behaviour arises from the non-monotonic chemical potential of Li as a function of the particle's composition 17 . On the other hand, a concurrent intercalation pathway, whereby most particles intercalate at once, has also been observed in LFP 18,19 .Despite its crucial importance, the active population has been largely neglected in models describing electrode cycling [20][21][22][23] . Differing approximations in the active population may have contributed to the vast range of experimentally-measured specific exchange current densities, which range from 10 -6 A m -2 to 10 -1 A m -2 in LFP [20][21][22][23] .…”

mentioning

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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Study of the LiFePO₄/FePO₄ Two-Phase System by High-Resolution Electron Energy Loss Spectroscopy

Cited by 508 publications

References 37 publications

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

Advanced analytical electron microscopy for lithium-ion batteries

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

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Study of the LiFePO4/FePO4 Two-Phase System by High-Resolution Electron Energy Loss Spectroscopy

Cited by 508 publications

References 37 publications

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy

Advanced analytical electron microscopy for lithium-ion batteries

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

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Study of the LiFePO₄/FePO₄ Two-Phase System by High-Resolution Electron Energy Loss Spectroscopy