Effect of Electrode Parameters on LiFePO[sub 4] Cathodes

Yu, Yaming; Donoue, Kazunori; Inoue, Takao; Fujimoto, Masahisa; Fujitani, S.

doi:10.1149/1.2179199

Cited by 117 publications

(98 citation statements)

References 15 publications

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“…We obtain good fits, with an of 0.2 and a of 0.6 A m -2 , yielding an average exchange current density of ~ 0.3 A m -2 . The exchange current density is higher than most reported values in literature; however, past work did not consider the active particle fraction and likely overestimated the active reaction area [20][21][22][23] . The fittings may also be affected by departures from Butler-Volmer kinetics at high rates that that lead to curved Tafel plots and small effective values of 27 .…”

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confidence: 57%

“…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%

“…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%

“…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] . The active population has sometimes been considered in terms of an electrode-level lithiation front from the separator to the current collector 24 .…”

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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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confidence: 99%

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

et al. 2014

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“…The set-up consists of an aluminum vacuum chamber where a Canberra PIPS detector is used to measure the energy of the emitted 3 H particles, as illustrated in Figure 1. All results are based on measurements on pouch cells (Gustafsson et al, 1992;Yu et al, 2006;Mohanty et al, 2013;Lv et al, 2018), also known as coffee bag cells (Singh et al, 2015), their flexible design allows the straightforward sealing of current collector window (Villevieille, 2015), as is also described in Zhang et al (2014). Also pouch cell type constructions are common practice in industrial applications (Trask et al, 2014).…”

Section: Methodsmentioning

confidence: 99%

Operando Neutron Depth Profiling to Determine the Spatial Distribution of Li in Li-ion Batteries

Verhallen

Wagemaker

2018

Front. Energy Res.

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Neutron Depth Profiling (NDP) allows determination of the spatial distribution of specific isotopes, via neutron capture reactions. In a capture reaction charged particles with fixed kinetic energy are formed, where their energy loss through the material of interest can be used to provide the depth of the original isotope. As lithium-6 has a relatively large probability for such a capture reaction, it can be used by battery scientists to study the lithium concentration in the electrodes even during battery operation. The selective measurement of the 6 Li isotope makes it a direct and sensitive technique, whereas the penetrative character of the neutrons allows practical battery pouch cells to be studied. Using NDP lithium diffusion and reaction rates can be studied operando as a function of depth, opening a large range of opportunities including the study of alloying reactions, metal plating, and (de) intercalation in insertion hosts. In the study of high rate cycling of intercalation materials the relatively low Li density challenges counting statistics while the limited change in electrode density due to the Li-ion insertion and extraction allows straightforward determination of the Li density as a function of electrode depth. If an electrode can be (dis)charged reversibly, data can be acquired and accumulated over multiple cycles to increase the time resolution. For Li metal plating and alloying reactions, the large lithium density allows good time resolution, however the large change of the electrode composition and density makes extracting the Li-density as a function of depth more challenging. Here an effective method is presented, using calibration measurements of the individual components, based on which the ratio of the components as a function of depth can be determined as well as the total Li-density. The same principles can be applied to insertion host materials, where the differences in density due to electrolyte infiltration yield the electrode porosity as a function of depth. This is of particular importance for battery electrodes where porosity has a direct influence on the energy density and charge transport.

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Conducting‐Polymer/Iron‐Redox‐ Couple Composite Cathodes for Lithium Secondary Batteries

Park¹,

Schougaard²,

Goodenough³

2007

Advanced Materials

404

220

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Conducting polymers, such as polyacetylene, polyaniline, and polypyrrole (PPy), have been studied as electrode materials for rechargeable batteries because they are electrochemically active and permit penetration of the electrolyte into the polymer mass. These polymers can be charged and discharged by a redox reaction involving lithium ions or counter anions of the electrolyte.[ /3dn + 1 pair of a first-row transition element. The operating voltage of the lithium-ion rechargeable battery should then reflect the energy level of the redox couple over the capacity range of the attached couple, which is expected to flatten the charge-discharge curves over this capacity range and add this capacity to that of the polymer.As an example of the chemical bonding of a redox couple to the polymer, we have covalently anchored ferrocene groups to the PPy backbone. Previous work on ferrocene tethered to PPy was mostly focused on membrane materials. [3] In this study, [(ferrocenyl) amidopropyl]pyrrole is used in conjunction with pure pyrrole to make the copolymer chains (Fig. 1).To examine the physical binding of redox couples to the polymer, we have incorporated the oxide LiFePO 4 into PPy; this oxide exhibits a flat V OC value of 3.4 V versus Li + /Li 0 and has a theoretical specific capacity of 170 mA h g -1 .[4] Although LiFePO 4 is inexpensive, thermally safe, and environmentally friendly, it is plagued by a low conductivity because of a subtle first-order phase change that distinguishes it from FePO 4 .[4]This phase change is responsible for the desirable flat V OC behavior, but has made it difficult to realize the theoretical capacity, particularly at high charge-discharge rates. Previous work has shown that the conductivity problems can be somewhat alleviated by a partial surface coating of carbon on the LiFePO 4 particles. [5] By physically incorporating fine carbon-coated LiFePO 4 particles into PPy, we have fabricated a cathode that is sufficiently porous to allow good penetration of the electrolyte to the surfaces of the oxide particles; the conducting polymer eliminates the need for carbon-black and polymer binder additives while providing additional capacity. In these proofof-concept experiments, no attempts have been made to optimize the polymer/oxide ratio of the composite cathodes. PPy/ferrocene polymer films with a uniform thickness have been electrodeposited onto a stainless-steel mesh (Fig. 2a). These films show an uneven surface morphology, which is typical of nucleation events, causing uneven current distribution. COMMUNICATION 848

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Effect of Electrode Parameters on LiFePO[sub 4] Cathodes

Cited by 117 publications

References 15 publications

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

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

Operando Neutron Depth Profiling to Determine the Spatial Distribution of Li in Li-ion Batteries

Conducting‐Polymer/Iron‐Redox‐ Couple Composite Cathodes for Lithium Secondary Batteries

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