Effects of Particle Size, Electronic Connectivity, and Incoherent Nanoscale Domains on the Sequence of Lithiation in LiFePO<sub>4</sub> Porous Electrodes

Li, Yiyang; Meyer, Sophie; Lim, Jongwoo; Lee, Sang Chul; Gent, William E.; Marchesini, Stefano; Krishnan, Harinarayan; Tyliszczak, Tolek; Shapiro, David A.; Kilcoyne, A. L. D.; Chueh, William C.

doi:10.1002/adma.201502276

Cited by 80 publications

(127 citation statements)

References 55 publications

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“…Afterwards, we could confirm many individual nanoparticles with uniform single-crystal like orientation exhibiting both, LFP and FP phases, in agreement with published experimental observations [4,5,14,16] and theoretical modellings [25,26], especially a recent in-situ X-ray study confirmed the coexistence of both phases (LFP+FP) in individual single crystalline particles [27]. Some of the particles in figure 1a containing both phases are shown in detail in figure 2.…”

Section: Crystallographic Analysis Of the Acom-tem Data: Properties Osupporting

confidence: 77%

“…Transmission electron microscopy (TEM) offers various sophisticated methods for LiFePO 4 /FePO 4 (LFP/FP) phase mapping with high spatial resolution [6][7][8][9][10][11][12][13][14][15][16]. The mapping methods can be sorted into two families: one are spectroscopy methods based on the chemical information encoded in the energy spectra; the other are diffraction methods relying on the crystallographic information recorded in diffraction patterns or high resolution (HR)TEM images.…”

Section: Introductionmentioning

confidence: 99%

“…Efforts to experimentally detect the lithium distribution in partially charged/discharged states at nanoscale resolution are therefore essential. Many advanced techniques have been developed to obtain Li distribution maps: Scanning transmission X-ray microscopy (STXM) [1,2] or ptychography techniques [3][4][5] in synchrotron based setups were used to observe de/lithiation phase boundaries that started the discussion around its relationship to cycling current; Electron back scatter diffraction (EBSD) techniques in a scanning electron microscope (SEM) [6] was used to investigate the influence of the distance of particles to current collectors for the de/lithiation process.…”

Section: Introductionmentioning

confidence: 99%

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Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

Kobler

Wang

et al. 2016

Ultramicroscopy

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Transmission electron microscopy (TEM) has been used intensively in investigating battery materials, e.g. to obtain phase maps of partially (dis)charged (lithium) iron phosphate (LFP/FP), which is one of the most promising cathode material for next generation lithium ion (Li-ion) batteries. Due to the weak interaction between Li atoms and fast electrons, mapping of the Li distribution is not straightforward. In this work, we revisited the issue of TEM measurements of Li distribution maps for LFP/FP. Different TEM techniques, including spectroscopic techniques (energy filtered (EF)TEM in the energy range from low-loss to core-loss) and a STEM diffraction technique (automated crystal orientation mapping (ACOM)), were applied to map the lithiation of the same location in the same sample. This enabled a direct comparison of the results. The maps obtained by all methods showed excellent agreement with each other. Because of the strong difference in the imaging mechanisms, it proves the reliability of both the spectroscopic and STEM diffraction phase mapping. A comprehensive comparison of all methods is given in terms of information content, dose level, acquisition time and signal quality. The latter three are crucial for the design of in-situ experiments with beam sensitive Li-ion battery materials. Furthermore, we demonstrated the power of STEM diffraction (ACOM-STEM) providing additional crystallographic information, which can be analyzed to gain a deeper understanding of the LFP/FP interface properties such as statistical information on phase boundary orientation and misorientation between domains.

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Section: Crystallographic Analysis Of the Acom-tem Data: Properties Osupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

Kobler

Wang

et al. 2016

Ultramicroscopy

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“…Given the geometric area and thickness of the electrode, LFP density and assuming a nominal capacity of ∼170 mAh g −1 , the total volume fraction of LFP is estimated to be 0.39. Assuming ∼10 vol.% of the electrode is filled with binder and conductive material in the LFP electrode, 43 the porosity of the LFP electrode is then calculated to be ∼0.51. The rate constant for the electrode reaction at the surface of the Li foil has been measured using Li/Li symmetric cells, as reported in a previous study.…”

Section: Resultsmentioning

confidence: 99%

“…40,41 In summary, three major lithiation/delithiation mechanisms have been proposed: i) intra-particle phase transformation causing mechanical damage (incoherent or semi-coherent), [32][33][34][35] ii) intra-particle phase transformation with no mechanical damage (coherent) 33 and iii) interparticle phase transformation in an ensemble of electronically and ionically connected particles which are present in a solid-solution phase away from equilibrium. [29][30][31][36][37][38][39] The dominant mechanism is determined by factors such as particle size and shape, 33,42 quality of ionically and electronically conductive coatings, synthesis route, structural defects, electrode formulation and microstructure, 43 temperature, applied potential/current 38,39 and the conditioning cycles or the cycling history. 32 Core-shell-type 14,44 and non-ideal solid-solution 26,27 models have been used to describe the juxtaposition of the two phases in a single particle observed during chemical lithiation/delithiation.…”

mentioning

confidence: 99%

Mesoscopic Modeling of a LiFePO₄Electrode: Experimental Validation under Continuous and Intermittent Operating Conditions

Farkhondeh¹,

Pritzker²,

Fowler³

2017

J. Electrochem. Soc.

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The previously presented mesoscopic model [Phys. Chem. Chem. Phys., 16, 22555, (2014)] for battery electrodes consisting of phase-change insertion materials is incorporated into porous-electrode theory and validated by comparing the simulation results with experimental data from continuous and intermittent galvanostatic discharge of a LiFePO 4 electrode under various operating conditions. The model features mesoscopic LiFePO 4 units that undergo non-equilibrium lithiation/delithiation and fast solid-state diffusion. Good agreement with the experimental data supports the validity of this model. GITT analysis suggests that the slow evolution of the electrode polarization during each pulse and the subsequent relaxation period is due to Li transport between LiFePO 4 units rather than diffusion within the units. Galvanostatic pulse techniques commonly used to determine diffusivities of inserted species in solid-solution systems may also be used to estimate the equilibrium potential of individual mesoscopic units for which no actual measurement has been reported to date. Further analysis of the GITT experiments suggests an alternative pathway for the intermittent charge/discharge of LFP electrodes. Depending on the overall depth-of-discharge/charge of the electrode, relaxation time and the incremental depth-of-discharge/charge of each pulse, the solid-solution capacity available in the Li-rich/Li-poor end-member may be able to accommodate Li insertion/extraction entirely without phase transformation during each pulse. LiFePO 4 (LFP) has proved promising as a high-power active material for the positive electrodes in Li-ion batteries. Its outstanding performance has been subject of intensive research since its discovery in 1997.1 LFP undergoes a phase separation between the Li-poor Li ε FePO 4 and Li-rich Li 1−ε FePO 4 phases (ε and ε 1) during lithiation/delithiation, which is manifested by its equilibrium potential remaining virtually constant over a range of intermediate compositions.1,2 In spite of this phase separation, electrodes consisting of either nano-scale LFP particles 3,4 and/or particles coated with ionically/electronically conducting materials 5-8 exhibit a high rate capability and long cycle life. However, the seeming contradiction between the biphasic nature of the material and its high performance is not reflected in conventional models 9-27 describing the movement of phase boundaries and associated mechanical effects inside the particles during lithiation/delithiation.The advent of high resolution phase mapping tools has lead to more accurate characterization of the charge/discharge dynamics of LFP electrodes. [28][29][30][31][32][33][34][35][36][37][38][39] Maier et al. 32 tracked the phase boundary propagation in a large millimeter-scale LFP single crystal during chemical delithiation and observed the formation of a large amount of microstructural defects such as pores and cracks. Cabana et al. 33 used soft X-ray ptychographic microscopy (with a spatial resolution of ∼5 nm) and X-ray absorption spec...

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Persistent State‐of‐Charge Heterogeneity in Relaxed, Partially Charged Li₁₋_xNi_1/3Co_1/3Mn_1/3O₂ Secondary Particles

et al. 2016

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Ex situ transmission X-ray microscopy reveals micrometer-scale state-of-charge heterogeneity in solid-solution Li1- x Ni1/3 Co1/3 Mn1/3 O2 secondary particles even after extensive relaxation. The heterogeneity generates overcharged domains at the cutoff voltage, which may accelerate capacity fading and increase impedance with extended cycling. It is proposed that optimized secondary structures can minimize the state-of-charge heterogeneity by mitigating the buildup of nonuniform internal stresses associated with volume changes during charge.

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Effects of Particle Size, Electronic Connectivity, and Incoherent Nanoscale Domains on the Sequence of Lithiation in LiFePO₄ Porous Electrodes

Cited by 80 publications

References 55 publications

Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

Mesoscopic Modeling of a LiFePO₄Electrode: Experimental Validation under Continuous and Intermittent Operating Conditions

Persistent State‐of‐Charge Heterogeneity in Relaxed, Partially Charged Li₁₋_xNi_1/3Co_1/3Mn_1/3O₂ Secondary Particles

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Effects of Particle Size, Electronic Connectivity, and Incoherent Nanoscale Domains on the Sequence of Lithiation in LiFePO4 Porous Electrodes

Cited by 80 publications

References 55 publications

Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

Mesoscopic Modeling of a LiFePO4Electrode: Experimental Validation under Continuous and Intermittent Operating Conditions

Persistent State‐of‐Charge Heterogeneity in Relaxed, Partially Charged Li1−xNi1/3Co1/3Mn1/3O2 Secondary Particles

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Effects of Particle Size, Electronic Connectivity, and Incoherent Nanoscale Domains on the Sequence of Lithiation in LiFePO₄ Porous Electrodes

Mesoscopic Modeling of a LiFePO₄Electrode: Experimental Validation under Continuous and Intermittent Operating Conditions

Persistent State‐of‐Charge Heterogeneity in Relaxed, Partially Charged Li₁₋_xNi_1/3Co_1/3Mn_1/3O₂ Secondary Particles