Jason R. Croy

Argonne National Laboratory, Lemont, Illinois, United States

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Publications (38)140.01 Total impact

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    ABSTRACT: Direct observations of structure-electrochemical activity relationships continue to be a key challenge in secondary battery research. 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the only structural probe currently available that can quantitatively characterize local lithium environments on the subnanometer scale that dominates the free energy for site occupation in lithium ion (Li-ion) intercalation materials. In the present study, we use this local probe to gain new insights into the complex electrochemical behavior of activated 0.56Li2MnO3•0.56LiMn0.5Ni0.5O2, lithium- and manganese-rich transition metal oxide intercalation electrodes. We show direct evidence of path-dependent lithium site occupation, correlated to structural reorganization of the metal oxide and the electrochemical hysteresis, during lithium insertion and extraction. We report new 6Li resonances centered at ~1600ppm that are assigned to LiMn6-TMtet sites, specifically, a hyperfine shift related to a small fraction of reentrant tetrahedral transition metals (Mntet), located above or below lithium layers, coordinated to LiMn6 units. The intensity of the TM layer lithium sites correlated with tetrahedral TMs loses intensity after cycling, indicating limited reversibility of TM migrations upon cycling. These findings reveal that defect sites, even in dilute concentrations, can have a profound effect on the overall electrochemical behavior.
    Journal of the American Chemical Society 01/2015; 137(6). DOI:10.1021/ja511299y · 11.44 Impact Factor
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    ABSTRACT: Both in situ high-energy X-ray diffraction and in situ X-ray absorption spectroscopy were used to investigate the structural evolution of materials during the solid-state synthesis of Li2MnO3. Combing X-ray absorption spectroscopy and factor analysis techniques, we were able to capture the spectrum and evolution of an intermediate phase (MnO2) that could not be detected by the diffraction technique. Meanwhile, the X-ray diffraction data clearly showed the anisotropic crystallization of Li2MnO3 during sintering above 600 °C.
    Journal of Power Sources 11/2014; 266:341–346. DOI:10.1016/j.jpowsour.2014.05.032 · 5.21 Impact Factor
  • M. M. Thackeray, J. R. Croy
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    ABSTRACT: Lithium- and manganese rich xLi2MnO3•(1-x)LiMO2 composite structures (M=Mn, Ni, Co) are currently one of the most promising classes of cathode materials for advanced Li-ion batteries. When charged below 4.3 V, and when used in low concentration (typically 0.03<x<0.1), the electrochemically inactive Li2MnO3 component acts as a structural stabilizer to enable modest improvements in electrochemical properties. When higher concentrations of Li2MnO3 are embedded in the matrix (typically 0.3<x<0.5), and when the cells are electrochemically-activated above 4.5 V, significantly higher capacities (250 mAh/g or more) can be achieved. Unfortunately, these high capacity electrode structures are unstable when charged repeatedly to such a high cell voltage. On cycling, the transition metals (M) migrate into the lithium layers; this migration leads to hysteresis, voltage fade, rate impairment and energy inefficiency - despite the retention of electrode capacity. We have addressed these limitations by strategically introducing a small amount of LiM2O4 spinel (M=Mn, Ni, Co) to form ‘layered-layered-spinel’ composite structures. The advantage of this approach is that the M cations of the spinel component occupy alternate layers of an oxygen array, which is structurally compatible with the LiMO2 component, in a 3:1 ratio, thereby imparting stability to the parent ‘layered-layered’ structure. This presentation will provide our recent results in tailoring and improving the structural, compositional and electrochemical properties of structurally-integrated electrode materials that mitigate the voltage fade phenomenon and energy decay of lithium cells.
    17th International Meeting on Lithium Batteries 2014; 06/2014
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    ABSTRACT: The results of a detailed structural investigation on the influence of cooling rates in the synthesis of lithium- and manganese-rich 0.5Li2MnO3·0.5LiCoO2 composite electrode materials, which are of interest for Li-ion battery applications, are presented. It is shown that a low-temperature, intermediate firing step, often employed in cathode synthesis, yields a minor secondary component representing a polydisperse distribution of lattice parameters, not found in the absence of low-temperature treatments. However, regardless of the heating and cooling conditions employed, all samples present two distinctly different local environments as evidenced by X-ray absorption fine structure spectroscopy (XAFS) and nuclear magnetic resonance (NMR) analysis. Transmission electron microscopy (TEM) data show discrete domain structures that are consistent with the XAFS and NMR findings. Furthermore, high resolution synchrotron X-ray diffraction (HR-XRD), as well as the XAFS and NMR data show no discernible differences between sample sets heated in similar fashion and subsequently cooled at different rates. The results contradict recent reports, using X-ray diffraction, that rapidly quenched samples of the same composition are true solid solutions. This apparent discrepancy is assigned, in part, to the inherent nature of conventional diffraction, which firmly elucidates the average long-range structure but does not capture the local domain microstructure of these nanocomposite materials. The combined use of HR-XRD, XAFS, NMR, and TEM data indicate that charge ordering, which is initiated at relatively low temperatures, is the dominant force that produces a nanoscale, inhomogeneous composite structure, irrespective of the cooling rate.
    Chemistry of Materials 05/2014; 26(11):3565–3572. DOI:10.1021/cm501229t · 8.54 Impact Factor
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    ABSTRACT: The commercialization of lithium-ion batteries has intimately changed our lives and enabled portable electronic devices, which has revolutionized communications, entertainment, medicine, and more. After three decades of commercial development, researchers around the world are now pursuing major advances that would allow this technology to power the next generation of light-duty, electric, and hybrid-electric vehicles. If this goal is to be met, concerted advances in safety and cost, as well as cycle-life and energy densities, must be realized through advances in the properties of the highly correlated, but separate, components of lithium-ion energy-storage systems.
    MRS Bulletin 05/2014; 39(05):407-415. DOI:10.1557/mrs.2014.84 · 5.07 Impact Factor
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    ABSTRACT: It is well known that Li-ion cells containing manganese oxide-based positive electrodes and graphite-based negative electrodes suffer accelerated capacity fade, which has been attributed to the deposition of dissolved manganese on the graphite electrodes during electrochemical cell cycling. However, the reasons for the accelerated capacity fade are still unclear. This stems, in part, from conflicting reports of the oxidation state of the manganese species in the negative electrode. In this communication, the oxidation state of manganese deposited on graphite electrodes has been probed by X-ray absorption near edge spectroscopy (XANES). The XANES features confirm, unequivocally, the presence of fully reduced manganese (Mn(0)) on the surface of graphite particles. The deposition of Mn(0) on the graphite negative electrode acts as a starting point to understand the consequent electrochemical behavior of these electrodes; possible reasons for the degradation of cell performance are proposed and discussed.
    Physical Chemistry Chemical Physics 03/2014; 16(15). DOI:10.1039/c4cp00764f · 4.20 Impact Factor
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    ABSTRACT: presented. Three distinct processes have been identified and tracked during extended electrochemical cycling. In addition to the standard intercalation behavior typical of layered metal oxide electrodes, two additional electrochemical phenomena, manifest as hysteresis and continuous voltage fade, are found to be directly related to one another. These two processes are a consequence of the Li2MnO3 component in the electrochemical reaction. This finding, coupled to X-ray absorption data, reveals that lithium and manganese ordering plays a significant role in the voltage degradation mechanisms of high-capacity lithium-and manganese-rich composite electrode structures. In general, all xLi(2)MnO(3)center dot(1-x)LiMO2 (M = Mn, Ni, Co) electrode materials possess this feature and are subject to similar degradation after activation (>4.5 V) and during high voltage (>4.0 V) cycling. The data highlight the practical importance of limiting the amount of Li2MnO3 and/or the extent of activation in these composite structures, thereby providing electrode stability to counteract voltage and hysteresis.
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    224th ECS Meeting; 10/2013
  • 224th ECS Meeting; 10/2013
  • 224th ECS Meeting; 10/2013
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    ABSTRACT: Electrochemical studies demonstrate a strong correlation between the phenomena of hysteresis and voltage fade in lithium- and manganese-rich layered transition-metal oxide electrodes. A mechanism is proposed that entails both the reversible and irreversible migration of transition metal ions. Their reversible migration to a metastable configuration, suggested to involve the occupation of tetrahedral sites in the lithium layer, is manifested as a 1 V hysteresis in site energy for 10–15% of the lithium content. The irreversible migration of the transition metal ions through the metastable ‘hysteresis’ sites to localized and lower energy cubic environments results in the observed voltage fade phenomenon.
    Electrochemistry Communications 10/2013; 33:96–98. DOI:10.1016/j.elecom.2013.04.022 · 4.29 Impact Factor
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    ABSTRACT: This paper reports the results of an initial investigation into the phenomenon of hysteresis in the charge-discharge profile of high-capacity, lithium- and manganese-rich "layered-layered" xLi(2)MnO(3)center dot(1-x)LiMO2 composite cathode structures (M = Mn, Ni, Co) and "layered-layered-spinel" derivatives that are of interest for Li-ion battery applications. In this study, electrochemical measurements, combined with in situ and ex situ X-ray characterization, are used to examine and compare electrochemical and structural processes that occur during charge (lithium extraction) and discharge (lithium insertion) of preconditioned cathodes. Electrochemical measurements of the open-circuit voltage versus lithium content demonstrate a similar to 1 V hysteresis in site energy for approximately 12% of the total lithium content during the early cycles, which is markedly different from the hysteresis commonly observed in other intercalation materials. X-ray absorption data indicate structural differences in the cathode at the same state of charge (i.e., the same lithium content) during lithium insertion and extraction reactions. The data support an intercalation mechanism whereby the total number of lithium ions extracted at the top of charge is not reaccommodated in the structure until low states of charge are reached. The hysteresis in this class of materials is attributed predominantly to an inherent structural reorganization after an electrochemical activation of the Li2MnO3 component that alters the crystallographic site energies.
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    ABSTRACT: Electrochemical studies demonstrate a strong correlation between the phenomena of hysteresis and voltage fade in lithium-and manganese-rich layered transition-metal oxide electrodes. A mechanism is proposed that entails both the reversible and irreversible migration of transition metal ions. Their reversible migration to a metastable configuration, suggested to involve the occupation of tetrahedral sites in the lithium layer, is manifested as a 1 V hysteresis in site energy for 10–15% of the lithium content. The irreversible migration of the transition metal ions through the metastable 'hysteresis' sites to localized and lower energy cubic envi-ronments results in the observed voltage fade phenomenon.
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    ABSTRACT: We have gained insight into the internal degree of atomic disorder in isolated size-selected Fe nanoparticles (NPs) (∼2–6 nm in size) supported on SiO2/Si(111) and Al2O3(0001) from precise measurements of the low-energy (low-E) part of the phonon density of states [PDOS, g(E)] via 57Fe nuclear resonant inelastic x-ray scattering (NRIXS) combined with transmission electron microscopy (TEM) measurements. An intriguing size-dependent trend was observed, namely, an increase of the low-E excess density of phonon states (as compared to the PDOS of bulk bcc Fe) with increasing NP size. This is unexpected, since usually the enhancement of the density of low-E phonon modes is attributed to low-coordinated atoms at the NP surface, whose relative content increases with decreasing NP size due to the increase in the surface-to-volume ratio. Our NPs are covered by a Ti-coating layer, which essentially restores the local neighborhood of surface Fe atoms towards bulk-like coordination, reducing the surface effect. Our data can be qualitatively explained by the existence of low-coordinated Fe atoms located at grain boundaries or other defects with structural disorder in the interior of the large NPs (∼3–6 nm), while our small NPs (∼2 nm) are single grain and, therefore, characterized by a higher degree of structural order. This conclusion is corroborated by the observation of Debye behavior at low energy [g(E) ∼ En with n ∼ 2] for the small NPs, but non-Debye behavior (with n ∼ 1.4) for the large NPs. The PDOS was used to determine thermodynamic properties of the Fe NPs. Finally, our results demonstrate that, in combination with TEM, NRIXS is a suitable technique to investigate atomic disorder/defects in NPs. We anticipate that our findings are universal for similar NPs with bcc structure.
    Physical review. B, Condensed matter 10/2012; 86(16). DOI:10.1103/PhysRevB.86.165406 · 3.66 Impact Factor
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    ABSTRACT: This study presents a systematic detailed experimental and theoretical investigation of the electronic properties of size-controlled free and γ-Al(2)O(3)-supported Pt nanoparticles (NPs) and their evolution with decreasing NP size and adsorbate (H(2)) coverage. A combination of in situ X-ray absorption near-edge structure (XANES) and density functional theory (DFT) calculations revealed changes in the electronic characteristics of the NPs due to size, shape, NP-adsorbate (H(2)) and NP-support interactions. A correlation between the NP size, number of surface atoms and coordination of such atoms, and the maximum hydrogen coverage stabilized at a given temperature is established, with H/Pt ratios exceeding the 1 : 1 ratio previously reported for bulk Pt surfaces.
    Physical Chemistry Chemical Physics 07/2012; 14(33):11766-79. DOI:10.1039/c2cp41928a · 4.20 Impact Factor
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    ABSTRACT: The thermal stability of inverse micelle prepared Pt nanoparticles (NPs) supported on nanocrystalline γ-Al(2)O(3) was monitored in situ under different chemical environments (H(2), O(2), H(2)O) via extended X-ray absorption fine-structure spectroscopy (EXAFS) and ex situ via scanning transmission electron microscopy (STEM). Drastic differences in the stability of identically synthesized NP samples were observed upon exposure to two different pre-treatments. In particular, exposure to O(2) at 400 °C before high temperature annealing in H(2) (800 °C) was found to result in the stabilization of the inverse micelle prepared Pt NPs, reaching a maximum overall size after moderate coarsening of ∼1 nm. Interestingly, when an analogous sample was pre-treated in H(2) at ∼400 °C, a final size of ∼5 nm was reached at 800 °C. The beneficial role of oxygen in the stabilization of small Pt NPs was also observed in situ during annealing treatments in O(2) at 450 °C for several hours. In particular, while NPs of 0.5 ± 0.1 nm initial average size did not display any significant sintering (0.6 ± 0.2 nm final size), an analogous thermal treatment in hydrogen leads to NP coarsening (1.2 ± 0.3 nm). The same sample pre-dosed and annealed in an atmosphere containing water only displayed moderate sintering (0.8 ± 0.3 nm). Our data suggest that PtO(x) species, possibly modifying the NP/support interface, play a role in the stabilization of small Pt NPs. Our study reveals the enhanced thermal stability of inverse micelle prepared Pt NPs and the importance of the sample pre-treatment and annealing environment in the minimization of undesired sintering processes affecting the catalytic performance of nanosized particles.
    Physical Chemistry Chemical Physics 07/2012; 14(32):11457-67. DOI:10.1039/c2cp41339f · 4.20 Impact Factor
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    16th International Meeting on Lithium Batteries, Jeju, Korea; 06/2012
  • APS/CNM/EMC 2012 Users Meeting, Argonne National Laboratory, Argonne, IL; 05/2012
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    ABSTRACT: A new approach to synthesizing high capacity lithium-metal-oxide cathodes for lithium-ion batteries from a Li2MnO3 precursor is described. The technique, which is simple and versatile, can be used to prepare a variety of integrated 'composite' electrode structures, such as 'layered-layered' xLi(2)MnO(3)center dot(1-x)LiMO2, 'layered-spinel' xLi(2)MnO(3)center dot(1-x)LiM2O4, 'layered-rocksalt' xLi(2)MnO(3)center dot(1-x)MO and more complex arrangements, in which M is typically Mn, Ni, and/or Co. Early indications are that electrodes prepared by this method are effective in 1) countering the voltage decay that occurs on cycling 'layered-layered' xLi(2)MnO(3)center dot(1-x)LiMO2 electrodes without compromising capacity, and 2) reducing the extent of electrochemical activation required above 4.5 V on the initial charge. In particular, a 0.5Li(2)MnO(3)center dot 0.5LiMn(0.5)Ni(0.5)O(2) electrode, after activation at 4.6 V, delivers a steady capacity of 245 mAh/g between 4.4 and 2.5 V at 15 mA/g (similar to C/15 rate) with little change to the voltage profile; a first cycle capacity loss of 12%, which is significantly less than usually observed for 'layered-layered' electrodes, has been achieved with a manganese-rich 0.1Li(2)MnO(3)center dot 0.9LiMn(0.50)Ni(0.37)Co(0.13)O(2) electrode. These results have implications for enhancing the performance of the next generation of high-energy lithium-ion batteries. The flexibility of the method and the variation in electrochemical properties of various composite electrode structures and compositions are demonstrated.
    Journal of The Electrochemical Society 01/2012; 159(6):A781. DOI:10.1149/2.080206jes · 2.86 Impact Factor