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Papers by donghan kim

Journal of Physical Chemistry C, Mar 25, 2013

ABSTRACT This paper reports the results of an initial investigation into the phenomenon of hyster... more 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.

Meeting abstracts, Jun 10, 2014

One objective in sodium-ion battery (SIB) research is to increase the capacity of the cathode in ... more One objective in sodium-ion battery (SIB) research is to increase the capacity of the cathode in order to increase the SIB energy densities. Because of the lower nominal Na content in stoichiometric P2 layered i.e. NaxMO2 (x ~ 0.67; M= Mn, Ni, Co), the extractable capacity for the cathode and hence its energy density in a sodium-ion battery (SIB) is generally too low. In previous work, as an effort to up the reversible capacity, we introduced Li for charge balancing and charge ordering stabilization in order to increase the x Na content and its full removal in NaaLib(Ni0.25Mn0.75)Oδ (a+b = 1.2) (1). However, despite the Li addition to form a single phase P2 layered material, the capacity was still too low because of a limited amount (25%) of redox active divalent Ni (~ 100 mAhg-1). Thus, in the present work we increased the redox active Ni(II) content to 0.5 mole stoichiometry (Na/Li = 1.0) in Na1-xLixNi0.5Mn0.5O2 in an attempt to maximize the capacity to a theoretical value of ~ 180 mAhg-1. In so doing we caused the unexpected formation of an intergrowth of P2 and O3 layered phases in this material. Figure 1 shows the HRTEM of the Na0.7Li0.3Ni0.5Mn0.5O2+δsample. It is noted that the domains have an orientation relationship. In fact the intergrowth structures are topotactic layers with nanometer thickness. This would suggest that the crystal structure changes of the O3 – P3 layer during electrochemical cycle may be influenced by the adjacent P2 layer. This type of phase stabilization is a well-known phenomenon in artificially grown heterostructures, and as such may stabilize the composite phase to variable Na content, particularly during cycling. The results of electrochemical high power rate tests in Na half cells have been established. The rate capability of the x=0.3 sample is superior being 140 mAhg-1 specific capacity at a rate of 125 mAg-1. At the same time, the percentage of P2 is the greatest in the x=0.3 composite thus suggesting that the P2 portion of the composite is responsible for the material’s high-rate. The improvement is nearly linear with x value. The x=0 material, which is O3 stacked is the lowest performer; this cathode material is full of phase changes from O3-P3-P’3-O’3(‘ = monoclinic distortion) during cycling, as manifested by a series of voltage humps, plateaus, and kinks that in turn can adversely affect the cycling behavior particularly at high voltages necessary to extract more Na (2). In this presentation we will describe and highlight the synthesis, materials chemistry and its relation to structure-function-property relationships. References (1) D. Kim, et.al., Advanced Energy Materials, 1, 333 (2011) (2) S. Komaba et al., Inorg. Chem. 51, 6211 (2012) Acknowledgments Funding from the Department of Energy under Contract DE-AC02-06CH11357 is gratefully acknowledged. The transmission electron microscopy was accomplished at the Electron Microscopy Center at Argonne National Laboratory, a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The submitted document has been created by UChicago Argonne LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrecovable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

ChemPhysChem, 2017

Thermal stability of Lithium-rich layered oxide with the composition Li(Li1/6Ni1/6Co1/6Mn1/2)O2-x... more Thermal stability of Lithium-rich layered oxide with the composition Li(Li1/6Ni1/6Co1/6Mn1/2)O2-xFx (x=0.00 and 0.05) was evaluated for use as a cathode material in lithium ion batteries. Thermogravimetric analysis, evolved gas analysis, and differential scanning calorimetry showed that upon fluorine doping, degradation of the lithium-rich layered oxides commences at higher temperatures, and the exothermic reaction is suppressed. Hot box tests also revealed that the prismatic cell with the fluorine-doped powder did not explode, while that with undoped one exploded at ~135°C with a sudden temperature increase. X-ray diffraction analysis indicated that fluorine doping imparts the lithium-rich layered oxide with better thermal stability by mitigating the oxygen release at elevated temperatures that causes the exothermic reaction with electrolyte. The origin of the reduced oxygen release from the fluorinated lithium-rich layered oxide was also discussed.

The Journal of Physical Chemistry C, 2013

ABSTRACT This paper reports the results of an initial investigation into the phenomenon of hyster... more 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.

Journal of Power Sources, 2006

Nanocrystalline TiO 2 particles were precipitated from the ethanol solution of titanium isopropox... more Nanocrystalline TiO 2 particles were precipitated from the ethanol solution of titanium isopropoxide (Ti(O-iPr) 4) and H 2 O 2 by refluxing at 80 • C for 48 h. The obtained particles were filtered and dried at 100 • C for 12 h. The dried powder itself, the sample with heating at 400 • C, and the sample with ultrasonically treating were prepared to investigate the effects of post treatments on materials characteristics and electrochemical properties of nanocrystalline TiO 2. The X-ray diffraction patterns of all of the samples were fitted well to the anatase phase. The field emission-TEM image of as-prepared sample shows a uniform spherical morphology with 5 nm particle size and the sample heated at 400 • C shows slightly increased particle size of about 10 nm while maintaining spherical shape. The sample treated with ultrasonic for 5 h or more at room temperature shows high aspect ratio particle shape with an average diameter of 5 nm and a length of 20 nm. According to the results of the electrochemical testing, as-prepared sample, the sample heated at 400 • C for 3 h, and the sample treated with ultrasonic show initial capacities of 270, 310 and 340 mAh g −1 , respectively.

Advanced Energy Materials, 2014

Advanced Energy Materials, 2014

Chemistry of Materials, 2011

We have taken advantage of the element specific nature of X-ray absorption spectroscopy to elucid... more We have taken advantage of the element specific nature of X-ray absorption spectroscopy to elucidate the chemical and structural details of a surface treatment intended for the protection of high-capacity cathode materials. Electrochemical data have shown that surface treatments of 0.5Li 2 MnO 3 •0.5LiCoO 2 (Li 1.2 Mn 0.4 Co 0.4 O 2) with an acidic solution of lithium− nickel-phosphate significantly improves electrode capacity, rate, and cycling stability. XAS data reveal that the surface treatment results in a modification of the composite structure itself, where Ni 2+ cations, intended to be present in a lithium−nickel-phosphate coating, have instead displaced lithium in the transition metal layers of Li 2 MnO 3-like domains within the 0.5Li 2 MnO 3 •0.5LiCoO 2 structure. X-ray diffraction data show the presence of Li 3 PO 4 , suggesting that phosphate ions from the acidic solution are responsible for lithium extraction and nickel insertion with the formation of vacancies and/or manganese reduction for charge compensation. Furthermore, we show that the above effects are not limited to lithium−nickelphosphate treatments. The studies described are consistent with a novel approach for synthesizing and tailoring the structures of high-capacity cathode materials whereby a Li 2 MnO 3 framework is used as a precursor for synthesizing a wide variety of composite metal oxide insertion electrodes for Li-ion battery applications.

Nano Energy, 2016

Abstract Li-rich layered oxides show high reversible capacities (≥250 mA h/g) in rechargeable lit... more Abstract Li-rich layered oxides show high reversible capacities (≥250 mA h/g) in rechargeable lithium-ion batteries. However, their energy densities are considerably reduced upon cycling due to a voltage depression originated from the layered-to-spinel phase transition. In this study, the influence of site-specific Ga-doping on the electrochemical properties of Li-rich layered oxide is investigated. A powder of Li-rich layered oxide is treated in acid, and then annealed with a Ga source at low temperature (300 °C) to insert Ga ions into the powder. Transmission electron microscopy and extended X-ray absorption fine structure analyses indicate that the Ga ions are predominantly doped into the tetrahedral sites of Li2MnO3-like nano-domains in Li-rich layered oxide. Cyclability tests with 18650 full cells clearly reveal that the voltage depression is suppressed by the treatment. Ex-situ X-ray diffraction and first principles calculation results imply that the formation of tetrahedral GaO4 unit in the Li2MnO3-like domain improves the structural stability of Li-rich layered oxide upon cycling.

Electrochemistry Communications, 2013

Abstract An electrochemical study of structurally-integrated xLi 2 MnO 3 •(1 − x )LiMn 0.5 Ni 0.5... more Abstract An electrochemical study of structurally-integrated xLi 2 MnO 3 •(1 − x )LiMn 0.5 Ni 0.5 O 2 ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li 2 MnO 3 -rich end of the Li 2 MnO 3 –LiMn 0.5 Ni 0.5 O 2 tie-line, i.e., for 0.7 ≤ x ≤ 0.95. Excellent performance was observed for x = 0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content ( x ≥ 0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed.

ECS Meeting Abstracts

Composite cathodes with the general composition Li1.05Na0.02Ni0.21Mn0.63O2 (by ICP and XANES) pos... more Composite cathodes with the general composition Li1.05Na0.02Ni0.21Mn0.63O2 (by ICP and XANES) possess chemically-integrated ‘layered-layeredspinel’ [Li2MnO3-Li(Ni0.5Mn0.5)O2]●[LiNi0.5Mn1.5O4]) domains in a composite matrix. In contrast to direct reaction, these materials were synthesized via Na for Li ion-exchange from a layered P2 type Na1.0Li0.2Ni0.25Mn0.75Oy precursor compound [1]. Cathodes formed from these materials have demonstrated nearly 250 mAhg (C15) (Fig. 1) with good cycle life (Fig. 2). Products are nanocrystalline and have structures that show high strain in the layered component indicative of a reaction process that consists of layer gliding, creation of stacking faults, and a release of internal stress in the Li-substitued Na precursor upon ion-exchange. When the powders are heat-treated at 550 °C in air then 5 V spinel (i.e.LiNi0.5Mn1.5O4) is formed at the surface of the composite (TEM) and this component in the composite is observed in the voltage profile (Fig. 1, inset). The majority of the voltage profile, however, consists of the layered component. Interestingly, not all powders show a 5 V spinel character upon heat-treatment (Fig. 3), and this appears to be related to both the type of precursor used and the ion-exchange conditions. Recent evaluation of the Na for Li ion-exchange under various reaction procedures has provided insight into conditions whereby a 5 V spinel component in the composite material forms. With a high-surface area precursor (sol-gel (Fig. 3)) and/or the solvent is water (Fig. 1), then the opening up of the layers is preferred and exposure to the Li reagent appears to be more aggressive. These ‘layered-layered-spinel’ composites actually exhibit improved cycling performance, a higher overall average voltage as compared to ‘layered-layered-spinel’ composites (with the same stochiometry) made from direct reaction in air from Li2CO3 and co-precipitated Ni0.25Mn0.75CO3 (see Fig. 1; see dark blue line versus the thick light blue (cyan) line)). Clearly, these numerous variables have to be understood and optimized in order to make a material with the best cycling properties.

ECS Meeting Abstracts

Recent advances of lithium-ion batteries have made the technology the most viable option for the ... more Recent advances of lithium-ion batteries have made the technology the most viable option for the transportation and grid energy storage applications. Accordingly, a huge increase in the cell production is projected in the near future. However, concerns also have been raised because the stable and economic access to the limited Li resources, which are mostly in remote or politically sensitive areas, is in doubt, and sharp increase in the future cost of Li precursors may become a critical factor that hinders the wide application of the technology. In this context, ambient temperature sodium-ion batteries are attracting more attention, recently, as sodium resource is unlimited and evenly distributed around the world. The Na-ion batteries, furthermore, have similar intercalation chemistry to the Li-ion counterpart, the knowledge and experience obtained from the development of current Liion batteries can be leveraged in the development of Naion batteries to facilitate its commercialization. Indeed, there are increasing volume of reports on materials for Na-ion batteries, and among them, layered transition metal oxides, NaMeO2 (Me = transition metals), are promising as cathode electrodes. However, unlike layered LiMeO2, where LiO6 units of the Li layer form only octahedral configuration, the layered NaMeO2 compounds form versatile structures as Na ions can occupy not only the octahedral site but also a trigonal prismatic site in their Na layer, and hence requires rigorous investigation on their structure-property relationship. For example, NaNi0.5Mn0.5O2, which is one of the promising cathode materials, exhibits complex voltage profile corresponding to its sequential phase transformations ranging from O3to P2-structures upon cycling. Therefore, we present here the lithium substituted Na1-xLixNi0.5Mn0.5O2 cathodes prepared by hightemperature (800C) reaction of Ni0.5Mn0.5(OH)2 precursor with appropriate amounts of Na2CO3 and Li2CO3, and their structure-property relationship for a cathode of Na-ion batteries. It is observed that different ratio of O3-Na phase, P2-Na phase, and O3-Li phase comprises the series of Na1-xLixNi0.5Mn0.5O2 compounds according to the degree of Li substitution, and the rate performance is greatly improved by incorporating Li into NaNi0.5Mn0.5O2. The effect of structural and morphological modification is discussed.

Phys. Chem. Chem. Phys.

Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large c... more Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large capacities.

Electrochemical and Solid State Letters, Sep 1, 2006

Scientific Reports, 2016

The real time detection of quantitative oxygen release from the cathode is performed by in-situ G... more The real time detection of quantitative oxygen release from the cathode is performed by in-situ Gas Chromatography as a tool to not only determine the amount of oxygen release from a lithium-ion cell but also to address the safety concerns. This in-situ gas chromatography technique monitoring the gas evolution during electrochemical reaction presents opportunities to clearly understand the effect of surface modification and predict on the cathode stability. The oxide cathode, 0.5Li 2 MnO 3 •0.5LiNi 0.4 Co 0.2 Mn 0.4 O 2 , surface modified by amorphous cobalt-phosphate nanoparticles (a-CoPO 4) is prepared by a simple co-precipitation reaction followed by a mild heat treatment. The presence of a 40 nm thick a-CoPO 4 coating layer wrapping the oxide powders is confirmed by electron microscopy. The electrochemical measurements reveal that the a-CoPO 4 coated overlithiated layered oxide cathode shows better performances than the pristine counterpart. The enhanced performance of the surface modified oxide is attributed to the uniformly coated CoP -O layer facilitating the suppression of O 2 evolution and offering potential lithium host sites. Further, the formation of a stable SEI layer protecting electrolyte decomposition also contributes to enhanced stabilities with lesser voltage decay. The in-situ gas chromatography technique to study electrode safety offers opportunities to investigate the safety issues of a variety of nanostructured electrodes. Since Li[Li 1/3−2x/3 Ni x Mn 2/3−x/3 ]O 2-type materials were first reported by Dahn and Ohzuku et al., overlithiated layered oxides Li 1+x M 1−x O 2 (M = Ni, Co, Mn, Cr, or combinations thereof) have attracted significant interest as potential alternatives to conventional cobalt and/or nickel-based cathode materials for high energy lithium-ion batteries because of their high capacity (≥200 mAh g −1), low-cost manganese (Mn) element, and high thermal stability in deeply charged states 1-9. The layered-type structural characteristics of the overlithiated layered oxides Li 1+x M 1−x O 2 (hereafter, denoted as OLO) facilitate the occupation of excess lithium ions amidst the transition metal layers 10. The stoichiometric composition of these composite materials is also generally represented as "xLi[Li 1/3 Mn 2/3 ]O 2 •(1− x)LiMO 2 " since the Li[Li 1/3 Mn 2/3 ]O 2 − like region plays a decisive role in evaluating their structural stability and electrochemical characteristics during charge/discharge cycling. This specific notation also offers a convenient method of determining precursor molar concentrations to prepare OLO materials with a targeted stoichiometry. OLO composites are generally represented as a combination of monoclinic (Li[Li 1/3 Mn 2/3 ]O 2 or Li 2 MnO 3) and rhombohedral/trigonal (LiMO 2) phases (or xLi[Li 1/3 Mn 2/3 ]O 2 •(1− x)LiMO 2). The monoclinic and rhombohedral phases are essentially identified by the corresponding major diffraction planes of (001) and (003), respectively, in

Journal of Physical Chemistry C, Mar 25, 2013

ABSTRACT This paper reports the results of an initial investigation into the phenomenon of hyster... more 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.

Meeting abstracts, Jun 10, 2014

One objective in sodium-ion battery (SIB) research is to increase the capacity of the cathode in ... more One objective in sodium-ion battery (SIB) research is to increase the capacity of the cathode in order to increase the SIB energy densities. Because of the lower nominal Na content in stoichiometric P2 layered i.e. NaxMO2 (x ~ 0.67; M= Mn, Ni, Co), the extractable capacity for the cathode and hence its energy density in a sodium-ion battery (SIB) is generally too low. In previous work, as an effort to up the reversible capacity, we introduced Li for charge balancing and charge ordering stabilization in order to increase the x Na content and its full removal in NaaLib(Ni0.25Mn0.75)Oδ (a+b = 1.2) (1). However, despite the Li addition to form a single phase P2 layered material, the capacity was still too low because of a limited amount (25%) of redox active divalent Ni (~ 100 mAhg-1). Thus, in the present work we increased the redox active Ni(II) content to 0.5 mole stoichiometry (Na/Li = 1.0) in Na1-xLixNi0.5Mn0.5O2 in an attempt to maximize the capacity to a theoretical value of ~ 180 mAhg-1. In so doing we caused the unexpected formation of an intergrowth of P2 and O3 layered phases in this material. Figure 1 shows the HRTEM of the Na0.7Li0.3Ni0.5Mn0.5O2+δsample. It is noted that the domains have an orientation relationship. In fact the intergrowth structures are topotactic layers with nanometer thickness. This would suggest that the crystal structure changes of the O3 – P3 layer during electrochemical cycle may be influenced by the adjacent P2 layer. This type of phase stabilization is a well-known phenomenon in artificially grown heterostructures, and as such may stabilize the composite phase to variable Na content, particularly during cycling. The results of electrochemical high power rate tests in Na half cells have been established. The rate capability of the x=0.3 sample is superior being 140 mAhg-1 specific capacity at a rate of 125 mAg-1. At the same time, the percentage of P2 is the greatest in the x=0.3 composite thus suggesting that the P2 portion of the composite is responsible for the material’s high-rate. The improvement is nearly linear with x value. The x=0 material, which is O3 stacked is the lowest performer; this cathode material is full of phase changes from O3-P3-P’3-O’3(‘ = monoclinic distortion) during cycling, as manifested by a series of voltage humps, plateaus, and kinks that in turn can adversely affect the cycling behavior particularly at high voltages necessary to extract more Na (2). In this presentation we will describe and highlight the synthesis, materials chemistry and its relation to structure-function-property relationships. References (1) D. Kim, et.al., Advanced Energy Materials, 1, 333 (2011) (2) S. Komaba et al., Inorg. Chem. 51, 6211 (2012) Acknowledgments Funding from the Department of Energy under Contract DE-AC02-06CH11357 is gratefully acknowledged. The transmission electron microscopy was accomplished at the Electron Microscopy Center at Argonne National Laboratory, a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The submitted document has been created by UChicago Argonne LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrecovable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

ChemPhysChem, 2017

Thermal stability of Lithium-rich layered oxide with the composition Li(Li1/6Ni1/6Co1/6Mn1/2)O2-x... more Thermal stability of Lithium-rich layered oxide with the composition Li(Li1/6Ni1/6Co1/6Mn1/2)O2-xFx (x=0.00 and 0.05) was evaluated for use as a cathode material in lithium ion batteries. Thermogravimetric analysis, evolved gas analysis, and differential scanning calorimetry showed that upon fluorine doping, degradation of the lithium-rich layered oxides commences at higher temperatures, and the exothermic reaction is suppressed. Hot box tests also revealed that the prismatic cell with the fluorine-doped powder did not explode, while that with undoped one exploded at ~135°C with a sudden temperature increase. X-ray diffraction analysis indicated that fluorine doping imparts the lithium-rich layered oxide with better thermal stability by mitigating the oxygen release at elevated temperatures that causes the exothermic reaction with electrolyte. The origin of the reduced oxygen release from the fluorinated lithium-rich layered oxide was also discussed.

The Journal of Physical Chemistry C, 2013

ABSTRACT This paper reports the results of an initial investigation into the phenomenon of hyster... more 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.

Journal of Power Sources, 2006

Nanocrystalline TiO 2 particles were precipitated from the ethanol solution of titanium isopropox... more Nanocrystalline TiO 2 particles were precipitated from the ethanol solution of titanium isopropoxide (Ti(O-iPr) 4) and H 2 O 2 by refluxing at 80 • C for 48 h. The obtained particles were filtered and dried at 100 • C for 12 h. The dried powder itself, the sample with heating at 400 • C, and the sample with ultrasonically treating were prepared to investigate the effects of post treatments on materials characteristics and electrochemical properties of nanocrystalline TiO 2. The X-ray diffraction patterns of all of the samples were fitted well to the anatase phase. The field emission-TEM image of as-prepared sample shows a uniform spherical morphology with 5 nm particle size and the sample heated at 400 • C shows slightly increased particle size of about 10 nm while maintaining spherical shape. The sample treated with ultrasonic for 5 h or more at room temperature shows high aspect ratio particle shape with an average diameter of 5 nm and a length of 20 nm. According to the results of the electrochemical testing, as-prepared sample, the sample heated at 400 • C for 3 h, and the sample treated with ultrasonic show initial capacities of 270, 310 and 340 mAh g −1 , respectively.

Advanced Energy Materials, 2014

Advanced Energy Materials, 2014

Chemistry of Materials, 2011

We have taken advantage of the element specific nature of X-ray absorption spectroscopy to elucid... more We have taken advantage of the element specific nature of X-ray absorption spectroscopy to elucidate the chemical and structural details of a surface treatment intended for the protection of high-capacity cathode materials. Electrochemical data have shown that surface treatments of 0.5Li 2 MnO 3 •0.5LiCoO 2 (Li 1.2 Mn 0.4 Co 0.4 O 2) with an acidic solution of lithium− nickel-phosphate significantly improves electrode capacity, rate, and cycling stability. XAS data reveal that the surface treatment results in a modification of the composite structure itself, where Ni 2+ cations, intended to be present in a lithium−nickel-phosphate coating, have instead displaced lithium in the transition metal layers of Li 2 MnO 3-like domains within the 0.5Li 2 MnO 3 •0.5LiCoO 2 structure. X-ray diffraction data show the presence of Li 3 PO 4 , suggesting that phosphate ions from the acidic solution are responsible for lithium extraction and nickel insertion with the formation of vacancies and/or manganese reduction for charge compensation. Furthermore, we show that the above effects are not limited to lithium−nickelphosphate treatments. The studies described are consistent with a novel approach for synthesizing and tailoring the structures of high-capacity cathode materials whereby a Li 2 MnO 3 framework is used as a precursor for synthesizing a wide variety of composite metal oxide insertion electrodes for Li-ion battery applications.

Nano Energy, 2016

Abstract Li-rich layered oxides show high reversible capacities (≥250 mA h/g) in rechargeable lit... more Abstract Li-rich layered oxides show high reversible capacities (≥250 mA h/g) in rechargeable lithium-ion batteries. However, their energy densities are considerably reduced upon cycling due to a voltage depression originated from the layered-to-spinel phase transition. In this study, the influence of site-specific Ga-doping on the electrochemical properties of Li-rich layered oxide is investigated. A powder of Li-rich layered oxide is treated in acid, and then annealed with a Ga source at low temperature (300 °C) to insert Ga ions into the powder. Transmission electron microscopy and extended X-ray absorption fine structure analyses indicate that the Ga ions are predominantly doped into the tetrahedral sites of Li2MnO3-like nano-domains in Li-rich layered oxide. Cyclability tests with 18650 full cells clearly reveal that the voltage depression is suppressed by the treatment. Ex-situ X-ray diffraction and first principles calculation results imply that the formation of tetrahedral GaO4 unit in the Li2MnO3-like domain improves the structural stability of Li-rich layered oxide upon cycling.

Electrochemistry Communications, 2013

Abstract An electrochemical study of structurally-integrated xLi 2 MnO 3 •(1 − x )LiMn 0.5 Ni 0.5... more Abstract An electrochemical study of structurally-integrated xLi 2 MnO 3 •(1 − x )LiMn 0.5 Ni 0.5 O 2 ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li 2 MnO 3 -rich end of the Li 2 MnO 3 –LiMn 0.5 Ni 0.5 O 2 tie-line, i.e., for 0.7 ≤ x ≤ 0.95. Excellent performance was observed for x = 0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content ( x ≥ 0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed.

ECS Meeting Abstracts

Composite cathodes with the general composition Li1.05Na0.02Ni0.21Mn0.63O2 (by ICP and XANES) pos... more Composite cathodes with the general composition Li1.05Na0.02Ni0.21Mn0.63O2 (by ICP and XANES) possess chemically-integrated ‘layered-layeredspinel’ [Li2MnO3-Li(Ni0.5Mn0.5)O2]●[LiNi0.5Mn1.5O4]) domains in a composite matrix. In contrast to direct reaction, these materials were synthesized via Na for Li ion-exchange from a layered P2 type Na1.0Li0.2Ni0.25Mn0.75Oy precursor compound [1]. Cathodes formed from these materials have demonstrated nearly 250 mAhg (C15) (Fig. 1) with good cycle life (Fig. 2). Products are nanocrystalline and have structures that show high strain in the layered component indicative of a reaction process that consists of layer gliding, creation of stacking faults, and a release of internal stress in the Li-substitued Na precursor upon ion-exchange. When the powders are heat-treated at 550 °C in air then 5 V spinel (i.e.LiNi0.5Mn1.5O4) is formed at the surface of the composite (TEM) and this component in the composite is observed in the voltage profile (Fig. 1, inset). The majority of the voltage profile, however, consists of the layered component. Interestingly, not all powders show a 5 V spinel character upon heat-treatment (Fig. 3), and this appears to be related to both the type of precursor used and the ion-exchange conditions. Recent evaluation of the Na for Li ion-exchange under various reaction procedures has provided insight into conditions whereby a 5 V spinel component in the composite material forms. With a high-surface area precursor (sol-gel (Fig. 3)) and/or the solvent is water (Fig. 1), then the opening up of the layers is preferred and exposure to the Li reagent appears to be more aggressive. These ‘layered-layered-spinel’ composites actually exhibit improved cycling performance, a higher overall average voltage as compared to ‘layered-layered-spinel’ composites (with the same stochiometry) made from direct reaction in air from Li2CO3 and co-precipitated Ni0.25Mn0.75CO3 (see Fig. 1; see dark blue line versus the thick light blue (cyan) line)). Clearly, these numerous variables have to be understood and optimized in order to make a material with the best cycling properties.

ECS Meeting Abstracts

Recent advances of lithium-ion batteries have made the technology the most viable option for the ... more Recent advances of lithium-ion batteries have made the technology the most viable option for the transportation and grid energy storage applications. Accordingly, a huge increase in the cell production is projected in the near future. However, concerns also have been raised because the stable and economic access to the limited Li resources, which are mostly in remote or politically sensitive areas, is in doubt, and sharp increase in the future cost of Li precursors may become a critical factor that hinders the wide application of the technology. In this context, ambient temperature sodium-ion batteries are attracting more attention, recently, as sodium resource is unlimited and evenly distributed around the world. The Na-ion batteries, furthermore, have similar intercalation chemistry to the Li-ion counterpart, the knowledge and experience obtained from the development of current Liion batteries can be leveraged in the development of Naion batteries to facilitate its commercialization. Indeed, there are increasing volume of reports on materials for Na-ion batteries, and among them, layered transition metal oxides, NaMeO2 (Me = transition metals), are promising as cathode electrodes. However, unlike layered LiMeO2, where LiO6 units of the Li layer form only octahedral configuration, the layered NaMeO2 compounds form versatile structures as Na ions can occupy not only the octahedral site but also a trigonal prismatic site in their Na layer, and hence requires rigorous investigation on their structure-property relationship. For example, NaNi0.5Mn0.5O2, which is one of the promising cathode materials, exhibits complex voltage profile corresponding to its sequential phase transformations ranging from O3to P2-structures upon cycling. Therefore, we present here the lithium substituted Na1-xLixNi0.5Mn0.5O2 cathodes prepared by hightemperature (800C) reaction of Ni0.5Mn0.5(OH)2 precursor with appropriate amounts of Na2CO3 and Li2CO3, and their structure-property relationship for a cathode of Na-ion batteries. It is observed that different ratio of O3-Na phase, P2-Na phase, and O3-Li phase comprises the series of Na1-xLixNi0.5Mn0.5O2 compounds according to the degree of Li substitution, and the rate performance is greatly improved by incorporating Li into NaNi0.5Mn0.5O2. The effect of structural and morphological modification is discussed.

Phys. Chem. Chem. Phys.

Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large c... more Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large capacities.

Electrochemical and Solid State Letters, Sep 1, 2006

Scientific Reports, 2016

The real time detection of quantitative oxygen release from the cathode is performed by in-situ G... more The real time detection of quantitative oxygen release from the cathode is performed by in-situ Gas Chromatography as a tool to not only determine the amount of oxygen release from a lithium-ion cell but also to address the safety concerns. This in-situ gas chromatography technique monitoring the gas evolution during electrochemical reaction presents opportunities to clearly understand the effect of surface modification and predict on the cathode stability. The oxide cathode, 0.5Li 2 MnO 3 •0.5LiNi 0.4 Co 0.2 Mn 0.4 O 2 , surface modified by amorphous cobalt-phosphate nanoparticles (a-CoPO 4) is prepared by a simple co-precipitation reaction followed by a mild heat treatment. The presence of a 40 nm thick a-CoPO 4 coating layer wrapping the oxide powders is confirmed by electron microscopy. The electrochemical measurements reveal that the a-CoPO 4 coated overlithiated layered oxide cathode shows better performances than the pristine counterpart. The enhanced performance of the surface modified oxide is attributed to the uniformly coated CoP -O layer facilitating the suppression of O 2 evolution and offering potential lithium host sites. Further, the formation of a stable SEI layer protecting electrolyte decomposition also contributes to enhanced stabilities with lesser voltage decay. The in-situ gas chromatography technique to study electrode safety offers opportunities to investigate the safety issues of a variety of nanostructured electrodes. Since Li[Li 1/3−2x/3 Ni x Mn 2/3−x/3 ]O 2-type materials were first reported by Dahn and Ohzuku et al., overlithiated layered oxides Li 1+x M 1−x O 2 (M = Ni, Co, Mn, Cr, or combinations thereof) have attracted significant interest as potential alternatives to conventional cobalt and/or nickel-based cathode materials for high energy lithium-ion batteries because of their high capacity (≥200 mAh g −1), low-cost manganese (Mn) element, and high thermal stability in deeply charged states 1-9. The layered-type structural characteristics of the overlithiated layered oxides Li 1+x M 1−x O 2 (hereafter, denoted as OLO) facilitate the occupation of excess lithium ions amidst the transition metal layers 10. The stoichiometric composition of these composite materials is also generally represented as "xLi[Li 1/3 Mn 2/3 ]O 2 •(1− x)LiMO 2 " since the Li[Li 1/3 Mn 2/3 ]O 2 − like region plays a decisive role in evaluating their structural stability and electrochemical characteristics during charge/discharge cycling. This specific notation also offers a convenient method of determining precursor molar concentrations to prepare OLO materials with a targeted stoichiometry. OLO composites are generally represented as a combination of monoclinic (Li[Li 1/3 Mn 2/3 ]O 2 or Li 2 MnO 3) and rhombohedral/trigonal (LiMO 2) phases (or xLi[Li 1/3 Mn 2/3 ]O 2 •(1− x)LiMO 2). The monoclinic and rhombohedral phases are essentially identified by the corresponding major diffraction planes of (001) and (003), respectively, in