{ "sample": "02-acs-excluded-blocks", "threshold": 0.35, "cache_status": { "exists": true, "usable": true, "reason": "cache_page_count_ok", "expected_pdf_pages": 8, "cached_docling_pages": 8, "cached_docling_max_page": 8, "formula_enrichment_enabled": false, "formula_enrichment_scale": 3.0, "formula_nodes": 0, "recognized_formula_nodes": 0 }, "candidate_blocks": [ { "page": 1, "page_count": 8, "bbox": [ 228.08, 504.04, 389.46, 608.65 ], "text": "of cations, and phase stability upon lithium extraction and insertion. Structurally, these layered structures are often composed of the intergrowth of LiMO2 R3m and Li2MO3 C2/m phases.7,13 Nevertheless, it is not clear how each individual phase affects the per- formance of these materials. Further, the cations are not necessarily uniformly distrib- uted at nanometer scale. Recently, Gu et al.7", "category": "front_summary", "coverage": 0.034, "words": 62 }, { "page": 1, "page_count": 8, "bbox": [ 228.08, 611.65, 389.46, 716.25 ], "text": "reported a nanoscale phase separation caused by the preferential segregation of Ni atoms on the particle surface and bound- aries in the layered lithium nickel manga- nese oxide cathode materials. They further predicted that the formation of the Ni-rich surface layer would affect the diffusion of Li ions, and thus possibly have an impact on the rate performance of this cathode.7", "category": "front_summary", "coverage": 0.0, "words": 63 }, { "page": 1, "page_count": 8, "bbox": [ 51.82, 504.05, 213.17, 740.12 ], "text": "i-ion batteries have been widely used as an energy storage device for mod- ern electric devices, grid application, and renewable energy.1\u00017 Cathodes with a layered structure such as Li1.2Ni0.2Mn0.6O2 (LNMO) andLi1.2Ni0.1Mn0.525Co0.175O2(LNMCO) can provide much higher capacity than the traditional cathode materials such as LiCoO2 and LiMn2O4 spinel.8\u000112 Therefore, these layered structures are one of the most pro- mising candidates for future heavy duty applications such as hybrid and electric vehicles. However, the application of these materials faces three fundamental chal- lenges: (1) voltage instability, (2) capacity fad- ing, and (3) slow charge/discharge rate. Collective experimental observations indicate these challenges are closely related to the structural characteristics of these materials, suchasthecrystalstructure,spatialdistribution", "category": "front_summary", "coverage": 0.0, "words": 121 }, { "page": 2, "page_count": 8, "bbox": [ 64.74, 64.44, 266.01, 426.44 ], "text": "the release of oxygen and Liþ(removal of the Li2O part).2 However, the effect of the removal of the Li2O part on the lattice stability has not been established. The layered-to-spinel transformation has long been postulated as an important factor to account for the capacity fading and poor rate performance of the layered structure materials.2,9,10,13\u000117 However, it is not clear where the spinel phase nucleates and how the spinel phase grows on the consumption of the layered structured phase. The answers to these ques- tions critically depends on the atomic level structural and chemical analysis of materials and their correlation with the cyclic performance of the battery. On the basis of atomic scale Z-contrast imaging, Xu et al. have found that the migration of transition metal (TM) cations into the Li layers can initiate the formation of spinel near the particle surface region.15 Apparently, a far more detailed microscopic understanding of the phase transformation characteristics in these layered structures will lead to tailoring of the materials struc- ture for better electrochemical performance. In this paper, we use aberration-corrected scanning/ transmission electron microscopy (S/TEM) imaging and energy dispersive X-ray spectroscopy (EDS) to probe the atomic structure of the layer structured cathode materials before and after high voltage cycling.18 The STEM high angle annular dark field (HAADF) detector collects all the incoherently scattered electrons. The image intensity of each atomic column reflects the average atomic number of each atomic column (∼Z1.5", "category": "scientific_body", "coverage": 0.04, "words": 254 }, { "page": 2, "page_count": 8, "bbox": [ 64.74, 425.75, 266.0, 585.58 ], "text": "to Z1.8),18 which is therefore termed as Z-contrast imaging and is chemical sensitive, allowing us to intuitively interpret the atomic structure changes di- rectly. We found that both LNMO and LNMCO layer structured cathodes are a random mixing of LiMO2 R3m and Li2MO3 C2/m phases, with both phases able to coexist in a single nanoparticle. Extraction of Li from the lattice of the layer-structured material leads to lattice break down, crack and porosity formation, and nucleation and growth of spinel. Mechanisti- cally, the formation of spinel from LiMO2 R3m is distinctively different from the transition of Li2MO3 C2/m to spinel.", "category": "scientific_body", "coverage": 0.01, "words": 105 }, { "page": 2, "page_count": 8, "bbox": [ 283.92, 436.81, 485.19, 744.66 ], "text": "of 82.8%. However, the material shows faster capacity fading after 100 cycles, which would be ascribed to the spinel transformation, lattice break down, and possi- ble deteriorated electrode/electrolyte interface that hampers the reversible lithium ion intercalation/ deintercalation.19\u000121 The AlF3-coated-LNMCO exhib- ited higher capacity in most of the cycling range and the fast capacity decay is delayed to after ∼150 cycles. This means that the AlF3 surface coating can partially relieve the formation of spinel phase in the layered structure, but it will not totally stop the spinel forma- tion. The detailed voltage/capacity curves of an LNMO cathode at the first (C/10), and subsequent cycles at C/3 are presented in Figure 1b. The initial charge profile is accompanied with an irreversible voltage plateau at ca. 4.4\u00014.6 V for oxidation beyond the formal oxidation potential of Ni2þ to Ni4þ. The voltage plateaus have been assigned to an irreversible loss of oxygen from the lattice based on differential electrochemical mass spectrometry (DEMS) results2,19 and in situ X-ray diffraction studies.22 During the oxygen loss plateau, the Li2MnO3 component is activated and thus the material could deliver high discharge capacity during the subsequent discharge process. However, the ex- tensive removal of the lithium ion and oxygen evolu- tion results in the instability of the electrode structure,", "category": "scientific_body", "coverage": 0.945, "words": 221 }, { "page": 2, "page_count": 8, "bbox": [ 64.74, 614.49, 266.02, 745.0 ], "text": "Electrochemical Performance Measurements. Cycling per- formance and the corresponding charge/discharge profile evolution of the lithium-rich cathode material LNMO and AlF3-coated LNMCO are shown in Figure 1. During formation cycles at C/10, these electrode ma- terials could deliver a capacity higher than 250 mAh g\u00011. After three formation cycles, despite increasing the current density to C/3 and lowering the charge cutoff voltage to 4.6 V, a capacity of 220 mAh g\u00011 could still be achieved for LNMO. LNMO only shows gradual capa- city decay in the first 100 cycles, with capacity retention", "category": "scientific_body", "coverage": 1.0, "words": 96 }, { "page": 3, "page_count": 8, "bbox": [ 64.74, 364.52, 266.06, 745.05 ], "text": "involving lattice breakdown and phase transformation from layered to spinel during initial activation and subsequent cycling.15,23 This structural transforma- tion leads to a layered-spinel intergrowth structure and the evolution of the redox reaction at ca. 3.2 V region, as observed for 0.7Li2MnO3 3 0.3LiNi1/3Co1/3- Mn1/3O2.23 As a result, the discharge profile shows obvious voltage decay with the increase in cycle numbers. The midpoint voltage (MPV) of discharge decreases from 3.57 V at the fourth to 3.37 V at 100 cycles. Similar voltage/capacity curves are observed for LNMCO. The voltage profile decay, which signals the layered-to-spinel transformation, is further char- acterized by comparing pristine and cycled samples using S/TEM. Structure of the Pristine Materials. The layered LNMO is a nanocomposite composed of the intergrowth of LiMO2 R3m and Li2MO3 C2/m phases (M denotes transiton metal cations) as shown in Figure 2 and Figure 3.7,13 The pristine LNMO maintains a layered structure with the stacking sequence of TM/O/Li/O as illustrated in Figure 2a. There is ∼10% (or less) Ni/Li disorder;Ni replaces 10% of the the Li ions in the Li layer and Li replaces 10% of the transition metal ions in the TM layer for the R3m phase.24\u000126 Both Li and TM cations are in octahedral sites. As shown by the Z-contrast images in Figure 2, the pristine LNMO cathode shows nanoplate-like morphology with open Li fast-diffusion channels. The Li channel direction is labeled with a red arrow in Figure 2a. The magnified region in Figure 2b shows that the Li-diffusion chan- nels are very dark in the Z-contrast image. The atomic", "category": "scientific_body", "coverage": 0.933, "words": 288 }, { "page": 4, "page_count": 8, "bbox": [ 283.92, 365.26, 485.19, 708.94 ], "text": "ions also show visible contrast. The Li layer in the pristine LNMO nanoparticle shows no visible contrast as illustrated in Figures 2c and 5d. However, following the charge/discharge cycles, the atomic columns in the Li layers both at the surface and in the bulk regions becomes visible, indicating the TM ions have migrated to the Li layer during the cyclic charge/discharge. As shown clearly in Figure 5d, the intensity of atomic columns in the Li layer at the surface region is stronger than that in the inner part of the particle in the cyclic charged/discharged sample. This observation likely indicates that the TM ions migration into the Li layer starts from the surface of the LNMO nanoparticles and extends to the inner region of the particle with the progression of the charge/discharge cycle. This con- clusion is consistently supported by the observation reported by Xu et al.15 They noticed that after high voltage cycling, the migration of the TM ions to the Li layers leads to the layered-to-spinel phase transforma- tion, which only occurs at the very surface area of the particle. Essentially, they found that after 10 cycles, a few unit cells of spinel is formed at the surface region. For our present observation, the battery was charged/ discharged to 100 cycles. Therefore the spinel forma- tion extended to the inner part of the particle. Crystal- lographically, the transformation from layered R3m structure to spinel involves the migration of TM cations into the Li site, movement of Li cations into the tetrahedral sites, and a distortion of oxygen lattices.9", "category": "scientific_body", "coverage": 0.981, "words": 264 }, { "page": 5, "page_count": 8, "bbox": [ 64.74, 364.13, 266.03, 480.7 ], "text": "Associated with these structural transformation char- acteristics, the spinels formed within a parental layered particle show features of a mosaic structure as seen in Figure 4. Formation of spinel destroyed the layered characteristics of the R3m phase, which resulted in poor rate performance due to the block of the Li fast diffusion channel. This phase transformation is one of the primary factors contributing to the capacity fading and poor rate performance of these cathode materials.15", "category": "scientific_body", "coverage": 0.875, "words": 76 }, { "page": 5, "page_count": 8, "bbox": [ 64.74, 483.69, 266.01, 744.71 ], "text": "Ni concentration appears to play a role on the layered structure to spinel transformation.27 Gu et al. used STEM and EDS mapping to analyze the composi- tion and phase distribution in pristine LNMO.7 The Li2MO3 phase contains Ni in most regions (∼20% Ni/ (Ni þ Mn)) atomic ratio).7 Hence, LNMO cannot be simply written as 0.5LiNi0.5Mn0.5O2 3 0.5Li2MnO3. The average Ni/(Ni þ Mn) ratio in the LiMO2 phase should be less than 50% as in LiNi0.5Mn0.5O2. The decreased Ni content may be one of the reasons that the LiMO2 R3m phase transformed to spinel after cycling.27 A very similar phase transformation process has also been identified in the LNMCO cathode after high voltage cycling. Disoriented Spinel Domains Generation, Porosity and Crack Formation. In the cycled sample, spinel particles that are typically several nanometers show random orientation and are often found to be dispersed in an amorphous region as representatively shown in Figure 6. Most of the spinel domains are distributed with nanometer sizes within the whole particle (not only in the sur- face layer, but also in the bulk crystal) in Figure 6a.", "category": "scientific_body", "coverage": 0.952, "words": 191 }, { "page": 6, "page_count": 8, "bbox": [ 64.74, 66.26, 265.99, 158.96 ], "text": "circled in red) and [111] (diffraction spots circled in blue) zone axis. The amorphous ring patterns indicate that amorphous regions must exist in this region in the TEM image in Figure 7a. A higher magnification TEM image is shown in Figure 7c, where the lattice shows a high degree of distortion in the phase boundaries of crystals with different orientations as labeled in red. In the meantime, porosity formation has been detected", "category": "scientific_body", "coverage": 1.0, "words": 72 }, { "page": 6, "page_count": 8, "bbox": [ 283.92, 66.26, 485.23, 554.37 ], "text": "in both the LNMO and LNMCO cathode nanoparticles. As shown in Figure 8, simultaneously taken Z-contrast and bright field images have been used to map the porosity formation in the cathode nanoparticles after cycling. Pores with sizes varying from 2 to15 nm are distributed evenly in the LNMO nanoparticle (Figure 8a,b). In the Z-contrast image, the formation of pores would reduce the average atomic number of these regions, resulting in a darker contrast on the pore region. On the other hand, in the bright field image, the pore region shows up with brighter contrast according to the mass\u0001thickness contrast theory. A detailed comparison of the contrast shown in the simulta- neously acquired Z-contrast and bright field images is presented in Figure 8c,d. In addition, the formation of pores in the cycled LNMCO has also been seen and mapped out using EDS mapping in Figure 8e. The porosity formation may be related to the strain generation due to removal of Li or O upon cycling and collapse of the crystal lattices.28 The surface of the LNCMO particles is covered with a uniformly thin layer of carbon-containing solid electrolyte layer as shown by the C map. In addition, the signatures of O, Mn, Ni, and Co are all observed by EDS mapping, confirming that this particle is truly the cathode nanoparticle. Last but not least, crack formation has been found to exist as evidenced by the results of S/TEM imaging and EDS mapping in the cycled LNMCO samples in Figure 9. A comparison of the STEM Z-contrast image of the pristine LNMCO sample is shown in Figure S1 in the Supporting Information, which exhibits no such cracks. The cracks are labeled with red arrows in the STEM Z-contrast image in Figure 9. Crack formation has been reported by early researchers28 and believed to origi- nate from the large strain generated by removal of the cations during charging. As discussed above, the pris- tine cathode also contains the cation-ordered Li2MO3 phase. It has been reported that Li2MO3 can be acti- vated and would release oxygen and lithium ions (in the form of Li2O) during high voltage cycling.2,14", "category": "scientific_body", "coverage": 0.986, "words": 364 }, { "page": 7, "page_count": 8, "bbox": [ 283.92, 66.26, 485.22, 206.76 ], "text": "surface coating or the chemical additive is not clear. Typically, in the present work, a thin layer of AlF3 coating on the surface of the LNMCO leads to a better capacity retention as illustrated in Figure 1. The surface layer coating may relieve the forma- tion of spinel in the R3m phase. However, it cannot stop the formation of spinel in the C2/m, where the phase transformation proceeds through nuclea- tion and growth process. More systematic work is needed to fully understand the mechanism of the surface coating on the lattice stability of cathode materials.", "category": "scientific_body", "coverage": 0.889, "words": 94 }, { "page": 7, "page_count": 8, "bbox": [ 283.92, 234.13, 485.24, 530.02 ], "text": "The LNMO and LNMCO layered cathode materials consist of an intergrowth of LiMO2 R3m and Li2MO3 C2/m phases. Migration of TM cations into the Li layer initiated the transformation to spinel for the R3m phase region during cycling. However, the Li2MO3 phase releases the Li2O portion during high voltage cycling, resulting in the breakdown of the crystal lattices. As a result, lattice distortion/ amorphization, crack formation, and porosity forma- tion are clearly observed as evidenced by the S/TEM imaging and EDS mapping. In this case, the layered- to-spinel phase transformation follows a nucleation and growth mechanism, which yields spinel clusters with different orientations in the distorted/amor- phized lattices. Coatings of the surface of cathode particles with AlF3 may delay the formation of spinel in the R3m phase. Nevertheless, it cannot stop the formation of spinel in the C2/m phase, where the phase transformation proceeds through nucleation and growth of spinel domains inside the broken lattice upon cycling. The structural changes of the layered structures observed in this work are believed to be the main factors influencing the capacity fading and poor rate performance of these layer- structured cathode materials.", "category": "scientific_body", "coverage": 0.835, "words": 192 }, { "page": 7, "page_count": 8, "bbox": [ 64.74, 294.05, 266.03, 530.19 ], "text": "and lattice break-up in the LiMO2 R3m phase region due to the Liþ removal during high voltage cycling. The overall phase transformation characteristic of the layer structured materials is schematically shown in Figure 10. The layered-to-spinel transformation process is achieved either by cation migration in the stable R3m phase region, or the nucleation and growth mechan- ism in an polycrystalline/amorphous matrix in the C2/m phase region after lattice break-up upon cyclic charge/discharge. The layered-to-spinel transforma- tion, lattice break-up, and porosity formation are strik- ing observations, which explain the loss of capacity during cycling in the Li-ion batteries. A lot of research effort has been made intending to stabilize the struc- ture of the cathode materials during the cyclic charge/ discharge. Coating of a surface layer on the particles of the cathode and modification of the chemistry of the cathode materials appear to prevent such a phase transformation in some way. However, the exact mechanism of the stabilization of the structure by the", "category": "scientific_body", "coverage": 0.826, "words": 171 }, { "page": 7, "page_count": 8, "bbox": [ 283.92, 575.48, 485.31, 744.77 ], "text": "dissolved in ethyl carbonate (EC) and dimethyl carbonate (DMC) (1:2 in volume) as electrolyte in an argon-filled MBraun glovebox. The electrochemical performance tests were per- formed galvanostatically between 2.0 and 4.6 V at C/3 (1C = 250 mA g\u00011) after three formation cycles at C/10 between 2.0 and 4.8 V on an Arbin BT-2000 battery tester at a controlled temperature of 30 \u0002C. Microstructures of the freshly prepared and electrochemically tested materials were analyzed using a probe-aberration corrected FEI Titan STEM and image-corrected FEIETEMat300 kV. The EDSmapswereacquired usinga 200 kV FEI Tecnai Osiris S/TEM microscope equipped with a FEI Super-X detector system, which combines four symmetrically placed Si drift detectors (SDD) around the objective lens with a high- brightness gun. This combination provides enhanced generation of X-rays and together with high detector efficiency results in a faster mapping of larger areas in EDS maps. In this work, the EDS maps with 512 \u0003 512 pixels are obtained within less than 5 min. This helps to reduce specimen damage as the beam is not parked on any specimen region for a long period of time. The atomic", "category": "scientific_body", "coverage": 0.881, "words": 198 }, { "page": 7, "page_count": 8, "bbox": [ 64.74, 588.4, 266.01, 745.51 ], "text": "The LNMO and LNMCO were synthesized via a coprecipita- tion method.29 Nickel sulfate hexahydrate (NiSO4.6H2O), man- ganese sulfate monohydrate (MnSO4.H2O), sodium hydroxide (NaOH), and ammonium hydroxide (NH3.H2O) were used as the starting materials to prepare Ni0.25Mn0.75(OH)2 or Ni0.125Mn0.656- Co0.219(OH)2 precursor. The precursors were well mixed with Li2CO3 and then calcined at 900 \u0002C for 15 h to get the cathode materials. For electrochemical measurement, the cathode elec- trodes were prepared by coating a mixture containing 80% Li[Li0.2Ni0.2Mn0.6]O2, 10% super P (from Timcal), and 10% poly- (vinylidene fluoride) (PVDF, Kynar HSV900, Arkema Inc.) binder onto Al current collector foil. After drying, the electrodes were punched into disks with ø = 1.27 cm. The active material loading was 3\u00015 mg cm\u00012. Coin cells were assembled with the cathode electrodes as-prepared, metallic lithium foil as counter elec- trode, Celgard K1640 monolayer polyethylene (PE) membrane as separator, and 1 M lithium hexafluorophosphate (LiPF6)", "category": "scientific_body", "coverage": 0.926, "words": 166 }, { "page": 8, "page_count": 8, "bbox": [ 64.74, 133.21, 266.12, 311.29 ], "text": "Acknowledgment. The research described in this paper is part of the Chemical Imaging Initiative at Pacific North- west National Laboratory (PNNL). It was conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle under Contract DE-AC05-76RLO1830 for the U.S. Department of Energy (DOE). The work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a na- tional scientific user facility sponsored by DOE's Office of Bio- logical and Environmental Research and located at PNNL. J. Zhang and J. Xiao would like to acknowledge the support of the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of DOE under Contract No. DE-AC02-05CH11231, Subcontract No. 18769 under the Batteries for Advanced Transportation Technologies (BATT) program. J. Liu would like to acknowledge the support of the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award KC020105-FWP12152. I. Belharouak and K. Amine would like to acknowledge the support from DOE's Freedom CAR and Vehicle Technologies Office.", "category": "back_matter", "coverage": 0.0, "words": 184 }, { "page": 8, "page_count": 8, "bbox": [ 64.74, 315.7, 266.13, 350.35 ], "text": "Supporting Information Available: The Supporting Informa- tion includes STEM image of the prestine LNMCO cathode nano- particles. No cracks are visible in the pristine particles. This material is available free of charge via the Internet at http://pubs.acs.org.", "category": "back_matter", "coverage": 0.0, "words": 38 } ], "low_coverage_blocks": [ { "page": 1, "page_count": 8, "bbox": [ 228.08, 504.04, 389.46, 608.65 ], "text": "of cations, and phase stability upon lithium extraction and insertion. Structurally, these layered structures are often composed of the intergrowth of LiMO2 R3m and Li2MO3 C2/m phases.7,13 Nevertheless, it is not clear how each individual phase affects the per- formance of these materials. Further, the cations are not necessarily uniformly distrib- uted at nanometer scale. Recently, Gu et al.7", "category": "front_summary", "coverage": 0.034, "words": 62 }, { "page": 1, "page_count": 8, "bbox": [ 228.08, 611.65, 389.46, 716.25 ], "text": "reported a nanoscale phase separation caused by the preferential segregation of Ni atoms on the particle surface and bound- aries in the layered lithium nickel manga- nese oxide cathode materials. They further predicted that the formation of the Ni-rich surface layer would affect the diffusion of Li ions, and thus possibly have an impact on the rate performance of this cathode.7", "category": "front_summary", "coverage": 0.0, "words": 63 }, { "page": 1, "page_count": 8, "bbox": [ 51.82, 504.05, 213.17, 740.12 ], "text": "i-ion batteries have been widely used as an energy storage device for mod- ern electric devices, grid application, and renewable energy.1\u00017 Cathodes with a layered structure such as Li1.2Ni0.2Mn0.6O2 (LNMO) andLi1.2Ni0.1Mn0.525Co0.175O2(LNMCO) can provide much higher capacity than the traditional cathode materials such as LiCoO2 and LiMn2O4 spinel.8\u000112 Therefore, these layered structures are one of the most pro- mising candidates for future heavy duty applications such as hybrid and electric vehicles. However, the application of these materials faces three fundamental chal- lenges: (1) voltage instability, (2) capacity fad- ing, and (3) slow charge/discharge rate. Collective experimental observations indicate these challenges are closely related to the structural characteristics of these materials, suchasthecrystalstructure,spatialdistribution", "category": "front_summary", "coverage": 0.0, "words": 121 }, { "page": 2, "page_count": 8, "bbox": [ 64.74, 64.44, 266.01, 426.44 ], "text": "the release of oxygen and Liþ(removal of the Li2O part).2 However, the effect of the removal of the Li2O part on the lattice stability has not been established. The layered-to-spinel transformation has long been postulated as an important factor to account for the capacity fading and poor rate performance of the layered structure materials.2,9,10,13\u000117 However, it is not clear where the spinel phase nucleates and how the spinel phase grows on the consumption of the layered structured phase. The answers to these ques- tions critically depends on the atomic level structural and chemical analysis of materials and their correlation with the cyclic performance of the battery. On the basis of atomic scale Z-contrast imaging, Xu et al. have found that the migration of transition metal (TM) cations into the Li layers can initiate the formation of spinel near the particle surface region.15 Apparently, a far more detailed microscopic understanding of the phase transformation characteristics in these layered structures will lead to tailoring of the materials struc- ture for better electrochemical performance. In this paper, we use aberration-corrected scanning/ transmission electron microscopy (S/TEM) imaging and energy dispersive X-ray spectroscopy (EDS) to probe the atomic structure of the layer structured cathode materials before and after high voltage cycling.18 The STEM high angle annular dark field (HAADF) detector collects all the incoherently scattered electrons. The image intensity of each atomic column reflects the average atomic number of each atomic column (∼Z1.5", "category": "scientific_body", "coverage": 0.04, "words": 254 }, { "page": 2, "page_count": 8, "bbox": [ 64.74, 425.75, 266.0, 585.58 ], "text": "to Z1.8),18 which is therefore termed as Z-contrast imaging and is chemical sensitive, allowing us to intuitively interpret the atomic structure changes di- rectly. We found that both LNMO and LNMCO layer structured cathodes are a random mixing of LiMO2 R3m and Li2MO3 C2/m phases, with both phases able to coexist in a single nanoparticle. Extraction of Li from the lattice of the layer-structured material leads to lattice break down, crack and porosity formation, and nucleation and growth of spinel. Mechanisti- cally, the formation of spinel from LiMO2 R3m is distinctively different from the transition of Li2MO3 C2/m to spinel.", "category": "scientific_body", "coverage": 0.01, "words": 105 }, { "page": 8, "page_count": 8, "bbox": [ 64.74, 133.21, 266.12, 311.29 ], "text": "Acknowledgment. The research described in this paper is part of the Chemical Imaging Initiative at Pacific North- west National Laboratory (PNNL). It was conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle under Contract DE-AC05-76RLO1830 for the U.S. Department of Energy (DOE). The work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a na- tional scientific user facility sponsored by DOE's Office of Bio- logical and Environmental Research and located at PNNL. J. Zhang and J. Xiao would like to acknowledge the support of the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of DOE under Contract No. DE-AC02-05CH11231, Subcontract No. 18769 under the Batteries for Advanced Transportation Technologies (BATT) program. J. Liu would like to acknowledge the support of the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award KC020105-FWP12152. I. Belharouak and K. Amine would like to acknowledge the support from DOE's Freedom CAR and Vehicle Technologies Office.", "category": "back_matter", "coverage": 0.0, "words": 184 }, { "page": 8, "page_count": 8, "bbox": [ 64.74, 315.7, 266.13, 350.35 ], "text": "Supporting Information Available: The Supporting Informa- tion includes STEM image of the prestine LNMCO cathode nano- particles. No cracks are visible in the pristine particles. This material is available free of charge via the Internet at http://pubs.acs.org.", "category": "back_matter", "coverage": 0.0, "words": 38 } ], "high_risk_body_missing_blocks": [ { "page": 2, "page_count": 8, "bbox": [ 64.74, 64.44, 266.01, 426.44 ], "text": "the release of oxygen and Liþ(removal of the Li2O part).2 However, the effect of the removal of the Li2O part on the lattice stability has not been established. The layered-to-spinel transformation has long been postulated as an important factor to account for the capacity fading and poor rate performance of the layered structure materials.2,9,10,13\u000117 However, it is not clear where the spinel phase nucleates and how the spinel phase grows on the consumption of the layered structured phase. The answers to these ques- tions critically depends on the atomic level structural and chemical analysis of materials and their correlation with the cyclic performance of the battery. On the basis of atomic scale Z-contrast imaging, Xu et al. have found that the migration of transition metal (TM) cations into the Li layers can initiate the formation of spinel near the particle surface region.15 Apparently, a far more detailed microscopic understanding of the phase transformation characteristics in these layered structures will lead to tailoring of the materials struc- ture for better electrochemical performance. In this paper, we use aberration-corrected scanning/ transmission electron microscopy (S/TEM) imaging and energy dispersive X-ray spectroscopy (EDS) to probe the atomic structure of the layer structured cathode materials before and after high voltage cycling.18 The STEM high angle annular dark field (HAADF) detector collects all the incoherently scattered electrons. The image intensity of each atomic column reflects the average atomic number of each atomic column (∼Z1.5", "category": "scientific_body", "coverage": 0.04, "words": 254 }, { "page": 2, "page_count": 8, "bbox": [ 64.74, 425.75, 266.0, 585.58 ], "text": "to Z1.8),18 which is therefore termed as Z-contrast imaging and is chemical sensitive, allowing us to intuitively interpret the atomic structure changes di- rectly. We found that both LNMO and LNMCO layer structured cathodes are a random mixing of LiMO2 R3m and Li2MO3 C2/m phases, with both phases able to coexist in a single nanoparticle. Extraction of Li from the lattice of the layer-structured material leads to lattice break down, crack and porosity formation, and nucleation and growth of spinel. Mechanisti- cally, the formation of spinel from LiMO2 R3m is distinctively different from the transition of Li2MO3 C2/m to spinel.", "category": "scientific_body", "coverage": 0.01, "words": 105 } ], "front_summary_missing_blocks": [ { "page": 1, "page_count": 8, "bbox": [ 228.08, 504.04, 389.46, 608.65 ], "text": "of cations, and phase stability upon lithium extraction and insertion. Structurally, these layered structures are often composed of the intergrowth of LiMO2 R3m and Li2MO3 C2/m phases.7,13 Nevertheless, it is not clear how each individual phase affects the per- formance of these materials. Further, the cations are not necessarily uniformly distrib- uted at nanometer scale. Recently, Gu et al.7", "category": "front_summary", "coverage": 0.034, "words": 62 }, { "page": 1, "page_count": 8, "bbox": [ 228.08, 611.65, 389.46, 716.25 ], "text": "reported a nanoscale phase separation caused by the preferential segregation of Ni atoms on the particle surface and bound- aries in the layered lithium nickel manga- nese oxide cathode materials. They further predicted that the formation of the Ni-rich surface layer would affect the diffusion of Li ions, and thus possibly have an impact on the rate performance of this cathode.7", "category": "front_summary", "coverage": 0.0, "words": 63 }, { "page": 1, "page_count": 8, "bbox": [ 51.82, 504.05, 213.17, 740.12 ], "text": "i-ion batteries have been widely used as an energy storage device for mod- ern electric devices, grid application, and renewable energy.1\u00017 Cathodes with a layered structure such as Li1.2Ni0.2Mn0.6O2 (LNMO) andLi1.2Ni0.1Mn0.525Co0.175O2(LNMCO) can provide much higher capacity than the traditional cathode materials such as LiCoO2 and LiMn2O4 spinel.8\u000112 Therefore, these layered structures are one of the most pro- mising candidates for future heavy duty applications such as hybrid and electric vehicles. However, the application of these materials faces three fundamental chal- lenges: (1) voltage instability, (2) capacity fad- ing, and (3) slow charge/discharge rate. Collective experimental observations indicate these challenges are closely related to the structural characteristics of these materials, suchasthecrystalstructure,spatialdistribution", "category": "front_summary", "coverage": 0.0, "words": 121 } ], "back_matter_low_overlap_blocks": [ { "page": 8, "page_count": 8, "bbox": [ 64.74, 133.21, 266.12, 311.29 ], "text": "Acknowledgment. The research described in this paper is part of the Chemical Imaging Initiative at Pacific North- west National Laboratory (PNNL). It was conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle under Contract DE-AC05-76RLO1830 for the U.S. Department of Energy (DOE). The work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a na- tional scientific user facility sponsored by DOE's Office of Bio- logical and Environmental Research and located at PNNL. J. Zhang and J. Xiao would like to acknowledge the support of the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of DOE under Contract No. DE-AC02-05CH11231, Subcontract No. 18769 under the Batteries for Advanced Transportation Technologies (BATT) program. J. Liu would like to acknowledge the support of the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award KC020105-FWP12152. I. Belharouak and K. Amine would like to acknowledge the support from DOE's Freedom CAR and Vehicle Technologies Office.", "category": "back_matter", "coverage": 0.0, "words": 184 }, { "page": 8, "page_count": 8, "bbox": [ 64.74, 315.7, 266.13, 350.35 ], "text": "Supporting Information Available: The Supporting Informa- tion includes STEM image of the prestine LNMCO cathode nano- particles. No cracks are visible in the pristine particles. This material is available free of charge via the Internet at http://pubs.acs.org.", "category": "back_matter", "coverage": 0.0, "words": 38 } ] }