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Single atom catalysts exhibit particularly high catalytic activities in contrast to regular nanomaterial-based catalysts. Until recently, research has been mostly focused on single atom catalysts, and it remains a great challenge to synthesize bimetallic dimer structures. Herein, we successfully prepare high-quality one-to-one A-B bimetallic dimer structures (Pt-Ru dimers) through an atomic layer deposition (ALD) process. The Pt-Ru dimers show much higher hydrogen evolution activity (more than 50 times) and excellent stability compared to commercial Pt/C catalysts. X-ray absorption spectroscopy indicates that the Pt-Ru dimers structure model contains one Pt-Ru bonding configuration. First principle calculations reveal that the Pt-Ru dimer generates a synergy effect by modulating the electronic structure, which results in the enhanced hydrogen evolution activity. This work paves the way for the rational design of bimetallic dimers with good activity and stability, which have a great potential to be applied in various catalytic reactions., Atomically precise control over elemental distributions presents a challenge in the preparation of catalytic nanomaterials. Here the authors report Pt-Ru bimetallic dimer structures through atomic layer deposition process and identify the roles of Pt and Ru in hydrogen evolution reaction.

Pt single-atom catalysts are receiving more and more attention due to their different properties compared with nanostructures. As one typical kind of single-atom catalysts, Pt-based single-atom all...

Glycerol partial electrooxidation was studied on NixPd1–x (x = 100, 95, 90, and 80 atom %) nanoparticles synthesized using a polyol method. The shape-controlled urchin-like monometallic Ni and sphe...

Electrochemical promotion of Ni9Pd nanoparticles (NPs) with low Pd content (Ni:Pd = 9:1 atomic ratio) supported on yttria-stabilized zirconia (YSZ) solid-electrolyte was evaluated for the first time for complete methane oxidation. Electron Energy Loss Spectroscopy (EELS) showed a Pd core with a Ni first shell surrounded by 3–4 nm layer of Pd outer shell. This core double-shell structure of Ni9Pd NPs enhanced the catalytic activity and stability compared to mono-metallic Pd and Ni NPs under open-circuit. The reversible electrochemical promotion of Ni9Pd was obtained upon positive polarization between 425 and 500 °C. At 425 °C, the reaction rate increase reached 240% corresponding to apparent Faradaic efficiency of 25. On Ni9Pd NPs the reaction exhibited electrophobic behavior, i.e., the rate increased with anodic polarization, under all experimental conditions of this study. The results demonstrate the advantage of using Ni9Pd bi-metallic nanoparticles with core double-shell structure for methane complete oxidation due to the synergetic effect between Pd and Ni and very low amount of expensive Pd phase. EPOC with this type of highly dispersed and low noble metal content catalysts may find a way in the real world catalytic converters for gas exhaust treatment.

Decreasing Pt loading in the anode layer below ∼0.025 mg·cm–2 is found to reduce the hydrogen oxidation reaction rate during polymer electrolyte membrane fuel cells (PEMFCs) normal operation, when using conventional Pt/C catalysts and electrode coating methods. To achieve extremely low Pt loading in the anode catalyst layer while maintaining high PEMFC performance and durability, a series of membrane electrode assemblies (MEAs) with low Pt loading in the anode layer are successfully prepared using an atomic layer deposition (ALD) technique. When the ALD cycle number is controlled, the Pt nanoparticles (NPs) with different sizes and loadings are directly deposited on the carbon layer to form the anode catalyst layer. The ALDPt NPs with uniform particle sizes are highly distributed on the carbon surface, which promotes the ALDPt with high electrochemical active surface area and enables enhanced performance of ALDPt-MEAs. Particularly, the 50ALDPt-MEA with the anode Pt prepared by 50ALD cycles shows excellen...

The development of smartphone Micro-Electro-Mechanical Systems (MEMS) inertial sensors has provided opportunities to improve indoor navigation and positioning for location-based services. One area of indoor navigation research uses pedestrian dead reckoning (PDR) technology, in which the mobile phone must typically be held to the pedestrian’s chest. In this paper, we consider navigation in three other mobile phone carrying modes: “calling,” “pocket,” and “swinging.” For the calling mode, in which the pedestrian holds the phone to their face, the rotation matrix method is used to convert the phone’s gyroscope data from the calling state to the holding state, allowing calculation of the stable pedestrian forward direction. For a phone carried in a pedestrian’s trouser pocket, a heading complementary equation is established based on principal component analysis and rotation approach methods. In this case, the pedestrian heading is calculated by determining a subset of data that avoid 180° directional ambiguity and improve the heading accuracy. For the swinging mode, a heading capture method is used to obtain the heading of the lowest point of the pedestrian’s arm swing as they hold the phone. The direction of travel is then determined by successively adding the heading offsets each time the arm droops. Experimental analysis shows that 95% of the heading errors of the above three methods are less than 5.81°, 10.73°, and 9.22°, respectively. These results present better heading accuracy and reliability.

Configuring metal single-atom catalysts (SACs) with high electrocatalytic activity and stability is one efficient strategy in achieving the cost-competitive catalyst for fuel cells' applications. Herein, the atomic layer deposition (ALD) strategy for synthesis of Pt SACs on the metal-organic framework (MOF)-derived N-doped carbon (NC) is proposed. Through adjusting the ALD exposure time of the Pt precursor, the size-controlled Pt catalysts, from Pt single atoms to subclusters and nanoparticles, are prepared on MOF-NC support. X-ray absorption fine structure spectra determine the increased electron vacancy in Pt SACs and indicate the Pt-N coordination in the as-prepared Pt SACs. Benefiting from the low-coordination environment and anchoring interaction between Pt atoms and nitrogen-doping sites from MOF-NC support, the Pt SACs deliver an enhanced activity and stability with 6.5 times higher mass activity than that of Pt nanoparticle catalysts in boosting the oxygen reduction reaction (ORR). Density functional theory calculations indicate that Pt single atoms prefer to be anchored by the pyridinic N-doped carbon sites. Importantly, it is revealed that the electronic structure of Pt SAs can be adjusted by adsorption of hydroxyl and oxygen, which greatly lowers free energy change for the rate-determining step and enhances the activity of Pt SACs toward the ORR.

The dissolution of transition metal ions from positive electrodes and loss of (both electroactive and transport) Li+ ions seriously impair the durability of lithium ion batteries. We show herein that the improvement in the cycle life of lithium manganate spinel-graphite cells effected by multifunctional separators results from smaller interfacial resistances at both positive and negative electrodes, that can in turn be traced back to thinner, more uniform, and chemically different surface films, due to lessened parasitic reactions and a decreased accumulation of parasitic reaction products at electrode surfaces, as evidenced by HR-SEM, FIB-SEM, EDX, 19F MAS NMR, and ICP-OES data.

Lithium-rich layered oxides are promising cathode candidates because of their exceptional high capacity. The commercial application of these high-energy cathodes, however, is thwarted by the undesired rapid performance decay during cycling. Surface degradation has been widely considered to correlate with the performance decay of the cathodes, whereas, in this work, we demonstrate that the degradation of Li-rich high-energy Li1.2Ni0.13Mn0.54Co0.13O2 (HENMC) cathode material not only takes place at surfaces but also proceeds from its internal structure. In addition to demonstrating the surface reconstruction and the formation of a cathode–electrolyte interphase (CEI) layer of cycled HENMC cathode, this study uncovers the irreversible bulk phase transition from a Li-excess monoclinic (C2/m) solid solution into a conventional “layered” (R3m) phase, accompanied by complete loss of Li+ from the TM layers during cycling. Furthermore, the internal grains of HENMC bear lattice distortions, leading to the formatio...

Nowadays, lithium-ion batteries (LIBs) have been widely used in the automotive industry as power sources for electric vehicles (EVs). Nevertheless, the rapid development of EVs requires LIBs to enable higher energy density, enhanced safety, lower cost and longer cycle life. Ni-rich LiNixMnyCo1-x-yO2 (NMC) layered oxides have attracted great attention due to their high specific capacity (≈ 200 mAh/g), which are promising cathode materials for high-energy-density LIBs. The capability of high-voltage operation of the cathode can largely influence the energy density of LIB. Whereas, it is reported that Ni-rich cathode materials are unstable at high-voltage cycling conditions, leading to severe performance deterioration. (1, 2) Attempts have been made in developing synthesis and modification methods of Ni-rich cathode materials in order to improve their high-voltage performance.(3, 4) However, the design of better materials relies intensively on the deep understanding of the cycling behavior of cathode. There are a few studies looking into the degradation process of Ni-rich cathodes upon high-voltage cycling. Most of the work mainly focuses on investigating structural changes of the active material, for example, phase transformation at the surface,(2) crack generation within active particles.(5) Whereas, less attention was paid to the evolutions within the whole electrode. Herein, we study the cycling behavior of LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode at high cut-off voltages and look into the structural evolutions of cathode. In this work, Ni-rich NMC811 cathodes were cycled at different upper cut-off voltages to investigate their charge-discharge behavior under high-voltage cycling conditions. The NMC811 cathodes were assembled into coin cells with Li foil as counter electrode. The cells were cycled under different upper cut-off voltages of 4.3V, 4.6V and 4.8V with a C/10 cycling rate. Electrochemical impedance spectroscopy (EIS) measurements were conducted to analyze the ionic conduction and charge transfer at the electrolyte/particle interface of coin cells cycled at different cut-off voltages. The microstructure of pristine and cycled NMC811 cathodes were characterized in order to understand the structural evolution among different phases during high-voltage cycling. Our results show that high cut-off voltages have a negative influence on cell performance. The specific capacity of the cells cycled at 4.6V upper cut-off voltage showed a faster decrease compared to the 4.3V cells. In addition, more severe voltage decay is observed from cells cycled at 3.0V-4.6V. Whereas, when increasing the upper cut-off voltage from 4.6V to 4.8V, the cells exhibited less pronounced voltage decay, comparing to the difference observed between 4.3V and 4.6V cells. Significant increases in the charge transfer resistance (Rct) of cells cycling under higher voltages were observed from EIS measurements, which may indicate an elevated irreversible phase transformation of the active materials under high voltage cycling.(2) The microstructural evolution of NMC811 cathodes were observed under higher cycling voltages which could contribute to the poor performance of the high-voltage cells. The different behaviors of NMC811 cathode at high-voltages were analyzed in order to understand the degradation mechanisms of NMC811 cathodes under increasing cycling voltages. References: J. Li, L. E. Downie, L. Ma, W. Qiu and J. R. Dahn, Journal of The Electrochemical Society, 162, A1401 (2015). S.-K. Jung, H. Gwon, J. Hong, K.-Y. Park, D.-H. Seo, H. Kim, J. Hyun, W. Yang and K. Kang, Advanced Energy Materials, 4 (2014). X. Dong, J. Yao, W. Zhu, X. Huang, X. Kuai, J. Tang, X. Li, S. Dai, L. Shen, R. Yang, L. Gao and J. Zhao, Journal of Materials Chemistry A, 7, 20262 (2019). J. Zhang, J. Zhang, X. Ou, C. Wang, C. Peng and B. Zhang, ACS Appl Mater Interfaces, 11, 15507 (2019). Y. Mao, X. Wang, S. Xia, K. Zhang, C. Wei, S. Bak, Z. Shadike, X. Liu, Y. Yang, R. Xu, P. Pianetta, S. Ermon, E. Stavitski, K. Zhao, Z. Xu, F. Lin, X. Q. Yang, E. Hu and Y. Liu, Advanced Functional Materials, 29 (2019).

Indium (In) doped zinc oxide (ZnO) nanowires-gated AlGaAs/GaAs high electron mobility transistor (HEMT) was demonstrated for the detection of lactic acid. The In-doped ZnO nanowires were synthesized via chemical vapor deposition (CVD) method. Such In-doped ZnO nanowires offered an effective surface area with high surface area-to-volume ratio as well as a favorable environment for the immobilization of lactate oxidase (LOX) on the HEMT gate area. The In-doped ZnO nanowires have better conductivity than pure ZnO nanowires and retained the electroactivity of enzymes. Due to the novel structure of the Si-doped GaAs cap layer, the drain–source current of the AlGaAs/GaAs HEMT sensor showed a rapid response when lactic acid solutions at various concentrations were introduced to the gate area of the HEMT. The fabricated sensor exhibited a wide detection range from 3 pM to 3 mM and a low detection limit of 3 pM. The result indicated that a portable, fast response and high sensitivity lactic acid detector can be realized by AlGaAs/GaAs HEMT sensor.

State-of-the-art image acquisition, image analysis, and modern homogenization theory are used to study the effects of cycling on commercial lithium-ion battery cathodes’ ability to conduct electronic current. This framework allows for a rigorous computation of an effective, or macroscale, electronic conductivity given an arbitrarily complicated three-dimensional microstructure comprised of three different material phases, i.e., active material, binder (polymer mixed with conductive carbon black), and electrolyte. The approach explicitly takes into account the geometry and is thus a vast improvement over the commonly used Bruggeman approximation. We apply our framework to two different types of lithium-ion battery cathodes before and after cycling. This leads us to predict an appreciable decrease in the effective electronic conductivity as a direct result of cycling. In addition, we present an ad-hoc “neighbor counting” methodology which meaningfully quantifies the effect of binder detaching from the surface of the active material due to the internal mechanical stresses experienced under operating conditions, thereby supporting the results of the homogenization calculations.

A ZnO nanowire (NW) array ultraviolet photodetector (PD) with Pt Schottky contacts has been fabricated on a glass substrate. Under UV light illumination, this PD showed a high photo-to-dark current ratio of 892 at 30 V bias. Interestingly, it was also found that this PD had a high sensitivity of 475 without external bias. This phenomenon could be explained by the asymmetric Schottky barrier height (SBH) at the two ends causing different separation efficiency of photogenerated electron–hole pairs, which resulted in the formation of photocurrent. It is anticipated to have potential applications in self-powered UV detection field.

Layered lithium transition metal oxides are one of the most important types of cathode materials in lithium-ion batteries (LIBs) that possess high capacity and relatively low cost. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and not yet fully understood. We herein systematically investigate the chemical evolution and structural transformation of the LiNixMnyCo1−x−yO2 (NMC) cathode material in order to understand the battery performance deterioration driven by the cathode degradation upon cycling. Using high-resolution electron energy loss spectroscopy (HR-EELS) we clarify the role of transition metals in the charge compensation mechanism, particularly the controversial Ni2+ (active) and Co3+ (stable) ions, at different states-of-charge (SOC) under 4.6 V operation voltage. The cathode evolution is studied in detail from the first-charge to long-term cycling using complementary diagnostic tools. With the bulk sensitive 7Li nuclear magnetic resonance (NMR) measurements, we show that the local ordering of transition metal and Li layers (Rm structure) is well retained in the bulk material upon cycling. In complement to the bulk measurements, we locally probe the valence state distribution of cations and the surface structure of NMC particles using EELS and scanning transmission electron microscopy (STEM). The results reveal that the surface evolution of NMC is initiated in the first-charging step with a surface reduction layer formed at the particle surface. The NMC surface undergoes phase transformation from the layered structure to a poor electronic and ionic conducting transition-metal oxide rock-salt phase (Rm → Fmm), accompanied by irreversible lithium and oxygen loss. In addition to the electrochemical cycling effect, electrolyte exposure also shows non-negligible influence on cathode surface degradation. These chemical and structural changes of the NMC cathode could contribute to the first-cycle coulombic inefficiency, restrict the charge transfer characteristics and ultimately impact the cell capacity.

In this paper, we aim to discover the mechanics-related novel phenomena on high-quality ZnO microwires through nanoindentation method. The mechanical property parameters of ZnO microwires were determined and a distinctive creep damage phenomenon was revealed. By using the cycles load mode in the nanoindentation experiments, the indentation size effect was demonstrated to exist in the ZnO microwires: the elastic modulus ranged from 65.9 GPa to 12.3 GPa and the hardness changed from 11.1 GPa to 1.8 GPa with the increase of indentation depth. Furthermore, the indentation-induced mechanical and electrical damage caused a permanent plastic deformation and an increase of 41% in the longitudinal conductance of the ZnO microwires.

The synergistic scale inhibition effect of rare-earth permanent magnetic material and polyaspartic acid is studied. The performance of synergistic scale inhibition is studied in different magnetic field intensity, water hardness and rate of concentration. Static and dynamic scale inhibition tests show that the two water treatment ways have good synergistic scale inhibition effect. The scale inhibition performance of polyaspartic acid can be increased greatly by the magnetization of water.

Polyaspartic acid (PASP) composite material, a scale and corrosion inhibitor, is prepared from PASP, acrylic acid-acrylic ester- itaconic acid tripolymer (IA-AA-AE) and 2-phosphonobutane- 1,2,4-tricarboxylic acid (PBTCA). The scale inhibition effects of PASP and PASP composite are investigated. Calcium carbonate crystals in scale samples are characterized by means of SEM. Experimental results show that the scale inhibition rate can reach 98.7 % and corrosion inhibition rate 96.5 % under the conditions of Ca2+ 639 mg.L-1 and PASP composite material 40 mg.L-1. SEM results show that calcite and aragonite can be transformed into vaterite completely by using PASP composite material.

For vehicle electrification, one of the biggest issues for lithium ion batteries is cycle life. Within this context, the mechanisms at the source of capacity degradation during cycling are not yet to be fully understood. In this work, we use state-of-the-art FIB-SEM serial sectioning and imaging techniques to determine the effect of cycling on lithium-ion battery cathodes. The three-dimensional (3D) microstructural study was performed on both pristine and cycled LiNixMnyCo1−x−yO2 (NMC) and Li(Li0.2Ni0.13Mn0.54Co0.13)O2 (HE-NMC) cathodes. The spatial distribution of active material, carbon-doped binder and pore spaces were successfully reconstructed by appropriate image processing. Comparisons of NMC and HE-NMC cathodes after different number of cycles showed only minor increases in the number of smaller active particles, possibly negligible, considering the intrinsic microstructure variation within the cathodes. However, the connectivity between carbon-doped binder additives and active particles in NMC and HE-NMC cathodes, assessed using a “neighbor counting” method, showed an appreciable decrease after cycling which indicates a detachment of carbon-doped binder from active particles. This significant cycling-induced detachment effect between the two phases (e.g., ∼22% for HE-NMC) could indicate a loss in electrical connectivity, which may partially explain the capacity fade in the cells.

A novel two-step surface modification method that includes atomic layer deposition (ALD) of TiO2 followed by post-annealing treatment on spinel LiNi0.5 Mn1.5 O4 (LNMO) cathode material is developed to optimize the performance. The performance improvement can be attributed to the formation of a TiMn2 O4 (TMO)-like spinel phase resulting from the reaction of TiO2 with the surface LNMO. The Ti incorporation into the tetrahedral sites helps to combat the impedance growth that stems from continuous irreversible structural transition. The TMO-like spinel phase also alleviates the electrolyte decomposition during electrochemical cycling. 25 ALD cycles of TiO2 growth are found to be the optimized parameter toward capacity, Coulombic efficiency, stability, and rate capability enhancement. A detailed understanding of this surface modification mechanism has been demonstrated. This work provides a new insight into the atomic-scale surface structural modification using ALD and post-treatment, which is of great importance for the future design of cathode materials.

With the rapid development of electronic devices and hybrid-electric/electric vehicles (H/EVs), lithium-ion batteries have become the most promising electrical storage system due to its high volumetric and gravimetric energy density. However, the high energy density of lithium-ion batteries is difficult to maintain after extended cycles due to capacity fading, which can be attributed to multiple possible reasons including SEI formation,[1] electrolyte decomposition,[2] and structural changes in electrode materials.[3] These issues generate important concerns to the stability and lifetime of the battery. Layered lithium-transition metal oxides represent a major type of cathode materials that are widely used in the commercial market. However, these materials are suggested to suffer structural transformation during electrochemical cycling. Previous studies suggest the possible surface structural transitions from the layered structure to spinel[4], and/or rock-salt structures,[5] or possible further decomposition of the transformed phase.[6]A clear explanation of these surface phenomenon is still under debate. An in-depth investigation of the structural reconstruction is necessary to elucidate the degradation mechanisms of the layered cathode materials. In the present study, we investigated the chemical evolution and structural transformation of a prominent layered cathode material for lithium-ion batteries, LiNi1/3Mn1/3Co1/3O2 (NMC). The redox reaction of NMC cathode during charge-discharge process was analyzed in detail using high-resolution electron-energy loss spectroscopy (EELS) and 7Li magic-angle spinning (MAS) NMR. Our results suggest that the charge compensation of the NMC cathode during the delithiation-lithiation process is mainly achieved by the oxidation and reduction of Ni2+↔Ni4+, whereas Mn4+ and Co3+ remain mostly unchanged. This is consistent with the NMR findings, from which a trend to lower chemical shift upon lithium extraction is well-correlated with the oxidation change from paramagnetic Ni2+ to diamagnetic Ni4+. Furthermore, the electronic structure of the NMC cathode during initial charging process is found to be inhomogeneous from the particle surface to the bulk using spatially resolved STEM-EELS technique (Figure 1a-1d). It is revealed that the particle surface is at lower oxidation state compared with the bulk region, indicating that the surface evolution of NMC cathode material occurs during the initial cycle. This surface evolution is further analyzed at different numbers of cycles using atomic-resolution high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) imaging combined with EELS and nano-beam electron diffraction (NBED). Figure 1e shows a HAADF-STEM image of the NMC particle after 50 cycles. It can be clearly seen from the image that the bulk of the cycled NMC particle shows identical layered structure symmetry, the NBED (Figure 1h) obtained from the bulk can be indexed to the R-3m space group. In contrast, the Li layers are occupied by transition metal ions at the particle surface, and this surface reconstruction layer thickens with extended cycles. When probing to the outer-most surface, the corresponding NBED can be indexed to an Fm-3m rock-salt structure, as shown in Figure 1f. The valence change of the transition metal cations is analyzed using STEM-EELS. The results indicate that the transition metal ions are reduced to divalent states at the surface. In addition, the TM:O ratio increases almost twice at the surface than the bulk. The results indicating that the surface layer is a MO-type rock-salt phase with small amount of residual Li ions and/or vacancies. In addition, a transition zone is observed (Figure 1e) between the bulk layered region and the surface rock-salt layer, where the Li sites are partially occupied by the transition metal ions (some are marked by the red arrows), and the diffraction spots corresponding to the alternating arrangement of Li-containing layers and transition metal layers (some are marked with arrows) become weaker (Figure 1g). 7Li NMR studies of the local Li-environments, following ten cycles and ending at the top of charge, indicate that the order of the TM layers remains unchanged in the bulk of the material. This highlights the importance of complementary studies that are sensitive to different length scales. Further data, including EELS and NMR of the NMC cathode at different cycling state and electrolyte effect will be discussed in the presentation. [1] K. Edström, T. Gustafsson, J. Thomas, Electrochim. Acta 2004, 50, 397. [2] L. Terborg, S. Weber, F. Blaske, et al. J. Power Sources 2013, 242, 832. [3] B. Xu, C.R. Fell, M. Chi, et al. Energy Environ. Sci. 2011, 4, 2223. [4] A. Boulineau, L. Simonin, J.F. Colin, et al. Chem. Mater. 2012, 24, 3558. [5] F. Lin, I. M. Markus, D. Nordlund, et al. Nat. Commun. 2014, 5, 3529. [6] J. Zheng, M. Gu, J. Xiao, et al. Nano Lett. 2013, 13, 3824. Figure 1

Lithium ion batteries are one of the most promising energy storage systems that have been widely used in portable electronic devices and electric vehicles. Nevertheless, advanced automotive electrification requires greater capacity, longer cycle life and reduced cost. With respect to cycle life, the mechanisms of capacity degradation are not yet to be fully understood. What is known is that solid electrolyte interface (SEI) formation [1] and structural distortion of active materials adversely impacts battery performance.[2,3] Furthermore, next generation negative electrodes are known to suffer huge volume changes during Li+ intercalation/deintercalation upon cycling, which induce local stresses and lead to microstructure degradation of the electrode.[4] While the smaller volume changes of the cathode materials are less well recognized, they may also turn out to be significant for battery performance and life.[5] In the present work, the structural evolution of the LiNixMnyCo1-x-yO2 (NMC) and Li1.2Ni0.13Mn0.54Co0.13O2 (HE-NMC) cathodes in lithium-ion batteries following electrochemical cycling were studied three-dimensionally.[6] The cathodes were successfully reconstructed in 3D using state–of-the-art focus ion beam-scanning electron microscope (FIB-SEM) serial sectioning and imaging techniques. The acquired 2D images were digitally segmenting into three distinct phases before reconstruction. In this study, a segmentation algorithm was developed to apply refined threshold values and gradient analysis to the 2D images, thereby avoiding the necessity of epoxy infiltration to the sample [7] and protect the integrity of the small features of the phases. As shown in Figures 1a-1b, each of the three phases: active material (AM), carbon-doped binder (CB), and pore spaces (which are filled with electrolyte during cycling) were clearly resolved after the image processing step. In order to evaluate the evolution of the relative positions of the important phases within the cathode, the segmented 3D structure was quantified with a “neighbor counting” method, by which the connectivity between CB and the AM was analyzed for cathodes that underwent different number of cycles. This approach provides statistical analysis-based assessment of the degree of connectivity between the surface of active particles and the binder matrix as a function of depth into the cathode (i.e., in the direction perpendicular to the separator and current collector). The probability of carbon-doped binder being adjacent to the active particles (PBA) of cycled NMC cathode is shown in Figure 1c. Each data point represents the probability of CB being in direct contact with the active particle surface of each slice perpendicular to the depth of the 3D structure in units of pixels, each pixel corresponding to the slice thickness (35 nm), as shown in the schematic diagram in Figure 1c. It is shown that the average PBA of the pristine sample decreases from 0.54 to 0.48 after 20 cycles, and further drops to 0.43 after 50 cycles. The value of the average PBA, e.g., 0.54, means that 54% of the AM surface is in contact with the CB phase within the 3D volume. The results therefore indicate that the connectivity between AM and CB decreases with the increased number of cycles, where a cycling-induced detachment between the two phases was observed. Similar detachment phenomenon is also observed in the HE-NMC cathode after 50 cycles, for which a 22.5% loss of AM and CB contact was detected. Since the CB phase contains the carbon black additive for the enhancement of electrical conductivity of the cathode, our results thus suggest that the detachment between the conductive CB phase and the active particles will reduce the efficiency of electron transport from the active particles (where Li+ intercalation/deintercalation happens) to the current collector. The loss of electrical conductivity of the cycled cathode will have an adverse effect on the cyclic performance as a consequence of the detachment between the conductive binder matrix and active particles. [1] P. Verma, P. Maire, P. Novak, Electrochem. Acta. 2010, 55, 6332-6341. [2] F. Lin, I.M. Markus, D. Nordlund, et al. Nat. Commun. 2014, 5, 3529. [3] A. Boulineau, L Simonin, J.F. Colin, et al. Nano Lett. 2013, 13, 3857-3863. [4] D. Larcher, S. Beattie, M. Morcrette, et al. J. Mater. Chem. 2007, 17, 3759–3772. [5] D.S. Eastwood, V. Yufit, J. Gelb, et al. Adv. Energy Mater. 2014, 4, 1300506. [6] H. Liu, J. M. Foster, A. Gully, et al. J. Power Sources. 2016, 306, 300-308. [7] Z. Liu, J. Scott Cronin, Y.K. Chen-Wiegart, et al. J. Power Sources. 2013, 227, 267–274. Figure 1

High energy density lithium ion batteries that are cheaper, safer, and with longer lifetimes need to be developed in order to meet the increasing demand for applications such as electric vehicles. LiNi0.8Mn0.1Co0.1O2 (NMC811) can deliver a high capacity of ∼200 mAh/g with an average discharge potential of ∼3.8 V (vs. Li+/Li), making it a promising positive electrode material for high energy density lithium ion batteries. However, electrochemical tests of NMC811 from half cells and full cells show poor cycling performance when charged to potentials above 4.2 V. In our previous report1, it was shown the there are no significant structural changes in the bulk of the material during charge-discharge cycling. Instead, the parasitic reactions between the electrolyte and the highly reactive delithiated cathode surface at high potentials were suggested as the main reason for the failure of cells cycled above 4.2 V. Recently, Lin et al 2 showed that the surface of LiNi0.42Mn0.42Co0.16O2 went through a structural reconstruction from layered (Rm) to rocksalt (Fmm), which caused a significant increase in cell impedance under high voltage cycling conditions. Takamatsu et al 3 also reported that Co3+ at the surface of LiCoO2 was reduced to Co2+ after soaking in the electrolyte, however, the reduction of Co was suppressed with the presence of vinylene carbonate (VC) additives. This suggests that appropriate electrolyte additives might be able to suppress surface reconstructions of NMC materials. In this work, the impact of electrolyte additives and cell upper cut-off potential on the formation of a rocksalt surface layer in NMC811 cells was studied. NMC811/graphite pouch cells (220 mAh) were cycled for 100 cycles between 2.8 to 4.1 or 2.8 to 4.3 V. The rate used was C/5 for 5 cycles and followed by one C/20 cycle. The control electrolyte was 1M LiPF6in 3:7 v:v EC:EMC. The electrolyte additives studied in this work were 2% VC and “PES211”. PES211 is a blend of 2% prop-1-ene-1,3-sultone (PES) + 1% methylene methane disulfonate + 1% tris(trimethylsilyl) phosphate in control electrolyte. The cycled cells were discharged to 3.0 V and held for 24 h before disassembly in an argon-filled glovebox. The recovered positive electrodes were then washed with diethyl carbonate (DEC). Thick layers of carbon (~3 µm) and tungsten (~10 µm) were first deposited on the surface of the electrode to avoid beam damage during the FIB process. The samples were then analyzed with HAADF, EELS and NBD in aberration-corrected STEM mode. Figure 1A shows the HAADF-STEM images of the pristine NMC811 electrode near the surface before contacting any electrolyte. Every other column of the transition metal atoms, as indicated by the blue arrows, observed at the surface disappeared when moving into the bulk region, indicating a reconstructed rocksalt surface layer. This is likely due to the reaction between the electrode surface, that has high nickel content, with moisture in the air. The thickness of the rocksalt layer is ~2 nm. Figures 1B, 1C and 1D show the HAADF-STEM images of the electrodes after 100 cycles between 2.8 – 4.3 V with control, control plus 2% VC and control plus PES211 electrolyte in the cells respectively. The thickness of the surface layer on the control electrode was ~4 nm, while the thickness of surface layer in the electrodes in cells with 2% VC and PES 211 was about ~2 nm, almost the same as the pristine electrode. This suggests that both the VC and PES211 additives can suppress the formation of the rocksalt surface in NMC811 electrodes. Our previous report1showed that NMC811/graphite pouch cells with PES211 additives had worse cycling performance than the cells with only control electrolyte. Hence, at least for NMC811 cells, failure cannot only be ascribed to a growing rocksalt surface layer. Instead, other processes, for example associated with electrolyte oxidation, are believed to be responsible for failure. Figures 1E and 1F show the nano beam diffraction (NBD) from the surface and bulk of the control electrode shown in Figure 1B, respectively. The red dashed lines showed the remaining diffraction spots while the blue dashed lines showed the diffraction spots which disappeared when the beam moved from the bulk to the surface. This result confirms the that the surface was reconstructed. More results about EELS results will be discussed. References 1. J. Li, L. E. Downie, L. Ma, W. Qiu, and J. R. Dahn, J. Electrochem. Soc., 162, A1401–A1408 (2015). 2. F. Lin et al., Nat. Commun., 5, 3529 (2014). 3. D. Takamatsu et al., J. Phys. Chem. C, 9791–9797 (2015). Figure 1

Core-shell (CS) structured positive electrode materials based on layered Li-Ni-Mn-Co oxide could be the next generation of positive electrode materials for high energy density lithium-ion batteries. This is because a high energy core material with poor stability against the electrolyte can be protected by a thin layer of a stable shell material. In our previous report1–2, Li and Mn-rich materials were used as the protecting shell, and Ni-rich materials were used as the core. It was shown that the Mn-rich shell can effectively protect the Ni-rich core from reactions with the electrolyte while the Ni-rich core renders a high and stable average voltage.1 However, diffusion of the cations between the core and shell phases occurs during sintering 2. In this work, the effect of the initial shell thickness, sintering temperature and the interdiffusion in a ternary system on the electrochemical performance of CS cathodes was studied. CS precursors with (Ni0.6Mn0.2Co0.2)(OH)2 as the core and 10 mol% (CS10), 20 mol% (CS20) or 33 mol% (CS33) (Ni0.2Mn0.6Co0.2)(OH)2 shell were first synthesized. Lithiated samples were then prepared by sintering the precursor and LiOH with three different lithium contents (average Li/TM of 1.02, 1.04 and 1.06) for each shell content at 850 or 900oC for 10 h. The samples were labeled as CS10 (20, 33) - 850 (900) - 1 (2,3), which indicate the initial shell content, sintering temperature and lithium content, respectively. For example, CS20-900-3 indicates a sample with 20 mol.% shell, sintered at 900oC with a Li/TM ratio of 1.06. Figure 1 shows a SEM image and energy dispersive spectroscopy (EDS) mapping results of CS33-850-2. Figures 1c, 1d and 1e show that the Mn-rich shell was maintained, while the Ni and Co content at the surface is lower than that in the core (less bright) after sintering. Figures 1a and 1b clearly show that the core and shell have two different morphologies where the core was sintered to a polycrystalline monolith nearly free of interior voids (besides some big pores), whereas the shell was composed of spiky flakes with pores in between. This could be improved by adjusting the synthesis approach in the future. In order to further examine the interdiffusion phenomena in spherical CS particles, a focused ion-beam (FIB) was used to cut a thin slice (~100 nm) through the center of a randomly selected particle. Figure 2a shows a scanning transimission electron microscope (STEM) image of the prepared slice. The yellow line shows the path where EDS point analysis was performed. Figure 2b shows the measured concentration profiles with symbols, calculated profiles with solid lines and simulated initial concentration profiles with dashed lines respectively. Ni moved from the core to the shell and the Ni content on the surface changed from ~21% to ~30% during sintering, while Mn moved from the shell into the bulk, and the Mn content on the surface changed from ~57% to ~55%. Surprisingly, Co moved into the core from the shell, even though the initial Co content in the core and shell was the same, in order to compensate for the increase of Ni content in the surface. This is because the interdiffusion between Ni/Co is much faster than Ni/Mn as discussed in Ref. 2. This suggests that the present of Co in the shell can accelerate the diffusion of Ni from the core to the shell. Samples CS20-850-3 and CS33-900-3 were selected from 24 synthesized samples for testing in full cell coin cells with graphite as the counter electrode using two different electrolytes, in comparison to a commercial material (Umicore coated NMC622) designed for high voltages. The control electrolyte was 1M LiPF6in 3:7 v:v ethylene carbonate (EC): diethylcarbonate (DEC). PES211 electrolyte is the control electrolyte plus 2% prop-1-ene-1,3-sultone + 1% Methylene methane disulfonate + 1% tri(trimethylsilyl) phosphite (PES). The cells were tested between 2.8 and 4.6 V with a rate of C/5 followed by one cycle of C/20 in every 20 cycles. Figure 3 shows the capacity of the cells as a function of cycle number. It is seen that cells with PES 211 have slightly higher capacity than the control cells. Figure 3a shows that the cells have similar capacity retention with control electrolyte, while Figure 3b shows that CS20-850-3 has slightly better capacity retention (~90% after 100 cycles ) comparing to CS33-900-3 and coated NMC622, References (1) Li, J.; Camardese, J.; Shunmugasundaram, R.; Glazier, S.; Lu, Z.; Dahn, J. R. Chem. Mater. 2015, 27, 3366–3377. (2) Li, J.; Doig, R.; Camardese, J.; Plucknett, K.; Dahn, J. R.;Chem. Mater. 2015, 27 (22), 7765–7773. . Figure 1

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An excellent biosensor with ZnO nanowires-gated AlGaAs/GaAs high electron mobility transistor (HEMT) was used to detect lactic acid. Due to the new structure, addition of the Si-doped GaAs cap layer, the HEMT biosensor could detect a wide range of lactic acid concentrations from 0.03 nM to 300 mM. The novel biosensor exhibiting good performance along with fast response, high sensitivity, wide detection range, and long-term stability, can be integrated with a commercially available transmitter to realize lactic acid detection.