This study investigates the degradation mechanisms of high-nickel (Ni) layered oxide (LiNi0.83Co0.11Mn0.06O2) under varying discharge C-rates at a high cut-off voltage (4.3 V) during long-term cycling. Contradictory to conventional knowledge, a low discharge rate (0.1C) results in worse cycle performance than a high discharge rate (1C) at a high cut-off voltage. In-depth transmission electron microscopy analysis reveals that at a high C-rate discharge condition, more Ni ions are reduced from +3 to +2, yet the layered structure is maintained. In contrast, at a low C-rate, more Ni ions retain their +3 valence but the phase transition to the periodically ordered spinel occurs at some portion. The prolonged dwell time at high voltage forces Ni ions in Li layers to be locally ordered, and this phase transition more critically affects the cycling. Therefore, this study underscores that setting a proper cut-off voltage can be more significant to the cycle performance than the discharge C-rate.

This study presents a novel method for fabricating composite gel polymer electrolytes through breath-figure self-assembly for Na metal batteries.

Despite the enormous efforts to control the growth behavior of Li, achieving a dendrite-free Li deposition and high-energy-density have remained an inevitable challenge of Li metal batteries. Here, the conformal deposition of Li metal is reported on electroactive organic materials to achieve a high-energy-density and electrochemical longevity. To this end, Li2C8H4O4 (Li2TP), which can act as both the electrode material (providing the redox capacity) and Li host (inducing the dendrite-free Li deposition), is used as the model electroactive organic material. The Li2TP host exhibits reversible sequential lithiation/delithiation and Li deposition/stripping reactions. Consequently, a Li-free full cell constructed by the Li2TP host (without pre-charging) and a LiFePO4 cathode delivered a high areal capacity (approximate to 3.8 mAh cm-2), exceptional rate performance (<= 12 mA cm-2), and superior cyclability (80% capacity retention after 100 cycles). This electroactive organic material-based Li host strategy can provide a new perspective for the development of practical Li metal batteries. A conformal and dendrite-free deposition of lithium metal on electroactive organic materials (Li2C8H4O4) is demonstrated, which can achieve both redox capacity and lithium electrodeposition stabilization. This work provides a new design concept for electroactive Li hosts that enable practical Li metal batteries with high energy density and electrochemical longevity. image

Materials that undergo combined conversion and alloying reactions are promising as anodes for lithium storage application because they can accommodate multiple lithium ions. However, irreversible conversion reactions, large voltage hysteresis, poor rate capabilities, and low initial Coulombic efficiencies during continuous discharge-charge cycling make practical applications of conversion-alloying materials challenging. Herein, we present cobalt-bismuth oxide (CBO) nanoneedles, a new bimetallic material in which Li+-ion uptake proceeds stepwise, thus effectively suppressing volume expansion. During the initial lithiation stage, the CBO nanoneedles undergo a conversion reaction to form nanodomains of low-oxidation-state Co delta+ ( delta <= 2) in a Li2O matrix. At the next potential platform, the Bi phase attracts Li+ ions via an alloying reaction, while the Co delta+/Li2O phase hinders excessive volume expansion. Consequently, the CBO electrode delivers a high reversible discharge capacity of 392 mAh g(-1) at 50 mA g(-1) for up to 100 cycles. Further, an ultrastable long-term capacity of 300 mAh g(-1) at 250 mA g(-1) is realized over 1000 cycles. The stepwise lithiation process decreases volume expansion significantly (by similar to 10%), which leads to good cyclability. Owing to their ease of preparation and excellent performance characteristics, CBO nanoneedles are an attractive long-life anode material for lithium-ion batteries.

The use of carbon-based supports, such as graphene and porous carbon, is a well-established approach to overcome the rapid capacity fading issues associated with alloy-based anode materials in lithium-ion batteries (LIBs). However, adopting carbonaceous materials that typically exhibit a low density eventually diminishes the primary purpose of alloys as high-energy-density anode materials. In this study, we introduce three-dimensional hierarchically porous molybdenum carbide (PMC) with high energy density, robust mechanical strength, and high electronic conductivity, which make it a promising alternative support for suppressing the huge volume expansion of alloying-based materials. Carbon-coated, ultrasmall Bi nanodots with an average size of 6.4 nm are uniformly embedded on the PMC surface (denoted as C-Bi/PMC) by facilitating heterogeneous nucleation. When tested as an anode in an LIB, the C-Bi/PMC electrode exhibits a high reversible capacity of 422 mAh g(-1) at 50 mA g(-1), high-rate capacity of 268 mAh g(-1) at 1000 mA g(-1), and long-term stability of 400 mAh g-1 at 250 mA g-1 over 500 cycles followed by 0.002 mAh g(-1)& nbsp;decay per cycle at 5000 mA g(-1)& nbsp;over subsequent 1000 cycles. When paired with LiNi0.5Co0.2Mn0.3O2 cathode as full-cell LIBs, the C-Bi/PMC anode deliver high gravimetric and volumetric energy densities of 352 Wh kg(-1) and 563 Wh L-1, respectively. In-situ X-ray diffraction patterns captured during cycling reveal that the Li+-ion insertion mechanism in the voltage plateau region at 0.7-1.0 V consists of the intercalation between Bi layers followed by the formation of triclinic LiBi phase and the subsequent transition of triclinic LiBi to cubic Li3Bi phase.

Metallic Sn is a promising anode material for Na-ion batteries owing to its high theoretical capacity. However, its practical implementation is hindered by large volumetric changes, interfacial instability, and sluggish sodiation kinetics. Here, a hierarchical yolk-shell nanohybrid composed of Sn yolk and C/SiOC bilayer shell is prepared via simple pyrolysis of silicone oil dispersion containing Sn-precursor. The multifunctional bilayer boosts the sodiation kinetics by providing conductive pathways, enhancing reversible capacity through surface capacitive reactions, and stabilizing the electrode/electrolyte interface. Moreover, abundant void interspaces inside the yolk-shell structure further accommodate large volume changes of the Sn yolk. Such Sn@C/SiOC nanohybrid demonstrates high specific capacity (~500 mAh g-1 at 1 A g-1), remarkable rate performance up to 10 A g-1, and ultrastable cyclability (91.1% retention after 1500 cycles at 5 A g-1). The proposed yolk-shell nanohybrid structure is expected to provide guidance in the development of various high-capacity anodes for energy storage applications.

The authors reveal the mechanisms of degradation of capacity, charge voltage, and discharge voltage of commercially‐available high‐nickel cathode material when it is cycled without a voltage margin by two different charge protocols: constant‐current charging and constant‐current, constant‐voltage charging. With repeated constant‐current charging, the cathode material changes to a non‐periodic cation‐mixed state, which causes a relatively low voltage degradation, whereas during constant‐current, constant‐voltage charging, the cathode material changes from a layered structure to a periodic cation‐mixed spinel‐like phase, with consequent severe voltage decay. This decay results from a reduction in the equilibrium electrode potential and an increase of overpotential which are aggravated in a periodic cation‐mixed state. The findings provide insights into the use of excess Li without charge‐voltage margin in high‐Ni cathode materials.

본 연구에서는 O3형 층상계산화물의 전구체에 나이오븀 코팅 실시하였고 이 방법이 O3형 층상계산화물의 전기화학적 특성을 크게 향상 시킨다는 것을 확인하였다. 코팅된 층상계산화물은 0.2 C에서 충/방전 100 사이클 이후 83 mAh gSUP-1/SUP의 우수한 용량을 보이고 5C의 고율의 충/방전에서는 코팅이 안된 층상계산화물에 비해 약 2.5 배 큰 97.6 mAh gSUP-1/SUP의 용량을 보여주었다.

In article number 1903658, Wonyoung Chang, Kyung Yoon Chung, Sang-Young Lee and co-workers present DNA-wrapped MWCNT as an eco-friendly chemical activation strategy for overlithiated layered oxides (OLO) cathode materials. The Li4Mn5O12-type spinel nanolayers are formed on an OLO surface through a cation exchange reaction of Na+–Li+. The spinel nanolayers significantly improve the charge-discharge kinetics, cyclability, and thermal stability. This unique behavior is comprehensively investigated by in-depth structural/electrochemical characterization.

Integrated material design for insertion materials for Mg batteries is realized utilizing lithium titanate through Cr-doping and particle size reduction.

Silicon oxycarbides (SiOCs) are considered promising anode materials for sodium-ion batteries. However, the mechanisms of Nation storage in SiOCs are not clear. In this study, the mechanism of Nation storage in high-temperature-synthesized SiOCs (1200-1400 degrees C) is examined. Phase separation of the oxygen (O)-rich and carbon (C)-rich SiOxCy domains of SiOC during synthesis was accompanied by the evolution of micropores, graphitic layers, and a silicon carbide (SiC) phase. The high-temperature-synthesized SiOCs exhibited a large voltage plateau capacity below 0.1 V (45-63% of the total capacity). Ex situ measurements and density functional theory simulations revealed that within the sloping voltage region, Nation uptake occurs mainly in the defects, micropores, C-rich SiOxCy phase, and some O-rich SiOxCy phases. In contrast, in the voltage plateau below 0.1 V, Na+-ion insertion into the O-rich SiOxCy phase and formation of Na-rich Si compounds are the main Nation uptake mechanisms. The generated SiC phase confers excellent long-term cyclability to the high-temperature-synthesized SiOxCy.

Hierarchically porous anatase TiO2 microparticles are synthesized in supercritical methanol (scMeOH) in the presence of organic surface modifiers such as oleylamine, oleic acid, and poly(ethylene glycol)methyl ether/citric acid (PEGME/CA) mixture. Primary TiO2 nanoparticles (5-9 nm) that loosely aggregate to form secondary micron-sized particles (0.2-1.5 mu m) are obtained in the presence of PEGME/CA. The surface modifier aids the effective suppression of undesirable crystal growth because their molecules cap the surfaces of growing particles in scMeOH. An ultrathin, conformal and uniform carbon layer with 1-2 nm thickness is then formed on the surface of the TiO2 particles by heat treatment. The carbon-coated TiO2 particles delivers 231 mAh g(-1) at 0.1 C after 50 cycles and 85 mAh g(-1) at 10 C in a lithium-ion battery cell, 275 mAh g(-1) at 0.1 C after 50 cycles, 40 mAh g(-1) at 10 C, and high capacity retention of 94% after 450 cycles in a sodium-ion battery cell. The excellent electrochemical performance of the TiO2 particles is attributed to the small crystallite size, continuous electronic network formed by the close contact of individual carbon-coated primary TiO2 particles, and the effective penetration of the mesopores by the electrolytes. (C) 2019 Elsevier Ltd. All rights reserved.

Lithium-ion batteries (LIBs) using organic liquid electrolytes have been applied in portable devices such as laptops and cellular phones owing to its wide electrochemical stability, high voltages, and excellent energy density. LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode have attracted significant interest as the cathode materials for LIBs owing to their high capacity, excellent rate capability and low cost. NCM523 cathode materials have a disadvantage of structural instability, which caused by the reduction of Ni ions releases oxygen from the crystal structure at the high temeprature or high charged state, which can lead thermal runaway by reacting with the flammable electrolyte. The use of organic liquid electrolytes in LIBs raises safety issues due to its flammable character and the impact on the explosion is greater in particular for relatively large systems such as electrical vehicles and grid storage. To overcome the safety issues, solid state batteries (SSBs) using a non-combustible solid state Li-ion conductor are regarded as the realistic alternative to prohibit the leakage of liquid electrolytes and the resultant fire hazards. However, due to the large resistance in the electrode-electrolyte interface, the capacity retention and cycle effieciency of the SSBs become worse. Previous studies on SSBs have been mainly focused on developing solid state electrolytes with high ion conductivity. Despite growing interest in stability, the systematic studies of safety of SSBs depending on the type of electrolyte has never been evaluated so far. It is necessary for understanding structural deformations on the cathode material in the effects of the reactions beween the electrode and various types of electrolytes, which is essential for ensuring the safety of the batteries. In this study, we investigate the structural degradation and thermal stability on NCM523 cathode materials by taking an advantage of in situ transmission electron microscopy (TEM) in various electrolyte conditions, including conventional liquid electrolyte, poly(ethylene oxide) (PEO) complexes with LiClO4 (PEO-based solid electrolyte), and PEO/LiClO4/Li1.3Al0.3Ti1.7(PO4)3 (LATP) composite electrolyte (PEO-inorganic composite electrolyte). Since the LATP oxide electrolyte has brittleness and the PEO has flexibility, it adopts a composite electrolyte having inorganic and organic phases with good interface contact with the cell electrode. A cell composed of each electrolyte was prepared and charged with cut-off voltages of 3.9 V and 4.3 V at a rate of 0.05 C after the second formation process for stabilzing the cell. The capacity at the same cut-off voltage decreases in the order of conventional liquid electrolyte, PEO-based solid electrolyte, and PEO-inorganic composite electrolytes. To understand the thermal stability and the degradation mechanism, modifications in selected-area electron diffraction (SAED) and electron energy-loss (EEL) spectra of oxygen K-edge and transition metal (Ni, Co, Mn) L-edges of each of charged NCM523 cathode materials are monitored in real time at the range from room temperature to 300°C. Our work demonstrated that contact resistance at the interface between the electrode and electrolyte is important factor. This work provides important information on the relationship with structural deformation and thermal stability of the cathode materials, which is an essential part of the rational design to develope for high engergy densities and safe SSBs. All the details will be available at the meeting. Acknowledgement This work was supported by the Korea Institute of Science and Technology (KIST) Institutional Program (Project 2E28142). This work was also supported by the National Research Foundation of Korea (NRF) grant (No. 2018R1A2B2005205).

Journal Article Using In-Situ Methods to Characterize Phase Changes in Charged Lithium Nickel Cobalt Aluminum Oxide Cathode Materials Get access Eric Stach, Eric Stach Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104 Corresponding author: stach@seas.upenn.edu Search for other works by this author on: Oxford Academic Google Scholar Sooyeon Hwang, Sooyeon Hwang Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973 Search for other works by this author on: Oxford Academic Google Scholar Khim Karki, Khim Karki Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973Department of Mechanical Engineering, Binghamton University, Binghamton, NY 13902 Search for other works by this author on: Oxford Academic Google Scholar Seung Min Kim, Seung Min Kim Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Jeonbuk 565-905, Republic of Korea Search for other works by this author on: Oxford Academic Google Scholar Wonyoung Chang, Wonyoung Chang Center for Energy Convergence, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea Search for other works by this author on: Oxford Academic Google Scholar Kyung-Yoon Chung, Kyung-Yoon Chung Center for Energy Convergence, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea Search for other works by this author on: Oxford Academic Google Scholar Guangwen Zhuo, Guangwen Zhuo Department of Mechanical Engineering, Binghamton University, Binghamton, NY 13902 Search for other works by this author on: Oxford Academic Google Scholar Qiao-Xing Yang, Qiao-Xing Yang Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11973 Search for other works by this author on: Oxford Academic Google Scholar M Stanley Whittingham M Stanley Whittingham Department of Chemistry, Binghamton University, Binghamton, NY 13902 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages 2030–2031, https://doi.org/10.1017/S1431927619010882 Published: 01 August 2019

Ultrathin and uniform carbon layer-coated layered Na2Ti3O7 and tunnel Na2Ti6O13 hybrids were synthesized via a facile and fast method using supercritical methanol and subsequent carbon coating with liquid carbon dioxide as a coating solvent. The carbon content and relative composition of the layered Na2Ti3O7 and tunnel Na2Ti6O13 phases in the hybrids were controlled by adjusting the calcination temperature. The drawbacks of each material could be overcome in the hybrid by taking advantage of the low volume expansion and high electronic conductivity (Na2Ti6O13), the high capacity (Na2Ti3O7), and a carbon coating. A careful examination of the cyclic voltammetry profiles of the sodium titanate hybrids revealed the existence of two different Na+1 ion diffusion pathways in the layered Na2Ti3O7 phase. Under high discharge-charge conditions, some of the Na+ ion uptake in the layered Na2Ti3O7 and the structural integrity of tunnel Na2Ti6O13 resulted in excellent high-rate performance and long-term cyclability in the hybrid.

Concerned about the environmental pollutant such as greenhouse gas emission caused by extensive use of diesel, gasoline vehicle operation, being increased. Implementation of rechargeable battery in EV application because of EV’s zero emission has become very popular. Lithium ion battery (LIB) is one of the successfully commercialized system due to their high operating potential, high energy density and long cycle life [1]. However, high price and limited resources of lithium still makes hard to produce for reasonable price of EV. In contrast of LIB issue, sodium-ion batteries (SIBs) have drawn a considerable attention as an alternative to LIBs in the EV applications because of its relative abundance in the earth crust, global distribution, and drastically lower cost [2]. However, the fundamental differences between sodium and lithium make it challenging to develop a suitable anode material to host Na+ ions such as well-known graphite intercalation affair in NIB system [3]. Moreover, the higher reduction potential of sodium (–2.71 V vs. S.H.E.) as compared to lithium (–3.04 V vs S.H.E) inherently reduces the energy density of battery system. Therefore, there is still considerable efforts underway to develop a potential anode material that allows to host a large amount of Na+ ions at a low voltage potential. Among the various electrode material, sodium titanates (NTOs) have considered one of promising anode materials for SIBs because of their low starting material cost, environmental friendly, and abundance [4]. Among various type of sodium titanate, layered Na2Ti3O7 is one of the most promising phase. It can uptake two Na+ ions per formula unit into its interlayer space at a low average potential of 0.3 V vs Na/Na+ , which could deliver a high theoretical capacity of 177 mAh g-1 [5]. It makes particularly promising to design an anode material with high energy density. However, the poor electronic conductivity of Na2Ti3O7 associated with its large bandgap (3.7 eV) and structural distortion upon Na+ ion uptake leds to sluggish Na+ ion diffusion and cycling stability [6]. In this study, ultrathin and uniform carbon layer-coated, layered Na2Ti3O7 and tunnel Na2Ti6O13 hybrids anode materials synthetic route was successfully developed using facile and fast supercritical methanol and subsequent carbon coating with low viscosity liquid carbon dioxide as a coating solvent. The deficiency of each material, e.g., poor rate performance and cyclability caused by sluggish Na+ ion diffusion and structural distortion of Na2Ti3O7 and the low capacity of Na2Ti6O13, could be overcome in the hybrid by taking advantages of low volume expansion and high electronic conductivity of Na2Ti6O13 and high capacity of Na2Ti3O7 with enhanced conductivity by carbon coating. Through the HR-TEM technique, conformal, uniform and ultrathin carbon layers on the NTO surface with an average thickness of 15 nm was observed. Moreover, significantly decreased charge transfer resistance was confirmed by way of the EIS measurement. A careful analysis of the cyclic voltammetry profiles of this sodium titanate hybrids revealed that the existence of two different Na+ ion diffusion pathways in the layered structure of Na2Ti3O7 phase. Among two different Na+ diffusion pathways, one is kinetically more favorable but energetically less favorable site and the other is kinetically less favorable but energetically more favorable site. Under the high discharge–charge condition, some of Na+ ion uptake in the layered structure of Na2Ti3O7 and structural integrity of tunnel structure of Na2Ti6O13 resulted in excellent high-rate performance and long-term cyclability in the hybrid. ACKNOWLEDGEMENTS This research was supported by a National Research Foundation of Korea (NRF) grant provided by the Korean Government (MSIP) (No. 2016R1A2B3008800, NRF-2018R1A6A3A01012498). REFERENCES [1] D. Larcher, J.M. Tarascon, Towards greener and more sustainable batteries for electrical energy storage, Nat Chem 7 (2015) 19-29. [2] N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, Research Development on Sodium-Ion Batteries, Chem. Rev. 114 (2014) 11636-11682. [3] H. Moriwake, A. Kuwabara, C.A. Fisher, Y. Ikuhara, Why is sodium-intercalated graphite unstable?, RSC Adv. 7 (2017) 36550-36554. [4] F. Xie, L. Zhang, D. Su, M. Jaroniec, S.-Z. Qiao, Na2Ti3O7@N-Doped Carbon Hollow Spheres for Sodium-Ion Batteries with Excellent Rate Performance, Adv. Mater. 29 (2017) 1700989. [5] J. Nava-Avendaño, A. Morales-García, A. Ponrouch, G. Rousse, C. Frontera, P. Senguttuvan, J.-M. Tarascon, M. Arroyo-de Dompablo, M.R. Palacín, Taking steps forward in understanding the electrochemical behavior of Na2Ti3O7, J. Mater. Chem. A 3 (2015) 22280-22286. [6] J. Ni, S. Fu, C. Wu, Y. Zhao, J. Maier, Y. Yu, L. Li, Superior Sodium Storage in Na2Ti3O7 Nanotube Arrays through Surface Engineering, Adv. Energy Mater. 6 (2016) 1502568.

The surface of a spinel LiNi0.5Mn1.5O4 cathode was modified with a nano-LiNbO3 coating layer by employing a Nb citrate-coated Ni0.25Mn0.75(OH)2 precursor and subsequent single calcination with LiOH at 900 °C.

In this work, we investigate the structural evolution and reaction kinetics of LixNi0.8Co0.15Al0.05O2. (NCA) cathode materials induced by the initial charge/ discharge as a function of the state of charge (SOC SO and 90%) and C-rates (0.1-10C), with a combination of high resolution transmission electron microscopy (HRTEM) imaging, selected area electron diffraction (SAED), and electron energy loss spectroscopy (EELS). During initial charging, the effects of C-rates on the structural modifications of NCA cathode materials are strongly dependent on how much the lithium is extracted from the pristine NCA. The structural modifications become more substantial as the extent of the charge increases, particularly at higher C-rates. In the highly delithiated state (90% SOC), even the particles charged at the same C-rate show significant variations in the degree of the structural modifications. The changes in the crystallographic and electronic structures at the subsurface scales, which were induced by the initial charging to 90% SOC at the rate of 0.1C, are nearly recovered during the initial discharge, except for the NCA discharged at the rate of 10C. To quantify the extent of the irreversible phase transition at the nanoscale, we have utilized HRTEM imaging and scanning transmission electron microscopy (STEM) EELS line scanning techniques, which enable us to draw complementary results. This comparative analysis provides valuable information that is useful not only for obtaining a complete understanding of the mechanisms by which the degradation is initiated, but also for improving and designing Ni-rich layered cathode materials with better charging and discharging kinetics.

A simple, effective, and ultra-fast one-pot route is developed to synthesize molybdenum disulfide (MoS2)-reduced graphene oxide (RGO) composites. The method to tightly anchor MoS2 particles on the surface of RGO includes simultaneous reduction of graphene oxide (GO) and heterogeneous nucleation and growth of MoS2 on the RGO surface in supercritical ethanol (scEtOH) medium. The synthesized MoS2-RGO composites have a mesoporous structure with high porosity. The MoS2-RGO composites show an enhanced electrochemical performance due to their unique nanostructure and the synergetic effect of MoS2 and RGO nanosheets when compared to those of compared with bare MoS2 and bare RGO. The MoS2-RGO composite with a MoS2 loading of 74.0 wt% can deliver a high reversible discharge capacity up to 1102 mAh g(-1) at a rate of 0.05 A g(-1) after 80 cycles and an excellent cycling stability of 951 mAh g(-1) at 0.05 A g(-1) after 140 cycles.

The effect of nitrogen on deformation-induced martensitic transformation (DIMT) in metastable 301 austenitic stainless steel has been studied based on the inelastic deformation theory. DIMT is regarded here as continuous relaxation process of internal strain energy accumulated during inelastic deformation. Using the kinetics equation based on the inelastic deformation theory the relationship between the volume fraction of transformed martensite and inelastic strain for DIMT has been successfully verified with the parameter representing the stability of austenite. The addition of nitrogen is experimentally found to increase austenite stability and the critical inelastic strain below which any DIMT is not observed to occur and to decrease the saturation volume fraction of α’ martensite. On the other hand, DIMT has been analyzed with its effect on stress-strain curve shape and mechanical properties in relation to the addition of nitrogen. The characteristic transition from sigmoidal to parabolic curve shape in stress-strain response has disappeared with the addition of nitrogen.