Nitriding-Induced Degradation of Structural Steels in High-Temperature Ammonia Utilizing Systems

Fast development of portable electronic devices (such as a smart phone, iPad, and Galaxy Note) and electrified vehicles (such as EVs and HEVs) require better and smaller lithium ion batteries as their energy storages. What is needed for the cathode of the lithium ion battery is a material capable of a higher volumetric energy density as well as gravimetric energy density. However, not only the development of cathode material but also the commercialization of high energy density anode material has been limited due to cathode material’s much lower energy density compared to anode material. In this regard, Li-rich material (Li2MnO3-LiMO2, M=Ni, Mn and Co) that has 150 % higher energy density than commercialized LiCoO2 is the unique next generation cathode material to solve the problem of cathode material’s low energy density. In the past decade, many researches have focused on the surface stabilization method of this material to improve its intrinsic problems of poor cycle/ rate capability and such surface treatment methods have been demonstrated in a few examples, including AlF3 coating and spinel heterostructures, yielding noticeable improvements in rate and cycle ability. Although such surface treatments showed improved rate and cycle performances, achieving the high volumetric energy density and long-term cycle life which are more critical factors for the commercialization of Li-rich material still remained unsatisfied. In general, Li-rich material’s reversible capacity is related with its particle size since the Li2MnO3 phase in large Li-rich material, which is a major component to realize high energy density, is not fully activated in low voltage range below 4.6 V. For this reason, many previous papers reported their results with only small primary particle size below 100nm. The high surface area induced by the small particle size increases side reactions with electrolyte resulting poor long-term cycle life as well as lowers the volumetric energy density. Note that Li-rich material’s deteriorations are generated from its surface and continue to affect its cycling capability and the deteriorations can be divided into two mechanisms: one is side reactions with electrolyte, and another is the phase collapse. The side reactions with electrolyte at its high working voltage yield active material attack speiceses such as HF and electrolyte exhaustion causing Li-rich material’s fast discharge capacity decay during cycles. Furthurmore, it is hardly show long-term cycle life with over 200 cycles since the phase transition from layered structure to spinel-like and NiO rock salt is generated on the surface of active material, and followed by expention of this transition into the bulk. For instance, AlF3 coated Li-rich LNCMO has abrupt capacity fade after 100 cycles, although it showed good rate and cycle capability within 100 cycles. Hence, new active material design, rather than simple surface modification methods such as coating or doping, is required to solve above previous limits.The new material design needs to start with a simple question: how to minimize the damages of surface deteriorations such as side reasction with electrolyte and phase trasnsition on bulk material and maximize volumetric energy density. The most effective solution for the question is increasing the primary particle size with the stable activation method, since the volumetric energy density of cathode material is maximized from synthesis of micron secondary particles consisted of primary particles by using co-precipitation method in industry. Here we demonstrate a novel approach for lithium storage, which is a material design of a secondary structure which consists of large flake shaped primary particle (hundred nanometers x mictrometers) with a novel activation method using simple chemical treatment to achieve superior long-term cycle life with high volumetric energy density. In this design, the large primary particle effectively reduced its surface area producing markedly decreased surface instability reaction as well as high tap density. Interstingly, the chemical approach activated only surface Li2MnO3 phase of large primary particle and the very surface activation effectively overcame the activation problem, which is limit of large primary particle have. This novel concept is very meaningful in that it is the first and unique method to achieve cathode material’s high volumetric energy density with long-term cycle life. As a result, this novel designed material affords remarkable battery performance with extremely high cycle retention during 400 cycles and high volumetric energy density ever reported before.

High Volumetric Energy and Power Density Li2TiSiO5 Battery Anodes via Graphene Functionalization

Simultaneously high mass-loading and volumetric energy density in Ag2O-intercalated MnO2-based supercapacitor with rapid electron/ion transport channels

Fast development of portable electronic devices (such as a smart phone, iPad, and Galaxy Note) and electrified vehicles (such as EVs and HEVs) require better and smaller lithium ion batteries as their energy storages. What is needed for the cathode of the lithium ion battery is a material capable of higher energy density. However, not only the development of cathode material but also the commercialization of high energy density anode material has been limited due to the cathode material’s much lower energy density compared to anode material. In this regard, Li-rich material (Li2MnO3-LiMO2, M=Ni, Mn and Co) that has 150 % higher energy density than commercialized LiCoO­2 is the unique next generation cathode material to solve the problem. In the past decade, many researches have focused on the surface stabilization method of this material to improve its intrinsic problems of poor cycle/ rate capability and such surface treatment methods have been demonstrated in a few examples, including AlF3 coating and spinel heterostructures, yielding noticeable improvements in rate and cycle ability. Although such surface treatments showed improved rate and cycle performances, the realization of the Li-rich material’s high volumetric energy density and long-term cycle life which are more critical factors for the commercialization of Li-rich material still remained unsatisfied. For instance, AlF3 coated Li-rich LNCMO has abrupt capacity fade after 100 cycles, while it showed good rate and cycle capability within 100 cycles. Hence, new active material design, instead of simple surface modification methods such as coating or doping, is required to solve above previous limits. Here we demonstrate a novel approach for lithium storage, which is a material design of a secondary structure which consists of large primary particle with a novel activation method using simple chemical treatment, to achieve superior long-term cycle life with high volumetric energy density. In this design, the large primary particle effectively reduced its surface area producing markedly decreased surface instability reaction as well as high tap density. Interestingly, the chemical approach activates only surface Li2MnO3 phase of large primary particle and the very surface activation effectively overcome the activation problem, which is limit of large primary particle have. This novel concept is very meaningful in that it is the first and unique method to achieve cathode material’s high volumetric energy density with long-term cycle life. As a result, this novel designed material affords remarkable battery performance with high volumetric energy density of ~1980 Wh L-1 and extremely high cycle retention of 90% during 300 cycles.

Calendering of free-standing electrode for lithium-sulfur batteries with high volumetric energy density

Limited by the size of microelectronics, as well as the space of electrical vehicles, there are tremendous demands for lithium-ion batteries with high volumetric energy densities. Current lithium-ion batteries, however, adopt graphite-based anodes with low tap density and gravimetric capacity, resulting in poor volumetric performance metric. Here, by encapsulating nanoparticles of metallic tin in mechanically robust graphene tubes, we show tin anodes with high volumetric and gravimetric capacities, high rate performance, and long cycling life. Pairing with a commercial cathode material LiNi0.6Mn0.2Co0.2O2, full cells exhibit a gravimetric and volumetric energy density of 590 W h Kg−1 and 1,252 W h L−1, respectively, the latter of which doubles that of the cell based on graphite anodes. This work provides an effective route towards lithium-ion batteries with high energy density for a broad range of applications.

As rechargeable Li-ion batteries have expanded their applications into on-board energy storage for electric vehicles, the energy and power must be increased to meet the new demands. Li-rich layered oxides are one of the most promising candidate materials; however, it is very difficult to make them compatible with high volumetric energy density and power density. Here, we develop an innovative approach to synthesize three-dimensional (3D) nanoporous Li-rich layered oxides Li[Li0.144Ni0.136Co0.136Mn0.544]O2, directly occurring at deep chemical delithiation with carbon dioxide. It is found that the as-prepared material presents a micrometer-sized spherical structure that is typically composed of interconnected nanosized subunits with narrow distributed pores at 3.6 nm. As a result, this unique 3D micro-/nanostructure not only has a high tap density over 2.20 g cm-3 but also exhibits excellent rate capability (197.6 mA h g-1 at 1250 mA g-1) as an electrode. The excellent electrochemical performance is ascribed to the unique nanoporous micro-nanostructures, which facilitates the Li+ diffusion and enhances the structural stability of the Li-rich layered cathode materials. Our work offers a comprehensive designing strategy to construct 3D nanoporous Li-rich layered oxides for both high volumetric energy density and power density in Li-ion batteries.

Development of electric vehicles and portable electronics triggers a research boom for the advanced lithium ion batteries (LIBs) with high energy density. For these reasons, High specific capacity anodes including Sn, Si and Ge with the specific capacity over 1500 mAh g−1 has been highlighted as alternative anodes to achieve the high energy LIBs. Although the huge volume change considered as the main reason of short cycle life upon repeated charging-dischrage process has been recently handled through the nano-engineering, its utilization as a commercial anodes has been still hindered when considering the low volumetric energy density affected by the several factors (low coulombic efficiency, high electrode swelling ratio, high working voltage and low cycling performance). On the other hand, conventional graphite exhibits the low working voltage and high cycling stability, and its high true density of 2.25 g cc−1 and low expansion ratio of 8% during cycling could lead to the high theoretical volumetric energy density of over 770 Wh L−1. However, density of the currently used electrode using conventional graphite anodes is 1.4 ~ 1.6 g cc−1 bringing about volumetric energy density of 550 Wh L−1. In case of the high electrode density of over 1.9 g cc−1, the poor electrolyte impregnation causes the unreacted active material with electrolyte upon cycling, which leads to the unbalance of N/P ratio (much higher areal capacity of cathode than those of anode) resulting in the Li metal plating. Therefore, Promoting the electrolyte penetration to electrode which is comprised of the highly densified active materials is key factors to meet the high energy density lithium ion batteries by using conventional graphite anodes. In this study, we synthesized cyanoethyl polyvinyl alcohol (PVA-CN) having feature of high degree of impregnation and coated on conventional graphite surface. Because of the PVA-CN with the higher permittivity which is one of critical factors determining the impregnation of electrolyte than these of other polymer such as SBR and PVDF, PVA-CN coated graphite composite demonstrated high cycling performance under the high electrode density of 1.9 g cc−1 without any Li plating, leading to the high volumetric energy density of over 650 Wh L−1.

Direct assembly of micron-size porous graphene spheres with a high density as supercapacitor materials

Alternately stacked thin film electrodes for high-performance compact energy storage

Supercapacitors are increasingly in demand among energy storage devices. Due to their abundant porosity and low cost, activated carbons are the most promising electrode materials and have been commercialized in supercapacitors for many years. However, their low packing density leads to an unsatisfactory volumetric performance, which is a big obstacle for their practical use where a high volumetric energy density is necessary. Inspired by the dense structure of irregular pomegranate grains, a simple yet effective approach to pack activated carbons into a compact graphene network with graphene as the “peels” is reported here. The capillary shrinkage of the graphene network sharply reduces the voids between the activated carbon particles through the microcosmic rearrangement while retaining their inner porosity. As a result, the electrode density increases from 0.41 to 0.76 g cm−3. When used as additive‐free electrodes for supercapacitors in an ionic liquid electrolyte, this porous yet dense electrode delivers a volumetric capacitance of up to 138 F cm−3, achieving high gravimetric and volumetric energy densities of 101 Wh kg−1 and 77 Wh L−1, respectively. Such a graphene‐assisted densification strategy can be extended to the densification of other carbon or noncarbon particles for energy devices requiring a high volumetric performance.

In the past few years, considerable effort has been devoted to the study of graphene as energy storage material for supercapacitors. More recently other 2D materials have emerged such as MXenes and transition metal dichalcogenides. In this study, chemically exfoliated and restacked nanosheets of metallic 1T phase MoS2 has been introduced as a supercapacitor electrode and its electrochemical charge storage mechanism has been investigated in aqueous and organic electrolytes. High volumetric capacitance values (650F/cm3) have been obtained with 1T phase MoS2 even at high scan rates. High volumetric energy density (0.1Wh/cm3) and power density (51W/cm3) values were measured with organic electrolytes. During chemical exfoliation and restacking process, structural, chemical and electronic properties of MoS2 change via phase transformation from semiconducting 2H MoS2 to metallic 1T MoS2. High charge storage performances can be explained with the distinct structural and electronic properties of metallic 1T phase MoS2. The good electrical conductivity of the 1T phase enables thicker and binder free film fabrication. Interestingly the capacitance obtained from 1T MoS2 is surprisingly high comparing the modest surface area of MoS2. In order to understand the charge storage mechanism, ex-situ XRD measurements were conducted. Our results demonstrate that cations (Proton, Li+, Na+, K+, TEA+) intercalate to the two dimensional MoS2 flakes and enhance the accessible surfaces for the charge storage. Charge storage performance is stable over 5000cycles (97% capacitance retention). Our study provides insight into the electrochemical behavior of the phase engineered exfoliated and restacked nanosheets.

Lithium polysulfide batteries possess several favorable attributes including low cost and high energy density for grid energy storage. However, the precipitation of insoluble and irreversible sulfide species on the surface of carbon and lithium (called “dead” sulfide species) leads to continuous capacity degradation in high mass loading cells, which represents a great challenge. To address this problem, herein we propose a strategy to reactivate dead sulfide species by reacting them with sulfur powder with stirring and heating (70 °C) to recover the cell capacity, and further demonstrate a flow battery system based on the reactivation approach. As a result, ultrahigh mass loading (0.125 g cm–3, 2 g sulfur in a single cell), high volumetric energy density (135 Wh L–1), good cycle life, and high single-cell capacity are achieved. The high volumetric energy density indicates its promising application for future grid energy storage.

Graphene oxide-modified zinc anode for rechargeable aqueous batteries

High volumetric energy density of LiFePO4/C microspheres based on xylitol-polyvinyl alcohol complex carbon sources