Nickel Current Collector Research Articles

The effect of current collectors on polymer-based energy-generating units inspired by the electric organs of eels

Bioinspired energy generation systems, particularly focusing on replicating the electrocytes, which are the cells of electric discharging organs of electric eels, have attracted much attention for battery cell development. Motivated by this trend, this study explores the effects of different current collectors (Au, Cu, Ni foils, and multilayer graphene-coated Ni foam) on the cell performance and open-circuit potentials of bioinspired energy-generating units. The results indicate that asymmetric current collectors, particularly the Cu-cell-Al configurations, yielded higher open circuit voltages and more stable power outputs over extended cycles. A polymer-based stacked energy unit between nickel current collectors achieved a high open circuit voltage of 230 mV and had a 75 % capacity decrease after 500 cycles. The developed devices, especially with asymmetric current collectors, provided a promising energy density (6541μWh.cm−2) and power density (50 mW.cm−2) while maintaining stability over thousands of cycles. In conclusion, flexible energy-generating units with potential applications in long-term energy needs were proposed in this study by incorporating electrochemical interactions to enhance the power output.

PANI-Coated VOx Nanobelts with Core-Shell Architecture for Flexible All-Solid-State Supercapacitor.

As a typical pseudocapacitor material, VOx possesses mixed valence states, making it an ideal electrode material for symmetric screen-printed supercapacitors. However, its high internal resistance and low energy density are the main hurdles to its widespread application. In this study, a two-dimensional PANI@VOx nanobelt with a core-shell architecture was constructed via a two-step route. This strategy involves the preparation of VOx using a solvothermal method, and a subsequent in situ polymerization process of the PANI. By virtue of the synergistic effect between the VOx core and the PANI shell, the optimal VOx@PANI has an enhanced conductivity of 0.7 ± 0.04 S/Ω, which can deliver a high specific capacitance of 347.5 F/g at 0.5 A/g, a decent cycling life of ~72.0%, and an outstanding Coulomb efficiency of ~100% after 5000 cycles at 5 A/g. Moreover, a flexible all-solid-state symmetric supercapacitor (VOx@PANI SSC) with an in-planar interdigitated structure was screen-printed and assembled on a nickel current collector; it yielded a remarkable areal energy density of 115.17 μWh/cm2 at an areal power density of 0.39 mW/cm2, and possessed outstanding flexibility and mechanical performance. Notably, a "Xiaomi" hygrothermograph (3.0 V) was powered easily by tandem SSCs with an operating voltage of 3.1 V. Therefore, this advanced pseudocapacitor material with core-shell architecture opens novel ideas for flexible symmetric supercapacitors in powering portable/wearable products.

Enhancing supercapacitor performance through graphene flame synthesis on nickel current collectors and active carbon material from plant biomass

This study introduces a novel approach utilizing flame-synthesized few-layer graphene on a metal current collector for energy storage devices. The graphene was synthesized through a scalable, one-step method involving a flame generated by pre-mixed propane/oxygen/argon gases. To ensure purity and eliminate undesired amorphous structures, ultrasonication was employed. The method successfully produced 5 to 10 layers of graphene on a nickel substrate with rapid growth rates (30–60 s) facilitated by a steady supply of precursors at a stable temperature. The resulting current collector was utilized in the assembly of a supercapacitor, where activated carbon derived from barley straw served as the active electrode material. The cycling stability test reveals that all electrodes maintain approximately 98 % of their initial specific capacitance over 5000 charge-discharge cycles, except for the Ni/Flame-based graphene current collector, which experiences a substantial decrease in capacitance. This study presents a scalable and straightforward concept for incorporating thin layers of graphene onto a metal current collector to enhance the electrochemical characteristics of the electrode. The continuous processing capability and high growth rate of graphene contribute to the method's effectiveness. The study demonstrates the potential of flame-synthesized few-layer graphene for improving the electrochemical properties of supercapacitor electrodes, and its suitability for large-scale production, making it a promising avenue for future energy storage advancements.

Insights into the Lithium Nucleation and Plating/Stripping Behavior from Ionic Liquid-Based Battery Electrolytes

Lithium-metal batteries are anticipated to become the next-generation battery technology, allowing for substantially higher energy densities. To maximize the energy density, however, a “zero excess” of lithium in the cell is a must, e.g., by initially storing all electrochemically active lithium in the positive electrode.1 Nevertheless, this requires the fully reversible deposition of metallic lithium, i.e., a Coulombic efficiency of essentially 100%.2 Herein, the investigation of the lithium nucleation and plating/stripping from ionic liquid-based electrolytes composed of N-butyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) on nickel current collectors is reported, involving a comprehensive set of electrochemical techniques coupled with operando and in situ atomic force microscopy and ex situ X-ray photoelectron spectroscopy. It was found that the morphology of the deposited lithium, the chemical composition of the interphase formed on the nickel current collector, and the reversibility of the lithium plating and stripping is highly dependent on the ratio of the ionic liquid and the lithium salt. Moreover, the addition of suitable film-forming additives allows for lower overpotentials and greater reversibility by tuning the interphase composition. The results are anticipated to contribute to the development of advanced electrolyte systems for “zero excess” lithium-metal batteries.(1) Nanda, S., Gupta, A., and Manthiram, A. Anode-Free Full Cells: A Pathway to High-Energy Density Lithium-Metal Batteries. Adv. Energy Mater. 2021, 11, 2000804. DOI: 10.1002/aenm.202000804(2) Hobold, G.M., Lopez, J., Guo, R. et al. Moving beyond 99.9% Coulombic efficiency for lithium anodes in liquid electrolytes. Nat. Energy 2021, 6, 951–960. DOI: 10.1038/s41560-021-00910-w

(Invited, Digital Presentation) Understanding Interfacial Chemo-Mechanics of Two-Dimensional Materials-Based Heterogeneous Functional Materials for Energy Storage

Two-dimensional (2D) materials and their heterostructures (2D + nD, n = 0,1,2,3) attracted enormous interest in wide range of applications including electrochemical systems, e.g., batteries. Electro-chemo-mechanics, the coupling of mechanics and electrochemistry, plays a crucial role in designing these systems. This talk considers battery as a model system and demonstrates the role of 2D materials in overcoming various interfacial electro-chemo-mechanical challenges. 2D materials are engineered as the van der Waals (vdW) “slippery” interface. For example, silicon (Si) electrodes can be placed over the graphene-coated current collector for Lithium-Ion Batteries (LIBs). This arrangement provides less stress build-up and less stress “cycling” on the vdW slippery substrate instead of a fixed interface. 2D materials such as MXenes can also be used to replace polymer binders, e.g., in Si-based LIBs. Our DFT studies show more stable performance and higher Coulombic efficiency for Si films deposited on graphene-coated nickel (i.e., slippery interface) than conventional nickel current collectors. The interface strength of monoclinic Se (selenium) is 0.43 J/m2, which is similar in magnitude in amorphous Si with graphene (0.41 J/m2). However, the interface strength of c-Se on a 3D aluminum (Al) current collector is higher (0.99 J/m2), suggesting a stronger adhesion for 3D/3D interface than 3D/2D interface. Furthermore, interface strength variation between a-Si and Ti3C2Tx MXenes are determined for various surface functional groups (Tx). The completely hydroxylated Ti3C2 has the highest interface strength of 0.60 J/m2 with a-Si. The talk also summarizes our recent efforts in developing High Dimensional Deep Learning Potential (HDDLP) to study interfacial electro-chemo-mechanics in 2D materials-based systems. Our computational results are in good agreement with experiments. Besides batteries, our comprehensive interface analyses are beneficial in advancing understanding of other 2D materials-based systems, e.g., sensors, fuel cells, solar cells, nanomedicine, soft-actuators, etc.

All‐Direct‐Ink‐Writing of Artistic Supercapacitors: Toward On‐Demand Embodied Power Sources

AbstractDespite the extensive studies on printed power sources for user‐customized shape‐versatile electronics, most of them have still focused on printing of electrochemically active materials, with little attention to passive components such as current collectors and packaging, thus hindering their versatile application. Here, all‐direct‐ink‐writing (DIW) of artistic supercapacitors (ASCs) as a facile and scalable strategy to enable power source‐unitized monolithic electronic devices with various form factors is demonstrated. Interdigitated nickel current collectors embedded inside a polyurethane support layer are fabricated using DIW printing, which can facilitate the subsequent printing of multi‐scale, ultrathick electrodes. Interstitial voids between the DIW‐printed adjacent electrode layers are densely infiltrated by click‐crosslinkable electrolyte inks with well‐tuned rheological properties. The void‐free electrode/electrolyte assembly is conformally printed with a waterproof packaging ink to enable hermetic encapsulation, eventually producing all‐DIW‐printed ASCs with efficient space utilization, design diversity, and dimensional scalability. Notably, the resulting ASC can be seamlessly unitized with arbitrary‐shaped 3D objects (e.g., miniature pagodas), allowing for the potential development of on‐demand embodied power sources for electronic devices.

Powder metallurgical 3D nickel current collectors with plasma-induced Ni3N nanocoatings enabling long-life and dendrite-free lithium metal anode

Building three-dimensional (3D) current collectors is a promising strategy to surmount the bottlenecks of lithium metal anodes (LMAs), but the regulation methodology of a 3D current collector has seldom been considered comprehensively concerning both skeleton architectures and surface coatings. Herein, a robust porous 3D nickel skeleton (NS) with lithiophilic Ni3N nanocoatings (Ni3N@NS) is synthesized via an integrative route of powder metallurgy/plasma-enhanced nitridation technics. The facile powder metallurgical method facilitates the adjustment of NS architectures toward sufficient electrolyte adsorption and even current density distribution, while the followed plasma-enhanced chemical vapor deposition (PECVD) method can induce compact Ni3N nanocoatings on NS, which reduces the Li nucleation overpotential, accelerates the Li-ion transfer, and facilitates a highly reversible oriented texture of Li deposition morphology owing to the dense and homogenous deposition of Li into the pores. The optimized Ni3N@NS current collector shows a high averaged Coulombic efficiency (CE) of 98.8% over 350 cycles, a prolonged lifespan of 1000 h (at 2 mA cm−2) in symmetrical cells, together with the significant performance in full cells. The ingenious methodology reported in this work can also be broadly applicable for the controllable production of other 3D skeletons with nitride nanocoatings for various applications.

Exploiting Super-Lithiation in 3D Mesostructured Polyimide Electrodes: Towards Practical Organic Batteries

Recent developments in redox-active organic molecules appear to be providing sustainable and cost-effective electrode materials as potential alternatives to conventional metal-based electrodes for lithium-ion batteries (LIBs). However, utilization of the organic battery electrodes in practical applications has been quite limited. The rational design principles of the electrode structure would be beneficial in concurrently achieving practical performance demands of high energy, fast charging rate, and long-term cyclability. In this work, we conceive a lithographic fabrication strategy for realizing a 3D mesostructured organic electrode that exploits a ‘super-lithiation’ phenomenon of nearly all unsaturated C=C bonds in multi-carbonyl polyimide. The polyimide layer grown on the ordered porous nickel current collector which is prepared via proximity-field nanopatterning (PnP), generates promoted super-lithiation and shows a much higher specific capacity of 1300 mAh g−1 compared to that of the 2D electrode (270 mAh g−1). We attribute the high electrochemical activity to fast reaction kinetics through the efficient pathways for Li-ions and electrons within the electrode, as well as pathways for rapid transport of ions within the interconnected, electrolyte-filled porous network. The effect of the 3D structure is further corroborated by the unprecedented high-rate capability (achieved rates up to 400 C) and 83% capacity retention at 10 C (15 A g−1) after 250 cycles. Finally, the full electrode-basis capacity reaches 2800 mAh cm−3, surpassing the target lines required to meet the energy density target of 1500 Wh L−1 (on half-cell level) for hybrid electric vehicles. Our findings suggest that our strategic electrode design may contribute to spurring the commercialization of organic electrodes for practical systems in near future. Furthermore, the 3D nickel with the continuous, periodic porous network used in this study is expected to accommodate the severe volume expansion and induce uniform Li deposition as an effective current collector. It could be further studied for the development of Si- and Sn-based anodes for advanced LIBs or dendrite-free Li anode for lithium-metal batteries.

Thermally-enhanced microstructures of Si/TiNi film electrodes for improved electrochemical properties

The structural and electrochemical properties of annealed Si film electrodes with titanium–nickel (TiNi) current collectors have been investigated to identify compounds and microstructures that improve electrochemical performances. The as-deposited Si/TiNi electrode consisted of amorphous Si (α–Si) and crystalline B2–TiNi alloy at room temperature. Only a thin oxide layer was formed at the interface, and any significant microstructural change was not found at 500 °C compared to the as-deposited electrode. The Ni atoms started to migrate from the TiNi alloy to the Si film at 600 °C, which resulted in the formation of a Ti-rich (Ti2Ni) layer at the interface. A large amount of Ni diffused into the Si film at 700 °C led to the formation of nickel silicide (NiSi2) particles being dispersed in the film. The Si/TiNi electrodes that were annealed at a temperature exceeding 600 °C showed improved electrochemical properties such as initial efficiency (~90%) and cycle performance (50% capacity retention after 300 cycles). The excellent electrochemical performance was achieved by enhancing the structural stability in annealed Si/TiNi electrodes.

Characterizations of nickel mesh and nickel foam current collectors for supercapacitor application

Nickel (Ni) current collectors having a three-dimensional and porous structure are considered attractive contestants for high-efficiency supercapacitors. Therefore, Ni current collectors have a unique architecture and outstanding electrochemical properties. This study reports the effect of electrochemical characterizations on the electrochemical behavior and physical properties of Ni mesh and Ni foam. Cyclic voltammetry (CV) and galvanostatic charge discharge (GCD) are used to examine the electrochemical properties and life span of the Ni mesh and Ni foam as a current collector in a supercapacitor application. Structural and microstructural characterizations are performed to verify the formation of an oxide layer after 1000 cycles of CV analysis. Results show that Ni foam can increase the yield electrochemical performance of the supercapacitor. Ni foam present better efficiency (35 F g−1) compared to the Ni mesh (12 F g−1) at 10 mV s−1 scan rate by using 2 mg imaginary mass of active material. This result shows that Ni foam has good electrochemical performance and reversibility, higher pseudocapacitance, weaker polarization, and enhance rotating performance as to Ni mesh. The porous structure of Ni foam is in control for improving of the electrochemical properties, therefore, the electrochemical region was increased and shortened ion diffusion. Structural analysis shows that Ni mesh and Ni foam are oxidized after the electrochemical analysis and transformed to nickel oxide hydroxide (NiOOH). Higher specific surface area between the electrode and electrolyte leads to excellent electrochemical and pseudocapacitive performance of the Ni foam compared to the Ni mesh, even if the materials of current collectors are the same. Hence, the physical structure of the current collectors have a critical part in improving the energy density of the supercapacitor.

Nickel percolation and coarsening in sintered Li4Ti5O12 anode composite

AbstractInherently safe all‐solid‐state lithium‐ion battery anodes with high electronic and ionic conductivity are sought to enable next‐generation electric propulsion systems. In novel architectural concepts, multifunctionality of battery materials will provide simultaneous mechanical load bearing and electrochemical energy storage functionality for systems level mass savings. Co‐processing of strain‐free lithium titanate anode and nickel current collector was explored to provide structural integrity and electrical conductivity for a load‐bearing anode with bulk current collection capability. In this study, the effects of processing conditions on densification, electrical conductivity, and microstructural evolution were characterized for Li4Ti5O12‐Ni (LTO‐Ni) composites. Densification of LTO‐Ni was achieved at 900°C and above, and nickel content had minimal effect on final density compared to sintering temperature and time. Electronic conductivity was modeled by percolation theory, exhibiting a large dependence on nickel content and bulk density. Bulk electrical conductivity greater than 1 S/cm was achieved at volume fractions above the percolation threshold. Modeling of microstructural evolution applied Ostwald ripening theories to describe diffusion governing the growth of average nickel particle size and the change in size distributions. Volume fraction effects resulted in larger average Nickel particle sizes and an activation energy of 1.04 eV was measured for nickel particle coarsening.

Effect of internal hydrocarbon reforming during coupled operation of a biomass gasifier with hot gas cleaning and SOFC stacks

AbstractIn the context of energy transition and climate change, a combination of highly efficient modern solid oxide fuel cells (SOFC) and thermo‐chemical conversion of biogenic residues could complement other intermittent renewable sources such as wind and solar. In order to reduce required gas cleaning efforts and to increase the process efficiency, the influence of hydrocarbons on SOFC performance is experimentally investigated in this study. For the first time, the operation of Ni/YSZ anode‐supported cells in Jülich F10 stacks is performed with pre‐reformed and with bio‐syngas containing full hydrocarbon content at realistic current densities. Sulfur and other impurities were removed in both cases. No degradation could be observed within normal operation on clean gas. With the tar reformer bypassed, the pressure drop over the stack increased due to severe carbon deposition on the anode substrate and the nickel current collector mesh inside the SOFC stack, so that operation had to be terminated after five hours. This behavior is different from single‐cell tests, where electrochemical degradation is the limiting factor. The results show that improvements are not only necessary for cell materials and that future research must also consider other stack components.

Excellent electrochemical stability of graphite nanosheet-based interlayer for electric double layer capacitors

Characterized by high power density and long cycle life, electric double layer capacitors have been considered to be most promising energy storage devices. However, the use of low electrolyte concentration due to the degradation of current collector in high electrolyte concentration involves their limitation for ionic diffusion at high current densities during cycling, leading to a low electrochemical behavior. Therefore, the sensible design of the interfacial structure between the current collector and the active material is a supreme technology for accomplishing desired requirements as the improved performance of current collector. In the present paper, by applying the graphite nanosheet as an interlayer on the nickel (Ni) current collector, the electrochemical performance is improved with high specific capacitance (236 F g−1 at the current density of 0.2 A g−1), outstanding high-rate ability (87%), and excellent cycling stability (93% after 10,000 cycles in the high-concentration electrolyte). Hence, the advantages of this unique approach include the improvement of the contact area between the current collector and the active material and prevention of the oxidation of the Ni current collector. This enhanced electrochemical performance suggests that this interface engineering is a powerful strategy for potential applications in electric double layer capacitors.

A Flexible Supercapacitor with High True Performance

SummaryThe demand for better “true performance” of supercapacitors, which is defined as the energy density based on the packaged cell with high active mass loading, is spurred by the ever-increasing energy storage market. The true performance of present supercapacitors is unsatisfactory, greatly limited by the currently used current collectors. Here, we develop a through-pore structured nickel current collector with excellent flexibility by electrodepositing nickel on laser-drilled stainless steel sheets filled with epoxy resin. Based on the new current collector, the electrodes possess higher performance than those fabricated by employing conventional current collectors. At a high active mass loading, the assembled supercapacitors show superior flexibility and high energy densities of 50.4 W hr L−1 and 30.1 W hr kg−1, respectively, based on the packaged cell, outperforming the present supercapacitors. Our strategy provides a new opportunity for promoting the further development of supercapacitors by enhancing the true performance.

A Flexible Supercapacitor with High True Performance

The demand for better “true performance” of supercapacitors, which is defined as the energy density based on the packaged cell with high active mass loading, is spurred by the ever-increasing energy storage market. The true performance of present supercapacitors is unsatisfactory, which is greatly limited by the currently used current collectors. Here, we develop an ultrathin ultralight through-pore structured nickel current collector with excellent flexibility by electrodepositing nickel on laser drilled stainless steel sheets filled with epoxy resin. Based on the new current collector, the electrodes possess higher performance than those fabricated by employing conventional current collectors. At a high active mass loading, the assembled supercapacitors show superior flexibility and high energy densities of 50.4 W hr L−1 and 30.1 W hr kg−1 based on the packaged cell, outperforming the present supercapacitors. Our strategy provides a new opportunity for promoting the further development of supercapacitors by enhancing the true performance.

Active role of inactive current collector in aqueous aluminum-ion battery

The recent revival of research interest in rechargeable aluminum-ion batteries has opened up avenues to overcome its inherent challenges. While there are fierce attempts to find suitable electrode materials for aluminum-ion batteries, it is very important to carefully evaluate them. We show here that an essential criterion for correct electrochemical evaluation of aqueous aluminum-ion batteries is to appropriately select the current collector. Considering anatase TiO2 as a model electrode material, it is demonstrated that type of current collector could transform an inactive electrode material to an active one. TiO2 could exhibit initial Al3+ ion storage capacity of 256 mAhg−1 at a current density of 4 Ag−1 with graphite current collector, whereas it is only 82 mAhg−1 with titanium current collector at similar current density. Interestingly, no charge/discharge characteristics could be obtained with stainless steel and nickel current collectors at any current densities.

Utilizing van der Waals Slippery Interfaces to Enhance the Electrochemical Stability of Silicon Film Anodes in Lithium-Ion Batteries.

High specific capacity anode materials such as silicon (Si) are increasingly being explored for next-generation, high performance lithium (Li)-ion batteries. In this context, Si films are advantageous compared to Si nanoparticle based anodes since in films the free volume between nanoparticles is eliminated, resulting in very high volumetric energy density. However, Si undergoes volume expansion (contraction) under lithiation (delithiation) of up to 300%. This large volume expansion leads to stress build-up at the interface between the Si film and the current collector, leading to delamination of Si from the surface of the current collector. To prevent this, adhesion promotors (such as chromium interlayers) are often used to strengthen the interface between the Si and the current collector. Here, we show that such approaches are in fact counter-productive and that far better electrochemical stability can be obtained by engineering a van der Waals "slippery" interface between the Si film and the current collector. This can be accomplished by simply coating the current collector surface with graphene sheets. For such an interface, the Si film slips with respect to the current collector under lithiation/delithiation, while retaining electrical contact with the current collector. Molecular dynamics simulations indicate (i) less stress build-up and (ii) less stress "cycling" on a van der Waals slippery substrate as opposed to a fixed interface. Electrochemical testing confirms more stable performance and much higher Coulombic efficiency for Si films deposited on graphene-coated nickel (i.e., slippery interface) as compared to conventional nickel current collectors.

Three-Dimensional Lithium-Iodine Microbatteries for Implantable Devices

Conventional batteries use thick electrodes that provide high energy density, but have large ion transport lengths that limit their current densities. Thin film batteries utilize thin layers of material and small transport lengths for higher power, but are limited in their total energy due to low mass loading. Three-dimensional batteries combine both high mass loading and small ion transport lengths due to their architected design, allowing for both high energy and power densities over a small footprint area. Accessing height in battery design permits much more active material than a planar thin film battery. Modern nanofabrication techniques, such as two-photon lithography, can fabricate 3D structures at the micro and nano scale that can be incorporated into a small-scale architected 3D cell. This type of battery could power the next generation of bio-implantable devices and miniaturized wearable sensors. We demonstrate the fabrication of architected anodes using two-photon lithography to form a polymer scaffold. A gold layer on the nickel current collector alloys with lithium, creating an adhesion layer that assists lithium electrodeposition. The cathode used is iodine mixed with poly(2-vinylpyridine) (P2VP), which forms a lithium iodide solid electrolyte in situ when the anode and cathode come in contact and can be poured into the structure in its molten state. The geometry of the anode is determined by surface area and the pore size is determined to accommodate the thickness of the lithium iodide layer and infiltration of cathode. The increase in surface area and decrease in ion transport lengths from the 3D architecture provide improved performance of the primary battery over planar cells with the same footprint area. Other battery chemistries could be investigated with such a battery design to enhance performance.

High Capacity Li-S Secondary Battery Using Vertically-Aligned CNT Electrode

In recent years, the lithium-sulfur (Li-S) secondary battery has been energetically researched worldwide as a good candidate for next-generation secondary batteries. The sulfur active material has a theoretical capacity of 1675 mAh g-1and is abundant and highly inexpensive. However, several issues are associated with the use of Li-S secondary batteries, such as low utilization due to the insulating property of sulfur and the redox shuttle phenomenon caused by the dissolution of polysulfides generated during the discharge process. In the present work, we have developed a Li-S secondary battery using the carbon nanotube (CNT) technoloy. Multiwalled-CNTs were directly grown on a nickel current collector by using the thermal chemical vapor deposition (CVD) method. The CNT films were used as the electrode for the Li-S battery. The S-CNT cathode was fabricated by impregnating it with molten sulfur. Then, sulfur powder was uniformly placed on the CNT film and heated at more than the melting point of 113°C. Our CNT has a diameter of 10-15 nm and a length of 200-600 µm. Therefore, the CNT electrode has a wide reaction area owing to its large specific surface area. In addition, the active materials can react rapidly because the electrons quickly access through the CNTs that connect directly with the current collector. At IMLB 2014, we reported that coin-cell-type Li-S batteries with a sulfur loading of up to 10 mg cm-2 operate at a current density of 0.5 mA cm-2 [1]. However, more sulfur loading is required, in order to achieve the electrode capacity of 300 Wh kg-1 for practical usage. As sulfur loading increased to more than 10 mg cm-2, the discharge capacity decreased dramatically, probably owing to be attributed to inhomogeneous sulfur distribution in the CNT film. Moreover, the CNT films fell off the nickel current collector because of the shrinkage of the CNT bundles owing to the absorption of sulfur. Therefore, we attempted to synthesize harder CNT films with homogeneously impregnated sulfur. A thick amorphous carbon layer was coated on the CNTs by optimizing the thermal CVD process, thus making the CNT films harder. Moreover, the adhesiveness between the CNTs and the nickel current collector was enhanced, which improved CNT exfoliation. For homogeneous distribution, sulfur impregnation was performed in vacuum. The sulfur was considered to spread over the CNT films more uniformly. We could obtain the stable coin-cell-battery performance with sulfur loading of up to 20 mg cm-2, and the capacity was estimated to be more than 300 Wh kg-1 [2]. We manufactured 1 Ah-class pouch cell, with electrode surface area of 50 cm2. Reference [1] N.Tsukahara, presented at The 17thInternational Meeting on Lithium Batteries, Como, 2014 (unpublished) [2] T. Yamada, presented at The 56th Battery Symposium, Nagoya, 2015 (unpublished) Figure 1

Enhanced Lithiation Cycle Stability of ALD-Coated Confined a-Si Microstructures Determined Using In Situ AFM.

Microfabricated amorphous silicon (a-Si) pits ∼4 μm in diameter and 100 nm thick were fabricated to be partially confined in a nickel (Ni) current collector. Corresponding unconfined pillars were also fabricated. The samples were coated with 1.5, 3, or 6 nm of Al2O3 ALD. These samples were tested in electrolytes of 3:7 by weight ethylene carbonate:ethyl methyl carbonate (EC:EMC) with 1.2 M LiPF6 salt with and without 2% fluoroethylene carbonate (FEC) and in a pure FEC electrolyte with 10 wt % LiPF6. The samples were imaged with an atomic force microscope during electrochemical cycling to evaluate morphology evolution and solid electrolyte interphase (SEI) formation. The partially confined a-Si structures had superior cycle efficiency relative to the unconfined a-Si pillars. Additionally, samples with 3 nm of ALD achieved higher charge capacity and enhanced cycle life compared to samples without ALD, demonstrated thinner SEI formation, and after 10 cycles at a 1 C rate remained mostly intact and had actually decreased in diameter. Finally, the samples with 3 nm of ALD had better capacity retention in the baseline 3:7 EC:EMC than in either of the FEC containing electrolytes.