Naoki Nitta

Lithium Iodide as a Promising Electrolyte Additive for Lithium–Sulfur Batteries: Mechanisms of Performance Enhancement

Lithium Iodide (LiI) is reported as a promising electrolyte additive for lithium-sulfur batteries. It induces formation of Li-ion-permeable protective coatings on both positive and negative electrodes, which prevent the dissolution of polysulfides on the cathode and reduction of polysulfides on the anode. In addition to enhancing the cell cycle stability, LiI addition also decreases the cell overpotential and voltage hysteresis.

A Hierarchical Particle–Shell Architecture for Long‐Term Cycle Stability of Li2S Cathodes

A hierarchical particle-shell architecture for long-term cycle stability of Li2S cathodes is described. Multiscale and multilevel protection prevents mechanical degradation and polysulfide dissolution in lithium-sulfur battery chemistries.

Lithographically Patterned Thin Activated Carbon Films as a New Technology Platform for On-Chip Devices

Continuous, smooth, visibly defect-free, lithographically patterned activated carbon films (ACFs) are prepared on the surface of silicon wafers. Depending on the synthesis conditions, porous ACFs can either remain attached to the initial substrate or be separated and transferred to another dense or porous substrate of interest. Tuning the activation conditions allows one to change the surface area and porosity of the produced carbon films. Here we utilize the developed thin ACF technology to produce prototypes of functional electrical double-layer capacitor devices. The synthesized thin carbon film electrodes demonstrated very high capacitance in excess of 510 F g(-1) (>390 F cm(-3)) at a slow cyclic voltammetry scan rate of 1 mV s(-1) and in excess of 325 F g(-1) (>250 F cm(-3)) in charge-discharge tests at an ultrahigh current density of 45,000 mA g(-1). Good stability was demonstrated after 10,000 galvanostatic charge-discharge cycles. The high values of the specific and volumetric capacitances of the selected ACF electrodes as well as the capacity retention at high current densities demonstrated great potential of the proposed technology for the fabrication of various on-chip devices, such as micro-electrochemical capacitors.

In situ small angle neutron scattering revealing ion sorption in microporous carbon electrical double layer capacitors.

Experimental studies showed the impact of the electrolyte solvents on both the ion transport and the specific capacitance of microporous carbons. However, the related structure-property relationships remain largely unclear and the reported results are inconsistent. The details of the interactions of the charged carbon pore walls with electrolyte ions and solvent molecules at a subnanometer scale are still largely unknown. Here for the first time we utilize in situ small angle neutron scattering (SANS) to reveal the electroadsorption of organic electrolyte ions in carbon pores of different sizes. A 1 M solution of tetraethylammonium tetrafluoroborate (TEATFB) salt in deuterated acetonitrile (d-AN) was used in an activated carbon with the pore size distribution similar to that of the carbons used in commercial double layer capacitors. In spite of the incomplete wetting of the smallest carbon pores by the d-AN, we observed enhanced ion sorption in subnanometer pores under the applied potential. Such results suggest the visible impact of electrowetting phenomena counterbalancing the high energy of the carbon/electrolyte interface in small pores. This behavior may explain the characteristic butterfly wing shape of the cyclic voltammetry curve that demonstrates higher specific capacitance at higher applied potentials, when the smallest pores become more accessible to electrolyte. Our study outlines a general methodology for studying various organic salts-solvent-carbon combinations.

Stabilization of selenium cathodes via in situ formation of protective solid electrolyte layer

The lithium/selenium (Li/Se) rechargeable battery chemistry offers a higher energy density than traditional Li ion battery cells. However, high solubility of polyselenides in suitable electrolytes causes Se loss during electrochemical cycling, and leads to poor cycle stability. This study presents a simple technique to form a protective, solid electrolyte layer on the cathode surface. This protective layer remains permeable to Li ions, but prevents transport of polyselenides, thus dramatically enhancing cell cycle stability. The greatly reduced reactivity of polyselenides with fluorinated carbonates (such as fluoroethylene carbonates [FEC]) permits using their in situ reduction for low-cost formation of protective coatings on Se cathodes.

Electrodeposition of Nanostructured Magnesium Coatings

In this work, we report on the electroplating of ultrafine and uniform magnesium (Mg) films on copper (Cu) and carbon nanotube (CNT) paper substrates. By controlling the process parameters and utilizing the pulsed deposition method, the average grain size of Mg was reduced to nano-dimensions. Surface pretreatment of the substrates by depositing a seed layer was found to be an efficient strategy for reducing the energy barrier for nucleation, thus improving nucleation density and the uniformity of deposited coatings. This work provides important guidance for the fabrication of smooth nanostructured Mg films on different substrates for a wide variety of applications.

Toward a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellency of Polyethylene Terephthalate (PET) Films Modified with Perfluoropolyether-Based Polyesters

Original perfluoropolyethers (PFPE)-based oligomeric polyesters (FOPs) of different macromolecular architecture were synthesized via polycondensation as low surface energy additives to engineering thermoplastics. The oligomers do not contain long-chain perfluoroalkyl segments, which are known to yield environmentally unsafe perfluoroalkyl carboxylic acids. To improve the compatibility of the materials with polyethylene terephthalate (PET) we introduced isophthalate segments into the polyesters and targeted the synthesis of lower molecular weight oligomeric macromolecules. The surface properties such as morphology, composition, and wettability of PET/FOP films fabricated from solution were investigated using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. It was demonstrated that FOPs, when added to PET film, readily migrate to the film surface and bring significant water and oil repellency to the thermoplastic boundary. We have established that the wettability of PET/FOP films depends on three main parameters: (i) end-groups of fluorinated polyesters, (ii) the concentration of fluorinated polyesters in the films, and (iii) equilibration via annealing. The most effective water/oil repellency FOP has two C4F9-PFPE-tails. The addition of this oligomeric polyester to PET allows (even at relatively low concentrations) reaching a level of oil repellency and surface energy comparable to that of polytetrafluorethylene (PTFE/Teflon). Therefore, the materials can be considered suitable replacements for additives containing long-chain perfluoroalkyl substances.

Nanostructured composites for high energy batteries and supercapacitors

High power energy storage devices, such as Li-ion batteries and supercapacitors, are critical for the development of zero-emission electric vehicles, large scale smart grid, energy efficient ships and locomotives, wearable devices and portable electronics. This review will focus on our progress with the developments of nanocomposite electrodes capable to improve both the energy and power storage characteristics of the state of the art devices. We review recent advancements in ultra-high capacity conversion-type anodes and cathodes for Li ion batteries as well as carbon-metal oxide and carbon-conductive polymer (nano)composite electrodes for supercapacitors. Various routes to overcome existing challenges will be discussed, including various solution deposition techniques, atomic layer deposition (ALD), chemical vapor deposition (CVD) and electro-deposition. Several designs and implementations of multi-functional electrodes will also be presented.

Lithium Sulfide Cathodes: A Hierarchical Particle–Shell Architecture for Long-Term Cycle Stability of Li2S Cathodes (Adv. Mater. 37/2015)

Hierarchical Li2 S-carbon-nanocomposite particles are synthesized by G. Yushin and co-workers, as described on page 5579, using a simple solution-based method followed by vapor deposition. The multiscale and multilevel protection enabled by the proposed architecture prevents mechanical degradation and polysulfide dissolution in lithium-sulfur batteries. The proposed hierarchical particle-shell design can be effectively utilized for a variety of other conversion-type cathode materials.