Cryopreservation technology allows long‐term banking of biological systems. However, a major challenge to cryopreserving organs remains in the rewarming of large volumes (>3 mL), where mechanical stress and ice formation during convective warming cause severe damage. Nanowarming technology presents a promising solution to rewarm organs rapidly and uniformly via inductive heating of magnetic nanoparticles (IONPs) preloaded by perfusion into the organ vasculature. This use requires the IONPs to be produced at scale, heat quickly, be nontoxic, remain stable in cryoprotective agents (CPAs), and be washed out easily after nanowarming. Nanowarming of cells and blood vessels using a mesoporous silica‐coated iron oxide nanoparticle (msIONP) in VS55, a common CPA, has been previously demonstrated. However, production of msIONPs is a lengthy, multistep process and provides only mg Fe per batch. Here, a new microporous silica‐coated iron oxide nanoparticle (sIONP) that can be produced in as little as 1 d while scaling up to 1.4 g Fe per batch is presented. sIONP high heating, biocompatibility, and stability in VS55 is also verified, and the ability to perfusion load and washout sIONPs from a rat kidney as evidenced by advanced imaging and ICP‐OES is demonstrated.
Doped Li8ZrO6 (LZO) is a pseudolayered material under consideration for lithium-ion battery cathodes and solid electrolyte coatings. The effects of doping LZO with Ce, Ti, Mg, Nb, and Y on structure, band gaps, conductivity, and activation energy for ion migration are investigated both experimentally and by quantum mechanical calculations. Optical band gaps decrease for all doped materials compared to undoped LZO. While all dopants reduce the electronic conductivity at room temperature slightly, doping with Mg or Nb increases ionic conductivity by an order of magnitude. Introducing a high loading of Nb into LZO decreases the activation energy for Li-ion diffusion in the 22–120 °C range. Calculations on lithium-ion diffusion in LZO show that it occurs by a polaron–vacancy complex mechanism. The energy barrier is lowest for the lithium hopping in a zigzag fashion between tetrahedral voids within adjacent layers. The diffusion barrier is reduced as the number of Li vacancies increases during battery charging. We calculated surface energies for 10 surfaces, and we find that the most stable surface is the (001) surface with the tetrahedral Li layer being exposed. The delithiation energy on the (001) surface was found to be slightly higher than that in the bulk. The Li-ion diffusion barriers from the surface to the bulk were also calculated on the (001) surface, and the diffusion energy barrier across the (001) surface was found to be smaller than the energy barrier along the (001) direction in the bulk, and also lower than the barrier for the lowest-energy path in the bulk (which is a hop between tetrahedral voids in adjacent layers as shown in the related graphic). These characterizations of surface and doping effects will assist future materials design.
is a pseudolamellar compound with high lithium content. Even though it is intrinsically a poor conductor and does not contain a transition metal with easily variable oxidation states, a new synthetic approach to preparing it in nanocomposite form with intimate contact to a conductive carbon by mechanical delamination enabled galvanostatic cycling of coin halfcells containing Li 8 ZrO 6 /C as the cathode and Li metal as the anode at 221 mAh/g (which corresponds to extracting 2 Li per formula unit) over at least 140 cycles. With a higher capacity limit, a discharge capacity of 331 mAh/g (which corresponds to extracting 3 Li per formula unit) was maintained over 15−20 cycles. Ex situ and operando X-ray diffraction (XRD) studies of galvanostatically cycled cells showed that at these levels of charge, delithiation follows a reversible, topotactic path with only small distortions around Zr atoms. During this process, crystalline grain sizes decrease continuously, shortening diffusion lengths within grains but increasing the number of grain boundaries and electrode/electrolyte interfaces. Charge storage in Li 8 ZrO 6 appears to involve partial oxidation of oxygen atoms and production of small-polaron holes, as supported by XRD, X-ray photoelectron spectroscopy, and pair-distribution function studies and predicted by quantum mechanical calculations. At higher depths of charge, delithiation results in amorphization of the active electrode material. The charge storage mechanism in Li 8 ZrO 6 is unusual among lithium-ion battery electrode materials and involves a combination of mechanisms that resemble intercalation and conversion reactions. With further refinement, Li 8 ZrO 6 /C based materials open up opportunities to develop new cathode materials for lithium-ion batteries that may improve on currently existing capacity barriers.
High areal performance from high cathode mass loading is an essential requirement to bring battery chemistries beyond the lithium (Li) ion, such as lithium–sulfur (Li–S) or lithium–selenium (Li–Se), toward practical applications. These conversion chemistry cathodes have been typically prepared by using conventional slurry-based techniques widely used for Li ion battery electrodes, requiring the use of solvent and binder and multiple steps such as mixing, casting, drying, and collecting and proper disposing of organic solvents. To increase active material mass loading, the processing steps become even more time-consuming when multiple casting-drying cycles are needed. Here we report an extremely facile procedure to prepare ultrahigh mass loading (>15 mg/cm2) with high active material content (>70%) conversion chemistry cathodes in a single step directly from neat active material, such as sulfur (S), selenium (Se), or selenium sulfide (SeS2), without the need of solvent or binder. This is achieved by the use of holey graphene (hG), a unique lightweight material that can be dry pressed by itself or as a host into neat or composite electrode forms. In the electrode preparation, hG, the neat active material, and hG are sequentially added to the pressing die, resulting in a sandwich architecture containing a neat active material layer with conveniently tunable ultrahigh mass loading. The sandwich electrodes exhibit excellent overall electrochemical performance with great active material utilization. Mechanistically, when Se is used as the example active material, the neat Se layer becomes electrochemically redistributed throughout the entire cathode thickness after the first cycle. The sandwich cathode not only does not crack or fail but also spontaneously densifies for stable and prolonged cycling. The sandwich electrode architecture is also compatible with the use of a fluorinated electrolyte solvent to significantly reduce polyselenide solubility and shuttling for improved cycling performance. Such sandwich electrodes from the hG-enabled, one-step, dry-press method offer an attractive fast fabrication option in bulk production of ultrahigh mass loading cathodes for practical applications.
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