High voltage electrolytes for lithium-ion batteries with micro-sized silicon anodes.

Micro-sized silicon anodes can significantly increase the energy density of lithium-ion batteries with low cost. However, the large silicon volume changes during cycling cause cracks for both organic-inorganic interphases and silicon particles. The liquid electrolytes further penetrate the cracked silicon particles and reform the interphases, resulting in huge electrode swelling and quick capacity decay. Here we resolve these challenges by designing a high-voltage electrolyte that forms silicon-phobic interphases with weak bonding to lithium-silicon alloys. The designed electrolyte enables micro-sized silicon anodes (5 µm, 4.1 mAh cm-2) to achieve a Coulombic efficiency of 99.8% and capacity of 2175 mAh g-1 for >250 cycles and enable 100 mAh LiNi0.8Co0.15Al0.05O2 pouch full cells to deliver a high capacity of 172 mAh g-1 for 120 cycles with Coulombic efficiency of >99.9%. The high-voltage electrolytes that are capable of forming silicon-phobic interphases pave new ways for the commercialization of lithium-ion batteries using micro-sized silicon anodes.

A stable atmospheric-pressure plasma for extreme-temperature synthesis.

Plasmas can generate ultra-high-temperature reactive environments that can be used for the synthesis and processing of a wide range of materials1,2. However, the limited volume, instability and non-uniformity of plasmas have made it challenging to scalably manufacture bulk, high-temperature materials3-8. Here we present a plasma set-up consisting of a pair of carbon-fibre-tip-enhanced electrodes that enable the generation of a uniform, ultra-high temperature and stable plasma (up to 8,000 K) at atmospheric pressure using a combination of vertically oriented long and short carbon fibres. The long carbon fibres initiate the plasma by micro-spark discharge at a low breakdown voltage, whereas the short carbon fibres coalesce the discharge into a volumetric and stable ultra-high-temperature plasma. As a proof of concept, we used this process to synthesize various extreme materials in seconds, including ultra-high-temperature ceramics (for example, hafnium carbonitride) and refractory metal alloys. Moreover, the carbon-fibre electrodes are highly flexible and can be shaped for various syntheses. This simple and practical plasma technology may help overcome the challenges in high-temperature synthesis and enable large-scale electrified plasma manufacturing powered by renewable electricity.

Lithium-Induced Optimization Mechanism for an Ultrathin-Strut Biodegradable Zn-Based Vascular Scaffold.

To reduce incidences of in-stent restenosis and thrombosis, the use of a thinner-strut stent has been clinically proven to be effective. Therefore, the contemporary trend is toward the use of ultrathin-strut (≤70 µm) designs for durable stents. However, stents made from biodegradable platforms have failed to achieve intergenerational breakthroughs due to their excessively thick struts. Here, microalloying is used to create an ultrathin-strut (65 µm) zinc (Zn) scaffold with modified biodegradation behavior and improved biofunction, by adding lithium (Li). The scaffold backbone consists of an ultrafine-grained Zn matrix (average grain diameter 2.28 µm) with uniformly distributed nanoscale Li-containing phases. Grain refinement and precipitation strengthening enable it to achieve twice the radial strength with only 40% of the strut thickness of the pure Zn scaffold. Adding Li alters the thermodynamic formation pathways of products during scaffold biodegradation, creating an alkaline microenvironment. Li2 CO3  may actively stabilize this microenvironment due to its higher solubility and better buffering capability than Zn products. The co-release of ionic zinc and lithium enhances the beneficial differential effects on activities of endothelial cells and smooth muscle cells, resulting in good endothelialization and limited intimal hyperplasia in porcine coronary arteries. The findings here may break the predicament of the next-generation biodegradable scaffolds.

Salt-in-Salt Reinforced Carbonate Electrolyte for Li Metal Batteries.

The instability of carbonate electrolyte with metallic Li greatly limits its application in high-voltage Li metal batteries. Here, a "salt-in-salt" strategy is applied to boost the LiNO3 solubility in the carbonate electrolyte with Mg(TFSI)2 carrier, which enables the inorganic-rich solid electrolyte interphase (SEI) for excellent Li metal anode performance and also maintains the cathode stability. In the designed electrolyte, both NO3 - and PF6 - anions participate in the Li+ -solvent complexes, thus promoting the formation of inorganic-rich SEI. Our designed electrolyte has achieved a superior Li CE of 99.7 %, enabling the high-loading NCM811||Li (4.5 mAh cm-2 ) full cell with N/P ratio of 1.92 to achieve 84.6 % capacity retention after 200 cycles. The enhancement of LiNO3 solubility by divalent salts is universal, which will also inspire the electrolyte design for other metal batteries.

Interactive effects of cerium and copper to tune the microstructure of silicocarnotite bioceramics towards enhanced bioactivity and good biosafety.

Endowing biomaterials with functional elements enhances their biological properties effectively. However, improving bioactivity and biosafety simultaneously is still highly desirable. Herein, cerium (Ce) and copper (Cu) are incorporated into silicocarnotite (CPS) to modulate the constitution and microstructure for degradability, bioactivity and biosafety regulation. Our results demonstrated that introducing Ce suppressed scaffold degradation, while, co-incorporation of both Ce and Cu accelerated degradability. Osteogenic effect of CPS in vitro was promoted by Ce and optimized by Cu, and Ce-induced angiogenic inhibition could be mitigated by cell coculture method and reversed by Ce-Cu co-incorporation. Ce enhanced osteogenic and angiogenic properties of CPS in a dose-dependent manner in vivo, and Cu-Ce coexistence exhibited optimal bioactivity and satisfactory biosafety. This work demonstrated that coculture in vitro was more appropriately reflecting the behavior of implanted biomaterials in vivo. Interactive effects of multi-metal elements were promising to enhance bioactivity and biosafety concurrently. The present work provided a promising biomaterial for bone repair and regeneration, and offered a comprehensive strategy to design new biomaterials which aimed at adjustable degradation behavior, and enhanced bioactivity and biosafety.

Rapid liquid phase-assisted ultrahigh-temperature sintering of high-entropy ceramic composites.

High-entropy ceramics and their composites display high mechanical strength and attractive high-temperature stabilities. However, properties like strong covalent bond character and low self-diffusion coefficients make them difficult to get sintered, limiting their mass popularity. Here, we present a rapid liquid phase-assisted ultrahigh-temperature sintering strategy and use high-entropy metal diboride/boron carbide composite as a proof of concept. We use a carbon-based heater to fast-heat the composite to around 3000 K, and a small fraction of eutectic liquid was formed at the interface between high-entropy metal diborides and boron carbide. A crystalline dodecaboride intergranular phase was generated upon cooling to ameliorate the adhesion between the components. The as-sintered composite presents a high hardness of 36.4 GPa at a load of 0.49 N and 24.4 GPa at a load of 9.8 N. This liquid phase-assisted rapid ultrahigh-temperature strategy can be widely applicable for other ultrahigh-temperature ceramics as well.

PDLLA-Zn-nitrided Fe bioresorbable scaffold with 53-µm-thick metallic struts and tunable multistage biodegradation function.

Balancing the biodegradability and mechanical integrity of a bioresorbable scaffold (BRS) with time after implantation to match the remodeling of the scaffolded blood vessel is important, but a key challenge in doing so remains. This study presents a novel intercalated structure of a metallic BRS by introducing a nanoscale Zn sacrificial layer between the nitrided Fe platform and the sirolimus-carrying poly(d,l-lactide) drug coating. The PDLLA-Zn-FeN BRS shows a multistage biodegradation behavior, maintaining mechanical integrity at the initial stage and exhibiting accelerated biodegradation at the subsequent stage in both rabbit abdominal aortas and human coronary arteries, where complete biodegradation was observed about 2 years after implantation. The presence of the nanoscale Zn sacrificial layer with an adjustable thickness also contributes to the tunable biodegradation of BRS and allows the reduction of the metallic strut thickness to 53 µm, with radial strength as strong as that of the current permanent drug-eluting stents.

Effective easing of the side effects of copper intrauterine devices using ultra-fine-grained Cu-0.4Mg alloy.

Copper intrauterine device is one of the most adopted contraceptive methods with high effectiveness (over 99 %), low cost, spontaneous reversibility and long-lasting usage. However, the side effects induced from the initial burst release of copper ions (Cu2+) hinder the continuation of the Cu-IUD made of Coarse-Grained Copper (CG Cu). We proposed to tailor the bio-corrosion behaviors of better control of Cu2+ release via the addition of bioactive Mg into the Ultra-Fine Grained (UFG) Bulk Cu. Thus, UFG bulk Cu with 0.4 wt.% Mg was produced via equal-channel angular pressing. The microstructures of the UFG Cu-0.4Mg was observed using electron backscatter diffraction and transmission electron microscopy techniques. The in vitro long-term corrosion behaviors in simulated uterine fluid, cytotoxicity to four cell lines, in vivo biocompatibility and contraceptive efficacy were all studied on CG Cu, UFG Cu and UFG Cu-0.4Mg materials. The results demonstrate that both the ultrafine grains and the addition of bioactive Mg into Cu contribute to the suppression of the burst release of Cu2+ in the initial stage and the maintenance of high level Cu2+ in long-term release. Moreover, the UFG Cu-0.4Mg also exhibited much improved cell and tissue biocompatibility from both the in vitro and in vivo evaluations. Therefore, the contraceptive efficacy of UFG Cu-0.4Mg is still maintained as high as the CG Cu and UFG Cu while the side effects are significantly eased, suggesting the high potential of the UFG Cu-0.4Mg alloy as a new upgrading or alternative material for Cu-IUD. STATEMENT OF SIGNIFICANCE: The side effects from burst release of Cu2+ at the initial implantation stage of Cu-containing intrauterine devices (Cu-IUD) is one of the main drawbacks of these devices. In this work, an ultra-fine-grained Cu (UFG Cu) alloyed with a low amount of bioactive Mg was used for a Cu-IUD. The UFG Cu-0.4Mg alloy exhibited suppressed burst release of Cu2+ at initial implantation, while active Cu2+ release for long-term usage was maintained, comparable to coarse-grained pure Cu. Furthermore, the UFG Cu-0.4Mg alloy displayed significantly improved biocompatibility with human uterus cells and a much decreased inflammatory response within the uterus. Therefore, the side effects from Cu-IUD were eased, while high antifertility efficacy of the UFG Cu-0.4Mg alloy was maintained. The UFG Cu-0.4Mg alloy is promising for Cu-IUD.

Fabrication of enamel-like structure on polymer-infiltrated zirconia ceramics.

OBJECTIVES: The aim of this study is to improve the biological and mechanical properties of zirconia-based PICN (polymer-infiltrated-ceramic-network) materials by fabrication an enamel-like structure on its surface. METHODS: Fluorapatite (FA) arrays were fabricated on zirconia discs by hydrothermal treatment. After polymer infiltration, an enamel-like structure was obtained on zirconia-based PICN materials. Effects of hydrothermal treatment conditions on the FA arrays were investigated by XRD, FTIR and SEM. Human gingival fibroblast cells (HGFs) and Escherichia coli (E. coli) were used to evaluate the cytocompatibility and antibacterial properties. Nanoindentation method was employed to determine elastic modulus and hardness. RESULTS: A facile and pervasive method was developed in this study to fabricate an enamel-like structure constituted of controlled FA arrays and interstitial resin on zirconia-based PICN materials. The obtained FA arrays can significantly promote the adhesion and proliferation of human gingival fibroblasts (HGFs), and further effectively inhibit the growth of Escherichia coli. Owing to the hierarchical structure, the enamel-like structure has achieved a hardness of 1.79 GPa and a lower Young's modulus of 37.4 GPa. SIGNIFICANCES: The enamel-like structure, with excellent biological and mechanical properties, is promising for various applications in dentistry.

Ferric oxide: A favorable additive to balance mechanical strength and biological activity of silicocarnotite bioceramic.

Ideal materials for bone regeneration should have not only a good bioactivity, but also a good mechanical strength to provide an initial support for new bone formation. How to get a balance between high mechanical property and good bioactivity is a challenging issue for bone regeneration materials. In the present work, a biocompatible additive Fe2O3 was selected to optimize the comprehensive properties of a novel calcium phosphate silicate (CPS) ceramic using a mechanical mixing method. The effects of Fe2O3 content on microstructure, bending strength, apatite formation ability and cytocompatibility of Fe-CPS bioceramics were investigated and the related mechanism was also discussed. The obtained Fe-CPS bioceramics showed enhanced mechanical and favorable bioactivity performances. Especially, the Fe-CPS bioceramic with 1.5 wt% Fe2O3 sintered at 1250 °C presented the highest bending strength of 91.9 MPa. While, Fe-CPS bioceramics still exhibited a good ability on apatite formation in simulated body fluid (SBF), and cytocompatibility test revealed that Fe-CPS bioceramics were favorable for cell adhesion and proliferation. All the results indicated that Fe-CPS bioceramics are promising candidate materials for bone regeneration at load bearing applications.

An Electron/Ion Dual-Conductive Alloy Framework for High-Rate and High-Capacity Solid-State Lithium-Metal Batteries.

The solid-state Li battery is a promising energy-storage system that is both safe and features a high energy density. A main obstacle to its application is the poor interface contact between the solid electrodes and the ceramic electrolyte. Surface treatment methods have been proposed to improve the interface of the ceramic electrolytes, but they are generally limited to low-capacity or short-term cycling. Herein, an electron/ion dual-conductive solid framework is proposed by partially dealloying the Li-Mg alloy anode on a garnet-type solid-state electrolyte. The Li-Mg alloy framework serves as a solid electron/ion dual-conductive Li host during cell cycling, in which the Li metal can cycle as a Li-rich or Li-deficient alloy anode, free from interface deterioration or volume collapse. Thus, the capacity, current density, and cycle life of the solid Li anode are improved. The cycle capability of this solid anode is demonstrated by cycling for 500 h at 1 mA cm-2 , followed by another 500 h at 2 mA cm-2 without short-circuiting, realizing a record high cumulative capacity of 750 mA h cm-2 for garnet-type all-solid-state Li batteries. This alloy framework with electron/ion dual-conductive pathways creates the possibility to realize high-energy solid-state Li batteries with extended lifespans.

Electrochemically Controlled Solid Electrolyte Interphase Layers Enable Superior Li-S Batteries.

Lithium-sulfur (Li-S) batteries suffer from shuttle reactions during electrochemical cycling, which cause the loss of active material sulfur from sulfur-carbon cathodes, and simultaneously incur the corrosion and degradation of the lithium metal anode by forming passivation layers on its surface. These unwanted reactions therefore lead to the fast failure of batteries. The preservation of the highly reactive lithium metal anode in sulfur-containing electrolytes has been one of the main challenges for Li-S batteries. In this study, we systematically controlled and optimized the formation of a smooth and uniform solid electrolyte interphase (SEI) layer through electrochemical pretreatment of the Li metal anode under controlled current densities. A distinct improvement of battery performance in terms of specific capacity and power capability was achieved in charge-discharge cycling for Li-S cells with pretreated Li anodes compared to pristine untreated ones. Importantly, at a higher power density (1 C rate, 3 mA cm-2), the Li-S cells with pretreated Li anodes protected by a controlled elastomer (Li-Protected-by-Elastomer, LPE)) show the suppression of the Li dendrite growth and exhibit 3-4 times higher specific capacity than the untreated ones after 100 electrochemical cycles. The formation of such a controlled uniform SEI was confirmed, and its surface chemistry, morphology, and electrochemical properties were characterized by X-ray photoelectron spectroscopy, focused-ion beam cross sectioning, and scanning electron microscopy. Adequate pretreatment current density and time are critical in order to form a continuous and uniform SEI, along with good Li-ion transport property.

A cubic room temperature polymorph of thermoelectric TAGS-85.

The alloy (GeTe)85(AgSbTe2)15, commonly known as TAGS-85, is one of the best performing p-type thermoelectric materials in the temperature range 200-500 °C. In all reports thus far, TAGS-85 adopts a rhombohedral crystal structure at room temperature and undergoes a reversible transition to a cubic phase in the middle of the operating temperature range. Here, we report on a novel, metrically cubic polymorph of TAGS-85 that can be obtained at room temperature using a particular cooling protocol during initial synthesis. This polymorph transforms irreversibly on initial heating to a 21-layer trigonal structure containing ordered cation vacancy layers, driven by the spontaneous precipitation of argyrodite-type Ag8GeTe6. We show that the precipitation of Ag8GeTe6 is detrimental to the thermoelectric performance of TAGS-85 due to an increase in the vacancy concentration, which makes the samples more metallic in character and significantly reduces the Seebeck coefficient. The precipitation of Ag8GeTe6 can be suppressed by careful control of the synthesis conditions.

Phase Transitions of Thermoelectric TAGS-85.

The alloys (GeTe)x(AgSbTe2)100-x, commonly known as TAGS-x, are among the best performing p-type thermoelectric materials for the composition range 80 ≤ x ≤ 90 and in the temperature range 200-500 °C. They adopt a rhombohedrally distorted rocksalt structure at room temperature and are reported to undergo a reversible phase transition to a cubic structure at ∼250 °C. However, we show that, for the optimal x = 85 composition (TAGS-85), both the structural and thermoelectric properties are highly sensitive to the initial synthesis method employed. Single-phase rhombohedral samples exhibit the best thermoelectric properties but can only be obtained after an annealing step at 600 °C during initial cooling from the melt. Under faster cooling conditions, the samples obtained are inhomogeneous, containing multiple rhombohedral phases with a range of lattice parameters and exhibiting inferior thermoelectric properties. We also find that when the room-temperature rhombohedral phase is heated, an intermediate trigonal structure containing ordered cation vacancy layers is formed at ∼200 °C, driven by the spontaneous precipitation of argyrodite-type Ag8GeTe6 which alters the stoichiometry of the TAGS-85 matrix. The rhombohedral and trigonal phases of TAGS-85 coexist up to 380 °C, above which a single cubic phase is obtained and the Ag8GeTe6 precipitates redissolve into the matrix. On subsequent cooling a mixture of rhombohedral, trigonal, and Ag8GeTe6 phases is again obtained. Initially single-phase samples exhibit thermoelectric power factors of up to 0.0035 W m-1 K-2 at 500 °C, a value that is maintained on subsequent thermal cycling and which represents the highest power factor yet reported for undoped TAGS-85. Therefore, control over the structural homogeneity of TAGS-85 as demonstrated here is essential in order to optimize the thermoelectric performance.

Evolution of Phase, Microstructure and ZrC Lattice Parameter in Solid-solution-treated W-ZrC Composite.

Zirconium carbide (ZrC) reinforced tungsten (W) composite was hot-pressed at 2200 °C for 1 h in vacuum, which was subsequently heat treated in the temperature range of 2200 to 2500 °C for 1.5 or 2 h. The relative ratios of ZrC phase were 21.0, 23.3 and 25.9 mol.% for the mixture of starting powders, composites sintered for 1 h and solid-solution treated at 2500 °C for 1.5 h, respectively. The solid solubility of W in ZrC increased with the increment in heat-treating temperature and time to a maximum value of 18.9 mol.% at 2500 °C for 1.5 h. The lattice parameter of cubic ZrC phase diminished from 0.4682 nm in the starting powder to 0.4642 nm in the solid-solution composite treated at 2500 °C for 1.5 h. This work demonstrated that the relationship between the solid solubility of W in ZrC and the lattice parameter of ZrC is linear, with a slope of -1.93 × 10-4 nm/at.%. Overall, more W atoms diffused into ZrC lattice after heat treatment, meanwhile, the previous precipitated nano-sized W dissolved in the supersaturated (Zr,W)C solid-solution, as detected by SEM and TEM.

Mechanism of superior luminescent and high-efficiency photocatalytic properties of Eu-doped calcium aluminate by low-cost self-propagating combustion synthesis technique.

Eu-doped calcium aluminate was synthesized via the low-cost self-propagating combustion synthesis (SPCS) technique, whose phase constitutions were identified as Ca9Al6O18 and Ca3Al2O6. The Ca2+ ions in Ca9Al6O18 rather than Ca3Al2O6 phase were replaced by Eu3+ ions. The product exhibits the superior luminescent property and photocatalytic activity, which may find potential applications in the display devices and environment treatments.

Metal-Insulator Transition Induced by Spin Reorientation in Fe7Se8 Grain Boundaries.

Fe7Se8 exists as a hexagonal NiAs-like crystal structure with a large number of ordered intrinsic vacancies. It is an ideal candidate for studying the effect of defects on properties such as magnetism and electrical transport. In this work, highly crystalline Fe7Se8 with the 3c crystal structure was synthesized by a solid-state reaction. Sharp changes in the magnetization at 100 K confirm a rotation of the spins from the ab plane to the c axis with decreasing temperature. We observe an interesting metal-insulator transition at the same temperature as the spin-direction changes. We propose that locked spins in the grain boundaries induce electron localization and result in the metal-insulator transition. Electron localization is confirmed by X-ray photoelectron spectroscopy of the Fe 2p peaks, which exhibit two characteristic satellite peaks. This mechanism is also verified by comparing it with the properties of the 4c-Fe7Se8 crystal structure.