All-in-one assembly based on 3D-intertangled and cross-jointed architectures of Si/Cu 1D-nanowires for lithium ion batteries

All-in-one assemblies of separator, electrode and current collector (SECA) for lithium ion batteries are presented by using 1D nanowires of Si and Cu (nwSi and nwCu). Even without binders, integrity of SECA is secured via structural joints based on ductility of Cu as well as entanglement of nwSi and nwCu. By controlling the ratio of the nanowires, the number of contact points and voids accommodating volume expansion of Si active material are tunable. Zero volume expansion and high energy density are simultaneously achievable by the architectureopen0

Lord of the x86 Rings: A Portable User Mode Privilege Separation Architecture on x86

Modern applications often involve processing of sensitive information. However, the lack of privilege separation within the user space leaves sensitive application secret such as cryptographic keys just as unprotected as a "hello world" string. Cutting-edge hardware-supported security features are being introduced. However, the features are often vendor-specific or lack compatibility with older generations of the processors. The situation leaves developers with no portable solution to incorporate protection for the sensitive application component. We propose LOTRx86, a fundamental and portable approach for user-space privilege separation. Our approach creates a more privileged user execution layer called PrivUser by harnessing the underused intermediate privilege levels on the x86 architecture. The PrivUser memory space, a set of pages within process address space that are inaccessible to user mode, is a safe place for application secrets and routines that access them. We implement the LOTRx86 ABI that exports the privcall interface to users to invoke secret handling routines in PrivUser. This way, sensitive application operations that involve the secrets are performed in a strictly controlled manner. The memory access control in our architecture is privilege-based, accessing the protected application secret only requires a change in the privilege, eliminating the need for costly remote procedure calls or change in address space. We evaluated our platform by developing a proof-of-concept LOTRx86-enabled web server that employs our architecture to securely access its private key during an SSL connection. We conducted a set of experiments including a performance measurement on the PoC on both Intel and AMD PCs, and confirmed that LOTRx86 incurs only a limited performance overhead

Nanoporous Films and Nanostructure Arrays Created by Selective Dissolution of Water-Soluble Materials.

Highly porous thin films and nanostructure arrays are created by a simple process of selective dissolution of a water-soluble material, Sr3Al2O6. Heteroepitaxial nanocomposite films with self-separated phases of a target material and Sr3Al2O6 are first prepared by physical vapor deposition. NiO, ZnO, and Ni1- x Mg x O are used as the target materials. Only the Sr3Al2O6 phase in each nanocomposite film is selectively dissolved by dipping the film in water for 30 s at room temperature. This gentle and fast method minimizes damage to the remaining target materials and side reactions that can generate impurity phases. The morphologies and dimensions of the pores and nanostructures are controlled by the relative wettability of the separated phases on the growth substrates. The supercapacitor properties of the porous NiO films are enhanced compared to plain NiO films. The method can also be used to prepare porous films or nanostructure arrays of other oxides, metals, chalcogenides, and nitrides, as well as films or nanostructures with single-crystalline, polycrystalline, or amorphous nature

Breathing silicon anodes for durable high-power operations

Silicon anode materials have been developed to achieve high capacity lithium ion batteries for operating smart phones and driving electric vehicles for longer time. Serious volume expansion induced by lithiation, which is the main drawback of silicon, has been challenged by multi-faceted approaches. Mechanically rigid and stiff polymers (e.g. alginate and carboxymethyl cellulose) were considered as the good choices of binders for silicon because they grab silicon particles in a tight and rigid way so that pulverization and then break-away of the active mass from electric pathways are suppressed. Contrary to the public wisdom, in this work, we demonstrate that electrochemical performances are secured better by letting silicon electrodes breathe in and out lithium ions with volume change rather than by fixing their dimensions. The breathing electrodes were achieved by using a polysaccharide (pullulan), the conformation of which is modulated from chair to boat during elongation. The conformational transition of pullulan was originated from its a glycosidic linkages while the conventional rigid polysaccharide binders have beta linkagesopen1

Superoxide stability for reversible Na-O2 electrochemistry

Stabilizing superoxide (O-2(-)) is one of the key issues of sodium-air batteries because the superoxide-based discharge product (NaO2) is more reversibly oxidized to oxygen when compared with peroxide (O-2(2-)) and oxide (O2-). Reversibly outstanding performances of sodium-oxygen batteries have been realized with the superoxide discharge product (NaO2) even if sodium peroxide (Na2O2) have been also known as the discharge products. Here we report that the Lewis basicity of anions of sodium salts as well as solvent molecules, both quantitatively represented by donor numbers (DNs), determines the superoxide stability and resultantly the reversibility of sodium-oxygen batteries. A DN map of superoxide stability was presented as a selection guide of salt/solvent pair. Based on sodium triflate (CF3SO3-)/dimethyl sulfoxide (DMSO) as a high-DN-pair electrolyte system, sodium ion oxygen batteries were constructed. Pre-sodiated antimony (Sb) was used as an anode during discharge instead of sodium metal because DMSO is reacted with the metal. The superoxide stability supported by the high DN anion/solvent pair (CF3SO3-/DMSO) allowed more reversible operation of the sodium ion oxygen batteries

A Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium-Oxygen Batteries

Reactive oxygen species or superoxide (O2-) to damage or age biological cells is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from the superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium-oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C60) was used as a superoxide disproportionation chemo-catalyst mimicking the function of SOD. As expected, MA-C60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm-2) with 0.5 mAh cm-2 cut-off survived up to 50 cycles after MA-C60 was introduced to electrolyte. Moreover, the SOD-mimetic catalyst increased capacity: e.g., more than six-fold increase at 0.2 mA cm-2. Experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li2O2) and density functional theory calculation confirmed that the solution mechanism of Li2O2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C60

Bipolymer-Cross-Linked Binder to Improve the Reversibility and Kinetics of Sodiation and Desodiation of Antimony for Sodium-Ion Batteries

Although the volume of antimony tremendously expands during the alloying reaction with sodium, it is considered a promising anode material for sodium-ion batteries (SIBs). Repeated volume changes along the sodiation/desodiation cycles encourage capacity fading by triggering pulverization accompanying electrolyte decomposition. Additionally, the low cation transference number of sodium ions is another hindrance for application in SIBs. In this work, a binder was designed for the antimony in SIB cells to ensure bifunctionality and improve (1) the mechanical toughness to suppress the serious volume change and (2) the transference number of sodium ions. A cross-linked composite of poly(acrylic acid) and cyanoethyl pullulan (pullulan-CN) was presented as the binder. The polysaccharide backbone of pullulan-CN was responsible for the mechanical toughness, while the cyanoethyl groups of pullulan-CN improved the lithium-cation transfer. The antimony-based SIB cells using the composite binder showed improved cycle life with enhanced kinetics. The capacity was maintained at 76% of the initial value at the 200th cycle of 1C discharge following 1C charge, while the capacity at 20C was 61% of the capacity at 0.2C, implying that the composite binder significantly improved the sodiation/desodiation reversibility of antimony

Shifting Target Reaction from Oxygen Reduction to Superoxide Disproportionation by Tuning Isomeric Configuration of Quinone Derivative as Redox Mediator for Lithium-Oxygen Batteries

Quinones having a fully conjugated cyclic dione structure have been used as redox mediators in electrochemistry. 2,5-Ditert-butyl-1,4-benzoquinone (DBBQ or DB-p-BQ) as a para-quinone derivative is one of the representative discharge redox mediators for facilitating the oxygen reduction reaction (ORR) kinetics in lithium-oxygen batteries (LOBs). Herein, we presented that the redox activity of DB-p-BQ for electron mediation was possibly used for facilitating superoxide disproportionation reaction (SODR) by tuning the isomeric config-uration of the carbonyl groups of the substituted quinone to change its reduction potentials. First, we expected a molecule having its reduction potential between oxygen/superoxide at 2.75 V versus Li/Li+ and superoxide/peroxide at 3.17 V to play a role of the SODR catalyst by transferring an electron from one superoxide (O-2(-)) to another superoxide to generate dioxygen (O2) and peroxide (O-2(2-)). By changing the isomeric configuration from para (DB-p-BQ) to ortho (DB-o-BQ), the reduction potential of the first electron transfer (Q/Q(-)) of the ditert-butyl benzoquinone shifted positively to the potential range of the SODR catalyst. The electrocatalytic SODR-promoting functionality of DB-o-BQ kept the reactive superoxide concentration below a harmful level to suppress superoxide-triggered side reaction, improving the cycling durability of LOBs, which was not achieved by the para form. The second electron transfer process (Q(-)/Q(2-)) of the DB-o-BQ, even if the same process of the para form was not used for facilitating ORR, played a role of mediating electrons between electrode and oxygen like the Q/Q(-) process of the para form. The ORR-promoting functionality of the ortho form increased the LOB discharge capacity and reduced the ORR overpotential

Rational Structure Design of Fast-Charging NiSb Bimetal Nanosheet Anode for Lithium Ion Batteries

Although bimetallic materials with various structures have been used as anodes for advanced lithium ion batteries, structural degradation, caused during electrochemical reactions, leads to a shorter cycle lifespan. Herein, we propose a rational structural design, carbon-wrapped porous bimetallic nickel-antimony nanosheets (NiSbNS@C), with the help of dual-functional organic acid acting as a reducing agent and a carbon coating source upon the synthetic process. The structural evolution of NiSbNS@C is further confirmed as the NiSb crystal is transformed into a Ni-rich phase on fast charging. A well-constructed NiSbNS@C electrode exhibits outstanding high rate performance and structure stability owing to the fast electrochemical kinetics of the porous NiSb nanostructure and uniform carbon decoration in both half and full cells. This approach opens up an avenue to make a desirable structure for bimetallic anode materials toward high rate and stable lithium ion batteries