Fluorinated Artificial Solid-Electrolyte-Interphase Layer for Long-Life Sodium Metal Batteries.

Sodium metal batteries have garnered significant attention due to their high theoretical specific capacity, cost effectiveness, and abundant availability. However, the propensity for dendritic sodium formation, stemming from the highly reactive nature of the sodium metal surface, poses safety concerns, and the uncontrollable formation of the solid-electrolyte interphase (SEI) leads to large cell impedance and battery failures. In this study, we present a novel approach where we have successfully developed a stable fluorinated artificial SEI layer on the sodium metal surface by employing various weight percentages of tin fluoride in a dimethyl carbonate solution, utilizing a convenient, cost-effective, and single-step method. The resulting fluoride-rich protective layer effectively stabilized the Na metal surfaces and significantly enhanced cycling stability. The engineered artificial SEI layer demonstrated an enhanced lifetime of Na metal symmetric cells of over 3.5 times, over 700 h at the current density of 0.25 mA/cm2, in cycling performance compared to the untreated sodium, which is attributed to the suppression of dendrite formation and the reduction of undesired SEI formation during high-current cycling.

Mg2+ ion-catalyzed polymerization of 1,3-dioxolane in battery electrolytes.

Electrolyte salts with Mg2+ and Al3+ Lewis acidic cations demonstrate polymerization of 1,3-dioxolane. The speed and extent of the reaction depends on coordination of the anion with the Mg2+ cation catalyst. Weakly coordinating anions such as TFSI- aid faster polymerization while strongly coordinating anions such as ClO4- hinder the polymerization.

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.

Epitaxial Welding of Carbon Nanotube Networks for Aqueous Battery Current Collectors.

Carbon nanomaterials are desirable candidates for lightweight, highly conductive, and corrosion-resistant current collectors. However, a key obstacle is their weak interconnection between adjacent nanostructures, which renders orders of magnitude lower electrical conductivity and mechanical strength in the bulk assemblies. Here we report an "epitaxial welding" strategy to engineer carbon nanotubes (CNTs) into highly crystalline and interconnected structures. Solution-based polyacrylonitrile was conformally coated on CNTs as "nanoglue" to physically join CNTs into a network, followed by a rapid high-temperature annealing (>2800 K, overall ∼30 min) to graphitize the polymer coating into crystalline layers that also bridge the adjacent CNTs to form an interconnected structure. The contact-welded CNTs (W-CNTs) exhibit both a high conductivity (∼1500 S/cm) and a high tensile strength (∼120 MPa), which are 5 and 20 times higher than the unwelded CNTs, respectively. In addition, the W-CNTs display chemical and electrochemical stabilities in strong acidic/alkaline electrolytes (>6 mol/L) when potentiostatically stressing at both cathodic and anodic potentials. With these exceptional properties, the W-CNT films are optimal as high-performance current collectors and were demonstrated in the state-of-the-art aqueous battery using a "water-in-salt" electrolyte.

Nanoscale Protection Layers To Mitigate Degradation in High-Energy Electrochemical Energy Storage Systems.

In the pursuit of energy storage devices with higher energy and power, new ion storage materials and high-voltage battery chemistries are of paramount importance. However, they invite-and often enhance-degradation mechanisms, which are reflected in capacity loss with charge/discharge cycling and sometimes in safety problems. Degradation mechanisms are often driven by fundamentals such as chemical and electrochemical reactions at electrode-electrolyte interfaces, volume expansion and stress associated with ion insertion and extraction, and profound inhomogeneity of electrochemical behavior. While it is important to identify and understand these mechanisms at some reasonable level, it is even more critical to design strategies to mitigate these degradation pathways and to develop means to implement and validate the strategies. A growing set of research highlights the mitigation benefits achievable by forming thin protection layers (PLs) intentionally created as artificial interphase regions at the electrode-electrolyte interface. These advances illustrate a promising-perhaps even generic-pathway for enabling higher-energy and higher-voltage battery configurations. In this Account, we summarize examples of such PLs that serve as mitigation strategies to avoid degradation in lithium metal anodes, conversion-type electrode materials, and alloy-type electrodes. Examples are chosen from a larger body of electrochemical degradation research carried out in Nanostructures for Electrical Energy Storage (NEES), our DOE Energy Frontier Research Center. Overall, we argue on the basis of experimental and theoretical evidence that PLs effectively stabilize the electrochemical interfaces to prevent parasitic chemical and electrochemical reactions and mitigate the structural, mechanical, and compositional degradation of the electrode materials at the electrode-electrolyte interfaces. The evidenced improvement in performance metrics is accomplished by (1) establishing a homogeneous interface for ion insertion and extraction, (2) providing mechanical constraints to maintain structural integrity and robust electronic and ionic conduction pathways, and (3) introducing spatial confinements on the electrode material matrix to alter the phase transformation (delaying the occurrence of the conversion reaction) upon Li insertion, which results in superior electrode performance, excellent capacity retention, and improved reversibility. Taken together, these examples portray a valuable role for thin protection layers synthesized over electrode surfaces, both for their benefit to cycle stability and for revealing insights into degradation and mitigation mechanisms. Furthermore, they underscore the impact of complex electrochemical behavior at nanoscale materials and nanostructure interfaces in modulating the behavior of energy storage devices at the mesoscale and macroscale.

Reducing Interfacial Resistance between Garnet-Structured Solid-State Electrolyte and Li-Metal Anode by a Germanium Layer.

Substantial efforts are underway to develop all-solid-state Li batteries (SSLiBs) toward high safety, high power density, and high energy density. Garnet-structured solid-state electrolyte exhibits great promise for SSLiBs owing to its high Li-ion conductivity, wide potential window, and sufficient thermal/chemical stability. A major challenge of garnet is that the contact between the garnet and the Li-metal anodes is poor due to the rigidity of the garnet, which leads to limited active sites and large interfacial resistance. This study proposes a new methodology for reducing the garnet/Li-metal interfacial resistance by depositing a thin germanium (Ge) (20 nm) layer on garnet. By applying this approach, the garnet/Li-metal interfacial resistance decreases from ≈900 to ≈115 Ω cm2 due to an alloying reaction between the Li metal and the Ge. In agreement with experiments, first-principles calculation confirms the good stability and improved wetting at the interface between the lithiated Ge layer and garnet. In this way, this unique Ge modification technique enables a stable cycling performance of a full cell of lithium metal, garnet electrolyte, and LiFePO4 cathode at room temperature.

[Risk factors of cubitus varus in humeral condylar fracture after conservative treatment in child].

OBJECTIVE: To further investigate the risk factors of cubitus varus in humeral condylar fracture after conservative treatment in children through Logistic regression analysis, so as to guide the clinical treatment. METHODS: Children with humeral condylar fracture who were treated by manipulative reduction and plaster fixation in our hospital from March 2008 to December 2014 were studied. The clinical data including age, gender, BMI, time from injury to reduction, direction of displacement, rotation displacement, fixed position, and epiphyseal injury were collected. First, preliminary screen the risk factors through univariate analysis of the above data, then determine the risk factors of cubitus varus through multivariate Logistic regression analysis of the significant factors from univariate analysis. RESULTS: Univariate analysis showed that time from injury to reduction, direction of displacement, rotation displacement and epiphyseal injury were significantly correlated with the cubitus varus. Multivariate Logistic regression analysis showed that time from injury to reduction which was longer than 8 h [P=0.017, OR=3.303(1.243-8.774)], ulnar displacement [P=0.001, OR=11.951(2.895-49.335)], rotation displacement [P=0.003, OR=4.190(1.643-10.685)]and epiphyseal injury [P=0.000, OR=7.092(2.557-19.671)] were independent risk factors of cubitus varus. CONCLUSIONS: Time from injury to reduction, ulnar displacement, rotation displacement and epiphyseal injury are independent risk factors of cubitus varus. So it need corresponding treatment according to different risk factors.

Solid Electrolyte Lithium Phosphous Oxynitride as a Protective Nanocladding Layer for 3D High-Capacity Conversion Electrodes.

Materials that undergo conversion reactions to form different materials upon lithiation typically offer high specific capacity for energy storage applications such as Li ion batteries. However, since the reaction products often involve complex mixtures of electrically insulating and conducting particles and significant changes in volume and phase, the reversibility of conversion reactions is poor, preventing their use in rechargeable (secondary) batteries. In this paper, we fabricate and protect 3D conversion electrodes by first coating multiwalled carbon nanotubes (MWCNT) with a model conversion material, RuO2, and subsequently protecting them with conformal thin-film lithium phosphous oxynitride (LiPON), a well-known solid-state electrolyte. Atomic layer deposition is used to deposit the RuO2 and the LiPON, thus forming core double-shell MWCNT@RuO2@LiPON electrodes as a model system. We find that the LiPON protection layer enhances cyclability of the conversion electrode, which we attribute to two factors. (1) The LiPON layer provides high Li ion conductivity at the interface between the electrolyte and the electrode. (2) By constraining the electrode materials mechanically, the LiPON protection layer ensures electronic connectivity and thus conductivity during lithiation/delithiation cycles. These two mechanisms are striking in their ability to preserve capacity despite the profound changes in structure and composition intrinsic to conversion electrode materials. This LiPON-protected structure exhibits superior cycling stability and reversibility as well as decreased overpotentials compared to the unprotected core-shell structure. Furthermore, even at very low lithiation potential (0.05 V), the LiPON-protected electrode largely reduces the formation of a solid electrolyte interphase.

Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition.

Lithium metal is considered to be the most promising anode for next-generation batteries due to its high energy density of 3840 mAh g(-1). However, the extreme reactivity of the Li surface can induce parasitic reactions with solvents, contamination, and shuttled active species in the electrolyte, reducing the performance of batteries employing Li metal anodes. One promising solution to this issue is application of thin chemical protection layers to the Li metal surface. Using a custom-made ultrahigh vacuum integrated deposition and characterization system, we demonstrate atomic layer deposition (ALD) of protection layers directly on Li metal with exquisite thickness control. We demonstrate as a proof-of-concept that a 14 nm thick ALD Al2O3 layer can protect the Li surface from corrosion due to atmosphere, sulfur, and electrolyte exposure. Using Li-S battery cells as a test system, we demonstrate an improved capacity retention using ALD-protected anodes over cells assembled with bare Li metal anodes for up to 100 cycles.

Directed Kinetic Self-Assembly of Mounds on Patterned GaAs (001): Tunable Arrangement, Pattern Amplification and Self-Limiting Growth.

We present results demonstrating directed self-assembly of nanometer-scale mounds during molecular beam epitaxial growth on patterned GaAs (001) surfaces. The mound arrangement is tunable via the growth temperature, with an inverse spacing or spatial frequency which can exceed that of the features of the template. We find that the range of film thickness over which particular mound arrangements persist is finite, due to an evolution of the shape of the mounds which causes their growth to self-limit. A difference in the film thickness at which mounds at different sites self-limit provides a means by which different arrangements can be produced.