Structure Dependent Electrochemical Behaviors of Hard Carbon Anode Materials Derived from Natural Polymer for Next-Generation Sodium Ion Battery.

Hard carbons are one of the most promising anode materials for next-generation sodium-ion batteries due to their high reversible capacity, long cycle life, and low cost. The advantage in terms of price of hard carbons can be further improved by using cheaper resources such as biomass waste as precursors. Lignin is one of the richest natural bio-polymer in the earth which can be obtained from woods. As the lignin has three-dimensional amorphous polymeric structure, it is considered as good precursor for producing carbonaceous materials under proper carbonization processes for energy storage devices. In this study, structural properties of lignin-derived hard carbons such as interlayer spacing, degree of disorder and surface defects are controlled. Specifically, lignin-derived hard carbons were synthesized at 1000 °C, 1250 °C, and 1500 °C, and it was confirmed that the structure gradually changed from a disordered structure to ordered structure through X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Hard carbons exhibit sloping regions at high voltage and plateau region at low voltage during the electrochemical processes for sodium ions. As the heat treatment temperature increases, the contribution to the overall reversible capacity of the sloping region decreases and the contribution of the plateau region increases. This trend confirms that it affects reversible capacity, rate-capability, and cycling stability, meaning that an understanding of structural properties and related electrochemical properties is necessary when developing hard carbon as a negative electrode material for sodium ion batteries.

Electrochemical Sodiation Mechanism in Magnetite Nanoparticle-Based Anodes: Understanding of Nanoionics-Based Sodium Ion Storage Behavior of Fe3O4.

Electrochemical ion storage behaviors of Fe3O4 nanoparticles, as a representative transition metal oxide for an environmentally benign and low-cost anode for a sodium-ion battery, are thoroughly investigated through a combination of electrochemical analysis and diagnostics of Fe3O4 electrode cells, X-ray-based and spectroscopic analysis of material structure evolution as functions of depth of discharge (DoD) and state of charge (SoC), and first principle modeling. The gravimetric capacity is found to be 50 mA h/g for bulk Fe3O4 (50 nm average crystallite size) and 100 mA h/g─about a tenth of the theoretical prediction for complete conversion─for Fe3O4 nanoparticles (8.7 nm average particle size), respectively. A fundamental and mechanistic study of material evolution as functions of DoD and SoC shows that Fe3O4 does not allow electrochemical incorporation of Na+ ions into the empty cation positions of the inverse spinel structure, leading to our assertion that electrochemical intercalation of Na+ ions to conversion of the Fe3O4 anode in sodium-ion batteries is nonviable. A density functional theory investigation points to the impracticality of the intercalation of Na+ ions into Fe3O4 and further validates our experimental findings. We propose several possible mechanisms corresponding to the observed low capacity, including formation of solid electrolyte interphases with unfavorable properties and adsorption of Na+ ions onto surfaces of nanoparticles and/or at heterointerfaces in Fe3O4 composite electrodes in a NaPF6-based electrolyte system.

Understanding Degradation at the Lithium-Ion Battery Cathode/Electrolyte Interface: Connecting Transition-Metal Dissolution Mechanisms to Electrolyte Composition.

Lithium transition-metal oxides (LiMn2O4 and LiMO2 where M = Ni, Mn, Co, etc.) are widely applied as cathode materials in lithium-ion batteries due to their considerable capacity and energy density. However, multiple processes occurring at the cathode/electrolyte interface lead to overall performance degradation. One key failure mechanism is the dissolution of transition metals from the cathode. This work presents results combining scanning electrochemical microscopy with inductively coupled plasma (ICP) and electron paramagnetic resonance (EPR) spectroscopies to examine cathode degradation products. Our effort employs a LiMn2O4 (LMO) thin film as a model cathode to monitor the Mn dissolution process without the potential complications of conductive additive and polymer binders. We characterize the electrochemical behavior of LMO degradation products in various electrolytes, paired with ICP and EPR, to better understand the properties of Mn complexes formed following metal dissolution. We find that the identity of the lithium salt anions in our electrolyte systems [ClO4-, PF6-, and (CF3SO2)2N-] appears to affect the Mn dissolution process significantly as well as the electrochemical behavior of the generated Mn complexes. This implies that the mechanism for Mn dissolution is at least partially dependent on the lithium salt anion.

Effect of Water Concentration in LiPF6-Based Electrolytes on the Formation, Evolution, and Properties of the Solid Electrolyte Interphase on Si Anodes.

A trace amount of water in an electrolyte is one of the factors detrimental to the electrochemical performance of silicon (Si)-based lithium-ion batteries that adversely affect the formation and evolution of the solid electrolyte interphase (SEI) on Si-based anodes and change its properties. Thus far, a lack of fundamental and mechanistic understanding of SEI formation, evolution, and properties in the presence of water has inhibited efforts to stabilize the SEI for improved electrochemical performance. Thus, we investigated the SEI formed in a Gen2 electrolyte (1.2 M LiPF6 in ethylene carbonate/ethyl methyl carbonate, 3:7 wt %, water content: <10 ppm) with and without additional water (50 ppm) at varying potentials (1.0, 0.5, 0.2, and 0.01 V vs Li/Li+). The impact of additional water on the morphological, (electro)chemical, and structural properties of SEI was studied using microscopic (atomic force microscopy and scanning spreading resistance microscopy) and spectroscopic (X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform infrared spectroscopy, and time-of-flight secondary ion mass spectrometry) techniques. The SEI exhibits both potential- and water concentration-dependent trends in its morphology and chemical composition. The presence of additional water in the electrolyte causes parasitic reactions, which onset at ∼1.0 V, resulting in a reduction of electrolyte components and result in the formation of an insulating, fluorophosphate-rich SEI. In addition, hydrolysis of LiPF6 creates hydrofluoric acid, which reacts with the surface oxide layer on the Si electrode, leading to a pitted and inhomogeneous SEI structure.

Three-Dimensional Mapping of Resistivity and Microstructure of Composite Electrodes for Lithium-Ion Batteries.

Nanoparticle silicon-graphite composite electrodes are a viable way to advance the cycle life and energy density of lithium-ion batteries. However, characterization of composite electrode architectures is complicated by the heterogeneous mixture of electrode components and nanoscale diameter of particles, which falls beneath the lateral and depth resolution of most laboratory-based instruments. In this work, we report an original laboratory-based scanning probe microscopy approach to investigate composite electrode microstructures with nanometer-scale resolution via contrast in the electronic properties of electrode components. Applying this technique to silicon-based composite anodes demonstrates that graphite, SiOx nanoparticles, carbon black, and LiPAA binder are all readily distinguished by their intrinsic electronic properties, with measured electronic resistivity closely matching their known material properties. Resolution is demonstrated by identification of individual nanoparticles as small as ∼20 nm. This technique presents future utility in multiscale characterization to better understand particle dispersion, localized lithiation, and degradation processes in composite electrodes for lithium-ion batteries.

Structural Stabilization of P2-type Sodium Iron Manganese Oxides by Electrochemically Inactive Mg Substitution: Insights of Redox Behavior and Voltage Decay.

Layered P2-type Na0.8 Mn0.5 Fe0.5 O2 cathode material is a promising candidate for next-generation sodium-ion batteries due to the economical and environmentally benign characteristics of Mn and Fe. The poor cycling stability of the material, however, is still a problem that must be solved. To address the problem, electrochemically inactive Mg2+ was introduced into the structure by substituting some of the Fe ions. It was shown that Mg substitution led to a smoother voltage profile with improved cycling performance and rate capability. These observations were attributed to the suppressed structural changes during electrochemical processes. Detailed redox mechanisms, associated local structural changes, and phase transitions were investigated by X-ray absorption spectroscopy and X-ray diffraction. From the detailed analysis of electrochemical behaviors, it was also identified how the redox reactions and structural disordering occurred in the high- and low-voltage regions and how Mg substitution stabilized the structure.

Heterogeneity in liver histopathology is associated with GSK-3ß activity and mitochondrial dysfunction in end-stage diabetic rats on differential diets.

While liver histopathology is heterogeneous in diabetes, the underlying mechanisms remain unclear. We investigated whether glycemic variation resulting from differential diets can induce heterogeneity in diabetic liver and the underlying molecular mechanisms. We generated end-stage non-obese diabetic model rats by subtotal-pancreatectomy in male Sprague- Dawley rats and ad libitum diet for 7 weeks (n = 33). The rats were then divided into three groups, and fed a standard- or a low-protein diet (18 or 6 kcal%, respectively), for another 7 weeks: to maintain hyperglycemia, 11 rats were fed ad libitum (18AL group); to achieve euglycemia, 11 were calorierestricted (18R group), and 11 were both calorie- and proteinrestricted with the low-protein diet (6R group). Overnightfasted liver samples were collected after the differential diets together with sham-control (18S group), and histology and molecular changes were compared. Hyperglycemic-18AL showed glycogenic hepatopathy (GH) without steatosis, with the highest GSK-3ß inactivation because of Akt activation during hyperglycemia; mitochondrial function was not impaired, compared to the 18S group. Euglycemic-18R showed neither GH nor steatosis, with intermediate GSK-3ß activation and mitochondrial dysfunction. However, euglycemic-6R showed both GH and steatosis despite the highest GSK-3ß activity and no molecular evidence of increased lipogenesis or decreased ApoB expression, where mitochondrial dysfunction was highest among the groups. In conclusion, heterogeneous liver histopathology developed in end-stage non-obese diabetic rats as the glycemic levels varied with differential diets, in which protein content in the diets as well as glycemic levels differentially influenced GSK-3ß activity and mitochondrial function in insulin-deficient state. [BMB Reports 2020; 53(2): 100-105].

Diet control to achieve euglycaemia induces tau hyperphosphorylation via AMPK activation in the hippocampus of diabetic rats.

Alzheimer's disease (AD) is a chronic neurodegenerative disease, and typical pathologic findings include abnormally hyperphosphorylated tau aggregation and neurofibrillary tangles. Insulin resistance and hyperglycaemia have been proposed as risk factors for AD development. As the maintenance of optimal blood glucose level is an important indicator of diabetes mellitus (DM) treatment, diet control is essential. AMPK is a crucial sensor of cellular bioenergetics for controlling anabolic and catabolic metabolism. Since AMPK is a direct regulator of tau phosphorylation, we hypothesized that strict diet control to achieve euglycaemia affects tau protein phosphorylation through increased AMPK activity in the hippocampus of DM rats. To test this hypothesis, we generated insulin-deficient DM rats by subtotal pancreatectomy and the animals were categorized into the diet-restriction (R) group and ad libitum (AL) feeding group. We found that tau phosphorylation was significantly higher in the R group than that in the sham-control (C) or AL group. AMPK activity in the R group was significantly higher than that in the C or AL group, as expected. Furthermore, the R group showed more critical tau pathology in the hippocampus than the other groups. These results suggest that diet control to achieve euglycaemia in an insulin-deficient DM condition may be harmful because of the greater possibility of AD development through increased tau phosphorylation by AMPK activation in the hippocampus.

Probing the Evolution of Surface Chemistry at the Silicon-Electrolyte Interphase via In Situ Surface-Enhanced Raman Spectroscopy.

We present a novel spectroscopic technique for in situ Raman microscopy studies of battery electrodes. By creating nanostructures on a copper mesh current collector, we were able to utilize surface-enhanced Raman spectroscopy (SERS) to monitor the evolution of the silicon anode-electrolyte interphase. The spectra show reversible Si peak intensity changes upon lithiation and delithiation. Moreover, an alkyl carboxylate species, lithium propionate, was detected as a significant SiEI component. Our experimental setup showed reproducible and stable performance over multiple cycles in terms of both electrochemistry and spectroscopy.

Intrinsic Properties of Individual Inorganic Silicon-Electrolyte Interphase Constituents.

Because of the complexity, high reactivity, and continuous evolution of the silicon-electrolyte interphase (SiEI), "individual" constituents of the SiEI were investigated to understand their physical, electrochemical, and mechanical properties. For the analysis of these intrinsic properties, known SiEI components (i.e., SiO2, Li2Si2O5, Li2SiO3, Li3SiOx, Li2O, and LiF) were selected and prepared as amorphous thin films. The chemical composition, purity, morphology, roughness, and thickness of prepared samples were characterized using a variety of analytical techniques. On the basis of subsequent analysis, LiF shows the lowest ionic conductivity and relatively weak, brittle mechanical properties, while lithium silicates demonstrate higher ionic conductivities and greater mechanical hardness. This research establishes a framework for identifying components critical for stabilization of the SiEI, thus enabling rational design of new electrolyte additives and functional binders for the development of next-generation advanced Li-ion batteries utilizing Si anodes.

Mechanical Properties and Chemical Reactivity of Li xSiO y Thin Films.

Silicon (Si) is a commonly studied candidate material for next-generation anodes in Li-ion batteries. A native oxide SiO2 on Si is often inevitable. However, it is not clear if this layer has a positive or negative effect on the battery performance. This understanding is complicated by the lack of knowledge about the physical properties of the SiO2 lithiation products and by the convolution of chemical and electrochemical effects during the anode lithiation process. In this study, Li xSiO y thin films as model materials for lithiated SiO2 were deposited by magnetron sputtering at ambient temperature, with the goal of (1) decoupling chemical reactivity from electrochemical reactivity and (2) evaluating the physical and electrochemical properties of Li xSiO y. X-ray photoemission spectroscopy analysis of the deposited thin films demonstrate that a composition close to previous experimental reports of lithiated native SiO2 can be achieved through sputtering. Our density functional theory calculations also confirm that the possible phases formed by lithiating SiO2 are very close to the measured film compositions. Scanning probe microscopy measurements show that the mechanical properties of the film are strongly dependent on lithium concentration, with a ductile behavior at a higher Li content and a brittle behavior at a lower Li content. The chemical reactivity of the thin films was investigated by measuring the AC impedance evolution, suggesting that Li xSiO y continuously reacts with the electrolyte, in part because of the high electronic conductivity of the film determined from solid-state impedance measurements. The electrochemical cycling data of the sputter-deposited Li xSiO y/Si films also suggest that Li xSiO y is not beneficial in stabilizing the Si anode surface during battery operation, despite its favorable mechanical properties.

Mechanical Properties and Chemical Reactivity of LixSiOy Thin Films.

Silicon (Si) is a commonly studied candidate material for next-generation anodes in Li-ion batteries. A native oxide SiO2 on Si is often inevitable. However, it is not clear if this layer has positive or negative effect on the battery performance. This understanding is complicated by the lack of knowledge about the physical properties, and by convolution of chemical and electrochemical effects during the anode lithiation process. In this study, LixSiOy thin films as model materials for lithiated SiO2 were deposited by magnetron sputtering at ambient temperature, with the goal of 1) decoupling chemical reactivity from electrochemical reactivity, and 2) evaluating the physical and electrochemical properties of LixSiOy. XPS analysis of the deposited thin films demonstrate that a composition close to previous experimental reports of lithiated native SiO2, can be achieved through sputtering. Our density functional theory calculations also confirm that possible phases formed by lithiating SiO2 are very close to the measured film compositions. Scanning probe microscopy measurements show the mechanical properties of the film are strongly dependent on lithium concentration, with ductile behavior and higher Li content and brittle behavior at lower Li content. Chemical reactivity of the thin films was investigated by measuring AC impedance evolution, suggesting that LixSiOy continuously reacts with electrolyte, in part due to high electronic conductivity of the film determined from solid state impedance measurements. Electrochemical cycling data of sputter deposited LixSiOy/Si films also suggest that LixSiOy is not beneficial in stabilizing the Si anode surface during battery operation, despite its favorable mechanical properties.

Directing the Lithium-Sulfur Reaction Pathway via Sparingly Solvating Electrolytes for High Energy Density Batteries.

The lithium-sulfur battery has long been seen as a potential next generation battery chemistry for electric vehicles owing to the high theoretical specific energy and low cost of sulfur. However, even state-of-the-art lithium-sulfur batteries suffer from short lifetimes due to the migration of highly soluble polysulfide intermediates and exhibit less than desired energy density due to the required excess electrolyte. The use of sparingly solvating electrolytes in lithium-sulfur batteries is a promising approach to decouple electrolyte quantity from reaction mechanism, thus creating a pathway toward high energy density that deviates from the current catholyte approach. Herein, we demonstrate that sparingly solvating electrolytes based on compact, polar molecules with a 2:1 ratio of a functional group to lithium salt can fundamentally redirect the lithium-sulfur reaction pathway by inhibiting the traditional mechanism that is based on fully solvated intermediates. In contrast to the standard catholyte sulfur electrochemistry, sparingly solvating electrolytes promote intermediate- and short-chain polysulfide formation during the first third of discharge, before disproportionation results in crystalline lithium sulfide and a restricted fraction of soluble polysulfides which are further reduced during the remaining discharge. Moreover, operation at intermediate temperatures ca. 50 °C allows for minimal overpotentials and high utilization of sulfur at practical rates. This discovery opens the door to a new wave of scientific inquiry based on modifying the electrolyte local structure to tune and control the reaction pathway of many precipitation-dissolution chemistries, lithium-sulfur and beyond.

Degradation Mechanisms of Magnesium Metal Anodes in Electrolytes Based on (CF3SO2)2N- at High Current Densities.

The energy density of rechargeable batteries utilizing metals as anodes surpasses that of Li ion batteries, which employ carbon instead. Among possible metals, magnesium represents a potential alternative to the conventional choice, lithium, in terms of storage density, safety, stability, and cost. However, a major obstacle for metal-based batteries is the identification of electrolytes that show reversible deposition/dissolution of the metal anode and support reversible intercalation of ions into a cathode. Traditional Grignard-based Mg electrolytes are excellent with respect to the reversible deposition of Mg, but their limited anodic stability and compatibility with oxide cathodes hinder their applicability in Mg batteries with higher voltage. Non-Grignard electrolytes, which consist of ethereal solutions of magnesium(II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), remain fairly stable near the potential of Mg deposition. The slight reactivity of these electrolytes toward Mg metal can be remedied by the addition of surface-protecting agents, such as MgCl2. Hence, ethereal solutions of Mg(TFSI)2 salt with MgCl2 as an additive have been suggested as a representative non-Grignard Mg electrolyte. In this work, the degradation mechanisms of a Mg metal anode in the TFSI-based electrolyte were studied using a current density of 1 mA cm-2 and an areal capacity of ∼0.4 mAh cm-2, which is close to those used in practical applications. The degradation mechanisms identified include the corrosion of Mg metal, which causes the loss of electronic pathways and mechanical integrity, the nonuniform deposition of Mg, and the decomposition of TFSI- anions. This study not only represents an assessment of the behavior of Mg metal anodes at practical current density and areal capacity but also details the outcomes of interfacial passivation, which was detected by simple cyclic voltammetry experiments. This study also points out the absolute absence of any passivation at the electrode-electrolyte interface for the premise of developing electrolytes compatible with a metal anode.

Macroscopic Innervation of the Dura Mater Covering the Middle Cranial Fossa in Humans Correlated to Neurovascular Headache.

The trigeminovascular system within the cranial dura mater is a possible cause of headaches. The aim of this study is to investigate macroscopically dural innervation around the middle meningeal artery (MMA) in the middle cranial fossa. Forty-four sides of the cranial dura overlying the skull base obtained from 24 human cadavers were stained using Sihler's method. Overall, the nervus spinosus (NS) from either the maxillary or mandibular trigeminal divisions ran along the lateral wall of the middle meningeal vein rather than that of the MMA. Distinct bundles of the NS running along the course of the frontal branches of the MMA were present in 81.8% of cases (N = 36). Others did not form dominant nerve bundles, instead giving off free nerve endings along the course of the MMA or dural connective tissue. The distribution of these nerve endings was similar to that of the course of the frontal, parietal and petrosal branches of the MMA (11.4%). The others were not restricted to a perivascular plexus, crossing the dural connective tissues far from the MMA (6.8%). These findings indicate that the NS generally travels alongside the course of the frontal branches of the MMA and terminates in the vicinity of the pterion.

"Rocking-Chair"-Type Metal Hybrid Supercapacitors.

Hybrid supercapacitors that follow a "rocking-chair"-type mechanism were developed by coupling divalent metal and activated carbon electrodes in nonaqueous electrolytes. Conventional supercapacitors require a large amount of electrolyte to provide a sufficient quantity of ions to the electrodes, due to their Daniell-type mechanism that depletes the ions from the electrolyte while charging. The alternative "rocking-chair"-type mechanism effectively enhances the energy density of supercapacitors by minimizing the necessary amount of electrolyte, because the ion is replenished from the metal anode while it is adsorbed to the cathode. Newly developed nonaqueous electrolytes for Mg and Zn electrochemistry, based on bis(trifluoromethylsulfonyl)imide (TFSI) salts, made the metal hybrid supercapacitors possible by enabling reversible deposition on the metal anodes and reversible adsorption on an activated carbon cathode. Factoring in gains through the cell design, the energy density of the metal hybrid supercapacitors is projected to be a factor of 7 higher than conventional devices thanks to both the "rocking-chair"-type mechanism that minimizes total electrolyte volume and the use of metal anodes, which have substantial merits in capacity and voltage. Self-discharge was also substantially alleviated compared to conventional supercapacitors. This concept offers a route to build supercapacitors that meet dual criteria of power and energy densities with a simple cell design.

Advanced hybrid battery with a magnesium metal anode and a spinel LiMn2O4 cathode.

Two Mg-Li dual salt hybrid electrolytes are developed, which exhibit excellent oxidative stability up to around 3.8 V (vs. Mg/Mg(2+)) on an aluminum current collector, enabling the successful coupling of several state-of-the-art lithium-ion intercalation cathodes (LiMn2O4, LiCoO2 and LiNi1/3Mn1/3Co1/3O2) with magnesium metal anodes. The Mg-LiMn2O4 battery delivers an initial discharge capacity of about 106 mA h g(-1) with a working voltage of around 2.8 V (vs. Mg/Mg(2+)), highlighting the highest working voltage of rechargeable batteries with magnesium metal anodes to date.

Origin of Electrochemical, Structural, and Transport Properties in Nonaqueous Zinc Electrolytes.

Through coupled experimental analysis and computational techniques, we uncover the origin of anodic stability for a range of nonaqueous zinc electrolytes. By examination of electrochemical, structural, and transport properties of nonaqueous zinc electrolytes with varying concentrations, it is demonstrated that the acetonitrile-Zn(TFSI)2, acetonitrile-Zn(CF3SO3)2, and propylene carbonate-Zn(TFSI)2 electrolytes can not only support highly reversible Zn deposition behavior on a Zn metal anode (≥99% of Coulombic efficiency) but also provide high anodic stability (up to ∼3.8 V vs Zn/Zn(2+)). The predicted anodic stability from DFT calculations is well in accordance with experimental results, and elucidates that the solvents play an important role in anodic stability of most electrolytes. Molecular dynamics (MD) simulations were used to understand the solvation structure (e.g., ion solvation and ionic association) and its effect on dynamics and transport properties (e.g., diffusion coefficient and ionic conductivity) of the electrolytes. The combination of these techniques provides unprecedented insight into the origin of the electrochemical, structural, and transport properties in nonaqueous zinc electrolytes.