Synergistic dual conversion reactions assisting Pb-S electrochemistry for energy storage.

SignificanceBased on the analysis of three thermodynamic parameters of various M-S systems (solubility of metal sulfides [MxSy] in aqueous solution, volume change of the metal-sulfur [M-S] battery system, and the potential of S/MxSy cathode redox couple), an aqueous Pb-S battery operated by synergistic dual conversion reactions (cathode: S⇄PbS, anode: Pb2+⇄PbO2) has been officially reported. Benefitting from the inherent insolubility of PbS and a conversion-type counter electrode, the aqueous Pb-S battery exhibited two advantages: it is shuttle effect free and has a dendrite-free nature. Moreover, the practical value of the Pb-S battery was further certified by the prototype S|Pb(NO3)2ǁZn(NO3)2|Zn hybrid cell, which afforded an energy density of 930.9 Wh kg-1sulfur.

Revealing the Dynamic Lithiation Process of Copper Disulfide by in Situ TEM.

Transition metal oxides, fluorides, and sulfides are extensively studied as candidate electrode materials for lithium-ion batteries driven by the urgency of developing next-generation higher energy density lithium batteries. These conversion-type electrode materials often require nanosized active materials to enable a "smooth" lithiation and de-lithiation process during charge/discharge cycles, determined by their size, structure, and phase. Herein, the structural and chemical changes of Copper Disulfide (CuS2) hollow nanoparticles during the lithiation process through an in situ transmission electron microscopy (TEM) method are investigated. The study finds the hollow structure of CuS2 facilitates the quick formation of fluidic Li2S "drops," accompanied by a de-sulfurization to the Cu7S4 phase. Meanwhile, the metallic Cu phase emerges as fine nanoparticles and grows into nano-strips, which are embedded in the Li2S/Cu7S4 matrix. These complex nanostructured phases and their spatial distribution can lead to a low de-lithiation barrier, enabling fast reaction kinetics.

SnO2/SnS heterojunction anchoring on CMK-3 mesoporous network improves the reversibility of conversion reaction for lithium/sodium ions storage.

Tin oxide-based (SnO2) materials show high theoretical capacity for lithium and sodium storage benefiting from a double-reaction mechanism of conversion and alloying reactions. However, due to the limitation of the reaction thermodynamics and kinetics, the conversion reaction process of SnO2usually shows irreversibility, resulting in serious capacity decay and hindering the further application of the SnO2anode. Herein, SnO2/SnS heterojunction was anchored on the surface and inside of CMK-3 byinsitusynthesis method, forming a stable 3D structural material (SnO2/SnS@CMK-3). The electrochemical properties of SnO2/SnS@CMK-3 composite show high capacity and reversible conversion reaction, which was attributed to the synergistic effect of CMK-3 and SnO2/SnS heterojunction. To further investigate the influence of the heterojunction on the reversibility of the conversion reaction, the Gibbs free energy (ΔG) was calculated using density functional theory. The results show that SnO2/SnS heterojunction has a closer to zero ΔGfor lithium/sodium ion batteries compared to SnO2, indicating that the heterojunction enhances the reversibility of the conversion reaction in chemical reaction thermodynamics. Our work provides insights into the reversibility of the conversion reaction of SnO2-based materials, which is essential for improving their electrochemical performance.

Design Principles for Fluorinated Interphase Evolution via Conversion-Type Alloying Processes for Anticorrosive Lithium Metal Anodes.

Over the past decade, lithium metal has been considered the most attractive anode material for high-energy-density batteries. However, its practical application has been hindered by its high reactivity with organic electrolytes and uncontrolled dendritic growth, resulting in poor Coulombic efficiency and cycle life. In this paper, we propose a design strategy for interface engineering using a conversion-type reaction of metal fluorides to evolve a LiF passivation layer and Li-M alloy. Particularly, we propose a LiF-modified Li-Mg-C electrode, which demonstrates stable long-term cycling for over 2000 h in common organic electrolytes with fluoroethylene carbonate (FEC) additives and over 700 h even without additives, suppressing unwanted side reactions and Li dendritic growth. With the help of phase diagrams, we found that solid-solution-based alloying not only facilitates the spontaneous evolution of a LiF layer and bulk alloy but also enables reversible Li plating/stripping inward to the bulk, compared with intermetallic compounds with finite Li solubility.

Recent Advances in the Reverse Water-Gas Conversion Reaction.

The increase in carbon dioxide emissions has significantly impacted human society and the global environment. As carbon dioxide is the most abundant and cheap C1 resource, the conversion and utilization of carbon dioxide have received extensive attention from researchers. Among the many carbon dioxide conversion and utilization methods, the reverse water-gas conversion (RWGS) reaction is considered one of the most effective. This review discusses the research progress made in RWGS with various heterogeneous metal catalyst types, covering topics such as catalyst performance, thermodynamic analysis, kinetics and reaction mechanisms, and catalyst design and preparation, and suggests future research on RWGS heterogeneous catalysts.

GeO2 Nanoparticles Decorated in Amorphous Carbon Nanofiber Framework as Highly Reversible Lithium Storage Anode.

Germanium oxide (GeO2) is a high theoretical capacity electrode material due to its alloying and conversion reaction. However, the actual cycling capacity is rather poor on account of suffering low electron/ion conductivity, enormous volume change and agglomeration in the repeated lithiation/delithiation process, which renders quite a low reversible electrochemical lithium storage reaction. In this work, highly amorphous GeO2 particles are uniformly distributed in the carbon nanofiber framework, and the amorphous carbon nanofiber not only improves the conduction and buffers the volume changes but also prevents active material agglomeration. As a result, the present GeO2 and carbon composite electrode exhibits highly reversible alloying and conversion processes during the whole cycling process. The two reversible electrochemical reactions are verified by differential capacity curves and cyclic voltammetry measurements during the whole cycling process. The corresponding reversible capacity is 747 mAh g-1 after 300 cycles at a current density of 0.3 A g-1. The related reversible capacities are 933, 672, 487 and 302 mAh g-1 at current densities of 0.2, 0.4, 0.8 and 1.6 A g-1, respectively. The simple strategy for the design of amorphous GeO2/carbon composites enables potential application for high-performance LIBs.

Accelerated Multi-step Sulfur Redox Reactions in Lithium-Sulfur Batteries Enabled by Dual Defects in Metal-Organic Framework-based Catalysts.

The sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium-sulfur (Li-S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li-S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual-defect (missing linker and missing cluster defects) metal-organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi-step conversion reaction of LiPSs. Electrochemical tests and first-principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S8 →Li2 S4 , while the missing cluster defects can catalyze the reaction of Li2 S4 →Li2 S, so as to effectively inhibit the shuttle effect. Hence, the Li-S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g-1 delivers a capacity of 1087 mAh g-1 at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm-2 and E/S=3.9 mL g-1 , an areal capacity of 10.4 mAh cm-2 for 45 cycles can still be obtained.

Macro/Micro-Environment Regulating Carbon-Supported Single-Atom Catalysts for Hydrogen/Oxygen Conversion Reactions.

Single-atom catalysts (SACs) have attracted tremendous research interest due to their unique atomic structure, maximized atom utilization, and remarkable catalytic performance. Among the SACs, the carbon-supported SACs have been widely investigated due to their easily controlled properties of the carbon substrates, such as the tunable morphologies, ordered porosity, and abundant anchoring sites. The electrochemical performance of carbon-supported SACs is highly related to the morphological structure of carbon substrates (macro-environment) and the local coordination environments of center metals (micro-environment). This review aims to provide a comprehensive summary on the macro/micro-environment regulating carbon-supported SACs for highly efficient hydrogen/oxygen conversion reactions. The authors first summarize the macro-environment engineering strategies of carbon-supported SACs with altered specific surface areas and porous properties of the carbon substrates, facilitating the mass diffusion kinetics and structural stability. Then the micro-environment engineering strategies of carbon-supported SACs are discussed with the regulated atomic structure and electronic structure of metal centers, boosting the catalytic performance. Insights into the correlation between the co-boosted effect from the macro/micro-environments and catalytic activity for hydrogen/oxygen conversion reactions are summarized and discussed. Finally, the challenges and perspectives are addressed in building highly efficient carbon-supported SACs for practical applications.

A Composite of Two Dimensional GeSe2 /Nitrogen-Doped Reduced Graphene Oxide for Enhanced Capacitive Lithium-Ion Storage.

A composite of two-dimensional (2D) GeSe2 nanosheets dispersed on N-doped reduced graphene oxide (GeSe2 /N-rGO) is fabricated via a simple hydrothermal method combined with post-selenization process. The high electronic conductivity and the substantial void spaces of the wrinkled N-rGO can improve the electrical conductivity of the active material and accommodate the volume evolution of GeSe2 nanosheets during the (de)lithiation processes, while GeSe2 nanosheets can reduce ion diffusion length effectively. Meanwhile, the unique layered structure is beneficial to the contact of the active material and electrolyte, and the reversibility of conversion reaction has also been improved. Furthermore, kinetics analysis reveals a pseudocapacitance-dominated Li+ -storage mechanism at high rates. In-situ X-ray diffraction analysis discloses that the conversion reaction has played a certain part in Li+ -storage. Thus, the GeSe2 /N-rGO composite delivers excellent rate capability and good long-term stability with a high reversible capacity of 711.0 mA h g-1 after 2000 cycles at 1 A g-1 .

Elaborated Reaction Pathway of Photothermal Catalytic CO2 Conversion with H2 O on Gallium Oxide-Decorated and -Defective Surfaces.

Ga2 O3 -decorated and -defective surface models based on anatase TiO2 have been established. The thermodynamic reaction pathways, including protonation, deoxygenation and hydroxylation steps, during CO2 conversion with H2 O to C1 products were calculated. The calculation results demonstrate that a Ga2 O3 cocatalyst enhances the selective adsorption of CO2 and slightly weakens the competitive adsorption of H2 O. The promotion effect of Ga2 O3 on the subsequent reaction depends on the availability of protons and electrons. Free-energy calculations revealed that the basic functional site generated by Ga2 O3 not only suppresses the back reaction of the OH group after H2 O directly provides protons but also maintains the surface defect oxygen vacancy (VO ), which promotes the reaction thermodynamics but tends to be consumed in the process. Additionally, Ga2 O3 decoration promotes VO formation, and the coexistence of Ga2 O3 and VO further decreases the reaction rate-determining step energy barrier, promoting C1 production.

Unusual pseudocapacitive lithium-ion storage on defective Co3O4nanosheets.

Secondary lithium-ion batteries are restricted in large-scale applications including power grids and long driving electric vehicles owing to the low specific capacity of conventional intercalation anodes possessing sluggish Li-ion diffusion kinetics. Herein, we demonstrate an unusual pseudocapacitive lithium-ion storage on defective Co3O4nanosheet anodes for high-performance rechargeable batteries. Cobalt-oxide nanosheets presented here composed of various defects including vacancies, dislocations and grain boundaries. Unique 2D holey microstructure enabled efficient charge transport as well as provided room for volume expansions associated with lithiation-delithiation process. These defective anodes exhibited outstanding pseudocapacitance (up to 87%), reversible capacities (1490 mAh g-1@ 25 mA g-1), rate capability (592 mAh g-1@ 30 A g-1), stable cycling (85% after 500 cycles @ 1 A g-1) and columbic efficiency (∼100%). Exceptional Li-ion storage phenomena in defective Co3O4nanosheets is accredited to the pseudocapacitive nature of conversion reaction resulting from ultrafast Li-ion diffusion through various crystal defects. The demonstrated approach of defect-induced pseudocapacitance can also be protracted for various low-cost and/or eco-friendly transition metal-oxides for next-generation rechargeable batteries.

Improved Li storage performance of SnO nanodisc on SnO2quantum dots embedded carbon matrix.

Li-ion batteries with conversion type anode are attractive choice, for electric vehicles and portable electronic devices, because of their high theoretical capacity and cycle stability. On the contrary, enormous volume change during lithiation/delithiation and irreversible conversion reaction limits use of such anodes. To overcome these challenges, incorporating nano-sized SnOxon flexible carbonaceous matrix is an efficient approach. A facile and scalable fabrication of SnO nanodisc decorated on SnO2quantum dots embedded carbon (SnOx@C) is reported in the present study. Detailed structural and morphological investigation confirms the successful synthesis of SnOx@C composite with 72.3 wt% SnOxloading. The CV profiles of the nanocomposite reveal a partial reversibility of conversion reaction for the active materials SnOx. Such partial reversible conversion enhances the overall capacity of the nanocomposite. It delivers a very high discharge capacity of 993 mAh g-1at current density of 0.05 A g-1after 200 cycles; which is 2.6 times higher than that of commercial graphitic anode (372 mAh g-1) and very close to the calculated capacity of the SnOx@C composite. This unique nanocomposite remarkably improves Li storage performance in terms of reversible capacity, rate capability and cycling performance. It is established that such engineered anode can efficiently reduce the electrode pulverization and in turn make conversion reaction of tin partially reversible.

Gender differences in risk factors and psychosocial functioning in children with psychogenic nonepileptic seizures.

OBJECTIVE: Female predominance is evident in childhood-onset psychogenic nonepileptic seizures (PNES). Understanding gender-specific vulnerability to PNES may provide a unique insight into its cause and management. We aimed to investigate gender differences in demographic characteristics, triggering factors and psychosocial functioning in children and youth with PNES. METHODS: We retrospectively reviewed patients who were evaluated in the PNES clinic at Children's Healthcare of Atlanta from July 2019 to March 2020 and completed questionnaires to assess adverse life events, psychosocial function (Pediatric Symptom Checklist-17 [PSC-17]), and somatic symptoms (Children's Somatic Symptom Inventory-8, [CSSI-8]). RESULTS: Forty-nine consecutive patients (38 girls, 11 boys) with a median age of 15.0 (9-19) years were included in the study. We performed univariate analysis and evaluated significant variables related to PNES according to sex. Majority of both genders experienced daily to weekly PNES, came from dysfunctional families, scored high on PSC-17, were treated for neuropsychiatric illnesses, and experienced bothersome somatic symptoms. The variables significantly different between genders were suicidal thoughts, history of trauma, and learning disability. Suicidal thoughts and trauma, particularly sexual abuse, were significantly more prevalent in girls (p = 0.03) whereas learning disability was more common in boys (p = 0.03). CONCLUSION: Females predominated in our PNES clinic (F:M = 3.5:1). Gender differences in predisposing factors were sexual abuse in females and learning disability in males. Our data highlight the gender-specific risk factors and vulnerability to PNES. The awareness of gender difference may guide more targeted intervention for children and youth with PNES.

Polymorphic Effects on Electrochemical Performance of Conversion-Based MnO2 Anode Materials for Next-Generation Li Batteries.

In this study, four different MnO2 polymorphs are synthesized with a controlled morphology of hollow porous structures to systematically investigate the influences of polymorphs in conversion-based material. As the structure of these materials transforms into nanosized metal and maintains an extremely low-crystalline phase during cell operation, the effects of polymorphs are overlooked as compared to the case of insertion-based materials. Thus, differences in the ion storage behaviors among various MnO2 polymorphs are not well identified. Herein, the structural changes, charge storage reaction, and electrochemical performance of the different MnO2 polymorphs are investigated in detail. The experimental results demonstrate that the charge storage reactions, as part of which spinel-phased MnO2 formation is observed after lithiation and delithiation instead of recovery of the original phases, are similar for all the samples. However, the electrochemical performance varies depending on the initial crystal structure. Among the four polymorphs, the spinel-type λ-MnO2 delivers the highest reversible capacity of ≈1270 mAh g-1 . The structural similarity between the cycled and pristine states of λ-MnO2 induces faster kinetics, resulting in the better electrochemical performance. These findings suggest that polymorphs are another important factor to consider when designing high-performance materials for next-generation rechargeable batteries.

Studying the Conversion Mechanism to Broaden Cathode Options in Aqueous Zinc-Ion Batteries.

Aqueous Zn-ion batteries (ZIBs) are regarded as alternatives to Li-ion batteries benefiting from both improved safety and environmental impact. The widespread application of ZIBs, however, is compromised by the lack of high-performance cathodes. Currently, only the intercalation mechanism is widely reported in aqueous ZIBs, which significantly limits cathode options. Beyond Zn-ion intercalation, we comprehensively study the conversion mechanism for Zn2+ storage and its diffusion pathway in a CuI cathode, indicating that CuI occurs a direct conversion reaction without Zn2+ intercalation due to the high energy barrier for Zn2+ intercalation and migration. Importantly, this direct conversion reaction mechanism can be readily generalized to other high-capacity cathodes, such as Cu2 S (336.7 mA h g-1 ) and Cu2 O (374.5 mA h g-1 ), indicating its practical universality. Our work enriches the Zn-ion storage mechanism and significantly broadens the cathode horizons towards next-generation ZIBs.

Synthesis Process of CoSeO3 Microspheres for Unordinary Li-ion Storage Performances and Mechanism of Their Conversion Reaction with Li ions.

Multicomponent materials with various double cations have been studied as anode materials of lithium-ion batteries (LIBs). Heterostructures formed by coupling different-bandgap nanocrystals enhance the surface reaction kinetics and facilitate charge transport because of the internal electric field at the heterointerface. Accordingly, metal selenites can be considered efficient anode materials of LIBs because they transform into metal selenide and oxide nanocrystals in the first cycle. However, few studies have reported synthesis of uniquely structured metal selenite microspheres. Herein, synthesis of high-porosity CoSeO3 microspheres is reported. Through one-pot oxidation at 400 °C, CoSex -C microspheres formed by spray pyrolysis transform into CoSeO3 microspheres showing unordinary cycling and rate performances. The conversion mechanism of CoSeO3 microspheres for lithium-ion storage is systematically studied by cyclic voltammetry, in situ X-ray diffraction and electrochemical impedance spectroscopy, and transmission electron microscopy. The reversible reaction mechanism of the CoSeO3 phase from the second cycle onward is evaluated as CoO + xSeO2 + (1 - x)Se + 4(x + 1)Li+ + 4( x + 1)e- ↔ Co + (2x + 1)Li2 O + Li2 Se. The CoSeO3 microspheres show a high reversible capacity of 709 mA h g-1 for the 1400th cycle at a current density of 3 A g-1 and a high reversible capacity of 526 mA h g-1 even at an extremely high current density of 30 A g-1 .

Enhancing the Sequential Conversion-Alloying Reaction of Mixed Sn-S Hybrid Anode for Efficient Sodium Storage by a Carbon Healed Graphene Oxide.

To date, the possible depletion of lithium resources has become relevant, giving rise to the interest in Na-ion batteries (NIBs) as promising alternatives to Li-ion batteries. While extensive investigations have examined various transition metal oxides and chalcogenides as anode materials for NIBs, few of these have been able to utilize their high specific capacity in sodium-based systems because of their irreversibility in a charge/discharge process. Here, the mixed Sn-S nanocomposites uniformly distributed on reduced graphene oxide are prepared via a facile hydrothermal synthesis and a unique carbothermal reduction process, producing ultrafine nanoparticle with the size of 2 nm. These nanocomposites are experimentally confirmed to overcome the intrinsic drawbacks of tin sulfides such as large volume change and sluggish diffusion kinetics, demonstrating an outstanding electrochemical performance: an excellent specific capacity of 1230 mAh g-1 , and an impressive rate capability (445 mAh g-1 at 5000 mA g-1 ). The electrochemical behavior of a sequential conversion-alloying reaction for the anode materials is investigated, revealing both the structural transition and the chemical state in the discharge/charge process. Comprehension of the reaction mechanism for the mixed Sn-S/rGO hybrid nanocomposites makes it a promising electrode material and provides a new approach for the Na-ion battery anodes.

Fast-Charging and High Volumetric Capacity Anode Based on Co3 O4 /CuO@TiO2 Composites for Lithium-Ion Batteries.

This paper presents an investigation of anodic TiO2 nanotube arrays (TNAs), with a Co3 O4 /CuO coating, for lithium-ion batteries (LIBs). The coated TNAs are investigated using various analytical techniques, with the results clearly suggesting that the molar ratio of Co3 O4 /CuO in the TiO2 nanotubes substantially influences its battery performance. In particular, a cobalt/copper molar ratio of 2:1 on the TNAs (Co2 Cu1 @TNAs) features the best LIBs anode performance, exhibiting high reversible capacity and enhanced cycling stability. Noticeably, Co2 Cu1 @TNAs achieve excellent rate capability even after quite a high current density of 20.0 A g-1 (≈25 C, where C corresponds to complete discharge in 1 h) and superior volumetric reversible capacity of ≈3330 mA h-1 cm-3 . This value is approximately seven times higher than those of a graphite-based anode. This outstanding performance is attributed to the synergistic effects of Co2 Cu1 @TNAs: 1) the structural advantage of TNAs, with their large amount of free space to accommodate the large volume expansion during Li+ insertion/extraction and 2) the optimized ratio of Co3 O4 and CuO in the composite for improved capacity. In addition, no binder or conductive agent is used, which is partly responsible for the overall improved volumetric capacity and electrochemical performance.

Nontopotactic Reaction in Highly Reversible Sodium Storage of Ultrathin Co9 Se8 /rGO Hybrid Nanosheets.

Transition metal chalcogenide with tailored nanosheet architectures with reduced graphene oxide (rGO) for high performance electrochemical sodium ion batteries (SIBs) are presented. Via one-step oriented attachment growth, a facile synthesis of Co9 Se8 nanosheets anchored on rGO matrix nanocomposites is demonstrated. As effective anode materials of SIBs, Co9 Se8 /rGO nanocomposites can deliver a highly reversible capacity of 406 mA h g-1 at a current density of 50 mA g-1 with long cycle stability. It can also deliver a high specific capacity of 295 mA h g-1 at a high current density of 5 A g-1 indicating its high rate capability. Furthermore, ex situ transmission electron microscopy observations provide insight into the reaction path of nontopotactic conversion in the hybrid anode, revealing the highly reversible conversion directly between the hybrid Co9 Se8 /rGO and Co nanoparticles/Na2 Se matrix during the sodiation/desodiation process. In addition, it is experimentally demonstrated that rGO plays significant roles in both controllable growth and electrochemical conversion processes, which can not only modulate the morphology of the product but also tune the sodium storage performance. The investigation on hybrid Co9 Se8 /rGO nanosheets as SIBs anode may shed light on designing new metal chalcogenide materials for high energy storage system.

In Situ Chemical Synthesis of Lithium Fluoride/Metal Nanocomposite for High Capacity Prelithiation of Cathodes.

The initial lithium loss during the formation stage is a critical issue that significantly reduces the specific capacity and energy density of current rechargeable lithium-ion batteries (LIBs). An effective strategy to solve this problem is using electrode prelithiation additives that can work as a secondary lithium source and compensate the initial lithium loss. Herein we show that nanocomposites of lithium fluoride and metal (e.g., LiF/Co and LiF/Fe) can be efficient cathode prelithiation materials. The thorough mixing of ultrafine lithium fluoride and metal particles (∼5 nm) allows lithium to be easily extracted from the nanocomposites via an inverse conversion reaction. The LiF/Co nanocomposite exhibits an open circuit voltage (OCV, 1.5 V) with good compatibility with that of existing cathode materials and delivers a high first-cycle "donor" lithium-ion capacity (516 mA h g(-1)). When used as an additive to a LiFePO4 cathode, the LiF/Co nanocomposite provides high lithium compensation efficiency. Importantly, the as-formed LiF/metal nanocomposites possess high stability and good compatibility with the regular solvent, binder, and existing battery processing conditions, in contrast with the anode prelithiation materials that usually suffer from issues of high chemical reactivity and instability. The facile synthesis route, high stability in ambient and battery processing conditions, and high "donor" lithium-ion capacity make the LiF/metal nanocomposites ideal cathode prelithiation materials for LIBs.