Densification of Alloying Anodes for High Energy Lithium-Ion Batteries: Critical Perspective on Inter- Versus Intra-Particle Porosity.

High Li-storage-capacity particles such as alloying-based anodes (Si, Sn, Ge, etc.) are core components for next-generation Li-ion batteries (LIBs) but are crippled by their intrinsic volume expansion issues. While pore pre-plantation represents a mainstream solution, seldom do this strategy fully satisfy the requirements in practical LIBs. One prominent issue is that porous particles reduce electrode density and negate volumetric performance (Wh L-1) despite aggressive electrode densification strategies. Moreover, the additional liquid electrolyte dosage resulting from porosity increase is rarely noticed, which has a significant negative impact on cell gravimetric energy density (Wh kg-1). Here, the concept of judicious porosity control is introduced to recalibrate existing particle design principles in order to concurrently boost gravimetric and volumetric performance, while also maintaining the battery's cycle life. The critical is emphasized but often neglected role that intraparticle pores play in dictating battery performance, and also highlight the superiority of closed pores over the open pores that are more commonly referred to in the literature. While the analysis and case studies focus on silicon-carbon composites, the overall conclusions apply to the broad class of alloying anode chemistries.

Palladium-Phosphide-Modified Three-Dimensional Phospho-Doped Graphene Materials for Hydrogen Storage.

The development of efficient hydrogen storage materials is crucial for advancing hydrogen-based energy systems. In this study, we prepared a highly innovative palladium-phosphide-modified P-doped graphene hydrogen storage material with a three-dimensional configuration (3D Pd3P0.95/P-rGO) using a hydrothermal method followed by calcination. This 3D network hindering the stacking of graphene sheets provided channels for hydrogen diffusion to improve the hydrogen adsorption kinetics. Importantly, the construction of the three-dimensional palladium-phosphide-modified P-doped graphene hydrogen storage material improved the hydrogen absorption kinetics and mass transfer process. Furthermore, while acknowledging the limitations of primitive graphene as a medium in hydrogen storage, this study addressed the need for improved graphene-based materials and highlighted the significance of our research in exploring three-dimensional configurations. The hydrogen absorption rate of the material increased obviously in the first 2 h compared with two-dimensional sheets of Pd3P/P-rGO. Meanwhile, the corresponding 3D Pd3P0.95/P-rGO-500 sample, which was calcinated at 500 °C, achieved the optimal hydrogen storage capacity of 3.79 wt% at 298 K/4 MPa. According to molecular dynamics, the structure was thermodynamically stable, and the calculated adsorption energy of a single H2 molecule was -0.59 eV/H2, which was in the ideal range of hydrogen ad/desorption. These findings pave the way for the development of efficient hydrogen storage systems and advance the progress of hydrogen-based energy technologies.

Enhanced interface stability of ammine magnesium borohydride by in situ decoration of MgBr2·2NH3 nanoparticles.

A novel Mg(BH4)2·1.9NH3-MgBr2·2NH3 composite was demonstrated as a solid-state Mg2+ electrolyte. The in situ decoration of MgBr2·2NH3 nanoparticles with an average size of 3.7 nm on the surface of Mg(BH4)2·1.9NH3 improves the Mg2+ conductivity to 2.1 × 10-4 S cm-1 at 50 °C and offers long-term stability towards the Mg metal anode.

Texture and High Yield Strength of Rapidly Solidified AZ31 Magnesium Alloy Extruded at 250 °C.

In this study, commercial AZ31B magnesium alloy was used to compare the differences between the microstructure, texture, and mechanical properties of conventional solidification (as homogenized AZ31) and rapid solidification (as RS AZ31). The results demonstrate that a rapidly solidified microstructure leads to better performance after hot extrusion with a medium extrusion rate (6 m/min) and extrusion temperature (250 °C). The average grain size of as-homogenized AZ31 extruded rod is 100 µm after annealing and 4.6 µm after extrusion, respectively, but that of the as-RS AZ31 extruded rod is only about 5 µm and 1.1 µm, correspondingly. The as-RS AZ31 extruded rod attains a high average yield strength of 289.6 MPa, which is superior to the as-homogenized AZ31 extruded rod, and is improved by 81.3% in comparison. The as-RS AZ31 extruded rod shows a more random crystallographic orientation and has an unconventional weak texture component in <112¯1>/<202¯1> direction, which has not been reported yet, while the as-homogenized AZ31 extruded rod has an expected texture with prismatic <101¯0>/<1¯21¯0>//ED.

Microstructure and Air Trace Defects of the Rapidly Solidified ZK60 Magnesium Alloy Ribbon.

ZK60 alloy metal ribbons were prepared successfully in a carbon dioxide atmosphere by varying the speeds of melt spinning. The thin metal ribbon with different solidification speeds was prepared by controlling different rotation speeds, and the influence of solidification speed on the ZK60 ribbon was studied. The results show that the gas mark has a significant effect on the local structure of the ribbon. The gas mark's proportional area of the ZK60 ribbon increases first and then decreases with the increase in roll speed, and the gas mark proportion area is the smallest at 17.6 m/s. With the increase in the solidification rate, the base texture of the ribbon is enhanced, and the proportion of columnar crystals in the ribbon gradually increases. At the rate of 17.6 m/s, columnar crystals run through the entire side of the ribbon, and uniformly distributed spherical-particle phases are found inside the grain. At the speed of 17.6 m/s, the mechanical properties of different areas of the ribbon are close and different from those of the other two speeds, and the performance of the quenching zone is better than that of the slow-cooling zone.

Migration of solidification grain boundaries and prediction.

Solidification processing is essential to the manufacture of various metal products, including additive manufacturing. Solidification grain boundaries (SGBs) result from the solidification of the last liquid film between two abutting grains of different orientations. They can migrate, but unlike normal GB migration, SGB migration (SGBM) decouples SGBs from solidification microsegregation, further affecting material properties. Here, we first show the salient features of SGBM in magnesium-tin alloys solidified with cooling rates of 8-1690 °C/s. A theoretical model is then developed for SGBM in dilute binary alloys, focusing on the effect of solute type and content, and applied to 10 alloy systems with remarkable agreement. SGMB does not depend on cooling rate or time but relates to grain size. It tends to occur athermally. The findings of this study extend perspectives on solidification grain structure formation and control for improved performance (e.g. hot or liquation cracking during reheating, intergranular corrosion or fracture).

Hierarchal Porous Graphene-Structured Electrocatalysts with Fe-N5 Active Sites Modified with Fe Clusters for Enhanced Performance Toward Oxygen Reduction Reaction.

The local coordination environment around the active centers has a major impact on tuning the intrinsic activity of M-N-C catalysts. Herein, a porous graphene with Fe-N5 active sites modified with Fe clusters is successfully fabricated by using Fe3+-SCN- and NaHCO3 as the metal precursor and pore-forming agent, respectively. The unique Fe-N5 configuration accompanying Fe clusters and the improved ORR activity are confirmed by various characterization techniques and theoretical calculations. Benefiting from the pores, mass and electron transfer channels are successfully constructed, making more active sites accessible and facilitating the ORR process. As a consequence, the as-prepared catalyst has an excellent ORR activity with a half-wave potential of 0.89 V, comparable selectivity, and superior stability. In addition, a homemade primary zinc-air battery using this material as the cathode catalyst has a maximum power density of 0.205 W/cm2, revealing the potential of the as-constructed CSA-Fe-N-C catalyst to replace precious Pt catalysts.

Ni3Sn2/nitrogen-doped graphene composite with chemisorption and electrocatalysis as advanced separator modifying material for lithium sulfur batteries.

Lithium-sulfur batteries have been widely studied because of their advantages of abundant reserves, environmental friendliness, low cost andhighspecific capacity. However, the volume expansionand the low electrical conductivity of sulfur, and the shuttle effect of polysulfides limit their application. Herein,wesynthesizea two-dimensional layered Ni3Sn2/nitrogen-doped graphene (NG) composite asseparator modifying material for lithium-sulfur batteries. The Ni3Sn2formed by dual metal salts Ni(NO3)2·6H2O and SnCl2·2H2O can adsorb polysulfide and catalyze its transformation to improve the electrochemical reaction kinetics. Moreover, the layered NG can not only disperse the Ni3Sn2particles, but alsoensure rapid electron transfer. Therefore, the lithium-sulfur battery with the Ni3Sn2/NG modified separator shows excellent electrochemical performance. At a current rate of 1 C, the lithium-sulfur battery with the Ni3Sn2/NG modified separator can provide a high initial discharge capacity of 1022.1 mAh g-1and maintain a reversible specific capacity of 758.3 mAh g-1after 400 cycles.

Controllable synthesis of few-layer ammoniated 1T'-phase WS2 as an anode material for lithium-ion batteries.

Two-dimensional transition metal dichalcogenide (TMDC) nanosheets have received significant attention as anode materials for lithium-ion batteries, especially in their metallic 1T/1T' phase. However, controllable synthesis of few-layer 1T/1T' phase is still a challenge. In the present study, we report a facile two-step hydrothermal method to controllably synthesize few-layer 1T'-phase WS2. By tuning the redox-temperature of (NH4)2WS4 from 160 to 200 °C, the thickness of 1T'-phase WS2 can be adjusted from 4-6 to 20 layers. A higher reversible capacity is achieved in 1T'-phase WS2 with a smaller thickness, but the cycling stability decreases due to the lower crystallinity. The 1T'-phase WS2 synthesized by reduction of (NH4)2WS4 at 180 °C shows a moderate thickness of 10 layers and crystallinity, exhibiting the optimal Li-ion storage properties, i.e. a reversible capacity of 855.9 mA h g-1 at 100 mA g-1 and a good rate performance of 354.4 mA h g-1 at 5000 mA g-1. These results provide new insights into understanding the impacts of layer number on the Li-ion storage properties of 1T'-phase WS2.

Size Effect of MgO on the Ionic Conduction Properties of a LiBH4·1/2NH3-MgO Nanocomposite.

A solid-state electrolyte (SSE) is the core component for fabricating solid-state batteries competitive with the currently commercial Li-ion batteries. In the present study, a LiBH4·1/2NH3-MgO nanocomposite has been developed as a fast Li-ion conductor. The conductive properties depend strongly on the size of MgO nanopowders. By adding MgO nanoparticles, the first-order transition at 55 °C observed in the crystalline LiBH4·1/2NH3 is suppressed due to the conversion of LiBH4·1/2NH3 into the amorphous state. When the size of MgO decreases from 163.6 to 13.9 nm, the MgO amount required for the phase-transition suppression of LiBH4·1/2NH3 decreases linearly from 92 to 75 wt %, accompanied by a significant enhancement of ionic conductivity. The optimized nanocomposite with 75 wt % MgO of size 13.9 nm exhibits a pronouncedly high conductivity of 4.0 × 10-3 S cm-1 at room temperature, which is 20 times higher than that of the crystalline LiBH4·1/2NH3. Furthermore, a smaller size MgO contributes to a higher electrochemical stability window (ESW) owing to the stronger interfacial interaction via B-O bonds, i.e., an ESW of 4.0 V is achieved with the addition of 75 wt % MgO of size 13.9 nm.

Li-Ion Conductivity Enhancement of LiBH4·xNH3 with In Situ Formed Li2O Nanoparticles.

Interfacial engineering is an efficient approach to improve the ionic conductivity of solid-state electrolytes. In the present study, we report the enhancement of in situ formed nanocrystalline Li2O on the thermal stability and electrochemical properties of amide lithium borohydride, LiBH4·xNH3 (x = 0.67-0.8). LiBH4·xNH3-Li2O composites with different amounts of Li2O are prepared by a one-step synthesis process by ball milling the mixture of LiBH4, LiNH2, and LiOH in molar ratios of 1:n:n (n = 1, 2, 3, 4). Owing to the strong interfacial effect with nanocrystalline Li2O, LiBH4·xNH3 is converted to the amorphous state in the presence of 78 wt % Li2O at n = 4. Consequently, the ionic conductivity of LiBH4·xNH3 at 20 °C is improved by orders of magnitude up to 5.4 × 10-4 S cm-1, the NH3 desorption temperature is increased by more than 20 °C, and the electrochemical window is widened from 0.5 to 3.8 V.

Heterostructured Ni3S2-Ni3P/NF as a Bifunctional Catalyst for Overall Urea-Water Electrolysis for Hydrogen Generation.

Urea oxidation reaction (UOR) has been proposed to replace the formidable oxygen evolution reaction (OER) to reduce the energy consumption for producing hydrogen from electrolysis of water owing to its much lower thermodynamic oxidation potential compared to that of the OER. Therefore, exploring a highly efficient and stable hydrogen evolution and urea electrooxidation bifunctional catalyst is the key to achieve economical and efficient hydrogen production. In this paper, we report a heterostructured sulfide/phosphide catalyst (Ni3S2-Ni3P/NF) synthesized via one-step thermal treatment of Ni(OH)2/NF, which allows the simultaneous occurrence of phosphorization and sulfuration. The obtained Ni3S2-Ni3P/NF catalyst shows a sheet structure with an average sheet thickness of ∼100 nm, and this sheet is composed of interconnected Ni3S2 and Ni3P nanoparticles (∼20 nm), between which there are a large number of accessible interfaces of Ni3S2-Ni3P. Thus, the Ni3S2-Ni3P/NF exhibits superior performance for both UOR and hydrogen evolution reaction (HER). For the overall urea-water electrolysis, to achieve current densities of 10 and 100 mA cm-2, cell voltage of only 1.43 and 1.65 V is required using this catalyst as both the anode and the cathode. Moreover, this catalyst also maintains fairly excellent stability after a long-term testing, indicating its potential for efficient and energy-saving hydrogen production. The theoretical calculation results show that the Ni atoms at the interface are the most efficient catalytically active site for the HER, and the free energy of hydrogen adsorption is closest to thermal neutrality, which is only 0.16 eV. A self-driven electron transfer at the interface, making the Ni3S2 sides become electron donating while Ni3P sides become electron withdrawing, may be the reason for the enhancement of the UOR activity. Therefore, this work shows an easy treatment for enhancing the catalytic activity of Ni-based materials to achieve high-efficiency urea-water electrolysis.

Enhanced room temperature ionic conductivity of the LiBH4·1/2NH3-Al2O3 composite.

A novel LiBH4·1/2NH3-Al2O3 composite was demonstrated, in which amorphous LiBH4·1/2NH3 was in situ formed on the surface of Al2O3 owing to the strong interfacial interaction via B-O bonds. The ionic conductivity of LiBH4·1/2NH3 is improved by one order of magnitude to 10-3 S cm-1 and the electrochemical window up to 3.6 V.

Enhanced Catalytic Conversion of Polysulfides Using Bimetallic Co7Fe3 for High-Performance Lithium-Sulfur Batteries.

Practical applications of lithium-sulfur (Li-S) batteries have been severely hindered by their low capacity, poor rate performance, and fast capacity degradation, which mainly originate from the notorious polysulfide shuttle effect. Herein, with density functional theory calculations, we show that the alloying of Fe into carbon-coated Co not only provides moderate binding interactions with the polysulfides to hinder their diffusion but also serves as an active catalyst in the spontaneous and successive lithiation of S8 to Li2S. Based on the fast migration of Li ions and the spontaneous lithiation of Li2S2 on the carbon-coated Fe-Co alloy, the entrapping-conversion processes of polysulfides are both thermodynamically and kinetically promoted in redox cycling. Experimentally, rationally designed Co7Fe3@porous graphite carbon-carbon nanotubes (Co7Fe3@PGC-CNT) electrocatalysts are introduced into Li-S batteries through separator functionalization. Consistent with theoretical predictions, Li-S batteries with Co7Fe3@PGC-CNT modified separators exhibit a dramatically enhanced rate capacity (788 and 631 mAh g-1 at 10 and 15 C rates, respectively) and cycling stability (a slow capacity decay of 0.05% per cycle over 1000 cycles at 2.0 C), which are superior to those of most reported Li-S batteries coupled with state-of-the-art separators. Furthermore, it is shown that the excellent hindering of the shuttle effects enables a high areal capacity of 4.7 mAh cm-2 after 90 cycles at a high sulfur loading of 6.7 mg cm-2. Our work provides a feasible method for developing high-energy and long-life Li-S batteries, which might drive the commercialization of Li-S batteries.

Hierarchical NiSe2 Nanosheet Arrays as a Robust Cathode toward Superdurable and Ultrafast Ni-Zn Aqueous Batteries.

Zn-based aqueous batteries are enjoying the hotspots of worldwide research as their significant merits in economic cost and safety. However, the lack of a robust cathode (positive electrode) owning excellent rate ability, high capacity, and stability challenges their practical application. Herein, we propose hierarchical NiSe2 nanosheet arrays as a robust cathode toward high-performance Ni-Zn aqueous batteries. Attributed to in situ anion exchange and Kirkendall effects, the nanosheet arrays are hierarchically constructed by NiSe2 nanoparticles and abundant mesopores, which fully expose the active sites and accelerate the electrode kinetics. This unique structure endows the NiSe2 electrode with remarkable specific capacity (245.1 mAh g-1) and extraordinary high-rate ability (maintains 58% at 72.8 A g-1) together with 10,000 cycles without any obvious capacity degeneration. As a result, based on the total active weight, our NiSe2//Zn battery is capable of record-high power density (91.22 kW kg-1/639.1 mW cm-2), imposing energy density (328.8 Wh kg-1/2.303 mWh cm-2), and ultralong lifespan (only 8.3% capacity loss after 10,000 cycles), surpassing most of the aqueous batteries and supercapacitors recently reported. Moreover, this NiSe2//Zn battery is also affordable (US$40 per kWh) and safe. These results open a new avenue for developing superdurable and ultrafast high-energy Ni-Zn batteries toward affordable and practical energy storage.

Highly Graphitized Porous Carbon-FeNi3 Fabricated from Oleic Acid for Advanced Lithium-Sulfur Batteries.

Improving the electrical conductivity of sulfur, suppressing shuttle/dissolution of polysulfide, and enhancing reaction kinetics in Li-S batteries are essential for practical applications. Here, for the first time, we have used inexpensive oleic acid as a single carbon source, and have added commercial SiO2 as a template to form a porous structure, whereas introducing Fe(NO3 )3 and Ni(NO3 )2 as catalysts to increase the degree of graphitization. Moreover, the dual metal salts Fe(NO3 )3 and Ni(NO3 )2 can also form FeNi3 alloy, and our results show that FeNi3 nanoparticles accelerate the kinetic conversion reactions of polysulfide. By virtue of the well-developed porous structure and high degree of graphitization, the highly graphitized porous carbon-FeNi3 (GPC-FeNi3 ) has high conductivity to ensure fast charge transfer, and the hierarchically porous structure facilitates ion diffusion and traps polysulfide. Thus, a GPC-FeNi3 /S cathode displays excellent electrochemical performance. At current rates of 0.2 and 1 C, a cathode of the GPC-FeNi3 /S composite with a sulfur content of 70 % delivers high initial discharge capacities of 1108 and 880 mA h g-1 , respectively, and retains reversible specific capacities of 850 mA h g-1 after 200 cycles at 0.2 C and 625 mA h g-1 after 400 cycles at 1 C.

Hollow Boron-Doped Si/SiOx Nanospheres Embedded in the Vanadium Nitride/Nanopore-Assisted Carbon Conductive Network for Superior Lithium Storage.

SiOx-based anode materials with high capacity and outstanding cycling performance have gained numerous attentions. Nevertheless, the poor electrical conductivity and non-negligible volume change hinder their further application in Li-ion batteries. Herein, we propose a new strategy to construct a hollow nanosphere with boron-doped Si/SiOx decorated with vanadium nitride (VN) nanoparticles and embedded in a nitrogen-doped, porous, and partial graphitization carbon layer (B-Si/SiOx@VN/PC). Benefiting from such structural and compositional features, the B-Si/SiOx@VN/PC electrode exhibits a stable cycling capacity of 1237.1 mA h g-1 at a current density of 0.5 A g-1 with an appealing capacity retention of 87.0% after 300 cycles. Additionally, it delivers high-rate capabilities of 1139.4, 940.7, and 653.4 mA h g-1 at current densities of 2, 5, and 10 A g-1, respectively, and ranks among the best SiOx-based anode materials. The outstanding electrochemical performance can be ascribed to the following reasons: (1) its hollow structure makes the Li+ transportation length decreased. (2) The existing nanopores facilitate the Li+ insertion/desertion and accommodate the volume variation. (3) The nitrogen-doped partial graphitization carbon enhances the electrical conductivity and promotes the formation of stable solid electrolyte interface layers during the repetitive Li+ intercalation/extraction process.

Synergy of Epoxy Chemical Tethers and Defect-Free Graphene in Enabling Stable Lithium Cycling of Silicon Nanoparticles.

We report a new approach for nanosilicon-graphene hybrids with uniquely stable solid electrolyte interphase. Expanded graphite is gently exfoliated creating "defect-free" graphene that is non-catalytic towards electrolyte decomposition, simultaneously introducing high mass loading (48 wt. %) Si nanoparticles. Silane surface treatment creates epoxy chemical tethers, mechanically binding nano-Si to CMC binder through epoxy ring-opening reaction while stabilizing the Si surface chemistry. Epoxy-tethered silicon pristine-graphene hybrid "E-Si-pG" exhibits state-of-the-art performance in full battery opposing commercial mass loading (12 mg cm-2 ) LiCoO2 (LCO) cathode. At 0.4 C, with areal capacity of 1.62 mAh cm-2 and energy of 437 Wh kg-1 , achieving 1.32 mAh cm-2 , 340.4 Wh kg-1 at 1 C. After 150 cycles, it retains 1.25 mAh cm-2 , 306.5 Wh kg-1 . Sputter-down XPS demonstrates survival of surface C-Si-O-Si groups in E-Si-pG after repeated cycling. The discovered synergy between support defects, chemical-mechanical stabilization of Si surfaces, and SEI-related failure may become key LIB anode design rule.

An Electrolytic Zn-MnO2 Battery for High-Voltage and Scalable Energy Storage.

Zinc-based electrochemistry is attracting significant attention for practical energy storage owing to its uniqueness in terms of low cost and high safety. However, the grid-scale application is plagued by limited output voltage and inadequate energy density when compared with more conventional Li-ion batteries. Herein, we propose a latent high-voltage MnO2 electrolysis process in a conventional Zn-ion battery, and report a new electrolytic Zn-MnO2 system, via enabled proton and electron dynamics, that maximizes the electrolysis process. Compared with other Zn-based electrochemical devices, this new electrolytic Zn-MnO2 battery has a record-high output voltage of 1.95 V and an imposing gravimetric capacity of about 570 mAh g-1 , together with a record energy density of approximately 409 Wh kg-1 when both anode and cathode active materials are taken into consideration. The cost was conservatively estimated at

Chromium deposition and poisoning of La2NiO4 cathode of solid oxide fuel cell.

Chromium deposition and poisoning of La2NiO4 cathode of solid oxide fuel cell were studied. La2NiO4 cathode showed stable performance in the presence of metallic interconnects. Comparing with the polarization resistance (R p) of La2NiO4 cathode in the absence of metallic interconnects, R p did not change in the presence of metallic interconnect. After electrical conductivity relaxation method, La2NiO4 with high surface oxygen diffusion coefficients working under Cr atmosphere improved the oxygen reduction kinetics and increased cathode O2 reduction reaction rates. No chromium deposition was observed on the La2NiO4 cathode surface after polarization for 20 h at 800°C. The chemical compatibility of La2NiO4/Cr2O3 and La2NiO4/Gd0.1Ce0.9O1.95 (GDC) study indicates that La2NiO4 did not react with Cr2O3 and GDC under the operating temperature. The results indicate that La2NiO4 cathode is a potential chromium-tolerant material of solid oxide fuel cell.