Fluorine-Doped Li7La3Zr2O12 Fiber-Based Composite Electrolyte for Solid-State Lithium Batteries with Enhanced Electrochemical Performance.

Garnet-based electrolytes with high ionic conductivity and excellent stability against lithium metal anodes are promising for commercial applications in solid-state lithium batteries (SSLBs). However, the further development of SSLBs is inhibited by issues such as low ionic conductivity and uncontrolled lithium dendrite growth. Herein, we report the synthesis of fluorine-doped Li7La3Zr2O12 (LLZO-F0.2) fibers by electrospinning and the subsequent calcination at high temperatures. The solid composite electrolyte with LLZO-F0.2 exhibits an ionic conductivity of 5.37 × 10-4 S cm-1 and a high lithium-ion transference number of 0.61 at room temperature. Meanwhile, it exhibits lower resistance and more uniform lithium metal stripping and deposition in symmetric cells. The full cell with LiFePO4 cathode exhibits excellent rate capability and cycling stability for 800 cycles at 0.5 C with a discharge specific capacity retention of 97.7%. This fluorine-doped fibrous garnet-type electrolyte provides a viable option for preparing high-performance SSLBs.

Superhydrophilic/superaerophobic CoP/CoMoO4 multi-level hierarchitecture electrocatalyst for urea-assisted hydrogen evolution reaction in alkaline media.

Utilizing the thermodynamically favorable urea oxidation reaction instead of the anodic oxygen precipitation reaction is an alternative pathway for the energy-saving hydrogen production. Therefore, it is significant to explore advanced electrocatalysts for both HER and UOR. In this work, a dendritic heteroarchitectures of 2D CoMoO4 nanosheets deposited on 1D CoP nanoneedles (CoP/CoMoO4-CC) was fabricated as bifunctional electrocatalyst. 1D CoP nanostructure with fast charge transport pathways and 2D CoMoO4 nanostructure with large specific surface area and short paths for electron/mass transport. The unique morphology endows the superhydrophilic and superaerophobic properties, allowing for the rapid contact with the reactants and rapid removal of surface-generated gases. As a result, the CoP/CoMoO4-CC shows efficient bifunctional activity. This work offers a new avenue to rationally design bifunctional electrocatalysts for large-scale practical hydrogen production.

Robust Solid-State Na-CO2 Battery with Na2.7Zr2Si2PO11.7F0.3-PVDF-HFP Composite Solid Electrolyte and Na15Sn4/Na Anode.

Solid-state Na-CO2 batteries are a kind of energy storage devices that can immobilize and convert CO2. They have the advantages of both solid-state batteries and metal-air batteries. High-performance solid electrolyte and electrode materials are important for improving the performance of solid-state Na-CO2 batteries. In this work, we investigate the influence of fluorine doping on the structure and ionic conductivity of Na3Zr2Si2PO12 (NZSP). An ionic conductive solid electrolyte membrane was prepared by compositing the inorganic solid electrolyte Na2.7Zr2Si2PO11.7F0.3 (NZSPF3) with poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP). It shows an ionic conductivity of up to 2.17 × 10-4 S cm-1 at room temperature, a high sodium ionic transfer number of ∼0.70, a broad electrochemical window of ∼5.18 V, and better mechanical strength. Furthermore, we studied the Na15Sn4/Na composite foil with the ability to inhibit dendrite as the anode for solid-state Na-CO2 batteries. Through density functional theory (DFT) calculations, the Na15Sn4 particle has been verified with a strong sodiophilic property, which reduces the nucleation barrier during the deposition process, leading to a lower overpotential. The symmetric cell assembled with the composite solid-state electrolyte NZSPF3-PVDF-HFP and Na15Sn4/Na composite anode can inhibit the growth of Na dendrites effectively and maintain the stability of the whole cell structure. Solid-state Na-CO2 batteries assembled with Ru-carbon nanotube (Ru-CNTs) as cathode catalysts exhibit a high discharge capacity of 6371.8 mAh g-1 at 200 mA g-1, excellent cycling stability for 1100 h, and good rate performance. This work provides a promising strategy for designing high-performance solid-state Na-CO2 batteries.

Dendrite-Free Lithium Metal Anodes Enabled by an Ordered Conductive Ni-Based Catecholate Interlayer for Solid-State Lithium Batteries.

The large-scale commercial application of Li metal batteries is hindered by uncontrolled Li dendrite growth. Most of the present interfacial engineering strategies in lithium metal batteries can only prolong the nucleation time of lithium dendrites but cannot prevent the growth of lithium dendrites in three-dimensional space. In this work, a nickel-based catecholate (Ni-CAT) conductive interlayer that can guide the orderly migration of lithium ions and inhibit the disordered deposition of lithium dendrites is successfully constructed between the solid electrolyte and lithium metal through a reasonable design. The experimental analysis proves that the Ni-CAT nanorod arrays with unique vertical structures are closely connected to the solid electrolyte, which can reduce the charge-transfer resistance at the interface and guide lithium ions to be preferentially deposited on the surface of the Ni-CAT intermediate layer through the conduction gradient. Hence, this structure effectively avoids the phenomenon of apical growth during lithium deposition. In addition, the rich pores and inherent nanochannels of Ni-CAT itself act as an "ion sieve", successfully inducing the uniform deposition of lithium metal, which greatly reduces the occurrence of dead lithium due to the loss of electrical contact of lithium during cycling. This strategy holds promise for solving the lithium dendrite problem.

Modulating the electronic structure of Mo2C/MoP heterostructure to boost hydrogen evolution reaction in a wide pH range.

Interface engineering is an effective strategy for the design of electrochemical catalysts with attractive performance for hydrogen evolution reaction. Herein, the Molybdenum carbide/molybdenum phosphide (Mo2C/MoP) heterostructure deposited on nitrogen (N), phosphorous (P) co-doped carbon substrate (Mo2C/MoP-NPC) is fabricated by one-step carbonization. The electronic structure of Mo2C/MoP-NPC is changed by optimizing the ratio of phytic acid and aniline. The calculation and experimental results also show that there is an electron interaction on the Mo2C/MoP interface, which optimizes the adsorption free energy of hydrogen (H) and improves the performance of hydrogen evolution reaction. Mo2C/MoP-NPC exhibits significant low overpotentials at 10 mA·cm-2 current density, 90 mV in 1 M KOH and 110 mV in 0.5 M H2SO4, respectively. In addition, it shows superior stability over a broad pH range. This research provides an effective method for the construction of novel heterogeneous electrocatalysts and is conducive to the development of green energy.

Recent advances in lithium-rich manganese-based cathodes for high energy density lithium-ion batteries.

The development of society challenges the limit of lithium-ion batteries (LIBs) in terms of energy density and safety. Lithium-rich manganese oxide (LRMO) is regarded as one of the most promising cathode materials owing to its advantages of high voltage and specific capacity (more than 250 mA h g-1) as well as low cost. However, the problems of fast voltage/capacity fading, poor rate performance and the low initial Coulombic efficiency severely hinder its practical application. In this paper, we review the latest research advances of LRMO cathode materials, including crystal structure, electrochemical reaction mechanism, existing problems and modification strategies. In this review, we pay more attention to recent progress in modification methods, including surface modification, doping, morphology and structure design, binder and electrolyte additives, and integration strategies. It not only includes widely studied strategies such as composition and process optimization, coating, defect engineering, and surface treatment, but also introduces many relatively novel modification methods, such as novel coatings, grain boundary coating, gradient design, single crystal, ion exchange method, solid-state batteries and entropy stabilization strategy. Finally, we summarize the existing problems in the development of LRMO and put forward some perspectives on the further research.

Recent advances in dendrite-free lithium metal anodes for high-performance batteries.

With the merits of high energy density, light weight, and low electrode potential, lithium metal anodes (LMAs) have lately sparked worldwide attention in the field of batteries. However, their low Coulombic efficiency, tremendous volume expansion, and serious dendrite growth make lithium metal batteries (LMBs) unsuitable for a wide variety of applications. Moreover, when lithium dendrite crosses the electrolyte and reaches the cathode material, it may cause short circuit and safety issues for batteries. Herein, to accelerate the development of LMBs, we give a brief summary of the dendrite growth mechanisms in both liquid and solid systems of electrolytes. In particular, various modification approaches to dendrite-free lithium metal batteries are discussed. Furthermore, advanced in situ characterization techniques for the real-time observation of lithium dendrite growth are presented. To address the application issues, various potential research routes for improving the performance of LMBs are provided as well.

Platinum atomic clusters embedded in polyoxometalates-carbon black as an efficient and durable catalyst for hydrogen evolution reaction.

Platinum-based catalysts are regarded as the Holy Grail of hydrogen evolution reaction (HER). As a benchmark catalyst for HER, the commercial Pt/C catalyst has low Pt utilization efficiency and high cost, which hinders its commercialization. Atomic clusters-based catalysts show high efficiency of atom utilization and high performance toward electrocatalysis. Herein, an environmentally friendly preparation strategy is proposed to construct Pt atomic clusters on the polyoxometalates-carbon black (Pt-POMs-CB) support. Density functional theory (DFT) calculations reveal that the Pt clusters can be stably anchored on the surface with the driving force arising from the charge transfer from Pt atoms to O atoms of the POMs. Benefiting from metal-support interaction, Pt atomic clusters embedded in silicotungstic acid-carbon black (Pt-STA-CB) exhibit excellent HER activity with an overpotential of 33.8 mV at 10 mA cm-2, and high mass activity is 1.62 A mg-1Pt at 33.8 mV, which is 5.4 times that of the commercial Pt/C. In addition, the catalyst displays high stability of 800 h at current density of 500 mA cm-2. It provides a platform for facile and low-cost preparation of stable Pt-based catalysts, which is crucial for their large-scale production and practical application in the industry.

FeCo Nanoparticles Encapsulated in N-Doped Carbon Nanotubes Coupled with Layered Double (Co, Fe) Hydroxide as an Efficient Bifunctional Catalyst for Rechargeable Zinc-Air Batteries.

Low-cost bifunctional nonprecious metal catalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical for the commercialization of rechargeable zinc-air batteries (ZABs). However, the preparation of highly active and durable bifunctional catalysts is still challenging. Herein, an efficient catalyst is reported consisting of FeCo nanoparticles embedded in N-doped carbon nanotubes (FeCo NPs-N-CNTs) by an in situ catalytic strategy. Due to the encapsulation and porous structure of N-doped carbon nanotubes, the catalyst shows high activity toward ORR and excellent durability. Furthermore, to enhance the OER activity, CoFe-layer double hydroxide (CoFe-LDH) is coupled with FeCo NPs-N-CNTs by in situ reaction approach. As the air electrode for rechargeable ZABs, the cell with CoFe-LDH@FeCo NPs-N-CNTs catalyst exhibits high open-circuit potential (OCP) of 1.51 V, high power density of 116 mW cm-2 , and remarkable durability up to 100 h, demonstrating its great promise for the practical application of the rechargeable ZABs.

A Monolithic Solid-State Sodium-Sulfur Battery with Al-Doped Na3.4Zr2(Si0.8P0.2O4)3 Electrolyte.

The limit of the energy density and increasing security issues on sodium-ion batteries (SIBs) impede their further development. Solid-state sodium metal batteries are potential candidates to replace the present SIBs. However, low ionic conductivity and poor interface contact hinder their progress. In this work, the impact of Al doping on the crystalline structure and ionic transport in Na3.4Zr2(Si0.8P0.2O4)3 was studied by neutron powder diffraction. The ionic conductivity of Na3.5Zr1.9Al0.1Si2.4P0.6O12 achieves 4.43 × 10-3 S cm-1 at 50 °C. The polarization voltage of the Na||Na symmetric battery is about 40 mV after cycling for more than 1600 h. Moreover, a solid-state sodium-sulfur battery with a monolithic structure was constructed to alleviate the interfacial resistance problems. Its specific discharge capacity can still keep 300 mA h g-1 after 480 cycles at 300 mA g-1. The work provides a promising strategy to design solid-state sodium-sulfur batteries with high performances.

Composite Lithium Protective Layer Formed In Situ for Stable Lithium Metal Batteries.

Lithium metal is considered as the ideal anode for next-generation rechargeable batteries due to its highest theoretical specific capacity and lowest electrochemical potential. However, lithium dendrite growth during lithium deposition could lead to a short circuit and even cause severe safety issues. Here, we use solid-state electrolyte Li3InCl6 as an additive in nonaqueous electrolytes because of its high ionic conductivity (10-3 to 10-4 S cm-1) and good electrochemical stability. It is found that Li3InCl6 can in situ react with metallic lithium to form a ternary composite solid electrolyte interphase (SEI) consisting of a Li-In alloy, LiCl, and codeposited Li3InCl6. The composite SEI can effectively suppress Li dendrite growth and thereby maintain stable long-term cycling performance in lithium metal batteries. The protected lithium electrode exhibits stable cycling performance in a symmetric Li|Li battery for nearly 1000 h at a current density of 1 mA cm-2. Besides, the full battery with a LiFePO4 cathode and a metallic lithium anode delivers a stable capacity of 140.6 mA h g-1 for 500 cycles with a capacity retention of 95%. The Li|S battery with Li3InCl6-added LiTFSI in 1,3-dioxolane/1,2-dimethoxyethane electrolyte also shows significant improvement in capacity retention at 0.5 C. This work demonstrates an effective approach to design dendrite-free metal anodes.

Recent Advances in Single-Atom Electrocatalysts for Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) plays significant roles in electrochemical energy storage and conversion systems as well as clean synthesis of fine chemicals. However, the ORR process shows sluggish kinetics and requires platinum-group noble metal catalysts to accelerate the reaction. The high cost, rare reservation, and unsatisfied durability significantly impede large-scale commercialization of platinum-based catalysts. Single-atom electrocatalysts (SAECs) featuring with well-defined structure, high intrinsic activity, and maximum atom efficiency have emerged as a novel field in electrocatalytic science since it is promising to substitute expensive platinum-group noble metal catalysts. However, finely fabricating SAECs with uniform and highly dense active sites, fully maximizing the utilization efficiency of active sites, and maintaining the atomically isolated sites as single-atom centers under harsh electrocatalytic conditions remain urgent challenges. In this review, we summarized recent advances of SAECs in synthesis, characterization, oxygen reduction reaction (ORR) performance, and applications in ORR-related H2O2 production, metal-air batteries, and low-temperature fuel cells. Relevant progress on tailoring the coordination structure of isolated metal centers by doping other metals or ligands, enriching the concentration of single-atom sites by increasing metal loadings, and engineering the porosity and electronic structure of the support by optimizing the mass and electron transport are also reviewed. Moreover, general strategies to synthesize SAECs with high metal loadings on practical scale are highlighted, the deep learning algorithm for rational design of SAECs is introduced, and theoretical understanding of active-site structures of SAECs is discussed as well. Perspectives on future directions and remaining challenges of SAECs are presented.

Flexible Quasi-Solid-State Sodium Battery for Storing Pulse Electricity Harvested from Triboelectric Nanogenerators.

In order to satisfy the increasing requirements on operation time of wearable and portable electronic devices, novel self-powered systems by integrating triboelectric nanogenerator (TENG) with an energy storage device have emerged as a promising technology to provide sustainable power. Here, a flexible sodium composite anode (Na@CC) was prepared by infusing the molten sodium into flexible sodiophilic carbon cloth. The symmetric cell with the Na@CC anode shows stable sodium plating and stripping for 400 h. The full cell with a flexible quasi-solid-state electrolyte, Na3V2(PO4)3@C nanofiber cathode, and Na@CC anode delivers an excellent rate capacity of 72.5 mAh g-1 at 5 C and also exhibits stable cycling performance under different bent degrees. By combining with TENG to form a self-powered system, the flexible quasi-solid-state sodium battery can effectively store the pulse current and shows stable discharging capacity for over 100 cycles. The advanced flexible battery demonstrates its capability as a promising energy storage part in combination with TENGs and shows great potential in powerful flexible self-powered systems.

Effects of Pulse Charging by Triboelectric Nanogenerators on the Performance of Solid-State Lithium Metal Batteries.

Solid-state lithium metal batteries (SSLMBs) are an emerging technology because they can effectively solve the safety problem facing the lithium-ion batteries with nonaqueous liquid electrolyte. However, the lithium dendrite problem in SSLMBs can still occur at the sites of grain boundaries and defects. It is reported that effective charge procedures enable to suppress the growth of lithium dendrite, especially the pulse charging mode. In this work, SSLMBs were charged by a vertical contact-separation triboelectric nanogenerator (TENG). The effects of the pulse current on the lithium dendrite growth of SSLMBs are studied. It is found that the lithium ions can diffuse uniformly during the intermittent period of the pulse current compared to the constant current charge, so the growth rate of the lithium dendrites is effectively inhibited by the pulse current. At the same time, it is found that the lower the frequency of TENG is, the slower the growth rate of lithium dendrites is. This work provides a guideline for designing an appropriate charging method for durable SSLMBs.

Fluorinated Ether Based Electrolyte Enabling Sodium-Metal Batteries with Exceptional Cycling Stability.

Sodium-metal batteries with conventional organic liquid electrolytes have disadvantages including dendrite deposition and safety concern. In this work, we report a low-flammable electrolyte (NaPF6-FRE) consisting of 1 M NaPF6 in 1,2-dimethoxyethane (DME), fluoroethylene carbonate (FEC), and 1,1,1,3,3,3-hexafluoroisopropylmethyl ether (HFPM) (2:1:2, in volume ratio). The symmetric Na and Na||Cu cells with a 1 M NaPF6-DME electrolyte absorbed in a porous separator, such as the porous glass-fiber, show very poor cycling performance. In addition, the cell with a Na3V2(PO4)3 (NVP) cathode and 1 M NaPF6-DME electrolyte shows low Coulombic efficiency. FEC was added into the NaPF6-DME-based electrolyte to reduce the irreversible capacity of the NVP cathode and improve the Coulombic efficiency of the cell. However, the high reactivity of FEC with the Na electrode leads to formation of an unstable solid electrolyte interphase (SEI) and large interfacial resistance, and HFPM was further added to stabilize the Na electrode surface by forming a new fluorine-containing organic layer. The new prepared low-flammable electrolyte (NaPF6-FRE) with 1 M NaPF6 in DME, FEC, and HFPM (2:1:2, in volume ratio) shows a wide electrochemical window of 5.2 V. The Na symmetric cells with this low-flammable electrolyte show superior cycling performance for 800 h with a stable voltage profile at 0.5 mA cm-2, 0.5 mA h cm-2 and 1 mA cm-2, 1 mA h cm-2, respectively. The NVP||Na cells show an excellent capacity retention of 94% after 2000 cycles and superior Coulombic efficiency of 99.9% on average at 5 C.

Carbon Formation Mechanism of C2H2 in Ni-Based Catalysts Revealed by in Situ Electron Microscopy and Molecular Dynamics Simulations.

Understanding the carbon formation mechanism is critical for designing catalysts in various applications. Here, we report the observation of the carbon formation mechanism on Ni-based catalysts by environmental transmission electron microscopy (ETEM) over a wide temperature range in combination with molecular dynamics simulations and density functional theory calculations. In situ TEM observation performed in a C2H2/H2 atmosphere provides real-time evidence that Ni3C is an intermediate phase that decomposes to graphitic carbon and metallic Ni, leading to carbon formation. Mechanisms of acetylene decomposition and evolution of carbon atom configuration are revealed by molecular dynamics simulations, which corroborate the experimental results. The modification of MgO on NiO can effectively decrease the formation of graphitic layers and thus enhance the catalytic performance of NiO. This finding may provide an insight into the origin of the carbon deposition and aid in developing effective approaches to mitigate it.

Fe2+ -Doped Layered Double (Ni, Fe) Hydroxides as Efficient Electrocatalysts for Water Splitting and Self-Powered Electrochemical Systems.

Developing nonprecious electrocatalysts with superior activity and durability for electrochemical water splitting is of great interest but challenging due to the large overpotential required above the thermodynamic standard potential of water splitting (1.23 V). Here, in situ growth of Fe2+ -doped layered double (Ni, Fe) hydroxide (NiFe(II,III)-LDH) on nickel foam with well-defined hexagonal morphology and high crystallinity by a redox reaction between Fe3+ and nickel foam under hydrothermal conditions is reported. Benefiting from tuning the local atomic structure by self-doping Fe2+ , the NiFe(II,III)-LDH catalyst with higher amounts of Fe2+ exhibits high activity toward oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER) activity. Moreover, the optimized NiFe(II,III)-LDH catalyst for OER (O-NiFe(II,III)-LDH) and catalyst for HER (H-NiFe(II,III)-LDH) show overpotentials of 140 and 113 mV, respectively, at a current density of 10 mA cm-2 in 1 m KOH aqueous electrolyte. Using the catalysts for overall water splitting in two-electrode configuration, a low overpotential of just 1.54 V is required at a benchmark current density of 10 mA cm-2 . Furthermore, it is demonstrated that electrolysis of the water device can be drived by a self-powered system through integrating a triboelectric nanogenerator and battery, showing a promising way to realize self-powered electrochemical systems.

Oxygen Deficient LaMn0.75Co0.25O3-δ Nanofibers as an Efficient Electrocatalyst for Oxygen Evolution Reaction and Zinc-Air Batteries.

The rational design of efficient and durable oxygen evolution reaction (OER) is important for energy conversion and storage devices. Here, we develop a two-step calcination method to prepare cobalt nanoparticles uniformly dispersed on perovskite oxide nanofibers and to tune oxygen vacancies in perovskite LaMn0.75Co0.25O3-δ nanofibers. The obtained product shows enhanced activity toward OER. In particular, the oxygen deficient LMCO-2 catalyst prepared by a two-step calcination shows excellent OER performance that is 27.5 times that of the LMO catalyst and is comparable to that of the commercial RuO2 catalyst. It also demonstates good stability because of its novel structure, abundant oxygen vacancies, and larger number of metal ions with a high oxidation state. As an air electrode for a flexible zinc-air battery, the cell with the LMCO-2 catalyst delivers a higher power density of 35 mW cm-2 and excellent cycling stability for 70 h. Moreover, the cell exhibits excellent flexibility under different bending conditions.

Effects of Fluorine Doping on Structural and Electrochemical Properties of Li6.25Ga0.25La3Zr2O12 as Electrolytes for Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) are promising technologies with great potential in improving safety and energy density, compared with the traditional liquid based lithium ion batteries. However, the bottleneck of SSLBs lies in the issues of poor interface contact and low electrolyte conductivity. In this work, the crystal structure of garnet-type Li6.25Ga0.25La3Zr2O12 (LGLZO) was engineered more rigidly with subdued atoms displacement by fluorine doping and thus smoother and faster lithium ion diffusion paths are formed. The ionic conductivity of garnet-type electrolyte is significantly increased from 5.43 × 10-4 S/cm to 1.28 × 10-3 S/cm at 25 °C and the activation energy is reduced from 0.33 to 0.28 eV. The solid-state symmetric cell consisting of F doped Li6.25Ga0.25La3Zr2O12 electrolyte and lithium metal has lower resistance and displays stable lithium plating/stripping for over 650 h with smaller overpotentials than those on LGLZO electrolyte. Moreover, the all solid-state lithium battery with F-LGLZO electrolyte and LiFePO4 composite electrode exhibits an improved rate capability, which can still keep 132.9 mAh/g at 1 C. Fluorine substitution in garnet-type electrolyte opens new avenues to design new solid-state electrolytes for practical applications of SSLBs.

Effects of F-Doping on the Electrochemical Performance of Na2Ti3O7 as an Anode for Sodium-Ion Batteries.

The effects of fluorine (F) doping on the phase, crystal structure, and electrochemical performance of Na2Ti3O7 are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. F-doping does not change the crystal structure of NTO, although it has an effect on the morphology of the resultant product. As an anode material for sodium-ion batteries, the specific capacity of Na2Ti3O7 exhibits a 30% increase with F-doping owing to the improved sodium ion diffusion coefficient. F-doped Na2Ti3O7 also displays an enhanced rate capability and favourable cycling performance for more than 800 cycles.