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.

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.

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.

Visualization of the Diffusion Pathway of Protons in (NH4)2Si0.5Ti0.5P4O13 as an Electrolyte for Intermediate-Temperature Fuel Cells.

We demonstrate that (NH4)2Si0.5Ti0.5P4O13 is an excellent proton conductor. The crystallographic information concerning the hydrogen positions is unraveled from neutron-powder-diffraction (NPD) data for the first time. This study shows that all the hydrogen atoms are connected though H bonds, establishing a two-dimensional path between the [(Si0.5Ti0.5)P4O132-]n layers for proton diffusion across the crystal structure by breaking and reconstructing intermediate H-O═P bonds. This transient species probably reduces the potential energy of the H jump from an ammonium unit to the next neighboring NH4+ unit. Both theoretical and experimental results support an interstitial-proton-conduction mechanism. The proton conductivities of (NH4)2Si0.5Ti0.5P4O13 reach 0.0061 and 0.024 S cm-1 in humid air at 125 and 250 °C, respectively. This finding demonstrates that (NH4)2Si0.5Ti0.5P4O13 is a promising electrolyte material operating at 150-250 °C. This work opens up a new avenue for designing and fabricating high-performance inorganic electrolytes.

Growth of Hollow Transition Metal (Fe, Co, Ni) Oxide Nanoparticles on Graphene Sheets through Kirkendall Effect as Anodes for High-Performance Lithium-Ion Batteries.

A general strategy based on the nanoscale Kirkendall effect has been developed to grow hollow transition metal (Fe, Co or Ni) oxide nanoparticles on graphene sheets. When applied as lithium-ion battery anodes, these hollow transition metal oxide-based composites exhibit excellent electrochemical performance, with high reversible capacities and long-term stabilities at a high current density, superior to most transition metal oxides reported to date.

P2-Type Na0.67Ni0.23Mg0.1Mn0.67O2 as a High-Performance Cathode for a Sodium-Ion Battery.

There is intense interest in sodium-ion batteries as an alternative to lithium-ion batteries for electric storage applications because of the low-cost and abundant sodium resources. Na0.67Ni0.33-xMgxMn0.67O2 compounds (x = 0, 0.02, 0.05, 0.1, or 0.15) were prepared by a sol-gel method and used as a cathode for sodium-ion batteries. The X-ray powder diffraction measurements demonstrated that the obtained samples have a pure P2 phase. Na0.67Ni0.23Mg0.1Mn0.67O2 delivers an initial reversible capacity of 105 mAh g(-1) in the potential region from 2.0 to 4.5 V at a charge/discharge current density of 48 mA g(-1). Moreover, the cyclability is improved by doping Mg. The capacity of Na0.67Ni0.23Mg0.1Mn0.67O2 can remain at approximately 84.9 mAh g(-1) at a current density of 48 mA g(-1) after 100 cycles. The improved high rate performance of Na0.67Ni0.23Mg0.1Mn0.67O2 was attributed to the increased lattice parameters and d spacing of the Na(+) layer. Therefore, Mg-doped Na0.67Ni0.23Mg0.1Mn0.67O2 is a promising cathode for sodium-ion batteries with excellent rate and cyclic performance.

Dynamic Octahedral Breathing in Oxygen-Deficient Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) Perovskite Performing as a Cathode in Intermediate-Temperature SOFC.

Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) outperforms as a cathode in solid-oxide fuel cells (SOFC), at temperatures as low as 700-750 °C. The microscopical reason for this performance was investigated by temperature-dependent neutron powder diffraction (NPD) experiments. In the temperature range of 25-800 °C, Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) shows a perfectly cubic structure (a = a0), with a significant oxygen deficiency in a single oxygen site, that substantially increases at the working temperatures of a SOFC. The anisotropic thermal motion of oxygen atoms considerably rises with T, reaching B(eq) ≈ 5 Å(2) at 800 °C, with prolate cigar-shaped, anisotropic vibration ellipsoids that suggest a dynamic breathing of the octahedra as oxygen ions diffuse across the structure by a vacancies mechanism, thus implying a significant ionic mobility that could be described as a molten oxygen sublattice. The test cell with a La(0.8)Sr(0.2)Ga(0.83)Mg(0.17)O(3-δ) electrolyte (∼300 µm in thickness)-supported configuration yields a peak power density of 0.20 and 0.40 W cm(-2) at temperatures of 700 and 750 °C, respectively, with pure H2 as fuel and ambient air as oxidant. The electrochemical impedance spectra (EIS) evolution with time of the symmetric cathode fuel cell measured at 750 °C shows that the Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) cathode possesses a superior ORR catalytic activity and long-term stability. The mixed electronic-ionic conduction properties of Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) account for its good performance as an oxygen-reduction catalyst.

Insight into the structure and functional application of the Sr0.95Ce0.05CoO3-δ cathode for solid oxide fuel cells.

A new perovskite cathode, Sr0.95Ce0.05CoO3-δ, performs well for oxygen-reduction reactions in solid oxide fuel cells (SOFCs). We gain insight into the crystal structure of Sr1-xCexCoO3-δ (x = 0.05, 0.1) and temperature-dependent structural evolution of Sr0.95Ce0.05CoO3-δ by X-ray diffraction, neutron powder diffraction, and scanning transmission electron microscopy experiments. Sr0.9Ce0.1CoO3-δ shows a perfectly cubic structure (a = a0), with a large oxygen deficiency in a single oxygen site; however, Sr0.95Ce0.05CoO3-δ exhibits a tetragonal perovskite superstructure with a double c axis, defined in the P4/mmm space group, that contains two crystallographically different cobalt positions, with distinct oxygen environments. The structural evolution of Sr0.95Ce0.05CoO3-δ at high temperatures was further studied by in situ temperature-dependent NPD experiments. At 1100 K, the oxygen atoms in Sr0.95Ce0.05CoO3-δ show large and highly anisotropic displacement factors, suggesting a significant ionic mobility. The test cell with a La0.8Sr0.2Ga0.83Mg0.17O3-δ-electrolyte-supported (∼300 µm thickness) configuration yields peak power densities of 0.25 and 0.48 W cm(-2) at temperatures of 1023 and 1073 K, respectively, with pure H2 as the fuel and ambient air as the oxidant. The electrochemical impedance spectra evolution with time of the symmetric cathode fuel cell measured at 1073 K shows that the Sr0.95Ce0.05CoO3-δ cathode possesses superior ORR catalytic activity and long-term stability. Mixed ionic-electronic conduction properties of Sr0.95Ce0.05CoO3-δ account for its good performance as an oxygen-reduction catalyst.

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.

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.

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.

Three-dimensional hierarchical architectures constructed by graphene/MoS2 nanoflake arrays and their rapid charging/discharging properties as lithium-ion battery anodes.

Charged up: Three-dimensional architectures constructed from graphene/MoS2 nanoflake arrays have been successfully fabricated by a one-step hydrothermal method. MoS2 nanoflakes with thicknesses less than 13 nm grow vertically on both sides of graphene sheets (see figure), which allows the architectures to be more stable during charging and discharging. Even at a high current density of 8000 mA g(-1), their discharge capacity is still up to 516 mA h g(-1).

In situ Raman spectroscopy of LiFePO4: size and morphology dependence during charge and self-discharge.

Previous studies of the size dependent properties of LiFePO4 have focused on the diffusion rate or phase transformation pathways by bulk analysis techniques such as x-ray diffraction (XRD), neutron diffraction and electrochemistry. In this work, in situ Raman spectroscopy was used to study the surface phase change during charge and self-discharge on a more localized scale for three morphologies of LiFePO4: (1) 25 ± 6 nm width nanorods, (2) 225 ± 6 nm width nanorods and (3) ∼2 µm porous microspheres. Both the large nanorod and microsphere geometries showed incomplete delithiation at the end of charge, which was most likely caused by anti-site defects along the 1D diffusion channels in the bulk of the larger particles. Based on the in situ Raman measurements, all of the morphologies studied exhibited self-discharge with time. Among them, the smallest FePO4 particles self-discharged (lithiated) the fastest. While nanostructuring LiFePO4 can offer advantages in terms of lowering anti-site defects within particles, it also creates new problems due to high surface energies that allow self-discharge. The in situ Raman spectroscopy also showed that carbon coating did not provide significant improvement to the stability of the lithiated particles.

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.

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.

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.

Monodisperse porous LiFePO4 microspheres for a high power Li-ion battery cathode.

A novel solvothermal approach combined with high-temperature calcinations was developed to synthesize on a large scale LiFePO(4) microspheres consisting of nanoplates or nanoparticles with an open three-dimensional (3D) porous microstructure. These micro/nanostructured LiFePO(4) microspheres have a high tap density and, as electrodes, show excellent rate capability and cycle stability.

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.