Rational design and accessible fabrication of bifunctional electrocatalysts with high electrocatalytic activity, low price and good durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are urgently required for metal-air batteries, but it remains as a difficult and hot subject. Herein, we report a novel cobalt-ion-exchange and pyrolysis strategy with the well-designed bio-MOF-1 as the self-template to prepare ultra-small cobalt nanoparticles embedded into N-doped hierarchical porous carbon (Co@N-HPC-800) with excellent electrical conductivity, high surface area and abundant Co-N-4 active sites. The electrochemical test results verify the outstanding bifunctional electrocatalytic activity and stability of Co@N-HPC-800 in alkaline condition, even outperforming the commercial Pt/C + RuO2 electrocatalysts. The in situ Raman technique demonstrates the ORR and OER catalytic process occur through the redox of Co(II) and Co(III) species. The rechargeable Zn-air battery (ZAB) assembled with Co@N-HPC-800 cathode deliveries an open circuit voltage of 1.42 V, a specific capacity of 129 mAh cm(-2), a peak power density of 89.1 mW cm(-2), and stable cyclability over 85 h at 5 mA cm(-2) by refreshing the electrolyte. The Co@N-HPC-800 cathode in a flexible quasi-solid-state ZAB exhibits good flexibility and stability under different bending states. This work paves a simple and valuable way for designing non-noble high-efficient bifunctional electrocatalysts in Zn-air batteries and related energy storage and conversion technologies.

Polymer binders that combine active materials with conductive agents have played a critical role in maintaining the structural integrity of phosphorus anodes with a huge volume change upon sodiation/desodiation. Herein, the role of binders on the structural/chemical stability of phosphorus/carbon anode is spectroscopically uncovered through unexpected mechanism. Surprisingly, the selection of different binders is found to determine the oxidation degree of active phosphorus in various electrodes, which correlate well with their electrochemical properties. At a high oxidation degree, the electrode applying a conventional poly(vinylidene difluoride) binder displays the worst electrochemical properties, while the electrode using a sodium alginate binder delivers the best electrochemical performance (a highly reversible capacity of 1064 mAh g −1 with a 90.1% capacity retention at 800 mA g −1 after 200 cycles and an outstanding rate capability of 401 mAh g −1 at 8000 mA g −1 ) for its negligible oxidation. Additionally, the emergence/decomposition of surface intermediates, including (PO 2 ) 3− and (PO 4 ) 3− species, are observed in the discharging/charging processes via the ex situ P K‐edge X‐ray absorption spectroscopies. This novel discovery of the unique role of binders in phosphorus anodes, not only provides an opportunity to ameliorate their electrochemical properties, but also enables their practical applications in high‐energy sodium‐ion batteries.

Efficient and stable electrocatalysts for oxygen reduction reaction and freestanding electrode structure were developed to reduce the use of polymer binders in the cathode of metalair batteries. Considering the unique geometrical configurations of helical carbon nanotubes (CNTs) and improved properties compared with straight CNTs, we prepared high-purity Co@CoOx/helical nitrogen-doped carbon nanotubes (Co@CoOx/HNCNTs) on a carbon fiber paper by hydrothermal and single-step in situ chemical vapor deposition strategies. Under an optimized growth time (1 h), the synthesized Co@CoOx/HNCNTs provide richer edge defects and active sites and show prominent electrocatalytic performance toward oxygen reduction reaction (ORR) under alkaline media compared with Co@CoOx/HNCNTs-0.5 h and Co@CoOx/HNCNTs-2 h. The soft X-ray absorption spectroscopy technique is used to investigate the influences of different growth times on the electronic structure and local chemical configuration of Co@CoOx/HNCNTs. Furthermore, the Alair coin cell employing Co@CoOx/HNCNTs-1 h as the binder-free cathode exhibits an open-circuit voltage of 1.48 V, a specific capacity of 367.31 mA h g1 at the discharge current density of 1.0 mA cm(2), and a maximum power density (Pmax) of 3.86 mW cm(2), which are superior to those of Co@CoOx/HNCNTs-0.5 h and Co@CoOx/HNCNTs-2 h electrodes. This work provides valuable insights into the development of scalable binder-free cathodes, exploiting HNCNT composite materials with an outstanding electrocatalytic performance for ORR in Alair systems.

Great efforts have been focused on studying high-efficiency and stable catalysts toward oxygen reduction reaction (ORR) in metal-air batteries. In view of synergistic effects and improved properties, carbon nanotubes and three-dimensional graphene (CNTs-3D graphene) hybrid catalysts developed via a well-controlled route are urgently required. Herein, a CoMn2O4 (CMO) nanoneedle-supported nitrogen-doped carbon nanotubes/3D graphene (NCNTs/3D graphene) composite was prepared by in situ chemical vapor deposition (CVD) along with hydrothermal methods over a Ni foam substrate. The cyclic voltammetry and linear sweep voltammograms results indicate that the CMO/NCNTs/3D graphene hybrid possesses remarkable electrocatalytic performance toward ORR in alkaline conditions compared with NCNTs/3D graphene, CMO/3D graphene, and 3D graphene catalysts, even outperforming the commercial 20 wt % Pt/C catalyst. Moreover, the Al-air coin cell employing CMO/NCNTs/3D graphene as cathode catalysts obtains an open circuit voltage of 1.55 V and a specific capacity of 312.8 mA h g-1, which are superior to the Al-air coin cell with NCNTs/3D graphene as catalysts. This work supplies new insights to advanced electrocatalysts introducing NCNTs/3D graphene as a catalyst support to develop scalable transition-metal oxide/NCNTs/3D graphene hybrids with excellent catalytic activity toward ORR in Al-air systems.

All-solid-state batteries (ASSBs) have attracted much attention due to their enhanced energy density and safety as compared to traditional liquid-based batteries. However, cyclic performance depreciates due to microcrack formation and propagation at the interface of the solid-state electrolytes (SSEs) and electrodes. Herein, we studied the elastic and fracture behavior of atomic layer deposition (ALD) synthesized glassy lithium phosphate (LPO) and lithium tantalate (LTO) thin films as promising candidates for SSEs. The mechanical behavior of ALD prepared SSE thin films with a thickness range of 5 nm to 30 nm over suspended single-layer graphene was studied using an atomic force microscope (AFM) film deflection technique. Scanning transmission electron microscopy (STEM) coupled with AFM was used for microstructural analysis. LTO films exhibited higher stiffness and higher fracture forces as compared to LPO films. Fracture in LTO films occurred directly under the indenter in a brittle fashion, while LPO films failed by a more complex fracture mechanism including significant plastic deformation prior to the onset of complete fracture. The results and methodology described in this work open a new window to identify the potential influence of SSEs mechanical performance on their operation in flexible ASSBs.

As a competitive anode material for sodium-ion batteries (SIBs), a commercially available red phosphorus, featured with a high theoretical capacity (2596 mA h g(-1)) and a suitable operating voltage plateau (0.1-0.6 V), has been confronted with a severe structural instability and a rapid capacity degradation upon large volumetric change. In particular, the fundamental determining factors for phosphorus anode materials are yet poorly understood, and their interfacial stability against ambient air has not been explored and clarified. Herein, a high-performance phosphorus/carbon anode material has been fabricated simply through ball-milling the carbon black and red phosphorus, delivering a high reversible capacity of 1070 mA h g(-1) at 400 mA g(-1) after 200 cycles and a superior rate capability of 479 mA h g(-1) at 3200 mA g(-1). More importantly, we first reveal the significance of inhibiting the exposure of phosphorus/carbon electrode materials to air, even for a short period, for achieving a good electrochemical performance, which would sharply decrease the reversible capacities. With the assistance of synchrotron-based X-ray techniques, the formation and accumulation of insulating phosphate compounds can be spectroscopically identified, leading to the decay of electrochemical performance. At the same time, these passivation layers on the surface of electrode were found to occur via a self-oxidation process in ambient air. To maintain the electrochemical advantages of phosphorus anodes, it is necessary to inhibit their contact with air through a rational coating or an optimal storage condition. Additionally, the employment of a fluoroethylene carbonate (FEC) additive facilitates the decomposition of the electrolyte and favors the formation of a robust solid electrolyte interphase layer, which may suppress the side reactions between the active Na-P compounds and the electrolyte. These findings could help improve the surface protection and interfacial stability of phosphorus anodes for high-performance SIBs.

All-solid-state batteries are expected to be promising next-generation energy storage systems with increased energy density compared to the state-of-the-art Li-ion batteries. Nonetheless, the electrochemical performances of the all-solid-state batteries are currently limited by the high interfacial resistance between active electrode materials and solid-state electrolytes. In particular, elemental interdiffusion and the formation of interlayers with low ionic conductivity are known to restrict the battery performance. Herein, we apply a nondestructive variable-energy hard X-ray photoemission spectroscopy to detect the elemental chemical states at the interface between the cathode and the solid-state electrolyte, in comparison to the widely used angle-resolved (variable-angle) X-ray photoemission spectroscopy/X-ray absorption spectroscopy methods. The accuracy of variable-energy hard X-ray photoemission spectroscopy is also verified with a focused ion beam and high-resolution transmission electron microscopy. We also show the significant suppression of interdiffusion by building an artificial layer via atomic layer deposition at this interface.

A stable and conductive interface is one of the decisive factors in manipulating the performance of high voltage LiNi0.5Mn1.5O4 (LNMO) cathode for Li-ion batteries. Herein, a hybrid Li3PO4–TiO2 coating layer is designed as an interfacial material via controllable atomic layer deposition (ALD) on LNMO. The coating acts not just as a physical barrier to prevent the side-reactions between cathode and electrolyte at high voltage, more importantly, the hybrid coating material improves both interfacial ionic and electronic conductivities to build facile Li-ion and electron diffusion pathways for LNMO. The optimized LNMO demonstrates improved rate capability and long-life stability. The capacity retention is 81.2% comparing with 47.4% of bare LNMO at 0.5C after 300 cycles. Detailed surface structural evolution is studied via X-ray absorption near edge spectroscopy and transmission electron microscopy. This work provides new insights of hybrid interfacial design via ALD and promotes novel electrode architectures for batteries.

Aluminum-air batteries are a promising power supply for electronics due to their low cost and high energy density. However, portable coin-type Al-air batteries operating under ambient air condition for small electronic appliances have rarely been reported. Herein, coin cell-type Al-air batteries using cost-effective and eco-friendly chitosan hydrogel membranes modified by SiO2, SnO2, and ZnO have been prepared and assembled. The Al-air coin cell employing chitosan hydrogel membrane containing 10 wt % SiO2 as a separator exhibits better discharge performance with a higher flat voltage plateau, longer discharge duration, and higher power density than the cells using a chitosan hydrogel membrane containing SnO2 or ZnO. Moreover, we also demonstrate that the presented Al-air coin cell can be recycled by a series of eco-friendly procedures using food-grade ingredients, resulting in recycled products that are environmentally safe and ready for reuse. The Al-air coin cell adopting a recycled cathode from a fully discharged Al-air coin cell using the above-mentioned procedure has shown comparable performance to cells assembled with a new cathode. With these merits of enhanced electrochemical performance and recyclability, this new Al-air coin cell with modified chitosan hydrogel membrane can find wide applications for powering portable and small-size electronics.

Na metal anode attracts increasing attention as a promising candidate for Na metal batteries (NMBs) due to the high specific capacity and low potential. However, similar to issues faced with the use of Li metal anode, crucial problems for metallic Na anode remain, including serious moss-like and dendritic Na growth, unstable solid electrolyte interphase formation, and large infinite volume changes. Here, the rational design of carbon paper (CP) with N-doped carbon nanotubes (NCNTs) as a 3D host to obtain Na@CP-NCNTs composites electrodes for NMBs is demonstrated. In this design, 3D carbon paper plays a role as a skeleton for Na metal anode while vertical N-doped carbon nanotubes can effectively decrease the contact angle between CP and liquid metal Na, which is termed as being "Na-philic." In addition, the cross-conductive network characteristic of CP and NCNTs can decrease the effective local current density, resulting in uniform Na nucleation. Therefore, the as-prepared Na@CP-NCNT exhibits stable electrochemical plating/stripping performance in symmetrical cells even when using a high capacity of 3 mAh cm-2 at high current density. Furthermore, the 3D skeleton structure is observed to be intact following electrochemical cycling with minimum volume change and is dendrite-free in nature.

Carbonate-based electrolytes demonstrate safe and stable electrochemical performance in lithium-sulfur batteries. However, only a few types of sulfur cathodes with low loadings can be employed and the underlying electrochemical mechanism of lithium-sulfur batteries with carbonate-based electrolytes is not well understood. Here, we employ in operando X-ray absorption near edge spectroscopy to shed light on a solid-phase lithium-sulfur reaction mechanism in carbonate electrolyte systems in which sulfur directly transfers to Li 2 S without the formation of linear polysulfides. Based on this, we demonstrate the cyclability of conventional cyclo-S 8 based sulfur cathodes in carbonate-based electrolyte across a wide temperature range, from −20 °C to 55 °C. Remarkably, the developed sulfur cathode architecture has high sulfur content (>65 wt%) with an areal loading of 4.0 mg cm −2 . This research demonstrates promising performance of lithium-sulfur pouch cells in a carbonate-based electrolyte, indicating potential application in the future.

Solid-state batteries have been considered as one of the most promising next-generation energy storage systems because of their high safety and energy density. Solid-state electrolytes are the key component of the solid-state battery, which exhibit high ionic conductivity, good chemical stability, and wide electrochemical windows. LATP [Li1.3Al0.3Ti1.7 (PO4)3] solid electrolyte has been widely investigated for its high ionic conductivity. Nevertheless, the chemical instability of LATP against Li metal has hindered its application in solid-state batteries. Here, we propose that atomic layer deposition (ALD) coating on LATP surfaces is able to stabilize the LATP/Li interface by reducing the side reactions. In comparison with bare LATP, the Al2O3-coated LATP by ALD exhibits a stable cycling behavior with smaller voltage hysteresis for 600 h, as well as small resistance. More importantly, on the basis of advanced characterizations such as high-resolution transmission electron spectroscope-electron energy loss spectroscopy, the lithium penetration into the LATP bulk and Ti4+ reduction are significantly limited. The results suggest that ALD is very effective in improving solid-state electrolyte/electrode interface stability.

The biggest challenge for the commercialization of layered structured nickel rich lithium transition metal oxide cathode is the capacity and voltage fading. Resolving this problem over the years follows an incremental progress. In this work, we report our finding of totally a new approach to revolutionize the cycle stability of aggregated cathode particles for lithium ion battery at both room and elevated temperatures. We discover that infusion of a solid electrolyte into the grain boundaries of the cathode secondary particles can dramatically enhance the capacity retention and voltage stability of the battery. We find that the solid electrolyte infused in the boundaries not only acts as a fast channel for Li ion transport, but also most importantly prevents penetration of the liquid electrolyte into the boundaries, consequently eliminating the detrimental factors that include solid-liquid interfacial reaction, intergranular cracking, and layer to spinel phase transformation. The present work, for the first time, reveals unprecedented insight as how the cathode behaves in the case of not contacting with the liquid electrolyte, ultimately points toward a general new route, via grain boundary engineering, for designing of better batteries of both solid-liquid and solid state systems.

Lithium-ion sulfur batteries use nonlithium materials as the anode for extended cycle life. However, polysulfide shuttle reactions still occur on the nonmetal anodes (such as graphite and Si), and result in undesirable low Coulombic efficiency. In this work, we used Al2O3 layers coated by atomic layer deposition (ALD) technique to suppress the shuttle reactions. With the optimal thickness of 2 nm Al2O3 coated on graphite anode, the Coulombic efficiency of the sulfur cathode was improved from 84% to 96% in the first cycle, and from 94% to 97% in the subsequent cycles. As a result, the discharge capacity of the sulfur cathode was increased to 550 mAh g-1 in the 100th cycle, as compared with 440 mAh g-1 when the pristine graphite anode was used. The Al2O3 passivation layer minimizes the formation of insoluble sulfide (Li2S2, Li2S) on the surface of graphite anode and improves the efficiency and capacity retention of the graphite-sulfur batteries. The surface passivation strategy could also be used in other sulfur based battery systems (with Li, Si, and Sn anodes), to minimize side reactions and enable high-performance sulfur batteries.

The Li metal anode is considered as a promising alternative candidate for next-generation Li metal batteries with high specific capacity, low potential, and light weight. However, the crucial problem for the Li metal anode is one of the biggest challenges. Mossy or dendritic growth of Li occurs in the repetitive Li stripping/plating process with an unstable solid electrolyte interphase (SEI) layer of nonuniform ionic flux, which can not only lead to low Coulombic efficiency, but can also create the risk of a short-circuit, resulting in possible burning or explosion. Here, an advanced molecular-layer-deposition (MLD) Alucone protective layer is first demonstrated for Li metal anodes. By protecting Li foil with a controllable Alucone layer, the dendrites and mossy Li formation are effectively suppressed and the lifetime is significantly improved in different electrolytes (carbonate-based and ether-based). Furthermore, the detailed surface changes are studied by the advanced characterization technique of Rutherford backscattering spectrometry. The novel design of the MLD-protected Li metal anode may bring in new opportunities to the realization of the next-generation high-energy-density Li metal batteries.

The enhancement of catalyst activity and stability by controlling the metal-support interaction is significantly important for the long-term operation of polymer electrolyte membrane fuel cells (PEMFCs). In this work, an extremely stable electrocatalyst of platinum nanoparticles (Pt NPs) immobilized on a carbon support via the bridge layer of nitrogen-doped tantalum oxide (N-Ta2O5) is proposed. The novel N-Ta2O5 bridge layer in between the Pt NPs and carbon surface is synthesized by an atomic layer deposition technique (ALD). It effectively prevents Pt nanocrystals from detachment, migration, and aggregation during the PEMFCs' operation. Electrochemical results indicate that the Pt/N-ALDTa(2)O(5)/C electrocatalyst exhibits superior durability and sufficient catalytic activity for the oxygen reduction reaction, compared to the Pt/C catalyst. X-ray absorption spectroscopy illustrates the strong interactions between the Pt NPs and the N-Ta2O5-decorated carbon support. It is found that the bridge layer of N-Ta2O5 alters the electronic structure of the Pt nanocrystals and contributes to the significantly enhanced catalytic activity and durability for the Pt/ N-ALDTa(2)O(5)/C catalyst. This strategy, by using ALD of N-doped metal oxide to tune the metal-support interface and results in strong metal-support interactions, will benefit the future design of new-generation electrocatalysts with even better activity and longterm durability for PEMFCs application.

To achieve the high-power sodium-ion batteries, the solid-state ion diffusion in the electrode materials is a highly concerned issue and needs to be solved. In this study, a simple and effective strategy is reported to weaken and degrade this process by engineering the intensified surface and near-surface reactions, which is realized by making use of a sandwich-type nanoarchitecture composed of graphene as electron channels and few-layered MoS2 with expanded interlayer spacing. The unique 2D sheet-shaped hierarchical structure is capable of shortening the ion diffusion length, while the few-layered MoS2 with expanded interlayer spacing has more accessible surface area and the decreased ion diffusion resistance, evidenced by the smaller energy barriers revealed by the density functional theory calculations. Benefiting from the shortened ion diffusion distance and enhanced electron transfer capability, a high ratio of surface or near-surface reactions is dominated at a high discharge/charge rate. As such, the composites exhibit the high capacities of 152 and 93 mA h g-1 at 30 and 50 A g-1 , respectively. Moreover, a high reversible capacity of 684 mA h g-1 and an excellent cycling stability up to 4500 cycles can be delivered. The outstanding performance is attributed to the engineered structure with increased contribution of surface or near-surface reactions.

Spinel LiNi0.5Mn1.5O4 (LNMO) is a promising high voltage cathode material for lithium ion batteries (LIBs). However, dissolution of Mn and unwanted side reactions between LNMO and the electrolyte raises several safety issues while also resulting in deteriorated electrochemical performance of LIBs at high working voltages. Here, we report the use of ultrathin atomic layer deposited (ALD) AlPO4 thin film as a coating material for LNMO electrodes to circumvent the stated issues. The as-prepared AlPO4 coated LNMO demonstrates excellent capacity retention with prolonged cycle life compared to the bare one. Synchrotron based X-ray spectroscopy was employed to understand how ultrathin coating layer improve the cycle life, and then develop a detailed mechanism for the effect of coating layer. Our studies revealed that using atomic scale coating layer with improved thermal stability effectively impede the side-reactions occurrence at high voltage, resulting in significantly improved safety and electrochemical performances.

Nanostructured sodium titanate has great potential for various applications such as sodium-ion batteries, photocatalysts, and waste treatment. Understanding the phase-transition mechanism in sodium titanate after annealing is fundamentally important to tune the structure, morphology, and property for targeted applications. In this work, we adopted amorphous sodium titanate grown on carbon nanotubes by an atomic layer deposition technique as a reference and used X-ray absorption spectroscopy (XAS) and scanning transmission X-ray microscopy (STXM), as well as a high-temperature in situ X-ray diffraction (XRD) technique, to elucidate the phase-transition mechanism of sodium titanate from amorphous to crystalline upon annealing from 25 °C to 900 °C. XAS and XRD analysis disclosed that anatase TiO2 first formed in the matrix of amorphous sodium titanate at 500 °C and then recrystallized into Na0.23TiO2 at 700 °C and 900 °C. XAS studies also revealed that the Ti atoms in sodium titanate were oxidized during the annealing process and reached an oxidation state about 3.8+ for Na0.23TiO2. The elevated annealing temperature increased the coordination number of Ti atoms and the crystallinity of sodium titanate. STXM chemical map provided spatial information and visualized evidence on the phase transition among amorphous sodium titanate, anatase TiO2, and Na0.23TiO2 in the samples annealed at intermediate temperatures (500 °C and 700 °C). This work provides a comprehensive understanding on the evolution of sodium titanate, in terms of crystal structure, electronic structure, chemical environment, and morphology, under different post annealing conditions.

Graphene has been integrated in many heterogeneous structures in order to take advantage of its superior mechanical properties. However, the complex mechanical response of heterogeneous films incorporating graphene is not well understood. Here, we studied the mechanical behavior of atomic layer deposition (ALD) synthesized TiO2/graphene, as a representative building block of a typical composite, to understand the mechanical behavior of heterostructures using an experiment-computational approach. The inclusion of graphene was found to significantly enhance the Young's modulus of TiO2/graphene hetero-films for films below a critical thickness of 3 nm, beyond which the Young's modulus approaches that of pure TiO2 film. A rule-of-mixtures was found to reasonably estimate the modulus of the TiO2/graphene hetero-film. Experimentally, these hetero-films were observed to fail via brittle fracture. Complimentary density functional theory and finite element modeling demonstrates strong adhesion at the graphene TiO2 interface and that graphene serves as a reinforcement, providing the hetero-film with an ability to sustain significantly high stresses at the point of failure initiation. The results and methodology described herein can contribute to the rational design of strong and reliable ultrathin hetero-films for versatile applications.