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Manganese-rich layered oxide materials hold great potential as low-cost and high-capacity cathodes for Na-ion batteries. However, they usually form a P2 phase and suffer from fast capacity fade. In this work, an O3 phase sodium cathode has been developed out of a Li and Mn-rich layered material by leveraging the creation of transition metal (TM) and oxygen vacancies and the electrochemical exchange of Na and Li. The Mn-rich layered cathode material remains primarily O3 phase during sodiation/desodiation and can have a full sodiation capacity of ca. 220 mAh g-1 . It delivers ca. 160 mAh g-1 specific capacity between 2-3.8 V with >86 % retention over 250 cycles. The TM and oxygen vacancies pre-formed in the sodiated material enables a reversible migration of TMs from the TM layer to the tetrahedral sites in the Na layer upon de-sodiation and sodiation. The migration creates metastable states, leading to increased kinetic barrier that prohibits a complete O3-P3 phase transition.

Sodium-ion batteries are promising candidates for energy storage application, but the absence of high-capacity and low-cost anode materials significantly limits their practical specific energy and ...

Lithium-ion batteries (LIBs) with high-nickel (Ni) content LiNixMnyCozO2 (x + y + z = 1) (NMC with Ni ≥ 0.6) cathodes operated at high charge voltages have been considered as one of the most promising candidates for addressing the challenge of increasing energy density demand. Conventional LiPF6-organocarbonate electrolytes exhibit incompatibility with such cell chemistries under certain testing conditions because of the instability of electrode/electrolyte interphases. In response to this challenge, ether-based electrolytes with finely tuned structure and composition of solvation sheaths were developed and evaluated in graphite (Gr)∥NMC811 cell chemistry in 2.5-4.4 V, despite ethers being conventionally considered to be unfavorable electrolyte solvents for LIBs because of their anodic instability above 4.0 V and cointercalation into Gr electrodes. The functional ether-based electrolytes in this work enable both excellent cycle life and high rate capability of Gr∥NMC811 cells. Mechanistic studies reveal that the unique structure and composition of the solvation sheath of the functional ether electrolytes are the main reasons behind their excellent anodic stability and effective protection of the Gr electrode and, consequently, the extraordinary cell performances when operated at high charge cutoff voltages. This work also provides a feasible approach in developing highly stable functional electrolytes for high-energy density LIBs.

O3-layered metal oxides are promising cathode materials for high-energy Na-ion batteries (SIBs); however, they suffer from fast capacity fade. Here, we develop a high-performance O3-NaNi0.68Mn0.22C...

Ni-rich layered oxide (LiNixMnyCozO2 (NMC), x > 60%), one of the most promising cathode materials for high-energy lithium ion batteries (LIBs), still suffers from surface instability even with the state-of-art protective coatings, which normally are limited to ≤10 nm to maintain the required kinetics. Here we demonstrate a highly conductive protective layer with bio-tissue structure that can enable high-rate operation of NMC cathodes even with a thickness exceeding 40 nm. With this thick protection layer, the modified LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode retains 90.1% and 88.3% of its initial capacity after 1000 cycles in coin cells and pouch cells, respectively. This novel membrane is composed of crystalline nano-domains surrounded by ~1 nm amorphous phase, which is an effective distance to enable tunneling of electrons and Li+ ions between these domains. The coated NMC811 cathode releases ~55.3% less heat under thermal abuse and largely enhances his safety feature during puncture test. The coating also enables excellent electrochemical stability of NMC811 even after it was exposed to a moist environment for four weeks at 55 °C, which is critical for large-scale production of high-energy-density LIBs.

Alloy-based nanostructure anodes have the privilege of alleviating the challenges of large volume expansion and improving the cycling stability and rate performance for high energy lithium- and sodium-ion batteries (LIBs and SIBs). Yet, they face the dilemma of worsening the parasitic reactions at the electrode-electrolyte interface and low packing density for the fabrication of practical electrodes. Here, pomegranate Sb@C yolk-shell microspheres were developed as a high-performance anode for LIBs and SIBs with controlled interfacial properties and enhanced packing density. Although the same yolk-shell nanostructure (primary particle size, porosity) and three-dimensional architecture alleviated the volume change induced stress and swelling in both batteries, the SIBs show 99% capacity retention over 200 cycles, much better than the 78% capacity retention of the LIBs. The comparative electrochemical study and X-ray photoelectron spectroscopy characterization revealed that the different SEIs, besides the distinct phase transition mechanism, played a critical role in the divergent cycling performance.

The pursuit of a high-capacity anode material has been urgently required for commercializing sodium-ion batteries with a high energy density and an improved working safety. In the absence of thermodynamically stable sodium intercalated compounds with graphite, constructing nanostructures with expanded interlayer distances is still the mainstream option for developing high-performance carbonaceous anodes. In this regard, a surface-functionalized and pore-forming strategy through a facile CO2 thermal etching route was rationally adopted to engineer negligible oxygenated functionalities on commercial carbon for boosting the sodium storage process. Benefitted from the abundant ionic/electronic pathways and more active reaction sites in the microporous structure with noticeable pseudocapacitive behaviors, the functionalized porous carbon could achieve a highly reversible capacity of 505 mA h g-1 at 50 mA g-1, an excellent rate performance of 181 mA h g-1 at 16,000 mA g-1, and an exceptional rate cycle stability of 176 mA h g-1 at 3200 mA g-1 over 1000 cycles. These outstanding electrochemical properties should be ascribed to a synergistic mechanism, fully utilizing the graphitic and amorphous structures for synchronous intercalations of sodium ions and solvated sodium ion compounds, respectively. Additionally, the controllable generation and evolution of a robust but thin solid electrolyte interphase film with the emergence of obvious capacitive reactions on the defective surface, favoring the rapid migration of sodium ions and solvated species, also contribute to a remarkable electrochemical performance of this porous carbon black.

Phase purity plays a vital role in achieving high capacity and long cycle life for lithium iron phosphate. Given that LiFePO4 has lower electronic and ionic conductivity, carbon coating on fine particle surface is often used in order to improve the electrochemical performance of LiFePO4. Unfortunately, the carbon coating process is an inherently reducing process that is difficult to control and often results in the over-reduction of LiFePO4, turning it into iron phosphide. Our research here demonstrates the formation of a non-conductive Fe2P2O7 phase during the carbon coating process on LiFePO4. This phase formation is found to be dependent on particle size, temperature, and annealing atmosphere. Furthermore, these changes are found to directly associate with the change of the reducing potential. The finding in this work aims to guide and control the phase purity of carbon coated LiFePO4 by identifying important parameters that need to be taken under consideration during the carbon coating process in an effort to realize excellent electrochemical performance.

Carbon coating is a commonly employed technique for improving the conductivity of active materials in lithium ion batteries. The carbon coating process involves pyrolysis of organic substance on lithium iron phosphate particles at elevated temperature to create a highly reducing atmosphere. This may trigger the formation of secondary phases in the active materials. Here, we observe a conductive phase during the carbon coating process of lithium iron phosphate and the phase content is size, temperature, and annealing atmosphere dependent. The formation of this phase is related to the reducing capability of the carbon coating process. This finding can guide us to control the phase composition of carbon-coated lithium iron phosphate and to tune its quality during the manufacturing process., Coating the active materials of interest with carbon is a widely employed way to boost the performance of lithium ion batteries. Here the authors show the formation of a conductive phase on LiFePO4 during carbon coating, which is size, annealing temperature and reduction atmosphere dependent.

High-performance and low-cost transition metal (TM) layered oxides using earth abundant elements are promising cathodes for Na-ion batteries. However, it is challenging to obtain desired materials because the large Na size, different Na occupations and various layer stacking sequences multiply the complication in determining the structure of a given composition and exacerbate uncertainty to the structure-property correlation. In this work, we use the attainment of desired NaxMnyNizTM1−y-zO2-based cathode materials as an example to demonstrate a general roadmap for batch development of sodium layered cathodes towards practical applications. A synthesis phase diagram of NaxMnyNi1−yO2 was created for pre-screening and rational selection of the platform material of P2/O3-structured Na0.85Mn0.6Ni0.4O2. Cationic potential was leveraged in elemental substitution to further promote the material structural stability and electrochemical performance. Several cost-effective O3 and P2/O3 hybrid cathode materials have been obtained, all of which demonstrate excellent performance. In particular, the Na0.85Mn0.5Ni0.4Ti0.1O2 delivers a high specific capacity of ~130 mAh/g between 2 and 4 V and 91% retention after 500 cycles. The work discovers multiple materials as high-performance and cost-effective Na-ion battery cathodes and offers critical guidance to the rational design of future layered cathode materials.

Utilizing both cationic and anionic oxygen redox reactions is regarded as an important approach to exploit high-capacity layered cathode materials with earth abundant elements. It has been popular strategies to effectively elevate the oxygen redox activities by Li-doping to introduce unhybridized O 2p orbitals in Nax MnO2 -based chemistries or enabling high covalency transition metals in P2-Na0.66 Mnx TM1-x O2 (TM = Fe, Cu, Ni) materials. Here, we investigated the effect of Li doping on regulating the oxygen redox activities P2-structured Na0.66 Ni0.25 Mn0.75 O2 materials. Systematic X-ray characterizations and ab initio simulations have shown that the doped Li has uncommon behavior in modulating the density of states of the neighboring Ni, Mn and O, leading to the suppression of the existing oxygen and Mn redox reactivities and the promotion of the Ni redox. The findings provide a complementary scenario to current oxygen redox mechanisms and shed lights on developing new routes for high-performance cathodes. This article is protected by copyright. All rights reserved.

Carbonaceous materials have long been considered promising anode materials for Na-ion batteries. However, the electrochemical performance of conventional carbon anodes is generally poor because the sodium ion storage solely relies on the disordered region of the carbon materials in a carbonate-based electrolyte. The solvent co-intercalation mechanism for Na ions has been recently reported in natural graphite anodes for Na-ion batteries with ether-based electrolytes, but their capacities are still unsatisfactory. We show here for the first time that by combining regular Na ion storage in the disordered carbon layer and solvent co-intercalation mechanism in the graphitized layer of a commercial N330 carbon black as an anode material for Na-ion batteries in ether-based electrolyte, the reversible capacity could be fully realized and doubled in magnitude. This unique sodium intercalation process resulted in a significantly improved electrochemical performance for the N330 electrode with an initial reversible capacity of 234 mAh·g–1 at 50 mA·g–1 and a superior rate capability of 105 mAh·g–1 at 3,200 mA·g–1. When cycled at 3,200 mA·g–1 over 2,000 cycles, the electrode still exhibited a highly reversible capacity of 72 mAh·g–1 with a negligible capacity loss per cycle (0.0167%). Additionally, surface-sensitive C K-edge X-ray absorption spectroscopy, with the assistance of electrochemical and physicochemical characterizations, helped in identifying the controlled formation and evolution of a thin and robust solid electrolyte interphase film. This film not only reduced the resistance for sodium ion diffusion, but also maintained the structural stability of the electrode for extended cycle reversibility. The superior electrochemical performance of N330 carbon black strongly demonstrated the potential of applying ether-based electrolytes for a wide range of carbon anodes apart from natural graphite.

Despite great advances in sodium-ion battery developments, the search for high energy and stable anode materials remains a challenge. Alloy or conversion-typed anode materials are attractive candidates of high specific capacity and low voltage potential, yet their applications are hampered by the large volume expansion and hence poor electrochemical reversibility and fast capacity fade. Here, we use antimony (Sb) as an example to demonstrate the use of yolk-shell structured anodes for high energy Na-ion batteries. The Sb@C yolk-shell structure prepared by controlled reduction and selective removal of Sb 2 O 3 from carbon coated Sb 2 O 3 nanoparticles can accommodate the Sb swelling upon sodiation and improve the structural/electrical integrity against pulverization. It delivers a high specific capacity of ~ 554 mAh g −1 , good rate capability (315 mhA g −1 at 10 C rate) and long cyclability (92% capacity retention over 200 cycles). Full-cells of O3-Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ]O 2 cathodes and Sb@C-hard carbon composite anodes demonstrate a high specific energy of ~ 130 Wh kg −1 (based on the total mass of cathode and anode) in the voltage range of 2.0–4.0 V, ~ 1.5 times energy of full-cells with similar design using hard carbon anodes.

The fast-growing demand of energy storage devices has prompted diverse battery techniques, while the state-of-the-art Li-ion batteries (LIBs) continue to flourish, Na-ion batteries (SIB) have been identified to be a promising alternative to share the burden with LIBs, particularly for large scale grid storage applications. Both LIBs and SIBs techniques work based on similar fundamental mechanisms, with a heavy focus on intercalation chemistry of layered transition metal (TM) oxides. However, the differences between Li-ion and Na-ion in terms of their size and Lewis acidity induce many different behaviors when crystallizing or diffusing in layered cathode materials. This minireview summarizes some typical cases where Li and Na-ion differ in layered cathode materials and discusses potential approaches to leverage their similarities and dissimilarities for future developments of high-performance Na-ion batteries.

Spinel LiNi 0.5 Mn 1.5 O 4 (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) AlPO 4 thin film as a coating material for LNMO electrodes to circumvent the stated issues. The as-prepared AlPO 4 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.

Herein we report the fabrication, optimization, and characterization of inkjet-printed thin film silicon anodes for lithium-ion batteries using commercial silicon nanoparticles. By comparing four different polymer binders, we demonstrate the critical role of binder on achieving good electrochemical performance of inkjet-printed silicon electrodes. Inkjet-printed silicon nanoparticle electrodes with conductive polymer PEDOT:PSS binder exhibit superior performance and durablity, with a capacity retention of over 1000 cycles at a depth-of-discharge of 1000 mA h g −1 . The working mechanism of the impact of the binders on inkjet-printed silicon electrodes is investigated and explained in detail via various characterization techniques, including scanning electron microscopy, Raman and infrared spectroscopy.

Li-O 2 batteries with ultrahigh theoretical energy density have triggered worldwide research interests and hold the prospect for powering electric vehicles. However, the poor cycling stability and low energy efficiency of Li-O 2 batteries still remain and hamper their practical application. Configuring desirable porous cathodes with uniformly dispersed and highly active catalysts is a noteworthy and feasible approach to overcoming these critical obstacles. Herein, we report on a novel strategy for the fabrication of Mn 3 O 4 nanowires and carbon nanotubes composite film (Mn 3 O 4 /CNTs film) with ultrafine RuO 2 nanoparticles (Mn 3 O 4 /CNTs-RuO 2 film), in which the Mn 3 O 4 /CNTs film was employed as a conductive and porous matrix and extremely low amount of RuO 2 (just 2.84 wt%) are uniformly dispersed onto this matrix by using atomic layer deposition method, and reveal its electrochemical behaviors as a free-standing air electrode for Li-O 2 batteries. The Mn 3 O 4 /CNTs-RuO 2 film delivers a high specific capacity, improved round-trip energy efficiency and ultra-long cycle life (251 cycles). The superior electrochemical performance can be attributed to the enhanced catalytic activity of the grafted RuO 2 with modulated electronic structure as the result of the interaction with substrate, which is evidenced by the corresponding X-ray absorption spectroscopy results and the unique nanosheet-shaped discharge product which can be smoothly decomposed.

Lithium-rich layered material is one of the most promising candidates of cathode materials for next-generation electric vehicles. However, one of the major issues that pertains to this material is the oxygen release during initial charge, which results in low initial coulombic efficiency (CE), intense electrolyte oxidation and thermal instability. In this study, we have conducted aluminum phosphate (AlPO 4 ) coating via atomic layer deposition (ALD) approach to protect the surface of this cathode material powders. It was found that part of the C2/m Li 2 MnO 3 phase turned into a spinel-like phase during the ALD process. The oxygen release has been effectively suppressed by such transformation, the initial CE increased from 75.2% for the bare electrode to 86.2% for the electrode with only 5 ALD cycles of AlPO 4 coating. Furthermore, AlPO 4 was also found to be more effective in improving the thermal stability of the cathode material comparing to bare or Al 2 O 3 coated samples. Our study has provided a new possible solution towards cathode materials with high thermal resistance via conformal coating.

Developing an economical, highly active and durable material to replace the conventional, expensive noble metal electrocatalyst is an important milestone in the development of fuel cell technology. Nanocarbon materials are considered as promising catalysts toward the oxygen reduction reaction (ORR) in fuel cells, due to their reasonable balance between low-cost, long-life durability and high catalytic activity in alkaline media. In this work, we present the fabrication of N,S-co-doped nanocarbon derived from a metal-organic framework (MOF) precursor for use as an electrocatalyst towards ORR. High resolution transmission electron microscopy (HRTEM) mapping demonstrates the uniform distribution of N and S atoms into the nanocarbon skeleton. The nitrogen absorption–desorption isotherms indicate that the MOF-derived N,S-co-doped nanocarbon has a high specific surface area (2439.9 m2 g−1) and a porous structure. Importantly, the N,S-co-doped nanocarbon exhibits higher catalytic activity toward ORR, better long-term stability and methanol tolerance than commercial Pt/C catalyst. First-principles calculations demonstrate that the remarkable electrochemical properties of N,S-co-doped nanocarbon are mainly attributed to the synergistic effect from the N and S dopants. Moreover, for the first time, it is revealed that the N,S-coupled dopants in nanocarbon can create active sites with higher catalytic activity for ORR than the isolated N and S-dopants. This finding on the structure–performance relationship of the co-doped nanocarbon provides guidelines for the design of high performance electrocatalysts.

To understand the role of functional groups and defects in improving the anti-poisoning performance of platinum (Pt) catalysts for formate oxidation, four kinds of supports originated from carbon nanotubes (CNTs) were prepared with varying amounts of functional groups (FGs) and varying degrees of defects. Pt particles with controlled similarity were deposited onto the four supports for precisely comparing the difference between the four supports. The catalysts structures were characterized using X-ray diffraction, high-resolution transmission electron microscope, Raman spectra and X-ray photoelectron spectra. The electrochemical performances of the four catalysts were characterized using cyclic voltammetry and chronoamperometry methods. The results showed that using fully-unzipped CNTs, with a higher degree of defects and lower amount of FGs, as a support results in the greatest improvement in anti-poisoning performance of Pt, compared to oxidized CNTs with a higher amount of FGs and lower degree of defects. These results indicate that CNT defects play more important role in promoting anti-poisoning performance for the supported catalyst than FGs. We believe that this conclusion is helpful for guiding the supports design to improve anti-poisoning performance of formate oxidation catalysts.

Platinum-based catalysts have been considered the most effective electrocatalysts for the hydrogen evolution reaction in water splitting. However, platinum utilization in these electrocatalysts is extremely low, as the active sites are only located on the surface of the catalyst particles. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their efficiency by utilizing nearly all platinum atoms. Here we report on a practical synthesis method to produce isolated single platinum atoms and clusters using the atomic layer deposition technique. The single platinum atom catalysts are investigated for the hydrogen evolution reaction, where they exhibit significantly enhanced catalytic activity (up to 37 times) and high stability in comparison with the state-of-the-art commercial platinum/carbon catalysts. The X-ray absorption fine structure and density functional theory analyses indicate that the partially unoccupied density of states of the platinum atoms' 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance., Downsizing platinum based nanocatalysts has the twin advantages of lower platinum usage and increased activity per platinum atom. Here, the authors report an atomic layer deposition technique for single platinum atom catalyst fabrication and assess their hydrogen evolution activity.

For the first time, we report a facile approach to fabricate metal organic framework derived carbon (MOF-C) with tunable porous structure. Different from direct pyrolysis of MOFs and blind attempt in application, the in-situ ammonia treatment enables MOF-C with desired porous structure from enriched microporous structure to hierarchically mesoporous structure. Further, NH 3 treated MOF-C as carbon host for sulfur loading performing as the cathode for Li–S batteries results in twice higher capacity retention than that of pristine MOF-C. Besides, different Li–S electrochemical mechanisms regarding the different porous structures of carbon are also revealed and investigated in this paper.

The understanding of the intrinsic properties of Pt and Pd is important for the rational design of catalysts for methanol and ethanol oxidation in alkaline media. In this paper, Pd catalysts, Pt catalysts and bimetallic PtPd catalysts supported on nitrogen-doped graphene are investigated. The cyclic voltammograms (CVs) for the bimetallic catalysts in 1 M KOH solution demonstrate the increasing surface composition of Pt versus Pd. The linear sweep voltammetry results show that the onset potential for OH formation on Pt is lower than on Pd, indicating that Pt has a higher affinity for OH than Pd. The CVs recorded for methanol and ethanol oxidation show that ethanol oxidation occurs at lower potentials, suggesting that ethanol is a more active fuel than methanol. Ethanol and methanol oxidation occurs at lower potentials on Pt than on Pd, revealing that Pt is intrinsically more active than Pd. Chronoamperometry results show that the rate of catalysts deactivation during ethanol oxidation is more severe compared with methanol oxidation, especially for catalysts with higher Pt content. The possible reason for the deactivation behaviors is presented and recommendations are given for future catalysts development.

Here we present a novel way to grow aluminum alkoxide films with tunable conductivity with molecular level accuracy with the use of molecular layer deposition (MLD). Alternating exposures of trimethylaluminum (TMA), ethylene glycol (EG), and terephthaloyl chloride (TC) are used to grow the aluminium alkoxide films. Control over film composition was accomplished by alternating cycles of EG and TC between cycles of TMA and EG. In this fashion the aluminum to carbon ratio can be accurately controlled. These films were then pyrolyzed under a reducing atmosphere to yield a conductive Al2O3/carbon composite. Raman spectroscopy determined that nanocrystalline sp2-graphitic carbon was formed following pyrolysis while sheet resistance measurements determined that conductivity of the film is directly related to aluminium–carbon ratio. To further elucidate the origin of conductivity within the film, synchrotron based XPS was performed.

Ni-rich NMC (LiNixMnyCo1-x-yO2, x ≥ 0.6) has the attributes of high specific capacity (greater than 180 mAh/g), high operating voltage (ca. 3.8 V) and low cost, which is therefore deemed as one of the most promising cathode candidates for next-generation high-energy Li-ion batteries (LIBs). However, challenges exist before the large-scale commercialization of Ni-rich cathode such as gas generation, capacity degradation especially at high rates or elevated temperatures. From thin film to densely packed high loading cathode, this work investigates the rate-limiting steps in Ni-rich cathode e.g., phase structure, electronic and ionic conductivity to understand the reaction kinetics at different scales. This work provides new insights in understanding the electrochemical properties of Ni-rich cathode at different levels to inspire revolutionary ideas to address the fundamental issues of Ni-rich cathode from material to relevant electrode levels.

The porous carbon blacks rationally designed by a facile yet efficient NH3 thermal etching route have been investigated as anode materials in an ether-based electrolyte for sodium-ion batteries. The as-synthesized CBN35 carbon black with a 35% weight loss after NH3 thermal etching exhibited a large specific charge capacity of 352 mAh g−1 at 50 mA g−1 and a superior rate capability of 101 mAh g−1 at 16000 mA g−1, due to its highest microporosity, an appropriate surface area, a desirable microstructure, and a promising hybrid intercalation mechanism. Impressively, even cycled at 1600 mA g−1 over 3200 cycles, an outstanding reversible capacity of 103 mAh g−1 with a negligible 0.0162% capacity loss per cycle can still be achieved. Based on the multimodal characterizations including the structural probes of phase evolution for carbon materials, the electrochemical techniques, and the surface-sensitive XAS measurements, the exceptional electrochemical properties should stem from several merits of modified carbon black system. While the particular microporous structure provides relatively more accessible sodium storage sites, a novel hybrid intercalation mechanism in ether-based electrolyte would incorporate the sodium ion insertion into the disordered structure with the solvated sodium ion species co-intercalation into the graphitic phase. In addition to the diffusion-controlled redox reactions, the noticeable surface-induced pseudocapacitive reactions also significantly contribute to the charge storage upon sodiation and guarantee the rapid migrations of sodium ions/solvated compounds. This system further features a controlled emergence of a robust but thin solid electrolyte interphase layer, which could suppress the side reactions of active electrode with reactive electrolyte, maintain the fragile porous structure upon cycling, and facilitate the migrations of sodium ions and solvated sodium ion compounds.

Room temperature sodium–air batteries have a similar design and concept as lithium–air batteries. Using ambient air instead of pure oxygen as oxygen source is challenging because the minor components in air could lead to various side reactions and influence the electrochemical reaction route. Although water is an innegligible component in air, its impact on Li– and Na–air batteries is often underestimated. In this study, the electrochemical behavior of Na–air batteries under different relative humidity (RH) has been systemically investigated by galvanic cycling and cyclic voltammetry tests, as well as the identification of corresponding discharge products by physical characterizations such as XRD, FT-IR, and SEM. The reaction mechanisms of Na–air batteries under humid conditions are revealed and discussed. Na–air batteries suffer from more severe impact from the water content in air than Li–air batteries. NaOH and its derivatives are found to form and are proven to be fatal to the cells under humid ambien...

A binder-free three-dimensional (3D) nanostructured air electrode composed of vertically grown nitrogen doped carbon nanotubes on carbon paper (NCNT-CP) is developed and applied to Na–O2 cells. The 3D architecture of the air electrode results in increased discharge capacity by optimizing the utilized area of the electrode material. The chemical and electrochemical reaction mechanisms of the cell are also explored with the use of synchrotron-based X-ray absorption spectroscopy (XAS). Investigation of the discharge product of Na–O2 cells during discharge and charge cycles using X-ray absorption near-edge structure (XANES) indicates that both sodium superoxide and peroxide are produced under various physicochemical conditions and can be subsequently decomposed with different overpotentials. Furthermore, formation of carbonate-based parasitic products is also shown to restrict the cyclability of the cell.

A non-aqueous approach was developed to synthesize iron phosphate cathode materials by the atomic layer deposition (ALD) technique. Deposition of iron phosphate thin films was achieved on nitrogen-doped carbon nanotubes (NCNTs) by combining ALD subcycles of Fe2O3 (ferrocene-ozone) and POx (trimethyl phosphate-water) at 200 – 350 °C. The thickness of iron phosphate thin films depends linearly on the ALD cycle, indicating their self-limiting growth behavior. The growth per cycle of iron phosphate thin films was determined to be ∼ 0.2, 0.4, 0.6, and 0.5 A, at 200, 250, 300, and 350 °C, respectively. Characterization by SEM, TEM, and HRTEM techniques revealed uniform and conformal coating of amorphous iron phosphates on the surface of NCNTs. XANES analysis confirmed Fe O P bonding in the iron phosphates prepared by ALD. Furthermore, electrochemical measurement verified the high electrochemical activity of the amorphous iron phosphate as a cathode material in lithium-ion batteries. It is expected that the amorphous iron phosphate prepared by this facile and cost-effective ALD approach will find applications in the next generation of lithium-ion batteries and thin film batteries as either cathode materials or surface coating materials.

Self-stacked nitrogen-doped carbon nanotubes (NCNTs) and pristine carbon nanotubes (CNTs) on commercial porous polypropylene substrates have been applied as air electrodes for sodium-air batteries (SAB). Both NCNT and CNT air electrodes exhibit highly reversible electrochemical activities and large capacities under low current densities in SABs, while NCNT electrodes show much higher rate performance and extended cycling life under high current densities. The superior electrochemical behavior of NCNT electrodes is attributed to the robust network of aligned NCNTs, which enables rapid oxygen and liquid electrolyte transport while accommodating the volume change originating from discharge product aggregation during cycling. Moreover, uniform coverage of the discharge product has been observed on the NCNT air electrodes, in contrast to the random and discrete dispersion of discharge product on the CNT air electrodes. The unique morphologies and growth mechanism of discharge products on NCNT electrodes are believed to be due to the outstanding catalytic activity of the nitrogen-doped sites in the NCNTs, which play a critical role in the high cycling stability of NCNT air electrodes for SABs.

Sodium-ion batteries (SIBs) have received increasing attention for applications in large-scale energy storage systems due to their low cost, high energy density, and high abundance of the sodium element. Nanosizing electrode materials becomes a key strategy to overcome the problems resulting from the sluggish kinetics of large sodium ions, thereby achieving good performance in SIBs. Herein, we developed an atomic layer deposition (ALD) approach for atomically precise fabrication of sodium titanate anode materials. This ALD process shows excellent controllability over the growth rate, film thickness, composition of sodium titanates, and high flexibility of coating uniform sodium titanate films onto various dimensions of substrates. Moreover, the amorphous sodium titanate deposited on carbon nanotubes exhibits high specific capacity, excellent rate capability, and ultra-long cycling life (∼100 mA h g−1 after 3500 cycles). It is expected that the ALD approach developed herein can be extended to well-defined fabrication of other sodium-containing electrode materials for SIBs.

The development of active, durable, and low-cost catalysts to replace noble metal-based materials is highly desirable to promote the sluggish oxygen reduction reaction in fuel cells. Herein, nitrogen and fluorine-codoped three-dimensional carbon nanowire aerogels, composed of interconnected carbon nanowires, were synthesized for the first time by a hydrothermal carbonization process. Owing to their porous nanostructures and heteroatom-doping, the as-prepared carbon nanowire aerogels, with optimized composition, present excellent electrocatalytic activity that is comparable to commercial Pt/C. Remarkably, the aerogels also exhibit superior stability and methanol tolerance. This synthesis procedure paves a new way to design novel heteroatom-doped catalysts.

Graphene nanoribbons (GNRs) from chemical unzipping of carbon nanotubes (CNTs) have been reported to be a suitable candidate for lithium ion battery materials, but very few of them focused on controlling GNRs with different unzipping levels. Here we present a study of GNRs with controlled unzipping level and the prevailing factors that affect the lithium storage performance at early and final unzipping level; besides, the effect of thermal reduction has been investigated. On the basis of Raman and BET surface area tests, we found that the unzipping of CNTs starts with surface etching and then proceeds to partial and full unzipping and finally fragmentation and aggregation. Galvanostatic charge–discharge reveals that defect increase is mainly responsible for the capacity enhancement at the early unzipping level; surface area drop is associated with the capacity fade at the final unzipping level. Surface functional groups can result in low electrical conductivity and therefore cause capacity drop within sev...