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• The metal phosphates coated P3-NaMN is synthesized via co-precipitation route. • The modified samples show a great improvement of cycling performance. • The metal phosphates coating could promote the air stability of the materials. • The coated layer could inhibit the loss of lattice oxygen in high voltage region. Cathode materials are considered to be the most critical component of the sodium-ion batteries, which determine the overall electrochemical performance of the battery to some degree. Currently, the layered oxides receive significant attention due to the high operating voltage and high capacity. However, the instability in the air and unsatisfactory cycling performance limit their commercial application. Based on excellent electrochemical performance of the P3-type Na 0.65 Mn 0.75 Ni 0.25 O 2 material, here AlPO 4 and Mg 3 (PO 4) 2 protective coatings are employed to modify P3-type Na 0.65 Mn 0.75 Ni 0.25 O 2. The metal phosphate layers cover the surfaces of the pristine particles via a co-precipitation route. It has been found that the two modified samples exhibit an obvious improvement of cycling performance with the capacity retentions about 93% at a current density of 0.2 C within 100 cycles. In addition, the coated metal phosphate layer can effectively suppress the irreversible oxidation of oxygen in the high voltage redox region. Furthermore, after exposure to the air, the coating samples still retain a high electrochemical activity. Therefore, the metal phosphates coating provides a meaningful exploration for the research and development of long-term cycling life and high air stability of cathode materials in sodium-ion batteries. [ABSTRACT FROM AUTHOR]

The hollow Si nanospheres modified by the mechanically robust titanium dioxide (TiO 2 ) shell and the uniform carbon layer are intentionally designed and successfully prepared as the anode active material of high performance lithium-ion batteries. The effects of the robust TiO 2 shell and the uniform carbon layer on the structure and electrochemical performances for the Si@TiO 2 @C nanospheres are studied in detail by X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction and charge/discharge tests. The results show that the hollow structure of the Si core can spontaneously absorb the huge volume expansion stress, the robust TiO 2 shell is used as a compact fence to promote the expansion towards the interior of the Si cavity instead of the exterior in the processes of charge/discharge, and the uniform carbon layer can effectively enhance the electrical conductivity and further control the integrity and stability of the well-wrapped core-shell-shell framework. Typically, the resultant hollow Si@TiO 2 @C nanospheres exhibit a high initial discharge capacity of 2557.1 mAh g −1 with coulombic efficiency of 86.06% as well as a large recuperative discharge capacity of 1270.3 mAh g −1 after 250 cycles at 1 A g −1 with a mean coulombic efficiency of 99.53%. Therefore, the hollow Si@TiO 2 @C nanospheres prepared by one-step sol-gel coating process show outstanding electrochemical properties and are considered as a prospective candidate to the adhibitions of the anode material for new generation power LIBs. [ABSTRACT FROM AUTHOR]

The structure design strategy for LRO based on the reversible anionic redox and spinel-layered coherent structure is propitious to maintaining high specific capacity and improving the reversible anionic redox and stable cyclic performance of LRO. [Display omitted] • LRO cathode with reversible anionic redox and spinel-layered coherent structure is designed. • The specific capacity and initial Coulombic efficiency are enhanced by the introduction of S-anions. • Stable interface structure and enhanced electrochemical kinetics are realized by the spinel-layered coherent structure. • Improved specific capacity and excellent cyclic stability are revealed in the modified LRO. Initiating effective strategies to improve the reversibility of anionic redox and structural stabilization is crucial to the development and industrial application of Li-rich cathode materials (LRO), which are regarded as the preferred option of the cathode materials for the next-generation lithium-ion battery with high energy density. To remit the unexpected behavior of structural destruction and capacity attenuation, this paper proposes a strategy for maintaining high specific capacity and improving the reversible anionic redox and stable cyclic performance of LRO by introducing the spinel-layered coherent structure and S-anions. Proved by the ex-situ X-ray photoelectron spectroscopy, S-anions can regulate the anionic redox reversibility and thus enhance the reversible discharge capacity and initial Coulombic efficiency. Moreover, the structural stability is greatly improved by the introduction of spinel-layered coherent structure and S-anions in LRO, which has been confirmed by abundant structural characterizations. Besides, the results reveal that the optimized material exhibits a high reversible discharge capacity of 289.52 mAh/g and good cyclic performance with a retention rate of 88.21% after 200 cycles. Evidently, the structure design strategy for LRO based on the reversible anionic redox and spinel-layered coherent structure is a significant exploration, which will bring a new clew for the design of the cathode materials with high-energy–density and excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile strategy is developed to synthesize multiphase Fe-based catalyst. • The Fe/Fe 3 C/FeN 0.0324 @N-GC exhibits excellent pH-universal ORR activity. • It possesses better battery performance than Pt/C in alkaline and neutral media. • The activity is attributed to the synergy among Fe-based sites dominated by Fe 3 C. • The active of Fe-based sites is probed by DFT calculation: Fe 3 C > Fe > FeN 0.0324. Iron-based nitrogen-doped carbonaceous materials are currently the most promising alternative towards oxygen reduction reaction (ORR) electrocatalysts due to the highly efficient active sites of single-atom Fe-N X coordination. However, the fact that iron-containing nanocrystals are easier to form during pyrolysis without additional tuning while providing activity comparable to single-atom sites cannot be ignored. Herein, we propose a facile and efficient strategy to synthesize iron nanocrystals sites with multiphase embedded in porous nitrogen-doped graphitized carbon (Fe/Fe 3 C/FeN 0.0324 @N-GC-X, X = 700, 850, and 1000). Based on highly active Fe 3 C@N-GC sites and the synergistic effect of Fe 3 C-dominated multiple iron-based, Fe/Fe 3 C/FeN 0.0324 @N-GC-850 exhibits excellent electrocatalytic activity towards ORR in pH-universal media. Specifically, it exhibits satisfactory onset potential (E onset), half-wave potential (E 1/2) and stability, and thus surpassing the benchmark Pt/C in both alkaline and neutral media as well as approaching Pt/C in acidic media. When employed as an air cathode in zinc-air batteries (ZABs), it also presents higher open-circuit voltage (OCV), discharge voltage plateaus, capacity, and peak power density compared with Pt/C. Density functional theory (DFT) calculations demonstrate that Fe 3 C (2 2 0)/N-GC has lower activation energy during ORR process and the overpotential generated by Fe 3 C/N-GC (0.7 V) is obviously less than one of Fe/N-GC (1.37 V) and FeN 0.0324 /N-GC (1.69 V). [ABSTRACT FROM AUTHOR]

• Construct Mn 3 O 4 protective shell to alleviate Jahn-Teller distortion. • Oxygen vacancy can effectively restrain the release of oxygen. • The designed LRNMO@Mn 3 O 4 cathode has higher electron/ion conductivity. • The Mn 3 O 4 -coated electrode exhibited excellent cycle stability. Herein, we put forward a feasible interfacial modification strategy in virtue of Mn 3 O 4 surface coating to construct protective shell and alleviate Jahn-Teller distortion during the charge/discharge process. It has been found that the increase of the oxygen vacancy on the surface of Li 1.2 Ni 0.27 Mn 0.54 O 2 of (LRNMO) after Mn 3 O 4 protective layer modification can effectively restrain the release of oxygen and enhancing rate capability, and thus improving its comprehensive electrochemical performances. In particular, the initial coulombic efficiency of the optimized LRNMO-1 electrode is improved from 72.3% to 84.3%. The capacity retention rate is up to 95.6% at 250 mA g−1 (1C) after 200 cycles. In addition, the LRNMO-1 electrode also has a good capacity retention rate (96.4% after 100 cycles) at a high current density of 5C. Moreover, the designed LRNMO@Mn 3 O 4 cathode exhibits higher ionic conductivity and better interface stability. As a result, this work offers a practicable and valuable exploration for the development and industrialization of Co-free Li-rich Mn-based cathode materials with high energy density. [ABSTRACT FROM AUTHOR]

• Co-free lithium-rich material was prepared by simple oxalate co-precipitation way. • The nano-micron combined structure was favorable to the infiltration of electrolyte. • The anions regulated the valence of surface transition metal ions. • The F-doped electrode exhibited excellent cycle stability. Co-free cathode materials are gradually attracted wide attention due to the low budget and environmental friendliness, but their application is still prevented by the poor rate performance and cyclic stability. Herein, the Co-free lithium-rich cathode materials (Li 1.2 Ni 0.2 Mn 0.6 O 2 , LRNMO) with a nano-micron combined morphology is prepared by a simple oxalate co-precipitation route and further modified by an anion doping strategy. It has been found that the F− anion doping can increase the content of Mn4+ in LRNMO, reduce the influence of the Jahn-Teller effect, and further impede the transition from layered phase to spinel phase. As a result, the as-obtained Li 1.2 Ni 0.2 Mn 0.6 O 2-x F x (x = 0.04, named as F4-LRNMO) shows an optimal electrochemical performance, for instance, high discharge capacity (243 mAh g−1) with a satisfactory initial coulombic efficiency of 84.37% at 0.1C. Meanwhile, the F4-LRNMO sample also can display high capacity retention of 92.2% after 200 cycles at 1C, and a remarkably high discharge capacity of 151 mAh g−1 with capacity retention of 95.4% after 100 cycles even at high rate of 5C. In consequence, this work can not only ameliorate the defects of poor stability and low initial coulomb efficiency, but also offer a meaningful exploration for the development of Co-free lithium-rich cathode materials with high capacity and high performance-price ratio. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polar and conductive titanium carbide is introduced for redox regulation. • Lithium sulfide plays as sulfur source in this study. • Sulfur redox and lithium sulfide precipitation are remarkably promoted. • The electrochemical characteristics of as-prepared batteries are boosted. The lithium-sulfur batteries (LSBs) have attracted more and more attention in recent years owing to its high theoretical energy density, abundant sulfur source and relatively low cost. However, the serious polysulfides shuttle and sluggish sulfur redox kinetics hinder the development and commercial application of high-performance lithium-sulfur batteries. In this paper, the titanium carbide (TiC)-decorated carbon matrix is considered as the mediator, anchor and electrocatalyst for polysulfides redox reaction. It has been proved that the conductive and polar titanium carbide can not only chemisorbs lithium polysulfides via titanium-sulfur (Ti-S) coordination, but also optimize the lithium sulfide (Li 2 S) nucleation/precipitation mechanism for better redox reaction. Especially, the graphene oxide and carbon nanotube matrix (GO-CNT) in this case can act as both host for Li 2 S loading and TiC precipitation. Accordingly, the as-fabricated lithium sulfide-graphene oxide–carbon nanotube-titanium carbide (LS-GO-CNT-TiC) cathode delivers the high initial discharge capacity of 956 mAh g−1 at 0.1C and good rate capability of 508 mAh g−1 at 2C. These results consequently manifest that the conductive and polar matrix of LS-GO-CNT-TiC can perform as a promising cathode of the high performance LSBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • An ultralow-potential H 2 Ti 3 O 7 ·xH 2 O anode is first introduced for zinc-ion batteries. • The storage mechanism of H+ and Zn2+ co-insertion is demonstrated on the H 2 Ti 3 O 7 ·xH 2 O anode. • The H 2 Ti 3 O 7 ·xH 2 O anode features excellent electrochemical performance. • The assembled Zn x MnO 2 //H 2 Ti 3 O 7 ·xH 2 O full battery exhibits the high output voltage. Developing the alternative anode materials that can completely resolve the dendrite concern of Zn metal anodes are desirable for reliable aqueous zinc-ion batteries. However, the sub-optimal charging potentials of reported anodes inevitably cause the discounted output voltage and energy density on a zinc-ion full battery. Herein, it is firstly demonstrated that the hydrated titanic acid (H 2 Ti 3 O 7 ·xH 2 O) can be applied as an ultralow-potential anode for the aqueous zinc-ion full battery. The depressed potential (0.2 V vs. Zn2+/Zn) of the H 2 Ti 3 O 7 ·xH 2 O compared to that of reported candidates could significantly enhance the operating voltage level of the zinc-ion full battery. Furthermore, the comprehensive analyses demonstrate that the expanded lattice spacings and interlayer crystal water stimulate Zn2+ along with H+ to jointly insert and extract on the H 2 Ti 3 O 7 ·xH 2 O anode. The low-potential H 2 Ti 3 O 7 ·xH 2 O anode exhibits an impressive cycling performance and coulombic efficiency by virtue of the assistance from interlayer crystal water. The assembled Zn x MnO 2 //H 2 Ti 3 O 7 ·xH 2 O zinc-ion full battery delivers the decent electrochemical performance, especially a high output voltage of over 1 V. This low-potential, high-stable H 2 Ti 3 O 7 ·xH 2 O anode reveals the exceptional potential for aqueous zinc-ion full batteries. [ABSTRACT FROM AUTHOR]

We present a separator modification strategy to suppress polysulfide shuttle and accelerate polysulfide conversion through transition metal coordinated g-C 3 N 4 with crystalline carbons. The Li-S batteries with Ni-C 3 N 4 /C-modified separator manifest improved electrochemical performance even at high sulfur loading and lean electrolyte condition, due to catalytic effect. • Transition metal coordinated g-C 3 N 4 with crystalline carbons is prepared. • Hybrid nanosheets efficiently prevent polysulfide diffusion by absorption effect. • This structure endows the lean-electrolyte Li-S batteries higher capacity. • Cell with Ni-C 3 N 4 /C-modified separator exhibits the best electrochemical performances. Lithium-sulfur batteries have been regarded as promising energy storage candidates because of their high energy density and low cost. However, the low electrical conductivity of sulfur, infamous polysulfides shuttle and slow redox kinetics result in fast capacity fade and poor rate capabilities. To solve these barriers, herein a modification strategy of functional separator is presented by coating transition metal coordinated graphitic carbon nitride (g-C 3 N 4) with crystalline carbons (M-C 3 N 4 /C) on the surface of a commercial separator. The coating layer exhibits both satisfactory interception ability for polysulfides shuttle and fast polysulfides conversion ability. It has been found that the uniformly distributed transition metal on g-C 3 N 4 /C acts as an active center to regulate polysulfides behavior via strong chemisorption capability and high catalytic activity towards polysulfide conversion, while the transition metal-interface guarantees the rapid electron transfer, which can consequently facilitate the utilization of active sulfur species. Notably, after considerable assessments from density functional theory calculations, spectroscopy and electrochemical performances, it can be concluded that the Ni-C 3 N 4 /C can strongly bind polysulfides and expedite polysulfides conversion kinetics as well as promote electrons/ion transfer. As a result, the lithium-sulfur batteries with Ni-C 3 N 4 /C-modified separator can deliver 999 mAh g−1 at 0.5 A g−1 with high capacity retention of 89.4% after 300 cycles. Even at a great sulfur loading of 4.6 mg cm−2 and a low electrolyte/sulfur ratio of 6 µL mg−1, a large initial capacity of 724.6 mAh g−1 is still obtained at 1.0 A g−1. The separator reported in this work initiates the exploration of transition metals coordination as dynamic regulators of high-performance lithium-sulfur batteries and also reveals an understanding of the catalytic reactions. [ABSTRACT FROM AUTHOR]