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Spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode candidate for the next‐generation high energy‐density lithium‐ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site‐selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fd3‾ m structure. This site‐selective doping not only suppresses unfavorable two‐phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg‐doped LNMOs exhibit extraordinarily stable electrochemical performance in both half‐cells and prototype full‐batteries with novel TiNb2O7 counter‐electrodes. This work pioneers an atomic‐doping engineering strategy for electrode materials that could be extended to other energy materials to create high‐performance devices. [ABSTRACT FROM AUTHOR]

Li-rich layered oxides have been regarded as valuable cathode materials for high energy density lithium-ion batteries. However, high initial irreversible capacity, bad rate capability, as well as serious capacity fading and voltage decay hinder their commercial application. In this paper, a nano CoF 2 protective layer is coated on the surface of Li 1.2 Ni 0.2 Mn 0.6 O 2 via a facial wet chemistry method. A high initial discharge capacity of 264.4 mAh g −1 is obtained for 0.5% CoF 2 -coated sample and 259.1 mAh g −1 for 1% CoF 2 -coated sample owing to the suppression of irreversible release of O 2 and the contribution of electrochemical conversion of CoF 2 /LiF. Furthermore, 1% CoF 2 -coated sample exhibits the excellent rate capability of 167.5 mAh g −1 at 5 C rate, the superior cycling stability with the capacity retention of 241.0 mAh g −1 and the ameliorative voltage drop of 0.312 V at 0.1C after 100 cycles. The enhanced rate performance as well as stability of capacity and voltage can be attributed to the nano coatings which inhibit the electrolyte-electrode side reaction, enhance the electrochemical kinetics and mitigate structure transition from layered to spinel phase. [ABSTRACT FROM AUTHOR]

• We developed an all-solid-state flexible micro-supercapacitor with 145 mF cm−2 areal capacitance and 20.14 μWh cm−2 energy density. • A hierarchical porous carbon material was prepared by a facile method, which was then utilized in 3D-printed micro-supercapacitors. • Hierarchical porous structure can facilitate ion diffusion of supercapacitors and deliver high energy density. • Hierarchical porous carbon material is cheaper and delivers better performance than commonly used electrode materials such as graphene and carbon nanotubes, promoting the commercialization of micro-supercapacitors. Porous carbon proves a crucial electrode material for micro-supercapacitors (MSCs) due to its favourable electrical conductivity, along with chemical and thermal stability. Nevertheless, the low area accessible to ions and the long electron diffusion paths commonly result in a low energy density for carbon-based MSCs. Here, an alga-based carbon sieve with an interconnected and hierarchical porous structure was prepared and employed as the electrode material to construct MSCs by 3D printing. The interconnected and hierarchical structure facilitates electrolyte diffusion and ion transport, resulting in a high specific capacitance of 145 mF cm−2 and an impressive energy density of 20.14 μWh cm−2 for the MSC. Moreover, the device exhibits excellent mechanical properties and long cycle life. These findings demonstrate the potential of devices for application in microelectronic devices. [ABSTRACT FROM AUTHOR]

The functional combination of riboflavin and activated carbon successfully introduced a significant redox reaction in the activated carbon, increasing the specific capacitance of the material and significantly improving the rate performance. Potential control significantly enhances the cycling stability of AC/VB2. [Display omitted] • AC/VB2 has a low charge/discharge plateau of −0.65 to −0.9 V (vs. Hg/HgO). • AC/VB2 as a negative electrode shows high specific capacitance (419.1 F g−1) and outstanding rate performance. • Potential control significantly enhances the cycling stability of AC/VB2. • An AC/VB2(–)||LDH(+) device delivers a high energy density of 58.5 Wh kg−1 and a high power density of 27,410 W kg−1. Pseudocapacitive materials are used to increase the energy density of supercapacitors, but their rate performance and cycling stability are frequently unsatisfactory. Herein, we report a riboflavin-functionalized activated carbon (AC/VB2) as a negative electrode with high specific capacitance (419.1 F g−1) and outstanding rate performance. The potent combination of VB2 and AC renders VB2 insoluble in alkaline liquids and fully exploits its redox characteristics. VB2 contributes additional redox reactions to AC and its reaction plateau is from −0.65 to −0.9 V (vs. Hg/HgO), favoring the storage of large amounts of energy. Based on the detailed analysis of the surface state of the material during the reaction, a strategy to improve cycling stability by controlling the charge/discharge potential window is proposed, which can effectively inhibit the desorption and overreaction of VB2, thus greatly enhancing cycling stability. The electrode can be operated stably for 100,000 cycles without any decline at high current densities. An AC/VB2(–)||LDH(+, Co-doped Ni(OH) 2) device delivered a high energy density of 58.6 Wh kg−1 at a power density of 686 W kg−1 and a high power density of 27,410 W kg−1 at an energy density of 13.2 Wh kg−1. This work offers a practical manual for making high–energy pseudocapacitive negative electrodes and enhancing their cycling stability. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) batteries have attracted enormous attentions as new-generation energy storage devices due to their high theoretical energy density, high theoretical specific capacity, low cost and environmental friendliness. However, polysulfide shuttle and the growth of lithium dendrites significantly restrain the practical application of the Li-S batteries. In this work, a modified PP separator with nanoscale rod-like α-MnO 2 supported on carbon nanotubes was prepared. The α-MnO 2 @CNT modified separator can effectively inhibit the shuttle of polysulfide, enhance the electrochemical activity and accelerate the transfer of ions and electrons. The density functional theory (DFT) calculations demonstrate that α-MnO 2 @CNT can efficiently adsorb and catalyze the conversion of polysulfides. Due to these advantages, the α-MnO 2 @CNT-based Li-S battery delivers a initial discharge capacity of 1469 mAh g−1 at 0.05 C, 1039 mAh g−1 at 0.5 C and the capacity can still maintain 648 mAh g−1 over 500 cycles at 0.5 C (capacity decay rate of 0.075%). Expressly, the capacity decay rate is only 0.022% after 600 cycles at a high current density of 2 C. The excellent performance could be attributed to the α-MnO 2 @CNT modified separator not only accelerating the transmission of electrons but also effectively inhibiting the shuttle of polysulfides. Moreover, this work provides a better idea for practical applications of lithium-sulfur batteries in the future. [Display omitted] • The synthesized α-MnO 2 is in the shape of nanorods. • The α-MnO 2 @CNT composite has good polysulfide adsorption and catalytic conversion ability. • The α-MnO 2 @CNT modified separator shows an excellent long-term cycling stability and rate performance. [ABSTRACT FROM AUTHOR]

The functional combination of methylene blue and activated carbon successfully introduced a significant redox reaction in the activated carbon, increasing the specific capacitance of the material and significantly improving the rate performance. The methylene blue adsorbed on the surface of activated carbon enables fast proton-coupled electron transfer. [Display omitted] • Anthracite can be activated at low temperature and show large specific surface area. • Oxygen groups could effectively contribute the pseudo-capacitance to AC. • The π-π binding endows AC/MB excellent electrochemical properties. • The optimized AC/MB as positive can deliver ultrahigh energy and power density. • Mathematical simulation can optimize the ratio of positive to negative electrodes. Supercapacitors are desired to deliver high power and energy density concurrently, and the introduction of a redox reaction is an effective strategy to improve their capacitive performance. Herein, methylene blue (MB) with redox was employed to functionalize coal-based activated carbons (ACs) as electrode materials for energy storage. The optimized AC shows a high specific capacitance of 408.1 F g−1 in 6 M KOH, deriving from the contribution of the electrical double-layer capacitance of pores and pseudocapacitance of oxygen groups. Interestingly, pure MB shows no capacitive performance mainly due to its low conductivity, while the optimized composite of AC adsorbed MB (AC/MB) surpasses the pure MB and optimized AC in any capacitive performance, displaying a relationship of mutual promotion based on functional combination. The best AC/MB sample exhibits a high specific capacitance of 431.8 F g−1 at 1 A g−1, and 356.1 F g−1 (82.5%) at an ultrahigh current density of 180 A g−1, implying an excellent rate performance. Aiming to deliver maximum energy density, an accurate universal method is proposed to match the mass ratio of negative to positive. The optimized asymmetric supercapacitor AC/MB(+) || AC(-) delivers an energy density of 11.0 Wh kg−1, a power density up to 15.3 kW kg−1 and a high capacity retention rate of 96.3% after 10,000 cycles, displaying good chemical stability. This work proposes a promising strategy for ultrafast store/release energy at high energy density, and also provides an application direction for AC and MB. [ABSTRACT FROM AUTHOR]

• The power density of the activated carbon reached 8.8 Wh ∙ kg−1 at 0.25 kW ∙ kg−1. • The activated carbons are rich in carbonyl groups and quinone type oxygen. • The oxygen-rich activated carbons were prepared without oxidation by strong acid. • The fluxing effect of KOH as activation agent was discovered for the first time. Heteroatom-doped activated carbons are ideal materials for energy storage devices. In this work, a series of nitrogen/oxygen codoped activated carbons with an inverse opal-like structure derived from cellulose diacetate are successfully synthesized through hydrothermal reaction and subsequent chemical activation during which the fluxing effect of KOH is discovered for the first time. The introduction of nitrogen and intrinsic oxygen (especially carbonyl and quinone groups) contributes to additional pseudocapacitance. The experimental results show that the obtained product delivers 400.3 F · g−1 at a current density of 1 A · g−1 in a three-electrode system and achieves extraordinary capacity retention of 90% after 10,000 charge-discharge cycles at 5 A · g−1. The energy density reaches as high as 8.8 Wh · kg−1 at a power density of 0.25 kW · kg−1 as symmetric supercapacitors, indicating a promising electrode material for high performance supercapacitors. The simple and cost-effective method requires no extra oxidation and excessive urea and thus provides new approaches for the future design of electrode materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Ce-doped MnO 2 was prepared by the potentiostatic electrodeposition strategy. • The assembled flexible Zn//Ce-MnO 2 @CC battery exhibits long cycle-life. • The doped cerium ions could stabilize the structure of the cathode materials. • A H+/Zn2+ co-insertion mechanism of the Mn-based oxides cathode was demonstrated. With the development of flexible electronic devices, power sources' higher safety, lighter, and bending ability have been demanded in recent years. While, aqueous zinc-ion batteries (ZIBs) have gained much attention due to their low cost, rich zinc resources, and high safety. Hence, they have been considered the most promising secondary battery in the near future. However, the practical application of aqueous ZIBs is still impeded by the unsatisfied performance of the cathode materials and the complex manufacturing process. Moreover, the electrochemical energy storage process and mechanism of the cathodes at the flexible ZIBs still remain ambiguous and under discussion, which severely limited the development of the ZIBs. Herein, a Ce doped-MnO 2 binder-free cathode electrode was prepared via a one-step potentiostatic electrodeposition strategy. A flexible ZIB assembled based on the Ce-MnO 2 @CC cathode and a homemade gel electrolyte exhibits a high reversible specific capacity (∼311 mAh g−1), a significant energy density (370 Wh kg−1), an excellent stability performance, and achieves good electrochemical behavior even under different bending conditions. Furthermore, the energy storage mechanism of the flexible ZIBs with Mn-based oxides cathode was monitored by the in-situ Raman, XRD, SEM, and TEM, revealing the reversible insertion/extraction of Zn2+ and H+ during the charge/discharge process. Moreover, the results also demonstrate that the structural shedding, and dissolution of the MnO 2 structure are the major factors in reducing capacity. This research opens up new opportunities for flexible ZIBs in the field of portable and wearable electronics. [ABSTRACT FROM AUTHOR]

Porous activated carbon material is successfully prepared with anthracite through KOH activation. The obtained activated carbon delivers a large specific surface area of 3550.7 m2 g−1 with existence of porous structure. The KOH activation introduces numerous hydroxyl groups on the surface of carbon material, improving the wettability of carbon. As electrode for supercapacitor, the material delivers the high specific capacity of 433 F g−1 at the current density of 0.5 A g−1 and it maintains 230 F g−1 even current density reaches up to 50 A g−1. Especially, as electrode for symmetric capacitor, the porous activated carbon exhibits a high specific capacitance of 280 F g−1 and energy density of 38.9 Wh kg−1 at 0.5 A g−1. The material also displays superior cyclic stability without distinct decay in capacity after 30000 cycles. The porous activated carbon material derived from coal, which embodies characteristics of capacitance behavior, may broaden the horizon of electrode materials and provide application prospect for specialized hybrid supercapacitor applications. Image 1 • The activated carbon produced by anthracite reveals porous microstructure. • The material delivers an ultrahigh specific surface area of 3550.7 m2 g−1. • The material delivers the high energy density of 38.9 Wh kg−1 at 0.5 A g−1. • The facile prepared route provides the train of thought for practical application. [ABSTRACT FROM AUTHOR]

• A high-efficient and cost-effective direct methanol fuel cell is proposed. • The peak power density is higher than both electrodes with noble catalysts. • Faradic efficiency of 85.1% and energy efficiency of 42.2% were obtained. • Enhanced O 2 adsorption and transfer capacity were obtained on cathode. • The half-wave potential of Fe 2 O 3 /Mn 2 O 3 outperforms commercial Pt/C. The development of power density and energy conversion efficiency of direct methanol fuel cells (DMFCs) is of great significance. This study presents a high-efficiency passive DMFC consisting of hetero-structured Fe 2 O 3 /Mn 2 O 3 as the cathode catalyst, PtRu/C as the anode catalyst and polymer fiber membrane (PFM) as the electrolyte membrane. The peak power densities reached up to 60.6, 121.2 and 186.6 mW cm−2 at 20, 50 and 70 °C, respectively, which was approximately 2.7 times greater than a normal cell composed of commercialized Nafion membrane and Pt/C cathode catalyst at 20 °C. Faradic efficiency of 85.1% and energy efficiency exceeding 42.2% were obtained. Herein, Fe 2 O 3 /Mn 2 O 3 displays framework structure with edge lengths of 1 to 2 μm homogeneous micro-cubes. A synergistic effect between α-Fe 2 O 3 and α-Mn 2 O 3 matrix in Fe 2 O 3 /Mn 2 O 3 significantly enhances its oxygen reduction reaction (ORR) catalyzed activity. α-Fe 2 O 3 with abundant oxygen vacancies could store and release O 2 through the transformation of Fe3+/Fe2+ redox couple. The three-dimensional mesoporous channel structure of Fe 2 O 3 /Mn 2 O 3 could act as effective mass transfer reactors, in which O 2 and electrolyte is uninhibited accessed to active sites. On the other hand, numerous heterogeneous interfaces can boost electron transfer efficiency, which is investigated using the electron transfer number, narrow band gap and lower charge transfer resistance. The output performance and the energy conversion efficiency of DMFCs is considerably improved through boosting oxygen and charge transfer capability in cathode. Overall, our result provides a promising strategy to fabricate high-efficient and cost-effective fuel cells for the enhanced power conversion. [ABSTRACT FROM AUTHOR]