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Lithium-oxygen (Li-O 2) batteries are facing challenges in capacity, cycling stability, and kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Advanced catalysts should have a high and bifunctional catalytic activity for ORR and OER. Moreover, the trade-off carbon in catalysts should have good oxidation resistance and high electronic conductivity and be used in a tiny amount. Up to now, it is still a challenge. Therefore, this work introduces a low-carbon CeO x /Ru@RuO 2 nanosheet as efficient cathode catalysts for Li-O 2 batteries and studies the preparation and working mechanisms using a variety of characterization and electrochemical techniques. The air oxidation treatment oxidizes Ru into Ru@RuO 2 and simultaneously removes unstable C into CO 2, leaving a tiny amount of stable carbon. CeO x /Ru@RuO 2 has enormous mesopores, well-distributed sub-5 nm CeO x and Ru@RuO 2 nanocrystals, a tiny amount of anti-oxidation carbon (1.2 %), and a high specific surface area of 159.3 m² g−1. These aspects optimize the Li-O reaction and regulate the Li 2 O 2 nucleation to form uniform and ultrathin Li 2 O 2 nanoflakes. As a result, the ORR and OER overpotentials are only 0.17 V and 0.45 V, respectively. This work provides a novel material combination and structure design for developing bifunctional catalyst materials in Li-O 2 batteries. [Display omitted] • Sub-5 nm CeO x and Ru@RuO 2 and 1.2 % carbon form a mesoporous nanosheet. • The nanosheet (~25 nm thick) has massive mesopores and specific surface area. • The average ORR and OER overpotentials are 0.17 V and 0.65 V, respectively. • The nanosheet optimizes the Li-O reaction to form ultrathin Li 2 O 2 nanoflakes. [ABSTRACT FROM AUTHOR]

BiSe has recently emerged as a new promising Te-free thermoelectric material due to its superlattice structure and intrinsic low thermal conductivity. However, the inherent high carrier concentration of BiSe limits its thermoelectric performance. In this paper, Ag and Na were doped in polycrystalline BiSe to tune its thermoelectric transport properties. A series of Ag-doped and (Ag, Na) co-doped samples were synthesized via solid-phase sintering method and spark plasma sintering (SPS). It is found that Ag doping can effectively reduce the lattice thermal conductivity of BiSe, thereby reducing the total thermal conductivity, which increases the ZT value of Bi 0.97 Ag 0.03 Se from 0.24 to 0.28. Along with the co-doping of 1% Na, the carrier concentration of the (Ag, Na) co-doped sample effectively reduces from 32 × 1019 cm−3 to 6 × 1019 cm−3, while the mobility greatly increases, so that the electrical conductivities are maintained in a high range, and the Seebeck coefficients are slightly increased. A maximum ZT value of 0.31 at 523 K is achieved in Bi 0.96 Ag 0.03 Na 0.01 Se along the SPS pressing direction as a result of the higher power factor and lower total thermal conductivity, which is about 30% higher than that of undoped BiSe. • (Ag, Na) co-doping optimizes thermal and electrical transport simultaneously. • Ag dopant prefers to occupying the Bi site of Bi2Se3 quintuple layers. • A 30% promotion of ZT value for (Ag, Na) co-doped BiSe is achieved. [ABSTRACT FROM AUTHOR]

● A facile sol-gel method is first proposed to synthesize NASICON-type Li 2 Zn 2 (MoO 4) 3 and Li 2 Cu 2 (MoO 4) 3. ● Rietveld refinement indicated the structure evolution in Cu-doped Li 2 Zn 2−x Cu x (MoO 4) 3. ● The Li 2 Zn 2 (MoO 4) 3 and Li 2 Cu 2 (MoO 4) 3 electrode display excellent lithium storage performance. ● In-situ XRD confirmed the existence of mesophase Li 4 MoO 5 in Li 2 M 2 (MoO 4) 3 (M=Zn, Cu) during the initial lithium insertion. NASICON (Na superionic conductor) type electrode materials are known for their wide range of electrochemical potentials, high ionic conductivity, and most importantly their structural and thermal stabilities. Li 2 M 2 (MoO 4) 3 (M=Zn, Cu), belonging to molybdenum-based NASICON family, are successfully synthesized by simple sol-gel method. The structure evolution caused by the substitution of Zn2+ by Cu2+ within Li 2 Zn 2- x Cu x (MoO 4) 3 (0 ≤ x ≤ 2) has been investigated. Rietveld refinement results reveals that the priority order of copper atoms replacing zinc atoms in Li 2 Zn 2 (MoO 4) 3. Furthermore, both Li 2 Zn 2 (MoO 4) 3 and Li 2 Cu 2 (MoO 4) 3 electrodes deliver excellent electrochemical performance, and high reversible capacities of 864 mAh g−1 and 747 mAh g−1 can be acquired at a current density of 0.1 A g−1, respectively. In addition, the in-operando X-ray diffraction measurements indicate the formation of cubic mesophase Li 4 MoO 5 both in Li 2 Zn 2 (MoO 4) 3 and Li 2 Cu 2 (MoO 4) 3 during the initial lithium insertion, which irreversibly converts into the amorphous phases on further discharge at subsequent discharge and charge process. [ABSTRACT FROM AUTHOR]

Herein, pure orthorhombic LiMnO 2 (o-LiMnO 2) was prepared via a one-step and short time EDTA-2Na assisted dynamic hydrothermal method, in which the electrolytic MnO 2 and C 4 H 6 MnO 4 ·4H 2 O were used as manganese source. The effects of EDTA-2Na concentration, hydrothermal temperature and stirring rate on the purity of o-LiMnO 2 were investigated. EDTA-2Na served as both chelating reagent and reductant, the oxidation of Mn2+ before reaction and the formation of Li 2 MnO 3 by residual oxygen in reaction system were suppressed due to coordination and reduction effects of EDTA-2Na, respectively. Furthermore, the solid-liquid reaction kinetics could be accelerated by stirring, then final expected pure phase o-LiMnO 2 was generated in short time and a low alkali concentration. The obtained product showed high crystallinity with an average diameter of 200–500 nm. When utilized as a lithium ion battery cathode material, the o-LiMnO 2 could deliver a high capacity of 166.1 mAh g−1 at 0.1 C at the voltage range of 2.0–4.5 V. • The pure orthorhombic LiMnO 2 can be prepared via a facile one-step dynamic hydrothermal method with MnO 2 as precursor. • EDTA-2Na serves as both chelating reagent and reductant in reaction system to minimize the impurities in final product. • o-LiMnO 2 delivers initial capacity of 166.1 mAh g−1 at 0.1 C and achieves 87% capacity retention rate after 50 cycles. [ABSTRACT FROM AUTHOR]

Due to the limited resources of lithium source and their high price, lithium-ion batteries (LIBs) cannot meet the demands of future large-scale energy storage. Sodium-ion batteries (SIBs) with advantages of the abundant sodium resources and low cost, are one of the most promising alternatives to LIBs. Here, we firstly synthesize a new manganese-based polyanionic compound (Na 3 Mn 2 P 3 O 11) through a simple sol-gel method. The resolved crystal structure indicates that single-phase Na 3 Mn 2 P 3 O 11 compound belongs to the orthorhombic structure. When tested as for cathodes, it displays a poor electrochemical performance with a potential window of 1.8–4.3 V (versus Na/Na+), caused by the Jahn-Teller effect of Mn3+ generated during charging process. In this context, a series of Fe-doped Na 3 Mn 2-x Fe x P 3 O 11 (0.1 ≤ x ≤ 0.5) are prepared to improve the electrochemical performance. Results indicate that Fe substitution of Mn in Na 2 Mn 2-x Fe x P 3 O 11 structure can not only enhance the electrochemical performance, but also increase conductivity and achieve fast reaction kinetics. Noticeably, when iron-doped amount is 0.4, Na 3 Mn 1.6 Fe 0.4 P 3 O 11 exhibits the best cycling (62.7 mA h g−1 at 0.1 C over 100 cycles) and rate performance (19.7 mA h g−1 at 5 C). A novel manganese-based polyanionic compound (Na 3 Mn 2 P 3 O 11) was successfully prepared via a simple sol-gel way, which belongs to orthorhombic system (space group P 2 1 2 1 2 1). The reasonably small Rp and Rwp factors of the Rietveld refinement reveal that single phase can be obtained, and no impurity phases can be detected in Fe-doped Na 3 Mn 2-x Fe x P 3 O 11 (0 ≤ x ≤ 0.5). Moreover, when iron-doped amount is 0.4, it exhibited the best cycling and rate performance. Image 1 • Na 3 Mn 2 P 3 O 11 (space group P 2 1 2 1 2 1) was firstly prepared via a simple sol-gel method. • Rietveld refinement proved existence of Na 3 Mn 2-x Fe x P 3 O 11 (x = 0–0.5) solid solution. • Carbon-coated Fe-doped samples were prepared to improve electrochemical property. • Na3Mn1.6Fe0.4P3O11@C shows a capacity of 62.7 mA h g−1 at 0.1 C over 100 cycles. [ABSTRACT FROM AUTHOR]