•A strategy to prepare graphene ─ polypyrrole/sulfur ─ graphene electrode.•This sandwich-like structural paper shows excellent electrochemical performance.•This free-standing electrodes can satisfy these recent battery market demands.Lithium sulfur batteries have been regarded as next-generation battery technology due to its high energy density, environmental benignity and abundance. However, the poor electric/ionic conductivity of sulfur limits the practical use of sulfur in an electrode. The main problem is the high solubility of long-chain polysulfides, which are the intermediates of the electrochemical processes in the liquid electrolyte. The dissolved polysulfide ions shuttle between the cathode and anode, thus causing precipitation of insulating Li2S2/Li2S on the surface of the electrode. The unavoidable phenomenon results in loss of active materials and fast capacity fading. In this regard, we show one simple method to prepare free-standing paper electrode used as cathode material for lithium sulfur batteries. Binder-free graphene-polypyrrole (PPy)/S-graphene (G-PPy/S-G) paper-like sandwich structural electrode was prepared by using the vacuum filtration method. In this structure, the unique graphene layers of sandwich-like framework not only serve as a conductive film, but also effectively block the diffusion of polysulfides, leading to suppression of the shuttle effect and low self-discharge behaviour. In addition, the middle layer, the PPy nanofibers can limit the diffusion of dissolved polysulfides due to the special bond with sulfur, and furthermore maintain the structural stability of the paper electrode because the nanofibers can serve as elastic springs to accommodate the huge volume changes in charging-discharging processes. When tested as cathode for Li-S batteries, the as-prepared sample G-PPy/S-G exhibits excellent electrochemical performance. We believe that our strategy could provide a useful pathway towards commercial utilizing of sulfur.Download high-res image (248KB)Download full-size image

•The specific influence of calcination atmosphere (oxygen or air) on the structure, morphology and electrochemical properties of Ni-rich LiNi0.6Co0.2Mn0.2O2 material was individually investigated in detail.•The functional mechanism of oxygen instead of air atmosphere during heat-treatment on improving electrochemical performance of LiNi0.6Co0.2Mn0.2O2 was revealed using electrochemical charge/discharge test, EIS and XPS.Layered Ni-rich LiNi0.6Co0.2Mn0.2O2 (LNCMO) materials are prepared by calcining the mixture of Ni0.6Co0.2Mn0.2(OH)2 precursor (co-precipitation method) and Li salts (Li2CO3). Two different caicination atmosphere (air and oxygen) are adopted to obtain final two samples of LNCMO-A (air) and LNCMO-O (oxygen) to individually investigate the influence of oxygen instead of air atmosphere on the structure and electrochemical behavior of the LNCMO materials. Both two samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical charge/discharge tests including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). XRD and SEM results show the LNCMO-O sample possesses relatively smaller Li+/Ni2+ cation mixing, better layer-structure ordering and smaller primary particle size. The electrochemical charge/discharge test results show the LNCMO-O sample exhibits superior discharge capacity (184.6 mAh g−1 at 0.1C), higher cycling retention (91.4% after 100 cycles at 0.5C) and promoted rate performance. Further XPS, CV and EIS analyses on the promotion mechanism demonstrate that the oxygen-atmosphere calcination is important and beneficial to improve the electrochemical performance for Ni-rich LiNi0.6Co0.2Mn0.2O2 material.

In this work, Ni-doped manganite perovskite oxides (La0.8Sr0.2Mn1–xNixO3, x = 0.2 and 0.4) and undoped La0.8Sr0.2MnO3 were synthesized via a general and facile sol–gel route and used as bifunctional catalysts for oxygen cathode in rechargeable lithium–air batteries. The structural and compositional characterization results showed that the obtained La0.8Sr0.2Mn1–xNixO3 (x = 0.2 and 0.4) contained more oxygen vacancies than did the undoped La0.8Sr0.2MnO3 as well as a certain amount of Ni3+ (eg = 1) on their surface. The Ni-doped La0.8Sr0.2Mn1–xNixO3 (x = 0.2 and 0.4) was provided with higher bifunctional catalytic activities than that of the undoped La0.8Sr0.2MnO3. In particular, the La0.8Sr0.2Mn0.6Ni0.4O3 had a lower total over potential between the oxygen evolution reaction and the oxygen reduction reaction than that of the La0.8Sr0.2MnO3, and the value is even comparable to that of the commercial Pt/C yet is provided with a much reduced cost. In the lithium–air battery, oxygen cathodes containing the La0.8Sr0.2Mn0.6Ni0.4O3 catalyst delivered the optimized electrochemical performance in terms of specific capacity and cycle life, and a reasonable reaction mechanism was given to explain the improved performance.Keywords: oxygen evolution reaction; oxygen reduction reaction; oxygen vacancy; perovskite; rechargeable lithium−air battery

•LaNi1−xMgxO3 is used for bi-functional air electrode in Li–air batteries.•LaNi1−xMgxO3 has higher Ni3+/Ni2+ ratio and will absorb hydroxyl on the surface.•Higher initial capacities of LaNi1−xMgxO3 in Li–air batteries are reported.Mg-doped perovskite oxides LaNi1−xMgxO3 (x = 0, 0.08, 0.15) electrocatalysts are synthesized by a sol–gel method using citric acid as complex agent and ethylene glycol as thickening agent. The intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity of as-prepared perovskite oxides in aqueous electrolyte are examined on a rotating disk electrode (RDE) set up. Li–air primary batteries on the basis of Mg-doped perovskite oxides LaNi1−xMgxO3 (x = 0, 0.08, 0.15) and nonaqueous electrolyte are also fabricated and tested. In terms of the ORR current densities and OER current densities, the performance is enhanced in the order of LaNiO3, LaNi0.92Mg0.08O3 and LaNi0.85Mg0.15O3. Most notably, partially substituting nickel with magnesium suppresses formation of Ni2+ and ensures high concentration of both OER and ORR reaction energy favorable Ni3+ (eg = 1) on the surface of perovskite catalysts. Nonaqueous Li–air primary battery using LaNi0.92Mg0.08O3 and LaNi0.85Mg0.15O3 as the cathode catalysts exhibit improved performances compared with LaNiO3 catalyst, which are consistent with the ORR current densities.

Three kinds of Co3O4 nanomaterials with different morphologies were synthesized controllably by a post-anneal-assisted hydrothermal method in this study. X-ray diffraction and scanning electron microscopy indicated that all three kinds of samples were pure cubic phase of Co3O4 with morphologies of nanorods, nanoclusters, and nanoplates. Moreover, the transmission electron microscopy (TEM) and high-resolution TEM showed that the Co3O4 nanorods were bamboo-like and highly crystalline structures. When these materials were applied to the lithium-ion batteries (LIBs) as anode materials, the Co3O4 of nanorods demonstrated the best performance. It has a stable reversible capacity of 954 mAh g−1 as the anode of a LIB, much higher than the other two kinds of Co3O4 of rod-like nanoclusters and nanoplates, even after 35 cycles. All results showed that the morphology and microstructure take very important roles in the performance of Co3O4 as the anode materials in LIBs.

Sn–Co alloy films are deposited electrochemically directly onto nickel foam in an aqueous solution. The influence of electrochemical current density and heat treatment on the structure and morphology of the electrodeposited films is studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the Sn–Co alloy films are further investigated by galvanostatic charge–discharge tests. As anodes for lithium ion batteries, the Sn–Co alloy-film anodes, after further heat treatment at 200 °C for 30 min, delivers a specific capacity of 663 mAh g−1 after 60 cycles. This high capacity retention is attributed to the unique electrode configuration with an enhanced interface strength between the active material and the current collector formed in the heat-treatment process.Highlights► Sn–Co alloy film is used as anode in Li-ion batteries. ► Sn–Co alloy film is deposited electrochemically directly onto nickel foam. ► This Ni foam supported Sn–Co anode can buffer the large volume change during lithium insertion and extraction. ► Heat treatment can furtherly improve the electrochemical properties.

Exfoliation from multiwalled carbon nanotubes (MWCNTs) during electrochemical insertion of lithium is shown to depend on the inner diameter of the tubes and the wall thickness. Those with core diameters of 10 nm and walls 5 nm thick showed no incorporation of solvated Li+ ions into the core and exfoliation as a result of solvated Li+ ions entering the walls; those with core diameters of 40 nm with walls 30 nm thick showed no exfoliation in an electrolyte based on ethylene carbonate (EC) and little exfoliation even in electrolytes based on propylene carbonate (PC). Exfoliation of graphene layers from a MWCNT on lithium insertion depends not only on the size of the solvated Li+ ions, but also on the concentration of the solvated Li+ ions between the graphene layers in the walls.

•We proposed a method to prepare Sr-doped perovskite oxide La1-xSrxMnO3 for Li-O2 batteries.•The Sr-doped perovskite oxide demonstrates enhanced catalytic effects as catalyst for lithium air batteries.•To understand the superior catalytic effect, we conducted relative measurements to study the ORR/OER.Strontium (Sr)-doped perovskite oxide La1-xSrxMnO3 (x = 0, 0.2, 0.6) composites are prepared by sol-gel process assisted with chelating effect of citric acid, which was used as catalysts for oxygen cathode in rechargeable lithium−air batteries. Sr-doped perovskite oxide La1-xSrxMnO3 composites demonstrate higher catalytic activities than that of the pure LaMnO3. In particular, the La0.4Sr0.6MnO3 had a lower total over potential between the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) than that of the La0.8Sr0.2MnO3 and LaMnO3 .When the Li-O2 cells were tested at the current density of 50 mA g−1, the discharge capacities of the oxygen cathode with different La1-xSrxMnO3 (x = 0, 0.2, 0.6) catalysts were 3573, 4408, and 5624 mA h g−1，respectively. Additionally, the cell employed La0.4Sr0.6MnO3 as catalyst can be cycled at a limited capacity of 200 mA h g−1 for about 71cycles, which is much higher than the 42 cycles for LaMnO3 electrode.