Hierarchical and Highly Stable Conductive Network Cathode for Ultraflexible Li–S Batteries

Flexible Li–S batteries have great potential for next-generation energy storage which can meet the rising demand of rollable displays and wearable electronic devices because of the high theoretical energy density and competitive price. Here, we design and fabricate an integrated electrode with hierarchical structure and interconnected 3D conductive networks as a cathode of flexible Li–S batteries. The composite cathode exhibits high electrochemical performance and cycling stability. The initial reversible discharge capacity is 1312 mA h g^–1 at 0.2 C with sulfur load 2.0 mg cm^–2, and the capacity decay rate is 0.09% per cycle within 500 cycles at current of 1 C. Notably, the composite electrode can sustain 15.2 MPa stress with 10% strain and retain structural integrity after 200 000 bending cycles, the highest number of bending cycles found to date for any flexible S cathodes. The soft package batteries with different sizes and shapes are fabricated, and they exhibit extraordinary flexibility and stability after bending and flattening over 2100 times. Moreover, their potential applications in rollable displays, flexible lighting, and wearable electronic devices are also investigated

Binary Mixtures of Highly Concentrated Tetraglyme and Hydrofluoroether as a Stable and Nonflammable Electrolyte for Li–O₂ Batteries

Developing a long-term stable electrolyte is one of the most enormous challenges for Li–O₂ batteries. Equally, the high flammability of frequently used solvents seriously weakens the electrolyte safety in Li–O₂ batteries, which inevitably restricts their commercial applications. Here, a binary mixture of highly concentrated tetraglyme electrolyte (HCG4) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) was used for a novel electrolyte (HCG4/TTE) in Li–O₂ batteries, which exhibit good wettability, enhanced ionic conductivity, considerable nonflammability, and high electrochemical stability. Being a co-solvent, TTE can contribute to increasing ionic conductivity and to improving flame retardance of the as-prepared electrolyte. The cell with this novel electrolyte displays an enhanced cycling stability, resulting from the high electrochemical stability during cycling and the formation of electrochemically stable interfaces prevents parasitic reactions occurring on the Li anode. These results presented here demonstrate a novel electrolyte with a high electrochemical stability and considerable safety for Li–O₂ batteries

Hierarchical and Highly Stable Conductive Network Cathode for Ultraflexible Li–S Batteries

Flexible Li–S batteries have great potential for next-generation energy storage which can meet the rising demand of rollable displays and wearable electronic devices because of the high theoretical energy density and competitive price. Here, we design and fabricate an integrated electrode with hierarchical structure and interconnected 3D conductive networks as a cathode of flexible Li–S batteries. The composite cathode exhibits high electrochemical performance and cycling stability. The initial reversible discharge capacity is 1312 mA h g^–1 at 0.2 C with sulfur load 2.0 mg cm^–2, and the capacity decay rate is 0.09% per cycle within 500 cycles at current of 1 C. Notably, the composite electrode can sustain 15.2 MPa stress with 10% strain and retain structural integrity after 200 000 bending cycles, the highest number of bending cycles found to date for any flexible S cathodes. The soft package batteries with different sizes and shapes are fabricated, and they exhibit extraordinary flexibility and stability after bending and flattening over 2100 times. Moreover, their potential applications in rollable displays, flexible lighting, and wearable electronic devices are also investigated

3D Foam-Like Composites of Mo₂C Nanorods Coated by N‑Doped Carbon: A Novel Self-Standing and Binder-Free O₂ Electrode for Li–O₂ Batteries

The development of self-standing and binder-free O₂ electrodes is significant for enhancing the total specific energy density and suppressing parasitic reactions for Li–O₂ batteries, which is still a formidable challenge thus far. Here, a three-dimensional foam-like composite composed of Mo₂C nanorods decorated by different amounts of N-doped carbon (Mo₂C-NR@<i>x</i>NC (<i>x</i> = 5, 11, and 16 wt %)) was directly employed as the O₂ electrode without applications of any binders and current collectors. Mo₂C-NR@<i>x</i>NC presents a network microstructure with interconnected macropore and mesoporous channels, which is beneficial to achieving fast Li⁺ migration and O₂ diffusion, facilitating the electrolyte impregnation, and providing enough space for Li₂O₂ storage. Additionally, the coated N-doped carbon layer can largely improve the electrochemical stability and conductivity of Mo₂C. The cell with Mo₂C-NR@11NC shows a considerable cyclability of 200 cycles with an overpotential of 0.28 V in the first cycle at a constant current density of 100 mA g^–1, a superior reversibility associated with the formation and decomposition of Li₂O₂ as desired, and a high electrochemical stability. On the basis of the experimental results, the electrochemical mechanism for the cell using Mo₂C-NR@11NC is proposed. These results represent a promising process in the development of a self-standing and binder-free foam-based electrode for Li–O₂ batteries

Insights into Electrochemistry and Mechanical Stability of α- and β‑Li₂MnP₂O₇ for Lithium-Ion Cathode Materials: First-Principles Comparison

With the aid of first principle calculations, structural characteristics, mechanical stability, and electronic and electrochemical properties of two polymorphs of manganese-based pyrophosphate α- and β-phases of Li₂MnP₂O₇ and their relevant delithiated structures are explored for comparison. Our results indicate that, although these two polymorphs of Li₂MnP₂O₇ belong to the monoclinic space group, considerable differences are discovered in Mn local environment of crystal structures. The cell voltage vs Li/Li⁺ are 4.68 and 4.16 V for α- and β-phases of the Li₂MnP₂O₇/LiMnP₂O₇ platform, respectively, comparable to the experimental values (4.45 and 4.00 V) for first voltage plateaus. All of the lithium atoms are practically fully ionized in the α- and β-Li₂MnP₂O₇ and their relative half delithiated states, charge transfer mainly concentrated upon Mn and O, which leads to the oxidization state of Mn from Mn²⁺ to Mn³⁺ and then from Mn³⁺ to Mn⁴⁺. The band gaps of delithiated configurations decrease gradually with removing lithium ions, and the conductivity changed from insulator nature to conductor characteristic. By the elastic properties calculations, the Pugh ratios (<i>B/G</i>) are 3.28 and 2.86 for the α- and β-Li₂MnP₂O₇, respectively, indicating their high mechanical stability. However, small <i>B/G</i> values are observed for the relevant delithiated phases. In addition, Young’s modulus (<i>E</i>) and Poisson’s ratio (ν) for α- and β-phases of Li₂MnP₂O₇ and their delithiated configurations are also presented to explore the hardness and bond characteristics

Multiporous MnCo₂O₄ Microspheres as an Efficient Bifunctional Catalyst for Nonaqueous Li–O₂ Batteries

Multiporous MnCo₂O₄ microspheres are fabricated via the solvothermal method followed by pyrolysis of carbonate precursor to demonstrate excellent bifunctional catalytic activity toward both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Because of this multiporous structure, the resulting MnCo₂O₄ microspheres show an efficient electrocatalytic performance in LiTFSI/TEGDME electrolyte-based Li–O₂ batteries. MnCo₂O₄ microspheres as the air cathode deliver better performance during the discharging and charging processes and good cycle stability compared with that of the Super P. This preliminary result manifests that multiporous MnCo₂O₄ microspheres are promising cathode catalysts for nonaqueous Li–O₂ batteries

Porous Carbon with Willow-Leaf-Shaped Pores for High-Performance Supercapacitors

A novel kind of biomass-derived, high-oxygen-containing carbon material doped with nitrogen that has willow-leaf-shaped pores was synthesized. The obtained carbon material has an exotic hierarchical pore structure composed of bowl-shaped macropores, willow-leaf-shaped pores, and an abundance of micropores. This unique hierarchical porous structure provides an effective combination of high current densities and high capacitance because of a pseudocapacitive component that is afforded by the introduction of nitrogen and oxygen dopants. Our synthetic optimization allows further improvements in the performance of this hierarchical porous carbon (HPC) material by providing a high degree of control over the graphitization degree, specific surface area, and pore volume. As a result, a large specific surface area (1093 m² g^–1) and pore volume (0.8379 cm³ g^–1) are obtained for HPC-650, which affords fast ion transport because of its short ion-diffusion pathways. HPC-650 exhibits a high specific capacitance of 312 F g^–1 at 1 A g^–1, retaining 76.5% of its capacitance at 20 A g^–1. Moreover, it delivers an energy density of 50.2 W h kg^–1 at a power density of 1.19 kW kg^–1, which is sufficient to power a yellow-light-emitting diode and operate a commercial scientific calculator

Porous Carbon with Willow-Leaf-Shaped Pores for High-Performance Supercapacitors

A novel kind of biomass-derived, high-oxygen-containing carbon material doped with nitrogen that has willow-leaf-shaped pores was synthesized. The obtained carbon material has an exotic hierarchical pore structure composed of bowl-shaped macropores, willow-leaf-shaped pores, and an abundance of micropores. This unique hierarchical porous structure provides an effective combination of high current densities and high capacitance because of a pseudocapacitive component that is afforded by the introduction of nitrogen and oxygen dopants. Our synthetic optimization allows further improvements in the performance of this hierarchical porous carbon (HPC) material by providing a high degree of control over the graphitization degree, specific surface area, and pore volume. As a result, a large specific surface area (1093 m² g^–1) and pore volume (0.8379 cm³ g^–1) are obtained for HPC-650, which affords fast ion transport because of its short ion-diffusion pathways. HPC-650 exhibits a high specific capacitance of 312 F g^–1 at 1 A g^–1, retaining 76.5% of its capacitance at 20 A g^–1. Moreover, it delivers an energy density of 50.2 W h kg^–1 at a power density of 1.19 kW kg^–1, which is sufficient to power a yellow-light-emitting diode and operate a commercial scientific calculator