Reinforced Conductive Confinement of Sulfur for Robust and High-Performance Lithium-Sulfur Batteries

Tailoring 3D Carbon Foam using CNTs and MnO2 to Fabricate Stable Lithium/Dissolved Lithium Polysulfide Batteries

The lithium-sulfur (Li-S) battery is an ideal electrochemical energy storage system owing to the high theoretical energy density and acceptable cost of finance and the environment. However, some disadvantages, including low electrical conductivity, poor sulfur utilization, and rapid capacity fading, obstruct its practical application. In this work, 3D carbon foam from a melamine resin is synthesized via high-temperature calcination. Carbon nanotubes (CNTs) and MnO₂ are utilized to tailor the properties of the 3D cathode collector in the liquid Li₂S₆-containing Li-S battery without additional conductive agents, binders, and aluminum foil. Herein, the decorated MnO₂ on the carbon fiber foam prolongs the lifespan of the Li-S battery, and adding CNTs is beneficial to enhance the capacity and cyclic performance of the Li-S battery under high sulfur loading. The Li-S battery with a sulfur loading of 3 mg cm^-2 possesses a reversible capacity of 437.9 mA h g^-1 after 400 cycles at 0.1 C. The capacity could be maintained at 568 mA h g^-1 at 0.1 C after 80 cycles when the sulfur loading increases to 6 mg cm^-2.

Suppressing the Shuttle Effect and Dendrite Growth in Lithium-Sulfur Batteries

Practical applications of lithium-sulfur batteries are simultaneously hindered by two serious problems occurring separately in both electrodes, namely, the shuttle effects of lithium polysulfides and the uncontrollable growth of lithium dendrites. Herein, to explore a facile integrated approach to tackle both problems as well as guarantee the efficient charge transfer, we used two-dimension hexagonal VS₂ flakes as the building blocks to assemble nanotowers on the separators, forming a symmetrical double-side-modified polypropylene separator without blocking the membrane pores. Benefiting from the "sulfiphilic" and "lithiophilic" properties, high interfacial electronic conductivity, and the unique hexagonal tower-form nanostructure, the D-HVS@PP separator not only guarantees the effective suppression of the lithium polysulfide shuttle and the rapid ion/electron transfer but also realizes uniform and stable lithium nucleation and growth during cycling. Hence, just at the expense of an 11% increase in the separator weight (0.14 mg cm^-2), the D-HVS@PP separator delivers an over 16 times higher initial areal capacity (8.3 mAh cm^-2) than a conventional PP separator (0.5 mAh cm^-2) under high sulfur-loading conditions (9.24 mg cm^-2). Even when used under a low electrolyte/sulfur ratio of 4 mL g^-1 and a practically relevant N/P ratio of 1.7, the D-HVS@PP separator still enabled stable cycling with a high cell-level gravimetric energy density. The potentials in broader applications (Li-S pouch battery and Li-LiFePO₄ battery) and the promising commercial prospect (large-scale production and recyclability) of the developed separator are also demonstrated.

Nitrogen-Doped Hierarchical Porous Carbon-Promoted Adsorption of Anthraquinone for Long-Life Organic Batteries

Organic quinone molecules are attractive electrochemical energy storage devices because of their high abundance, multielectron reactions, and structural diversity compared with transition metal-oxide electrode materials. However, they have problems like poor cycle stability and low rate performance on account of the inherent low conductivity and high solubility in the electrolyte. Solving these two key problems at the same time can be challenging. Herein, we demonstrate that using a nitrogen-doped hierarchical porous carbon (NC) with mixed microporous/low-range mesoporous can greatly alleviate the shuttle effect caused by the dissolution of organic molecules in the electrolyte through physical binding and chemisorption, thereby improving the electrochemical performances. Lithium-ion batteries based on the anthraquinone (AQ) electrode exhibit dramatic capacity decay (5.7% capacity retention at 0.2 C after 1000 cycles) and poor rate performance (14.2 mA h g^-1 at 2 C). However, the lithium-ion battery based on the NC@AQ cathode shows excellent cycle stability (60.5% capacity retention at 0.2 C after 1000 cycles, 82.8% capacity retention at 0.5 C after 1000 cycles), superior rate capability (152.9 mA h g^-1 at 2 C), and outstanding energy efficiency (98% at 0.2 C). Our work offers a new approach to realize the next-generation organic batteries for long life and high rate performance.

Hierarchical porous CoxFe3−xO4 nanocubes obtained by calcining Prussian blue analogues as anodes for lithium-ion batteries

Prussian blue analogue derived hierarchical porous Co_xFe_3−xO₄ nanocubes applied as LIBs anode material can provide large space to buffer volume expansion during the Li⁺ insertion/extraction processes and enhanced electrochemical performance.

Formation and Effect of Residual Lithium Compounds on Li-Rich Cathode Material Li1.35[Ni0.35Mn0.65]O2

Li-rich cathode materials are regarded as ideal cathode materials, owing to their excellent electrochemical capacity. However, residual lithium compounds, which are formed on the surface of the materials by reacting with moisture and carbon dioxide in ambient atmosphere, can impair the surface structure, injure the capacity, and impede the electrode fabrication using Li-rich materials. Exposure to air atmosphere causes the formation of residual lithium compounds; the formation of such compounds is believed to be related to humidity, temperature, and time during handling and storage. In this study, we demonstrated for the first time an artificial strategy for controlling time, temperature, and humidity to accelerate exposure. The formation and effect of residual lithium compounds on Li-rich cathode material Li_1.35[Ni_0.35Mn_0.65]O₂ were systematically investigated. The residual lithium compounds formed possessed primarily an amorphous structure and were partially coated on the surface. These compounds include LiOH, Li₂O, and Li₂CO₃. Li₂CO₃ is the major component in residual lithium compounds. The presence of residual lithium compounds on the material surface led to a high discharge capacity loss and large discharge voltage fading. Understanding the formation and suppressing the effect of residual lithium compounds will help prevent their unfavorable effects and improve the electrochemical performance.

Free-Standing Porous Carbon Nanofiber/Carbon Nanotube Film as Sulfur Immobilizer with High Areal Capacity for Lithium-Sulfur Battery

Low sulfur utilization and poor cycle life of the sulfur cathode with high sulfur loadings remain a great challenge for lithium-sulfur (Li-S) battery. Herein, the free-standing carbon film consisting of porous carbon nanofibers (PCNFs) and carbon nanotubes (CNTs) is successfully fabricated by the electrospinning technology. The PCNF/CNT film with three-dimensional and interconnected structure is promising for the uniformity of the high-loading sulfur, good penetration of the electrolyte, and reliable accommodation of volumetric expansion of the sulfur cathode. In addition, the abundant N/O-doped elements in PCNF/CNT film are helpful to chemically trap soluble polysulfides in the charge-discharge processes. Consequently, the obtained monolayer S/PCNF/CNT film as the cathode shows high specific capacity, excellent cycle stability, and rate stability with the sulfur loading of 3.9 mg cm^-2. Moreover, the high areal capacity of 13.5 mA h cm^-2 is obtained for the cathode by stacking three S/PCNF/CNT layers with the high sulfur loading of 12 mg cm^-2. The stacking-layered cathode with high sulfur loading provides excellent cycle stability, which is beneficial to fabricate high-energy-density Li-S battery in future.

Improved Performances of LiNi0.8Co0.15Al0.05O2 Material Employing NaAlO2 as a New Aluminum Source

To prepare a high-performance LiNi_0.8Co_0.15Al_0.05O₂ material (LNCA) for Li-ion batteries, a new aluminum source, NaAlO₂, is employed in the coprecipitation step for the first time, and the effect of aluminum sources on the performances is systematically investigated. Different from the traditional preparation process using Al(NO₃)₃ as the aluminum source, the preparation process of the Ni_0.8Co_0.15Al_0.05(OH)_2.05 precursor from NaAlO₂ is a hydrolysis process, during which the fast precipitation of Al³⁺ and the formation of a flocculent precipitate can be effectively avoided. As expected, stoichiometric LNCA with uniform element distribution, low cation mixing and well-ordered layered structure is obtained from NaAlO₂, which is designed as LNCA-NaAlO₂. The characterization and electrochemical measurements show that LNCA-NaAlO₂ exhibits significantly improved performances (such as tap density, initial discharge capacity and volumetric energy density, rate performance, cycle performance, electrochemical stability, microstructure stability, and storage stability) compared to the performances of those prepared from Al(NO₃)₃ (LNCA-Al(NO₃)₃), indicating that it is an effective strategy to preparing high-performance LNCA employing NaAlO₂ as the aluminum source.

General Strategy for Integrated SnO2/Metal Oxides as Biactive Lithium-Ion Battery Anodes with Ultralong Cycling Life

Integration of bicomponents into a greater object or assemblage is a new avenue to acquire multifunctionality for metal oxide-based anodes for lithium-ion batteries (LIBs). Herein, we report a versatile means by which precursors serve as self-sacrificing templates to form architectures of SnO₂ phase and other metal oxides. The vital challenge is the determination of appropriate synthetic system that can benefit the formation of respective precursors in a structure or single-source precursors of tin and other metal species. In the current work, by the aids of synergy action between l-proline and ethylene glycol (EG), precursors containing two metal ions are generally fabricated. Adequate flexibility of the present method has been achieved for SnO₂/M _x O _y hierarchical hybrids, including Mn₂O₃, Co₃O₄, NiO, and Zn₂SnO₄, by calcination of their corresponding SnMn, SnCo, SnNi, and SnZn precursors, respectively. When evaluated as anode materials for LIBs, the obtained SnO₂/Mn₂O₃ homogeneous hybrids, as expected, show higher specific capacity and ultralong cycling stability, gaining a reversible specific capacity of 610.3 mA h g^-1 after 600 cycles with only decay of 0.29 mA h g^-1 per cycle at 1 A g^-1 and 487 mA h g^-1 after 1001 cycles at a high current density of 2 A g^-1.

Porous Carbon Paper as Interlayer to Stabilize the Lithium Anode for Lithium-Sulfur Battery

The lithium-sulfur (Li-S) battery is expected to be the high-energy battery system for the next generation. Nevertheless, the degradation of lithium anode in Li-S battery is the crucial obstacle for practical application. In this work, a porous carbon paper obtained from corn stalks via simple treating procedures is used as interlayer to stabilize the surface morphology of Li anode in the environment of Li-S battery. A smooth surface morphology of Li is obtained during cycling by introducing the porous carbon paper into Li-S battery. Meanwhile, the electrochemical performance of sulfur cathode is partially enhanced by alleviating the loss of soluble intermediates (polysulfides) into the electrolyte, as well as the side reaction of polysulfides with metallic lithium. The Li-S battery assembled with the interlayer exhibits a large capacity and excellent capacity retention. Therefore, the porous carbon paper as interlayer plays a bifunctional role in stabilizing the Li anode and enhancing the electrochemical performance of the sulfur cathode for constructing a stable Li-S battery.

Multifunctional Nitrogen-Doped Loofah Sponge Carbon Blocking Layer for High-Performance Rechargeable Lithium Batteries

Low-cost, long-life, and high-performance lithium batteries not only provide an economically viable power source to electric vehicles and smart electricity grids but also address the issues of the energy shortage and environmental sustainability. Herein, low-cost, hierarchically porous, and nitrogen-doped loofah sponge carbon (N-LSC) derived from the loofah sponge has been synthesized via a simple calcining process and then applied as a multifunctional blocking layer for Li-S, Li-Se, and Li-I2 batteries. As a result of the ultrahigh specific area (2551.06 m(2) g(-1)), high porosity (1.75 cm(3) g(-1)), high conductivity (1170 S m(-1)), and heteroatoms doping of N-LSC, the resultant Li-S, Li-Se, and Li-I2 batteries with the N-LSC-900 membrane deliver outstanding electrochemical performance stability in all cases, i.e., high reversible capacities of 623.6 mA h g(-1) at 1675 mA g(-1) after 500 cycles, 350 mA h g(-1) at 1356 mA g(-1) after 1000 cycles, and 150 mA h g(-1) at 10550 mA g(-1) after 5000 cycles, respectively. The successful application to Li-S, Li-Se, and Li-I2 batteries suggests that loofa sponge carbon could play a vital role in modern rechargeable battery industries as a universal, cost-effective, environmentally friendly, and high-performance blocking layer.

Rational Design of NiCoO2@SnO2 Heterostructure Attached on Amorphous Carbon Nanotubes with Improved Lithium Storage Properties

It still remains very challenging to design proper heterostructures to enhance the electrochemical performance of transition metal oxide-based anode materials for lithium-ion batteries. Here, we synthesized the NiCoO2 nanosheets@SnO2 layer heterostructure supported by amorphous carbon nanotubes (ACNTs) which is derived from polymeric nanotubes (PNTs) by a stepwise method. The inner SnO2 layer not only provides a considerable capacity contribution but also produces the extra Li2O to promote the charge process of NiCoO2 and thus results in a rising cycling performance. Combining with the contribution of ACNTs backbone and ultrathin NiCoO2 nanosheets, the specific capacities of these one-dimensional nanostructures show an interesting gradually increasing trend even after 100 cycles at 400 mA g(-1) with a final result of 1166 mAh g(-1). This approach can be an efficient general strategy for the preparation of mixed-metal-oxide one-dimensional nanostructures and this innovative design of hybrid electrode materials provides a promising approach for batteries with improved electrochemical performance.

Self-Assembly of Polyethylene Glycol-Grafted Carbon Nanotube/Sulfur Composite with Nest-like Structure for High-Performance Lithium-Sulfur Batteries

The novel polyethylene glycol-grafted multiwalled carbon nanotube/sulfur (PEG-CNT/S) composite cathodes with nest-like structure are fabricated through a facile combination process of liquid phase deposition and self-assembly, which consist of the active material core of sulfur particle and the conductive shell of PEG-CNT network. The unique architecture not only provides a short and rapid charge transfer pathway to improve the reaction kinetics but also alleviates the volume expansion of sulfur during lithiation and minimizes the diffusion of intermediate polysulfides. Such an encouraging electrochemical environment ensures the excellent rate capability and high cycle stability. As a result, the as-prepared PEG-CNT/S composite with sulfur content of 75.9 wt % delivers an initial discharge capacity of 1191 and 897 mAh g(-1) after 200 cycles at 0.2 C with an average Coulombic efficiency of 99.5%. Even at a high rate of 2 C, an appreciable capacity of 723 mAh g(-1) can still be obtained.