One-Pot Synthesized Amorphous Cobalt Sulfide With Enhanced Electrochemical Performance as Anodes for Lithium-Ion Batteries

In order to solve the poor cycle stability and the pulverization of cobalt sulfides electrodes, a series of amorphous and crystalline cobalt sulfides were prepared by one-pot solvothermal synthesis through controlling the reaction temperatures. Compared to the crystalline cobalt sulfide electrodes, the amorphous cobalt sulfide electrodes exhibited superior electrochemical performance. The high initial discharge and charge capacities of 2,132 mAh/g and 1,443 mAh/g at 200 mA/g were obtained. The reversible capacity was 1,245 mAh/g after 200 cycles, which is much higher than the theoretical capacity. The specific capability was 815 mAh/g at 800 mA/g and increased to 1,047 mAh/g when back to 100 mA/g, indicating the excellent rate capability. The outstanding electrochemical performance of the amorphous cobalt sulfide electrodes could result from the unique characteristics of more defects, isotropic nature, and the absence of grain boundaries for amorphous nanostructures, indicating the potential application of amorphous cobalt sulfide as anodes for lithium-ion batteries.

Binder and Conductive Diluents Free NaVPO4F Based Free-standing Positive Electrodes for Sodium-Ion Batteries

Herein, we report a carbon-fiber based freestanding electrode for NaVPO4F cathodes in sodium-ion batteries. The replacement of conventional aluminum foil with a carbon fiber mat-based current collector results in significant improvement in capacity at high rates and charge-discharge cycle stability. Petroleum-pitch (P-Pitch) has dual functions. P-pitch is used as a binder to bind NaVPO4F particles onto the carbon fiber mat, which helps to eliminate typical organic binders. At the same time, P-Pitch acts as a conducting precursor to coat onto NaVPO4F particles. The amount of P-pitch required to achieve stable electrochemical performance is optimized. As a result, 15 and 20 % of P-pitch in the composite NaVPO4F electrodes (15P_NVPF@CF and 20P_NVPF@CF) shows stable electrochemical performances. A reversible capacity of 120 and 119 mAh g−1 are observed for 15P_NVPF@CF and 20P_NVPF@CF, with 97 and 98 % retention in capacity after 300 cycles, respectively. Further, at a 0.5 C current rate, 15P_NVPF@CF and 20P_NVPF@CF electrodes show 86 and 87 % capacity retention after 1000 cycles. The significant electrochemical performance of these freestanding electrodes is ascribed to the interlinked carbon matrix with NaVPO4F particles and carbon-fiber mat, which provides a continuous path for electronic conduction and faster kinetics of NaVPO4F particles

Module-Designed Carbon-Coated Separators for High-Loading, High-Sulfur-Utilization Cathodes in Lithium–Sulfur Batteries

Lithium–sulfur batteries have great potential as next-generation energy-storage devices because of their high theoretical charge-storage capacity and the low cost of the sulfur cathode. To accelerate the development of lithium–sulfur technology, it is necessary to address the intrinsic material and extrinsic technological challenges brought about by the insulating active solid-state materials and the soluble active liquid-state materials. Herein, we report a systematic investigation of module-designed carbon-coated separators, where the carbon coating layer on the polypropylene membrane decreases the irreversible loss of dissolved polysulfides and increases the reaction kinetics of the high-loading sulfur cathode. Eight different conductive carbon coatings were considered to investigate how the materials’ characteristics contribute to the lithium–sulfur cell’s cathode performance. The cell with a nonporous-carbon-coated separator delivered an optimized peak capacity of 1112 mA∙h g−1 at a cycling rate of C/10 and retained a high reversible capacity of 710 mA∙h g−1 after 200 cycles under lean-electrolyte conditions. Moreover, we demonstrate the practical high specific capacity of the cathode and its commercial potential, achieving high sulfur loading and content of 4.0 mg cm−2 and 70 wt%, respectively, and attaining high areal and gravimetric capacities of 4.45 mA∙h cm−2 and 778 mA∙h g−1, respectively.

PPy coated nanoflower like CuCo2O4 based on in situ growth of nanoporous copper for high-performance supercapacitor electrodes

General CuCo2O4 electrodes suffer a very low reversible capacity and poor cycling stability because of easily fading phenomena and volume change during cycling. To optimize the electrode, a facile method is conducted to fabricate a novel electrode of Cu@CuCo2O4@polypyrrole (Cu@CCOP) nanoflowers. Due to larger specific surface area and more electrochemical reactive areas of Cu@CCOP nanoflowers, the pseudocapacitance of the in-situ grown Cu@CCOP (912 F g-1 at 2 A g-1) is much higher than the pristine CuCo2O4 (CCO) (618 F g-1 at 2 A g-1). Remarkably, the Cu@CCOP (cathode) and active carbon (anode) are used to assemble an asymmetric supercapacitor, which exhibits a relatively high energy density of 90 Wh kg-1 at a power density of 2519 W kg-1 and 35 Wh kg-1 at a high-power density of 9109 W kg-1, and excellent cycling stability (about 90.4% capacitance retention over 10000 cycles). The prominent performance of Cu@CCOP makes it as a potential electrode for supercapacitor.

Biomass-Derived Porous Carbon from Agar as an Anode Material for Lithium-Ion Batteries

New porous activated carbons with a high surface area as an anode material for lithium-ion batteries (LIBs) were synthesized by a one-step, sustainable, and environmentally friendly method. Four chemical activators—H2SO4, H3PO4, KOH, and ZnCl2—have been investigated as facilitators of the formation of the porous structure of activated carbon (AC) from an agar precursor. The study of the materials by Brunauer–Emmett–Teller (BET) and scanning electron microscopy (SEM) methods revealed its highly porous meso- and macro-structure. Among the used chemical activators, the AC prepared with the addition of KOH demonstrated the best electrochemical performance upon its reaction with lithium metal. The initial discharge capacity reached 931 mAh g−1 and a reversible capacity of 320 mAh g−1 was maintained over 100 cycles at 0.1 C. High rate cycling tests up to 10 C demonstrated stable cycling performance of the AC from agar.

Green and Highly-Efficient Microwave Synthesis Route for Sulfur/Carbon Composite for Li-S Battery

Multiporous carbons (MPCs) are prepared using ZnO as a hard template and biomass pyrolysis oil as the carbon source. It is shown that the surface area, pore volume, and mesopore/micropore ratio of the as-prepared MPCs can be easily controlled by adjusting the ZnO/oil ratio. Sulfur/MPC (S/MPC) composite is prepared by blending sulfur powder with the as-prepared MPCs followed by microwave heating at three different powers (100 W/200 W/300 W) for 60 s. The unique micro/mesostructure characteristics of the resulting porous carbons not only endow the S/MPC composite with sufficient available space for sulfur storage, but also provide favorable and efficient channels for Li-ions/electrons transportation. When applied as the electrode material in a lithium-ion battery (LIB), the S/MPC composite shows a reversible capacity (about 500 mAhg−1) and a high columbic efficiency (>95%) after 70 cycles. Overall, the method proposed in this study provides a simple and green approach for the rapid production of MPCs and S/MPC composite for high-performance LIBs.

Hierarchical Mg-Birnessite Nanowall Arrays with Enriched (010) Planes for High Performance Aqueous Mg-Ion Batteries

Birnessite MnO2 is a promising cathode material for aqueous Mg-ion batteries due to its layered structure with large interlayer distance. However, the two-dimensional growth mode of birnessite induces nanosheet morphology with preferred growth of inactive (001) planes with sluggish ion transport kinetics. In this work, a high Mg content birnessite with hierarchical nanowall arrays morphology is prepared by in situ electro-conversion using spinel Mn3O4 nanowall arrays. The electro-conversion Mg-birnessite (ECMB) nanowall arrays are assembled by ultrasmall nanosheets with reduced (001) planes but increased active (010) planes, affording enriched open intercalation channels and shortened Mg2+ diffusion length. Consequently, the ECMB cathode exhibits a large specific reversible capacity of about 255.1 mAh/g at a current density of 200 mA/g, and outstanding cycling stability with 73.6% capacity retention after 3000 cycles. Finally, a 2.2 V aqueous full cell is constructed by using ECMB as positive electrode and polyimide as negative electrode, which achieves a high energy density of 65.2 Wh/kg at a power density of 96 W/kg. This work demonstrates effective crystal plane modulation for Mg-birnessite to achieve superior Mg2+ storage in aqueous batteries.

Coaxial Electrospinning Construction Si@C Core–Shell Nanofibers for Advanced Flexible Lithium-Ion Batteries

Silicon (Si) is expected to be a high-energy anode for the next generation of lithium-ion batteries (LIBs). However, the large volume change along with the severe capacity degradation during the cycling process is still a barrier for its practical application. Herein, we successfully construct flexible silicon/carbon nanofibers with a core–shell structure via a facile coaxial electrospinning technique. The resultant Si@C nanofibers (Si@C NFs) are composed of a hard carbon shell and the Si-embedded amorphous carbon core framework demonstrates an initial reversible capacity of 1162.8 mAh g−1 at 0.1 A g−1 with a retained capacity of 762.0 mAh g−1 after 100 cycles. In addition, flexible LIBs assembled with Si@C NFs were hardly impacted under an extreme bending state, illustrating excellent electrochemical performance. The impressive performances are attributed to the high electric conductivity and structural stability of the porous carbon fibers with a hierarchical porous structure, indicating that the novel Si@C NFs fabricated using this electrospinning technique have great potential for advanced flexible energy storage.