Enhancing the Cycle Performance of Lithium-Sulfur Batteries by Coating the Separator with a Cation-Selective Polymer Layer.

Lithium-sulfur batteries are believed to possess the feasibility to power electric vehicles in the future ascribed to the competitive energy density. However, soluble polysulfides continuously shuttle between the sulfur electrode and lithium anode across the separator, which dramatically impairs the battery's capacity. Herein, the surface of a polypropylene separator (PP film) is successfully modified with a delicately designed cation-selective polymer layer to suppress the transport of polysulfides. In principle, since bis-sulfonimide anions groups on the backbone of the polymer are immobilized, only cations can pass through the polymer layer. Furthermore, plenty of ethoxy chains in the polymer can facilitate lithium-ion mobility. Consequently, in addition to obstructing the movement of negatively charged polysulfides by the electrostatic repulsive force of fixed anions, the coated multi-functional layer on the PP film also guarantees the smooth conduction of lithium ions. The investigations demonstrate that the battery with the pristine PP film only delivers 228.5 mAh g-1 after 300 cycles at 2 C with a high capacity fading rate of 60.9 %. By contrast, the polymer-coated sample can release 409.4 mAh g-1 under the identical test condition and the capacity fading rate sharply declines to 43.2 %, illustrating superior cycle performance.

Exploring the Effect of a MnO2 Coating on the Electrochemical Performance of a Li1.2Mn0.54Ni0.13Co0.13O2 Cathode Material.

The effect of electrochemically active MnO2 as a coating material on the electrochemical properties of a Li1.2Mn0.54Ni0.13Co0.13O2 (LTMO) cathode material is explored in this article. The structural analysis indicated that the layered structure of the LTMO was unchanged after the modification with MnO2. The morphology inspection demonstrated that the rod-like LTMO particles were encapsulated by a compact coating layer. The MnO2 layer was able to hinder the electrolyte solution from corroding the LTMO particles and optimized the formation of a solid electrolyte interface (SEI). Meanwhile, lithium ions were reversibly inserted into and extracted from MnO2, which afforded an additional capacity. Compared with the bare LTMO, the MnO2-coated sample exhibited enhanced electrochemical performance. After the MnO2 coating, the first discharge capacity rose from 224.2 to 239.1 mAh/g, and the initial irreversible capacity loss declined from 78.2 to 46.0 mAh/g. Meanwhile, the cyclic retention climbed up to 88.2% after 100 cycles at 0.5 C, which was more competitive than that of the bare LTMO with a value of 71.1%. When discharging at a high current density of 2 C, the capacity increased from 100.5 to 136.9 mAh/g after the modification. These investigations may be conducive to the practical application of LTMO in prospective automotive Li-ion batteries.

Controllable Synthesis of Co@CoOx/Helical Nitrogen-Doped Carbon Nanotubes toward Oxygen Reduction Reaction as Binder-free Cathodes for Al-Air Batteries.

Efficient and stable electrocatalysts for oxygen reduction reaction and freestanding electrode structure were developed to reduce the use of polymer binders in the cathode of metal-air batteries. Considering the unique geometrical configurations of helical carbon nanotubes (CNTs) and improved properties compared with straight CNTs, we prepared high-purity Co@CoOx/helical nitrogen-doped carbon nanotubes (Co@CoOx/HNCNTs) on a carbon fiber paper by hydrothermal and single-step in situ chemical vapor deposition strategies. Under an optimized growth time (1 h), the synthesized Co@CoOx/HNCNTs provide richer edge defects and active sites and show prominent electrocatalytic performance toward oxygen reduction reaction (ORR) under alkaline media compared with Co@CoOx/HNCNTs-0.5 h and Co@CoOx/HNCNTs-2 h. The soft X-ray absorption spectroscopy technique is used to investigate the influences of different growth times on the electronic structure and local chemical configuration of Co@CoOx/HNCNTs. Furthermore, the Al-air coin cell employing Co@CoOx/HNCNTs-1 h as the binder-free cathode exhibits an open-circuit voltage of 1.48 V, a specific capacity of 367.31 mA h g-1 at the discharge current density of 1.0 mA cm-2, and a maximum power density (Pmax) of 3.86 mW cm-2, which are superior to those of Co@CoOx/HNCNTs-0.5 h and Co@CoOx/HNCNTs-2 h electrodes. This work provides valuable insights into the development of scalable binder-free cathodes, exploiting HNCNT composite materials with an outstanding electrocatalytic performance for ORR in Al-air systems.

Effect of Micromorphology on Alkaline Polymer Electrolyte Stability.

Recent studies demonstrated that the chemical stability of alkaline polymer electrolytes (APEs) could be improved by reducing the inductive effect between cations and backbones. Therefore, pendent cations were recommended. However, microphase-separated morphologies would be generated by elongating the spacer between cations and backbones, which have a significant influence on the chemical stability of APEs too. In order to analyze how the patterns of micromorphology affect the chemical stability of the materials, in the present work, four APEs ( a1-QAPS, a3-QAPS, a5-QAPS, and a7-QAPS) with different lengths of side chain between polysulfone and quaternary ammonium are synthesized. The longer the side chain is, the more obvious the microphase separation for the a x-QAPS membranes is observed. After immersing in a hot alkaline solution (80 °C, 1 M KOH) for 30 days, a5-QAPS exhibits the highest chemical stability. The ion exchange capacity and ionic conductivity of  a5-QAPS film are reduced by 10.0 and 10.5%, respectively. The weight loss of  a5-QAPS membrane is 8.0%, which is similar to the value of the pristine backbone. The increased chemical stability can be ascribed to the suitable micromorphology constructed in  a5-QAPS sample. Besides,  a5-QAPS membrane shows a high conductivity of 75.5 mS cm-1, whereas the swelling ratio is limited to 15.0% in liquid water at 80 °C. In addition, a peak power density of 339.1 mW cm-2 is obtained by applying a5-QAPS as the APE to the H2-O2 fuel cell at 60 °C.

Step-by-Step Assembly of Metal-Organic Frameworks from Trinuclear Cu3 Clusters.

Two novel metal-organic frameworks (MOFs), HBNU-1 and HBNU-2, have been synthesized successfully. We adopt a step-by-step assembly strategy, which first synthesize the Cu3 cluster Cu3(µ3-OH)(pz)3(CH3COO)2(Hpz), and then react it with H2BDC under different conditions to form final frameworks. In both MOF structures, the Cu3 clusters are maintained, although certain differences are observed. Compared with HBNU-1, the Cu3 cluster dimerizes into Cu6 cluster in HBNU-2. With this step-by-step cluster assembly strategy, MOF structure predicting becomes possible and may give some reference for MOF structure designing.

Organic amines as templates: pore imprints with exactly matching sizes in a series of metal-organic frameworks.

Three kinds of organic amines have been used as soft templates for constructing a series of metal-organic frameworks with variable pores. The pore sizes of these MOFs exactly matched those of amines, confirming the template effect of these amines.

A gel single ion conducting polymer electrolyte enables durable and safe lithium ion batteries via graft polymerization.

Concentration polarization issues and lithium dendrite formation, which associate inherently with the commercial dual-ion electrolytes, restrict the performance of lithium ion batteries. Single ion conducting polymer electrolytes (SIPEs) with high lithium ion transference numbers (t + ≈ 1) are being intensively studied to circumvent these issues. Herein, poly(ethylene-co-vinyl alcohol) (EVOH) is chosen as the backbone and then grafted with lithium 3-chloropropanesulfonyl(trifluoromethanesulfonyl)imide (LiCPSI) via Williamson's reaction, resulting in a side-chain-grafted single ion polymer conductor (EVOH-graft-LiCPSI). The ionomer is further blended with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) by solution casting for practical use. The SIPE membrane with ethylene carbonate and dimethyl carbonate (EC/DMC = 1 : 1, v/v) as plasticizer (i.e., gel SIPE) exhibits an ionic conductivity of 5.7 × 10-5 S cm-1, a lithium ion transference number of 0.88, a wide electrochemical window of 4.8 V (vs. Li/Li+) and adequate mechanical strength. Finally, the gel SIPE is applied in a lithium ion battery as the electrolyte as well as the separator, delivering an initial discharge capacity of 100 mA h g-1 at 1C which remains at 95 mA h g-1 after 500 cycles.

A hyperbranched conjugated Schiff base polymer network: a potential negative electrode for flexible thin film batteries.

A hyperbranched conjugated Schiff base polymer network was synthesized by condensation between 4,4',4''-nitrilotribenzaldehyde and p-phenylenediamine. The material exhibits excellent rate capability and long cycle life for lithium storage. Coupled with lower electrode potential (0.7 V vs. Li(+)/Li), it may be well suited for fully flexible thin film polymeric batteries as the negative electrode.