Fabrication of a Covalent Triazine Framework Functional Interlayer for High-Performance Lithium–Sulfur Batteries

The shuttling effect of polysulfides is one of the major problems of lithium–sulfur (Li–S) batteries, which causes rapid capacity fading during cycling. Modification of the commercial separator with a functional interlayer is an effective strategy to address this issue. Herein, we modified the commercial Celgard separator of Li–S batteries with one-dimensional (1D) covalent triazine framework (CTF) and a carbon nanotube (CNT) composite as a functional interlayer. The intertwined CTF/CNT can provide a fast lithium ionic/electronic transport pathway and strong adsorption capability towards polysulfides. The Li–S batteries with the CTF/CNT/Celgard separator delivered a high initial capacity of 1314 mAh g−1 at 0.1 C and remained at 684 mAh g−1 after 400 cycles−1 at 1 C. Theoretical calculation and static-adsorption experiments indicated that the triazine ring in the CTF skeleton possessed strong adsorption capability towards polysulfides. The work described here demonstrates the potential for CTF-based permselective membranes as separators in Li–S batteries.

Quantitative Estimation of Turning Point of Ageing Based on a Two-Stage Model for Lithium-Ion Batteries

The capacity fading of lithium-ion batteries (LIBs) is reported by a linear dependency followed by a nonlinear ageing process, where the former is dominated by solid electrolyte interphase formation and reformation (SEI and SEI-re), while the latter is by lithium plating. In this work, a two-stage model is developed to quantitatively predict the turning point during the capacity fading of LIBs, which couples the electrochemical and thermal models accounting for SEI, SEI-re and lithium plating. Accordingly, a quantitative evaluation method of the turning point is proposed by attributing the transition of the capacity fading to the balance of consumption of active lithium for SEI growth and lithium plating per cycle in the two stages. The characteristics of capacity fading of LIBs are quantitatively analyzed under various operation conditions and design parameters. An NCM111/graphite battery is used to validate the proposed model. The results shows the validity of the proposed model. The turning points of the capacity fading processes are influenced by operation and design parameters of LIBs, where lithium plating or SEI growth reign. According to the effect on the turning point, the order of significance of the factors are charging current, charging cut-off voltage, temperature and N/P ratio, respectively.

Single-dispersed polyoxometalate clusters embedded on multilayer graphene as a bifunctional electrocatalyst for efficient Li-S batteries

The redox reactions occurring in the Li-S battery positive electrode conceal various and critical electrocatalytic processes, which strongly influence the performances of this electrochemical energy storage system. Here, we report the development of a single-dispersed molecular cluster catalyst composite comprising of a polyoxometalate framework ([Co4(PW9O34)2]10−) and multilayer reduced graphene oxide. Due to the interfacial charge transfer and exposure of unsaturated cobalt sites, the composite demonstrates efficient polysulfides adsorption and reduced activation energy for polysulfides conversion, thus serving as a bifunctional electrocatalyst. When tested in full Li-S coin cell configuration, the composite allows for a long-term Li-S battery cycling with a capacity fading of 0.015% per cycle after 1000 cycles at 2 C (i.e., 3.36 A g−1). An areal capacity of 4.55 mAh cm−2 is also achieved with a sulfur loading of 5.6 mg cm−2 and E/S ratio of 4.5 μL mg−1. Moreover, Li-S single-electrode pouch cells tested with the bifunctional electrocatalyst demonstrate a specific capacity of about 800 mAh g−1 at a sulfur loading of 3.6 mg cm−2 for 100 cycles at 0.2 C (i.e., 336 mA g−1) with E/S ratio of 5 μL mg−1.

Effects of Mg Doping at Different Positions in Li-Rich Mn-Based Cathode Material on Electrochemical Performance

Li-rich Mn-based layered oxides are among the most promising cathode materials for next-generation lithium-ion batteries, yet they suffer from capacity fading and voltage decay during cycling. The electrochemical performance of the material can be improved by doping with Mg. However, the effect of Mg doping at different positions (lithium or transition metals) remains unclear. Li1.2Mn0.54Ni0.13Co0.13O2 (LR) was synthesized by coprecipitation followed by a solid-state reaction. The coprecipitation stage was used to introduce Mg in TM layers (sample LR-Mg), and the solid-state reaction (st) was used to dope Mg in Li layers (LR-Mg(st)). The presence of magnesium at different positions was confirmed by XRD, XPS, and electrochemical studies. The investigations have shown that the introduction of Mg in TM layers is preferable in terms of the electrochemical performance. The sample doped with Mg at the TM positions shows better cyclability and higher discharge capacity than the undoped sample. The poor electrochemical properties of the sample doped with Mg at Li positions are due to the kinetic hindrance of oxidation of the manganese-containing species formed after activation of the Li2MnO3 component of the composite oxide. The oxide LR-Mg(st) demonstrates the lowest lithium-ion diffusion coefficient and the greatest polarization resistance compared to LR and LR-Mg.

Modelling the effect of anode particle radius and anode reaction rate constant on capacity fading of Li-ion batteries

This paper investigates the effect of anode particle radius and anode reaction rate constant on the capacity fading of lithium-ion batteries. It is observed through simulation results that capacity fade will be lower when the anode particle size is smaller. Simulation results also show that the reaction rate constant for the anode reaction has a good impact on the capacity loss of a lithium-ion battery. The potential drop across the SEI layer (solid electrolyte interphase) is studied as a function of the anode particle radius and anode reaction rate constant. Modelling results are compared with experimental data and found to compare well.

The Electrochemical Performance of δ-MnO2 Cathode Material for Aqueous Zinc-Ion Batteries: The Role of Current Collector

Electrochemical properties of δ-MnO2-based cathode materials were studied in dependence on current collector used for electrode casting (stainless steel mesh, carbon paper and titanium foil) by galvanostatic charge/discharge measurements and cyclic voltammetry. It was shown that δ-MnO2-based electrodes cast on carbon paper demonstrate the most stable electrochemical performance in comparison with two other current collectors. This can be explained by corrosion of steel and passivation of titanium in mild aqueous electrolytes. Detailed study of carbon paper as current collector shows that pressing of electrodes leads to decreasing the porosity and fast capacity fading.

High Voltage Redox-Meditated Flow Batteries with Prussian Blue Solid Booster

This work presents Prussian blue solid boosters for use in high voltage redox-mediated flow batteries (RMFB) based on non-aqueous electrolytes. The system consisted of sodium iodide as a redox mediator in an acetonitrile catholyte containing solid Prussian blue powder. The combination enabled the solid booster utilization in the proposed systems to reach as high as 66 mAh g−1 for hydrated Prussian blue and 110 mAh g−1 for anhydrous rhombohedral Prussian blue in cells with an average potential of about 3 V (vs. Na+/Na). Though the boosted system suffers from capacity fading, it opens up possibilities to develop non-aqueous RMFB with low-cost materials.