Construction of two-dimensional bimetal (Fe-Ti) oxide/carbon/MXene architecture from titanium carbide MXene for ultrahigh-rate lithium-ion storage

The development of battery systems with high specific capacity and power density could fuel various energy-related applications from personal electronics to grid storage. (Fe_2.5Ti_0.5)_1.04O₄ possessing high theoretical specific capacity has been considered as a promising high rate anode material for lithium ion batteries due to the replacement of Fe³⁺ (0.64 Å) by Ti⁴⁺ (0.68 Å) with a larger radius to expand the interlayer space for ion intercalation. However, its extreme volume variation upon cycling as well as poor electrical conductivity hinder its further application. To tackle the above problems, in this work, we successfully synthesized two-dimensional (2D) (Fe_2.5Ti_0.5)_1.04O₄/C/MXene architecture derived from Ti₃C₂T_x MXene via solvo-hydrothermal, ultrasound hybridizing and high temperature annealing processes. The (Fe_2.5Ti_0.5)_1.04O₄/C/MXene shows a high discharge capacity of 757.2 mAh g^-1 after 800 cycles at a current density of 3 A g^-1 with excellent rate performance. The superior electrochemical performances are triggered primarily by the incorporation of carbon and MXene into (Fe_2.5Ti_0.5)_1.04O₄ moiety to construct a 2D layered structure, which can improve the ion diffusion and electron transport. In addition, the synergistic contributions from diffusion controlled and capacitive processes for (Fe_2.5Ti_0.5)_1.04O₄/C/MXene improve the ion diffusion rate and offer high specific capacity at high current density. The MXene-derived synthesis strategy in this work should be a promising pathway to synthesize other anode materials with 2D layered architecture for high performance lithium storage.

Synthesis of zinc sulfide/copper sulfide/porous carbonized cotton nanocomposites for flexible supercapacitor and recyclable photocatalysis with high performance

The composite material composed of zinc sulfide, copper sulfide and porous carbon is prepared in this study, exhibiting excellent performances in the field of supercapacitor electrode and photocatalysts. In the degradation process of organic pollutants, zinc sulfide/copper sulfide with heterostructure effectively reduce the recombination rate of photo-generated electron-hole pairs. And the porous carbon substrate can not only accelerate the separation of photo-carriers but also provide numerous active sites. Furthermore, the sample can be easily separated after decomposing the organic pollutants. As a supercapacitor electrode, the combination of zinc sulfide/copper sulfide with large pseudo-capacitance and porous carbon material with excellent double-layercapacitance results in superior electrochemical performances. The composite electrode shows a high specific capacitance of 1925 mF cm^-2/0.53 mAh cm^-2 at 4 mA cm^-2. And the symmetric flexible supercapacitor based on the composite electrode achieves an outstanding energy density (0.39 Wh cm^-2 at the power density of 4.32 W cm^-2). Therefore, the zinc sulfide/copper sulfide/porous carbonized cotton nanocomposites (pCZCS) prepared herein exhibit dual functions of photocatalysts with high efficiency as well as energy storage materials with high energy density, which is interesting and important for expanding the practical applications in cross fields.

Hydrogen peroxide-induced growth of hierarchical Ni3S2 nanorod/sheet arrays for high performance supercapacitors

The rational design and simple synthesis of high performance electrodes are important aspects of energy storage fields. However, it is difficult to determine a facile preparation method to obtain hierarchical Ni₃S₂ nanorod/sheet arrays. Herein, hydrogen peroxide-induced growth by the hydrothermal method is used to fabricate the hierarchical Ni₃S₂ nanorod/sheet arrays on nickel foam substrates. Hydrogen peroxide can accelerate the hydrolysis of Na₂S₂O₃ to release sulfur ions and then induce formation of the hierarchical nanorod/sheet. The one-dimensional nanorod skeleton acting as high-speed electron transfer channels can support the nanosheets. The two-dimensional nanosheets can provide abundant active edge sites and protect the backbone from electrochemical corrosion. The hierarchical structure integrates the advantages of sufficient active sites, effective protection and high-speed electron transfer. The electrode based on the Ni₃S₂ nanorod/sheet delivers a high specific capacitance of 6.87 F cm^-2 at 2 mV s^-1 (6.24 F cm^-2 at 5 mA cm^-2) and long cycling stability (85.7% capacitance retention at 15 mA cm^-2 after 3000 cycles). The asymmetric supercapacitor gains a high energy density of 1.16 mWh cm^-3 at 15.00 W cm^-3. The hierarchical Ni₃S₂ nanorod/sheet arrays are expected to be candidates for the electrodes of practical supercapacitors.

Recent Development of Polyolefin-Based Microporous Separators for Li-Ion Batteries: A Review

Secondary Li-ion batteries have been paid attention to wide-range applications of power source for the portable electronics, electric vehicle, and electric storage reservoir. Generally, lithium-ion batteries are comprised of four components including anode, cathode, electrolyte and separator. Although separators do not take part in the electrochemical reactions in a lithium-ion (Li-ion) battery, they conduct the critical functions of physically separating the positive and negative electrodes to prevent electrical short circuit while permitting the free flow of lithium ions through the liquid electrolyte that fill in their open porous structure. Hence, the separator is directly related to the safety and the power performance of the battery. Among a number of separators developed thus far, polyethylene (PE) and polypropylene (PP) porous membrane separators have been the most dominant ones for commercial Li-ion batteries over the decades because of their superior properties such as cost-efficiency, good mechanical strength and pore structure, electrochemical stability, and thermal shutdown properties. However, there are main issues for vehicular storage, such as nonpolarity, low surface energy and poor thermal stability, although the polyolefin separators have proven dependable in portable applications. Hence, in this review, we decide to provide an overview of the types of polyolefin microporous separators utilized in Li-ion batteries and the methods employed to modify their surface in detail. The remarkable results demonstrate that extraordinary properties can be exhibited by mono- and multilayer polyolefin separators if they are modified using suitable methods and materials.

Surface Carbon Shell-Functionalized ZrO2 as Nanofiller in Polymer Gel Electrolyte-Based Dye-Sensitized Solar Cells

We prepare dye-sensitized solar cells (DSSCs) fabricated with a poly (ethylene glycol) based polymer gel electrolytes (PGEs) incorporating surface carbon shell-functionalized ZrO2 nanoparticles (ZrO2-C) as nanofillers (NFs). ZrO2 are polymerized via atom transfer radical polymerization (ATRP) using poly (ethylene glycol) methyl ether methacrylate (POEM) as a scaffold to prepare the ZrO2-C through carbonization. The power conversion efficiency of DSSC with 12 wt% ZrO2-C/PGEs is 5.6%, exceeding that with PGEs (4.4%). The enhanced efficiency is attributed to Lewis acid-base interactions of ZrO2-C and poly (ethylene glycol), catalytic effect of the carbon shells of ZrO2-C, which results in reduced crystallinity, enhanced ion conductivity of electrolytes, decreased counterelectrode/electrolyte interfacial resistance, and improved charge transfer rate. These results demonstrate that ZrO2-C introduction to PGEs effectively improves the performance of DSSCs.

A Heavily Surface-Doped Polymer with the Bifunctional Catalytic Mechanism in Li-O2 Batteries

The application of conducting polymers (CPs) in energy storage systems is greatly limited by insufficient reversibility and stability. Here, we successfully incorporated functionalized dopants (Fe(CN)63- [FCN] and PO43- ions) in CPs matrixes to achieve a preferable electrochemical performance. A stable cation inserting/expulsing behavior of surface-doped polycarbazole (PCz) is demonstrated in our work, where doping levels and semiconductor properties of PCz are effectively controlled to adjust their redox properties and stability. With carbon nanotube (CNT) films as the substrate, the CNT/PCz:FCN composite is initially adopted as a free-standing catalytic electrode in Li-O2 cells. The molecule-level dispersed FCN dopants on the surface can work as bifunctional redox mediators on the charge-discharge process. Thus, this composite can not only achieve a low charge plateau of 3.62 V and a regular growth of capacities from 1,800 to 4,800 mAh/gCNT, but also maintain the most of charge voltages under 4.0 V for 150 cycles.