Research Progress of Liquid Electrolytes for Lithium Metal Batteries at High Temperatures.

Lithium metal batteries (LMBs) are the most promising high energy density energy storage technologies for electric vehicles, military, and aerospace applications. LMBs require further improvement to operate efficiently when chronically or routinely exposed to high temperatures. Electrolyte engineering with high temperature tolerance and electrode compatibility has been essential to the development of LMBs. In this review, the primary obstacles to achieving high-temperature LMBs are first explored. Subsequently, electrolyte tailoring options, such as lithium salt optimization, solvation structure modification, and the addition of additives are reviewed in detail. In addition, the feasibility of utilizing LMBs at high temperatures has been investigated. In conclusion, this study provides insights and perspectives for future research on electrolyte design at high temperatures.

An integrated flexible film as cathode for High-Performance Lithium-Sulfur battery.

Poor cycling stability and low volumetric capacity of sulfur cathode prevents practical application of Lithium-sulfur (Li-S) batteries. Herein, we demonstrate a strategy to address the two drawbacks of sulfur cathode by synthesizing a compact and flexible film cathode with bilayer structure using a two-step vacuum filtration method. Two layers make up the sulfur cathode, active layer (sulfur-acethlene black (SC) spheres) and barrier layer (three dimensional MnO2-graphene oxide-multi-walled carbon nanotubes (MnO2-GO-CNTs) composites), which are integrated together by reduced graphene oxide (rGO) through self-binding. The rGO sheets provide an electrical conductive framework and a stable architecture to accommodate volume changes of sulfur. SC spheres stacked orderly between the rGO layers facilitate fast Li+ storage and energy release. Polar MnO2-GO-CNTs composites with large specific surface area have not only afforded efficient sites for chemically binding polysulfides, but also provided fast electron transfer for accelerating polysulfides redox reaction. Consequently, the integrated film cathode exhibits an unprecedented cycling stability of ~0.0279% capacity decay per cycle over more than 600 cycles at 1C and high volumetric capacity of 1021.9 Ah L-1 at 2C. Meanwhile, a foldable Li-S battery based on this flexible cathode is fabricated and shows excellent mechanical and electrochemical properties. The integrated flexible sulfur cathode of this study sheds light on the design strategies for application in flexible high volumetric capacity system.

A low-overpotential sodium/fluorinated graphene battery based on silver nanoparticles as catalyst.

Fluorinated graphene (F-GNS) was synthesized using commercial graphene (GNS) as starting material and introduced in sodium batteries, which exhibited good rate performance, but large voltage gap between discharge and charge process. Ag nanoparticles were employed in freestanding and binder-free F-GNS electrode (the composite film electrode was labeled as FGA) as catalyst, which were shown to strongly facilitate the decomposition of NaF during charge process in sodium/carbon fluorides (Na/CFx) secondary batteries. During discharge process, the discharge voltage with Ag was about the same as that of Na/F-GNS cell. During charge process, the charge voltage of Na/FGA cell was substantially lower (by 480 mV) than that of Na/F-GNS cell, thus leading to a lower overpotential and a higher electric efficiency. Nanosized amorphous discharge products of NaF formed in Na/FGA cells were ascribed as the key role in reducing the polarization.

A flexible copper sulfide @ multi-walled carbon nanotubes cathode for advanced magnesium-lithium-ion batteries.

The hybrid magnesium-lithium-ion batteries (MLIBs) are promising alternatives in large-scale energy storage field owing to low cost and high safety of magnesium batteries and fast diffusion rate of Li-ion in the electrode. Herein, a free-standing and binder-free copper sulfide/Multi-walled carbon nanotubes film cathode (F-CuS-CNT), along with Mg-Li dual-salt electrolyte and dendrite-free Mg anode, is employed to construct the MLIBs. At room temperature (25 °C), the F-CuS-CNT electrode with a CuS content up to 70% exhibits a high initial specific capacity of 479 mAh g-1 (∼85.5% of the theoretical capacity) and a considerable cycling stability (165 mAh g-1 even after 100 cycles at the current density of 30 mA g-1), which far surpasses those of conventional CuS electrode. The excellent electrochemical performances of the F-CuS-CNTs electrode can be attributed to its excellent flexible network architecture as well as abundant pores, which provide more stable conductive buffering layers for CuS particles and higher Li+ diffusion dynamics during the charging/discharging process. This work demonstrates that constructing a flexible and free-standing film electrode could improve the electrochemical performances of MLIBs and may be an appropriate select of preparing flexible MLIBs.

Long-life sodium/carbon fluoride batteries with flexible, binder-free fluorinated mesocarbon microbead film electrodes.

Home-made fluorinated mesocarbon microbeads (F-MCMBs) were synthesised and employed in sodium batteries. Flexible, binder-free F-MCMB film electrodes were fabricated to enhance the cycle stability, and 65 cycles were achieved, which is the longest lifespan reported thus far. Nitrogen-doped graphene nanosheets (N-GNS) were also introduced as a catalyst, with the aim of lowering the voltage gap.

Free-standing reduced graphene oxide/MnO2-reduced graphene oxide-carbon nanotube nanocomposite flexible membrane as an anode for improving lithium-ion batteries.

To solve the barriers of poor rate capability and inferior cycling stability for the MnO2 anode in lithium ion batteries, we present a highly flexible membrane anode employing two-dimensional (2D) reduced graphene oxide sheets (rGO) and a three-dimensional (3D) MnO2-reduced graphene oxide-carbon nanotube nanocomposite (MGC) by a vacuum filtration and thermal annealing approach. All the components in the 2D/3D thin film anode have a synergistic effect on the improved performance. The initial discharge specific capacity of the electrode with the MnO2 content of 56 wt% was 1656.8 mA h g-1 and remains 1172.5 mA h g-1 after 100 cycles at a density of 100 mA g-1. On enhancing the density to 200 mA g-1, the membrane-electrode still exhibits a large reversible discharging capacity of ∼948.9 mA h g-1 after 300 cycles. Moreover, the flexible Li-ion battery with a large area also shows excellent electrochemical performance in different bending positions, which provides the potential for wearable energy storage devices.

A three-dimensional core-shell nanostructured composite of polypyrrole wrapped MnO(2)/reduced graphene oxide/carbon nanotube for high performance lithium ion batteries.

Manganese oxides are promising anode materials for their high-energy density. However, they suffer from poor rate capability and fast capacity fading. Herein, we construct a three-dimensional (3D) core-shell structured polypyrrole (PPy)/MnO2-reduced graphene oxide (rGO)-carbon nanotubes (CNTs) composite via a facile two-step method. In the structure, the CNTs can facilitate fast electron conduction and keep structural integrity. The flexible and conductive rGO nanosheets work as both a reactive material and a carrier for MnO2 in-situ growth. The MnO2 nanosheets well distributed on the rGO/CNTs scaffold favor the energy storage by way of fast Li+ insertion and extraction. PPy nanoparticles (∼10nm) well wrapped on the MnO2 nanosheets not only enable the interfacial stabilization, but also provide a buffer layer to accommodate the volume expansion. As a result, the as-prepared PPy/MnO2-rGO-CNTs composite exhibits high specific capacity, excellent cycling stability and good rate capability. A reversible specific capacity of 1748.1mAhg-1 is achieved at the current density of 100mAg-1 after 200 cycles. Even at a high current density of 1000mAg-1, the composite still exhibits 941.1mAhg-1 after 1200 cycles. The design strategy of the composite can be extended to other high-capacity metal oxide material.

A MnO2/Graphene Oxide/Multi-Walled Carbon Nanotubes-Sulfur Composite with Dual-Efficient Polysulfide Adsorption for Improving Lithium-Sulfur Batteries.

Lithium-sulfur batteries can potentially be used as a chemical power source because of their high energy density. However, the sulfur cathode has several shortcomings, including fast capacity attenuation, poor electrochemical activity, and low Coulombic efficiency. Herein, multi-walled carbon nanotubes (CNTs), graphene oxide (GO), and manganese dioxide are introduced to the sulfur cathode. A MnO2/GO/CNTs-S composite with a unique three-dimensional (3D) architecture was synthesized by a one-pot chemical method and heat treatment approach. In this structure, the innermost CNTs work as a conducting additive and backbone to form a conducting network. The MnO2/GO nanosheets anchored on the sidewalls of CNTs have a dual-efficient absorption capability for polysulfide intermediates as well as afford adequate space for sulfur loading. The outmost nanosized sulfur particles are well-distributed on the surface of the MnO2/GO nanosheets and provide a short transmission path for Li+ and the electrons. The sulfur content in the MnO2/GO/CNTs-S composite is as high as 80 wt %, and the as-designed MnO2/GO/CNTs-S cathode displays excellent comprehensive performance. The initial specific capacities are up to 1500, 1300, 1150, 1048, and 960 mAh g-1 at discharging rates of 0.05, 0.1, 0.2, 0.5, and 1 C, respectively. Moreover, the composite cathode shows a good cycle performance: the specific capacity remains at 963.5 mAh g-1 at 0.2 C after 100 cycles when the area density of sulfur is 2.8 mg cm-2.