Spinel oxide cathode material for high power lithium ion batteries for electrical vehicles

Electrical Vehicles (EVs) are very important in reducing fossil oil consumption and carbon emission in cities. Spinel LiNi0.5Mn1.5O4 is one promising cathode material for lithium ion batteries used in EVs owing to its high power density. Here AlF3 coated LiNi0.5Mn1.5O4 is prepared through an newly developed method. The spinel oxide sintered at 900 ̊C presents the best electrochemical performance with a specific discharge capacity of 132.4 mAh/g at 0.5 C. 81.0% of the initial specific capacity can be retained after 50 cycles. AlF3 coating can further improve the electrochemical performance. The initial specific capacity at 10 C is enhanced from 104.6 to 109.1 mAh g-1 with the capacities retention increasing from 80.6 to 92.1% after 100 cycles

Ultrahigh and Durable Volumetric Lithium/Sodium Storage Enabled by a Highly Dense Graphene-Encapsulated Nitrogen-Doped Carbon@Sn Compact Monolith

2020 American Chemical Society. Tin-based composites hold promise as anodes for high-capacity lithium/sodium-ion batteries (LIBs/SIBs); however, it is necessary to use carbon coated nanosized tin to solve the issues related to large volume changes during electrochemical cycling, thus leading to the low volumetric capacity for tin-based composites due to their low packing density. Herein, we design a highly dense graphene-encapsulated nitrogen-doped carbon@Sn (HD N-C@Sn/G) compact monolith with Sn nanoparticles double-encapsulated by N-C and graphene, which exhibits a high density of 2.6 g cm-3 and a high conductivity of 212 S m-1. The as-obtained HD N-C@Sn/G monolith anode exhibits ultrahigh and durable volumetric lithium/sodium storage. Specifically, it delivers a high volumetric capacity of 2692 mAh cm-3 after 100 cycles at 0.1 A g-1 and an ultralong cycling stability exceeding 1500 cycles at 1.0 A g-1 with only 0.019% capacity decay per cycle in lithium-ion batteries. Besides, in situ TEM and ex situ SEM have revealed that the unique double-encapsulated structure effectively mitigates drastic volume variation of the tin nanoparticles during electrode cycling. Furthermore, the full cell using HD N-C@Sn/G as an anode and LiCoO2 as a cathode displays a superior cycling stability. This work provides a new avenue and deep insight into the design of high-volumetric-capacity alloy-based anodes with ultralong cycle life

Effect of Process Parameters on Tensile Mechanical Properties of 3D Printing Continuous Carbon Fiber-Reinforced PLA Composites

Three-dimensional (3D) printing continuous carbon fiber-reinforced polylactic acid (PLA) composites offer excellent tensile mechanical properties. The present study aimed to research the effect of process parameters on the tensile mechanical properties of 3D printing composite specimens through a series of mechanical experiments. The main printing parameters, including layer height, extrusion width, printing temperature, and printing speed are changed to manufacture specimens based on the modified fused filament fabrication 3D printer, and the tensile mechanical properties of 3D printing continuous carbon fiber-reinforced PLA composites are presented. By comparing the outcomes of experiments, the results show that relative fiber content has a significant impact on mechanical properties and the ratio of carbon fibers in composites is influenced by layer height and extrusion width. The tensile mechanical properties of continuous carbon fiber-reinforced composites gradually decrease with an increase of layer height and extrusion width. In addition, printing temperature and speed also affect the fiber matrix interface, i.e., tensile mechanical properties increase as the printing temperature rises, while the tensile mechanical properties decrease when the printing speed increases. Furthermore, the strengthening mechanism on the tensile mechanical properties is that external loads subjected to the components can be transferred to the carbon fibers through the fiber-matrix interface. Additionally, SEM images suggest that the main weakness of continuous carbon fiber-reinforced 3D printing composites exists in the fiber-matrix interface, and the main failure is the pull-out of the fiber caused by the interface destruction

Transparent and Self-Supporting Graphene Films with Wrinkled- Graphene-Wall-Assembled Opening Polyhedron Building Blocks for High Performance Flexible/Transparent Supercapacitors

Improving mass loading while maintaining high transparency and large surface area in one self-supporting graphene film is still a challenge. Unfortunately, all of these factors are absolutely essential for enhancing the energy storage performance of transparent supercapacitors for practical applications. To solve the above bottleneck problem, we produce a novel self-supporting flexible and transparent graphene film (STF-GF) with wrinkled-wall-assembled opened-hollow polyhedron building units. Taking advantage of the microscopic morphology, the STF-GF exhibits improved mass loading with high transmittance (70.2% at 550 nm), a large surface area (1105.6 m²/g), and good electrochemical performance: high energy (552.3 μWh/cm³), power densities (561.9 mW/cm³), a superlong cycle life, and good cycling stability (the capacitance retention is ∼94.8% after 20,000 cycles)

Ultra-thick, dense dual-encapsulated Sb anode architecture with conductively elastic networks promises potassium-ion batteries with high areal and volumetric capacities

Ultra-thick, dense alloy-type anodes are promising for achieving large areal and volumetric performance in potassium-ion batteries (PIBs), but severe volume expansion as well as sluggish ion and electron diffusion kinetics heavily impede their widespread application. Herein, we design highly dense (3.1 ​g ​cm−3) Ti3C2Tx MXene and graphene dual-encapsulated nano-Sb monolith architectures (HD-Sb@Ti3C2Tx-G) with high-conductivity elastic networks (1560 ​S ​m−1) and compact dually encapsulated structures, which exhibit a large volumetric capacity of 1780.2 ​mAh cm−3 (gravimetric capacity: 565.0 ​mAh g−1), a long-term stable lifespan of 500 cycles with 82% retention, and a large areal capacity of 8.6 ​mAh cm−2 (loading: 31 ​mg ​cm−2) in PIBs. Using ex-situ SEM, in-situ TEM, kinetic investigations, and theoretical calculations, we reveal that the excellent areal and volumetric performance mechanism stems from the three dimensional (3D) high-conductivity elastic networks and the dual-encapsulated Sb architecture of Ti3C2Tx and graphene; these effectively mitigate against volume expansion and the pulverization of Sb, offering good electrolyte penetration and rapid ionic/electronic transmission. Ti3C2Tx also decreases the K+ diffusion energy barrier, and the ultra-thick compact electrode ensures volumetric and areal performance. These findings provide a feasible strategy for fabricating ultra-thick, dense alloy-type electrodes to achieve high areal and volumetric capacity energy storage via highly-dense, dual-encapsulated architectures with conductive elastic networks

Improvement in capacity retention of cathode material for high power density lithium ion batteries: The route of surface coating

Using electrical vehicles instead of traditional ones is very important for reducing fossil oil consumption and carbon emissions. Spinel LiNi0.5Mn1.5O4 is considered as a promising cathode material for advanced lithium ion batteries owing to its high power density. Nevertheless, it suffers badly from the interfacial reactions with the electrolyte at high operation potential, which degrades its electrochemical performance. The strategy of the present study is to prevent direct contact between LiNi0.5Mn1.5O4 and the electrolyte by using a surface coating in order to reduce solid electrolyte interfacial reactions and consequently enhance its cycling performance. The experimental results indicated that as-prepared LiNi0.5Mn1.5O4 sintered at 900 °C possessed the highest initial specific capacity of 132.4 mA h·g−1 at 0.2 C rate, with 81.0% initial capacity retention after 50 cycles. Coating AlF3 on the particle surfaces of LiNi0.5Mn1.5O4 using a modified solid-state method can improve its electrochemical properties by enhancing its initial specific capacity from 104.6 to 109.1 mA h·g−1 and increasing its capacity retention from 80.6 to 92.1% at the 10 C rate after 100 cycles