Summary
In this paper, a systematic method has been developed to produce highly flexible and robust graphene/LiMn2O4 (G/LMO) and graphene/LiCr0.05Mn1.95O4 (G/LCMO) free‐standing composite cathode electrodes with increased specific capacity and improved electrochemical capability. Spinel LMO nanorods are synthesized by calcination method followed by a hydrothermal reaction technique. As‐synthesized nanorods were then embedded in a graphene layer which will in turn serve as a self‐standing binder‐free cathode electrode. Spinel LMO and LCMO nanorods with a length of 600 nm and width of 50 nm were then homogenously entrapped and distributed within the layers of conductive graphene structure. This hybrid structure will help to eliminate the use of heavy metal current collectors and electrically resistant binders or even conductive additives. A discharge capacity of 114.5 mAh g−1 is obtained after first cycle and %72 capacity retention is obtained after 250 cycles from G/LCMO freestanding samples. The enhancement in the electrochemical properties is due to the unique freestanding structure of the cathode electrodes.
The cathode electrodes in commercial Li-ion cells are usually coated on aluminum foils, while the anode part is coated on copper current collector. However, these metallic foils of the electrodes are relatively heavy counterparts when compared with the total cell weight. To overcome this issue, we comparatively studied LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC); NMC/graphene positive electrodes reinforced with graphene were produced in the form of freestanding electrodes by a facile sol-gel and vacuum filtration method. To confirm our results obtained with the half-cells, graphite@NMC@graphene full-cells were also produced and a specific capacity of 220 mAh g −1 after 250 cycles. Extraordinary electrochemical cycling, high conductivity, and enhanced rate properties are obtained by anchoring the NMC particles between the graphene layers. The results have also indicated that the freestanding graphene-based electrodes could be a useful tool for high-capacity lithium-ion batteries.
Different polymorphs of MnO2 (α-, β-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers’ method. Freestanding graphene/MnO2 cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO2 nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge–discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm−2 using CR2016 coin cells. The initial specific capacity of graphene/α-, β-, and γ-MnO2 freestanding cathodes was found to be 321 mAhg−1, 198 mAhg−1, and 251 mAhg−1, respectively. Finally, the graphene/α-MnO2 cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO2 freestanding cathodes exhibited a specific capacity of 229 mAhg−1 after 200 cycles with 72% capacity retention.
Summary
In this paper, nanosized Ni3Sn4 nanoparticles were synthesized by chemical reduction technique. A facile strategy is also developed to synthesize the yolk‐shell Ni3Sn4 nanoparticles decorated between the layers of multilayer graphene to obtain high‐capacity, long service life with comparable cost Li‐ion batteries. Ni3Sn4 nanoparticles in the form of yolk‐shell morphology were synthesized between 30 and 130 nm in size and homogeneously anchored on graphene layers as spacers preventing the layers merging after vacuum filtration. The characterization of the as‐synthesized composite electrodes was performed by scanning electron microscopy and X‐ray diffraction methods. As an anode electrode, yolk‐shell Ni3Sn4/graphene composite electrodes revealed a stable capacity of 324.5 mAh g−1 after 250 cycles, indicating that the composites might have a promising future application in Li‐ion batteries. The results have shown that unique yolk‐shell Ni3Sn4/graphene hybrid composite structure shows extraordinary electrochemical performance with superior reversible capacity and improved cyclic performance, indicating that the stacking of the active electrode nanoparticles between the graphene layers is a good method for maximum specific capacity outputs.
Significant climate change and variable fossil energy prices are forcing us to minimize fossil fuel consumption and develop innovative energy conversion and storage systems capable of reducing carbon dioxide emissions. Batteries are the most common form of alternative energy systems, and cathode materials are critical for their performance. Their low-rate performance and short lifespan severely hamper the efficiency of cathode materials. The adoption of nanotechnology is essential to improve the cathode life cycle and maintain capacity. Conventional synthetic techniques face serious problems in producing complex nanomaterials with precise design, high efficiency, and long life. Recent efforts have been made to utilize bio-inspired materials in a variety of applications, emphasizing the importance of biomimetics due to their unique advantages and excellent properties. This review examines the synthesis mechanism, properties, and advances of bioinspired materials in the production of nanomaterials in order to pave the way for the future study of rechargeable batteries. Subsequently, the solutions and problems encountered by cathode materials in the main categories of secondary rechargeable batteries are addressed. The aim of this study is to alert scientists toward this promising development trend in bio-inspired battery materials.
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