The increasing demand for large-scale energy storage propels the development of lithium-ion batteries with high energy and high power density. Low tortuosity electrodes with aligned straight channels have proved to be effective in building such batteries. However, manufacturing such low tortuosity electrodes in large scale remains extremely challenging. In contrast, high-performance electrodes with customized gradients of materials and porosity are possible to be made by industrial roll-to-roll coating process. Yet, the desired design of gradients combining materials and porosity is unclear for high-performance gradient electrodes. Here, triple gradient LiFePO 4 electrodes (TGE) are fabricated featuring distribution modulation of active material, conductive agent, and porosity by combining suction filtration with the phase inversion method. The effects and mechanism of active material, conductive agent, and porosity distribution on electrode performance are analyzed by experiments. It is found that the electrode with a gradual increase of active material content from current collector to separator coupled with the distribution of conductive agent and porosity in the opposite direction, demonstrates the best rate capability, the fastest electrochemical reaction kinetics, and the highest utilization of active material. This work provides valuable insights into the design of gradient electrodes with high performance and high potential in application.
Jinyue Yang,Jianxin Wang,Yongwen Lin,Xin Huang,Guangming Yin,Haixia Yu,Wendi Wang,Xinyou Zhang,Hong Pan
Transition metal sulfides are considered potential electrode materials for supercapacitors because of their low electronegativity, high electrochemical activity, and rich oxidation–reduction properties , but they also have the disadvantages of poor cycle stability and low magnification performance. In-situ growth sulfides on the current collector can strengthen the structural stability of the electrode to a certain extent, but this method only obtains a weak binding of the sulfide and current collector. With the progress of cycling, repeated structural evolution will inevitably lead to metal dissolution and sulfide shedding. In this study, nickel-poor reactants were cleverly adopted to synthesize one in-situ sulfide on nickel foam (NF) by activating the nickel element in NF to participate in the formation of sulfide, so as to obtain the in-situ electrode material with flower shape and gradient Ni content, named as Ni (2-x) CoS 4 /Ni 2 CoS 4 /Ni electrode. By further compounding polyaniline (PANI) on the surface of Ni (2-x) CoS 4 /Ni 2 CoS 4 /Ni electrode, the in-situ gradient Ni (2-x) CoS 4 /Ni 2 CoS 4 /Ni-PANI composite electrode (ISG-NCS-PANI) was obtained. This in-situ bimetallic sulfide has not only high stability, but also high reactivity. The flower shape with a large specific surface area is also beneficial to enhance the rate performance. As a result, the specific capacitance of the composite electrode is up to 2909.4 F g −1 at 1 A g −1 . After 5000 cycles, the capacity remains 83.8 %. The asymmetric supercapacitor (ASC) composed of activated carbon (AC) negative electrode has a specific capacitance of 211.11 F g −1 at 1 A g −1 . The power density of 749.99 W kg −1 shows the maximum energy density of 65.97 Wh kg −1 . The above results prove that ISG-NCS-PANI electrode holds significant potential for application prospect in the domain of energy storage and conversion.
Min Wu,Shumin Liu,Haofu Yuan,Zichao Zhao,Lin Qiao,Xiangkun Ma
Iron-chromium flow batteries (ICFBs) are regarded as one of the most potential large-scale energy storage devices. Nevertheless, the slow dynamics of the Cr 3+ /Cr 2+ redox couples hinder the development of ICFBs. Here, a high-efficiency carbon-loaded bismuth (Bi/C) catalyst is fabricated and introduced on the electrode in situ to improve the dynamics with the assistance of polyvinylpyrrolidone (PVP). To derive the greatest value, we explore the current density anisotropy in ICFB and design a strategy of anisotropy engineering to meet the requirements of the anisotropy for catalysts. In the work, the gradient electrode (G-PBiC/TCF) with a high-efficiency Bi/C catalyst is successfully prepared. In addition, the ICFB assembled with the G-PBiC/TCF(M/m, the side of more catalysts facing the Membrane side) shows excellent battery performance. It can run over 500 cycles with EE of 81.36% at 120 mA cm −2 , which is the longest cycle life reported. Furthermore, the catalytic mechanism and the effect of the catalyst distribution on the performance are explained by the DFT calculation and multi-physical field simulation. This work provides a novel pathway to design that catalyst-supported gradient electrode with high performance and low cost.
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