Stability For Electrooxidation Research Articles

Quasi-solid polymer electrolytes with binary and ternary salt mixtures for high-voltage lithium metal batteries

Quasi-solid polymer electrolytes (QSPEs) are considered a promising alternative to liquid electrolytes for high-voltage lithium metal batteries. Herein, we present their properties and performance supported on polyolefin microporous separators. These QSPEs consist of a poly(vinylidene-fluoride-co-hexafluoropropylene) polymer matrix, ethylene carbonate as a plasticizer, and various lithium salt mixtures, including lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalate)borate (LiBOB), and LiNO3 as a solid electrolyte interface-forming additive. They exhibit an ionic conductivity of ca. 1 mS cm-1 at room temperature and excellent resistance against lithium dendrites, attributed to the presence of the tough polyolefin separator. The effect of the lithium salt mixture composition on lithium plating/stripping performance and electrooxidation stability was studied in detail, showing that LiNO3, while having a clear positive effect on the plating/stripping performance, may also adversely affect the oxidative stability of the electrolyte, accelerating the degradation of the cathode/electrolyte interface. QSPEs with binary LiFSI/LiBOB salt mixtures were tested at room temperature in a LiNi0.8Mn0.1Co0.1O2||Li monolayer pouch cell with a cathode area capacity of ca. 2.5 mAh cm-2. This cell delivered an initial capacity close to 200 mAh g-1 at C/20, 150 mAh g-1 at C/1, and 80% capacity retention after 100 cycles at 25 °C. The results demonstrate the viability of supported QSPEs, based on poly(vinylidene-fluoride-co-hexafluoropropylene), ethylene carbonate, LiFSI and LiBOB, for application in high-voltage quasi solid-state lithium metal batteries.

Nanocomposite solid polymer electrolytes based on semi-interpenetrating hybrid polymer networks for high performance lithium metal batteries

This research reports the synthesis of nanocomposite solid polymer electrolytes (ncSPEs) for solid state lithium metal batteries. These materials are composed of a controlled hybrid organic-inorganic network of glycidyl POSS® and Jeffamine® ED2003, in which linear high molecular weight poly (ethylene oxide) (PEO) chains are entangled to improve both mechanical and electrochemical properties of the ncSPE. Synthesis and preparation of self-standing membranes are achieved with a facile one-pot catalyst-free method with considerably reduced amount of organic solvent, which is a plus toward a future scale-up. We found that the component ratio plays a crucial role in ncSPEs’ performance as a simple variation (i.e. cross-linking degree) is sufficient to completely change the electrochemical behavior of the solid state cell. For instance, increasing POSS® amount guarantees better resistance to lithium dendrites penetration, better electro-oxidation stability, and significantly extends cycle life in Li/ncSPE/LiFePO4 solid state cells. Furthermore, besides improving cell performance at higher C-rate of Li/LiFePO4 cells, this PEO-based ncSPE gives better response than reference PEO-LiTFSI electrolyte in high voltage Li/LiNi0.6Mn0.2Co0.2O2 cells with up to 10 cycles at 60 °C with discharge capacity retention above 80%. Despite the poor performance, to the best of our knowledge, this electrolyte is one of the few examples of PEO-based solid polymer electrolytes being capable of cycling with high voltage cathodes.

Mesoporous NiCo2O4 nanoneedles grown on 3D graphene-nickel foam for supercapacitor and methanol electro-oxidation

Mesoporous NiCo2O4 nanoneedles were directly grown on three dimensional (3D) graphene-nickel foam which was prepared by chemical vapor deposition, labeled as NCO/GNF. The structure and morphology of NCO/GNF were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, element mapping and Raman spectroscopy. The NCO/GNF was employed as electrodes for supercapacitor and methanol electro-oxidation. When used for supercapacitor, the NiCo2O4 nanoneedles exhibit hi exhibit high specific capacitance (1588Fg−1 at 1Ag−1), high power density and energy density (33.88Whkg−1 at 5kWkg−1) as well as long cycling stability. In methanol electro-oxidation, the NiCo2O4 nanoneedles deliver high electro-oxidation activity (93.3Ag−1 at 0.65V) and electro-oxidation stability. The good electrochemical performance of NiCo2O4 nanoneedles is attributed to the 3D structure with large specific area, high conductivity and fast ions/electrons transport.

CNT–Ni/SiC hierarchical nanostructures: preparation and their application in electrocatalytic oxidation of methanol

CNT–Ni/SiC composites with three-dimensional hierarchical nanostructures were fabricated via in situ pyrolysis of methane to grow CNTs on a novel flake-like NiO/SiC material. The NiO/SiC was prepared by hydrothermally growing Ni(OH)2 on SiC. After calcination, Ni(OH)2 was converted to porous NiO flakes. During the methane pyrolysis, NiO was in situ converted to Ni nanoparticles, which acted as the catalyst for growing CNTs. Due to the combination of Ni nanoparticles, in situ grown CNTs and the SiC support, the CNT–Ni/SiC composites exhibit excellent catalytic activity and stability in electro-oxidation of methanol. The catalytic activity shows a dependence on the pyrolysis temperature of methane, and a pyrolysis temperature of 700 °C can lead to a mass activity of 10 A mg−1 Ni, which is about 15 times higher than that of the catalyst obtained from methane pyrolysis at 500 °C and about 4000 times higher than that of the original NiO/SiC catalyst.