ABSTRACT
The electrochemical performance of ionic liquid electrolytes containing different sodium salts dissolved in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI) evaluated in a half-cell configuration using spherical P2-Na0.6Co0.1Mn0.9O2+z (NCO) cathodes are reported. Among the various electrolytes investigated, sodium bis(fluorosulfonyl)imide (NaFSI) (0.5 M) in BMPTFSI shows the best electrochemical performance with a significant improvement in cycling stability (90% capacity retention after 500 cycles at 50 mA g-1 in a half cell versus Na metal anode) compared with conventional NaClO4 (1 M) in ethylene carbonate/propylene carbonate electrolytes (39% retention after 500 cycles). Cyclic voltammetry (CV) studies reveal that ionic liquid electrolytes are stable up to 4.8 V versus Na/Na+. When NaFSI and NaTFSI are used as conducting salts, X-ray photoelectron spectroscopy results prove that the cathode electrolyte interface (CEI) is composed of components resulting from the decomposition of the TFSI anion and the deposition of the BMP cation. On the other hand, the CEI layer of the electrode cycled in an electrolyte containing NaClO4 in BMPTFSI follows a different pathway of TFSI decomposition and consists mainly of sodium fluoride. Similarly, plating studies were used to understand the stability of different ionic liquids in contact with metallic sodium. It was found that the excellent capacity retention for the electrolyte consisting of NaFSI salt is related to the formation of a stable CEI and solid electrolyte interphase layers.
ABSTRACT
Sodium ion batteries (SIBs) based on IL electrolytes have attracted great attention, particularly in large-scale energy storage systems for renewable energy due to the abundance of sodium and the excellent safety resulting from the use of non-flammable ionic liquid (IL) electrolytes. In this article, a series of 15 functionalized room temperature ionic liquids (RTILs) suitable as electrolytes is presented. Special emphasis was laid on the purity of the synthesized RTILs and a consistent and uniform characterization of their physicochemical properties. Evaluation of the viscosity, conductivity, and thermal and electrochemical stabilities resulted in clear structure-property relationships, rendering the ether functionalized RTILs most promising for application in SIBs. Electrochemical investigations of the ether functionalized IL electrolytes in SIB half cells (Na0.6Mn0.9Co0.1O2 as cathode material) proved their compatibility with a SIB system. Stable cycling performance was achieved with the piperidinium based RTIL IL 6 outperforming the organic electrolyte by far with a retention of 81% after 350 cycles. These results show the suitability of RTILs to enhance the performance of SIB systems and serve as a basis for the design of high performance IL electrolytes.
ABSTRACT
Formation of vanadium oxide nanofilm-coated graphene oxide (GO) is achieved by thermally induced explosive disintegration of a microcrystalline ammonium peroxovanadate-GO composite. GO sheets isolate the microcrystalline grains and capture and contain the microexplosion products, resulting in the deposition of the nanoscale products on the GO. Thermal treatment of the supported nanofilm yields a sequence of nanocrystalline phases of vanadium oxide (V3O7, VO2) as a function of temperature. This is the first demonstration of microexplosive disintegration of a crystalline peroxo compound to yield a nanocoating. The large number of recently reported peroxide-rich crystalline materials suggests that the process can be a useful general route for nanofilm formation. The V3O7@GO composite product was tested as a sodium ion battery anode and showed high charge capacity at high rate charge-discharge cycling (150 mAh g-1 at 3000 mA g-1 vs 300 mAh g-1 at 100 mA g-1) due to the nanomorphology of the vanadium oxide.
ABSTRACT
High-charge-capacity sodium-ion battery anodes made of Sb2Te3@reduced graphene oxide are reported for the first time. Uniform nano-coating of graphene oxide is carried out from common sol of peroxotellurate and peroxoantimonate under room temperature processing. Reduction by hydrazine under glycerol reflux yields Sb2Te3@reduced graphene oxide. The electrodes exhibit exceptionally high volumetric charge capacity, above 2300mAhcm-3 at 100mAg-1 current density, showing very good rate capabilities and retaining 60% of this capacity even at 2000mAg-1. A comparison of sodiation and lithiation shows that lithiation exhibits better volumetric charge capacity, but surprisingly only marginally better relative rate capability retention at 2000mAg-1. Tellurium-based electrodes are attractive due to the high volumetric charge capacity of Te, its very high electric conductivity, and the low relative expansion upon lithiation/sodiation.
ABSTRACT
Due to its potential cost advantage, sodium ion batteries could become a commercial alternative to lithium ion batteries. One promising cathode material for this type of battery is layered sodium manganese oxide. In this investigation we report on the influence of morphology on cycle performance for the layered NaxMnO2+z. Hollow spheres of NaxMnO2+z with a diameter of â¼5 µm were compared to flake-like NaxMnO2+z. It was found that the electrochemical behavior of both materials as measured by cyclic voltammetry is comparable. However, the cycle stability of the spheres is significantly higher, with 94 mA h g(-1) discharge capacity after 100 cycles, as opposed to 73 mA h g(-1) for the flakes (50 mA g(-1)). The better stability can potentially be attributed to better accommodation of volume changes of the material due to its spherical morphology, better contact with the added conductive carbon, and higher electrode/electrolyte interface owing to better wetting of the active material with the electrolyte.
