PDF Publication Title:
Text from PDF Page: 065
Review Article Chem Soc Rev presence of NaF in NaPF6 using X-ray diffraction and the observa- tion of the insoluble fraction in NaPF6/EC:DMC solution by the naked eye when exceeding concentrations of 0.4 M.576 Recently, Kubota et al. discuss the influence of the NaPF6 salts with different purities on the solubility of the organic solvents and the electrochemical properties.18 When they tried to dissolve the reagent grade NaPF6, 1 M NaPF6 was not completely dissolved in PC. However, by selecting the battery grade NaPF6, 1 M NaPF6 in the PC solution was revealed to be colorless and transparent because of the complete dissolution of 1 M NaPF6. As anticipated from the electrolyte coloration, the hard carbon anode exhibited better electrochemical performances in the battery grade NaPF6 containing electrolyte solution (Fig. 42d). The above results convinced that the choice of a well-balanced mixture solvent and high purity Na-salt is very important for identifying suitable electrolyte solutions.567,568,570 Recently, for improving the Na storage performances, ether-based electrolytes also have been reported for SIBs.259,261,262,413,429,453,578–581 Especially in graphite anodes, it is found that by using ether- based electrolytes rather than conventionally used ester-based electrolytes, the co-insertion of solvent and sodium ions can be successfully achieved. Kim et al. and Zhu et al. systematically studied the application and the mechanism of graphite as an anode material for SIBs in some ether-based electrolytes.259,262 Some research groups enabled transition-metal disulfides to achieve high-rate capability and long-term cyclability by optimizing the electrolytes and voltage windows in ether-based electrolytes. With regard to transition-metal chalcogenides, ether-based electrolytes exhibited a higher solvent-salt stability and a lower reaction energy barrier than those of carbonate- based electrolytes.407,413,429,578 4.2. Additives Another major component, often needed to create a functional electrolyte is the choice of additives. Generally, additives are used in functional electrolyte formulations for stable SEI formation and to enhance its electrochemical stability, and are also required for battery safety issues such as reducing flammability and preventing overcharging processes.99,569,577 Komaba et al. examined and compared the electrochemical performance of Na cells with several additives in 1 M NaClO4 in PC solution, including fluoroethylene carbonate (FEC), trans- difluoroethylene carbonate (DFEC), ethylene sulfite (ES), and vinylene carbonate (VC), which are well-known to be efficient electrolyte additives for Li-ion batteries.577 The results demon- strated that FEC is the only efficient electrolyte additive for both the cathode and anode. According to Komaba et al.’s reports, an appropriate amount of FEC additive (2 volume%) is helpful for forming high quality passivation films on the electrode surface, as well as for suppressing the side reactions between the Na metal and propylene carbonate solution containing Na salts (Fig. 42e). Meanwhile, Ponrouch et al. observed a decrease in specific capacity and Coulombic efficiency of the hard carbon electrode when FEC was used in the EC:PC solution containing 1 M NaClO4 salt.249 Unlike the PC only based electrolyte, the EC:PC mixture based electrolyte promoted efficient SEI layer mixture solutions. Interestingly, VC is commonly accepted as a suitable additive to modify the interface via thin film forming of the electrodes; however, the addition of VC in a PC solvent was not found to play the same role in hard carbon electrodes. Appropriate additives for SIBs are specifically discussed in the additive part. On the other hand, anodic stability without electrolyte decomposition at high voltage is also a crucial issue for achieving practical SIBs without gas evolution and battery swelling.568 Recently, Oh et al. proposed an ethyl methanesulfonate-based (EMS) electrolyte containing the NaClO4 salt (Fig. 42b). A high anodic stability (up to 5.6 V versus Na/Na+) and ionic conduc- tivity (6.0 103 S cm1) can be achieved by replacing the PC with EMS.51 On the other hand, in order to realize practical SIBs, many researchers have explored alternative Na salts with high battery performances as well as good battery safety. Ponrouch et al. systematically investigated the most appropriate electrolyte formulation so as to minimize the interface reactions and enhance both cell performances and safety aspects.28 They evaluated the basic properties of the electrolyte solution such as viscosity, ionic conductivity, and thermal and electrochemi- cal stability in diverse solvent mixtures and Na-based salts having either F-based or perchlorate anions. Especially, safety issues, in which they evaluated the thermal stability using fully reduced hard carbon powders in the selected electrolytes via DSC measurements: (i) NaClO4 in PC, (ii) NaClO4 in EC:PC, (iii) NaClO4 in EC:DEC and (iv) NaPF6 in EC:PC. Among them, NaPF6 in the EC:PC electrolyte exhibited the high thermal stability with a first exothermic peak onset temperature of 156.2 1C and a low heat generation of 717.2 J g1 (Fig. 42c). The appearance of an exothermic peak at a high temperature of NaPF6 in the EC:PC electrolyte can be ascribed to how a significantly more thermally stable SEI layer is formed on a hard carbon surface after cycling compared to those of the other electrolytes. On the other hand, Komaba et al. observed the stable cycling performances in hard carbon electrodes with the NaPF6-based electrolyte solution in comparison to those of the NaClO4-based electrolyte.27 Bhide et al. carried out a comparative study of the physico-chemical properties of non- aqueous liquid electrolytes based on NaPF6, NaClO4 and NaCF3SO3 salts in the binary mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC).576 Bhide et al. also observed that the NaPF6-based electrolyte demonstrated a higher ionic conductivity as a function of composition and temperature. Additionally, in view of practical Na-ion battery systems, the electrolytes are electrochemically tested with Na0.7CoO2 as a cathode. The results showed that the electrolyte NaPF6–EC:DMC is favorable for the formation of a stable surface film and the reversibility of the Na0.7CoO2 cathode material. Ponrouch et al. also achieved a high rate capability for the Na3V2(PO4)2F3 cathode and the hard carbon/Na3V2(PO4)2F3 full cell in 1 M NaPF6 in the EC:PC:DMC (45:45:10, v/v) electrolyte.574 However, when using the NaPF6 containing electro- lyte for the electrode materials, negative effects also occurred, such as low ionic conductivity of the SEI formation associated with the presence of NaF. In addition, Bhide et al. proved the View Article Online 3592 | Chem. Soc. Rev., 2017, 46, 3529--3614 This journal is © The Royal Society of Chemistry 2017 Open Access Article. Published on 28 March 2017. Downloaded on 7/1/2019 3:41:21 AM. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.PDF Image | Sodium-ion batteries present and future
PDF Search Title:
Sodium-ion batteries present and futureOriginal File Name Searched:
Sodium-ion batteries present and future.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Salt water flow battery technology with low cost and great energy density that can be used for power storage and thermal storage. Let us de-risk your production using our license. Our aqueous flow battery is less cost than Tesla Megapack and available faster. Redox flow battery. No membrane needed like with Vanadium, or Bromine. Salgenx flow battery
| CONTACT TEL: 608-238-6001 Email: greg@salgenx.com | RSS | AMP |