PDF Publication Title:
Text from PDF Page: 026
J. Phys. Energy 3 (2021) 031503 N Tapia-Ruiz et al 2.2. Titanium-based oxides Sara I R Costa1,3, Rebecca R Boston2,3 and Nuria Tapia-Ruiz1,3 1 Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom 2 Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom 3 The Faraday Institution, Quad One, Harwell Science and Innovation Campus, OX11 0RA, United Kingdom Status Titanium-based oxides are among the most promising and versatile Na anode materials, due to their low cost, ease of processing, and non-toxicity. These materials are safer than carbon-based anodes given their higher operating voltage, which prevents metallic sodium plating. This occurs, however, at the cost of delivering lower energy density. In most cases, the storage of Na+ ions occurs through a (de)insertion mechanism driven by the Ti4+/Ti3+ redox couple. The most representative oxides include TiO2, Li4Ti5O12, Na2Ti6O13, and Na2Ti3O7, which will be briefly described herein. TiO2-based anodes are a promising avenue of research, due to their high structural stability and theoretical capacity (335 mAh g−1). Microsized TiO2 is inactive in NIBs; however, reducing the particle size to the nanoscale activates reversibility, achieving practical capacities of ca. 155 mAh g−1 [103]. The various TiO2 polymorphs exhibit different electrochemical performances, with anatase (crystalline and amorphous) generally being the favoured form [104]. Li4Ti5O12 (Fd-3m) has been widely studied as an anode in LIBs due to its zero-strain behaviour [105]. In NIBs, it delivers a reversible capacity of 155 mAh g−1 by inserting three Na+ ions into the structure at a relatively low potential (0.9 V) [106]. Among the Na–Ti–O ternary compounds, Na2Ti6O13 (C2/m) shows high Na+ ion diffusion due to its tunnel structure and small volume change (<1%) upon Na+ ion (de)insertion. However, it displays an impractical storage capacity of 49.5 mAh g−1 [107]. Control of the morphology, particle size, and exposed crystal facets has significantly increased the capacity to 109 mAh g−1 (at a rate of 1 A g−1) after 2800 cycles [108]. On the other hand, Na2Ti3O7 (P21/m) has been widely investigated in recent years due to its low working potential (0.3 V); it delivers the highest energy density among this family of compounds (figure 11). Na2Ti3O7 exhibits a specific capacity of 177 mAh g−1 through the reversible insertion of two Na+ ions per formula unit [109]. Current challenges to be overcome before this compound can be used in practical applications include poor electronic conductivity and sluggish Na+ ion (de)insertion kinetics. These will be described in detail below. Recent advances in this area include the discovery of a new Na2Ti3O7 triclinic phase (P-1) with a similar working potential to the monoclinic phase, but with an outstanding capacity retention of 94.7% (after 20 cycles at 20 mA g−1) [110], and the development of Na2Ti3O7/Na2Ti6O13 hybrids, which combine the higher storage capacity and ionic conductivity of their respective phases, resulting in excellent cycling stability and superior rate performance [111]. Current and future challenges The main factors limiting the commercialisation of Na2Ti3O7 (NTO) in NIBs are the low electronic conductivity and sluggish Na+ ion (de)intercalation kinetics, which result in poor rate performance and cycling stability. The presence of Ti4+ ions (d0) makes NTO an electrical insulator (bandgap energy ≈ 3.7 eV) [112], which hampers Na+ ion diffusion within the crystal structure (DNa+ in NTO is ≈ 2–3 orders of magnitude lower than that in hard carbon). Thus, a major area of research encompasses the development of strategies to enhance long-term cycling stability, particularly at high current densities. These mainly involve: (a) bulk and surface structural control through doping and the introduction of defects; (b) nanostructuring; and (c) composite fabrication with carbon allotropes. Furthermore, the formation of an SEI layer on the surface of the electrode and the consumption of Na+ ions by carbon additives below 1 V result in low initial coulombic efficiency (ICE) (40%–60%). These phenomena are particularly critical in full cells, where there is limited sodium available. Methodologies are therefore required to mitigate the initial capacity irreversibility, although, to date, such procedures are underdeveloped. Additionally, the high reactivity of Na metal when used in half cells contributes to the underperformance of NTO due to the formation of an unstable SEI layer, requiring the use of three-electrode cells and full cells to gain a better insight into the Na contribution to the overall performance. Few studies have demonstrated the complex nature of the SEI composition. For example, Casas-Cabanas et al reported the formation of various SEI inorganic and organic species, such as Na2CO3, alkyl carbonates and PEO during discharge when using 1 M NaClO4 in an EC:PC electrolyte [113]. Moreover, NaCl and NaF products have been observed before cycling, as a result of the decomposition of the NaClO4 inorganic electrolyte salt and the Polyvinylidene fluoride (PVDF) binder, respectively. Alternative inorganic salts, such 25PDF Image | 2021 roadmap for sodium-ion batteries
PDF Search Title:
2021 roadmap for sodium-ion batteriesOriginal File Name Searched:
roadmap-sodium-ion-batteries_031503.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 (Standard Web Page)