Bilayered V2O5 Batteries - ACS

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Glyme-Based Electrolyte for Na/Bilayered V2O5 Batteries Xu Liu, Bingsheng Qin, Huang Zhang, Arianna Moretti, and Stefano Passerini ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00128 • Publication Date (Web): 11 Mar 2019 Downloaded from http://pubs.acs.org on March 17, 2019

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ACS Applied Energy Materials

Glyme-Based Electrolyte for Na/Bilayered V2O5 Batteries Xu Liu,†,§ Bingsheng Qin,†,§ Huang Zhang,†,§ Arianna Moretti,†,§ Stefano Passerini*,†,§ †Helmholtz

Institute Ulm (HIU), Electrochemistry I, 89081 Ulm, Germany

§Karlsruhe

*Corresponding

Institute of Technology (KIT), 76021 Karlsruhe, Germany

author

Email: [email protected]

ABSTRACT: Due to its large interlayer space and multivalent redox capability, bilayered-V2O5 is a very interesting host material for sodium metal batteries. However, the severe capacity fading upon cycling occurring with conventional organic carbonate-based electrolytes largely prevents its application. Herein, we report the outstanding performance of a Na-metal battery using GO/bilayered-V2O5 (GVO) composite positive electrode in glyme-based electrolyte. The battery shows excellent cycling stability benefiting from the stabilization of the Na metal anode due to the use of the glyme-based electrolyte, yielding to low polarization of the negative electrode as revealed via three-electrode cells tests. Interestingly, the cycle performance of presodiated-GVO//GVO (symmetric) cells suggests that the intercalation/de-intercalation is a very stable process also in conventional carbonate 1

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electrolyte, which is in contrast with previous reports proposing the intrinsic fading of V2O5 electrodes. Overall, the results demonstrate that the stabilization of the Na metal anode/electrolyte interface is the critical step to improve the cycling performance of Na-metal batteries using vanadium oxide-based cathodes.

KEYWORDS: bilayered-V2O5 cathode; sodium batteries; glyme-based electrolytes; cycling ability; rate performance; sodium anode

1. INTRODUCTION

Lithium-ion batteries are the most successful energy storage technology over the past few decades. However, the increasing demand of energy storage is leading to geopolitical concerns regarding the availability of lithium and, especially, cobalt supplies motivating the research interests towards alternative secondary battery chemistries.1 Because of the low cost, wide distribution, and abundance of sodium resource, as well as the high specific capacity offered by sodium metal anodes, roomtemperature sodium metal batteries are considered among the candidates to back up LIBs in applications characterized by less stringent requirements.2 In comparison with lithium ions, sodium ions possess larger radius, which leads to slower insertion kinetics and induces higher mechanical stress in the host structure.3 Bilayered-V2O5, characterized by an interlayer distance larger than 10 Å and offering multivalent redox centers (V3+, V4+, and V5+),4,5 is an appealing host material for Na, delivering high specific capacity and standing fast cycling rates. However, a severe capacity

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fading upon cycling has been always observed so far.6-10 In fact, the reported cycle life (which is generally fixed at 80% retention of the initial capacity) is limited to 100 cycles or even less, seriously hindering the application of bilayered-V2O5 as cathode material. Therefore, enhancing its cycling stability by deciphering the fading mechanism upon the sodiation/de-sodiation process is a crucial issue for both the fundamental understanding and the practical application. Presently, the collapse of the layered structure during sodiation/de-sodiation process is thought to be the main reason for the rapid capacity fading. Based on this hypothesis, structural engineering has been commonly adopted to promote the cycling ability of vanadium oxide. For instance, Wei et al. utilized iron as dopant to relieve the lattice breathing, which improved cycling stability.10 However, the capacity retention after 50 cycles at 100 mA g-1 was still limited to only 80%. In this respect, H+, Na+ and K+ were also used as pillaring agents to stabilize the vanadium slabs and suppress the structural collapse.11-15 These pillaring agents were very effective to enhance the cyclability, but in spite of inferior specific capacity (less than 100 mAh g-1) even at low specific currents (e.g., 50 mA g-1). On the other hand, the electrolyte plays an important role in determining the cells’ performance as well.16,17 In our previous work, the lifespan of bilayered-V2O5 cathode in lithium metal batteries was extended from 50 cycles to 628 cycles at 56 mA g-1 by replacing the conventional organic carbonate-based electrolyte with an ionic liquidbased electrolyte.18 Glyme-based electrolytes are awakening interests in sodiumbased battery chemistry.19 Jache et al. observed the co-intercalation of sodium ions 3



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and glyme solvent molecules into graphite leading to superior cycling stability and rate capability.20 Seh et al. found that the glyme-based electrolyte enabled highly reversible and non-dendritic plating/stripping of sodium metal anodes.21 Moreover, the use of glyme-based electrolytes can significantly promote the electrochemical performance of a series of anode materials, including bulk metals,22,23 metal sulfides24-27 and phosphides28. Owing to these successes, exploring the effectiveness of glyme-based electrolytes for bilayered-V2O5 is of interests. Since bilayered-V2O5 has a very large interlayer distance enabling the intercalation of various mono- and multivalent cations (e.g., Li+, Na+, K+, Mg2+, Ba2+, Ca2+, and Zn2+),5,

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and even

polymers,33 the occurrence of Na+-solvent co-intercalation cannot be excluded. However, this might lead to better cyclability and rate performance as already observed for other host materials. Together with the protection of the sodium metal anode, by avoiding the consumption of electrolyte through irreversible side reactions, glyme-based electrolytes can effectively improve the reversibility and cycling stability of Na-metal batteries.34 Herein, the graphene oxide/bilayered-V2O5 (GVO) composite synthesized via a highly efficient microwave reaction was used as a model to investigate the sodium storage behavior of bilayered-V2O5 in glyme-based electrolytes. To the best of our knowledge, these characterization has not been reported yet. The effects of various sodium salts (NaPF6, NaClO4, NaTFSI, and NaFSI) and electrolyte solvents (glyme, diglyme, and tetraglyme) on the cycling stability were evaluated. Compared with conventional carbonate-based electrolytes, the use of glyme-based electrolytes not 4


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only enhanced the cycling stability, but also remarkably promoted the rate performance. The reasons for the highly enhanced performance were also systematically investigated.

2. EXPERIMENTAL DETAILS 2.1. Synthesis of GVO composite The room-temperature sol-gel method is commonly used to prepare bilayeredV2O5.4 However, the aging process needing several days to transform the V2O5 sol into gel limits its effectiveness. In this work, an innovative, highly efficient synthesis of bilayered-V2O5 is reported for the first time based on a microwave driven reaction. Making use of the dielectric heating mode, the bilayered-V2O5 composite containing 5 wt.% GO, was obtained within 30 min at 140 °C while the yield was as high as 91%. Notably, only 100 s were needed to reach 140 °C, after which a power as low as 15 W was sufficient to keep the temperature constant (see Fig. S1). In a typical procedure, 25 mg GO prepared according to the modified Hummers’ method35 were dispersed in 18.25 mL ultrapure water via ultrasonic water bath for 1 h. After this, 1.75 mL H2O2 solution (Sigma Aldrich, 30 wt. %) was added to the GO suspension. The mixture was kept under stirring in a water/ice bath while adding 500 mg V2O5 (Pechiney). After 1 h, the suspension was placed in a water bath at 25 ºC for an additional hour and then transferred into a glass reactor (30 mL, Anton Paar). The reactor was heated in a microwave oven (Monowave 300, Anton Paar) up to 140 ºC in 5 min, and held at such a temperature for 30 min. The obtained product was

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centrifuged and rinsed with anhydrous acetone (VWR, 99.5%) to exchange the residual water. After the final drying with supercritical CO2 at 32 ºC and 82 bar, the graphene oxide-vanadium oxide (GVO) composite was obtained. To avoid the uptake of water, GVO was stored in sealed vessels inside the dry room (dew point

Bilayered V2O5 Batteries - ACS

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