Elsevier

Journal of Power Sources

Volume 300, 30 December 2015, Pages 453-459
Journal of Power Sources

The electrochemical performance improvement of LiMn2O4/Zn based on zinc foil as the current collector and thiourea as an electrolyte additive

https://doi.org/10.1016/j.jpowsour.2015.09.096Get rights and content

Highlights

  • For the first time we used the sulfate salt system as a mixture electrolyte.

  • Thiourea as an additive improved the electrochemical performance of the battery.

  • Float charge current density and the self-discharge of Zn were decreased quickly.

Abstract

The polished commercial zinc foil as the current collector and thiourea (TU) as the electrolyte additive are studied systematically to improve the performance of LiMn2O4/Zn aqueous battery. The results show that the coulombic efficiency and the cycling performance are significantly improved by using the polished zinc foil as the anode current collector. Moreover, the TU addition increases the cycling performance of LiMn2O4/Zn battery and decreases the float charge current density of the battery at room as well as high temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests confirm that there is nearly no effect of TU in the electrolyte on the crystal structure of LiMn2O4 electrode. However, the addition of TU has an indirect effect on the morphology. Cyclic voltammetry (CV) and deposition–dissolution measurement demonstrate that TU is stable on the cathode electrode and it is able to adsorb to the surface of the zinc anode current collector. As such, the deposition–dissolution efficiency and energy efficiency are improved, which also can be attributed to faster deposition–dissolution and smaller self-discharge process of zinc.

Introduction

To lessen the energy shortage and environment pollution, it is of great significance to explore new energy storage and conversion systems such as lead-acid, nickel cadmium (Ni–Cd), nickel–metal hydride (Ni–MH) and non-aqueous lithium ion batteries (LIBs) [1]. However, Ni–Cd and lead-acid batteries present serious ecological threat due to the toxic heavy metals Pb and Cd. Ni–MH is expensive due to the low abundance of the precursors for anode material. Non-aqueous LIBs are not safe and economical because of highly toxic and flammable organic electrolytes. Moreover, there is a very high cost for battery assembly in the atmosphere without oxygen and water.

Compared to non-aqueous LIBs, the aqueous rechargeable lithium-ion batteries (ARLIBs) can overcome above mentioned disadvantages. Firstly, the fabrication costs can be reduced significantly since its electrode and electrolyte materials are not expensive. Secondly, the assembly process of ARLIBs is simple because they can be packaged in air [2]. Thirdly, it is inherently safe by avoiding the use of flammable organic electrolytes. Finally, the ionic conductivity of ARLIBs is about two orders of magnitude higher than that of non-aqueous LIBs, which can ensure high rate capability and high specific power density. Therefore, ARLIBs are more competitive as compared with that of lead-acid or Ni–Cd batteries. However, the cycling performance of ARLIBs is originally very poor due to the evolution of hydrogen and oxygen [3], [4].

During the past decades, many efforts have been made to improve the performance of the ARLIBs since it was proposed firstly by Dahn's group in 1994 [5]. Some researchers focus on studying the potential anode materials such as vanadium oxides including VO2 [6], TiO2 [7], LiV3O8 [8], NASICON-type LiTi2(PO4)3 [9] and pyrophosphate compounds TiP2O7 [10]. Although different systems of ARLIBs have shown compatible performance with these anode materials, including LiMn2O4/VO2 [6], LiCoO2/LiV3O8 [11], LiMn2O4/TiP2O7 [10], LiMn2O4/LiTi2(PO4)3 [12], Li[Ni1/3Co1/3Mn1/3]O2/LiV3O8 [13], LiFePO4/LiV3O8 [14] and so on [15], [16], the cycling performance of the batteries still needs to be improved substantially.

Recently, a novel aqueous battery system based on acid electrolyte called rechargeable hybrid aqueous battery (ReHAB) was reported firstly by Chen's group. This system shows a great prospect due to high working voltage and cheap electrode materials of LiMn2O4 and Zn [17]. After that, the LiMnPO4/Zn [18], LiCo1/3Mn1/3Ni1/3PO4/Zn [19], LiNiPO4/Zn [20] systems were also reported. According to Chen's report, the cycling performance is pretty good in ZnCl2 + LiCl system and the capacity retention is up to 90.0% after 1000 charge–discharge cycles. However, the float charge current density, Zn corrosion and Zn dendrite were ignored. Different from other ARLIBs, ReHAB operates in mild acidic aqueous electrolyte, and the charge–discharge mechanism in the anode side is not the intercalation and deintercalation of lithium ion but the reaction of Zn2+ deposition–dissolution. Thus, the charge–discharge efficiency, voltage efficiency and energy efficiency for the deposition–dissolution of Zn2+ will affect the overall electrochemical performance of ReHAB, including cycling performance, float charge current density, Zn corrosion and Zn dendrite.

Thiourea has been widely demonstrated as an additive in the Cu and Zn electrowinning in sulfate salt system, and it can increase the electrolytic efficiency of these metals due to the inhibition of hydrogen evolution [21], [22].

Herein, for the first time the thiourea is added into sulfate-salt-contained mixture electrolyte, and polished Zn is used as the current collector. We expect that such strategies will improve the cycling performance, decrease float charge current density and the self-discharge of Zn. Meanwhile, the reasonable explanations are figured out and discussed further.

Section snippets

Experimental

The working electrodes were prepared by casting slurries of LiMn2O4 (MTI Co.), KS-6 (Alfa Aesar Co.), and polyvinylidene fluoride (PVDF, Arkema Inc.) (86:7:7 wt.%) in N-methyl-2-pyrrolidinone (NMP, Sigma–Aldrich Co.) on graphite or polyethylene (PE) foil (SGL Group Co.), followed by drying in vacuum oven at 60 °C for 4 h. Disks of 12 mm diameter were cut (typical active material load of 7–8 mg cm−2) and soaked in the electrolyte solution under vacuum for 15 min. A 12 mm of commercial Zn foil

Different Zn current collectors

Contrary to the “rocking-chair” type LIBs and ARLIBs, exchange of lithium and zinc ions in the electrolyte occurs simultaneously upon cycling in LiMn2O4/Zn battery. The Zn2+ in the electrolyte for the Swagelok™-type battery is not only an ionic conductive medium but also the source of anode, which is formed by Zn deposition upon charge process and also regenerated because of Zn dissolution during the discharge process. Therefore, the Zn foil as the current collector affects the anode

Conclusions

In summary, the coulombic efficiency of the battery after 300 cycles is much more stable by using polished commercial zinc foil as the current collector as compared to that of without polished one, and the capacity retention of the former is more than 75.0% for polished commercial Zn, which is much higher than those of unpolished commercial Zn foil. Moreover, the capacity retention of the battery with unpolished Zn foil in the presence of thiourea is up to 75.0% of the initial discharge

Acknowledgments

This research was financially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), Scientific Research Start-up Funding of Jishou University (No. jsdxrcyjkyxm2014007), the National Natural Science Foundation of China (No. 51142001, No. 51262008, No. 51202087, No. 51364009), and Natural Science Foundation of Hunan Province, China (No. 12JJ2005, No. 14JJ4048), The Collaborative Innovation Center of Manganese-Zinc-Vanadium Industrial Technology (the 2011 Plan of

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