The eminent global energy crisis and growing ecological concerns in the past two decades lead to intensive development in the fields of clean energy sources such as wind and solar power. The successful penetration of green energy technologies highly depends on the deployment of large scale energy storage systems (ESS) with low cost, safe, and longevity. Lithium ion batteries (LIB) have been well acknowledged as EES with high energy density and long cycling life, and are superior to other conventional batteries. However, their inherent safety and cost issues related to the use of expensive, toxic and flammable organic electrolyte and superfast charging performance are still challenges for their applications in large-scale EES such as electric vehicles and smart grids ^[1].

To meet the needs of EES, batteries based on aqueous electrolytes are attractive candidates compared to the present LIB utilizing flammable and expensive organic electrolytes because of their improved safety and low cost. For these reasons, aqueous batteries, including Pb-Acid, Ni-Cd and Ni-MH batteries, are widely used in many markets such as electric scooters and automatically guided vehicles. However, the Pb-Acid batteries and Ni-Cd batteries raise the problem of toxic heavy-metal pollution, while the market of Ni-MH batteries is limited by its high cost due to the use of rare-earth metal for anodes ^[2]. So it is necessary to develop a new type of aqueous battery with qualities of low cost, safety, environmental benignity, long cycle life and acceptable energy density.

Zn is an ideal anode for aqueous rechargeable batteries due to its abundance in the nature and possesses a high theoretical capacity (820 mAh/g) and a low negative potential (-0.762 V vs. SHE). Various rechargeable Zn-based batteries have been investigated (Ni-Zn, Zn-air and Zn-Br flow battery etc.) ^[3]. Recently, a promising aqueous Zn-LiMn₂O₄ (LMO) rechargeable battery system has attracted attentions as a low cost, ecologically friendly and safe battery. The estimated energy density of the system is 50-80 Wh/kg, which is comparable to conventional aqueous systems such as Lead-Acid batteries ^[4]. However, shape change and dendritic shorting of the Zn electrode prevent the commercialization of these battery technologies ^[3].

Herein, we present an innovative design of aqueous battery based on Zn-LMO system, which used the concept of immobilized Zn²⁺ions to prevent the metal dendrite in Zn-based batteries and optimized a nontoxic, high conductivity, noncorrosive, and low-cost neutral aqueous solution as electrolyte. Therefore, this new design of Zn-LMO aqueous battery exhibits an improved rate capability and delivers good cycling performance while still maintaining an acceptable energy density. As shown in Fig.1 and Fig.2, the Zn-LMO pouch cell provides a high discharge capacity of 120 mAh/g (based on the weight of LMO) at 0.5C at room temperature with an average discharge potential of 1.88 V. The system showed a good rate capability, maintaining 99, 92.5, and 74.3% of the 0.5C value at rates of 1C, 2C, and 4C, respectively. In addition, the battery also exhibited an excellent good cycle performance even at higher temperature of 60℃（Fig.2）which were attributed to the well optimized negative, positive and electrolyte combination and composition. Given the unique advantages (performance, scalability, low cost, safety and environmental benignity) of this cell, it’s optimal for stationary storage applications of renewable energies, such as solar and wind, and energy integration into the grid.

Fig. 1. Charge/Discharge profiles (25℃) of Zn-LMO battery at various current densities from 0.5C to 4C. Cut voltage is 1.5 V-2.3 V.

Fig. 2. Cycle performances and coulombic efficiency (25℃ and 60℃) of Zn-LMO battery at 4C.

Reference

 

[1]      J.M. Tarascon, Nature 414 (2001) 359.

[2]      F. Beck, Electrochimica Acta 45 (2000) 2467.

[3]      X.G. Zhang, Encyclopedia of Electrochemical Power Sources (2009) 454.

[4]      J. Yan, Journal of Power Sources 216 (2012) 222.