High Cycle Stability of Zinc Anode Battery Using Ni-Co Layered Double Hydroxide Cathode
Authors: Sugihara Hikaru , Ogawa Satoshi , Ajiki Yoshiharu 
Published: December 2024

The current storage battery market is dominated by water-based lead-acid batteries. Since lead-acid batteries are water-based, there is no risk of fire, and they are inexpensive and highly reliable storage batteries. In addition, lead, which is a toxic substance, can be used safely if recycled, so it has been used for a long time. However, in recent years, lead import regulations have become stricter and lead poisoning in developing countries has become a problem, and new storage batteries that can replace lead-acid batteries are required from a life cycle assessment perspective [1]. Therefore, in this study, we are considering a water-based storage battery that uses zinc as the negative electrode. Zinc is an abundant resource, non-toxic, and has a proven track record in practical batteries [2]. On the other hand, we are considering various materials for the positive electrode that can be driven by an aqueous electrolyte, but we have not yet found a material that achieves both a large capacity and good cycle performances. Therefore, the purpose of our research is to develop a positive electrode material that can be used successfully in combination with a zinc negative electrode. Here, we focused on the intercalation reaction, which performs redox by inserting and deintercalation ions without destroying the crystal structure, as a stable battery reaction. Furthermore, in order to realize the intercalation of hydroxide ions in alkaline electrolytes, we investigated layered double hydroxide (LDH) as a material that can reversibly incorporate anions. In LDH, the layer consisting of divalent and trivalent metal ions is positively charged, and anions are inserted between the layers to compensate for the increased positive charge. Taking advantage of this property, hydroxide ions can move between the layers and function as a positive electrode, thereby achieving high cycle stability for zinc negative electrode batteries.
We will explain how to prepare LDH samples. This time, we chose hydrothermal synthesis to create a homogeneous and highly crystalline sample. First, cobalt nitrate hexahydrate, crystals of cobalt nitrate hexahydrate, and hexamethylenetetramine as a precipitant were mixed in a molar ratio of 2:1:1 and dissolved in 25 g of water. The solution was placed in a PTFE container, which was sealed with a metal container, and the synthesis was performed at 220°C for 24 hours. The resulting precipitate was filtered and dried to create a powder sample. Crystal structure analysis and charge/discharge tests were performed on the prepared samples. Crystal structure analysis was performed using X-ray diffraction (XRD). In the charge/discharge test, the positive electrode was made by sandwiching 10 mg of LDH between foamed Ni current collectors. The negative electrode was created by applying zinc oxide as an active material to 10 mAh/cm² using a current collector made of a thin and uniform layer of zinc formed by plating on a mesh. A nonwoven fabric separator was placed on the positive electrode side of the LDH, and a cellophane separator was placed on the negative electrode side. The electrode stack was introduced into an acrylic cell, and a 30wt% KOH aqueous solution was added to complete the device. The measurement conditions were to charge at 100mAh/g with a current of 5mA, and then discharge to 1.0V with a current of 5mA.
From the diffraction pattern of the XRD measurement, we were able to confirm peaks at positions 003 and 006, which are derived from LDH. Next, we conducted a charge/discharge test, and the results shown in Figure (a) were obtained. The discharge efficiency was approximately 98%, confirming reversible charge and discharge behavior. Furthermore, the voltage position is different from the Ni-Zn battery, which was tested at a SOC of 0.85% and a current rate of 0.5C. From this, it is possible that even the same nickel material is a substance like this. Furthermore, looking at the cycle characteristics shown in Figure (b), it is confirmed that while the capacity of Ni-Zn batteries decreases around the 60th cycle, LDH-Zn operates stably for more than 100 cycles. Ta. Based on this, we believe that it is possible to create a zinc anode battery that has both a large capacity and good cycle performances by using LDH.
[1] Songsak Srianujata, LEAD-THE TOXIC METAL TO STAY WITH HUMAN, The Journal of Toxicological Sience, Vol.23, Supplement II, (1998), 237-240
[2]Wenxu Shang, Wentao Yu, Yongfu Liu, Ruixin Li, Yawen Dai, Chun Cheng, Peng Tan, Meng Ni，Rechargeable alkaline zinc batteries: Progress and challenges，Energy Storage Materials, 31, (2020), 44-57

Figure 1