Recently, Tang Yongbing, Research Fellow of Functional Film Materials Research Center, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, and Tsinghua Berkeley Shenzhen Institute jointly developed a high-performance calcium ion, Cheng Huiming, a researcher at Shenyang Institute of Materials Science, Chinese Academy of Sciences Institute of Metal Research. The battery. They through the innovation of the battery structure, so that the calcium ion battery has a new electrochemical reaction mechanism, and to achieve a stable charge-discharge reaction at room temperature. Related research results with Reversible calcium alloying enables a practical room-temperature charging calcium-ion Battery with a high discharge voltage ("High-voltage calcium-ion battery operated stably at room temperature based on the calcium-tin alloying reaction"), published online in the Nature Journal, Nature Chemistry, doi:10.1038 /s41557-018-0045-4), and applied for China's invention patent (201710184368.1) and PCT patent (PCT/CN2017/078203).
In the alkaline-earth metal element, calcium has a low polarization, the standard electrode potential is close to that of lithium (Ca2+/Ca: −2.868 V vs. SHE, which is only 170 mV higher than lithium), and the ion is +2 (charged number is lithium ion). The calcium ion battery has the potential to become an efficient and low cost energy storage battery. However, in 1991, Aurbach et al. found that calcium ions are difficult to penetrate in traditional organic electrolytes. The passivation film on the surface of the calcium metal negative electrode causes the calcium ion to not undergo a reversible redox reaction like lithium ion (J. Electrochem. Soc. 1991, 138, 3536). Since then, the research progress of the calcium ion battery has been slow. Until 2016, MIT's Sadoway et al. used molten CaCl2 and LiCl as electrolytes while using molten Ca-Mg alloy and Bi metal as anode and cathode materials, respectively, to develop a new type of calcium ion liquid battery with a low operating voltage. (<1V) , 但在高温下 (550-700°C) 表现出良好的循环稳定性(Nat. Commun. 2016, 7, 10999). 而西班牙科学家Palacin等人虽然在室温下未发现钙离子的可逆氧化还原反应, 但在75-100°C温度下发现钙离子在碳酸酯类电解液中能在钙负极表面发生可逆沉积反应, 并且在100°C 下能循环30周以上(Nat. Mater. 2016, 15, 169). 虽然高温下的可逆充放电现象的发现为钙离子电池的发展带来了希望, 但要想使钙离子电池具有实用价值, 其工作温度还须降低到室温附近, 需要找到能实现可逆钙离子嵌入/脱出的正负极材料并提高其电化学性能, 包括室温循环特性, 倍率特性和工作电压(目前<2V).
After studying the binary phase diagram, the team found that calcium and sodium, zinc, tin and other metals can form alloy phases, and further charge and discharge characteristics of various metal anodes in carbonate electrolytes containing Ca(PF6)2. A study was conducted and it was found that tin has a good reversible reaction and specific capacity in the calcium ion electrolyte. During the first charging process, the calcium ion in the electrolyte and the tin negative electrode are alloyed to form a Ca7Sn6 alloy, and Ca7Sn6 de- alloying occurs during discharge. Reactions. Theoretical simulations and in-situ electrochemical stress tests have shown that the four bonding states of calcium and tin in the Ca7Sn6 alloy phase have lower binding energy, and the electrochemical stress when calcium ions are inserted into the tin negative electrode is pressure. Stress, This compressive stress not only helps to maintain the structural stability of the material but also has a good reversibility in the process of calcium ion insertion/extraction.
Based on the above findings, the team proposed a new type of calcium ion battery: a reversible alloying reaction of titanium foil with a negative electrode and calcium ions, and an integrated design of an active material and a current collector; and anion with graphite as a positive electrode (PF6−) The reversible intercalation/deintercalation reaction is based on a carbonate-based solvent with calcium hexafluorophosphate and 5V high pressure resistance. The calcium-ion battery has excellent electrochemical performance with an average discharge pressure of up to 4.45V. , After the cycle of 350 cycles at room temperature, the capacity retention rate is greater than 95%.
The work expands the calcium ion battery system, enriches the selection range of key materials such as positive electrode, negative electrode, and electrolyte in the calcium ion battery system, and has important implications for the research and development of novel energy storage devices based on multivalent state ions.
Figure 1. (a) First charge and discharge curves of tin metal negative electrodes in a calcium ion electrolyte; (b,c) XRD analysis shows that during the charging process, calcium ions and tin negative electrode alloyed to form Ca7Sn6 alloy during discharge. Demetallization of Ca7Sn6 occurs; (d,e) Four bond formations and corresponding binding energies of calcium ions and tin in Ca7Sn6 alloy phase; (f) In-situ electrochemical stress test of tin negative electrode during first charge and discharge curve.
Figure 2. (a) Structure and working principle of new calcium ion battery; (b) XRD pattern of graphite cathode at different voltages; (c) Linear scanning of quaternary pressure-resistant electrolyte system in different anodes on tin anode batteries. Volt-ampere curve; (d) High-voltage test curve of quaternary electrolyte system at a charge current density of 100 mA/g; (e) Charge-discharge curve of a calcium ion battery (a calcium ion button cell can light up two (Yellow LEDs in series), (f) Rate capability, (g) Variation of discharge medium pressure with number of cycles (inset is a charge-discharge curve of 320-350 cycles), and (h) Charge-discharge curve at different cycle numbers .
