Advances in research on anode electrodes and electrolyte materials for aluminum ion batteries

With the increase in the world's demand for renewable energy development, the short board of the grid energy storage system is increasingly prominent. In lead-acid, nickel-metal hydride, lithium-ion and other mainstream battery systems, lithium-ion batteries have the best overall performance, but lithium reserves are limited, and there are hidden safety issues; lead-acid batteries, although low-cost, lead pollution problems. Therefore, the development of inexpensive, safe, long-life, fast-charging battery systems has become a hot topic in the world.

In recent years, the emergence of aluminum ion batteries has provided new solutions to solve the above problems. It uses "aluminum", which is one of the most abundant metallic elements on the earth's crust, as a battery material. Due to the conversion between an aluminum ion and an aluminum atom, it can have the gains and losses of three electrons, making its theoretical specific capacity second only to lithium. Development potential.

Since the 1980s, United States Letters, Cornell University, Oak Ridge National Laboratory, Sandia National Laboratories, and the Indian Institute of Technology have all gradually invested in the development of aluminum-ion batteries, using graphite and fluorinated graphite. Metal oxides, conductive polymers, and other materials are used as positive electrodes, but neither ideal discharge voltage (<1.7 V) nor sufficient charge and discharge cycles (<100 times) have been obtained.

The research group headed by Academician Dai Hongjie of the Department of Chemistry at Stanford University in the US used foamed graphite as the positive electrode and ionic liquid as the electrolyte in 2015. It successfully developed the first discharge voltage at 2V and was able to charge and discharge thousands of times in the past 30 years. Aluminum-ion batteries, and propose a complete battery reaction mechanism, related research results published in the Nature (Nature) magazine.

Recently, the study group led by the Institute of Internal Medicine has addressed the problems of insufficient capacity of graphite electrodes and high electrolyte costs, and proposed a new process for low-cost, high-capacity graphite cathodes. At the same time, a low-cost ionic liquid electrolyte based on urea was developed. The combination of the two has made the industrialization of aluminum ion batteries a big step forward. Relevant research results have been published in the recently published "Nature Communications" and "Proceedings of the National Academy of Sciences" magazine.

"Natural Communications" reported an aluminum ion battery using a natural graphite foil as a cathode electrode. The battery exhibited excellent performance with a capacitance of about 110 mAhg-1 and a Coulomb efficiency of about 98%. At 6 C rate, the battery capacitance is 60 mAh/g, and after more than 6000 charge-discharge cycles, the Coulomb efficiency is about 99%. In addition, the behavioral mechanism of chloroaluminate ion-implanted graphite layer was simulated by theoretical calculations.

The "American Academy of Sciences" reported an aluminum ion battery using an aluminum chloride and urea ionic liquid electrolyte. The battery has an excellent Coulomb efficiency of 99.7%. At a rate of 1.4C, the battery capacity is 73 mAh/g, which can stably charge and discharge more than 200 times. The cost of aluminum chloride and urea electrolyte is low, with natural graphite material as cathode, aluminum foil as anode, the above-mentioned materials constitute aluminum ion battery with low cost and excellent electrochemical performance, making the aluminum ion battery an ideal grid storage Electrical system.

Recently, aluminum-ion batteries have become a new research hotspot in the field of electrochemical energy storage batteries. Researchers in Europe, the United States, Japan, South Korea, and Australia have all research teams engaged in relevant research work. In China, several research groups including graphite as a cathode material were published after 2015, including Professor Lin Mengchang from Shandong University of Science and Technology, Professor Jiao Shuqiang from Beijing University of Science and Technology, Professor Gao Chao from Zhejiang University, and Professor Ouyang Chuying from Jiangxi Normal University. These efforts have aroused the development advantages of aluminum ion batteries in science and engineering.

At present, AB Systems Inc., a Silicon Valley start-up company in the United States, specializes in the industrialization of aluminum-ion batteries and has obtained the exclusive authorization for aluminum-ion battery patents from Stanford University (patent filing date: 1st US provisional filed on Feb 28, 2014; 2nd US provisional filed on Nov 6, 2014; PCT application filed on Feb 27, 2015). The company has successfully gathered the resources of domestic and foreign multi-industry research institutes and is striving to bring aluminum ion batteries to market applications.