According to the "Japan Economic News" on January 26, Argonne National Laboratory and other institutions in the United States have greatly improved the durability of lithium-air batteries by increasing their capacity, and have achieved 1,000 times of charging and discharging, reaching practical standards. In addition to extending the range of electric vehicles (EVs), this achievement will also contribute to the electrification of airplanes and trucks, and is expected to be put into use after 2030.
Argonne National Laboratory and the Illinois Institute of Technology have trial-produced lithium-air batteries known as the "Dream Battery." Its theoretical capacity is about 3,000 Wh per kilogram, which is 10 times the upper limit of 300 Wh for lithium batteries.
Argonne National Laboratory expert Larry Curtis said lithium-air batteries have the highest energy density among the new generation of batteries. The lab's goal is to make lithium-air batteries four times more capable of lithium-ion batteries. This level will allow the EV to have a range of more than 1,000 miles (about 1,609 km) on a single charge, which is about four times that of the current standard EV.
It is difficult to further increase the capacity of traditional lithium-ion batteries. In addition to lithium-air batteries, lithium-sulfur batteries that use sulfur as the positive electrode, lithium-metal batteries that use lithium as the negative electrode, and all-solid-state batteries that replace liquid electrolytes with solid electrolytes are also being developed.
However, no matter what kind of battery you have, you can only increase its capacity up to 15 to 2 times. Lithium-air batteries store a large number of electron-carrying lithium ions in the lithium metal anode, and the weight of the battery can be reduced by using oxygen in the air instead of lithium compounds as the positive electrode.
However, in the past, lithium ions combined with oxygen during the discharge process were prone to the formation of impurities lithium peroxide. This substance is difficult to convert back into lithium ions during charging, so it is easy to cause excessive voltage to be applied to the battery, which can cause the battery to age.
Lithium metal crystals have the potential to grow in a needle-like pattern on the negative electrode, and extending to the positive electrode can cause a short circuit, so such batteries can only be charged and discharged a few dozen times.
To overcome this shortcoming, Argonne National Laboratory uses solid electrolytes instead of liquid electrolytes. The solid electrolyte is made by incorporating a lithium-phosphorus compound specially developed for this purpose into a complex of lithium salts and resins.
The researchers trialled the electrolyte between the positive and negative electrodes to make a battery. It has a capacity of 685 Wh per kilogram, which is more than double that of lithium batteries. The solid electrolyte is difficult to break down, and because it adheres tightly to the negative electrode, it prevents the formation of needle-like lithium crystals. It is difficult to produce lithium peroxide during discharge, and it can maintain 88% capacity even if it is repeatedly charged and discharged 1000 times.
However, solid electrolytes have problems such as poor ion transport capacity and difficulty in generating high voltages and currents. Ion transport capacity varies depending on the type and proportion of elements used in the electrolyte. In the future, researchers will continue to look for the optimal electrolyte ratio to improve battery performance by several times, and make the solid electrolyte thinner and lighter, increasing the unit capacity of the battery.
Curtis believes that these improvements are expected to increase the capacity of the new battery to 1,200 watt-hours per kilogram equivalent to four times that of lithium-ion batteries, and they are working with car companies to commercialize the new batteries.
At present, the electrification of large vehicles in the automotive field is lagging behind. If new batteries can be put into practical use, it will be possible to electrify long-distance trucks in the United States, and the electrification of aircraft may no longer be a dream.
While Argonne National Laboratory is leading the way in research using solid electrolytes to extend the life of lithium-air batteries, progress is being made around the world. South Korea's Ulsan Institute of Science and Technology achieved 100 times of charging and discharging such batteries in 2020, and has applied for and published a number of related patents.
The Japan Institute of Materials and Materials (NIMS) has collaborated with SoftBank and other companies to achieve more than 20 charge-discharge cycles by combining a solid electrolyte film with a liquid electrolyte in 2023.
Tohoku University in Japan extends battery cathode life by using electrolyte. Carbon materials with many pores of 7 nanometers in diameter are used at the cathode of the battery to heat treat areas that are susceptible to deterioration due to adhesion of oxygen and other substances. In this way, even if the battery is charged and discharged, the positive electrode will not deteriorate.
With the support of the Japan Science and Technology Agency (JST), Professor Shuji Nakanishi of Osaka University and others will conduct international joint research with researchers from the United States, Germany, and the United Kingdom from February until the end of fiscal 2028. The goal is to commercialize new batteries in the first half of the 2030s. (Compiled by Li Ziyue).
Scientists at Argonne National Laboratory in the United States conduct research on lithium batteries (Argonne National Laboratory**).