New strategy for cathode materials in lithium-chlorine battery

A team led by Prof. Chen Wei, Prof. Jiang Hailong and Prof. Li Zhenyu from the University of Science and Technology of China (USTC) adopted NH₂-functionalized metal-organic frameworks (MOFs) in lithium-chlorine (Li-Cl₂) batteries to achieve high specific capacities, cycle stability and superior low-temperature performance. Their work was published in Joule on March 15.

Traditional lithium-thionyl chloride (Li-SOCl₂) batteries are widely used for their high energy density and other advantages, but alternatives are still needed since Li-SOCl₂ batteries are not rechargeable. Rechargeable Li-Cl₂ battery was first invented in 2021, with a high specific capacity of 1200 mAh/g and a high output voltage of ~3.6 V.

However, the following problems stand in the way of the practical application of Li-Cl₂ battery. First, the Cl₂ reaction is limited by the weak physical adsorption of porous carbon to Cl₂ molecules. Second, the excessive LiCl generation into the carbon pores blocks the channels for Li⁺ transportation and Cl₂ diffusion, hindering further electrochemical reactions. Furthermore, the shuttle effect of unbonded Cl₂ leads to battery capacity decay, especially at high output capacities. Therefore, the cathode materials with highly porous structures are vital to realize high-performance Li-Cl₂ batteries.

To overcome these difficulties, the team proposed that MOFs with Lewis basic functional groups should be applied to improve the cathode Cl₂/LiCl reactions. Guided by theoretical predictions, MOFs with -NH₂ functional groups were screened out using first-principles calculation and applied in Li-Cl₂ batteries. Cryo-TEM and low-dose high-resolution TEM showed that UiO-66-NH₂ maintains a very stable structure during cycling, and XPS verified -NH2 groups' strong affinity to Cl₂ and LiCl, thus enhancing its redox reaction kinetics. Li-Cl₂@MOF batteries designed by the team reached a maximum discharge specific capacity of 2000 mAh/g and are stable for more than 500 cycles at a specific capacity of 1000 mAh/g. Meanwhile, the batteries performed stable function under the temperature of -40°C.