High entropy alloy formulation for trivalent anode materials in sustainable batteries

Abstract

Lithium-ion batteries are hitting limits regarding resource availability and energy density.Trivalent metals like Aluminum (Al) and Chromium (Cr) are strong alternatives because they exchange three electrons per atom. This gives them huge theoretical volumetric capacities approximately 8,047 mAh cm-3 for Al and 11,117 mAh cm-3 for Cr, which is significantly higher than lithium. However, using these metals in rechargeable batteries has been difficult because they spontaneously form insulating oxide layers (Al2O3 and Cr2O3). These layers block ion transport and cause high overpotentials, effectively preventing the battery from working. This thesis explores the use of High Entropy Alloys (HEAs) to solve these passivation issues. First, we developed an Al-based HEA to stabilize the interface between the metal and aqueous electrolytes. Calculations show that the alloy structure forces aluminum atoms to share electrons with neighboring elements (Cu, Fe, Ni, Sn). This suppresses oxidation and keeps the interface "open" for Al3+ transport. We used this mechanism to demonstrate a stable, high-performance aqueous Al–Selenium battery. Second, this work addresses the long-standing problem that chromium metal cannot be recharged. By engineering a Cr-rich HEA (Cr-Bi-Cu-Sn-Ni), we created a native oxide layer filled with different heterointerfaces. Some of these interfaces, such as Cr2O3/Bi2O3, lower the barrier for chromium diffusion, while others stop oxygen from entering. This allowed us to build the first rechargeable chromium battery, which cycled reversibly for over 10,000 hours. These results show that HEAs are a practical way to control surface chemistry and finally unlock the potential of high- density multivalent batteries.