The Reverse of Electrostatic Interaction Force for Ultrahigh-Energy Al-Ion batteries.

The two-dimensional (2D) MXenes with sufficient interlayer spacing are promising cathode materials for aluminum-ion batteries (AIBs), yet the electrostatic repulsion effect between the surface negative charges and the active anions (AlCl 4 - ) hinders the intercalation of AlCl 4 - and is usually ignored. Here, we propose a charge regulation strategy for MXene cathodes to overcome this challenge. By doping N and Co, the zeta potential is gradually transformed from negative (Ti 3 C 2 T x ) to near-neutral (Ti 3 CNT x ), and finally positive (Ti 3 CNT x @Co). Therefore, the electrostatic repulsion force can be greatly weakened between Ti 3 CNT x and AlCl 4 - , or even formed a strong electrostatic attraction between Ti 3 CNT x @Co and AlCl 4 - , which can not only accommodate more AlCl 4 - ions in the Ti 3 CNT x @Co interlayers to increase the capacity, but also solve the stacking and expansion problems. As a result, the optimized Al-MXene battery exhibits an ultrahigh capacity of up to 240 mAh g -1 (2-4 times the capacity of graphite cathode, 60-120 mAh g -1 ) and a potential ultrahigh energy density (432 Wh kg -1 , 2-4 times the value of graphite, 110-220 Wh kg -1 ) based on the mass of cathode materials, comparable to LiFePO 4 -based lithium-ion batteries (350-450 Wh kg -1 , based on the mass of LiFePO 4 ).