Flexible aqueous lithium-ion batteries with ultrahigh areal capacity and long cycle life

Practical application of flexible batteries have been hindered by low areal capacity, low stability, and safety concerns. This work reports a facile and scalable infiltration method to fabricate free-standing three-dimensional (3D) flexible electrodes using LiTi 2 (PO 4 ) 3 (LTP) and LiMn 2 O 4 (LMO) as examples for aqueous Li-ion batteries. Benefiting from the unique 3D electrode architecture with fast electron and ion transport, flexible LTP-LMO pouch cells deliver an ultrahigh areal capacity (e.g., 3–23 mAh cm −2 , LTP loading = 24–200 mg cm −2 ), high rate capability, and stable cycling stability (e.g., 93% and 72% capacity retention after 500 and 3000 cycles, respectively, at 14–15 mA cm −2 ). High mechanical and electrochemical stability of the cell is demonstrated with a high capacity retention of 96% after 1000 dynamic bending cycles. Pouch cells with a high capacity (0.53 Ah for 4 × 6 cm 2 cell) and high voltage (3 V/9 V) are demonstrated. This work offers a low-cost and effective strategy to fabricate high areal capacity electrodes with stable electrochemical performance, high mechanical strength, and excellent flexibility. • A facile infiltration method was developed to fabricate flexible electrodes. • Flexible aqueous lithium-ion batteries achieved an ultrahigh areal capacity of 23 mAh cm −2 . • High mechanical and electrochemical stability of the battery was demonstrated.