Bipolar electrode architecture enables high-energy aqueous rechargeable sodium ion battery

Aqueous rechargeable sodium ion batteries (ARSIBs), with intrinsic safety, low cost, and greenness, are attracting more and more attentions for large scale energy storage application. However, the low energy density hampers their practical application. Here, a battery architecture designed by bipolar electrode with graphite/amorphous carbon film as current collector shows high energy density and excellent rate-capability. The bipolar electrode architecture is designed to not only improve energy density of practical battery by minimizing inactive ingredient, such as tabs and cases, but also guarantee high rate-capability through a short electron transport distance in the through-plane direction instead of in-plane direction for traditional cell architecture. As a proof of concept, a prototype pouch cell of 8 V based on six Na₂MnFe(CN)₆||NaTi₂(PO₄)₃ bipolar electrodes stacking using a “water-in-polymer” gel electrolyte is demonstrated to cycle up to 4,000 times, with a high energy density of 86 Wh·kg⁻¹ based on total mass of both cathode and anode. This result opens a new avenue to develop advance high-energy ARSIBs for grid-scale energy storage applications.