A novel aqueous Li+ (or Na+)/Br− hybrid-ion battery with super high areal capacity and energy density

Abstract

With the explosive growth in intermittent renewable sources and the global drive toward decarbonizing the energy economy, reliable large-scale electrical energy storage technologies with high safety and low cost are urgently needed. Aqueous batteries hold the intrinsic advantages of nonflammability and low cost; the zinc//bromine flow battery and LiMn₂O₄//NaTi₂(PO₄)₃ aqueous rechargeable ion battery are two representative systems with relatively high voltages (1.6 V to 1.8 V in common aqueous solutions). However, the long-term cycling stability of intercalation/de-intercalation type cathode materials is easily impaired by pH fluctuance, while the deposition/dissolution-type zinc anode suffers from zinc dendrites and uneven deposition issues. To avoid these two issues, we propose a novel bromine//NaTi₂(PO₄)₃ hybrid ion battery, involving an aqueous redox pair (Br₃⁻/Br⁻, with high reactivity in a pH range from 0 to 9) and a high-loading ion intercalation anode (NaTi₂(PO₄)₃, with low working voltage and little volume change). First, the high-performance NTP@C nanoparticles are synthesized by a modified sol–gel method. Then, the three-dimensional NTP@C anode with super high mass loading is designed by employing a porous and conductive carbon substrate. The crossover of bromine in aqueous catholyte is suppressed by an effective bromine complexing agent and the insufficient ion transport in a thick solid anode is conquered by a negative flowing electrolyte. As a result, the hybrid ion battery shows high areal energy density, high power density and promising cycling stability. The full cell can deliver a high energy density and power density of 12.8 mW h cm⁻² (109 W h kg⁻¹ based on NTP@C and reacted LiBr) and 29.4 mW cm⁻² (250 W kg⁻¹ based on NTP@C and reacted LiBr), respectively. Moreover, the power density can reach 106 mW cm⁻² with energy density remaining at 7.95 mW h cm⁻² (68 W h kg⁻¹ based on NTP@C and reacted LiBr) at a super high current density of 100 mA cm⁻². An average capacity loss of 0.075% per cycle is obtained during a 200-cycle test, demonstrating the great feasibility of the new system. Therefore, this hybrid battery has great potential in large scale electrical energy storage.