Pillarquinone-based sodium-ion batteries using a highly concentrated electrolyte

Sodium-ion batteries using organic electrode materials are a promising alternative to state-of-the-art lithium-ion batteries. However, their practical viability is hindered by challenges such as a low specific capacity of the organic electrode materials, suboptimal interfacial compatibility, the availability of suitable electrolytes, or intrinsic dissolution issues associated with the organic materials. Previous research primarily addressed dissolution mitigation through electrode or materials engineering, often neglecting the substantial influence of the electrolyte. Herein, we use a highly concentrated electrolyte with a small-molecule organic positive electrode based on pillar[5]quinone (P5Q) with a high theoretical specific capacity of 446 mAh g−1, encapsulated within CMK-3 as mesoporous carbon, achieving record cycling performance with improved cycling stability even at elevated temperature (40 °C). Using 5 M sodium bis(fluorosulfonyl)imide in succinonitrile as electrolyte, the P5Q@CMK-3 composite electrode delivers 430 mAh g−1 specific discharge capacity at 0.2C and retains 90% of this value over 200 cycles. This corresponds to an impressive energy density of 831 Wh kg−1 (based on P5Q mass) and surpasses previous reports based on pillarquinones as electrode material. When operated at 40 °C, the P5Q@CMK-3 composite electrodes deliver a record-specific discharge capacity of 438 mAh g−1 with 88% capacity retention over 500 cycles, which translates to a minimal capacity decay of only 0.02% per cycle, and with ca. 100% Coulombic efficiency. This study underscores the crucial role of the electrolyte in advancing the prospect of organic sodium batteries for large-scale energy storage applications, offering a promising avenue for the future of sustainable energy technologies.