Xu Liu, Haiyan Yu, Xiaotong Deng, Jianyue He, Xuri Zhang, Junjie Huang, Zengrong Wang, Chenjing Liu, Xin Zhang, Gang He*. Angew. Chem. Int. Ed. 2026, DOI: 10.1002/anie.202522442

Neutral aqueous organic redox flow batteries (AORFBs), as pivotal candidate systems for new energy-complementary storage technologies, have their overall energy efficiency directly determined by the physicochemical properties of organic electrolyte materials. However, design strategies based on traditional empirical exploration via the “trialand-error” approach frequently lack universal theoretical guidance, resulting in significant performance variations among materials, particularly manifesting in a ubiquitous solubility-stability trade-off within high-concentration battery systems. Viologen derivatives have attracted significant attention as promising anolyte templates for neutral AORFBs due to their favorable optoelectronic properties and structural tunability. Current mainstream molecular design strategies concentrate on the functionalization of the bipyridine core structure (steric hindrance modulation, conjugation extension, etc) to achieve performance optimization. Critically, these modification schemes universally involve terminal N-alkylation reactions to construct hydrophilic functional layers, thereby enabling gradient enhancement of solubility. Furthermore, conventional N-alkylated viologen electrolytes in AORFBs undergo irreversible nucleophilic S_N2 dealkylation degradation.

Figure 1. Literature information extraction pipeline powered by large language models

Here we report a machine learning (ML) strategy using large language models (LLMs) trained on over 1300 AORFB studies to predict chiral viologens with ortho-dihydroxy motifs. This bonding network forms a dynamic, pH-adaptive “solvation armor” that stabilizes the viologen structure. The R-/S-enantiomers (2.75/2.76 M) exhibit 1.66 times higher solubility versus RS-racemate. Molecular simulations and in situ spectroscopy confirm that the dihydroxy groups protect reactive C-N bonds via a solvation structure (unrelated to chiral effect), enhancing stability to pH 11. The 1 M R²⁺/R^+• redox couple sets a new record by achieving 99.42% capacity retention over 3652 cycles. The 1 M R-based AORFB shows 100% retention over 533 cycles, outperforming quaternary ammonium- ([(NPr)₂V]Cl₄, 94.92%) and sulfonate-modified viologen ((SPr)₂V), 65.49%). Stable cycling across 0.1 ∼ 2.5 M demonstrates decoupling of degradation from concentration. This strategy is validated by 2.5 kg-scale synthesis and Ah-class stack testing (98.65% retention over 77 cycles), demonstrating industrial scalability. This work establishes a generalizable, ML-enabled platform for electrolyte development, bridging molecular design and practical AORFB deployment.

Figure 2. Structural diagram of chiral viologens and battery performance test

First Author: Liu Xu, Asst. Prof., Xi’an Jiaotong University

Correspondence Author: Prof. He Gang, Xi’an Jiaotong University

Full Text Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.202522442