Associative metal-free ElectROlytes for Battery Energy STorage

Project Information

AERO BEST

Grant agreement ID: 101189530

DOI

10.3030/101189530

Project closed

EC signature date 1 October 2024

Start date 1 October 2024

End date 31 March 2026

Funded under

• European Research Council (ERC)

Total cost

No data

EU contribution

€ 150 000,00

Coordinated by

THE CHANCELLOR MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom

Periodic Reporting for period 1 - AERO BEST (Associative metal-free ElectROlytes for Battery Energy STorage)

Reporting period: 2024-10-01 to 2026-03-31

Summary of the context and overall objectives of the project

AERO-BEST addresses the urgent need for safe, sustainable and geopolitically resilient battery energy storage systems (BESS) to support the growth of renewable electricity. At present, grid‑scale BESS are dominated by lithium‑ion and vanadium redox‑flow technologies that rely on geographically concentrated critical metals with volatile prices and safety and environmental concerns, creating cost, supply‑chain and deployment risks just as storage capacity must expand to integrate high shares of intermittent solar and wind generation.

The project develops and de‑risks a new class of metal‑free associative bis‑pyridinium electrolytes (APEs) for aqueous redox‑flow batteries. These fully organic electrolytes are designed to self‑assemble in solution, providing intrinsic protection against detrimental reactions with oxygen and enabling stable operation in air. By combining earth‑abundant elements, tunable redox properties and excellent cycling stability, APEs have the potential to deliver lower‑cost, safer and more sustainable flow batteries that are less constrained by geography and critical‑metal supply chains.

The overall objective is to take APE technology from laboratory proof‑of‑principle to a robust proof of concept at application level. This includes scaling synthesis from gram to hundreds of grams with a clear path to kilogram scale, validating long‑term performance in flow‑battery hardware under both anaerobic and air‑exposed conditions, and assessing chemical stability and regeneration potential over extended cycling. In parallel, the project undertakes techno‑economic analysis, market research and business model development to determine how APE‑based electrolytes can be manufactured and commercialised, culminating in the creation and initial funding of a dedicated spin‑out company.

The expected impact is to establish a new platform for stationary energy storage that can lower electrolyte costs relative to metal‑based systems, improve safety and simplify operation and maintenance, while de‑risking supply chains by eliminating dependence on critical metals. In the medium term, this should facilitate wider deployment of flow‑battery storage, including in regions with weaker infrastructure and in applications where air‑stable, low‑maintenance systems are essential, such as off‑grid and microgrid settings. By jointly addressing technological feasibility and the commercial pathway of APE electrolytes, the project aims to support decarbonisation of power systems and the development of a more sustainable and geopolitically robust energy ecosystem.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project has delivered substantial scientific and technical progress towards establishing associative bis‑pyridinium electrolytes (APEs) as a viable platform for metal‑free aqueous redox‑flow batteries. Work was organised around three technical objectives: synthesis scale‑up and cost reduction, validation of battery performance in flow‑cell hardware, and assessment of long‑term stability and regeneration potential.

On the synthetic side, we identified promising APE anolyte structures for air‑stable operation and developed an optimised, scalable route. Reactions were scaled from gram to reproducible 10–100 g batches, a two‑order‑of‑magnitude increase over the original laboratory scale. Key improvements included lowering palladium catalyst loading from around 5% to below 0.5%, shortening reaction times and reducing the equivalents of boronic acid required. These changes improve projected manufacturing costs and process robustness and indicate that further scale‑up to kilogram batches should be straightforward once demand justifies larger quantities.

For electrochemical performance, APE‑based electrolytes were implemented in commercial‑style flow‑battery hardware and tested at higher concentrations (towards 1 M), corresponding to tens of grams of active material. Multigram‑scale cells were cycled over extended periods, delivering more than 1,000 charge–discharge cycles with very high per‑cycle stability, good Coulombic and energy efficiencies, and low capacity fade. Tests under both controlled and air‑exposed conditions confirmed that the self‑associative nature of the electrolytes provides effective protection against oxygen, enabling stable operation without stringent exclusion of air. Although a full 1 kg / 100 Wh demonstrator was not built within the project timeframe, the observed performance and synthetic scalability together provide strong evidence that the technology can be translated to larger systems.

In terms of stability and regeneration, cycling studies indicated negligible crossover of the anolyte into the catholyte compartment and catholyte crossover that depended on the chosen catholyte but did not impair cell operation over the observed period. The high per‑cycle retention shows that the APE chemistry is intrinsically robust under realistic flow‑battery conditions, including in the presence of oxygen. Given the low degradation observed and the limited duration of the action, a full regeneration protocol was not implemented, and work on degradation mechanisms and regeneration strategies has instead been prioritised for follow‑on research.

Overall, the action has moved the APE concept from a laboratory curiosity to a technically credible option for stationary energy storage: the chemistry has been scaled by two orders of magnitude, long‑term cycling stability has been demonstrated in flow‑cell hardware, and the key parameters affecting cost and performance are now well understood.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project has delivered results that clearly advance the state of the art in organic redox‑flow batteries and metal‑free electrolytes. Most existing organic flow‑battery systems require strict exclusion of oxygen and avoid molecular association, because dimerisation has been linked to capacity fade. In contrast, this project shows that associative, fully organic bis‑pyridinium electrolytes can be engineered to self‑assemble in solution and that this association can be harnessed to protect against oxygen, enabling stable operation in air. This overturns prevailing assumptions that organic electrolytes must be run under air‑free conditions and that association is necessarily detrimental to performance.

The optimised APE structures combine metal‑free composition, aqueous and near‑neutral pH operation, and tunable redox properties in a single platform. We demonstrate that these electrolytes can be synthesised on the multi‑10‑gram scale with reduced catalyst loadings and more efficient use of key reagents, indicating compatibility with future industrial production rather than remaining a purely academic curiosity. On the device side, long‑term cycling in flow‑cell hardware—with per‑cycle stability greater than 99.99%, low crossover and stable operation under exposure to air—shows that APE‑based systems can match or surpass the durability benchmarks of vanadium and other metal‑based technologies, while potentially offering advantages in safety and sustainability.

The potential impacts are substantial. If developed to industrial scale, APE electrolytes could enable lower‑cost, safer and more sustainable stationary energy storage, supporting higher penetrations of renewables and facilitating deployment in settings with weaker infrastructure or challenging environmental conditions. Because the chemistry avoids critical metals and uses precursors that can be sourced and manufactured in many regions, the technology also supports more resilient and geopolitically robust energy systems.

For further uptake and success, several needs have been identified. Additional research and demonstration at larger scale are required, in particular construction and testing of higher‑capacity demonstrators (100 Wh and beyond) and deeper study of long‑term degradation mechanisms and regeneration strategies. Access to markets and finance will be essential to support scale‑up of electrolyte production and integration into commercial flow‑battery products, alongside continued engagement with manufacturers and project developers. Ongoing commercialisation and IPR support are needed to consolidate the patent position, structure partnerships and licensing agreements, and refine the business model of the spin‑out company. As the technology matures, engagement with relevant standards and regulatory frameworks for grid‑scale storage will help ensure efficient deployment and formal recognition of safety and environmental benefits.

In summary, the project has: (i) established a scalable, cost‑aware synthetic route to associative, metal‑free bis‑pyridinium electrolytes; (ii) demonstrated long‑term, air‑stable operation of these electrolytes in aqueous flow‑battery hardware with very high per‑cycle stability and low crossover; and (iii) defined a credible commercial pathway, including creation and initial funding of a spin‑out, to advance this electrolyte platform towards real‑world deployment in stationary energy storage.