The RAMSES project, funded jointly by the German Federal Ministry of Education and Research (BMBF) and the French National Research Agency (ANR) through a 2+2 call on sustainable energy, ran from 1 September 2019 to 31 March 2023, with a six‑month extension. Its goal was to produce a 6 V, 15 Ah rechargeable zinc‑manganese dioxide (Zn‑MnO₂) battery demonstrator using an alkaline electrolyte, with a particular emphasis on developing a MnO₂ cathode that could deliver an areal capacity of at least 10 mA cm⁻².
The consortium comprised the French SME Sunergy, the CNRS research institute ICMCB (Bordeaux), the German research institute ZSW, and initially the German battery manufacturer Hoppecke. Hoppecke withdrew as a full partner during the project and became an associate partner; consequently, ZSW assumed responsibility for building the battery demonstrator. The partners pursued divergent strategies for the cathode: Sunergy produced electrochemically deposited MnO₂ (EMD), ICMCB synthesized a Mn‑Ni mixed‑phase (Ni‑Asbolan), and ZSW fabricated α‑phase MnO₂. Both French partners also explored hybrid structures rich in Ni(OH)₂ to enhance areal capacity and cycle life. ZSW’s key breakthrough was a selective anion‑exchange membrane that blocks Zn²⁺ ions generated at the anode during discharge, preventing irreversible poisoning of the MnO₂ cathode. This design enabled fully reversible discharge and charge of the active MnO₂ material. Electrodes fabricated with this architecture achieved areal capacities roughly three times the original target, reaching about 30 mA cm⁻², and were scaled to a 63 cm² active area after overcoming several technical challenges.
The demonstrator consisted of three cells in series, each comprising 13 parallel anode‑cathode pairs. Under controlled manufacturing conditions, the full battery delivered results that matched single‑cell tests. In the first phase, with a 25 % depth of discharge (DoD) and a load of 0.82 A, the battery supplied 8.2 Ah over eight cycles at a nominal voltage near 3 V. Doubling the required capacity to 50 % DoD (16.4 Ah, 20 mA cm⁻²) yielded promising performance, albeit with a slightly lower nominal voltage. Increasing the current to 1.6 A to accelerate cycling, however, caused the demonstrator to fail irreversibly after about a dozen cycles. Analysis indicated that the failure stemmed from wiring errors between electrodes rather than from the electrode design itself. The successful electrode architecture prompted an EU patent application for the fully discharged and reversibly rechargeable MnO₂ cathode.
A second demonstrator, built on Sunergy’s hybrid cathode, achieved a nominal voltage of 4.7 V, operated for 180 cycles, and stored 37 Wh of energy. The majority of this capacity was attributed to the Ni(OH)₂ redox pair, underscoring the synergistic effect of combining MnO₂ with nickel species. Across all partners, the integration of Ni components and the specific electrode geometry were found to positively influence durability, though further investigation is required to fully understand the underlying mechanisms.
The RAMSES effort was framed as a friendly competition among the partners, yet it also fostered close collaboration. The project’s outcomes lay the groundwork for a follow‑up BMBF‑supported initiative that aims to deliver Zn‑MnO₂ batteries with energy contents exceeding 1 kWh and energy densities above 100 Wh kg⁻¹, thereby advancing the technology toward practical grid‑scale storage solutions.