Scientists from Peking University jointly with researchers from Nankai University, the Harbin Institute of Technology and the City University of Hong Kong have presented a concept for a next-generation battery. These rechargeable magnesium carbon dioxide batteries not only store energy but also directly use CO₂ as an active component.
In this solution, traditional lithium chemistry is replaced with a system that uses magnesium and carbon dioxide. During discharging, magnesium oxidizes at the anode, donating electrons to the external circuit. At the cathode, carbon dioxide accepts these electrons and combines with magnesium ions to form solid compounds, i.e., magnesium carbonates or oxalates. In other words, power generation is accompanied by the chemical binding of carbon in a stable form. During charging, the process should reverse: the solid products decompose and release CO₂, while the magnesium is reprecipitated as a metal.
The choice of magnesium is not accidental. This metal is more abundant in Earth’s crust than lithium, which opens up prospects for large-scale and relatively inexpensive production. Plus, magnesium donates two electrons per atom, providing a high theoretical capacity. Another important advantage is a more uniform metal deposition during charging. Unlike lithium, magnesium is less prone to forming dendrites, needle-like structures that can cause short circuits and fires. This improves the potential safety of these systems.
However, practical implementation has met with major scientific challenges. Magnesium ions have a double charge and high charge density, which causes them to interact strongly with surrounding electrolyte molecules and reaction products. This results in the formation of highly stable magnesium carbonates. Although these are thermodynamically favorable, they decompose poorly during charging. This leads to high energy losses and rapid battery degradation.
To overcome this limitation, the researchers put an emphasis on controlling the reaction mechanism. They found that it was crucial not only to accelerate processes at the cathode, but also to change the very CO₂ conversion pathway. Instead of forming hard-to-reverse carbonates, the scientists directed the reaction towards forming oxalates, compounds in which two carbon atoms bond. These products decompose more easily during charging, which increases reversibility and extends the battery’s lifespan.
It should be noted that, rather than limiting themselves to improving a single battery element, the scientists essentially rebuilt its chemistry. The cathode was purposefully modified: they introduced defects into its structure and fine-tuned its electronic properties so that the surface would interact more actively with CO₂ and stabilize the desired intermediate compounds. At the same time, they altered the composition of the electrolyte, the medium in which magnesium ions move. This made it possible to reorganize their coordination and select specific products to be formed during discharging. As a result, reaction control became predictable. This brought about more reversible and stable battery operation.
The most realistic application for these batteries is stationary power generation. While charging speed requirements are lower in energy storage systems for solar and wind farms than in transportation, such properties as safety, durability and material cost are very important. Magnesium carbon dioxide batteries can operate in conjunction with concentrated CO₂ sources, such as industrial emissions or carbon capture plants. During periods of excess electricity production, CO₂ will be electrochemically converted into solid compounds with simultaneous energy storage and released back if necessary.
