Sodium-ion batteries are attracting growing attention as a greener and more affordable alternative to today’s lithium-ion batteries.
Sodium is abundant, widely available, and cheaper than lithium, making it appealing for large-scale energy storage.
But despite this promise, sodium-ion batteries have struggled with a major technical problem that has slowed their progress—until now.
Researchers at the Federal Institute for Materials Research and Testing (BAM) in Germany have developed a new anode design that dramatically improves both efficiency and energy storage.
Their approach tackles one of the biggest weaknesses of sodium-ion batteries: the loss of capacity during the very first charge.
This early loss happens because of a chemical reaction between the anode and the electrolyte, the liquid that carries charged particles inside the battery.
When a sodium-ion battery is first charged, electrolyte molecules break down on the surface of the anode and seep into tiny pores inside it. These pores are supposed to store sodium ions, but once they are filled with unwanted by-products, that storage space is lost for good.
Eventually, a thin protective layer forms on the anode and stops further damage. However, this layer itself traps sodium ions, reducing the number of charge carriers available for the battery.
As a result, much of the battery’s potential energy is lost before it ever reaches the user.
Lithium-ion batteries rarely face this issue because their anodes are made of dense graphite, which allows the protective layer to form quickly and efficiently. Sodium ions, however, cannot be stored in graphite.
Instead, sodium-ion batteries rely on “hard carbon,” a porous form of carbon that can hold sodium but also makes unwanted chemical reactions more likely.
The BAM team realized that one single material cannot do two conflicting jobs well: store large amounts of sodium and form a protective layer efficiently. Their solution was to separate these roles using a clever core-shell design.
In this new anode, the core is made of porous hard carbon that stores sodium ions. Around it, the researchers added an ultra-thin outer layer that acts like a selective filter. Sodium ions can pass through easily, but larger electrolyte molecules are blocked. This prevents damage to the core while still allowing the battery to charge and discharge normally.
The shell is made from activated carbon, a low-cost and environmentally friendly material already used in water filters and other applications. This makes the technology not only effective, but also practical for real-world use.
The results are striking. The new anode reaches an initial efficiency of 82 percent, compared with just 18 percent for an uncoated version. The researchers believe there is still room for further improvement.
By separating protection and storage into two layers, this design opens new possibilities for sodium-ion batteries. It brings them a big step closer to becoming a reliable, sustainable option for future energy storage.
Source: KSR.
