Researchers have found a way to make sodium-ion batteries more durable by changing the shape of their cathode crystals rather than altering their chemical composition. By reducing the thickness of a key crystal dimension, the team limited internal stress and cracking that normally develops as sodium ions repeatedly enter and leave the material. The optimized cathode retained 96.7% of its capacity after 300 cycles at 5 C, pointing to a practical design route for more durable sodium-ion battery materials.

Sodium-ion batteries are attracting growing interest for large-scale energy storage because sodium is abundant, widely distributed, and compatible with low-cost battery chemistry. Layered transition-metal oxides offer high capacity and good scalability as positive electrode materials, but their mechanical stability remains a major barrier.

During sodium-ion intercalation and deintercalation, the crystal lattice expands and contracts unevenly, especially along the c-axis. This non-uniform lattice strain can concentrate stress inside the grains, causing cracks, exposing fresh surfaces to the electrolyte, and accelerating side reactions and capacity loss. Based on these challenges, there is a need to develop microstructure-level strategies that can relieve internal stress before it damages the cathode.

A team led by Wuhan University of Technology said the study offers a way to think about battery failure before visible damage appears. They said sodium-ion storage creates a repeated “breathing” motion in layered oxides, and thick grains allow this strain to build up until cracks form. By shortening the most vulnerable direction, the material can release stress earlier and more evenly. They said this principle could help guide cathode design beyond composition tuning, giving researchers a clearer mechanical strategy for building sodium-ion batteries that remain stable over prolonged cycling.

The findings have practical implications for next-generation energy storage. Simply reducing overall particle size can improve stress release, but it may also increase surface side reactions and reduce tap density.

Source: The National Law Review

Image: Sodium-ion battery