A new cathode design reduces lattice stress in sodium-ion batteries, helping one material retain 96.7% capacity after 300 high-rate charging cycles under demanding laboratory conditions.
A study published by Elsevier in eScience Energy has demonstrated a promising route to longer-lasting sodium-ion batteries, using carefully tailored cathode crystals to reduce structural stress. The modified P2-type cathode retained 96.7% of its capacity after 300 cycles at a demanding 5C rate, while also showing improved structural stability.
The research addresses a major problem affecting layered oxide cathodes: repeated sodium-ion insertion and extraction can cause uneven lattice strain. As stress accumulates inside the crystal grains, it can eventually produce deformation and internal cracking, accelerating capacity loss.
Researchers focused on the crystal’s c-axis dimension, creating prism-like grains with a smaller c-axis size. This morphology helped accommodate mechanical strain more effectively and allowed stress to dissipate before it became concentrated enough to damage the material.
Microscopy and finite-element analysis supported the approach. The thinner grains showed more uniform strain distribution, while conventional thicker grains developed greater localised distortion and stress. The tailored structure also facilitated sodium-ion transport and reduced resistance during electrochemical testing.
The modified material, P2-Na₀.₇₅Ni₀.₂₅Mn₀.₇₅O₂, demonstrated not only strong cycling stability but also useful high-rate performance, retaining 80.7% of its capacity between 0.2C and 10C. A full cell pairing the material with hard carbon achieved an energy density of 218.3 Wh kg⁻¹ and retained 92.6% capacity after 300 cycles at 2C.
The findings suggest that controlling crystal morphology could complement chemical approaches to improving sodium-ion batteries. By reducing internal mechanical stress rather than simply changing the battery’s composition, the strategy offers another pathway towards more durable energy-storage materials.
