Thinner crystal grains improve sodium-ion battery durability

A new study from Wuhan University of Technology and Xi’an Jiaotong University shows that reshaping layered oxide cathode grains can reduce hidden cracking in sodium-ion batteries. The design boosted cycling stability and could help make grid-storage batteries more durable and practical.

Why it matters: - Sodium-ion batteries are gaining attention for large-scale energy storage because sodium is abundant, widely distributed and compatible with lower-cost chemistry. - Mechanical failure inside layered oxide cathodes remains a major barrier to longer battery life. - The study shows that grain geometry, not just chemical composition, can help manage internal stress and delay crack formation.

What happened: - Researchers led by Wuhan University of Technology, with collaborators from Xi’an Jiaotong University, published the study online on May 20, 2026, in eScience Energy. - The team focused on layered P2-type Na0.75Ni0.25Mn0.75O2 cathodes and tuned the c-axis dimension to make the crystal grains thinner. - The optimized cathode retained 96.7% of its capacity after 300 cycles at 5 C. - In a full cell paired with a hard carbon negative electrode, the optimized material reached about 218.3 Wh kg−1 and kept 92.6% capacity after 300 cycles at 2 C. - The paper is identified by DOI 10.1016/j.esen.2026.100070.

The details: - The researchers compared morphology-tailored NaNMO (MT-NaNMO) with a control sample (C-NaNMO) that had the same chemical composition. - X-ray diffraction, scanning electron microscopy and electron microscopy confirmed both materials kept the P2 layered structure. - MT-NaNMO formed thinner prism-like primary grains of about 200 nm along the c-axis, compared with about 800 nm in C-NaNMO. - In situ XRD showed similar unit-cell-level lattice changes in both samples during charging and discharging. - High-resolution transmission electron microscopy and geometric phase analysis showed stable lattice fringes and more uniform strain fields in MT-NaNMO. - The control sample showed lattice distortion and localized strain. - Finite element analysis showed that shortening the c-axis produced a more even stress distribution. - Electrochemical impedance spectroscopy and cycling tests showed faster sodium-ion transport, lower resistance and stronger long-term stability in MT-NaNMO.

Between the lines: - The study points to a mechanical design strategy for cathodes that goes beyond composition tuning. - The authors argue that layered oxides “breathe” during sodium insertion and removal, and thick grains let strain build until cracks appear. - By reducing the most vulnerable dimension, the material can release stress earlier and more evenly. - That approach may avoid some tradeoffs of simply shrinking particles, which can raise surface side reactions and lower tap density.

What’s next: - The directional microstructure strategy could inform new cathode designs for longer-lasting sodium-ion batteries. - The work suggests a path toward more reliable, lower-cost storage systems for renewable energy and grid-scale use. - The funding came from China’s National Key Research and Development Program and the National Natural Science Foundation of China.