Why do some of the most promising next-generation batteries fail—and how can we stop it? A new peer-reviewed study led by Imperial College London answers that by watching the failure process unfold as the battery operates. Using simultaneous dual-polarity secondary-ion mass spectrometry (SIMS) alongside controlled electrochemical cycling, the team directly observed where, when, and why degradation starts inside solid-state sodium-ion batteries.
Why this matters:
Sodium-ion batteries are attracting interest as a lower-cost, abundant alternative to lithium-ion. One leading architecture uses NASICON, a ceramic solid electrolyte that transports sodium ions between electrodes. However, the sodium metal | NASICON interface is fragile. Charging and discharging can trigger:
- Interfacial cracking and unwanted side reactions
- Growth of metallic “dendrites” that short-circuit the cell
- Progressive loss of ion-transport pathways
Historically, researchers had to take cells apart post-mortem, which can alter the chemistry and hide what really happened during operation. This work changes that by providing operando visibility.
What the researchers did:
The team paired normal battery cycling with a dual-polarity SIMS instrument in high vacuum. By applying tiny, precisely controlled currents to micron-scale regions of a sodium|NASICON half-cell, they captured synchronised electrochemical and chemical data from the exact same spot—operando. That combination delivers performance metrics and nanoscale chemical maps in real time.
What they found:
- Failure threshold: NASICON withstood current densities up to ~0.04 μA μm⁻² before instability set in. Above this, irregular sodium deposits formed quickly, leading to short circuits.
- Interfacial chemistry: A solid-electrolyte interphase (SEI) formed at the sodium|NASICON contact, dominated by sodium oxides and silicates. Crucially, the SEI did not self-limit—it kept growing and impeded ion transport. Pathway-driven degradation: 3D chemical maps showed sodium moving through narrow “transport columns” within NASICON, often along grain boundaries. SEI thickened on these routes, causing local Na⁺ build-up and, ultimately, metallic dendrites that pierced the electrolyte.
Why it’s important:
- This is the first demonstration of a solid-state battery being monitored for both chemistry and electrical behaviour in situ, exposing the earliest moments of failure rather than the aftermath. The takeaways:
- Degradation is pathway-specific, initiating along transport columns and grain boundaries.
- The SEI at sodium|NASICON is dynamically growing rather than protective, progressively blocking ion flow.
- Operando dual-polarity SIMS now provides a diagnostic route to design more stable interfaces.
Although focused on sodium systems, the insights—and the measurement approach—translate to other solid-state platforms, including advanced lithium cells and hybrid supercapacitors.
Implications for materials and device design:
- Interface engineering: Use interlayers/surface terminations that suppress SEI overgrowth at grain boundaries.
- Microstructure control: Tune NASICON processing to refine grain size and boundary chemistry, guiding transport paths.
- Operating windows: Set current-density limits that avoid dendritic onset during formation and fast-charge regimes.
- Qualification: Employ operando SIMS maps as go/no-go criteria for interface recipes before scale-up.
How Hiden Analytical supports this work:
Hiden’s SIMS platforms are built for high-sensitivity chemical imaging and are customisable for operando workflows. Fine control of primary ion conditions, simultaneous acquisition of complementary ion polarities, and robust charge compensation enable quantitative depth profiles and high-contrast maps from delicate solid-state interfaces—exactly what’s needed to see failure precursors before they become catastrophic.
Dual-Polarity SIMS: capture both sides of the chemistry in one pass
Many species are preferentially detected as either positive or negative secondary ions. Running those measurements sequentially risks mis-registration—especially on evolving, one-off samples. Dual-polarity SIMS acquires positive and negative ions simultaneously, preserving spatial and depth alignment while boosting overall information content. For complex solid-state battery interfaces, that means clearer identification of oxides, silicates and metallic species as they nucleate and grow.
Learn more: Dual Polarity SIMS Workstation
Paper reference: Sukumaran, S., Chater, R.J., Fearn, S., Cooke, G., Smith, N. and Skinner, S.J. (2025) ‘Probing dynamic degradation and mass transport in solid-state sodium-ion batteries using operando simultaneous dual-polarity SIMS’, EES Batteries, 1, pp. 964–974. doi:10.1039/D5EB00071H
