Scanning Electron Microscopy (SEM) plays a critical role in the failure analysis of lithium-ion batteries by providing high-resolution imaging and elemental analysis of battery materials at micro- and nanoscales. The technique is indispensable for identifying structural and chemical degradation mechanisms that lead to performance loss or catastrophic failure. Key applications include dendrite detection, electrode delamination analysis, and post-thermal runaway investigation, as well as cross-sectional studies of aged cells to correlate physical degradation with electrochemical behavior.
Dendrite formation is a major failure mode in lithium-ion batteries, particularly in cells with lithium metal or silicon anodes. SEM enables direct observation of lithium dendrites, which appear as needle-like or mossy structures growing from the anode surface. High-resolution imaging reveals dendrite morphology, penetration depth into the separator, and interaction with the cathode. Energy-dispersive X-ray spectroscopy (EDS) coupled with SEM confirms the elemental composition of dendrites, distinguishing between lithium metal deposits and electrolyte decomposition products. In some cases, dendrites exhibit branching patterns that correlate with local current density variations, providing insights into uneven plating behavior. Cross-sectional SEM analysis of cycled anodes shows how dendrites initiate at defects in the solid-electrolyte interphase (SEI) and propagate through repetitive stripping and plating cycles.
Electrode delamination is another critical failure mechanism that SEM helps diagnose. Delamination occurs when active material separates from the current collector due to mechanical stress, gas evolution, or binder degradation. SEM imaging reveals cracks, voids, and detachment zones at the electrode-current collector interface. Secondary electron imaging highlights topographical changes, while backscattered electron imaging differentiates material phases based on atomic contrast. In aged cathodes, delamination often coincides with particle cracking and transition metal dissolution, which SEM-EDS maps can quantify. Anode delamination is frequently associated with excessive SEI growth or gas accumulation, visible as blistering or lifting of the coating layer. Cross-sectional analysis of delaminated electrodes provides depth-resolved information on failure progression, linking mechanical degradation to capacity fade or impedance rise.
Post-thermal runaway analysis with SEM reveals microstructural changes induced by extreme heat and gas generation. Cells subjected to thermal runaway exhibit melted separators, coalesced electrode particles, and reaction products from electrolyte decomposition. SEM imaging identifies localized hot spots where thermal propagation initiated, often marked by distinct phase transformations or pore formation. EDS analysis detects fluorine and phosphorus-rich deposits from electrolyte breakdown, as well as oxidized transition metals from cathode decomposition. In some cases, SEM reveals how thermal runaway pathways correlate with manufacturing defects such as electrode misalignment or contaminant particles. Cross-sectional studies of thermally abused cells show gradient damage patterns, with severe degradation near the initiation point tapering to milder effects in peripheral regions.
Cross-sectional SEM analysis of aged lithium-ion cells provides critical insights into degradation mechanisms. Focused ion beam (FIB)-SEM allows precise site-specific cross-sectioning of battery components, preserving delicate structures like the SEI. In cycled anodes, cross-sections reveal SEI thickness evolution, lithium plating penetration, and particle fracture. Aged cathodes show phase segregation, particle cracking, and loss of electrical contact between active material and conductive additives. SEM imaging quantifies porosity changes in electrodes, which directly impact ionic transport and rate capability. Combining cross-sectional data with electrochemical impedance spectroscopy measurements establishes structure-property relationships, such as how pore closure correlates with diffusion polarization growth.
SEM also contributes to understanding interfacial degradation in solid-state batteries. For ceramic electrolytes, SEM identifies grain boundary failures and lithium filament penetration paths. In polymer-ceramic composites, it reveals phase separation and contact loss at interfaces. High-resolution imaging of cycled solid-state interfaces shows reaction layer formation and mechanical deformation from volume changes. These observations help explain impedance rise and capacity fade in solid-state systems.
Operando SEM studies, though technically challenging, provide dynamic views of battery degradation. Specialized stages allow researchers to observe dendrite growth in real time under controlled electrochemical conditions. These experiments capture dendrite nucleation, propagation kinetics, and mechanical interactions with separator materials. Similarly, operando studies of electrode particles reveal crack initiation and propagation during cycling, linking mechanical damage to state of charge variations.
Sample preparation is critical for reliable SEM analysis of battery materials. Argon ion milling produces artifact-free cross-sections for interface studies. Cryogenic techniques preserve liquid electrolyte distribution and prevent lithium metal reactions during sample handling. Conductive coatings mitigate charging effects while minimizing interference with EDS signals. Advanced techniques like low-voltage SEM reduce beam damage to sensitive materials like lithium metal or organic SEI components.
SEM’s limitations in battery analysis include difficulty in distinguishing lithium compounds due to their low atomic number and sensitivity to beam damage. However, combining SEM with complementary techniques like Raman spectroscopy or atomic force microscopy overcomes these challenges. Correlative microscopy approaches provide comprehensive views of battery degradation by merging SEM’s high-resolution imaging with chemical and mechanical property mapping.
The technique’s value extends beyond failure analysis to quality control and materials development. SEM inspection of electrode coatings detects manufacturing defects like agglomerates, pinholes, or uneven thickness that could lead to field failures. In materials research, SEM screens novel electrode architectures or coatings for structural stability before electrochemical testing. This proactive application prevents costly failures downstream in battery development cycles.
Quantitative image analysis of SEM data enables statistical evaluation of degradation phenomena. Particle size distributions track active material fragmentation over cycles. Fractal dimension calculations quantify dendrite complexity and its relationship to cycling conditions. Porosity measurements from image segmentation correlate with electrolyte wetting and ionic transport properties. These metrics provide objective criteria for comparing degradation across cell designs or operating protocols.
In summary, SEM serves as an essential tool for lithium-ion battery failure analysis by visualizing and characterizing degradation at multiple length scales. Its ability to resolve dendrites, delamination, thermal damage, and aging effects provides mechanistic understanding that informs safer, more durable battery designs. When integrated with electrochemical data, SEM analysis establishes clear connections between physical degradation modes and performance loss, guiding both troubleshooting and predictive modeling efforts. The technique’s continued evolution, particularly in operando capabilities and correlative microscopy, will further enhance its role in advancing battery reliability and performance.