Infrared microscopy systems with sub-10µm resolution have emerged as a critical tool for analyzing heat generation in battery materials, particularly in single electrode particles or micro-wires. These systems enable researchers to map thermal behavior at microscale resolutions, providing insights into localized heating effects that influence battery performance, safety, and degradation. By integrating with scanning electron microscopy (SEM) and focused ion beam (FIB) systems, IR microscopy offers a multimodal approach to correlating structural, compositional, and thermal properties. However, challenges remain in sub-surface thermal profiling and quantifying local Joule heating effects, driving ongoing research to refine these techniques.

The principle of IR microscopy for thermal analysis relies on detecting mid-infrared radiation emitted by materials due to temperature-dependent blackbody emission. Advanced detectors, such as mercury cadmium telluride (MCT) or quantum well infrared photodetectors (QWIPs), achieve spatial resolutions below 10µm, allowing visualization of heat distribution in individual electrode particles. This capability is particularly valuable for studying heterogeneous materials like lithium-ion battery electrodes, where localized hotspots can lead to accelerated degradation or thermal runaway.

Coupling IR microscopy with SEM or FIB systems enhances the depth of analysis by combining high-resolution imaging with thermal mapping. SEM provides nanoscale structural details, while FIB enables cross-sectional analysis or site-specific sample preparation. By aligning IR thermal data with SEM/FIB images, researchers can correlate heat generation with microstructural features such as grain boundaries, cracks, or porosity. For example, studies have shown that lithium plating on graphite anodes produces distinct thermal signatures detectable by IR microscopy, which can be further investigated using FIB cross-sectioning to examine subsurface morphology.

Despite these advantages, sub-surface thermal profiling remains a limitation for IR microscopy. Infrared radiation is absorbed or scattered by overlying material, making it difficult to resolve thermal gradients beneath the surface. The penetration depth depends on the material’s optical properties, but in most battery materials, useful thermal data is limited to the top few microns. To address this, researchers employ techniques such as lock-in thermography, which modulates the heat source to improve signal-to-noise ratios and isolate subsurface contributions. Alternatively, combining IR data with computational modeling helps reconstruct 3D thermal profiles, though this requires precise knowledge of material properties.

Local Joule heating effects are another area of active investigation using high-resolution IR microscopy. In battery systems, Joule heating arises from resistive losses during charge-discharge cycles, particularly in high-current applications or materials with poor conductivity. Micro-wires or single particles with defects exhibit uneven current distribution, leading to microscale temperature variations. IR microscopy can quantify these effects by measuring temperature rises with high spatial and temporal resolution. For instance, experiments on silicon anode particles have revealed that cracking during lithiation increases local resistance, resulting in measurable Joule heating that accelerates capacity fade.

Quantitative analysis of thermal data requires careful calibration and validation. Emissivity variations between materials can introduce errors in temperature measurements, necessitating sample-specific calibration curves. Additionally, the dynamic nature of battery operation means that transient heating effects must be captured with fast response detectors. Modern IR systems achieve frame rates exceeding 100 Hz, enabling real-time observation of thermal phenomena during electrochemical cycling.

Research into advanced IR microscopy techniques continues to push the boundaries of thermal analysis. Hyperspectral IR imaging, for example, combines spatial and spectral resolution to identify chemical changes accompanying heat generation. This is particularly useful for studying electrolyte decomposition or phase transitions in electrode materials. Another development is the integration of atomic force microscopy (AFM) with IR detection, which can achieve nanoscale thermal resolution by measuring local thermal expansion or conductivity.

The application of these techniques extends beyond lithium-ion batteries to emerging technologies such as solid-state batteries or lithium-sulfur systems. In solid-state batteries, interfacial resistance between electrodes and solid electrolytes generates heat that can be mapped with IR microscopy to optimize material combinations. Similarly, in lithium-sulfur batteries, localized heating due to polysulfide shuttling can be visualized to design better cathode architectures.

In summary, IR microscopy systems with sub-10µm resolution provide a powerful platform for investigating heat generation in battery materials. Integration with SEM/FIB systems enhances structural-thermal correlations, while ongoing research aims to overcome sub-surface profiling challenges and refine Joule heating analysis. These insights are critical for developing safer, more efficient energy storage systems, particularly as batteries evolve toward higher energy densities and faster charging capabilities. Future advancements in detector technology and multimodal imaging will further expand the utility of IR microscopy in battery research.