Scanning Electron Microscopy (SEM) plays a critical role in the study of lithium metal anodes, offering high-resolution imaging capabilities that reveal morphological details essential for understanding performance and degradation mechanisms. The technique provides direct visualization of dendrite formation, stripping and plating behavior, and the solid electrolyte interphase (SEI) layer, all of which influence battery safety and efficiency. Cryogenic SEM (cryo-SEM) further enhances these observations by preserving the highly reactive lithium metal in its native state, preventing artifacts from air exposure or beam damage.

Dendrite growth remains a major challenge in lithium metal batteries due to its propensity to cause short circuits and capacity loss. SEM enables researchers to examine dendrite morphology at nanoscale resolution, distinguishing between needle-like, mossy, or fractal structures. Needle-like dendrites, often observed under high-current conditions, exhibit sharp protrusions that penetrate separators, while mossy lithium forms porous, uneven deposits that increase interfacial resistance. By correlating SEM images with electrochemical data, researchers identify conditions that promote or suppress dendritic growth, such as electrolyte composition, current density, and cycling protocols.

Stripping and plating behavior directly impacts Coulombic efficiency and cycle life. SEM captures the evolution of lithium metal surfaces during repeated deposition and dissolution. Uneven stripping leads to dead lithium—detached fragments that no longer participate in electrochemical reactions—while non-uniform plating creates rough surfaces that exacerbate dendrite formation. High-resolution SEM images reveal pitting, cracking, and void formation, which contribute to capacity fade. Researchers use these observations to evaluate the effectiveness of artificial SEI layers, electrolyte additives, and 3D host structures in promoting uniform lithium deposition.

The SEI layer, a passivating film that forms on lithium metal surfaces, influences interfacial stability and ion transport. SEM, combined with energy-dispersive X-ray spectroscopy (EDS), provides insights into SEI composition and morphology. A homogeneous, compact SEI prevents excessive electrolyte decomposition, while a porous or fractured SEI leads to continuous side reactions and lithium corrosion. SEM analysis helps identify how different electrolytes—such as carbonate-based, ether-based, or solid-state systems—affect SEI structure. For instance, inorganic-rich SEI layers often exhibit better mechanical stability than organic-dominated ones.

Cryo-SEM has become indispensable for lithium metal anode research due to its ability to stabilize reactive samples. Traditional SEM requires conductive coatings or vacuum conditions that alter lithium morphology. Cryo-SEM involves rapidly freezing samples to cryogenic temperatures, immobilizing the lithium and SEI in their operational states. This technique prevents beam-induced melting, oxidation, or SEI dissolution, allowing for accurate imaging of dendrites, grain boundaries, and SEI nanostructures. Cryo-SEM has revealed that some lithium deposits initially assumed to be dendritic are instead granular or columnar, highlighting the importance of proper sample preservation.

Quantitative SEM analysis provides metrics such as dendrite density, SEI thickness, and porosity. For example, studies have measured SEI thickness ranging from 20 to 500 nanometers depending on electrolyte formulation and cycling history. Dendrite aspect ratios—calculated from SEM images—help predict penetration risks through separators. Automated image processing tools extract statistical data on particle size distributions and surface roughness, enabling correlations between morphology and electrochemical performance.

Despite its advantages, SEM has limitations. Beam sensitivity can cause sample damage, necessitating low accelerating voltages or fast imaging protocols. Cryo-SEM requires specialized equipment and careful sample transfer to avoid condensation or warming artifacts. Additionally, SEM alone cannot provide chemical bonding information, requiring complementary techniques like X-ray photoelectron spectroscopy (XPS) or Fourier-transform infrared spectroscopy (FTIR) for complete SEI characterization.

Recent advances in in-situ SEM allow real-time observation of lithium deposition and dissolution within miniaturized electrochemical cells. These setups capture dynamic processes such as dendrite nucleation, SEI formation, and crack propagation, providing mechanistic insights unavailable through post-mortem analysis. For example, in-situ SEM has demonstrated how mechanical pressure suppresses dendrite growth by promoting lateral lithium spreading instead of vertical protrusion.

In summary, SEM is a powerful tool for lithium metal anode research, offering detailed morphological insights into dendrite growth, stripping/plating behavior, and SEI layer evolution. Cryo-SEM extends these capabilities by preserving reactive interfaces in their native states. The technique supports the development of safer, longer-lasting lithium metal batteries by enabling precise characterization of failure modes and material innovations. Future advancements in resolution, speed, and correlative microscopy will further enhance its utility in battery research.