Lithium-Ion Battery Analysis: Four Years of Spectroscopic Advances in Research, Manufacturing, and Quality Assessment

Lithium-ion batteries (LIBs) are important to modern energy storage systems for electric vehicles, portable electronics, and grid applications. Over the past four years, advances in spectroscopy, chemometrics, and artificial intelligence have significantly improved LIB research, manufacturing, and quality assessment. This review summarizes developments in near-infrared (NIR), infrared (IR), Raman, X-ray fluorescence (XRF), laser-induced breakdown spectroscopy (LIBS), nuclear magnetic resonance (NMR), and hyperspectral imaging for battery material characterization and process monitoring.

Applications include raw material verification, electrode coating analysis, electrolyte characterization, degradation studies, and failure analysis. Emphasis is placed on multivariate analysis, machine learning (ML), and explainable AI for interpreting spectral data and enabling real-time process analytical technology (PAT). The review also discusses analytical challenges and emerging spectroscopic methods for next-generation battery chemistries, including solid-state and sodium-ion systems.

Lithium-ion batteries (LIBs) have become the dominant rechargeable energy storage technology of the 21st century.¹ Since their commercial introduction in 1991, LIBs have powered the revolution in portable electronics and are now the engine of the global transition to electric mobility and renewable-energy integration.² A modern LIB consists of a layered-oxide, spinel, or olivine cathode; a graphite, silicon-composite, or lithium-metal anode; a non-aqueous liquid or solid electrolyte; and a microporous polymer separator. The electrochemical energy storage and release cycle depends on the reversible intercalation and de-intercalation of lithium ions between cathode and anode, a process governed by atomic and molecular phenomena that can only be fully characterized through spectroscopic investigation.

The analytical requirements for LIB research, manufacturing, and quality assessment span an exceptionally broad range of measurement objectives. At the research frontier, scientists need techniques capable of monitoring structural phase transitions in electrode materials operando—in real time, inside a working cell under current flow—with spatial resolution down to the micrometer scale. At the manufacturing scale, quality engineers need rapid, non-destructive, high-throughput methods that can verify coating uniformity, detect trace metal contamination, and confirm electrolyte stoichiometry on timescales of milliseconds to seconds per sample. In the recycling and sustainability domain, analysts need to quantify the composition of black mass recovered from spent cells and certify the purity of resynthesized cathode precursors.

No single spectroscopic technique fulfills all of these requirements, and a central theme of Spectroscopy Online's coverage over the past four years has been the articulation and systematic development of multi-technique analytical strategies.³ The following sections survey the major spectroscopic methods covered in our pages during 2022–2025, describe their applications across the LIB value chain, and situate the published work within the broader scientific and technical literature.

Molecular Spectroscopy of Lithium-Ion Battery Materials

Raman Spectroscopy: Structural Fingerprinting from Cathode to Solid Electrolyte Interface

Raman spectroscopy has emerged as perhaps the most versatile and widely adopted molecular technique in LIB analysis, and it has commanded sustained attention in Spectroscopy Online. The technique's sensitivity to the vibrational modes of crystalline and amorphous solids, its compatibility with aqueous and non-aqueous environments, its minimal sample preparation requirements, and its amenability to in situ and operando experimental configurations make it uniquely suited to the demands of battery research and manufacturing.

In the cathode domain, Raman spectroscopy is the gold standard for verifying the crystalline structure of layered NMC oxides (LiNi_xMn_yCo_zO₂), spinel LiMn₂O₄, and olivine LiFePO₄. The sharp A_1g Raman mode of NMC serves as a direct indicator of the R-3m hexagonal structure; deviations signal phase impurities or cation disordering. The sensitivity of Raman to hydrated forms of lithium salts, which is a critical concern for LiPF₆, which hydrolyzes to form corrosive HF, has been highlighted as a key quality-control application in manufacturing environments.⁴

The most scientifically rich application of Raman in the LIB field is operando monitoring of electrode structural evolution during electrochemical cycling. During charge, lithium de-intercalation from layered cathodes drives a sequence of structural phase transitions—from the rhombohedral phase through monoclinic distortions to a fully delithiated hexagonal phase—each producing characteristic shifts in the Raman peak positions of the E_g and A_1g modes.⁵ Operando Raman experiments, in which a custom optical cell with a transparent window is cycled under a spectrometer's laser, can resolve these transitions with sub-cycle temporal resolution, providing kinetic information inaccessible by ex situ diffraction. Spectroscopy Online has published multiple reviews of in situ and operando Raman methodology, documenting both bulk and confocal micro-Raman approaches to electrode analysis.⁶

The solid electrolyte interface (SEI), which is the passivation layer that forms on graphite anodes during the first charge cycle via electrolyte reduction, is one of the most analytically challenging objects in battery science: nanometrically thin, chemically heterogeneous, and mechanically fragile. Raman spectroscopy, particularly surface-enhanced and tip-enhanced variants, has been employed to identify organic (lithium alkyl carbonates, lithium ethylene dicarbonate) and inorganic (Li₂CO₃, LiF, Li₂O) components of the SEI, with the D and G bands of graphitic carbon providing a parallel probe of anode structural integrity and degree of graphitization.⁷

FT-IR and NIR Spectroscopy: Electrolyte Analysis and Binder Quality Control

Fourier transform infrared (FT-IR) and near-infrared (NIR) spectroscopy address a complementary set of analytical challenges in LIB analysis, primarily the characterization of electrolyte solvents, salt speciation, binder polymers, and separator materials. Spectroscopy Online has published application notes demonstrating FT-IR-based monitoring of carbonate solvent composition (ethylene carbonate/dimethyl carbonate mixtures are most common in commercial cells), detection of electrolyte degradation products such as CO₂ and organic acid fragments, and assessment of polyvinylidene fluoride (PVDF) binder uniformity on coated electrode films.

NIR spectroscopy has attracted growing interest for LIB applications because it enables rapid, non-contact analysis through glass or polymer packaging and is well suited to inline process analytical technology (PAT) in manufacturing environments.³ Published work covered by Spectroscopy Online includes NIR-based methods for determining lithium salt concentration in electrolyte solutions, monitoring electrode slurry water content during the aqueous processing of LFP cathodes, and assessing state-of-charge and state-of-health in finished cells through the measurement of overtone and combination bands associated with lithium-ion coordination environments in the electrolyte.

The 2024 comprehensive review by Julien and Mauger, published in the International Journal of Molecular Sciences, provided a systematic treatment of Raman and FT-IR spectra for all major LIB electrode material classes—layered, spinel, and olivine cathodes; graphitic, hard-carbon, and silicon-based anodes—and highlighted the diagnostic power of vibrational spectroscopy for amorphous and nanostructured materials for which X-ray diffraction gives weak or ambiguous signals.⁸

NMR Spectroscopy: Ion Dynamics and Electrolyte Structure

Nuclear magnetic resonance (NMR) spectroscopy occupies a specialized but indispensable role in LIB research, offering unique access to the local chemical environment of lithium nuclei and to the dynamics of ion transport in electrolytes and solid electrolytes. ⁷Li and ⁶Li solid-state NMR have been used to measure lithium chemical shifts in layered cathode materials as a function of state of charge, directly probing the occupancy of lithium sites in the transition-metal oxide lattice. Solution-state ⁷Li and ¹⁹F NMR allow direct measurement of ion-pairing equilibria, solvation numbers, and diffusion coefficients in non-aqueous electrolytes, providing molecular-level understanding of how electrolyte formulation affects lithium-ion transport.

A proof-of-principle in situ high-resolution NMR technique for operating LIB cells was described in a 2023 article in Solid State Nuclear Magnetic Resonance and highlighted in Spectroscopy Online's coverage of emerging operando methods. The cylindrical mini-pellet approach allows NMR spectra to be acquired from an electrochemically active cell, offering a direct window on how the lithium coordination environment in the electrolyte evolves during cycling, which is a capability previously unavailable by any other technique.⁹

Atomic Spectroscopy of Lithium-Ion Battery Materials

ICP-OES and ICP-MS: Elemental Purity Across the Value Chain

Inductively coupled plasma–optical emission spectrometry (ICP-OES) and ICP–mass spectrometry (ICP-MS) are the workhorses of elemental analysis in LIB research and manufacturing, and they have been among the most consistently covered techniques in Spectroscopy Online. Their role spans every stage of the battery value chain: from the qualification of lithium carbonate and lithium hydroxide feedstocks extracted from brine or spodumene; through the purity certification of cathode precursors (NiSO₄, MnSO₄, CoSO₄) and active materials; to the quality control of electrolyte salts and solvents; and finally to the compositional analysis of recycled materials from spent cells.

A May 2023 application note published in Spectroscopy Online by Agilent Technologies provided a detailed practical guide to ICP-OES analysis of LIB electrode materials, documenting challenges in digesting refractory oxide cathode powders, the interferences from high-matrix electrolyte solutions, and validated methods for the simultaneous determination of Li, Ni, Mn, Co, Al, Fe, Cu, and Zn across the full production workflow.¹⁰ The authors emphasized that accurate multi-element analysis at the trace level is critical during incoming material inspection, as even part-per-million levels of magnetic metal contaminants (Fe, Ni, Cr, Zn) in cathode powders can cause internal short circuits and thermal runaway events in finished cells.

The analysis of LIB electrolytes by ICP-MS has posed distinct analytical challenges owing to the high organic solvent content of carbonate electrolyte matrices. A 2025 column in Spectroscopy Online documented methods for the elemental compositional analysis of LiPF₆-based electrolytes by ICP-MS, including organic matrix management strategies, the use of internal standards, and collision/reaction cell approaches for the elimination of polyatomic interferences from carbon- and phosphorus-containing fragments.¹¹ The article cited the work of Liu et al. on organic matrix effects in ICP-MS as foundational for method development in this analytically demanding matrix.¹²

In the recycling domain, ICP-MS and ICP-OES are used to verify the purity of lithium, cobalt, nickel, and manganese recovered by hydrometallurgical processes from black mass, confirming suitability for re-entry into the cathode precursor supply chain. The role of XRF as a complementary and faster technique for incoming cathode material inspection—requiring no sample dissolution—has been emphasized as part of a multi-platform quality-control architecture in which ICP provides certification-level accuracy while XRF provides screening-level speed.³

LIBS: From Laboratory Research to Inline Manufacturing

Laser-induced breakdown spectroscopy (LIBS) has undergone a remarkable transition over the period 2022–2025 from a niche research tool to a production-relevant inline analytical technology for LIB manufacturing, and Spectroscopy Online has been at the forefront of documenting this development. LIBS offers a unique combination of attributes for battery applications: instantaneous elemental response without sample preparation, spatial mapping capability with micrometer resolution, compatibility with moving electrode foils on production lines, and the ability to provide depth-resolved compositional profiles through thin-film electrode coatings.

A December 2024 article in Spectroscopy Online reported on research from the Université de Lyon, led by Vincent Motto-Ros and published in Spectrochimica Acta Part B: Atomic Spectroscopy, describing a micro-LIBS device capable of generating 2D elemental maps of lithium distribution across electrode cross-sections with spatial resolution sufficient to resolve individual particles in NMC cathode coatings.¹³ The technique's ability to image lithium directly, which is an element invisible to XRF because of its low atomic number, represents a critical advance for cathode uniformity verification.

Inline LIBS for production quality control has been documented in Spectroscopy Online through multiple publications. Nanosecond-pulsed LIBS systems optimized for quality-control applications on moving electrode foils have been shown capable of providing quasi-depth-resolved concentration profiles for carbon, nickel, manganese, cobalt, lithium, and aluminum at line speeds up to 17 m/min.¹⁴ These systems allow manufacturing defects such as coating non-uniformities, delamination zones, and current-collector contamination to be detected in real time rather than discovered through costly post-production testing. The homogeneity work of Lochbrunner et al. demonstrated that spot-to-spot LIBS signal variations in cathode foil measurements reflect genuine microstructural features of the coating rather than instrumental noise, establishing the technique's suitability for statistical quality mapping.¹⁵

LIBS has also been applied to the analysis of lithium-bearing geological materials in the context of battery-grade lithium supply chain qualification, and to the sorting and characterization of black mass components during battery recycling. Spectroscopy Online's coverage of recent developments in LIBS surveyed applications ranging from lithium ore grade estimation to identification of cathode chemistry in mixed spent-cell streams.¹⁶

X-ray Fluorescence: Speed and Non-Destructive Testing at Scale

X-ray fluorescence (XRF) spectroscopy has been widely adopted in LIB manufacturing as a rapid, non-destructive screening tool for elemental composition verification. Although XRF cannot directly detect lithium because of its low fluorescence yield, it provides fast, accurate measurements of the transition-metal composition of cathode active materials (Ni:Mn:Co ratios in NMC; Fe:P stoichiometry in LFP), the aluminum and copper loadings on current collector foils, and the sulfur and phosphorus content of electrolyte residue films. Spectroscopy Online has published vendor-contributed technical notes and editorial reviews describing the integration of XRF into LIB quality management systems, including the use of handheld XRF for incoming material inspection and benchtop wavelength-dispersive XRF for high-precision stoichiometric analysis.³

XPS: Surface Chemistry of Electrode Interfaces

X-ray photoelectron spectroscopy (XPS) is the definitive technique for the chemical characterization of electrode surfaces and interfaces, including the SEI on graphite anodes and the cathode electrolyte interphase (CEI) on oxide cathodes. XPS provides binding-energy-resolved spectra of Li 1s, C 1s, O 1s, F 1s, and N 1s core levels that allow unambiguous identification of the organic and inorganic species constituting these nanometric passivation layers. Spectroscopy Online has covered XPS studies documenting how SEI composition varies with electrolyte formulation, cycling history, and temperature, and how CEI chemistry on high-nickel NMC cathodes evolves during aggressive fast-charging cycles—information essential for designing electrolyte additives that promote stable interfacial chemistry.¹⁷

Electrochemical Impedance Spectroscopy: Health Monitoring, Aging, and State Estimation

Although electrochemical impedance spectroscopy (EIS) is not an optical technique in the conventional sense, it is recognized within the broader spectroscopic community as a powerful frequency-domain measurement tool, and Spectroscopy Online has devoted extensive coverage to its application in LIB diagnostics. EIS measures the complex impedance of a cell or electrode assembly across a frequency range, typically from millihertz to megahertz, and the resulting Nyquist and Bode plots encode information about ohmic resistance, double-layer capacitance, charge-transfer kinetics, and solid-state lithium diffusion. These parameters respond sensitively to the degradation mechanisms that reduce battery capacity and safety over time: SEI thickening; lithium plating; active material cracking; and electrolyte decomposition.

A 2024 article covered by Spectroscopy Online reported research by Zabara et al. at Bilkent and Sabancı Universities, who used temperature-dependent EIS with a symmetric cell configuration to isolate and quantify charge-transfer dynamics in lithium batteries. The authors demonstrated that activation energies and exchange current densities extracted from EIS spectra provide mechanistic insight into rate-limiting interfacial processes governing power performance, which is information essential for fast-charging protocol design.¹⁸

The Spectroscopy Online article "Evaluating Battery Health for Electric Vehicles Using Electrochemical Impedance Spectroscopy Measurements," published in 2024, provided a practical review of EIS-based state-of-health estimation methods relevant to electric vehicle battery management systems.¹⁹ The article examined how EIS parameters, particularly the mid-frequency semicircle diameter associated with charge-transfer resistance, evolve predictably with cycle number and serve as leading indicators of capacity fade well before the battery reaches end-of-life. A companion February 2026 article described a novel non-invasive EIS-based method for real-time temperature prediction in LIBs, a capability with significant implications for thermal runaway prevention.²⁰

The integration of machine learning (ML) with EIS has been among the most rapidly developing themes in battery analytics, and Spectroscopy Online has tracked this development closely. Zhang et al. demonstrated that Gaussian process ML applied to a data set of more than 20,000 EIS spectra collected at different states of health, charge, and temperature could accurately predict remaining useful life without complete knowledge of a cell's prior operating history.²¹ Building on this foundation, a September 2025 Spectroscopy Online article highlighted how LIBs play a major role in many application areas, including mobile phones and electric vehicles, and how spectroscopic techniques, including EIS, are routinely used to test battery performance, safety, and lifespan in combination with ICP-OES, Raman, NIR, ICP-MS, XRF, and micro-discharge optical emission spectroscopy (μDOES).²²

A further advance reported in Spectroscopy Online came from Knott et al. in the International Journal of Energy Research (2024), who investigated dynamic EIS (DEIS) measurements on LIBs under real-world conditions of simultaneous SOC change and temperature fluctuation—conditions encountered routinely in electric vehicle service but typically excluded from laboratory EIS protocols. Their results demonstrated that EIS measurements vary significantly even with temperature changes of 5 °C, underscoring the need for thermally corrected impedance models in field-deployed battery management systems.²³

Operando and In Situ Spectroscopy: Watching Batteries Work

The most demanding and scientifically rewarding category of spectroscopic LIB investigation is operando analysis: acquisition of spectroscopic data from a functioning cell under electrochemical control, in real time, without disassembly. Operando methods are essential for understanding the dynamic processes that govern battery performance and failure, including phase transformation kinetics in cathode materials, electrolyte decomposition pathways, SEI formation mechanisms, and lithium plating on anodes during fast charging.

A 2022 article in Nature Energy by Gervillié-Mouravieff et al., discussed in Spectroscopy Online's research coverage, described operando fiber-optic infrared (IR) spectroscopy performed inside commercial sodium- and lithium-ion cells. The technique unlocked cell chemistry evolution, including electrolyte decomposition and SEI formation, in real time, with spatial and temporal resolution that ex situ analysis cannot approach. The authors showed that fiber-optic IR probes can be embedded into commercial-format cylindrical cells without compromising their electrochemical performance, opening a route to in-operando quality monitoring of production cells.²⁴

Optical resonance comb spectroscopy, which is a technique that uses laser frequency combs to obtain broadband, high-resolution absorption spectra at millisecond timescales, was reported in a 2023 Nature Communications article cited in Spectroscopy Online as enabling operando monitoring of electrolyte chemical dynamics in lithium–sulfur batteries, providing mechanistic insights into the polysulfide shuttle reactions responsible for capacity decay in that emerging battery chemistry.²⁵

Operando plasmonic fiber-optic sensors for monitoring ion activities in aqueous batteries, published in Nature Communications (2022) and covered in Spectroscopy Online, demonstrated the monitoring of lithium and sodium ion concentrations in real time during cycling through changes in surface plasmon resonance of gold-coated optical fibers embedded in the electrolyte.²⁶ These fiber-optic and plasmon-based operando approaches represent a frontier in which spectroscopic instrumentation is being physically integrated into battery architecture rather than merely applied to samples removed from it.

Manufacturing, Quality Control, and the Multi-Platform Analytical Approach

A unifying theme across Spectroscopy Online's four years of LIB coverage has been the articulation of integrated, multi-technique analytical frameworks that apply the right spectroscopic tool to each measurement challenge along the manufacturing value chain. The 2024 comprehensive review by Workman, published in the Spectroscopy Supplement, provided the most complete treatment of this multi-platform philosophy, systematically mapping more than a dozen spectroscopic techniques to the specific quality requirements of LIB raw material qualification, electrode coating production, electrolyte manufacturing, cell assembly, formation cycling, and end-of-line testing.³

The review delineated the roles of spectroscopic techniques at each stage as follows. For raw material qualification, ICP-MS and ICP-OES are used to analyze recovered metals (lithium, cobalt, nickel) from spent batteries to evaluate purity and suitability for reuse, while XRF monitors the composition of recycled cathode materials, and Raman spectroscopy verifies phase purity of precursor powders.³ For electrode manufacturing, LIBS and μDOES monitor electrode composition during the manufacturing process to ensure consistent material properties, XRF provides fast non-destructive testing of electrode materials to confirm proper elemental composition, and Raman spectroscopy verifies crystalline structure to confirm no phase transitions have occurred during high-temperature calcination. For electrolyte analysis, FT-IR monitors the composition of binders and electrolyte solvents during manufacturing, UV-vis spectroscopy measures the stability of electrolyte additives during production, and NMR analyzes the mobility of lithium ions within the electrolyte to evaluate ion diffusion performance.

For finished-cell quality assurance, ICP-MS and ICP-OES perform routine quality checks for trace metal impurities in electrode and electrolyte materials, Raman checks for consistent crystallinity and phase purity across production batches, XRF ensures elemental composition is within specification, XPS inspects surface contaminants on electrodes that could negatively affect battery efficiency and longevity, and FTIR and NIR assess the purity of electrolytes and binders to ensure the absence of organic impurities.³

The production of high-performance NMC cathode coatings requires precise control of the nickel-to-manganese-to-cobalt ratio at the micron scale across electrode areas of several square meters per cell. Raman spectroscopy, particularly confocal Raman mapping, can verify crystallinity and phase uniformity across production batches, while LIBS provides inline depth-resolved elemental maps that detect coating thickness variations and substrate contamination events on timescales compatible with roll-to-roll manufacturing.^14,15

Sustainability, Recycling, and the Circular Battery Economy

The rapid growth in LIB deployment has created an urgent need for analytical methods capable of supporting the responsible end-of-life management and recycling of spent cells. Spectroscopy Online has published and reported on research across all analytical dimensions of the battery recycling challenge: characterizing black mass composition to optimize hydrometallurgical recovery processes; certifying the purity of recovered lithium, cobalt, nickel, and manganese for re-entry into cathode precursor manufacturing; and assessing performance recovery achievable through direct cathode regeneration approaches.

A December 2023 article in Spectroscopy Online by Hroncich reported on research by Sim et al., published in Solar Energy Materials and Solar Cells, which described a simplified process for recovering high-purity silicon from expired photovoltaic panels and converting it into high-performance LIB anodes.²⁷ This cross-sectoral material circularity was enabled by rigorous spectroscopic characterization of the recovered silicon's purity and surface chemistry using XPS, Raman, and ICP-OES. The study demonstrated that photovoltaic-grade silicon, once freed of its aluminum contact metallization and surface passivation layers, can be directly incorporated into silicon-graphite composite anodes with capacity retention comparable to commercially sourced silicon feedstock.

The analytical requirements for recycled LIB materials are stringent because trace-level contamination introduced during recycling can compromise the electrochemical performance of regenerated cells. ICP-MS is the preferred technique for certifying that recovered transition metals meet the part-per-billion purity specifications required for battery-grade precursor materials. Raman spectroscopy and XRD are used to verify that resynthesized NMC or LFP active materials have the correct crystalline phase and no residual impurity phases. XPS confirms the absence of surface contaminants that could impede lithium-ion transport at electrode interfaces in regenerated cells. Petzold and Flamme reviewed recycling strategies for spent consumer LIBs and identified analytical characterization as the rate-limiting step in establishing confidence in the quality of secondary battery materials.²⁸

Emerging Technologies: Artificial Intelligence, Machine Learning, and Portable Spectroscopy

The period 2022–2025 witnessed an accelerating integration of artificial intelligence and machine learning with spectroscopic LIB analysis, and Spectroscopy Online has been attentive to these developments. Machine learning algorithms—including Gaussian processes, convolutional neural networks, variational autoencoders, and gradient-boosted ensembles—have been trained on large spectroscopic datasets (EIS spectra, Raman spectra, NIR spectra) to deliver rapid, automated predictions of battery state-of-health, remaining useful life, and degradation mode without requiring expert interpretation of individual spectra.²¹

An October 2024 article in Spectroscopy Online reported on the use of variational autoencoders applied to large EIS datasets to reveal degradation patterns in aging LIBs, demonstrating that unsupervised machine learning can identify degradation modes—SEI growth, lithium plating, active material loss—from impedance spectra without prior labeling of failure modes.²⁹ A 2025 study from Sungkyunkwan University demonstrated that four machine learning algorithms applied to EIS data could predict the state-of-health of lithium metal batteries with errors below 2%, establishing a new benchmark for AI-assisted battery diagnostics.³⁰

The miniaturization and portabilization of spectroscopic instrumentation, including handheld Raman spectrometers, portable XRF analyzers, and compact NIR sensors, has opened new application domains for LIB analysis in the field and at the point of use. Spectroscopy Online has covered the development and validation of portable instruments for battery material identification, state-of-health screening of EV packs in service stations, and rapid sorting of spent cells for recycling based on cathode chemistry identification by handheld Raman. These developments align with the publication's broader coverage of miniaturized spectroscopy for field applications.³

Overview of Spectroscopy Online Coverage, 2022–2025

The articles, reviews, application notes, and research reports constituting Spectroscopy Online's LIB coverage during 2022–2025 can be grouped into five thematic streams, each of which is represented in this special supplement:

1. Technique-focused reviews and tutorials. In-depth treatments of individual spectroscopic methods—Raman, FTIR, ICP-OES, ICP-MS, LIBS, XRF, XPS, EIS, NMR, NIR, UV-vis—describing their physical principles, instrumental requirements, sample preparation protocols, and performance benchmarks for LIB applications.

2. Application notes and case studies. Vendor-contributed and independently authored articles presenting validated analytical methods for specific LIB manufacturing and quality-control tasks, typically including method validation data, uncertainty estimates, and comparison with reference techniques.

3. Research news and translation. Timely reports summarizing peer-reviewed research from leading journals—Journal of Power Sources, Journal of the Electrochemical Society, ACS Energy Letters, Nature Energy, Angewandte Chemie, and others—with editorial commentary on analytical significance and technological implications.

4. Manufacturing and process analytical technology. Articles addressing the integration of spectroscopic methods into LIB manufacturing workflows, including inline and at-line measurement systems, statistical process control, and multi-technique quality management architectures.

5. Sustainability, recycling, and the circular economy. Coverage of spectroscopic methods applied to battery end-of-life assessment, black mass characterization, recycled material certification, and life-cycle analytical strategies.

Together, these five thematic streams constitute a comprehensive record of how spectroscopy has been applied to, and has in turn advanced, LIB science and technology over a pivotal four-year period during which the global battery industry underwent transformative growth. Spectroscopy Online has been uniquely positioned to document this convergence because it bridges the analytical chemistry community, with its expertise in measurement science, instrumentation, and method validation, and the battery technology community, with its demand for reliable, scalable analytical solutions.

Conclusion

The story of LIBs is, at its molecular and atomic core, a spectroscopic story. From the vibrational modes of NMC crystals to the impedance arcs of aging graphite anodes, from the plasma emission of a LIBS laser ablating a moving electrode foil to the chemical shift of a lithium nucleus in a cycling cell, spectroscopic measurement is not merely a diagnostic adjunct to LIB technology—it is the language in which battery chemistry speaks and through which battery engineers listen.

Spectroscopy Online's four years of coverage in this domain have documented an extraordinary convergence: analytical techniques developed over decades for other applications—mineralogy, pharmaceutical quality control, semiconductor manufacturing, petrochemical process control—are being adapted, refined, and, in some cases, fundamentally reimagined to meet the specific and demanding requirements of a battery industry operating at global scale under intense performance and sustainability pressure.

The articles collected in this special supplement represent the state of that convergence as of 2026. They are addressed to every analytical chemist who wants to understand how their expertise can contribute to one of the great technological challenges of the century, and to every battery scientist and engineer who wants to deploy the full power of modern spectroscopy in their work. We are confident that the work reported here will serve as both a resource for current practitioners and a foundation for the analytical innovations that the next decade of battery technology will demand.

References

1. International Energy Agency. Global EV Outlook 2024: Moving Towards Increased Affordability; International Energy Agency: Paris, France, 2024. https://www.iea.org/reports/global-ev-outlook-2024 (accessed 2026-06-03).
2. Tarascon, J.-M.; Armand, M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359–367. https://doi.org/10.1038/35104644.
3. Workman, J., Jr. A Comprehensive Review of Spectroscopic Techniques for Lithium-Ion Battery Analysis. Spectroscopy 2024, 39 (Suppl. 11), 6–16. https://doi.org/10.56530/spectroscopy.ii3689u3.
4. Beccard, B.; Karavadra, S. N.; Dahal, S. Lithium-Ion Battery Manufacturing and Quality Control: Raman Spectroscopy, an Analytical Technique of Choice. Spectroscopy 2022, June 1. https://www.spectroscopyonline.com/view/lithium-ion-battery-manufacturing-and-quality-control-raman-spectroscopy-an-analytical-technique-of-choice (accessed 2026-06-03).
5. Flores, E.; Novák, P.; Berg, E. J. In Situ and Operando Raman Spectroscopy of Layered Transition Metal Oxides for Li-Ion Battery Cathodes. Front. Energy Res. 2018, 6, 82. https://doi.org/10.3389/fenrg.2018.00082.
6. Wieboldt, D.; Hahn, M.; Ruff, I. Techniques for Raman Analysis of Lithium-Ion Batteries. Spectroscopy 2015, 30 (6). https://www.spectroscopyonline.com/view/techniques-raman-analysis-lithium-ion-batteries (accessed 2026-06-03).
7. Adams, R. A.; Li, B.; Kazmi, J.; Adams, T. E.; Tomar, V.; Pol, V. G. Dynamic Impact of LiCoO₂ Electrodes for Li-Ion Battery Aging Evaluation. Electrochim. Acta 2018, 292, 586–593. https://doi.org/10.1016/j.electacta.2018.08.101.
8. Julien, C. M.; Mauger, A. Raman and Infrared Spectroscopy of Materials for Lithium-Ion Batteries. Int. J. Mol. Sci. 2025, 26, 11879. https://doi.org/10.3390/ijms262411879.
9. Mohammad, I.; Cambaz, M. A.; Samoson, A.; Fichtner, M.; Witter, R. Development of In Situ High Resolution NMR: Proof-of-Principle for a New (Spinning) Cylindrical Mini-Pellet Approach Applied to a Lithium-Ion Battery. Solid State Nucl. Magn. Reson. 2024, 129, 101914. https://doi.org/10.1016/j.ssnmr.2023.101914.
10. Agilent Technologies. A Practical Guide to Elemental Analysis of Lithium-Ion Battery Materials Utilizing ICP-OES. Spectroscopy 2023, May 26. https://www.spectroscopyonline.com/view/a-practical-guide-to-elemental-analysis-of-lithium-ion-battery-materials-utilizing-icp-oes (accessed 2026-06-03).
11. McCurdy, E. Benefits of ICP-MS for the Elemental Compositional Analysis of Lithium-Ion Battery Electrolytes. Spectroscopy 2025, 40, (3), 6–9. https://doi.org/10.56530/spectroscopy.eg1583l1.
12. Liu, S., Han, Z., Kong, X., Zhang, J., Lv, Z., & Yuan, G. Organic Matrix Effects in Inductively Coupled Plasma Mass Spectrometry: A Tutorial Review. Appl. Spectrosc. Rev. 2022, 57, 461–489. https://doi.org/10.1080/05704928.2021.1897991.
13. Fernandes, J.; Sorbier, L.; Hermelin, S.; Benoit, J.-M.; Dujardin, C.; Lienemann, C.-P.; Bernard, J.; Motto-Ros, V. Looking Inside Electrodes at the Microscale with LIBS: Li Distribution. Spectrochim. Acta, Part B 2024, 221, 107047. https://doi.org/10.1016/j.sab.2024.107047.
14. Basler, C.; Kappeler, M.; Carl, D. Depth-Resolved Elemental Analysis on Moving Electrode Foils with Laser-Induced Breakdown Spectroscopy. Sensors 2023, 23 (3), 1082. https://doi.org/10.3390/s23031082.
15. Kappeler, M.; Basler, C.; Brandenburg, A.; Carl, D.; Wöllenstein, J. Homogeneity Measurements of Li-Ion Battery Cathodes Using Laser-Induced Breakdown Spectroscopy. Sensors 2022, 22 (2), 8816. https://doi.org/10.3390/s22228816.
16. Wetzel, W. Recent Developments in Laser-Induced Breakdown Spectroscopy. Spectroscopy 2024. May 17. https://www.spectroscopyonline.com/view/recent-developments-in-laser-induced-breakdown-spectroscopy (accessed 2026-06-03).
17. Schulz, N.; Hausbrand, R.; Dimesso, L.; Jaegermann, W. XPS-Surface Analysis of SEI Layers on Li-Ion Cathodes: Part I. Investigation of Initial Surface Chemistry. J. Electrochem. Soc. 2018, 165, A819–A832. https://doi.org/10.1149/2.0061805jes.
18. Zabara, M. A.; Katırcı, G.; Civan, F. E.; Yürüm, A.; Gürsel, S. A.; Ülgüt, B. Insights into Charge Transfer Dynamics of Li Batteries through Temperature-Dependent Electrochemical Impedance Spectroscopy Utilizing Symmetric Cell Configuration. Electrochim. Acta 2024, 485, 144080. https://doi.org/10.1016/j.electacta.2024.144080.
19. Wetzel, W. Evaluating Battery Health for Electric Vehicles Using Electrochemical Impedance Spectroscopy Measurements. Spectroscopy 2024, October 22. https://www.spectroscopyonline.com/view/evaluating-battery-health-for-electric-vehicles-using-electrochemical-impedance-spectroscopy-measurements (accessed 2026-06-03).
20. Wetzel, W. Leveraging Electrochemical Impedance Spectroscopy for Lithium-Ion Battery Temperature Prediction. Spectroscopy 2025, January 17. https://www.spectroscopyonline.com/view/leveraging-electrochemical-impedance-spectroscopy-for-lithium-ion-battery-temperature-prediction (accessed 2026-06-04).
21. Zhang, Y.; Tang, Q.; Zhang, Y.; Wang, J.; Stimming, U.; Lee, A. A. Identifying Degradation Patterns of Lithium-Ion Batteries from Impedance Spectroscopy Using Machine Learning. Nat. Commun. 2020, 11, 1706. https://doi.org/10.1038/s41467-020-15235-7.
22. Wetzel, W. New Model Enhances Lithium-Ion Battery Management Using Real-Time Impedance Analysis. Spectroscopy 2025, September 30. https://www.spectroscopyonline.com/view/new-model-enhances-lithium-ion-battery-management-using-real-time-impedance-analysis (accessed 2026-06-04).
23. Knott, A.; Long, E.; Garner, C.P.; Fly, A.; Reid, B.; Atkins, A. Insights into Lithium-Ion Battery Cell Temperature and State of Charge Using Dynamic Electrochemical Impedance Spectroscopy. Int. J. Energy Res. 2024, 9657360. https://doi.org/10.1155/2024/9657360.
24. Gervillié-Mouravieff, C.; Boussard-Plédel, C.; Huang, J.; et al. Unlocking Cell Chemistry Evolution with Operando Fibre Optic Infrared Spectroscopy in Commercial Na(Li)-Ion Batteries. Nat. Energy 2022, 7, 1157–1169. https://doi.org/10.1038/s41560-022-01141-3.
25. Liu, F.; Lu, W.; Huang, J.; et al. Detangling Electrolyte Chemical Dynamics in Lithium Sulfur Batteries by Operando Monitoring with Optical Resonance Combs. Nat. Commun. 2023, 14, 7350. https://doi.org/10.1038/s41467-023-43110-8.
26. Wang, R.; Zhang, H.; Liu, Q.; et al. Operando Monitoring of Ion Activities in Aqueous Batteries with Plasmonic Fiber-Optic Sensors. Nat. Commun. 2022, 13, 547. https://doi.org/10.1038/s41467-022-28267-y.
27. Sim, Y.; Tay, Y. B.; Lin, X.; Mathews, N. Simplified Silicon Recovery from Photovoltaic Waste Enables High Performance, Sustainable Lithium-Ion Batteries. Sol. Energy Mater. Sol. Cells 2023, 257, 112394. https://doi.org/10.1016/j.solmat.2023.112394.
28. Petzold, M.; Flamme, S. Recycling Strategies for Spent Consumer Lithium-Ion Batteries. Metals 2024, 14, 151. https://doi.org/10.3390/met14020151.
29. Liu, Y.; Li, Q.; Wang, K. Revealing the Degradation Patterns of Lithium-Ion Batteries from Impedance Spectroscopy Using Variational Auto-Encoders. Energy Storage Mater. 2024, 69, 103394. https://doi.org/10.1016/j.ensm.2024.103394.
30. Yoon, J.; Chae, S.; Jeong, C.; Lee, M.; Jang, S.; Woo, K.; Cho, H.; Yang, W. Machine Learning-Assisted Prediction of State of Health in Lithium Metal Batteries with Electrochemical Impedance Spectroscopy. Small Sci. 2025, 5, 2500277. https://doi.org/10.1002/smsc.202500277.