Chemistry Analysis

There are a broad range of techniques in the area of battery chemistry analysis, spanning the full lifecycle from raw material qualification through to cell production, benchmarking, ageing investigation, failure mode analysis, and pack material compatibility. This document lists the primary testing categories and techniques.

Raw Materials

Raw material quality directly impacts cell performance and consistency. Key analytical techniques include:

  • Elemental Analysis of Lithium
    • Method: Inductively Coupled Plasma (ICP) techniques — ICP-OES and ICP-MS
    • Application: Quantification of trace-level impurities in lithium brines and refined lithium salts
    • Performance benchmark: Measurement accuracy within 90–110% for brines containing 0.5 mg·L⁻¹ of trace analytes and 3,000 mg·L⁻¹ Li
    • Relevance: Impurity control in precursor materials (Li₂CO₃, LiOH) critical for cathode yield and cycle life
elemental analysis

Elemental Analysis of Lithium – the analysis demonstrated that for all analytes the measurement accuracy was in the range of 90% to 110% for brines containing 0.5 mg·L-1 of the trace level analytes and 3,000 mg·L-1 of Li.

  • Cathode Precursor Purity Analysis
    • Method: ICP-MS, XRF (X-Ray Fluorescence)
    • Application: Verification of Ni, Mn, Co, Al ratios in NMC/NCA/LFP precursors
  • Anode Material Characterisation
    • Method: Laser diffraction particle size analysis, BET surface area measurement
    • Application: Graphite, silicon, and hard carbon particle size distribution and surface area
  • Electrolyte Solvent and Salt Purity
    • Method: Karl Fischer titration (moisture), IC (ion chromatography), NMR
    • Application: Water content and ionic impurity screening in LiPF₆ salts and carbonate solvents

Elemental analysis such as ICP-OES/ICP-MS is also how the material-composition obligations of the EU Battery Regulation get verified in practice — recycled-content declarations for cobalt, lithium, nickel and lead, and the restricted-substance limits it sets, both rely on the same techniques used here for raw-material characterisation.

Battery Cell Research

Open Circuit Voltage (OCV) & Diffusion Coefficient

Accurate OCV and diffusion coefficient data are foundational inputs for electrochemical models. The two primary approaches are:

  • Galvanostatic Intermittent Titration Technique (GITT)
    • Principle: Applies short current pulses followed by extended rest periods; relaxation voltage used to extract OCV and solid-state diffusion coefficient (D_Li)
    • Limitation: Experimental duration of multiple days; impractical for routine screening
    • Output: Full OCV–SOC curve, diffusion coefficient vs. stoichiometry
  • Intermittent Current Interruption (ICI)
    • Principle: Fast alternative to GITT; current is interrupted at intervals and rest durations varied to balance accuracy vs. test time
    • Advantage: Significantly reduced test duration while retaining acceptable accuracy for modelling purposes

The established methodology for Open Circuit Voltage measurement is the Galvanostatic Intermittent Titration Technique (GITT). However, its significant limitation is the large experimental duration, requiring multiple days.

To simulate a battery, the open circuit voltage (OCV) and diffusion coefficient of its active materials must be determined.

Here, Intermittent Current Interruption (ICI) was used as a fast alternative. The rest durations were varied to optimise between accuracy and test duration

Laboratory Preparation & Handling Techniques

  • Solid-State Battery Testing Mould Preparation & Cleaning
    • Criticality: Moulds for solid-state cell assembly are extremely sensitive to residual powder, water stains, and surface scratches
    • Effect of contamination: Poor electrode contact, inadequate densification, and compromised experimental results
    • Procedure: Controlled cleaning protocols in dry-room or glovebox environments; surface inspection under magnification prior to use
solid state mould cleaning
Solid State Battery Testing Mould Cleaning

Solid-state battery moulds are extremely sensitive to leftover powder, water stains, or surface scratches. Any of these can lead to poor electrode contact, low densification, and ultimately, wasted experiments…

  • Electrode Slurry Characterisation
    • Method: Rheometry, solid content measurement, particle size distribution
    • Application: Coating quality control and mixing process validation
  • Coin Cell and Pouch Cell Assembly (Half-Cell / Full-Cell)
    • Application: Baseline electrochemical characterisation of new active materials in controlled laboratory format
In Production Testing

Changes in chemistry formulation, electrode coating, and formation protocols require ongoing in-line and at-line analytical capability. Key production testing techniques include:

Gas Chromatography–Mass Spectrometry (GC-MS)

  • Single-Quadrupole GC-MS
    • Application: Electrolyte composition analysis — identification and quantification of solvents (EC, DMC, EMC, etc.), functional additives, and degradation products
    • Capability: Reliable analysis of major components, minor additives, and trace impurity/degradation species
    • Use case: Formation gas analysis, electrolyte QC, post-cycle electrolyte sampling
    • Output data: Component retention times, fragmentation patterns, concentration vs. standard calibration
  • Headspace GC-MS
    • Application: Volatile organic compound (VOC) and gas evolution monitoring during formation and cycling

Single quadrupole Gas Chromatography-Mass Spectroscopy instruments can reliably analyse the electrolyte composition and provide information on major components, additives and degradation products.

How Can GC-MS Provide the Data Needed to Improve Lithium-ion Battery Performance?

Electrode Coating Quality

  • X-Ray Fluorescence (XRF)
    • Application: Coating weight and elemental distribution mapping across electrode sheets
  • Scanning Electron Microscopy (SEM)
    • Application: Surface morphology of coated electrodes; porosity and cracking assessment
  • Energy-Dispersive X-Ray Spectroscopy (EDS/EDX)
    • Application: Elemental mapping of electrode cross-sections; binder and conductive additive distribution

Electrolyte Fill & Wetting

  • Karl Fischer Titration
    • Application: Moisture content verification in electrolyte prior to fill and in dry-room atmosphere
  • Neutron Imaging / X-Ray Tomography
    • Application: Non-destructive assessment of electrolyte distribution and wetting completeness inside sealed cells
Cell Benchmarking Chemistry Analysis

Techniques used to analyse the chemical composition of benchmarked cells — enabling inference of cost, environmental impact, and electrochemical performance characteristics.

Destructive Chemical Analysis

  • ICP-OES / ICP-MS (Cathode Composition)
    • Application: Determination of Ni/Mn/Co/Li ratios in harvested cathode material; identification of chemistry type (NMC811, LFP, NCMA, etc.)
  • X-Ray Diffraction (XRD)
    • Application: Crystal structure identification of cathode and anode active materials; phase purity assessment
    • Relevance: Distinguishes between LFP, NMC, LMO, and other crystal phases
  • Thermal Gravimetric Analysis (TGA)
    • Application: Binder content quantification; active material loading per electrode
  • BET Surface Area & Pore Size Analysis
    • Application: Active material surface area, correlating with rate capability and electrolyte accessibility

Non-Destructive / Imaging Methods

  • X-Ray Computed Tomography (X-Ray CT)
    • Application: Internal structure imaging — electrode alignment, separator integrity, electrolyte distribution, winding defects
  • Neutron Diffraction
    • Application: Lithium distribution mapping within electrodes during cycling (lithium is low contrast for X-ray but detectable by neutron)
Ageing Analysis

Calendar and cycle ageing investigation benefits significantly from analytical characterisation of chemistry and cell structure to identify degradation mechanisms.

Electrochemical Techniques

  • Electrochemical Impedance Spectroscopy (EIS)
    • Application: Quantification of SEI growth, charge-transfer resistance increase, and electrolyte resistance evolution with ageing
    • Output: Nyquist plots; equivalent circuit model fitting for component isolation
  • Incremental Capacity Analysis (ICA) / Differential Voltage Analysis (DVA)
    • Application: Identifying loss of lithium inventory (LLI) and loss of active material (LAM) from charge/discharge curves without disassembly
    • Advantage: Non-destructive; trackable through cell life

Post-Mortem Chemical Analysis

  • SEM / TEM (Transmission Electron Microscopy)
    • Application: Cathode particle cracking, SEI layer morphology, lithium plating on anode
  • XRD on Aged Electrodes
    • Application: Phase transitions, structural disordering, and capacity fade attribution in cathode materials
  • XPS (X-Ray Photoelectron Spectroscopy)
    • Application: Surface chemistry of SEI and CEI (cathode electrolyte interphase) layers; oxidation state mapping
  • TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry)
    • Application: Depth profiling of SEI composition; lithium distribution in near-surface electrode regions
Failure Mode Analysis

When a cell fails, understanding the root cause at an atomic or molecular level is often essential to implement an effective engineering remedy. Key techniques include:

  • SEM / FIB-SEM (Focused Ion Beam SEM)
    • Application: Cross-section preparation and imaging of internal failure sites; dendrite, crack, and delamination analysis
  • EDS / EDX Elemental Mapping
    • Application: Localised compositional analysis at failure sites; contamination identification
  • XRD and XPS
    • Application: Phase identification and surface chemistry at failure locations
  • Gas Analysis (Thermal Runaway Gases)
    • Method: GC-MS, FTIR (Fourier Transform Infrared Spectroscopy)
    • Application: Identification of gas species evolved during venting, thermal runaway, or overcharge events (H₂, CO, CO₂, HF, etc.)
  • Thermal Runaway Product Analysis
    • Application: Characterisation of solid and gaseous decomposition products to understand runaway propagation mechanisms
  • Lithium Plating Detection
    • Method: Optical inspection, SEM, EDS
    • Application: Anode surface inspection for metallic lithium deposition; failure mode in fast-charge or low-temperature scenarios
  • Electrolyte Post-Mortem Analysis (GC-MS, NMR)
    • Application: Identification of electrolyte decomposition products and additive depletion at end of life
Battery Pack Materials Analysis

Battery packs incorporate a wide range of materials — structural, thermal, electrical, and sealing — each requiring characterisation for compatibility with the pack environment and intended operational life.

Chemical Compatibility Testing

  • Electrolyte Compatibility / Immersion Testing
    • Application: Assessment of polymer, elastomer, and adhesive materials exposed to electrolyte solvents and vapours
  • Outgassing Analysis (FTIR / GC-MS)
    • Application: Identification of volatile compounds released by thermal interface materials, foams, and adhesives at operating temperatures

Thermal Interface Materials (TIMs)

  • Thermal Conductivity Measurement (Laser Flash / Hot Disk)
    • Application: Verification of TIM thermal performance and ageing stability
  • Rheology and Viscosity
    • Application: Dispensing process qualification for gap-fill TIMs and potting compounds

Structural and Sealing Materials

  • DSC (Differential Scanning Calorimetry)
    • Application: Melting point, glass transition temperature (Tg), cure characterisation of adhesives and sealants
  • Mechanical Property Testing (Tensile, Compression, Creep)
  • Application: Structural polymer and foam components — load bearing, vibration damping, and crush zone performance
  • Corrosion Analysis
    • Method: Salt spray, electrochemical corrosion, SEM/EDS on corroded surfaces
    • Application: Cooling plate materials, busbars, and housing metals in humid/corrosive environments

See also: Cell Measurement Techniques, Making energy greener – what role does elemental analysis play?