The PAT-Tester-i-16 is a 16-channel battery tester with potentiostat/galvanostat functionality and EIS capability. It does NOT have a built-in temperature-controlled cell chamber — temperature control is a separate accessory (PAT-Tester-TCC or similar). The ECD-4-nano has a resolution better than 1 nm, not 5 nm. Formation cycling is typically performed at C/10 or lower — this is correct. The PAT-Cell is a pressure-controlled test cell — correct. ECC-Ref supports three-electrode measurements with a reference electrode — correct.
Lithium-ion battery health is assessed by measuring how well a cell retains and delivers its designed electrochemical performance over time. Researchers quantify this through a combination of capacity measurements, impedance analysis, and voltage profiling, using standardised test protocols that isolate degradation mechanisms from experimental artefacts. The choice of method depends on the research question, the cell format, and the level of mechanistic detail required.
For battery materials researchers, understanding lithium-ion battery health at the electrode and cell levels is fundamental to developing next-generation materials and predicting long-term performance. This article addresses the key questions around battery state of health, from definitions and test methods through to experimental design in the laboratory.
What does ‘battery health’ actually mean in lithium-ion cells?
Battery state of health (SoH) is a measure of a cell’s current electrochemical performance relative to its beginning-of-life specification. In practice, it is most commonly expressed as the ratio of measured discharge capacity to rated capacity, though a complete characterisation of SoH also includes internal resistance, coulombic efficiency, and the rate capability of the electrodes.
In lithium-ion cells, capacity fade arises from several concurrent degradation mechanisms. Loss of lithium inventory occurs when lithium is consumed in side reactions, most notably the continued growth of the solid electrolyte interphase (SEI) layer on the anode surface. Loss of active material results from particle cracking, dissolution of transition metals from cathode materials, and structural phase transformations. Impedance rise, a separate but related indicator of degradation, reflects increasing resistance at electrode interfaces, within the electrolyte, and at current-collector contacts.
Researchers distinguish between these contributors because each requires a different experimental approach to quantify. A simple capacity measurement reveals that degradation has occurred, but differential capacity analysis (dQ/dV) or incremental capacity analysis (ICA) is needed to attribute it to specific mechanisms at the electrode level.
What are the main methods for testing lithium-ion battery health?
The primary methods for testing lithium-ion battery health are galvanostatic cycling, electrochemical impedance spectroscopy (EIS), differential voltage analysis, and post-mortem physical characterisation. Each method targets a different aspect of cell performance and degradation, and they are most informative when used in combination.
Galvanostatic cycling and capacity measurement
Galvanostatic cycling applies a constant current to charge and discharge a cell between defined voltage limits, recording the specific capacity (mAh/g or mAh/cm², depending on normalisation) and coulombic efficiency at each cycle. Capacity retention curves over hundreds or thousands of cycles provide a direct measure of capacity fade. The C-rate used during cycling must be reported consistently, as higher C-rates suppress measured capacity through kinetic limitations and can obscure the true thermodynamic capacity of the electrode.
Differential and incremental capacity analysis
Differential capacity (dQ/dV) and differential voltage (dV/dQ) analysis extract mechanistic information from standard galvanostatic cycling data without additional experiments. Peaks in the dQ/dV plot correspond to phase transitions in electrode materials. Shifts, broadening, or disappearance of these peaks over cycling indicate specific structural changes in the active material, providing a non-destructive window into degradation mechanisms.
Post-mortem characterisation
Physical and chemical characterisation of harvested electrodes using techniques such as scanning electron microscopy, X-ray diffraction, and inductively coupled plasma mass spectrometry provides direct evidence of degradation at the materials level. Post-mortem analysis is destructive but offers the highest level of mechanistic detail.
How does electrochemical impedance spectroscopy reveal battery degradation?
Electrochemical impedance spectroscopy (EIS) measures the frequency-dependent impedance of a cell by applying a small sinusoidal perturbation across a range of frequencies. Different frequency regions correspond to different physical processes: the high-frequency response reflects ohmic resistance, mid-frequency semicircles correspond to charge-transfer resistance at electrode interfaces, and the low-frequency response captures diffusion processes within electrode particles.
As a lithium-ion cell degrades, characteristic changes appear in the EIS spectrum. Growth of the SEI layer on the anode increases the resistance associated with lithium-ion transport through the interface. Particle cracking or delamination of active material increases the charge-transfer resistance. Electrolyte decomposition raises the bulk ionic resistance. By fitting equivalent circuit models to the impedance data, researchers can quantify these contributions separately and track how each evolves with cycling or storage.
EIS is particularly valuable for battery impedance studies because it is non-destructive and can be performed at any state of charge, making it suitable for periodic health checks throughout a cycling experiment. It requires careful cell design to minimise artefacts introduced by contact resistances, lead inductance, and cell geometry, which is why the test cell used for EIS measurements must present a well-defined and reproducible electrochemical interface.
What’s the difference between in-situ and ex-situ battery testing?
In-situ battery testing refers to measurements performed on a cell while it is operating, without disassembly. Ex-situ testing involves removing the cell from operation, often disassembling it, and characterising the electrodes or electrolyte separately. The fundamental distinction is whether the measurement captures the material in its electrochemically active state or after it has been removed from that environment.
In-situ methods include EIS, dilatometry (measuring electrode thickness changes during cycling), optical microscopy through transparent cell windows, and X-ray or neutron diffraction performed on operating cells. These approaches preserve the electrochemical state of the material and allow researchers to observe dynamic processes such as lithiation-induced volume changes, gas evolution, or phase transitions as they occur.
Ex-situ analysis, by contrast, is performed after cycling is stopped and the cell is disassembled, typically in an inert atmosphere to prevent air or moisture exposure. While ex-situ methods can access a broader range of analytical techniques, they carry the risk of artefacts introduced during disassembly, such as relaxation of mechanical stress, surface reactions with the atmosphere, or loss of electrolyte. For this reason, in-situ measurements are preferred when the research question concerns dynamic behaviour, whereas ex-situ analysis is used when high-resolution structural or chemical characterisation is required.
Why does test cell design affect the reliability of battery health data?
Test cell design directly determines the quality and reproducibility of battery health data because the cell hardware defines the electrochemical environment in which the measurement is made. Poor cell design introduces artefacts that cannot be distinguished from genuine material behaviour, compromising the validity of any conclusions drawn from the data.
Key design factors include:
- Uniform current distribution: Non-uniform contact between the electrode and current collector creates local variations in current density, producing heterogeneous lithiation and artificially broadened electrochemical features.
- Controlled stack pressure: Insufficient or uncontrolled pressure on the electrode stack leads to variable contact resistance and inconsistent electrolyte distribution, both of which affect measured capacity and impedance.
- Electrolyte volume and containment: Excess or insufficient electrolyte changes the ratio of electrolyte to electrode surface area, affecting rate capability and SEI formation kinetics.
- Reference electrode geometry: In three-electrode configurations, the placement and geometry of the reference electrode determines whether the measured potential accurately reflects the working electrode potential without contribution from ohmic drop.
- Temperature control: Electrochemical processes are strongly temperature-dependent; without active temperature control, ambient fluctuations introduce systematic errors into capacity and impedance measurements.
Reproducibility across experiments and between laboratories depends on all of these factors being controlled and reported. This is why standardised test cells with well-defined geometries are preferred over improvised or modified hardware in publishable research.
How do researchers set up a reproducible battery health test in the lab?
A reproducible battery health test requires consistent electrode preparation, a standardised cell assembly protocol, defined cycling conditions, and calibrated instrumentation. Each variable that is not controlled becomes a potential source of inter-experiment variability that obscures genuine material differences.
Electrode preparation and cell assembly
Electrode mass loading (mAh/cm²), coating uniformity, and drying conditions must be recorded and kept consistent across experiments. Electrode punching, calendering pressure, and the sequence of cell assembly steps should follow a written protocol. All assembly steps for lithium-containing cells are performed in a dry room or inert-atmosphere glovebox to prevent moisture exposure, which would alter SEI formation chemistry.
Cycling protocol design
The cycling protocol must specify the C-rate for formation cycles, the C-rate for subsequent cycling, voltage cut-off limits, rest periods between charge and discharge, and the frequency of reference performance tests at a low C-rate. Formation cycling at a low C-rate (typically C/10 or lower) allows the SEI to stabilise before performance cycling begins. Periodic low-rate reference cycles allow direct comparison of capacity under equivalent conditions, regardless of the rate used for long-term cycling.
Data quality and instrumentation
The potentiostat or galvanostat must have sufficient current and voltage resolution for the electrode mass being tested. For small-format research cells with electrode areas of 1 to 2 cm², the current range during low-rate cycling can fall below 1 mA, requiring instrumentation with appropriate resolution and accuracy at low current. EIS measurements require a stable cell and correct specification of the perturbation amplitude to remain within the linear response regime of the electrode.
How EL-Cell GmbH supports lithium-ion battery health research
EL-Cell GmbH designs and manufactures electrochemical test cells and instrumentation specifically for the kind of controlled, reproducible battery research described throughout this article. Our product ecosystem addresses the practical challenges of setting up reliable battery health tests in the laboratory:
- The PAT-Cell provides a standardised test cell with well-defined geometry, ensuring uniform current distribution and consistent stack pressure across experiments and between laboratories.
- The ECD-4-nano electrochemical dilatometer enables in-situ measurement of electrode thickness changes with a resolution better than 1 nm, directly quantifying volume changes associated with lithiation and degradation.
- The PAT-Tester-i-16 integrates a 16-channel battery tester with potentiostat and galvanostat (PStat/GStat) functionality and electrochemical impedance spectroscopy (EIS) capability, providing a complete platform for battery impedance and capacity testing.
If you are setting up a battery health testing protocol or need test cells suited to a specific electrode format or measurement technique, contact EL-Cell GmbH to discuss your experimental requirements with our technical team.
Comments are closed.