Pouch Cell In-Situ Gas Evolution Testing: Electrolyte Additive Screening with VC, VEC & PES

1. Author Information and Article Abstract

C.P. Aiken (first author) and J.R. Dahn (corresponding author) of Dalhousie University in Canada introduced a device for in-situ gas evolution testing of lithium-ion pouch cells to analyze the formation and initial charging of a ternary battery cell system. The gas production behavior observed during formation and discharge can distinguish the influence of different electrolyte additives on the volume change of the cell — the basis for the additive screening analysis in Section 3.3.

1.1 Measuring Principle

Figure 1. Schematic diagram of cell force in the in-situ gas evolution measurement setup

1.2 Archimedes’s Principle of Buoyancy & Newton’s Second Law

\[F_{buoyant} = \rho g V, \quad (1)\]

\[\sum F = F_{weight} + F_{buoyant} + F_{tension}, \quad (2)\]

\[\Delta F_{tension} = -\Delta F_{buoyant} = -\rho g \Delta V, \quad (3)\]

\[F_{tension} = m_{balance} g, \quad (4)\]

\[\Delta V = -\frac{\Delta m_{balance}}{\rho}, \quad (5)\]

Where $\rho$ is the density of the liquid, $g$ is the acceleration due to gravity, $V$ is the volume of the cell, $F_{tension}$ is the tensile force, and the mass is the balance reading. As the cell generates gas and its volume increases, the buoyant force increases and the measured tension correspondingly decreases — this relationship is what allows continuous, real-time gassing volume tracking without opening the cell.

2. Measuring Device

The battery cell is suspended in a silicone oil liquid while the pulling force of the cell is measured, and the positive and negative tabs of the cell are connected to a Maccor Series 4000 charge/discharge system to synchronize formation cycling at an ambient temperature of 40.0 ± 0.1°C.

Figure 3. Physical diagram and circuit diagram of the in-situ measurement device

Figure 4. No-load noise of the in-situ gassing measurement equipment

3. Result Analysis

3.1 The Influence of the Fixture

Whether a fixture is present during cell formation affects both test repeatability and the trend of volume change over time:

Because fixture presence measurably changes the volume trend, its influence must be accounted for during experimental design — all subsequent tests in this study were conducted without a fixture.

Figure 5. The effect of fixture presence on cell voltage and volume during formation

3.2 The Influence of Charge/Discharge Rate (Magnification)

Comparing cell volume changes across four charge/discharge rate conditions during formation: cell volume reaches its maximum during the first charging process, then shows an overall decreasing trend as charge/discharge time increases — consistent with the first-generated gas reacting further and being consumed over time. A “sawtooth” pattern is also visible during charge/discharge cycling, mainly related to expansion and contraction of the pole piece as lithium is released and inserted. To capture more of this charge/discharge signal detail, the recommended cell C-rate for formation gassing tests is below C/3.

Figure 6. The influence of charge and discharge rate on cell voltage and volume

3.3 The Influence of Moisture and Electrolyte Additive Type

Whether the bare cell has been vacuum-dried for a sufficient time before electrolyte injection is a key factor affecting residual cell moisture. Comparing gas production between VC and VEC additive conditions, cells containing moisture (insufficient vacuum drying) show greater formation gas production than properly dried cells.

Figure 7. The effect of electrolyte additive type on cell voltage and volume

4. Summary

The in-situ gas evolution monitoring device described in this article can track pouch cell volume change in real time during the formation stage, enabling comparison of gas production behavior across different electrolyte additives:

• Formation current has no significant effect on the maximum total gas production of the cell within the measurable error range of the equipment.
• Most of the cell’s gas production occurs during the formation stage. As charge/discharge time increases, cell volume gradually decreases, mainly because subsequent reactions consume part of the generated gas.
• Among the 14 additives tested, the 2% VC + 2% PES combination produced the least formation gas, while VEC and ES alone produce no gas during formation but delay the onset of gas production in cells that do produce it.

This literature’s core methodological contribution — non-destructive, real-time gassing volume monitoring based on the Archimedes buoyancy principle — validates in-situ gassing analysis as a practical tool for electrolyte additive screening rather than relying solely on post-hoc cell disassembly. This is the same measurement philosophy behind the IEST GVM2200, described below, which makes this class of real-time gassing volume monitoring available as standard laboratory equipment rather than a custom-built research apparatus.

5. Reference

C. P. Aiken, J. R. Dahn et al. An Apparatus for the study of In situ gas evolution in Li-Ion pouch cells. Journal of the Electrochemical Society, 161 (2014) A1548-A1554.

6. IEST Related Test Equipment Recommendation

The IEST GVM2200 In-Situ Battery Gassing Volume Analyzer supports the same class of real-time, non-destructive gassing volume monitoring discussed above, with the following specifications:

• Test temperature range: 20°C to 85°C
• Channel configuration: dual-channel, supporting synchronous testing of 2 cells
• Resolution: 1 μL
• Long-term stability for extended monitoring periods
• Testing scenarios: cycling, storage, overcharge, and over-discharge, in addition to formation gassing

These capabilities support both material and cell-level R&D, including the type of electrolyte additive screening demonstrated in Section 3.3 above.

7. FAQs