Vacuum degassing chamber for lithium-ion battery electrolyte: removing gas from the liquid without boiling off its solvents
Battery electrolyte, before it reaches the cell · vacuum level against solvent vapour pressure, staged pump-down, bubbles in the dosing volume
Electrolyte for lithium-ion cells is a lithium salt dissolved in organic carbonates, and it picks up gas while it is mixed, pumped and stored. A vacuum degassing chamber is the sealed reservoir in which that liquid is held under reduced pressure so gas comes out before the electrolyte is dosed into a cell. The difficulty is that the low-boiling carbonates in the blend start to boil at pressures not far below the level needed for degassing, so the chamber is defined as much by how precisely it holds its vacuum as by how deep that vacuum is.
Sealed vacuum reservoirs and chambers that degas liquid organic electrolyte for lithium-ion cells before filling: vacuum level relative to solvent vapour pressure, pressure difference to the cell, staged pump-down, and protection of valves and pumps from solvent vapour. Electrolyte filling machines, dosing pumps and wetting stations are covered on the Electrolyte filling systems page; general-purpose process and test vacuum chambers on the Vacuum chamber page; rotary degassing of molten aluminium on the Degassing chamber for molten aluminium page. Removal of formation gas from pouch cells, planetary vacuum mixers and drilling-mud degassers are outside this page.
CNFX editorial research · Sources checked October 12, 2026 · 5 sources
Solvent vapour pressure sets how far the electrolyte can be pumped down
Lowering the pressure pulls gas out of the liquid, but it also pulls solvent. The linear carbonates used in electrolyte blends differ by more than three orders of magnitude in vapour pressure from the cyclic ethylene carbonate, so the safe vacuum level depends on which solvents are in the blend.
Matsushita's filling patent states the risk directly: if the reduced pressure is not set correctly, the organic electrolyte, which it calls one of the expensive battery materials, boils, and the exhausted low-boiling components are corrosive to the solenoid valves and vacuum pump in the vacuum line and leave an electrolyte whose composition differs from the original. Its method therefore keeps the vacuum within a range below the boiling point of the electrolyte. [1]
Editorial calculation, taking atmospheric pressure as 101.3 kPa: a gauge reading of −95 kPa is about 6.3 kPa absolute and −90 kPa about 11.3 kPa absolute. Pure DMC at 25 °C has a vapour pressure of 7.4 kPa, between those two figures, while EC's 9.8 × 10⁻³ mmHg is about 0.0013 kPa. A blend's vapour pressure depends on its composition and temperature, so the absolute pressure at which a given electrolyte starts to boil has to come from the electrolyte supplier, not from a gauge setting copied from another line. [1][3][5]
Give the chamber supplier the solvent blend and salt, the electrolyte temperature in the chamber, and the absolute pressure at which that blend boils, and ask how the chamber measures and holds absolute pressure.
02
Reservoir at −90 kPa, cell at −95 kPa: staged pump-down and the pressure difference
In Matsushita's patent the electrolyte waits in a temporary storage chamber above the filling hopper. The storage chamber is pumped to −90 kPa and the battery case to −95 kPa, so the electrolyte is degassed in the reservoir and then driven into the case by a 5 kPa pressure difference when the hopper opens. [1]
The patent cites earlier injection devices in which the electrolyte was degassed by depressurising the storage part and the battery case was then pumped to a higher vacuum than the storage part. Against conventional methods that pump the case and the hopper to the same pressure, the patent states that the pressure difference shortens injection time, improving productivity to about 1.5 to 2 times, and improves injection accuracy by 10 to 20%. It also explains why gas left in the liquid causes trouble later: bubbles trapped between electrode plates expand when pressure returns to atmosphere and can throw electrolyte out of the case. [1]
Nagano Automation's patent on an electrolyte supply apparatus adds the dosing side. Gas that separates from the electrolyte inside the measuring space is compressible, so it degrades metering precision, and if it expands under reduced pressure it scatters electrolyte from the discharge nozzle inside the reduced-pressure chamber. Its dispenser feeds electrolyte into the measuring space from below and discharges the liquid layer closest to gas-liquid separation first, before bubbles can form. [2]
Setting in the patent
Value
Purpose stated
Battery case vacuum
−70 to −95 kPa claimed; −95 kPa in the embodiment [1]
Shorten electrolyte absorption time while staying below the boiling point; chosen to suit electrolyte viscosity [1]
Ask for the chamber's vacuum set points and tolerance, how many pump stages it uses, whether reservoir and cell pressures are controlled independently, and how solvent vapour is kept out of valves and pumps.
03
Describe the electrolyte and the vacuum it must hold
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Electrolyte: [salt and concentration; solvent blend; viscosity]
Temperature: [in the chamber; at filling]
Vacuum: [set point in absolute kPa; tolerance; boiling-point limit from electrolyte supplier]
Pressure difference: [reservoir to cell, kPa]
Volume: [chamber volume L; dose per cell mL; cycle time]
Materials: [wetted materials; seals compatible with the electrolyte]
Vacuum line: [pump type and stages; solvent trap; valve materials]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Why not pull the deepest possible vacuum on battery electrolyte?
Low-boiling solvents start to boil: PubChem lists dimethyl carbonate at 7.4 kPa vapour pressure at 25 °C, and Matsushita's patent warns that boiling loses expensive electrolyte, changes its composition and sends corrosive vapour into valves and pumps. [3][1]
What vacuum levels does a published electrolyte degassing reservoir use?
In Matsushita's patent the electrolyte reservoir is held at −90 kPa and the battery case at −95 kPa, a 5 kPa difference that drives the electrolyte into the case. [1]
Why do bubbles in the electrolyte matter at filling?
Nagano Automation's patent notes that gas in the measuring space is compressible and spoils metering precision, and expanding gas can scatter electrolyte from the nozzle under vacuum. [2]
Which electrolyte solvent is least affected by vacuum?
Ethylene carbonate: PubChem lists 9.8 × 10⁻³ mmHg at 25 °C, against 10.8 mmHg for diethyl carbonate and 55.36 mmHg for dimethyl carbonate. [5][4][3]
Sources and what still needs a direct check
Sources checked 2026-10-12. Matsushita's and Nagano Automation's patents describe electrolyte reservoirs and dispensers on lithium-ion filling lines; PubChem, run by the US National Library of Medicine, supplies the vapour pressures and boiling points of the carbonate solvents.
