How to monitor ultra-low humidity environments for safety and yield
Lithium is a fascinating alkali metal. It is found widely in the earth’s crust, where it normally occurs at low levels of dispersion in pegmatitic (coarse crystalline igneous materials) minerals, granite and in clay deposits and aqueous sources. This can make it difficult to mine or extract. Yet, once this soft silver-colored metal has been processed and converted to different compounds, it offers a range of unique properties. As lithium stearate, it is used as a thickener in industrial greases; as lithium oxide, it is used in the manufacture of pottery glazes; and, in the form of lithium salts, it is used as an additive in anti-depressant medicines.
Lithium is probably best known for its use in lithium ion (Li-ion) batteries, where its low atomic mass, high electrical potential, and excellent charge – and power-to-weight ratio – offer considerable advantages over other battery technologies. As a result, Li-Ion batteries are now widely used in mobile phones, laptops and electric vehicles.
Moisture and lithium don’t mix!
One of the properties of lithium is that it is potentially explosive if it comes into contact with water. The subsequent reaction is exothermic and releases lithium hydroxide, which is soluble, and hydrogen, which is given off as a gas and is extremely flammable. This can be a potential challenge for the manufacturers of batteries and, depending on the scale of production, requires the use of sealed environmental chambers, glove boxes or large anhydrous or dry rooms.
If moisture, even in low concentrations, is present during battery manufacture, there is the risk of corrosion forming on metal surfaces, including battery components and production equipment. Humidity can also affect the chemical and physical properties of electrolytes and separators, causing defects in the finished products.
Creating a suitable manufacturing facility with anhydrous rooms requires meticulous attention to detail to ensure that ultra-low levels of humidity are achieved and then safely maintained. Typically, this will require a relative humidity below 1 %, or a dew point of at least -40 °C or lower, which is the equivalent of just 0.15 g of moisture in each kilo of dry air.
If the production operation is fully automated, then establishing this type of environment can be achieved relatively easily. However, things become far more complex if there is the need for laboratory, production or maintenance staff to enter the area, or if there are multiple access points for conveyors or other equipment, or leaks occur in fluid handling systems.
Anhydrous battery production rooms will be fitted with dehumidifiers and dryers to create a steady and positive flow of dry air. Equally important are the use of reliable dew-point measurement instruments, to provide continuous monitoring of environmental conditions to ensure optimal levels of safety and improve product yield. Note that dew point is the preferred method of measuring the concentration of water vapor, as relative humidity analyzers are not sufficiently sensitive to detect extremely small changes in environmental conditions, which can have a disproportionate impact on production quality.
Typically, dew-point sensors will be installed at key stages of the production operation. These include monitoring the performance of dryers, where sensors are normally fitted in the outlet of PSA towers or membrane cartridges, as well as gas supply lines, work areas and ventilation and exhaust ducts.
Detecting and measuring extremely low levels of humidity
Two of the most effective technologies for measuring ultra-low levels of humidity are chilled mirror analyzers and transmitters using either thick-film or ceramic metal-oxide sensors.
Chilled mirror analyzers represent the gold standard. For example, our S8000 Precision Chilled Mirror Hygrometer can measure dew point to -60 °Cdp, while the S8000 RS version can be used in applications down to -90 °Cdp; both instruments have an accuracy of within ±0.1 °Cdp, repeatability within 0.05 °C, zero drift and advanced communication options for integration with plant-wide analysis and control systems.
For less demanding applications, or where budgets are limited, robust and reliable thick-film dew-point hygrometers, such as our quick-install SF82, or our Easidew ceramic metal-oxide transmitter, can offer cost-effective options. These are ideal for use in dryers, production areas, environmental chambers and ventilation systems, where they offer a combination of fast response, accuracy and repeatability with a wide range of options.
Throughout, we provide comprehensive technical and application support, plus sensor calibration, repair and exchange services.
With over 40 years’ experience in the development of innovative precision instruments, we are the application experts in dew point and moisture measurements for all battery manufacturing applications. If you would like to discuss your requirements, please contact our team today.
Lithium has just three protons in its nucleus and a very loosely held outer electron. This makes it relatively unstable and easy to ionize. But how is it formed?
According to a recent study from NASA (North American Space Agency), much of the element was formed right at the beginning of our universe, during what has become known as the ‘Big Bang’. From a sea of protons and neutrons, the elements hydrogen, helium and a miniscule amount of beryllium-7 initially formed. The beryllium-7 had a short half-life and swiftly decayed; in so doing, it captured an extra electron to form stable lithium-7.
Lithium is also formed by collisions between high-energy cosmic rays colliding with atoms of heavy elements, which shatter to form lithium, along with other lighter elements.
The NASA study has also found, for the first time, that lithium is formed from the stars themselves. When a star dies, it can collapse into a White Dwarf. This is a small body with an extremely dense mass, that consists primarily of carbon and oxygen atoms. If the White Dwarf is orbited by an active star, the denser dwarf star will slowly attract matter to its surface until it reaches the point where a nuclear reaction takes place, leading to an explosion that ejects matter into space and subsequently forms a nova. This matter can include beryllium-7, which decays to form lithium-7.
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Why is moisture measurement critical in lithium-ion battery manufacture? Part One
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