Figure 1: DAQ6510 is a precision data acquisition and logging system that creates a new level of simplicity compared with the often complicated configuration and control found in the industry
Li-Ion Batteries Manufacturing: a quick look into production
Li-Ion battery production is an extremely interesting market; LIBs are a popular choice for several applications that, for simplicity, we will group into three main categories:
- The consumer market, which includes battery-operated IoT, medical wearables, smart home and general portable electronics
- The transportation market, which is in large part the automotive EV market
- The broad and complex stationary applications market, which includes uninterruptible power supply (UPS), data centers, renewable energy systems (RES), and batteries for grid-level storage.
Each of these main macro applications not only differ in energy and power density requirements, the battery form factor, discharge rate, efficiency, and safety, but must adapt in order to support ever-changing lifetime requirements. This translates to more complex specs, such as the number of charge/discharge cycles and other performance-related parameters.
Also, the needs of each from a test and measurement perspective differ significantly. Over the last several years, many national and international industry projects and consortiums have been created to work throughout the entire battery value stream, growing and sharing their expertise.
Multiple associations in Europe assembled players focused on battery production technology in different departments, from the machine and component supply, raw material provisioning and preparation, electrode production and the stages of assembly, from the cell level to module and pack production. All of these were propaedeutic steps in preparation to support the need for several battery plants in Europe—the so called “Gigafactories”.
These large facilities are supposed to produce battery systems for electric vehicles, which fall in the second of the three aforementioned markets: transportation/automotive.
Battery System Testing in Automotive
An automotive battery system is complex with a lot of electronics incorporated in a solid, protected housing. It contains a battery pack with relatively complex cooling and control systems, electrical and thermal sensors, and some communication wiring. The control unit acts as a “brain” and is called BMS or battery management system.
A battery pack is a system composed of several battery modules. Each battery module is composed of several individual battery cells.
If the chemistry is efficient at the cell level, you need to make sure that the optimization still exists at the module or system/pack level as well.
Different test sets are developed at the cell level, module level and system level. The same test Instrument may find space in different production stages and for different levels of batteries.
Let’s take a quick look at some of the value chain phases.
Cell-level Materials and Subcomponents, Electrode Manufacturing Testing
There is a lot of material (like complex polymers) processing in the early stages of the production of key components used in cell manufacturing. You need to make the separators, the case, the electrodes etc.
Tektronix and Keithley solutions relate to the electrical measurements taken on electrodes for instance. It is necessary to trace the impedance on electrodes to make sure the materials chosen for the anode and cathode do not massively contribute to the battery input impedance and stay in the range of a fraction of an ohm across a certain frequency range. Generally, customers design a specific fixture capable of accessing all interfaces between collectors and other layers; it is a necessary step for the accurate determination of electrical conductivity of different samples. A special chuck can be used to connect to it with the four-point probe technique.
Keithley state-of-the-art Nanovoltmeter 2182A combined with 622x Current AC and DC sources support such measurements. As said in the previous paragraph, these measurements are made mostly in the research stages and considered particularly useful when dealing with electrochemical noise measurements. The DC source applies a very precise constant current on the electrodes while the digital nanovoltmeter measures the correspondent drop in voltage.
Cell-level Assembly, Stacking, Tab Welding, Filling
Before filling the electrolyte into the cell, defective products need to be removed from production. To identify defective products, you can run a test on the insulator (also called the separator) that involves a charging-dwelling-discharging sequence and measure the leakage current.
When issues with the separator exist (membrane problems, decomposition etc.), the failure is easy to detect as the level of current is in the range of tens of mA. When insulation is good, the leakage current can be quite low (in the pico Ampere range). The insulation resistance test is also repeated in the module assembly and pack assembly stages to prove the insulation is good for different parts with respect to ground (chassis).
The Keithley model 6517B Electrometer/ High Resistance Meter offers insulation resistance measurements at various calibrated insulation test voltages. The 6517B has very low current sensitivity and a built-in 1kV voltage source with sweep capabilities. This simplifies performing leakage, breakdown, and high-resistance testing as well as surface resistivity measurement on insulating materials.