The Gamry Interface 1010 series Top 10 list: Channel-to-channel Isolation Gamry Instruments uses only low-profile components to drastically lower any electromagnetic interference, and places a conductive fence between channels. Ultimate Resolution Gamry Instruments starts with a 16-bit A/D converter for the best analog-to-digital resolution and add controllable noise filters to remove any noise in the Read more about The Gamry Potentiostat Difference[…]
A new partnership between Bitrode and Gamry was announced today. The collaboration in the development of battery test equipment shows the strength of the two companies. A ‘One Stop‘ product has been created by integrating Gamry’s EIS […]
Corrosion can be viewed as the natural return of metals to their ores and will occur anywhere a galvanic cell or field can be or has established. To establish the field all that is needed is two dissimilar metals that are connected directly or indirectly by an electrolyte, such as water. This is the same Read more about Corrosion as an Electrochemical Process[…]
Purpose of This Note
This application note discusses the differences between 2‑point and 4‑point measurements of batteries. These two typical setups are compared with Gamry’s battery holders for CR2032 coin cells and cylindrical 18650 batteries. Both holders allow direct‑contact Kelvin sensing.
EIS measurements are performed with two types of lithium‑ion batteries and different experimental setups. In addition, shorted lead measurements show the low‑impedance limits of Gamry’s 18650 and CR2032 battery holders.
It is crucial to know the exact specifications when testing batteries or any other energy storage device. Many parameters affect the capability of a battery, e.g. electrolyte, electrode materials, and temperature.
Batteries have to pass different tests to check their capacity, voltage window, current rating, internal impedance, leakage current, cycle life, operational temperature range, as well as several impact tests.
In order to get correct, reliable, and reproducible results, researchers have to rely on their experimental setup. Wrong setups can heavily affect and falsify measurement results leading to inaccurate conclusions.
The following sections show by means of EIS experiments the influence of the setup on the actual result. Common battery setups are compared with Gamry’s direct‑contact 4‑terminal battery holders. Shorted lead measurements with dummy cells show the lower limits of Gamry’s battery holders.
Dual Cell CR2032 and 18650 Battery Holder
Figure 1 shows typical options to connect cylindrical batteries and coin cells. Some batteries can be purchased with soldered tabs on each electrode. They allow connecting alligator clips for measurements. If no tabs are available, simple battery holders with two contacts are often used.
A potentiostat is an electronic instrument that controls the voltage difference between a Working Electrode and a Reference Electrode. Both electrodes are contained in an electrochemical cell. The potentiostat implements this control by injecting current into the cell through an Auxiliary or Counter electrode.
In almost all applications, the potentiostat measures the current flow between the Working and Counter electrodes. The controlled variable in a potentiostat is the cell potential and the measured variable is the cell current.
This Application Note may be difficult to follow unless you have some familiarity with electrical terms such as voltage, current, resistance, frequency, and capacitance. If you feel your knowledge in this area is lacking, we suggest review of a very basic electronics or physics book.
A potentiostat requires an electrochemical cell with three electrodes as shown below. W/WS denote the working and working sense. R denotes the reference electrode and C denotes the counter electrode.