With the global proliferation of electric vehicles (EVs) and energy storage systems (ESSs), the demand for lithium-ion batteries is rapidly expanding. Leading Tier-1 manufacturers in the battery industry are beginning to explore the use of EIS (Electrochemical Impedance Spectroscopy) measurement¹ for internal resistance² inspection.

To pursue a paradigm shift brought about by new measurement methods, or to pursue improving current measurement methods—this is the choice that manufacturers striving to produce high-capacity lithium-ion batteries may be forced to make in the near future.
 

• 1 EIS (Electrochemical Impedance Spectroscopy) measurement: A method for analyzing the electrochemical characteristics inside a battery. It measures the impedance (AC resistance) by applying an AC voltage to the battery while varying the frequency.
• 2 Internal resistance: One of the important indicators of the battery’s condition. It represents the difficulty of current flow within the battery itself. It is commonly measured on battery production lines using a battery tester that applies a 1 kHz AC signal.

Background

To ensure the sustainable use of limited resources, realizing a battery circular economy³ has become an urgent issue in the battery market. This would be done through promoting the reuse and recycling of batteries. For efficient battery recycling, it is important to have detailed data recording and management throughout the entire battery lifecycle, from production to disposal. The EU is attempting to do this by adopting their Battery Passport⁴. Through this program, they plan to increase transparency, circularity, and sustainability in the battery value chain. The passport, as with other global actions to further the battery circular economy, are expected to create new value, such as increasing recycling efficiency and improving the evaluation of the value of used batteries through the use of recorded data. 

• 3 Battery Circular Economy: An economic model that aims to minimize environmental impact of batteries while maximizing economic value. Efficient resource utilization and circulation are required at each stage of batteries’ production, use, reuse, and recycling.
• 4 Battery Passport: A system that ensures data traceability throughout the battery lifecycle by digitally recording information on battery manufacturing, use, and recycling.

Furthermore, developers have been increasing the battery capacity of large batteries for the purpose of extending EV driving ranges and creating ESSs of that can store more energy. This is resulting in new batteries installed in high-performance EVs and ESSs undergoing significant changes in size and internal structure. As battery capacity increases, internal resistance decreases. A consequence of this recent dramatic increase in battery capacity is that the extremely low internal resistance has become difficult to measure accurately. Moreover, there are other factors related to the significant changes in size and internal structure that affect the measurement. Most significant of these new challenges is that internal resistance cannot be accurately evaluated using the standard 1 kHz battery tester.

Leading Tier-1 manufacturers in the battery industry are beginning to explore next-generation internal resistance inspection methods. New solutions that enable the realization of a circular economy are needed for internal resistance measurement of batteries with new structures or high capacities.

Battery Impedance Meter BT4560, and Battery Tester BT6075 

Obtaining Detailed Data through EIS Measurement

To introduce battery passports, battery manufacturers are exploring methods for obtaining and managing detailed production data. EIS internal resistance measurement is one of such methods attracting attention. Measurement using multiple frequencies over a wide frequency range enables detailed analysis and recording of the internal state of battery cells. Hioki’s Battery Impedance Meter BT4560 is a perfect fit for this type of measurement. It can perform EIS measurements in the frequency range of 0.01 Hz to 1.05 kHz. Today, the BT4560 is gaining attention not only for research and development purposes but also as an inspection device on production lines.

Measuring Lithium-ion batteries at multiple frequencies (EIS) has many benefits. For example, internal resistance measurement at 0.01 Hz is so close to DC (i.e. 0 Hz, the actual state of operating batteries), it gives insight into the condition in which battery cells actually operate. Moreover, in high-capacity battery cells, sometimes internal resistance measurement at 100 Hz is more accurate than at the traditional 1 kHz. This is because 100 Hz measurement is less affected by inductance components compared to 1 kHz measurement. Having multiple measurement frequencies provides flexibility to respond to dramatic changes in new battery designs. Furthermore, the accumulation of measurement data at multiple frequencies will clarify the differences between batteries under development and old ones. These are just a few examples of how Tier-1 manufacturers are finding EIS measurement to be more suitable for the latest batteries. 
 

High-Precision Measurement for High-Capacity Batteries

The miniaturization of internal resistance values resulting from the increased capacity of batteries is increasing cases of measurement accuracy and reproducibility issues. The Battery Tester BT6075 boasts the world's highest level of performance in accuracy, stability, and measurement speed in the category of 1 kHz battery testers. It is a model through which Hioki has pursued the limit of performance for users seeking further advancement in internal resistance measurement using the conventional method.

The battery industry is now at a major turning point, or paradigm shift. They face the decision to either seek out new measurement methods to respond to changes in large Lithium-ion designs, or to strive to enhance conventional measurement methods. Hioki approaches this with two solutions: the BT4560 enabling EIS measurement, and the BT6075 pursuing conventional methods to the limit. Hioki strongly supports the realization of a battery circular economy and the development of next-generation batteries.
 

Features of Battery Impedance Meter BT4560

A battery impedance meter capable of measuring internal resistance of various types of batteries over a wide frequency range. The lower limit of the measurement frequency has been expanded in this newer model (BT4560-50) from 0.1 Hz to 0.01 Hz.

• Measurement frequency : 0.01 Hz to 1.05 kHz
• Maximum input voltage : 5 V
• Resistance measurement range : 3 mΩ, 10 mΩ, 100 mΩ
• Minimum resolution : 0.1 μΩ (3 mΩ range, 10 mΩ range)

Link: Battery Impedance Meter BT4560

Features of Battery Tester BT6075

Enables high-precision, high-speed, and stable internal resistance measurement of batteries at a measurement frequency of 1 kHz. Top-class model of traditional battery testers.

• Measurement frequency : 1 kHz
• Maximum input voltage : 100 V
• Resistance measurement range : 3 mΩ, 30 mΩ, 300 mΩ, 3 Ω, 30 Ω
• Resolution : 0.01 μΩ (3 mΩ range)

Link: Battery Tester BT6075

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