Challenges of the battery of tests
Li-ion batteries can be used in both small electronic devices and very large applications, so they can vary greatly in size, voltage and shape. However, this breadth means that battery manufacturers must purchase and maintain battery of tests solutions for each battery type. The associated capital investment can become very large, directly accounting for 20 percent of the final cost of the battery.
Clearly, there is a need for a battery of tests solutions that can handle a wider range of battery voltages, capacities, and physical dimensions. Creating a comprehensive universal test facility is challenging because the market illustrated in figure below requires a cost-effective solution.
A test battery consists of a series of tests administered to assess different facets of a child’s or adult’s functioning
Just like any other device, batteries need to be tested to determine if they are airworthy. That is, to determine if they will perform properly when required under normal conditions and more so when needed in emergency situations.
Test methods range from taking a voltage reading, to measuring the internal resistance by a pulse or AC impedance method, to coulomb counting, and to taking a snapshot of the chemical battery with Electrochemical Impedance Spectroscopy (EIS).
Challenges of the battery of tests
After the battery assembly process, each lithium-ion battery undergoes a gradual charging process so that it forms a solid electrolyte membrane (SEI) layer. So it is critical for the long-term function of lithium-ion batteries. If this process is not properly controlled, the battery can lose up to 50% of its capacity. Therefore, the test equipment must be able to accurately control the thickness of the SEI layer, which can reduce capacity losses to less than 5%. Many applications use battery packs consisting of multiple cells connected in series and parallel configurations to achieve higher output voltage and greater energy capacity.
A test battery designed specifically for a battery pack adds its own complexity. Because all cells in a battery pack need to be identical not only in size and capacity, but also in parameters such as impedance and service life. Given the inherent process changes in battery impedance and capacity, The battery of tests become critical not only to eliminate defective cells, but also to pick out identical cells to form a battery pack. As with all mass-produced things, a small percentage of batteries will prove defective. The potential explosive characteristics and energy storage density of lithium-ion batteries require high operational safety when charging and discharging in battery test environments. Therefore, the battery tester must include protection measures against various system failures to improve the robustness and reliability of the overall equipment.
Today’s battery test equipment is designed for specific battery types. Testing larger batteries requires more current, so battery testers require larger silicon wafers, inductors, magnetic components and wiring, as well as thicker wires. Battery manufacturers producing small cells (with lower current requirements) often leave high-current battery testers idle by using testers optimized for lower current levels. Having a tester that can test both smaller and larger batteries would reduce this redundancy and thus the overall cost of battery production. In order to improve the capacity and quality of the battery as much as possible, battery manufacturers constantly improve the charge-discharge curve during the battery formation process.
Moreover, because test equipment can be used to develop new battery technologies, try new technologies and gain a competitive advantage, battery manufacturers expect test equipment manufacturers to provide more features. Let’s take a closer look at why designing an integrated solution for this application is so difficult.
Integration solution challenges
The battery tester requirements are very unique, and there is no technical node in place to enable designers to meet all requirements. Combining speed, power, and accuracy in a single design risks sacrificing other aspects of performance, either by not being fast enough, or by not being precise enough, or by limiting high current transfer efficiency. On the one hand, there are some requirements for the power of lithium-ion batteries. The efficiency of the process is a key consideration because of the high levels of energy needed to transfer when a battery is charged and discharged. On the other hand, there are precision requirements. It doesn’t just convert power and transfer it to the battery, or from the battery to the power supply.
The process must be extremely precise. It has always been difficult to design a product that can deliver high power with great precision. The technologies used in the power products focus on achieving low drain-source conduction resistances and gate capacitors to provide higher power at low cost. The techniques used in precision products aim to achieve low offset voltages and drifts by introducing other steps into the manufacturing process, which can increase the cost of integrated circuits (ics). Power products designed with precision techniques may be suitable for low power levels where the switching power field-effect transistor (FET) has a small area relative to the rest of the circuit. However, for high current applications above 1A, integrating the power FETS on the same bare sheet with the rest of the precision circuit is not optimal. because the size of the power FEts is relatively large compared to the rest of the circuit. At this point, discrete FETs become a more logical solution.
Conclusion
The wide variety of lithium-ion batteries available today requires battery of tests equipment that is flexible and comprehensive. But it still can be very accurate without the high cost of large batteries, multiple phases and add-ons. The modular battery tester reference design shows that the problems of high accuracy, high current, high speed and flexibility can be solved without large investment in battery test equipment. Instead of investing in multiple architectures for different current levels, you now test a series of currents so that high-current devices are no longer idle when testing low-current batteries. This reference design allows you to save money by investing in lower current battery test equipment, while providing the ability and flexibility to test high current applications without sacrificing accuracy.
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