Create a cost-effective multifunctional lithium-ion battery test solution

With the increasing application of lithium-ion batteries in drones, electric vehicles (EV), and solar energy storage, battery manufacturers are also using modern technology and chemical composition to push the limits of battery testing and manufacturing capabilities.

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Figure 1: The battery that powers modern electric vehicles

Nowadays, the performance and life of each battery, regardless of size, are determined in the manufacturing process, and the test equipment is designed for a specific battery. However, because the lithium-ion battery market covers all shapes and capacities, it is difficult to create a single, integrated tester that can handle different capacities, currents and physical shapes with the required accuracy and accuracy.

In view of the increasingly diversified demand for lithium-ion batteries, we urgently need high-performance and flexible test solutions to minimize the trade-offs and achieve cost-effectiveness.

Lithium-ion batteries are complex and diverse

Nowadays, lithium-ion batteries have a variety of sizes, voltages and application ranges, but this technology was not realized when it was first put on the market. Lithium-ion batteries were originally designed for use in relatively small devices, such as notebook computers, mobile phones, and other portable electronic devices. Now, their dimensions are much larger, such as electric cars and solar battery storage. This means that a larger series-parallel battery pack has a higher voltage and a larger capacity, and the physical volume is also larger. For example, the battery packs of some electric vehicles can be configured with up to 100 in series and more than 50 in parallel.

Stacked batteries are nothing new. A typical rechargeable lithium-ion battery pack in an ordinary notebook computer consists of multiple batteries in series, but due to the larger volume of the battery pack, the test becomes more complicated and may affect the overall performance. In order for the performance of the entire battery pack to reach a level, each battery must be almost the same as its neighboring battery. Batteries will affect each other, so if a battery in a series has a low capacity, the other batteries in the battery pack will be below the state, because their capacity will be downgraded by the battery monitoring and rebalancing system to match the performance of the battery. As the saying goes, a rat poop spoils a pot of porridge.

The 　　 charge-discharge cycle further illustrates how a single battery can reduce the performance of the entire battery pack. The capacity of the battery in the battery pack will reduce its state of charge at a rapid rate, resulting in an unsafe voltage level, and the entire battery pack can no longer be discharged. When the battery pack is charged, the capacity battery will be fully charged first, and the remaining batteries will not be charged further. In electric vehicles, this will result in a reduction in the effective overall available battery pack capacity, thereby reducing the vehicle's cruising range. In addition, the degradation of low-capacity batteries will accelerate because it reaches an excessively high voltage at the end of charging and discharging before the safety protection measures take effect.

Regardless of the terminal device, the more batteries in the battery pack are stacked in series and parallel, the more serious the problem. The obvious solution is to ensure that each battery is made exactly the same, and to combine the same batteries in the same battery pack. However, due to the inherent manufacturing process differentiation of battery impedance and capacity, testing has become critical-not only to exclude defective parts, but also to distinguish which batteries are the same and which battery packs to put in. In addition, the charging and discharging curve of the battery during the production process has a great influence on its characteristics and is constantly changing.

Why do modern lithium-ion batteries bring new test challenges?

Battery testing is not a new thing, but since its advent, lithium-ion batteries have put new pressure on test equipment, production volume and circuit board density.

Lithium-ion batteries are unique because they have extremely dense energy storage capacity. If they are charged and discharged improperly, they may cause fires and explosions. In the process of manufacturing and testing, this energy storage technology is very demanding, and many emerging applications further exacerbate this requirement. In terms of shape, size, capacity and chemical composition, the types of lithium-ion batteries are more extensive. On the contrary, they will also affect the test equipment, because they need to ensure that the correct charge and discharge curves are followed accurately to achieve the storage capacity, reliability and quality.

Since there is no one size suitable for all batteries, choosing suitable test equipment and different manufacturers for different lithium-ion batteries will increase the test cost. In addition, continuous industrial innovation means that the ever-changing charge-discharge curve is further optimized, making the battery tester an important development tool for new battery technology. Regardless of the chemical and mechanical properties of lithium-ion batteries, there are countless charging and discharging methods in their manufacturing process, which makes battery manufacturers put pressure on battery testers to require them to have unique test functions.

is obviously a necessary capability. It not only means the ability to keep high current control at a very low level, but also includes the ability to switch very quickly between charging and discharging modes and between different current levels. These requirements are not only driven by the need to mass-produce lithium-ion batteries with consistent characteristics and quality. Battery manufacturers also hope to use test procedures and equipment as innovative tools to create a competitive advantage in the market, such as modifying charging. Algorithm to increase capacity.

Although a variety of tests are required for different types of batteries, today's testers are optimized for specific battery sizes. For example, if you are testing a large battery, you need a larger current, which translates to larger inductance and thicker wires and other characteristics. So there are many aspects involved when creating a tester that can handle high currents. However, many factories do not only produce one type of battery. They may produce a complete set of large batteries for a customer while meeting all the test requirements for these batteries, or they may produce a set of smaller batteries with a smaller current for a smartphone customer. .

This is the reason for the rising cost of testing-the battery tester is optimized for current. Testers that can handle higher currents are generally larger and more expensive because they not only require larger silicon wafers, but also magnetic components and wiring to meet electromigration rules and minimize parasitic voltage drops in the system. The factory needs to prepare a variety of test equipment at any time to meet the production and inspection of various types of batteries. Due to the different types of batteries produced by the factory at different times, some testers may be incompatible with these specific batteries and may be left unused, which further increases the cost because the tester is a large investment.

Whether it is for common and emerging factories for mass production of ordinary lithium-ion batteries, or battery manufacturers who want to use the test process to innovate and create new battery products, they need to use flexible test equipment to adapt to a wider range of batteries. Capacity and physical size, thereby reducing capital investment, and improving the return on investment of test equipment.

When trying to properly optimize a single integration test solution, there are many conflicting requirements. There is no panacea for all types of lithium-ion battery test solutions, but Texas Instruments (TI) has proposed a reference design that reduces the trade-off between cost-effectiveness and the cost-effectiveness.

High test solution, suitable for high current applications

Unique battery test scenario requirements will always exist, and it needs an equally unique solution accordingly. However, for many types of lithium batteries, whether it is a small smart phone battery or a large battery pack for an electric vehicle, there can be a cost-effective test equipment.

In order to achieve the full-scale charge and discharge current control required by many lithium-ion batteries on the market, Texas Instruments’ modular battery tester reference design for 50-A, 100-A, and 200-A applications uses 50-A and 100 -A combination of battery test design to create a modular version that can reach 200-A charge and discharge levels. The block diagram of this solution is shown in Figure 2.

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Figure 2: Texas Instruments battery tester solution

For example, TI adopts a constant current and constant voltage control loop for the battery tester reference design for high current applications, which supports up to 50A charge and discharge rates. This reference design uses the LM5170-Q1 multiphase bidirectional current controller and the INA188 instrumentation amplifier to regulate the current flowing into or out of the battery. INA188 implements and monitors the constant current control loop, and since the current may flow in either direction, the SN74LV4053A multiplexer can adjust the input of the INA188 accordingly.

This particular solution creates a modifiable platform for applications requiring higher current or multiphase by combining several key TI technologies, demonstrating the feasibility of building a cost-effective test solution. This flexible and forward-looking solution not only meets today's needs, but also predicts the future growth trend of automotive batteries, which will soon increase the demand for the tester's current capability to exceed 50A.

Lithium-ion battery testing equipment investment

The modular battery tester reference design of Texas Instruments solves the problems of high, high current and flexibility of lithium-ion battery test equipment. This reference design covers a variety of available battery shapes, sizes, and capacities, and can cope with emerging applications, such as large battery packs in electric vehicles and solar power plants, and small-sized batteries commonly found in consumer electronics such as smart phones.

The reference design for lithium-ion battery testing enables you to invest in lower current battery test equipment and use them in parallel, eliminating the need for expensive investments in multiple architectures with different current levels. The ability to use test equipment in a variety of current ranges can optimize the investment in battery test equipment, reduce overall costs, and provide flexibility to adapt to the changing needs of lithium-ion battery testing.