Lithium battery system technical bottleneck -Lithium - Ion Battery Equipment

What technical bottlenecks exist in lithium battery systems? -Lithium - Ion Battery Equipment

As an electronic component with real-time monitoring, automatic balancing, and intelligent charging and discharging, the battery management system (BMS) plays important functions such as ensuring safety, extending life, and estimating remaining power. Through a series of management and control, it ensures the normal operation of electric vehicles.

Regarding the current market, Cha Yong, sales director of Littel Company in my country, said that the current demand for improving air quality based on low or zero emissions puts forward higher efficiency requirements for cars. With the increase of electrical loads in the entire car (such as The improvement of automobile power, multimedia power consumption, etc.) requires high-voltage power supply and a more powerful power supply system.

At present, there are four main types of electric vehicle/hybrid vehicle architecture: one is HEV (Hybrid), which is a hybrid of oil and electricity, and the battery is charged by the engine; the other is PEV (Plug-in), which is a hybrid of oil and electricity, and the battery requires external charging; The third is BEV (Battery Electric Vehicle), which is powered by pure batteries; the fourth is powered by chemical fuel-powered lithium batteries. Cha Yong said that at present, gasoline and electric hybrid vehicles occupy a relatively large proportion of the market, and they will gradually transform to pure electric vehicles in the future.(Lithium - Ion Battery Equipment)

So, what are the advantages of lithium batteries?

We understand that the power supply system of electric vehicles is composed of several lithium batteries.

Lithium battery packs are composed of battery cells. Each battery pack has approximately 500 to 7,000 cells, which puts forward higher requirements for battery management and control.

Lithium battery technology will be the basis for any type of electric vehicle. Cha Yong said that it is still being improved and will provide the best cost and functionality required in the future. The relevant costs are expected to be reduced by one-quarter to one-third in the next few years, while the energy density has the same of increase. Comparative table of lead-acid batteries, nickel-metal hydride batteries, and lithium batteries. It can be seen that the advantages of lithium batteries in power density and charging cycle life are irreplaceable.

What are the technical bottlenecks in lithium battery systems?

Regarding lithium battery technology, there are still many areas that need to be further improved. Cha Yong mentioned three important points:

First, the charging and discharging state. The battery can operate safely and reliably only when the charge and discharge state is within a certain range. High discharge and overcharge will reduce the efficiency and life of the lithium battery. The ideal state of charge is about 20% to 90% of the maximum charge capacity;

Second, safe battery operating voltage. Keep the battery voltage between a minimum of 2V and a maximum of 4.2V, too high a battery voltage can cause too much current to flow, and in the worst case, a short circuit can destroy the battery;

Third, thermal management. Temperature control is particularly important because too high temperatures can cause a interlock reaction in the anode process, leading to dangerous situations due to possible electrode short circuits and outgassing of flammable gases from the organic solvent (electrolyte).

To make the battery work in a reliable and safe state, it is necessary to manage the charging and discharging status of the battery and supervise the safe working voltage of the battery. Currently, active balancing and passive balancing technologies are mostly used. Cha Yong added that for protection device fuses, small size and high voltage are still technical difficulties.

How to control security?

Lithium batteries must be carefully monitored and regulated by the battery management system. Protection of the battery management system itself is to ensure that this important system is safe and reliable under all circumstances (assembly, maintenance, normal operation).

In the event of a short circuit, strong currents can be induced on the power lines. Cha Yong said that for such a situation, it is recommended to use appropriate fusing technology with fuses with higher breaking capacity, such as Littel's 0HEV series. Battery management systems are usually connected via high-impedance sensing lines, so the short-circuit current is significantly reduced, allowing the use of electronic fuses, although the voltage requirements depend on the battery construction.

For battery protection, Litfuse fuses and TVS diode protection have great advantages:

1) As a global leader in protection devices, Littel supplies a full range of protection devices, including Fuse, PPTCTVSDiode, TVSDiodeArray, and different protection methods;

2) All devices meet AEC-Q101 and AEC-Q200 automotive certification;

3) LAB can provide various testing needs for customers.

Cha Yong pointed out that as more and more automotive applications (such as battery sensor circuit protection) rely on electronic fuses, and there is currently no official standard for electronic fuses used in cars, Litfuse has developed a standard based on the AEC-Q200 guidelines. A test plan to test the suitability and reliability of fuses in automotive applications. This test plan includes 18 tests, such as 1,000 hours of high temperature and humidity test, 1,000 cycle temperature shock test, special mechanical shock and vibration test, etc. There are also more stringent requirements for sample size. "Just one test is not enough. How to ensure that every batch of goods passes this test? The entire quality control system can ensure the consistency and continuity of high quality. This is something that some manufacturers do not have, so we must pay special attention to it."

In addition, Littelfuse continues to supply more products within the qualified range of electronic fuses for automotive applications. Regarding the protection of DC filter capacitors and IGBTs, Zener diodes have been used in the past, but they cannot provide the same advantages as TVS diodes, such as fast response, higher surge capability and higher reliability.

For example, on-board chargers communicate with other systems via the CAN bus. In dense automotive environments, CAN lines are subject to overvoltage stress caused by ESD or other transients caused by other automotive systems through coupling or conduction. In this regard, Cha Yong said that special protection devices have been developed for the CAN bus, SM24CANA and SM24CANB. They not only have ESD capabilities, but also have certain surge resistance capabilities, and also meet AEC-Q101 automotive certification.

It is not difficult to find that the lithium battery system is composed of several single cells with a relatively complex structure. It is the key to whether the entire system can work reliably. It is also extremely susceptible to static electricity, switching power loads, inductive surges, overloads, and short circuits. There are threats of over-current and over-voltage, so it is particularly important to carefully select and correctly place protective components for over-voltage and short-circuit protection.

Finally, Cha Yong said that vigorously developing new energy vehicles has become a consensus among all countries. Important countries in the world such as the United States, my country, Japan, Germany, South Korea, and the United Kingdom have all established their own ambitious new energy vehicle industry plans. The safety of new energy vehicles has always been one of the key tasks of the automobile industry. While looking forward to the rapid development of new energy vehicles, we must realize that stable, efficient, safe and reliable battery management system products are the key to ensuring the safety of electric vehicles. The key to normal operation is that only in this way can new energy vehicles have a sustainable future.

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