Why do electric car batteries explode? These battery security chips, you need to know!

[Introduction]Driven by the trend of electrification, automobiles are undergoing earth-shaking changes. The three core components have changed from the engine, chassis and gearbox of fuel vehicles to the “three-electric system” of electric vehicles – electric drive, battery, Electric control. According to the cost data released by car companies, the battery system is the component with the highest cost in electric vehicles, accounting for nearly 40% of the total cost.

On the one hand, the battery system of an electric vehicle “cannot afford to fail”. In the maintenance project of electric vehicles, once it is linked to the battery system, the maintenance cost will increase sharply. Counting the premium of parts for the maintenance system, once there is a problem with the battery system, it often takes nearly 60% of the cost of the whole vehicle for maintenance. On the other hand, the occasional electric vehicle spontaneous combustion accident proves that the deflagration of the electric vehicle battery has greater destructive power and leaves the driver and passengers with shorter escape time. Therefore, ensuring the safety and stability of the battery system is the common goal of the entire electric vehicle industry.

In fact, since the explosion accident of mobile phones and electric bicycles, the public and the industry have begun to pay attention to the safety of lithium batteries, but in the field of automobiles, the concept of safety has been further strengthened. In this article, we will specifically interpret the safety protection of lithium batteries, and recommend components distributed by Mouser Electronics that can ensure battery safety.

About lithium battery safety

As we all know, lithium batteries are quite dangerous due to their own physical properties. When a lithium battery is charged, it converts electrical energy into chemical energy for energy storage, and when discharged, it converts chemical energy into electrical energy for energy release. Once the lithium battery stores energy, the uncontrollable energy release will cause deflagration. As smartphones, electric vehicles, and electric vehicles are all pursuing long battery life, the high energy density of battery systems has become a product advantage, but this actually further increases the destructive power of deflagration.

Of course, the final destructive power of lithium batteries is presented by deflagration, but this is not done instantaneously, but has a gradual process in the form of thermal runaway. What will cause the thermal runaway of lithium batteries? The industry refers to these situations collectively as abusive conditions.

After checking the Chinese national standard GBT31485-2015 “Safety Requirements and Experimental Methods for Power Batteries for Electric Vehicles”, it is found that the abuse conditions include over-discharge, over-charge, internal and external short circuits, extrusion and drop.

Taking the electric vehicle power battery system as an example, it generally consists of cells, BMS (battery management system), structural parts (boxes, wires, connectors, etc.) and thermal management systems.

The cell is a single-cell lithium-ion battery, which consists of a positive electrode sheet, a negative electrode sheet, a diaphragm, an electrolyte and structural parts. Many power battery system accidents, such as spontaneous combustion, are caused by short circuits in the cells. After an internal short circuit occurs, the cell temperature will rise rapidly. When the temperature reaches a certain level, the diaphragm protecting the active material of the negative electrode in the battery cell will disappear, resulting in the complete exposure of the negative electrode, and a large amount of electrolyte decomposes on the surface of the electrode to release heat. This is the first of a series of exothermic side reactions inside the battery. step. Then a lot of heat and flammable gases are released, which eventually causes the system to detonate.

In addition, there are two abuse situations that can cause the battery system to detonate: high temperature and overcharge. BMS is responsible for monitoring battery terminal voltage, energy balance between batteries, total battery voltage/current, battery terminal/battery temperature, etc. As mentioned above, when these indicators mutate, the battery will enter the abuse condition. If it cannot be stopped in time, it will cause a deflagration accident.

Electric vehicles have an urgent need for high-performance BMS. At the same time, the rapid growth of the electric vehicle market also has a positive driving effect on BMS products.

According to the analysis data of QYReaserch, the global automotive BMS market will reach 21.7 billion yuan in 2020 and is expected to reach 88.5 billion yuan in 2027, with a compound annual growth rate (CAGR) of 26.19%.

BMS is called “battery nanny” or “battery housekeeper” by many industry players. Its main function is to intelligently and dynamically manage and maintain each battery unit, prevent overcharging and overdischarging of the battery, prolong the service life of the battery, and monitor the battery life. state. In terms of battery management, the BMS can accurately obtain the State of Charge (SOC) of the power battery pack to ensure that the SOC is maintained within a reasonable range and prevent damage to the battery due to overcharge or overdischarge. When the voltage or capacity of some cells in the battery pack is found to be too high or too low, the BMS has the ability to balance between the single cells, which is a key part of preventing the cells from being abused, which not only prolongs the life of the system, It also eliminates security risks and provides safe and stable operating conditions for fast charging.

To sum up, in the application of electric bicycles and electric vehicles, the BMS system mainly realizes the following functions:

● Accurately obtain the SOC of the power battery pack, and maintain the SOC within a reasonable range through the system algorithm;

● Balanced management of battery packs and cells, including thermal management, charge and discharge management, etc.;

● Provide a variety of protection functions for the battery pack, including overcharge protection, overdischarge protection, short circuit protection, etc.;

● Use the communication bus to exchange information with the vehicle system.

In addition to making innovations in key technical fields such as BMS and battery materials, in order to promote the safe use of lithium batteries, the policy side is also stepping up the promulgation of relevant regulations, trying to play a correct guiding role in the industry.


Multi-Cell Battery Balancer for Electric Vehicles

In the above analysis, we took the automotive power battery system as an example to interpret which abuses will lead to the deflagration risk of the power battery pack, and mentioned the important role of the BMS system in the safety of the power battery system. Next, the first product we want to introduce is the LTC3300 multi-cell battery balancer that can be used in electric vehicle BMS systems. This product is available from the manufacturer, ADI, and the supplier part number for this product on Mouser Electronics is LTC3300HLXE-2#WPBF.

The LTC3300 Bidirectional Multi-Cell Battery Balancer is a fault-protected controller IC for transformer-based bidirectional active charge balancing of battery packs with multiple cells. As can be seen from Figure 1, the LTC3300 has rich pin functions, and integrates various related gate drive circuits, high-precision battery sensing, fault detection circuits and a ruggedized watchdog timer inside the device. serial interface.

Why do electric car batteries explode? These battery security chips, you need to know!

Figure 1: LTC3300 pinout (Image source: ADI)

Figure 2 is a block diagram of a typical application of the LTC3300, which can charge up to 6 series-connected batteries with an input common-mode voltage up to 36V, solving the problem of unidirectional balancing when the battery voltage is low in the battery pack. efficiency issues, thereby achieving charge balancing for each cell in a long string of series-connected cells. Minimize equilibration time and reduce power consumption. By external setting, the balance current can reach 10A.

Why do electric car batteries explode? These battery security chips, you need to know!

Figure 2: LTC3300 typical application block diagram (Image source: ADI)

At the same time, the LTC3300 has industry-leading scalability. With its level-shifting SPI-compatible serial interface, it can complete the series connection of multiple LTC3300-1 devices without using optocouplers or isolators, and can be stacked to support 1000V above system. And the LTC3300-1 connected in series can work at the same time, so all the cells in the battery pack can be charged independently at the same time. In addition, the LTC3300 can be seamlessly integrated with the LTC680x family of multi-cell battery stack monitors.

As shown in Figure 3, the LTC3300 has a balancer efficiency of up to 92%.

Why do electric car batteries explode? These battery security chips, you need to know!

Figure 3: Measured efficiency of the LTC3300 (Image source: ADI)

Comprehensive protection performance is a highlight of the LTC3300 device, which provides a variety of fault protection features, including readback capability, cyclic redundancy check (CRC) error detection, maximum on-time volt-second clamping and overvoltage shutdown. break.

When applied to a BMS system of series-connected lithium-ion batteries, the battery pack balancer composed of the LTC3300-1 is a key component in the system and can work in conjunction with a monitor, charger, microprocessor or microcontroller. Figure 4 is the schematic diagram of LTC3300-1 applied to the BMS system. The function of the battery pack balancer in the system is to charge a given unbalanced battery with an adjacent larger battery pack (which contains unbalanced batteries). Transfer to achieve voltage or capacity balance of the single cell and the entire battery pack.

Why do electric car batteries explode? These battery security chips, you need to know!

Figure 4: Schematic diagram of LTC3300-1 applied to BMS (Image source: ADI)

In BMS systems, the seamless integration of the LTC3300 and LTC680x series of multi-cell battery stack monitors provides highly accurate voltage monitoring protection. The balancing efficiency of up to 92% allows the LTC3300 to more than double the balancing current compared to a solution with the same balancer power consumption but with an efficiency of only 80%.

This efficient balancing method extends the life of the power battery pack and helps achieve faster charging speeds. From a system safety point of view, more efficient cell balancing could prevent the situation from getting worse. When the cell voltage or energy imbalance occurs, if it cannot be solved quickly, it is easy to further deteriorate into overcharge or overdischarge, which is the abuse situation we mentioned above.

In terms of potential application scenarios, LTC3300 is not only suitable for BMS systems of electric vehicles or plug-in hybrid electric vehicles (HEV), but also can be used in general-purpose multi-cell battery pack monitoring, high-power UPS/grid energy storage systems, etc. market.

For more LTC3300 information, please click here >>


Battery Front-End IC for Accurate Monitoring

In the above content, we have repeatedly mentioned the important role of BMS in electric vehicles, and introduced a component that can be used for BMS battery balancing in electric vehicles. In fact, BMS systems are also extremely important in the field of electric bicycles. Frequent accidents have made electric bicycles banned from entering residential buildings, but to prevent such accidents, it is necessary to fundamentally improve the battery safety of various types of light electric vehicles.

The next device that can be used in BMS systems for light electric vehicles is the ISL94216x battery front-end IC from manufacturer Renesas Electronics. Engineer friends can find it precisely by searching for the manufacturer’s part number ISL94216IRZ on Mouser Electronics.

Why do electric car batteries explode? These battery security chips, you need to know!

Figure 5: ISL94216x battery front-end IC (Image source: Renesas Electronics)

Figure 6 is a system block diagram of the ISL94216x battery front-end IC, showing the integrated features of the device. The device supports I²C, SPI, and 1-wire protocol stacks to interface with MCUs in battery management solutions.

Why do electric car batteries explode? These battery security chips, you need to know!

Figure 6: ISL94216x battery front-end IC system block diagram (Source: Renesas Electronics)

The ISL94216x battery front-end ICs feature several battery monitoring functions that periodically scan the battery status and operating environment to optimize battery life and prevent catastrophic failures. The device’s differential multiplexer and 16-bit ADC accurately monitor battery voltage, temperature, and load current in the overall state of the battery pack. At the same time, the charge/load wake-up detection circuit in the device can dynamically obtain the working condition of the battery pack.

The core function of a BMS system is monitoring and balancing. For cell balancing, the ISL94216x battery front-end ICs have an internal cell balancing circuit that provides 8mA balancing current per cell. Therefore, the device can provide multiple operation modes and monitoring/protection functions when applied to light-duty electric vehicle BMS systems.

The open circuit detection function of the ISL94216x battery front-end IC is emphasized here. The circuit block diagram is shown in Figure 7, where VC0-VC16 check the wire (blue) between the connector and the battery, and VSS and VBAT1 OW check the red connection to This is to judge whether the connection between the BMS and the battery unit is disconnected.

Why do electric car batteries explode? These battery security chips, you need to know!

Figure 7: ISL94216x battery front-end IC open circuit detection function (Image source: Renesas Electronics)

Open circuit detection is a very important function in BMS self-diagnosis. Once the connector is disconnected from the battery pack, the BMS will not be able to continue to provide system monitoring and adjustment functions. If other circuits continue to work at this time, it will not only damage the battery pack, but even damage the battery pack. will cause an accident.

For more information on ISL94216x, please click here >>

Nip danger in the bud

Judging from the current technology status of the industry, the risk of lithium batteries will continue to exist for a long time in the future, but the industry is not helpless. From system monitoring to battery balancing, battery protection components provided by major manufacturers can nip the dangers of lithium batteries in the bud.

The importance of the BMS system has been recognized by the whole industry. Facing the future, BMS needs better state estimation technology, battery diagnosis technology, and active balancing technology, and cloud-based BMS will also become an inevitable trend; in terms of product form, distributed management makes the functions of BMS clearer and separated, and with the help of integration The technology is integrated into different domain controllers; in addition, the BMS will pursue more advanced functional safety to achieve the safety management of the battery life cycle; in addition, low-cost technology is the main implementation method of the future BMS.

Of course, Electronic components are the cornerstone of all this. These components with excellent protection performance can be easily obtained by engineers and friends under the “Battery Management” column of Mouser Electronics, and there are a wealth of development tools associated with components to help engineers and friends make good use of lithium batteries. the “safety switch”.

This article is reproduced from: Mouser Electronics WeChat Official Account

The Links:   SKM111AR G156HTN010

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