button cell battery cr2025

What is the difference between energy storage battery BMS and button cell battery cr2025?

1 Application scenarios of large-scale energy storage systems

In order to achieve the purpose of smoothing output power fluctuations, more and more power plants are equipped with energy storage systems, such as new energy power stations, wind power stations or solar power stations.

Independent energy storage power stations, as the reform of the power system gradually enters people's field of vision, independent energy storage power stations that make a living by reselling electricity gradually appear.

Indoor energy storage power station

2 Differences between energy storage battery management system (ESBMS) and power lithium battery management system (BMS)

The energy storage battery management system is very similar to the power lithium battery management system. However, the power lithium battery system is in high-speed electric vehicles, and has higher requirements for the power response speed and power characteristics of the battery, the SOC estimation accuracy, and the number of state parameter calculations.

The scale of energy storage systems is extremely large, and there are obvious differences between centralized battery management systems and energy storage battery management systems. Here we only compare them with the distributed battery management system of power lithium batteries.

2.1 The positions of batteries and their management systems in their respective systems are different.

In the energy storage system, the energy storage battery only interacts with the energy storage converter at high voltage. The converter draws power from the AC power grid to charge the battery pack; or the battery pack supplies power to the converter, and the power is converted into AC by the converter and sent to the AC power grid.

For the communication of the energy storage system, the battery management system has an important information interaction relationship with the converter and the energy storage power station dispatching system. On the one hand, the battery management system sends important status information to the converter to determine the high-voltage power interaction; on the other hand, the battery management system sends the most comprehensive monitoring information to the PCS of the energy storage power station dispatching system. As shown in the figure below.

Basic topology of energy storage system

The BMS of electric vehicles has energy exchange relationships with both motors and chargers at high voltage; in terms of communication, it has information interaction with the charger during the charging process, and has the most detailed information interaction with the vehicle controller during the entire application process. As shown in the figure below.

Electric vehicle electrical topology

2.2 Different hardware logical structures

For energy storage management systems, the hardware generally adopts a two-layer or three-layer model, and the larger scale tends to adopt a three-layer management system, as shown in the figure below.

Three-layer energy storage battery management system block diagram

Power lithium battery management system, only one layer of centralized or two distributed, basically will not appear three-layer situation. Small cars mainly use one layer of centralized battery management system. Two-layer distributed power lithium battery management system, as shown in the figure below.

Distributed electric vehicle battery management system block diagram

From the functional point of view, the first and second layer modules of the energy storage battery management system are basically equivalent to the first layer acquisition module and the second layer main control module of the power lithium battery. The third layer of the energy storage battery management system is a new layer added on this basis to cope with the huge scale of energy storage batteries.

Let's make a not so appropriate analogy. The best number of subordinates for a manager is 7 people. If the department continues to expand and 49 people appear, then 7 people have to choose a team leader, and then appoint a manager to manage these 7 team leaders. Beyond personal ability, management is prone to confusion.

Mapped to the energy storage battery management system, this management capability is the computing power of the chip and the complexity of the software program.

2.3 Communication protocols are different

Energy storage battery management systems basically use CAN protocol for internal communication, but they often use TCP/IP protocol for external communication, especially the PCS of energy storage power station dispatching system.

Power lithium batteries and electric vehicle environments all use CAN protocol, but they are distinguished by using internal CAN between components in the battery pack and using vehicle CAN between the battery pack and the whole vehicle.

2.4 Different types of batteries used in energy storage power stations will result in different management system parameters.

For safety and economic considerations, energy storage power stations often use lithium iron phosphate when selecting lithium-ion batteries, and some energy storage power stations use lead-acid batteries and lead-carbon batteries. The current mainstream battery types for electric vehicles are lithium iron phosphate ion batteries and ternary lithium ion batteries.

Different battery types have different external characteristics, and battery models are completely incompatible. The battery management system and battery cell parameters must be one-to-one. The same type of battery cells produced by different manufacturers will not have the same detailed parameter settings.

2.5 Different threshold setting tendencies

Energy storage power stations have more space and can accommodate more batteries, but some power stations are located in remote areas and transportation is inconvenient, so large-scale replacement of batteries is difficult. Energy storage power stations expect the battery cells to have a long life and not to fail. Based on this, the upper limit of its working current will be set relatively low to prevent the battery cells from working at full load. The energy and power characteristics of the battery cells should not be particularly high. The most important thing is to look at the cost performance.

Power lithium batteries are different. In the limited space of the vehicle, the battery that is finally installed is expected to be used to the extreme. Therefore, the system parameters will refer to the battery's limit parameters, and such application conditions are harsh for the battery.

2.6 The number of state parameters required to be calculated by both is different

SOC is a state parameter that both need to calculate. But until today, there is no unified requirement for energy storage systems, and what state parameter calculation capabilities the energy storage battery management system must have. In addition, the application environment of energy storage batteries has relatively abundant space and a stable environment, and small deviations are not easily perceived in large systems. Therefore, the computing power requirements of the energy storage battery management system are relatively lower than those of the power lithium battery management system, and the corresponding single-string battery management cost is not as high as that of the power lithium battery.

2.7 The passive balancing conditions for the application of the energy storage battery management system are relatively good

The energy storage power station has an urgent requirement for the balancing ability of the management system. The scale of the energy storage battery module is relatively large, and multiple strings of batteries are connected in series. The larger single-cell voltage difference will cause the capacity of the entire box to decrease. The more batteries are connected in series, the more capacity is lost. From the perspective of economic efficiency, the energy storage power station must be fully balanced.

In addition, due to the ample space and good heat dissipation conditions, passive balancing can play a better role. With a relatively large balancing current, there is no need to worry about excessive temperature rise. Low-cost passive balancing can be used in energy storage power stations. According to the forecast of my country's power lithium battery installed capacity in 2017 released by Zhenli Research, since the market size of electric passenger cars will surpass that of electric buses in 2017, they have high requirements for driving range, which determines that they will use ternary lithium-ion batteries. Therefore, the installed capacity of ternary lithium-ion batteries will increase from 26.27% in 2016 to 44%, and the installed capacity of lithium iron phosphate batteries will drop from 71.69% to 55.16%. However, the position of lithium iron phosphate in the electric bus market of 94% will not be shaken.

2. What is the difficulty in promoting electric buses?

Since the Ministry of Industry and Information Technology announced in 2016 that it would suspend the inclusion of ternary lithium-ion battery buses in the "Recommended Model Catalog for the Promotion and Application of New Energy Vehicles", ternary lithium-ion batteries have gradually withdrawn from the electric bus market, and lithium iron phosphate batteries have quickly dominated the electric bus market with a 94% share. However, the four major problems it has cannot be ignored. First, the battery life is short and cannot meet the requirements of a single-day driving mileage on a single charge; second, the vehicle charging time is long, and it takes 4-6 hours to fully charge once, which restricts the operating efficiency of the bus; third, the power lithium battery has a short life, usually 5-8 years, which directly affects the service life of the vehicle; finally, the power lithium battery has weak resistance to low temperatures, and its ideal operating temperature is 0℃～60℃. Once it is below 0℃, its charging capacity will drop rapidly, and the cruising range will continue to shorten, so it is not suitable for promotion in the northern market.

3. How does Yinlong lithium titanate beat lithium iron phosphate?

Yinlong lithium titanate has the same safe and stable properties as lithium iron phosphate, but it can surpass lithium iron phosphate in the following three aspects. First, it has a faster charging speed and can be fully charged in 6 minutes without affecting the battery life, which greatly improves the operating efficiency of buses. Secondly, it has strong resistance to low temperatures, and its ideal operating temperature is -40℃～60℃, which is suitable for promotion in the northern market. Moreover, the life of lithium titanate ion batteries is said to be more than 10 years, which can increase the service life of electric buses. However, Brother Mao questioned what positive electrode materials lithium titanate ion batteries use, which can be used with lithium titanate as negative electrode materials to achieve a battery life of more than 10 years.

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