A recent event that has caught the attention of the energy storage industry is the explosion of the integrated solar energy storage and charging power station project that occurred in Beijing last week. The accident resulted in the sacrifice of two firefighters involved in firefighting, causing a significant impact and will inevitably draw attention to energy storage safety issues in industry policies. Today we will talk about the security risks of energy storage and how to eliminate them through technology.



First of all, let's review this accident: According to the official Weibo account of Beijing Fire Protection, at 12:17 on April 16th, the 119 Command Center in Beijing received an alarm about a fire at the energy storage power station at No. 14, Ximachang, Yongwai Dahongmen, South Fourth Ring Road, Fengtai District. Fifteen fire stations, 47 fire trucks, and 235 firefighters were dispatched to the scene for disposal. At around 14:15, during the disposal process of the southern area of the power station, there was a sudden explosion in the northern area without warning, resulting in the sacrifice of two firefighters, injury to one firefighter, and loss of contact with one employee inside the power station.



The incident occurred at the Beijing Jimei Dahongmen 25MWh DC optical storage and charging integrated power station project, and the power station was undergoing debugging at the time of the accident. According to public information, the energy storage power station was put into operation in 2019 and belongs to the user side photovoltaic energy storage charging pile integrated system. The energy storage battery is a retired 25MWh lithium iron phosphate battery. The power station first caught fire, and then firefighters exploded during the disposal process, resulting in casualties, that is, starting with fire and then exploding. From the phenomenon, it is very similar to the fire and explosion process of the APS energy storage system in the United States in 2019. The investigation results of the APS accident show that the main cause of the accident was the production of a large amount of explosive gas and accumulation after the battery burned. When the first batch of emergency personnel opened the cabin door and oxygen entered the cabin, the explosive gas began to burn and explode.



It is currently unknown whether the fire was caused by the battery itself or by other reasons that led to the battery explosion. However, based on the above information, there are two safety hazards that should be noted:

1. The energy storage battery is a retired lithium iron phosphate battery. Although lithium iron phosphate batteries are relatively safe compared to ternary lithium batteries, retirement means that the battery has been used in other places for several years, and there may be internal deformation caused by physical collisions, uneven distribution of electrochemical performance due to too many cycles of electrode charging and discharging, which will become weak links inside the battery and easily lead to short circuits and combustion.





2. This is a charging station project, which means the output power is very high, that is, the output current is very high. With the constant internal resistance of the battery, as the current increases, the heat generated by the internal resistance increases in a square order. Moreover, as this is a retired battery, its internal resistance is often much higher than that of a newly manufactured battery, making it highly susceptible to generating a large amount of heat and causing combustion. At the time of the incident, the power station was undergoing debugging, so it cannot be ruled out that combustion may have been caused during the debugging of high output current.



In the past few years, the energy storage market has gradually heated up, and various types of capital have entered one after another. In the early stages of the industry, the market was inevitably mixed, with unicorns like CATL and BYD, as well as a large number of small and medium-sized enterprises attempting to make quick money. In an immature market, from owners, investors to equipment suppliers, they are more concerned about price and cost, and do not have sufficient understanding of product risk control and safety. The fire accident also reflects a lack of regulatory capacity. Compared with over 100 national standards in the electric vehicle industry, there are less than 20 national standards in the energy storage industry, and their fire safety national standards do not yet exist. From a technical perspective, there are several ways to improve the safety level of energy storage projects.



1. Increase the surface area of the energy storage battery pack appropriately to enhance its heat dissipation capacity. Compared with 3C product batteries and power batteries, energy storage batteries usually have a capacity several orders of magnitude larger, so their battery pack aggregation is very high, resulting in a very small surface area per unit capacity, which is not conducive to the diffusion of heat to the outside world. If you want to increase the surface area per unit capacity, you need to reduce the capacity of each battery pack, which will cause a certain cost increase.





2. Improve the heat dissipation capacity of the battery pack gap. The most widely used and cost-effective cooling method currently is air cooling, which uses a fan to accelerate the air flow between battery packs and promptly remove heat from the energy storage area. The biggest drawback of this heat dissipation method is its low heat dissipation efficiency, as the specific heat capacity of the air is still too small. Liquid cooling technology, commonly known as water cooling, can greatly improve heat dissipation efficiency, but the installation cost is high, and once leaked, it may also cause battery damage. Other available heat dissipation technologies, including phase change material heat dissipation (similar to the principle of air conditioning), are too expensive to be used in energy storage projects that pursue low costs.






3. It is necessary to appropriately tighten the State of Charge (SOC) range for battery charging and discharging. Generally speaking, when lithium batteries operate in the SOC range of 20% to 80%, the internal resistance of charging and discharging is relatively small, and the heat generation is also relatively small. Moreover, working in this range is not easy to cause overcharging and discharging problems in the battery, which is conducive to avoiding the risks caused by this. Due to the limitation of the operating range of SOC to 60% of the maximum theoretical capacity, it will also result in a significant increase in energy storage costs.



4. Use non combustible battery technology. Solid state batteries can achieve higher safety by removing flammable organic solvents. However, solid-state batteries have not yet been mass-produced and have high costs, making them difficult to use in energy storage projects. Another battery technology specifically designed for energy storage applications is flow batteries: they use water as a solvent, so there is no need to worry about combustion hazards; Its power and capacity can be independently regulated, providing great application flexibility; It can maintain a long service life in deep charge discharge cycling applications, and replacing the electrolyte is very simple and convenient. Its biggest drawback compared to lithium batteries is its low energy density. However, for energy storage applications, space is generally not a problem, and relying on other advantages, flow batteries are bound to become the mainstream technology in the future.






In the following series of articles, we will begin to enter the field of flow battery technology and explore together how this energy storage technology will change the future energy storage market.





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Author Introduction:

Dr. Xie Wei, Bachelor and Master of Materials Science from Tsinghua University, and Ph.D. in Chemical Engineering from the University of Texas (Austin) in the United States. Mainly engaged in the development of energy storage batteries, has held important positions in multinational corporations and startups, led multiple research and development projects funded by the US Department of Energy, and won the 2013 US Annual 100 Best Research and Development Technology Award. Published 17 papers in top journals in materials science and energy storage, served as a reviewer for 5 international journals, and has applied for 17 international invention patents.



Introduction to ZH Energy Storage Company:

Shenzhen ZH Energy Storage Technology Co., Ltd. is committed to the research and development, promotion, and application of energy storage technology, aiming to help achieve China's goal of "carbon neutrality" through the application of electrochemical energy storage technology. In the early stages of development, the company focused on providing technical support and consulting services to the Chinese energy storage market by leveraging its accumulated industry experience and outstanding research and development capabilities in the field of energy storage. At the same time, the company focuses on conducting research and analysis on the Chinese energy storage market, and developing or introducing the most advanced and effective energy storage technologies for the Chinese market.

Company's technical research and development direction: water-based energy storage batteries, lithium-ion battery materials, fuel cells, ion exchange membranes, coatings and adhesives, membrane separation technology.

Domestic business: Technical cooperation and academic exchange between liquid flow batteries and high-energy density lithium-ion batteries, technical lectures on the company's technology research and development direction, research and development consulting, and guidance on paper writing.