Recently, the editor has noticed that many companies are paying attention to and planning immersion liquid cooling energy storage. After a period of silence, immersion liquid cooling technology has attracted attention again and seems to be becoming popular again. I believe that many peers are also paying attention to this development.

1- Features of immersion liquid cooling technology

Energy storage cells are moving towards 300+Ah, and energy storage systems are moving towards 5MWh+. The larger the cell, the more heat it generates, the more difficult it is to dissipate heat, and the more difficult it is to ensure temperature consistency. In addition, the energy storage system is composed of a large number of stacked cells, and the operating conditions are complex and changeable, which is more likely to cause uneven heat generation and uneven temperature distribution. If the problems of heat dissipation and temperature uniformity are not properly solved, the battery's charging and discharging performance, capacity and life will decline, affecting the performance of the entire system. In addition, safety has always been the "Sword of Damocles" hanging over lithium battery energy storage, and the most common way to improve safety is to move towards the three dimensions of intrinsic safety, active safety, and passive safety.

Immersion liquid cooling is to immerse the battery cell in an insulating, non-toxic, heat-dissipating liquid. The coolant has a higher thermal conductivity and specific heat capacity. This direct contact method can provide extremely high heat transfer efficiency while also improving better temperature uniformity. In addition, in addition to being a temperature control medium, the coolant can also be used as a fire-fighting fluid for energy storage systems, combining temperature control and fire protection, which is also a significant feature of immersion liquid cooling technology. Immersion liquid cooling will undoubtedly have more advantages in the context of an industry that requires higher heat dissipation performance and stronger safety.

Figure 1: Immersed liquid-cooled energy storage battery Pack box

2- Immersed liquid cooling energy storage system solution

As a branch of liquid cooling technology, immersion liquid cooling technology is not the first to be used in the energy storage industry. It was initially used in the field of high-performance computing, and later gradually expanded to data centers, artificial intelligence, cryptocurrency, etc.

The original intention of the design of the immersion liquid cooling energy storage system is to solve the shortcomings of traditional air cooling and indirect liquid cooling in cooling efficiency and battery temperature difference control. The official commissioning of the Southern Power Grid Meizhou Baohu project marks the successful application of immersion liquid cooling, a cutting-edge technology, in the field of new energy storage engineering.

l Cooling method and coolant circulation method

The cooling methods are divided into single-phase and phase change. Single-phase immersion liquid cooling is used, mainly including mineral oil, silicone oil, natural ester, etc. Other schemes use two-phase immersion liquid cooling, mainly represented by hydrofluoroether, and use phase change latent heat to dissipate heat and improve heat dissipation efficiency. According to incomplete statistics, the "single-phase immersion cooling" scheme is the most common among the currently released immersion liquid cooling energy storage systems.

According to the difference in the circulation mode of the coolant, there are three technical routes in single-phase immersion liquid cooling: natural convection, pump drive, and immersion coupled cold plate liquid cooling. Natural convection uses the characteristics of liquid volume expansion and density reduction after heating to achieve the floating of hot coolant and sinking after cooling, thereby completing the circulation heat dissipation; the core of the pump drive system is that the liquid cooling unit drives the coolant to circulate between the liquid cooling pipeline and the battery immersion box to complete the entire circulation heat dissipation process; and in the immersion coupled plate liquid cooling scheme, the battery is immersed in the dielectric fluid, and the cold plate in contact with the dielectric fluid is used to take away the heat, avoiding the use of complex secondary circuits to cool the dielectric fluid.

l Product form and integration solution

The integration solution iteration of the immersion liquid-cooled energy storage system is a process from the whole to the part and then to the details. Each step is optimized and improved on the basis of the previous stage to achieve higher performance and safety.

From the cabin level to the pack level, the system integration technology presents the characteristics of scene customization. The diversification of energy storage scenarios makes the demand for energy storage systems different. A single product cannot meet market demand. The modular design allows energy storage products to be optimized and expanded according to the scale and power demand of the project, allowing energy storage solutions to be quickly adjusted and deployed according to different application scenarios and needs.

3-Challenges and implementation scenarios in the industrialization process

Immersed liquid-cooled energy storage systems face many challenges during the commercialization process, including economic feasibility, technical complexity, market acceptance, and industry chain maturity.

l Technical complexity: Compared with cold plate liquid cooling systems, immersion liquid cooling systems are more complex to design and implement.

l Industry chain maturity: The industry chain of immersion liquid cooling technology is not yet fully mature, which limits its application in a wider range of fields. The maturity of the industry chain directly affects the promotion and commercialization of the technology.

l Economic challenges: The energy storage industry is still in the early stages of commercial development, and the lack of profitability makes it difficult for high-cost technology routes to be favored by the market. Many companies compete with low prices for temporary orders, which limits the penetration of immersion liquid cooling.

At present, the main market of the energy storage industry is still dominated by air cooling and cold plate liquid cooling, and immersion liquid cooling has not yet been fully accepted by the market. Although the market penetration and acceptance of immersion liquid cooling technology are not high, it may not show considerable potential in some special scenarios, such as:

l Hazardous chemicals industry: Hazardous chemicals companies have extremely strict safety controls on energy storage equipment, because most of the chemicals they produce and store are highly flammable, explosive, toxic or corrosive. Once an accident occurs, it will not only cause serious losses to the company itself, but may also cause environmental pollution and harm to surrounding communities.

l Base stations and data centers: Base stations and data centers have a low tolerance for thermal runaway. Data center energy storage systems must have batteries with stable performance and are not prone to thermal runaway to ensure system safety. The requirements for power quality are high, and the energy storage system needs to have a fast response capability. In the event of an emergency such as a grid failure or power outage, the energy storage system must be able to directly switch to discharge mode to ensure the continuity and stability of power.

l Fast charging station: When charging and discharging at high rates, the battery generates a large amount of heat in a short period of time, which will cause the battery temperature to be too high and uneven, posing a threat to the battery's performance, life and safety. This means that battery thermal management becomes particularly important in high-rate charging and discharging scenarios.

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