Lithium battery immersion liquid cooling system and control method

Abstract

The present disclosure relates to the technical field of battery, in particular to a lithium battery immersion liquid cooling system and control method. The present disclosure comprises a sealed box, a refrigeration cycle circuit and a fluid distribution assembly, and the box is filled with a non-azeotropic mixed working medium. The fluid distribution assembly guides the working medium to flow in the box from the bottom to the top of the battery cell, and uses the temperature glide characteristics of the non-azeotropic mixed working medium in the phase change process to make the phase change temperature variation trend of the working medium match the temperature distribution trend of the battery cell from the bottom to the top, so as to realize constant heat transfer temperature difference. In addition, by setting multiple inlet and outlet branch circuits and flow regulating valves, the working medium flow is dynamically adjusted according to the real-time temperature of each battery cell, so as to realize dynamic stability of the temperature field in the box. The present disclosure solves the problem of mismatch between the existing fixed boiling point refrigerant and the temperature distribution of the battery cell, and significantly improves the cooling effect and system energy efficiency.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and in particular to a lithium battery immersion liquid cooling system and control method. Background Technology

[0002] The mainstream cooling methods for lithium batteries include air cooling, indirect liquid cooling, and immersion liquid cooling (direct liquid cooling). Immersion liquid cooling involves completely immersing the battery in coolant for cooling, resulting in better cooling effect, stronger temperature uniformity, and lower cooling energy consumption.

[0003] Immersion liquid cooling can be further divided into single-phase immersion liquid cooling and two-phase immersion liquid cooling. Two-phase immersion liquid cooling involves both gas and liquid phases, and can remove a large amount of heat through phase change, making it the most effective of the main cooling methods. In existing technologies, most two-phase immersion liquid cooling systems use a single refrigerant, thus having a fixed boiling point. However, the temperature of a battery cell varies within a certain range depending on its charge and discharge state, and the top of the cell is typically warmer than the bottom. Therefore, a single refrigerant with a fixed boiling point is not perfectly suited for this, resulting in limited and fluctuating heat exchange performance.

[0004] Existing immersion liquid cooling solutions do not consider or design the flow direction of the cooling medium, and the inlet and outlet settings are arbitrary, failing to adapt to the characteristic that the temperature at the top of the battery cell is higher than that at the bottom. In existing immersion liquid cooling solutions, a single enclosure contains multiple battery cells, but the operating conditions and aging degradation of different cells vary. However, there is only one outlet and one inlet for the cooling medium, lacking regulation of the overall temperature field distribution within the enclosure.

[0005] In summary, the key challenge is how to overcome the problems caused by the mismatch between the fixed boiling point of a single refrigerant and the temperature distribution of the battery cells, such as limited heat exchange, unreasonable fluid flow direction design, and lack of overall temperature field regulation of the enclosure. Summary of the Invention

[0006] To address the aforementioned issues, this disclosure provides a lithium battery immersion liquid cooling system and control method.

[0007] In a first aspect, a lithium battery immersion liquid cooling system includes: A sealed enclosure for housing at least one lithium battery cell; The refrigeration cycle circuit includes a compressor, condenser, expansion valve, and sealed enclosure connected in sequence by piping; A fluid distribution assembly, connected between the refrigeration cycle loop and the sealed housing, is used to control the inflow and outflow of refrigerant into and out of the sealed housing; The system is filled with a non-azeotropic working fluid. The fluid distribution component is used to guide the non-azeotropic working fluid to flow from the bottom to the top of the battery cell within the sealed housing. By utilizing the temperature slip characteristics of the non-azeotropic working fluid during the phase change process, the phase change temperature change trend of the non-azeotropic working fluid is matched with the temperature distribution trend of the battery cell from bottom to top.

[0008] Furthermore, the fluid distribution assembly includes multiple inlet branches located at the bottom of the sealed housing and multiple outlet branches located at the top.

[0009] Furthermore, flow regulating valves are installed on the inlet and outlet branches.

[0010] Furthermore, the system also includes a controller connected to a flow regulating valve. The controller is used to control the opening of the flow regulating valve based on the real-time temperature data of the battery cell, so as to regulate the flow rate of the non-azeotropic working fluid entering different battery cell regions and achieve dynamic stability of the temperature field inside the sealed enclosure.

[0011] Furthermore, the non-azeotropic working fluids include R141b refrigerant and R123 refrigerant.

[0012] Furthermore, the mass fraction ratio of R141b refrigerant to R123 refrigerant is 1:1.

[0013] Furthermore, the non-azeotropic working fluid exists in a gas-liquid two-phase mixed state within the sealed chamber; During the process of the non-azeotropic working fluid flowing from the bottom to the top of the cell, the low-boiling-point components in the non-azeotropic working fluid preferentially vaporize, and the boiling point of the remaining liquid phase components gradually increases with the vaporization process, forming a phase change temperature distribution that gradually increases along the flow direction. The direction of the boiling temperature increase is consistent with the direction of the cell temperature increase.

[0014] Furthermore, the condenser is used to utilize the variable-temperature condensation characteristics of the non-azeotropic working fluid. During the condensation process, the temperature of the non-azeotropic working fluid gradually decreases as heat is released during condensation, thereby reducing the heat exchange temperature difference between the working fluid and the cooling medium.

[0015] Secondly, a lithium battery immersion liquid cooling control method, based on the aforementioned lithium battery immersion liquid cooling system, includes: Obtain real-time temperature distribution data of each battery cell inside the sealed enclosure; Based on real-time temperature distribution data, determine the cooling requirements of each battery cell; The fluid distribution component controls the flow rate of the non-azeotropic working fluid to each cell, so that the non-azeotropic working fluid flows from the bottom to the top of the cell, and the phase change temperature of the non-azeotropic working fluid gradually increases along the flow direction to follow the temperature gradient of the cell.

[0016] Thirdly, the application of a non-azeotropic working fluid in immersion liquid cooling of lithium batteries. Non-azeotropic working fluids include R141b refrigerant and R123 refrigerant; A non-azeotropic working fluid is filled into the lithium battery immersion liquid cooling system as described above. The non-azeotropic working fluid undergoes a phase change during its flow from the bottom to the top of the cell, and the phase change temperature range covers the operating temperature range of the cell. The temperature glide characteristics of the non-azeotropic working fluid are used to match the temperature gradient of the cell.

[0017] This disclosure includes at least the following beneficial effects: This disclosure selects R141b refrigerant and R123 refrigerant (50% by mass each) as non-azeotropic refrigerants, whose boiling temperature range is highly matched with the temperature range of lithium batteries, and whose cooling effect and energy efficiency are significantly higher than those of single refrigerant and azeotropic refrigerant solutions in the past. The flow direction of the non-azeotropic refrigerant was specifically designed to flow from the bottom of the cell to the top and gradually boil, which better matches the characteristic that the temperature at the top of the cell is higher than that at the bottom, thus achieving a stable heat exchange temperature difference and better cooling effect. To address the temperature differences among the individual cells within the enclosure, multiple refrigerant inlets and outlets were designed. Based on the real-time temperature and cooling requirements of each cell, the distribution valves were dynamically adjusted to achieve dynamic stability of the temperature field within the enclosure.

[0018] Other features and advantages of this disclosure will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the disclosure. The objects and other advantages of this disclosure may be realized and obtained by means of the structures pointed out in the description and the accompanying drawings. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the liquid cooling system architecture according to an embodiment of the present disclosure; Figure 2 This is a schematic diagram of the liquid cooling principle in an embodiment of this disclosure. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0022] like Figure 1 As shown, a lithium battery immersion liquid cooling system includes: A sealed enclosure for housing at least one lithium battery cell; The refrigeration cycle circuit includes a compressor, condenser, expansion valve, and sealed enclosure connected in sequence by piping; A fluid distribution assembly, connected between the refrigeration cycle loop and the sealed housing, is used to control the inflow and outflow of refrigerant into and out of the sealed housing; The system is filled with a non-azeotropic working fluid. The fluid distribution component is used to guide the non-azeotropic working fluid to flow from the bottom to the top of the battery cell within the sealed housing. By utilizing the temperature slip characteristics of the non-azeotropic working fluid during the phase change process, the phase change temperature change trend of the non-azeotropic working fluid is matched with the temperature distribution trend of the battery cell from bottom to top.

[0023] In this embodiment, the fluid distribution assembly includes multiple inlet branches disposed at the bottom of the sealed housing and multiple outlet branches disposed at the top.

[0024] In this embodiment, flow regulating valves are provided on the inlet branch and the outlet branch.

[0025] In this embodiment, the system further includes a controller connected to a flow regulating valve. The controller is used to control the opening of the flow regulating valve according to the real-time temperature data of the battery cell, so as to regulate the flow rate of the non-azeotropic working fluid entering different battery cell regions and achieve dynamic stability of the temperature field inside the sealed box.

[0026] In this embodiment, the non-azeotropic working fluid includes R141b refrigerant and R123 refrigerant.

[0027] In this embodiment, the mass fraction ratio of R141b refrigerant to R123 refrigerant is 1:1.

[0028] In this embodiment, the non-azeotropic working fluid is in a gas-liquid two-phase mixed state inside the sealed box; During the process of the non-azeotropic working fluid flowing from the bottom to the top of the cell, the low-boiling-point components in the non-azeotropic working fluid preferentially vaporize, and the boiling point of the remaining liquid phase components gradually increases with the vaporization process, forming a phase change temperature distribution that gradually increases along the flow direction. The direction of the boiling temperature increase is consistent with the direction of the cell temperature increase.

[0029] In this embodiment, the condenser is used to utilize the variable temperature condensation characteristics of the non-azeotropic working fluid. During the condensation process, the temperature of the non-azeotropic working fluid gradually decreases as heat is released during condensation, thereby reducing the heat exchange temperature difference between the working fluid and the cooling medium.

[0030] This disclosure provides a lithium battery immersion liquid cooling control method, based on the above-mentioned lithium battery immersion liquid cooling system, including: Obtain real-time temperature distribution data of each battery cell inside the sealed enclosure; Based on real-time temperature distribution data, determine the cooling requirements of each battery cell; The fluid distribution component controls the flow rate of the non-azeotropic working fluid to each cell, so that the non-azeotropic working fluid flows from the bottom to the top of the cell, and the phase change temperature of the non-azeotropic working fluid gradually increases along the flow direction to follow the temperature gradient of the cell.

[0031] In practice: This disclosure includes a sealed enclosure, a refrigeration cycle loop, and a fluid distribution assembly. The enclosure is filled with a non-azeotropic working fluid. The fluid distribution assembly guides the working fluid to flow from the bottom to the top of the battery cell within the enclosure. Utilizing the temperature glide characteristics of the non-azeotropic working fluid during the phase change process, the phase change temperature change trend of the working fluid matches the temperature distribution trend of the battery cell from bottom to top, achieving a constant heat exchange temperature difference. Furthermore, by setting multiple inlet and outlet branches and flow regulating valves, the working fluid flow rate is dynamically adjusted according to the real-time temperature of each battery cell, achieving dynamic stability of the temperature field within the enclosure. This disclosure solves the problem of mismatch between existing fixed-boiling-point refrigerants and battery cell temperature distribution, significantly improving cooling effect and system energy efficiency.

[0032] This disclosure uses a non-azeotropic mixture of R141b and R123 as the working fluid, utilizing its "temperature glide" characteristic during phase change (i.e., the boiling temperature varies within a certain range rather than being a fixed value). By designing the refrigerant flow path from the bottom to the top of the battery cell, the phase change temperature of the working fluid increases synchronously with the increase of the battery cell temperature during the endothermic boiling process (usually the temperature at the top of the battery cell is higher than that at the bottom). This design makes the phase change temperature curve of the refrigerant highly matched with the longitudinal temperature gradient of the battery cell, thereby maintaining a stable and small heat exchange temperature difference (e.g., around 2°C) throughout the entire path. This avoids the problem of excessive heat exchange at low levels and insufficient heat exchange at high levels caused by the fixed boiling point of traditional single refrigerants, significantly improving the overall heat exchange efficiency and cooling effect.

[0033] To address the temperature differences (i.e., "hot spots") caused by varying operating conditions and degradation levels among different cells within the battery pack, this disclosure presents a multi-inlet, multi-outlet fluid distribution assembly, combined with a flow regulating valve for dynamic control. The system can allocate refrigerant flow to different areas of the battery pack based on real-time temperature monitoring data. This refined flow regulation strategy effectively eliminates localized overheating, achieving dynamic stability and uniform temperature distribution throughout the sealed enclosure. This helps suppress the bottleneck effect within the battery pack, thereby extending the overall cycle life of the lithium battery group.

[0034] This disclosure utilizes the variable temperature characteristics of the non-azeotropic working fluid not only on the evaporation side (battery housing) but also on the condensation side. In the condenser, the temperature of the non-azeotropic mixture gradually decreases during its exothermic liquefaction process, creating a favorable counter-current heat exchange balance with the gradually increasing temperature of the cooling medium (such as circulating water). Compared to a single working fluid, this balance results in a more uniform and reasonable temperature difference within the condenser, reducing irreversible heat transfer losses, thereby lowering system operating energy consumption and improving the overall energy efficiency of the cooling system.

[0035] This disclosure provides an application of a non-azeotropic working fluid in immersion liquid cooling for lithium batteries. Non-azeotropic working fluids include R141b refrigerant and R123 refrigerant; A non-azeotropic working fluid is filled into the lithium battery immersion liquid cooling system as described above. The non-azeotropic working fluid undergoes a phase change during its flow from the bottom to the top of the cell, and the phase change temperature range covers the operating temperature range of the cell. The temperature glide characteristics of the non-azeotropic working fluid are used to match the temperature gradient of the cell.

[0036] To enable those skilled in the art to better understand this disclosure, the principles of this disclosure are explained as follows: Most existing immersion liquid cooling systems use single-phase coolant, resulting in mediocre cooling performance. Even when using two-phase coolant, they typically employ only a single refrigerant or an azeotropic refrigerant.

[0037] Liquid-phase single / azeotropic refrigerant (taking single R123 refrigerant as an example, with a boiling point of 28°C) enters the immersion-type liquid-cooled sealed enclosure from the bottom. As the refrigerant cools the battery cells, it reaches its boiling point of 28°C, absorbs a large amount of heat, and transforms into a gaseous phase, forming a clear gas-liquid interface between the liquid and gas phases. The liquid and gaseous phase temperatures of the refrigerant are generally around the boiling point of 28°C. However, during operation, the battery cell temperature is typically lower at the bottom and higher at the top. Therefore, the heat exchange temperature difference and heat transfer coefficient at different locations are constantly changing, resulting in poor heat exchange efficiency.

[0038] After the cooling process, the gaseous refrigerant enters the compressor and then the condenser to dissipate heat, turning into a liquid phase. It then passes through a throttling valve and returns to the sealed enclosure, similar to the air conditioning refrigeration cycle. In the condenser heat exchanger, the refrigerant releases heat on one side and changes from a gaseous phase to a liquid phase, maintaining a constant temperature. The other side typically uses circulating cooling water, whose temperature gradually rises and carries away the heat from the refrigerant.

[0039] like Figure 1 As shown, this disclosure uses a non-azeotropic refrigerant, composed of R141b and R123 refrigerants (each 50% by mass), with a boiling temperature range of 28-32°C. The system circulation is as follows: Figure 1 As shown.

[0040] like Figure 2 As shown, the non-azeotropic liquid refrigerant is dynamically distributed via a distribution valve according to the cooling requirements of each battery cell, entering the immersion-type liquid-cooled sealed enclosure through multiple inlets at the bottom. The refrigerant cools the battery cells (top 34°C, bottom 30°C), bringing them to their boiling point (28°C-32°C). By controlling the refrigerant flow rate, the refrigerant within the enclosure can be kept in a state of continuous gas-liquid two-phase mixing and boiling, maintaining a constant temperature difference of approximately 2°C between the refrigerant and the battery cells from bottom to top, achieving excellent cooling performance and heat exchange efficiency.

[0041] After the cooling process, the non-azeotropic refrigerant is almost entirely converted to a gaseous phase, then enters the compressor and the condenser to dissipate heat, becoming a liquid phase. It then passes through a throttling valve and returns to the sealed enclosure. The difference lies in the condenser heat exchanger: on one side, the refrigerant releases heat and gradually changes from a gaseous phase to a liquid phase, with its temperature gradually decreasing; on the other side, circulating cooling water is typically used, with the water temperature gradually rising and carrying away the heat from the refrigerant. Compared to single / azeotropic refrigerants, the non-azeotropic refrigerant in the condenser has a more stable heat exchange temperature difference and higher heat exchange efficiency.

[0042] In addition, a distribution valve is also installed at the top of the cabinet, corresponding to the distribution valve at the bottom of the cabinet, which can better control the flow of non-azeotropic refrigerant in the cabinet and achieve dynamic adjustment and localized targeted cooling.

[0043] This solution specifically targets the temperature range of the battery cell, selecting a non-azeotropic refrigerant composed of R141b and R123 refrigerants. The boiling temperature range closely matches the temperature distribution from the bottom to the top of the battery cell, thus significantly improving cooling performance and heat exchange efficiency. Simultaneously, a more uniform heat exchange temperature difference and higher heat exchange efficiency are achieved in the condenser, resulting in higher overall energy efficiency for the cooling system.

[0044] This solution also specifically designs the flow direction of the non-azeotropic refrigerant to align with the temperature distribution direction of the battery cells. Furthermore, to address the temperature differences among the individual battery cells within the same enclosure due to inconsistent operating conditions, multiple refrigerant inlets and outlets are designed. The distribution valves are dynamically adjusted based on the real-time temperature and cooling requirements of each battery cell, achieving dynamic stability of the temperature distribution within the enclosure.

[0045] For the temperature range of lithium battery cells, a non-azeotropic refrigerant composed of R141b refrigerant and R123 refrigerant (each 50% by mass) is specifically selected for immersion liquid cooling to achieve continuous boiling cooling within a certain temperature range. The cooling effect and energy efficiency are significantly higher than those of single refrigerant and azeotropic refrigerant.

[0046] The flow direction of the non-azeotropic refrigerant was specifically designed so that it flows from the bottom of the cell to the top, gradually boiling and transforming into a gas phase. The direction of the boiling temperature increase is consistent with the direction of the cell temperature increase, achieving a stable heat exchange temperature difference and better cooling effect.

[0047] To address the temperature differences between individual cells within the same enclosure due to inconsistent operating conditions, multiple refrigerant inlets and outlets were designed. Based on the real-time temperature and cooling requirements of each cell, the distribution valves were dynamically adjusted to achieve dynamic stability of the temperature distribution within the enclosure.

[0048] Compared to existing immersion liquid cooling solutions, this solution has the following advantages: 1. Selecting a non-azeotropic refrigerant consisting of R141b and R123 refrigerants (50% by mass each) has a boiling temperature range that closely matches the temperature range of lithium batteries, resulting in significantly higher cooling performance and energy efficiency compared to existing single-refrigerant and azeotropic refrigerant solutions. 2. Existing immersion liquid cooling solutions do not consider or design the flow direction of the cooling medium, and the inlet and outlet settings are arbitrary. This solution specifically designs the flow direction of the non-azeotropic refrigerant, allowing it to flow from the bottom of the cell to the top and gradually boil, better matching the characteristic that the temperature at the top of the cell is higher than that at the bottom, thus achieving a stable heat exchange temperature difference and better cooling effect; 3. Existing immersion liquid cooling solutions have only one outlet and one inlet for the cooling medium, lacking adjustment of the temperature field distribution within the enclosure. This solution addresses the temperature differences among the individual cells within the enclosure by designing multiple refrigerant inlets and outlets. Based on the real-time temperature and cooling requirements of each cell, the distribution valves are dynamically adjusted to achieve dynamic stability of the temperature field within the enclosure.

[0049] Although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A lithium battery immersion liquid cooling system, characterized in that, include: A sealed enclosure for housing at least one lithium battery cell; The refrigeration cycle circuit includes a compressor, condenser, expansion valve, and sealed enclosure connected in sequence by piping; A fluid distribution assembly, connected between the refrigeration cycle loop and the sealed housing, is used to control the inflow and outflow of refrigerant into and out of the sealed housing; The system is filled with a non-azeotropic working fluid. The fluid distribution component is used to guide the non-azeotropic working fluid to flow from the bottom to the top of the battery cell within the sealed housing. By utilizing the temperature slip characteristics of the non-azeotropic working fluid during the phase change process, the phase change temperature change trend of the non-azeotropic working fluid is matched with the temperature distribution trend of the battery cell from bottom to top.

2. The lithium battery immersion liquid cooling system as described in claim 1, characterized in that, The fluid distribution assembly includes multiple inlet branches located at the bottom of the sealed housing and multiple outlet branches located at the top.

3. The lithium battery immersion liquid cooling system as described in claim 2, characterized in that, Flow regulating valves are installed on the inlet and outlet branches.

4. The lithium battery immersion liquid cooling system as described in claim 3, characterized in that, The system also includes a controller connected to a flow regulating valve. The controller controls the opening of the flow regulating valve based on the real-time temperature data of the battery cells to adjust the flow rate of the non-azeotropic working fluid entering different battery cell regions, thereby achieving dynamic stability of the temperature field inside the sealed enclosure.

5. The lithium battery immersion liquid cooling system as described in claim 1, characterized in that, Non-azeotropic working fluids include R141b refrigerant and R123 refrigerant.

6. The lithium battery immersion liquid cooling system as described in claim 5, characterized in that, The mass fraction ratio of R141b refrigerant to R123 refrigerant is 1:

1.

7. The lithium battery immersion liquid cooling system as described in claim 1, characterized in that, The non-azeotropic working fluid exists in a gas-liquid two-phase mixed state within the sealed chamber; During the process of the non-azeotropic working fluid flowing from the bottom to the top of the cell, the low-boiling-point components in the non-azeotropic working fluid preferentially vaporize, and the boiling point of the remaining liquid phase components gradually increases with the vaporization process, forming a phase change temperature distribution that gradually increases along the flow direction. The direction of the boiling temperature increase is consistent with the direction of the cell temperature increase.

8. The lithium battery immersion liquid cooling system as described in claim 1, characterized in that, Condensers are used to utilize the variable-temperature condensation characteristics of non-azeotropic working fluids. During the condensation process, the temperature of the non-azeotropic working fluid gradually decreases as heat is released during condensation, thereby reducing the heat exchange temperature difference between it and the cooling medium.

9. A method for controlling immersion liquid cooling of lithium batteries, characterized in that, A lithium battery immersion liquid cooling system according to any one of claims 1-8 includes: Obtain real-time temperature distribution data of each battery cell inside the sealed enclosure; Based on real-time temperature distribution data, determine the cooling requirements of each battery cell; The fluid distribution component controls the flow rate of the non-azeotropic working fluid to each cell, so that the non-azeotropic working fluid flows from the bottom to the top of the cell, and the phase change temperature of the non-azeotropic working fluid gradually increases along the flow direction to follow the temperature gradient of the cell.

10. The application of a non-azeotropic working fluid in immersion liquid cooling of lithium batteries, characterized in that, Non-azeotropic working fluids include R141b refrigerant and R123 refrigerant; A non-azeotropic working fluid is filled into the lithium battery immersion liquid cooling system as described in any one of claims 1-8. The non-azeotropic working fluid undergoes a phase change during its flow from the bottom to the top of the cell, and the phase change temperature range covers the operating temperature range of the cell. The temperature glide characteristics of the non-azeotropic working fluid are used to match the temperature gradient of the cell.

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