Battery cell with uniform temperature characteristic

Abstract

The invention provides a battery cell with uniform temperature characteristic, the battery cell is provided with a heat dissipation surface and a heat transfer path which are perpendicular to each other, the temperature difference between two ends of the heat transfer path is less than or equal to 5 DEG C, and the ratio of the area of the heat dissipation surface to the length of the heat transfer path is 0.11-6 m. The method provides a direction for the size design of the battery cell, and can scientifically quantify the ratio of the area of the heat dissipation surface of the battery cell to the length of the heat transfer path by limiting the temperature rise and the temperature difference of the battery cell, so that the size design direction of the battery cell is optimized, the design efficiency and the heat dissipation performance of the battery cell are improved, and the cycle life of the battery cell is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a battery cell with a uniform temperature characteristic. Background Art

[0002] With the development of electrochemical energy storage technology, under the pressure of reducing costs and increasing efficiency, battery companies and system integrators have flocked to the track of larger capacity batteries and higher capacity energy storage systems. The research and development of larger capacity, safer and longer life large-capacity batteries has become a starting point for battery companies to build core competitiveness. As the smallest unit of the energy storage system, the battery cell directly affects the life and safety of the energy storage system.

[0003] For lithium batteries, operating temperature and temperature consistency have a significant impact on their efficiency, life and safety. The optimal operating temperature range of lithium batteries is 10-35°C. Too high a temperature will accelerate the attenuation rate of lithium batteries, reduce the cycle life of the battery cells, and in severe cases will cause thermal runaway. In addition, the inconsistency of the battery cell temperature will directly reduce the service life of the system. A research report shows that when the temperature difference of each battery cell in the module reaches 5°C, the life of the module is reduced by 30% compared to the life of the module with a temperature difference controlled within 2°C. The maximum temperature difference exceeding 5°C will form a hot spot inside the module, seriously affecting the safety and life of the battery cell. Summary of the invention

[0004] The object of the present invention is to provide a battery cell with a uniform temperature characteristic, by limiting the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path by limiting the temperature rise of the battery cell, so as to better guide the design of the battery cell size and improve the safety and service life of the battery cell.

[0005] The technical solution of the present invention includes: a battery cell with uniform temperature characteristics, the battery cell has a heat dissipation surface and a heat transfer path that are perpendicular to each other, the temperature difference at both ends of the heat transfer path is ≤5°C, and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 0.111~6m.

[0006] Specifically, the battery cell is a square battery cell with internal structural layers stacked in a transverse direction, the product of the height, width and thickness of the square battery cell is constant, and the width is greater than the thickness.

[0007] Specifically, the area of ​​the heat dissipation surface is the product of the width and thickness of the square battery cell.

[0008] The length of the heat transfer path is the height of the square battery cell.

[0009] The ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 0.111-1 m.

[0010] Specifically, the temperature difference between the two ends of the heat transfer path is ≤3° C., and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 0.25-0.58 m.

[0011] Specifically, the maximum temperature rise of the square battery core is ≤3° C., and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥0.3 m.

[0012] Specifically, the area of ​​the heat dissipation surface is the product of the height and width of the square battery cell.

[0013] The length of the heat transfer path is the thickness of the square battery cell.

[0014] The ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 1 to 6 m.

[0015] Specifically, the temperature difference between the two ends of the heat transfer path is ≤3° C., the maximum temperature rise of the square battery cell is ≤3° C., and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 2.4 to 3.7 m.

[0016] The beneficial effects of the present invention are as follows: the two thermal management methods of bottom liquid cooling and side liquid cooling of square battery cells provide direction for battery cell size design, and by limiting the temperature rise and temperature difference of the battery cells, the ratio of the area of ​​the battery cell heat dissipation surface to the length of the heat transfer path can be scientifically quantified, thereby optimizing the battery cell size design direction, improving the battery cell design efficiency and heat dissipation performance, and extending the cycle life of the battery cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the structure of a battery cell in an embodiment of the present invention;

[0018] Figure 2 It is a line graph of the maximum temperature rise and the area of ​​the heat dissipation surface / the length of the heat transfer path of the battery cells of the embodiment of the present invention and the comparative example when the bottom surface is liquid-cooled;

[0019] Figure 3 It is a line graph of the temperature difference at both ends of the heat transfer path and the area of ​​the heat dissipation surface / the length of the heat transfer path when the battery cells of the embodiment of the present invention and the comparative example are liquid-cooled on the bottom surface;

[0020] Figure 4 It is a line graph of the pole temperature difference and the area of ​​the heat dissipation surface / the length of the heat transfer path when the battery cells of the embodiment of the present invention and the comparative example are liquid-cooled on the bottom surface;

[0021] Figure 5 It is a line graph of the maximum temperature rise of the battery cells of the embodiment of the present invention and the comparative example when the side liquid is cooled and the area of ​​the heat dissipation surface / the length of the heat transfer path;

[0022] Figure 6It is a line graph of the temperature difference at both ends of the heat transfer path and the area of ​​the heat dissipation surface / the length of the heat transfer path when the battery cells of the embodiment of the present invention and the comparative example are liquid-cooled on the side;

[0023] Figure 7 It is a line graph of the pole temperature difference and the area of ​​the heat dissipation surface / the length of the heat transfer path when the battery cells of the embodiments of the present invention and the comparative examples are liquid-cooled on the side. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the embodiments of the present invention, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings and other implementation methods can be obtained based on these accompanying drawings without creative work.

[0025] Currently, the cooling methods of energy storage battery boxes on the market are mainly air cooling and liquid cooling. Air cooling has low and uneven heat dissipation efficiency and can no longer meet the heat dissipation requirements of high-power batteries. Liquid cooling has high heat dissipation efficiency and is effective in reducing the maximum temperature of batteries and improving the temperature consistency of battery modules. Liquid cooling will be an important research direction for thermal management of high-power lithium batteries under complex working conditions in the future. However, the thermal conductivity of batteries is low, so the technical solution of this application is mainly aimed at improving the temperature rise and temperature consistency of batteries by adjusting the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path when using liquid cooling thermal management.

[0026] Reference Figure 1 The battery cell with uniform temperature characteristics of the present invention is described in detail by taking a square battery cell as an example. The internal structural layers (such as pole pieces, diaphragms, electrolyte layers, etc.) of the square battery cell are stacked in the horizontal direction, and the product of the height, width and thickness is constant, and the width is greater than the thickness. Due to the difference in the properties of the structural layers, there is a large difference in the heat transfer efficiency within the layer and the heat transfer efficiency between the layers. Therefore, this embodiment will respectively explain the technical solutions in which the heat transfer path is mainly heat transfer within the layer and the heat transfer path is mainly heat transfer between the layers.

[0027] When the bottom liquid cooling solution is adopted, the heat dissipation surface of the square battery cell is the bottom surface, and its heat transfer path is perpendicular to the bottom surface, which is mainly intra-layer heat transfer. Therefore, at this time: the area of ​​its heat dissipation surface = width × thickness, and the length of the heat transfer path = height; when the side liquid cooling solution is adopted, the heat dissipation surface of the square battery cell is the side surface, and its heat transfer path is perpendicular to the side surface, which is mainly inter-layer heat transfer. In order to improve the liquid cooling effect, a liquid cooling structure is usually constructed on the side with a larger area. Therefore, at this time: the area of ​​its heat dissipation surface = height × width, and the length of the heat transfer path = thickness.

[0028] (1) For the bottom liquid cooling solution, the size of the battery cell is optimized according to the battery cell temperature rise specification: the thickness of the battery cell is fixed, and the ratio of the area of ​​the battery cell heat dissipation surface to the length of the heat transfer path is changed by adjusting the height and width of the battery cell. The square battery cells are assembled into a 1P52S square module, and the square module is charged and discharged at 0.5P. The maximum temperature rise, the temperature difference at both ends of the heat transfer path, and the pole temperature difference of different battery cells are recorded in Table 1.

[0029] Table 1 - Temperature records under 0.5P discharge for 2 hours

[0030]

[0031] It can be seen from Table 1 that when the area of ​​the heat dissipation surface = width × thickness and the length of the heat transfer path = height, as the width of the battery cell increases, the height of the battery cell continues to decrease, that is, the area of ​​the heat dissipation surface of the battery cell increases and the length of the heat transfer path decreases, the maximum temperature rise, the temperature difference at both ends of the heat transfer path and the temperature difference of the poles all continue to decrease.

[0032] Plot the data as a line graph (such as Figure 2-4 As shown in the figure, it can be found intuitively that as the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path increases, the maximum temperature rise, the temperature difference at both ends of the heat transfer path and the pole temperature difference all show a trend of getting smaller and smaller, and gradually tend to balance.

[0033] Take a point on the line graph. When the square battery cell adopts the bottom surface heat dissipation method, when the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥0.111m, the temperature difference at both ends of the heat transfer path is ≤5℃, the consistency of the battery cell body is good, and the safety and normal service life of the battery cell can be guaranteed; when the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥0.25m, the temperature difference at both ends of the heat transfer path is ≤3℃, and the pole temperature difference is ≤1.5℃. The consistency of the battery cell body is good, which can ensure the safety and normal service life of the battery cell; when the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥0.14m, the maximum temperature rise is ≤5℃, and the working temperature of the battery cell is appropriate. When the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥0.3m, the maximum temperature rise is ≤3℃, and the working temperature of the battery cell is further reduced, which can effectively ensure the stable performance of its performance.

[0034] When the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥0.58m, the maximum temperature rise, the temperature difference at both ends of the heat transfer path and the pole temperature difference gradually tend to balance. Therefore, considering the process difficulty, cost and performance improvement, when the square battery cell adopts the bottom surface heat dissipation method, the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path can be adjusted in the range of 0.111 to 0.58m according to the requirements of the battery cell temperature rise and temperature difference, to ensure that the battery cell is always in the appropriate operating temperature range, and effectively avoid the adverse effects of heat accumulation and uneven temperature on the battery cell cycle.

[0035] (2) For the side liquid cooling solution, the size of the battery cell is optimized according to the battery cell temperature rise specification: the height of the battery cell is fixed, and the ratio of the area of ​​the battery cell heat dissipation surface to the length of the heat transfer path is changed by adjusting the width and thickness of the battery cell. The square battery cells are assembled into a 1P52S square module, and the square module is charged and discharged at 0.5P. The maximum temperature rise, the temperature difference at both ends of the heat transfer path, and the pole temperature difference of different battery cells are recorded in Table 2.

[0036] Table 2 - Temperature records under 0.5P discharge for 2 hours

[0037]

[0038]

[0039] It can be seen from Table 2 that when the area of ​​the heat dissipation surface = height × width and the length of the heat transfer path = thickness, as the width of the battery cell increases, the thickness of the battery cell continues to decrease, that is, the area of ​​the heat dissipation surface of the battery cell increases and the length of the heat transfer path decreases, the maximum temperature rise, the temperature difference at both ends of the heat transfer path and the temperature difference of the poles all continue to decrease.

[0040] Plot the data as a line graph (such as Figure 5-7 As shown in the figure, it can be found intuitively that as the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path increases, the maximum temperature rise, the temperature difference at both ends of the heat transfer path and the pole temperature difference all show a trend of getting smaller and smaller, and gradually tend to balance.

[0041] Take a point on the line graph. When the square battery cell adopts the side heat dissipation method, when the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥1.3m, the temperature difference at both ends of the heat transfer path is ≤5℃, the consistency of the battery cell body is good, and the safety and normal service life of the battery cell can be guaranteed; when the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥2.4m, the temperature difference at both ends of the heat transfer path is ≤3℃, the pole temperature difference is ≤1.2℃, the consistency of the battery cell body is good, and the safety and normal service life of the battery cell can be guaranteed; when the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥1.3m, the maximum temperature rise is ≤5℃, and the working temperature of the battery cell is appropriate. When the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥2.4m, the maximum temperature rise is ≤3℃, and the working temperature of the battery cell is further reduced, which can ensure the stable performance of its performance.

[0042] When the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥3.7m, the maximum temperature rise, the temperature difference at both ends of the heat transfer path and the pole temperature difference gradually tend to balance. Therefore, considering the process difficulty, cost and performance improvement, when the square battery cell adopts the side heat dissipation method, the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path can be adjusted in the range of 2.4 to 3.7m according to the requirements of the battery cell temperature rise and temperature difference, to ensure that the battery cell is always in the appropriate operating temperature range, and effectively avoid the adverse effects of heat accumulation and uneven temperature on the battery cell cycle.

[0043] The beneficial effects of the embodiments of the present invention are as follows: the two thermal management methods of bottom liquid cooling and side liquid cooling of square battery cells provide direction for battery cell size design. By limiting the temperature rise and temperature difference of the battery cells, the ratio of the area of ​​the battery cell heat dissipation surface to the length of the heat transfer path can be scientifically quantified, thereby optimizing the battery cell size design direction, improving the battery cell design efficiency and heat dissipation performance, and extending the cycle life of the battery cells.

[0044] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A battery cell with uniform temperature characteristics, characterized in that: The battery core has a heat dissipation surface and a heat transfer path which are perpendicular to each other, the temperature difference between the two ends of the heat transfer path is ≤5°C, and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 0.111-6m.

2. The battery cell with uniform temperature characteristics according to claim 1, characterized in that: The battery cell is a square battery cell with internal structural layers stacked in a transverse direction. The product of the height, width and thickness of the square battery cell is constant, and the width is greater than the thickness.

3. The battery cell with uniform temperature characteristics according to claim 2, characterized in that: The area of ​​the heat dissipation surface is the product of the width and thickness of the square battery cell. The length of the heat transfer path is the height of the square battery cell. The ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 0.111-1 m.

4. The battery cell with uniform temperature characteristics according to claim 3, characterized in that: The temperature difference between the two ends of the heat transfer path is ≤3°C, and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 0.25-0.58m.

5. The battery cell with uniform temperature characteristics according to claim 3 or 4, characterized in that: The maximum temperature rise of the square battery core is ≤3°C, and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is ≥0.3m.

6. The battery cell with uniform temperature characteristics according to claim 2, characterized in that: The area of ​​the heat dissipation surface is the product of the height and width of the square battery cell. The length of the heat transfer path is the thickness of the square battery cell. The ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 1 to 6 m.

7. The battery cell with uniform temperature characteristics according to claim 5, characterized in that: The temperature difference between the two ends of the heat transfer path is ≤3°C, the maximum temperature rise of the square battery cell is ≤3°C, and the ratio of the area of ​​the heat dissipation surface to the length of the heat transfer path is 2.4-3.7m.

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