Battery pack, energy storage device and method for monitoring state of charge of battery pack

Abstract

The embodiment of the invention provides a battery pack, an energy storage device and a method for monitoring the state of charge of the battery pack, the battery pack comprises a plurality of battery cells, each battery cell comprises a shell, a positive tab and a negative tab, the positive tab and the negative tab are contained in the shell, and the battery cells comprise a sodium ion battery and a lithium ion battery. The negative tab of the sodium ion battery is electrically connected with the shell of the sodium ion battery, the positive tab of the lithium ion battery is electrically connected with the shell of the lithium ion battery, and the shell of the sodium ion battery is electrically connected with the shell of the lithium ion battery. According to the lithium iron phosphate battery system, the sodium ion battery is introduced into the lithium iron phosphate battery system to reduce the cost, and the sodium ion battery and the lithium iron phosphate battery are integrated without wire connection, so that the connection complexity and the total internal resistance can be reduced. In addition, the estimation precision of the SOC of the battery pack is estimated through the charge-discharge curve of the sodium ion battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a battery pack, an energy storage device, and a method for monitoring the state of charge of the battery pack. Background Technology

[0002] Among related technologies, lithium-ion batteries are widely used due to their reasonable price and mature technology. However, lithium-ion batteries have a relatively long charge and discharge plateau during the charging and discharging process. The voltage SOC-OCV (State of Charge-Voltage) curve of the cell during the charging and discharging process is flat and has a small slope. This leads to a large error in the accuracy of the BMS (Battery Management System) when monitoring the SOC of the battery pack using the voltage of the lithium-ion battery. Inaccurate SOC measurement of the battery pack can lead to overcharging and over-discharging of the battery pack, resulting in damage to the battery pack. Moreover, inaccurate SOC measurement of the battery pack will reduce the system performance and reliability of the energy storage system using the battery pack, and will also cause the vehicle using the battery pack to make incorrect range estimations, resulting in low battery utilization efficiency. Therefore, inaccurate SOC measurement of the battery pack seriously affects the user experience. Summary of the Invention

[0003] Embodiments of this application provide a battery pack, an energy storage device, and a method for monitoring the state of charge (SOC) of the battery pack, thereby improving the accuracy of SOC detection for the battery pack.

[0004] In a first aspect, embodiments of this application provide a battery pack, which includes multiple battery cells. Each battery cell includes a housing and a positive electrode tab and a negative electrode tab housed within the housing. The multiple battery cells include sodium-ion batteries and lithium-ion batteries. The negative electrode tab of the sodium-ion battery is electrically connected to the housing of the sodium-ion battery, the positive electrode tab of the lithium-ion battery is electrically connected to the housing of the lithium-ion battery, and the housing of the sodium-ion battery is electrically connected to the housing of the lithium-ion battery.

[0005] In this embodiment, since the negative electrode tab of the sodium-ion battery is electrically connected to its casing, the casing can be considered the negative terminal of the sodium-ion battery. Similarly, since the positive electrode tab of the lithium-ion battery is electrically connected to its casing, the casing can be considered the positive terminal. Therefore, when the casings of the sodium-ion and lithium-ion batteries are in contact, it can be considered that the negative terminal of the sodium-ion battery and the positive terminal of the lithium-ion battery are electrically connected, thus representing a series connection between the sodium-ion and lithium-ion batteries. Because the voltage of the sodium-ion battery changes at a relatively steep rate during charging and discharging, there is a good correlation between the sodium-ion battery voltage and the state of charge (SOC) of the battery pack. Therefore, the BMS can more accurately and reliably monitor the SOC of the battery pack using the sodium-ion battery voltage. Thus, in this embodiment, by connecting the sodium-ion and lithium-ion batteries in series, the SOC of the battery pack can be accurately monitored by monitoring the voltage of the sodium-ion battery, effectively solving the problem of low accuracy in monitoring the SOC of the battery pack.

[0006] In some embodiments, the battery pack further includes a battery management unit (BMU) for collecting voltage data from the sodium-ion batteries and calculating the state of charge (SOC) of the battery pack based on this data. In this embodiment, because the voltage change slope during the charging and discharging process of the sodium-ion batteries is relatively large, real-time voltage data during charging and discharging can be accurately detected. The BMU then collects this voltage data and feeds it back to the data processing module, which calculates the SOC of the battery pack based on the voltage data collected by the BMU. This allows for real-time and accurate monitoring of the SOC of the battery pack in this embodiment.

[0007] In some embodiments, the battery management unit includes a first voltage acquisition line and a second voltage acquisition line, the first voltage acquisition line being electrically connected to the positive terminal of the sodium-ion battery, and the second voltage acquisition line being electrically connected to the casing of the sodium-ion battery or the casing of the lithium-ion battery.

[0008] In some embodiments, the voltage acquisition line includes a first voltage acquisition line, a third voltage acquisition line, and a second voltage acquisition line. The first voltage acquisition line is connected to the positive terminal of the sodium-ion battery, and the third voltage acquisition line is connected to the negative terminal of the lithium iron phosphate battery. The second voltage acquisition line is connected to the surface of the sodium-ion battery casing or the surface of the lithium-ion battery casing. In this embodiment, because the voltage change slope of the sodium-ion battery during charging and discharging is relatively large, there is a good correspondence between the voltage of the sodium-ion battery and the SOC state of the battery pack. Therefore, the voltage of the sodium-ion battery between the first and second voltage acquisition lines, as well as the total voltage of the sodium-ion battery and the lithium iron phosphate battery connected in series between the third and first voltage acquisition lines, can be accurately monitored. Thus, by monitoring the voltage of the sodium-ion battery between the first and second voltage acquisition lines, or the total voltage of the sodium-ion battery and the lithium iron phosphate battery connected in series between the third and first voltage acquisition lines, accurate prediction of the SOC of the battery pack can be achieved.

[0009] In some embodiments, the casings of the sodium-ion battery and the lithium-ion battery are arranged along a first direction, with the length direction of both the lithium-ion and sodium-ion batteries being the same as the first direction. In this embodiment, the arrangement of the casings of the sodium-ion and lithium-ion batteries along the first direction not only facilitates the connection between the sodium-ion and lithium-ion batteries but also meets the arrangement requirements of the sodium-ion and lithium-ion batteries in certain specific scenarios.

[0010] In some embodiments, the first direction is the same as the width direction of the battery pack. In this embodiment, since the first direction is the width direction of the battery pack, and the arrangement direction of the sodium-ion batteries and lithium-ion batteries is the first direction, the arrangement can be more reasonable when the lengths of the sodium-ion batteries and lithium-ion batteries are different.

[0011] In some embodiments, the width of the lithium-ion battery is the same as the width of the sodium-ion battery, and the height of the lithium-ion battery is the same as the height of the sodium-ion battery. The sodium-ion battery and the lithium-ion battery are arranged facing each other in the first direction. In this embodiment, because the sodium-ion battery and the lithium-ion battery are arranged facing each other in the first direction, it is beneficial to make the overall layout of the sodium-ion battery and the lithium-ion battery more reasonable.

[0012] In some embodiments, the sodium-ion battery is longer than the lithium-ion battery, and the sodium-ion battery has the same capacity and charge / discharge rate as the lithium-ion battery. In this embodiment, the sodium-ion battery has the same capacity and charge / discharge rate as the lithium-ion battery. The series-connected battery pack can achieve a more balanced current distribution and more efficient energy utilization. This avoids energy waste and performance inconsistencies caused by differences between battery cells.

[0013] In some embodiments, the sodium-ion battery casing includes a first top wall, a first bottom wall, and a plurality of first side walls connected between the first top wall and the first bottom wall. The first top wall and the first bottom wall are arranged opposite each other in a first direction, and the first bottom wall, the first top wall, and the plurality of first side walls form a first sealed cavity. The lithium-ion battery casing includes a second top wall and a plurality of second side walls. The second top wall and the first bottom wall are arranged opposite each other in a first direction, and the plurality of second side walls are connected between the first bottom wall and the second top wall, and the three together form a second sealed cavity. In this embodiment, since the first bottom wall is both part of the first sealed cavity and part of the second sealed cavity, and the sodium-ion battery and the lithium-ion battery are arranged along the first direction, the lithium-ion battery casing does not need to have an additional bottom wall to form the second sealed cavity with the plurality of second side walls and the second top wall. If the bottom wall of the second casing were to be provided, it would have a certain thickness. Since the second casing does not need an additional bottom wall, the length of the second casing in the first direction can be effectively reduced, thereby effectively reducing the overall length of the sodium-ion battery and the lithium-ion battery in the first direction after arrangement. This can effectively improve the energy density of the battery pack. Furthermore, the lithium-ion battery casing saves on the cost of casing materials because it eliminates the need for a bottom wall.

[0014] In some embodiments, the lithium iron phosphate battery casing is defined as having a height of H1, a width of T1, and a length of L1. The sodium-ion battery casing is defined as having a height of H2, a width of T2, and a length of L2. L2 = XL2, where X = 1.2-3, to ensure that the lithium iron phosphate and sodium-ion batteries operate within the same voltage range and have the same charge / discharge capacity.

[0015] In some embodiments, the first bottom wall is welded to the first side wall, and the first bottom wall is welded to the second side wall. In this embodiment, welding allows for a convenient and quick connection of the first bottom wall, the first side wall, and the second side wall together. It is understood that in other embodiments, the first bottom wall, the first side wall, and the second side wall may be integrally injection molded. Alternatively, the first bottom wall and the first side wall may be integrally injection molded, while the second side wall is welded to the first bottom wall.

[0016] In some embodiments, the negative electrode tab of the sodium-ion battery is electrically connected to the first bottom wall, and the positive electrode tab of the lithium-ion battery is electrically connected to the first bottom wall. In this embodiment, because both the negative electrode tab of the sodium-ion battery and the first bottom wall are electrically connected, the first bottom wall can be considered as both the positive and negative electrode posts of the sodium-ion battery, thus achieving a series connection between the sodium-ion and lithium-ion batteries. Compared to the indirect connection between the negative electrode tab of the sodium-ion battery and the positive electrode tab of the lithium-ion battery through contact between the casings of the sodium-ion and lithium-ion batteries, this embodiment, with both the negative electrode tab and the positive electrode tab of the lithium-ion battery electrically connected, effectively reduces or avoids contact resistance, thereby further reducing internal losses in both the sodium-ion and lithium-ion batteries.

[0017] In some embodiments, the sodium-ion battery further includes a positive terminal post disposed on the first top wall, which is electrically connected to the positive tab of the sodium-ion battery. The lithium-ion battery further includes a negative terminal post disposed on the second top wall, which is electrically connected to the negative tab of the lithium-ion battery. This design of the position of the positive terminal post of the sodium-ion battery and the negative terminal post of the lithium-ion battery allows for a more rational layout of the two batteries, resulting in a more rational overall structure after their connection. Furthermore, since the first direction is the same as the width direction of the battery pack, placing the positive terminal post on the first top wall and the negative terminal post on the second top wall effectively reduces the height dimension of the battery pack. Therefore, when the battery pack is applied to a vehicle, its vertical proportion can be effectively reduced, thereby effectively increasing the size of the vehicle's passenger compartment.

[0018] In some embodiments, the lithium-ion battery is a lithium iron phosphate battery, and the sodium-ion battery has an aluminum casing. The negative electrode of the sodium-ion battery is electrically connected to its casing, and the positive electrode of the lithium iron phosphate battery is also electrically connected to its casing. Furthermore, the casings of the sodium-ion and lithium iron phosphate batteries are in contact and electrically connected. In this embodiment, because the sodium-ion battery casing is aluminum and the positive electrode material is a sodium-containing compound or polymer, the sodium-ion battery casing will not undergo an intercalation reaction with sodium ions in the electrolyte at either high or low potentials. Therefore, the electrical connection between the negative electrode and the casing of the sodium-ion battery does not affect the overall stability of the sodium-ion battery. Similarly, because the lithium-ion battery casing is aluminum and the positive electrode material is a lithium-containing compound or polymer, the lithium-ion battery casing will not undergo an intercalation reaction with lithium ions at high potentials. Thus, the electrical connection between the positive electrode and the casing of the lithium-ion battery still ensures the stability of the lithium-ion battery. Sodium-ion and lithium-ion batteries can be connected in series by making their casings in contact, thus avoiding the use of wires, reducing internal losses caused by wires, and simplifying the series connection. This also ensures the stability of both the sodium-ion and lithium-ion batteries.

[0019] Furthermore, because sodium-ion batteries are sodium-ion batteries, and the voltage change during charging and discharging has a relatively large slope, there is a good correlation between the voltage of the sodium-ion battery and the state of charge (SOC) of the battery pack. Therefore, the BMS can more accurately and reliably monitor the SOC of the battery pack using the sodium-ion battery voltage. In this embodiment, since the sodium-ion battery is a sodium-ion battery and the sodium-ion battery is connected in series, the SOC of the battery pack can be accurately monitored simply by monitoring the voltage of the sodium-ion battery, thus effectively solving the problem of low SOC monitoring accuracy in battery packs using only lithium iron phosphate batteries.

[0020] In some embodiments, the positive electrode tab of the sodium-ion battery includes an aluminum foil and a positive electrode material disposed on the aluminum foil. The positive electrode material includes layered oxides and polyanions, with the proportion of polyanions ranging from 0% to 40%, for example, the proportion of polyanions can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc. In this embodiment, layered oxides can simultaneously achieve high energy density and cycle life. The advantage of layered oxides is that they can provide high specific capacity while having good cycle performance. Polyanion compounds have diverse and stable three-dimensional structures, resulting in good long-term cycle stability and high safety. Since the proportion of polyanions in the positive electrode material is 0% to 40%, within this range, it is possible to provide high specific capacity, good cycle performance, and good long-term cycle stability and high safety. Furthermore, when the proportion of polyanions in the cathode material is within the range of 0-40%, the slope of the SOC-OCV (state of charge-voltage) curve of the sodium-ion battery during the charge and discharge process can be ensured to be large enough to provide accurate voltage change measurement. Thus, the SOC of the battery pack can be accurately obtained by measuring the voltage of the sodium-ion battery.

[0021] In some embodiments, the lithium-ion battery includes a second bottom wall, a second top wall, and a second side wall connected between the second bottom wall and the second top wall. The second bottom wall, the second side wall, and the second top wall enclose a second sealed cavity, and the sodium-ion battery and the lithium-ion battery are arranged along a first direction, with the first bottom wall and the second bottom wall in contact and electrically connected.

[0022] In some embodiments, the lithium-ion battery includes a second bottom wall, a second top wall, and a second side wall connecting the second bottom wall and the second top wall. The second bottom wall, the second side wall, and the second top wall enclose a second sealed cavity for housing the positive electrode tab, the negative electrode tab, and the electrolyte of the lithium-ion battery. The sodium-ion battery and the lithium-ion battery are arranged along a second direction, wherein the second direction is perpendicular to the first direction. The first side wall of the sodium-ion battery contacts and is electrically connected to the second side wall of the lithium-ion battery.

[0023] In some implementations, both the current collectors of the positive and negative tabs of the sodium-ion battery are made of aluminum, which effectively reduces the cost of the sodium-ion battery. It also effectively reduces the weight of the sodium-ion battery.

[0024] In some embodiments, multiple lithium iron phosphate (LFP) batteries are connected in series, and the casing of a sodium-ion battery is in contact with and electrically connected to the casing of one of the LFP batteries. In this embodiment, by connecting a sodium-ion battery in series among multiple LFP batteries, the state of charge (SOC) of the battery pack can be accurately predicted by monitoring the voltage of the sodium-ion battery.

[0025] In some embodiments, the length of the sodium-ion battery is twice the length of the lithium-ion battery. The sodium-ion battery and one of the lithium-ion batteries are arranged along a first direction to form a first battery pack; three lithium-ion batteries are arranged along the first direction to form a second battery pack. The first and second battery packs are arranged along the length of the battery pack. In this embodiment, since the length of the sodium-ion battery is twice the length of the lithium-ion battery, the second battery pack, composed of three lithium-ion batteries, has the same dimensions as the first battery pack in the first direction, thus making the arrangement of the sodium-ion and lithium-ion batteries in the battery pack casing more reasonable.

[0026] In some embodiments, the length direction of the lithium-ion battery is the same as the first direction, and the length direction of the sodium-ion battery is the same as the first direction. One lithium-ion battery and one sodium-ion battery are arranged along the first direction to form a first battery pack. The first direction is perpendicular to the length direction of the battery pack, and multiple first battery packs are arranged along the length direction of the battery pack. In this embodiment, the first battery packs composed of sodium-ion batteries and lithium-ion batteries are arranged along the length direction of the battery pack, and each first battery pack is the same size, which allows for a more reasonable arrangement within the battery pack.

[0027] In some embodiments, the length direction of the lithium-ion battery is the same as the first direction, and the length direction of the sodium-ion battery is the same as the first direction. One lithium-ion battery and one sodium-ion battery are arranged along the first direction to form a first battery pack. The first direction is parallel to the length direction of the battery pack. The battery pack also includes multiple lithium-ion batteries, which are arranged along the length direction of the battery pack to form a second battery pack. In the length direction of the battery pack, the length of the second battery pack is the same as the length of the first battery pack. In this embodiment, since the lengths of the first and second battery packs are the same in the length direction of the battery pack, it is easier to rationally arrange the first and second battery packs within the battery pack.

[0028] In some embodiments, the lithium-ion battery is a ternary lithium battery, and both the casing of the sodium-ion battery and the casing of the ternary lithium battery are aluminum. The negative electrode tab of the sodium-ion battery is electrically connected to the casing of the sodium-ion battery, and the positive electrode tab of the ternary lithium battery is electrically connected to the casing of the ternary lithium battery. The casing of the sodium-ion battery and the casing of the ternary lithium battery are in contact and electrically connected.

[0029] Secondly, embodiments of this application provide an energy storage device, which includes a battery management system and a plurality of battery packs as described in any of the first aspects. The battery management system is used to collect voltage data of sodium-ion batteries and calculate the state of charge of the battery packs based on the collected voltage data of sodium-ion batteries.

[0030] Thirdly, embodiments of this application provide a method for measuring the state of charge of a battery pack as described in any of the first aspects above, wherein the sodium-ion battery is a sodium-ion battery;

[0031] The methods include:

[0032] Collect voltage data from sodium-ion batteries;

[0033] The state of charge of the battery pack is calculated based on the collected voltage data of the sodium-ion batteries.

[0034] In some embodiments, prior to the step of acquiring voltage data from the sodium-ion battery, the method further includes the following steps:

[0035] Measure and obtain the corresponding curves of voltage and state of charge of the sodium-ion battery pack under different states;

[0036] In the step of calculating the state of charge of the battery pack based on the collected voltage data of the sodium-ion batteries, the collected voltage data of the sodium-ion batteries is used to calculate the state of charge of the battery pack based on the corresponding curve.

[0037] Fourthly, embodiments of this application provide a vehicle, the vehicle including a body and a plurality of battery packs such as any one of the first aspects disposed within the body. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0039] Figure 1 A simplified structural diagram of an energy storage device provided in this application embodiment;

[0040] Figure 2 This is a schematic diagram of the structure of a battery pack provided in an embodiment of this application;

[0041] Figure 3 for Figure 2 A schematic diagram of the structure of the sodium-ion battery and the lithium-ion battery in the battery pack of the embodiment;

[0042] Figure 4 for Figure 3 A schematic diagram of the winding structure of the battery cell in the embodiment;

[0043] Figure 5 for Figure 3 A schematic diagram showing the exploded structure of the casings of sodium-ion and lithium-ion batteries.

[0044] Figure 6 Charge-discharge curves for lithium iron phosphate batteries and sodium-ion batteries;

[0045] Figure 7 for Figure 3 Top view of the sodium-ion battery and lithium-ion battery in the embodiments;

[0046] Figure 8 for Figure 3 Front view of the sodium-ion battery and lithium-ion battery in the embodiments;

[0047] Figure 9 This is a schematic diagram of the structure of another sodium-ion battery and lithium-ion battery provided in the embodiments of this application;

[0048] Figure 10 A schematic diagram of the structure of another sodium-ion battery and a lithium-ion battery provided in the embodiments of this application;

[0049] Figure 11A A schematic diagram showing the connection of some cells in a battery pack according to an embodiment of this application;

[0050] Figure 11B A schematic diagram showing the connection of some cells in a battery pack according to an embodiment of this application;

[0051] Figure 11C A schematic diagram showing the connection of some cells in a battery pack according to an embodiment of this application;

[0052] Figure 12 This application provides a method for measuring the state of charge of a battery pack. Attached image description:

[0054] X, first direction; Y, second direction;

[0055] 1. Energy storage device; 2. Housing; 3. Battery pack; 4. Casing; 5. Battery cell; 6. Sodium-ion battery; 7. Lithium-ion battery; 8. Battery management unit;

[0056] 10. Shell; 11. First bottom wall; 12. First top wall; 13. First side wall; 14. First sealing cavity; 15. Second top wall; 16. Second side wall; 17. Second sealing cavity; 18. Second bottom wall;

[0057] 21. Positive electrode plate; 22. Negative electrode plate; 23. Separator;

[0058] 31. The positive electrode post of a sodium-ion battery;

[0059] 32. The negative electrode post of a lithium-ion battery;

[0060] 40. Voltage acquisition line; 41. First voltage acquisition line; 42. Second voltage acquisition line; 43. Third voltage acquisition line;

[0061] 91. First battery pack; 92. Second battery pack. Detailed Implementation

[0062] The following section will first explain some of the terms used in the embodiments of this application.

[0063] The terms "first," "second," "third," "fourth," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0064] In this specification, the terms "vertical" and "parallel" are explained.

[0065] Perpendicularity: The perpendicularity defined in this application is not limited to an absolute perpendicular intersection (with an included angle of 90 degrees). It is permissible for non-absolute perpendicular intersections caused by factors such as assembly tolerances, design tolerances, and structural flatness. It is permissible for errors within a small angular range, such as an assembly error range of 80 to 100 degrees, which can all be understood as a perpendicular relationship.

[0066] Parallelism: The parallelism defined in this application is not limited to absolute parallelism. This definition of parallelism can be understood as basic parallelism, allowing for situations where the parallelism is not absolute due to factors such as assembly tolerances, design tolerances, and structural flatness. These situations may lead to the sliding mating part and the first door panel not being absolutely parallel, but this application also defines such situations as parallelism.

[0067] Figure 1 This is a simplified structural diagram of an energy storage device 1 provided in an embodiment of this application.

[0068] Reference Figure 1 The energy storage device 1 includes a housing 2 and multiple battery packs 3 and a battery management system (BMS) housed within the housing 2. The multiple battery packs 3 are stacked within the housing 2. Electrical energy can be stored or output through the multiple battery packs 3. The battery management system is used for intelligent management and maintenance of each battery pack 3, preventing overcharging and over-discharging of the battery packs 3, extending the service life of the battery packs 3, and monitoring the status of the battery packs 3.

[0069] To facilitate understanding of the energy storage device 1 provided in this application embodiment, its application scenarios are first introduced below. The energy storage device 1 is a system that can store electrical energy through a certain medium and release the stored energy to generate electricity when needed. It can be used as a load balancing device and backup power source in scenarios such as industrial and commercial parks, large ground-based power stations, or photovoltaic-storage systems. The application of the energy storage device 1 will be briefly explained using a photovoltaic-storage system scenario as an example. A photovoltaic-storage system typically includes photovoltaic modules, an energy storage converter, the energy storage device 1, and a grid-connected inverter. The photovoltaic modules can convert light energy into direct current (DC) electrical energy and output it to the grid-connected inverter; the grid-connected inverter can convert the DC electrical energy into alternating current (AC) electrical energy and transmit the AC electrical energy to the power grid, thereby realizing grid connection of the photovoltaic-storage system.

[0070] Figure 2 This is a schematic diagram of the structure of a battery pack 3 provided in an embodiment of this application. Figure 2 The battery pack 3 in the embodiment can be applied not only to Figure 1 The energy storage device 1 in the embodiment can also be applied to the automotive field or other fields that require the use of battery pack 3.

[0071] Reference Figure 2 The battery pack 3 includes a housing 4 and multiple battery cells 5 inside the housing 4. The multiple battery cells 5 are arranged inside the housing 4. It can be understood that the multiple battery cells 5 can be arranged in one row or in multiple rows.

[0072] In some embodiments, multiple battery cells 5 are connected in series. In other embodiments, multiple battery cells 5 may also be connected in parallel, or some battery cells 5 may be connected in series and some battery cells 5 may be connected in parallel.

[0073] In some implementations, the casing of the battery cell 5 is a metal casing, such as an aluminum casing.

[0074] In some embodiments, the battery cell 5 is generally rectangular. Of course, in other embodiments, the battery cell 5 can also be other shapes.

[0075] Figure 3 for Figure 2 A schematic diagram of the structure of the sodium-ion battery 6 and the lithium-ion battery 7 in the battery pack 3 in the embodiment; Figure 4 for Figure 3 A schematic diagram of the winding core of cell 5 in the embodiment. Figure 5 for Figure 3 A schematic diagram of the exploded structure of the casing 10 of the sodium-ion battery 6 and the lithium-ion battery 7. Figure 6The graph shows the charge / discharge curves of lithium iron phosphate battery and sodium-ion battery 6; the horizontal axis represents the charge or discharge ratio of lithium iron phosphate battery and sodium-ion battery 6, and the vertical axis represents the voltage value, where a positive slope indicates charging and a negative slope indicates discharging. Figure 3 Cell 5 in the middle is used Figure 2 Battery pack 3 in the embodiment.

[0076] Reference Figure 4 and Figure 5 In some embodiments, the multiple cells 5 of the battery pack 3 each include a housing 10 and an electrolyte, a positive electrode tab (not shown in the figure), a negative electrode tab (not shown in the figure), a positive electrode plate 21, a negative electrode plate 22, and a separator 23 located between the positive electrode plate 21 and the negative electrode plate 22, wherein the positive electrode tab is connected to the positive electrode plate 21 and the negative electrode tab is connected to the negative electrode plate 22.

[0077] Reference Figures 3-5 In some embodiments, the multiple battery cells 5 include sodium-ion batteries 6 and lithium-ion batteries 7. For example, the lithium-ion battery 7 can be a lithium iron phosphate battery or a ternary lithium battery.

[0078] The negative electrode tab of the sodium-ion battery 6 is electrically connected to the casing 10 of the sodium-ion battery 6, and the positive electrode tab of the sodium-ion battery 6 is electrically connected to the positive terminal 31 of the sodium-ion battery 6. Because the negative electrode tab and the casing 10 of the sodium-ion battery 6 are electrically connected, the casing 10 of the sodium-ion battery 6 can be considered as the negative terminal of the sodium-ion battery 6, and a potential difference exists between the positive terminal 31 of the sodium-ion battery 6 and the casing 10 of the sodium-ion battery 6.

[0079] The positive electrode tab of the lithium-ion battery 7 is electrically connected to the casing 10 of the lithium-ion battery 7, and the negative electrode tab of the lithium-ion battery 7 is electrically connected to the negative terminal 32 of the lithium-ion battery 7. Since the positive electrode tab of the lithium-ion battery 7 is electrically connected to the casing 10 of the lithium-ion battery 7, the casing 10 of the lithium-ion battery 7 can be regarded as the positive terminal of the lithium-ion battery 7, and there is a potential difference between the casing 10 of the lithium-ion battery 7 and the negative terminal 32 of the lithium-ion battery 7.

[0080] In some embodiments, the casing 10 of the sodium-ion battery 6 is made of aluminum. Aluminum does not undergo an alloying reaction with the electrolyte of the sodium-ion battery 6 under both high and low potentials. This means that sodium ions in the electrolyte of the sodium-ion battery 6 will not embed into the aluminum casing to form a sodium-aluminum alloy. Therefore, the casing 10 of the sodium-ion battery 6 will not be corroded by the electrolyte of the sodium-ion battery 6 at either high or low potentials, thus ensuring the stability of the sodium-ion battery 6. It is understood that in other embodiments, the casing 10 of the sodium-ion battery 6 may also be made of other materials. However, it must ensure that when the negative electrode tab of the sodium-ion battery 6 is connected to the casing 10, the casing 10 of the sodium-ion battery 6 will not undergo an alloying reaction with sodium ions in the electrolyte of the sodium-ion battery 6 under low potentials.

[0081] In some embodiments, the casing 10 of the lithium-ion battery 7 is made of aluminum. Aluminum is less prone to alloying with lithium ions in the electrolyte of the lithium-ion battery 7 at high potentials. That is, lithium ions in the electrolyte of the lithium-ion battery 7 will not embed into the aluminum to form an aluminum-lithium alloy. Therefore, at high potentials, the casing 10 of the lithium-ion battery 7 will not be corroded by the electrolyte of the lithium-ion battery 7, thus ensuring the stability of the casing 10. It is understood that in other embodiments, the casing 10 of the lithium-ion battery 7 may also be made of other materials, but it must ensure that when the positive electrode tab of the lithium-ion battery 7 is connected to the casing 10, the casing 10 of the lithium-ion battery 7 will not alloy with lithium ions in the electrolyte of the lithium-ion battery 7 at high potentials.

[0082] In some embodiments, the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7 are electrically connected. This is because the voltage change during the charging and discharging process of the sodium-ion battery has a relatively large slope (see reference). Figure 6 The voltage of the sodium-ion battery and the state of charge (SOC) of the battery pack 3 have a good correlation, thus the BMS can more accurately and reliably monitor the SOC of the battery pack 3 using the sodium-ion battery voltage. Therefore, in this embodiment, by connecting the sodium-ion battery 6 and the lithium-ion battery 7 in series, the SOC of the battery pack 3 can be accurately monitored by monitoring the voltage of the sodium-ion battery 6, effectively solving the problem of low SOC monitoring accuracy of the battery pack 3.

[0083] Among related technologies, lithium iron phosphate batteries are widely used in energy storage due to their reasonable price and mature technology. However, the positive electrode system of lithium iron phosphate batteries exhibits a relatively long charge-discharge plateau during the charging and discharging process (see reference). Figure 6The SOC-OCV (State of Charge-Voltage) curve during the voltage charging and discharging process is very flat with a small slope, resulting in a significant error in the accuracy of the BMS's monitoring of the SOC of battery pack 3 using the voltage of the lithium iron phosphate battery. This discrepancy in capacity estimation can negatively impact the user experience.

[0084] In some embodiments, the lithium-ion battery 7 is a lithium iron phosphate battery, and both the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7 are aluminum casings. This ensures the stability of the negative electrode tab of the sodium-ion battery 6 after electrical connection with the casing 10, and also ensures the stability of the positive electrode tab of the lithium-ion battery 7 after electrical connection. Furthermore, because the voltage change slope of the sodium-ion battery 6 during charging and discharging is relatively large (see reference...), Figure 6 The voltage of the sodium-ion battery 6 and the state of charge (SOC) of the battery pack 3 have a good correlation, thus the BMS can more accurately and reliably monitor the SOC of the battery pack 3 using the voltage of the sodium-ion battery 6. In this embodiment, by connecting the sodium-ion battery 6 and the lithium iron phosphate battery in series, the SOC of the battery pack 3 can be accurately monitored by monitoring the voltage of the sodium-ion battery 6, thereby effectively solving the problem of low SOC monitoring accuracy of the battery pack 3 using only lithium iron phosphate batteries. At the same time, because lithium iron phosphate batteries are reasonably priced and have mature technology, costs can be reduced and safety performance can be improved.

[0085] In some embodiments, the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7 are in contact and electrically connected. Since the casing 10 of the sodium-ion battery 6 can be considered as the negative terminal of the sodium-ion battery 6, and the casing 10 of the lithium-ion battery 7 can be considered as the positive terminal of the lithium-ion battery 7, when the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7 are in contact, it can be considered as an electrical connection between the negative terminal of the sodium-ion battery 6 and the positive terminal of the lithium-ion battery 7, thus it can be considered as a series connection between the sodium-ion battery 6 and the lithium-ion battery 7. By using the method of contacting and electrically connecting the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7, the use of wires to connect the sodium-ion battery 6 and the lithium-ion battery 7 can be avoided. This not only facilitates the electrical connection between the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7, reducing the complexity of the connection between the sodium-ion battery 6 and the lithium-ion battery 7, but also improves the stability of the connection between the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7, preventing the connection from being easily broken like a wire connection. Furthermore, by eliminating the use of wires, the internal resistance caused by wires can be effectively reduced, and the internal loss caused by wires can be effectively avoided, thereby improving the overall energy output of battery pack 3.

[0086] It is understood that the electrical connection between the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7 in this embodiment is conditional. It requires that the casing 10 of the sodium-ion battery 6 and the negative electrode tab of the sodium-ion battery 6 be electrically connected and maintain a stable state, and that the casing 10 of the lithium-ion battery 7 and the positive electrode tab of the lithium-ion battery 7 be electrically connected and maintain a stable state.

[0087] In some embodiments, the positive electrode material of a sodium-ion battery can be a sodium-containing compound or polymer. For example, some sodium-ion battery positive electrode materials are formed by a mixture of layered oxides and polyanions. The layered oxides can include transition metals such as nickel, iron, manganese, and copper, and the polyanions can be sodium iron pyrophosphate.

[0088] In some implementations, the cathode material of a lithium-ion battery is a lithium-containing compound or polymer. For example, some lithium-ion batteries use lithium iron phosphate as the cathode material, while others use ternary polymers of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0089] In some embodiments, the positive electrode 21 of the sodium-ion battery 6 includes an aluminum foil and a positive electrode material disposed on the aluminum foil. The positive electrode material includes layered oxides and polyanionic compounds, wherein the proportion of polyanionic compounds in the positive electrode material is 0-40%, for example, the proportion of polyanionic compounds can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc. Layered oxides can simultaneously achieve high energy density and cycle life. The advantage of layered oxides is that they can provide high specific capacity and good cycle performance. Polyanionic compounds have diverse and stable three-dimensional structures, resulting in good long-term cycle stability and high safety. The proportion of polyanionic compounds in the positive electrode material is 0-40%, which within this range can meet the requirements of providing high specific capacity, good cycle performance, and good long-term cycle stability and high safety. Furthermore, when the proportion of polyanions in the cathode material is within the range of 0-40%, the slope of the SOC-OCV (state of charge-voltage) curve of the sodium-ion battery 6 during the charge and discharge process can be ensured to be large enough to provide accurate voltage change measurement. Thus, the SOC of the battery pack 3 can be accurately obtained by measuring the voltage of the sodium-ion battery 6.

[0090] In some embodiments, both the current collector of the positive electrode 21 and the current collector of the negative electrode 22 of the sodium-ion battery 6 can be made of aluminum, which effectively reduces the cost of the sodium-ion battery 6. It can also effectively reduce the weight of the sodium-ion battery 6.

[0091] Reference Figure 3 and Figure 5In some embodiments, the housings 10 of the sodium-ion battery 6 and the lithium-ion battery 7 are arranged along a first direction X, wherein the length direction of the lithium-ion battery 7 is the same as the first direction X, and the length direction of the sodium-ion battery 6 is the same as the first direction X. This arrangement not only facilitates the connection between the sodium-ion battery 6 and the lithium-ion battery 7, but also meets the arrangement requirements of the sodium-ion battery 6 and the lithium-ion battery 7 in certain specific scenarios.

[0092] In some embodiments, the first direction X is the same as the width direction b of the battery pack 3. Since the first direction X is the width direction b of the battery pack 3, and the sodium-ion battery 6 and lithium-ion battery 7 are arranged in the first direction X, the arrangement of the sodium-ion battery 6 and lithium-ion battery 7 can be more reasonable when their lengths are different.

[0093] To effectively reduce the overall length of the sodium-ion battery 6 and lithium-ion battery 7 arranged in the first direction X, in some embodiments, the housing 10 of the sodium-ion battery 6 includes a first bottom wall 11, a first top wall 12, and a plurality of first side walls 13 connected between the first bottom wall 11 and the first top wall 12. The first bottom wall 11, the first top wall 12, and the plurality of first side walls 13 enclose a first sealed cavity 14, and the first direction X is the direction in which the first bottom wall 11 and the first top wall 12 are opposite to each other. The housing 10 of the lithium-ion battery 7 includes a second top wall 15 and a plurality of second side walls 16 connected to the periphery of the second top wall 15. The first bottom wall 11 and the second top wall 15 are disposed opposite each other in the first direction X, and the second side walls 16 are connected between the first bottom wall 11 and the second top wall 15. The first bottom wall 11, the second top wall 15, and the plurality of second side walls 16 enclose a second sealed cavity 17. In this embodiment, since the first bottom wall 11 is part of both the first sealed cavity 14 and the second sealed cavity 17, and the sodium-ion battery 6 and the lithium-ion battery 7 are arranged along the first direction X, the casing 10 of the lithium-ion battery 7 does not need an additional bottom wall to form the second sealed cavity 17 with the second side wall 16 and the second top wall 15. The bottom wall of the second casing 10, if provided, would have a certain thickness. Since the second casing 10 does not need an additional bottom wall, its length in the first direction X can be effectively reduced, thereby effectively reducing the overall length of the sodium-ion battery 6 and the lithium-ion battery 7 arranged in the first direction X. This effectively improves the energy density of the battery pack 3. Furthermore, since the casing 10 of the lithium-ion battery 7 saves on a bottom wall, the material cost of the casing 10 can also be saved. Furthermore, since the casings 10 of the sodium-ion battery 6 and the lithium-ion battery 7 are arranged along the first direction X, a bottom wall is not required on the casing 10 of the lithium-ion battery 7. Not having a bottom wall on the casing 10 of the lithium-ion battery 7 eliminates the need for additional processes to remove the bottom wall and also saves the step of welding the bottom wall of the casing 10 of the lithium-ion battery 7. Therefore, because the casings 10 of the sodium-ion battery 6 and the lithium-ion battery 7 are arranged along the first direction X, the manufacturing of the second casing 10 is facilitated.

[0094] In some embodiments, the first bottom wall 11 is welded to the first side wall 13, and the first bottom wall 11 is welded to the second side wall 16. In this embodiment, welding can conveniently and quickly connect the first bottom wall 11, the first side wall 13, and the second side wall 16 together.

[0095] It is understood that in some other embodiments, the first bottom wall 11, the first side wall 13, and the second side wall 16 may be integrally injection molded. Alternatively, the first bottom wall 11 and the first side wall 13 may be integrally injection molded, and the second side wall 16 may be welded to the first bottom wall 11.

[0096] In some embodiments, the negative electrode tab of the sodium-ion battery 6 is electrically connected to the first bottom wall 11, and the positive electrode tab of the lithium-ion battery 7 is electrically connected to the first bottom wall 11. In this embodiment, since the negative electrode tab of the sodium-ion battery 6 is electrically connected to the first bottom wall 11, and the positive electrode tab of the lithium-ion battery 7 is electrically connected to the first bottom wall 11, the first bottom wall 11 can be regarded as both the positive electrode post 31 of the sodium-ion battery 6 and the negative electrode post 32 of the lithium-ion battery 7, thus realizing the series connection of the sodium-ion battery 6 and the lithium-ion battery 7. Moreover, since the first bottom wall 11 can be directly electrically connected to the negative electrode tab of the sodium-ion battery 6 and the positive electrode tab of the lithium-ion battery 7, the series connection of the sodium-ion battery 6 and the lithium-ion battery 7 can be realized. Compared to the indirect electrical connection between the negative electrode of the sodium-ion battery 6 and the positive electrode of the lithium-ion battery 7 through contact between the casing 10 of the sodium-ion battery 6 and the casing 10 of the lithium-ion battery 7, this embodiment effectively reduces or avoids contact resistance by electrically connecting the negative electrode of the sodium-ion battery 6 to the first bottom wall 11, and simultaneously electrically connecting the positive electrode of the lithium-ion battery 7 to the first bottom wall 11, thereby further reducing the internal losses of the sodium-ion battery 6 and the lithium-ion battery 7. It is understood that the first bottom wall 11 in this embodiment can be considered both the positive electrode post 31 of the sodium-ion battery 6 and the negative electrode post 32 of the lithium-ion battery 7. Similarly, the first side wall 13, the first top wall 12, the second side wall 16, and the second top wall 15, all connected to the first bottom wall 11, have the same potential as the first bottom wall 11 and can all be considered both the positive electrode post 31 of the sodium-ion battery 6 and the negative electrode post 32 of the lithium-ion battery 7.

[0097] Figure 7 for Figure 3 Top view of sodium-ion battery 6 and lithium-ion battery 7 in the embodiment; Figure 8 for Figure 3 Front view of sodium-ion battery 6 and lithium-ion battery 7 in the embodiment.

[0098] Reference Figure 7 and Figure 8In some embodiments, the casing 10 of the sodium-ion battery 6 is generally rectangular, and the casing 10 of the lithium-ion battery 7 is also generally rectangular. The first direction X is the same as the length direction of both the sodium-ion battery 6 and the lithium-ion battery 7. The width of the casing 10 of the sodium-ion battery 6 is the same as the width of the casing 10 of the lithium-ion battery 7, and the height of the casing 10 of the sodium-ion battery 6 is the same as the height of the lithium-ion battery 7. The sodium-ion battery 6 and the lithium-ion battery 7 are positioned opposite each other in the first direction X, meaning that the height direction of the sodium-ion battery 6 is the same as the height direction of the lithium-ion battery 7, and the width direction of the sodium-ion battery 6 is the same as the width direction of the lithium-ion battery 7. Furthermore, the outer surfaces of the first sidewall 13 and the second sidewall 16 are flush. Because the sodium-ion battery 6 and the lithium-ion battery 7 are positioned opposite each other in the first direction X, it is beneficial to make the overall layout of the sodium-ion battery 6 and the lithium-ion battery 7 more rational.

[0099] In some implementations, the lithium-ion battery 7 is a lithium iron phosphate battery, and the length of the casing 10 of the sodium-ion battery 6 is greater than the length of the casing 10 of the lithium-ion battery 7. The capacity of the sodium-ion battery 6 is the same as that of the lithium-ion battery 7, and the charge / discharge rate of the sodium-ion battery 6 is the same as that of the lithium-ion battery 7. For example, when the sodium-ion battery 6 is a sodium-ion battery and the lithium-ion battery 7 is a lithium iron phosphate battery, in order to achieve the same capacity and charge / discharge rate for both the sodium-ion battery 6 and the lithium-ion battery 7, the length of the casing 10 of the sodium-ion battery 6 needs to be greater than the length of the casing 10 of the lithium-ion battery 7. It is understandable that if the two cells 5 have different capacities, the series-connected battery pack will be limited by the cell 5 with the smallest capacity, causing the larger capacity cell 5 to be underutilized, while the smaller capacity cell 5 may be over-discharged. This situation not only reduces energy utilization but may also adversely affect lifespan and performance. If the charge / discharge rates of the two cells 5 are different, then during discharge, since the current flows through each of the series-connected cells 5, the cell 5 with the lower charge / discharge rate will limit the current output of the entire battery pack, thus affecting the performance and efficiency of the battery pack 3. Since the sodium-ion battery 6 in this embodiment has the same capacity as the lithium-ion battery 7, and the charge / discharge rates of the sodium-ion battery 6 and lithium-ion battery 7 are also the same, the series-connected battery pack can achieve a more balanced current distribution and more efficient energy utilization. This avoids energy waste and performance inconsistencies caused by differences between the cells 5.

[0100] Because lithium iron phosphate (LFP) batteries and sodium-ion batteries have different volumetric energy densities, but the series current draw is the same, their casing dimensions (10) differ. The LFP battery casing (10) is defined as having a height of H1, a width of T1, and a length of L1. The sodium-ion battery casing (10) is defined as having a height of H2, a width of T2, and a length of L2. L2 = XL2, where X = 1.2-3, to ensure that the LFP and sodium-ion batteries operate within the same voltage range and have the same charge / discharge capacity. For example, if the LFP battery operates at 2.0-3.65V 0.2C, then the sodium-ion battery will also operate at 2.0-3.65V 0.2C.

[0101] It is understood that in some other embodiments, the sodium-ion battery 6 and the lithium-ion battery 7 may not be directly opposite each other in the first direction X. The widths of the sodium-ion battery 6 and the lithium-ion battery 7 may also be different, as may their heights. The lengths of the sodium-ion battery 6 and the lithium-ion battery 7 may also be the same.

[0102] Reference Figure 7 and Figure 8 In some embodiments, the positive electrode post 31 of the sodium-ion battery 6 is located on the first top wall 12 and is electrically connected to the positive electrode tab of the sodium-ion battery 6. The negative electrode post 32 of the lithium-ion battery 7 is located on the second top wall 15 and is electrically connected to the negative electrode tab of the lithium-ion battery 7. This design of the position of the positive electrode post 31 of the sodium-ion battery 6 and the negative electrode post 32 of the lithium-ion battery 7 allows for a reasonable layout of the sodium-ion battery 6 and the lithium-ion battery 7, resulting in a more rational overall structure after the sodium-ion battery 6 and the lithium-ion battery 7 are connected.

[0103] Furthermore, since the first direction X is the same as the width direction b of the battery pack 3, the positive terminal 31 is placed on the first top wall 12 and the negative terminal 32 is placed on the second top wall 15, which can effectively reduce the size of the battery pack 3 in the height direction c. Thus, when the battery pack 3 is applied to a vehicle, the proportion of the battery pack 3 in the vertical direction can be effectively reduced, thereby effectively increasing the size of the vehicle's passenger compartment.

[0104] It is understood that in some other embodiments, the positive electrode post 31 of the sodium-ion battery 6 may also be disposed on the first sidewall 13, and the negative electrode post 32 of the lithium-ion battery 7 may also be disposed on the second sidewall 16. It is understood that the positive electrode post 31 of the sodium-ion battery 6 is insulated from the casing 10 of the sodium-ion battery 6, and the negative electrode post 32 of the lithium-ion battery 7 is insulated from the casing 10 of the lithium-ion battery 7.

[0105] In some embodiments, the battery pack 3 further includes a Battery Management Unit (BMU) 8. The BMU 8 collects voltage data from the sodium-ion battery 6 and feeds this data back to a data processing module. The data processing module calculates the State of Charge (SOC) of the battery pack 3 based on the voltage data collected by the BMU 8. The data processing module is a module within the Battery Management System (BMS) of the energy storage device. In this embodiment, because the voltage change slope of the sodium-ion battery 6 during charging and discharging is relatively large, the real-time voltage data of the sodium-ion battery 6 during charging and discharging can be accurately detected. The voltage data of the sodium-ion battery 6 is then collected by the BMU 8 and fed back to the data processing module, which can then calculate the SOC of the battery pack 3 based on this data. This allows the SOC of the battery pack 3 in this embodiment to be monitored accurately in real time.

[0106] In some embodiments, the battery management unit 8 includes a voltage acquisition line 40, which is used to monitor the voltage of the sodium-ion battery 6 and / or the voltage of the lithium-ion battery 7 and / or the total voltage of the sodium-ion battery 6 and the lithium-ion battery 7 connected in series.

[0107] In some embodiments, the voltage acquisition line 40 includes a first voltage acquisition line 41, a second voltage acquisition line 42, and a third voltage acquisition line 43. The first voltage acquisition line 41 is connected to the positive terminal of the sodium-ion battery, and the third voltage acquisition line 43 is connected to the negative terminal of the lithium-ion battery 7. The second voltage acquisition line 42 can be connected to the surface of the housing 10 of the sodium-ion battery 6, and the second voltage acquisition line 42 can also be connected to the surface of the housing 10 of the lithium-ion battery 7. Specifically, the second voltage acquisition line 42 can be connected to any one of the first bottom wall 11, the first side wall 13, the first top wall 12, the second side wall 16, and the second top wall 15. The voltage between the third voltage acquisition line 43 and the first voltage acquisition line 41 is the total voltage of the sodium-ion battery and the lithium-ion battery 7 connected in series; the voltage between the first voltage acquisition line 41 and the second voltage acquisition line 42 is the voltage of the sodium-ion battery; and the voltage between the second voltage acquisition line 42 and the third voltage acquisition line 43 is the voltage of the lithium-ion battery 7. In this embodiment, since the slope of the voltage change during the charging and discharging process of the sodium-ion battery is relatively large, there is a good correspondence between the voltage of the sodium-ion battery and the SOC state of the battery pack 3. Therefore, the voltage of the sodium-ion battery between the first voltage acquisition line 41 and the second voltage acquisition line 42, as well as the total voltage of the sodium-ion battery and the lithium-ion battery 7 connected in series between the third voltage acquisition line 43 and the first voltage acquisition line 41, can be accurately monitored. Thus, by monitoring the voltage of the sodium-ion battery between the first voltage acquisition line 41 and the second voltage acquisition line 42, or the total voltage of the sodium-ion battery and the lithium-ion battery 7 connected in series between the third voltage acquisition line 43 and the first voltage acquisition line 41, the SOC of the battery pack 3 can be accurately predicted.

[0108] Figure 9 This is a schematic diagram of the structure of another sodium-ion battery 6 and lithium-ion battery 7 provided in the embodiments of this application. Figure 9 Examples and Figure 3 The main difference in the embodiment is that the lithium-ion battery 7 also includes a second bottom wall 18.

[0109] Reference Figure 9 In some embodiments, the lithium-ion battery 7 includes a second bottom wall 18, a second top wall 15, and a plurality of second side walls 16 connecting the second bottom wall 18 and the second top wall 15. The second bottom wall 18, the plurality of second side walls 16, and the second top wall 15 enclose a second sealed cavity 17 for housing the positive electrode 21, the negative electrode 22, and the electrolyte of the lithium-ion battery 7.

[0110] Sodium-ion battery 6 and lithium-ion battery 7 are arranged along a first direction X, and the first bottom wall 11 and the second bottom wall 18 are in contact and electrically connected. For example, in some embodiments, the first bottom wall 11 and the second bottom wall 18 can be welded together. In this embodiment, sodium-ion battery 6 and lithium-ion battery 7 can be manufactured independently, and then connected together through subsequent processes. This can effectively improve production efficiency.

[0111] It should be noted that the sodium-ion battery 6, the first bottom wall 11, the second top wall 15, the second side wall 16, the second sealing cavity 17, the first direction X, etc. in this embodiment can all refer to the previous embodiment, and will not be repeated here.

[0112] Figure 10 This is a schematic diagram of another sodium-ion battery 6 and a lithium-ion battery 7 provided in the embodiments of this application. Figure 10 Compared to the example Figure 3 The main difference in the embodiments is that the lithium-ion battery 7 also includes a second bottom wall 18, and the sodium-ion battery 6 and the lithium-ion battery 7 are arranged in different directions.

[0113] Reference Figure 10 In some embodiments, the lithium-ion battery 7 includes a second bottom wall 18, a second top wall 15, and a plurality of second side walls 16 connecting the second bottom wall 18 and the second top wall 15. The second bottom wall 18, the plurality of second side walls 16, and the second top wall 15 enclose a second sealed cavity 17 for housing the positive electrode 21, the negative electrode 22, and the electrolyte of the lithium-ion battery 7.

[0114] Sodium-ion battery 6 and lithium-ion battery 7 are arranged along a second direction Y, wherein the second direction Y is perpendicular to the first direction X, and the first sidewall 13 of sodium-ion battery 6 is in contact with and electrically connected to the second sidewall 16 of lithium-ion battery 7.

[0115] In some embodiments, the first top wall 12 and the second top wall 15 are flush. This ensures that the positive terminal on the first top wall 12 and the negative terminal on the second top wall 15 both face the same direction and are effectively brought closer together, facilitating the connection of the voltage acquisition line 40 and reducing its length.

[0116] It should be noted that the sodium-ion battery 6, the first sidewall 13, the first top wall 12, the second top wall 15, the second sidewall 16, the second sealed cavity 17, the first direction X, the voltage acquisition line 40, the positive electrode post 31 of the sodium-ion battery 6 and the negative electrode post 32 of the lithium-ion battery 7 in this embodiment can all refer to the previous embodiment, and will not be repeated here.

[0117] Understandable Figure 3 , Figure 9 and Figure 10This is just one of three ways to arrange the sodium-ion battery 6 and the lithium-ion battery 7. In this embodiment, the sodium-ion battery 6 and the lithium-ion battery 7 can also be arranged in other ways, as long as the housing 10 of the sodium-ion battery 6 and the housing 10 of the lithium-ion battery 7 are in contact and electrically connected.

[0118] Figure 11A This is a schematic diagram showing the connection of some cells 5 in another battery pack 3 provided in an embodiment of this application.

[0119] Reference Figure 11A In some embodiments, there are multiple lithium-ion batteries 7, and these batteries are connected in series. The casing 10 of the sodium-ion battery 6 is in contact with and electrically connected to the casing 10 of one of the lithium-ion batteries 7. The lithium-ion battery 7 can be a lithium iron phosphate battery or a ternary lithium battery. In this embodiment, a sodium-ion battery 6 is connected in series among the multiple lithium-ion batteries 7. By monitoring the voltage of the sodium-ion battery 6, the SOC of the battery pack 3 can be accurately predicted.

[0120] Understandably, multiple lithium-ion batteries 7 can be connected in series via wires.

[0121] In some embodiments, the length of the sodium-ion battery 6 is twice the length of the lithium-ion battery 7. The sodium-ion battery 6 and one of the lithium-ion batteries 7 are arranged along the first direction X to form a first battery pack 91; the three lithium-ion batteries 7 are arranged along the first direction X to form a second battery pack 92. The first battery pack 91 and the second battery pack 92 are arranged in the length direction a of the battery pack 3. In this embodiment, since the length of the sodium-ion battery 6 is twice the length of the lithium-ion battery 7, the second battery pack 92, which is composed of three lithium-ion batteries 7, and the first battery pack 91 have the same dimensions in the first direction X, thereby making the arrangement of the sodium-ion battery 6 and the lithium-ion battery 7 in the outer casing 4 of the battery pack 3 more reasonable.

[0122] It is understandable that there can be multiple first battery packs 91 and multiple second battery packs 92, or there can be only one.

[0123] Figure 11B This is a schematic diagram showing the connection of some cells 5 in another battery pack 3 provided in an embodiment of this application.

[0124] Reference Figure 11BIn some embodiments, there are multiple sodium-ion batteries 6 and multiple lithium-ion batteries 7. The casing 10 of the sodium-ion battery 6 is in contact with and electrically connected to the casing 10 of the lithium-ion battery 7. One lithium-ion battery 7 and one sodium-ion battery 6 are arranged along a first direction X to form a first battery pack 91. The first direction X is perpendicular to the length direction a of the battery pack 3. Multiple first battery packs 91 are arranged along the length direction a of the battery pack 3. In this embodiment, the first battery packs 91 composed of sodium-ion batteries 6 and lithium-ion batteries 7 are arranged along the length direction a of the battery pack 3. Each first battery pack 91 is the same size, which allows for a more reasonable arrangement within the battery pack 3.

[0125] To facilitate the series connection between two adjacent first battery packs 91 along the length a of the battery pack 3, the sodium-ion battery 6 and the lithium-ion battery 7 of the two adjacent first battery packs 91 are positioned opposite each other along the length a of the battery pack 3, so that the positive and negative terminals of the two adjacent first battery packs 91 are exactly opposite, thus facilitating the series connection of the two adjacent first battery packs 91.

[0126] Figure 11C This is a schematic diagram showing the connection of some cells 5 in another battery pack 3 provided in an embodiment of this application.

[0127] Reference Figure 11C In some embodiments, the casing 10 of the sodium-ion battery 6 is in contact with and electrically connected to the casing 10 of the lithium-ion battery 7. A lithium-ion battery 7 and a sodium-ion battery 6 are arranged along a first direction X to form a first battery pack 91, where the first direction X is consistent with the length direction a of the battery pack 3. The battery pack 3 also includes multiple lithium-ion batteries 9, which are arranged along the length direction a of the battery pack 3 to form a second battery pack 92. In the length direction a of the battery pack 3, the length of the second battery pack 92 is the same as the length of the first battery pack 91. Because the lengths of the first battery pack 91 and the second battery pack 92 are the same in the length direction a of the battery pack 3, it is easier to rationally arrange the first battery pack 91 and the second battery pack 92 within the battery pack 3.

[0128] Specifically, in the first direction X, the total length of a sodium-ion battery 6 and a lithium-ion battery 7 is an integer multiple of the length of a lithium-ion battery 9. For example, in the first direction X, the total length of a sodium-ion battery 6 and a lithium-ion battery 7 is four times the length of a lithium-ion battery 9. This allows for a reasonable arrangement of the sodium-ion battery 6, lithium-ion battery 7, and lithium-ion battery 9.

[0129] In some embodiments, the positive and negative terminals of the lithium-ion battery 9 are both located on the top wall of the lithium-ion battery 9 to facilitate series connection between adjacent lithium-ion batteries 9.

[0130] In some embodiments, the height of the lithium-ion battery 9 is the same as the width of the lithium-ion battery 7, and the width of the sodium-ion battery 6 is the same as the height of the lithium-ion battery 9. The arrangement direction of the plurality of lithium-ion batteries 9 in the second battery pack 92 is consistent with the width direction of the lithium-ion batteries 9. The total length of one sodium-ion battery 6 and one lithium-ion battery 7 is an integer multiple of the width of one lithium-ion battery 9.

[0131] Figure 12 This application provides a method for measuring the state of charge (SOC) of a battery pack 3. Figure 12 The battery pack 3 in the embodiment includes the sodium-ion battery 6 and the lithium-ion battery 7 mentioned above, wherein the sodium-ion battery 6 is a sodium-ion battery 6.

[0132] Reference Figure 12 The method for measuring the state of charge of battery pack 3 includes the following steps:

[0133] S100. Measure and obtain the corresponding curves of the voltage of the sodium-ion battery 6 in different states and the state of charge (SOC) of the battery pack 3. The corresponding curves of the voltage of the sodium-ion battery 6 in different states and the SOC of the battery pack 3 in step S100 are usually measured and obtained before the battery pack 3 leaves the factory, so that it can be directly applied through the battery management system (BMS) when the battery pack 3 is subsequently applied to energy storage devices or vehicles. Specifically, these curves can be obtained experimentally, such as by obtaining the voltage of the sodium-ion battery 6 after it is fully charged and left to rest, and by obtaining the voltage of the sodium-ion battery 6 after it is fully discharged and left to rest. Then, based on the two voltages, the corresponding curves of the voltage of the sodium-ion battery 6 and the SOC of the battery pack 3 can be estimated using an appropriate method.

[0134] S200: Collect voltage data of sodium-ion battery 6, and / or monitor the total voltage of sodium-ion battery 6 and lithium-ion battery 7. This step can be achieved by collecting voltage data of sodium-ion battery 6 and / or monitoring the total voltage of sodium-ion battery 6 and lithium-ion battery 7 through battery management unit 8.

[0135] For example, voltage data can be acquired using the first voltage acquisition line 41, the third voltage acquisition line 43, and the second voltage acquisition line 42 mentioned above. The first voltage acquisition line 41 is connected to the positive terminal of the sodium-ion battery 6, and the third voltage acquisition line 43 is connected to the negative terminal of the lithium-ion battery 7. The second voltage acquisition line 42 can be connected to the surface of the casing 10 of the sodium-ion battery 6, or it can be connected to the surface of the casing 10 of the lithium-ion battery 7. The voltage between the third voltage acquisition line 43 and the first voltage acquisition line 41 is the total voltage of the sodium-ion battery 6 and the lithium-ion battery 7 connected in series. The voltage between the first voltage acquisition line 41 and the second voltage acquisition line 42 is the voltage of the sodium-ion battery 6. The voltage between the second voltage acquisition line 42 and the third voltage acquisition line 43 is the voltage of the lithium-ion battery 7. In this step, because the voltage of the sodium-ion battery 6 changes at a relatively large slope during the charging and discharging process, there is a good correspondence between the voltage of the sodium-ion battery 6 and the SOC state of the battery pack 3. Therefore, the voltage of the sodium-ion battery 6 between the first voltage acquisition line 41 and the second voltage acquisition line 42, as well as the total voltage of the sodium-ion battery 6 and the lithium-ion battery 7 connected in series between the third voltage acquisition line 43 and the first voltage acquisition line 41, can be accurately monitored. Thus, by monitoring the voltage of the sodium-ion battery 6 between the first voltage acquisition line 41 and the second voltage acquisition line 42, or the total voltage of the sodium-ion battery 6 and the lithium-ion battery 7 connected in series between the third voltage acquisition line 43 and the first voltage acquisition line 41, the SOC of the battery pack 3 can be accurately predicted.

[0136] S300. Calculate the state of charge of battery pack 3 based on the collected voltage data of sodium-ion battery 6.

[0137] Before step S200, since the corresponding curve of the voltage of sodium-ion battery 6 and the SOC of battery pack 3 has been obtained, the data processing module can calculate the SOC value of battery pack 3 based on the corresponding curve of the voltage of sodium-ion battery 6 and the SOC of battery pack 3.

[0138] It should be noted that when estimating the SOC of battery pack 3, the influence of other factors such as operating temperature and charging / discharging current also needs to be considered.

[0139] When estimating State of Charge (SOC), other factors also need to be considered, such as the battery's operating temperature and charging / discharging current. Changes in these factors will affect the battery voltage, thus impacting the SOC estimation results.

[0140] It is understood that the voltage detection method for the SOC of the battery pack 3 in this embodiment can also be used in combination with the ampere-hour integration method to improve the prediction accuracy of the SOC of the battery pack 3.

[0141] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A battery pack, characterized in that, The battery pack includes a battery management unit and multiple battery cells. Each battery cell includes a housing and a positive electrode tab and a negative electrode tab housed within the housing. The multiple battery cells include sodium-ion batteries and lithium-ion batteries. The negative electrode tab of the sodium-ion battery is electrically connected to the housing of the sodium-ion battery, the positive electrode tab of the lithium-ion battery is electrically connected to the housing of the lithium-ion battery, and the housing of the sodium-ion battery is electrically connected to the housing of the lithium-ion battery. The battery management unit is used to collect voltage data of the sodium-ion battery and calculate the state of charge of the battery pack based on the voltage data of the sodium-ion battery collected by the battery management unit.

2. The battery pack according to claim 1, characterized in that, The battery management unit includes a first voltage acquisition line and a second voltage acquisition line. The first voltage acquisition line is electrically connected to the positive terminal of the sodium-ion battery, and the second voltage acquisition line is electrically connected to the casing of the sodium-ion battery or the casing of the lithium-ion battery.

3. The battery pack according to claim 1 or 2, characterized in that, The casings of the sodium-ion battery and the lithium-ion battery are arranged along a first direction, the length direction of the lithium-ion battery is the same as the first direction, the length direction of the sodium-ion battery is the same as the first direction, and the first direction is the same as the width direction of the battery pack.

4. The battery pack according to claim 3, characterized in that, The width of the lithium-ion battery is the same as the width of the sodium-ion battery, the height of the lithium-ion battery is the same as the height of the sodium-ion battery, the sodium-ion battery and the lithium-ion battery are arranged facing each other in the first direction, and the length of the sodium-ion battery is greater than the length of the lithium-ion battery.

5. The battery pack according to claim 3 or 4, characterized in that, The housing of the sodium-ion battery includes a first top wall, a first bottom wall, and a plurality of first side walls connected between the first top wall and the first bottom wall. The first top wall and the first bottom wall are disposed opposite to each other in the first direction, and the first bottom wall, the first top wall, and the plurality of first side walls form a first sealed cavity. The lithium-ion battery casing includes a second top wall and a plurality of second side walls. The second top wall and the first bottom wall are disposed opposite each other in the first direction. The plurality of second side walls are connected between the first bottom wall and the second top wall. The first bottom wall, the second top wall and the plurality of second side walls form a second sealed cavity.

6. The battery pack according to claim 5, characterized in that, The sodium-ion battery further includes a positive electrode post disposed on the first top wall, the positive electrode post being electrically connected to the positive electrode tab of the sodium-ion battery, and the lithium-ion battery further includes a negative electrode post disposed on the second top wall, the negative electrode post being electrically connected to the negative electrode tab of the lithium-ion battery.

7. The battery pack according to any one of claims 1-6, characterized in that, The positive electrode tab of the sodium-ion battery includes an aluminum foil and a positive electrode material disposed on the aluminum foil. The positive electrode material includes a layered oxide and a polyanion, and the proportion of the polyanion is 0-40%.

8. The battery pack according to claim 3, characterized in that, The number of lithium-ion batteries is multiple, and the multiple lithium-ion batteries are connected in series. The casing of the sodium-ion battery is in contact with and electrically connected to the casing of one of the lithium-ion batteries.

9. The battery pack according to claim 8, characterized in that, The length of the sodium-ion battery is twice the length of the lithium-ion battery. The sodium-ion battery and one of the lithium-ion batteries are arranged along the first direction to form a first battery pack. The three lithium-ion batteries are arranged along the first direction to form a second battery pack. The first battery pack and the second battery pack are arranged along the length of the battery pack.

10. The battery pack according to claim 3, characterized in that, One lithium-ion battery and one sodium-ion battery are arranged along the first direction to form a first battery pack, the first direction being perpendicular to the length direction of the battery pack, and a plurality of the first battery packs are arranged along the length direction of the battery pack.

11. The battery pack according to claim 1 or 2, characterized in that, The casings of the sodium-ion battery and the lithium-ion battery are arranged along a first direction. One lithium-ion battery and one sodium-ion battery are arranged along the first direction to form a first battery pack. The first direction is parallel to the length direction of the battery pack. The battery pack also includes a plurality of lithium-ion batteries. The plurality of lithium-ion batteries are arranged along the length direction of the battery pack to form a second battery pack. In the length direction of the battery pack, the length of the second battery pack is the same as the length of the first battery pack.

12. An energy storage device, characterized in that, The energy storage device includes a battery management system and a plurality of battery packs as described in any one of claims 1-11. The battery management system is used to collect voltage data of the sodium-ion batteries and calculate the state of charge of the battery packs based on the collected voltage data of the sodium-ion batteries.

13. A method for measuring the state of charge of a battery pack as described in any one of claims 1-11, characterized in that, The method includes: Collect voltage data of the sodium-ion battery; The state of charge of the battery pack is calculated based on the collected voltage data of the sodium-ion battery.

14. The method for measuring the state of charge of a battery pack according to claim 13, characterized in that, Before the step of acquiring the voltage data of the sodium-ion battery, the method further includes the following steps: Measure and obtain the voltage of the sodium-ion battery in different states and the corresponding curves of the state of charge of the battery pack; In the step of calculating the state of charge of the battery pack based on the collected voltage data of the sodium-ion battery, the collected voltage data of the sodium-ion battery is used to calculate the state of charge of the battery pack based on the corresponding curve.

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