Energy storage battery pack, energy storage system, and state-of-charge (SOC) equalization method
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-05
- Publication Date
- 2026-08-13
Smart Images
Figure CN2026077323_13082026_PF_FP_ABST
Abstract
Description
Energy storage battery packs, energy storage systems and SOC balancing methods Technical Field
[0001] This application relates to the field of power electronics technology, and in particular to an energy storage battery pack, an energy storage system, and a method for balancing the state of charge (SOC). Background Technology
[0002] Estimating the state of charge (SOC) of energy storage batteries is a core issue in battery management systems (BMS), so accurately estimating the battery's SOC will help extend the battery's lifespan.
[0003] Currently, lithium iron phosphate (LFP) cells exhibit excellent safety performance, leading to a surge in the number of energy storage products using LFP cells in recent years. However, due to the plateauing characteristic of LFP batteries, their state of charge (SOC) cannot be accurately estimated. Summary of the Invention
[0004] In view of the above, this application provides an energy storage battery pack, an energy storage system, and a method for balancing the state of charge (SOC). The energy storage battery pack and energy storage system of this application can solve the problem that existing lithium iron phosphate batteries cannot accurately estimate their SOC due to their plateau period characteristics and the fact that their performance is affected by low temperature environments.
[0005] A first aspect of this application provides an energy storage battery pack, the energy storage battery pack comprising:
[0006] At least one sodium-ion battery cell or solid-state battery cell;
[0007] Multiple lithium iron phosphate cells; the at least one sodium-ion cell or solid-state cell is connected in series with the multiple lithium iron phosphate cells to form a hybrid battery pack;
[0008] The capacity of the sodium-ion battery cell or the solid-state battery cell is greater than that of the lithium iron phosphate battery cell, and the proportion of the sodium-ion battery cell or the solid-state battery cell in the energy storage battery pack is between 10% and 50%.
[0009] The energy storage battery pack of this application is based on a series connection of lithium iron phosphate cells and sodium-ion cells to form an energy storage battery pack. Compared with the existing lithium iron phosphate battery pack, by introducing sodium-ion cells into the energy storage battery pack and setting the proportion of sodium-ion cells in the energy storage battery pack to be between 10% and 50%, the problem that the existing lithium iron phosphate batteries cannot accurately estimate their state of charge can be solved.
[0010] As an optional implementation, the operating voltage range of the lithium iron phosphate battery cell is within the operating voltage range of the sodium-ion battery cell or the solid-state battery cell.
[0011] As an optional implementation, the capacity of the sodium-ion battery cell or the solid-state battery cell is at least 1.5 times greater than the capacity of the lithium iron phosphate battery cell.
[0012] As an optional implementation, the discharge current of the sodium-ion battery cell or the solid-state battery cell is greater than the discharge current of the lithium iron phosphate battery cell, and the charging current of the sodium-ion battery cell or the solid-state battery cell is greater than the charging current of the lithium iron phosphate battery cell.
[0013] As an optional implementation, the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells are arranged in space according to a first preset number of rows and a second preset number of columns.
[0014] As an optional implementation, the at least one sodium-ion battery cell or solid-state battery cell is disposed at the positive and negative terminals of the energy storage battery pack or at the corner of the cell array of the energy storage battery pack.
[0015] A second aspect of this application provides an energy storage system, the energy storage system including a battery management system and at least one energy storage battery pack as described in the first aspect, the battery management system being electrically connected to the energy storage battery pack, the battery management system being used to acquire parameters of the sodium-ion battery cell or the solid-state battery cell and parameters of the plurality of lithium iron phosphate battery cells, and to determine the state of charge of the energy storage system based on the parameters of the sodium-ion battery cell or the solid-state battery cell and the parameters of the plurality of lithium iron phosphate battery cells.
[0016] As an optional implementation, it also includes a power converter electrically connected between the energy storage battery pack and the power generation system, or the power converter electrically connected between the energy storage battery pack and the electrical device.
[0017] As an alternative implementation, the battery management system can estimate the SOC of the energy storage battery pack using the SOC of the sodium-ion cell or the solid-state cell.
[0018] As an optional implementation, the battery management system can perform a fusion calculation based on the SOC of the at least one sodium-ion cell or solid-state cell and the maximum and minimum SOC of the cells among the plurality of lithium iron phosphate cells to estimate the SOC of the energy storage battery pack.
[0019] As an optional implementation, the battery management system can control the SOC balancing operation among the cells in the energy storage battery pack based on the capacity of the at least one sodium-ion cell or solid-state cell and the capacity of the plurality of lithium iron phosphate cells.
[0020] As an optional implementation, the SOC equalization operation includes:
[0021] Real-time calculation of the average SOC of all battery cells;
[0022] Based on the average SOC, perform SOC equalization on each of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells; and
[0023] SOC balancing is performed between the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells based on the minimum and maximum SOC of each cell of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells, or based on the total SOC of the at least one sodium-ion battery cell or solid-state battery cell and the total SOC of the plurality of lithium iron phosphate battery cells.
[0024] As an optional implementation, the step of performing SOC balancing on the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells respectively based on the average SOC includes:
[0025] Based on the SOC of each cell, the cells in the at least one sodium-ion cell or solid-state cell and the plurality of lithium iron phosphate cells are sorted, and the SOC of the at least one sodium-ion cell or solid-state cell and the SOC of the plurality of lithium iron phosphate cells are balanced according to the sorting results and the difference between the SOC of each cell and the average SOC.
[0026] As an optional implementation, the step of performing SOC balancing between the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells based on the minimum and maximum SOC of each cell of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells, or based on the total SOC of the at least one sodium-ion battery cell or solid-state battery cell and the total SOC of the plurality of lithium iron phosphate battery cells, includes:
[0027] Compare the minimum SOC of one of the at least one sodium-ion battery cell or solid-state battery cell and the maximum SOC of one of the plurality of lithium iron phosphate battery cells with the maximum SOC of the other.
[0028] If the minimum SOC of one of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells is greater than the maximum SOC of the other battery cell, then an overall mutual power compensation strategy is adopted to perform SOC balancing operation between the two.
[0029] If the minimum SOC of one of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells is less than or equal to the maximum SOC of the cells in the other, then a single-cell mutual charging strategy is used to perform SOC balancing between the two, or
[0030] Compare the total SOC of the at least one sodium-ion battery cell or solid-state battery cell with the total SOC of the plurality of lithium iron phosphate battery cells;
[0031] If the difference between the total SOC of the at least one sodium-ion battery cell or solid-state battery cell and the total SOC of the plurality of lithium iron phosphate battery cells is greater than or equal to a first predetermined threshold, then an overall mutual charging strategy is adopted to perform SOC balancing between the two.
[0032] The first predetermined threshold is related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
[0033] As an optional implementation, the method of employing an overall mutual power compensation strategy to perform SOC balancing operation between the two includes:
[0034] If the difference in average SOC between the at least one sodium-ion battery cell and the plurality of lithium iron phosphate battery cells is less than a second predetermined threshold, the SOC balancing between the two cells is stopped.
[0035] The second predetermined threshold is related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
[0036] As an optional implementation, the method of employing a single-unit mutual power compensation strategy to perform SOC balancing operation between the two includes:
[0037] Based on the difference between the SOC of each of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells and the average SOC, the SOC between the two is balanced using a one-to-one correspondence method between the cells.
[0038] As an optional implementation, the SOC balancing operation further includes: at the end of charging and discharging, determining the difference between the average SOC of the at least one sodium-ion cell or solid-state cell and the average SOC of the plurality of lithium iron phosphate cells; if the difference between their average SOCs is greater than a third predetermined threshold, then performing SOC balancing between them, until the difference between their average SOCs is less than a fourth predetermined threshold.
[0039] The third and fourth predetermined thresholds are related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
[0040] A third aspect of this application provides a state-of-charge (SOC) balancing method for the energy storage system, the method comprising: performing an SOC balancing operation among the cells in the energy storage battery pack based on the capacity of the at least one sodium-ion cell or solid-state cell and the capacity of the plurality of lithium iron phosphate cells.
[0041] The energy storage system of this application is based on a hybrid series connection of lithium iron phosphate cells and sodium-ion cells to form an energy storage battery pack. Compared with existing lithium iron phosphate battery packs, by introducing sodium-ion cells (or solid-state cells) into the energy storage battery pack and setting the proportion of sodium-ion cells (or solid-state cells) in the energy storage battery pack to between 10% and 50%, the state parameters of the entire energy storage system can be estimated by using the state of charge of sodium-ion cells (or solid-state cells). This solves the problem that existing lithium iron phosphate batteries cannot accurately estimate their state of charge. Attached Figure Description
[0042] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0043] Figure 1 is an application scenario diagram of an energy storage system provided in an embodiment of this application.
[0044] Figure 2 is a diagram of another application scenario of an energy storage system provided in an embodiment of this application.
[0045] Figure 3 is a schematic diagram of an energy storage system provided in an embodiment of this application.
[0046] Figure 4 is a schematic diagram of an energy storage battery pack provided in an embodiment of this application.
[0047] Figure 5 is another schematic diagram of an energy storage battery pack provided in an embodiment of this application.
[0048] Figure 6 is another schematic diagram of an energy storage battery pack provided in an embodiment of this application.
[0049] Figure 7 is another schematic diagram of an energy storage battery pack provided in an embodiment of this application.
[0050] Figure 8 is a schematic diagram of a battery management system provided in an embodiment of this application.
[0051] Figure 9 is a schematic diagram of the SOC balancing operation of a battery management system provided in an embodiment of this application. Detailed Implementation
[0052] In the embodiments of this application, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or order. For example, "first application" and "second application" are used to distinguish different applications, not to describe a specific order of applications. Features specified as "first" or "second" may explicitly or implicitly include one or more of those features.
[0053] Estimating the state of charge (SOC) of energy storage batteries is a core issue in battery management systems (BMS), so accurately estimating the battery's SOC will help extend the battery's lifespan.
[0054] Currently, lithium iron phosphate (LFP) cells exhibit excellent safety performance, leading to a surge in the number of energy storage products using LFP cells in recent years. However, due to the plateauing characteristics of LFP cells and their performance degradation at low temperatures, it is difficult to accurately estimate the battery's state of charge.
[0055] To address the aforementioned problems, embodiments of this application provide an energy storage battery pack, an energy storage system, and a method for balancing the state of charge (SOC). This application can construct a hybrid series battery pack by using a combination of lithium iron phosphate cells and sodium-ion cells or solid-state cells connected in series within the energy storage battery pack.
[0056] Sodium-ion batteries or solid-state cells outperform lithium iron phosphate batteries in low-temperature environments. For example, at -20°C, sodium-ion batteries retain approximately 90% of their capacity, while lithium iron phosphate batteries retain about 70%. This means that sodium-ion batteries can provide higher actual capacity in cold regions or low-temperature applications.
[0057] This application is based on an energy storage battery pack that uses a mixture of lithium iron phosphate cells and sodium-ion cells or solid-state cells connected in series. Compared to lithium-ion battery packs, this application introduces sodium-ion cells or solid-state cells into the energy storage battery pack, and sets the proportion of sodium-ion cells in the energy storage battery pack to between 10% and 50%. The state parameters of the entire energy storage system can be estimated by the state of charge of the sodium-ion cells or solid-state cells. The state parameters can include the state of charge (SOC), state of health (SOH), and state of power (SOP). This application can solve the problem that existing lithium iron phosphate batteries cannot accurately estimate their state parameters, especially the state of charge, due to their plateau characteristics and the fact that their performance is affected by low-temperature environments.
[0058] Please refer to Figure 1, which is a schematic diagram of an application of an energy storage system 200 provided in an embodiment of this application.
[0059] In one application scenario, the energy storage system 200 is electrically connected to the electrical device 300. The energy storage system 200 can be used to supply power to the electrical device 300.
[0060] In this application, electrical equipment 300 refers to equipment powered by electrical energy, including household appliances such as electric water heaters, electric fans, electric hair dryers, vacuum cleaners, and robot vacuum cleaners.
[0061] Please refer to Figure 2, which is a schematic diagram of another application of the energy storage system 200 provided in one embodiment of this application.
[0062] In another application scenario, the energy storage system 200 is electrically connected to the power generation system 400. The power generation system 400 can be used to supply power to the energy storage system 200.
[0063] It is understood that, in one alternative implementation, the power generation system 400 can be a photovoltaic power generation system, which can convert solar energy into usable electrical energy and output the electrical energy to the energy storage system 200 to charge the energy storage system 200. In other alternative implementations, the power generation system 400 can also be other new energy power generation systems or a power grid.
[0064] Please refer to Figure 3, which is a schematic diagram of an energy storage system 200 provided in one embodiment of this application.
[0065] In this embodiment, the energy storage system 200 may include a power converter 201, a battery management system 202, and multiple energy storage battery packs connected in series. Figure 3 illustrates this with three energy storage battery packs 100a, 100b, and 100c as an example. In possible embodiments, the number of energy storage battery packs may be more than three or less than three. As shown in Figure 3, the multiple energy storage battery packs 100a, 100b, and 100c are connected in series. It can be understood that in other possible implementations, the multiple energy storage battery packs 100a, 100b, and 100c may also be connected in parallel.
[0066] Energy storage battery pack 100a can be connected to battery management system 202 via communication bus 101a to enable communication between them. Energy storage battery pack 100b can be connected to battery management system 202 via communication bus 101b to enable communication between them. Energy storage battery pack 100c can be connected to battery management system 202 via communication bus 101c to enable communication between them. Battery management system 202 can also be connected to power converter 201 via communication bus 101d to enable communication between them. In one possible example, energy storage battery pack 100a can be connected to battery management system 202 via Controller Area Network (CAN) bus, and energy storage battery pack 100b and energy storage battery pack 100c can be connected to battery management system 202 via CAN communication bus. The battery management system 202 can also be connected to the power converter 201 via a CAN communication bus. It is understood that, in another possible example, the aforementioned communication buses 101a, 101b, 101c, and 101d could also be RS485 buses.
[0067] In one example, one end of the power converter 201 is electrically connected to the positive terminal of the energy storage battery pack 100a, and the other end of the power converter 201 is also electrically connected to the negative terminal of the energy storage battery pack 100a. One end of the battery management system 202 is electrically connected to the connection point between the positive terminal of the energy storage battery pack 100a and the power converter 201, and the other end of the battery management system 202 is electrically connected to the connection point between the negative terminal of the energy storage battery pack 100a and the power converter 201.
[0068] Based on this approach, in the embodiments of this application, the battery management system 202 can obtain the battery parameters of the energy storage battery packs 100a, 100b, and 100c, and the battery management system 202 can also estimate the state parameters of the energy storage system 200 based on the obtained parameters.
[0069] In the scenario where the energy storage system 200 supplies power to the electrical device 300, the electrical device 300 is electrically connected to the power converter 201, and the energy storage battery packs 100a, 100b, and 100c connected in series provide power to the electrical device 200 through the power converter 201.
[0070] In the scenario where the power generation system 400 supplies power to the energy storage system 200, the power generation system 400 is electrically connected to the power converter 201, and the power generation system 400 provides power to the energy storage battery packs 100a, 100b, and 100c connected in series through the power converter 201.
[0071] In this embodiment, energy storage battery packs 100a, 100b, and 100c are hybrid battery packs. A hybrid battery pack refers to a battery pack assembled from two or more types of battery cells.
[0072] It is understood that the structures of energy storage battery packs 100a, 100b, and 100c may be the same or different. In a preferred implementation, the structures of energy storage battery packs 100a, 100b, and 100c are the same. The following explanation will use the structure of energy storage battery pack 100a as an example.
[0073] It is understood that the energy storage battery pack in this application may include at least one sodium-ion battery cell (or solid-state battery cell) and multiple lithium iron phosphate battery cells. At least one sodium-ion battery cell may be connected in series with multiple lithium iron phosphate battery cells to form a hybrid battery pack. The capacity of the sodium-ion battery cell is greater than that of the lithium iron phosphate battery cell, and the proportion of sodium-ion battery cells in the energy storage battery pack is between 10% and 50% (i.e., the proportion of sodium-ion battery cells in the energy storage battery pack is greater than 10% and less than 50%).
[0074] The energy storage battery pack of this application will be described in detail below with reference to specific embodiments.
[0075] Please refer to Figure 4, which is a schematic diagram of an energy storage battery pack 100a provided in one embodiment of this application.
[0076] As shown in Figure 4, the energy storage battery pack 100a may include multiple battery cells. Specifically, the energy storage battery pack 100a includes at least one lithium iron phosphate battery cell and at least one sodium-ion battery cell. Of course, in other examples, the energy storage battery pack 100a may also include at least one lithium iron phosphate battery cell and at least one solid-state battery cell. The various positional and parameter settings of the solid-state battery cell are the same as those of the sodium-ion battery cell. The following description uses the sodium-ion battery cell as an example.
[0077] Figure 4 illustrates the example using one sodium-ion battery cell and seven lithium iron phosphate battery cells. It is understood that in other possible embodiments, the number of lithium iron phosphate battery cells may be more than seven or less than seven, and the number of sodium-ion battery cells may be greater than one.
[0078] In a specific implementation, in one example, the energy storage battery pack 100a includes a sodium-ion battery cell 21a, a lithium iron phosphate battery cell 31a, a lithium iron phosphate battery cell 32a, a lithium iron phosphate battery cell 33a, a lithium iron phosphate battery cell 34a, a lithium iron phosphate battery cell 35a, a lithium iron phosphate battery cell 36a, and a lithium iron phosphate battery cell 37a connected in series.
[0079] More specifically, the positive electrode of lithium iron phosphate cell 31a is electrically connected to the negative electrode of sodium-ion cell 21a; the negative electrode of lithium iron phosphate cell 31a is electrically connected to the positive electrode of lithium iron phosphate cell 32a; the negative electrode of lithium iron phosphate cell 32a is electrically connected to the positive electrode of lithium iron phosphate cell 33a; the negative electrode of lithium iron phosphate cell 33a is electrically connected to the positive electrode of lithium iron phosphate cell 34a; the negative electrode of lithium iron phosphate cell 34a is electrically connected to the positive electrode of lithium iron phosphate cell 35a; the negative electrode of lithium iron phosphate cell 35a is electrically connected to the positive electrode of lithium iron phosphate cell 36a; and the negative electrode of lithium iron phosphate cell 36a is electrically connected to the positive electrode of lithium iron phosphate cell 37a. Therefore, the positive electrode of sodium-ion cell 21a can be used as the positive electrode of energy storage battery pack 100a, and the negative electrode of lithium iron phosphate cell 37a can be used as the negative electrode of energy storage battery pack 100a. In an alternative implementation, in order to ensure that the energy storage battery pack 100a can be assembled smoothly and to reduce the volume of the energy storage battery pack 100a, the sodium-ion battery cell 21a, lithium iron phosphate battery cell 31a, lithium iron phosphate battery cell 32a, lithium iron phosphate battery cell 33a, lithium iron phosphate battery cell 34a, lithium iron phosphate battery cell 35a, lithium iron phosphate battery cell 36a, and lithium iron phosphate battery cell 37a can be arranged in an array structure.
[0080] In one alternative implementation, the lithium iron phosphate cells and sodium-ion cells in the energy storage battery pack 100a can be arranged in space according to a preset number of rows and columns.
[0081] As an example, the multiple cells of the energy storage battery pack 100a in this embodiment can be arranged in a 2-row, 4-column array structure. As shown in Figure 4, the first row, from left to right, contains one sodium-ion cell and three lithium iron phosphate cells, while the second row contains four lithium iron phosphate cells. It is understood that due to the plateau characteristic of the open circuit voltage (OCV) curve of lithium iron phosphate cells, the estimation of the state of charge (SOC) of these cells will have a relatively large error, especially at low temperatures where the capacity of the lithium iron phosphate cells changes significantly, leading to even greater deviations in the SOC estimation.
[0082] The OCV curve of a sodium-ion battery cell is a directly proportional curve, meaning there is no plateau period. In this application, the energy storage battery pack 100a is a hybrid battery pack of sodium-ion and lithium iron phosphate cells, i.e., sodium-ion cells are connected in series with multiple lithium iron phosphate cells. Therefore, in this application, the battery management system 202 can accurately estimate the state of charge (SOC) of the energy storage system 200 by using the SOC of the sodium-ion cells.
[0083] In its specific implementation, the energy storage battery pack 100a includes a controller (not shown in the figure). The controller collects the voltages of the sodium-ion cells and the lithium iron phosphate cells, and transmits these voltages to the battery management system 202 via a communication bus. The battery management system 202 can sample the parameters of the sodium-ion cells (i.e., voltage, current, and temperature) and the parameters of multiple lithium iron phosphate cells (i.e., voltage, current, and temperature), and obtain the state of charge (SOC) parameters of the sodium-ion cells and the SOC parameters of the multiple lithium iron phosphate cells based on the parameters of the multiple lithium iron phosphate cells. The battery management system 202 can perform a fusion calculation based on the SOC of the sodium-ion cells, the highest SOC among the multiple lithium iron phosphate cells, and the lowest SOC among the multiple lithium iron phosphate cells, thereby accurately estimating the SOC of the energy storage system 200.
[0084] In one alternative implementation, to ensure the full release of the energy storage battery pack's capacity, the capacity of the sodium-ion battery cell is greater than that of the lithium iron phosphate battery cell. Taking sodium-ion battery cell 21a and lithium iron phosphate battery cell 31a as examples, the capacity of sodium-ion battery cell 21a is greater than that of lithium iron phosphate battery cell 31a.
[0085] In another, more specific implementation, the capacity of the sodium-ion battery cell is at least 1.5 times greater than that of the lithium iron phosphate battery cell; that is, the capacity of the sodium-ion battery cell is at least 1.5 times that of the lithium iron phosphate battery cell. Taking sodium-ion battery cell 21a and lithium iron phosphate battery cell 31a as examples, the capacity of sodium-ion battery cell 21a is at least 1.5 times greater than that of lithium iron phosphate battery cell 31a.
[0086] Because the discharge rate of sodium-ion cells is greater than that of lithium iron phosphate cells, and the decay rate of sodium-ion cells is greater than that of lithium iron phosphate cells at low temperatures, the capacity of sodium-ion cell 21a is set to be greater than that of lithium iron phosphate cell 31a. In other words, the capacity of sodium-ion cell 21a is redundantly designed. This not only ensures that the energy storage battery pack can be fully released, but also makes it easier to estimate the overall SOC of the energy storage battery pack at low temperatures.
[0087] Under normal ambient temperature or specific scenarios, this redundant design may result in the sodium-ion cell 21a's capacity never being fully utilized, while the lithium iron phosphate cell's capacity is relatively low, causing a "weakest link" effect in the overall energy storage battery pack. Therefore, in order to solve this problem, this application adopts a battery SOC balancing method to balance the SOC of the above-mentioned energy storage battery pack, in order to solve the problem that the redundant design causes the sodium-ion cell 21a's capacity to never be fully utilized, the lithium iron phosphate cell's capacity to be relatively low, and the overall energy storage battery pack to exhibit a "weakest link" effect.
[0088] The SOC equalization operation includes:
[0089] Real-time calculation of the average SOC of all battery cells;
[0090] Based on the average SOC, SOC balancing is performed on each of the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells; and
[0091] SOC balancing is performed between the at least one sodium-ion cell (or solid-state cell) and the plurality of lithium iron phosphate cells based on the minimum and maximum SOC of each cell of the at least one sodium-ion cell (or solid-state cell) and the plurality of lithium iron phosphate cells, or based on the total SOC of the at least one sodium-ion cell (or solid-state cell) and the total SOC of the plurality of lithium iron phosphate cells.
[0092] In one example, the step of performing SOC balancing on the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells respectively based on the average SOC includes:
[0093] Based on the SOC of each cell, the cells in the at least one sodium-ion cell (or solid-state cell) and the plurality of lithium iron phosphate cells are sorted, and the SOC balancing of the at least one sodium-ion cell (or solid-state cell) and the SOC balancing of the plurality of lithium iron phosphate cells are performed according to the sorting results and the difference between the SOC of each cell and the average SOC.
[0094] In one example, performing SOC balancing between the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells based on the minimum and maximum SOC of each cell of the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells, or based on the total SOC of the at least one sodium-ion battery cell (or solid-state battery cell) and the total SOC of the plurality of lithium iron phosphate battery cells, includes:
[0095] Compare the minimum SOC of one of the at least one sodium-ion battery cell (or solid-state battery cell) and the maximum SOC of one of the plurality of lithium iron phosphate battery cells.
[0096] If the minimum SOC of one of the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells is greater than the maximum SOC of the other, then an overall mutual power supplementation strategy is adopted to perform SOC balancing operation between the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells.
[0097] If the minimum SOC of one of the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells is less than or equal to the maximum SOC of the other, then a single-cell mutual charging strategy is used to perform SOC balancing operation between the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells, or
[0098] Compare the total SOC of the at least one sodium-ion battery cell (or solid-state battery cell) with the total SOC of the plurality of lithium iron phosphate battery cells;
[0099] If the difference between the total SOC of the at least one sodium-ion battery cell (or solid-state battery cell) and the total SOC of the plurality of lithium iron phosphate battery cells is greater than or equal to a first predetermined threshold, then an overall mutual charging strategy is adopted to perform SOC balancing between the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells.
[0100] The first predetermined threshold is related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
[0101] In one example, the capacity of one lithium iron phosphate cell is 1, and the capacity of one sodium-ion cell is 1.5. Assuming the number of lithium iron phosphate cells is n and the number of sodium-ion cells is n*0.25, the total capacity of at least one sodium-ion cell is 1.5*0.25*n, and the total capacity of multiple lithium iron phosphate cells is 1*n. The difference between the total capacity of at least one sodium-ion cell (or solid-state cell) and the total capacity of multiple lithium iron phosphate cells is -0.625n. As the battery is used, the capacity of both will decrease. Assuming that the discharge rates of sodium-ion cells and lithium iron phosphate cells are basically the same, after a period of time, the difference between the total SOC of at least one sodium-ion cell and the total SOC of multiple lithium iron phosphate cells will be -0.625*0.8n. Therefore, the first predetermined threshold can be set to -0.625*0.8n*k, where k takes a value between 1.1 and 1.6.
[0102] In one example, the SOC balancing operation between the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells using an overall mutual power compensation strategy includes:
[0103] If the difference in average SOC between the at least one sodium-ion battery cell and the plurality of lithium iron phosphate battery cells is less than a second predetermined threshold, the SOC balancing between the at least one sodium-ion battery cell (or solid-state battery cell) and the plurality of lithium iron phosphate battery cells is stopped.
[0104] The second predetermined threshold is related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
[0105] In one example, the capacity of one lithium iron phosphate cell is 1, and the capacity of one sodium-ion cell is 1.5. The difference in average SOC between the two types of batteries at the start of discharge is 0.5. Assuming that the discharge rates of the sodium-ion and lithium iron phosphate cells are essentially the same, the second predetermined threshold is set to m times the difference of 0.5, where m ranges from 0.2 to 0.6.
[0106] In one example, the SOC balancing operation between the at least one sodium-ion cell (or solid-state cell) and the plurality of lithium iron phosphate cells using a single-cell mutual charging strategy includes:
[0107] Based on the difference between the SOC of each of the at least one sodium-ion cell (or solid-state cell) and the plurality of lithium iron phosphate cells and the average SOC, SOC balancing between the at least one sodium-ion cell (or solid-state cell) and the plurality of lithium iron phosphate cells is performed in a one-to-one correspondence manner.
[0108] In one example, the SOC balancing operation further includes: at the end of charging and discharging, determining the difference between the average SOC of the at least one sodium-ion cell (or solid-state cell) and the average SOC of the plurality of lithium iron phosphate cells; if the difference between the average SOC of the at least one sodium-ion cell (or solid-state cell) and the average SOC of the plurality of lithium iron phosphate cells is greater than a third predetermined threshold, then performing SOC balancing between the two until the difference between their average SOCs is less than a fourth predetermined threshold.
[0109] The third and fourth predetermined thresholds are related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
[0110] In one example, the capacity of one lithium iron phosphate cell is 1, and the capacity of one sodium-ion cell is 1.5. At the start of discharge, the difference in average SOC between the two types of batteries is 0.5. Assuming that the charge and discharge rates of the sodium-ion and lithium iron phosphate cells are essentially the same, then the third predetermined threshold is set to t times the difference of 0.5, where t ranges from 0.6 to 0.9. The fourth predetermined threshold is set to m times the difference of 0.5, where m ranges from 0.2 to 0.6.
[0111] Referring to Figure 9, taking a sodium-ion battery cell as an example (the same applies to solid-state batteries), the SOC equalization operation includes:
[0112] Step 1: Calculate the current average SOC in real time based on the current SOC of all individual cells;
[0113] Step 2: Sort the individual cell SOC sizes of nano- and lithium-ion batteries, and match and balance them one by one according to the difference from the average SOC.
[0114] Step 3: After both have completed internal cell balancing, determine whether mutual power replenishment is needed;
[0115] Step 4: Determine whether to activate individual cell mutual charging or overall mutual charging based on the lowest and highest SOC of each cell;
[0116] Step 5: At the end of the charge / discharge cycle, determine the difference between the nano-current SOC and the lithium-ion battery SOC. If the nano-current SOC is much higher than the lithium-ion battery SOC, then the nano-current is used to charge the lithium-ion battery, and vice versa.
[0117] Referring to Figure 8, taking sodium-ion cells as an example (the same applies to solid-state cells), the specific steps of the SOC equalization operation include:
[0118] Step 1: Begin;
[0119] Step 2: Calculate the average SOC of all individual cells in real time;
[0120] Step 3: Determine if it is the end of the charge / discharge cycle;
[0121] Step 4: If it is the end of the charge / discharge cycle, calculate the average SOC of the sodium-ion battery cell and the average SOC of multiple lithium iron phosphate battery cells, denoted as SOC-NaAvg and SOC-LiAvg respectively; if it is not the end of the charge / discharge cycle, proceed directly to step 7.
[0122] Step 5: Compare the average SOC of the sodium-ion battery cell with the average SOC of multiple lithium iron phosphate battery cells, and determine whether the difference between the two is greater than the end-on threshold ΔCurrEnd (corresponding to the third predetermined threshold mentioned above).
[0123] Step 6: If the difference between the two is greater than the end-to-end threshold ΔCurrEnd, enable equalization and calculate SOC in real time.- NaAvg and SOC-LiAvg, until the difference between their thresholds is less than the closing threshold ΔCurrEnd1 (corresponding to the fourth predetermined threshold mentioned above); if the difference between them is not greater than the end opening threshold ΔCurrEnd, then proceed directly to step 7.
[0124] Step 7: Sort the SOC of each individual cell in at least one sodium-ion cell and multiple lithium iron phosphate cells, and perform matching and balancing based on the difference from the average SOC until SOC balancing is completed.
[0125] Step 8: Calculate the average SOC of the sodium-ion battery cell and the average SOC of multiple lithium iron phosphate battery cells, and denote them as SOC. - NaAvg and SOC-LiAvg;
[0126] Step 9: Compare the highest SOC of one of the sodium-ion cells and the lowest SOC of the other of the multiple lithium iron phosphate cells to see if the lowest SOC of one is higher than the highest SOC of the other.
[0127] Step 10: If the lowest SOC of one party is equal to or lower than the highest SOC of the other party, then select the individual cells to be balanced one by one according to the difference between the individual SOC and the average SOC of both parties; after the individual cells are balanced one by one, or if the lowest SOC of one party is higher than the highest SOC of the other party, then compare the average SOC of at least one sodium-ion cell and multiple lithium iron phosphate cells to see if it is greater than the end-turn-on threshold Δ1.
[0128] Step 11: If the difference is greater than the threshold, start the equalization process and calculate SOC-NaAvg and SOC-LiAvg in real time until the difference between their thresholds is less than the closing threshold Δ2 (corresponding to the second predetermined threshold mentioned above); if the difference is not greater than the threshold, the equalization process ends.
[0129] In one alternative implementation, the operating voltage range of the lithium-ion battery cell covers the operating voltage range of the lithium iron phosphate battery cell; that is, the operating voltage range of the lithium iron phosphate battery cell is within the operating voltage range of the lithium-ion battery cell. As an example, taking sodium-ion battery cell 21a and lithium iron phosphate battery cell 31a, the operating voltage of lithium iron phosphate battery cell 31a is greater than a first voltage threshold and less than a second voltage threshold. The minimum operating voltage of sodium-ion battery cell 21a is less than or equal to the first threshold, and the maximum operating voltage of sodium-ion battery cell 21a is greater than or equal to the second threshold. For example, the operating voltage of lithium iron phosphate battery cell 31a is greater than 2.5V and less than 3.6V. The minimum operating voltage of sodium-ion battery cell 21a is less than or equal to 2.5V, and the maximum operating voltage of sodium-ion battery cell 21a is greater than or equal to 3.6V.
[0130] In one alternative implementation, the charging current of the sodium-ion battery cell is greater than that of the lithium iron phosphate battery cell. The discharging current of the sodium-ion battery cell is also greater than that of the lithium iron phosphate battery cell.
[0131] In the embodiment shown in Figure 4 above, the sodium-ion battery cell is located at the positive terminal of the energy storage battery pack 100a. Furthermore, the energy storage battery pack 100a contains 1 sodium-ion battery cell and 8 lithium iron phosphate battery cells, meaning that the sodium-ion battery cell accounts for 12.5% of the total number of cells in the energy storage battery pack 100a. In other words, in this embodiment, the sodium-ion battery cell accounts for between 10% and 50% of the total number of cells in the energy storage battery pack 100a.
[0132] Please refer to Figure 5, which is a schematic diagram of an energy storage battery pack 100a provided in another embodiment of this application.
[0133] The difference from the embodiment shown in FIG4 is that, as shown in FIG5, in this embodiment, the energy storage battery pack 100a includes two sodium-ion cells, and the two sodium-ion cells are respectively located at the positive terminal and the negative terminal of the energy storage battery pack 100a.
[0134] Specifically, the energy storage battery pack 100a in this embodiment includes a sodium-ion battery cell 21a, a lithium iron phosphate battery cell 31a, a lithium iron phosphate battery cell 32a, a lithium iron phosphate battery cell 33a, a lithium iron phosphate battery cell 34a, a lithium iron phosphate battery cell 35a, a lithium iron phosphate battery cell 36a, and a sodium-ion battery cell 22a connected in series.
[0135] More specifically, the positive electrode of lithium iron phosphate cell 31a is electrically connected to the negative electrode of sodium-ion cell 21a; the negative electrode of lithium iron phosphate cell 31a is electrically connected to the positive electrode of lithium iron phosphate cell 32a; the negative electrode of lithium iron phosphate cell 32a is electrically connected to the positive electrode of lithium iron phosphate cell 33a; the negative electrode of lithium iron phosphate cell 33a is electrically connected to the positive electrode of lithium iron phosphate cell 34a; the negative electrode of lithium iron phosphate cell 34a is electrically connected to the positive electrode of lithium iron phosphate cell 35a; the negative electrode of lithium iron phosphate cell 35a is electrically connected to the positive electrode of lithium iron phosphate cell 36a; and the negative electrode of lithium iron phosphate cell 36a is electrically connected to the positive electrode of sodium-ion cell 22a. Therefore, the positive electrode of sodium-ion cell 21a can serve as the positive electrode of energy storage battery pack 100a, and the negative electrode of sodium-ion cell 22a can serve as the negative electrode of energy storage battery pack 100a.
[0136] In this embodiment, the multiple cells of the energy storage battery pack 100a are arranged in a 2-row, 4-column array structure. As shown in Figure 5, the first row from left to right consists of 1 sodium-ion cell and 3 lithium iron phosphate cells, and the second row from right to left consists of 3 lithium iron phosphate cells and 1 sodium-ion cell.
[0137] It is understood that in this embodiment, there are 6 lithium iron phosphate cells between the two sodium-ion cells 21a and 22a.
[0138] In the embodiment shown in Figure 5 above, two sodium-ion cells are located at the positive and negative terminals of the energy storage battery pack 100a, respectively. Furthermore, the energy storage battery pack 100a contains 2 sodium-ion cells and 6 lithium iron phosphate cells, meaning that sodium-ion cells account for 25% of the total number of cells in the energy storage battery pack 100a. In other words, in this embodiment, the proportion of sodium-ion cells in the energy storage battery pack 100a is between 10% and 50%.
[0139] Please refer to Figure 6, which is a schematic diagram of an energy storage battery pack 100a provided in another embodiment of this application.
[0140] The difference from the embodiment shown in Figure 5 is that, as shown in Figure 6, in this embodiment, the energy storage battery pack 100a includes four sodium-ion cells, and the four sodium-ion cells are located at the four corners of the array structure. The sodium-ion cells are located at the four corners of the array structure because sodium-ion batteries perform better than lithium iron phosphate batteries in low-temperature environments. The temperature at the four corners is slightly lower than that at the inner side. This arrangement makes the overall performance of the energy storage battery pack better and the predicted SOC of the energy storage battery pack more accurate.
[0141] Specifically, the energy storage battery pack 100a in this embodiment includes sodium-ion battery cell 21a, lithium iron phosphate battery cell 30a, lithium iron phosphate battery cell 35a, lithium iron phosphate battery cell 32a, sodium-ion battery cell 22a, sodium-ion battery cell 23a, lithium iron phosphate battery cell 33a, lithium iron phosphate battery cell 36a, lithium iron phosphate battery cell 34a, and sodium-ion battery cell 24a connected in series.
[0142] More specifically, in the embodiments of this application, the positive electrode of the lithium iron phosphate cell 30a is electrically connected to the negative electrode of the sodium-ion cell 21a, the negative electrode of the lithium iron phosphate cell 30a is electrically connected to the positive electrode of the lithium iron phosphate cell 35a, the negative electrode of the lithium iron phosphate cell 35a is electrically connected to the positive electrode of the lithium iron phosphate cell 32a, the negative electrode of the lithium iron phosphate cell 32a is electrically connected to the positive electrode of the sodium-ion cell 22a, the negative electrode of the sodium-ion cell 22a is electrically connected to the positive electrode of the sodium-ion cell 23a, the negative electrode of the sodium-ion cell 23a is electrically connected to the positive electrode of the lithium iron phosphate cell 33a, the negative electrode of the lithium iron phosphate cell 33a is electrically connected to the positive electrode of the lithium iron phosphate cell 36a, the negative electrode of the lithium iron phosphate cell 36a is electrically connected to the positive electrode of the lithium iron phosphate cell 34a, and the negative electrode of the lithium iron phosphate cell 34a is electrically connected to the positive electrode of the sodium-ion cell 24a. Therefore, the positive electrode of the sodium-ion battery cell 21a can be used as the positive electrode of the energy storage battery pack 100a, and the negative electrode of the sodium-ion battery cell 24a can be used as the negative electrode of the energy storage battery pack 100a.
[0143] In the embodiments of this application, the multiple cells of the energy storage battery pack 100a are arranged in a 2-row, 4-column array structure. As shown in the spatial arrangement in Figure 6, the first row from left to right consists of 1 sodium-ion cell, 3 lithium iron phosphate cells, and 1 sodium-ion cell, and the second row from right to left consists of 1 sodium-ion cell, 3 lithium iron phosphate cells, and 1 sodium-ion cell.
[0144] It is understood that in this embodiment, there are 3 lithium iron phosphate cells between sodium ion cell 21a and sodium ion cell 22a, and there are 3 lithium iron phosphate cells between sodium ion cell 23a and sodium ion cell 24a.
[0145] It is understandable that if the number of sodium-ion cells in the energy storage battery pack is greater than two, in addition to placing two sodium-ion cells at each end of the energy storage battery pack, the remaining sodium-ion cells need to be evenly interspersed among the lithium iron phosphate cells. Therefore, in the embodiment shown in Figure 6 above, four sodium-ion cells are located at the four corners of the array structure, and two sodium-ion cells are located at the positive and negative terminals of the energy storage battery pack 100a, respectively, so that the energy storage battery pack 100a achieves overall balance. Furthermore, the number of sodium-ion cells in the energy storage battery pack 100a is 4, and the number of lithium iron phosphate cells is 6, that is, the proportion of sodium-ion cells in the energy storage battery pack 100a is 40%. In other words, in this embodiment, the proportion of sodium-ion cells in the energy storage battery pack 100a is between 10% and 50%.
[0146] Please refer to Figure 7, which is a schematic diagram of an energy storage battery pack 100a provided in another embodiment of this application.
[0147] The difference from the embodiment shown in Figure 5 is that, as shown in Figure 7, in this embodiment, the energy storage battery pack 100a includes two sodium-ion cells located in the middle of the array structure, and four lithium iron phosphate cells located at the four corners of the array structure.
[0148] The energy storage battery pack 100a in this embodiment includes lithium iron phosphate cell 31a, sodium-ion cell 21a, lithium iron phosphate cell 32a, lithium iron phosphate cell 33a, lithium iron phosphate cell 34a, lithium iron phosphate cell 35a, sodium-ion cell 22a, and lithium iron phosphate cell 36a connected in series.
[0149] Specifically, the positive electrode of sodium-ion battery cell 21a is electrically connected to the negative electrode of lithium iron phosphate battery cell 31a; the negative electrode of sodium-ion battery cell 21a is electrically connected to the positive electrode of lithium iron phosphate battery cell 32a; the negative electrode of lithium iron phosphate battery cell 32a is electrically connected to the positive electrode of lithium iron phosphate battery cell 33a; the negative electrode of lithium iron phosphate battery cell 33a is electrically connected to the positive electrode of lithium iron phosphate battery cell 34a; the negative electrode of lithium iron phosphate battery cell 34a is electrically connected to the positive electrode of lithium iron phosphate battery cell 35a; the negative electrode of lithium iron phosphate battery cell 35a is electrically connected to the positive electrode of sodium-ion battery cell 22a; and the negative electrode of sodium-ion battery cell 22a is electrically connected to the positive electrode of lithium iron phosphate battery cell 36a. Therefore, the positive electrode of lithium iron phosphate battery cell 31a can be used as the positive electrode of energy storage battery pack 100a, and the negative electrode of lithium iron phosphate battery cell 36a can be used as the negative electrode of energy storage battery pack 100a.
[0150] It is understood that in this embodiment, there are four lithium iron phosphate cells between sodium ion cell 21a and sodium ion cell 22a.
[0151] In the embodiment shown in Figure 7 above, two lithium iron phosphate cells are located at the positive and negative terminals of the energy storage battery pack 100a, respectively. Furthermore, the energy storage battery pack 100a contains 2 sodium-ion cells and 6 lithium iron phosphate cells, meaning that sodium-ion cells account for 25% of the total number of cells in the energy storage battery pack 100a. In other words, in this embodiment, the proportion of sodium-ion cells in the energy storage battery pack 100a is between 10% and 50%.
[0152] It is understood that the embodiment in Figure 5 places the sodium-ion battery cell at both the positive and negative terminals of the battery pack. The difference between the embodiment in Figure 5 and the embodiment in Figure 7 is that the sodium-ion battery cell is placed in the middle of the six lithium iron phosphate battery cells. The energy storage battery packs of the embodiments in Figure 5 and Figure 7 have similar performance in estimating the state of charge.
[0153] Sodium-ion batteries exhibit better thermal stability than lithium iron phosphate batteries. However, when placed in the middle of a battery pack, sodium-ion batteries experience a significant temperature rise and have a poor cycle life. If exposed to high temperatures for extended periods, their state of health deteriorates rapidly, negatively impacting the estimation of state of charge. Therefore, in some possible implementations, such as the battery pack 100a shown in Figure 5, sodium-ion batteries are positioned at either the positive or negative terminal to ensure they are kept at a suitable temperature.
[0154] It is understood that the energy storage battery pack 100a shown in the embodiments of Figure 4, Figure 5, Figure 6 and Figure 7 above is a possible example of the structure of the energy storage battery pack, and this application does not limit the number and location of sodium-ion cells and lithium iron phosphate cells in the energy storage battery pack.
[0155] It's understandable that in some traditional energy storage battery pack structures, if sodium-ion cells account for less than 10% of the total number of cells, meaning the state of charge (SOC) of one sodium-ion cell needs to be adjusted to match the SOC of multiple (e.g., 15 or 20) lithium iron phosphate (LFP) batteries, the adjustment effect will be affected by slight inconsistencies within these LFP batteries. This results in poor adjustment performance and low stability, leading to inaccurate SOC estimation. If sodium-ion cells account for more than 50% of the total number of cells, their shorter cycle life compared to LFP batteries means that placing too many sodium-ion cells in a single pack will cause uneven battery health due to their faster degradation. This uneven health will negatively impact the overall health of the battery pack, thus affecting the accuracy of SOC estimation.
[0156] It is understood that, compared with the traditional energy storage battery pack structure, in the energy storage battery pack 100a shown in the embodiments of Figures 4, 5, 6 and 7 of this application, the proportion of sodium-ion cells in the energy storage battery pack 100a is between 10% and 50%. This design can make the energy storage battery pack more accurate in estimating the state of charge.
[0157] To make the inventive objectives, technical solutions, and technical effects of this application clearer, the following detailed description is provided in conjunction with comparative examples and embodiments. Comparative Examples 1 and 2 described below both use existing energy storage battery pack structures to estimate the state of charge. Embodiment 1 uses the energy storage battery pack structure of this application to estimate the state of charge.
[0158] Comparative Example 1
[0159] It should be noted that Comparative Example 1 discloses an energy storage battery pack structure using existing technology to perform state of charge estimation.
[0160] In Comparative Example 1, the energy storage battery pack includes one sodium-ion battery cell and 15 lithium iron phosphate battery cells. The sodium-ion battery cell and the 15 lithium iron phosphate battery cells are connected in series, and the sodium-ion battery cell is located at the positive terminal of the energy storage battery pack. In Comparative Example 1, the sodium-ion battery cell accounts for 6.25% of the total number of cells in the energy storage battery pack.
[0161] Comparative Example 2
[0162] It should be noted that Comparative Example 2 discloses an energy storage battery pack structure using existing technology to perform state of charge estimation.
[0163] In Comparative Example 2, the energy storage battery pack includes eight lithium iron phosphate cells connected in series. In other words, the energy storage battery pack in Comparative Example 2 does not contain any sodium-ion cells.
[0164] Example 1
[0165] It should be noted that Embodiment 1 discloses the use of the energy storage battery pack structure shown in Figure 4 to perform state of charge estimation.
[0166] In Example 1, the energy storage battery pack 100a includes one sodium-ion battery cell and seven lithium iron phosphate battery cells. The sodium-ion battery cell and the seven lithium iron phosphate battery cells are connected in series, and the sodium-ion battery cell is located at the positive terminal of the energy storage battery pack. In the energy storage battery pack of Example 1, the sodium-ion battery cell accounts for 12.5% of the total number of cells.
[0167] The estimated state of charge of the energy storage battery packs of Comparative Examples 1, 2 and Example 1 was recorded, and the results are recorded in Table 1 below.
[0168] Table 1
[0169] As shown in Table 1 above, the proportion of sodium-ion cells in the energy storage battery packs of Comparative Examples 1 and 2 is not between 10% and 50%, while the proportion of sodium-ion cells in the 100a energy storage battery pack of Example 1 is between 10% and 50%. The state of charge (SOC) estimation of the energy storage battery packs of Example 1 and Comparative Example 1 is better than that of the energy storage battery pack of Comparative Example 2. The energy storage battery pack of Comparative Example 1 exhibits greater fluctuations at high or low SOC levels, resulting in low stability in its SOC estimation. The energy storage battery pack of Example 1 also provides more accurate estimation during the plateau period. Compared to the structure of the energy storage battery pack of Comparative Example 1, the energy storage battery pack of Example 1 has a smaller average error, and its SOC estimation is more stable. The SOC estimation of the energy storage battery packs of Comparative Examples 1 and 2 deviates significantly from that of the energy storage battery pack of Example 1.
[0170] This application is based on a hybrid series connection of lithium iron phosphate cells and sodium-ion cells. Compared with existing lithium iron phosphate battery packs, by introducing sodium-ion cells and setting the proportion of sodium-ion cells in the energy storage battery pack to between 10% and 50%, the state parameters of the entire energy storage system can be estimated by the state of charge of the sodium-ion cells. This solves the problem that existing lithium iron phosphate batteries cannot accurately estimate their state of charge.
[0171] Figure 8 is a schematic diagram of a battery management system provided in an embodiment of this application.
[0172] Referring to Figure 8, the battery management system 202 of this application includes: multiple battery voltage sampling modules for measuring the voltage value V of each cell in each battery string within the battery module; a temperature sampling module for measuring the temperature value T of the battery module; a microcontroller for receiving the voltage value V of each cell measured by the battery voltage sampling module and the temperature value T of the battery module measured by the temperature sampling module, and determining the cells that need to be balanced; a PWM charging controller and multiple balancing gating control modules, which are controlled by the microcontroller to perform the battery state of charge (SOC) balancing method on the cells that need to be balanced, wherein the battery management system can estimate the overall SOC of the energy storage battery pack by using the SOC of sodium-ion cells or solid-state batteries.
[0173] The battery management system can perform a fusion calculation based on the SOC of at least one sodium-ion cell or solid-state cell and the maximum and minimum SOC of the cells among the plurality of lithium iron phosphate cells to estimate the SOC of the energy storage battery pack.
[0174] The battery management system can perform SOC balancing operations among the cells in the energy storage battery pack based on the capacity of at least one sodium-ion or solid-state cell and the capacity of the plurality of lithium iron phosphate cells. The specific details of the SOC balancing operation are described above and will not be repeated here.
[0175] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application should fall within the scope of protection claimed by this application.
Claims
1. An energy storage battery pack, characterized in that, The energy storage battery pack includes: At least one sodium-ion battery cell or solid-state battery cell; Multiple lithium iron phosphate cells; the at least one sodium-ion cell or solid-state cell is connected in series with the multiple lithium iron phosphate cells to form a hybrid battery pack; The capacity of the sodium-ion battery cell or the solid-state battery cell is greater than that of the lithium iron phosphate battery cell, and the proportion of the sodium-ion battery cell or the solid-state battery cell in the energy storage battery pack is between 10% and 50%.
2. The energy storage battery pack according to claim 1, characterized in that, The operating voltage range of the lithium iron phosphate battery cell is within the operating voltage range of the sodium ion battery cell or the solid-state battery cell.
3. The energy storage battery pack according to claim 1 or 2, characterized in that, The capacity of the sodium-ion battery cell or the solid-state battery cell is at least 1.5 times greater than the capacity of the lithium iron phosphate battery cell.
4. The energy storage battery pack according to claim 1, characterized in that, The discharge current of the sodium-ion battery cell or the solid-state battery cell is greater than the discharge current of the lithium iron phosphate battery cell, and the charging current of the sodium-ion battery cell or the solid-state battery cell is greater than the charging current of the lithium iron phosphate battery cell.
5. The energy storage battery pack according to claim 1, characterized in that, The at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells are arranged in space according to a first preset number of rows and a second preset number of columns.
6. The energy storage battery pack according to any one of claims 1-5, characterized in that, The at least one sodium-ion battery cell or solid-state battery cell is disposed at the positive and negative terminals of the energy storage battery pack or at the corner of the cell array of the energy storage battery pack.
7. An energy storage system, characterized in that, The energy storage system includes a battery management system and at least one energy storage battery pack as described in any one of claims 1-6. The battery management system is electrically connected to the energy storage battery pack. The battery management system is used to acquire parameters of the sodium-ion battery cell or the solid-state battery cell and parameters of the plurality of lithium iron phosphate battery cells, and to determine the state of charge of the energy storage system based on the parameters of the sodium-ion battery cell or the solid-state battery cell and the parameters of the plurality of lithium iron phosphate battery cells.
8. The energy storage system according to claim 7, characterized in that, It also includes a power converter, which is electrically connected between the energy storage battery pack and the power generation system, or the power converter is electrically connected between the energy storage battery pack and the electrical equipment.
9. The energy storage system according to any one of claims 7-8, characterized in that, The battery management system can estimate the SOC of the energy storage battery pack by using the SOC of the sodium-ion battery cell or the solid-state battery cell.
10. The energy storage system according to claim 9, characterized in that, The battery management system can perform a fusion calculation based on the SOC of at least one sodium-ion cell or solid-state cell and the maximum and minimum SOC of the cells among the plurality of lithium iron phosphate cells to estimate the SOC of the energy storage battery pack.
11. The energy storage system according to any one of claims 7-10, characterized in that, The battery management system can control the SOC balancing operation among the cells in the energy storage battery pack based on the capacity of the at least one sodium-ion cell or solid-state cell and the capacity of the plurality of lithium iron phosphate cells.
12. The energy storage system according to claim 11, characterized in that, The SOC equalization operation includes: Real-time calculation of the average SOC of all battery cells; Based on the average SOC, perform SOC equalization on each of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells; and SOC balancing is performed between the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells based on the minimum and maximum SOC of each cell of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells, or based on the total SOC of the at least one sodium-ion battery cell or solid-state battery cell and the total SOC of the plurality of lithium iron phosphate battery cells.
13. The energy storage system according to claim 12, characterized in that, The step of performing SOC balancing on the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells respectively based on the average SOC includes: Based on the SOC of each cell, the cells in the at least one sodium-ion cell or solid-state cell and the plurality of lithium iron phosphate cells are sorted, and the SOC of the at least one sodium-ion cell or solid-state cell and the SOC of the plurality of lithium iron phosphate cells are balanced according to the sorting results and the difference between the SOC of each cell and the average SOC.
14. The energy storage system according to claim 12, characterized in that, The step of performing SOC balancing between the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells based on the minimum and maximum SOC of each cell of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells, or based on the total SOC of the at least one sodium-ion battery cell or solid-state battery cell and the total SOC of the plurality of lithium iron phosphate battery cells, includes: Compare the minimum SOC of one of the at least one sodium-ion battery cell or solid-state battery cell and the maximum SOC of one of the plurality of lithium iron phosphate battery cells with the maximum SOC of the other. If the minimum SOC of one of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells is greater than the maximum SOC of the other battery cell, then an overall mutual power compensation strategy is adopted to perform SOC balancing operation between the two. If the minimum SOC of one of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells is less than or equal to the maximum SOC of the cells in the other, then a single-cell mutual charging strategy is used to perform SOC balancing between the two, or Compare the total SOC of the at least one sodium-ion battery cell or solid-state battery cell with the total SOC of the plurality of lithium iron phosphate battery cells; If the difference between the total SOC of the at least one sodium-ion battery cell or solid-state battery cell and the total SOC of the plurality of lithium iron phosphate battery cells is greater than or equal to a first predetermined threshold, then an overall mutual charging strategy is adopted to perform SOC balancing between the two. The first predetermined threshold is related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
15. The energy storage system according to claim 14, characterized in that, The method of performing SOC balancing between the two using an overall mutual power compensation strategy includes: If the difference in average SOC between the at least one sodium-ion battery cell and the plurality of lithium iron phosphate battery cells is less than a second predetermined threshold, the SOC balancing between the two cells is stopped. The second predetermined threshold is related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
16. The energy storage system according to claim 14, characterized in that, The method of employing a single-unit mutual power compensation strategy to perform SOC balancing operation between the two includes: Based on the difference between the SOC of each of the at least one sodium-ion battery cell or solid-state battery cell and the plurality of lithium iron phosphate battery cells and the average SOC, the SOC between the two is balanced using a one-to-one correspondence method between the cells.
17. The energy storage system according to any one of claims 12-16, characterized in that, The SOC balancing operation further includes: at the end of charging and discharging, determining the difference between the average SOC of the at least one sodium-ion cell or solid-state cell and the average SOC of the plurality of lithium iron phosphate cells; if the difference between their average SOCs is greater than a third predetermined threshold, then performing SOC balancing between them, until the difference between their average SOCs is less than a fourth predetermined threshold. The third and fourth predetermined thresholds are related to the difference between the capacity of the sodium-ion battery cell or solid-state battery cell and the capacity of the lithium iron phosphate battery cell.
18. A state-of-charge (SOC) balancing method for the energy storage system of claim 7, characterized in that, The method includes performing a state-of-charge (SOC) balancing operation among the individual cells in the energy storage battery pack based on the capacity of the at least one sodium-ion cell or solid-state cell and the capacity of the plurality of lithium iron phosphate cells.