Secondary battery manufacturing method, energy storage system, and electric device

Abstract

The application provides a secondary battery preparation method, an energy storage system and a power utilization device, relates to the technical field of secondary battery preparation, and comprises the following steps: providing a formed secondary battery, sending the formed secondary battery into a restraint liquid cooling temperature control device to perform load regulation, and obtaining the charge-discharge data of the secondary battery in the load regulation process; determining a target first polarization interval and a target first polarization capacity corresponding to the target first polarization interval according to the charge-discharge data in the load regulation process; determining a target second polarization capacity according to the target first polarization capacity and the corresponding relationship between the first polarization capacity and the second polarization capacity; determining the target non-polarization capacity of the secondary battery according to the corresponding relationship between the winding core weight of the battery and the non-polarization capacity; and determining the predicted capacity of the secondary battery according to the target first polarization capacity, the target second polarization capacity and the target non-polarization capacity. The method provided by the application is helpful to improve the prediction accuracy of the capacity of the secondary battery and realize the free sorting of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery preparation technology, and in particular to a secondary battery preparation method, energy storage system, and electrical equipment. Background Technology

[0002] Battery capacity is one of the important technical indicators for evaluating battery quality. In the production process of rechargeable batteries, a full capacity assessment process is usually used to determine the battery capacity. This involves collecting the actual capacity of the battery through a complete charge and discharge cycle, and then classifying the batteries according to their capacity to meet the required shipment capacity.

[0003] In related technologies, capacity prediction can be performed using predictive models based on process control and characteristic data from formation and capacity testing. Partial capacity confirmation is then conducted after self-discharge testing to verify the accuracy of the predicted capacity. However, the capacity prediction methods for secondary batteries in these technologies suffer from low prediction accuracy. Summary of the Invention

[0004] This application provides a method for preparing a secondary battery, an energy storage system, and an electrical device, which helps to improve the prediction accuracy of secondary battery capacity, achieve capacity grading-free secondary batteries, reduce production costs, and ensure consistent performance and quality of secondary batteries upon shipment.

[0005] In a first aspect, this application provides a method for preparing a secondary battery, comprising:

[0006] The formed secondary battery is provided and sent to the restraint liquid cooling temperature control device for load adjustment. The charging and discharging data of the secondary battery during the load adjustment process are obtained. The load adjustment process includes constant power discharge and constant power charging.

[0007] The target first polarization range and the target first polarization capacity corresponding to the target first polarization range are determined based on the charge and discharge data during the load adjustment process.

[0008] The target second polarization capacity is determined based on the correspondence between the first and second polarization capacities and the target first polarization capacity.

[0009] The target non-polarized capacity of the secondary battery is determined based on the relationship between the battery core weight and the non-polarized capacity.

[0010] The predicted capacity of the secondary battery is determined based on the target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity.

[0011] In one possible implementation, the constant power discharge and constant power charging processes include:

[0012] The secondary battery is discharged to the first cutoff voltage at a first power.

[0013] After the constant power discharge ends, the secondary battery is charged to the target state of charge with the second power; the first power is equal to the second power.

[0014] In one possible implementation, the target first polarization region includes a first endpoint and a second endpoint, and the state of charge corresponding to the first endpoint is the state of charge corresponding to the starting point of constant power charging.

[0015] The target first polarization range and the corresponding target first polarization capacity are determined based on the charge and discharge data during the load adjustment process, including:

[0016] The charging voltage curve of the secondary battery is plotted based on the charging voltage data during constant power charging. The charging voltage curve of the secondary battery includes a stage of significant voltage change. The state of charge corresponding to the termination point of the stage of significant voltage change is the state of charge corresponding to the second endpoint.

[0017] The target first polarization capacity is determined based on the difference in the state of charge between the first and second endpoints.

[0018] In one possible implementation, determining the correspondence between the first polarization capacity and the second polarization capacity includes:

[0019] The test cell is subjected to capacity grading to obtain charge and discharge test data of the test cell during the capacity grading process. The capacity grading process includes the charge and discharge process from the second cutoff voltage to the third cutoff voltage.

[0020] The charging voltage curve of the test cell is plotted based on the charging voltage data in the charge and discharge test data.

[0021] The charging voltage curve of the test cell is divided into a first polarization segment and a second polarization segment. The voltage changes between the first polarization segment and the second polarization segment are significant, and the state of charge corresponding to the first polarization segment is smaller than that corresponding to the second polarization segment.

[0022] The first polarization capacity is determined based on the change in the state of charge corresponding to the first polarization segment, and the second polarization capacity is determined based on the change in the state of charge corresponding to the second polarization segment.

[0023] By fitting the first polarization capacity and the second polarization capacity, the corresponding relationship between the first polarization capacity and the second polarization capacity is obtained.

[0024] In one possible implementation, the correspondence between the first polarization capacity and the second polarization capacity includes a linear relationship.

[0025] One possible implementation involves determining the predicted capacity of the secondary battery based on the target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity, including:

[0026] The target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity are added together to obtain the predicted capacity of the secondary battery.

[0027] One possible implementation of the method also includes:

[0028] If the predicted capacity of the secondary battery meets the preset capacity requirement, it will be sorted into different storage areas according to the predicted capacity. If the predicted capacity of the secondary battery does not meet the preset capacity requirement, the battery will be recycled or downgraded for use.

[0029] In one possible implementation, the restraint liquid-cooled temperature control device includes a clamp and a liquid-cooled temperature control module. The clamp is used to hold the secondary battery, and the liquid-cooled temperature control module is used to control the temperature within the range of 25±2℃ during the load adjustment process.

[0030] Secondly, this application provides an energy storage system including a plurality of secondary batteries, which are prepared using the secondary battery preparation method described in the first aspect.

[0031] Thirdly, this application provides an electrical device including the energy storage system described in the second aspect.

[0032] The beneficial effects of this application are as follows:

[0033] This application provides a method for preparing a secondary battery. The method involves providing a formed secondary battery, then feeding it into a confinement liquid-cooled temperature control device for load adjustment to obtain charge and discharge data during the load adjustment process. Based on the charge and discharge data, a target first polarization range and a target first polarization capacity corresponding to the target first polarization range are determined. A target second polarization capacity is determined based on the correspondence between the first and second polarization capacities and the target first polarization capacity. A target non-polarization capacity of the secondary battery is determined based on the correspondence between the battery core weight and the non-polarization capacity. Finally, a predicted capacity of the secondary battery is determined based on the target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity. By utilizing a confinement liquid-cooled temperature control device to ensure consistent interlayer spacing of battery electrodes during the formation and load adjustment processes of secondary batteries, temperature control becomes more precise. This eliminates the influence of temperature and interlayer spacing of battery electrodes on the charged and discharged polarized capacity of secondary batteries. Furthermore, by establishing a correlation between the battery core weight and the non-polarized capacity, the non-polarized capacity of the secondary battery can be determined. Based on the polarized and non-polarized capacities of the secondary battery, the predicted capacity can be determined, which helps improve the accuracy of secondary battery capacity prediction, achieves capacity grading-free operation of secondary batteries, reduces production costs, and ensures consistent performance and quality of secondary batteries upon shipment. Attached Figure Description

[0034] Figure 1 This is a process flow diagram for the fabrication of secondary batteries in related technologies;

[0035] Figure 2 This is a process flow diagram for the fabrication of secondary batteries provided in the embodiments of this application;

[0036] Figure 3 A schematic diagram of an exemplary battery charging curve provided for embodiments of this application;

[0037] Figure 4 This is a schematic flowchart of the secondary battery preparation method provided in the embodiments of this application;

[0038] Figure 5a A front view schematic diagram of a restraint liquid cooling temperature control device provided in an embodiment of this application;

[0039] Figure 5b for Figure 5a A top view of the restraint liquid cooling temperature control device in the middle;

[0040] Figure 6 A schematic diagram of the charge-discharge curves for the load adjustment process provided in the embodiments of this application;

[0041] Figure 7 A flowchart illustrating the correspondence between the first polarization capacity and the second polarization capacity provided in an embodiment of this application;

[0042] Figure 8 This is a schematic diagram of the charge-discharge curves of the test cell capacity testing process provided in an embodiment of this application. Detailed Implementation

[0043] In this embodiment of the application, unless otherwise stated, the character " / " indicates that the preceding and following objects are in an OR relationship. For example, A / B can represent A or B. "AND / OR" describes the relationship between the associated objects, indicating that three relationships can exist. For example, A AND / OR B can represent: A existing alone, A and B existing simultaneously, and B existing alone.

[0044] It should be noted that the terms "first" and "second" used in the embodiments of this application are used only for distinguishing descriptive purposes and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated, nor should they be construed as indicating or implying order.

[0045] In the embodiments of this application, "at least one" refers to one or more items, and "more than one" refers to two or more items. Furthermore, "at least one of the following" or similar expressions refer to any combination of these items, which may include any combination of a single item or a plurality of items. For example, at least one of A, B, or C can represent: A, B, C, A and B, A and C, B and C, or A, B, and C. Each of A, B, and C can be an element itself or a set containing one or more elements.

[0046] In this application, terms such as "exemplary," "in some embodiments," and "in another embodiment" are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the term "exemplary" is intended to present the concept in a concrete manner.

[0047] In the embodiments of this application, "of", "corresponding (relevant)" and "corresponding" can sometimes be used interchangeably. It should be noted that when their differences are not emphasized, their meanings are consistent.

[0048] In the embodiments of this application, the term "equal to" can be used in conjunction with "greater than" to apply to technical solutions employing the condition of "greater than", and can also be used in conjunction with "less than" to apply to technical solutions employing the condition of "less than". It should be noted that when "equal to" is used with "greater than", it cannot be used with "less than"; and when "equal to" is used with "less than", it cannot be used with "greater than".

[0049] Secondary batteries are batteries that can be charged and reused repeatedly by an external power source. Secondary batteries include: lithium-ion batteries (charging cut-off voltage: 4.2V, discharging cut-off voltage: 2.5V-3.0V) and lithium iron phosphate batteries (charging cut-off voltage: 3.65V, discharging cut-off voltage: 2.0V-2.5V), etc.

[0050] The typical manufacturing process of a secondary battery includes: preparation of positive and negative electrodes, preparation of the electrode core, heat sealing, electrolyte injection, formation, aging, and capacity testing. A process flow diagram for secondary battery manufacturing in related technologies is shown below. Figure 1 As shown, it includes:

[0051] (1) Formation: The battery is charged for the first time after being injected with electrolyte. The purpose is to activate the active materials in the battery so that they have electrochemical activity, and at the same time, a solid electrolyte interphase (SEI) film is formed on the surface of the negative electrode.

[0052] (2) Aging: After the battery is formed, it is placed under certain temperature and time conditions to allow the chemical reaction inside the battery to proceed fully in order to achieve a more stable state.

[0053] (3) Second injection: The process of injecting electrolyte into the battery again after the battery has been formed. This is mainly to replenish the electrolyte consumed during the formation process and ensure that the battery has enough electrolyte for subsequent use.

[0054] (4) Sealing: The battery is sealed with sealing nails to seal the electrolyte filling port and prevent electrolyte leakage and outside air from entering.

[0055] (5) Chlorine detection: Perform chloride ion detection on the battery to ensure that there is no chloride ion contamination inside the battery.

[0056] (6) Room temperature 1, room temperature 2, room temperature 3: During the battery production process, the battery is placed in a room temperature environment for a certain period of time. This is mainly to further stabilize the internal chemical reaction of the battery, and also helps to test the battery's performance at room temperature.

[0057] (7) OCV1, OCV2, OCV3: OCV (Open Circuit Voltage) refers to the voltage of the battery in the open circuit state. OCV1, OCV2, and OCV3 refer to the open circuit voltage tests performed on the battery at different stages to evaluate the battery's performance and consistency.

[0058] (8) SOC Adjustment: SOC (State of Charge) refers to the state of charge of a battery. SOC adjustment refers to adjusting the battery's state of charge to the required level through charging and discharging operations to meet the requirements of subsequent use or testing.

[0059] (9) Capacity testing: A portion of the batteries are subjected to capacity testing to verify the accuracy of the predicted capacity of the batteries.

[0060] (10) Coating and sorting before storage: Coating refers to wrapping the battery with a protective film to protect it and prevent external environmental factors from affecting it. Sorting refers to classifying and screening batteries according to their capacity. Storage refers to placing the sorted batteries into a warehouse for storage.

[0061] exist Figure 1The process flow diagram for secondary battery manufacturing shown illustrates how a predictive model is used to predict capacity based on process control and characteristic data from formation and capacity grading processes. Partial capacity confirmation is performed after self-discharge testing to verify the accuracy of the predicted capacity. However, due to variations in secondary battery manufacturing processes, the interlayer spacing of the positive or negative electrode sheets is inconsistent during formation and capacity grading. Furthermore, since formation and capacity grading are primarily conducted in a test cabinet, the heat generated by other equipment within the test cabinet (such as the power supply motor) can affect the temperature during these processes, reducing the accuracy of temperature control. For example, the formation and capacity grading temperatures in the test cabinet are 45±5℃ and 25±5℃ respectively, a large temperature range. Even ±5℃ significantly impacts capacity polarization and interface dynamics, resulting in insufficient accuracy in capacity prediction and making it difficult to meet the required capacity for shipment.

[0062] Based on the above problems, this application proposes a method for preparing a secondary battery, which helps to improve the prediction accuracy of the secondary battery capacity, realize the elimination of capacity testing for secondary batteries, reduce production costs, and ensure consistent performance and quality of secondary batteries upon shipment.

[0063] Now combined Figures 2-8 The method for preparing a secondary battery provided in the embodiments of this application will be described.

[0064] Figure 2 The process flow diagram for the fabrication of secondary batteries provided in the embodiments of this application is as follows: Figure 2 As shown, the secondary battery manufacturing process includes: formation, aging, secondary injection, sealing, chlorine detection, charging to the post-formation charged state, room temperature 1, room temperature 2, room temperature 3, OCV1, OCV2, OCV3, and charging to the shipment state (corresponding to...). Figure 1 The process includes SOC adjustment, capacity testing, coating, and sorting / discharging. For the operations of aging, secondary injection, sealing, chlorine testing, ambient temperature 1, ambient temperature 2, ambient temperature 3, OCV1, OCV2, OCV3, SOC adjustment, capacity testing, coating, and sorting / discharging, please refer to the section on... Figure 1 A detailed description of the preparation process.

[0065] Unlike the secondary battery manufacturing processes in related technologies, this application utilizes a confinement liquid-cooled temperature control device to simulate the environment of a test chamber for secondary battery formation and load adjustment. This ensures consistent interlayer spacing of the battery electrodes and precise temperature control during formation and load adjustment. For example, the temperature during load adjustment can be controlled within the range of 25±2℃, reducing the impact of temperature on the battery's polarization capacity. After secondary battery formation, load adjustment (i.e., adjusting the state of charge of the secondary battery) is performed to the post-formation state of charge, which refers to a state of charge between 21% and 36% of the battery capacity. The polarization capacity of the secondary battery is calculated based on the charge-discharge curve during this load adjustment process. The non-polarization capacity of the battery is determined by the weight of the positive electrode active material. The predicted capacity of the secondary battery is determined based on its polarization and non-polarization capacities, which helps improve the accuracy of secondary battery capacity prediction, achieves capacity grading-free secondary batteries, reduces production costs, and ensures consistent performance and quality of the shipped secondary batteries.

[0066] The applicant discovered that during battery charging, polarization phenomena (including ohmic polarization, concentration polarization, and electrochemical polarization) are prone to occur in low charge state (SOC<20%) and high charge state (SOC>80%), resulting in significant voltage changes. Figure 3 An exemplary battery charging curve diagram provided for embodiments of this application, such as... Figure 3 As shown, within the SOC range of 0-5%, the voltage increases from 2.5V to 3.3V, and within the SOC range of 95%-100%, the voltage increases from 3.4V to 3.45V. Significant voltage changes occur in these two ranges. The voltage change is stable in the intermediate state of charge (SOC between 5% and 95%). Therefore, battery capacity is composed of the polarized capacity in the low state of charge, the non-polarized capacity in the intermediate state of charge, and the polarized capacity in the high state of charge. When predicting battery capacity, both polarized and non-polarized capacities need to be considered.

[0067] Based on this, the present application proposes a method for preparing a secondary battery. Figure 4 This is a schematic flowchart of a secondary battery fabrication method provided in an embodiment of this application, which specifically includes the following steps:

[0068] Step S41: Provide the formed secondary battery, send the formed secondary battery into the restraint liquid cooling temperature control device for load adjustment, and obtain the charge and discharge data of the secondary battery during the load adjustment process.

[0069] In order to precisely control the temperature during the formation and loading processes, and to ensure the consistency of the interlayer spacing of the battery electrodes, thereby improving the consistency of the formation and loading processes and enhancing the accuracy of the predicted battery capacity, this application proposes to use a confinement liquid cooling temperature control device for formation and loading.

[0070] In some embodiments, the restraint liquid-cooled temperature control device includes a clamp and a liquid-cooled temperature control module. The clamp is used to hold the secondary battery, and the liquid-cooled temperature control module is used to control the temperature during the load adjustment process within the range of 25±2℃ (i.e., 23℃~27℃) and the temperature during the formation process within the range of 45±2℃ (i.e., 43℃~47℃). In other embodiments, the liquid-cooled temperature control module can also be used to control the temperature during the load adjustment process within the range of 25±0.5℃ (i.e., 24.5℃~25.5℃) and the temperature during the formation process within the range of 45±0.5℃ (i.e., 44.5℃~45.5℃), achieving higher temperature control accuracy.

[0071] like Figure 5a and Figure 5b As shown, Figure 5a This is a front view schematic diagram of a restraint liquid cooling temperature control device provided in an embodiment of this application. Figure 5b for Figure 5a The diagram shows a top view of a liquid-cooled temperature control device, which includes a cooling channel and a heat-dissipating copper plate. The cooling channel and copper plate are positioned in close contact with the battery. Cooling water or other coolant flows through the cooling channel, and the temperature is controlled by adjusting the flow rate of the cooling water. The close contact between the cooling channel and the heat-dissipating copper plate and the battery facilitates direct and accurate temperature control. Figure 5a and Figure 5b Not shown, but it is understood that the clamp can be positioned outside the heat dissipation copper plate to hold the battery and control the spacing between the battery electrodes. Optionally, the restraint liquid cooling temperature control device can be a restraint liquid cooling temperature control tray. It is understood that... Figure 5a and Figure 5b The restraint liquid cooling temperature control device shown is a schematic diagram provided in the embodiment of this application, and is used as an example for illustration purposes only, without any limiting effect.

[0072] The secondary battery is placed into a clamping liquid-cooled temperature control device, held, and maintained at 45±0.5℃ for formation, ensuring consistent incoming material conditions (consistent interlayer spacing of battery electrodes), and SEI stabilization is performed. The formed secondary battery is then placed into the clamping liquid-cooled temperature control device, held, and maintained at 25±0.5℃ for load adjustment, obtaining charge and discharge data during the load adjustment process. Optionally, after formation, the secondary battery undergoes aging, secondary injection, sealing, and chlorine testing before being placed into the clamping liquid-cooled temperature control device for load adjustment, which includes constant power discharge and constant power charging.

[0073] In some optional embodiments, the constant power discharge process includes discharging the secondary battery at a first power to a first cutoff voltage. After the constant power discharge is completed, a constant power charge is performed, the constant power charge process including charging the secondary battery at a second power to a target state of charge. The first power is equal to the second power.

[0074] The target state of charge (SOC) is the post-formation SOC (a SOC representing 21%-36% of the battery capacity, located in the non-polarized range). The first cutoff voltage is the discharge cutoff voltage of the secondary battery, which is set according to the type of secondary battery. For example, the discharge cutoff voltage for lithium-ion batteries is 2.5V-3.0V, and for lithium iron phosphate batteries it is 2.0V-2.5V. The purpose of constant power discharge is to deplete the capacity of the secondary battery, while the purpose of constant power charging is to charge the secondary battery to the target SOC.

[0075] Optionally, the first power and the second power can be values ​​within the range of 0.3P to 0.7P, such as 0.3P, 0.4P, 0.5P, 0.6P, 0.7P, etc. For example, charging a secondary battery at a constant power of 0.5P means that the charging power of the secondary battery is 50% of the battery's rated power (P). If the rated power of the secondary battery is 100W, then 0.5P = 50W, that is, the charging power is 50W. When the battery is charged and discharged within the constant power range of 0.3P to 0.7P, the battery polarization is smaller, and the predicted battery capacity is more accurate. Optionally, the cell is discharged to 2.5V at a constant power of 0.5P, and then charged to the target state of charge at a constant power of 0.5P.

[0076] The above-mentioned load adjustment process can obtain the charging and discharging data of the secondary battery. The charging and discharging data of the secondary battery includes the charging voltage, discharging voltage, charging current, discharging current, SOC (state of charge), charging capacity, and discharging capacity during the load adjustment process.

[0077] Step S42: Determine the target first polarization range and the target first polarization capacity corresponding to the target first polarization range based on the charge and discharge data during the load adjustment process.

[0078] Specifically, the charge-discharge curves of the secondary battery can be plotted based on the voltage data during the above-mentioned load adjustment process. The charge-discharge curves include the discharge voltage curve plotted based on the discharge voltage data during the constant power discharge process and the charging voltage curve plotted based on the charging voltage data during the constant power charging process.

[0079] Figure 6 A schematic diagram of the charge-discharge curves for the load adjustment process provided in the embodiments of this application, as shown below. Figure 6 As shown, load adjustment is performed within the time period 0-T4. During the time period 0-T2, constant power discharge is performed until the voltage reaches the first cutoff voltage V1, where the first cutoff voltage V1 represents the discharge cutoff voltage of the secondary battery. During the time period T2-T4, constant power charging is performed until the target state of charge (a state of charge between 21% and 36% SOC) is reached. That is, the state of charge corresponding to time T4 is the target state of charge.

[0080] In some optional embodiments, the target first polarization interval corresponds to the interval where the voltage of the secondary battery changes significantly during constant power charging. The target first polarization interval includes a first endpoint and a second endpoint. The state of charge corresponding to the first endpoint is the state of charge corresponding to the starting point of constant power charging.

[0081] The target first polarization range and the target first polarization capacity corresponding to the target first polarization range are determined based on the charging and discharging data during the load adjustment process. This includes: plotting the charging voltage curve of the secondary battery based on the charging voltage data during the constant power charging process. The charging curve includes a stage of significant voltage change, and the state of charge corresponding to the termination point of the stage of significant voltage change is the state of charge corresponding to the second endpoint. The target first polarization capacity is determined based on the difference between the state of charge of the first endpoint and the second endpoint.

[0082] according to Figure 6 The charge-discharge curves of the load adjustment process are shown. The charging voltage curve is the voltage curve for the time period T2-T4. The two endpoints of the target first polarization interval (the stage of significant voltage change) are the first endpoint A and the second endpoint B, respectively. The time of the first endpoint A corresponds to the start time T2 of constant power charging, and the voltage of the first endpoint A is the first cutoff voltage V1. The time of the second endpoint B is T3, and the voltage of the second endpoint B is V3. The state of charge (SOC) corresponding to the first endpoint A is the SOC corresponding to the start point of constant power charging (i.e., SOC at time T2), and the state of charge corresponding to the second endpoint B is the SOC corresponding to the end point of the stage of significant voltage change (i.e., SOC at time T3). By calculating the SOC difference between the first endpoint A and the second endpoint B (i.e., subtracting the SOC at time T2 from the SOC at time T3), the target first polarization capacity can be obtained.

[0083] In this embodiment, the calculated target first polarization capacity is the charging polarization capacity in the low charge state.

[0084] In some alternative embodiments, the target first polarization interval may also correspond to the interval where the voltage of the secondary battery changes significantly during constant power discharge. The target first polarization interval includes a first endpoint and a second endpoint, and the state of charge corresponding to the first endpoint is the state of charge corresponding to the termination point of constant power discharge.

[0085] The target first polarization range and the target first polarization capacity corresponding to the target first polarization range are determined based on the charge and discharge data during the load adjustment process. This includes: plotting the discharge voltage curve of the secondary battery based on the discharge voltage data during the constant power discharge process. The discharge curve includes a stage of significant voltage change. The state of charge corresponding to the starting point of the stage of significant voltage change is the state of charge corresponding to the second endpoint. The target first polarization capacity is determined based on the difference between the state of charge of the first endpoint and the second endpoint.

[0086] according to Figure 6The charge and discharge curves of the load adjustment process are shown. The discharge voltage curve is the voltage curve during the time period from 0 to T2. The two endpoints of the target first polarization interval (the stage of significant voltage change) are the first endpoint A and the second endpoint C, respectively. The time of the first endpoint A corresponds to the termination time T2 of constant power discharge (T2 is also the start time of constant power charging). The voltage of the first endpoint A is the first cutoff voltage V1. The time of the second endpoint C is T1, and the voltage of the second endpoint C is V2.

[0087] The state of charge (SOC) at the first endpoint A corresponds to the termination point of constant power discharge (i.e., the SOC at time T2, which is also the SOC at the start point of constant power charging). The state of charge at the second endpoint C corresponds to the start point of the significant voltage change phase (i.e., the SOC at time T1). By calculating the SOC difference between the first endpoint A and the second endpoint C (i.e., subtracting the SOC at time T2 from the SOC at time T1), the target first polarization capacity can be obtained.

[0088] In this embodiment, the calculated target first polarization capacity is the discharge polarization capacity in the low charge state.

[0089] Step S43: Determine the target second polarization capacity based on the correspondence between the first polarization capacity and the second polarization capacity, and the target first polarization capacity.

[0090] When performing capacity grading on some battery cells, the applicant discovered a correlation between the polarization capacity in the low-charge state and the polarization capacity in the high-charge state. Therefore, the target second polarization capacity can be calculated using the correspondence between the polarization capacity in the low-charge state and the polarization capacity in the high-charge state. In this application, the target first polarization capacity refers to the polarization capacity in the low-charge state of the secondary battery (including the charging polarization capacity or the discharging polarization capacity in the low-charge state), and the target second polarization capacity refers to the polarization capacity in the high-charge state of the secondary battery (including the charging polarization capacity or the discharging polarization capacity in the high-charge state). It is understood that in other embodiments, the target first polarization capacity may also refer to the polarization capacity in the high-charge state of the secondary battery, and the target second polarization capacity may also refer to the polarization capacity in the low-charge state of the secondary battery.

[0091] Figure 7 The flowchart illustrating the determination of the correspondence between the first polarization capacity and the second polarization capacity provided in this application embodiment specifically includes the following steps:

[0092] Step S71: Perform capacity testing on the test cell to obtain charge and discharge test data of the test cell during the capacity testing process.

[0093] Specifically, a portion of the batteries manufactured in the same batch as the aforementioned secondary batteries are selected as test cells. These test cells are then subjected to capacity testing, which includes a charge-discharge process from the second cutoff voltage to the third cutoff voltage. The second cutoff voltage is the discharge cutoff voltage of the test cell, and the third cutoff voltage is the charge cutoff voltage of the test cell. For example, if the aforementioned secondary battery and the test cell are both lithium iron phosphate batteries, then the discharge cutoff voltage (second cutoff voltage) of the test cell is equal to the discharge cutoff voltage (first cutoff voltage) of the aforementioned secondary battery.

[0094] The charging and discharging process from the second cutoff voltage to the third cutoff voltage includes a full charge process (charging from the second cutoff voltage to the third cutoff voltage) and a full discharge process (discharging from the third cutoff voltage to the second cutoff voltage). For example, a full charge process from 2.5V to 3.65V and a full discharge process from 3.65V to 2.5V.

[0095] Optionally, to ensure the accuracy of the results, it is necessary to control the temperature and charge / discharge power of the test cell's capacity grading process and the aforementioned secondary battery's load adjustment process to be the same.

[0096] Step S72: Plot the charging voltage curve of the test cell based on the charging voltage data in the charge and discharge test data.

[0097] Specifically, a charging voltage curve is plotted based on the charging voltage data from the second cutoff voltage to the third cutoff voltage during the full charge process. In other embodiments, a discharge voltage curve for the test cell can also be plotted based on the discharge voltage data from the charge-discharge test data; specifically, a discharge voltage curve is plotted based on the discharge process from the third cutoff voltage to the second cutoff voltage during the full discharge process.

[0098] Step S73: Divide the charging voltage curve of the test cell into a first polarization segment and a second polarization segment.

[0099] Figure 8 This is a schematic diagram of the charge-discharge curves of the test cell capacity grading process provided in the embodiments of this application, as shown below. Figure 8 As shown, the capacity testing process of the battery cell includes a constant power (e.g., 0.5P) charging process from 2.5V to 3.65V, and a constant power (e.g., 0.5P) discharging process from 3.65V to 2.5V. Figure 8 The test includes the charge and discharge curves of three test cells (cells 1#, 2#, and 3#) during the capacity testing process, including the charging capacity curve s1, the discharging capacity curve s2, the charging voltage curve s3, and the discharging voltage curve s4. Figure 8 The horizontal axis represents time in seconds (S), the vertical axis on the left represents charge / discharge capacity in ampere-hours (Ah), and the vertical axis on the right represents voltage in volts (V).

[0100] In some optional embodiments, the charging voltage curve s3 can be divided into a first polarization segment (corresponding to the time period 0-t1) and a second polarization segment (corresponding to the time period t2-t3) based on the voltage change or the slope of the charging voltage curve. The voltage changes between the first and second polarization segments are significant, and the state of charge corresponding to the first polarization segment is lower than that corresponding to the second polarization segment. In other words, the first polarization segment is a low-charge state polarization segment, and the second polarization segment is a high-charge state polarization segment.

[0101] In some alternative embodiments, the discharge voltage curve s4 can be divided into a first polarization segment (corresponding to the time period t5-t6) and a second polarization segment (corresponding to the time period t3-t4) by the voltage change or the slope of the discharge voltage curve. The first polarization segment is the polarization segment of the low charge state, and the second polarization segment is the polarization segment of the high charge state.

[0102] Step S74: Determine the first polarization capacity based on the change in state of charge corresponding to the first polarization segment, and determine the second polarization capacity based on the change in state of charge corresponding to the second polarization segment.

[0103] In some alternative embodiments, such as Figure 8 As shown, the first polarization capacity can be obtained by calculating the change in SOC (i.e., charging capacity) of the first polarization segment (0-t1) of the charging capacity curve s3, and the second polarization capacity can be obtained by calculating the change in SOC (i.e., charging capacity) of the second polarization segment (t2-t3) of the charging capacity curve s3.

[0104] In some other alternative embodiments, such as Figure 8 As shown, the first polarization capacity can be obtained by calculating the change in SOC (i.e., discharge capacity) of the first polarization segment (t5-t6) of the discharge capacity curve s4, and the second polarization capacity can be obtained by calculating the change in SOC (i.e., discharge capacity) of the second polarization segment (t3-t4) of the discharge capacity curve s4.

[0105] The first polarization capacity is the polarization capacity of the test cell in its low-charge state, and the second polarization capacity is the polarization capacity of the test cell in its high-charge state.

[0106] As shown in Table 1, Table 1 is Figure 8 The table shows the charging capacity of the three test cells.

[0107] Table 1. Charging Capacity of Tested Battery Cells

[0108]

[0109] In Table 1, the first polarization capacity corresponds to a voltage range of 2.5V-3.36V (time period 0-t1), the non-polarization capacity corresponds to a voltage range of 3.36V-3.43V (time period t1-t2), and the second polarization capacity corresponds to a voltage range of 3.43V-3.65V (time period t2-t3).

[0110] As shown in Table 2, Table 2 is Figure 8 The table shows the discharge capacity of the three test cells.

[0111] Table 2. Discharge Capacity of Test Cells

[0112]

[0113] In Table 2, the first polarization capacity corresponds to a voltage range of 3.19V-2.5V (time period t5-t6), the non-polarization capacity corresponds to a voltage range of 3.26V-3.19V (time period t4-t5), and the second polarization capacity corresponds to a voltage range of 3.65V-3.26V (time period t3-t4).

[0114] Step S75: Fit the first polarization capacity and the second polarization capacity to obtain the correspondence between the first polarization capacity and the second polarization capacity.

[0115] In some embodiments, the relationship between the first polarization capacity and the second polarization capacity includes a linear relationship, which can be expressed as: y = k*x + b. Here, y represents the second polarization capacity, and x represents the first polarization capacity. Optionally, the relationship between the first polarization capacity and the second polarization capacity may also include a non-linear relationship, such as an exponential relationship or a logarithmic relationship, and the relationship between the first polarization capacity and the second polarization capacity is affected by the electrode material characteristics of the secondary battery.

[0116] Taking lithium iron phosphate battery as an example, this application finds that the first polarization capacity and the second polarization capacity of lithium iron phosphate battery have a linear relationship. According to Table 1 above, the function expression of the first polarization capacity and the second polarization capacity during constant power charging can be obtained by fitting: y1=-1.003*x1+122.5, where y1 represents the second charging polarization capacity and x1 represents the first charging polarization capacity.

[0117] According to Table 2 above, the functional expressions of the first polarization capacity and the second polarization capacity during constant power discharge process can be obtained by fitting: y2=-0.932*x2+146.3, where y2 represents the second discharge polarization capacity and x2 represents the first discharge polarization capacity.

[0118] By performing capacity grading on the test cells, the functional relationship between the first polarization capacity and the second polarization capacity can be obtained, thus revealing the correlation between the polarization capacity in the low-charge state and the polarization capacity in the high-charge state. Substituting the target first polarization capacity obtained during the load adjustment process into the functional relationship, the target second polarization capacity can be obtained.

[0119] For example, according to Figure 6 The charging voltage curve of the load adjustment process shown gives the target first polarization capacity (target first charging polarization capacity) Q1 for the time period T2-T3. Substituting into the function expression y1=-1.003*x1+122.5 of the first polarization capacity and the second polarization capacity in the constant power charging process, we get the target second polarization capacity (target second charging polarization capacity) P1=-1.003*Q1+122.5.

[0120] Or it can also be based on Figure 6 The discharge voltage curve of the load adjustment process shown gives the target first polarization capacity (target first discharge polarization capacity) for the time period T1-T2 as Q2. Substituting this into the function expression y2=-0.932*x2+146.3 of the first polarization capacity and the second polarization capacity in the constant power charging process, we get the target second polarization capacity (target second discharge polarization capacity) P2=-0.932*Q2+146.3.

[0121] Therefore, secondary batteries only need to undergo the above-mentioned load adjustment process to obtain the target first polarization capacity and the target second polarization capacity, without the need for a complete capacity grading process, thereby achieving capacity grading-free secondary batteries and reducing production costs.

[0122] Step S44: Determine the target non-polarized capacity of the secondary battery based on the correspondence between the battery core weight and the non-polarized capacity.

[0123] The non-polarized capacity of a battery is related to the weight and specific capacity of the positive electrode active material. Specifically, the non-polarized capacity of the battery is calculated by multiplying the weight of the positive electrode active material by its specific capacity. According to the applicant's research, for batteries of the same model, batch, and with identical material ratios and structures, and manufactured using the same process, the battery core weight has a linear relationship with the non-polarized capacity (including non-polarized charging capacity or non-polarized discharging capacity). Therefore, knowing only the core weight of the battery whose capacity is to be predicted allows the calculation of the non-polarized capacity of the battery to be determined based on the correspondence between the core weight and the non-polarized capacity. Furthermore, the core weight of the battery can be directly measured, making the calculation of the battery's non-polarized capacity simpler.

[0124] According to Table 1 above, the relationship between the non-polarized charging capacity and the battery core weight can be obtained by fitting: y3=0.0489*x3+2.71, where x3 represents the battery core weight and y3 represents the non-polarized charging capacity.

[0125] According to Table 2 above, the relationship between the non-polarized discharge capacity and the battery core weight can be obtained by fitting: y4=0.00492*x4+154.56, where x4 represents the battery core weight and y4 represents the non-polarized discharge capacity.

[0126] For example, Figure 6 The weight of the secondary battery core shown is Z. Substituting this into the formula y3=0.0489*x3+2.71, we obtain the target non-polarized capacity (non-polarized charging capacity) during the charging process: R1=0.0489*Z+2.71;

[0127] Alternatively, by substituting into the formula y4=0.00492*x4+154.56, we can obtain the target non-polarized capacity (non-polarized discharge capacity) during the discharge process: R2=0.00492*Z+154.56.

[0128] Step S45: Determine the predicted capacity of the secondary battery based on the target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity.

[0129] Specifically, the target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity are added together to obtain the predicted capacity of the secondary battery.

[0130] In some embodiments, the predicted capacity of the secondary battery is the sum of the target first charging polarization capacity, the target second charging polarization capacity, and the target non-polarization charging capacity.

[0131] In other embodiments, the predicted capacity of the secondary battery is the sum of the target first discharge polarization capacity, the target second discharge polarization capacity, and the target non-polarization discharge capacity.

[0132] by Figure 6 Taking the secondary battery shown as an example, the target first polarization capacity for the time period T2-T3 is Q1. Based on the formula and Q1, the target second planned capacity P1 is derived, and the target non-polarization capacity R1 is derived from the formula. Then the predicted capacity of the secondary battery is Q1+P1+R1.

[0133] Alternatively, if the target first polarization capacity for the time period T1-T2 is Q2, the target second planned capacity P2 is derived from the formula and Q2, and the target non-polarization capacity R2 is derived from the formula. Then the predicted capacity of the secondary battery is Q2+P2+R2.

[0134] This application provides a method for manufacturing a secondary battery. It utilizes a confinement liquid-cooled temperature control device to ensure consistent interlayer spacing of the battery electrodes during formation and load adjustment, resulting in more precise temperature control. The method also utilizes the water flow rate of the confinement liquid-cooled temperature control device to control the temperature, achieving closed-loop regulation of battery temperature detection and water flow rate. This eliminates the influence of temperature and interlayer spacing of the battery electrodes on the battery's charge-discharge polarization capacity, ensuring the accuracy of the polarization capacity. Furthermore, by determining the non-polarization capacity of the secondary battery based on the correspondence between the battery core weight and non-polarization capacity, and by determining the predicted capacity of the battery based on its polarization and non-polarization capacities, it helps improve the accuracy of battery capacity prediction, enabling capacity grading-free operation, reducing production costs, and ensuring consistent performance and quality of the shipped batteries.

[0135] Conventional capacity prediction methods involve a capacity sampling rate of 10%-20% and a capacity accuracy of ±6Ah. The method provided in this application involves a capacity sampling rate of 1%-2% and a capacity accuracy of ±0.5Ah. Furthermore, it relies on the test cabinet conditions for formation and capacity assessment, calculates the corresponding non-polarized capacity for cells with different core weights, and combines this with the polarized capacity to ensure the accuracy and reliability of the predicted cell capacity.

[0136] Optionally, the method provided in this application further includes: if the predicted capacity of the secondary battery meets the preset capacity requirements, then the secondary battery is sorted into different storage areas according to its predicted capacity; or if the predicted capacity of the secondary battery does not meet the preset capacity requirements, then the battery is recycled or downgraded for use. For example, according to the battery capacity, the shipment standard of capacity ≤3Ah is sorted, and batteries of the same grade that meet the requirements are removed from the production line. Through accurate capacity prediction and sorting, it is ensured that the capacity of cells of the same grade is highly consistent and meets the shipment standards.

[0137] Optionally, the target state of charge (SOC) is the shipment SOC. Battery cells are typically shipped in a charged state. After a complete charge-discharge capacity test, the cells need to be recharged before shipment, which prolongs the overall cell shipment time and increases energy consumption. Therefore, if the accuracy of the predicted battery capacity is verified through capacity sampling, and the charge-discharge curves of the secondary battery to be predicted are consistent with those of the battery meeting the preset capacity requirements during formation and load adjustment, and the core weight is consistent, then it can be determined that the secondary battery to be predicted also meets the preset capacity requirements. In this case, the secondary battery to be predicted can be directly charged to the shipment SOC during the constant current charging stage of the load adjustment process. This will significantly shorten the cell production process, increase production capacity, and save energy.

[0138] This application also provides an energy storage system including a plurality of secondary batteries, which are prepared using the secondary battery preparation method described above.

[0139] This application provides an electrical device including the above-mentioned energy storage system.

[0140] The above description is merely a specific embodiment of this application. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. The protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A method for preparing a secondary battery, characterized in that, The method includes: A secondary battery after formation is provided, and the secondary battery after formation is sent into a restraint liquid cooling temperature control device for load adjustment. The charging and discharging data of the secondary battery during the load adjustment process are obtained. The load adjustment process includes constant power discharge and constant power charging. The target first polarization range and the target first polarization capacity corresponding to the target first polarization range are determined based on the charge and discharge data during the load adjustment process. The target first polarization range is the range in which the voltage of the secondary battery changes significantly during constant power charging. The target first polarization capacity is determined based on the change in the state of charge within the target first polarization range. The target second polarization capacity is determined based on the correspondence between the first polarization capacity and the second polarization capacity, and the target first polarization capacity. The determination of the correspondence between the first polarization capacity and the second polarization capacity includes: performing capacity grading on the test cell, plotting a charging voltage curve based on the charging voltage data during the capacity grading process, dividing the charging voltage curve into a first polarization segment and a second polarization segment with significant voltage changes, determining the first polarization capacity and the second polarization capacity based on the change in state of charge corresponding to each segment, and fitting the two to obtain the correspondence. The target non-polarized capacity of the secondary battery is determined based on the correspondence between the battery core weight and the non-polarized capacity. The predicted capacity of the secondary battery is determined based on the target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity. The constant power discharge and constant power charging processes include: The secondary battery is discharged to a first cutoff voltage at a first power. After the constant power discharge is completed, the secondary battery is charged to the target state of charge with a second power; the first power is equal to the second power. Determining the target non-polarized capacity of the secondary battery based on the correspondence between the battery core weight and the non-polarized capacity includes: Obtain the core weight of the secondary battery; Based on the linear fitting relationship between the core weight and non-polarized capacity of the secondary battery, which is predetermined for the same model and batch of secondary batteries, the target non-polarized capacity of the secondary battery is determined. The linear fitting relationship is a linear function in one variable, and the slope and intercept of the linear function in one variable are determined by the core weight sample data and the non-polarized capacity sample data in the sample data of secondary batteries of the same model and batch. The step of determining the predicted capacity of the secondary battery based on the target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity includes: The target first polarization capacity, the target second polarization capacity, and the target non-polarization capacity are added together to obtain the predicted capacity of the secondary battery.

2. The method for preparing a secondary battery according to claim 1, characterized in that, The target first polarization region includes a first endpoint and a second endpoint, and the state of charge corresponding to the first endpoint is the state of charge corresponding to the starting point of the constant power charging. Determining the target first polarization capacity based on the change in state of charge within the target first planning interval includes: The charging voltage curve of the secondary battery is plotted based on the charging voltage data during the constant power charging process. The charging voltage curve of the secondary battery includes a stage of significant voltage change, and the state of charge corresponding to the termination point of the stage of significant voltage change is the state of charge corresponding to the second endpoint. The target first polarization capacity is determined based on the difference in the state of charge between the first endpoint and the second endpoint.

3. The method for preparing a secondary battery according to claim 1, characterized in that, Determining the correspondence between the first polarization capacity and the second polarization capacity includes: The test cell is subjected to capacity testing to obtain charge and discharge test data of the test cell during the capacity testing process. The capacity testing process includes a charge and discharge process from the second cutoff voltage to the third cutoff voltage. The charging voltage curve of the test cell is plotted based on the charging voltage data in the charge-discharge test data. The charging voltage curve of the test cell is divided into a first polarization segment and a second polarization segment. The voltage changes between the first polarization segment and the second polarization segment are significant, and the state of charge corresponding to the first polarization segment is smaller than that corresponding to the second polarization segment. The first polarization capacity is determined based on the change in state of charge corresponding to the first polarization segment, and the second polarization capacity is determined based on the change in state of charge corresponding to the second polarization segment. By fitting the first polarization capacity and the second polarization capacity, the correspondence between the first polarization capacity and the second polarization capacity is obtained.

4. The method for preparing a secondary battery according to claim 1, characterized in that, The correspondence between the first polarization capacity and the second polarization capacity includes a linear relationship.

5. The method for preparing a secondary battery according to any one of claims 1 to 4, characterized in that, The method further includes: If the predicted capacity of the secondary battery meets the preset capacity requirement, it will be sorted into different storage areas according to the predicted capacity. If the predicted capacity of the secondary battery does not meet the preset capacity requirement, it will be recycled or downgraded for use.

6. The method for preparing a secondary battery according to claim 1, characterized in that, The restraint liquid cooling temperature control device includes a clamp and a liquid cooling temperature control module. The clamp is used to hold the secondary battery, and the liquid cooling temperature control module is used to control the temperature within the range of 25±2℃ during the load adjustment process.

7. An energy storage system, characterized in that, It includes multiple secondary batteries, which are prepared using the secondary battery preparation method as described in any one of claims 1 to 6.

8. An electrical appliance, characterized in that, Including the energy storage system as described in claim 7.

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