Preparation method of lithium iron phosphate cell, lithium iron phosphate cell and secondary battery
By using a rate of 0.01C to 0.1C to perform constant current charging and discharge during the decomposition and capacity testing of lithium iron phosphate battery cells, the problem of cycling slope climbing of lithium iron phosphate batteries is solved, and the battery cell is fully activated and the capacity of the battery cell is maximized.
Patent Information
- Application Number
- CN202411618883.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-13
- Publication Date
- 2025-03-28
AI Technical Summary
Lithium iron phosphate batteries have cycling slope climbing during the normal temperature cycle, resulting in the failure to fully utilize the capacity and the sub-capacity capacity is low.
During the decomposition and capacity test of lithium iron phosphate battery cells, constant current charging and discharge of the battery cells was used to ensure that the battery cells were fully activated within the range of 10% SOC-90% SOC.
By fully activating the lithium iron phosphate battery cell, the capacity climbing situation is reduced, so that the battery cell can exert its maximum or relatively close to the maximum capacity when discharged in the capacity separation process, and the economic benefits of the battery are improved.
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Figure CN119725815A_ABST
Abstract
Description
Technical Field
[0001] The present application belongs to the technical field of lithium batteries, and more specifically, relates to a method for preparing a lithium iron phosphate battery cell and a lithium iron phosphate battery cell and a secondary battery. Background Art
[0002] Lithium-ion batteries have outstanding advantages such as high energy density, no memory effect, long cycle life, fast charging and discharging, and low self-discharge. They are widely used in energy storage fields such as portable devices, electric vehicles, and aerospace, and have great market demand. In particular, lithium iron phosphate batteries have a long cycle life, stable positive electrode materials that do not decompose, and safety that other positive electrode materials cannot match. In addition, lithium iron phosphate resources are abundant and environmentally friendly, making lithium iron phosphate particularly widely used.
[0003] However, during the normal temperature cycle, the capacity of lithium iron phosphate batteries will first climb for a period of time, reach the highest point, and then gradually decrease, which is called the cycle climbing phenomenon. The climbing phenomenon will cause the capacity of the lithium iron phosphate battery to not be fully utilized, and the capacity of the capacity is low, so it cannot be sold at the highest capacity and performance. Summary of the invention
[0004] Based on this, one object of the present application is to provide a method for preparing a lithium iron phosphate battery cell to solve the technical problem of cycle climbing of lithium iron phosphate batteries existing in the prior art.
[0005] Another object of the present application is to provide a lithium iron phosphate battery cell.
[0006] Another object of the present application is to provide a secondary battery.
[0007] To achieve the above purpose, the technical solution adopted in this application is:
[0008] A preparation method for a lithium iron phosphate battery cell comprises: during formation and capacity test, in the range of 10% SOC to 90% SOC of the lithium iron phosphate battery cell, using at least one rate between 0.01C and 0.1C to perform constant current charging and discharging on the lithium iron phosphate battery cell at least once.
[0009] Optionally, during the formation and capacity separation test, in the step of performing at least one constant current charge and discharge on the lithium iron phosphate battery cell at least once within the range of 10% SOC-90% SOC of the lithium iron phosphate battery cell using at least one rate between 0.01C and 0.1C, the formation step includes:
[0010] Use 0.1C constant current to charge the lithium iron phosphate battery to 5%-10% SOC;
[0011] Then, the lithium iron phosphate battery cell is charged at a constant current to 20% SOC-35% SOC using at least one rate of 0.01C-0.1C;
[0012] The sub-capacity test includes the following steps;
[0013] The lithium iron phosphate battery cell is charged at a constant current to 40% SOC-90% SOC using at least one rate of 0.01C-0.1C;
[0014] The lithium iron phosphate battery cell is discharged at a constant current to 10% SOC-90% SOC using at least one rate of 0.01C-0.1C.
[0015] Optionally, the step of charging the lithium iron phosphate battery cell with a constant current to 20% SOC-35% SOC at at least one rate of 0.01C-0.1C comprises:
[0016] The lithium iron phosphate battery is charged to 35% at a constant current of 0.05C-0.1C.
[0017] Optionally, the forming temperature is 25°C-45°C.
[0018] Optionally, the surface pressure of a single lithium iron phosphate battery cell is 0.8Mpa-1.5Mpa.
[0019] Optionally, the step of charging to 40% SOC-90% SOC using at least one constant current of 0.01C-0.1C rate comprises:
[0020] The battery is charged to 60% SOC-90% SOC using a constant current of 0.01C-0.1C.
[0021] Optionally, between the step of charging the lithium iron phosphate battery cell to 40% SOC-90% SOC at a constant current using at least one rate of 0.01C-0.1C and the step of discharging the lithium iron phosphate battery cell to 10% SOC-90% SOC at a constant current using at least one rate of 0.01C-0.1C, the following steps are further included:
[0022] The lithium iron phosphate battery cell is charged at a constant current of 0.33C-0.5C to 100% SOC.
[0023] Optionally, in the capacity division test, after the step of discharging the lithium iron phosphate battery cell at a constant current to 10% SOC-90% SOC at at least one rate of 0.01C-0.1C, the method further includes:
[0024] Use 0.33C-0.5C to discharge the lithium iron phosphate battery to 0% SOC;
[0025] Use 0.33C-0.5C constant current and constant voltage to charge the lithium iron phosphate battery to 100% SOC;
[0026] Use 0.33C-0.5C constant current discharge to 0% SOC for lithium iron phosphate battery;
[0027] The lithium iron phosphate battery is charged to 60% at a constant current of 0.33C-0.5C.
[0028] And, a lithium iron phosphate battery cell manufactured by the above-mentioned lithium iron phosphate battery cell preparation method.
[0029] And, a secondary battery includes the above-mentioned lithium iron phosphate battery cell.
[0030] The beneficial effects of this application are:
[0031] The preparation method of the lithium iron phosphate battery cell provided in the present application is that the impedance of the lithium iron phosphate battery cell is relatively small in the range of 10% SOC-90% SOC, and one or more combinations of 0.01C-0.1C are used for charging and discharging in this range, so as to fully activate the lithium iron phosphate battery cell in the state where its impedance is minimum, so that it can exert the maximum or close to the maximum capacity when discharging in the capacity division process, thereby reducing the capacity climbing situation;
[0032] The lithium iron phosphate battery cell and secondary battery provided by the present application are manufactured by the preparation method of the present application. The lithium iron phosphate battery cell is fully activated, which reduces the problem of capacity climbing and can accurately divide the capacity. The secondary battery manufactured by the lithium iron phosphate battery cell provided by the present application can be sold with the highest capacity and performance, thereby improving the economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, in which:
[0034] Figure 1 The cycle capacity curves of the lithium iron phosphate batteries of Examples 1-4 and Comparative Example 1 of the present application. DETAILED DESCRIPTION
[0035] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.
[0036] Terminology
[0037] SOC, State Of Charge, refers to the ratio of available power in the battery cell to the nominal capacity, and is an important monitoring parameter of the battery management system.
[0038] Lithium iron phosphate batteries produced by existing technology generally have capacity climbing when cycled at room temperature, and the climbing ratio of lithium iron phosphate batteries with more large particles is greater than that of lithium iron phosphate batteries with more small particles. The capacity climbing ratio of lithium iron phosphate batteries cycled at a high rate is higher than that of lithium iron phosphate batteries cycled at a low rate.
[0039] As we all know, lithium iron phosphate cells have a slope section with a large voltage change as the capacity changes at the SOC at the beginning and end of charge and discharge, and the impedance of this area is significantly greater than the SOC in the middle platform area of charge and discharge. During the charge and discharge process, different SOC areas and charge and discharge rates will affect the activation effect of lithium iron phosphate cells.
[0040] After research, a method for preparing a lithium iron phosphate battery cell of an embodiment of the present application was obtained. The preparation method includes performing constant current charging and discharging on the lithium iron phosphate battery cell at least once in the range of 10% SOC-90% SOC of the lithium iron phosphate battery cell during formation and capacity separation testing, using at least one rate between 0.01C and 0.1C.
[0041] The impedance of lithium iron phosphate cells is relatively small in the range of 10% SOC-90% SOC. In this range, charging and discharging at a rate of 0.01C-0.1C or one or more combinations of rates will have the most obvious activation effect, which can fully activate the lithium iron phosphate cells and enable them to exert their maximum or close to maximum capacity during discharge in the capacity division process, thereby reducing capacity creep.
[0042] In some embodiments, during the formation and capacity test, in the step of performing constant current charging and discharging of the lithium iron phosphate battery cell at least once using at least one rate between 0.01C and 0.1C within the range of 10% SOC to 90% SOC of the lithium iron phosphate battery cell, the formation step includes:
[0043] (1): Use 0.1C constant current to charge the lithium iron phosphate battery to 5%-10% SOC.
[0044] (2): Then, the lithium iron phosphate battery cell is charged at a constant current to 20% SOC-35% SOC using at least one rate between 0.01C and 0.1C.
[0045] In some embodiments, step (2) comprises:
[0046] The lithium iron phosphate battery is charged to 35% at a constant current of 0.05C-0.1C.
[0047] Optionally, the forming temperature is 25°C-45°C.
[0048] Optionally, the surface pressure of a single lithium iron phosphate battery cell is 0.8Mpa-1.5Mpa. If the surface pressure is too small, for example, less than 0.8Mpa, the adhesion between the diaphragm and the electrode may be weak, affecting the battery molding; if the surface pressure is too large, for example, greater than 1.5Mpa, the pores of the diaphragm of the lithium iron phosphate battery cell may be too large, or even break, resulting in a short circuit and posing a safety hazard.
[0049] It can be understood that the formation method in the preparation method of the embodiment of the present application also includes a conventional discharge process.
[0050] The sub-capacity test includes the following steps;
[0051] (a): The lithium iron phosphate battery cell is charged at a constant current to 40% SOC-90% SOC using at least one rate between 0.01C and 0.1C.
[0052] Optionally, step (a) comprises:
[0053] The battery is charged to 60% SOC-90% SOC using a constant current of 0.01C-0.1C.
[0054] (b): The lithium iron phosphate battery cell is discharged at a constant current to 10% SOC-90% SOC using at least one rate between 0.01C and 0.1C.
[0055] Optionally, between step (a) and step (b), the following steps are further included:
[0056] The lithium iron phosphate battery cell is charged at a constant current of 0.33C-0.5C to 100% SOC.
[0057] That is, the lithium iron phosphate battery is fully charged with constant current and then discharged.
[0058] In at least one charging process, the lithium iron phosphate battery cell is charged to 10% SOC-90% SOC at a constant current of at least one rate of 0.01C-0.1C, for example, to 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, 80% SOC or 90% SOC, etc., and then charged to 100% SOC at a higher frequency current such as 0.33C, and then discharged.
[0059] In at least one discharge process, the lithium iron phosphate battery cell is charged to 10% SOC-90% SOC at a constant current using at least one rate among 0.01C-0.1C. For example, from a fully charged state, it is discharged to 90% SOC, 80% SOC, 70% SOC, 60% SOC, 50% SOC, 40% SOC, 30% SOC, 20% SOC, etc. at a rate among 0.01C-0.1C, and then discharged to 0% SOC at a constant current using a higher frequency current, such as 0.5C.
[0060] In some embodiments, in the volume fractionation test, after step (b), the following steps are further included:
[0061] Use 0.33C-0.5C to discharge the lithium iron phosphate battery to 0% SOC;
[0062] Use 0.33C-0.5C constant current and constant voltage to charge the lithium iron phosphate battery to 100% SOC;
[0063] Use 0.33C-0.5C constant current discharge to 0% SOC for lithium iron phosphate battery;
[0064] The lithium iron phosphate battery is charged to 60% at a constant current of 0.33C-0.5C.
[0065] It can be understood that in the preparation method of the embodiment of the present application, after the formation, the lithium iron phosphate battery cell is also degassed and double-sealed, and then a capacity test is performed.
[0066] The preparation method of the lithium iron phosphate battery cell provided in the embodiment of the present application has a small impedance in the range of 10% SOC-90% SOC, and is charged and discharged at a rate of one or more combinations of 0.01C-0.1C. The lithium iron phosphate battery cell is activated in the formation stage, and then charged and discharged at a frequency of 0.01C-0.1C in a state of small impedance in the capacity division test stage, and is further fully activated, so that the lithium iron phosphate battery cell can exert a maximum or relatively close to maximum capacity when discharged in the capacity division process, effectively reducing the capacity climbing.
[0067] The embodiment of the present application also provides a lithium iron phosphate battery cell, which is manufactured using the above-mentioned lithium iron phosphate battery cell preparation method.
[0068] An embodiment of the present application also provides a secondary battery, comprising the above-mentioned lithium iron phosphate battery cell.
[0069] The lithium iron phosphate battery cell and secondary battery provided in the embodiment of the present application are manufactured by the preparation method of the embodiment of the present application. The lithium iron phosphate battery cell is fully activated, which reduces the problem of capacity climbing and can accurately divide the capacity. The secondary battery made of the lithium iron phosphate battery cell provided in the embodiment of the present application can be sold with the highest capacity and performance, thereby improving the economic benefits.
[0070] The following uses a number of embodiments to illustrate the preparation method of lithium iron phosphate batteries and their products, as well as product performance and other aspects.
[0071] Example 1
[0072] The preparation method of the lithium iron phosphate battery cell of this embodiment includes formation and capacity testing.
[0073] The formation includes the following steps:
[0074] 1) Set the temperature of the formation cabinet to 45°C and the surface pressure of a single lithium iron phosphate cell to 1.3MPa;
[0075] 2) 0.1C constant current charging to 10% SOC; leave for 10 minutes;
[0076] 3) Charge at 0.01C constant current to 35% SOC; leave for 10 min.
[0077] 4) Increase the constant current by 0.01C and charge to 90% SOC; leave for 30 minutes;
[0078] After formation, the lithium iron phosphate battery cell is degassed and sealed twice, and then the capacity test is carried out. The capacity test includes the following steps:
[0079] a) 0.33C constant current and constant voltage charging to 3.65V, 0.05C cut-off (0.05C cut-off is 100% SOC); leave for 30 minutes;
[0080] b) 0.33C constant current discharge to 90% SOC; leave for 30 minutes;
[0081] c) 0.01C constant current discharge to 10% SOC; leave for 30 minutes;
[0082] d) 0.33C constant current discharge to 2.5V (0% SOC when constant current discharge to 2.5V); leave for 30 minutes;
[0083] e) 0.5C constant current and constant voltage charging to 3.65V, 0.05C cut-off; leave for 30 minutes;
[0084] f) 0.5C constant current discharge to 2.5V; leave for 30 minutes;
[0085] g) Charge at 0.5C constant current to 60% SOC; leave for 30 min.
[0086] Example 2
[0087] The preparation method of the lithium iron phosphate battery cell of this embodiment includes formation and capacity testing.
[0088] The formation includes the following steps:
[0089] 1) Set the temperature of the formation cabinet to 45°C and the surface pressure of a single cell to 1.3MPa;
[0090] 2) 0.1C constant current charging to 10% SOC; leave for 10 minutes;
[0091] 3) Charge at 0.01C constant current to 35% SOC; leave for 10 min.
[0092] 4) Increase the constant current by 0.05C to charge to 90% SOC; leave for 30 minutes;
[0093] After formation, the lithium iron phosphate battery cell is degassed and sealed twice, and then the capacity test is carried out. The capacity test includes the following steps:
[0094] a) 0.33C constant current and constant voltage charging to 3.65V, 0.05C cut-off (0.05C cut-off is 100% SOC); leave for 30 minutes;
[0095] b) Increase the constant current to 0.33C and discharge to 90% SOC; leave for 30 minutes;
[0096] c) 0.05C constant current discharge to 10% SOC; leave for 30 minutes;
[0097] d) 0.33C constant current discharge to 2.5V (0% SOC is defined as constant current discharge to 2.5V); leave for 30 minutes;
[0098] e) 0.5C constant current and constant voltage charging to 3.65V, 0.05C cut-off; leave for 30 minutes;
[0099] f) 0.5C constant current discharge to 2.5V; leave for 30 minutes;
[0100] g) Charge at 0.5C constant current to 60% SOC; leave for 30 min.
[0101] Example 3
[0102] The preparation method of the lithium iron phosphate battery cell of this embodiment includes formation and capacity testing.
[0103] The formation includes the following steps:
[0104] 1) Set the temperature of the formation cabinet to 45°C and the surface pressure of a single cell to 1.3MPa;
[0105] 2) 0.1C constant current charging to 10% SOC; leave for 10 minutes;
[0106] 3) Charge at 0.1C constant current to 35% SOC; leave for 10 minutes.
[0107] 4) Charge at 0.1C constant current to 90% SOC; leave for 30 minutes.
[0108] After formation, the lithium iron phosphate battery cell is degassed and sealed twice, and then the capacity test is carried out. The capacity test includes the following steps:
[0109] 1) 0.33C constant current and constant voltage charging to 3.65V, 0.05C cut-off (defined as constant current and constant voltage charging to 3.65V, 0.05C cut-off is 100% SOC); leave for 30 minutes;
[0110] 2) Increase the constant current of 0.33C to 90% SOC and leave for 30 minutes;
[0111] 3) 0.1C constant current discharge to 10% SOC; leave for 30 minutes;
[0112] 4) 0.33C constant current discharge to 2.5V (0% SOC is defined as constant current discharge to 2.5V); leave for 30 minutes;
[0113] 5) 0.5C constant current and constant voltage charging to 3.65V, 0.05C cut-off; leave for 30 minutes;
[0114] 6) 0.5C constant current discharge to 2.5V; leave for 30 minutes;
[0115] 7) Charge at 0.5C constant current to 60% SOC; leave for 30 minutes.
[0116] Example 4
[0117] The preparation method of the lithium iron phosphate battery cell of this embodiment includes formation and capacity testing.
[0118] The formation includes the following steps:
[0119] 1) Set the temperature of the formation cabinet d to 45°C and the surface pressure of a single cell to 1.3MPa;
[0120] 2) 0.1C constant current charging to 10% SOC; leave for 10 minutes;
[0121] 3) Charge at 0.1C constant current to 35% SOC; leave for 10 minutes.
[0122] 4) Increase the constant current by 0.05C to charge to 40% SOC; leave for 30 minutes;
[0123] 5) 0.01C constant current charge to 60% SOC; leave for 30 minutes;
[0124] 6) 0.05C constant current charge to 80% SOC; leave for 30 minutes;
[0125] 7) Charge at 0.1C constant current to 90% SOC; leave for 30 minutes;
[0126] After formation, the lithium iron phosphate battery cell is degassed and sealed twice, and then the capacity test is carried out. The capacity test includes the following steps:
[0127] 1) 0.33C constant current and constant voltage charging to 3.65V, 0.05C cut-off (defined as constant current and constant voltage charging to 3.65V, 0.05C cut-off is 100% SOC); leave for 30 minutes;
[0128] 2) Increase the constant current of 0.33C to 90% SOC and leave for 30 minutes;
[0129] 3) 0.1C constant current discharge to 80% SOC; leave for 30 minutes;
[0130] 4) 0.05C constant current discharge to 60% SOC; leave for 30 minutes;
[0131] 5) 0.01C constant current discharge to 40% SOC; leave for 30 minutes;
[0132] 6) 0.05C constant current discharge to 20% SOC; leave for 30 minutes;
[0133] 7) 0.1C constant current discharge to 10% SOC; leave for 30 minutes;
[0134] 8) 0.33C constant current discharge to 2.5V (defined as 0% SOC when the constant current discharge reaches 2.5V); leave for 30 minutes;
[0135] 9) 0.5C constant current and constant voltage charging to 3.65V, 0.05C cut-off; leave for 30 minutes;
[0136] 10) 0.5C constant current discharge to 2.5V; leave for 30 minutes;
[0137] 11) Charge at 0.5C constant current to 60% SOC; leave for 30 minutes.
[0138] Comparative Example 1
[0139] The preparation method of the lithium iron phosphate battery cell of this comparative example includes formation and capacity separation test.
[0140] The formation includes the following steps:
[0141] 1) Set the temperature of the formation cabinet to 45°C and the surface pressure of a single cell to 1.3MPa;
[0142] 2) 0.1C constant current charging to 5% SOC; leave for 10 minutes;
[0143] 3) Charge at 0.15C constant current to 35% SOC; leave for 10 minutes.
[0144] After formation, the lithium iron phosphate battery cell is degassed and sealed twice, and then the capacity test is carried out. The capacity test includes the following steps:
[0145] 1) 0.33C constant current and constant voltage charging to 3.65V, 0.05C cut-off (defined as constant current and constant voltage charging to 3.65V, 0.05C cut-off is 100% SOC); leave for 30 minutes;
[0146] 2) 0.33C constant current discharge to 2.5V (0% SOC is defined as constant current discharge to 2.5V); leave for 30 minutes;
[0147] 3) 0.5C constant current and constant voltage charging to 3.65V, 0.05C cut-off; leave for 30 minutes;
[0148] 4) 0.5C constant current discharge to 2.5V; leave for 30 minutes;
[0149] 5) Charge at 0.5C constant current to 60% SOC; leave for 30 minutes.
[0150] The preparation methods of Examples 1-4 are compared with the preparation method of Comparative Example 1 as shown in Table 1 below, and the gray shading represents the differences between the Examples and Comparative Example 1. During the formation process, each charge / discharge was left alone for 10 minutes; during the capacity separation test, each charge / discharge was left alone for 30 minutes.
[0151] Table 1
[0152]
[0153] Comparing the capacity data of the lithium iron phosphate cells of Examples 1-4 and Comparative Example 1 in the capacity division test at 0.5C discharge, and performing normal OCV and other tests after the lithium iron phosphate cells of Examples 1-4 and Comparative Example 1 are divided into different capacities, the cells with no abnormal 3EA process data are subjected to 0.5C cycle test to observe their climbing trend. The specific data are shown in Table 2 below, and the cycle capacity curve is shown in the attached table. Figure 1 .
[0154] Table 2
[0155]
[0156] It can be seen from the results that the lithium iron phosphate batteries in Examples 1-4 reach the maximum or close to the maximum capacity when the capacity is divided. Compared with Comparative Example 1, the capacity climbing amplitude of the lithium iron phosphate batteries in Examples 1-4 at the initial stage of the cycle is much smaller than that in Comparative Example 1 or there is no capacity climbing, indicating that the lithium iron phosphate batteries in the embodiments of the present application are fully activated in the capacity division stage and there is no obvious climbing in the cycle.
[0157] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims
1. A method for preparing a lithium iron phosphate battery cell, characterized in that: Including during the formation and capacity test process, within the range of 10% SOC-90% SOC of the lithium iron phosphate battery cell, the lithium iron phosphate battery cell is charged and discharged at least once at a constant current rate of 0.01C-0.1C.
2. The method for preparing a lithium iron phosphate battery cell according to claim 1, characterized in that: During the formation and capacity division test, in the step of performing at least one constant current charge and discharge on the lithium iron phosphate battery cell at least once within the range of 10% SOC-90% SOC of the lithium iron phosphate battery cell using at least one rate between 0.01C and 0.1C, the formation step comprises: The lithium iron phosphate battery cell is charged at a constant current of 0.1C to 5%-10% SOC; Then, the lithium iron phosphate battery cell is charged at a constant current to 20% SOC-35% SOC using at least one rate of 0.01C-0.1C; The sub-capacity test comprises the following steps: The lithium iron phosphate battery cell is charged at a constant current to 40% SOC-90% SOC using at least one rate of 0.01C-0.1C; The lithium iron phosphate battery cell is discharged at a constant current to 10% SOC-90% SOC using at least one rate of 0.01C-0.1C.
3. The method for preparing a lithium iron phosphate battery cell according to claim 2, characterized in that: The step of charging the lithium iron phosphate battery cell with a constant current to 20% SOC-35% SOC using at least one rate of 0.01C-0.1C comprises: The lithium iron phosphate battery cell is charged to 35% at a constant current of 0.05C-0.1C.
4. The method for preparing a lithium iron phosphate battery cell according to any one of claims 1 to 3, characterized in that: The formation temperature is 25°C-45°C.
5. The method for preparing a lithium iron phosphate battery cell according to any one of claims 1 to 3, characterized in that: In the formation step, the surface pressure of a single lithium iron phosphate battery cell is 0.8 MPa-1.5 MPa.
6. The method for preparing a lithium iron phosphate battery cell according to claim 1, characterized in that: The step of charging to 40% SOC-90% SOC by using at least one constant current of 0.01C-0.1C rate comprises: The battery is charged to 60% SOC-90% SOC using a constant current of 0.01C-0.1C.
7. The method for preparing a lithium iron phosphate battery cell according to claim 1, characterized in that: The step of charging the lithium iron phosphate battery cell with a constant current to 40% SOC-90% SOC using at least one rate of 0.01C-0.1C and the step of discharging the lithium iron phosphate battery cell with a constant current to 10% SOC-90% SOC using at least one rate of 0.01C-0.1C also includes: The lithium iron phosphate battery cell is charged at a constant current of 0.33C-0.5C to 100% SOC.
8. The method for preparing a lithium iron phosphate battery cell according to claim 1, characterized in that: In the capacity division test, after the step of discharging the lithium iron phosphate battery cell to 10% SOC-90% SOC at a constant current using at least one rate of 0.01C-0.1C, the step further includes: Discharging the lithium iron phosphate battery cell at a constant current of 0.33C-0.5C to 0% SOC; The lithium iron phosphate battery is charged to 100% SOC at constant current and constant voltage using 0.33C-0.5C; Discharging the lithium iron phosphate battery cell at a constant current of 0.33C-0.5C to 0% SOC; The lithium iron phosphate battery cell is charged to 60% at a constant current of 0.33C-0.5C.
9. A lithium iron phosphate battery cell, characterized in that: The lithium iron phosphate battery cell is manufactured by the preparation method of any one of claims 1 to 8.
10. A secondary battery, characterized in that: Including the lithium iron phosphate battery cell as described in claim 9.