Battery capacity grading method

Abstract

A battery capacity grading method comprises the following steps: charging at a constant first power to a charging cut-off voltage of a battery, and standing for a first time length; carrying out constant second power discharge until the discharge cut-off voltage of the battery is reached, and standing for a second duration; discharging at a constant third power until the discharging cut-off voltage of the battery is reached, and standing for a third duration; and charging at constant fourth power, charging to the limiting voltage of the battery, and standing for a fourth time period, so that the state of charge of the battery is A, 21% < = A < = 30%, regulating and controlling the capacity grading temperature by using a temperature control piece, the capacity grading temperature is t, and 30 DEG C < = t < = 40 DEG C. The consistency of the batteries subjected to capacity grading by using the battery capacity grading method is high.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery capacity assessment method. Background Technology

[0002] Batteries produced in the same batch may have different actual capacities (e.g., ±5% or even higher). If directly assembled into a battery pack, the lower-capacity batteries will reach their discharge cutoff voltage prematurely, causing the entire battery pack to stop working early and reducing usable capacity. Therefore, it is necessary to improve the consistency between multiple batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a battery capacity grading method to solve the problem of poor consistency among multiple batteries.

[0004] To achieve the objectives of this invention, the following technical solution is provided: This invention provides a battery capacity testing method, comprising the following steps: Charge at constant first power until the battery reaches its charging cutoff voltage, then let it rest for a first period of time; Discharge at a constant second power until the battery's discharge cutoff voltage is reached, then leave it to stand for a second duration; Discharge at a constant third power until the battery reaches its discharge cutoff voltage, and then leave it to stand for a third duration. The battery is charged at a constant fourth power until it reaches its limit voltage, and then left to stand for a fourth time to ensure that the battery's state of charge is A, satisfying the condition: 21% ≤ A ≤ 30%. Among them, a temperature control device is used to regulate the volumetric temperature, and the volumetric temperature is t, which satisfies: 30℃≤t≤40℃.

[0005] In one embodiment, the second power is b2 and the third power is b3, satisfying that b2 > b3.

[0006] In one implementation, 0.4P≤b2≤0.6P; 0.05P≤b3≤0.1P.

[0007] In one embodiment, the fourth power is b4, which satisfies: b4 > b3.

[0008] In one implementation, the constant fourth power charging time is h1, which satisfies: A = b4 × h1 / 60, where h1 is in minutes.

[0009] In one embodiment, the first power is b1, which satisfies: 0.4P≤b1≤0.6P.

[0010] In one embodiment, the charging cutoff voltage is V1, which satisfies: 3.5V≤V1≤4.2V; The discharge cutoff voltage is V2, which satisfies the condition: 2.4V≤V2≤2.6V.

[0011] In one embodiment, the limiting voltage is V3, which satisfies: 3.5V≤V3≤4.2V.

[0012] In one embodiment, the first duration, the second duration, the third duration, and the fourth duration are all equal. In one embodiment, the first duration is h2, which satisfies: 3min≤h2≤30min.

[0013] The battery capacity grading method of the present invention uses a constant power mode to charge and discharge the battery. In the constant power mode, the heat generated by the battery is directly related to the power, which facilitates dynamic adjustment of the battery temperature and avoids local overheating. The constant power mode can more realistically reflect the performance differences of the battery under actual power output, making it easier to select battery cells with highly consistent parameters such as capacity, internal resistance, and self-discharge rate, thereby improving the overall performance of the battery pack. Furthermore, the SOC of the batteries selected by the capacity grading method is limited to 21%≤A≤30%, which can also effectively improve the capacity utilization rate of multiple batteries. Therefore, the batteries obtained by the battery capacity grading method of the present invention have high consistency. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0015] Figure 1 This is a flowchart illustrating the steps of a battery capacity grading method according to one embodiment; Figure 2 This is a diagram showing the relationship between voltage (V) and state of charge (SOC) in one embodiment; Figure 3 This is a graph showing the relationship between voltage (V), state of charge (SOC), and their derivatives (dV / dQ) in one embodiment. Figure 4 This is a schematic diagram illustrating a battery undergoing 0.5P capacity testing at different temperatures according to one embodiment. Figure 5 This is a schematic diagram of a battery of another embodiment undergoing 0.5P capacity testing at different temperatures. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

[0018] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used in this invention includes any and all combinations of one or more of the associated listed items.

[0019] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0020] Please refer to Figure 1 A battery capacity grading method includes the following steps: Step S10: Charge at constant first power until the battery reaches its charging cutoff voltage, then let stand for a first duration.

[0021] Step S20: Discharge at constant second power until the battery's discharge cutoff voltage is reached, and then allow to stand for a second duration.

[0022] Step S30: Discharge at constant third power until the battery's discharge cutoff voltage is reached, then let stand for a third duration.

[0023] Step S40: Charge at constant fourth power until the battery's limiting voltage is reached, then let it rest for a fourth duration to ensure that the battery's state of charge is A, satisfying: 21%≤A≤30%.

[0024] Optionally, in step S10, the positive electrode of the first power lithium iron phosphate cell adopts a solid-phase or liquid-phase positive electrode. The cell needs to be fully charged to activate the electrode, so as to effectively release the capacity and reduce the polarization of the cell during initial discharge.

[0025] Optionally, step S10 may also include resting the device before performing constant first power charging.

[0026] Optionally, in step S10, the positive electrode of the battery is a solid-phase or liquid-phase positive electrode. The battery needs to be fully charged to activate the electrode, so as to effectively release the capacity and reduce the polarization of the battery during the initial discharge.

[0027] Optionally, in step S20, during the first discharge of the battery, the SEI film undergoes structural reorganization under stress during the discharge process (Li ions are removed from the negative electrode), defects are repaired, and a denser and more stable protective layer is formed, reducing electrolyte decomposition and gas generation in subsequent cycles. The first discharge can also eliminate batteries with abnormal capacity (such as those below 80% of rated capacity), reducing waste in subsequent processes.

[0028] Optionally, in step S30, by discharging to the discharge cutoff voltage, the discharge termination conditions of different batteries are standardized, which facilitates horizontal comparison of capacity differences (such as capacity screening). After the discharge is completed, there is residual polarization inside the battery (such as ohmic polarization and electrochemical polarization). After standing, the charge is redistributed and the voltage gradually rises back to the open circuit voltage, reflecting the true remaining charge.

[0029] Optionally, in step S30, the battery is charged to its limit voltage to calibrate the final capacity of the battery, optimize electrochemical performance, ensure safety boundaries, and provide a precise basis for the long-term use and graded management of the battery.

[0030] Optionally, in steps S10-S40, using constant power mode for charging and discharging can avoid high current surges (such as instantaneous high currents during startup) in constant current mode, reduce damage to the SEI film (solid electrolyte interface film), and delay capacity decay. Optionally, the first duration, second duration, third duration, and fourth duration can be the same or different, without restriction.

[0031] Please refer to Figure 2 and Figure 3 , Figure 2 These are the voltage values ​​of LFP batteries (lithium iron phosphate batteries) at different SOC levels. Figure 3 This represents the battery voltage values ​​at different SOCs and the derivative of voltage with respect to SOC. Figure 2 and Figure 3 As shown in 'a', with the increase of SOC, the voltage first rises and then stabilizes. The stress distribution in the voltage stabilization region is uniform, reducing active material shedding and SEI film rupture, which helps to increase the battery's cycle life. Figure 2 This indicates that the battery's SOC needs to be ≥21%. Figure 3As shown in b, when the State of Charge (SOC) is 30%, dV / dQ is close to zero, meaning the voltage plateau is flat. Small capacity changes hardly cause voltage fluctuations, thus significantly reducing voltage differences between multiple cells within the group and improving the capacity utilization of multiple cells. Therefore, the SOC of the battery should be 21% ≤ A ≤ 30%.

[0032] Optionally, the first power, the second power, and the fourth power can be the same or different, without restriction.

[0033] The battery capacity grading method of the present invention uses a constant power mode to charge and discharge the battery. In the constant power mode, the heat generated by the battery is directly related to the power, which facilitates dynamic adjustment of the battery temperature and avoids local overheating. The constant power mode can more realistically reflect the performance differences of the battery under actual power output, making it easier to select battery cells with highly consistent parameters such as capacity, internal resistance, and self-discharge rate, thereby improving the overall performance of the battery pack. Furthermore, the SOC of the batteries selected by the capacity grading method is limited to 21%≤A≤30%, which can also effectively improve the capacity utilization rate of multiple batteries. Therefore, the batteries obtained by the battery capacity grading method of the present invention have high consistency.

[0034] In one embodiment, the battery capacity grading method further includes: using a temperature control device to regulate the capacity grading temperature, wherein the capacity grading temperature is t, and satisfies: 30℃≤t≤40℃.

[0035] Optionally, the temperature control component can be liquid-cooled, air-cooled, etc., without limitation. Specifically, the cooling medium of the temperature control component can be liquid or gaseous; specifically, the cooling medium can be water, coolant, or heat transfer oil, without limitation. Specifically, when the temperature control component is liquid-cooled and the cooling medium is water, and each battery is placed in a container for capacity separation, with the container placed inside the temperature control component, the control of the capacity separation temperature is more accurate when the temperature control component is liquid-cooled.

[0036] Optionally, the test temperature can be 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, etc., without limitation.

[0037] When the capacity rating temperature t is too low, the battery's internal resistance increases at low temperatures, requiring a reduction in charging / discharging current to avoid overvoltage / overcurrent, thus prolonging the capacity rating cycle. When the capacity rating temperature t is too high, the high temperature accelerates the oxidative decomposition of organic solvents in the electrolyte, generating gases (such as CO2 and CO) and byproducts (such as HF), leading to electrolyte drying, increased internal resistance, and potential rupture of the SEI film (solid electrolyte interface film) at high temperatures, exposing fresh electrode surfaces and triggering continuous side reactions. A moderate capacity rating temperature t ensures a suitable diffusion rate of lithium ions in the electrolyte and electrode materials, avoiding electrolyte decomposition due to excessively high temperatures or hindered ion migration due to excessively low temperatures.

[0038] For details, please refer to Figure 4 and Figure 5 ,in Figure 4 The 0.5P capacity of LFP batteries (lithium iron phosphate batteries) was tested sequentially at different temperatures from 18℃ to 45℃. Figure 5 The LFP battery was subjected to 0.5P capacity tests at different temperatures from 45℃ to 18℃. The test results showed that when the battery was subjected to capacity testing at around 35℃, the polarization effect caused by lower temperature capacity testing could be eliminated, and lithium ions could be completely extracted and released.

[0039] In one implementation, the second power is b2 and the third power is b3, satisfying b2 > b3. If only a single high-power discharge (b2) is used, the polarization effect will cause the battery to reach the discharge cutoff voltage prematurely, resulting in the actual discharged capacity being lower than the true value. By quickly releasing most of the capacity with a first high-power discharge (b2), and then releasing the remaining capacity with a second low-power discharge (b3), the impact of the polarization effect on capacity measurement can be significantly reduced. During low-power discharge, polarization is weakened, the voltage drop is more gradual, and the measurement is closer to the battery's true capacity.

[0040] In one implementation, 0.4P≤b2≤0.6P; 0.05P≤b3≤0.1P.

[0041] Optionally, b2 can be 0.4P, 0.45P, 0.5P, 0.55P, 0.6P, etc., without restriction.

[0042] Optionally, b3 can be 0.05P, 0.06P, 0.07P, 0.08P, 0.09P, 0.1P, etc., without restriction.

[0043] When b2 is too large, the electrode reaction rate accelerates, causing the ion migration rate in the electrolyte to be unable to keep up, resulting in concentration polarization and reducing the effective output voltage; when b2 is too small, the discharge time is longer, which may reduce the capacity efficiency; when b2 is of a moderate size, the active materials inside the battery fully participate in the reaction, which helps to improve the actual effective capacity of the battery.

[0044] If b3 is too small, the battery internal resistance test result may be too low, making it impossible to accurately identify high internal resistance batteries during sorting, affecting the consistency and lifespan of the battery pack; if b3 is too large, the function of step S30, namely releasing polarization capacity, may not be possible; when b3 is of a moderate size, during the first discharge of the battery, due to the existence of polarization, the normal distribution of capacity shows a tail at the left end, requiring a low-power discharge to release polarization capacity. A lower-power b3 can more thoroughly release the battery capacity, ensuring the accuracy of capacity testing.

[0045] In one embodiment, the fourth power is b4, satisfying: b4 > b3. Optionally, 0.4P ≤ b4 ≤ 0.6P. Using the fourth power b4 for high-power charging at the end of step S40 can quickly increase the battery capacity to near full charge, significantly shortening the testing cycle and increasing production capacity. Furthermore, step S40 is the final stage of battery capacity assessment. The battery has already formed a stable SEI film and electrochemical system through previous tests (such as the first charge and discharge in steps S10-S30). At this point, using high-power charging can quickly charge the battery to the specified SOC state, significantly shortening the testing cycle and increasing production capacity.

[0046] In one implementation, 0.4P ≤ b1 ≤ 0.6P. Optionally, b1 can be 0.4P, 0.45P, 0.5P, 0.55P, 0.6P, etc., without limitation.

[0047] When b1 is too high, the rate at which lithium ions embed into the graphite anode may exceed their diffusion capacity, leading to the deposition of lithium metal on the anode surface and the formation of dendrites. These dendrites may pierce the separator, causing internal short circuits and even battery thermal runaway. When b1 is too low, although the risk of thermal runaway can be reduced, it will significantly affect testing efficiency, the accuracy of battery performance evaluation, equipment utilization, and production costs. Furthermore, at low power, battery polarization effects (such as concentration polarization and electrochemical polarization) are weakened, and voltage changes are gradual, making it difficult to reflect the dynamic response of the battery in actual use. When b1 is moderate, it can avoid battery thermal runaway, improve the efficiency of battery capacity assessment, and also help to reflect the true capacity of the battery.

[0048] In one embodiment, step S40 includes: the constant fourth power charging time is h1, satisfying: A=b4×h1 / 60, where h1 is minutes.

[0049] Correspondingly, h = 60A / b4, where 21% ≤ A ≤ 30%, and 0.4P ≤ b1 ≤ 0.6P. Specifically, when b1 is 0.5P and A is 21% (i.e., when the battery's SOC is 21%), b1 = 60 × 21% / 0.5 = 25.2 min; when b1 is 0.5P and A is 30% (i.e., when the battery's SOC is 30%), b1 = 60 × 30% / 0.5 = 36 min. By calculating the charging time to the specified battery SOC, the voltage difference between multiple batteries in the group is significantly reduced, thereby improving the capacity utilization of multiple batteries.

[0050] In one embodiment, the charging cutoff voltage is V1, which satisfies: 3.5V≤V1≤4.2V; the discharging cutoff voltage is V2, which satisfies: 2.4V≤V2≤2.6V.

[0051] Optionally, V1 can be 3.5V, 3.6V, 3.65V, 3.8V, 3.9V, 4V, 4.1V, 4.2V, etc., without restriction. Optionally, V2 can be 2.4V, 2.44V, 2.48V, 2.5V, 2.54V, 2.58V, 2.6V, etc., without restriction.

[0052] When V1 is too high, overcharging causes lattice distortion of the positive electrode material and thickening of the SEI film on the negative electrode surface, obstructing the electron conduction path. This may cause some batteries to experience a sharp drop in capacity due to structural damage, while other batteries only experience slight degradation. It is difficult to screen out inferior products through the capacity threshold during sorting. When V1 is too low, undercharging will cause the positive electrode active material to not be completely delithiated and the negative electrode to not be fully lithium-intercalated, resulting in the measured capacity being lower than the true value. When V1 is moderate, the battery can be fully delithiated, so that the measured battery capacity is close to the true value.

[0053] When V2 is too high, the battery's depth of discharge is insufficient, the battery's capacity is reduced, and the energy density is lowered. When V2 is too low, the battery's capacity increases, but it will cause irreversible side reactions of the active materials, accelerating battery aging. When V2 is moderate, the battery's capacity is moderate and will not affect the battery's active materials.

[0054] In one embodiment, the limiting voltage is V3, which satisfies: 3.5V≤V3≤4.2V.

[0055] Optionally, V3 can be 3.5V, 3.6V, 3.65V, 3.8V, 3.9V, 4V, 4.1V, 4.2V, etc., without restriction. V3 can be selected according to the type of battery. When the battery is an LFP battery, the corresponding V3 can be 3.65V, and when the battery is an NCM battery (nickel-cobalt-manganese lithium battery), the corresponding V3 can be 4.2V.

[0056] When V3 is too high, lithium is excessively extracted from the positive electrode material, causing the crystal structure to collapse (such as the transformation of the layered structure into a spinel structure), resulting in permanent capacity decay. When V3 is too low, lithium ions are extracted from the negative electrode and embedded in the positive electrode. If the voltage is too low, lithium is excessively extracted from the negative electrode, causing the graphite layered structure to collapse and forming irreversible "dead lithium". When V3 is moderate, lithium plating in the battery can be effectively prevented, avoiding local overcharging or over-discharging.

[0057] In one implementation, the first duration, the second duration, the third duration, and the fourth duration are all equal. The first duration is h2, which satisfies: 3min ≤ h2 ≤ 30min.

[0058] Optionally, h2 can be 3 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc., without restriction.

[0059] The core purpose of each resting step in the battery capacity testing process is to ensure that the chemical substances inside the battery reach dynamic equilibrium, stabilize key parameters, and provide accurate data for subsequent testing. Specifically, during charging and discharging, polarization (including ohmic polarization, concentration polarization, and electrochemical polarization) occurs on the electrode surface due to the mismatch between ion migration rate and chemical reaction rate, resulting in voltage lag. Resting allows ions to redistribute, and the polarization voltage gradually disappears, ensuring that the voltage value measured later accurately reflects the battery state. If h2 is too small, the battery polarization is not completely eliminated, and voltage lag still exists, leading to increased capacity testing errors. Unstable internal temperature and electrolyte distribution may also cause abnormal self-discharge rates. If h2 is too large, the extended resting time will significantly increase the capacity testing cycle and reduce production capacity.

[0060] The technical solution of the present invention will be described in detail below through specific embodiments.

[0061] Example 1 Step S10: Let stand for 3 minutes, the first power b1 is 0.5P, charge at the constant first power until the battery charging cutoff voltage is 3.65V, and let stand for 3 minutes. Step S20: The second power b2 is 0.5P, and the battery is discharged at a constant second power until the discharge cutoff voltage of the battery is 2.5V, and then left to stand for 3 minutes. Step S30: The third power b3 is 0.1P, and the battery is discharged at a constant third power until the discharge cutoff voltage of the battery is 2.5V, and then left to stand for 3 minutes. In step S40, the fourth power b4 is 0.5P, and the battery is charged at a constant fourth power until the battery's limiting voltage of 3.65V. After resting for 3 minutes, the charging time h1 is 25.2 minutes, and the corresponding battery SOC is 21%.

[0062] The volumetric temperature is 35℃.

[0063] Example 2 In step S40, the fourth power b4 is 0.5P, and the battery is charged at a constant fourth power until the battery's limiting voltage of 3.65V is reached, followed by a resting period of 3 minutes. The charging time h1 is 36 minutes, corresponding to a battery SOC of 30%.

[0064] All other parameters are the same as in Example 1.

[0065] Example 3 The volumetric temperature is 30℃.

[0066] All other parameters are the same as in Example 1.

[0067] Example 4 The volumetric temperature is 40℃.

[0068] All other parameters are the same as in Example 1.

[0069] Comparative Example 1 After resting for 3 minutes, charge the battery to 3.65V with a constant first current of 0.5C. Keep the charging voltage at 3.65V and gradually reduce the current to 0.05C as the battery approaches full charge. Then let it rest for 3 minutes. Discharge to 2.5V with a constant second current, where the second current is 0.5C, and let stand for 3 minutes; Discharge to 2.5V with a constant third current, where the third current is 0.05C, and let stand for 3 minutes; Charge to 3.65V with a constant fourth current, where the fourth current is 0.5C, and the charging time is 48 minutes, followed by a 3-minute rest period.

[0070] The volumetric temperature is 35℃.

[0071] Comparative Example 2 The fourth power, b4, is 0.5P. The battery is charged at this constant fourth power until it reaches its limit voltage of 3.65V, then left to rest for 3 minutes. The charging time, h1, is 60 minutes, corresponding to a battery SOC of 60%.

[0072] All other parameters are the same as in Example 1.

[0073] Comparative Example 3 The fourth power, b4, is 0.5P. The battery is charged at this constant fourth power until it reaches its limit voltage of 3.65V, then left to rest for 3 minutes. The charging time, h1, is 12 minutes, corresponding to a battery SOC of 10%.

[0074] All other parameters are the same as in Example 1.

[0075] Comparative Example 4 The volumetric temperature is 25℃.

[0076] All other parameters are the same as in Example 1.

[0077] Comparative Example 5 The volumetric temperature is 45℃.

[0078] All other parameters are the same as in Example 1.

[0079] The capacity grading methods provided in Examples 1-2 and Comparative Examples 1-5 were used to perform capacity grading on lithium iron phosphate batteries. The batteries after capacity grading were then subjected to capacity consistency testing, internal resistance stability testing, voltage characteristic testing, and cycle life verification under the following conditions: Capacity consistency test: Constant current constant voltage charge-discharge test (CC-CV), charge at standard current (1C) to cutoff voltage (3.65V), then charge at constant voltage until the current drops to 0.05C; after standing for 30 minutes, discharge at 1C current to cutoff voltage (2.5V), and record the discharge capacity; the test standard is that the capacity difference (maximum value - minimum value) of batteries in the same batch should be ≤ 3% of the design capacity. The specific design capacity is 280Ah, and 3% of the design capacity is 8400mAh.

[0080] Internal resistance stability test: DC internal resistance (DCIR) test, with the battery at 50% SOC, apply a 10-second pulse current (1C), record the voltage transient change, and calculate the internal resistance (R = ΔV / ΔI); the test standard is that the DCIR value should be ≤ the design upper limit, and the specific design upper limit is 0.6mΩ.

[0081] After the 1P13S module is manufactured, the voltage difference at the end of the discharge is tested: 13 batteries are connected in series to form a 1P13S module. The voltage of each individual battery in the module is monitored in real time by a battery charge and discharge tester or a battery management system (BMS), and the difference between the highest voltage and the lowest voltage at the end of the discharge is calculated.

[0082] The test results are shown in Table 1 below.

[0083] Table 1

[0084] Comparing Examples 1 to 4 and Comparative Examples 1 to 5 in Table 1, it can be seen that the discharge terminal voltage difference of the 1P13S module prepared by constant power capacity separation at a suitable capacity separation temperature is smaller than the discharge terminal voltage difference of the corresponding P13S module in the comparative examples.

[0085] Comparing Examples 1, 3, 4, 4, and 5 in Table 1, it can be seen that when the temperature is within a suitable range (35±5℃), the discharge terminal voltage difference is the smallest after fabricating the 1P13S module, indicating high consistency among multiple batteries. Changes in the capacity grading temperature affect the battery's internal resistance and the diffusion rate of the electrolyte and electrode materials; therefore, an appropriate capacity grading temperature should be selected.

[0086] Comparing Examples 1, 2, 2, and 3 in Table 1, it can be seen that when the battery's state of charge (SOC) is within a suitable range (21%-30%), the voltage drop at the discharge end of the 1P13S module is smaller, indicating high consistency among multiple batteries. The SOC affects the stress distribution in the voltage stability region, which in turn affects the shedding of active materials and the rupture of the SEI film inside the battery. Therefore, limiting the SOC can improve battery stability and reduce voltage differences between multiple batteries.

[0087] Comparing Example 1 and Comparative Example 1 in Table 1, it can be seen that the 1P13S module made from batteries obtained by the constant power charge-discharge method has a smaller discharge terminal voltage drop compared to batteries obtained by the constant current charge-discharge method. This indicates that the multiple batteries corresponding to Example 1 have high consistency. Because the constant power charge-discharge mode can dynamically adjust the battery temperature, avoid local overheating, and thus select cells with highly consistent parameters such as capacity, internal resistance, and self-discharge rate, the overall performance of the battery pack can be improved.

[0088] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0089] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A battery capacity testing method, characterized in that, Includes the following steps: Charge at constant first power until the battery reaches its charging cutoff voltage, then let it rest for a first period of time; Discharge at a constant second power until the battery's discharge cutoff voltage is reached, then leave it to stand for a second duration; Discharge at a constant third power until the battery reaches its discharge cutoff voltage, and then leave it to stand for a third duration. The battery is charged at a constant fourth power until it reaches its limit voltage, and then left to stand for a fourth time to ensure that the battery's state of charge is A, satisfying the condition: 21% ≤ A ≤ 30%. Among them, a temperature control device is used to regulate the volumetric temperature, and the volumetric temperature is t, which satisfies: 30℃≤t≤40℃.

2. The battery capacity assessment method according to claim 1, characterized in that, The second power is b2, and the third power is b3, satisfying the condition: b2 > b3.

3. The battery capacity testing method according to claim 2, characterized in that, 0.4P≤b²≤0.6P; 0.05P≤b3≤0.1P.

4. The battery capacity assessment method according to claim 2, characterized in that, The fourth power is b4, which satisfies: b4 > b3.

5. The battery capacity testing method according to claim 4, characterized in that, The charging time for the constant fourth power is h1, which satisfies: A = b4 × h1 / 60, where h1 is in minutes.

6. The battery capacity testing method according to claim 1, characterized in that, The first power is b1, which satisfies: 0.4P≤b1≤0.6P.

7. The battery capacity testing method according to claim 1, characterized in that, The charging cutoff voltage is V1, which satisfies the following condition: 3.5V≤V1≤4.2V; The discharge cutoff voltage is V2, which satisfies the condition: 2.4V≤V2≤2.6V.

8. The battery capacity testing method according to claim 1, characterized in that, The limiting voltage is V3, which satisfies the following condition: 3.5V≤V3≤4.2V.

9. The battery capacity testing method according to any one of claims 1 to 8, characterized in that, The first duration, the second duration, the third duration, and the fourth duration are all equal.

10. The battery capacity testing method according to claim 9, characterized in that, The first duration is h2, which satisfies: 3min≤h2≤30min.

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