A method for capacity testing of lithium-ion batteries

Abstract

This invention discloses a capacity grading method for lithium-ion batteries, comprising a charging stage and a discharging stage. The charging stage sequentially includes a first charging stage where the charging current increases from OC to I, a second charging stage where the charging current remains constant at I, a third charging stage where the charging current decreases from I to OC, and a constant-voltage charging stage where the voltage remains constant. The discharging stage sequentially includes a first discharging stage where the discharging current increases from OC to I, a second discharging stage where the discharging current remains constant at I, and a third discharging stage where the discharging current decreases from I to OC. In this capacity grading method, the binding or separation of lithium ions and lithium base is more effective during the gradual increase or decrease of the current, saving the passive time after capacity grading of the lithium battery. It also reduces the damage to the lithium-ion lattice of the battery during high-rate charging and discharging, improving the initial efficiency and cycle life of the battery, and has excellent application prospects.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery production technology, and specifically relates to a lithium-ion battery capacity assessment method. Background Technology

[0002] Driven by environmental protection needs and energy shortages, the demand for power batteries has exploded. Although technological advancements have led to significant improvements in the safety and performance of power batteries, manufacturing costs remain high and are still a major factor influencing their development.

[0003] Among the many processes in battery production, capacity grading equipment accounts for a significant portion of the cost, making the introduction of new capacity grading technologies and methods imperative. Capacity grading involves classifying the produced batteries into capacity grades to ensure the consistency of battery capacity within the same battery pack, thereby extending the battery's cycle life. However, existing traditional capacity grading methods rely on excessive amounts of capacity grading equipment, resulting in excessively high investment costs for battery manufacturers. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a lithium-ion battery capacity grading method. This invention utilizes a stepped current grading method to save the passive time after lithium battery capacity grading, while reducing the damage to the lithium-ion lattice of the lithium battery during high-rate charging and discharging, thereby improving the battery's initial efficiency and cycle life. This reduces the process time of the capacity grading process, improves battery quality, indirectly saves factory floor space, reduces factory energy consumption, and lowers battery costs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A lithium-ion battery capacity assessment method includes a charging stage and a discharging stage, wherein:

[0007] The charging stages sequentially include a first charging stage where the charging current increases from 0C to I, a second charging stage where the charging current remains constant at I, a third charging stage where the charging current decreases from I to 0C, and a constant voltage charging stage where the voltage remains constant; furthermore, the voltage value of the constant voltage charging stage is 3.65V or 4.2V.

[0008] The discharge stages sequentially include a first discharge stage in which the discharge current increases from 0C to I, a second discharge stage in which the discharge current remains constant at I, and a third discharge stage in which the discharge current decreases from I to 0C.

[0009] The temperature I is 0.5C to 0.8C.

[0010] Capacity is the integral of time with respect to current as shown in formula (1). In the preferred technical solution, the capacity of the battery charged from the first stage to the third stage of charging is Q = I / 2*(t1+t3)+t2*I.

[0011] Q(I n )=t∫I n Formula (1) for dt.

[0012] As a preferred technical solution, the duration of the first charging stage is 3-5 minutes; the duration of the second charging stage is 115-117 minutes; and the duration of the third charging stage is 3-5 minutes.

[0013] As a preferred technical solution, the duration of the first discharge stage is 3-5 minutes; the duration of the second discharge stage is 115-117 minutes; and the duration of the third discharge stage is 3-5 minutes.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] In the capacity grading method provided by this invention, the current in the first charging stage and the first discharging stage gradually increases, while the current in the third charging stage and the third discharging stage gradually decreases. During the gradual increase or decrease of the current, the binding or separation effect between lithium ions and lithium base is better, saving the passive time after capacity grading of lithium batteries. At the same time, it reduces the damage to the lithium ion lattice of the battery during high-rate charging and discharging, improves the initial efficiency of the battery and the cycle life of the battery, and saves passive time, thereby reducing the process time of capacity grading. The shorter the capacity grading process time, the fewer capacity grading equipment are required, indirectly saving at least 8.57% of the factory floor space, reducing factory energy consumption, and reducing battery production costs. Attached Figure Description

[0016] Figure 1 A schematic diagram of the current change process during the charging phase;

[0017] Figure 2 This is a schematic diagram of the current change process during the discharge phase; Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0019] Due to the different material systems, lithium iron phosphate and ternary materials have different material activities. The first charge and discharge stage of a lithium iron phosphate battery takes 3 minutes, while the third charge and discharge stage of a ternary material battery takes 5 minutes.

[0020] The lithium-ion batteries used in the following examples and comparative examples are all from the same batch and of the same specifications. The capacity grading method includes a charging stage and a discharging stage, wherein:

[0021] refer to Figure 1 The charging process consists of three stages: a first charging stage A1 where the charging current increases from 0C to I; a second charging stage A2 where the charging current remains constant at I; a third charging stage A3 where the charging current decreases from I to 0C; and a 3.65V constant voltage charging stage A4. The constant voltage charging stage A4 is the battery replenishment process, designed to fully charge the battery. This stage is a standard procedure during battery capacity testing. Figure 1 The 3.65V constant voltage charging stage A4 is not shown in the code; the time for stage A1 is t1, the time for stage A2 is t2, the time for stage A3 is t3, and the time for stage A4 is T. cv ;

[0022] refer to Figure 2 The discharge stages sequentially include a first discharge stage B1 where the discharge current increases from 0C to I, a second discharge stage B2 where the discharge current remains constant at I, and a third discharge stage B3 where the discharge current decreases from I to 0C; the time for stage B1 is t1, the time for stage B2 is t2, and the time for stage B3 is t3.

[0023] The principle behind the above-mentioned increase or decrease in current is as follows: the output current of a general charging power supply is DC / DC, and the current charging current is changed by changing the DC duty cycle; this invention controls the output current by controlling the change of the duty cycle, and the duty cycle of each stage satisfies the rate of change of the current in the corresponding stage. In this field, the principle of controlling the change of the duty cycle is a conventional technical means, which will not be elaborated here.

[0024] Comparative Example 1

[0025] In the battery industry, the charge / discharge rate in the capacity grading process of conventional lithium iron phosphate batteries is 0.5C; T0 is the constant current charging time, which requires 120 minutes to fully charge; T 00 The settling and negativeing ​​time is 30 minutes; T cv The constant voltage charging time is 10 minutes; t0 is the discharge time, which requires 120 minutes to fully discharge. The total capacity sizing time for the conventional scheme is T0 + T. 00 +T cv +t0 = 280min.

[0026] Comparative Example 2

[0027] In the capacity grading process of lithium iron phosphate batteries, when the charge / discharge rate is 0.8C, T0 is the constant current charging time, which requires 75 minutes to fully charge; T 00The settling and negativeing ​​time is 50 minutes; T cv The constant voltage charging time is 10 minutes; t0 is the discharge time, which requires 75 minutes to fully discharge. The total capacity sizing time is T0 + T... 00 +T cv +t0 = 210 min.

[0028] Example 1

[0029] A lithium-ion battery capacity assessment method includes a charging stage and a discharging stage. In this embodiment, the current I is 0.5C, wherein:

[0030] The charging phase times include the following: the first charging phase A1, where the charging current increases from 0C to 0.5C, requires t1 of 3 minutes; the second charging phase A2, where the charging current remains constant at 0.5C, requires t2 of 117 minutes; the third charging phase A3, where the charging current decreases from 0.5C to 0C, requires t3 of 3 minutes; and the 3.65V constant voltage charging phase A4 requires t1 of 3 minutes. cv It is 10 minutes;

[0031] The discharge phase times include the following: the time required for the first discharge phase B1, in which the discharge current increases from 0C to 0.5C, is t1, which is 3 minutes; the time required for the second discharge phase B2, in which the discharge current remains constant at 0.5C, is t2, which is 117 minutes; and the time required for the third discharge phase B3, in which the discharge current decreases from 0.5C to 0C, is t3, which is 3 minutes.

[0032] The total capacity dissipation time is: t1 + t2 + t3 + T cv +t1+t2+t3=256min.

[0033] Compared with Comparative Example 1, Example 1 showed a time saving ratio of 256 min < 280 min, which is (280-256) / 280 = 8.57%.

[0034] Example 2

[0035] A lithium-ion battery capacity assessment method includes a charging stage and a discharging stage. In this embodiment, the current I is 0.8C, wherein:

[0036] The charging phase times include the following: the first charging phase A1, where the charging current increases from 0C to 0.5C, requires a time t1 of 3 minutes; the second charging phase A2, where the charging current remains constant at 0.5C, requires a time t2 of 72 minutes; the third charging phase A3, where the charging current decreases from 0.5C to 0C, requires a time t3 of 3 minutes; and the 3.65V constant voltage charging phase A4 requires a time T... cv It is 10 minutes;

[0037] The discharge phase times include the following: the time required for the first discharge phase B1, in which the discharge current increases from 0C to 0.5C, is t1, which is 3 minutes; the time required for the second discharge phase B2, in which the discharge current remains constant at 0.5C, is t2, which is 72 minutes; and the time required for the third discharge phase B3, in which the discharge current decreases from 0.5C to 0C, is t3, which is 3 minutes.

[0038] The total capacity dissipation time is: t1 + t2 + t3 + T cv +t1+t2+t3=166min.

[0039] Compared with Comparative Example 2, Example 2 showed a time saving ratio of 166 min < 210 min, which is (210 - 166) / 210 = 20.95% (Performance Testing).

[0040] The batteries in Example 1 and Comparative Example 1 were subjected to initial efficiency and cycle life tests, respectively. The test results are shown in Table 1 below:

[0041] Table 1. Battery performance test results in the examples and comparative examples.

[0042]

[0043] As can be seen from Table 1, compared with the conventional charge-discharge capacity testing method in the comparative example, the capacity testing method provided by the present invention can not only shorten the time required for capacity testing, but also significantly improve the initial efficiency and cycle life of the resulting battery.

[0044] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for capacity testing of lithium-ion batteries, characterized in that: It includes a charging phase and a discharging phase, in which: The charging stages sequentially include a first charging stage where the charging current increases from 0C to I, a second charging stage where the charging current remains constant at I, a third charging stage where the charging current decreases from I to 0C, and a constant voltage charging stage where the voltage remains constant. The discharge stages sequentially include a first discharge stage in which the discharge current increases from 0C to I, a second discharge stage in which the discharge current remains constant at I, and a third discharge stage in which the discharge current decreases from I to 0C. The temperature I is 0.5C to 0.8C.

2. The lithium-ion battery capacity assessment method according to claim 1, characterized in that: The first charging phase lasts for 3-5 minutes.

3. The lithium-ion battery capacity assessment method according to claim 1, characterized in that: The second charging phase lasts for 115-117 minutes.

4. The lithium-ion battery capacity assessment method according to claim 1, characterized in that: The duration of the third charging stage is 3-5 minutes.

5. The lithium-ion battery capacity assessment method according to claim 1, characterized in that: The duration of the first discharge phase is 3-5 minutes.

6. The lithium-ion battery capacity assessment method according to claim 1, characterized in that: The second discharge phase lasts for 115-117 minutes.

7. The lithium-ion battery capacity assessment method according to claim 1, characterized in that: The duration of the third discharge stage is 3-5 minutes.

8. The lithium-ion battery capacity testing method according to any one of claims 1 to 7, characterized in that: The voltage value during the constant voltage charging phase is 3.65V or 4.2V.

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