Lithium battery self-discharge screening method

Abstract

The invention relates to a lithium battery self-discharge screening method, and belongs to the technical field of lithium ion batteries. The screening method comprises the following steps: S1, pressurizing and fixing a plurality of lithium ion batteries in a tray; s2, all the lithium ion batteries in the tray are charged to 100% SOC; s3, transferring the tray and all the lithium ion batteries into an environment of 50 + / -5 DEG C, standing for a period of time, recording first open-circuit voltages of all the lithium ion batteries, continuously standing for a period of time, recording second open-circuit voltages of all the lithium ion batteries, and calculating voltage drops, a mean value Xbar of the voltage drops and a standard deviation sigma of the voltage drops; and S4, according to the mean value Xbar of the voltage drop and the standard deviation sigma of the voltage drop, determining self-discharge standards of all the lithium ion batteries, and screening all the lithium ion batteries. According to the screening method, large-scale continuous production can be realized, and bad batteries with internal defects can be screened out as soon as possible.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium battery self-discharge screening method. Background Art

[0002] Self-discharge performance is an important performance indicator for lithium-ion batteries. Self-discharge performance is also called charge retention capacity, which refers to the ability of the battery to retain the amount of electricity stored in the open circuit under certain environmental conditions. Electric vehicles and energy storage have become the largest application areas for lithium-ion batteries.

[0003] In electric vehicles and energy storage systems, single cells are connected in series, parallel or series-parallel to form a battery pack, so the batteries in the battery pack must have good self-discharge consistency to ensure maximum performance and prevent over-discharge during discharge. With the advancement of technology, people have higher and higher requirements for battery self-discharge consistency. Summary of the invention

[0004] In view of this, in order to achieve the discharge consistency of a lithium battery pack, the present invention provides a lithium battery self-discharge screening method.

[0005] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows.

[0006] The lithium battery self-discharge screening method of the present invention comprises the following steps:

[0007] S1. Place multiple lithium-ion batteries in a tray and pressurize and fix them;

[0008] S2. Charge all lithium-ion batteries in the tray to 100% SOC;

[0009] S3. Place the tray and all lithium-ion batteries in an environment of 50±5°C, let them stand for a period of time, record the first open circuit voltage of all lithium-ion batteries, continue to let them stand for a period of time, record the second open circuit voltage of all lithium-ion batteries, and calculate the voltage drop, the mean value Xbar of the voltage drop, and the standard deviation σ of the voltage drop;

[0010] S4. According to the mean value Xbar of the voltage drop and the standard deviation σ of the voltage drop, the self-discharge standard of all lithium-ion batteries is determined, and all lithium-ion batteries are screened.

[0011] Preferably, in step S1, the pressurized pressure is 0.05MPa-0.3Mpa.

[0012] Preferably, in step S2, the charging current is 0.05C-1C.

[0013] Preferably, the number of the lithium-ion batteries is n. In step S3, all the lithium-ion batteries are first left to stand for T1, and the open circuit voltage OCV1 of all the lithium-ion batteries is tested. 电池1 、OCV1 电池2 ...OCV1 电池n ;

[0014] Then keep all lithium-ion batteries still for T2 and test the open circuit voltage OCV2 of all lithium-ion batteries. 电池1 、OCV2 电池2 ...OCV2 电池n ;

[0015] Calculate the voltage drop (OCV1) of each lithium-ion battery during the static time T2 电池1 -OCV2 电池1 )、(OCV1 电池2 -OCV2 电池2 )……(OCV1 电池n -OCV2 电池n );

[0016] The average value Xbar of all lithium-ion batteries is calculated according to formula 1:

[0017]

[0018] The standard deviation σ of all lithium-ion batteries is calculated according to formula 2:

[0019]

[0020] More preferably, T1=36-48h, T2=12-24h.

[0021] Preferably, in step S4, the self-discharge voltage drop standard is: upper limit USL = Xbar + 3σ, lower limit LSL = Xbar - 3σ, battery voltage drop (OCV1 电池i -OCV2 电池i ) Lithium-ion batteries whose voltage drop is within the range of (USL, LSL) are qualified self-discharge cells, and lithium-ion batteries whose voltage drop is not within the range of (USL, LSL) are unqualified self-discharge cells.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The lithium battery self-discharge screening method of the present invention affects the self-discharge screening by allowing the internal chemical reaction of the lithium ion battery to stand at high temperature when fully charged; increases the probability of burrs, particles, and metal impurities piercing the diaphragm under pressurized conditions of the lithium ion battery; formulates the self-discharge standard through statistical screening methods; and can realize large-scale continuous production, so that bad batteries with internal defects can be screened out as early as possible, greatly reducing the flow of self-discharge defective products into products. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the specific implementation modes of the present invention, the drawings required for use in the specific implementation modes will be briefly introduced below. Obviously, the drawings described below are only some specific implementation modes of the present invention and are not limitations of the present invention.

[0025] Figure 1 It is a process flow chart of the lithium battery self-discharge screening method of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings.

[0027] like Figure 1 As shown, the lithium battery self-discharge screening method of the present invention comprises the following steps:

[0028] S1. Place n lithium-ion batteries in a tray and fix them under pressure at a pressure of 0.05MPa-0.3Mpa;

[0029] S2. Charge all lithium-ion batteries in the tray to 100% SOC, with a charging current of 0.05C-1C;

[0030] S3. Transfer the tray and all lithium-ion batteries to a 50±5℃ environment, let all lithium-ion batteries stand for T1=36-48h, and test the open circuit voltage OCV1 of all lithium-ion batteries. 电池1 、OCV1 电池2 ...OCV1 电池n ;

[0031] Then, all lithium-ion batteries are left to stand for T2 = 12-24 hours, and the open circuit voltage OCV2 of all lithium-ion batteries is tested. 电池1 、OCV2 电池2 ...OCV2 电池n ;

[0032] Calculate the voltage drop (OCV1) of each lithium-ion battery during the static time T2 电池1 -OCV2 电池1 )、(OCV1 电池2 -OCV2 电池2 )……(OCV1 电池n -OCV2 电池n );

[0033] The average value Xbar of all lithium-ion batteries is calculated according to formula 1:

[0034]

[0035] The standard deviation σ of all lithium-ion batteries is calculated according to formula 2:

[0036]

[0037] S4. Determine the self-discharge standard of all lithium-ion batteries according to the mean value Xbar of the voltage drop and the standard deviation σ of the voltage drop, and screen all lithium-ion batteries;

[0038] The self-discharge voltage drop standard is: upper limit USL = Xbar + 3σ, lower limit LSL = Xbar - 3σ, battery voltage drop (OCV1 电池i -OCV2 电池i ) Lithium-ion batteries whose voltage drop is within the range of (USL, LSL) are qualified self-discharge cells, and lithium-ion batteries whose voltage drop is not within the range of (USL, LSL) are unqualified self-discharge cells.

[0039] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A lithium battery self-discharge screening method, characterized in that: The following steps are involved: S1. Place multiple lithium-ion batteries in a tray and pressurize and fix them; S2. Charge all lithium-ion batteries in the tray to 100% SOC; S3. Place the tray and all lithium-ion batteries in an environment of 50±5°C, let them stand for a period of time, record the first open circuit voltage of all lithium-ion batteries, continue to let them stand for a period of time, record the second open circuit voltage of all lithium-ion batteries, and calculate the voltage drop, the mean value Xbar of the voltage drop, and the standard deviation σ of the voltage drop; S4. According to the mean value Xbar of the voltage drop and the standard deviation σ of the voltage drop, the self-discharge standard of all lithium-ion batteries is determined, and all lithium-ion batteries are screened.

2. The lithium battery self-discharge screening method according to claim 1, characterized in that: In step S1, the pressurized pressure is 0.05MPa-0.3Mpa.

3. The lithium battery self-discharge screening method according to claim 1, characterized in that: In step S2, the charging current is 0.05C-1C.

4. The lithium battery self-discharge screening method according to claim 1, characterized in that: The number of the lithium-ion batteries is n. In step S3, First, let all lithium-ion batteries stand for T1 and test the open circuit voltage OCV1 of all lithium-ion batteries. 电池1 、OCV1 电池2 ...OCV1 电池n ; Then keep all lithium-ion batteries still for T2 and test the open circuit voltage OCV2 of all lithium-ion batteries. 电池1 、OCV2 电池2 ...OCV2 电池n ; Calculate the voltage drop (OCV1) of each lithium-ion battery during the static time T2 电池1 -OCV2 电池1 )、(OCV1 电池2 -OCV2 电池2 )……(OCV1 电池n -OCV2 电池n ); The average value Xbar of all lithium-ion batteries is calculated according to formula 1: The standard deviation σ of all lithium-ion batteries is calculated according to formula 2:

5. The lithium battery self-discharge screening method according to claim 4, characterized in that: T1 = 36-48h, T2 = 12-24h.

6. The lithium battery self-discharge screening method according to claim 1, characterized in that: In step S4, the self-discharge voltage drop standard is: upper limit USL = Xbar + 3σ, lower limit LSL = Xbar - 3σ, battery voltage drop (OCV1 电池i -OCV2 电池i ) Lithium-ion batteries whose voltage drop is within the range of (USL, LSL) are qualified self-discharge cells, and lithium-ion batteries whose voltage drop is not within the range of (USL, LSL) are unqualified self-discharge cells.

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