Method for shortening shipment period of finished lithium ion battery

Abstract

The invention relates to the technical field of lithium ion battery production, in particular to a method for shortening the shipment cycle of a finished lithium ion battery, which comprises the following steps: aging and infiltrating a battery after liquid injection, fully charging, storing for 3 days at 45 DEG C in a fully charged state, storing for 8 hours at 25 DEG C, testing an open-circuit voltage value, and recording as OCV0; storing for 7 days at the temperature of 25 DEG C, testing an open-circuit voltage value after the storage is finished, recording the open-circuit voltage value as OCV1, and recording a difference value between the OCV0 and the OCV1 as DOCV; the method comprises the following steps: grouping batteries, enabling the environments of pole piece preparation, roll core preparation and storage of each group of batteries to be the same, screening out the batteries of which the DOCV is beyond a DOCV standard range according to the DOCV standard range of the batteries, then taking the remaining good products in the group as samples, calculating the first mean value and standard deviation of the DOCV of the batteries in the group, iterating for 5 times, and calculating the second mean value and standard deviation of the DOCV of the batteries in the group; a good product of each iteration is used as a sample of the next iteration, and finally, the battery of which the DOCV is between the lower limit value of the DOCV standard range and the sum of the average value of the DOCV after the fifth iteration is 0-5 times of the standard deviation in the group is the good product.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery production, and in particular to a method for shortening the delivery cycle of finished lithium ion batteries. Background Art

[0002] Lithium-ion batteries are increasingly used in power tools or devices such as notebooks, digital cameras, and digital video cameras. They also have broad prospects in the fields of electric two-wheeled vehicles, automobiles, mobile base stations, energy storage power stations, etc. Due to the poor voltage of some lithium-ion batteries, they may face low voltage problems during use, which not only affects the normal operation of the equipment, but may also shorten the battery life and even bring safety hazards.

[0003] In order to avoid low voltage after lithium-ion batteries with poor voltage are shipped to customers, causing customer complaints and other problems, during the lithium battery production process, the process will store the batteries for a certain period of time after they come off the line, select the batteries with poor voltage, and ship the good batteries to customers. The existing method is: the process puts all the tray batteries together for overall selection, and then adds sorting, and stores them for a certain period of time after they come off the line for selection. Due to differences in the preparation of the electrode sheets, the preparation of the cores, and the storage temperature of the battery cells between different trays in the process, it is impossible to select all the batteries with poor voltage, resulting in some defective products flowing out to the customer, causing customer complaints. In addition, this screening method also has problems such as long production cycle, increased delivery rate, storage costs, and reduced capital turnover. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for shortening the delivery cycle of finished lithium-ion batteries, which can efficiently and quickly sort out defective lithium-ion batteries and prevent defective products from flowing to the client and causing customer complaints.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for shortening the delivery cycle of finished lithium-ion batteries, comprising the following steps: S1, aging and soaking several batteries after injection, and then fully charging; S2, store the fully charged batteries at 45°C for 3 days and then at 25°C for 8 hours, and then test the open circuit voltage of each battery, which is recorded as OCV0; S3, the batteries are stored at 25°C for another 7 days, and then the open circuit voltage of each battery is tested, recorded as OCV1, and the difference between OCV0 and OCV1 of each battery is recorded as DOCV; S4, grouping the batteries, the electrode sheet preparation, core preparation and storage environment of the batteries in each group are the same, and then subsequent operations are performed on the batteries in each group respectively; by grouping, batteries with similar performance are integrated together to avoid affecting the screening accuracy due to a large number of batteries with large differences sharing the same screening criteria; S5, screening each battery in the group according to the DOCV standard range of the battery, and screening out the battery whose DOCV is outside the DOCV standard range; S6, taking the remaining batteries in the group as samples, calculating the mean and standard deviation of DOCV of each battery in the sample, taking the sum of the sample mean and 3.8 times the sample standard deviation as the upper limit, taking the difference between the sample mean and 3.8 times the sample standard deviation as the lower limit, forming a new screening range, screening each battery in the sample according to the new screening range, and screening out batteries with DOCV outside the new screening range; S7, iterating step S6 5 times, using the batteries retained in each iteration as samples for the next iteration, and calculating and obtaining the mean and standard deviation of the DOCV of the remaining batteries after the fifth iteration; S8, using the lower limit of the standard range of battery DOCV used in S5 as the lower limit of the final screening, and the sum of the mean of the DOCV of the remaining batteries after the fifth iteration in S7 and the standard deviation of 0-5 times as the upper limit of the final screening, to form the final screening range of the group, and re-screening each battery of the group according to the final screening range, and the battery with DOCV within the final screening range is a good product. For each group, the accurate final screening range is obtained through multiple screening calculations and analyses, so that all defective products in the group can be screened out to ensure the screening effect.

[0006] As an optional solution, the upper limit of the final screening range is the sum of the mean and 3.8 times the standard deviation of the DOCV of the remaining batteries after the fifth iteration.

[0007] As an alternative, each group includes 256 cells.

[0008] As an optional solution, the grouping of batteries in step S4 can be completed before S1, S2 or S3.

[0009] Compared with the prior art, the present invention has the following beneficial effects: utilizing the method of the present invention can shorten the delivery cycle of finished lithium-ion batteries, and can effectively prevent products with poor voltage from flowing out to the client and causing customer complaints. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0011] Figure 1 is the scatter plot of OCV1-DOCV; Figure 2 Self-discharge settlement example diagram; DETAILED DESCRIPTION

[0012] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0013] A method for shortening the shipping cycle of finished lithium-ion batteries comprises the following steps: S1, after aging and soaking several injected batteries, fully charge them.

[0014] S2, store the fully charged batteries at 45°C for 3 days and then at 25°C for 8 hours, then test the open circuit voltage of each battery one by one, and record the open circuit voltage value of each battery as OCV0.

[0015] S3, store the batteries at 25°C for 7 days, and then test the open circuit voltage of each battery one by one. The open circuit voltage value of each battery is recorded as OCV1, and the difference between OCV0 and OCV1 of each battery is recorded as DOCV. The DOCV of each battery is used as a parameter for subsequent screening of the battery.

[0016] To avoid confusion, each battery can be labeled to facilitate measuring and recording the DOCV of each battery.

[0017] S4, grouping the batteries. The electrode preparation, winding core preparation and storage environment of the batteries in each group are the same. The battery grouping operation can also be completed before S1, S2 or S3 steps.

[0018] Then, the subsequent steps S5 to S8 are performed on each group of batteries.

[0019] S5, first find the corresponding DOCV standard range according to the battery specifications and models, combined with the industry's public data information, and perform preliminary screening on each battery in each group according to the DOCV standard range corresponding to the battery, screen out the batteries in the group whose DOCV is outside the DOCV standard range, and retain the batteries whose DOCV is within the DOCV standard range.

[0020] S6, in each group, the batteries whose DOCV is within the DOCV standard range retained in step S5 are used as samples, and the mean and standard deviation of DOCV of each battery in the sample are calculated. According to the calculation results, the sum of the sample mean and 3.8 times the sample standard deviation is used as the upper limit, and the difference between the sample mean and 3.8 times the sample standard deviation is used as the lower limit to form a new screening range. According to the new screening range, each battery in the sample is screened, and the batteries whose DOCV is outside the new screening range are screened out.

[0021] S7, iterate step S6 5 times, and the batteries retained after each iteration are used as samples for the next iteration, and finally calculate the mean and standard deviation of the DOCV of the remaining batteries after the fifth iteration.

[0022] S8, select the lower limit value of the DOCV standard range in step S5 as the lower limit value of the final screening, select the mean value of DOCV of the remaining batteries after the fifth iteration in S7 and the sum of 0-5 times the standard deviation as the upper limit value of the final screening, and form the final screening range of the group. According to the determined final screening range, re-screen each battery in the group, and the battery with DOCV within the final screening range is a good battery that can be delivered to the client.

[0023] By performing steps S5-S8 on the batteries in each group, all batteries can be tested and screened, and the batteries finally retained are good batteries that can be shipped to customers.

[0024] As a preferred embodiment, in step S8, the upper limit of the final screening range is the sum of the mean value of the DOCV of the remaining batteries after the fifth iteration and 3.8 times the standard deviation.

[0025] In the above-mentioned operation method, the batteries are grouped according to their conditions, so that the batteries in each group belong to the same production batch, or the parameters such as the ambient temperature in the process steps such as electrode preparation and core preparation are similar, and the storage environment of the batteries in each group is also the same, and then the operation steps S5-S8 are performed on each group respectively to obtain a final screening range suitable for each battery in the group, and the batteries in the group are screened using the obtained final screening range, so that defective products can be fully screened out, and by combining the battery grouping with the subsequent S5-S8 steps, it is possible to avoid detection errors caused by the use of the same final screening range for batteries with large differences in their own performance, which causes defective products to flow to the client and cause complaints.

[0026] Preferably, each grouping includes 256 batteries to facilitate use with trays used in existing battery production processes.

[0027] By utilizing the process method of the present invention, batteries with poor voltage can be screened out more accurately to prevent batteries with poor voltage from flowing out to the client. In addition, the screening speed is fast and the efficiency is high, which effectively shortens the delivery cycle of finished lithium batteries.

[0028] Figure 1 This is a scatter plot of OCV1-DOCV made by measuring batteries according to the existing method and the method according to the present invention. The horizontal axis in the figure indicates the OCV1 value, and the vertical axis indicates the DOCV value. The defective products detected by the existing method are all distributed above the black line in the figure. However, by using the method of the present invention, in addition to the defective products above the black line, the defective products below the black line can also be detected, which effectively avoids the flow of products with poor voltage to the client and causes customer complaints; Figure 2 Self-discharge settlement example diagram, by Figure 2 From the statistical information, it can be seen that the number of defects increases with the change of the number of iterations. In the method of the present invention, the number of iterations is 5, which can screen out all the defects.

[0029] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0030] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for shortening the shipping cycle of finished lithium-ion batteries, characterized in that: The following steps are involved: S1, aging and soaking several batteries after injection, and then fully charging; S2, store the fully charged batteries at 45°C for 3 days and then at 25°C for 8 hours, and then test the open circuit voltage of each battery, which is recorded as OCV0; S3, the batteries are stored at 25°C for another 7 days, and then the open circuit voltage of each battery is tested, recorded as OCV1, and the difference between OCV0 and OCV1 of each battery is recorded as DOCV; S4, grouping the batteries, the electrode sheet preparation, winding core preparation and storage environment of the batteries in each group are the same, and then subsequent operations are performed on the batteries in each group respectively; S5, screening each battery in the group according to the DOCV standard range of the battery, and screening out the battery whose DOCV is outside the DOCV standard range; S6, taking the remaining batteries in the group as samples, calculating the mean and standard deviation of DOCV of each battery in the sample, taking the sum of the sample mean and 3.8 times the sample standard deviation as the upper limit, taking the difference between the sample mean and 3.8 times the sample standard deviation as the lower limit, forming a new screening range, screening each battery in the sample according to the new screening range, and screening out batteries with DOCV outside the new screening range; S7, iterating step S6 5 times, using the batteries retained in each iteration as samples for the next iteration, and calculating and obtaining the mean and standard deviation of the DOCV of the remaining batteries after the fifth iteration; S8, taking the lower limit of the standard range of battery DOCV adopted in S5 as the lower limit of the final screening, taking the mean of DOCV of the remaining batteries after the fifth iteration in S7 and the sum of 0-5 times the standard deviation as the upper limit of the final screening, forming the final screening range of the group, and rescreening the batteries of the group according to the final screening range, and the batteries with DOCV within the final screening range are good products.

2. A method for shortening the shipping cycle of finished lithium-ion batteries according to claim 1, characterized in that: The upper limit of the final screening range is the sum of the mean and 3.8 times the standard deviation of the DOCV of the remaining cells after the fifth iteration.

3. A method for shortening the shipping cycle of finished lithium-ion batteries according to claim 2, characterized in that: Each group contains 256 batteries.

4. A method for shortening the shipping cycle of finished lithium-ion batteries according to claim 2 or 3, characterized in that: The grouping of batteries in step S4 may be completed before S1, S2 or S3.

Images