Optimized capacity grading method of lithium ion battery

Abstract

The invention discloses an optimized capacity grading method of a lithium ion battery, which comprises the following steps: S1, executing preset capacity grading operation on all multiple batteries to be subjected to capacity grading, and obtaining a charging capacity C1; s2, sorting according to the sequence of the charging capacities C1 from high to low, extracting a plurality of the charging capacities C1 as standard batteries, and recording the charging capacities C1; s3, performing constant volume operation on the plurality of standard batteries by using standard conditions to obtain a standard capacity C2; s4, drawing scatter diagrams of a plurality of standard batteries by taking the charging capacity C1 as an abscissa and the standard capacity C2 as an ordinate; s5, fitting the scatter diagram to obtain a quantitative relational expression; and S6, for any battery to be subjected to capacity grading, according to the charging capacity C1 and the quantitative relational expression, obtaining a corresponding standard capacity as a capacity grading capacity, and then taking the capacity grading capacity as a sorting basis of the batteries. According to the invention, the capacity grading efficiency of a plurality of batteries in a large batch can be improved, and the capacity grading accuracy is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery optimization capacity division method. Background Art

[0002] At present, lithium-ion batteries have been widely used in digital products, electric vehicles and energy storage fields due to their high energy density, good cycle performance, and green and pollution-free. As a basic characteristic of lithium-ion batteries, capacity plays a very important role in the experience and use of lithium-ion battery products. The capacity of the battery cell directly affects the battery life and service life of the product. Therefore, it is necessary to screen out the battery cells with unqualified capacity during production.

[0003] Capacity is an important performance indicator of lithium-ion batteries. During the later battery assembly (Pack), multiple single cells need to be connected in series and parallel to form modules and battery packs. Therefore, the capacity of the single cell needs to be clarified before assembly.

[0004] At present, the capacity division process of lithium-ion batteries generally adopts the following steps: full discharge operation, full charge operation, full discharge operation and charging to a specified SOC (state of charge) mode, that is, the battery is fully discharged first, and then a complete full charge and discharge cycle is performed, and the full discharge capacity is defined as the capacity division capacity as the basis for later assembly. However, the capacity division time of the above process is relatively long. Even if a charge and discharge rate of 0.7 to 1.0 C is used, it takes about 5 to 7 hours. However, the high rate of charge and discharge leads to greater polarization of the battery, which is not conducive to the performance of the initially activated battery cells.

[0005] In addition, it is well known that lithium ion transmission is greatly affected by temperature. When using high-rate discharge, when the battery cell temperature is high, the battery discharge capacity increases, which will affect the accuracy of the actual battery capacity. However, the existing lithium-ion battery capacity division process ignores the impact of the ambient temperature of the discharge process on the lithium-ion battery charge and discharge process, resulting in low accuracy of battery capacity division.

[0006] Therefore, there is an urgent need to develop a technology that can solve the above technical problems. Summary of the invention

[0007] The purpose of the present invention is to provide a lithium ion battery capacity optimization method in view of the technical defects in the prior art.

[0008] To this end, the present invention provides a method for optimizing capacity distribution of lithium-ion batteries, characterized in that it comprises the following steps:

[0009] Step S1, performing a preset capacity division operation on all the multiple batteries to be divided, and obtaining a charging capacity C1 of each battery to be divided;

[0010] The preset capacity division operation includes: a preset charging operation and a preset discharging operation performed successively;

[0011] Step S2, sorting all the multiple batteries to be divided that have completed the preset capacity division operation in descending order of the charging capacity C1, extracting the multiple batteries to be divided that have completed the preset capacity division operation as multiple standard batteries, and recording the charging capacity C1 of each standard battery;

[0012] Step S3, performing a constant capacity operation on a plurality of standard batteries using standard conditions to obtain a standard capacity C2 of each standard battery;

[0013] Step S4, drawing a scatter plot of a plurality of standard batteries with the charging capacity C1 of the standard battery as the abscissa and the standard capacity C2 of the standard battery as the ordinate;

[0014] Step S5, fitting the scatter plots of multiple standard batteries to obtain a quantitative relationship between the charging capacity C1 and the standard capacity C2 corresponding to the standard battery;

[0015] Step S6, for any battery to be divided, according to the charging capacity C1 obtained after the preset division operation is performed and according to the quantitative relationship, the standard capacity corresponding to the battery to be divided is obtained and used as the division capacity, and then the division capacity is used as the basis for battery sorting.

[0016] It can be seen from the technical solution provided by the present invention that, compared with the prior art, the present invention provides an optimized capacity division method for lithium-ion batteries, which is scientifically designed, can improve the efficiency of capacity division for a large number of batteries, and ensure the accuracy of capacity division, and has great practical significance.

[0017] The present invention provides a new capacity fractionation technology and data fitting model, which converts batch production data into standard test data, draws a scatter plot of the batch production test data and the standard condition test data in one-to-one correspondence, and then performs curve fitting to obtain a capacity correction model formula, thereby calculating the discharge capacity under standard conditions. The application of the present invention is conducive to significantly improving the production efficiency and accuracy of the capacity fractionation test. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of a lithium-ion battery optimization capacity division method provided by the present invention;

[0019] Figure 2 An overall flow chart of an embodiment of a lithium-ion battery optimization capacity division method provided by the present invention;

[0020] Figure 3A method for optimizing capacity division of a lithium-ion battery provided by the present invention is provided. In the embodiment, a scatter plot is drawn with the charging capacity of the battery as the horizontal axis and the standard capacity of the battery as the vertical axis. DETAILED DESCRIPTION

[0021] 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.

[0022] In the description of this patent, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0023] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and implementation modes.

[0024] See also Figures 1 to 3 The present invention provides a method for optimizing the capacity distribution of a lithium-ion battery, comprising the following steps:

[0025] Step S1, performing a preset capacity division operation on all the multiple batteries to be divided, and obtaining a charging capacity C1 of each battery to be divided;

[0026] The preset capacity division operation includes: a preset charging operation and a preset discharging operation performed successively;

[0027] Step S2, sorting all the multiple batteries to be divided that have completed the preset capacity division operation (including the preset charging operation and the preset discharging operation) in descending order of the charging capacity C1, and extracting the multiple batteries to be divided that have completed the preset capacity division operation (a part of the batteries to be divided) as multiple standard batteries, and recording the charging capacity C1 of each standard battery;

[0028] Step S3, performing a constant capacity operation on a plurality of standard batteries using standard conditions to obtain a standard capacity C2 of each standard battery;

[0029] Step S4, drawing a scatter plot of a plurality of standard batteries with the charging capacity C1 of the standard battery as the abscissa and the standard capacity C2 of the standard battery as the ordinate;

[0030] Step S5, fitting (specifically linear fitting) the scatter plots of multiple standard batteries to obtain a quantitative relationship between the charging capacity C1 and the standard capacity C2 corresponding to the standard battery;

[0031] Step S6, for any battery to be divided, according to the charging capacity C1 obtained after performing the preset division operation and according to the quantitative relationship, the standard capacity corresponding to the battery to be divided is obtained and used as the division capacity, and then the division capacity is used in the sorting process of multiple batteries to be divided, that is, the division capacity is used as the basis for battery sorting (that is, as the actual capacity of the battery), which is the basis for the subsequent battery module assembly, thereby improving the consistency of single cell capacity sorting and grouping consistency.

[0032] It should be noted that the capacity of lithium-ion batteries is a key indicator for evaluating battery performance, and the capacity directly affects the application of batteries. In the battery manufacturing process, the capacity of each battery is detected by the capacity separation process. The actual capacity of the battery is detected through the capacity separation process, so that the battery can be graded in the subsequent sorting process.

[0033] In step S1, in specific implementation, the battery to be divided is a battery that has been formed for the first time;

[0034] In step S1, in a specific implementation, the multiple batteries to be divided into different capacities are batteries of the same specification and model.

[0035] In step S1, in specific implementation, the charging capacity of the battery is equal to the total charging capacity of the batteries to be divided when performing a preset charging operation, that is, the sum of the charging capacities.

[0036] In the present invention, the preset charging operation of step S1 specifically includes the following steps:

[0037] Step S11, charging the battery with a constant current to a first SOC at a first rate of a preset magnitude;

[0038] Step S12, standing for a first preset time;

[0039] Step S13, charging the battery with a constant current to a second SOC at a second rate of a preset magnitude;

[0040] Step S14, charging the battery with a constant current and constant voltage to a preset charging cut-off voltage at a third rate of a preset magnitude;

[0041] In the present invention, in step S11, the value range of the first magnification is 0.5C to 1.0C;

[0042] In step S11, the first SOC is preferably 70%, which is close to the platform voltage of the battery cell. In this stage, charging with a large current can shorten the time and improve the working efficiency. The first SOC can also fluctuate up and down by a certain range (for example, 3%) based on 70%.

[0043] In step S12, the first preset time length is 1 to 5 minutes.

[0044] In step S13, the second magnification ranges from 0.1C to 0.3C;

[0045] In step S13, the second SOC is preferably 80%. According to the material characteristics, this interval is the cell charge period. Electric platform area, platform Charging at a low rate in the voltage range can increase the depth of charge and reduce polarization. Specifically, the SOC may fluctuate up or down by a certain range (for example, 3%) on the basis of 80%.

[0046] In step S14, the value range of the third magnification is 0.3C to 0.5C;

[0047] In step S14, regarding constant current and constant voltage charging, the constant current (i.e., the current magnitude of constant current charging) is a third rate magnitude, and constant current and constant voltage charging is performed to a cut-off voltage;

[0048] In step S14, the voltage of the constant voltage charging is preferably equal to the cut-off voltage of the battery for full charging (eg, 4.2V).

[0049] It should be noted that the voltage value of constant voltage charging is generally the cut-off voltage designed for the battery (i.e., the full-charge voltage).

[0050] In step S14, the preset charge cut-off voltage is preferably equal to the full charge cut-off voltage of the battery (eg, 4.2 V). The preset charge cut-off voltage is determined according to the designed cut-off voltage of the battery cell.

[0051] In step S1, in specific implementation, the charging capacity C1 of each battery to be divided is equal to the total charging capacity of the battery to be divided after executing steps S11 to S14, that is, the sum of the charging capacities.

[0052] In the present invention, after the preset charging operation in step S1, the preset discharging operation performed specifically includes the following steps:

[0053] Step S15, standing for a second preset time;

[0054] Step S16, discharging the battery to a third SOC at a fourth rate of a preset magnitude with a constant current or constant current and constant voltage;

[0055] In step S15, the second preset time length is 1 minute.

[0056] In step S16, the fourth magnification has a value range of 0.5C to 1.0C;

[0057] In step S16, the battery is discharged at a constant current or constant current constant voltage, wherein the constant current (i.e., the current magnitude of the constant current discharge) is a fourth rate magnitude;

[0058] Among them, the voltage of constant voltage discharge is a pre-required and set value, which is specifically determined according to the SOC required by the actual factory battery cell.

[0059] The third SOC is a pre-required and set value, which is the SOC value that the battery has when it leaves the factory according to customer requirements. The constant voltage value needs to be selected according to the SOC required by the customer when the battery cell is shipped (i.e., leaving the factory). Different customer requirements will result in different SOCs.

[0060] In step S2, in specific implementation, all the multiple batteries to be divided that have completed the preset capacity division operation are sorted in descending order of the charging capacity C1, and the multiple batteries to be divided that have completed the preset capacity division operation are extracted as multiple standard batteries, which specifically includes the following operations:

[0061] First, all the batteries to be divided are sorted in descending order according to the charging capacity C1;

[0062] Then, the total charging capacity C1 of all the multiple cells to be divided is divided into multiple value intervals of the same width.

[0063] Then, in each numerical range, a plurality of (at least 1, for example, 10) batteries are randomly selected as standard batteries.

[0064] In step S3, in specific implementation, standard conditions include standard temperature and standard ratio;

[0065] The standard temperature is 25 degrees Celsius;

[0066] The standard rate is C / 20, or C / 10, where C is the charge and discharge rate of the battery.

[0067] In step S3, in specific implementation, a plurality of standard batteries are subjected to a constant capacity operation using standard conditions, specifically including the following operations:

[0068] Place multiple standard batteries in an environment with the same standard temperature, and then perform charge and discharge operations at a standard rate, and obtain the full discharge capacity of each standard battery at the standard charge and discharge rate, which is defined as the standard capacity C2 (i.e., the discharge capacity of the standard battery in the constant capacity operation);

[0069] Among them, the standard rate charge and discharge operation is specifically as follows: first fully charge the standard battery at the standard rate, that is, charge it to the battery's full charge cut-off voltage (for example, 4.2V, that is, fully charged), and then fully discharge it at the standard rate, that is, discharge it to the battery's discharge cut-off voltage (for example, 2.5V).

[0070] In step S3, in a specific implementation, the battery capacity can be constant in a widely used constant temperature charging cabinet, that is, the standard capacity C2 test can be performed.

[0071] In step S5, in specific implementation, the quantitative relationship is as follows:

[0072] y = kx + b;

[0073] Where x is the charge capacity C1 of the standard battery;

[0074] y is the standard capacity C2 of the standard battery;

[0075] k and b are constants, and are obtained by linear fitting of the scatter plot in step S5. In specific implementation, the scatter plot can be automatically obtained by fitting the formula using a fitting software that is mature in the prior art and has been widely used. The fitting software, for example, can be the origin software produced by OriginLab.

[0076] It should be noted that, given that lithium ion transmission is greatly affected by temperature, when the temperature is high, the battery discharge capacity increases, affecting the accuracy of the actual capacity.

[0077] Therefore, the present invention fully considers the influence of the ambient temperature of the discharge process on the charging and discharging process of the lithium-ion battery, and considers that in the batch production workshop, the heat release of the battery cell is large during the capacity-divided discharge stage, resulting in The temperature difference between different areas is large. The inventors of the present invention have found that the test capacity is different. Production data analysis found that: the ambient temperature deviation during the charging process is small, and the dispersion of charging capacity compared to discharge capacity is also small. Therefore, the present invention adopts a step-by-step constant current plus constant current constant voltage charging mode according to the characteristics of the material system. The final battery charging capacity is less affected by temperature and polarization is also small. The present invention uses a charging capacity superimposed standard capacity correlation fitting method to derive capacity correction results and judgment criteria, which can effectively reduce the deviation caused by temperature and polarization in existing processes.

[0078] It should also be noted that the capacity splitting test is generally carried out after the first formation of the battery, so the SOC (state of charge) before the capacity splitting starts is the state of the last charging result. The present invention focuses on the charging capacity, so the capacity splitting can adopt a process of first fully charging and then discharging at a constant current or a constant current and constant voltage to a specified SOC (state of charge).

[0079] Among them, because what needs to be collected is the charging capacity of the battery, the discharge process current can be in the range of 0.5C to 1.0C.

[0080] Among them, in order to reduce the influence of polarization and shorten the time, the charging process can be carried out under the conditions of step-by-step variable current charging and constant voltage and constant current cut-off. The current of each step used in the charging process can be changed by 0.1~0.7C according to the electrochemical system.

[0081] The above process is carried out at the workshop management temperature.

[0082] In order to more clearly understand the technical solution of the present invention, the technical solution of the present invention is described below through specific embodiments.

[0083] Example

[0084] First, for multiple batteries to be divided into different capacities placed in the same capacity division tray, step S1 is performed (specifically including: Figure 2 The first to sixth steps in the process) collect the charging capacity C1 of each battery to be divided; wherein the charging capacity C1 of each battery to be divided is equal to the charging capacity of the battery to be divided. Figure 2 The total charging capacity after the first to fourth steps, that is, the sum of the charging capacities (specifically, the sum of the electricity charged in the first, third and fourth charging steps).

[0085] Then, the charging capacities C1 of the batteries to be divided in the same capacity division tray are arranged from low to high according to the values ​​(except for abnormal points); max -C min , calculate the range of data distribution (Range), and divide the Range into multiple intervals of batteries with equal gaps (i.e. equal amount and equal numerical intervals);

[0086] Among them, C max That is the maximum value of the charging capacity C1 (after removing abnormal values), C min That is the minimum value of the charging capacity C1 (after removing abnormal values); C max -C min The meaning is: the extreme value of charging capacity, which is used to confirm the interval of charging capacity data distribution.

[0087] Then, randomly select 15 to 20 batteries (as standard batteries) from the batteries in each interval, and record the capacity C1-1, C1-2, ..., C1-n (e.g., C1-20);

[0088] Then, the selected standard batteries are subjected to a constant capacity operation using standard conditions (temperature 25°C, standard rate), and the standard capacities C2-1, C2-2, ..., C2-n (e.g., C1-20) are recorded;

[0089] Then, a scatter plot is made by corresponding the divided capacities of multiple randomly selected batteries (i.e., standard batteries) to the standard capacities, such as Figure 3 As shown;

[0090] Then, curve fitting is performed based on the drawn scatter plot to obtain the fitting formula (i.e., quantitative relationship) for the standard capacity and the fractional capacity of the lithium-ion battery in each interval. A fitting coefficient of 0.9 or above is a valid relationship.

[0091] Among them, see Figure 3 As shown, in the embodiment, the quantitative relationship of the scatter plot is as follows:

[0092] y (i.e. battery standard capacity C2) = 0.9679x + 8.2669;

[0093] Quantitative relationship R 2 =0.9456.

[0094] Among them, 0.9679 and 8.2669 are coefficient constants, which are obtained by linear fitting of the scatter plot in step S4;

[0095] Fitting coefficient R 2 =0.9456, which indicates the degree of fit of the quantitative relationship, is automatically calculated when the scatter plot is fitted with the formula using existing fitting software. For example, the scatter plot function of Minitab software can be used for linear fitting.

[0096] Then, the capacity of each batch of batteries can be used to predict the standard capacity C2 corresponding to these batteries through the obtained fitting formula and the battery charging capacity C1. The standard capacity C2 can be used as the capacity, which can facilitate the subsequent sorting grade screening and low-capacity screening.

[0097] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for optimizing capacity distribution of lithium-ion batteries, characterized in that: The following steps are involved: Step S1, performing a preset capacity division operation on all the multiple batteries to be divided, and obtaining a charging capacity C1 of each battery to be divided; The preset capacity division operation includes: a preset charging operation and a preset discharging operation performed successively; Step S2, sorting all the multiple batteries to be divided that have completed the preset capacity division operation in descending order of the charging capacity C1, extracting the multiple batteries to be divided that have completed the preset capacity division operation as multiple standard batteries, and recording the charging capacity C1 of each standard battery; Step S3, performing a constant capacity operation on a plurality of standard batteries using standard conditions respectively, to obtain a standard capacity C2 of each standard battery; Step S4, drawing a scatter plot of a plurality of standard batteries with the charging capacity C1 of the standard battery as the abscissa and the standard capacity C2 of the standard battery as the ordinate; Step S5, fitting the scatter plots of multiple standard batteries to obtain a quantitative relationship between the charging capacity C1 and the standard capacity C2 corresponding to the standard battery; Step S6, for any battery to be divided, according to the charging capacity C1 obtained after the preset division operation is performed and according to the quantitative relationship, the standard capacity corresponding to the battery to be divided is obtained and used as the division capacity, and then the division capacity is used as the basis for battery sorting.

2. The method for optimizing capacity distribution of lithium-ion batteries according to claim 1, characterized in that: In step S1, the battery to be capacity-separated is a battery that has undergone the first formation.

3. The method for optimizing capacity distribution of lithium-ion batteries according to claim 1, characterized in that: In step S1 , the multiple batteries to be divided into different capacities are batteries of the same specification and model.

4. The method for optimizing capacity distribution of lithium-ion batteries according to claim 1, characterized in that: The preset charging operation of step S1 specifically includes the following steps: Step S11, charging the battery with a constant current to a first SOC at a first rate of a preset magnitude; Step S12, standing for a first preset time; Step S13, charging the battery with a constant current to a second SOC at a second rate of a preset magnitude; Step S14, charging the battery with a constant current and constant voltage to a preset charging cut-off voltage at a third rate of a preset magnitude; The charging capacity C1 of each battery to be divided is equal to the total charging capacity of the batteries to be divided after executing steps S11 to S14.

5. The method for optimizing capacity distribution of lithium-ion batteries according to claim 4, characterized in that: In step S11, the value range of the first magnification is 0.5C to 1.0C; In step S11, the first SOC is 70% In step S12, the first preset time length is 1 to 5 minutes; In step S13, the second magnification ranges from 0.1C to 0.3C; In step S13, the second SOC is 80%; In step S14, the value range of the third magnification is 0.3C to 0.5C; In step S14, the voltage of the constant voltage charging is equal to the cut-off voltage of the battery when it is fully charged; The preset charging cut-off voltage is equal to the full-charge cut-off voltage of the battery.

6. The method for optimizing capacity distribution of lithium-ion batteries according to claim 1, characterized in that: After the preset charging operation in step S1, the preset discharging operation performed specifically includes the following steps: Step S15, standing for a second preset time; Step S16, discharging the battery to a third SOC at a fourth rate of a preset magnitude with a constant current or constant current and constant voltage.

7. The method for optimizing capacity distribution of lithium-ion batteries according to claim 1, characterized in that: In step S2, all the multiple batteries to be divided that have completed the preset capacity division operation are sorted in descending order of the charging capacity C1, and the multiple batteries to be divided that have completed the preset capacity division operation are extracted as multiple standard batteries, which specifically includes the following operations: First, all the batteries to be divided are sorted in descending order according to the charging capacity C1; Then, the total charging capacity C1 of all the batteries to be divided is divided into multiple value intervals of the same width. Then, within each numerical interval, multiple batteries are randomly selected as standard batteries.

8. The method for optimizing capacity distribution of lithium-ion batteries according to claim 1, characterized in that: In step S3, standard conditions include standard temperature and standard ratio; The standard temperature is 25℃; The standard rate is C / 20, or C / 10, where C is the charge and discharge rate of the battery.

9. The method for optimizing capacity distribution of lithium-ion batteries according to claim 1, characterized in that: In step S3, a plurality of standard batteries are subjected to a constant capacity operation using standard conditions, specifically including the following operations: Place multiple standard batteries in an environment with the same standard temperature, and then perform charge and discharge operations at a standard rate, obtain the capacity of each standard battery during full discharge and define it as the standard capacity C2; The standard rate charge and discharge operation is as follows: first, fully charge the standard battery at the standard rate, that is, charge it to the full charge cut-off voltage of the battery, and then fully discharge it at the standard rate, that is, discharge it to the discharge cut-off voltage of the battery.

10. The method for optimizing capacity distribution of a lithium-ion battery according to any one of claims 1 to 9, characterized in that: In step S5, the quantitative relationship is as follows: y = kx + b; Where x is the charge capacity C1 of the standard battery; y is the standard capacity C2 of the standard battery; k is the slope of the straight line connecting the multiple scattered points in the scatter plot, and b is the intersection of the straight line connecting the multiple scattered points in the scatter plot and the y-axis.

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