Battery grading method and system

Abstract

The invention relates to a battery grading method and system. The method comprises the following steps: sequentially carrying out liquid injection formation and false capacity grading; the liquid injection formation comprises a formation process and at least two times of liquid injection, the formation process is carried out after the first time of liquid injection and before the last time of liquid injection, and the formation process comprises formation; the false capacity grading comprises the following steps: performing constant-current discharge on each battery until each battery reaches a preset first state parameter; each battery is subjected to constant-current charging until each battery reaches a preset second state parameter, a third state parameter of each battery after constant-current charging is actually measured, the second state parameter is charging cut-off voltage, and the third state parameter is actually measured capacity; or the second state parameter is charging cut-off SOC and the third state parameter is actually measured voltage; and grading the batteries according to the size of the third state parameter. The battery capacity can be accurately distinguished while the energy consumption is reduced and the production cost of the battery is reduced.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a method and system for grading batteries. Background Art

[0002] The manufacturing process of batteries is an extremely energy-consuming process, especially the formation and grading processes of batteries.

[0003] Currently, there are two ways to take batteries offline, which are specifically as follows:

[0004] One is full-capacity offline. It proceeds according to steps such as primary liquid injection, static formation, formation, aging, secondary liquid injection, grading, and packaging. Among them, during the grading process, all batteries are fully charged and then discharged. It can be seen that this offline method has the disadvantages of high energy consumption, long time, and high cost.

[0005] The other is virtual-capacity offline. Compared with full-capacity offline, virtual-capacity offline does not perform grading. The specific steps of virtual-capacity offline are primary liquid injection, static aging, formation, aging, secondary liquid injection, and packaging. In this way, it is not necessary to fully charge the batteries throughout the battery manufacturing process. Obviously, this method can reduce energy consumption, time, and cost.

[0006] The process that a battery has not undergone a full charge before offline is called virtual capacity. The definition of a virtual-capacity battery is a battery that has not undergone a full charge before offline. The advantage of virtual-capacity batteries is that they reduce production energy consumption and the production cost of batteries. Therefore, many enterprises choose to directly take the batteries offline after formation; the disadvantage is that the user side cannot accurately control the capacity difference and the self-discharge electrode difference of the batteries, and the failure rate of the user side will be relatively high. Summary of the Invention

[0007] The embodiments of this application provide a method and system for grading batteries, which can accurately distinguish the battery capacity while reducing energy consumption and the production cost of batteries.

[0008] In the first aspect, a method for grading batteries is provided, which includes:

[0009] Sequentially perform liquid injection formation and pseudo-grading; wherein, the liquid injection formation includes: a formation process and at least two liquid injections. The formation process is after the first liquid injection and before the last liquid injection, and the formation process includes formation;

[0010] The pseudo-grading includes:

[0011] First, perform constant current discharge on each battery until each battery reaches a preset first state parameter;

[0012] Then, constant current charging is performed on each battery until each battery reaches a preset second state parameter, and the third state parameter of each battery after the completion of the constant current charging is actually measured. Among them, the second state parameter is the charging cut-off voltage and the third state parameter is the actually measured capacity, or the second state parameter is the charging cut-off SOC and the third state parameter is the actually measured voltage;

[0013] According to the magnitude of the third state parameter, each battery is classified.

[0014] In some embodiments, the formation includes: at 25°C to 50°C, constant current charging is performed at a current magnitude of 0.1C to 0.5C until the charging cut-off SOC of each battery reaches 20% to 80%.

[0015] In some embodiments, before the formation, the formation process further includes aging; the aging includes: the aging time is 12h to 72h, the aging temperature is 40°C to 50°C, and the dew point is below -25°C;

[0016] And / or, after the formation, the formation process further includes aging; the aging includes: the standing time is 24h to 48h, the standing temperature is 40°C to 50°C, and the dew point is below -30°C.

[0017] In some embodiments, classifying each battery according to the magnitude of the third state parameter specifically includes:

[0018] When the third state parameter is the actually measured capacity, the actually measured capacities of each battery are arranged from small to large, and each battery is classified according to the arrangement order of the actually measured capacities;

[0019] When the third state parameter is the actually measured voltage, the actually measured voltages of each battery are arranged from large to small, and each battery is classified according to the arrangement order of the actually measured voltages.

[0020] In some embodiments, the first state parameter is the discharge cut-off voltage or the discharge cut-off SOC.

[0021] In some embodiments, the discharge cut-off voltage is 2.5V to 2.8V;

[0022] The discharge cut-off SOC is 0% to 10%.

[0023] In some embodiments, the constant current discharge is performed at room temperature;

[0024] And / or, the discharge current during the constant current discharge is 0.2C to 0.5C;

[0025] And / or, before the constant current charging, first stand for 1h to 3h;

[0026] And / or, the charging current during the constant current charging is 0.5C to 5C;

[0027] And / or, the charging cut-off voltage is 3.0V to 3.4V;

[0028] And / or, the charging cut-off SOC is 10% to 40%.

[0029] In some embodiments, after the false grading, the grading method further includes:

[0030] Performing a first static placement and a second static placement in sequence, and measuring the first voltage of each battery after the first static placement and the second voltage after the second static placement;

[0031] Calculating the absolute value of the voltage difference between the first voltage and the second voltage of each battery, and setting a voltage difference threshold. If the absolute value of the voltage difference between the first voltage and the second voltage of each battery is less than the voltage difference threshold, the battery is qualified; otherwise, it is unqualified.

[0032] In some embodiments, the first static placement includes: a time of 20h to 50h and a temperature of 20°C to 30°C;

[0033] The second static placement includes: a first stage with a time of 20h to 50h and a temperature of 40°C to 50°C; a second stage with a time of 20h to 50h and a temperature of 20°C to 30°C.

[0034] In a second aspect, a grading system for batteries is provided, which includes:

[0035] A charge and discharge unit, which is used for: first performing constant current discharge on each battery until each battery reaches a preset first state parameter, and then performing constant current charging on each battery until each battery reaches a preset second state parameter; wherein, the battery undergoes injection and formation, and the injection and formation includes: a formation process and at least two injections. The formation process is after the first injection and before the last injection, and the formation process includes formation;

[0036] A detection unit, which is used for: measuring the third state parameter of each battery after the constant current charging is completed, wherein the second state parameter is the charging cut-off voltage and the third state parameter is the measured capacity, or the second state parameter is the charging cut-off SOC and the third state parameter is the measured voltage;

[0037] A grading unit, which is used for: grading each battery according to the magnitude of the third state parameter.

[0038] The beneficial effects brought by the technical solution provided in this application include:

[0039] The embodiments of the present application provide a battery grading method and system. Through the dummy formation and grading of the present application, the capacity of the battery can be accurately distinguished, thereby achieving low energy consumption, reducing the production cost of the battery, and avoiding battery abnormalities at the user end. Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0041] Figure 1 It is a flowchart of the battery grading method provided by the embodiments of the present application;

[0042] Figure 2 It is a dummy formation flowchart provided by the embodiments of the present application. Detailed Embodiments

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0044] See Figure 1 As shown, the embodiments of the present application provide a battery grading method, which includes the following steps:

[0045] 101: Perform injection and formation.

[0046] The injection and formation includes: a formation process and at least two injections. The formation process is after the first injection and before the last injection, and the formation process includes formation.

[0047] It can be understood that when injecting electrolyte each time above, the proportions of the injected electrolyte in the total electrolyte add up to exactly 100%.

[0048] It can be understood that the minimum number of injections in the present application is two, and the number can be increased according to needs.

[0049] For example, when the number of injections is two, first perform the first injection, then perform the formation process, and then perform the second injection.

[0050] For another example, when there are multiple times of liquid injection, the formation process needs to be carried out after the first liquid injection and before the last liquid injection. As an example, if there are 5 times of liquid injection, the formation process can be placed between the first and the second liquid injection, or between the second and the third liquid injection, or between the third and the fourth liquid injection, or between the fourth and the fifth liquid injection. It can be understood that static treatment is usually carried out between two adjacent liquid injections.

[0051] 102: Perform dummy formation.

[0052] For step 102, refer to Figure 2 as shown, which specifically includes the following steps:

[0053] 201: First, perform constant current discharge on each battery until each battery reaches a preset first state parameter.

[0054] Among them, in step 201, constant current discharge can be carried out at room temperature. The purpose of discharging is to make the final states of all batteries consistent, that is, to reach the first state parameter.

[0055] It can be understood that the magnitude of the discharge current during constant current discharge can be set according to actual needs. For example, as an example, the discharge current is 0.2C to 0.5C.

[0056] The first state parameter can be the discharge cut-off voltage or the discharge cut-off SOC (State of Charge, which is used to reflect the remaining capacity of the battery and is numerically defined as the ratio of the remaining capacity to the battery capacity).

[0057] The magnitude of the discharge cut-off voltage or the discharge cut-off SOC can be set according to actual needs. For example, as an example, the discharge cut-off voltage is 2.5V to 2.8V, and the discharge cut-off SOC is 0% to 10%.

[0058] 202: Then, perform constant current charging on each battery until each battery reaches a preset second state parameter, and actually measure the third state parameter of each battery after the constant current charging is completed. Among them, the second state parameter is the charge cut-off voltage and the third state parameter is the actually measured capacity, or the second state parameter is the charge cut-off SOC and the third state parameter is the actually measured voltage.

[0059] Among them, in step 202, before performing constant current charging, first staticize for 1h to 3h, and the purpose is to make the voltage fluctuation stable.

[0060] It can be understood that the magnitude of the charging current during constant current charging can be set according to actual needs. For example, as an example, the charging current is 0.5C to 5C, preferably 0.5C to 1C.

[0061] It can be understood that in this application, a preset charging cut-off voltage can be used as the end flag of constant current charging, and then the measured capacity of each battery can be measured. Alternatively, a preset charging cut-off SOC can be used as the end flag of constant current charging, and then the measured voltage of each battery can be measured.

[0062] It can be understood that the magnitude of the charging cut-off voltage or charging cut-off SOC during constant current charging can be set according to actual needs. For example, as an example, the charging cut-off voltage is 3.0V to 3.4V, and the charging cut-off SOC is 10% to 40%.

[0063] 203: Classify each battery according to the magnitude of the third state parameter.

[0064] Specifically, if a preset charging cut-off voltage is used as the end flag of constant current charging, and then the measured capacity of each battery is measured, then arrange them in ascending order according to the measured capacity corresponding to the same charging cut-off voltage, and then divide the batteries into grades A1, A2, A3,..., An, where grade A1 is the grade with the highest full charge capacity.

[0065] For example, if the total number of batteries is 10, and the batteries need to be divided into the first grade and the second grade, and the number of batteries in each grade is 5 (the number of grades for dividing the batteries and the number of batteries in each grade can be selected according to actual needs); then sort the measured capacity values of the 10 batteries in ascending order, and the batteries corresponding to the first 5 measured capacity values in this sorting are the first grade, and the batteries corresponding to the last 5 measured capacity values in the remaining sorting are the second grade.

[0066] If a preset charging cut-off SOC is used as the end flag of constant current charging, and then the measured voltage of each battery is measured, then arrange them in descending order according to the measured voltage corresponding to the same charging cut-off SOC, and then divide the batteries into grades A1, A2, A3,..., An, where grade A1 is the grade with the highest full charge capacity.

[0067] For example, if the total number of batteries is 10, and the batteries need to be divided into the first grade and the second grade, and the number of batteries in each grade is 5 (the number of grades for dividing the batteries and the number of batteries in each grade can be selected according to actual needs); then sort the measured voltages of the 10 batteries in descending order, and the batteries corresponding to the first 5 measured voltages in this sorting are the first grade, and the batteries corresponding to the last 5 measured voltages in the remaining sorting are the second grade.

[0068] 103: Screen qualified batteries.

[0069] Due to the possible existence of unqualified batteries, battery screening is required to select qualified batteries.

[0070] This application realizes the capacity screening of batteries through pseudo-capacity grading. The principle of pseudo-capacity grading is that the electrolyte of the battery is divided into two parts. The first part of the electrolyte is injected before formation, and the second part of the electrolyte is injected after formation. During the formation process, the SOC of the battery is adjusted to a certain state, and this part is already activated for the battery. Pseudo-capacity grading is to perform capacity grading on this part of the active state, but it is different from traditional full-capacity grading. In traditional full-capacity grading, after one injection, formation, and secondary injection, first full charge is carried out, and then discharge. In this application, after one injection, formation, and secondary injection, first constant-current discharge is carried out, and then constant-current charging (this constant-current charging process does not fully charge the battery, and the SOC state of the battery after charging is lower than 100%, being 10% - 40%), so it is called pseudo-capacity grading. After pseudo-capacity grading, the capacity differences of the already activated part of the batteries are highlighted. If the charging cut-off voltage is used as the end mark of constant-current charging, the battery with a lower measured capacity after charging corresponds to a higher full-charge capacity of the battery; if the charging cut-off SOC is used as the end mark of constant-current charging, the battery with a higher measured voltage after charging corresponds to a higher full-charge capacity of the battery.

[0071] Through the pseudo-capacity grading of this application, the capacities of the batteries can be accurately distinguished. Since full charge is not required and the SOC state of the battery during pseudo-capacity grading is lower than 100%, low energy consumption is achieved, the production cost of the battery is reduced, and battery anomalies at the user end are avoided.

[0072] In addition, since the SOC state of pseudo-capacity grading is relatively low and the heat generation of the battery at a low SOC state is relatively small, the pseudo-capacity grading of the battery is not affected by battery temperature rise, there are fewer factors affecting the battery capacity, and the data is more reliable.

[0073] Further, the formation includes: at 25°C to 50°C, constant-current charging is carried out at a current magnitude of 0.1C to 0.5C until the charging cut-off SOC of each battery reaches 20% to 80%. Preferably, the charging cut-off SOC during formation reaches 45% to 55%.

[0074] Before the formation, the formation process further includes aging; after the formation, the formation process further includes conditioning.

[0075] Among them, exemplarily, the aging includes: the aging time is 12h to 72h, the aging temperature is 40°C to 50°C, and the dew point is below -25°C.

[0076] Exemplarily, the conditioning includes: the standing time is 24h to 48h, the standing temperature is 40°C to 50°C, and the dew point is below -30°C.

[0077] When measuring the open-circuit voltage (OCV), a 1 kHz alternating current is used for testing.

[0078] In step 103 above, screening qualified batteries specifically includes the following steps:

[0079] 301: Each battery in each gear is sequentially subjected to a first standing and a second standing, and the first voltage of each battery after the first standing and the second voltage after the second standing are measured.

[0080] Among them, exemplarily, the first standing includes: a time of 20 h to 50 h and a temperature of 20 °C to 30 °C.

[0081] Exemplarily, the second standing includes: a first stage with a time of 20 h to 50 h and a temperature of 40 °C to 50 °C; a second stage with a time of 20 h to 50 h and a temperature of 20 °C to 30 °C.

[0082] 302: Based on the absolute value of the pressure difference between the first voltage and the second voltage of each battery, qualified batteries are screened out.

[0083] Among them, when screening, a pressure difference threshold can be set. The pressure difference threshold can be determined according to actual needs. For example, for 5 mV, calculate the absolute value of the pressure difference between the first voltage and the second voltage of each battery in each gear. If the absolute value of the pressure difference is less than 5 mV, it indicates that the battery is qualified; otherwise, it indicates that the battery is unqualified.

[0084] Based on the above grading method, an embodiment of the present application further provides a battery grading system, which includes a charge and discharge unit, a detection unit, and a grading unit, where:

[0085] The charge and discharge unit is used for: first performing constant current discharge on each battery until each battery reaches a preset first state parameter, and then performing constant current charging on each battery until each battery reaches a preset second state parameter; among them, the battery has undergone injection and forming, and the injection and forming includes: a forming process and at least two injections. The forming process is after the first injection and before the last injection, and the forming process includes forming.

[0086] The detection unit is used for: measuring the third state parameter of each battery after the constant current charging is completed, where the second state parameter is the charging cut-off voltage and the third state parameter is the measured capacity, or the second state parameter is the charging cut-off state of charge (SOC) and the third state parameter is the measured voltage.

[0087] The grading unit is used for: grading each battery according to the magnitude of the third state parameter.

[0088] The present application will be described below through embodiments.

[0089] Six batteries to be tested are taken, and the nominal capacity of each battery is 115 Ah, and 1 C = 115 A;

[0090] S1. The batteries are subjected to the first liquid injection. After the liquid injection is completed, the batteries are aged. The aging time is 48 h, the temperature is 45 °C, and the dew point is -30 °C.

[0091] S2. After aging, the batteries are formed at 25 °C. The forming is divided into two stages. The forming current in the first stage is 0.1 C and the time is 7 minutes. The forming current in the second stage is 0.2 C until the charging cut-off SOC is 50%.

[0092] S3. After forming, the batteries are aged. The aging time is 24 h, the temperature is 45 °C, and the dew point is -30 °C.

[0093] S4. Then, the batteries are subjected to the second liquid injection. The sum of the proportion of the electrolyte in the first liquid injection to the total electrolyte and the proportion of the electrolyte in the second liquid injection to the total electrolyte is 100%, and the mass ratio of the first liquid injection to the second liquid injection is 4:1.

[0094] S5. The batteries are subjected to constant current discharge at room temperature. The discharge current is 0.2 C and the discharge cut-off voltage is 2.7 V.

[0095] S6. After the above batteries are left standing for 1 h, they are continuously charged at a constant current. The charging current is 1 C and the cut-off charging voltage is 3.4 V.

[0096] S7. Record the measured capacity of the batteries when the voltage is cut off.

[0097] S8. Arrange the measured capacities of the batteries from smallest to largest, and divide the batteries into three grades: A1, A2, and A3. Each grade contains two batteries. The actual charging capacities of the six batteries to be tested are shown in Table 1.

[0098] Test example:

[0099] The above six batteries are fully charged according to the following scheme, and the full charge capacity is measured;

[0100] 1) Test conditions: temperature 25 ± 2 °C, constant temperature oven.

[0101] 1) First, the batteries are subjected to constant current discharge. The current is 1 C and the cut-off voltage is 2.5 V, and then left standing for 5 h.

[0102] 2) The batteries are subjected to constant current and constant voltage charging, from 1 C to 3.65 V, and the cut-off current is 0.05 C, and then left standing for 60 min.

[0103] 3) The batteries are subjected to constant current discharge. The current is 1 C and the cut-off voltage is 2.5 V.

[0104] Record the actual full charge capacity and full charge and discharge capacity of six different batteries, as shown in Table 1 below.

[0105] It can be seen from Table 1 that the trend of the actual full charge and discharge capacity is exactly the same as that of the actual charge capacity obtained in step S8; that is, Battery #1 and Battery #2 are in the first gear; Battery #3 and Battery #4 are in the second gear; Battery #5 and Battery #6 are in the third gear, and the first gear batteries have the largest full charge capacity. Through the grading of this application, the full charge capacity of the batteries can be accurately distinguished, achieving low energy consumption, reducing the production cost of the batteries, and avoiding battery anomalies at the user end.

[0106] Table 1

[0107]

[0108] In the description of this application, it should be noted that the orientation or positional relationship indicated by terms such as "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to this application. Unless otherwise clearly specified and defined, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0109] It should be noted that in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0110] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for grading a battery, characterized in that, It includes: Successively performing injection liquefaction and dummy formation; wherein, the injection liquefaction includes: a formation process and at least two injections, the formation process is after the first injection and before the last injection, and the formation process includes formation; The dummy formation includes: First, performing constant current discharge on each battery until each battery reaches a preset first state parameter; Then, performing constant current charge on each battery until each battery reaches a preset second state parameter, and actually measuring the third state parameter of each battery after the constant current charge is completed, wherein the second state parameter is the charge cut-off voltage and the third state parameter is the actually measured capacity, or the second state parameter is the charge cut-off SOC and the third state parameter is the actually measured voltage; Classifying each battery according to the magnitude of the third state parameter.

2. The battery classification method according to claim 1, characterized in that: The formation includes: at 25°C to 50°C, performing constant current charge at a current magnitude of 0.1C to 0.5C until the charge cut-off SOC of each battery reaches 20% to 80%.

3. The battery classification method according to claim 1, characterized in that: Before the formation, the formation process further includes aging; the aging includes: the aging time is 12h to 72h, the aging temperature is 40°C to 50°C, and the dew point is below -25°C; And / or, after the formation, the formation process further includes curing; the curing includes: the standing time is 24h to 48h, the standing temperature is 40°C to 50°C, and the dew point is below -30°C.

4. The battery classification method according to claim 1, characterized in that: Classifying each battery according to the magnitude of the third state parameter specifically includes: When the third state parameter is the actually measured capacity, arranging the actually measured capacities of each battery from small to large, and classifying each battery according to the arrangement order of the actually measured capacities; When the third state parameter is the actually measured voltage, arranging the actually measured voltages of each battery from large to small, and classifying each battery according to the arrangement order of the actually measured voltages.

5. The battery classification method according to claim 1, characterized in that: The first state parameter is the discharge cut-off voltage or the discharge cut-off SOC.

6. The battery classification method according to claim 5, characterized in that: The discharge cut-off voltage is 2.5V to 2.8V; The discharge cut-off SOC is 0% to 10%.

7. The battery classification method according to claim 1, characterized in that: The constant current discharge is performed at room temperature; And / or, the discharge current during the constant current discharge is 0.2C to 0.5C; And / or, before the constant current charge, first stand for 1h to 3h; And / or, the charge current during the constant current charge is 0.5C to 5C; And / or, the charge cut-off voltage is 3.0V to 3.4V; And / or, the charge cut-off SOC is 10% to 40%.

8. The battery classification method according to claim 1, characterized in that: After the dummy formation, the classification method further includes: Perform the first static placement and the second static placement in sequence, and measure the first voltage of each battery after the first static placement and the second voltage after the second static placement; Calculate the absolute value of the voltage difference between the first voltage and the second voltage of each battery, and set a voltage difference threshold. If the absolute value of the voltage difference between the first voltage and the second voltage of each battery is less than the voltage difference threshold, the battery is qualified; otherwise, it is unqualified.

9. The battery grading method according to claim 8, wherein: The first static placement includes: a time of 20h to 50h and a temperature of 20°C to 30°C; The second static placement includes: a first stage with a time of 20h to 50h and a temperature of 40°C to 50°C; a second stage with a time of 20h to 50h and a temperature of 20°C to 30°C.

10. A grading system for a battery, characterized in that, It includes: A charge and discharge unit, which is used for: first performing constant current discharge on each battery until each battery reaches a preset first state parameter, and then performing constant current charging on each battery until each battery reaches a preset second state parameter; wherein, the battery undergoes injection liquefaction, and the injection liquefaction includes: a forming process and at least two injections. The forming process is after the first injection and before the last injection, and the forming process includes forming; A detection unit, which is used for: measuring the third state parameter of each battery after the constant current charging is completed, wherein the second state parameter is the charging cut-off voltage and the third state parameter is the measured capacity, or the second state parameter is the charging cut-off SOC and the third state parameter is the measured voltage; A grading unit, which is used for: grading each battery according to the magnitude of the third state parameter.

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