Preparation method of secondary battery, secondary battery and energy storage system

Abstract

The embodiment of the invention relates to the field of energy storage battery cells, and provides a preparation method of a secondary battery, the secondary battery and an energy storage system.The method comprises the steps that the weight difference of a battery cell assembly to be put into a shell is obtained, and under the condition of different weight differences, different charging, formation, charging and discharging and capacity grading treatment are adopted. When the weight difference is larger than the first difference threshold value and smaller than or equal to the second difference threshold value, the battery cell may face the risk of low capacity, the battery cell is subjected to first charging treatment, second formation treatment and second capacity grading treatment, and the current of the second formation treatment is lower than that of the first formation treatment; the current of the second capacity grading processing is lower than that of the first capacity grading processing. The smaller the formation current and the capacitance grading current are, the smaller the ohmic polarization is, the charging is completed under the lower voltage, the loss is reduced, the charging efficiency is improved, more charging is performed under the same time, and the capacity is increased. According to the preparation method of the secondary battery provided by the embodiment of the invention, at least the capacity of the secondary battery with relatively low capacity grading capacity can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage battery, in particular to a preparation method of secondary battery, secondary battery and energy storage system. BACKGROUND

[0002] In the field of energy storage, the battery capacity, i.e. the maximum amount of electricity that a battery can store and release under specified conditions, is one of the key indicators for evaluating battery performance. However, due to the non-uniformity of materials, slight fluctuations in process parameters, and the complexity of electrochemical environment, the battery capacity often deviates from the ideal design value, and sometimes even far below the expected level. That is, the battery capacity in the prior art is generally low. SUMMARY

[0003] The embodiments of the present application provide a preparation method of secondary battery, secondary battery and energy storage system, which at least helps to improve the battery capacity of the secondary battery.

[0004] According to some embodiments of the present application, the embodiments of the present application provide a preparation method of secondary battery, comprising: a step of obtaining a weight difference of a to-be-encapsulated battery assembly, wherein the weight difference is an absolute value of a difference between an actual weight of the to-be-encapsulated battery assembly and a target weight of the to-be-encapsulated battery assembly; a first determination step of determining whether the weight difference is greater than a first difference threshold value after the to-be-encapsulated battery assembly is subjected to encapsulation and liquid injection to obtain a to-be-processed battery; a first processing step of sequentially performing a first formation processing and a first capacity grading processing on the to-be-processed battery to obtain a to-be-tested battery if the weight difference is less than or equal to the first difference threshold value; a second determination step of determining whether the weight difference is greater than a second difference threshold value if the weight difference is greater than the first difference threshold value; a second processing step of sequentially performing a first charging processing, a second formation processing and a second capacity grading processing on the to-be-processed battery to obtain the to-be-tested battery if the weight difference is greater than the first difference threshold value and less than or equal to the second difference threshold value, wherein a charging current of the second formation processing is less than a charging current of the first formation processing, and a charging current of the second capacity grading processing is less than a charging current of the first capacity grading processing; a third determination step of determining whether the weight difference is greater than a third difference threshold value if the weight difference is greater than the second difference threshold value; a third processing step of sequentially performing a second charging processing, a third formation processing, a depolarization processing and a third capacity grading processing on the to-be-processed battery to obtain the to-be-tested battery if the weight difference is greater than the second difference threshold value and less than or equal to the third difference threshold value, wherein a current of the third formation processing is less than a current of the first formation processing, and a current of the third capacity grading processing is less than a current of the first capacity grading processing; and a detection step of detecting a capacity of the to-be-tested battery, and determining that the secondary battery is out of capacity grading when the capacity is greater than or equal to a capacity threshold value.

[0005] In some embodiments, if the weight difference is less than or equal to the first difference threshold, sequentially performing first formation processing and first trimming processing on the to-be-processed battery to obtain the to-be-tested battery, including: charging the to-be-processed battery at a first current for a first preset time period to realize the first formation processing, wherein the first current is 40-120 A, and the first preset time period is 2-4 h; charging the to-be-processed battery at a second current for a second preset time period and discharging the to-be-processed battery to realize the first trimming processing, wherein the second current is 100-300 A, and the second preset time period is 4-6 h.

[0006] In some embodiments, if the weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, sequentially performing first charging processing, second formation processing and second trimming processing on the to-be-processed battery to obtain the to-be-tested battery, including: charging the to-be-processed battery at a third current for a third preset time period until the state of charge of the to-be-processed battery reaches 1-2% to realize the first charging processing, wherein the third current is 300-900 A, and the third preset time period is 36 s-6 min; charging the to-be-processed battery at a fourth current for a fourth preset time period until the state of charge of the to-be-processed battery reaches 30-36% to realize the second formation processing, wherein the fourth current is 20-60 A, and the fourth preset time period is 4-6 h; charging the to-be-processed battery at a fifth current for a fifth preset time period until a first preset voltage is reached and discharging the to-be-processed battery to realize the second trimming processing, wherein the fifth current is 60-180 A, the fifth preset time period is 6-10 h, and the first preset voltage is 3.5-3.7 V.

[0007] In some embodiments, if the weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, the battery to be processed is sequentially subjected to a second charging treatment, a third formation treatment, a depolarization treatment, and a third capacity grading treatment, including: a first charging step, charging the battery to be processed at a sixth current for a sixth preset time period until the state of charge of the battery to be processed reaches 1% to 2%, to achieve the second charging treatment, wherein the sixth current is 300 to 900 A, and the sixth preset time period is 36 s to 6 min; a second charging step, charging the battery to be processed at a seventh current for a seventh preset time period until the state of charge reaches 30 to 36%, to achieve the third formation treatment, wherein the seventh current is 20 to 60 A, and the seventh preset time period is 4 to 6 h; a fourth treatment step, at least discharging the battery to be processed multiple times, and the current of the multiple discharges decreases in turn until a second preset voltage is reached, wherein the current of the discharging treatment is 2 to 300 A, and the second preset voltage is 1.8 to 2.1 V; a third charging step, charging the battery to be processed until the voltage of the battery to be processed reaches a third preset voltage, wherein the third preset voltage is 2.8 to 3.1 V; a repeating step, determining whether the voltage of the battery to be processed remains unchanged at the third preset voltage, and in the case that the voltage of the battery to be processed is greater than the third preset voltage, repeating the fourth treatment step at least once until the voltage of the battery to be processed remains unchanged at the third preset voltage, and charging the battery to be processed to 100% of the state of charge; and a fourth charging step, charging the battery to be processed at an eighth current for an eighth preset time period to achieve the third capacity grading treatment, wherein the eighth current is 60 to 180 A, and the eighth preset time period is 6 to 10 h.

[0008] In some embodiments, the fourth treatment step includes one of the following: continuously discharging the battery to be processed multiple times, and the current of the multiple discharges decreases in turn until a second preset voltage is reached; and alternatively discharging and charging the battery to be processed multiple times, and the current of the multiple discharges decreases in turn until the second preset voltage is reached.

[0009] In some embodiments, the method further comprises: discharging the battery to be tested by a ninth current until a fourth preset voltage is reached, wherein the ninth current is 80-360 A, and the fourth preset voltage is 2-3 V; discharging the battery to be tested by a tenth current until a fifth preset voltage is reached, wherein the tenth current is 4-60 A, and the fifth preset voltage is 1.8-2.1 V; and discharging the battery to be tested by an eleventh current until the second preset voltage is reached, wherein the eleventh current is 1-6 A.

[0010] In some embodiments, the first difference threshold is 90-110 g, the second difference threshold is 190-210 g, and the third difference threshold is 490-510 g.

[0011] In some embodiments, the current of the third formation treatment is less than the current of the second formation treatment, and the current of the third trimming treatment is less than the current of the second trimming treatment.

[0012] In some embodiments, after detecting the capacity of the battery to be tested, the method further comprises: repeating a predetermined treatment step if the capacity is less than the capacity threshold, and updating a first predetermined treatment in the predetermined treatment step to a second predetermined treatment in the predetermined treatment step in the last repetition, wherein the current of the first predetermined treatment is less than the current of the second predetermined treatment, until the capacity is greater than or equal to the capacity threshold, wherein the predetermined treatment step comprises one of the first treatment step, the second treatment step, and the third treatment step, the first predetermined treatment and the second predetermined treatment comprise the first formation treatment and the first trimming treatment respectively if the predetermined treatment step is the first treatment step, the first predetermined treatment and the second predetermined treatment comprise the first charging treatment, the second formation treatment, and the second trimming treatment respectively if the predetermined treatment step is the second treatment step, and the first predetermined treatment and the second predetermined treatment comprise the second charging treatment, the third formation treatment, the depolarization treatment, and the third trimming treatment respectively if the predetermined treatment step is the third treatment step.

[0013] According to some embodiments of the present application, another aspect of the present application provides a secondary battery prepared by any one of the methods for preparing a secondary battery.

[0014] According to some embodiments of the present application, another aspect of the embodiments of the present application provides an energy storage system comprising a plurality of the secondary batteries.

[0015] The technical scheme provided by the embodiments of the present application has at least the following advantages: the preparation method of the secondary battery adopts different charging, formation, charge-discharge and capacity grading processing in the case of different weight differences. In the case where the weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, the weight difference is larger, indicating that the battery cell may face the risk of lower capacity. The battery cell assembly is sequentially subjected to first charging processing, second formation processing and second capacity grading processing. The current of the second formation processing is lower than that of the first formation processing, and the current of the second capacity grading processing is also lower than that of the first capacity grading processing. According to Ohm's law, the smaller the formation current and the capacity grading current, the smaller the Ohmic polarization. The charging can be completed at a lower voltage, reducing the loss and increasing the charging efficiency. In the same time, the charging is more, so the capacity can be increased. In the case where the weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, the weight difference is larger, indicating that the battery cell may face the risk of lower capacity. The battery cell assembly is sequentially subjected to second charging processing, third formation processing, depolarization processing and third capacity grading processing. The current of the third formation processing is lower than that of the first formation processing, and the current of the second capacity grading processing is also lower than that of the first capacity grading processing. Based on the same reasons as above, the capacity can be increased. In addition, the depolarization processing can further remove the electrochemical polarization, achieve the purpose of adjusting the state of charge and stabilizing the SEI, and make the electrochemical polarization of the battery smaller, so that the active sites of the electrode active material can more fully undergo chemical reactions, further increase the charging capacity, increase the capacity grading capacity of the battery cell, and thus increase the capacity grading capacity rate, thereby ensuring the consistency of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0016] One or more embodiments are illustrated by way of example in the drawings that are for illustrative purposes only, and not for the purposes of limiting the embodiments, unless otherwise specifically stated herein. In order to more clearly illustrate the technical solutions of the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0017] Figure 1 FIG. 1 shows a flowchart of a preparation method of a secondary battery according to an embodiment of the present application;

[0018] Figure 2 FIG. 2 shows a flowchart of another preparation method of a secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION

[0019] As can be known from the background art, the existing battery capacity is generally low, because in the existing battery manufacturing process, the polarization is large, resulting in a small capacity of the battery cell.

[0020] In the early stage of battery manufacturing, after the battery cell is completed with liquid injection, it needs to undergo a standing process, which is usually carried out under high temperature conditions. This stage is the process of electrolyte soaking into the battery cell, especially filling into the pores of the electrode material. The purpose of soaking is to ensure the full contact of the electrode and the electrolyte, to provide the necessary environment for the subsequent electrochemical reaction, so that the battery can exert its designed performance. The soaking process of high-temperature standing in the prior art is mainly completed by physical means, that is, by increasing the temperature and adjusting the viscosity of the electrolyte to promote the fluidity and diffusion capacity of the electrolyte.

[0021] The SEI (Solid Electrolyte Interface) film is a protective layer formed on the surface of the electrode during the first charging of the battery, mainly composed of the products of electrolyte decomposition. The role of the SEI film is to form a stable interface on the surface of the electrode, reduce the direct reaction between the electrode material and the electrolyte, protect the internal structure of the battery, and prolong the service life of the battery. After completing the formation (SEI film formation) and the initial high-temperature standing, the battery is subjected to a second liquid injection (two injections), followed by a capacity test. Capacity test is an important test in battery manufacturing, which is used to determine the actual capacity of the battery. However, in this process, the SEI film may be broken and recombined, resulting in a large polarization, which leads to a lower discharge capacity of the battery during the capacity test than its theoretical capacity. This is because during the capacity test, the battery needs to be discharged to a certain state, and the reconstruction of the SEI film will cause energy loss, which is manifested as a decrease in capacity.

[0022] To solve the problem of low capacity of the secondary battery in the prior art, the embodiments of the present application provide a preparation method of a secondary battery, a secondary battery and an energy storage system. By improving the soaking effect and reducing the polarization of the SEI film in the capacity test process, the capacity of the battery cell can be effectively improved.

[0023] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0024] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in an embodiment” in various places in the specification are not necessarily referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combined with other embodiments in accordance with the application.

[0025] In the description of the embodiments of the application, the term“and / or” only means an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can mean that A exists, A and B exist, and B exists. In addition, the character“ / ” herein generally means that the front and rear associated objects are in an“or” relationship.

[0026] In the description of the embodiments of the application, the term“a plurality of” refers to two or more (including two), and similarly, “a plurality of groups” refers to two or more groups (including two groups), and “a plurality of pieces” refers to two or more pieces (including two pieces).

[0027] In the description of the embodiments of the application, the technical terms“center”,“longitudinal”,“transverse”,“length”,“width”,“thickness”,“upper”,“lower”,“front”,“rear”,“left”,“right”,“vertical”,“horizontal”,“top”,“bottom”,“inner”,“outer”,“clockwise”,“counterclockwise”,“axial”,“radial”,“circumferential” and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the application.

[0028] In the description of the embodiments of the application, unless otherwise explicitly specified and limited, the technical terms“mounting”,“connection”,“connection”,“fixing” and the like should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the embodiments of the application can be understood according to the specific circumstances.

[0029] In the drawings corresponding to the embodiments of the present application, the thickness and area of a layer are exaggerated for better understanding and ease of description. When describing that a component (such as a layer, a film, a region, or a substrate) is on or on the surface of another component, the component can be "directly" on the surface of the other component, or a third component can exist between the two components. Conversely, when describing that a component is on the surface of another component or that a component surface forms or is provided with another component, it is indicated that there is no third component between the two components. In addition, when describing that a component is "formed substantially" on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a part of the edge of the entire surface.

[0030] In the description of the embodiments of the present application, when a certain component "includes" another component, unless otherwise specified, other components are not excluded, and other components can also be further included. In addition, when a layer, a film, a region, or a plate, and the like, are referred to as "on / over" another component, it can be "directly on" another component (i.e., between the surface of another component and another component, there is no other component), or another component can exist therebetween. In addition, when a layer, a film, a region, a plate, and the like, are "directly on" another component, or when a layer, a film, a region, a plate, and the like, are on the surface of another component, it is indicated that there is no other component therebetween.

[0031] The terms used in the description of various described embodiments herein are only used to describe specific embodiments, and are not intended to be limiting. As used in the description of various described embodiments and the appended claims, "the part" is also intended to include the plural form, unless the context clearly indicates otherwise. Among them, the components include layers, films, regions, or plates, and the like.

[0032] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are presented in order to enable the reader to better understand the present application. However, the technical solutions claimed by the present application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0033] Figure 1 is a flowchart of a method for manufacturing a secondary battery according to an embodiment of the present application. As shown in Figure 1 the method includes the following steps:

[0034] An acquisition step (step S101) acquires a weight difference of a to-be-cased battery cell assembly, wherein the weight difference is an absolute value of a difference between an actual weight of the to-be-cased battery cell assembly and a target weight of the to-be-cased battery cell assembly;

[0035] Before step S101, there is also a step of providing a to-be-encased cell assembly. The target weight is a standard weight preset according to the cell design, material properties and manufacturing process, representing the weight of the cell assembly in an ideal state, which is an important parameter for production quality control. The weight difference is calculated to quantify the deviation of the cell assembly from the ideal state.

[0036] The first determination step (step S102) is to perform the encasing and liquid injection processes on the to-be-encased cell assembly to obtain a to-be-processed battery, and determine whether the weight difference is greater than a first difference threshold value;

[0037] The encasing process refers to placing the preliminarily assembled cell assembly into the battery shell. This usually occurs after the cell assembly (including positive and negative electrode sheets, separators, etc.) has been wound or stacked, but before it is packaged in the final battery housing. The encasing process not only involves physical installation, but also needs to ensure that the cell assembly is correctly placed, not damaged, and properly connected with other components (such as lead wires, safety valves, etc.) inside the battery shell. The liquid injection process is the process of adding electrolyte into the battery shell. The electrolyte is the medium for conducting ions and realizing electrochemical reactions in the battery, which is crucial for the performance and safety of the battery. After completing the above two steps, the cell assembly has been packaged in the battery shell and injected with an appropriate amount of electrolyte, forming a complete but not yet fully activated battery unit, referred to here as a "to-be-processed battery". The first difference threshold value is set to determine whether the to-be-encased cell assembly has a low capacity risk. Generally, the parameter range of the first difference threshold value can be 95g-105g, for example, it can be set to 98g, 100g, 103g, and preferably set to 100g. The selection of the first difference threshold value is related to historical production data and industry experience. Batteries with a weight deviation of about 100g may have a slight impact on their electrochemical performance (such as capacity, internal resistance, cycle life, etc.), but such impact is usually within an acceptable range. 100g as a difference threshold value can help identify batteries with slight unevenness in material distribution or structural assembly. Such deviations may be caused by minor variations in the production process, but can often be compensated or corrected through subsequent processing (such as adjusting the charge and discharge parameters).

[0038] The first processing step (step S103) is to sequentially perform the first formation and first capacity grading processes on the to-be-processed battery if the weight difference is less than or equal to the first difference threshold value, to obtain a to-be-tested battery.

[0039] If the weight difference is less than or equal to the first difference threshold value, it proves that the to-be-encapsulated battery cell assembly has a low risk of low capacity, and normal formation (i.e., first formation treatment) and normal distribution (i.e., first distribution treatment) can be adopted. The current of normal formation (i.e., first formation treatment) and normal distribution (i.e., first distribution treatment) is relatively high, and the normal formation and distribution current is usually set in the optimal interval of battery design and manufacturing process, which can ensure the smooth progress of the internal electrochemical process of the battery, thereby improving the consistency of battery performance. In the case that the to-be-encapsulated battery cell assembly is not prone to low capacity, normal formation current helps to form a good quality SEI film, which plays a crucial role in protecting the battery internally and reducing the risk of internal short circuit of the battery.

[0040] The second determination step (step S104) is to determine whether the weight difference is greater than a second difference threshold value if the weight difference is greater than the first difference threshold value, wherein the second difference threshold value is greater than the first difference threshold value;

[0041] If the weight difference is greater than the first difference threshold value, it proves that the to-be-encapsulated battery cell assembly has a certain risk of low capacity, and small current formation and / or small current distribution steps need to be adopted for the to-be-encapsulated battery cell assembly to improve the capacity of the battery cell. However, it is necessary to further screen the weight difference to determine whether the weight difference also exceeds the second difference threshold value of a higher level, that is, to determine whether the weight difference also exceeds the second difference threshold value of a higher level. This detailed decision-making process reflects strict control of production quality. According to different levels of weight difference, different treatments are performed to maximize the capacity of the to-be-encapsulated battery cell assembly while ensuring production efficiency and production cost. Generally, the parameter range of the second difference threshold value can be 195g-205g, for example, it can be set to 198g, 200g, 203g, and 200g is preferred. The second difference threshold value of 200g is a decision made on the basis of comprehensive consideration of battery performance, cost control, safety, and industry practice. It aims to identify and handle those batteries with large weight deviation but still have potential for recovery through specific technical means, thereby maximizing economic benefits while ensuring product quality and safety. Compared with slight weight deviation, a threshold value of 200g means that the battery may have a large performance loss. However, at the same time, through special processing techniques such as increasing the charging current to improve wetting, adjusting the formation current and distribution current, etc., it is still possible to partially or completely compensate for this performance loss.

[0042] The second processing step (step S105) is that if the weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, the battery to be processed is sequentially subjected to first charging processing, second formation processing, and second capacity grading processing, to obtain the battery to be tested, the charging current of the second formation processing is less than the charging current of the first formation processing, and the charging current of the second capacity grading processing is less than the charging current of the first capacity grading processing;

[0043] If the weight difference is between the first difference threshold and the second difference threshold, it proves that the shell-in battery cell assembly has a certain risk of lower capacity. At this time, the shell-in battery cell assembly is subjected to large-current charging processing to promote the infiltration of the electrolyte inside the cell, small-current formation processing to form a SEI film more gently and uniformly, reduce the instability or excessive growth of the SEI film caused by fast charging, and thus reduce the ohmic polarization and improve the battery performance. Small-current capacity grading processing reduces the polarization effect in the electrochemical reaction, so that the battery exhibits more true capacity characteristics during the test process, increasing the accuracy of the test, while also helping to stabilize the battery SEI film and reduce capacity decay.

[0044] The third determination step (step S106) is that if the weight difference is greater than the second difference threshold, it is determined whether the weight difference is greater than a third difference threshold, wherein the third difference threshold is greater than the second difference threshold;

[0045] If the weight difference is greater than the second difference threshold, it proves that the shell-in battery cell assembly has a very high risk of lower capacity. At this time, small-current formation and / or small-current capacity grading and capacity grading before load adjustment to stabilize the SEI are required to improve the capacity of the cell. The third difference threshold is a very strict upper limit. If the weight difference is greater than the third difference threshold, the batch of shell-in battery cell assemblies is directly determined to be unqualified. Generally, the parameter range of the third difference threshold can be 495g-505g, for example, it can be set to 498g, 500g, 503g, and is preferably set to 500g. When the weight difference reaches 500g, the performance and safety risk of the battery may increase significantly. This may be caused by excessive or insufficient active material, or serious uneven distribution of electrolyte. Although the cost of performance recovery is high, if the battery can reach the basic safety and performance standards through special processing, these batteries still have certain market value, especially in application scenarios where the performance requirement is not very extreme. The third difference threshold of 500g provides a clear decision boundary. Battery assemblies below this value will be attempted to be salvaged by various means; while batteries exceeding this value, due to high performance and safety risks, the cost and feasibility of salvage are dramatically reduced, so they are usually directly determined to be unqualified to avoid further resource investment and potential quality risks.

[0046] A third processing step (step S107) is performed on the battery to be processed, sequentially, if the weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, a second charging treatment, a third formation treatment, a depolarization treatment, and a third equalization treatment, to obtain the battery to be tested, the current of the third formation treatment is less than the current of the first formation treatment, and the current of the third equalization treatment is less than the current of the first equalization treatment.

[0047] If the weight difference is between the second difference threshold and the third difference threshold, it proves that the shell-in battery cell assembly has a high risk of low capacity, but certain process means can be used for optimization, at this time the shell-in battery cell assembly uses higher large current charging treatment to promote the infiltration of the electrolyte inside the battery cell, smaller small current formation treatment to form a SEI film more gently and uniformly, reduce the instability or excessive growth of the SEI film caused by fast charging, thereby reducing the ohmic polarization and improving the battery performance, and adding a depolarization treatment to reduce the polarization effect inside the battery, improve the electrochemical reaction efficiency and capacity release ability of the battery, and smaller small current equalization treatment to reduce the polarization effect in the electrochemical reaction, so that the battery shows more real capacity characteristics during the test process, increasing the accuracy of the test, while also helping to stabilize the SEI film of the battery and reduce capacity decay.

[0048] A detection step (step S108) is performed to detect the capacity of the battery to be tested. If the capacity is greater than or equal to a capacity threshold, the secondary battery is determined to be equalized and offline.

[0049] Specifically, the capacity threshold is a specific numerical value representing the minimum acceptable charge storage capacity of the battery. Typically, capacity detection is performed through standard charge and discharge cycles. In this process, the battery is fully charged and then discharged to a predetermined cut-off voltage, and the total charge output during discharge is recorded, which is the capacity of the battery. When the detected capacity of the battery reaches or exceeds this threshold, it is considered to meet the performance requirements and can proceed to the next equalization and offline operation. Conversely, if the capacity of the battery is lower than the set threshold, it will be considered as a defective product and needs to be isolated for further analysis or disposal.

[0050] The preparation method of the secondary battery is different in different weight difference sizes. In the case where the weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, the weight difference is large, indicating that the battery may face the risk of low capacity. The battery assembly is sequentially subjected to first charging treatment, second formation treatment and second capacity grading treatment. The current of the second formation treatment is lower than that of the first formation treatment, and the current of the second capacity grading treatment is also lower than that of the first capacity grading treatment. According to Ohm's law, the smaller the formation current and the capacity grading current, the smaller the Ohm polarization. The charging can be completed at a lower voltage, reducing the loss and increasing the charging efficiency. In the same time, the charging is more, so the capacity can be increased. In the case where the weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, the weight difference is larger, indicating that the battery may face a greater risk of low capacity. The battery assembly is sequentially subjected to second charging treatment, third formation treatment, depolarization treatment and third capacity grading treatment. The current of the third formation treatment is lower than that of the first formation treatment, and the current of the second capacity grading treatment is also lower than that of the first capacity grading treatment. Based on the same reasons, the capacity can be increased. In addition, the depolarization treatment can further remove the electrochemical polarization, adjust the state of charge and stabilize the SEI, and make the electrochemical polarization of the battery smaller, the point of the electrode active material more fully react chemically, further improve the charging capacity, improve the capacity grading capacity of the battery, thereby improve the capacity grading capacity rate, and ensure the consistency of the battery.

[0051] In some embodiments, if the weight difference is less than or equal to the first difference threshold, the battery to be treated is sequentially subjected to first formation treatment and first capacity grading treatment to obtain a battery to be tested, including the following steps:

[0052] Step S1031, the battery to be treated is charged at a first current for a first predetermined time to realize the first formation treatment, wherein the first current is 40-120 A, for example, it can be 60 A, 80 A, 100 A, and the first predetermined time is 2-4 h, for example, it can be 2.5 h, 3 h, 3.5 h;

[0053] The first current is a normalizing current. The minimum value of the first current range is calculated according to the formula 0.2C*200Ah=40A, and the maximum value of the first current range is calculated according to the formula 0.2C*600Ah=120A. It should be noted that 0.2C is the rate, 200Ah is a smaller value of battery milliampere, 600Ah is a larger value of battery milliampere. The value range of the rate is not fixed as 0.2C, and can be between 0.1C and 0.3C, for example, it can also be 0.15C or 0.25C. The battery milliampere is also not fixed as 200Ah and 600Ah. The above values are only a preferred range, and can be adjusted according to actual conditions.

[0054] In some embodiments, the value range of the rate can also be between 0.3C and 1.8C, for example, it can be 0.5C or 1.5C.

[0055] The range of the first current is set to 40-120A, for example, it can be 60A, 80A or 100A. This interval is generally considered to be a moderate current density, which can promote the internal reaction of the battery and form an SEI film, and also does not cause the SEI film to be unstable or the internal structure to be damaged due to too fast. The first preset time is set to 2-4 hours, for example, it can be 2.5h, 3h or 3.5h. This time is to ensure that the battery has enough time to react under the controlled current to form a uniform and stable SEI film. The stability and quality of the SEI film directly affect the cycle life and safety of the battery.

[0056] In step S1032, the battery to be processed is charged at a second current for a second preset time, and then discharged to achieve the first capacity grading process. The second current is 100-300A, for example, it can be 150A, 200A or 250A, and the second preset time is 4-6h, for example, it can be 4.5h, 5h or 5.5h.

[0057] The second current is a normal capacity distribution current. The minimum value of the second current range is calculated according to the formula 0.5Cx200Ah=100A, and the maximum value of the second current range is calculated according to the formula 0.5Cx600Ah=300A. It should be noted that 0.5C is the rate, 200Ah is a smaller value of battery milliampere, 600Ah is a larger value of battery milliampere. The value range of the rate is not fixed as 0.5C, and can be between 0.4C and 0.6C, for example, it can also be 0.45C or 0.55C. The value of battery milliampere is also not fixed as 200Ah and 600Ah. The above values are only a preferred range, which can be adjusted according to actual conditions.

[0058] The second current is set to a higher range of 100-300A, which helps to quickly determine the capacity characteristics of the battery, and also helps to find the performance bottleneck of the battery under high load. The second preset time period is 4-6 hours, during which the battery will undergo charge and discharge cycles to simulate actual use conditions, detect battery capacity and calibrate it to some extent. Appropriate charge and discharge cycles help to balance the distribution of ions inside the battery and reduce initial electrochemical polarization effects.

[0059] Specifically, by precisely controlling the current and time of formation and capacity distribution, it can be ensured that each battery cell can complete activation under similar conditions, thereby greatly improving the performance consistency between battery batches. This is particularly important for applications such as energy storage systems and electric vehicles that require high consistency. The SEI film is a solid electrolyte interface film formed on the surface of the battery electrode, and its quality and stability directly affect the cycle performance and safety of the battery. The set first current and preset time period help to form a high-quality and uniform SEI film, thereby prolonging the battery life and improving the safety. Appropriate capacity distribution processing can reduce the ohmic polarization and electrochemical polarization of the battery, so that the battery can reach a stable state faster in the initial stage of use, reduce capacity decay, and improve the efficiency and usability of the battery.

[0060] In some embodiments, if the above weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, the above to-be-processed battery is sequentially subjected to a first charging process, a second formation process, and a second capacity distribution process to obtain the above to-be-tested battery, including the following steps:

[0061] In step S1051, the battery to be processed is charged with a third current for a third preset time period until the state of charge of the battery to be processed reaches 1% to 2%, so as to realize the first charging process, wherein the third current is 300 to 900 A, for example, can be 450 A, 600 A, 850 A, the third preset time period is 36 s to 6 min, for example, can be 1 min, 3 min, 5 min;

[0062] The third current is a large charging current. The minimum value of the third current range is calculated according to the formula 1.5C*200 Ah=300 A, and the maximum value of the third current range is calculated according to the formula 1.5C*600 Ah=900 A. It should be noted that 1.5C is the rate, 200 Ah is a smaller example of the battery milliamperes, 600 Ah is a larger example of the battery milliamperes. 200 Ah is a smaller example of the battery milliamperes, and 600 Ah is a larger example of the battery milliamperes. The value range of the rate is not fixed as 1.5C, and can be between 1C and 2C, for example, can also be 1.2C, 1.4C, 1.6C. The battery milliamperes is also not fixed as 200 Ah and 600 Ah. The above values are only a preferred range, which can be adjusted according to actual conditions.

[0063] The third current range is set to 300 to 900 A, which is a large current charging, and the purpose is to realize the pre-wetting of the battery through fast charging, promote the rapid penetration of lithium ions and solvent molecules in the electrode material, and improve the wetting effect of the electrode surface. The third preset time period is 36 s to 6 min, and the short time high current charging helps to quickly increase the state of charge of the battery to 1% to 2%, which is sufficient to trigger the preliminary reaction of the electrode material, but is not enough to form an unstable SEI film, and the pre-wetting improves the effect of subsequent formation.

[0064] In step S1052, the battery to be processed is charged with a fourth current for a fourth preset time period until the state of charge of the battery to be processed reaches 30 to 36%, so as to realize the second formation process, wherein the fourth current is 20 to 60 A, for example, can be 30 A, 40 A, 50 A, the fourth preset time period is 4 to 6 h, for example, can be 4.5 h, 5 h, 5.5 h;

[0065] The fourth current is a small formation current. The minimum value of the fourth current range is calculated according to the formula 0.1C*200Ah=20A, and the maximum value of the fourth current range is calculated according to the formula 0.1C*600Ah=60A. It should be noted that 0.1C is the rate, 200Ah is a smaller value of battery milliampere, and 600Ah is a larger value of battery milliampere. The value range of the rate is not fixed as 0.1C, and can be between 0.05C and 0.1C, for example, it can also be 0.07C or 0.08C. The battery milliampere is also not fixed as 200Ah and 600Ah. The above values are only a preferred range, and can be adjusted according to actual conditions.

[0066] The fourth current range is 20-60A, which is a relatively moderate current suitable for the formation and stabilization of the SEI film. The formation time is 4-6h, which ensures that the battery cell has sufficient time to form a uniform and stable SEI film under controlled current, and the state of charge is 30%-36%, which is beneficial to the optimization of the SEI film, reduces the internal resistance, and improves the cycle performance and safety of the battery.

[0067] In step S1053, the battery to be processed is charged at a fifth current for a fifth preset time period until a first preset voltage is reached, and then discharged to achieve the second capacity sorting process. The fifth current is 60-180A, for example, it can be 80A, 100A or 150A. The fifth preset time period is 6-10h, for example, it can be 6.5h, 8h or 9h. The first preset voltage is 3.5-3.7V, for example, it can be 3.55V, 3.6V or 3.65V.

[0068] The fifth current is a small capacity sorting current. The minimum value of the fifth current range is calculated according to the formula 0.3C*200Ah=60A, and the maximum value of the fifth current range is calculated according to the formula 0.3C*600Ah=180A. It should be noted that 0.3C is the rate, 200Ah is a smaller value of battery milliampere, and 600Ah is a larger value of battery milliampere. The value range of the rate is not fixed as 0.3C, and can be between 0.2C and 0.3C, for example, it can also be 0.24C, 0.25C or 0.26C. The battery milliampere is also not fixed as 200Ah and 600Ah. The above values are only a preferred range, and can be adjusted according to actual conditions.

[0069] The fifth current range is 60-180 A, which is used to quickly determine the true capacity of the battery during the capacity formation process and optimize the electrochemical balance inside the battery. The fifth preset time length is 6-10 h, which ensures that the battery cell can fully experience the charge and discharge cycle to reach the first preset voltage of 3.5-3.7 V. The voltage control during the capacity formation process helps to stabilize the internal structure of the battery, reduce the polarization effect under high state of charge, and improve the capacity and cycle efficiency of the battery.

[0070] Specifically, by high-current charging in the first charging process, the wettability of the battery can be significantly improved, ensuring that the electrolyte can fully penetrate into the pores of the electrode material, improving the utilization rate of active materials, and thus increasing the capacity of the battery. The second formation process uses a mild small current and precise state of charge control, which helps to form a more uniform and stable SEI film, reduces the ohmic polarization and electrochemical polarization of the battery in subsequent use, and improves the cycle stability and service life of the battery. The second capacity formation process can make the ohmic polarization of the battery smaller.

[0071] In some embodiments, if the above weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, the above to-be-processed battery is sequentially subjected to a second charging process, a third formation process, a depolarization process, and a third capacity formation process, comprising:

[0072] A first charging step, charging the above to-be-processed battery at a sixth current and for a sixth preset time length until the state of charge of the above to-be-processed battery is 1-2%, to realize the second charging process, wherein the sixth current is 300-900 A, for example, it can take values such as 400 A, 600 A, 800 A, and the sixth preset time length is 36 s-6 min, for example, it can take values such as 1 min, 3 min, 5 min;

[0073] A second charging step, charging the above to-be-processed battery at a seventh current and for a seventh preset time length until the state of charge is 30-36%, to realize the third formation process, wherein the seventh current is 20-60 A, for example, it can take values such as 30 A, 40 A, 50 A, and the seventh preset time length is 4-6 h, for example, it can take values such as 4.5 h, 5 h, 5.5 h;

[0074] A fourth processing step, at least performing multiple discharge processes on the above to-be-processed battery, and the current of the multiple discharge processes decreases in turn until a second preset voltage is reached, wherein the current of the discharge process is 2-300 A, for example, it can take values such as 220 A, 250 A, 280 A, and the second preset voltage is 1.8-2.1 V, for example, it can take values such as 1.9 V, 2.0 V, 2.05 V;

[0075] The fourth processing step is depolarization processing. The current is gradually reduced through multiple discharging processes until the second preset voltage (1.8-2.1V) is reached. This process aims to remove the ohmic polarization and electrochemical polarization generated during the formation and charging process of the battery, ensuring uniform distribution of internal charges and reducing the negative effects of charge aggregation, such as local overheating or uneven lithium ion deposition.

[0076] The third charging step is to charge the battery until the voltage reaches the third preset voltage, which is 2.8-3.1V, for example, 2.9V or 3.0V.

[0077] The process is repeated to determine whether the voltage of the battery remains unchanged at the third preset voltage. If the voltage is greater than the third preset voltage, the fourth processing step is repeated at least once until the voltage of the battery remains unchanged at the third preset voltage, and the battery is charged to 100% state of charge.

[0078] After depolarization, the battery is charged until its voltage reaches the third preset voltage (2.8-3.1V), and after confirming that the battery voltage is stable and does not fall back, it is further charged to 100% state of charge. This step helps to further strengthen and stabilize the SEI film, ensuring that the battery does not experience capacity decline or safety issues due to unstable SEI film at high state of charge.

[0079] The fourth charging step is to charge the battery at an eighth current for an eighth preset duration to achieve the third capacity grading process. The eighth current is 60-180A, for example, 80A, 100A, or 150A, and the eighth preset duration is 6-10h, for example, 6.5h, 8h, or 9h.

[0080] Specifically, depolarization and deep optimization of the SEI film can significantly improve the performance of the battery cell, particularly capacity and cycle stability, even in cases of significant weight differences. Through depolarization processing and SEI film strengthening, the internal structure of the battery is more stable, reducing the risk of safety risks caused by overcharging and overdischarging, and improving the reliability and durability of the battery. Through large-current charging, gentle formation, deep depolarization processing, and optimization of the grading process, not only can the performance of the battery be maximized in cases of significant material and structural deviations, but also the safety, reliability, and consistency between batches can be significantly improved.

[0081] In some embodiments, the fourth processing step includes one of the following:

[0082] The above-mentioned battery to be processed is subjected to multiple continuous discharge treatments, and the current of each discharge treatment is gradually reduced until the second preset voltage is reached.

[0083] The polarization effect includes ohmic polarization and electrochemical polarization, which is the result of uneven distribution of internal charge and incomplete electrochemical reaction. After the battery is formed or charged, different degrees of polarization may occur inside, which reduces the battery efficiency, increases the internal resistance, and may cause poor performance of the battery during initial use. By multiple continuous discharge treatments, and gradually reducing the current of each discharge, the excess charge stored inside the battery can be gradually removed, reducing the unevenness of charge distribution, thereby reducing the polarization effect.

[0084] The above-mentioned battery to be processed is subjected to multiple continuous discharge treatments, and the current of each discharge treatment is gradually reduced until the second preset voltage is reached.

[0085] In addition, in addition to depolarization, alternating discharge and charge treatment also helps to optimize the structure of the SEI film, i.e. the solid electrolyte interface film. The SEI film is formed during the formation of the battery and is crucial to the performance and safety of the battery. Proper discharge and charge cycles can eliminate polarization while promoting the SEI film to a more uniform and stable state. By gradually reducing the discharge current, polarization can be eliminated gently without damaging the battery, and by charging treatment, the uniform distribution of internal charge state is ensured, promoting the optimization of the SEI film.

[0086] Specifically, whether continuous discharge treatment or alternating charge and discharge treatment can effectively reduce ohmic polarization and electrochemical polarization, reduce the internal resistance of the battery, and improve the charge and discharge efficiency and overall performance of the battery. Alternating discharge and charge treatment, especially when the current is gradually reduced, helps to optimize the SEI film and form a more uniform and stable interface layer, which has an important impact on the cycle life and safety of the battery. By eliminating polarization effect and optimizing SEI film, the battery is more stable during charging and discharging, reducing the safety hazards caused by local overheating, uneven charge distribution, etc., and improving the overall safety of the battery.

[0087] In some embodiments, the above-mentioned battery to be tested is subjected to multiple continuous discharge treatments, and the current of each discharge treatment is gradually reduced until the second preset voltage is reached, comprising the following steps:

[0088] Step S201, using the ninth current to discharge the above-mentioned battery to be processed until the fourth preset voltage is reached, wherein the ninth current is 80-360A, for example, it can take the value of 100A, 200A, 300A, and the fourth preset voltage is 2-3V, for example, it can take the value of 2.5V, 2.6V, 2.8V.

[0089] The battery is discharged using a larger current (80-360 A) to quickly consume the excess charge accumulated in the battery during previous processes (such as charging, formation), reducing the ohmic polarization of the battery, i.e. the energy loss caused by the increase in internal resistance of the battery. High-current discharge can promote more efficient movement of lithium ions, rapidly reducing the battery voltage to a fourth preset voltage (2-3 V), creating conditions for subsequent more delicate processing stages.

[0090] In step S202, the battery to be processed is discharged using a tenth current until a fifth preset voltage is reached, wherein the tenth current is 4-60 A, for example, it can take values such as 45 A, 50 A, 55 A, and the fifth preset voltage is 1.8-2.1 V, for example, it can take values such as 1.9 V, 2.0 V.

[0091] Compared to the first stage (step S201), the current in this stage (4-60 A) is reduced, but still maintains a certain intensity. This helps to further homogenize the charge distribution inside the battery on the basis of rapid depolarization, reduce electrochemical polarization, while avoiding excessive discharge of the battery. The battery voltage is reduced to a fifth preset voltage (1.8-2.1 V), which is usually a more ideal working voltage range that better reflects the true state of the battery and prepares for the next step of processing.

[0092] In step S203, the battery to be processed is discharged using an eleventh current until the second preset voltage is reached, wherein the eleventh current is 1-6 A, for example, it can take values such as 3 A, 4 A, 5 A.

[0093] In this stage, the current is further reduced to a very low level (1-6 A), which means that the processing process becomes more gentle and delicate. Low-current discharge can effectively remove residual polarization in the battery, especially the impact on the SEI film, ensuring the stability of the internal state of the battery. The battery voltage is reduced to the second preset voltage, which indicates that the battery has completed deep depolarization and reached a stable working state, providing a good starting point for subsequent charging, full charging, etc. of the battery.

[0094] Specifically, by gradually reducing the discharge current through the three stages, the ohmic polarization and electrochemical polarization of the battery can be significantly reduced, the energy conversion efficiency of the battery during charging and discharging can be improved, and the capacity decay can be reduced. Multi-stage discharge processing helps to optimize the electrochemical balance of the battery, ensures uniform distribution of lithium ions between the positive and negative electrodes, and makes the SEI film structure more stable, providing better cycle performance and life for the battery. The step-by-step decreasing current discharge avoids excessive current impact and reduces the risk of battery heating and damage during processing, thereby improving the safety of the battery.

[0095] In some embodiments, the first difference threshold is 90-110 g, the second difference threshold is 190-210 g, and the third difference threshold is 490-510 g. For example, the first difference threshold can be 95 g, 100 g, or 105 g, the second difference threshold can be 195 g, 200 g, or 205 g, and the third difference threshold can be 495 g, 500 g, or 505 g.

[0096] A weight difference in the range of 90-110 g often means that the performance of the battery deviates less, and the standard formation and capacity distribution process can meet the performance requirements. When the difference expands to 190-210 g, the performance of the battery can be more obviously affected, and additional processing measures need to be taken to ensure that the performance meets the standard. Further, when the difference reaches 490-510 g, the performance defects of the battery can be very significant, and more stringent, even customized, processing procedures need to be taken to try to restore the performance of the battery.

[0097] For batteries with a weight difference within the first difference threshold of 90-110 g, since the difference is small, only conventional formation, capacity distribution, and other processing may be required. This not only ensures the consistency of performance, but also avoids waste of resources caused by excessive processing. When the weight difference of the battery expands to the second difference threshold of 190-210 g, the performance of the battery can be more obviously affected. At this time, more complex processing strategies, such as enhanced soaking and depolarization processing, can effectively compensate for the performance loss caused by uneven distribution of active materials and improve the overall performance of the battery. When the weight difference reaches the third difference threshold of 490-510 g, the battery can have serious performance deviation, and it can even fail to meet the qualified standard. In this extreme case, a series of high-level processing methods such as deep depolarization and multi-stage formation are used to restore the basic performance of the battery to at least meet the usable standard, while also trying to reduce the large difference in performance to meet the consistency requirements of the battery pack.

[0098] Setting a lower first difference threshold means that most battery units with small weight differences can follow the standard processing procedure, avoiding waste of time, energy, and cost caused by excessive processing. The higher the difference threshold, the more complex the processing required, and the greater the resource consumption. By setting different thresholds, processing resources can be reasonably allocated while ensuring battery performance, ensuring that resources are mainly used for battery units with large performance deviations.

[0099] In some embodiments, the current of the third formation processing is less than the current of the second formation processing, and the current of the third capacity distribution processing is less than the current of the second capacity distribution processing.

[0100] Specifically, formation refers to the process of forming SEI (Solid Electrolyte Interface) film during the first charge-discharge process of the battery, and the formation and stability of SEI film are crucial to the performance and life of the battery. In traditional formation processing, a fixed or relatively high current may be used. However, if the current is too large, the SEI film may be formed too rough or uneven, resulting in increased internal resistance of the battery and decreased electrochemical performance. Therefore, by setting the current of the third formation processing to be smaller than that of the second formation processing, the growth process of the SEI film can be more finely controlled, making it more uniform, dense and stable, thereby reducing the ohmic polarization of the battery and improving the electrochemical performance of the battery. The capacity test is an important link in the battery manufacturing process, mainly used to test and calibrate the actual capacity of the battery. During the capacity test, the battery usually needs to be charged first, and then discharged to measure the maximum storage capacity of the battery. If too high a current is used during the capacity test (especially during the charging phase), it may cause local overheating inside the battery, damaging the battery structure, especially the integrity of the SEI film, resulting in inaccurate capacity readings or damaged battery performance. Therefore, by setting the current of the third capacity test to be smaller than that of the second capacity test, the battery can be treated more gently, reducing electrochemical polarization, ensuring that the battery is not overstressed during the capacity test, thereby obtaining more accurate and reliable battery capacity data while protecting the battery from damage.

[0101] In some embodiments, after detecting the capacity of the battery to be tested, the method further comprises: in the case that the capacity is less than the capacity threshold, repeating the predetermined processing steps, and in the repeating process, updating the first predetermined processing in the predetermined processing steps to the second predetermined processing in the predetermined processing steps in the last repeating process, wherein the charging current of the first predetermined processing is smaller than the current of the second predetermined processing, until the capacity is greater than or equal to the capacity threshold, wherein the predetermined processing steps include one of the first processing steps, the second processing steps and the third processing steps, in the case that the predetermined processing steps are the first processing steps, the first predetermined processing and the second predetermined processing include the first formation processing and the first capacity test respectively, in the case that the predetermined processing steps are the second processing steps, the first predetermined processing and the second predetermined processing include the first charging processing, the second formation processing and the second capacity test respectively, in the case that the predetermined processing steps are the third processing steps, the first predetermined processing and the second predetermined processing include the second charging processing, the third formation processing, the depolarization processing and the third capacity test respectively.

[0102] Specifically, when the initial capacity of the battery is below a set capacity threshold, the system automatically initiates a repetitive processing flow. In this flow, each repetition upgrades the processing strategy, i.e., the current "first predetermined processing" is replaced by the "second predetermined processing" in the previous processing, which usually has higher current or other more intense processing parameters. This iterative upgrade strategy is based on the understanding of the impact of current size on the internal structure and performance of the battery, i.e., higher current can promote electrochemical reactions, accelerate charge transfer, improve the formation and stability of SEI film, and thus improve the capacity of the battery.

[0103] Through the step-by-step upgrade of the processing flow, especially the increase of charging current, the capacity of the battery can be effectively improved until the capacity reaches or exceeds the set threshold. This helps to improve the yield of the battery and reduce the waste of raw materials and manufacturing costs due to insufficient performance. The flow design supports automation, and once the battery capacity is detected below the threshold, the system automatically performs processing and adjusts the strategy according to the results, without manual intervention, improving production efficiency and consistency. Compared with directly scrapping or downgrading the batteries that do not meet the standards, the iterative processing scheme can save a part of the batteries, thereby reducing the waste of raw materials and manufacturing costs. Each iteration of processing is aimed at specific performance defects of the battery, such as poor SEI film formation and internal polarization, which helps to optimize the performance of the battery and improve the overall quality and reliability of the battery.

[0104] Taking LFP314 battery as an example, according to the capacity lower limit of 320Ah, the capacity of the battery can be improved between 319-320Ah. By using different weight data of the incoming material, the capacity of the battery can be improved, and the capacity of the corresponding gear can be reduced by 1Ah.

[0105] Comparative Example 1

[0106] The weight difference of the shell assembly is 150g, and the battery to be processed is subjected to formation treatment using an 80A current and capacity treatment using a 200A current. The capacity of the secondary battery obtained finally is 318Ah.

[0107] Example 1

[0108] The weight difference of the shell assembly is 150g, and the battery to be processed is subjected to formation treatment using an 80A current and capacity treatment using a 200A current. The capacity of the secondary battery obtained finally is 318Ah.

[0109] Example 2

[0110] The weight difference of the shell entering battery cell assembly was 150 g, the battery to be treated was charged by using 400 A current, the battery to be treated was formed by using 30 A current, and the battery to be treated was divided into containers by using 80 A current. The capacity of the secondary battery finally obtained was 318.5 Ah. Among them, the difference between Example 2 and Example 1 was that small current formation and small current division were used. The difference between Example 2 and Comparative Example 1 was that large current charging before formation, small current formation and small current division were used.

[0111] Comparative Example 2

[0112] The weight difference of the shell entering battery cell assembly was 300 g, the battery to be treated was formed by using 80 A current, and the battery to be treated was divided into containers by using 200 A current. The capacity of the secondary battery finally obtained was 317 Ah.

[0113] Example 3

[0114] The weight difference of the shell entering battery cell assembly was 300 g, the battery to be treated was charged by using 400 A current, the battery to be treated was formed by using 30 A current, and the battery to be treated was divided into containers by using 80 A current. The capacity of the secondary battery finally obtained was 317.5 Ah. Among them, the difference between Example 3 and Comparative Example 2 was that large current charging before formation, small current formation and small current division were used.

[0115] Example 4

[0116] The weight difference of the shell entering battery cell assembly was 300 g, the battery to be treated was charged by using 400 A current, the battery to be treated was formed by using 30 A current, the battery to be treated was formed by using 2-300 A current, and the battery to be treated was divided into containers by using 80 A current. The capacity of the secondary battery finally obtained was 318 Ah. Among them, the difference between Example 4 and Example 3 was that the electrochemical depolarization treatment was used.

[0117] The comparison results of the final example and the comparative example are shown in Table 1:

[0118] Table 1. Comparison results of examples and comparative examples

[0119]

[0120] As shown in Table 1, by using large current charging before formation to strengthen infiltration, the capacity of the battery cell can be increased by 0.2 Ah; by using small current formation and small current division, the capacity of the battery cell can be increased by 0.3 Ah. By adjusting the load before division to stabilize SEI, the capacity of the battery cell can be increased by 0.5 Ah.

[0121] In order to enable a person skilled in the art to more clearly understand the technical solutions of the present application, the implementation process of the preparation method of the secondary battery of the present application will be described in detail below in conjunction with specific embodiments.

[0122] The present embodiment relates to a specific preparation method of a secondary battery, as shown in the following steps: Figure 2 As shown in the following steps, first, the weight difference of the to-be-housed battery assembly is determined, in the case of weight difference ≤ 100g, no pre-formation charging large current treatment is adopted, only normal formation and normal capacity distribution treatment are adopted, and then capacity detection is performed; in the case of 100 < weight difference ≤ 200g, pre-formation charging large current is adopted to strengthen infiltration, and small current formation and small current capacity distribution treatment are adopted, and then it is determined whether the capacity meets the capacity threshold, in the case of not meeting, the above predetermined processing steps are repeated; in the case of 200 < weight difference ≤ 500g, pre-formation charging large current is adopted to strengthen infiltration, small current formation and small current capacity distribution treatment are adopted, and load adjustment before capacity distribution is adopted to stabilize SEI, and then it is determined whether the capacity meets the capacity threshold, in the case of not meeting, the above predetermined processing steps are repeated.

[0123] According to some embodiments of the present application, another aspect of the present embodiment provides a secondary battery prepared by any one of the above preparation methods of a secondary battery.

[0124] The above-mentioned secondary battery is treated by large current charging, which significantly improves the infiltration effect of the battery, ensures that the electrolyte can fully penetrate into the pores of the electrode material, improves the utilization rate of active material, and thus improves the capacity of the battery. And by using small current formation, small current capacity distribution and depolarization, the ohmic polarization of the battery is smaller, which helps to form a more uniform and stable SEI film, reduces the ohmic polarization and electrochemical polarization of the battery in subsequent use, and improves the cycle stability and service life of the battery.

[0125] According to some embodiments of the present application, another aspect of the present embodiment provides an energy storage system comprising a plurality of the above-mentioned secondary batteries.

[0126] The above-mentioned secondary battery of the energy storage system is treated by large current charging, which significantly improves the infiltration effect of the battery, ensures that the electrolyte can fully penetrate into the pores of the electrode material, improves the utilization rate of active material, and thus improves the capacity of the battery. And by using small current formation, small current capacity distribution and depolarization, the ohmic polarization of the battery is smaller, which helps to form a more uniform and stable SEI film, reduces the ohmic polarization and electrochemical polarization of the battery in subsequent use, and improves the cycle stability and service life of the battery.

[0127] From the above description, it can be seen that the above-mentioned embodiments of the application achieve the following technical effects:

[0128] 1) The preparation method of the secondary battery of the application adopts different charging, formation, charge-discharge and capacity grading treatment in the case of different weight differences. In the case where the weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, the weight difference is larger, indicating that the battery may face the risk of lower capacity. The battery assembly is sequentially subjected to first charging treatment, second formation treatment and second capacity grading treatment. The current of the second formation treatment is lower than that of the first formation treatment, and the current of the second capacity grading treatment is also lower than that of the first capacity grading treatment. According to Ohm's law, the smaller the formation current and the capacity grading current, the smaller the Ohmic polarization. The charging can be completed at a lower voltage, reducing loss and increasing charging efficiency. In the same time, the charging is more, so the capacity can be increased. In the case where the weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, the weight difference is larger, indicating that the battery may face the risk of lower capacity. The battery assembly is sequentially subjected to second charging treatment, third formation treatment, depolarization treatment and third capacity grading treatment. The current of the third formation treatment is lower than that of the first formation treatment, and the current of the second capacity grading treatment is also lower than that of the first capacity grading treatment. Based on the same reasons as above, the capacity can be increased. In addition, the depolarization treatment can further remove the electrochemical polarization, achieve the purpose of adjusting the state of charge and stabilizing SEI, and make the electrochemical polarization of the battery smaller, the point of the electrode active material more fully chemically react, further improve the charging capacity, improve the capacity grading capacity of the battery, thereby improve the capacity grading capacity rate, and ensure the consistency of the battery.

[0129] Those skilled in the art can understand that the above-mentioned embodiments are specific embodiments for implementing the application, and in actual application, various changes can be made in form and detail without departing from the spirit and scope of the application. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the application, therefore the protection scope of the application should be limited by the scope defined in the claims.

Claims

1. A method for preparing a secondary battery, characterized in that: include: An acquisition step of acquiring a weight difference of the battery cell assembly to be placed in the shell, wherein the weight difference is an absolute value of a difference between an actual weight of the battery cell assembly to be placed in the shell and a target weight of the battery cell assembly to be placed in the shell; In a first determination step, the battery cell assembly to be shelled is subjected to a shelling process and a liquid injection process to obtain a battery to be processed, and whether the weight difference is greater than a first difference threshold is determined; A first processing step, if the weight difference is less than or equal to the first difference threshold, sequentially performing a first formation treatment and a first capacity separation treatment on the battery to be processed to obtain a battery to be tested; a second determining step, if the weight difference is greater than the first difference threshold, determining whether the weight difference is greater than a second difference threshold; a second processing step, if the weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, sequentially performing a first charging process, a second formation process, and a second capacity division process on the battery to be processed to obtain the battery to be tested, wherein the charging current of the second formation process is less than the charging current of the first formation process, and the charging current of the second capacity division process is less than the charging current of the first capacity division process; a third determining step, if the weight difference is greater than the second difference threshold, determining whether the weight difference is greater than a third difference threshold; a third processing step, if the weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, sequentially performing a second charging process, a third formation process, a depolarization process, and a third capacity division process on the battery to be processed to obtain the battery to be tested, wherein the current of the third formation process is less than the current of the first formation process, and the current of the third capacity division process is less than the current of the first capacity division process; The detection step detects the capacity of the battery to be tested, and if the capacity is greater than or equal to a capacity threshold, determines that the secondary battery is offline.

2. The method for preparing a secondary battery according to claim 1, wherein: If the weight difference is less than or equal to the first difference threshold, performing a first formation treatment and a first capacity separation treatment on the battery to be processed in sequence to obtain a battery to be tested, including: Charging the battery to be processed with a first current for a first preset time to achieve the first formation treatment, wherein the first current is 40 to 120 A and the first preset time is 2 to 4 hours; The battery to be processed is charged with a second current for a second preset time, and the battery to be processed is discharged to achieve the first capacity division process, wherein the second current is 100-300A and the second preset time is 4-6h.

3. The method for preparing a secondary battery according to claim 1, wherein: If the weight difference is greater than the first difference threshold and less than or equal to the second difference threshold, sequentially performing a first charging process, a second formation process, and a second capacity separation process on the battery to be processed to obtain the battery to be tested, including: The battery to be processed is charged with a third current for a third preset time until the state of charge of the battery to be processed reaches 1% to 2%, thereby achieving the first charging process, wherein the third current is 300 to 900 A. The third preset duration is 36 seconds to 6 minutes; charging the battery to be processed with a fourth current for a fourth preset time until the state of charge of the battery to be processed reaches 30-36%, thereby performing the second formation treatment, wherein the fourth current is 20-60A and the fourth preset time is 4-6h; charging the battery to be processed with a fifth current for a fifth preset time period until the first preset voltage is reached, The battery to be processed is discharged to achieve the second capacity division process, wherein the fifth current is 60 to 180 A, the fifth preset time is 6 to 10 hours, and the first preset voltage is 3.5 to 3.7 V.

4. The method for preparing a secondary battery according to claim 1, wherein: If the weight difference is greater than the second difference threshold and less than or equal to the third difference threshold, the battery to be processed is sequentially subjected to a second charging process, a third formation process, a depolarization process, and a third capacity separation process, including: a first charging step of charging the battery to be processed with a sixth current and continuously for a sixth preset time until the state of charge of the battery to be processed reaches 1% to 2%, thereby implementing the second charging process, wherein the sixth current is 300 to 900 A and the sixth preset time is 36 seconds to 6 minutes; a second charging step of charging the battery to be processed with a seventh current and continuously for a seventh preset time until the state of charge reaches 30-36% to achieve the third formation treatment, wherein the seventh current is 20-60A and the seventh preset time is 4-6h; a fourth treatment step of performing at least a plurality of discharge treatments on the battery to be treated, wherein the current of the plurality of discharge treatments is successively reduced until a second preset voltage is reached, wherein the current of the discharge treatment is 2 to 300 A and the second preset voltage is 1.8 to 2.1 V; a third charging step of charging the battery to be processed until the voltage of the battery to be processed reaches a third preset voltage, wherein the third preset voltage is 2.8 to 3.1 V; Repeating the steps to determine whether the voltage of the battery to be processed is maintained at the third preset voltage without changing, and if the voltage of the battery to be processed is greater than the third preset voltage, repeating the fourth processing step at least once until the voltage of the battery to be processed is maintained at the third preset voltage without changing, and charging the battery to be processed to 100% of the state of charge; The fourth charging step is to charge the battery to be processed with an eighth current and continue for an eighth preset time to achieve the third capacity division treatment, wherein the eighth current is 60 to 180 A and the eighth preset time is 6 to 10 hours.

5. The method for preparing a secondary battery according to claim 4, wherein: The fourth processing step includes one of the following: Performing multiple consecutive discharge treatments on the battery to be treated, wherein the current of each of the multiple discharge treatments is reduced sequentially until a second preset voltage is reached; The battery to be processed is subjected to the discharge process and the charge process alternately for multiple times, and the current of the multiple discharge processes is reduced in sequence until the second preset voltage is reached.

6. The method for preparing a secondary battery according to claim 5, wherein: Performing multiple continuous discharge processes on the battery to be tested, wherein the current of each of the multiple discharge processes is sequentially reduced until a second preset voltage is reached, comprising: discharging the battery to be processed using a ninth current until a fourth preset voltage is reached, wherein the ninth current is 80 to 360 A and the fourth preset voltage is 2 to 3 V; discharging the battery to be processed using a tenth current until a fifth preset voltage is reached, wherein the tenth current is 4 to 60 A, and the fifth preset voltage is 1.8 to 2.1 V; The battery to be processed is discharged using an eleventh current until the second preset voltage is reached, wherein the eleventh current is 1-6A.

7. The method for preparing a secondary battery according to any one of claims 1 to 6, characterized in that: The first difference threshold is 90-110g, the second difference threshold is 190-210g, and the third difference threshold is 490-510g.

8. The method for preparing a secondary battery according to any one of claims 1 to 6, characterized in that: The current of the third formation process is smaller than the current of the second formation process, and the current of the third capacity division process is smaller than the current of the second capacity division process.

9. The method for preparing a secondary battery according to any one of claims 1 to 5, characterized in that: After detecting the capacity of the battery to be tested, the method further includes: When the capacity is less than the capacity threshold, the predetermined processing step is repeated, and during the repetition, the first predetermined processing in the predetermined processing step is updated to the second predetermined processing in the predetermined processing step in the previous repetition process, wherein the charging current of the first predetermined processing is less than the current of the second predetermined processing, until the capacity is greater than or equal to the capacity threshold, wherein the predetermined processing step includes one of the first processing step, the second processing step and the third processing step. When the predetermined processing step is the first processing step, the first predetermined processing and the second predetermined processing respectively include the first formation processing and the first capacity division processing. When the predetermined processing step is the second processing step, the first predetermined processing and the second predetermined processing respectively include the first charging processing, the second formation processing and the second capacity division processing. When the predetermined processing step is the third processing step, the first predetermined processing and the second predetermined processing respectively include the second charging processing, the third formation processing, the depolarization processing and the third capacity division processing.

10. A secondary battery, characterized in that: The secondary battery is prepared by the method for preparing a secondary battery according to any one of claims 1 to 9.

11. An energy storage system, characterized in that: The invention comprises a plurality of secondary batteries according to claim 10.

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