Secondary battery, method for preparing same, energy storage system, and power supply device

Abstract

The present application provides a secondary battery, a preparation method thereof, an energy storage system, and a power supply device, which are beneficial to solving the influence caused by gas generation of the lithium supplement agent. The method includes: providing an electric core, wherein the lithium supplement agent of the electric core is configured with a first charging platform and a second charging platform; charging the electric core with a first current to form a SEI film; performing a first formation exhaust treatment, after charging the electric core to a preset cut-off voltage with a second current, performing at least one breathing exhaust treatment on the electric core; performing an activation treatment, charging the electric core to the minimum value of the first charging platform with the second current; performing a second formation exhaust treatment, after charging the electric core to the maximum value of the first charging platform with a third current, performing at least one breathing exhaust treatment on the electric core; performing a third formation exhaust treatment, during the period of charging the electric core to the maximum value of the second charging platform with the first current, performing at least one breathing exhaust treatment on the electric core; charging the electric core to a termination voltage with the third current.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly to a secondary battery, a preparation method thereof, an energy storage system, and a power supply device. Background Art

[0002] During the first charging process of a lithium-ion battery, the organic electrolyte will be reductively decomposed on the surface of the negative electrode such as graphite to form a solid electrolyte interface (SEI) membrane, permanently consuming a large amount of lithium from the positive electrode, resulting in a low Coulomb efficiency (ICE) in the first cycle and reducing the capacity and energy density of the lithium-ion battery. In an energy storage system, from the analysis of the long-cycle capacity decay failure, the loss of active lithium is an important factor leading to a short cycle life. Summary of the Invention

[0003] Embodiments of this application provide a secondary battery, a preparation method thereof, an energy storage system, and a power supply device, which solve the influence caused by gas generation of the lithium supplement agent in view of the activation characteristics of the lithium supplement agent.

[0004] According to some embodiments of this application, on the one hand, a preparation method of a secondary battery provided by an embodiment of this application includes: providing an electric core, wherein the electric core includes a lithium supplement agent, the lithium supplement agent is configured with a first charging platform and a second charging platform, the first charging platform corresponds to the voltage range when the lithium supplement agent first reaches the decomposition platform, the second charging platform is the voltage range when the lithium supplement agent second reaches the decomposition platform, and the minimum value of the second charging platform is greater than or equal to the maximum value of the first charging platform; charging the electric core with a first current to form an SEI membrane; performing a first formation exhaust treatment, after charging the electric core to a preset cut-off voltage with a second current, performing at least one breathing exhaust treatment on the electric core, and the breathing exhaust treatment includes raising the internal pressure of the electric core to a first positive pressure and then lowering it to a first negative pressure, and the preset cut-off voltage is less than the minimum value of the first charging platform; performing an activation treatment, continuing to charge the electric core to the minimum value of the first charging platform with the second current; performing a second formation exhaust treatment, after charging the electric core to the maximum value of the first charging platform with a third current, performing at least one breathing exhaust treatment on the electric core; performing a third formation exhaust treatment, during the process of charging the electric core to the maximum value of the second charging platform with the first current, performing at least one breathing exhaust treatment on the electric core; charging the electric core to a termination voltage with the third current.

[0005] In some embodiments, in the step of the first formation exhaust treatment, the number of times of the breathing exhaust treatment is the first number; in the step of the second formation exhaust treatment, the number of times of the breathing exhaust treatment is the second number; in the step of the third formation exhaust treatment, the number of times of the breathing exhaust treatment is the third number; the third number is greater than the first number, and / or, the third number is greater than the second number.

[0006] In some embodiments, the ratio of the third number to the second number is a first ratio; the gas generation amount of the lithium supplement agent at the first charging platform is a first gas generation amount; the gas generation amount of the lithium supplement agent at the second charging platform is a second gas generation amount; the ratio of the second gas generation amount to the first gas generation amount is a second ratio; the first ratio is greater than or equal to the second ratio.

[0007] In some embodiments, the difference between the minimum value of the first charging platform and the preset cut-off voltage is greater than 0 and less than or equal to 0.5.

[0008] In some embodiments, in the step of forming the SEI film, the internal pressure of the battery cell is an initial negative pressure; in the step of performing the activation treatment, the internal pressure of the battery cell is a second negative pressure, and the absolute value of the second negative pressure is less than the absolute value of the initial negative pressure.

[0009] In some embodiments, the initial negative pressure is -80 Kpa ± 20 Kpa; the second negative pressure is -40 Kpa ± 20 Kpa.

[0010] In some embodiments, the second current is greater than the first current.

[0011] In some embodiments, the third current is less than the second current and greater than the first current.

[0012] In some embodiments, the first current is 0.02C to 0.1C; the second current is 0.2C to 0.4C; the third current is 0.1C to 0.3C.

[0013] In some embodiments, the absolute value of the first positive pressure is less than the absolute value of the first negative pressure.

[0014] In some embodiments, the first positive pressure is 0 Kpa ± 20 Kpa; the first negative pressure is -80 Kpa ± 20 Kpa.

[0015] According to some embodiments of the present application, on the other hand, the present application provides a secondary battery, which is manufactured by using the manufacturing method of the secondary battery in the above embodiments.

[0016] According to some embodiments of the present application, on the other hand, the present application provides an energy storage system, including a plurality of secondary batteries as in the above embodiments.

[0017] According to some embodiments of the present application, on the other hand, the present application provides a power supply device, which includes the secondary battery in the above embodiments; or includes the energy storage system in the above embodiments.

[0018] The technical solutions provided by the embodiments of the present application at least have the following advantages:

[0019] In the method for preparing a secondary battery provided by an embodiment of the present application, the first charging process of the secondary battery is divided into multiple stages according to the charging platform corresponding to the decomposition platform of the lithium supplement agent, and breathing exhaust treatment is performed separately for different stages to ensure that the gas generated in each stage of the battery cell can be discharged in time, thereby ensuring that the electrolyte fully infiltrates the electrode sheet and avoiding interface defects caused by gas generation, such as black spots or lithium deposition. The voltage range corresponding to the first time the lithium supplement agent reaches the decomposition platform is taken as the first charging platform, and the voltage range corresponding to the second time the lithium supplement agent reaches the decomposition platform is taken as the second charging platform. Before the battery cell is charged to the first charging platform, an SEI film is first formed and the battery cell is charged to a preset cut-off voltage close to the minimum value of the first charging platform, and then at least one breathing exhaust treatment is performed on the battery cell to discharge the gas generated during the formation of the SEI film in the previous stage; in the stage from activation treatment to the completion of the first charging platform, at least one breathing exhaust treatment is performed on the battery cell to discharge the gas generated in the first charging platform stage; during the second charging platform, at least one exhaust treatment is performed, and the generated gas is discharged in real time as the second charging platform progresses. Since the gas generation conditions in different stages are different, dividing the first charging process of the secondary battery into multiple stages according to the first charging platform and the second charging platform can perform breathing exhaust treatment in a targeted manner in different stages, fully ensuring the smooth progress of each stage, and at the same time avoiding the influence caused by gas generation in each stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a proportional limitation; in order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the following-described drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a flowchart of the method for preparing a secondary battery provided by an embodiment of the present application;

[0022] Figure 2 It is a schematic diagram of electrolyte reflux provided by an embodiment of the present application;

[0023] Figure 3 It is a graph of the liquid level change trend of the electrolyte during the first charging process corresponding to battery cell 1;

[0024] Figure 4 It is a schematic diagram of the negative electrode interface of battery cell 1;

[0025] Figure 5Schematic diagram of the negative electrode interface of the battery cell 2. Detailed implementation manners

[0026] To solve the loss of active lithium, "pre-lithiation" technology can be adopted. Among many pre-lithiation technologies, adding a lithium supplement agent can compensate for the loss of active lithium. Moreover, the lithium supplement agent has a high compatibility with the existing production line, and has advantages such as relatively low cost and good economic benefits, becoming the most promising method for practical application. However, a series of gas generation problems will also be caused while adding a lithium supplement agent for lithium supplementation. The formation of the SEI film in the formation process and the bubbles generated during the activation of the lithium supplement agent will hinder the migration of lithium ions from the positive electrode to the negative electrode (in severe cases, there may be an electrolyte bridge break), and then black spots or lithium deposition problems will appear on the negative electrode charging interface, resulting in the deterioration of the battery cell performance.

[0027] However, the current conventional formation process flow cannot timely and fully discharge the gas generated by the activation of the lithium supplement agent, and it is necessary to perform targeted optimization according to the activation characteristics of the lithium supplement agent.

[0028] Taking lithium-rich lithium ferrate (Li5FeO4) as an example of the lithium supplement agent for secondary batteries, the release of active lithium by Li5FeO4 in the first cycle includes two decomposition platforms. The first decomposition platform is a two-phase reaction, and the reaction formula is Li5FeO4 → Li3FeO 3.5 +0.25O2 (gas) + 2Li + +2e - , in the first decomposition platform, Li5FeO4 is transformed into pseudo-cubic Li3FeO 3.5 , and the first charging platform corresponding to the first decomposition platform is generally at 3.5V - 3.8V; the second decomposition platform is a single-phase reaction, and the reaction formula is Li3FeO 3.5 →LiFeO2 + 0.75O2 (gas) + 2Li + +2e - , in the second decomposition platform, pseudo-cubic Li3FeO 3.5 is transformed into another pseudo-cubic LiFeO2, and the second charging platform corresponding to the second decomposition platform is generally at 3.8V - 4.1V. Oxygen will be generated in both stages of Li5FeO4. The oxygen will cause some components in the electrolyte to undergo oxidative decomposition to generate carbon dioxide and water, thereby triggering a series of gas generation reactions, releasing a large amount of carbon dioxide and hydrogen, resulting in battery swelling and hindering the application of lithium-rich lithium ferrate as a lithium supplement agent for secondary batteries.

[0029] The embodiments of the present application provide a secondary battery, its preparation method, an energy storage system, and a power supply device, which solve the influence caused by gas generation of the lithium supplement agent according to the activation characteristics of the lithium supplement agent.

[0030] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order or primary-secondary relationship of the indicated technical features.

[0031] In the description of the embodiments of the present application, "a plurality of" means more than two, unless otherwise specifically and clearly defined.

[0032] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments may be included in at least one embodiment of the present application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: the existence of A, the simultaneous existence of A and B, and the existence of B. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0034] The following will elaborate on each embodiment of the present application in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that in each embodiment of the present application, many technical details are presented for the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0035] Figure 1 It is a flowchart of a method for preparing a secondary battery provided for the embodiments of the present application.

[0036] Reference Figure 1 , the method for preparing a secondary battery provided by the embodiments of the present application includes:

[0037] S101. Provide an electric core, the electric core includes a lithium supplement agent, the lithium supplement agent is configured with a first charging platform and a second charging platform. The first charging platform corresponds to the voltage range when the lithium supplement agent first reaches the decomposition platform, and the second charging platform is the voltage range when the lithium supplement agent second reaches the decomposition platform. The minimum value of the second charging platform is greater than or equal to the maximum value of the first charging platform.

[0038] The lithium supplement agent includes at least one of Li5FeO4, Li2NiO2 or Li2O2.

[0039] The lithium supplement reaching the decomposition plateau refers to different stages of the decomposition of the lithium supplement. Taking Li5FeO4 as an example, the process of Li5FeO4 transforming into pseudo-cubic Li3FeO 3.5 is the first decomposition plateau; the process of pseudo-cubic Li3FeO 3.5 transforming into another pseudo-cubic LiFeO2 is the second decomposition plateau. Correspondingly, the first charging plateau is 3.5V - 3.8V; the second charging plateau is 3.8V - 4.1V.

[0040] The ranges of the first charging plateau and the second charging plateau are related to the type of the lithium supplement. Corresponding first charging plateau and second charging plateau can be obtained according to the decomposition stages of different lithium supplements.

[0041] In some embodiments, the battery cell includes a housing, and a positive electrode sheet, a negative electrode sheet and a separator located inside the housing. The separator is disposed between the positive electrode sheet and the negative electrode sheet. There is also electrolyte inside the housing, and the positive electrode sheet, the negative electrode sheet and the separator are immersed in the electrolyte. The lithium supplement can be disposed in the positive electrode material layer of the positive electrode sheet, or in the negative electrode material layer of the negative electrode sheet, or in the material layer of the separator, or in the electrolyte. The embodiments of the present application do not limit the position of the lithium supplement in the battery cell.

[0042] S102: Charge the battery cell with a first current to form a SEI film.

[0043] In the step of forming the SEI film, the internal pressure of the battery cell is an initial negative pressure, and the initial negative pressure is -80Kpa ± 20Kpa, such as -100Kpa~-90Kpa, -90Kpa~-80Kpa, -80Kpa~-70Kpa or -70Kpa~-60Kpa. Specifically, it can be -100Kpa, -95Kpa, -90Kpa, -85Kpa, -80Kpa, -75Kpa, -70Kpa, -65Kpa or -60Kpa. The negative pressure is beneficial to reducing the bubbles in the electrolyte, reducing the occurrence of side reactions, and avoiding the interference to the formation of the SEI film caused by the decomposition and gas generation of the electrolyte. In addition, the negative pressure can also enhance the contact between the electrode and the electrolyte, promote ion transport, and thus improve the quality and stability of the SEI film.

[0044] The first current is 0.02C~0.1C, such as 0.02C~0.05C, 0.05C~0.08C or 0.08C~0.1C. Specifically, it can be 0.02C, 0.04C, 0.06C, 0.08C or 0.1C. When the current density is relatively large, it will accelerate the formation of the SEI film, but too large current density may cause the SEI film to be uneven or too thick, affecting the battery performance. A lower current density is beneficial to forming a SEI film with higher uniformity and density.

[0045] In the stage of forming the SEI film, the battery cell is charged to 2.0V to 2.2V, such as 2.0V to 2.03V, 2.03V to 2.05V, 2.05V to 2.08V, 2.08 to 2.1V, 2.1V to 2.14V, 2.14V to 2.16V or 2.16V to 2.2V, and specifically can be 2.0V, 2.05V, 2.1V, 2.16V or 2.2V.

[0046] S103: Perform the first full charge and exhaust treatment. After charging the battery cell to the preset cut-off voltage with the second current, perform at least one breathing exhaust treatment on the battery cell. The breathing exhaust treatment includes raising the internal pressure of the battery cell to the first positive pressure and then lowering it to the first negative pressure. The preset cut-off voltage is less than the minimum value of the first charge platform.

[0047] That is to say, before the battery cell reaches the first charge platform, at least one breathing exhaust treatment is performed on the battery cell to remove the gas generated before reaching the first charge platform, such as the gas generated during the formation of the SEI film. Thus, it is possible to avoid the impact between the gas accumulated in the early stage and the gas released by the decomposition of the subsequent lithium supplement agent at the charge platform, resulting in the problem of insufficient local electrolyte.

[0048] Figure 2 It is a schematic diagram of electrolyte reflux provided by an embodiment of the present application.

[0049] Reference Figure 2 , before the breathing exhaust treatment, a large amount of gas occupies the volume inside the battery cell, resulting in the inability of lithium ions to move through the electrolyte; during the breathing exhaust treatment, the internal pressure of the battery cell rises to the first positive pressure and then drops to the first negative pressure. Thus, first, the negative pressure is reduced to promote the reflux of the electrolyte to fill the local electrolyte deficiency caused by excessive negative pressure or air flow impact. Then, after dropping to the first negative pressure again, the generated gas is discharged, and the electrolyte fills the battery cell again to construct a lithium ion migration path, thereby avoiding problems such as interface black spots or lithium deposition caused by poor lithium intercalation.

[0050] In some embodiments, the second current is greater than the first current. After the formation of the SEI film, increasing the current density can accelerate the charging rate, improve the power performance of the battery cell to meet the requirements of high-power applications, and a larger current density can shorten the full charge time, improve production efficiency, and reduce the production cost of the battery cell.

[0051] The second current is 0.2C to 0.4C, such as 0.2C to 0.23C, 0.23C to 0.25C, 0.25C to 0.3C, 0.3C to 0.36C or 0.36C to 0.4C, and specifically can be 0.2C, 0.24C, 0.26C, 0.28C, 0.3C, 0.33C, 0.36C, 0.39C or 0.4C.

[0052] In some embodiments, the absolute value of the first positive pressure is less than the absolute value of the first negative pressure. The first positive pressure is used to break the vacuum state inside the battery cell to promote the movement of gas, which is beneficial to gas discharge. The fact that the absolute value of the first positive pressure is less than the absolute value of the first negative pressure can avoid the problem that the air pressure difference between the first positive pressure and the first negative pressure is too large, resulting in abnormal battery cell formation or bulging.

[0053] The first positive pressure is 0±20Kpa, for example, -20Kpa~-10Kpa, -10Kpa~0Kpa, 0Kpa~10Kpa, 10Kpa~20Kpa. Specifically, it can be -20Kpa, -15Kpa, -10Kpa, -5Kpa, 0Kpa, 5Kpa, 10Kpa, 15Kpa or 20Kpa. It should be noted that the first positive pressure adjusts the air pressure in the positive pressure direction relative to the initial negative pressure, so that the degree of vacuum of the first positive pressure is smaller than that of the initial negative pressure. Therefore, the pressure value of the first negative pressure can still be negative.

[0054] In some embodiments, the absolute value of the first negative pressure is greater than the absolute value of the initial negative pressure. That is to say, the degree of vacuum of the first negative pressure is greater than that of the initial negative pressure, so that it is beneficial to completely discharge the gas generated before reaching the first charging platform.

[0055] The first negative pressure is -80Kpa±20Kpa, for example, -100Kpa~-90Kpa, -90Kpa~-80Kpa, -80Kpa~-70Kpa, -70Kpa~-60Kpa. Specifically, it can be -100Kpa, -95Kpa, -90Kpa, -85Kpa, -80Kpa, -75Kpa, -70Kpa, -65Kpa or -60Kpa.

[0056] In some embodiments, the difference between the minimum value of the first charging platform and the preset cut-off voltage is greater than 0 and less than or equal to 0.5, that is, the gap between the cut-off voltage and the minimum value of the first charging platform is small, preparing for entering the first charging platform subsequently.

[0057] The difference between the minimum value of the first charging platform and the preset cut-off voltage can specifically be 0.1, 0.2, 0.3, 0.4 or 0.5.

[0058] S104: Perform an activation process, and continue to charge the battery cell to the minimum value of the first charging platform using the second current.

[0059] In some embodiments, during the step of activation treatment, the internal pressure of the battery cell is a second negative pressure, and the absolute value of the second negative pressure is less than the absolute value of the initial negative pressure. That is to say, the degree of vacuum of the second negative pressure is lower than that of the initial negative pressure. In this way, it can provide an appropriate buffer for the gas generation of the subsequent lithium supplement agent during the first charging plateau process, so as to avoid the problem of insufficient local electrolyte caused by the air flow impact between the excessive negative pressure and a large amount of gas, and further avoid the problems of interface black spots or lithium deposition caused by poor lithium intercalation.

[0060] The second negative pressure is -40Kpa ± 20Kpa, for example, -60Kpa to -50Kpa, -50Kpa to -40Kpa, -40Kpa to -30Kpa or -30Kpa to -20Kpa. Specifically, it can be -60Kpa, -55Kpa, -50Kpa, -45Kpa, -40Kpa, -35Kpa, -30Kpa, -25Kpa or -20Kpa.

[0061] S105: Perform the second formation exhaust treatment. After charging the battery cell to the maximum value of the first charging plateau with a third current, perform at least one breathing exhaust treatment on the battery cell. That is to say, after the battery cell is charged to complete the first charging plateau, the gas generated during the first charging plateau stage is discharged through the breathing exhaust treatment.

[0062] In some embodiments, the third current is less than the second current and greater than the first current. That is, a moderate charging rate is used to pass through the stage of the first charging plateau. Since a too high charging rate will lead to a relatively fast gas generation rate, which will cause the problem of air flow impact caused by a large amount of gas, and a too low charging rate will lead to a decrease in charging efficiency and production efficiency. Therefore, the third current being between the first current and the second current can be beneficial for the battery cell to smoothly pass through the second charging plateau.

[0063] The third current is 0.1C to 0.3C, for example, 0.1V to 0.15V, 0.15V to 0.2V, 0.2V to 0.25V or 0.25V to 0.3V. Specifically, it can be 0.1V, 0.13V, 0.16V, 0.18V, 0.2V, 0.22V, 0.25V, 0.28V or 0.3V.

[0064] In some embodiments, during the process of performing the second formation exhaust treatment, the internal pressure of the battery cell is the second negative pressure.

[0065] S106: Conduct the third formation exhaust treatment. During the process of charging the battery cell to the maximum value of the second charging platform using the first current, perform at least one breathing exhaust treatment on the battery cell. That is to say, during the second charging platform stage, perform at least one breathing exhaust treatment on the battery cell simultaneously. Since the gas generation amount of the lithium supplement agent is relatively large during the second charging platform stage, it is necessary to perform breathing exhaust treatment while charging. During the second charging platform stage, using a relatively small first current can slow down the gas generation rate of the lithium supplement agent to avoid the problem that a large amount of gas accumulates in a short time and the gas stays in the battery cell and cannot be discharged.

[0066] In some embodiments, in the step of the first formation exhaust treatment, the number of breathing exhaust treatments is the first number; in the step of the second formation exhaust treatment, the number of breathing exhaust treatments is the second number; in the step of the third formation exhaust treatment, the number of breathing exhaust treatments is the third number; the third number is greater than the first number, and / or, the third number is greater than the second number. Since the gas generation amount of the lithium supplement agent is relatively large during the second charging platform stage, more exhaust treatments are required during the second charging platform stage. In addition, a relatively large third number can also help to discharge the gas that was not discharged in time during the first formation exhaust treatment or the second formation exhaust treatment.

[0067] The third number being greater than the first number and the third number being greater than the second number means that the third number is greater than the larger one of the first number and the second number. For example, if the first number is 1 and the second number is 2, then the third number is greater than 2. The third number being greater than the first number or the third number being greater than the second number means that regardless of which one of the first number and the second number is larger, the third number can be only greater than the first number or only greater than the second number. For example, if the first number is 1 and the second number is 2, the third number can be greater than or equal to 2.

[0068] In some embodiments, the ratio of the third number to the second number is the first ratio; the gas generation amount of the lithium supplement agent at the first charging platform is the first gas generation amount; the gas generation amount of the lithium supplement agent at the second charging platform is the second gas generation amount; the ratio of the second gas generation amount to the first gas generation amount is the second ratio; the first ratio is greater than or equal to the third ratio. That is to say, set the third number according to the relationship between the gas generation amounts at the first charging platform and the second charging platform. Taking Li5FeO4 as an example, theoretically, the gas generation amount in the second charging platform stage is 3 times that in the first charging platform stage. However, due to the occurrence of other side reactions, the actual gas generation amount in the second charging platform stage may be as high as about 7 to 10 times that in the first charging platform stage. In this way, setting more times for the third number according to the ratio of the second gas generation amount to the first gas generation amount can not only help to discharge the gas generated in the second charging platform stage, but also help to discharge the gas generated by other side reactions.

[0069] In some embodiments, during the third formation exhaust treatment, the internal pressure of the battery cell is a second negative pressure.

[0070] S107: Charge the battery cell to the cut-off voltage using a third current.

[0071] In some embodiments, during the process of charging the battery cell to the cut-off voltage using a third current, the internal pressure of the battery cell is a first negative pressure. At this time, the formation process of the battery cell is approaching the end stage, and the gas generation in the battery cell is significantly reduced. Further reducing the internal pressure of the battery cell to the first negative pressure with a higher degree of vacuum can enable the electrolyte to be fully filled in the battery cell.

[0072] In some embodiments, the difference between the cut-off voltage and the maximum value of the second charging plateau is greater than 0 and less than or equal to 0.5. It can be 0.5, for example, specifically it can be 0.1, 0.2, 0.3, 0.4 or 0.5.

[0073] In the method for preparing a secondary battery provided by the embodiments of the present application, the first charging process of the secondary battery is divided into multiple stages according to the charging plateau corresponding to the decomposition plateau of the lithium supplement agent. Respiratory exhaust treatment is carried out separately for different stages to ensure that the gas generated by the battery cell in each stage can be discharged in time, thereby ensuring that the electrolyte fully infiltrates the electrode sheet and avoiding interface defects caused by gas generation, such as black spots or lithium deposition and other problems. Taking the voltage range corresponding to the first time the lithium supplement agent reaches the decomposition plateau as the first charging plateau, and the voltage range corresponding to the second time the lithium supplement agent reaches the decomposition plateau as the second charging plateau. Before the battery cell is charged to the first charging plateau, a SEI film is first formed and the battery cell is charged to a preset cut-off voltage close to the minimum value of the first charging plateau, and then at least one respiratory exhaust treatment is carried out on the battery cell to discharge the gas generated during the formation of the SEI film in the previous stage; during the stage from the activation treatment to the completion of the first charging plateau, at least one respiratory exhaust treatment is carried out on the battery cell to discharge the gas generated during the first charging plateau stage; during the second charging plateau, at least one exhaust treatment is carried out, and the gas generated is discharged in real time as the second charging plateau progresses. Since the gas generation conditions in different stages are different, dividing the first charging process of the secondary battery into multiple stages according to the first charging plateau and the second charging plateau can perform targeted respiratory exhaust treatment in different stages, fully guarantee the smooth progress of each stage, and at the same time avoid the influence caused by the gas generation in each stage.

[0074] Correspondingly, another embodiment of the present application further provides a secondary battery, which can be prepared by using the method for manufacturing a secondary battery provided in the above embodiments. The secondary battery includes a lithium iron phosphate battery, a lithium manganate battery, a lithium nickelate battery, a ternary lithium battery or a lithium iron manganese phosphate battery.

[0075] Correspondingly, another embodiment of the present application further provides an energy storage system, and the energy storage system includes multiple secondary batteries in the above embodiments.

[0076] Correspondingly, another embodiment of the present application further provides a power supply device, which includes the secondary battery in the above embodiment; or includes the energy storage system in the above embodiment.

[0077] The following are specific embodiments of the present application:

[0078] The electrolyte of the battery cell 1 includes Li5FeO4 as a lithium supplement agent. Correspondingly, the first charging platform is 3.5V to 3.8V; the second charging platform is 3.8V to 4.1V.

[0079] The following steps are adopted to perform the first charging on the battery cell 1:

[0080] 1. Charge the battery cell 1 with a current of 0.02C to 0.1C to 2.2V to form a SEI film, for a time of 2h to 3h, and the internal pressure of the battery cell 1 is -80Kpa ± 20Kpa;

[0081] 2. After charging the battery cell 1 to 3.3V with a current of 0.2C to 0.4C, perform a breathing exhaust treatment once, raise the internal pressure of the battery cell 1 to 0Kpa ± 20Kpa and then lower it to -80Kpa ± 20Kpa;

[0082] 3. Adjust the internal pressure of the battery cell 1 to -40Kpa ± 20Kpa, and continue to charge the battery cell 1 to 3.5V to 3.65V with a current of 0.2C to 0.4C;

[0083] 4. After charging the battery cell 1 to 3.8V with a current of 0.1C to 0.3C, perform a breathing exhaust treatment once, and then adjust the internal pressure of the battery cell 1 to -40Kpa ± 20Kpa;

[0084] 5. Charge the battery cell 1 to 4.1V with a current of 0.02C to 0.1C. During this process, perform three breathing exhaust treatments on the battery cell 1, and adjust the internal pressure of the battery cell 1 to -40Kpa ± 20Kpa after each breathing exhaust treatment;

[0085] 6. Adjust the internal pressure of the battery cell 1 to -80Kpa ± 20Kpa, and charge the battery cell 1 to 4.2V with a current of 0.1 to 0.3C.

[0086] Perform the first charging on the battery cell 2 which is the same as the battery cell 1, without performing breathing exhaust treatment during this period.

[0087] Figure 3 is the liquid level change trend diagram of the electrolyte during the first charging process corresponding to the battery cell 1; Figure 4 is the schematic diagram of the negative electrode interface of the battery cell 1; Figure 5 is the schematic diagram of the negative electrode interface of the battery cell 2.

[0088] According to Figure 3 It can be seen that during the charging of the battery cell 1 to the first charging platform, the electrolyte level has a slight upward trend; during the charging of the battery cell 1 to the second charging platform, the electrolyte level rises more significantly. After the end of the first charging platform, a breathing and exhaust treatment is carried out once to remove the gas generated in the previous stage, which can avoid the problem of the impact of a large amount of gas generated subsequently and the gas retained in the previous stage. During the second charging platform, three breathing and exhaust treatments are carried out, which can discharge the gas generated by the lithium supplement agent in real time during the second charging platform stage, so as to facilitate the stable progress of the second charging platform. Comparing Figure 4 and Figure 5 it can be found that Figure 4 compared with Figure 5 the black spots have been significantly improved. The black spots will cause problems of poor local lithium intercalation, significant loss of battery capacity (about more than 15%), and may also cause lithium deposition problems during subsequent cycling, resulting in a sharp decline in the capacity retention rate of the battery. The method for preparing a secondary battery provided by the embodiments of the present application performs multiple breathing and exhaust treatments during the first charging of the battery cell according to the activation characteristics of the lithium supplement agent, which can significantly reduce the impact of the gas generated by the lithium supplement agent on the negative electrode interface.

[0089] For different lithium supplement agents, it is necessary to distinguish different stages according to the characteristics of the lithium supplement agent, and adjust the charging current, air pressure and the number of breathing and exhaust treatments in the corresponding stages. For example, taking lithium trifluoromethanesulfonate in the battery cell as an example, the steps of its first charging are as follows:

[0090] 1. Charge the battery cell at a current of 0.05C to 0.1C to 1.8V to form a SEI film, for a time of 2h to 3h, and the internal pressure of the battery cell is -80Kpa ± 20Kpa;

[0091] 2. After charging the battery cell at a current of 0.05C to 0.1C to 2.0V, perform a breathing and exhaust treatment once, raise the internal pressure of the battery cell 1 to 0Kpa ± 20Kpa and then lower it to -80Kpa ± 20Kpa;

[0092] 3. Adjust the internal pressure of the battery cell to -40Kpa ± 20Kpa, and continue to charge the battery cell at a current of 0.05C to 0.1C to 2.5V, and perform 3 to 5 breathing and exhaust treatments during this period;

[0093] 4. Adjust the internal pressure of the battery cell to -20KPa to 0KPa, and charge the battery cell to 3.6V at a current of 0.2C to 0.5C;

[0094] 5. Charge the battery cell to 4.0V at a rate of increasing 0.1V every 10 minutes, and perform 5 to 8 breathing and exhaust treatments on the battery cell during the period from 3.8V to 4.0V;

[0095] 6. After charging the battery cell to 4.2V at a current of 0.1C to 0.3C, adjust the internal pressure of the battery cell to 0 KPa and let it stand for 2 to 4 hours.

[0096] Those of ordinary skill in the art can understand that the above embodiments are specific examples for implementing this application. In actual applications, various changes can be made in form and details without departing from the spirit and scope of this application. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of this application. Therefore, the protection scope of this application should be subject to the scope defined by the claims.

Claims

1. A method for preparing a secondary battery, characterized in that: include: A battery cell is provided, wherein the battery cell includes a lithium supplement agent, and the lithium supplement agent is configured with a first charging platform and a second charging platform, wherein the first charging platform corresponds to a voltage range corresponding to when the lithium supplement agent first reaches the decomposition platform, and the second charging platform corresponds to a voltage range corresponding to when the lithium supplement agent secondly reaches the decomposition platform, and a minimum value of the second charging platform is greater than or equal to a maximum value of the first charging platform; Charging the battery cell with a first current to form a SEI film, wherein during the step of forming the SEI film, the internal pressure of the battery cell is initially negative; Performing a first formation exhaust process, charging the battery cell to a preset cutoff voltage using a second current, and then performing at least one breathing exhaust process on the battery cell, wherein the breathing exhaust process includes increasing the internal pressure of the battery cell to a first positive pressure and then decreasing it to a first negative pressure, wherein the preset cutoff voltage is less than a minimum value of the first charging platform; performing an activation process, continuing to use the second current to charge the battery cell to the minimum value of the first charging platform, wherein during the activation process, the internal pressure of the battery cell is a second negative pressure, and the absolute value of the second negative pressure is less than the absolute value of the initial negative pressure; Performing a second formation exhaust treatment, after charging the battery cell to the maximum value of the first charging platform using a third current, performing the breathing exhaust treatment on the battery cell at least once; performing a third formation exhaust treatment, wherein the battery cell is charged to a maximum value of the second charging platform using the first current, and performing the breathing exhaust treatment on the battery cell at least once; The battery cell is charged to a termination voltage using the third current.

2. The method for preparing a secondary battery according to claim 1, wherein: In the step of the first formation and exhaust treatment, the number of times of the breathing and exhaust treatment is the first number; In the step of the second formation and exhaust treatment, the number of the breathing and exhaust treatment is the second number; In the step of the third formation and exhaust treatment, the number of times of the breathing and exhaust treatment is the third number; The third number is greater than the first number, and / or the third number is greater than the second number.

3. The method for preparing a secondary battery according to claim 2, wherein: The ratio of the third number to the second number is a first ratio; The gas production of the lithium supplement agent on the first charging platform is a first gas production; the gas production of the lithium supplement agent on the second charging platform is a second gas production; and the ratio of the second gas production to the first gas production is a second ratio; The first ratio is greater than or equal to the second ratio.

4. The method for preparing a secondary battery according to claim 1, wherein: A difference between the minimum value of the first charging platform and the preset cut-off voltage is greater than 0 and less than or equal to 0.

5.

5. The method for preparing a secondary battery according to claim 1, wherein: The initial negative pressure is -80Kpa±20Kpa; the second negative pressure is -40Kpa±20Kpa.

6. The method for preparing a secondary battery according to claim 1, wherein: The second current is greater than the first current.

7. The method for preparing a secondary battery according to claim 6, wherein: The third current is smaller than the second current and larger than the first current.

8. The method for preparing a secondary battery according to claim 7, wherein: The first current is 0.02C~0.1C; the second current is 0.2C~0.4C; and the third current is 0.1C~0.3C.

9. The method for preparing a secondary battery according to claim 1, wherein: An absolute value of the first positive pressure is smaller than an absolute value of the first negative pressure.

10. The method for preparing a secondary battery according to claim 9, wherein: The first positive pressure is 0Kpa±20Kpa; the first negative pressure is -80Kpa±20Kpa.

11. A secondary battery, characterized in that: The secondary battery is manufactured using the secondary battery manufacturing method according to any one of claims 1 to 10.

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

13. A power supply device, characterized in that: The power supply device includes the secondary battery according to claim 11; or includes the energy storage system according to claim 12.

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