Secondary battery and preparation method thereof, energy storage system and power supply equipment

Abstract

The invention provides a secondary battery and a preparation method thereof, an energy storage system and power supply equipment, which are beneficial to solving the influence caused by gas production of a lithium supplement agent. The method comprises the following steps: providing a battery cell, wherein a lithium supplement agent of the battery cell is configured with a first charging platform and a second charging platform; charging the battery cell by using a first current to form an SEI film; carrying out first formation exhaust treatment, and carrying out breathing exhaust treatment on the battery cell for at least one time after charging the battery cell to a preset cut-off voltage by adopting a second current; carrying out activation treatment, and charging the battery cell to the minimum value of the first charging platform by adopting a second current; second formation exhaust treatment is carried out, and after the battery cell is charged to the maximum value of the first charging platform through third current, breathing exhaust treatment is carried out on the battery cell at least once; carrying out third formation exhaust treatment, and carrying out breathing exhaust treatment on the battery cell for at least one time when the battery cell is charged to the maximum value of the second charging platform by adopting the first current; and charging the battery core to the final voltage by using a third current.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly relates 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 Coulombic efficiency (ICE) in the first cycle and reducing the capacity and energy density of the lithium-ion battery. In the energy storage system, from the analysis of the long-cycle capacity attenuation 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 is provided, including: providing 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, 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, 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 the 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 production of the lithium supplement agent at the first charging platform is a first gas production; the gas production of the lithium supplement agent at the second charging platform is a second gas production; 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.

[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 -80Kpa ± 20Kpa; the second negative pressure is -40Kpa ± 20Kpa.

[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 0Kpa ± 20Kpa; the first negative pressure is -80Kpa ± 20Kpa.

[0015] According to some embodiments of the present application, on the other hand, an embodiment of 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, an embodiment of 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, an embodiment of 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 solution provided by the embodiments of the present application has at least the following advantages: 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 and 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. The voltage range corresponding to the first time the lithium supplement agent reaches the decomposition platform is defined as the first charging platform, and the voltage range corresponding to the second time the lithium supplement agent reaches the decomposition platform is defined 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 and exhaust treatment is carried out on the battery cell to discharge the gas generated during the formation of the SEI film in the early stage; during the stage from the activation treatment to the completion of the first charging platform, at least one breathing and exhaust treatment is carried out on the battery cell to discharge the gas generated during the first charging platform stage; during the process of the second charging platform, at least one exhaust treatment is carried out, 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 carry out breathing and exhaust treatment in a targeted manner in different stages, fully ensuring the smooth progress of each stage and avoiding the influence caused by gas generation in each stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] One or more embodiments are illustrated by way of example in the accompanying drawings, which do not constitute a limitation to the embodiments unless otherwise stated. The figures in the drawings do not constitute a scale 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.

[0020] Figure 1 It is a flowchart of the method for preparing a secondary battery provided by an embodiment of the present application; Figure 2 It is a schematic diagram of electrolyte reflux provided by an embodiment of the present application; Figure 3 It is a graph showing the change trend of the liquid level of the electrolyte during the first charging process corresponding to battery cell 1; Figure 4 It is a schematic diagram of the negative electrode interface of battery cell 1; Figure 5 It is a schematic diagram of the negative electrode interface of battery cell 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] To address the loss of active lithium, "pre-lithiation" technology can be adopted. Among various pre-lithiation techniques, adding a lithium supplement can make up for the loss of active lithium. Moreover, the lithium supplement has a high compatibility with existing production lines, relatively low costs, good economic benefits, etc., making it the most promising method for practical application. However, adding a lithium supplement for lithium replenishment will also trigger a series of gas generation problems. The formation of the SEI film during the formation process and the bubbles generated during the activation of the lithium supplement will hinder the migration of lithium ions from the positive electrode to the negative electrode (in severe cases, there may be an electrolyte break), and then black spots or lithium deposition problems will appear at the negative electrode charging interface, resulting in the deterioration of the cell performance.

[0022] However, the current conventional formation process flow cannot timely and fully discharge the gas generated by the activation of the lithium supplement, and targeted optimization needs to be carried out according to the activation characteristics of the lithium supplement.

[0023] Taking lithium-rich lithium ferrite (Li 5 FeO 4 ) as an example of the lithium supplement for secondary batteries, Li 5 FeO 4 releases active lithium in the first cycle, including two decomposition platforms. The first decomposition platform is a two-phase reaction, and the reaction formula is Li 5 FeO 4 →Li 3 FeO 3.5 +0.25O 2 (gas)+2Li + +2e - . In the first decomposition platform, Li 5 FeO 4 is transformed into pseudo-cubic Li 3 FeO 3.5 . The first charging platform corresponding to the first decomposition platform is generally between 3.5V and 3.8V. The second decomposition platform is a single-phase reaction, and the reaction formula is Li 3 FeO 3.5 →LiFeO 2 +0.75O 2 (gas)+2Li + +2e - . In the second decomposition platform, pseudo-cubic Li 3 FeO 3.5 is transformed into another pseudo-cubic LiFeO 2 . The second charging platform corresponding to the second decomposition platform is generally between 3.8V and 4.1V. Oxygen is generated in both stages of Li 5 FeO 4 . The oxygen will cause some components in the electrolyte to oxidize and decompose 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 ferrite as a lithium supplement for secondary batteries.

[0024] An embodiment of the present application provides 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.

[0025] 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 indicating the quantity, specific order or primary-secondary relationship of the indicated technical features.

[0026] In the description of the embodiments of the present application, the meaning of "a plurality" is more than two, unless otherwise specifically defined.

[0027] Referring to "embodiment" herein means that a specific feature, structure or characteristic described in connection with the embodiment 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.

[0028] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there can be three relationships, for example, A and / or B, which can mean: there is A, there is both A and B at the same time, and there is B. In addition, the character " / " in this article generally indicates that the front and rear associated objects are an "or" relationship.

[0029] The embodiments of the present application will be described in detail below with reference to the drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are proposed 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 required to be protected by the present application can be implemented.

[0030] Figure 1 It is a flowchart of the preparation method of the secondary battery provided by the embodiment of the present application.

[0031] Refer to Figure 1 , the preparation method of the secondary battery provided by the embodiment of the present application includes: 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, 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.

[0032] The lithium supplement includes Li 5 FeO 4 、Li 2 NiO 2 or Li 2 O 2 or at least one of them.

[0033] The lithium supplement reaching the decomposition plateau refers to different stages of the lithium supplement decomposition. Taking Li 5 FeO 4 as an example, the process of Li 5 FeO 4 transforming into pseudo-cubic Li 3 FeO 3.5 is the first decomposition plateau; the process of pseudo-cubic Li 3 FeO 3.5 transforming into another pseudo-cubic LiFeO 2 is the second decomposition plateau. Correspondingly, the first charging plateau is 3.5V - 3.8V; the second charging plateau is 3.8V - 4.1V.

[0034] 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.

[0035] 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 an 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.

[0036] S102: Charge the battery cell with a first current to form a SEI film.

[0037] 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 of the electrolyte to generate gas. 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.

[0038] The first current is 0.02C to 0.1C, such as 0.02C to 0.05C, 0.05C to 0.08C, or 0.08C to 0.1C, and specifically can be 0.02C, 0.04C, 0.06C, 0.08C, or 0.1C. When the current density is relatively large, the formation of the SEI film will be accelerated, but an excessive 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 an SEI film with higher uniformity and density.

[0039] 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.

[0040] S103: Perform the first formation exhaust treatment. After charging the battery cell to the preset cut-off voltage using 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 charging platform.

[0041] That is to say, before the battery cell reaches the first charging platform, at least one breathing exhaust treatment is performed on the battery cell to remove the gas generated before reaching the first charging platform, such as the gas generated during the formation of the SEI film. In this way, 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 charging platform, causing the problem of insufficient local electrolyte.

[0042] Figure 2 This is a schematic diagram of electrolyte reflux provided by an embodiment of the present application.

[0043] 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 is raised to the first positive pressure and then lowered to the first negative pressure. In this way, 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. After that, when it is lowered to the first negative pressure again, the generated gas is discharged, and the electrolyte refills the battery cell to construct a lithium ion migration path, thereby avoiding problems such as interface black spots or lithium plating caused by poor lithium insertion.

[0044] In some embodiments, the second current is greater than the first current. After forming 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 formation time, improve production efficiency, and reduce the production cost of the battery cell.

[0045] 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.

[0046] 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, and thus is beneficial to gas discharge. The absolute value of the first positive pressure being less than the absolute value of the first negative pressure can avoid the problem of abnormal formation or bulging of the battery cell due to too large a pressure difference between the first positive pressure and the first negative pressure.

[0047] The first positive pressure is 0 ± 20 Kpa, such as -20 Kpa to -10 Kpa, -10 Kpa to 0 Kpa, 0 Kpa to 10 Kpa, 10 Kpa to 20 Kpa, and specifically can be -20 Kpa, -15 Kpa, -10 Kpa, -5 Kpa, 0 Kpa, 5 Kpa, 10 Kpa, 15 Kpa, or 20 Kpa. It should be noted that the first positive pressure is adjusted in the positive pressure direction relative to the initial negative pressure so that the vacuum degree of the first positive pressure is smaller relative to the initial negative pressure. Therefore, the pressure value of the first negative pressure can still be negative.

[0048] 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 vacuum degree of the first negative pressure is greater relative to the initial negative pressure, so that it is beneficial to thoroughly discharge the gas generated before reaching the first charging platform.

[0049] The first negative pressure is -80 Kpa ± 20 Kpa, such as -100 Kpa to -90 Kpa, -90 Kpa to -80 Kpa, -80 Kpa to -70 Kpa, -70 Kpa to -60 Kpa, and specifically can be -100 Kpa, -95 Kpa, -90 Kpa, -85 Kpa, -80 Kpa, -75 Kpa, -70 Kpa, -65 Kpa, or -60 Kpa.

[0050] 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, which prepares for entering the first charging platform subsequently.

[0051] 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.

[0052] 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.

[0053] In some embodiments, in the step of performing the activation process, the internal pressure of the battery cell is the 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 platform 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.

[0054] The second negative pressure is -40Kpa ± 20Kpa, such as -60Kpa~-50Kpa, -50Kpa~-40Kpa, -40Kpa~-30Kpa or -30Kpa~-20Kpa, and can specifically be -60Kpa, -55Kpa, -50Kpa, -45Kpa, -40Kpa, -35Kpa, -30Kpa, -25Kpa or -20Kpa.

[0055] S105: Perform a second formation exhaust process. After charging the battery cell to the maximum value of the first charging platform using the third current, perform at least one breathing exhaust process on the battery cell. That is to say, after the battery cell is charged to complete the first charging platform, the gas generated during the first charging platform stage is discharged through the breathing exhaust process.

[0056] 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 platform. Since too high a charging rate will lead to a faster gas generation rate, and thus cause the problem of air flow impact caused by a large amount of gas, while too low a charging rate will lead to a reduction 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 platform.

[0057] The third current is 0.1C to 0.3C, such as 0.1V to 0.15V, 0.15V to 0.2V, 0.2V to 0.25V or 0.25V to 0.3V, and specifically can be 0.1V, 0.13V, 0.16V, 0.18V, 0.2V, 0.22V, 0.25V, 0.28V or 0.3V.

[0058] In some embodiments, during the second formation exhaust treatment, the internal pressure of the battery cell is a second negative pressure.

[0059] S106: Perform a third formation exhaust treatment. During the period of charging the battery cell to the maximum value of the second charging platform using a 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, resulting in the gas staying in the battery cell and being unable to be discharged.

[0060] 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, the number of exhaust treatments required during the second charging platform stage is relatively large. 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.

[0061] The third number is greater than the first number and the third number is 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 is greater than the first number or the third number is 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.

[0062] In some embodiments, the ratio of the third number of times to the second number of times is the first ratio; the gas production of the lithium supplement agent at the first charging platform is the first gas production; the gas production of the lithium supplement agent at the second charging platform is the second gas production; the ratio of the second gas production to the first gas production is the second ratio; the first ratio is greater than or equal to the third ratio. That is to say, the third number of times is set according to the magnitude relationship of the gas production at the first charging platform and the second charging platform. Taking Li 5 FeO 4 as an example, theoretically, the gas production 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 gas production in the actual second charging platform stage may be as high as about 7 to 10 times that in the first charging platform stage. Thus, setting the third number of times more with reference to the ratio of the second gas production to the first gas production can not only facilitate the discharge of the gas generated in the second charging platform stage, but also facilitate the discharge of the gas generated by other side reactions.

[0063] In some embodiments, during the third formation exhaust treatment, the internal pressure of the battery cell is the second negative pressure.

[0064] S107: Charge the battery cell to the termination voltage using the third current.

[0065] In some embodiments, during the process of charging the battery cell to the termination voltage using the third current, the internal pressure of the battery cell is the first negative pressure. At this time, the formation process of the battery cell is approaching the end stage, and the gas production in the battery cell is greatly reduced. Reducing the internal pressure of the battery cell to the first negative pressure with a higher vacuum degree can make the electrolyte fully fill the battery cell.

[0066] In some embodiments, the difference between the termination voltage and the maximum value of the second charging platform is greater than 0 and less than or equal to 0.5. For example, it can specifically be 0.1, 0.2, 0.3, 0.4, or 0.5.

[0067] 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 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. The voltage range corresponding to the first time the lithium supplement agent reaches the decomposition platform is the first charging platform, and the voltage range corresponding to the second time the lithium supplement agent reaches the decomposition platform is 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 remove the gas generated during the formation of the SEI film in the early 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.

[0068] Correspondingly, another embodiment of the present application further provides a secondary battery, which can be prepared by using the manufacturing method of the secondary battery provided in the above embodiment. The secondary battery includes a lithium iron phosphate battery, a lithium manganese oxide battery, a lithium nickel oxide battery, a ternary lithium battery, or a lithium iron manganese phosphate battery.

[0069] Correspondingly, another embodiment of the present application further provides an energy storage system, which includes a plurality of secondary batteries in the above embodiments.

[0070] 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.

[0071] The following are specific embodiments of the present application: The electrolyte of the battery cell 1 includes Li 5 FeO 4 As the lithium supplement agent, correspondingly, the first charging platform is 3.5V to 3.8V; the second charging platform is 3.8V to 4.1V.

[0072] The following steps are used to perform the first charge on the battery cell 1: 1. Charge the battery cell 1 at a current of 0.02C to 0.1C until it reaches 2.2V to form the SEI film for 2h to 3h, and the internal pressure of the battery cell 1 is -80Kpa ± 20Kpa; 2. After charging the battery cell 1 to 3.3V at 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; 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 at a current of 0.2C to 0.4C; 4. After charging the battery cell 1 to 3.8V at 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; 5. Charge the battery cell 1 to 4.1V at 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; 6. Adjust the internal pressure of the battery cell 1 to -80Kpa ± 20Kpa, and charge the battery cell 1 to 4.2V at a current of 0.1 to 0.3C.

[0073] Perform the first charge on the battery cell 2 which is the same as the battery cell 1 without performing breathing exhaust treatment during this period.

[0074] Figure 3 It is the liquid level change trend diagram of the electrolyte during the first charge corresponding to the battery cell 1; Figure 4 It is the schematic diagram of the negative electrode interface of the battery cell 1; Figure 5 It is the schematic diagram of the negative electrode interface of the battery cell 2.

[0075] According to Figure 3 It can be seen that during the period when the battery cell 1 is charged to the first charging platform, the liquid level of the electrolyte has a slight upward trend; during the period when the battery cell 1 is charged to the second charging platform, the liquid level of the electrolyte rises more significantly. After the end of the first charging platform, perform a breathing exhaust treatment once to remove the gas generated in the early stage, which can avoid the problem of the impact of a large amount of gas generated later and the gas retained in the early stage. Perform three breathing exhaust treatments during the period of the second charging platform to discharge the gas generated by the lithium supplement agent in real time during the second charging platform stage, which is beneficial to the stable progress of the second charging platform. Comparing Figure 4 and Figure 5 it can be found that Figure 4 Compared with Figure 5For example, the black spots have been significantly improved. The black spots can cause problems of local lithium insertion deficiency, significant loss of battery capacity (more than about 15%), and may also cause lithium plating problems during subsequent cycling, resulting in a sharp decline in the capacity retention rate of the battery. The preparation method of the 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.

[0076] For different lithium supplement agents, it is necessary to distinguish different stages in combination with 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 the lithium trifluoromethanesulfonate in the battery cell as an example, the steps of its first charging are as follows: 1. Charge the battery cell at a current of 0.05C to 0.1C to 1.8V to form a SEI film for 2h to 3h, and the internal pressure of the battery cell is -80Kpa ± 20Kpa; 2. After charging the battery cell at a current of 0.05C to 0.1C to 2.0V, perform a breathing and exhaust treatment, raise the internal pressure of the battery cell 1 to 0Kpa ± 20Kpa and then lower it to -80Kpa ± 20Kpa; 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; 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; 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; 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 0KPa and let it stand for 2 hours to 4 hours.

[0077] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present application. In actual applications, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present 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 reaches the decomposition platform for the first time, and the second charging platform corresponds to a voltage range corresponding to when the lithium supplement agent reaches the decomposition platform for the second time, 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; Performing a first formation exhaust treatment, after charging the battery cell to a preset cut-off voltage using a second current, performing at least one breathing exhaust treatment on the battery cell, wherein the breathing exhaust treatment includes increasing the internal pressure of the battery cell to a first positive pressure and then reducing it to a first negative pressure, and the preset cut-off voltage is less than a minimum value of the first charging platform; Performing activation processing, and continuing to use the second current to charge the battery cell to the minimum value of the first charging platform; 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, during which the battery cell is charged to a maximum value of the second charging platform using the first current, performing the breathing exhaust treatment on the battery cell at least once; The third current is used to charge the battery cell to a termination voltage.

2. The method for preparing a secondary battery according to claim 1, characterized in that: 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 times 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, characterized in that: 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, characterized in that: 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, characterized in that: 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 smaller than the absolute value of the initial negative pressure.

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

7. The method for preparing a secondary battery according to claim 1, characterized in that: The second current is greater than the first current.

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

9. The method for preparing a secondary battery according to claim 8, characterized in that: 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.

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

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

12. A secondary battery, characterized in that: The secondary battery is manufactured by the method for manufacturing a secondary battery according to any one of claims 1 to 11.

13. An energy storage system, characterized in that: A plurality of secondary batteries as claimed in claim 12 are included.

14. A power supply device, characterized in that: The power supply device includes the secondary battery as claimed in claim 12; or includes the energy storage system as claimed in claim 13.

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