Battery secondary liquid injection formation process and battery

Abstract

The application relates to the technical field of batteries, in particular to a battery secondary liquid injection formation process and a battery. The provided battery secondary liquid injection formation process comprises the following steps: after one-time liquid injection of a battery, one-time formation, aging and discharging are carried out; after the discharging is completed, the battery is subjected to secondary liquid injection, centrifugation and standing; after the standing is completed, the battery is subjected to secondary formation. By adopting the battery secondary liquid injection formation process, the uniformity of electrolyte components in each region inside the battery at each stage can be greatly improved, the positive and negative electrode interface structure of the battery is optimized, the uniformity of the interface is improved, the state and performance of each region inside the battery tend to be consistent, and therefore the long-term performance of the battery and the consistency among individual batteries are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a secondary liquid injection formation process for batteries and a battery. Background Technology

[0002] With the development of lithium-ion battery technology, customers have increasingly higher requirements for its performance. As one of the three main materials, the electrolyte plays a crucial role in battery performance. Therefore, the design and setting of parameters such as electrolyte formulation, injection method, and formation process cannot be underestimated. Typically, electrolyte components mainly include lithium salts, solvents, and additives. Different components play different roles, especially additives, which are numerous, diverse, and mutually influential. Therefore, to fully utilize their respective roles, a secondary electrolyte injection method is sometimes used in battery manufacturing to achieve better battery performance. However, since the formulations of the primary and secondary electrolyte injections are usually different, secondary injection can easily lead to inconsistencies in electrolyte composition across different areas of the battery.

[0003] In related technologies, secondary electrolyte injection is used to protect the positive and negative electrodes of a battery in stages and in a targeted manner to optimize battery performance. However, these existing methods overlook the fact that after secondary electrolyte injection, the electrolyte composition differs between the two injections, leading to inconsistencies in the electrolyte composition across different regions of the battery. This results in variations in the state and performance of different areas within the battery, especially noticeable in large-size batteries, thus failing to achieve the desired effect. Furthermore, due to the inconsistent state and performance of different areas within the battery, the current density distributed across the electrode surface will be uneven during charging and discharging, causing long-term performance degradation, particularly at high temperatures. This also increases individual performance differences between batteries, making it difficult to guarantee consistency.

[0004] Therefore, there is an urgent need to provide a secondary liquid injection formation process to improve the long-term performance of batteries and the consistency between individual batteries. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a battery secondary liquid injection formation process and a battery that can improve the long-term performance of the battery and improve the consistency between individual batteries.

[0006] To solve the above-mentioned technical problems, this application is implemented as follows:

[0007] According to one aspect of this application, an embodiment of this application provides a battery secondary liquid injection formation process, including the following steps:

[0008] After the battery is filled with electrolyte once, it undergoes one formation, aging and discharge process.

[0009] After the discharge is completed, the battery will undergo a second electrolyte injection, centrifugation, and settling.

[0010] After the initial settling period, the battery undergoes a second formation process.

[0011] In addition, the battery secondary liquefaction formation process according to this application may also have the following additional technical features:

[0012] In some embodiments, the primary formation includes a first constant current charge and a second constant current charge performed sequentially, wherein the current of the second constant current charge is greater than the current of the first constant current charge.

[0013] In some of these embodiments, the current of the first constant current charging is 0.005C to 0.15C, and the charging time is 5min to 15min.

[0014] In some of these embodiments, the current of the second constant current charging is 0.02C to 1C, and the charging time is 60min to 120min.

[0015] In some of these embodiments, the aging temperature is 40°C to 50°C, and the aging time is 20h to 28h.

[0016] In some of these embodiments, the discharge current is greater than or equal to the minimum current of a single formation charge and less than or equal to the maximum current of a single formation charge.

[0017] Optionally, the discharge current is 0.005C to 1C, and the discharge is carried out to 0% SOC.

[0018] In some embodiments, after the initial injection and before the initial formation, an immersion and resting step is also included.

[0019] In some of these embodiments, the centrifugation includes a first centrifugation and a second centrifugation.

[0020] In some of these embodiments, during the first centrifugation, the bottom of the battery is oriented in the same or opposite direction to the centrifugal force.

[0021] In some embodiments, when the battery group margin is ≥89% and <91.5%, the rotation speed of the first centrifugation is 2000-6000 rpm and the time of the first centrifugation is 5 min-30 min; when the battery group margin is ≥91.5%, the rotation speed of the first centrifugation is 6000-9000 rpm and the time of the first centrifugation is 5 min-30 min.

[0022] In some of these embodiments, the bottom is oriented in the opposite direction to that of the first centrifugation during the second centrifugation.

[0023] In some embodiments, when the battery group margin is ≥89% and <91.5%, the rotation speed of the second centrifugation is 2000-6000 rpm, and the time of the second centrifugation is 5 min-30 min; when the battery group margin is ≥91.5%, the rotation speed of the second centrifugation is 6000-9000 rpm, and the time of the second centrifugation is 5 min-30 min.

[0024] In some embodiments, the settling process includes placing the battery vertically, the settling time being ≥2 hours, and the settling temperature being 25°C to 55°C.

[0025] In some embodiments, the secondary formation step involves charge-discharge cycles within the battery's state of charge (SOC) range of 5% to 90%.

[0026] In some embodiments, the charging and discharging currents of the secondary formation are both greater than or equal to the minimum current of the primary formation charge, and less than or equal to 1.5 times the maximum current of the primary formation charge.

[0027] In some of these embodiments, the charging and discharging currents of the secondary formation are in the range of 0.005C to 1.5C.

[0028] In some embodiments, when the battery's group margin is ≥89% and <91.5%, the number of cycles during secondary formation is ≥1 cycle, preferably 1 to 3 cycles; when the battery's group margin is ≥91.5%, the number of cycles during secondary formation is ≥2 cycles, preferably 2 to 5 cycles.

[0029] In some implementations, the secondary formation is followed by a capacity separation step.

[0030] In some of these embodiments, the volume of the single injection accounts for 60% to 95% of the total volume of the injection.

[0031] In some embodiments, the electrolyte for the first injection is a first electrolyte, and the electrolyte for the second injection is a second electrolyte.

[0032] According to another aspect of this application, an embodiment of this application provides a battery comprising a battery prepared by the aforementioned secondary liquefaction formation process.

[0033] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0034] In this application, after the battery undergoes its first electrolyte injection, a second formation and aging process, followed by a low-current discharge, can reduce the expansion of the battery electrodes and the volume of the core, providing more space for the second electrolyte injection. This facilitates the uniform mixing of the electrolyte within the battery after the second injection and further improves the battery's cycle life and high-temperature storage performance. Secondly, after the second electrolyte injection, centrifugation is performed. This centrifugation process ensures thorough and uniform mixing of the electrolyte from the first and second injections, with the first-injection electrolyte also including the electrolyte that permeated into the electrode sheets during the first injection. Furthermore, the second formation step can repair the SEI film aged after the first electrolyte injection, optimizing and stabilizing its structure. Simultaneously, the expansion and contraction of the electrodes during charging and discharging further homogenizes the electrolyte composition within the battery.

[0035] Furthermore, the technical solution of this invention can greatly improve the uniformity of electrolyte composition in each region of the battery at each stage, optimize the interface structure of the positive and negative electrodes, improve the uniformity of the interface, and make the state and performance of each region of the battery more consistent, thereby improving the long-term performance of the battery and the consistency between individual batteries.

[0036] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0037] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0040] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0042] In related technologies, several secondary electrolyte injection processes have been disclosed. For example, patent CN106784589A discloses a secondary electrolyte injection method for high-nickel systems, which uses a negative electrode SEI film-forming additive in the first injection and a positive electrode CEI film-forming additive in the second injection to balance the high-temperature performance and kinetic performance of high-nickel materials. Patent CN104577031A discloses a secondary electrolyte injection method for vinylene carbonate (VC), in which a high content of vinylene carbonate is added in the first injection, and a smaller content of vinylene carbonate (VC) is added in the second injection to improve the high-temperature storage and high-temperature cycle performance of the battery. Patent CN102201563A discloses a scheme in which isopropyl carbonate (PC) is not used in the first injection, but isopropyl carbonate (PC) is included in the second injection to reduce the expansion of the negative electrode material and ensure cycle performance. The patent with publication number CN114335925A discloses a method in which the first injection contains no or very little VC and contains sufficient FEC electrolyte, while the second injection contains sufficient VC and no or very little fluorinated FEC electrolyte. By forming a low-impedance SEI film through the first injection, good power performance is maintained, while the second injection of sufficient VC is used for long-term cycling, and good cycling performance is obtained.

[0043] The aforementioned existing technologies all employ a secondary electrolyte injection method. These disclosed methods are largely theoretical, aiming to optimize battery performance by providing phased and targeted protection for the positive and negative electrodes through secondary electrolyte injection. However, these existing methods overlook the fact that after secondary electrolyte injection, the electrolyte composition differs between the two injections, leading to inconsistencies in the electrolyte composition across different regions of the battery. This results in variations in the state and performance of different areas within the battery, especially noticeable in large-size batteries, ultimately failing to achieve the desired effect.

[0044] In view of this, the inventors of this application, after extensive research, have proposed a new improvement approach from the liquid injection formation process to address the shortcomings of existing secondary liquid injection processes. This aims to avoid or reduce the problem of inconsistent electrolyte composition in different regions of the battery due to different electrolyte compositions in the two liquid injections, resulting in different states and performance in different regions of the battery. This will improve the electrochemical performance of the battery. The following is a detailed description of this application.

[0045] In some embodiments, the present invention provides a battery secondary liquid injection formation process, comprising the following steps:

[0046] After the battery is filled with electrolyte once, it undergoes one formation, aging and discharge process.

[0047] After the discharge is complete, the battery is refilled with electrolyte, centrifuged, and allowed to stand.

[0048] After the settling period, the battery undergoes a second formation process.

[0049] In this embodiment, the provided secondary electrolyte injection formation process can alleviate the problem of inconsistent states and performance in different areas of the battery, which affects the electrochemical performance of the battery, as present in current secondary electrolyte injection methods. Overall, the secondary electrolyte injection formation process includes sequential steps such as primary electrolyte injection, primary formation, aging, discharge, secondary electrolyte injection, centrifugation, settling, and secondary formation. That is, the battery is injected with electrolyte twice, and the electrolytes used in the two injections can be different. Between the primary and secondary electrolyte injections, there are steps such as primary formation, aging, and discharge. After the secondary electrolyte injection, there are steps such as centrifugation, settling, and secondary formation.

[0050] It should be noted that, in addition to the above-mentioned process steps, other steps can be flexibly selected and adjusted, such as setting a settling step after secondary liquid injection and before centrifugation. This embodiment does not limit this.

[0051] Compared to conventional secondary electrolyte injection formation methods, firstly, this application performs a first formation and aging process after the initial electrolyte injection, followed by discharge, preferably using a low-current discharge method. This reduces the expansion of the battery electrodes and the volume of the core, providing more space for secondary electrolyte injection. This facilitates the uniform mixing of the electrolyte within the battery after secondary electrolyte injection and further improves the battery's cycle life and high-temperature storage performance. Secondly, in the secondary electrolyte injection formation process of this application, centrifugation is performed after the secondary electrolyte injection. Through centrifugation, the electrolyte from the first and second injections can be thoroughly and uniformly mixed within the battery. The electrolyte from the first injection also includes the electrolyte injected during the first injection that has permeated into the electrode sheets. This allows the mixed electrolyte to fully re-permeate throughout the battery, improving the uniformity of the electrolyte composition in different areas of the battery. Third, through the secondary formation process, the SEI film after the first electrolyte injection aging can be repaired, its structure optimized and stabilized. At the same time, through the expansion and contraction of the electrode during charging and discharging, the electrolyte composition in the battery can be further homogenized.

[0052] Therefore, the secondary electrolyte injection formation process of this application can greatly improve the uniformity of electrolyte composition in each region of the battery at each stage, optimize the interface structure of the positive and negative electrodes, improve the uniformity of the interface, and make the state and performance of each region of the battery more consistent, thereby improving the long-term performance of the battery and the consistency between individual batteries.

[0053] In some embodiments, the battery's group margin is ≥89%. Preferably, the battery's group margin is ≥90%. As an example, the battery's group margin can be 89%, 90%, 96%, 97%, 98%, or greater than 98%, etc., and of course, it can also be other values ​​within the above range, which are not limited here.

[0054] In this application, the secondary liquid injection formation process is applicable to batteries with a group margin greater than or equal to 89%, preferably 90% or more. It should be understood that battery group margin mainly refers to the gaps between individual cells within a battery pack. The group margin of a battery has a certain impact on its performance; generally, increasing the group margin helps improve battery quality and safety. Furthermore, excessively large or small group margins will adversely affect the performance of the battery pack. For example, excessive group margins will lead to reduced internal space utilization within the battery pack, thereby reducing the energy density; while excessively small group margins may cause cells to squeeze against each other during expansion, even leading to safety accidents.

[0055] In this application, the specific operating conditions for some steps in the secondary electrolyte injection formation process of the battery are related to the battery's group margin, such as the centrifugation step and the secondary formation step. For different group margins, the specific operating parameters can be adaptively adjusted to ensure more thorough and uniform mixing of the electrolyte. This is because, relatively speaking, the higher the group margin, the more difficult it is to mix the electrolyte uniformly. Therefore, setting different operating parameters for batteries with different group margins is more conducive to improving the uniformity of electrolyte composition in different regions within the battery at each stage.

[0056] It should be noted that in the battery secondary electrolyte injection formation process of this application, different electrolytes can be used for primary and secondary electrolyte injection, that is, the compositions of the electrolytes for primary and secondary electrolyte injection are different. For example, the additives in the electrolytes for primary and secondary electrolyte injection are different, and / or, the electrolyte salts in the electrolytes for primary and secondary electrolyte injection are different, and / or, the organic solvents in the electrolytes for primary and secondary electrolyte injection are different. The battery secondary electrolyte injection formation process of this application is applicable to scenarios where different electrolytes are used for secondary electrolyte injection, and there is no limitation on the specific type or composition of the electrolytes used for primary and secondary electrolyte injection, as long as the electrolytes used in the two injections are different and it does not limit the purpose of this application.

[0057] In some embodiments, the electrolytes injected twice can be different electrolytes. For example, a primary electrolyte injection using a small amount of high-voltage resistant film-forming agent may be used for high-voltage formation, while a secondary electrolyte injection using a large amount of conventional electrolyte containing gas-inhibiting agent may be used for conventional voltage capacity testing and cycling.

[0058] In some specific embodiments, the battery secondary liquid injection formation process specifically includes the following steps S1 to S6:

[0059] S1: After the battery is filled with electrolyte once, it undergoes one formation, aging and discharge.

[0060] In some embodiments, after one injection and before one formation, an immersion and resting step is also included.

[0061] Step S1 specifically includes: first, injecting electrolyte into the battery once; after the first injection, immersing and resting the battery; and then sequentially performing formation, aging, and discharge.

[0062] Preferably, a low-current discharge is used. Discharging with a low current can reduce the expansion of the battery electrodes, reduce the volume of the core, provide more space for secondary electrolyte injection, and also facilitate the uniform mixing of the electrolyte after secondary electrolyte injection and within the battery.

[0063] In step S1, the one-time formation and aging steps can be carried out in accordance with conventional operating methods in the art, such as using conventional process parameters in the art. This application does not limit this.

[0064] In some embodiments, the volume of a single injection accounts for 60% to 95% of the total injection volume. Preferably, the volume of a single injection accounts for 75% to 90% of the total injection volume. As an example, the volume of a single injection can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc., of course, other values ​​within the above range are also possible and are not limited here. Those skilled in the art will understand that the total injection volume is the sum of the volume of the single injection and the volume of the secondary injection.

[0065] In some embodiments, the soaking and resting time is 2 to 4 hours. As an example, the soaking and resting time can be 2 hours, 3 hours, or 4 hours, or other values ​​within the above range, which are not limited here. This soaking and resting can be carried out at room temperature.

[0066] After soaking and resting, it can ensure that the electrolyte fully wets the electrode, forms a stable SEI film, removes air bubbles, and balances the electrolyte distribution.

[0067] In some embodiments, primary formation includes sequentially performing a first constant current charge and a second constant current charge, wherein the current of the second constant current charge is greater than the current of the first constant current charge. The fact that the current of the second constant current charge is greater than the current of the first constant current charge ensures a milder chemical reaction during the primary formation process and reduces side reactions, which helps to form a more stable SEI film. It can also optimize the electrode structure and improve the safety and consistency of the battery.

[0068] In some embodiments, the current of the first constant current charging is 0.005C to 0.15C, preferably 0.05C to 0.15C, and more preferably 0.08C to 0.1C. As an example, the current of the first constant current charging can be 0.005C, 0.01C, 0.015C, 0.025C, 0.035C, 0.045C, 0.055C, 0.075C, 0.085C, 0.095C, 0.1C, 0.12C, 0.13C, 0.15C, etc., or other values ​​within the above range, which are not limited here.

[0069] In some embodiments, the first constant current charging time is 5 min to 15 min. As an example, the first constant current charging time can be 5 min, 6 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 15 min, etc., or other values ​​within the above range, which are not limited here.

[0070] In some embodiments, the current of the second constant current charging is 0.02C to 1C, preferably 0.1C to 0.5C, and more preferably 0.2C to 0.3C. As an example, the current of the second constant current charging can be 0.02C, 0.03C, 0.04C, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, 0.1C, 0.3C, 0.5C, 0.6C, 0.7C, 1C, etc., or other values ​​within the above range, which are not limited here.

[0071] In some embodiments, the second constant current charging time is 60 min to 120 min. As an example, the second constant current charging time can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc., or other values ​​within the above range, which are not limited here.

[0072] It should be noted that the values ​​of the first constant current charging current and the second constant current charging current must satisfy the condition that the second constant current charging current is greater than the first constant current charging current.

[0073] In some embodiments, the aging temperature is 40°C to 50°C, preferably 45°C. As an example, the aging temperature can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, etc., or other values ​​within the above range, which are not limited here.

[0074] In some embodiments, the aging time is 20h to 28h, preferably 24h. As an example, the aging time can be 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, etc., or other values ​​within the above range, which are not limited here.

[0075] In this application, after aging is complete, the battery is discharged with a small current. In some embodiments, the discharge current is greater than or equal to the minimum current of a single formation charge, and less than or equal to the maximum current of a single formation charge.

[0076] For example, the discharge current is 0.005C to 1C, discharging to 0% SOC; preferably, the discharge current is 0.01C to 0.5C. For example, the discharge current can be 0.005C, 0.01C, 0.015C, 0.025C, 0.035C, 0.045C, 0.055C, 0.075C, 0.085C, 0.095C, 0.1C, 0.12C, 0.13C, 0.15C, 0.3C, 0.5C, 0.6C, 0.7C, 1C, etc., or other values ​​within the above range, which are not limited here.

[0077] This application reduces electrode expansion and core volume by subjecting the battery to low-current discharge after primary formation, providing more space for secondary electrolyte injection. This facilitates uniform mixing of the electrolyte within the battery after secondary injection and further improves cycle life and high-temperature storage performance. Furthermore, excessive discharge current in this step can lead to lithium plating, affecting the negative electrode interface. Therefore, employing a low-current discharge method and controlling the discharge current within the aforementioned range helps avoid or reduce lithium plating and minimize its impact on the negative electrode interface.

[0078] S2: After the discharge is complete, the battery is refilled with electrolyte and then centrifuged for the first time.

[0079] In step S2, after the discharge step in step S1 is completed, the battery is injected with electrolyte a second time. After the battery is injected with electrolyte a second time, it is sealed and then subjected to the first centrifugation treatment.

[0080] Optionally, the volume of the secondary injection accounts for 5% to 40% of the total injection volume. Preferably, the volume of the secondary injection accounts for 10% to 25% of the total injection volume.

[0081] In some embodiments, during the first centrifugation, the bottom of the battery is oriented in the same or opposite direction to the centrifugal force.

[0082] Optionally, in step S2, during the first centrifugation process, the battery (core) is placed in a centrifuge with the bottom facing out along its horizontal direction.

[0083] The specific operating parameters for the first centrifugation process are related to the battery's group margin. For example, in some embodiments, when the battery's group margin is ≥89% and <91.5%, that is, 89% ≤ group margin < 91.5%, the rotation speed for the first centrifugation is 2000–6000 rpm. As an example, the rotation speed for the first centrifugation can be 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, 6000 rpm, etc., or other values ​​within the above range, which are not limited here.

[0084] In some embodiments, when the battery group margin is ≥89% and <91.5%, that is, 89% ≤ group margin < 91.5%, the first centrifugation time is 5 min to 30 min. As an example, the first centrifugation time can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc., or other values ​​within the above range, which are not limited here.

[0085] In some embodiments, when the battery group margin is ≥91.5%, the rotation speed of the first centrifugation is 6000-9000 rpm. As an example, the rotation speed of the first centrifugation can be 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm, etc., or other values ​​within the above range, which are not limited here.

[0086] In some embodiments, when the battery group margin is ≥91.5%, the first centrifugation time is 5 min to 30 min. As an example, the first centrifugation time can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc., or other values ​​within the above range, which are not limited here.

[0087] It should be noted that the centrifugation speed is related to the battery's group margin; a higher group margin makes it more difficult to mix the electrolyte evenly. Therefore, when the group margin is high, a higher centrifugation speed should be set. This allows the electrolyte to settle sufficiently to the bottom, promoting thorough and uniform mixing of the electrolyte components, thereby improving the uniformity of the positive and negative electrode interfaces and making the state and performance of different regions within the battery more consistent. This, in turn, improves the long-term performance of the battery and the consistency between individual batteries.

[0088] S3: After the first centrifugation is completed, perform the second centrifugation.

[0089] In some embodiments, the bottom is oriented in the opposite direction during the second centrifugation to the direction during the first centrifugation.

[0090] Optionally, in step S3, after the first centrifugation to allow the electrolyte to settle to the bottom, the battery is flipped over and centrifuged again along the horizontal direction of the battery (core), with the bottom facing inward. This is a second centrifugation process to ensure that the electrolyte injected in the first and second stages is fully mixed and homogeneous. The electrolyte includes the electrolyte injected in the first stage that has seeped into the battery electrode.

[0091] In some embodiments, when the battery group margin is ≥89% and <91.5%, that is, 89% ≤ group margin < 91.5%, the rotation speed of the second centrifugation is 2000-6000 rpm. As an example, the rotation speed of the second centrifugation can be 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, 6000 rpm, etc., or other values ​​within the above range, which are not limited here.

[0092] In some embodiments, when the battery group margin is ≥89% and <91.5%, that is, 89% ≤ group margin < 91.5%, the second centrifugation time is 5 min to 30 min. As an example, the second centrifugation time can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc., or other values ​​within the above range, which are not limited here.

[0093] In some embodiments, when the battery group margin is ≥91.5%, the rotation speed of the second centrifugation is 6000-9000 rpm, and the second centrifugation time is 5 min-30 min. As an example, the rotation speed of the second centrifugation can be 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm, etc., or other values ​​within the above range, which are not limited here.

[0094] In some embodiments, when the battery group margin is ≥91.5%, the second centrifugation time is 5 min to 30 min. As an example, the second centrifugation time can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc., or other values ​​within the above range, which are not limited here.

[0095] It should be noted that the centrifugation speed is related to the battery's group margin; a higher group margin makes it more difficult to mix the electrolyte evenly. Therefore, when the group margin is high, a higher centrifugation speed should be set. In this way, after the second centrifugation, the electrolyte from the first and second injections within the battery can be thoroughly and evenly mixed, thereby greatly improving the uniformity of electrolyte composition in different regions within the battery at each stage.

[0096] S4: Let the battery stand after the second centrifugation.

[0097] In some embodiments, resting includes placing the battery vertically.

[0098] In step S4, after the battery is centrifuged a second time, the battery is removed from the centrifuge, placed vertically with the bottom facing down for a certain period of time to allow the mixed electrolyte to fully permeate all areas of the battery again.

[0099] In some embodiments, the settling time is ≥2 hours; preferably, the settling time is 2 hours to 8 hours. As an example, the settling time can be 2 hours, 4 hours, 5 hours, 8 hours, etc., or other values ​​within the above range, which are not limited here.

[0100] In some embodiments, the settling temperature is 25°C to 55°C; preferably, the settling temperature is 25°C to 45°C. As an example, the settling temperature can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, etc., or other values ​​within the above range, which are not limited here.

[0101] By controlling the time and temperature of the above-mentioned settling steps within the above range, the mixed electrolyte can be fully reinfiltrated in all areas of the battery, which helps to improve the uniformity of various areas inside the battery.

[0102] S5: After the battery has been placed vertically for more than 2 hours, it is subjected to low-current charge and discharge cycles within a certain SOC range, which is called secondary formation.

[0103] In step S5, the main process is secondary formation. After the battery has been placed vertically for more than 2 hours, it is subjected to small-charge and discharge cycles, which is secondary formation. This process can repair the SEI after the first electrolyte injection aging, optimize and stabilize its structure, and further homogenize the electrolyte composition in the battery through the expansion and contraction of the electrode during the charging and discharging process.

[0104] In some embodiments, during the secondary formation step, charge-discharge cycles are performed within the battery's SOC range of 5% to 90%, preferably within the battery's SOC range of 30% to 70%. As an example, during the secondary formation step, the battery can be charged to 90% SOC and discharged to 5% SOC to complete one charge-discharge cycle; it can also be charged to 80% SOC and discharged to 10% SOC to complete one charge-discharge cycle; or it can be charged to 70% SOC and discharged to 30% SOC to complete one charge-discharge cycle. That is, during the charge-discharge cycle, the charging and discharging can be any value within the aforementioned SOC range.

[0105] In some embodiments, the charging and discharging currents during secondary formation are both greater than or equal to the minimum charging current during primary formation, and less than or equal to 1.5 times the maximum charging current during primary formation. By limiting the charging and discharging currents within this range, the negative electrode interface can be optimized, preventing lithium plating.

[0106] For example, the charging and discharging currents for secondary formation are both in the range of 0.005C to 1.5C; preferably, the charging and discharging currents for secondary formation are both in the range of 0.1C to 1C. For example, the charging current for secondary formation can be 0.005C, 0.01C, 0.015C, 0.025C, 0.035C, 0.045C, 0.055C, 0.075C, 0.085C, 0.095C, 0.1C, 0.12C, 0.13C, 0.15C, 0.3C, 0.5C, 0.6C, 0.7C, 1C, 1.5C, etc., or other values ​​within the above ranges, which are not limited here. The discharge current for secondary formation can be 0.005C, 0.01C, 0.015C, 0.025C, 0.035C, 0.045C, 0.055C, 0.075C, 0.085C, 0.095C, 0.1C, 0.12C, 0.13C, 0.15C, 0.3C, 0.5C, 0.6C, 0.7C, 1C, 1.5C, etc., or other values ​​within the above range. The charging and discharging currents for secondary formation can be the same or different.

[0107] In some embodiments, when the battery's group margin is ≥89% and <91.5%, that is, 89% ≤ group margin < 91.5%, the number of cycles during secondary formation is ≥1 cycle, preferably 1 to 3 cycles. As an example, when the battery's group margin is ≥89% and <91.5%, the number of cycles during secondary formation can be 1 cycle, 2 cycles, 3 cycles, 4 cycles, etc., or other values ​​within the above range, which are not limited here.

[0108] In some embodiments, when the battery's group margin is ≥91.5%, the number of cycles during secondary formation is ≥2, preferably 2 to 5. As an example, when the battery's group margin is ≥91.5%, the number of cycles during secondary formation can be 2, 3, 4, 5, etc., or other values ​​within the above range, which are not limited here.

[0109] The number of cycles during the secondary formation process is related to the battery's group margin. The higher the battery group margin, the more difficult it is to mix the electrolyte evenly. Therefore, multiple small-current charge-discharge cycles are required for mixing.

[0110] S6: After the battery undergoes two-stage formation, it is finally tested for capacity to obtain the finished battery.

[0111] In step S6, the main task is to perform capacity partitioning. The specific operation method of capacity partitioning can be any method known in the art and is not limited thereto.

[0112] Therefore, the above-mentioned technical solution, after the battery undergoes one electrolyte injection, one formation and aging process, and then discharge, can reduce the expansion of the battery electrodes and the volume of the core, providing more space for the second electrolyte injection. This facilitates the uniform mixing of the electrolyte within the battery after the second electrolyte injection and further improves the battery's cycle life and high-temperature storage performance. More specifically, the first formation includes a first constant current charge and a second constant current charge performed sequentially, with the current of the second constant current charge being greater than that of the first constant current charge. The higher current of the second constant current charge ensures a milder chemical reaction during the first formation process and reduces side reactions, contributing to the formation of a more stable SEI film. It also optimizes the electrode structure and improves battery safety and consistency. Secondly, after two centrifugations in opposite directions, the electrolyte from the first and second electrolyte injections within the battery can be thoroughly and uniformly mixed. The electrolyte from the first electrolyte injection also includes the electrolyte injected into the electrode plates during the first injection, which can significantly improve the uniformity of electrolyte composition in different regions within the battery at each stage. Furthermore, the secondary formation process can repair the SEI film after the first electrolyte injection aging, optimize and stabilize its structure, and further homogenize the electrolyte composition in the battery through the expansion and contraction of the electrode during charging and discharging.

[0113] Based on the same inventive concept, this application provides a battery, which includes the battery prepared by the aforementioned secondary liquid injection formation process.

[0114] The battery is prepared by the aforementioned secondary liquid injection formation process, and therefore has all the beneficial effects brought about by the technical solution of the above embodiments, which will not be repeated here.

[0115] In this embodiment, the battery can be a secondary battery. Optionally, the secondary battery can be a lithium-ion battery, a sodium-ion battery, or a magnesium-ion battery, etc. This application does not limit the specific type of battery.

[0116] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0117] Battery preparation

[0118] The battery is a large-size 150Ah aluminum-cased square battery.

[0119] (1) The composition of the positive electrode slurry includes:

[0120] The mass ratio of lithium iron phosphate (LFP), conductive carbon black (SuperP), binder polyvinylidene fluoride (PVDF_5130), and dispersant polyvinylpyrrolidone (PVP_30) is 100:2:2.5:0.5.

[0121] (2) The composition of the negative electrode slurry includes:

[0122] The mass ratio of graphite, conductive agent (SuperP), binder styrene-butadiene rubber (SBR), binder sodium carboxymethyl cellulose (CMC_500), and water is 100:2:2:0.8:99.

[0123] (3) Separator: Polyethylene film is used.

[0124] (4) Electrolyte:

[0125] The electrolyte used in both the first and second injections includes lithium salts, organic solvents, and additives.

[0126] The electrolyte used in the first injection includes 13% lithium hexafluorophosphate (LiPF6), organic solvents including ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), with a volume ratio of EC, EMC and DMC of 3:5:2, and additives including 1% vinylene carbonate (VC) and 1% fluoroethylene carbonate (FEC).

[0127] The electrolyte used in the secondary injection process includes 13% lithium hexafluorophosphate (LiPF6), organic solvents including ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC, EMC, and DMC of 3:5:2, and additives including 16% vinylene carbonate (VC) and 1% fluoroethylene carbonate (FEC).

[0128] (5) Battery preparation

[0129] The positive electrode, separator, and negative electrode are bonded, wound, and welded to obtain the battery cell. The bare battery cell is then placed in the battery outer packaging in preparation for the secondary liquefaction formation process.

[0130] Example 1

[0131] The battery secondary liquid injection formation process includes the following steps:

[0132] Step S1: Perform a first injection of electrolyte into the battery to be injected (the first injection volume accounts for 90% of the total electrolyte volume). After soaking and resting, first formation, and aging, perform a small current discharge. After the discharge is completed, perform a second injection of electrolyte.

[0133] Step S2: After the battery is refilled with electrolyte and sealed, place the battery in a centrifuge with the bottom facing out along the transverse direction of the winding core for centrifugation (first centrifugation).

[0134] Step S3: After the electrolyte has settled to the bottom, turn the battery over so that the bottom faces inward along the transverse direction of the core and continue to centrifuge the battery (secondary centrifugation).

[0135] Step S4: After the second centrifugation, remove the battery and place it vertically with the bottom facing down;

[0136] Step S5: After the battery is placed vertically, it is subjected to low-current charge and discharge cycles within a certain SOC range, which is called secondary formation.

[0137] Step S6: After the battery undergoes two injections of formation, it is finally subjected to capacity testing to obtain the finished battery.

[0138] For the secondary liquefaction formation step in Example 1, the parameters are detailed in Tables 1 and 2.

[0139] The specific parameters for the injection formation of Examples 2-14 and Comparative Examples 1-4 are shown in Tables 1 and 2. In Example 14, the injection volume in one injection accounted for 75% of the total injection volume, and the rest were the same as in Example 1.

[0140] Table 1

[0141]

[0142]

[0143] Table 2

[0144]

[0145]

[0146] Note: The " / " in Tables 1 and 2 indicates that this step was not performed in this embodiment or comparative example.

[0147] Performance testing

[0148] (1) 45℃ Cycling Test: The lithium-ion batteries prepared in each embodiment and comparative example were cycled at 45℃ for 1500 cycles at 1C / 1C to test the battery capacity retention rate and DCR rise rate. Specifically, the lithium-ion batteries prepared in each embodiment and comparative example were left to stand at 45℃ for 5 min, discharged at 1C to 2.5V, left to stand for 15 min, charged at 1C constant current to 3.65V, left to stand for 15 min, discharged at 1C to 2.5V, and the discharge capacity was recorded as C1. At the same time, the DCR1 was obtained according to the discharge curve. The above charge and discharge process was repeated for 1500 cycles, and the capacity Cn was recorded on the 1500th cycle. At the same time, the DCRn was obtained according to the discharge curve on the 1500th cycle. The capacity retention rate = Cn / C1×100%, and the DCR rise rate = ((DCRn / DCR1)-1)×100%.

[0149] (2) 60℃ high temperature storage test: After storing the lithium-ion batteries prepared in each example and comparative example at 60℃ for 100 days, the remaining capacity, capacity recovery rate and DCR increase rate were tested respectively. Specifically, the lithium-ion batteries prepared in each embodiment and comparative example were first charged at 25°C with a constant current and constant voltage of 1C to 3.65V, with a cutoff current of 0.05C, and then discharged at a constant current of 1C to 2.5V. The discharge capacity C0 was recorded, and the DCR1 was obtained according to the discharge curve. The batteries were then charged again with a constant current and constant voltage of 1C, and the cutoff voltage was 0.05C. The batteries were then transferred to a 60°C oven for high-temperature storage for 100 days. After that, they were discharged at 25°C with a constant current of 1C to 2.5V, and the discharge capacity at this time was recorded as the remaining capacity C1. Then, the batteries were charged again with a constant current and constant voltage of 1C to 3.65V, with a cutoff voltage of 0.05C, and then discharged again with a constant current of 1C to 2.5V. The discharge capacity was defined as the reversible capacity C2, and the DCR2 was obtained according to the discharge curve. The remaining capacity rate = C1 / C0 × 100%, the capacity recovery rate = C2 / C0 × 100%, and the DCR rise rate = ((DCR2 / DCR1) - 1) × 100%.

[0150] The specific test results are shown in Table 3.

[0151] Table 3

[0152]

[0153] Test data shows that after a single electrolyte injection, immersion and resting, a single formation and aging process, the battery's cycle performance and high-temperature storage performance can be significantly improved by increasing low-current discharge, secondary electrolyte injection, centrifugal mixing of electrolyte components, vertical standing after centrifugation, secondary formation, and low-current cycling after secondary formation. This effectively enhances capacity retention and recovery rate, effectively suppresses the rise of DCR, and further improves the overall performance of the battery.

[0154] Specifically, comparing the data from Examples 1-3, it can be seen that increasing the discharge current before the second electrolyte injection improves the battery's cycle life and high-temperature storage performance, and the smaller discharge current (e.g., around 0.2C) results in better performance. In other words, performing a small-current discharge after the first formation process can improve the battery's electrical and storage performance.

[0155] Comparing the data from Examples 1, 5, and 6, and comparing the data from Examples 8 and 9, it can be seen that appropriately increasing the centrifugation speed and centrifugation time improves both battery cycle performance and high-temperature storage performance, and the higher the group margin, the greater the impact.

[0156] Comparing the data from Examples 1 and 7, and from Examples 9 and 10, it can be seen that appropriately increasing the vertical placement time and temperature improves the battery cycle performance and high-temperature storage performance.

[0157] Comparing the data from Examples 1, 2, and 4, and from Examples 9 and 12, it can be seen that increasing secondary formation and low-current cycling improves battery cycle and high-temperature storage performance. Appropriately increasing the number of low-current cycles also contributes to performance improvement.

[0158] Comparing the data from Examples 9 and 11, it can be seen that appropriately increasing the secondary formation and low-current cycle SOC improves both battery cycle performance and high-temperature storage performance. Comparing the data from Examples 9 and 13, it can be seen that appropriately increasing the secondary formation and low-current cycle current has little impact on battery cycle performance and high-temperature storage performance.

[0159] A comparative analysis of Example 1 and Comparative Examples 1-4 shows that adding a centrifugation step after secondary electrolyte injection improves both the battery's cycle performance and high-temperature storage performance. For example, the capacity retention rate of Comparative Example 1 after cycling at 45°C is significantly lower than that of Example 1. Adding secondary formation after secondary electrolyte injection can also improve the battery's cycle performance and high-temperature storage performance. Furthermore, even with low group margins, good cycle performance and high-temperature storage performance can be achieved without centrifugation, secondary formation, and low-current cycling. Therefore, the technical solution of this invention can effectively alleviate the problems faced by batteries with high group margins.

[0160] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0161] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0162] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0163] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery secondary liquid injection formation process, characterized in that, Includes the following steps: After the battery is filled with electrolyte once, it undergoes one formation, aging and discharge process. After the discharge is completed, the battery will undergo a second electrolyte injection, centrifugation, and settling. After the settling period, the battery will undergo a second formation process. The primary formation includes a first constant current charge and a second constant current charge performed sequentially, wherein the current of the second constant current charge is greater than the current of the first constant current charge. The discharge current is greater than or equal to the minimum current of a single charge and less than or equal to the maximum current of a single charge. The centrifugation includes a first centrifugation and a second centrifugation; During the first centrifugation, the bottom of the battery is oriented in the same or opposite direction to the centrifugal force during centrifugation. The bottom orientation during the second centrifugation is opposite to that during the first centrifugation. The electrolyte composition of the primary injection and the electrolyte composition of the secondary injection are different.

2. The battery secondary liquid injection formation process according to claim 1, characterized in that, The current of the first constant current charging is 0.005C~0.15C, and the charging time is 5min~15min; And / or, the current of the second constant current charging is 0.02C~1C, and the charging time is 60min~120min; And / or, the aging temperature is 40℃~50℃, and the aging time is 20h~28h.

3. The battery secondary liquid injection formation process according to claim 1, characterized in that, The discharge current is 0.005C~1C, and the discharge is carried out until 0% SOC; And / or, after the first injection and before the first formation, the process further includes an immersion and resting step.

4. The battery secondary liquid injection formation process according to claim 1, characterized in that, When the battery's group margin is ≥89% and <91.5%, the rotation speed of the first centrifugation is 2000~6000 rpm, and the time of the first centrifugation is 5min~30min; When the battery's group margin is ≥91.5%, the rotation speed for the first centrifugation is 6000~9000 rpm, and the time for the first centrifugation is 5min~30min.

5. The battery secondary liquid injection formation process according to claim 4, characterized in that, When the battery's group margin is ≥89% and <91.5%, the rotation speed of the second centrifugation is 2000~6000 rpm, and the time of the second centrifugation is 5min~30min; When the battery's group margin is ≥91.5%, the rotation speed of the second centrifugation is 6000~9000 rpm, and the time of the second centrifugation is 5min~30min.

6. The battery secondary liquid injection formation process according to claim 1, characterized in that, The settling process includes placing the battery vertically, the settling time is ≥2 hours, and the settling temperature is 25℃~55℃.

7. The battery secondary liquid injection formation process according to claim 1, characterized in that, In the secondary formation step, charge-discharge cycles are performed within the battery's SOC range of 5% to 90%. And / or, the charging and discharging currents of the secondary formation are both greater than or equal to the minimum current of the primary formation charging, and less than or equal to 1.5 times the maximum current of the primary formation charging; And / or, the charging and discharging currents of the secondary formation are both in the range of 0.005C to 1.5C.

8. The battery secondary liquefaction formation process according to claim 7, characterized in that, When the battery's group margin is ≥89% and <91.5%, the number of cycles during secondary formation is ≥1. When the battery's group margin is ≥91.5%, the number of cycles during secondary formation is ≥2. And / or, after the secondary transformation, a capacity-sharing step is also included.

9. The battery secondary liquid injection formation process according to any one of claims 1 to 8, characterized in that, The volume of fluid injected in a single injection accounts for 60% to 95% of the total volume of fluid injected.

10. A battery, characterized in that, The battery includes the battery prepared by the secondary liquefaction formation process according to any one of claims 1 to 9.

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