Lithium ion battery and formation method thereof

Abstract

The invention provides a lithium ion battery and a formation method thereof, and relates to the technical field of lithium ion battery manufacturing, in the formation method, by optimizing a matching relationship between formation temperature and formation current and adding a constant-current discharge process, when the battery is charged to a charging cut-off voltage at constant current, the battery is continuously charged to the cut-off current at the constant voltage, and the constant-current discharge process is stopped; at the moment, the battery is in a full charge state, and then the battery is subjected to constant-current discharge at a certain discharge rate to a set charge state, so that the SEI film part is re-oxidized, the electrochemical performance of active substances is fully activated, the component proportion of the SEI film is stabilized, and the phenomenon that the capacity fading at the initial stage of circulation is relatively fast due to instability of the SEI film and insufficient activation of the active substances in the battery is avoided; and the cycle life of the lithium ion battery is prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of lithium ion battery manufacturing, and in particular to a lithium ion battery and a formation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in mobile electronic devices, electric vehicles and large-scale energy storage systems due to their high energy density, long life and good charge and discharge performance. The quality of battery performance depends largely on the performance of electrode materials and the interaction between electrodes and electrolytes. In the battery manufacturing process, the formation process is a key step in forming a stable electrode / electrolyte interface (i.e., solid electrolyte interface film, SEI film). During the formation charging process, the electrolyte additive undergoes a reduction reaction on the negative electrode and is deposited on the surface of the negative electrode to form an SEI film. This film is an insulator for electrons but a good conductor for lithium ions, allowing lithium ions to pass freely. The formation of the SEI film is crucial to battery performance because it prevents the irreversible consumption of electrolyte and lithium ions in subsequent cycles, thereby improving the cycle life and safety of the battery.

[0003] However, there are some problems with the formation methods in the prior art. Usually, charging formation is adopted, and the battery does not undergo a complete charge and discharge process, resulting in the SEI film generated being not ideal in terms of uniformity and stability. In addition, the matching problem between the formation temperature and the formation current is not considered, resulting in poor cycle performance, self-discharge performance and safety performance of the battery formed.

[0004] Therefore, there is an urgent need to provide a lithium-ion battery and a formation method thereof, which can improve the stability of the SEI film and improve the problem of rapid capacity decay of the battery in the early stage of the cycle, thereby increasing the overall cycle life. Summary of the invention

[0005] The present application provides a lithium-ion battery and a formation method thereof, which can solve the problem of poor matching between temperature and formation current, improve the stability of the SEI film, and improve the problem of rapid capacity decay of the battery in the early stage of the cycle, thereby increasing the overall cycle life.

[0006] In a first aspect, the present application provides a formation method for a lithium ion battery, comprising the steps of: setting a formation temperature to a preset temperature value, the preset temperature value being between 25°C and 80°C; determining a charge and discharge rate according to the preset temperature value, the charge and discharge rate comprising a first rate, a second rate, a third rate and a fourth rate; charging the lithium ion battery to a first state of charge at a first rate by a constant current method, the first state of charge being 0% to 10% SOC; charging the lithium ion battery to a second state of charge at a second rate by a constant current method, the second state of charge being 10% to 50% SOC; charging the lithium ion battery to a full charge state of 100% SOC by a constant current and constant voltage method at a third rate; standing for 5-10 minutes; discharging the lithium ion battery to a target state of charge at a fourth rate by a constant current discharge method, the target state of charge being 0% to 70% SOC; standing for 5-10 minutes to form a lithium ion battery.

[0007] Through the above scheme, when the formation temperature is set at 25℃~80℃, the viscosity of the electrolyte can be reduced, the transmission resistance of active lithium ions in the electrolyte can be reduced, thereby improving the conductivity of the electrolyte, and then improving the performance of the lithium-ion battery. The charging or discharging rate of each stage is determined by the formation temperature, so that the charging or discharging rate is optimized and matched according to the formation temperature, thereby obtaining a more stable SEI film and improving the cycle performance of the battery. The charging process adopts a three-stage charging system. The first stage uses a small current for formation. The small current charging at the initial stage of formation is conducive to the formation of a dense SEI film, which can effectively prevent the electrolyte from directly contacting the electrode interface; the second stage slightly increases the current, which is conducive to ensuring the formation of a dense SEI film while improving the formation efficiency; the third stage continues to increase the current and charges to 100% SOC at a constant current and constant voltage. The constant current and constant voltage charging mode combines the advantages of constant current charging (CC) and constant voltage charging (CV). It can charge quickly at a constant current at the initial stage of charging, and then convert to constant voltage charging to ensure that the battery is fully charged. Among them, constant voltage charging can alleviate the concentration polarization inside the battery and improve the quality of the SEI film. At the same time, full charging of 100% SOC can ensure the full progress of side reactions. After the battery is fully charged, it is discharged at the fourth rate constant current to 0%~70% SOC. In this process, the organic components in the SEI film are partially oxidized to inorganic components, and the resulting SEI film is denser and more stable. At the same time, the reduction of organic components in the SEI film reduces its impedance, which can reduce the initial internal resistance of the cycle to a certain extent, which is beneficial to slow down the attenuation rate of the battery capacity, thereby increasing the cycle life of the battery.

[0008] In a possible design, when the preset temperature value is 25°C to 45°C, the first multiplier is 0.01 to 0.1C, the second multiplier is 0.05 to 0.15C, the third multiplier is 0.1 to 0.2C, and the fourth multiplier is 0.2 to 0.3C.

[0009] Through the above scheme, the influence of temperature on the battery charging characteristics is taken into account, and the charge and discharge rate is adjusted according to the temperature range to optimize the formation process and performance of the battery. When the preset temperature value is 25℃~45℃, correspondingly, the first stage of formation charging uses a small current of 0.01~0.1C at the first rate for formation. The small current is conducive to the formation of a dense SEI film, which can effectively prevent the electrolyte from directly contacting the electrode interface; the second stage slightly increases the current, and the second rate is set to 0.05~0.15C current for formation according to the preset temperature value, which is conducive to improving the formation efficiency; the third stage continues to increase the current, and uses the third rate of 0.1~0.2C constant current and constant voltage charging to 100% SOC. 100% SOC full charging can ensure the full progress of side reactions. After the battery is fully charged, it is discharged at a constant current of 0.2-0.3C at the fourth rate. Discharging at a higher fourth rate helps to quickly discharge the battery to the target state of charge after it is fully charged, so that the organic components in the SEI film are partially reoxidized into inorganic components. The resulting SEI film is denser and more stable. At the same time, the SEI film impedance is reduced, which is beneficial to slow down the attenuation rate of the battery capacity and increase the cycle life of the battery.

[0010] In a possible design, when the preset temperature value is 45°C to 60°C, the first multiplier is 0.05 to 0.1°C, the second multiplier is 0.1 to 0.2°C, the third multiplier is 0.15 to 0.3°C, and the fourth multiplier is 0.3 to 0.5°C.

[0011] Through the above scheme, the influence of temperature on the battery charging characteristics is taken into account, and the charge and discharge rate is adjusted according to the temperature range to optimize the battery formation process and performance. For the higher preset temperature value range of 45℃~60℃, the corresponding first rate can be appropriately increased to 0.05~0.1C, but the current should not be increased excessively. A larger current is not conducive to the formation of a dense SEI film at the initial stage of formation, and is not conducive to controlling the heat generation of the battery at a temperature of 45℃~60℃. The corresponding second rate is 0.1~0.2C. When the battery temperature is 45℃~60℃, when the electrochemical reaction activity is strong, it can continue to charge at a faster speed while keeping the battery temperature and pressure within a safe range. The third rate is 0.15~0.3C for constant current and constant voltage charging, which helps to alleviate the concentration polarization inside the battery at a temperature of 45℃~60℃, improve the quality of the SEI film, and ensure that the battery reaches a full charge state. Finally, discharging at a higher fourth rate of 0.3-0.5C helps to discharge quickly after the battery is fully charged, so that the organic components in the SEI film are partially oxidized into inorganic components, and the resulting SEI film is denser and more stable. At the same time, the SEI film impedance is reduced, which is beneficial to slow down the attenuation rate of the battery capacity and increase the cycle life of the battery.

[0012] In a possible design, when the preset temperature value is 60°C to 80°C, the first multiplier is 0.1 to 0.3°C, the second multiplier is 0.15 to 0.5°C, the third multiplier is 0.2 to 0.5°C, and the fourth multiplier is 0.3 to 0.5°C.

[0013] Through the above scheme, when the corresponding preset temperature value is 60℃~80℃, the first rate is adjusted to 0.1~0.3C, the second rate is 0.15~0.5C, the third rate is 0.2~0.5C, and the fourth rate is 0.3~0.5C to optimize the formation process and performance of the battery. Using a rate of 0.1~0.3C for initial charging helps to control the heat generation of the battery under high temperature conditions and promote the formation of a stable SEI film. As the battery voltage rises to a certain threshold, the charging rate is increased to 0.15~0.5C, which helps to continue charging at a faster speed when the battery temperature is high and the electrochemical reaction activity is strong, thereby shortening the formation time to improve the formation efficiency. When the battery is close to a fully charged state, constant current and constant voltage charging is performed at a rate of 0.2~0.5C, which helps to alleviate the concentration polarization inside the battery at a higher temperature, improve the quality of the SEI film, and ensure that the battery reaches a fully charged state. Finally, discharge at a higher rate of 0.3-0.5C helps to quickly discharge the battery to the target state of charge after it is fully charged, so that the organic components in the SEI film are partially oxidized to inorganic components, and the resulting SEI film is more dense and stable. At the same time, the SEI film impedance is reduced, which is conducive to slowing down the attenuation rate of the battery capacity and increasing the cycle life of the battery. This design optimizes the battery formation process by carefully adjusting the charge and discharge rates at different temperatures, which helps to improve the performance and safety of the battery.

[0014] In a possible design, the method further includes the following steps: repeating step (4) according to a preset number of times to charge the lithium-ion battery at a third rate by constant current and constant voltage to a fully charged state of 100% SOC, and then standing for 5-10 minutes in step (7) to form a lithium-ion battery, wherein the preset number of times is 0-2 times.

[0015] According to the above scheme, low-current charging only needs to occur during the first charging of the battery, and there is no need to perform low-current charging again subsequently. Therefore, it is only necessary to add the charge and discharge process of steps (4) to (7) to reform and repair the unstable SEI film formed in the early stage of formation. When the charge and discharge process reaches 1-3 times, the reformation and repair of the SEI film can be completed well, so that a dense and stable SEI film is formed on the surface of the electrode material, and at the same time, the electrochemical properties of the active material are fully activated, so that it has a better capacity, which is beneficial to improving the cycle life and performance of the lithium-ion battery.

[0016] In one possible design, the lithium-ion battery is a lithium iron phosphate lithium-ion battery, a ternary lithium-ion battery, a lithium cobalt oxide lithium-ion battery, a lithium manganese oxide lithium-ion battery or a lithium iron manganese phosphate lithium-ion battery.

[0017] Through the above scheme, the above method is used to perform the above method on a lithium iron phosphate lithium ion battery, a ternary lithium ion battery, a lithium cobalt oxide lithium ion battery, a lithium manganese oxide lithium ion battery or a lithium iron manganese phosphate lithium ion battery, so that the cycle life of the lithium iron phosphate lithium ion battery, the ternary lithium ion battery, the lithium cobalt oxide lithium ion battery, the lithium manganese oxide lithium ion battery or the lithium iron manganese phosphate lithium ion battery can be improved.

[0018] In one possible design, the first state of charge is 5% SOC, and the second state of charge is 30% SOC.

[0019] Through the above scheme, charging with a small current constant current to the first state of charge is an initial charging process. The SEI film formed by charging with a small current at the 0-5% SOC stage is uniform and stable. The second state of charge is the amount of electricity charged at the second rate. Charging to 30% SOC is an intermediate step in the formation charging process, which is used to further form and stabilize the SEI film. Charging with a small current to 30% SOC can satisfy the formation of a dense SEI film, and then charging to 100% SOC at a larger rate can satisfy the formation of a dense SEI film while ensuring the formation efficiency.

[0020] In one possible design, the third rate ≤ the fourth rate; the target state of charge is 0% SOC.

[0021] Through the above scheme, the first rate and the second rate are both low-current charging rates. The purpose of low-current charging is to form a dense SEI film. The third rate is a relatively large charging rate, and the fourth rate is a discharge rate. The third rate ≤ the fourth rate, that is, discharge at a higher rate, which helps to quickly discharge to the target state of charge after the battery is fully charged, so that the organic components in the SEI film are partially reoxidized to inorganic components, and the resulting SEI film is more dense and stable, while reducing the SEI film impedance, which is conducive to slowing down the battery capacity decay rate and improving the battery cycle life. The target state of charge is 0% SOC, that is, discharging the battery to 0% SOC helps to ensure that the organic components in the SEI film are partially reoxidized to inorganic components, and the resulting SEI film is more dense and stable, while reducing the SEI film impedance, which is conducive to slowing down the battery capacity decay rate and improving the battery cycle life.

[0022] In a possible design, the formation time is controlled at 4h-12h.

[0023] Through the above scheme, the formation time has a significant impact on the long-term cycle performance of lithium-ion batteries. By optimizing the formation time, the number of formation equipment and power consumption can be reduced, and production costs can be reduced while ensuring battery performance. The formation time is controlled within the range of 4 hours to 12 hours, which can balance production efficiency and cost while ensuring the performance of lithium-ion batteries.

[0024] In a second aspect, the present application provides a lithium-ion battery, including a lithium-ion battery obtained according to any of the above-mentioned lithium-ion battery formation methods.

[0025] The beneficial effects of the lithium-ion battery provided in the second aspect and each possible design of the second aspect can refer to the beneficial effects brought about by the first aspect and each possible implementation method of the first aspect, which will not be repeated here.

[0026] The above description is only an overview of the technical solution of the embodiment of the present application. In order to more clearly understand the technical means of the embodiment of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiment of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, a brief introduction will be given below to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A flow chart of a lithium-ion battery and a formation method thereof provided in one embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used in the specification of the application herein are only for describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification, claims and accompanying drawings of this application are intended to cover non-exclusive inclusions.

[0031] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase "embodiments" in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] The term "and / or" in this article 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 can mean: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0033] In addition, the terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order, and may explicitly or implicitly include one or more of the features.

[0034] In the description of the present application, unless otherwise specified, "plurality" means more than two (including two), and similarly, "multiple groups" means more than two groups (including two).

[0035] Battery formation is a crucial part of the lithium-ion battery production process, which directly affects the quality and performance of the battery. Formation is the process of activating the internal positive and negative active materials through a certain charging and discharging method after the battery is manufactured, improving the battery's charging and discharging performance and comprehensive performance such as self-discharge and storage. The purpose of formation is to convert the active substances in the battery into substances with normal electrochemical effects with the help of the first charge, so that the electrode is mainly the negative electrode, forming an effective passivation film, namely the SEI film. During the formation process, the electrolyte is reduced on the surface of the negative electrode, and the insoluble reduction product is deposited on the surface of the negative electrode material to form a passivation layer, namely the solid electrolyte interface film (SEI film). The quality of the SEI film has a great influence on the cycle life, initial capacity loss, and rate performance of lithium-ion batteries.

[0036] As can be seen from the background art, the formation method in the prior art adopts charging formation, and does not consider the matching problem between the formation temperature and the formation current, so that the cycle performance, self-discharge performance and safety performance of the formed battery are poor.

[0037] In the related art, the formation temperature and formation current in the formation method used for lithium-ion batteries are not well matched, and when charging formation is used, the battery does not undergo a complete charge and discharge process, resulting in unsatisfactory quality of the generated SEI film such as uniformity and stability, which in turn leads to unsatisfactory cycle performance, self-discharge performance and safety performance of the lithium-ion battery.

[0038] In view of this, the embodiment of the present application provides a lithium ion battery and a formation method thereof, by optimizing the matching relationship between the formation temperature and the formation current, and adding a constant current discharge process, when the battery is charged with a constant current to the charging cut-off voltage, it continues to be charged with the voltage at a constant voltage to the cut-off current. At this time, the battery is fully charged, and then discharged with a certain rate constant current to a set charge state, so that the SEI film is partially reoxidized, the electrochemical properties of the active substance are fully activated, the proportion of the SEI film components is stabilized, and the phenomenon of rapid capacity decay in the initial stage of the cycle due to unstable SEI film and insufficient activation of active substances in the battery is avoided, thereby improving the cycle life of the lithium ion battery.

[0039] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0040] The present embodiment provides a formation method of a lithium-ion battery, wherein the lithium-ion battery can be a lithium-ion battery made of various materials, such as a lithium iron phosphate lithium-ion battery, a ternary lithium-ion battery, a lithium cobalt oxide lithium-ion battery, a lithium manganese oxide lithium-ion battery or a lithium iron manganese phosphate lithium-ion battery.

[0041] Figure 1 For the flow chart of the formation method provided in this embodiment, please refer to Figure 1 , the formation method of the lithium ion battery in this embodiment includes:

[0042] Step 1, setting the formation temperature to a preset temperature value, wherein the preset temperature value is between 25° C. and 80° C., and determining the charge and discharge rate according to the preset temperature value.

[0043] The charge and discharge rates include a first rate, a second rate, a third rate and a fourth rate, wherein the first rate is less than the second rate and less than the third rate.

[0044] When the formation temperature is set at 25°C to 80°C, the viscosity of the electrolyte can be reduced, and the transmission resistance of active lithium ions in the electrolyte can be reduced, thereby increasing the conductivity of the electrolyte and further improving the performance of the lithium-ion battery.

[0045] For example, the preset temperature value may be 25°C, 28°C, 30°C, 35°C, 40°C, 50°C, 60°C, 70°C or 80°C.

[0046] The first rate, the second rate, the third rate and the fourth rate are the charging rate or the discharging rate in each stage of the present embodiment. The charging or discharging rate of each stage is determined by the preset temperature value, so that the charging or discharging rate is optimized and matched according to the formation temperature, wherein the first rate < the second rate < the third rate, so that the electrochemical performance of the active material is fully activated, the SEI film component ratio is stabilized, thereby providing the compactness and stability of the SEI film, which is conducive to improving the cycle performance of the battery. The first rate and the second rate are both small current charging rates, and the purpose of small current charging is to form a compact SEI film. The third rate is a relatively large charging rate, and the fourth rate is a discharge rate. The third rate ≤ the fourth rate, that is, discharge at a higher rate, which helps to quickly discharge to the target state of charge after the battery is fully charged, so that the organic components in the SEI film are partially oxidized to inorganic components, and the obtained SEI film is more compact and stable, while reducing the SEI film impedance, which is conducive to slowing down the decay rate of the battery capacity and improving the cycle life of the battery.

[0047] Step 2: charging the lithium-ion battery at a first rate by constant current to a first state of charge, wherein the first state of charge is 0% to 10% SOC.

[0048] The charging process adopts a three-stage charging system. The charging rate in the first stage is the first rate. The first rate is charged to the first state of charge through constant current. The first state of charge is 0% to 10% SOC. The small current is conducive to the formation of a dense SEI film, which can effectively prevent the electrolyte from directly contacting the electrode interface. In the 0% to 10% SOC range, the electrode material can be initially activated and a stable SEI film can begin to form.

[0049] For example, the first state of charge may be 1% SOC, 5% SOC, 7% SOC, 9% SOC, or 10% SOC.

[0050] Step 3, charging the lithium-ion battery at a second rate by constant current to a second state of charge, wherein the second state of charge is 10% to 50% SOC.

[0051] The charging process adopts a three-stage charging system. The charging rate of the second stage is the second rate. The second stage slightly increases the current, which is conducive to ensuring the formation of a dense SEI film while improving the formation efficiency. The second state of charge is 10% to 50% SOC. Charging to 10% to 50% SOC is an intermediate step in the formation charging process, which is used to further form and stabilize the SEI film. By using a suitable current constant current charging in the 10% to 50% SOC range, the charging stress of the battery in the high SOC range can be reduced, thereby extending the battery life.

[0052] For example, the second state of charge may be 11% SOC, 13% SOC, 15% SOC, 18% SOC, 25% SOC, 35% SOC, 45% SOC, or 50% SOC.

[0053] Step 4: charge the lithium-ion battery at a third rate in a constant current and constant voltage manner to a fully charged state of 100% SOC.

[0054] The charging process adopts a three-stage charging system. The charging rate of the third stage is the third rate. The third stage continues to increase the current and charges to 100% SOC at constant current and constant voltage. The constant current and constant voltage charging mode combines the advantages of constant current charging (CC) and constant voltage charging (CV). It can charge quickly at a constant current in the early stage of charging, and then convert to constant voltage charging to ensure that the battery is fully charged. Among them, constant voltage charging can alleviate the concentration polarization inside the battery and improve the quality of the SEI film. At the same time, 100% SOC full charging can ensure the full progress of side reactions.

[0055] Step 5: Let stand for 5-10 minutes.

[0056] The 5-10 minute rest period can make the temperature distribution inside the battery more uniform, help the natural diffusion of heat inside the battery, and reduce the risk of local overheating. Adding a rest step between battery charging and discharging can effectively reduce the polarization effect and avoid battery performance degradation. It also helps the formation equipment to smoothly transition between charging and discharging states, reducing the impact on the equipment caused by state switching, thereby extending the service life of the formation equipment.

[0057] Step 6: discharging the lithium-ion battery at a fourth rate by constant current discharge to a target state of charge, wherein the target state of charge is 0% to 70% SOC.

[0058] After the battery is fully charged, it is discharged at the fourth rate constant current to 0% to 70% SOC. In this process, the organic components in the SEI film are partially oxidized into inorganic components, and the resulting SEI film is denser and more stable. At the same time, the reduction of organic components in the SEI film reduces its impedance, which can reduce the initial internal resistance of the cycle to a certain extent, which is beneficial to slow down the attenuation rate of the battery capacity, thereby increasing the cycle life of the battery.

[0059] For example, the fourth state of charge may be 0% SOC, 10% SOC, 15% SOC, 20% SOC, 25% SOC, 35% SOC, 45% SOC, 50% SOC, 60% SOC, or 70% SOC.

[0060] Step 7, let stand for 5-10 minutes to form a lithium-ion battery.

[0061] After discharge, the battery voltage will be higher or lower than the actual battery voltage due to polarization. Letting the battery stand for 5-10 minutes can gradually stabilize the battery voltage and approach the actual battery voltage. By letting the battery stand for 5-10 minutes during the charge and discharge process, the battery cycle stress can be reduced and the battery life can be extended.

[0062] In this embodiment, the method further includes repeating steps 4 to 7 according to a preset number of times, where the preset number of times is 0 to 2 times.

[0063] Low-current charging only needs to occur during the first charging of the battery, and there is no need to perform low-current charging again subsequently. Therefore, it is only necessary to add the charge and discharge process of steps (4) to (7) to reform and repair the unstable SEI film formed in the early stage of formation. When the charge and discharge process reaches 1-3 times, the reformation and repair of the SEI film can be completed well, so that a dense and stable SEI film is formed on the surface of the electrode material, and at the same time, the electrochemical properties of the active material are fully activated, so that it has a better capacity, which is beneficial to improving the cycle life and performance of the lithium-ion battery.

[0064] In this embodiment, repeating 2 times is equivalent to a total of 3 charge and discharge processes, which is sufficient to activate the battery and repair and reform the SEI film. According to actual production experience, too long formation time will affect the entire battery production progress. Under the premise of achieving the ideal formation effect, the number of repetitions should be reduced as much as possible, thereby shortening the formation time and reducing costs.

[0065] In some embodiments, step 1 includes: when the preset temperature value is 25°C to 45°C, the first magnification is 0.01 to 0.1C, the second magnification is 0.05 to 0.15C, the third magnification is 0.1 to 0.2C, and the fourth magnification is 0.2 to 0.3C.

[0066] Through the above scheme, the influence of temperature on the battery charging characteristics is taken into account, and the charge and discharge rate is adjusted according to the temperature range to optimize the formation process and performance of the battery. When the preset temperature value is 25℃~45℃, correspondingly, the first stage of formation charging uses a small current of 0.01~0.1C at the first rate for formation. The small current is conducive to the formation of a dense SEI film, which can effectively prevent the electrolyte from directly contacting the electrode interface; the second stage slightly increases the current, and the second rate is set to 0.05~0.15C current for formation according to the preset temperature value, which is conducive to improving the formation efficiency; the third stage continues to increase the current, and uses the third rate of 0.1~0.2C constant current and constant voltage charging to 100% SOC. 100% SOC full charging can ensure the full progress of side reactions. After the battery is fully charged, it is discharged at a constant current of 0.2-0.3C at the fourth rate. Discharging at a higher fourth rate helps to quickly discharge the battery to the target state of charge after it is fully charged, so that the organic components in the SEI film are partially reoxidized into inorganic components. The resulting SEI film is denser and more stable. At the same time, the SEI film impedance is reduced, which is beneficial to slow down the attenuation rate of the battery capacity and increase the cycle life of the battery.

[0067] In some embodiments, step 1 includes: when the preset temperature value is 45°C to 60°C, the first magnification is 0.05 to 0.1C, the second magnification is 0.1 to 0.2C, the third magnification is 0.15 to 0.3C, and the fourth magnification is 0.3 to 0.5C.

[0068] Through the above scheme, the influence of temperature on the battery charging characteristics is taken into account, and the charge and discharge rate is adjusted according to the temperature range to optimize the battery formation process and performance. For the higher preset temperature value range of 45℃~60℃, the corresponding first rate can be appropriately increased to 0.05~0.1C, but the current should not be increased excessively. A larger current is not conducive to the formation of a dense SEI film at the initial stage of formation, and is not conducive to controlling the heat generation of the battery at a temperature of 45℃~60℃. The corresponding second rate is 0.1~0.2C. When the battery temperature is 45℃~60℃, when the electrochemical reaction activity is strong, it can continue to charge at a faster speed while keeping the battery temperature and pressure within a safe range. The third rate is 0.15~0.3C for constant current and constant voltage charging, which helps to alleviate the concentration polarization inside the battery at a temperature of 45℃~60℃, improve the quality of the SEI film, and ensure that the battery reaches a full charge state. Finally, discharging at a higher fourth rate of 0.3-0.5C helps to discharge quickly after the battery is fully charged, so that the organic components in the SEI film are partially oxidized into inorganic components, and the resulting SEI film is denser and more stable. At the same time, the SEI film impedance is reduced, which is beneficial to slow down the attenuation rate of the battery capacity and increase the cycle life of the battery.

[0069] In some embodiments, step 1 includes: when the preset temperature value is 60°C to 80°C, the first magnification is 0.1 to 0.3°C, the second magnification is 0.15 to 0.5°C, the third magnification is 0.2 to 0.5°C, and the fourth magnification is 0.3 to 0.5°C.

[0070] Through the above scheme, when the corresponding preset temperature value is 60℃~80℃, the first rate is adjusted to 0.1~0.3C, the second rate is 0.15~0.5C, the third rate is 0.2~0.5C, and the fourth rate is 0.3~0.5C to optimize the formation process and performance of the battery. Using a rate of 0.1~0.3C for initial charging helps to control the heat generation of the battery under high temperature conditions and promote the formation of a stable SEI film. As the battery voltage rises to a certain threshold, the charging rate is increased to 0.15~0.5C, which helps to continue charging at a faster speed when the battery temperature is high and the electrochemical reaction activity is strong, thereby shortening the formation time to improve the formation efficiency. When the battery is close to a fully charged state, constant current and constant voltage charging is performed at a rate of 0.2~0.5C, which helps to alleviate the concentration polarization inside the battery at a higher temperature, improve the quality of the SEI film, and ensure that the battery reaches a fully charged state. Finally, discharge at a higher rate of 0.3-0.5C helps to quickly discharge the battery to the target state of charge after it is fully charged, so that the organic components in the SEI film are partially oxidized to inorganic components, and the resulting SEI film is more dense and stable. At the same time, the SEI film impedance is reduced, which is conducive to slowing down the attenuation rate of the battery capacity and increasing the cycle life of the battery. This design optimizes the battery formation process by carefully adjusting the charge and discharge rates at different temperatures, which helps to improve the performance and safety of the battery.

[0071] In the present embodiment, the time of step 2 to step 7 is controlled at 4h-12h.It is better to control the formation time 4h-12h, because the formation time has a significant impact on the long-term cycle performance of lithium ion battery, and by optimizing the formation time, the quantity and the power consumption of formation equipment can be reduced under the prerequisite of guaranteeing battery performance, and production costs can be reduced. The formation time is controlled in the scope of 4 hours to 12 hours, and when guaranteeing the lithium ion battery performance, production efficiency and cost can be balanced.

[0072] In this embodiment, when the preset temperature value is 25°C to 45°C, the formation time is 6h to 12h; when the preset temperature value is 45°C to 60°C, the formation time is 4h to 8h; when the preset temperature value is 60°C to 80°C, the formation time is 4h to 6h.

[0073] Based on the above embodiments, the present application further provides a lithium ion battery, including a lithium ion battery obtained according to any of the above-mentioned lithium ion battery formation methods. Since the steps and beneficial effects of the formation method have been described in detail in the previous embodiments, the present application will not repeat them here.

[0074] Example 1

[0075] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0076] (1) The preset temperature is 45°C.

[0077] (2) The first rate is 0.1C constant current charging to 5% SOC.

[0078] (3) Charge at a second rate of 0.15C constant current to 30% SOC.

[0079] (4) Charge at a third rate of 0.2C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C.

[0080] (5) Let stand for 10 minutes.

[0081] (6) 0.3C constant current discharge to 10% SOC.

[0082] (7) Let stand for 10 minutes.

[0083] (8) Finish the formation.

[0084] Example 2

[0085] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0086] (1) The preset temperature is 45°C.

[0087] (2) The first rate is 0.05C constant current charging to 5% SOC.

[0088] (3) Charge at a second rate of 0.1C constant current to 30% SOC.

[0089] (4) Charge at a third rate of 0.15C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C.

[0090] (5) Let stand for 10 minutes.

[0091] (6) 0.3C constant current discharge to 10% SOC.

[0092] (7) Let stand for 10 minutes.

[0093] (8) Finish the formation.

[0094] Example 3

[0095] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0096] (1) The preset temperature is 45°C.

[0097] (2) The first rate is 0.1C constant current charging to 5% SOC.

[0098] (3) Charge at a second rate of 0.2C constant current to 30% SOC.

[0099] (4) Charge at a third rate of 0.3C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C.

[0100] (5) Let stand for 10 minutes.

[0101] (6) 0.3C constant current discharge to 10% SOC.

[0102] (7) Let stand for 10 minutes.

[0103] (8) Finish the formation.

[0104] Example 4

[0105] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0106] (1) The preset temperature is 25°C.

[0107] (2) The first rate is 0.05C constant current charging to 10% SOC.

[0108] (3) Charge at a second rate of 0.1C constant current to 50% SOC.

[0109] (4) Charge at a third rate of 0.15C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C.

[0110] (5) Let stand for 10 minutes.

[0111] (6) 0.2C constant current discharge to 10% SOC.

[0112] (7) Let stand for 10 minutes.

[0113] (8) Forming a square aluminum shell lithium iron phosphate battery.

[0114] Example 5

[0115] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0116] (1) The preset temperature is 60°C.

[0117] (2) The first rate is 0.1C constant current charging to 5% SOC.

[0118] (3) Charge at a second rate of 0.2C constant current to 30% SOC.

[0119] (4) Charge at a third rate of 0.3C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C.

[0120] (5) Let stand for 10 minutes.

[0121] (6) 0.5C constant current discharge to 10% SOC.

[0122] (7) Let stand for 10 minutes.

[0123] (8) Finish the formation.

[0124] Example 6

[0125] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0126] (1) The preset temperature is 45°C.

[0127] (2) The first rate is 0.1C constant current charging to 5% SOC.

[0128] (3) Charge at a second rate of 0.15C constant current to 30% SOC.

[0129] (4) Charge at a third rate of 0.2C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C.

[0130] (5) Let stand for 10 minutes.

[0131] (6) 0.3C constant current discharge to 0% SOC.

[0132] (7) Let stand for 10 minutes.

[0133] (8) Finish the formation.

[0134] Example 7

[0135] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0136] (1) The preset temperature is 45°C.

[0137] (2) The first rate is 0.1C constant current charging to 5% SOC.

[0138] (3) Charge at a second rate of 0.15C constant current to 30% SOC.

[0139] (4) Charge at a third rate of 0.2C constant current and constant voltage to 3.65V, with a cut-off current of 0.05C.

[0140] (5) Let stand for 10 minutes.

[0141] (6) 0.3C constant current discharge to 0% SOC.

[0142] (7) Let stand for 10 minutes.

[0143] (8) The preset number of times is 1, and steps (4) to (7) are repeated once.

[0144] (9) Finish the formation.

[0145] Comparative Example 1

[0146] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0147] (1) The formation temperature is 45°C.

[0148] (2) 0.1C constant current charging to 5% SOC.

[0149] (3) 0.15C constant current charging to 30% SOC.

[0150] (4) End the formation.

[0151] Comparative Example 2

[0152] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0153] (1) The formation temperature is 45°C.

[0154] (2) 0.1C constant current charging to 5% SOC.

[0155] (3) 0.15C constant current charging to 30% SOC.

[0156] (4) 0.2C constant current and constant voltage charging to 3.65V, with a cut-off current of 0.05C.

[0157] (5) Finish the formation.

[0158] Comparative Example 3

[0159] A square aluminum shell lithium iron phosphate battery is formed using the following steps:

[0160] (1) The formation temperature is 45°C.

[0161] (2) 0.1C constant current charging to 5% SOC.

[0162] (3) 0.2C constant current charging to 30% SOC.

[0163] (4) 0.3C constant current and constant voltage charging to 3.65V, with a cut-off current of 0.05C.

[0164] (5) Finish the formation.

[0165] Performance Test:

[0166] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to a normal temperature discharge DCR test and a normal temperature cycle test. The test results are shown in Table 1. The specific test method is as follows:

[0167] Normal temperature discharge DCR test: set the temperature to 25℃, perform charge and discharge operations within the voltage range of 2.5-3.65V, first charge to 3.65V at 0.33C constant current and constant voltage, with a cut-off current of 0.05C, then discharge to 50% SOC at 0.33C constant current, let stand for 60min, record the voltage at the end of standing as V1, then perform 2C constant current discharge for 10s, record the voltage at the end of discharge as V2, calculate the discharge DCR value, the calculation method is discharge DCR = |V1-V2| / I;

[0168] Room temperature cycle performance test: set the temperature to 25℃, charge to 3.65V at 1C constant current and constant voltage, with a cut-off current of 0.05C, and then discharge to 2.5V at 1C constant current, which is recorded as the initial discharge capacity; the test is terminated when the capacity drops to 80% of the initial capacity, and the number of cycles is recorded.

[0169] Table 1:

[0170]

[0171] Combined with Table 1, it can be seen from Comparative Examples 1-3 that when conventional formation methods are used for formation treatment, due to the lack of a constant current discharge process, the unstable organic components in the SEI film cannot be reoxidized to form a dense and stable structure, resulting in a high initial DCR of the prepared lithium-ion battery. At the same time, the SEI film will be repaired and reformed during the cycle test, consuming electrolyte and active lithium ions, thereby deteriorating the cycle performance.

[0172] It can be seen from Examples 1-5 that the temperature in the formation stage and the size of the charge and discharge current will affect the impedance and cycle performance of the battery, but the formation temperature and the formation current can be reasonably matched, for example, a smaller formation current is matched when the formation temperature is low, and a larger formation current is matched when the formation temperature is high, so that the initial DCR difference of the battery can be reduced, the film formation is stable, and the cycle life difference is reduced; at the same time, it can be seen from Examples 1-3 that at the same formation temperature, a relatively better formation scheme can be screened out by adjusting the actual charge and discharge rate of the formation.

[0173] It can be seen from Examples 1 and 6 that when the constant current discharge is to 0% SOC, the organic components in the SEI film are further reoxidized into inorganic components, and the resulting SEI film is denser and more stable. At the same time, the reduction of the organic components in the SEI film reduces its impedance, which can reduce the initial internal resistance of the cycle to a certain extent, which is beneficial to slowing down the attenuation rate of the battery capacity and thereby improving the cycle life.

[0174] It can be seen from Examples 6 and 7 that by further increasing the number of formation charge and discharge cycles, the organic components in the SEI film will be further converted into inorganic components, the stability will be further increased, the DCR will be further reduced, and the cycle life will be increased.

[0175] The formation method provided by the present invention can effectively improve the cycle life of the battery, and at the same time has a high degree of matching with the equipment used in the existing normal production process, does not require the establishment of additional sites or the addition of adjustment equipment, and the formation process is simple to operate and is conducive to production.

[0176] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A formation method for a lithium ion battery, characterized in that: Includes steps: (1), setting the formation temperature to a preset temperature value, the preset temperature value is between 25°C and 80°C; determining the charge and discharge rate according to the preset temperature value, the charge and discharge rate including a first rate, a second rate, a third rate and a fourth rate, wherein the first rate < the second rate < the third rate; (2) charging the lithium-ion battery at a first rate by constant current to a first state of charge, wherein the first state of charge is 0% to 10% SOC; (3) charging the lithium-ion battery at a second rate by constant current to a second state of charge, wherein the second state of charge is 10% to 50% SOC; (4) charging the lithium-ion battery at a third rate by constant current and constant voltage to a full charge state of 100% SOC; (5) Let stand for 5-10 minutes; (6) discharging the lithium-ion battery at a fourth rate by constant current discharge to a target state of charge, wherein the target state of charge is 0% to 70% SOC; (7) Let stand for 5-10 minutes to form a lithium-ion battery.

2. The chemical formation method according to claim 1, characterized in that: Step (2) includes: when the preset temperature value is 25°C to 45°C, the first magnification is 0.01 to 0.1°C, the second magnification is 0.05 to 0.15°C, the third magnification is 0.1 to 0.2°C, and the fourth magnification is 0.2 to 0.3°C.

3. The chemical formation method according to claim 1, characterized in that: Step (2) includes: when the preset temperature value is 45°C to 60°C, the first magnification is 0.05 to 0.1°C, the second magnification is 0.1 to 0.2°C, the third magnification is 0.15 to 0.3°C, and the fourth magnification is 0.3 to 0.5°C.

4. The chemical formation method according to claim 1, characterized in that: Step (2) includes: when the preset temperature value is 60°C to 80°C, the first magnification is 0.1 to 0.3°C, the second magnification is 0.15 to 0.5°C, the third magnification is 0.2 to 0.5°C, and the fourth magnification is 0.3 to 0.5°C.

5. The chemical formation method according to claim 1, characterized in that: The method further includes the steps of: repeating steps (4) to (7) according to a preset number of times, wherein the preset number of times is 0 to 2 times.

6. The chemical formation method according to claim 1, characterized in that: The lithium ion battery is a lithium iron phosphate lithium ion battery, a ternary lithium ion battery, a lithium cobalt oxide lithium ion battery, a lithium manganese oxide lithium ion battery or a lithium iron manganese phosphate lithium ion battery.

7. The chemical formation method according to claim 1, characterized in that: The first state of charge is 5% SOC, and the second state of charge is 30% SOC.

8. The chemical formation method according to claim 1, characterized in that: The third rate ≤ the fourth rate; the target state of charge is 0% SOC.

9. The chemical formation method according to claim 1, characterized in that: The time from step (2) to step (7) is controlled at 4h-12h.

10. A lithium ion battery, characterized in that: A lithium ion battery obtained by the lithium ion battery formation method according to any one of claims 1 to 9.

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