Battery and formation method thereof
By adopting step-rate charging and multi-step charging and discharging steps under vacuum negative pressure during the decomposition process of lithium-ion batteries, the problems of SEI film density and lithium supplement decomposition are solved, and the effect of good battery interface and high cycleability is achieved.
Patent Information
- Application Number
- CN202510192462.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-20
- Publication Date
- 2025-05-13
AI Technical Summary
During the first charging and discharging process of lithium-ion batteries, solid electrolyte phase interface mask (SEI), resulting in permanent consumption of active lithium, reducing the battery capacity, energy density and cycle life. At the same time, the battery interface is prone to black spots, wrinkles, lithium evolution and other adverse phenomena.
A battery formation method is adopted, including step-rate charging and charging and discharging steps under vacuum negative pressure conditions. By using step-rate charging in steps S1-S3, the SEI film is densely stable, the voltage reaches 3.25V~3.4V in step S2 to stabilize the SEI film, the constant current and constant voltage are used to alleviate the polarization of the battery cell, the lithium supplement agent is activated in steps S4-S6 and the gas production rate is reduced, and the deep charging and discharging accelerates the decomposition of unstable solvents in steps S7-S9.
Through this method, the battery interface is good, without any adverse phenomena such as black spots, wrinkles, lithium separation, etc., the liquid loss in the transformation is extremely low, and the circulation and consistency of the battery are high, which solves the problem of the battery interface and improves the performance of the battery.
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Figure CN119994259A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of battery technology, and in particular to a battery and a formation method thereof. Background Art
[0002] In the preparation of lithium-ion batteries, when the battery is charged and discharged for the first time, the electrolyte will form a solid electrolyte interface film (SEI) on the surface of the negative electrode material such as graphite, and in this process, the active lithium from the positive electrode will be permanently consumed, resulting in a low efficiency (Coulomb efficiency) of the first charge and discharge cycle, thereby reducing the capacity, energy density and cycle life of the lithium-ion battery. In order to solve this problem, researchers have proposed a pre-lithiation method, that is, adding additional lithium sources to the positive electrode slurry during the homogenization process to compensate for the irreversible lithium loss consumed by the formation of the SEI film, thereby achieving the purpose of increasing the battery capacity and energy density. However, due to the particularity of the battery formation process and the high gas production characteristics of the lithium supplement, the battery interface is prone to black spots, wrinkles, lithium precipitation and other undesirable phenomena, which will lead to poor battery cycle performance. Summary of the invention
[0003] Based on this, in response to the above problems, the present application provides a battery and a formation method thereof to solve the above technical problems.
[0004] The first aspect of the present application provides a battery formation method, comprising the following steps:
[0005] S1, charging at a first current rate constant current to a power of Q1;
[0006] S2, charging at a second current rate until the voltage reaches 3.25V~3.4V;
[0007] S3, charging at a third current rate with constant current and constant voltage until the voltage reaches 3.5V~3.6V;
[0008] S4, charging at a fourth current rate constant current to a first cut-off voltage of 4.0V-4.1V;
[0009] S5, charging at a fifth current rate constant current to a first cut-off voltage of 4.0V-4.1V;
[0010] S6, charging at a sixth current rate constant current to a second cut-off voltage of 4.1V-4.3V;
[0011] S7, discharging at a constant current of the seventh current rate to a voltage of 1.9V~2.0V;
[0012] S8, charging at a constant current of the eighth current rate until the voltage reaches 3.65V~3.8V;
[0013] S9, discharging at a constant current of the ninth current rate to a power of Q2;
[0014] The positive electrode active material of the battery is lithium iron phosphate; the lithium supplement of the battery is lithium ferrite and / or lithium nickelate; the first cut-off voltage and the second cut-off voltage have different values;
[0015] Steps S1-S9 are all performed under vacuum negative pressure conditions. In step S3, the vacuum negative pressure condition K2 is set to -20KPa~0KPa; in steps S4-S6, the vacuum negative pressure condition K3 is set to -45KPa~-20KPa;
[0016] In steps S1-S9, a boss clamp is used to apply a restraining force to the battery.
[0017] In some implementations, in step S1 , the power Q1 is 5% SOC to 20% SOC; in step S9 , the power Q2 is 20% SOC to 80% SOC.
[0018] In some embodiments, in steps S1-S2, the vacuum negative pressure condition K1 is set to -65KPa~-35KPa; in steps S7-S9, the vacuum negative pressure condition K4 is set to -45KPa~-20KPa.
[0019] In some embodiments, the first current magnification is 0.01C~0.04C; the second current magnification is 0.05C~0.2C; and the third current magnification is 0.2C~0.5C.
[0020] In some embodiments, the fourth current multiplier is 0.05C~0.1C; the fifth current multiplier is 0.02C~0.07C; the sixth current multiplier is 0.01C~0.05C; the seventh current multiplier is 0.1C~0.5; the eighth current multiplier is 0.1C~0.5C; and the ninth current multiplier is 0.1C~1C.
[0021] In some embodiments, in steps S1-S9, a restraining force of 150 kg-450 kg is applied to the battery.
[0022] In some embodiments, in steps S1-S9, the battery is at an ambient temperature of 25°C to 48°C.
[0023] In some embodiments, before step S1, the following steps are also included: injecting liquid into the battery once, and the amount of liquid injected once accounts for 88% to 95% of the total injection amount.
[0024] In some embodiments, after any of steps S1 to S9 is completed, the battery is left to stand for 1 min to 10 min.
[0025] The second aspect of the present application provides a battery, which is obtained by the battery formation method provided by the first aspect.
[0026] The present application adopts a step rate charging method in steps S1-S3, so that the formed SEI film is in a relatively dense and stable state, thereby improving the cycle performance. By charging to a voltage of 3.25V~3.4V in step S2, a stable SEI film is obtained. By using constant current and constant voltage in step S3 to alleviate the polarization of the battery cell. By first charging to the first cut-off voltage twice at constant current in steps S4-S6, and then charging to the second cut-off voltage at constant current, it is ensured that the lithium supplement can be fully activated while reducing the gas production rate, so as to avoid a large amount of gas production in a short time from being discharged in time. By performing deep charging and discharging in steps S7-S9, it is helpful to accelerate the decomposition of the unstable solvent remaining in the electrolyte due to the decomposition of the lithium supplement through the redox process, thereby avoiding gas production during subsequent aging and volume separation. The battery formation interface problem of different contents and different types of positive electrode lithium supplements is solved, and the prepared battery interface is good, without black spots, wrinkles, lithium precipitation and other undesirable phenomena, and at the same time, the formation loss is extremely low, and the battery has high cyclability and consistency.
[0027] The battery formation method of the present application solves the problems of insufficient gas discharge and easy extraction of electrolyte by coordinating a boss clamp with a certain restraining force with the current and negative pressure in different charging intervals. It not only improves the consistency of the electrolyte retention and saves the cost of electrolyte loss, but also avoids the situation where the electrolyte is sucked away due to high negative pressure vacuuming, resulting in black spots or even lithium precipitation in the R corner area of the wound battery due to lack of liquid and poor dynamics.
[0028] The battery formation method of the present application applies a certain pressure to the battery through a boss clamp, so that the contact between the pole pieces is tighter during battery charging and discharging, which is more conducive to gas production and discharge. At the same time, the pole pieces expand more evenly and no wrinkles on the negative electrode interface occur. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 FIG. 1 is a process flow chart of a battery formation method in one embodiment of the present application.
[0030] Figure 2 This is a schematic diagram of the disassembly interface of the battery after secondary filling and full charging in Example 1 of the present application after formation.
[0031] Figure 3 This is a schematic diagram of the disassembly interface of the battery after secondary filling and full charging in Example 2 of the present application after formation.
[0032] Figure 4 This is a schematic diagram of the disassembly interface of the battery after secondary filling and full charging in Example 3 of the present application after formation.
[0033] Figure 5 This is a schematic diagram of the disassembly interface of the battery after secondary filling and full charging in Example 4 of the present application after formation.
[0034] Figure 6 This is a schematic diagram of the disassembly interface of the battery after secondary filling and full charging in comparative example 1 of the present application after formation. DETAILED DESCRIPTION
[0035] References to embodiments of the present application will now be provided in detail, one or more embodiments of which are described below. Each embodiment is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.
[0036] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.
[0037] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.
[0038] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.
[0039] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 100~150 nm means that the units of the left endpoint "100" and the right endpoint "150" are both nm (nanometers).
[0040] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.
[0041] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.
[0042] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
[0043] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or included, or may only include or include the listed components.
[0044] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
[0045] Based on this, in response to the above problems, the present application provides a battery and a formation method thereof to solve the above technical problems.
[0046] The first aspect of the present application provides a battery formation method, comprising the following steps:
[0047] S1, charging at a first current rate constant current to a power of Q1;
[0048] S2, charging at a second current rate until the voltage reaches 3.25V~3.4V;
[0049] S3, charging at a third current rate with constant current and constant voltage until the voltage reaches 3.5V~3.6V;
[0050] S4, charging at a fourth current rate constant current to a first cut-off voltage of 4.0V-4.1V;
[0051] S5, charging at a fifth current rate constant current to a first cut-off voltage of 4.0V-4.1V;
[0052] S6, charging at a sixth current rate constant current to a second cut-off voltage of 4.1V-4.3V;
[0053] S7, discharge at the seventh current rate to a constant current of 1.9V~2.0V;
[0054] S8, charging at a constant current of the eighth current rate until the voltage reaches 3.65V~3.8V;
[0055] S9, discharging at a constant current of the ninth current rate to a power of Q2;
[0056] The positive electrode active material of the battery is lithium iron phosphate; the lithium supplement of the battery is lithium ferrite and / or lithium nickelate; the first cut-off voltage and the second cut-off voltage have different values;
[0057] Steps S1-S9 are all performed under vacuum negative pressure conditions. In step S3, the vacuum negative pressure condition K2 is set to -20KPa~0KPa; in steps S4-S6, the vacuum negative pressure condition K3 is set to -45KPa~-20KPa;
[0058] In steps S1-S9, a boss clamp is used to apply a restraining force to the battery.
[0059] Exemplarily, in one embodiment, S4, constant current charging at a fourth current rate to a first cut-off voltage of 4.1V; S5, constant current charging at a fifth current rate to a first cut-off voltage of 4.1V; S6, constant current charging at a sixth current rate to a second cut-off voltage of 4.3V.
[0060] In another embodiment, S4, constant current charging at a fourth current rate to a first cut-off voltage of 4.05V; S5, constant current charging at a fifth current rate to a first cut-off voltage of 4.05V; S6, constant current charging at a sixth current rate to a second cut-off voltage of 4.2V.
[0061] The present application adopts step-rate charging in steps S1-S3 to make the growth of SEI film dense and stable during the formation process. In step S2, the voltage is charged to 3.25V~3.4V to obtain a stable SEI film. In step S3, constant current and constant voltage are used to alleviate the polarization of the battery cell.
[0062] By first charging to the first cut-off voltage twice at constant current in steps S4-S6, and then charging to the second cut-off voltage at constant current, since the first cut-off voltage is the main delithiation voltage platform of most lithium supplements, charging to the first cut-off voltage twice can decompose the lithium supplement to a greater extent; since the second cut-off voltage is the main delithiation cut-off voltage of most lithium supplements, the implementation of step S6 will help to completely decompose the lithium supplement; that is, through steps S4-S6, it is ensured that the lithium supplement can be fully activated, and at the same time the gas production rate is reduced to avoid a large amount of gas production in a short period of time that cannot be discharged in time, and S4-S6 can be applied to both iron-based and nickel-based lithium supplements.
[0063] By performing deep charge and discharge in steps S7-S9, the unstable solvent remaining in the electrolyte due to the decomposition of the lithium supplement agent is accelerated to decompose through the redox process, thereby avoiding gas production during subsequent aging and volume separation. The battery formation interface problem of different contents and different types of positive electrode lithium supplement agents is solved, and the prepared battery has a good interface without black spots, wrinkles, lithium precipitation and other undesirable phenomena. At the same time, the formation loss is extremely low and the battery consistency is high.
[0064] It can be understood that step S3 is the boundary voltage for the complete formation of the SEI film of the battery cell and the initial decomposition of the lithium supplement agent. Since the current rate of this step is large, the use of constant current and constant voltage can alleviate the polarization of the battery cell.
[0065] In some embodiments, in step S1, the power level Q1 is 5% SOC to 20% SOC, including but not limited to 5% SOC, 10% SOC, 15% SOC, and 20% SOC.
[0066] In step S9, if the SOC state is too low or too high, it is not conducive to the stability of the properties and composition of the SEI film during the aging process, so the power Q2 is set to 20% SOC~80% SOC, including but not limited to 20% SOC, 25% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, 80% SOC. When Q2 is at 20% SOC~80% SOC, the battery is in a voltage platform, which helps to avoid the attenuation of the battery capacity during aging due to excessive decomposition reaction of the electrolyte on the negative electrode.
[0067] In some embodiments, steps S1-S9 are all performed under vacuum negative pressure conditions. In steps S1-S2, the vacuum negative pressure condition K1 is set to -65KPa~-35KPa, including but not limited to -65KPa, -55KPa, -45KPa, and -35KPa. In step S3, the vacuum negative pressure condition K2 is set to -20KPa~0KPa, including but not limited to -20KPa, -15KPa, -10KPa, -5KPa, and 0KPa. In steps S4-S6, the vacuum negative pressure condition K3 is set to -45KPa~-20KPa, including but not limited to -45KPa, -35KPa, -25KPa, and -20KPa. In steps S7-S9, the vacuum negative pressure condition K4 is set to -45KPa~-20KPa, including but not limited to -45KPa, -35KPa, -30KPa, -25KPa, and -20KPa.
[0068] In some embodiments, the first current magnification is 0.01C to 0.04C, including but not limited to 0.01C, 0.02C, 0.03C, and 0.04C. The second current magnification is 0.05C to 0.2C, including but not limited to 0.05C, 0.1C, 0.15C, and 0.2C. The third current magnification is 0.2C to 0.5C, including but not limited to 0.2C, 0.3C, 0.4C, and 0.5C.
[0069] In step S1, if the first current rate is too large, the SEI film formed will be thicker and the cycle performance will be poor; if the first current rate is too small, the formation efficiency will be reduced. Therefore, by charging with a small first current rate in the range of 0.01C to 0.04C in step S1, the quality of the formed SEI film is more operable, and the formation time is more flexible.
[0070] In the above step S2, since the SEI film is basically stable, the second current rate can be appropriately higher than the first current rate. In the above step S3, since the SEI film has been formed and the lithium supplement in this interval has not yet begun to decompose, the third current rate does not need to be a small rate, otherwise it will affect the formation efficiency. That is, by adopting step rate charging in steps S1-S3, the growth of the SEI film during the formation process is more dense and stable, and the cycle performance is improved.
[0071] In the above step S4, the lithium supplement reacts and decomposes to produce a large amount of gas. If the current rate is too large, the decomposition effect will be poor, and a large amount of gas produced in a short time will be difficult to be discharged in time, thereby affecting the formation effect and the battery interface state. Therefore, in some embodiments, the fourth current rate is 0.05C~0.1C, including but not limited to 0.05C, 0.07C, 0.09C, and 0.1C.
[0072] In the above steps S5-S6, if the current magnification is too large, the lithium supplement agent will not be completely decomposed. Therefore, in some embodiments, the fifth current magnification is 0.02C-0.07C, including but not limited to 0.02C, 0.03C, 0.05C, and 0.07C. The sixth current magnification is 0.01C-0.05C, including but not limited to 0.01C, 0.02C, 0.03C, and 0.04C.
[0073] The present application uses multiple small current charging in steps S4-S6 to allow the lithium supplement to fully react, without leaving inactive residues in the positive electrode material and without continuing to react and produce gas during subsequent charging and discharging processes.
[0074] The deep charge and discharge in the above steps S7-S9 will help the unstable solvent remaining in the electrolyte due to the decomposition of the lithium supplement agent to accelerate the decomposition through the redox process, thereby avoiding gas production during subsequent aging and volume separation. Since this section of the process mainly focuses on the deep charge and discharge, the current rate does not need to be too small. Therefore, in some embodiments, the seventh current rate is 0.1C~0.5C, including but not limited to 0.1C, 0.3C, 0.4C, and 0.5C. The eighth current rate is 0.1C~0.5C, including but not limited to 0.1C, 0.3C, 0.4C, and 0.5C. The ninth current rate is 0.1C~1C, including but not limited to 0.1C, 0.4C, 0.7C, and 1C.
[0075] In one embodiment, the battery is charged at a constant current and voltage of 0.2C to 0.5C to a voltage of 3.5V to 3.6V under a negative pressure of -20KPa to 0KPa. A relatively low negative pressure of -20KPa to 0KPa is applied in step S3 to prevent the electrolyte from being easily drawn out due to excessive negative pressure; at the same time, the battery is charged at a constant current and voltage of 0.2C to 0.5C to a voltage of 3.5V to 3.6V in step S3. Since this voltage is lower than the initial gas production voltage range of most lithium supplements, the battery will not be unable to exhaust gas in time due to the use of a high rate current in the high gas production stage, and constant current and voltage charging can make the formed SEI film interface more stable.
[0076] In one embodiment, step S2 is specifically charged at a constant current of 0.05C to 0.2C until the voltage reaches 3.3V. Step S3 is specifically charged at a constant current and constant voltage of 0.2C to 0.5C until the voltage reaches 3.55V. By setting the voltage in step S2 to 3.3V, a more stable SEI film can be formed. The voltage in step S3 is set to 3.55V, which is lower than the initial gas production stage of most lithium supplements, and the result of using a high rate current in the high gas production stage and failing to exhaust in time will not occur.
[0077] In some embodiments, in steps S1-S9, a restraining force of 150 kg to 450 kg is applied to the battery, including but not limited to 150 kg, 200 kg, 350 kg, and 450 kg.
[0078] The present application uses a boss clamp to assist in the formation process. On the one hand, a boss clamp of a calculated appropriate thickness is used to apply a restraining force of 150kg-450kg to the battery, so that the expansion of the electrode is restrained by the boss clamp during the formation process. During the formation process, the electrode contact will be tighter and the overall expansion will be more uniform, which will greatly improve interface problems such as wrinkles. On the other hand, since more gas is produced during the formation process of the battery, if the boss clamp is not used to apply the restraining force, the gas will easily exist in the gap between the positive electrode sheet / diaphragm / negative electrode sheet, making it difficult to discharge. The application of the boss clamp has a better tightness of the interface, which has a greater positive effect on the discharge of gas.
[0079] In some embodiments, in steps S1-S9, the battery is at an ambient temperature of 25°C to 48°C, including but not limited to 25°C, 30°C, 35°C, 40°C, 45°C, and 48°C.
[0080] In some embodiments, before step S1, the following steps are also included: injecting liquid into the battery once, and the amount of liquid injected once accounts for 88% to 95% of the total injection amount, including but not limited to 88%, 89%, 90%, 91%, 92%, 93%, 94%, and 95%.
[0081] It is understandable that when the injection volume is too low, the wettability of the pole piece is insufficient for the lithium replenishment formation step of deep charge and discharge, which is easy to cause lithium precipitation due to insufficient electrolyte, especially the R angle of the wound battery cell is prone to this phenomenon. When the injection volume is too high, the amount of liquid loss during formation is usually relatively high, and the effective liquid retention volume during the formation process does not increase, while increasing the cost of the electrolyte. Therefore, due to the deep charging degree and high charging voltage during battery formation, the demand for electrolyte is relatively large. In this application, the amount of one injection is set to 88%~95% of the total injection volume, which can meet the amount of formation electrolyte and make the pole piece fully infiltrated.
[0082] In some embodiments, after any step S1-S9 is completed, the battery is left to stand for 1 min to 10 min, including but not limited to 1 min, 3 min, 5 min, 7 min, and 10 min.
[0083] The battery formation method of the present application adopts step rate charging in steps S1-S3, so that the growth of the SEI film is denser and more stable, thereby improving the cycle performance.
[0084] The battery formation method of the present application uses multiple small current charging in steps S4-S6 to allow the lithium supplement to fully react, without leaving inactive residues in the positive electrode material and without continuing to react and produce gas during subsequent charging and discharging processes.
[0085] The battery formation method of the present application, by performing deep charge and discharge in steps S7-S9, helps to accelerate the decomposition of unstable solvents remaining in the electrolyte due to the decomposition of the lithium supplement through the redox process, thereby avoiding gas production during subsequent aging and volume separation.
[0086] In the battery formation method of the present application, in steps S1-S2, gas is generated due to the formation of the SEI film. Therefore, by applying a vacuum negative pressure of -65KPa to -35KPa to the battery in steps S1-S2, the gas can be discharged in time and the electrolyte can be prevented from being sucked away.
[0087] In the battery formation method of the present application, in steps S4-S6, the lithium supplement agent gradually decomposes to generate gas. At this time, the battery cell is already in a high power state, the electrode is expanded, and the electrolyte is easily sucked away. Therefore, by applying a relatively smaller vacuum negative pressure of -45KPa~-20KPa to the battery in steps S4-S6, combined with multiple low-rate current charging, it is possible to completely discharge the gas while avoiding the electrolyte being sucked away, resulting in poor interface due to lack of liquid, especially the R corner of the wound battery cell is very prone to lack of liquid.
[0088] The battery formation method of the present application solves the problems of insufficient gas discharge and easy extraction of electrolyte by coordinating a boss clamp with a certain restraining force with the current and negative pressure in different charging intervals. It not only improves the consistency of the electrolyte retention and saves the cost of electrolyte loss, but also avoids the situation where the electrolyte is sucked away due to high negative pressure vacuuming, resulting in black spots or even lithium precipitation in the R corner area of the wound battery due to lack of liquid and poor dynamics.
[0089] The battery formation method of the present application applies a certain pressure to the battery through a boss clamp, so that the contact between the pole pieces is tighter during battery charging and discharging, which is more conducive to gas production and discharge. At the same time, the pole pieces expand more evenly and no wrinkles on the negative electrode interface occur.
[0090] The second aspect of the present application provides a battery, which is obtained by the battery formation method provided by the first aspect.
[0091] The present application will be further described below with reference to specific embodiments and comparative examples.
[0092] Example 1
[0093] The positive electrode composition of the battery in this embodiment is as follows: the mass ratio of the positive electrode active material, the conductive agent, the binder and the lithium supplement is 96.6:0.7:1.7:1. Among them, the positive electrode active material is lithium iron phosphate (LFP), the conductive agent is conductive carbon black (SP) and carbon nanotubes (CNT), the mass ratio of conductive carbon black and carbon nanotubes is 3:2, the binder is polyvinylidene fluoride (PVDF), and the lithium supplement is lithium ferrite (LFO).
[0094] The negative electrode of the battery is composed of a negative electrode active material, a conductive agent, and a binder in a mass ratio of 96:1:3. The negative electrode active material is graphite (Gr), the conductive agent is conductive carbon black (SP), and the binder is carboxymethyl cellulose sodium (CMC) and styrene-butadiene rubber (SBR), and the mass ratio of CMC to SBR is 1:1.
[0095] The battery has a designed capacity of 133Ah and a wound cell structure, and is formed according to the following steps.
[0096] The battery is injected once (the electrolyte composition of the first injection is: the mass ratio of solvent dimethyl carbonate (DMC), lithium salt LiPF6 and additive fluoroethylene carbonate (FEC) is 82:12:6), and the amount of the first injection accounts for 90% of the total injection amount. And the injection coefficient of the electrolyte is 3.15g / Ah, that is, the total injection amount is calculated according to the injection coefficient * the design capacity of the battery.
[0097] In one of the injections, the following steps are used for the formation:
[0098] S1. Charge at a constant current of 0.04C until the battery reaches 10% SOC and the negative pressure is -60KPa.
[0099] S2. Charge at a constant current of 0.1C until the voltage reaches 3.3V and the negative pressure is -60KPa.
[0100] S3. Charge at 0.2C constant current and constant voltage until the voltage reaches 3.55V and the negative pressure value is -10KPa.
[0101] S4, charge to 4.05V at a constant current of 0.05C, and the negative pressure value is -20KPa.
[0102] S5. Charge to 4.05V at a constant current of 0.03C and a negative pressure of -20KPa.
[0103] S6. Charge to 4.2V at a constant current of 0.02C and a negative pressure of -20KPa.
[0104] S7, discharge at a constant current of 0.3C to 2.0V, and the negative pressure value is -20KPa.
[0105] S8. Charge to 3.65V at a constant current of 0.5C and a negative pressure of -20KPa.
[0106] S9, discharge at 0.5C constant current to 40% SOC, negative pressure value is -20KPa.
[0107] During the formation process, a boss clamp is used to provide 400kg of restraint force for the battery. The formation environment temperature is 35°C. Each step in S1-S9 needs to be left to stand for 5 minutes.
[0108] Example 2
[0109] The positive electrode composition of the battery in this embodiment is as follows: the mass ratio of the positive electrode active material, the conductive agent, the binder and the lithium supplement is 96.6:0.7:1.7:1. Among them, the positive electrode active material is lithium iron phosphate (LFP), the conductive agent is conductive carbon black (SP) and carbon nanotubes (CNT), the mass ratio of conductive carbon black and carbon nanotubes is 3:2, the binder is polyvinylidene fluoride (PVDF), and the lithium supplement is lithium ferrite (LFO) and lithium nickelate (LNO), and the mass ratio of lithium ferrite (LFO) and lithium nickelate (LNO) is 1:1.
[0110] The negative electrode of the battery is composed of a negative electrode active material, a conductive agent, and a binder in a mass ratio of 96:1:3. The negative electrode active material is graphite (Gr), the conductive agent is conductive carbon black (SP), and the binder is carboxymethyl cellulose sodium (CMC) and styrene-butadiene rubber (SBR), and the mass ratio of CMC to SBR is 1:1.
[0111] The battery has a designed capacity of 133Ah and a wound cell structure, and is formed according to the following steps.
[0112] The battery is injected once (the electrolyte composition of the first injection is: the mass ratio of solvent DMC, lithium salt LiPF6 and additive FEC is 82:12:6), and the amount of the first injection accounts for 90% of the total injection amount. And the injection coefficient of the electrolyte is 3.15g / Ah, that is, the total injection amount is calculated according to the injection coefficient * the design capacity of the battery.
[0113] In one of the injections, the following steps are used for the formation:
[0114] S1. Charge at a constant current of 0.01C to 5% SOC, with a negative pressure of -60KPa.
[0115] S2. Charge at a constant current of 0.2C until the voltage reaches 3.4V and the negative pressure is -60KPa.
[0116] S3, charge at 0.35C constant current and constant voltage until the voltage reaches 3.5V, and the negative pressure value is -20KPa.
[0117] S4, charge to 4V at 0.1C constant current, negative pressure value is -30KPa.
[0118] S5. Charge to 4V at a constant current of 0.05C and a negative pressure of -30KPa.
[0119] S6. Charge to 4.1V at a constant current of 0.05C and a negative pressure of -30KPa.
[0120] S7, discharge at a constant current of 0.1C to 1.9V, and the negative pressure value is -30KPa.
[0121] S8. Charge to 3.7V at a constant current of 0.1C and a negative pressure of -30KPa.
[0122] S9, discharge at 0.1C constant current to 20% SOC, negative pressure value is -30KPa.
[0123] During the formation process, a boss clamp is used to provide 400kg of restraint force for the battery. The formation environment temperature is 35°C. Each step in S1-S9 needs to be left to stand for 5 minutes.
[0124] Example 3
[0125] The difference between this embodiment and embodiment 1 is that:
[0126] S1. Charge at a constant current of 0.04C until the battery reaches 20% SOC and the negative pressure is -60KPa.
[0127] S2. Charge at a constant current of 0.1C until the voltage reaches 3.25V and the negative pressure is -60KPa.
[0128] S3. Charge at 0.5C constant current and constant voltage until the voltage reaches 3.6V and the negative pressure value is -10KPa.
[0129] S4, charge at 0.05C constant current to 4.1V, negative pressure value is -45KPa.
[0130] S5. Charge to 4.1V at a constant current of 0.07C and a negative pressure of -45KPa.
[0131] S6. Charge to 4.3V at a constant current of 0.02C and a negative pressure of -45KPa.
[0132] S7, discharge at 0.5C constant current to 2.0V, negative pressure value is -45KPa.
[0133] S8, charge at 0.5C constant current to 3.8V, negative pressure value is -45KPa.
[0134] S9, discharge at 1C constant current to 80% SOC, negative pressure value is -45KPa.
[0135] Example 4
[0136] The difference between this embodiment and embodiment 1 is that in steps S4 and S5, the battery is charged to 4.0 V at constant currents of 0.08 C and 0.05 C respectively.
[0137] Comparative Example 1
[0138] The difference between this comparative example and Example 1 is that the negative pressure value in steps S4 to S6 is -80 KPa.
[0139] Comparative Example 2
[0140] The difference between this comparative example and Example 1 is that no boss clamp is used to provide clamping force for the battery during the formation process.
[0141] Comparative Example 3
[0142] The difference between this comparative example and Example 1 is that the negative pressure value in step S3 is set to -60 KPa.
[0143] Comparative Example 4
[0144] The difference between this comparative example and Example 1 is that step rate charging is not used in steps S1-S3. Specifically:
[0145] S1. Charge at a constant current of 0.1C until the battery reaches 10% SOC and the negative pressure is -60KPa.
[0146] S2. Charge at a constant current of 0.1C until the voltage reaches 3.3V and the negative pressure is -60KPa.
[0147] S3. Charge at 0.1C constant current and constant voltage until the voltage reaches 3.55V and the negative pressure is -10KPa.
[0148] Comparative Example 5
[0149] The difference between this comparative example and Example 1 is that the first cut-off voltage and the second cut-off voltage have the same value, both set to 4.05V.
[0150] Comparative Example 6
[0151] The difference between this comparative example and embodiment 1 is that step S4 is not provided.
[0152] Comparative Example 7
[0153] The difference between this comparative example and embodiment 1 is that step S2 is not provided.
[0154] Test Case
[0155] (1) The liquid loss during formation of the above-mentioned embodiments and comparative examples was tested, wherein the liquid loss during formation = the weight of the battery cell before formation - the weight of the battery cell after formation. The results are shown in Table 1 below.
[0156] (2) After the batteries of the above-mentioned embodiment and the comparative example are formed, the secondary injection (the electrolyte composition of the secondary injection and the primary injection is exactly the same, and the secondary injection + the primary injection = the total injection amount) are fully charged and disassembled to observe the negative electrode interface. Figure 2 , Figure 3 , Figure 4 and Figure 5 The results are respectively from Example 1, Example 2, Example 3 and Example 4. From the interface results, it can be seen that Examples 1-4 have good interfaces without black spots, wrinkles, lithium precipitation and the like. Figure 6 According to the results of Comparative Example 1, lithium deposition occurs at the R corner of the battery cell. The reason is that the lithium supplement decomposes to produce a large amount of gas. The high negative pressure value draws away a large amount of electrolyte while drawing away the gas, resulting in liquid deficiency at the R corner of the battery cell.
[0157] (3) Cycle performance: The batteries of the above-mentioned embodiments and comparative examples were subjected to conventional processes such as subsequent capacity division and aging to achieve normal battery offline. All batteries were compared for cycle performance under the same test conditions, i.e., 25°C, 1C constant current and constant voltage charging to 3.65V / 1C constant current and constant voltage discharging to 2V, and their capacity retention rate was tested.
[0158] Table 1
[0159] Cycle performance (600 cycles capacity retention %) Liquid loss / g Example 1 94.12 3.8 Example 2 94.23 4.3 Example 3 94.03 4.9 Example 4 94.09 3.6 Comparative Example 1 86.65 23.2 Comparative Example 2 90.26 3.3 Comparative Example 3 89.12 12.6 Comparative Example 4 92.86 4.6 Comparative Example 5 87.26 3.2 Comparative Example 6 89.36 3.1 Comparative Example 7 90.23 4.2
[0160] By comparing Example 1 with Comparative Examples 1-7, it can be found that the battery obtained by adopting the specific formation method defined in the present application has better cycle performance.
[0161] Comparison of Example 1 and Comparative Example 1 shows that due to the high negative pressure value, the liquid loss of the formation is significantly increased, and according to Figure 6 It can also be seen that the negative electrode plate interface of Comparative Example 1 is also bad, so the cycle performance is poor.
[0162] By comparing Example 1 and Comparative Example 2, it can be seen that since no clamping force is provided, the exhaust effect during the battery cell formation process will be poor, so the negative electrode interface also tends to be poor, resulting in poor cycle performance.
[0163] By comparing Example 1 and Comparative Example 3, it can be seen that since the negative pressure value in S3 is too large, the liquid loss during the formation is significantly increased, and the cycle performance is poor.
[0164] Comparing Example 1 with Comparative Example 4, since the current rates of S1-S3 are the same, the generated SEI film is too dense, which leads to a decrease in the cycle performance.
[0165] Comparing Example 1 with Comparative Example 5, since the first cut-off voltage and the second cut-off voltage have the same value, the lithium supplement agent is not completely decomposed, and thus the cycle performance is poor.
[0166] Compared with Example 1 and Comparative Example 6, since step S4 is not provided, the lithium supplement agent is not completely decomposed, so the cycle performance is poor.
[0167] Compared with Example 1 and Comparative Example 7, since step S2 is not provided, the growth of the SEI film during the formation process is relatively loose, and the cycle performance is also poor.
[0168] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0169] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.
Claims
1. A battery formation method, characterized in that: The following steps are involved: S1, charging at a first current rate constant current to a power of Q1; S2, charging at a second current rate until the voltage reaches 3.25V~3.4V; S3, charging at a third current rate with constant current and constant voltage until the voltage reaches 3.5V~3.6V; S4, charging at a fourth current rate constant current to a first cut-off voltage of 4.0V-4.1V; S5, charging at a fifth current rate constant current to a first cut-off voltage of 4.0V-4.1V; S6, charging at a sixth current rate constant current to a second cut-off voltage of 4.1V-4.3V; S7, discharging at a constant current of the seventh current rate to a voltage of 1.9V~2.0V; S8, charging at a constant current of the eighth current rate until the voltage reaches 3.65V~3.8V; S9, discharging at a constant current of the ninth current rate to a power of Q2; Wherein, the positive electrode active material of the battery is lithium iron phosphate; the lithium supplement of the battery is lithium ferrite and / or lithium nickelate; the first cut-off voltage and the second cut-off voltage have different values; Steps S1-S9 are all performed under vacuum negative pressure conditions. In step S3, the vacuum negative pressure condition K2 is set to -20KPa~0KPa; in steps S4-S6, the vacuum negative pressure condition K3 is set to -45KPa~-20KPa; In steps S1-S9, a boss clamp is used to apply a restraining force to the battery.
2. The chemical formation method according to claim 1, characterized in that: In step S1 , the power level Q1 is 5% SOC to 20% SOC; in step S9 , the power level Q2 is 20% SOC to 80% SOC.
3. The chemical formation method according to claim 1, characterized in that: In steps S1-S2, the vacuum negative pressure condition K1 is set to -65KPa~-35KPa; in steps S7-S9, the vacuum negative pressure condition K4 is set to -45KPa~-20KPa.
4. The chemical formation method according to claim 1, characterized in that: The first current magnification is 0.01C~0.04C; the second current magnification is 0.05C~0.2C; and the third current magnification is 0.2C~0.5C.
5. The chemical formation method according to claim 1, characterized in that: The fourth current multiplier is 0.05C~0.1C; the fifth current multiplier is 0.02C~0.07C; the sixth current multiplier is 0.01C~0.05C; the seventh current multiplier is 0.1C~0.5C; the eighth current multiplier is 0.1C~0.5C; and the ninth current multiplier is 0.1C~1C.
6. The chemical formation method according to claim 1, characterized in that: In steps S1-S9, a restraining force of 150kg-450kg is applied to the battery.
7. The chemical formation method according to claim 1, characterized in that: In steps S1-S9, the battery is at an ambient temperature of 25°C to 48°C.
8. The chemical formation method according to claim 1, characterized in that: Before step S1, the method further includes the following steps: injecting liquid into the battery once, wherein the amount of liquid injected once accounts for 88% to 95% of the total amount of liquid injected.
9. The chemical formation method according to claim 1, characterized in that: After any of steps S1 to S9 is completed, the battery is left to stand for 1 min to 10 min.
10. A battery, characterized in that: The battery is obtained by the battery formation method according to any one of claims 1 to 9.