Lithium battery and manufacturing method thereof

Abstract

The invention provides a lithium battery and a manufacturing method thereof. The manufacturing method comprises the following steps: S100, performing primary liquid injection and formation on a lithium battery; s200, the formed lithium battery is subjected to restrained electricity supplementation; and S300, carrying out aging and capacity grading on the lithium battery subjected to restrained power supply. According to the invention, the accuracy of lithium battery K value defect screening can be improved, defective products with too fast self-discharge can be more accurately screened out, and pole piece expansion and wrinkles are avoided, so that the manufacturing process of the lithium battery is improved, the electrochemical performance of the lithium battery is improved, and the outgoing quality of the product is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and more particularly, to a lithium battery and a manufacturing method thereof. Background Art

[0002] As an efficient and environmentally friendly energy storage device, lithium batteries have been widely used in many fields in recent years and have become an important driving force for the global energy transformation and the development of the green economy. Lithium batteries are the core components of electric vehicles. With the rapid development of the global new energy vehicle market, the demand for power batteries continues to grow. Lithium batteries also have great application potential in energy storage fields such as power grid peak shaving, renewable energy grid connection, home energy storage, and backup power supplies for communication base stations. In addition, lithium batteries are widely used in consumer electronic products such as smart phones, laptops, Bluetooth headsets, and wearable devices.

[0003] On the one hand, when manufacturing lithium batteries, by performing K - value defective screening, defective products with too fast self - discharge can be screened out. Therefore, the accuracy of K - value defective screening has a crucial impact on the ex - factory quality of products.

[0004] On the other hand, negative electrode swelling is a common problem during the use of lithium batteries. Negative electrode swelling will cause stress concentration inside the battery, thereby increasing the internal pressure of the battery, resulting in an increase in the battery thickness, and in severe cases, it may cause the rupture and leakage of the battery shell. In addition, negative electrode swelling will also cause the movement path of lithium ions inside the battery to become longer, increasing the resistance and affecting the charge - discharge efficiency of the battery. Finally, negative electrode swelling will limit the utilization rate of the battery capacity and reduce the battery's endurance. Therefore, how to reduce or avoid negative electrode swelling during the charge - discharge process in the manufacturing process of lithium batteries also has a crucial impact on the ex - factory quality of products.

[0005] The technical problems existing in the manufacturing process of lithium batteries in the prior art are that the accuracy of K - value defective screening is not ideal enough and how to avoid negative electrode swelling during the charge - discharge process. How to improve the manufacturing process of lithium batteries and enhance the electrochemical performance of lithium batteries is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] The problem solved by the present invention is how to improve the accuracy of K - value defective screening of lithium batteries and how to avoid negative electrode swelling during the charge - discharge process, thereby improving the manufacturing process of lithium batteries and enhancing the electrochemical performance of lithium batteries.

[0007] To solve the above problems, the present invention provides a manufacturing method of a lithium battery, and the manufacturing method includes:

[0008] S100. Perform primary liquid injection and formation on the lithium battery;

[0009] S200. Perform constrained charging on the lithium battery after formation;

[0010] S300. Age and capacity test the lithium battery after constrained charging.

[0011] In the above technical solution, the manufacturing method further includes: performing secondary liquid injection on the lithium battery after the formation process and before the constrained charging process; and / or aging the lithium battery before the formation process.

[0012] In any of the above technical solutions, the constrained charging is: charging and discharging the lithium battery while applying a constraining force to the lithium battery.

[0013] In any of the above technical solutions, the constrained charging process specifically includes:

[0014] A. Place the lithium battery after formation on a constrained tray, and adjust the extension distance of the extrusion rod of the constrained tray so that the extrusion rod applies a constraining force to the lithium battery;

[0015] B. Transport the constrained tray to a charging cabinet so that the lithium battery is charged and discharged with a charging current while being under the applied constraining force.

[0016] In any of the above technical solutions, in step A, control the extension distance of the extrusion rod to be 0 mm to 56 mm; and / or in step B, control the charging current to be 60 A to 200 A; and / or in step B, control the state of charge (SOC) at the end of the lithium battery charging to be 0% to 100%.

[0017] In any of the above technical solutions, the manufacturing method further includes: using the DOE experimental design method to verify the process parameters of the constrained charging. The verified process parameter factors include: the extension distance of the extrusion rod, the charging current, and the SOC at the end of charging; the response variables used for verification include: the number of wrinkles on the negative electrode sheet after battery disassembly, and the accuracy of K value screening.

[0018] In any of the above technical solutions, when only considering the number of wrinkles on the negative electrode sheet after battery disassembly as a single response variable, use the normal plot of standardized effects to determine that the extension distance of the extrusion rod and the charging current are significant factors, and the SOC at the end of charging is a non-significant factor; according to the variance analysis of the Pareto chart of standardized effects, determine that the significant influence degree of the extension distance of the extrusion rod is higher than that of the charging current; when only considering the accuracy of K value screening as a single response variable, use the normal plot of standardized effects to determine that the charging current and the SOC at the end of charging are significant factors, and the extension distance of the extrusion rod is a non-significant factor; according to the variance analysis of the Pareto chart of standardized effects, determine that the significant influence degree of the SOC at the end of charging is higher than that of the charging current.

[0019] In any of the above technical solutions, in step A, the extension distance of the extrusion rod is controlled to be 56 mm; in step B, the charging current is controlled to be 100 A; in step B, the SOC at the end of lithium battery charging is controlled to be 100%.

[0020] In any of the above technical solutions, in step A, after adjusting the extension distance of the extrusion rod of the restraint tray, hard pads are filled into the restraint tray to keep the extension distance of the extrusion rod constant.

[0021] The present invention also provides a lithium battery obtained by using the manufacturing method as described in any of the above technical solutions.

[0022] Beneficial effects

[0023] The present invention provides a manufacturing method of a lithium battery. The manufacturing method performs a single injection and aging on the assembled battery to obtain a lithium battery, and then performs formation and aging on the lithium battery. Among them, before the aging process, the present invention performs restraint charging on the lithium battery. Through restraint charging, the present invention sets a restraint charging process before the aging process to adjust the charged amount of the lithium battery, so that in the subsequent high-temperature aging process, its chemical self-discharge and battery side reactions can be fully carried out, thereby improving the accuracy of subsequent K value screening. In addition, setting a restraint charging process before the aging process can also solve the problem of negative electrode swelling caused by charging during the manufacturing process, and avoid the problems of increased thickness of the battery core roll and unreleased tension. This can avoid wrinkles caused by non-uniform swelling of the electrode sheet, thereby improving the manufacturing process of the lithium battery and enhancing the electrochemical performance of the lithium battery. Description of the drawings

[0024] Figure 1 It is the appearance of the negative electrode sheet after disassembling a lithium battery sample without restraint charging to 95% SOC;

[0025] Figure 2 It is the appearance of the negative electrode sheet after disassembling a lithium battery sample without restraint charging to 100% SOC;

[0026] Figure 3 It is the appearance of the negative electrode sheet after disassembling a lithium battery sample with restraint charging to 95% SOC;

[0027] Figure 4 It is the appearance of the negative electrode sheet after disassembling a lithium battery sample with restraint charging to 100% SOC;

[0028] Figure 5 It is the normal probability plot of the standardized effect when only considering the number of wrinkles on the negative electrode sheet after battery disassembly as a single response variable;

[0029] Figure 6 For Figure 5ANOVA results with a Pareto chart made from standardized effects;

[0030] Figure 7 Normal plot of standardized effects when only considering K value screening accuracy as a response variable;

[0031] Figure 8 Based on Figure 7 Pareto chart of ANOVA results made with standardized effects. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the following is a detailed description of the specific embodiments of the present invention.

[0033] Unless otherwise specified, the materials used in the present invention can be purchased through commercial channels. The experimental methods in the following examples without specifying specific conditions are selected according to conventional methods and conditions, or according to the product specifications.

[0034] The present invention provides a method for manufacturing a lithium battery, the manufacturing method comprising:

[0035] S100, injecting and forming the lithium battery once;

[0036] S200, controlling and charging the formed lithium battery;

[0037] S300, aging and capacity separation of the lithium battery after the battery is fully charged.

[0038] It is understood that in order to obtain the lithium battery to be injected once in S100, a series of components to be assembled including positive and negative electrodes need to be prepared. According to the type, model and specification of the lithium battery, those skilled in the art can select the components to be assembled and their preparation process according to actual needs.

[0039] Exemplarily, when preparing electrode materials, common cathode active materials include lithium iron phosphate (LFP), ternary materials (NCM / NCA), lithium cobalt oxide (LCO), etc. Common anode active materials include graphite, silicon-carbon composite materials, etc. The preparation processes of the cathode sheet and the anode sheet mainly include slurry preparation, coating, drying, and rolling. The method of slurry preparation is to mix electrode active substances (cathode active materials or anode active materials), conductive agents (such as carbon black), binders (such as polyvinylidene fluoride PVDF / carboxymethyl cellulose CMC / styrene-butadiene rubber SBR), and solvents (such as N-methylpyrrolidone NMP / water) in proportion to make uniform cathode slurry and anode slurry. The coating process refers to uniformly coating the cathode slurry and the anode slurry on the cathode current collector aluminum foil and the anode current collector copper foil to form the cathode sheet and the anode sheet. Subsequently, the cathode sheet and the anode sheet are dried in a high-temperature oven to remove the solvent. Then, the cathode sheet and the anode sheet are compacted by a rolling press to improve the energy density and mechanical strength, thereby obtaining the electrode materials. After separately preparing the cathode sheet and the anode sheet, the cathode sheet and the anode sheet need to be cut into strips according to the battery size requirements.

[0040] Exemplarily, the installation method of the positive electrode tab and the negative electrode tab is: welding the positive electrode tab (such as an aluminum strip) and the negative electrode tab (such as a nickel strip) to the positive current collector and the negative current collector respectively.

[0041] Exemplarily, the method for assembling the electrode assembly includes: stacking or winding. Among them, the stacking process stacks the cathode sheet, the separator, and the anode sheet in sequence to form a multi-layer structure. The winding process winds the cathode sheet, the separator, and the anode sheet in sequence into a cylindrical or elliptical shape.

[0042] After the above processes are completed, finally, encapsulation is carried out, and then the assembly of the battery can be completed. Exemplarily, among them, the encapsulation method of the soft-pack battery is to put the battery into an aluminum-plastic film and heat-seal the edge. The encapsulation method of the hard-shell battery is to put the battery into a metal shell (such as a steel shell or an aluminum shell) and weld and seal the top cover.

[0043] After the battery assembly is completed, a lithium battery is obtained, and the lithium battery is subjected to primary liquid injection and formation. The purpose of primary liquid injection is to inject the electrolyte into the battery to preliminarily wet the electrode sheets and the separator. Exemplarily, the electrolyte can be 15wt% lithium bis(fluorosulfonyl)imide (LiFSI), 24wt% ethylene carbonate (EC), 56wt% ethyl methyl carbonate (EMC), 2wt% vinylene carbonate (VC), 3wt% divinyl sulfone (DTD).

[0044] The manufacturing method also includes: aging the lithium battery before the formation process.

[0045] Aging needs to be carried out under high-temperature conditions. Standing still in a high-temperature environment can promote the full infiltration of the electrolyte. The aging temperature can be selected by those skilled in the art according to actual needs.

[0046] Formation refers to a process of performing the first charge and discharge on the battery with a small current. During formation, a passivation layer, namely a solid electrolyte interface film (SEI film), is formed on the negative electrode surface. The quality of the SEI film directly affects the performance of the battery, such as cycle life, stability, self-discharge property, and safety. The main purpose of formation is to activate the battery, charge the battery with a small current, activate the positive and negative active materials inside it, form an SEI film on the negative electrode surface, make the battery performance more stable. Only after the battery undergoes formation can its true performance be reflected. If the battery does not undergo formation, it cannot be normally charged and discharged. Only through the formation process can the battery reach the best performance state, improving the battery's capacity, cycle life, and safety performance.

[0047] The manufacturing method of the present invention further includes: performing secondary liquid injection on the lithium battery after the formation process and before the restraint charging process. The purpose of secondary liquid injection is to supplement the electrolyte after formation to ensure sufficient electrolyte.

[0048] The aging process is carried out under high-temperature conditions. The aging temperature can be selected by those skilled in the art according to actual needs. The main purpose of the aging process in the lithium battery preparation process is to screen out batteries with unstable performance and ensure the consistency and safety of the batteries. Specifically, the high-temperature environment can accelerate the side reactions inside the battery and screen out batteries with micro-short circuits, excessive self-discharge, or other potential defects. The aging process can also promote the balance of chemical reactions inside the battery, stabilize the interface between the electrode material and the electrolyte, and improve the cycle life and safety of the battery. The high-temperature storage conditions for the aging process are generally 45°C to 60°C, and the storage time is generally 5 days to 7 days. The aging process can be carried out in a constant-temperature aging chamber or an aging cabinet. Those skilled in the art can adjust the aging temperature and time according to the battery type (such as power batteries, energy storage batteries). After aging, the batteries can be divided into qualified products and unqualified products according to the voltage change and internal resistance test results. Qualified batteries can enter the next process (such as grading), and unqualified batteries are repaired or scrapped.

[0049] In the present invention, constrained charging is a new process between the formation process and the aging process, and its purpose is to improve the accuracy of subsequent K value screening and solve the problem of negative electrode expansion caused by charging of lithium batteries during the manufacturing process. It should be noted that in the present invention, the preparation process of lithium batteries includes not only one liquid injection, aging, formation, constrained charging, aging, and capacity separation, but also other processes. The order of liquid injection, aging, formation and aging, as well as other processes, can be adjusted by technicians in this field within a feasible range according to actual conditions and technical requirements. It is only necessary to ensure that the constrained charging is performed before the aging process.

[0050] After the aging process, the lithium battery is divided into different capacities. In the lithium battery manufacturing process, the main function of the capacity division process is to screen and grade the battery capacity to ensure the consistency of battery performance. Capacity division is preferably carried out after the battery has completed the formation and aging processes. At this time, the battery has basic electrochemical properties, and the capacity division can more accurately reflect its actual capacity and performance.

[0051] The K value of a lithium battery refers to the voltage drop of the battery per unit time under certain conditions. The K value is usually expressed in mV / d and is an indicator used to measure the self-discharge rate of a lithium battery. The smaller the K value, the slower the self-discharge rate of the battery and the better the battery performance. When manufacturing lithium batteries, defective products with too fast self-discharge can be screened out by performing K value screening. Therefore, the accuracy of K value screening has a crucial impact on the factory quality of the product.

[0052] The main factors affecting the accuracy of K value screening include: 1. Depolarization effect: After charging, the voltage of lithium-ion batteries gradually stabilizes with the increase of time. When depolarization is incomplete, the tested K value is too large, and misjudgment occurs; 2. Aging temperature and time: According to the Arrhenius equation, the increase in aging temperature can accelerate chemical reactions, increase the self-discharge rate, and lead to an increase in K value; 3. Test equipment: The K value test formula is: (OCV 2 -OCV 1 ) / ΔT, when testing the K value, the two OCV (Open Circuit Voltage) tests need to use the same equipment or highly consistent equipment to ensure the authenticity of the K value.

[0053] In addition to the above factors, the State of Charge (SOC) of lithium batteries also has an important impact on the accuracy of the K-value defective screening. The Open Circuit Voltage (OCV) changes in a curve as the SOC increases. When the slope k is relatively large, it is beneficial to the selection of the K value. Therefore, in the present invention, before the aging process, the lithium batteries are subjected to constrained charge replenishment. The batteries after constrained charge replenishment enter the high-temperature aging process while maintaining an appropriate SOC state, enabling the batteries to undergo sufficient chemical self-discharge and side reactions inside the batteries, which is thus beneficial to the screening accuracy of the subsequent K value.

[0054] The negative electrode active material of lithium batteries usually uses graphite as the main material, and there are also some batteries that use silicon-based materials (such as silicon-carbon composite materials) or other materials.

[0055] Negative electrode swelling is a common phenomenon during the use of lithium batteries, and the problem of negative electrode swelling in lithium batteries has always troubled the technical personnel in the research and production fields of lithium batteries. The main reasons for the negative electrode swelling problem include: 1. Material reasons: During the charge and discharge process of the battery, due to ion exchange, the structure of the negative electrode active material will change. Therefore, some negative electrode active materials may be more likely to change during charge and discharge due to their own structural weaknesses or improper preparation methods, generating gas inside the battery and causing the battery to swell; 2. Process reasons: Such as uneven pressing of the negative electrode active material, poor encapsulation, etc.; 3. Structural reasons: The positive and negative electrodes are strictly separated inside the battery, and the negative electrode is prone to chemical reactions with other parts of the battery, thereby promoting negative electrode swelling.

[0056] Negative electrode swelling will cause stress concentration inside the battery, thereby increasing the internal pressure of the battery, resulting in an increase in the battery thickness, and in severe cases, it may cause the rupture and leakage of the battery shell. In addition, negative electrode swelling will also cause the movement path of lithium ions inside the battery to become longer, increasing the resistance and affecting the charge and discharge efficiency of the battery. Finally, negative electrode swelling will limit the utilization rate of the battery capacity and reduce the battery's endurance ability.

[0057] It should be particularly noted that during the manufacturing process of lithium batteries, the negative electrode swelling caused by the charge and discharge process will lead to an increase in the thickness of the electrode assembly and the inability to release the tension. The non-uniform swelling generated therefrom will cause the electrode sheet to wrinkle. Therefore, how to reduce or avoid the negative electrode swelling during the charge and discharge process in the manufacturing process of lithium batteries also has a crucial impact on the ex-factory quality of the products.

[0058] Setting the constrained charge replenishment process before the aging process can also solve the negative electrode swelling caused by charging during the manufacturing process, avoid the problems of the increase in the thickness of the electrode assembly and the inability to release the tension, and thus avoid the wrinkles of the negative electrode sheet caused by non-uniform swelling.

[0059] Constrained charging is a process of charging and discharging a lithium battery while applying a constraining force to the lithium battery. The role of the constrained tray in constrained charging is to apply a fixed force to the battery, inhibit the internal stress generated by the expansion of the electrode during charging and discharging, and achieve the effect of eliminating the generation of electrode wrinkles and controlling the battery thickness.

[0060] The process of constrained charging specifically includes:

[0061] A. Place the formed lithium battery on the constrained tray and adjust the extended distance of the extrusion rod of the constrained tray so that the extrusion rod applies a constraining force to the lithium battery;

[0062] B. Transport the constrained tray to the charging cabinet so that the lithium battery is charged and discharged with a charging current while being under the applied constraining force.

[0063] In the present invention, the constrained tray is used to fix and limit the expansion of the battery during charging and discharging. The constrained tray can be made of metal or high-strength plastic, and preferably made of materials with high temperature resistance and corrosion resistance. The constrained tray can be applied to processes such as formation, grading, and aging. The present invention innovatively charges the battery before the aging process and uses the constrained tray to constrain the battery during the charging process, simultaneously achieving the purpose of inhibiting expansion and improving the accuracy of K value screening.

[0064] As Figures 1 to 4 shown, the appearance of the lithium battery sample charged to 100% SOC by constrained charging has significantly fewer wrinkles.

[0065] It can be understood that the extrusion rod of the constrained tray applies a constraining force to the lithium battery. By adjusting the extended distance of the extrusion rod, the magnitude of the constraining force can be adjusted. If the extended distance of the extrusion rod is long, the constraining force is greater. If the extended distance of the extrusion rod is fixed, the magnitude of the constraining force is constant. In step A, after adjusting the extended distance of the extrusion rod of the constrained tray, hard pads can be filled into the constrained tray to maintain the constant extended distance of the extrusion rod.

[0066] It can be understood that during the process of constrained charging, controlling the extended distance of the extrusion rod (i.e., the magnitude of the constraining force), the charging current, and the SOC at the end of the lithium battery charging all have a synergistic effect on the effect of constrained charging. Among them, the effect of constrained charging can be measured by two factors: the number of wrinkles on the negative electrode after the battery is disassembled and the accuracy of K value screening.

[0067] Preferably, in step A, control the extended distance of the extrusion rod to be 0 mm to 56 mm; and / or in step B, control the charging current of the charging cabinet to be 60 A to 200 A; and / or in step B, control the SOC of the lithium battery after charging ends to be 0% to 100%.

[0068] In order to further optimize the constrained charging process, the present invention verifies the design scheme through the DOE (Design of Experiments) experimental design method, and optimizes parameters such as the extended distance of the extrusion rod, the charging current, and the SOC at the end of charging.

[0069] The constrained charging process is specifically as follows:

[0070] Step 1: Match the lithium battery after secondary liquid injection into the constrained tray, adjust the extended distance of the extrusion rod of the constrained tray, and then fill a spacer with an appropriate thickness to fix the extrusion rod so that the extrusion rod applies a constraining force to the lithium battery.

[0071] Step 2: Transport the lithium battery in the constrained tray to the charging cabinet, and issue the charging process for charging and discharging; different charging currents and the SOC at the end of charging can be set for the charging process. By setting the SOC at the end of charging, it is ensured that the battery enters the high-temperature aging with the optimal storage SOC. By setting the charging current to adjust the charged amount, the chemical self-discharge and battery side reactions of the battery are fully carried out in the subsequent high-temperature aging process, which is beneficial to the accuracy of the subsequent K value screening.

[0072] Step 3: Replace the battery with a common tray for high-temperature aging.

[0073] Among them, the present invention uses the DOE (Design of Experiments) experimental design method for verification, and this method can be used to confirm the constrained charging process parameters of different models of batteries. The core goal of the DOE of the present invention is to obtain the most information through the least number of experiments, so as to optimize the constrained charging process. The detailed process of the DOE experimental design of the present invention is as follows: The three factors for experimental research on the constrained charging process are: the extended distance of the extrusion rod (A), the charging current (B), and the SOC at the end of charging (C); the two response variables to be observed are: the number of wrinkles on the negative electrode sheet after the battery is disassembled, and the accuracy of K value screening; design 2 3 factorial experiment; combined with the actual performance of the equipment, the factor levels are set as the extended distance of the pressure rod (A) is 0 - 56 mm, the charging current (B) is 60 - 200 A, and the SOC at the end of charging (C) is 0 - 100% SOC. As shown in Table 1, the present invention obtains 19 groups of experimental schemes.

[0074] Table 1

[0075]

[0076] Analyze according to the experimental data of DOE, such as Figure 5As shown, when only considering the number of wrinkles on the negative electrode sheet after battery disassembly as a single response variable, the effect estimates can be plotted on a normal plot of standardized effects to identify significant factor interactions and main factor effects. It is determined that the extended distance of the extrusion rod (A) and the charging current (B) are significant factors, while the SOC at the end of charging (C) is a non-significant factor. As Figure 6 shown, according to the analysis of variance of the Pareto chart of standardized effects, the significant influence degree of the extended distance (A) is higher than that of the charging current (B). That is to say, it can be judged that the significant influence degrees of the extended distance of the extrusion rod (A) and the charging current (B) are in the order of: the extended distance of the extrusion rod (A), the charging current (B); and when the extended distance of the extrusion rod (A) is 56 mm and the charging current (B) is 100 A, the number of wrinkles on the negative electrode sheet after battery disassembly, the response variable, is the least and the effect is the best.

[0077] Analyzing based on the experimental data of DOE, as Figure 7 shown, when only considering the screening accuracy of the K value as a single response variable, the effect estimates can be plotted on a normal plot of standardized effects to identify significant factor interactions and main factor effects. It is determined that the charging current (B) and the SOC at the end of charging (C) are significant factors, while the extended distance of the extrusion rod (A) is a non-significant factor. As Figure 8 shown, according to the analysis of variance of the Pareto chart of standardized effects, the significant influence degree of the SOC at the end of charging (C) is higher than that of the charging current (B). That is to say, it can be judged that the significant influence degrees of the charging current (B) and the SOC at the end of charging (C) are in the order of: the SOC at the end of charging (C), the charging current (B); and when the SOC at the end of charging (C) is 100% and the charging current (B) is 100 A, the screening accuracy rate of the response variable K value is the highest and the effect is the best.

[0078] Finally, the optimal process parameters for constrained charging are obtained through the DOE experimental design method. In step A, the extended distance of the extrusion rod is controlled at 56 mm; in step B, the charging current is controlled at 100 A; in step B, the SOC at the end of lithium battery charging is controlled at 100%.

[0079] According to the verification through the DOE experimental design scheme, the extended distance of the extrusion rod, the charging current, and the SOC at the end of charging are designed reasonably. After charging is completed, the lithium battery is disassembled and the thickness of the lithium battery is measured to check the interface and wrinkling conditions of the negative electrode sheet.

[0080] In summary, the restraint charging process for lithium-ion batteries provided by the present invention can adjust the charged amount before high-temperature aging of the lithium battery, enabling the lithium battery to undergo high-temperature aging in a suitable state of charge, allowing the chemical self-discharge and side reactions of the lithium battery to proceed fully, which is beneficial to the accuracy of subsequent K-value screening. At the same time, a restraint tray is added in the charging process, enabling the battery to be charged under the action of restraint force, which can ensure that all components of the lithium battery are in close contact, increase the contact area of the battery interface, and is beneficial to the uniform distribution of current during the charge and discharge process. The restraint force can eliminate the problems of the increase in the thickness of the electrode assembly caused by the expansion of the negative electrode plate during charging and the failure to release the tension, thereby avoiding the wrinkles caused by the non-uniform expansion of the negative electrode plate.

[0081] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A method for manufacturing a lithium battery, characterized in that: The manufacturing method comprises: S100, injecting and forming the lithium battery once; S200, controlling and charging the formed lithium battery; S300, aging and capacity separation of the lithium battery after the battery is fully charged.

2. The manufacturing method according to claim 1, characterized in that: The manufacturing method further comprises: After the formation process and before the restrained charging process, the lithium battery is injected with liquid for the second time; and / or Before the formation process, the lithium battery is aged.

3. The manufacturing method according to claim 1, characterized in that: The restrained power replenishment is to charge and discharge the lithium battery while applying a restraining force to the lithium battery.

4. The manufacturing method according to any one of claims 1 to 3, characterized in that: The restraint charging process specifically includes: A. placing the formed lithium battery on a restraint tray, and adjusting the extension distance of the extrusion rod of the restraint tray so that the extrusion rod applies a restraining force to the lithium battery; B. The restraint tray is transported to a charging cabinet so that the lithium battery is charged and discharged with a charging current while a restraint force is applied.

5. The manufacturing method according to claim 4, characterized in that: In step A, controlling the extension distance of the extrusion rod to be 0 mm to 56 mm; and / or In step B, the supplementary current is controlled to be 60A to 200A; and / or In step B, the SOC of the lithium battery at the end of charging is controlled to be 0% to 100%.

6. The manufacturing method according to claim 5, characterized in that: The manufacturing method further comprises: The DOE experimental design method was used to verify the process parameters of the constrained charging. The verified process parameter factors included: the extension distance of the extrusion rod, the charging current, and the SOC at the end of the charging. The response variables used in the verification included: the number of wrinkles on the negative electrode sheet after the battery was disassembled, and the accuracy of the K value screening.

7. The manufacturing method according to claim 6, characterized in that: When only one response variable, the number of wrinkles on the negative electrode sheet after disassembly of the battery, is considered, the normal plot of the standardized effect is used to determine that the extension distance of the extrusion rod and the supplementary current are significant factors, and the SOC at the end of supplementary power is a non-significant factor; according to the variance analysis of the Pareto chart of the standardized effect, it is determined that the significant influence of the extension distance of the extrusion rod is higher than the significant influence of the supplementary power current; When only one response variable, namely, the K value screening accuracy, is considered, the normal plot of the standardized effect is used to determine that the charging current and the SOC at the end of the charging are significant factors, and the extension distance of the extrusion rod is a non-significant factor; based on the variance analysis of the Pareto plot of the standardized effect, it is determined that the SOC at the end of the charging has a higher degree of significant influence than the charging current.

8. The manufacturing method according to claim 7, characterized in that: In step A, the extension distance of the extrusion rod is controlled to be 56 mm; In step B, the supplementary current is controlled to be 100A; In step B, the SOC of the lithium battery at the end of charging is controlled to be 100%.

9. The manufacturing method according to claim 5, characterized in that: In step A, after adjusting the extension distance of the squeezing rod of the restraining tray, a hard pad is filled into the restraining tray to maintain the extension distance of the squeezing rod constant.

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

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