Preparation method of lithium iron phosphate battery positive electrode slurry, slurry, positive electrode sheet, battery and battery preparation method

Abstract

This invention relates to the field of lithium battery technology, specifically disclosing a method for preparing a positive electrode slurry for lithium iron phosphate batteries, as well as the slurry, positive electrode sheet, battery, and battery manufacturing method. The positive electrode slurry is prepared through the following steps: S1. Mixing a binder and solvent and stirring to form a gel; S2. Adding a conductive agent to the gel and stirring to obtain a conductive phase; S3. Adding a lithium replenishing agent, lithium iron phosphate, and an synergist to the gel and dispersing them evenly, wherein the amount of synergist added is 1-6 wt% of the amount of lithium replenishing agent; simultaneously adding a binder and a conductive phase to achieve a solid content of 60-75% in the positive electrode slurry; dispersing and stirring the mixture to obtain the positive electrode slurry; wherein the lithium replenishing agent is lithium-rich nickel oxide, and the synergist for the lithium replenishing agent is lithium ferrocene sulfopropionate. This invention introduces an synergist and a lithium replenishing agent into the positive electrode slurry, which synergistically act on the lithium iron phosphate-graphite system, increasing the battery's lifespan without affecting its electrical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a method for preparing positive electrode slurry in lithium batteries, the slurry, electrode, and battery obtained by the method, and a method for preparing lithium batteries. Background Technology

[0002] With the rapid development of emerging applications such as renewable energy, large-scale energy storage, microgrids, and residential energy storage, lithium-ion batteries, especially those based on lithium iron phosphate (LiFePO4, LFP) cathodes / graphite anodes, have gained widespread application in the energy storage field due to their excellent safety, cost advantages, and environmental friendliness. However, in practical applications, especially for energy storage batteries intended for "long-term service" (e.g., over ten years, thousands of cycles, or even tens of thousands of cycles), higher requirements are placed on cycle life, calendar life, and reliability.

[0003] Currently, several key lifespan bottlenecks are gradually emerging in LFP-graphite system batteries:

[0004] (1) Initial lithium inventory loss: During the first charge and discharge process, the graphite negative electrode surface will react with the electrolyte to form a solid electrolyte interface film (usually called SEI film). This process will irreversibly consume some active lithium ions. According to publicly available information, the loss of lithium ions during this process is usually in the range of 8~12%, which will result in insufficient available lithium ions at the negative electrode, thereby reducing the available lithium reserves in the battery.

[0005] (2) Lithium content and interface loss during cycling: In subsequent cycles of the battery, due to volume changes and interfacial stress changes of the electrodes (especially graphite anodes) during charging and discharging, the SEI film may crack or detach. In this case, the electrolyte will directly penetrate the surface of the active material and regenerate a new SEI film, continuously consuming lithium ions. This "continuous lithium consumption" mechanism has become an important reason for limiting cycle life.

[0006] Therefore, although the LFP-graphite system theoretically has good stability, in real-world energy storage systems, many products can only achieve about 7,000 cycles and a capacity retention rate of about 70% in ambient temperature cycling, making it difficult to adapt to scenarios requiring a service life of more than 10 years or thousands of cycles, such as residential energy storage, industrial and commercial energy storage, and grid-side energy storage.

[0007] Based on the aforementioned shortcomings, lithium replenishment / pre-lithiation processes have become an important path to improve battery life. This involves introducing additional usable lithium into the battery system in advance to compensate for irreversible lithium consumption during the first or subsequent cycles. For example, patent US20210013555A1 uses a lithium replenishment structure as a technical solution to improve the capacity decay problem of lithium-ion batteries during the first or long-term cycles. Among various lithium replenishment methods, adding lithium replenishing agents to the cathode material is gradually becoming the preferred approach in industry due to its high chemical stability, good safety, and strong compatibility with existing production processes. For example, patent CN110218078A discloses a method for preparing the lithium replenishing material Li2NiO2 and its application in lithium-ion batteries.

[0008] However, while the batteries obtained after the aforementioned improvements in existing technologies have improved in terms of performance such as cycle life, they still do not meet the higher usage requirements such as "cycle life of more than 10,000 cycles". There are still obvious technological gaps in the improvement of lithium-ion battery performance. Summary of the Invention

[0009] This invention provides a method for preparing a positive electrode slurry, which improves the positive electrode slurry, thereby enabling the positive electrode slurry and the electrode sheet loaded with the positive electrode slurry to have better performance, and the battery composed of the corresponding positive electrode sheet to have stronger electrochemical performance and service life.

[0010] This invention is achieved through the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing a positive electrode slurry for a lithium iron phosphate battery, comprising the following steps: S1. Mixing a binder and a solvent at a mass ratio of 1:(8~12) and stirring to form a slurry; S2. Adding a conductive agent of 1~5 wt% by weight of the dry basis of the positive electrode slurry to the slurry and stirring to mix evenly to obtain a conductive phase; S3. Adding 0.5~5 parts of a lithium supplementer, 90~97.5 parts of lithium iron phosphate and a synergist of the lithium supplementer to the slurry and dispersing evenly according to the dry basis of the positive electrode, wherein the amount of the synergist added is 1~6% of the amount of the lithium supplementer added; simultaneously adding a total of 2~8 parts of binder and conductive phase to make the solid content of the positive electrode slurry reach 60~75%; dispersing and stirring the mixture to obtain the positive electrode slurry; wherein the lithium supplementer is lithium-rich nickel oxide and the synergist of the lithium supplementer is lithium ferrocene sulfide propionate.

[0012] The binders, solvents, and conductive agents used are all conventional materials in the field. For example, the binder can be polyvinylidene fluoride (hereinafter referred to as PVDF), the solvent can be N-methylpyrrolidone (hereinafter referred to as NMP), and the conductive agent can be at least one of SuperP carbon black and carbon nanotubes (hereinafter referred to as CNT).

[0013] In this invention, the first method for improving the performance of lithium iron phosphate batteries is to improve the positive electrode slurry. Further improvements to the positive electrode slurry are no longer limited to simply adding lithium supplementers or improving the performance of lithium supplementers. Instead, it involves introducing lithium-rich nickel oxide (hereinafter referred to as LNO) as a lithium supplementer and using lithium ferrocene sulfopropionate as a synergist for the lithium supplementer.

[0014] In this invention, the synergist can synergistically work with the LNO lithium replenisher in the lithium iron phosphate-graphite system. When the positive electrode slurry of this invention is prepared into a positive electrode sheet, and the positive electrode sheet is used in a battery, the synergist component can play multiple roles within the battery. Specifically, the ferrocene group in the synergist's molecular structure can optimize the electron transport environment inside the electrode, and the sulfur group can form a stable coordination with lithium elements, promoting the orderly insertion, extraction, and migration of active lithium in the lithium replenisher, reducing irreversible lithium-ion loss during transport. At the same time, the synergist can regulate the electrode interface reaction, inhibit the excessive growth and rupture of the solid electrolyte interphase (SEI) film, thereby reducing the continuous consumption of lithium during cycling, and thus synergistically improving the lithium inventory stability and cycle durability of the battery.

[0015] Therefore, by introducing this synergist in combination with a lithium replenisher, multiple improvements can be achieved, thereby enhancing the electrochemical performance and lifespan of batteries using this cathode slurry. Furthermore, the introduction and use of the lithium replenisher synergist also provides new insights into improving the performance of lithium batteries.

[0016] As a further improvement of the present invention, in S1, when preparing the adhesive solution, the stirring speed is 2500~4500 rpm and the duration is 20~50 min.

[0017] As a further improvement of the present invention, in S2, when preparing the conductive phase, the stirring speed is 2500~3000 rpm and the duration is 60~120 min. After preparation, it is necessary to ensure that the conductive network is uniform and free of agglomerated particles >5µm.

[0018] As a further improvement of the present invention, in S3, the ambient humidity is controlled to be 3~10%; at the same time, the present invention mainly disperses and stirs the material through a dispersion disc to ensure that the material in the positive electrode slurry is evenly dispersed, wherein the linear velocity of dispersion and stirring is controlled to be 7.5~12m / s.

[0019] As a further improvement of the present invention, the dispersion and stirring time is maintained for 3 to 5 hours, and the viscosity of the final positive electrode slurry must be 6000 to 15000 mPa·s, and the positive electrode slurry must not separate into layers or precipitate after standing for 24 hours.

[0020] As a further improvement of the present invention, the synergist is prepared by the following method: a. Under a protective atmosphere, 10-20 parts of 6-(mercaptohexyl)ferrocene and 400-600 parts of anhydrous tetrahydrofuran are added to a reaction vessel, stirred, and then 3-5 parts of lithium acrylate are added, and stirring is continued to obtain a suspension; b. 0.5-3 parts of azobisisobutyronitrile are added, and the mixture is heated to 60-80°C and refluxed and stirred for 4-8 hours; c. After the reaction is completed, the mixture is cooled to room temperature, and the anhydrous tetrahydrofuran is removed by vacuum distillation to obtain a crude product; d. The crude product is dried under vacuum to obtain lithium ferrocene sulfopropionate.

[0021] As a further improvement of the present invention, in step a, after 6-(mercaptohexyl)ferrocene is added to anhydrous tetrahydrofuran, it is stirred at 300~500 rpm for 10~30 min, and then lithium acrylate is added and stirred for another 20~100 min.

[0022] As a further improvement of the present invention, in step c, anhydrous tetrahydrofuran is removed by vacuum distillation at 40~50°C and -0.09MPa.

[0023] Secondly, the present invention provides a positive electrode slurry, which is prepared by any of the above-described preparation methods.

[0024] Thirdly, the present invention provides a positive electrode sheet coated with the aforementioned lithium iron phosphate battery positive electrode slurry, and the positive electrode surface density reaches 320~450 g / m². 2 In the process of manufacturing the positive electrode sheet, it is necessary to dry the positive electrode slurry. In this invention, the moisture content of the mixed sample after drying the positive electrode slurry is required to be <100~350 ppm, so as to avoid introducing too much moisture into the battery and affecting the battery's service life.

[0025] Fourthly, the present invention provides a lithium iron phosphate battery comprising the aforementioned positive electrode slurry or the aforementioned positive electrode sheet. In the battery, the negative electrode sheet and the active material thereon can be conventional materials. For example, the negative electrode active material used in the present invention is graphite, and the graphite content on the negative electrode sheet can be controlled at 94-98% based on the dry weight of the negative electrode, and the areal density of the negative electrode can be controlled at 160-200 g / m². 2 .

[0026] Fifthly, this invention provides a method for preparing a lithium iron phosphate battery to obtain the aforementioned battery. The pre-processing of the electrode sheet and battery assembly are mature existing technologies and will not be elaborated upon here. The formation activation process after battery assembly in this invention is as follows: Let the battery rest for 5-15 minutes to ensure the cell temperature reaches the target temperature; charge the battery with a constant current of 0.01C for 5-20 minutes; charge the battery with a constant current of 0.05C, with a cutoff voltage of 3.65 V, for 150-200 minutes; charge the battery with a constant current of 0.50C, with a cutoff voltage of 3.65 V, for 100-150 minutes; let the battery rest for 5-15 minutes; charge the battery with a constant current of 0.10C, with a cutoff voltage of 4.20 V, for 400-600 minutes; let the battery rest for 5-15 minutes; charge the battery with a constant current of 0.015C, with a cutoff voltage of 4.20 V, for 400-600 minutes; let the battery rest for 5-15 minutes. For 150-210 minutes, discharge the battery at a constant current of 0.50C with a cutoff voltage of 2.50 V; let the battery rest for 5-15 minutes; charge the battery at a constant current of 0.50C with a cutoff voltage of 3.65 V; let the battery rest for 20-40 minutes; let the battery rest for 2-10 minutes.

[0027] As a further improvement of the present invention, the target temperature is 45~60℃.

[0028] The beneficial effects of this invention are as follows: Firstly, it adopts a strategy of adding an additional lithium replenishing agent to the positive electrode slurry, i.e., without increasing the negative electrode areal density or overdrawing part of the cell's NP ratio. This strategy can minimize the drawback of reduced battery mass energy density caused by the introduction of the lithium replenishing agent, while simultaneously completing lithium replenishment. Furthermore, after introducing the lithium replenishing agent, the preparation and production process of the positive electrode slurry, etc., is fully compatible with the existing commercial lithium iron phosphate-graphite battery production process, requiring no equipment modification. Specifically, in the positive electrode homogenization stage, the LNO lithium replenishing agent can be directly integrated into the traditional wet dispersion process, and the prepared positive electrode slurry exhibits no stratification, no precipitation, and viscosity rises within a reasonable range.

[0029] This invention also improves lithium utilization by introducing a synergistic effect agent to enhance lithium replenishment, mitigating irreversible lithium loss during the first charge / discharge cycle and subsequent cycling, thus significantly extending battery cycle life and calendar life. The addition of the synergist optimizes electrode interface stability and electron / ion transport efficiency, suppresses internal resistance growth and self-discharge rate, and ensures the stability of the battery's electrochemical performance during long-term service. Furthermore, the use of this material is fully compatible with existing lithium iron phosphate-graphite battery production processes, requiring no modification to production equipment or significant adjustments to production steps, which facilitates the widespread adoption of this improved processing method.

[0030] Overall, this invention achieves an upgrade in battery life without degrading conventional electrochemical performance, and has good prospects for industrial application. Attached Figure Description

[0031] The accompanying drawings are provided below to illustrate the preferred embodiments of the invention and to aid in understanding the objectives and advantages of the invention, wherein:

[0032] Figure 1 The graph shows the viscosity of the cathode slurry in Examples 1-2 and Comparative Examples 1-2 as a function of time.

[0033] Figure 2 The graph shows the results of high-temperature cycling tests at 45°C for batteries prepared using the positive electrode slurry in Examples 1-2 and Comparative Examples 1-2.

[0034] Figure 3 The graph shows the results of the full-charge calendar life test at 25°C for batteries prepared using the positive electrode slurry in Examples 1-2 and Comparative Examples 1-2. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0037] Example 1:

[0038] This embodiment provides a positive electrode slurry, which is prepared by the following method:

[0039] Positive electrode homogenate:

[0040] S1. Mix the adhesive PVDF with the solvent NMP to prepare the adhesive solution. In this embodiment, the solid content of the adhesive solution is designed to be 8%, and the amount of adhesive and solvent is adjusted accordingly. After mixing the two, the stirring speed is kept at 3000 rpm for 4 hours to obtain the desired adhesive solution.

[0041] S2. Add the conductive agent carbon black and the slurry to the stirring tank, maintain the stirring speed at 2500 rpm, and stir for 2 hours to obtain the conductive phase; in this embodiment, the amount of carbon black is designed to be 3 wt% of the dry basis of the positive electrode slurry.

[0042] S3. Control the ambient humidity of the operation to not exceed 3~10%; weigh 95.91 parts of LFP, 1.25 parts of LNO and lithium ferrocene sulfide propionate as synergist based on the dry weight of the positive electrode, wherein the amount of synergist added is 2wt% of the lithium supplement. Then add the above materials into the slurry and disperse them evenly. During this period, use a dispersion disc to perform dispersion and stirring, maintaining the linear speed of the dispersion disc at 10m / s for 3 hours; then add the conductive phase and continue to disperse for 2 hours to obtain the positive electrode slurry.

[0043] The synergist used in the lithium supplement is lithium ferrocene sulfide propionate, which is prepared by the following method:

[0044] a. Under a nitrogen atmosphere, 10 g of 6-(mercaptohexyl)ferrocene and 400 g of anhydrous tetrahydrofuran (hereinafter referred to as THF) were added to a three-necked flask. The mixture was stirred at 300 rpm for about 30 min, and then 3 g of lithium acrylate was added and the stirring was continued for 20 min to obtain a suspension. b. 1 g of azobisisobutyronitrile was added to the suspension, and the mixture was heated to 60 °C and stirred under reflux for 8 h. c. After the reaction, the mixture was cooled to room temperature and THF was removed by vacuum distillation at 40 °C and -0.09 MPa to obtain a viscous crude product. d. The crude product was dried under vacuum at 50 °C for 12 h to obtain lithium ferrocene sulfopropionate.

[0045] The positive electrode slurry prepared in this invention shows no stratification or sedimentation after standing for 24 hours, which meets the basic requirements for the use of positive electrode slurry.

[0046] Example 2:

[0047] This embodiment provides a positive electrode slurry, the preparation method of which differs from that in Example 1. In this embodiment, the amount of LFP is 93.78 parts, the amount of LNO is 3.38 parts, and the amount of synergist is 4 wt% of the lithium supplement.

[0048] In this embodiment, the synergist used was prepared by the following method:

[0049] a. Under a nitrogen atmosphere, 20 g of 6-(mercaptohexyl)ferrocene and 600 g of anhydrous THF were added to a three-necked flask. The mixture was stirred at 500 rpm for about 10 min, and then 5 g of lithium acrylate was added and the stirring was continued for 100 min to obtain a suspension. b. 3 g of azobisisobutyronitrile was added to the suspension, and the mixture was heated to 80 °C and stirred under reflux for 4 h. c. After the reaction, the mixture was cooled to room temperature and THF was removed by vacuum distillation at 50 °C and -0.09 MPa to obtain a viscous crude product. d. The crude product was dried under vacuum at 60 °C for 8 h to obtain lithium ferrocene sulfopropionate.

[0050] Comparative Example 1:

[0051] The difference between this comparative example and Example 1 is that LNO and synergists were not introduced, and the amount of LFP was controlled at 97.16%.

[0052] Comparative Example 2:

[0053] The difference between this comparative example and Example 1 is that no synergist was introduced, and the amount of LNO was controlled at 1.25%.

[0054] Performance testing:

[0055] In this embodiment, the cathode slurries in Examples 1-2 and Comparative Examples 1-2 were tested. On one hand, the viscosity of the cathode slurries in Examples 1-2 and Comparative Examples 1-2 was measured, primarily by monitoring the viscosity changes of various cathode slurries over 24 hours to determine whether they met the basic requirements for use as cathode slurries. The relevant test results are as follows: Figure 1 As shown. On the other hand, positive electrode slurry is mainly used to make positive electrode sheets, and then the positive electrode sheets are combined with negative electrode sheets to form a battery. The battery performance is then tested to examine the impact of the positive electrode slurry on the battery performance.

[0056] For the positive electrode slurry in Example 1, after undergoing conventional processes such as sieving, coating, rolling, die-cutting, stacking, and assembly, it is dried, maintaining the positive electrode surface density at 385 g / m³. 2 The moisture content of the Honghu battery cell mixture sample was dried to <200ppm; then liquid was injected and high-temperature impregnation was performed; after formation, a second injection, impregnation, second sealing, and capacity separation process were carried out to complete the preparation.

[0057] The main difference in preparing the positive electrode sheet using the positive electrode slurry in Example 2 lies in controlling the positive electrode areal density to be 394 g / m². 2 .

[0058] The main difference in preparing the positive electrode sheet using the positive electrode slurry in Comparative Example 1 lies in controlling the positive electrode areal density to be 380 g / m². 2 .

[0059] The main difference in preparing the positive electrode sheet using the positive electrode slurry in Comparative Example 2 lies in controlling the positive electrode areal density to be 385 g / m³. 2 .

[0060] A lithium iron phosphate battery was obtained by assembling the positive electrode sheets from Examples 1-2 and Comparative Examples 1-2 with the negative electrode sheets and other components used in conventional lithium iron phosphate batteries. In this example, the negative electrode areal density of all negative electrode sheets was controlled to be 182 g / m³. 2The obtained battery was activated through the following steps: The battery was left to stand for approximately 10 minutes to allow the cell temperature to reach the target temperature of 50°C; the battery was charged at a constant current of 0.01C for 15 minutes; the battery was charged at a constant current of 0.05C with a cutoff voltage of 3.65 V for 180 minutes; the battery was charged at a constant current of 0.50C with a cutoff voltage of 3.65 V for 180 minutes; the battery was left to stand for 10 minutes; the battery was charged at a constant current of 0.10C with a cutoff voltage of 4.20 V for 500 minutes; the battery was left to stand for 10 minutes; the battery was charged at a constant current of 0.015C with a cutoff voltage of 4.20 V for 500 minutes; the battery was left to stand for 10 minutes; the battery was discharged at a constant current of 0.50C with a cutoff voltage of 2.50 V for 200 minutes; the battery was left to stand for 10 minutes; the battery was charged at a constant current of 0.50C with a cutoff voltage of 3.65 V for 30 minutes; the battery was left to stand for 10 minutes.

[0061] For batteries that have completed formation and activation, relevant performance tests were conducted. The test items and results are shown in Table 1 and below. Figures 2-3 As shown. For experimental methods where specific conditions are not specified, they are usually determined according to national standards. If there is no corresponding national standard, then generally accepted international standards, standard conditions, or conditions recommended by the manufacturer shall be followed.

[0062] Table 1 Summary of Battery Performance Test Results project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Initial charge capacity (Ah) 5.8159 5.8627 5.7171 5.7678 Capacity at breakout point / (Ah) 5.3402 5.4157 5.2437 5.3054 After capacitance adjustment, the internal resistance in ohms is / (mΩ) 3.23 3.14 3.06 3.28 K value / (mV / h) 0.0154 0.0134 0.0091 0.0167 50% SOC HPPC discharge internal resistance (mΩ) 15.05 14.91 14.40 15.56 50% SOC HPPC charging internal resistance (mΩ) 15.48 15.25 14.79 16.01 0.5P energy efficiency 94.64% 94.58% 94.79% 94.82% .

[0063] First, such as Figure 1 The test results show that the viscosity change trend of the cathode slurry in Examples 1-2 within 24 hours is similar to that of the cathode slurry in Comparative Examples 1-2, and the viscosity increase meets the actual production requirements. Therefore, the introduction of lithium supplement and synergist did not have a negative impact on the viscosity characteristics of the cathode slurry itself.

[0064] Secondly, the test results in Table 1 show that:

[0065] The batteries prepared with the cathode slurry in Examples 1 and 2 exhibited higher initial charge capacity and discharge capacity than the battery prepared with the cathode slurry in Comparative Example 2, while the battery prepared with the cathode slurry in Comparative Example 1 performed the worst in these aspects. These results further demonstrate that the addition of a lithium replenisher effectively provides more active lithium ions, thereby improving battery performance. Furthermore, the addition of an synergist further optimizes the electron transport environment within the electrode, enabling stable coordination between sulfur groups and lithium elements in the battery. This promotes the orderly insertion, extraction, and migration of active lithium in the lithium replenisher, reducing irreversible lithium ion loss during transport. Compared to simply adding a lithium replenisher, this further enhances lithium replenishment efficiency, thus further improving battery performance.

[0066] Regarding battery internal resistance and self-discharge, the batteries prepared using the cathode slurry in Examples 1-2 exhibited an ohmic internal resistance of 3.14-3.23 mΩ after capacity testing, and a charge / discharge internal resistance of 14.91-15.48 mΩ at 50% SOC HPPC. This performance deviation from the battery prepared using the cathode slurry in Comparative Example 1 was ≤5%. The K-value of the batteries prepared using the cathode slurry in Examples 1-2 was 0.0134-0.0154 mV / h, slightly higher than the K-value of the battery prepared using the cathode slurry in Comparative Example 1, but still far below the industry standard of ≤0.03 mV / h for energy storage batteries, thus posing no risk of self-discharge. The 0.5P energy efficiency of the batteries prepared using the cathode slurry in Examples 1-2 reached 94.58-94.64%, similar to the battery prepared using the cathode slurry in Comparative Example 1, demonstrating that the addition of lithium supplementers and synergists did not affect the lithium insertion / extraction activity of LFPs. The comparison of the above test results proves that the positive electrode slurry in Examples 1-2 can participate in the normal operation of the battery, and the addition of the synergist can improve its performance without affecting the normal use of the positive electrode slurry.

[0067] Based on this, the battery lifespan has been significantly improved. Specifically, for example... Figure 2 The cycle performance test results of the batteries shown at 45°C indicate that the cycle capacity retention of the batteries prepared using the positive electrode slurry in Examples 1-2 is significantly higher than that of Comparative Examples 1-2. This demonstrates that the combined use of the synergist and lithium supplement can further optimize cycle performance, i.e., battery life. Furthermore, the battery prepared using the positive electrode slurry in Example 2 is significantly superior to the battery prepared using the positive electrode slurry in Example 1. This indicates that when the dosage is kept within the reasonable addition range provided by this invention, the LNO lithium supplement and synergist can significantly improve cycle performance, and the improvement effect increases with increasing dosage.

[0068] At the same time, such as Figure 3The calendar life test results of the batteries at room temperature show that the trend of their life results is consistent with the results of high-temperature cycling at 45°C, and the life improvement trend of the batteries made using the positive electrode slurry in Examples 1 and 2 at room temperature is greater.

[0069] Taking the preparation of the positive electrode slurry in Examples 1-2 as an example, in the overall battery production process, the processes such as homogenization, coating, and formation do not require modification of existing equipment, but only parameter adjustments are needed; at the same time, the addition amounts of LNO and synergists are both low, and the unit cell cost increases by ≤5%. However, the above improvements can significantly improve the cycle life of the battery and significantly reduce the cost per kilowatt-hour of the cell over its entire life cycle.

[0070] Overall, this invention enhances the capability of the positive electrode slurry by improving its preparation method, thereby reducing the degradation of the electrical performance of the resulting battery and significantly extending its lifespan. This low-cost improvement technique achieves a substantial improvement in battery performance and shows promising application prospects.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a positive electrode slurry for lithium iron phosphate batteries, characterized in that, It includes the following steps: S1. Mix the adhesive and solvent at a mass ratio of 1:(8~12) and stir to prepare an adhesive solution; S2. Add 1-5 wt% of conductive agent by weight of the dry basis of the positive electrode slurry to the adhesive solution, and stir to mix evenly to obtain a conductive phase; S3. Based on the dry weight of the positive electrode, take 0.5-5 parts of lithium supplementer, 90-97.5 parts of lithium iron phosphate, and the lithium supplementer synergist and add them to the adhesive solution and disperse them evenly, wherein the amount of the synergist added is 1-6 wt% of the amount of lithium supplementer added; at the same time, add a total of 2-8 parts of the binder and the conductive phase to make the solid content of the positive electrode slurry reach 60-75%; disperse and stir the mixture to obtain the positive electrode slurry; The lithium replenishing agent is lithium nickel oxide rich in lithium, and the synergist of the lithium replenishing agent is lithium ferrocene sulfopropionate.

2. The method for preparing a lithium iron phosphate battery cathode slurry according to claim 1, characterized in that, In S3, the ambient humidity is controlled at 3~10%; the linear velocity of dispersion and stirring is controlled at 7.5~12m / s.

3. The method for preparing a lithium iron phosphate battery cathode slurry according to claim 1, characterized in that, The synergist is prepared by the following method: a. Under a protective atmosphere, add 10-20 parts of 6-(mercaptohexyl)ferrocene and 400-600 parts of anhydrous tetrahydrofuran to a reaction vessel, stir, then add 3-5 parts of lithium acrylate, and continue stirring to obtain a suspension. b. Add 0.5-3 parts of azobisisobutyronitrile and heat the mixture to 60-80℃, then reflux and stir for 4-8 hours; c. After the reaction is complete, cool to room temperature and remove anhydrous tetrahydrofuran by vacuum distillation to obtain the crude product; d. The crude product was vacuum dried to obtain lithium ferrocene sulfonylpropionate.

4. The method for preparing a lithium iron phosphate battery cathode slurry according to claim 3, characterized in that, In step a, after the 6-(mercaptohexyl)ferrocene is added to the anhydrous tetrahydrofuran, it is stirred at 300-500 rpm for 10-30 min, and then the lithium acrylate is added and stirred for another 20-100 min.

5. The method for preparing a lithium iron phosphate battery cathode slurry according to claim 3, characterized in that, In step c, the anhydrous tetrahydrofuran is removed by vacuum distillation at 40~50℃ and -0.09MPa.

6. A lithium iron phosphate battery cathode slurry, characterized in that, It is prepared by the method for preparing the positive electrode slurry of lithium iron phosphate battery according to any one of claims 1 to 5.

7. A positive electrode sheet, characterized in that, The cathode slurry of a lithium iron phosphate battery as described in claim 6 is coated; the areal density of the cathode is 320~450 g / m³. 2 .

8. A lithium iron phosphate battery, characterized in that, It comprises the lithium iron phosphate battery positive electrode slurry as described in claim 6 or the positive electrode sheet as described in claim 7.

9. A method for preparing a lithium iron phosphate battery, used to prepare the lithium iron phosphate battery as described in claim 8, characterized in that, The formation and activation process after battery assembly is as follows: Let the battery rest for 5 to 15 minutes to ensure that the cell temperature reaches the target temperature. Charge the battery at a constant current of 0.01C for 5~20 minutes; Charge the battery with a constant current of 0.05C, cutoff voltage 3.65V, for 150~200 minutes; Charge the battery at a constant current of 0.50C, with a cutoff voltage of 3.65V, for 100~150 minutes; Let the battery rest for 5-15 minutes; Charge the battery at a constant current of 0.10C, with a cutoff voltage of 4.20V, for 400~600 minutes; Let the battery rest for 5-15 minutes; Charge the battery with a constant current of 0.015C, cutoff voltage 4.20 V, for 400~600 min; Let the battery rest for 5-15 minutes; The battery was discharged at a constant current of 0.50C with a cutoff voltage of 2.50V for 150~210 minutes. Let the battery rest for 5-15 minutes; Charge the battery at a constant current of 0.50C, with a cutoff voltage of 3.65V, for 20~40 minutes; Let the battery rest for 2 to 10 minutes.

10. A method for preparing a lithium iron phosphate battery according to claim 9, characterized in that, The target temperature is 45~60℃.

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