Preparation method of lithium manganese iron phosphate positive electrode sheet and application thereof

Abstract

This invention discloses a method for preparing lithium manganese iron phosphate (LFP) cathode sheets and their applications. The preparation method includes the following steps: S1. Mixing LFP powder, binder, and water, and then spray-drying to obtain granulated dry powder; S2. Dry-mixing the granulated dry powder with conductive carbon black, and then adding PVDF, carbon nanotube slurry, solid electrolyte powder, polyethylene oxide, NMP, and dispersant to obtain LFP slurry; S3. Coating the LFP slurry onto carbon-coated aluminum foil, drying, and rolling to obtain LFP cathode sheets. Through the above steps, this application improves the problem of low compaction density, low areal density, and decreased proportion of positive electrode active material in LFP electrodes, which makes it difficult to improve battery energy density.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a method for preparing lithium manganese iron phosphate cathode sheets and their applications. Background Technology

[0002] Because lithium manganese iron phosphate has a higher voltage than lithium iron phosphate, its energy density is theoretically also higher, and its potential for utilization is very large.

[0003] However, practical applications have revealed that lithium manganese iron phosphate (LMP) electrodes have lower areal density and compaction, resulting in no significant improvement in energy density compared to lithium iron phosphate (LFP) batteries. The main reasons for this are as follows: First, the compaction of LMP electrodes is lower than that of LFP, reducing the mass of cathode material that can be accommodated per unit volume. Second, LMP primary particles are small, resulting in a larger specific surface area and more micropowder in the finished material, making coating prone to cracking and leading to a lower areal density and a reduced mass of cathode material per unit area. Third, LMP has lower conductivity than LFP, requiring more conductive agent to be added during cathode homogenization, thus reducing the proportion of active material and consequently lowering battery energy density.

[0004] Therefore, the key to achieving an energy density upgrade over lithium iron phosphate lies in how to prepare high-compact, high-area-density cathode sheets. Summary of the Invention

[0005] In view of this, this application provides a method for preparing lithium manganese iron phosphate cathode sheet and its application, which is used to solve the problem of how to improve battery energy density.

[0006] To achieve the above technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a method for preparing a lithium manganese iron phosphate cathode sheet, comprising the following steps: S1. After mixing lithium manganese iron phosphate powder, binder and water, spray dry to obtain granulated dry powder; S2. After dry mixing the granulated dry powder with conductive carbon black, PVDF, carbon nanotube slurry, solid electrolyte powder, polyethylene oxide, NMP and dispersant are added to obtain lithium manganese iron phosphate slurry; S3. Coat the lithium manganese iron phosphate slurry onto carbon-coated aluminum foil, dry and roll it to obtain the lithium manganese iron phosphate positive electrode sheet.

[0007] Preferably, the adhesive comprises polyvinyl alcohol.

[0008] Preferably, the mass ratio of lithium manganese iron phosphate powder, binder, and water is (60-65):(0.5-1.0):(30-37).

[0009] Preferably, in the lithium manganese iron phosphate slurry, the mass ratio of lithium manganese iron phosphate, conductive carbon black, carbon nanotubes, solid electrolyte powder, PVDF and dispersant is (94-96):(1.1-3.0):(0.5-1.5):(0.5-1.0):(0.1-1.0):(2.0-3.0):(0.1-0.5).

[0010] Preferably, the solid electrolyte powder is lithium titanium aluminum phosphate.

[0011] Preferably, step S3 is performed as follows: the lithium manganese iron phosphate slurry is coated onto the carbon-coated aluminum foil according to the areal density A, dried once, coated again according to the areal density B, dried a second time, and then rolled to obtain the lithium manganese iron phosphate positive electrode sheet.

[0012] Preferably, the areal density A is 25-30 mg / cm³ on both sides. 2 The primary drying temperature is 80-100℃; the areal density B is 10-15 mg / cm³ on both sides. 2 The secondary drying temperature is 100-120℃.

[0013] Preferably, the rolling process includes a primary rolling process and a secondary rolling process; the temperature of the rollers during rolling is 40-60℃.

[0014] Preferably, the target compaction density for a single roller compaction is 1.8~2.0 g / cm³. 3 The target compaction density for secondary roller compaction is 2.3~2.6 g / cm³. 3 .

[0015] Secondly, this application provides a pouch lithium-ion battery comprising a lithium manganese iron phosphate cathode sheet. The beneficial effects of this application are as follows: This application uses lithium manganese iron phosphate powder as raw material, and then adds binder for granulation to cause secondary agglomeration of small particles, reducing the risk of gelation during homogenization. Solid electrolyte powder is added during homogenization to improve the contact between the lithium manganese iron phosphate main material and the electrolyte under high electrode compaction. Then, a two-step coating method is adopted to improve the electrode load and prevent cracking during drying. Finally, hot rolling is used to improve the electrode compaction density. The positive electrode obtained by this application has high electrode compaction density and good electrochemical performance after being assembled into a soft-pack battery. Detailed Implementation

[0016] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0017] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0018] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0019] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0020] Unless otherwise explicitly defined and specified herein, all technical and scientific terms used in this application shall have the generally accepted meanings understood by one of ordinary skill in the field of chemical and chemical materials technology (including but not limited to polymer chemistry, inorganic chemistry, organic synthesis, catalysis chemistry, materials processing, and chemical unit operations) based on their professional knowledge and conventional practice. The use of any terminology herein is intended to describe the specific embodiments of this application in the clearest and most accurate manner, so as to fully disclose the technical solution. Such use shall not in any way be construed as a limitation on the scope of the claims, nor does it imply the exclusion of equivalent technical solutions that could be reasonably known by one of skill in the art based on the concept of this application.

[0021] The terms "comprising," "including," "having," "containing," and any grammatical variations or similar expressions used in the specification and claims of this application are all open-ended and non-exhaustive descriptive terms. Their purpose is to explicitly describe the existence of technical features, components, steps, or parts, while explicitly allowing and covering the possibility that other features, components, steps, parts, or any combinations thereof not explicitly listed may exist or be added to the technical solution, as long as such additions do not destroy the integrity and inventiveness of the original technical solution.

[0022] When the terms "embodiments," "some embodiments," or "specific embodiments" are mentioned in the specification, they refer to examples that, in conjunction with the specific parameters, materials, steps, and results described in that section, constitute one or a group of examples for implementing the technical solutions of this application. These embodiments are used for full disclosure and illustrative purposes, not for exhaustive enumeration. Those skilled in the art should understand that, without departing from the overall inventive concept of this application, the various technical features disclosed in different embodiments can be combined, substituted, modified, or deleted to form other implementation methods that are not listed one by one in the specification but also fall within the protection scope of this application.

[0023] Unless otherwise expressly specified and limited, all terms related to chemical process operations, material preparation, processing and analytical testing involved in this application shall be interpreted in the broadest sense based on the conventional understanding of those skilled in the art.

[0024] Regarding performance testing and structural characterization, all testing and characterization methods involved in this application, unless otherwise specified, refer to conventional methods known in the art. Specific testing conditions may be selected and adjusted according to the sample properties and relevant national standards, international standards, or industry-standard methods. Test items may include mechanical properties (such as tensile, bending, and impact strength), thermal properties (such as DSC and TGA analysis), and chemical stability (such as solvent resistance and acid / alkali corrosion resistance). Structural characterization methods may include FT-IR, NMR, XRD, SEM, TEM, and BET. All test results should be understood to be within the allowable range of conventional experimental errors.

[0025] Regarding numerical values ​​and ranges, all parameter ranges expressed in this application in the form of "from a certain value to a certain value" should be understood as explicitly disclosing the endpoints of the range, each specific numerical point between the endpoints, and all sub-ranges formed by any two numerical points within the range. For example, "30℃ to 80℃" discloses 30, 31, ..., 80℃, as well as sub-ranges such as 30-50℃, 45-70℃, etc. When a numerical value is preceded by "about," "approximately," or similar words, it indicates that the numerical value is allowed to have reasonable errors recognized in the art under the measurement or control conditions, which can generally be understood as the deviation allowed by relevant standards or a normal fluctuation range of ±5% or ±10%.

[0026] This application provides a method for preparing a lithium manganese iron phosphate cathode sheet, comprising the following steps: S1. After mixing lithium manganese iron phosphate powder, binder and water, spray dry to obtain granulated dry powder; S2. After dry mixing the granulated dry powder with conductive carbon black, PVDF, carbon nanotube slurry, solid electrolyte powder, polyethylene oxide, NMP and dispersant are added to obtain lithium manganese iron phosphate slurry; S3. Coat the lithium manganese iron phosphate slurry onto carbon-coated aluminum foil, dry and roll it to obtain the lithium manganese iron phosphate positive electrode sheet.

[0027] In this application, lithium manganese iron phosphate is sieved using a vibrating screen to obtain lithium manganese iron phosphate powder, removing ultra-large particles and ultrafine powders, thus improving the homogenization processing performance. Then, a binder is used for granulation to cause secondary agglomeration of small particles, reducing the risk of homogenization gelation. Solid electrolyte powder is added during the homogenization process to improve the contact between the lithium manganese iron phosphate main material and the electrolyte under high electrode compaction. A two-step coating method is used to increase the load of the electrode and prevent cracking during drying. Finally, a two-step hot rolling process is used to increase the electrode compaction density. Through the above methods, the problem of low compaction density, low areal density, and decreased proportion of positive electrode active material in lithium manganese iron phosphate electrodes, which makes it difficult to improve the battery energy density, is improved.

[0028] In some embodiments, lithium manganese iron phosphate material is sieved using a vibrating screen to obtain lithium manganese iron phosphate powder, wherein the compacted density of the lithium manganese iron phosphate powder is 2.20~2.40 g / cm³. 3 The vibrating screen is divided into two layers. The mesh size of the upper layer is smaller than that of the lower layer. After removing the material on the first layer and the material under the second layer, the powder after the screen is retained as the material on the second layer. Its particle size distribution satisfies D10 > 0.9 μm and D99 < 18 μm.

[0029] By adopting the above technical solution, the first sieve removes ultra-large particles, the second sieve removes ultra-fine powder, and the material retained on the second sieve has a concentrated particle size distribution, which is beneficial to improving the homogenization performance and coating quality of the slurry.

[0030] In some embodiments, the adhesive comprises polyvinyl alcohol.

[0031] By adopting the above technical solution, the binder granulation causes the small lithium manganese iron phosphate particles to agglomerate again, reducing the risk of gelation during the homogenization process.

[0032] In some embodiments, the mass ratio of lithium manganese iron phosphate powder, binder, and water is (60-65):(0.5-1.0):(30-37).

[0033] In some embodiments, the mass ratio of lithium manganese iron phosphate, conductive carbon black, carbon nanotubes, solid electrolyte powder, PVDF and dispersant in the lithium manganese iron phosphate slurry is (94-96):(1.1-3.0):(0.5-1.5):(0.5-1.0):(0.1-1.0):(2.0-3.0):(0.1-0.5).

[0034] In some embodiments, the solid electrolyte powder is lithium titanium aluminum phosphate.

[0035] By adopting the above technical solution, the solid electrolyte powder added during the homogenization process can improve the contact between the lithium manganese iron phosphate main material and the electrolyte under high electrode compaction.

[0036] In some embodiments, the discharged solids content of the lithium manganese iron phosphate slurry is 50-60%, the discharged viscosity is 4000-8000 cps, and the discharged fineness is <20μm.

[0037] In some embodiments, step S3 involves coating lithium manganese iron phosphate slurry onto carbon-coated aluminum foil according to surface density A, drying it once, coating it again according to surface density B, drying it a second time, and then rolling it to obtain the lithium manganese iron phosphate positive electrode sheet.

[0038] In some embodiments, the areal density A is 25-30 mg / cm² on both sides. 2 The primary drying temperature is 80-100℃; the areal density B is 10-15 mg / cm³ on both sides. 2 The secondary drying temperature is 100-120℃.

[0039] In this embodiment, coating and drying are performed in two steps, which can improve the electrode load and prevent cracking during drying.

[0040] In some embodiments, the rolling step includes a primary rolling process and a secondary rolling process; the temperature of the rollers during rolling is 40-60°C.

[0041] In some embodiments, the target compaction density for a single roll pressing is 1.8~2.0 g / cm³. 3 The target compaction density for secondary roller compaction is 2.3~2.6 g / cm³. 3 .

[0042] In this embodiment, the two-step hot rolling process gradually increases the compaction density of the electrode sheet, avoiding damage to the electrode sheet caused by a single high-pressure compaction.

[0043] This application provides a pouch lithium-ion battery comprising a lithium manganese iron phosphate cathode.

[0044] The preparation method of soft-pack lithium-ion battery includes the following steps: the above-mentioned high energy density lithium manganese iron phosphate positive electrode sheet is rolled, slited and die-cut to obtain the desired positive electrode sheet; the graphite material is homogenized, coated, rolled, slited and die-cut to obtain the desired negative electrode sheet; the positive electrode sheet, separator and negative electrode sheet are stacked in sequence, and then liquid injection, primary encapsulation, pre-formation, secondary encapsulation, continuous formation and capacity testing are performed to obtain the desired soft-pack battery.

[0045] The following specific embodiments further illustrate this solution.

[0046] Example 1 A method for preparing a lithium manganese iron phosphate cathode sheet includes the following steps: S1. Compact lithium manganese iron phosphate powder (powder compaction density 2.38 g / cm³) 3 The lithium manganese iron phosphate powder was sieved to obtain a particle size distribution of D10=1.0μm and D99=15.3μm. The lithium manganese iron phosphate powder, polyvinyl alcohol, and pure water were then granulated in a ratio of 62:1.0:37 and spray-dried to obtain granulated dry powder. S2. Granulated dry powder, conductive carbon black, carbon nanotubes, lithium titanium aluminum phosphate, polyethylene oxide, PVDF and dispersant vinyl polyether are homogenized in a mass ratio of 94:1.5:1.5:0.5:0.4:2.0:0.1. After high stirring for 3 hours, NMP solvent is added to adjust the viscosity. The solid content of the slurry is controlled at 55%. After sieving, a lithium manganese iron phosphate slurry with a viscosity of 5800 cps and a fineness of 15 μm is obtained. S3. The lithium manganese iron phosphate slurry is coated onto the carbon-coated aluminum foil in two steps, first with a double-sided areal density A=28mg / cm³. 2 The coating is applied and dried at 80°C, then coated with a double-sided surface density of B = 12 mg / cm³. 2 The electrode is coated again and dried at 120°C, followed by a two-step rolling process. The first rolling process brings the electrode compaction density to 1.9 g / cm³. 3 The second rolling process compacts the electrode sheet to 2.50 g / cm³. 3 The temperature of the rollers is 60℃ for both roller pressing processes, thus obtaining the lithium manganese iron phosphate positive electrode sheet.

[0047] Example 2 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that the ratio of lithium manganese iron phosphate powder, polyvinyl alcohol, and pure water is adjusted to 65:0.5:34.5.

[0048] Example 3 A method for preparing lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that the mass ratio of granulated dry powder, conductive carbon black, carbon nanotubes, lithium titanium aluminum phosphate, polyethylene oxide, PVDF and dispersant is 94:1.5:1.1:0.9:0.4:2.0:0.1.

[0049] Example 4 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that the mass ratio of granulated dry powder, conductive carbon black, carbon nanotubes, lithium titanium aluminum phosphate, polyethylene oxide, PVDF and dispersant is 94.4:1.1:1.5:0.5:0.4:2.0:0.1.

[0050] Example 5 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that the areal density A is adjusted to a bifacial areal density of 30 mg / cm³. 2 The areal density B is adjusted to a bifacial areal density of 15 mg / cm³. 2 .

[0051] Example 6 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that the areal density A is adjusted to a bifacial areal density of 30 mg / cm³. 2 The areal density B is adjusted to a bifacial areal density of 10 mg / cm³. 2 .

[0052] Example 7 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that the compaction of the primary roller-pressed electrode sheet is adjusted to 1.8 g / cm³. 3 .

[0053] Example 8 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that the compaction of the primary roller-pressed electrode sheet is adjusted to 2.0 g / cm³. 3 .

[0054] Comparative Example 1 A method for preparing lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that there is no granulation process.

[0055] Comparative Example 2 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that lithium titanium aluminum phosphate and polyethylene oxide are not added.

[0056] Comparative Example 3 A method for preparing a lithium manganese iron phosphate cathode sheet is the same as in Example 1, except that only one coating is applied to achieve a bifacial density of 40 mg / cm³. 2 With just one rolling process, the electrode compaction density can reach a maximum of 2.40 g / cm³. 3 .

[0057] Testing and Evaluation The positive electrode sheets from the above embodiments and comparative examples are rolled, slited, and die-cut to obtain the desired positive electrode sheets. Graphite material is homogenized, coated, rolled, slited, and die-cut to obtain the desired negative electrode sheets. The positive electrode sheets, separator, and negative electrode sheets are then stacked sequentially. After liquid injection, primary encapsulation, pre-formation, secondary encapsulation, continuous formation, and capacity testing, the desired soft-pack battery is obtained. The soft-pack battery is tested for charge and discharge within a voltage range of 2.0~4.3V. The test steps are as follows: Discharge capacity test: The battery was placed at an ambient temperature of 25±3℃ for 8 hours; constant current and constant voltage charging was performed at the specified rate, with a cutoff voltage of 4.3V and a cutoff current of 0.02C; constant current discharge was performed at the specified rate, with a cutoff voltage of 2.0V; the cycle was repeated twice, and the result of the second cycle was taken. Cyclic performance test: The battery was placed at an ambient temperature of 25±3℃ for 8 hours; constant current and constant voltage charging was performed at a 1C rate, with a cutoff voltage of 4.3V and a cutoff current of 0.02C; constant current discharging was performed at a 1C rate, with a cutoff voltage of 2.0V; after 100 cycles, the capacity retention rate was calculated as (capacity of the 100th cycle / capacity of the 1st cycle) x 100%.

[0058] The test results are shown in Table 1.

[0059] Table 1 Test Results of Lithium Manganese Iron Phosphate Pouch Batteries

[0060] Combining Example 1 and Comparative Example 1 with Table 1, it can be seen that in Comparative Example 1 without binder granulation, the electrode compaction density decreased from 2.50 g / cm³ to 2.40 g / cm³, the first-time efficiency decreased from 91.6% to 88.9%, the 1.0C discharge specific capacity decreased from 128.5 mAh / g to 119.6 mAh / g, and the capacity retention rate after 100 cycles at 1.0C decreased from 99.0% to 97.0%. This indicates that after binder granulation caused secondary agglomeration of small particles, the electrode compaction density and electrochemical performance were significantly improved.

[0061] Combining Example 1 and Comparative Example 2 with Table 1, it can be seen that Comparative Example 2, without the addition of lithium aluminum titanium phosphate and polyethylene oxide, has an electrode compaction density of 2.50 g / cm³, a 0.1C discharge specific capacity of only 134.0 mAh / g, an initial efficiency of only 88.4%, a 1.0C discharge specific capacity of only 117.8 mAh / g, and a 100-cycle capacity retention rate of only 96.3%, which is the lowest among all comparative examples. This indicates that adding solid electrolyte powder and polyethylene oxide during the homogenization process can effectively improve the contact between the lithium iron manganese phosphate main material and the electrolyte under high electrode compaction, and significantly contributes to capacity performance, initial efficiency, and cycle stability.

[0062] Combining Example 1 and Comparative Example 3 with Table 1, it can be seen that Comparative Example 3, which uses only one coating and rolling process, can only achieve an electrode compaction density of 2.40 g / cm³, with the first-time efficiency reduced to 88.5% and the capacity retention rate after 100 rolls reduced to 96.7%. This indicates that the two-step coating and two-step hot rolling process is necessary to obtain high-compact, stable electrode sheets under high areal density.

[0063] Combined with Examples 1-8 and Table 1, it can be seen that, under the conditions of varying granulation ratio, ratio of conductive carbon black to carbon nanotubes and lithium titanium aluminum phosphate, areal density A / B combination, and single-roll compaction density, the obtained positive electrode sheet compaction density is consistently maintained at 2.50 g / cm³, and the first-cycle efficiency of the soft-pack battery remains at 91.2%~92.3%, and the capacity retention rate after 100 cycles remains at 98.8%~99.3%, indicating that the method of this application has good process adaptability.

[0064] As can be seen from the data in Table 1, when the high-energy-density lithium manganese iron phosphate cathode sheet prepared in this application is assembled into a soft-pack battery, compared with the comparative example, the electrode compaction, first-time efficiency, capacity and cycle stability are all improved, indicating that the high-energy-density lithium manganese iron phosphate cathode sheet prepared by the method provided in this application has advantages.

[0065] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode sheet, characterized in that, Includes the following steps: S1. After mixing lithium manganese iron phosphate powder, binder and water, spray dry to obtain granulated dry powder; S2. After dry mixing the granulated dry powder with conductive carbon black, PVDF adhesive, carbon nanotube slurry, solid electrolyte powder, polyethylene oxide, NMP and dispersant are added to obtain lithium manganese iron phosphate slurry; S3. The lithium manganese iron phosphate slurry is coated onto carbon-coated aluminum foil, dried, and rolled to obtain the lithium manganese iron phosphate positive electrode sheet.

2. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 1, characterized in that, The adhesive includes polyvinyl alcohol.

3. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 1, characterized in that, The mass ratio of the lithium manganese iron phosphate powder, binder, and water is (60-65):(0.5-1.0):(30-37).

4. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 1, characterized in that, In the lithium manganese iron phosphate slurry, the mass ratio of lithium manganese iron phosphate, conductive carbon black, carbon nanotubes, solid electrolyte powder, and PVDF solid to dispersant in the PVDF adhesive is (94-96):(1.1-3.0):(0.5-1.5):(0.5-1.0):(0.1-1.0):(2.0-3.0):(0.1-0.5).

5. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 1, characterized in that, The solid electrolyte powder is lithium titanium aluminum phosphate.

6. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 1, characterized in that, Step S3 involves coating lithium manganese iron phosphate slurry onto carbon-coated aluminum foil according to surface density A, drying it once, coating it again according to surface density B, drying it a second time, and then rolling it to obtain the lithium manganese iron phosphate positive electrode sheet.

7. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 6, characterized in that, The areal density A is 25-30 mg / cm³ on both sides. 2 The primary drying temperature is 80-100℃; the areal density B is 10-15 mg / cm³ on both sides. 2 The secondary drying temperature is 100-120℃.

8. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 6, characterized in that, The rolling process includes a primary rolling process and a secondary rolling process; the temperature of the rollers in the rolling process is 40-60℃.

9. The method for preparing the lithium manganese iron phosphate cathode sheet according to claim 8, characterized in that, The target compaction density of the first roll pressing is 1.8~2.0 g / cm³. 3 The target compaction density for secondary roller compaction is 2.3~2.6 g / cm³. 3 .

10. A soft-pack lithium-ion battery, characterized in that, It includes lithium manganese iron phosphate cathode sheets prepared by the preparation method according to any one of claims 1-9.

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