Manganese iron oxalate precursor material and preparation method thereof, manganese iron lithium phosphate positive electrode material, positive electrode sheet and secondary battery

Abstract

The application provides a manganese iron oxalate precursor material and a preparation method thereof, a manganese iron lithium phosphate positive electrode material, a positive electrode sheet and a secondary battery, and relates to the technical field of secondary batteries. x Fe (1‑x) C2O4,0

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and particularly relates to a manganese iron oxalate precursor material, a preparation method thereof, a lithium manganese iron phosphate cathode material, a cathode electrode sheet and a secondary battery. Background Art

[0002] Lithium-ion batteries are widely used in fields such as 3C electronic products, new energy vehicles, energy storage devices, etc. due to their advantages such as fast charging ability, low self-discharge rate, and no memory effect. With the continuous development of the energy field, higher requirements are also put forward for the charge and discharge performance of lithium-ion batteries.

[0003] The cathode material is an important component of a lithium-ion battery, and its performance directly affects the cycle life and charge and discharge performance of the lithium-ion battery. Among them, lithium manganese iron phosphate has received wide attention due to its higher energy density and higher discharge voltage platform compared with lithium iron phosphate, which can provide a longer cruising range. Currently, the precursors of lithium manganese iron phosphate mainly include manganese iron phosphate, iron manganese oxide, and manganese iron oxalate. Manganese iron oxalate has been widely studied due to its advantages such as low cost, simple process, and low sintering difficulty. However, at present, when using the co-precipitation method to prepare the manganese iron oxalate precursor, the grain growth rate is relatively fast, the formed manganese iron oxalate precursor has a large particle size, the lithium manganese iron phosphate material prepared from this manganese iron oxalate precursor also has a large particle size, a low tap density, and the lithium ion migration path becomes longer, resulting in a decrease in the lithium ion transmission speed and the electrochemical reaction efficiency, thereby affecting its electrochemical performance, such as charge and discharge specific capacity, first Coulomb efficiency, rate performance, etc., making it difficult to improve the performance in the above aspects. Summary of the Invention

[0004] In view of the technical problems existing in the background art, the present application provides a manganese iron oxalate precursor material, a preparation method thereof, a lithium manganese iron phosphate cathode material, a cathode electrode sheet and a secondary battery, aiming to solve the technical problem that it is difficult to improve the electrochemical performance of the lithium manganese iron phosphate cathode material in terms of charge and discharge specific capacity, first Coulomb efficiency, rate performance, etc.

[0005] In a first aspect, an embodiment of the present application provides a manganese iron oxalate precursor material. The chemical formula of the manganese iron oxalate precursor material is Mn x Fe (1-x) C2O4, 0 < x < 1; the primary particles of the manganese iron oxalate precursor material are in a flaky structure, the length of the primary particles is 1000 nm - 1500 nm, the width of the primary particles is 400 nm - 870 nm, the thickness of the primary particles is 300 nm - 500 nm; the purity of the manganese iron oxalate precursor material ≥ 99.2%.

[0006] In the technical solution of this application embodiment, controlling the composition, purity, morphology, and size of the primary particles of the ferromanganese oxalate precursor material not only helps to improve the compaction density of the ferromanganese oxalate precursor material but also gives it a smaller particle size. This increases the compaction density of the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material and reduces the lithium-ion migration path in the resulting lithium iron phosphate cathode material. This improves the electronic conductivity and lithium-ion diffusion rate of the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material, thereby significantly improving the electrochemical performance of the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material in terms of charge / discharge specific capacity, initial coulombic efficiency, and rate performance. Simultaneously, controlling the purity of the ferromanganese oxalate precursor material to ≥99.2% helps to reduce impurities in the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material from the source, ensuring the controllability and consistency of the chemical composition, structure, and electrochemical performance of the lithium iron phosphate cathode material.

[0007] In some embodiments, the D0 particle size of the ferromanganese oxalate precursor material is 0.35 μm to 0.42 μm, the D10 particle size is 1 μm to 3 μm, the D50 particle size is 4 μm to 10 μm, the D90 particle size is 10 μm to 25 μm, the D99 particle size is 20 μm to 45 μm, and the D100 particle size is 20 μm to 60 μm.

[0008] In this embodiment, controlling the particle size distribution of the manganese iron oxalate precursor material results in a small and concentrated particle size, which is beneficial for the preparation of lithium manganese iron phosphate cathode material with a small and concentrated particle size distribution. This helps improve the electrochemical performance of the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material in terms of charge-discharge specific capacity, initial coulombic efficiency, and rate performance, while also enhancing the consistency of the electrical performance of the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material. Simultaneously, the particle size distribution of the manganese iron oxalate precursor material... The small particle size and concentrated particle size distribution of the manganese iron oxalate precursor material help to produce more active sites in the lithium manganese iron phosphate cathode material, increasing the lithium ion insertion and extraction efficiency, thereby improving the specific capacity and overall electrochemical activity of the aforementioned lithium manganese iron phosphate cathode material. In addition, the reasonable particle size distribution of the manganese iron oxalate precursor material is beneficial to optimizing the particle size distribution of the lithium manganese iron phosphate cathode material prepared from it, improving the processing performance of the lithium manganese iron phosphate cathode material, facilitating uniform coating during the manufacturing process of the cathode sheet, improving production efficiency, and thus reducing costs.

[0009] In some embodiments, the length of the primary particle is 1000nm~1400nm, the width of the primary particle is 400nm~700nm, and the thickness of the primary particle is 350nm~450nm.

[0010] This embodiment further controls the size of the primary particles of the ferromanganese oxalate precursor material, resulting in a smaller particle size. This further improves the compaction density of the lithium iron manganese phosphate cathode material prepared from the ferromanganese oxalate precursor material and reduces the lithium-ion migration path in the lithium iron manganese phosphate cathode material prepared from the ferromanganese oxalate precursor material. This further improves the electrochemical performance of the lithium iron manganese phosphate cathode material prepared from the ferromanganese oxalate precursor material in terms of charge / discharge specific capacity, initial coulombic efficiency, and rate performance.

[0011] In some embodiments, the specific surface area of ​​the manganese ferric oxalate precursor material is 1.0 m². 2 / g~5.0m 2 / g.

[0012] In this embodiment, controlling the specific surface area of ​​the ferromanganese oxalate precursor material is beneficial for controlling its reactivity, thereby improving the purity of the lithium iron phosphate cathode material prepared from it. Simultaneously, controlling the specific surface area of ​​the ferromanganese oxalate precursor material also helps to control the specific surface area of ​​the lithium iron phosphate cathode material prepared from it, providing suitable active sites and promoting lithium ion insertion and extraction, thus improving the purity of the lithium iron phosphate cathode material. The actual specific capacity of the material; in addition, the lithium manganese iron phosphate cathode material has a suitable specific surface area, which helps the electrolyte to more fully wet the surface of the lithium manganese iron phosphate cathode material, improves the transport efficiency of lithium ions at the solid-liquid interface, thereby reducing the interfacial impedance inside the secondary battery using the lithium manganese iron phosphate cathode material, and helps to promote good contact between the active sites of the lithium manganese iron phosphate cathode material and the electrolyte, optimizes lithium ion transport and intercalation during the first charge-discharge process, and thus improves the first coulombic efficiency of the lithium manganese iron phosphate cathode material when applied to secondary batteries.

[0013] Secondly, embodiments of this application provide a method for preparing a manganese iron oxalate precursor material, comprising the following steps:

[0014] The metal salt solution and the alkaline solution are mixed and subjected to a first reaction treatment to obtain the first slurry;

[0015] The first slurry is mixed with oxalate source and then subjected to a second reaction to obtain the second slurry;

[0016] The second slurry was aged to obtain manganese ferric oxalate precursor material;

[0017] Among them, the metal salt solution contains divalent manganese ions and divalent iron ions, and the first slurry includes an intermediate product. The general formula of the intermediate product is: Mn x Fe (1-x) (OH)2, where 0 < x < 1, and the particle size of the primary particles of the intermediate product is 30 nm to 100 nm;

[0018] The chemical formula of the manganese iron oxalate precursor material is Mn x Fe (1-x) C2O4, where 0 < x < 1;

[0019] The primary particles of the manganese iron oxalate precursor material are in a flaky structure. The length of the primary particles is 1000 nm to 1500 nm, the width of the primary particles is 400 nm to 870 nm, and the thickness of the primary particles is 300 nm to 500 nm;

[0020] The purity of the manganese iron oxalate precursor material is ≥99.2%.

[0021] In this embodiment, the present invention first coprecipitates divalent manganese ions (Mn 2+ ) and divalent iron ions (Fe 2+ ) to obtain a manganese iron hydroxide intermediate product. The intermediate product presents an ultrafine nanoscale structure, and its particle size is much smaller than that of the manganese iron oxalate particles prepared directly by the oxalate precipitation method; then, the intermediate product is mixed with oxalic acid source. In the second reaction treatment, oxalate ions replace the hydroxide ions in the intermediate product to generate manganese iron oxalate. The introduction of oxalate ions causes lattice rearrangement, further refines the particles, and obtains manganese iron oxalate with a further optimized microstructure. At the same time, in the second reaction treatment, the reducing property of oxalate ions effectively protects divalent iron ions and divalent manganese ions from oxidation. Even if there is a situation where divalent iron ions and / or divalent manganese ions are oxidized, the complexing effect of oxalate ions ensures that the oxidation by-products will not precipitate together with manganese iron oxalate, effectively improving the purity of the manganese iron oxalate precursor material; after oxalate replacement, the second slurry is subjected to aging treatment to allow sufficient lattice rearrangement of manganese iron oxalate, and the distribution of Mn and Fe elements is more uniform, which helps to improve the purity and crystallinity of the manganese iron oxalate precursor material. The finally obtained manganese iron oxalate precursor material exhibits a significantly reduced primary particle size and overall particle size, ensuring the uniform distribution of Mn and Fe elements in the manganese iron oxalate precursor material, greatly shortening the diffusion path of lithium ions in the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material, while improving the charge-discharge rate and kinetic performance of the lithium manganese iron phosphate cathode material when applied to secondary batteries, and improving the cycle stability of the lithium manganese iron phosphate cathode material when applied to secondary batteries.

[0022] The ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron in the metal salt solution can be 1:1, 1.1:1, 1.2:1, 1.3:1, or any combination thereof.

[0023] In some embodiments, the pH value of the first slurry is 9.0 to 11.0.

[0024] In this embodiment, the pH value of the first slurry is controlled to be 9.0~11.0, which is conducive to the growth of divalent manganese ions (Mn). 2+ ) and ferrous ions (Fe 2+ The co-precipitation of manganese ferrous hydroxide forms a highly uniform intermediate product. Simultaneously, the pH range described above is favorable for the reaction of metal ions and hydroxide ions to form a uniform precipitate, thus promoting the formation of ultrafine particles, facilitating the acquisition of nanoscale intermediate products, and improving the overall uniformity of the intermediate product. Secondly, the pH range helps reduce the occurrence of side reactions, ensuring the formation of the manganese ferrous hydroxide intermediate product and contributing to its purity. Furthermore, the pH range allows the surface charge state and hydration level of the intermediate product to be more suitable for subsequent oxalate replacement, thereby facilitating the formation of a high-purity, pure-phase manganese ferric oxalate precursor material.

[0025] In some embodiments, the ratio of the molar amount of hydroxide ions in the alkaline solution to the total molar amount of manganese and iron in the metal salt solution is (2~3):1.

[0026] In this embodiment, the molar ratio of hydroxide ions in the alkaline solution to the total molar ratio of manganese and iron in the metal salt solution is controlled to be (2~3):1, ensuring that divalent manganese ions (Mn) are present. 2+ ), divalent iron ions (Fe 2+ ) and OH - A full reaction helps promote the reaction of divalent manganese ions (Mn). 2+ ), divalent iron ions (Fe 2+ Effective and thorough co-precipitation, while also helping to avoid residual OH in the second slurry. - Excessive amounts can affect crystal transformation during aging and increase the purity of the manganese oxalate ferric precursor material.

[0027] In some embodiments, the ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron in the metal salt solution is (1.0~1.2):1.

[0028] In this embodiment, by controlling the molar ratio of oxalate ions in the oxalate source to the total molar ratio of manganese and iron in the metal salt solution to (1.0~1.2):1, it is ensured that oxalate ions efficiently replace hydroxide ions in the intermediate product, reducing residual hydroxides or unreacted metal salts. At the same time, it avoids unnecessary side reactions and waste of raw materials caused by excessive oxalate ions, thereby improving the conversion rate, purity, and structural integrity of the manganese iron oxalate precursor material, while also improving production efficiency and economic benefits.

[0029] In some embodiments, the ferrous salt containing ferrous ions includes at least one of ferrous chloride, ferrous nitrate, ferrous sulfate, and ferrous acetate.

[0030] In this embodiment, by using the above-mentioned widely available and low-cost divalent iron salt, it is beneficial to significantly reduce the production cost of manganese iron oxalate precursor materials and ensure the economic feasibility of the preparation process.

[0031] In some embodiments, the divalent manganese salt containing divalent manganese ions includes at least one of manganese chloride, manganese nitrate, manganese sulfate, and manganese acetate.

[0032] In this embodiment, by using the above-mentioned widely available and low-cost divalent manganese salt, it is beneficial to significantly reduce the production cost of manganese ferric oxalate precursor materials and ensure the economic feasibility of the preparation process.

[0033] In some embodiments, the alkaline solution includes at least one of sodium hydroxide solution and ammonia water.

[0034] In this embodiment, the use of the aforementioned widely available and low-cost alkaline solution helps to significantly reduce the production cost of the manganese iron oxalate precursor material and ensures the economic feasibility of the preparation process.

[0035] In some embodiments, the oxalate source includes at least one of oxalic acid, ammonium oxalate, and sodium oxalate.

[0036] In this embodiment, by using the above-mentioned widely available and low-cost oxalate source, it is beneficial to significantly reduce the production cost of manganese iron oxalate precursor materials and ensure the economic feasibility of the preparation process.

[0037] In some embodiments, the step of mixing a metal salt solution with an alkaline solution and subjecting it to a first reaction to obtain a first slurry includes: mixing the metal salt solution and the alkaline solution at a first mixing temperature and for a first mixing time to obtain a first mixture; and mixing the first mixture at a first reaction temperature and for a first reaction time to obtain a first slurry; wherein the first mixing temperature is 20°C to 60°C, the first mixing time is 15 min to 30 min, the first reaction temperature is 20°C to 60°C, and the first reaction time is 5 min to 15 min.

[0038] In this embodiment, controlling the mixing of the metal salt solution and the alkaline solution under the above conditions and performing the first reaction treatment helps to promote the uniform mixing and co-precipitation of metal ions and hydroxide ions in the alkaline solution, resulting in more uniform formation of nanoscale intermediate product particles. In some embodiments, the step of mixing the first slurry with an oxalate source and performing a second reaction treatment to obtain a second slurry includes: the first slurry and the oxalate source are mixed at a second mixing temperature and for a second mixing time to obtain a second mixture; the second mixture is mixed at a second reaction temperature and for a second reaction time to obtain a second slurry; wherein the second mixing temperature is 20℃~60℃, the second mixing time is 15min~30min, the second reaction temperature is 20℃~60℃, and the second reaction time is 15min~45min.

[0039] In this embodiment, the first slurry and oxalate source are mixed and subjected to a second reaction under the above conditions to promote a full reaction between the intermediate product in the first slurry and oxalate ions, thereby facilitating the generation of a high-purity manganese ferric oxalate precursor material. In some embodiments, the step of aging the second slurry to obtain the manganese ferric oxalate precursor material includes: aging the second slurry at an aging temperature and for an aging time to obtain an aged slurry; separating the aged slurry into solid and liquid components to obtain a first solid material; rinsing the first solid material until the conductivity of the rinsing solution is ≤120 μs / cm to obtain a second solid material; and drying the second solid material at a drying temperature and for a drying time to obtain the manganese ferric oxalate precursor material; wherein the aging temperature is 80℃~100℃, the aging time is 60min~150min, and the drying temperature is 60℃~80℃, and the drying time is 2h~4h.

[0040] In this embodiment, the aging process allows the manganese oxalate ferric crystals to grow optimally under the aforementioned conditions, improving the crystallinity and purity of the manganese oxalate ferric crystal precursor material. The rinsing process effectively removes residual soluble impurities, ensuring the purity of the manganese oxalate ferric crystal precursor material. The drying process under the aforementioned conditions facilitates the rapid and thorough removal of moisture from the manganese oxalate ferric crystal precursor material. Strictly controlled temperature and time parameters ensure the particle size and morphology of the prepared manganese oxalate ferric crystal precursor material, guaranteeing batch-to-batch consistency and repeatability.

[0041] Thirdly, this application provides a lithium manganese iron phosphate cathode material, which is prepared from a manganese iron oxalate precursor material. The manganese iron oxalate precursor material is selected from the manganese iron oxalate precursor material of the first aspect, or the manganese iron oxalate precursor material prepared by the preparation method of the manganese iron oxalate precursor material of the second aspect.

[0042] In the technical solution of this application embodiment, the composition, morphology, and size of the manganese iron oxalate precursor material are controlled to give the manganese iron oxalate precursor material a small particle size and high compaction density. This effectively improves the compaction density of the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material, reduces the lithium ion migration path in the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material, improves the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material, and thus significantly improves the electrochemical performance of the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material in terms of charge-discharge specific capacity, first coulombic efficiency, and rate performance.

[0043] In some embodiments, the compaction density of the lithium manganese iron phosphate cathode material is 1.85 g / cm³. 3 ~1.9g / cm 3 .

[0044] In this embodiment, the lithium manganese iron phosphate cathode material has a high compaction density, which is beneficial for the secondary battery using the lithium manganese iron phosphate cathode material to store more energy per unit volume, thereby improving the battery's range and energy output capability.

[0045] In some embodiments, the 0.1C charging specific capacity of the lithium manganese iron phosphate cathode material is ≥150mAh / g, and the 0.1C discharging specific capacity of the lithium manganese iron phosphate cathode material is ≥150mAh / g.

[0046] In this embodiment, at a charge-discharge rate of 0.1C, the lithium manganese iron phosphate cathode material stores a large amount of electrical energy, exhibiting excellent energy storage capacity. The discharge specific capacity of the lithium manganese iron phosphate cathode material at a charge-discharge rate of 0.1C is ≥150mAh / g, and the high charge release efficiency of the lithium manganese iron phosphate cathode material is beneficial for maintaining a stable discharge voltage platform, ensuring the energy output and service life of the secondary battery using the lithium manganese iron phosphate cathode material.

[0047] In some embodiments, the initial coulombic efficiency of the lithium manganese iron phosphate cathode material is ≥97.48%.

[0048] In this embodiment, the lithium manganese iron phosphate cathode material has a high initial coulombic efficiency, indicating that the lithium manganese iron phosphate cathode material has high energy conversion efficiency during the first charge-discharge process, which helps to reduce the irreversible energy loss of the secondary battery using the lithium manganese iron phosphate cathode material in the charge-discharge cycle and extend the cycle life of the secondary battery.

[0049] Fourthly, embodiments of this application provide a positive electrode sheet, including a current collector and a positive electrode active material, a conductive agent, and a binder located on one or both sides of the current collector; the positive electrode active material includes the lithium manganese iron phosphate positive electrode material of the third aspect.

[0050] In this embodiment, the positive electrode sheet contains the above-mentioned lithium manganese iron phosphate positive electrode material, thus having the advantages of high charge specific capacity, discharge specific capacity and first coulombic efficiency.

[0051] Fifthly, embodiments of this application provide a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the positive electrode is the same as the positive electrode of the fourth aspect.

[0052] In this embodiment, the secondary battery includes the aforementioned positive electrode plate, thus possessing the advantages of high charge specific capacity, discharge specific capacity, and initial coulombic efficiency.

[0053] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0055] Figure 1 This is a flowchart of the steps in the preparation method of the manganese iron oxalate precursor material in one embodiment of this application;

[0056] Figure 2 SEM of the intermediate product in Example 1 of this application Figure 1 ;

[0057] Figure 3 SEM of the intermediate product in Example 1 of this application Figure 2 ;

[0058] Figure 4 SEM image of the manganese iron oxalate precursor material in Example 1 of this application. Figure 1 ;

[0059] Figure 5 SEM image of the manganese iron oxalate precursor material in Example 1 of this application. Figure 2 ;

[0060] Figure 6 This is a SEM image showing the length of the primary particles of the manganese iron oxalate precursor material in Example 1 of this application.

[0061] Figure 7This is a SEM image showing the width measurement of the primary particles of the manganese iron oxalate precursor material in Example 1 of this application;

[0062] Figure 8 This is a SEM image showing the thickness of the primary particles of the manganese iron oxalate precursor material in Example 1 of this application.

[0063] Figure 9 SEM image of the manganese iron oxalate precursor material in Comparative Example 1 of this application Figure 1 ;

[0064] Figure 10 SEM image of the manganese iron oxalate precursor material in Comparative Example 1 of this application Figure 2 ;

[0065] Figure 11 The image shows the XRD pattern of the manganese iron oxalate precursor material in Example 1 of this application.

[0066] Figure 12 The image shows the XRD pattern of the manganese iron oxalate precursor material in Comparative Example 1 of this application. Detailed Implementation

[0067] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0073] In the description of the embodiments of this application, unless otherwise specified, the solvent used in the "solution" is selected from at least one of distilled water, deionized water, deionized water, pure water, and ultrapure water.

[0074] In the description of the embodiments of this application, unless otherwise specified, "purity" and "content" refer to the mass percentage of the tested elements, molecules or ions in the sample.

[0075] Compared to lithium iron phosphate (LFP), lithium manganese iron phosphate (LFP) has higher energy density and a higher discharge voltage platform, providing a longer driving range and is widely used in secondary batteries, especially in electric vehicles and energy storage systems. Iron manganese oxalate (MMO) precursors are widely used as precursor materials for LFP cathode materials due to their advantages such as low cost, simple processing, and low sintering difficulty. However, during the preparation of MMO precursors, the rapid grain growth rate results in a larger particle size, leading to lower compaction density, longer lithium-ion migration paths, and impacting lithium-ion transport speed and electrochemical reaction efficiency. This, in turn, affects the charge-discharge performance and initial coulombic efficiency of LFP materials.

[0076] To address the technical challenge of simultaneously improving the electrochemical performance of lithium manganese iron phosphate (LFP) cathode materials in terms of charge-discharge performance and initial coulombic efficiency, this application provides a manganese iron oxalate precursor material and its preparation method, an LFP cathode material, a cathode electrode, and a secondary battery. By controlling the composition, morphology, and size of the primary particles in the manganese iron oxalate precursor material, the compaction density of the precursor material is increased. This helps improve the compaction density, electronic conductivity, and lithium-ion diffusion rate of the LFP cathode material prepared from the manganese iron oxalate precursor material, thereby enhancing the charge specific capacity, discharge specific capacity, initial coulombic efficiency, and rate performance. Consequently, the electrochemical performance of the cathode electrode and the secondary battery is also improved.

[0077] In a first aspect, embodiments of this application provide a manganese ferric oxalate precursor material, the chemical formula of which is Mn. x Fe (1-x)C2O4, where 0 < x < 1; the primary particles of the manganese-iron oxalate precursor material are in a flaky structure, the length of the primary particles is 1000 nm to 1500 nm, the width of the primary particles is 400 nm to 870 nm, and the thickness of the primary particles is 300 nm to 500 nm; the purity of the manganese-iron oxalate precursor material is ≥99.2%.

[0078] In the manganese-iron oxalate precursor material of the embodiment of the present application, its chemical formula is Mn x Fe (1-x) C2O4, where 0 < x < 1, indicating that the manganese-iron oxalate precursor material contains both Mn element and Fe element. The presence of Mn element helps to improve the thermal stability of the lithium iron manganese phosphate cathode material prepared from the manganese-iron oxalate precursor material; while the presence of Fe element stabilizes the crystal structure of the lithium iron manganese phosphate cathode material prepared from the manganese-iron oxalate precursor material and helps to enhance the conductivity of the lithium iron manganese phosphate cathode material. Therefore, by controlling the value of x, the ratio between the two can be flexibly adjusted to optimize the conductivity, thermal stability, energy storage capacity, etc. of the lithium iron manganese phosphate cathode material prepared from the manganese-iron oxalate precursor material. At the same time, controlling the purity of the manganese-iron oxalate precursor material to be ≥99.2% is beneficial to reducing the impurities in the lithium iron manganese phosphate cathode material prepared from the manganese-iron oxalate precursor material from the source, ensuring the controllability and consistency of the chemical composition, structure and electrochemical performance of the lithium iron manganese phosphate cathode material.

[0079] Furthermore, 0.2 ≤ x ≤ 0.6. By controlling 0.2 ≤ x ≤ 0.6, it helps to further improve the thermal stability and conductivity of the lithium iron manganese phosphate cathode material prepared from the manganese-iron oxalate precursor material, avoiding reducing the conductivity of the lithium iron manganese phosphate cathode material prepared from the manganese-iron oxalate precursor material due to too high Mn element content, and at the same time avoiding reducing the thermal stability of the lithium iron manganese phosphate cathode material prepared from the manganese-iron oxalate precursor material due to too high Fe element content.

[0080] Specifically, x can be 0.2, 0.3, 0.4, 0.5, 0.6 or the range composed of any two of them. For example, the chemical formula of the manganese-iron oxalate precursor material can be Mn 0.2 Fe 0.8 C2O4 or Mn 0.6 Fe 0.4 C2O4.

[0081] Specifically, the length of a primary particle can be in the range of 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm or any two of these; the width of a primary particle can be in the range of 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm or any two of these; and the thickness of a primary particle can be in the range of 300nm, 350nm, 400nm, 450nm, 500nm or any two of these.

[0082] The ferromanganese oxalate precursor material comprises secondary particles, which are formed by the aggregation of primary particles. Specifically, the primary particles of the ferromanganese oxalate precursor material exhibit a plate-like structure. When preparing lithium iron manganese phosphate cathode materials using the ferromanganese oxalate precursor material, the plate-like primary particles act as templates during the preparation process. Lithium ions and other elements preferentially embed and align along the existing crystal lattice structure, causing the prepared lithium iron manganese phosphate cathode material to tend to retain a similar plate-like structure.

[0083] On the one hand, the aforementioned sheet-like structure provides a shorter diffusion path for lithium ions, enabling them to migrate more quickly. This helps to improve the lithium ion transport rate of secondary batteries using this lithium manganese iron phosphate cathode material, reduce charge transfer resistance, and thus significantly improve the charge and discharge rate and kinetic performance of secondary batteries using this lithium manganese iron phosphate cathode material.

[0084] On the other hand, the primary particles with a sheet-like structure have a high specific surface area. After preparing lithium iron phosphate cathode materials using iron manganese oxalate precursor materials, it is beneficial to provide more active sites for lithium ion adsorption and deintercalation and increase the lithium ion transport path, thereby helping to improve the electrochemical activity, charge specific capacity, and discharge specific capacity of lithium iron phosphate cathode materials prepared from iron manganese oxalate precursor materials.

[0085] Furthermore, the primary particles of the manganese iron oxalate precursor material, due to their flat geometry, are more tightly packed together during compaction compared to spherical or other irregularly shaped particles. This reduces the gaps between particles, which is beneficial for filling more active material in the same secondary battery space and helps to improve the compaction density of lithium manganese iron phosphate cathode material prepared from this manganese iron oxalate precursor material.

[0086] The thickness of the primary particles in the ferromanganese oxalate precursor material affects the length of the lithium-ion diffusion path. In the lamellar structure of lithium iron phosphate cathode material prepared from ferromanganese oxalate precursor material, the shortest lithium-ion transport path is in the direction perpendicular to the plane of the lamellar structure, i.e., the thickness direction of the primary particles. By controlling the thickness of the primary particles in the ferromanganese oxalate precursor material, the migration distance of lithium ions in this direction is significantly shortened, thereby reducing the resistance to lithium-ion transport and accelerating the charge and discharge rates. By controlling the length and width of the primary particles in the ferromanganese oxalate precursor material, more ion and electron conduction paths and active sites are provided in the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor, reducing the resistance to ion and electron transport, facilitating the formation of a continuous conductive network, ensuring rapid electron conduction, and thus improving the charge specific capacity, discharge specific capacity, and initial coulombic efficiency of the secondary battery of this lithium iron phosphate cathode material.

[0087] Furthermore, when preparing lithium iron manganese phosphate cathode materials using iron manganese oxalate precursor materials, impurities such as metal ions and organic residues in the iron manganese oxalate precursor materials will remain in the lithium iron manganese phosphate cathode materials. These impurities will not only reduce the conductivity of the lithium iron manganese phosphate cathode materials, but will also participate in unnecessary side reactions during the first charge-discharge process of the lithium iron manganese phosphate cathode materials, consuming lithium ions, thereby reducing the charge specific capacity, discharge specific capacity and first coulombic efficiency of the lithium iron manganese phosphate cathode materials used. The high-purity manganese iron oxalate precursor material of this invention participates more effectively in the electrochemical reaction when converted into lithium manganese iron phosphate cathode material, providing a higher actual specific capacity. Secondly, it reduces the participation of impurities in unnecessary side reactions and reduces the obstruction of lithium-ion diffusion paths by impurities, which is conducive to improving the rapid transport of lithium ions, thereby improving the charging specific capacity, discharging specific capacity, and first coulombic efficiency of the lithium manganese iron phosphate cathode material. In addition, the crystal structure of the high-purity manganese iron oxalate precursor material is more complete, avoiding the interference of impurities on the crystal structure, improving the structural stability of the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material, and extending the cycle life of the lithium manganese iron phosphate cathode material.

[0088] Therefore, the manganese iron oxalate precursor material in this application embodiment, by controlling the composition, purity, morphology, and size of the primary particles, not only helps to improve the compaction density of the manganese iron oxalate precursor material, but also gives it a small particle size. This improves the compaction density of the lithium iron manganese phosphate cathode material prepared from the manganese iron oxalate precursor material, reduces the lithium ion migration path in the lithium iron manganese phosphate cathode material prepared from the manganese iron oxalate precursor material, improves the electronic conductivity and lithium ion diffusion rate of the lithium iron manganese phosphate cathode material prepared from the manganese iron oxalate precursor material, and thus significantly improves the electrochemical performance of the lithium iron manganese phosphate cathode material prepared from the manganese iron oxalate precursor material in terms of charge specific capacity, discharge specific capacity, first coulombic efficiency, and rate performance.

[0089] It should be noted that any two of the length direction, width direction, and height direction of a primary particle are spatially perpendicular to each other, and the length of a primary particle is greater than its width, and the width of a primary particle is greater than its height.

[0090] Furthermore, in some embodiments, the D10 particle size of the ferromanganese oxalate precursor material is 1 μm to 3 μm, the D50 particle size is 4 μm to 10 μm, the D90 particle size is 10 μm to 25 μm, the D100 particle size is 20 μm to 60 μm, the D0 particle size is 0.35 μm to 0.42 μm, and the D99 particle size is 20 μm to 45 μm.

[0091] In the technical solution of this application embodiment, D10 particle size is the particle size corresponding to a cumulative volume distribution percentage of 10% for the ferromanganese oxalate precursor material; D50 particle size is the particle size corresponding to a cumulative volume distribution percentage of 50% for the ferromanganese oxalate precursor material; D90 particle size is the particle size corresponding to a cumulative volume distribution percentage of 90% for the ferromanganese oxalate precursor material; D99 particle size is the particle size corresponding to a cumulative volume distribution percentage of 99% for the ferromanganese oxalate precursor material; D0 particle size is the minimum particle size of the ferromanganese oxalate precursor material; and D100 particle size is the maximum particle size of the ferromanganese oxalate precursor material. The particle size distribution of the ferromanganese oxalate precursor material directly affects the particle size distribution, compaction density, lithium ion diffusion rate, and conductivity of the subsequently prepared lithium iron manganese phosphate cathode material.

[0092] Specifically, by controlling the D10 particle size of the manganese iron oxalate precursor material to be 1μm~3μm, ensuring the presence of a certain proportion of ultrafine particles in the manganese iron oxalate precursor material helps to shorten the diffusion path of lithium ions in the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material. This reduces the diffusion resistance of lithium ions during the insertion and extraction process, thereby improving the charge and discharge rate and kinetic performance of the secondary battery using this lithium manganese iron phosphate cathode material.

[0093] By controlling the D50 particle size of the manganese iron oxalate precursor material to 4μm~10μm, it is beneficial to form a more uniform compaction density of the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material, while ensuring good interparticle contact and the formation of an electron conduction network, thus balancing the lithium-ion transport efficiency and structural stability of the lithium manganese iron phosphate cathode material.

[0094] By controlling the D90 particle size of the manganese iron oxalate precursor material to be 10μm~25μm, and controlling the particle size of most manganese iron oxalate precursor materials to be suitable, the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material can be better arranged during the compaction process, forming a high compaction density lithium manganese iron phosphate cathode material.

[0095] By controlling the D100 particle size of the manganese ferric oxalate precursor material to 20μm~60μm, the presence of abnormally large particles is avoided, thus reducing the problem of excessive porosity caused by large particles affecting compaction density and electrical conductivity.

[0096] Therefore, controlling the particle size distribution of the ferromanganese oxalate precursor material to achieve a small and concentrated particle size is beneficial for the preparation of lithium iron phosphate cathode material with a small and concentrated particle size distribution. This helps improve the electrochemical performance of the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material in terms of charge specific capacity, discharge specific capacity, first coulombic efficiency, and rate performance, while also enhancing the consistency of the electrical performance of the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material. Furthermore, the ferromanganese oxalate precursor material... The small particle size and concentrated particle size distribution of the precursor material help to produce more active sites in the lithium iron manganese phosphate cathode material, increasing the lithium ion insertion and extraction efficiency, thereby improving the specific capacity and overall electrochemical activity of the lithium iron manganese phosphate cathode material. In addition, the reasonable particle size distribution of the precursor material is beneficial to the particle size distribution of the lithium iron manganese phosphate cathode material, improving the processing performance of the lithium iron manganese phosphate cathode material, facilitating uniform coating during the manufacturing process of the cathode sheet, improving production efficiency, and thus reducing costs.

[0097] Specifically, the D10 particle size of the ferromanganese oxalate precursor material can be in the range of 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, or any combination thereof; the D50 particle size of the ferromanganese oxalate precursor material can be in the range of 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination thereof; and the D90 particle size of the ferromanganese oxalate precursor material can be in the range of 10 μm, 11 μm, 12 μm, 13 μm, 15 μm, 20 μm, 25 μm, or any combination thereof. The D100 particle size of the material can be in the range of 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or any combination thereof; the D0 particle size of the manganese ferric oxalate precursor material can be in the range of 0.35μm, 0.36μm, 0.37μm, 0.38μm, 0.39μm, 0.40μm, 0.41μm, 0.42μm or any combination thereof; and the D99 particle size of the manganese ferric oxalate precursor material can be in the range of 20μm, 25μm, 30μm, 35μm, 40μm, 45μm or any combination thereof.

[0098] Furthermore, in some embodiments, the length of the primary particle is 1000nm~1400nm, the width of the primary particle is 400nm~700nm, and the thickness of the primary particle is 350nm~450nm.

[0099] In the technical solution of this application embodiment, the size of the primary particles of the manganese iron oxalate precursor material is further controlled, so that the manganese iron oxalate precursor material has a smaller particle size, thereby further improving the compaction density of the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material, and reducing the lithium ion migration path in the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material, thereby further improving the electrochemical performance of the lithium manganese iron phosphate cathode material prepared from the manganese iron oxalate precursor material in terms of charge-discharge specific capacity, first coulombic efficiency, and rate performance.

[0100] Furthermore, in some embodiments, the specific surface area of ​​the manganese ferric oxalate precursor material is 1.0 m². 2 / g~5.0m 2 / g.

[0101] In the technical solution of the embodiment of the present application, controlling the specific surface area of the manganese iron oxalate precursor material is beneficial to controlling the reaction activity of the manganese iron oxalate precursor material, thereby being beneficial to improving the purity of the lithium iron manganese phosphate cathode material prepared from the manganese iron oxalate precursor material; at the same time, controlling the specific surface area of the manganese iron oxalate precursor material is beneficial to controlling the specific surface area of the lithium iron manganese phosphate cathode material prepared from the manganese iron oxalate precursor material, which is beneficial for the lithium iron manganese phosphate cathode material to provide suitable active sites, promote the insertion and extraction of lithium ions, and thus be beneficial to improving the actual specific capacity of the lithium iron manganese phosphate cathode material; in addition, the lithium iron manganese phosphate cathode material has a suitable specific surface area, which helps the electrolyte to more fully wet the surface of the lithium iron manganese phosphate cathode material, improve the transport efficiency of lithium ions at the solid-liquid interface, thereby reducing the interfacial impedance inside the secondary battery using the lithium iron manganese phosphate cathode material, and helps to promote the good contact between the active sites of the lithium iron manganese phosphate cathode material and the electrolyte, optimize the transport and insertion of lithium ions during the first charge-discharge process, and further improve the first Coulomb efficiency when the lithium iron manganese phosphate cathode material is applied to a secondary battery.

[0102] In a second aspect, the embodiment of the present application provides a preparation method of a manganese iron oxalate precursor material, including the following steps:

[0103] Mix a metal salt solution and an alkaline solution, and obtain a first slurry through a first reaction treatment;

[0104] Mix the first slurry with an oxalic acid source, and obtain a second slurry through a second reaction treatment;

[0105] Age the second slurry to obtain a manganese iron oxalate precursor material;

[0106] Wherein, the metal salt solution contains divalent manganese ions and divalent iron ions, the first slurry includes an intermediate product, and the general formula of the intermediate product is: Mn x Fe (1-x) (OH)2, 0 < x < 1, and the particle size of the primary particles of the intermediate product is 30 nm to 100 nm;

[0107] The chemical formula of the manganese iron oxalate precursor material is Mn x Fe (1-x) C2O4, 0 < x < 1;

[0108] The primary particles of the manganese iron oxalate precursor material are in a flaky structure, the length of the primary particles is 1000 nm to 1500 nm, the width of the primary particles is 400 nm to 870 nm, and the thickness of the primary particles is 300 nm to 500 nm;

[0109] The purity of the manganese iron oxalate precursor material ≥ 99.2%;

[0110] The ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron in the metal salt solution is (1.0~1.3):1.

[0111] In the step of mixing a metal salt solution with an alkaline solution, the solution containing divalent manganese ions (Mn) is first mixed. 2+ ) and ferrous ions (Fe 2+ A metal salt solution is mixed with an alkaline solution, and the alkaline solution is used to adjust the pH value to facilitate the mixing of Mn in the metal salt solution. 2+ Fe 2+ The sediment precipitates, thus forming the first slurry through a first reaction treatment. Through this first reaction treatment, Mn... 2+ Fe 2+ With OH - A reaction occurs, forming a first slurry containing intermediate products. The chemical reaction involved in the first reaction treatment is: (1-x)Fe 2+ +xMn 2+ +OH - =Mn x Fe 1-x (OH)₂. The solubility product constant of Fe(OH)₂ is 4.87 × 10⁻⁶. -17 The solubility product constant of Mn(OH)2 is 2 × 10⁻⁶. -13 Compared to ferrous oxalate (solubility product constant is 3.2 × 10⁻⁶), ... -7 ) and manganese oxalate (solubility product constant is 1.7 × 10⁻⁶) -7 With a smaller solubility product constant, ferrous manganese hydroxide is more likely to precipitate, thus making it easier to prepare ultrafine particles.

[0112] The intermediate product is a hydroxide with a specific chemical formula, Mn. x Fe (1-x) (OH)₂, where x represents the proportion of manganese ions and 1-x represents the proportion of iron ions. By controlling the particle size of the primary particles of the intermediate product, the intermediate product is made to have a nanoscale structure. In the subsequent conversion process, the intermediate product is used as a template to prepare a manganese iron oxalate precursor material. The primary particles of the prepared manganese iron oxalate precursor material have a smaller particle size than those prepared by conventional processes. This helps to shorten the lithium ion diffusion path and accelerate lithium ion transport in the lithium iron phosphate material prepared from the manganese iron oxalate precursor material, resulting in improved charge-discharge performance and cycle stability.

[0113] Furthermore, 0.2 ≤ x ≤ 0.6, specifically, x can be a range of 0.2, 0.3, 0.4, 0.5, 0.6, or any combination of two of these. For example, the chemical formula of the intermediate product can be Mn. 0.2 Fe 0.8 (OH)2 or Mn 0.6Fe 0.4 (OH)2.

[0114] In some preferred embodiments, the particle size of the primary particles of the intermediate product is 35nm to 70nm, for example, a range of 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm or any combination thereof.

[0115] The first slurry is mixed with a source containing oxalate, and then treated in a second reaction to remove oxalate ions (C2O4). 2- ) replace hydroxide ions (OH) - The intermediate product is converted into ferromanganese oxalate to form the second slurry. During the substitution of hydroxide ions by oxalate ions, not only is the chemical composition of the material altered, but lattice rearrangement further refines the particles and optimizes the microstructure of the ferromanganese oxalate precursor material, helping to control its porosity and specific surface area. The chemical reaction involved in the second reaction is: Mn... x Fe (1-x) (OH)₂ + H₂C₂O₄ = Mn x Fe (1-x) C2O4 + 2H2O.

[0116] It should be noted that ferrous ions and manganese ions may be oxidized to ferric ions (Fe3+) in air or in the presence of an oxidizing agent. 3+ And high-valence manganese ions. In the second reaction treatment, the reducing power of oxalate ions can effectively prevent this oxidation process, thereby ensuring Fe... 2+ and Mn 2+ The stability of oxalate ions and ferric ions (Fe) 3+ The oxidation byproducts, such as high-valence manganese ions, form complexes that are difficult to decompose, and the resulting Fe is oxidized into Fe. 3+ Both ferric and high-valent manganese ions can be rapidly captured by oxalate ions to form stable complexes, hindering further reactions. These complexes formed by ferric and high-valent manganese ions do not transform into ferromanganese oxalate structures during subsequent aging and drying processes, thus effectively eliminating them from the ferromanganese oxalate precursor material and significantly improving its purity. Furthermore, due to the reducing and complexing properties of oxalate ions, an inert atmosphere is not required during the preparation of the ferromanganese oxalate precursor material, simplifying the process and reducing production costs. Therefore, oxalate, as a key component in the preparation of the ferromanganese oxalate precursor material, not only effectively protects divalent iron and divalent manganese ions due to its reducing properties but also prevents oxidation byproducts from contaminating the ferromanganese oxalate precursor material through its complexing effect, effectively improving its purity.

[0117] Finally, the second slurry is aged to further refine its crystal structure and morphology, ultimately yielding a pure manganese oxalate ferromanganese precursor material. Aging helps eliminate residual unreacted substances or byproducts, thereby improving the purity and crystallinity of the manganese oxalate ferromanganese precursor material and optimizing its microstructure.

[0118] In the technical solution of this application embodiment, the present invention first removes divalent manganese ions (Mn) 2+ ) and ferrous ions (Fe 2+The intermediate product of manganese ferrous hydroxide was obtained by co-precipitation. The intermediate product has an ultrafine nanoscale structure with a particle size much smaller than that of manganese ferric oxalate particles prepared directly by oxalate precipitation. Then, the intermediate product was mixed with oxalate source. In the second reaction treatment, oxalate ions replaced hydroxide ions in the intermediate product to generate manganese ferric oxalate. The introduction of oxalate ions causes lattice rearrangement, further refining the particles and resulting in ferromanganese oxalate with a further optimized microstructure. Simultaneously, in the second reaction, the reducing properties of oxalate ions effectively protect ferrous and manganese ions from oxidation. Even if ferrous and / or manganese ions are oxidized, the complexation effect of oxalate ions ensures that oxidation byproducts do not precipitate with the ferromanganese oxalate, effectively improving the purity of the ferromanganese oxalate precursor material. After oxalate replacement, the second slurry undergoes aging treatment, allowing for thorough lattice rearrangement of the ferromanganese oxalate, resulting in a more uniform distribution of Mn and Fe elements, which contributes to improving the purity and crystallinity of the ferromanganese oxalate precursor material. The resulting manganese iron oxalate precursor material exhibits a significantly reduced primary particle size and overall particle size, ensuring the uniform distribution of Mn and Fe elements in the precursor material. This greatly shortens the diffusion path of lithium ions in the lithium iron manganese phosphate cathode material prepared from the manganese iron oxalate precursor material. This improves the charge / discharge rate and kinetic performance of the lithium iron manganese phosphate cathode material when applied to secondary batteries, while also enhancing its cycle stability. Secondly, the uniform distribution of Mn and Fe elements in the ferromanganese oxalate precursor material was ensured, achieving atomic-level mixing. This uniform mixing helps the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material to form a stable solid solution structure, thereby improving the electrochemical activity and cycle stability of secondary batteries using this lithium iron phosphate cathode material. Furthermore, the ferromanganese oxalate precursor material, derived from ultrafine-sized intermediate products, possesses a more optimized pore structure and a higher specific surface area, which facilitates deeper electrolyte penetration, accelerates lithium-ion transport, and provides more active sites, improving the interaction efficiency between the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material and lithium ions. Simultaneously, the small particle size and uniform distribution help increase the compaction density of the lithium iron phosphate cathode material. Combined with optimized porosity and specific surface area, this significantly improves the electrochemical performance of the lithium iron phosphate cathode material prepared from the ferromanganese oxalate precursor material, specifically manifested in higher specific capacity, initial coulombic efficiency, and cycle stability.

[0119] Furthermore, in some embodiments, the pH value of the first slurry is 9.0 to 11.0.

[0120] In the technical solution of this application embodiment, controlling the pH value of the first slurry to be 9.0~11.0 is beneficial to divalent manganese ions (Mn). 2+) and ferrous ions (Fe 2+ The co-precipitation of manganese ferrous hydroxide forms a highly uniform intermediate product. Simultaneously, the pH range described above is favorable for the reaction of metal ions and hydroxide ions to form a uniform precipitate, thus promoting the formation of ultrafine particles, facilitating the acquisition of nanoscale intermediate products, and improving the overall uniformity of the intermediate product. Secondly, the pH range helps reduce the occurrence of side reactions, ensuring the formation of the manganese ferrous hydroxide intermediate product and contributing to its purity. Furthermore, the pH range allows the surface charge state and hydration level of the intermediate product to be more suitable for subsequent oxalate replacement, thereby facilitating the formation of a high-purity, pure-phase manganese ferric oxalate precursor material.

[0121] Specifically, the pH value of the first slurry can be a range of 9.0, 9.2, 9.5, 9.8, 10.0, 10.2, 10.5, 10.8, 11.0 or any combination thereof.

[0122] Furthermore, in some embodiments, the molar ratio of hydroxide ions in the alkaline solution to the total molar ratio of manganese and iron in the metal salt solution is (2~3):1.

[0123] In the technical solution of this application embodiment, the ratio of the molar amount of hydroxide ions in the alkaline solution to the total molar amount of manganese and iron elements in the metal salt solution is controlled to be (2~3):1, ensuring that divalent manganese ions (Mn) are present. 2+ ), divalent iron ions (Fe 2+ ) and OH - A full reaction helps promote the reaction of divalent manganese ions (Mn). 2+ ), divalent iron ions (Fe 2+ Effective and thorough co-precipitation, while also helping to avoid residual OH in the second slurry. - Excessive amounts can affect crystal transformation during aging, thus reducing the purity of the manganese ferric oxalate precursor material. When the molar ratio of hydroxide ions in the alkaline solution to the total molar ratio of manganese and iron in the metal salt solution is less than 2:1, divalent manganese ions (Mn)... 2+ ), divalent iron ions (Fe 2+ Incomplete precipitation not only wastes raw materials but also reduces the yield of intermediate products, thereby decreasing the yield of the manganese ferric oxalate precursor. When the molar ratio of hydroxide ions in the alkaline solution to the total molar ratio of manganese and iron in the metal salt solution is greater than 3:1, excess OH-... - It will promote the formation of byproducts (such as Fe(OH)3), leading to a decrease in the purity of the manganese ferric oxalate precursor material, and the excess OH... - It will also lead to waste of raw materials and increase production costs.

[0124] Specifically, the ratio of the molar amount of hydroxide ions in the alkaline solution to the total molar amount of manganese and iron in the metal salt solution can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, or any combination thereof.

[0125] Furthermore, in some embodiments, the ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron in the metal salt solution is (1.0~1.2):1.

[0126] In the technical solution of this application embodiment, the ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron elements in the metal salt solution is controlled to be (1.0~1.2):1. This ensures that oxalate ions efficiently replace hydroxide ions in the intermediate product, reducing residual hydroxides or unreacted metal salts. At the same time, it avoids unnecessary side reactions and waste of raw materials caused by excessive oxalate ions, thereby improving the conversion rate, purity, and structural integrity of the manganese iron oxalate precursor material, while also improving production efficiency and economic benefits.

[0127] Specifically, the ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron in the metal salt solution can be a range of 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.1:1, 1.15:1, 1.2:1, or any two of these.

[0128] Furthermore, in some embodiments, the ferrous salt containing ferrous ions includes at least one of ferrous chloride, ferrous nitrate, ferrous sulfate, and ferrous acetate.

[0129] In the technical solution of this application embodiment, by using the above-mentioned widely available and low-cost divalent iron salt, it is beneficial to significantly reduce the production cost of manganese iron oxalate precursor materials and ensure the economic feasibility of the preparation process.

[0130] Furthermore, in some embodiments, the divalent manganese salt containing divalent manganese ions includes at least one of manganese chloride, manganese nitrate, manganese sulfate, and manganese acetate.

[0131] In the technical solution of this application embodiment, by using the above-mentioned widely available and low-cost divalent manganese salt, it is beneficial to significantly reduce the production cost of manganese ferric oxalate precursor materials and ensure the economic feasibility of the preparation process.

[0132] Furthermore, in some embodiments, the alkaline solution includes at least one of sodium hydroxide solution and ammonia water.

[0133] In the technical solution of this application embodiment, by using the above-mentioned widely available and low-cost alkaline solution, it is beneficial to significantly reduce the production cost of manganese iron oxalate precursor material and ensure the economic feasibility of the preparation process.

[0134] Furthermore, in some embodiments, the oxalate source includes at least one of oxalic acid, ammonium oxalate, and sodium oxalate.

[0135] In the technical solution of this application embodiment, by using the above-mentioned widely available and low-cost oxalate source, it is beneficial to significantly reduce the production cost of manganese iron oxalate precursor materials and ensure the economic feasibility of the preparation process.

[0136] Further, in some embodiments, the step of mixing the metal salt solution and the alkaline solution and undergoing a first reaction treatment to obtain a first slurry includes: the metal salt solution and the alkaline solution are mixed at a first mixing temperature and for a first mixing time to obtain a first mixture; the first mixture is mixed at a first reaction temperature and for a first reaction time to obtain a first slurry; wherein the first mixing temperature is 20℃~60℃, the first mixing time is 15min~30min, the first reaction temperature is 20℃~60℃, and the first reaction time is 5min~15min.

[0137] In the technical solution of this application embodiment, controlling the mixing of the metal salt solution and the alkaline solution under the above conditions and carrying out the first reaction treatment helps to promote the uniform mixing and co-precipitation of metal ions and hydroxide ions in the alkaline solution, and more uniformly form nano-sized intermediate product particles; the setting of the first mixing time and the first reaction time is beneficial to effectively control the primary particle size of the intermediate product, and while fully precipitating, avoids the formation of large particles caused by excessively rapid precipitation, which is beneficial to the subsequent oxalate ion replacement reaction; the setting of the first mixing temperature and the first reaction temperature ensures the reaction rate and ensures that the formation of the intermediate product is sufficient and efficient.

[0138] Specifically, the first mixing temperature can be a range of 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃ or any two of these; the first mixing time can be a range of 15min, 18min, 20min, 22min, 25min, 28min, 30min or any two of these; the first reaction temperature can be a range of 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃ or any two of these; and the first reaction time can be a range of 5min, 8min, 10min, 12min, 15min or any two of these.

[0139] Further, in some embodiments, the step of mixing the first slurry with an oxalate source and subjecting it to a second reaction treatment to obtain a second slurry includes: the first slurry and the oxalate source being mixed at a second mixing temperature and for a second mixing time to obtain a second mixture; the second mixture being mixed at a second reaction temperature and for a second reaction time to obtain a second slurry; wherein the second mixing temperature is 20℃~60℃, the second mixing time is 15min~30min, the second reaction temperature is 20℃~60℃, and the second reaction time is 15min~45min.

[0140] In the technical solution of this application embodiment, the first slurry and oxalate source are mixed and subjected to a second reaction treatment under the above conditions to promote a sufficient reaction between the intermediate product in the first slurry and the oxalate ions, thereby facilitating the generation of a high-purity manganese ferrooxate precursor material. By controlling the second mixing time and the second reaction time, it is beneficial to ensure a sufficient reaction between the oxalate ions and the intermediate product; by controlling the second mixing temperature and the second reaction temperature, it is beneficial to control the reaction rate, thereby facilitating the acquisition of a high-purity manganese ferrooxate precursor material with small particle size and suitable particle size distribution.

[0141] Specifically, the second mixing temperature can be a range of 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃ or any two of these; the second mixing time can be a range of 15min, 18min, 20min, 22min, 25min, 28min, 30min or any two of these; the second reaction temperature can be a range of 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃ or any two of these; and the second reaction time can be a range of 15min, 18min, 20min, 25min, 30min, 35min, 40min or any two of these.

[0142] In some embodiments, the oxalate source can be mixed with the first slurry in solution form. That is, before mixing with the first slurry, the oxalate source is dissolved in a solvent to obtain an oxalate source solution. The concentration of oxalate in the oxalate source solution can be from 1 mol / kg to 3 mol / kg, for example, it can be a range of 1 mol / kg, 1.5 mol / kg, 2 mol / kg, 2.5 mol / kg, 3 mol / kg, or any combination thereof.

[0143] Further, in some embodiments, the step of aging the second slurry to obtain the manganese ferric oxalate precursor material includes: aging the second slurry at an aging temperature and for an aging time to obtain an aged slurry; separating the aged slurry into solid and liquid components to obtain a first solid material; rinsing the first solid material until the conductivity of the rinsing solution is ≤120 μs / cm to obtain a second solid material; and drying the second solid material at a drying temperature and for a drying time to obtain the manganese ferric oxalate precursor material; wherein the aging temperature is 80℃~100℃, the aging time is 60min~150min, and the drying temperature is 60℃~80℃, and the drying time is 2h~4h.

[0144] Specifically, in the preparation of the ferromanganese oxalate precursor material, controlling the aging temperature and time promotes the growth and maturation of ferromanganese oxalate crystals in the second slurry, helping to form a complete and stable crystal structure and improving the purity and performance of the ferromanganese oxalate precursor material. After aging, the aged slurry is filtered or subjected to other solid-liquid separation techniques to remove the liquid portion, obtaining the first solid material. This step helps to concentrate the target product. Rinsing the first solid material removes residual ions and impurities adhering to its surface, ensuring the purity of the final product. Conductivity monitoring quantifies the rinsing effect; when the conductivity reaches a specified standard (≤120 μS / cm), it indicates that most soluble impurities have been removed. By controlling the drying temperature and time, moisture in the material is effectively evaporated without damaging the ferromanganese oxalate crystal structure. In the specific implementation of this invention, drying ensures that the mass fraction of moisture in the ferromanganese oxalate precursor material is <0.5%.

[0145] In the technical solution of this application embodiment, through aging treatment, the manganese ferric oxalate crystals grow perfectly under the above conditions, which improves the crystallinity and purity of the manganese ferric oxalate precursor material; through rinsing treatment, residual soluble impurities are effectively removed, ensuring the purity of the manganese ferric oxalate precursor material; and the drying treatment under the above conditions is beneficial for quickly and fully removing moisture from the manganese ferric oxalate precursor material.

[0146] By strictly controlling the temperature and time parameters mentioned above, the particle size and morphology of the prepared manganese ferric oxalate precursor material were ensured, and the consistency and repeatability of the manganese ferric oxalate precursor material obtained from different batches were guaranteed.

[0147] Specifically, the aging temperature can be a range of 80℃, 82℃, 85℃, 88℃, 90℃, 92℃, 95℃, 100℃ or any two of these; the aging time can be a range of 60min, 70min, 80min, 90min, 100min, 110min, 120min, 150min or any two of these; the drying temperature can be a range of 60℃, 65℃, 70℃, 75℃, 80℃ or any two of these; and the drying time can be a range of 2h, 2.5h, 2.8h, 3h, 3.2h, 3.5h, 3.8h, 4h or any two of these.

[0148] Thirdly, embodiments of this application provide a lithium manganese iron phosphate cathode material, which is prepared from a manganese iron oxalate precursor material. The manganese iron oxalate precursor material is selected from the manganese iron oxalate precursor material of the first aspect, or the manganese iron oxalate precursor material prepared by the preparation method of the manganese iron oxalate precursor material of the second aspect.

[0149] Specifically, by mixing manganese iron oxalate precursor material with lithium phosphate, a sintering process can be used to promote the chemical reaction between the two, generating lithium manganese iron phosphate cathode material. The sintering temperature is 600℃~800℃, the sintering time is 5~20h, and the sintering atmosphere can be oxygen, inert gas, or vacuum, ensuring that the reaction between the manganese iron oxalate precursor material and lithium phosphate proceeds fully. This results in the lithium manganese iron phosphate cathode material exhibiting good crystal integrity, structural stability, and electrochemical activity.

[0150] In the technical solution of this application embodiment, the composition, morphology, and size of the manganese iron oxalate precursor material are controlled to give the manganese iron oxalate precursor material a small particle size and high compaction density. This effectively improves the compaction density of the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material, reduces the lithium ion migration path in the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material, improves the electronic conductivity and lithium ion diffusion rate of the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material, and thus significantly improves the electrochemical performance of the lithium iron phosphate cathode material prepared from the manganese iron oxalate precursor material in terms of charge specific capacity, discharge specific capacity, first coulombic efficiency, and rate performance.

[0151] Furthermore, in some embodiments, the compaction density of the lithium manganese iron phosphate cathode material is 1.85 g / cm³. 3 ~1.9g / cm 3 .

[0152] In the technical solution of this application embodiment, the lithium manganese iron phosphate cathode material has a high compaction density, which is beneficial for the secondary battery using the lithium manganese iron phosphate cathode material to store more energy in a unit volume, thereby improving the battery's endurance and energy output capability.

[0153] Specifically, the compaction density of lithium manganese iron phosphate cathode material can be 1.85 g / cm³. 3 1.86 g / cm 3 1.87 g / cm 3 1.88g / cm 3 1.89 g / cm 3 1.9g / cm 3 or a range consisting of any two of them.

[0154] Furthermore, in some embodiments, the 0.1C charging specific capacity of the lithium manganese iron phosphate cathode material is ≥150 mAh / g, and the 0.1C discharging specific capacity of the lithium manganese iron phosphate cathode material is ≥150 mAh / g. Specific capacity reflects the ability of a unit mass of material to store charge. High specific capacity plays a decisive role in improving battery energy density and extending battery life.

[0155] In the technical solution of this application embodiment, at a charge-discharge rate of 0.1C, the lithium manganese iron phosphate cathode material can store a large amount of electrical energy and has excellent energy storage capacity; by controlling the discharge specific capacity of the lithium manganese iron phosphate cathode material at a charge-discharge rate of 0.1C to ≥150mAh / g, the lithium manganese iron phosphate cathode material has high charge release efficiency, which is conducive to maintaining a stable discharge voltage platform and ensuring the energy output and service life of the secondary battery using the lithium manganese iron phosphate cathode material.

[0156] Furthermore, in some embodiments, the initial coulombic efficiency of the lithium manganese iron phosphate cathode material is ≥97.48%. Initial coulombic efficiency refers to the percentage of the ratio of the initial discharge specific capacity to the initial charge specific capacity when the lithium manganese iron phosphate cathode material is applied to a secondary battery, directly reflecting the reversibility of the electrochemical reaction during the initial charge-discharge process when the lithium manganese iron phosphate cathode material is applied to a secondary battery.

[0157] In the technical solution of this application embodiment, the lithium manganese iron phosphate cathode material has a high initial coulombic efficiency, indicating that the electrochemical reaction of the lithium manganese iron phosphate cathode material is almost completely reversible during the first charge-discharge process, and the energy conversion efficiency is high. This helps to reduce the irreversible energy loss of secondary batteries using lithium manganese iron phosphate cathode materials in charge-discharge cycles and extend the cycle life of secondary batteries.

[0158] Fourthly, embodiments of this application provide a positive electrode sheet, including a current collector and a positive electrode active material, a conductive agent, and a binder located on one or both sides of the current collector; the positive electrode active material includes the lithium manganese iron phosphate positive electrode material of the third aspect.

[0159] Due to the inclusion of the aforementioned high-performance lithium manganese iron phosphate cathode material, this cathode sheet exhibits high charge specific capacity, discharge specific capacity, and initial coulombic efficiency.

[0160] Fifthly, embodiments of this application provide a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the positive electrode is the same as the positive electrode of the fourth aspect.

[0161] Because of the high performance of lithium manganese iron phosphate cathode material mentioned above, when it is used as a cathode sheet in secondary batteries, the resulting secondary batteries have comprehensively improved electrochemical performance, including higher charge specific capacity, discharge specific capacity, and first coulombic efficiency.

[0162] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0163] I. Preparation Method

[0164] Example 1

[0165] Raw material preparation: Ferrous sulfate, manganese sulfate and water are mixed to obtain a metal salt solution with a metal cation concentration of 1.0 mol / kg, wherein the molar ratio of Mn to Fe is 6:4;

[0166] Sodium hydroxide was mixed with water to obtain an alkaline solution with a hydroxide ion concentration of 8 mol / kg.

[0167] Oxalic acid, ammonium oxalate, sodium oxalate and water were mixed to obtain an oxalate source with an oxalate concentration of 2.0 mol / kg.

[0168] The preparation method of the manganese iron oxalate precursor in this embodiment includes the following steps:

[0169] S1, using a metal salt solution as the base liquid, stirring is started, and an alkaline solution is added dropwise to the metal salt solution at 35°C for 20 minutes to obtain a first mixture; the first mixture is reacted at 35°C for 10 minutes to obtain a first slurry with a pH of 9.532; wherein, the ratio of the amount of hydroxide ions in the alkaline solution to the sum of the amounts of Fe and Mn elements in the metal salt solution is 2.5:1.0; the first slurry includes intermediate products with properties as shown in Table 1-1:

[0170] Table 1-1

[0171]

[0172] S2, at a temperature of 35°C, oxalate source is added dropwise to the first slurry for 20 minutes to obtain a second mixture; the second mixture is reacted at a temperature of 35°C for 30 minutes to obtain a second slurry; wherein, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.1:1;

[0173] S3, the second slurry is placed in a reaction vessel, and a water bath is turned on for heating. It is kept at 90℃ for 90 minutes to obtain an aged slurry. After solid-liquid separation, the aged slurry yields a first solid material. The first solid material is rinsed with pure water until the conductivity of the rinsing solution is ≤120μs / cm, yielding a second solid material. The second solid material is dried at 80℃ for 3 hours until the moisture content is <0.5%, yielding the manganese ferric oxalate precursor material (Mn). 0.6 Fe 0.4 C2O4).

[0174] Example 2

[0175] Raw material preparation: Ferrous sulfate, manganese sulfate and water are mixed to obtain a metal salt solution with a metal cation concentration of 0.5 mol / kg, wherein the molar ratio of Mn to Fe is 2:8;

[0176] Sodium hydroxide was mixed with water to obtain an alkaline solution with a hydroxide ion concentration of 5 mol / kg.

[0177] Oxalic acid, ammonium oxalate, sodium oxalate and water were mixed to obtain an oxalate source with an oxalate concentration of 1 mol / kg.

[0178] The preparation method of the manganese iron oxalate precursor in this embodiment includes the following steps:

[0179] S1, using a metal salt solution as the base liquid, stirring is started, and an alkaline solution is added dropwise to the metal salt solution at 20℃ for 30 minutes to obtain a first mixture; the first mixture is reacted at 20℃ for 15 minutes to obtain a first slurry with a pH of 9; wherein, the ratio of the amount of hydroxide ions in the alkaline solution to the sum of the amounts of Fe and Mn elements in the metal salt solution is 2:1; the first slurry includes intermediate products with properties as shown in Table 1-2:

[0180] Table 1-2

[0181]

[0182] S2, at 20℃, oxalate source is added dropwise to the first slurry for 30 min to obtain a second mixture; the second mixture is reacted at 20℃ for 45 min to obtain a second slurry; wherein, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.05:1;

[0183] S3, the second slurry is placed in a reaction vessel, and water bath heating is turned on. It is kept at 80℃ for 120 minutes to obtain an aged slurry. After solid-liquid separation, the aged slurry yields a first solid material. The first solid material is rinsed with pure water until the conductivity of the rinsing solution is ≤120μs / cm, yielding a second solid material. The second solid material is dried at 70℃ for 4 hours until the moisture content is <0.5%, yielding the manganese ferric oxalate precursor material (Mn). 0.2 Fe 0.8 C2O4).

[0184] Example 3

[0185] Raw material preparation: Ferrous sulfate, manganese sulfate and water are mixed to obtain a metal salt solution with a metal cation concentration of 1.5 mol / kg, wherein the molar ratio of Mn to Fe is 2:8;

[0186] Sodium hydroxide was mixed with water to obtain an alkaline solution with a hydroxide ion concentration of 10 mol / kg.

[0187] Oxalic acid, ammonium oxalate, sodium oxalate and water were mixed to obtain an oxalate source with an oxalate concentration of 3 mol / kg.

[0188] The preparation method of the manganese iron oxalate precursor in this embodiment includes the following steps:

[0189] S1, using a metal salt solution as the base liquid, stirring is started, and an alkaline solution is added dropwise to the metal salt solution at 60℃ for 15 minutes to obtain a first mixture; the first mixture is reacted at 60℃ for 5 minutes to obtain a first slurry with a pH of 11; wherein, the ratio of the amount of hydroxide ions in the alkaline solution to the sum of the amounts of Fe and Mn elements in the metal salt solution is 3:1; the first slurry includes intermediate products with properties as shown in Table 1-3:

[0190] Table 1-3

[0191]

[0192] S2, at 60℃, oxalate source is added dropwise to the first slurry for 15 minutes to obtain a second mixture; the second mixture is reacted at 60℃ for 15 minutes to obtain a second slurry; wherein, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.2:1;

[0193] S3, the second slurry is placed in a reaction vessel, and water bath heating is turned on. It is kept at 95℃ for 60 minutes to obtain an aged slurry. After solid-liquid separation, the aged slurry yields a first solid material. The first solid material is rinsed with pure water until the conductivity of the rinsing solution is ≤120μs / cm, yielding a second solid material. The second solid material is dried at 80℃ for 2 hours until the moisture content is <0.5%, yielding the manganese ferric oxalate precursor material (Mn). 0.2 Fe 0.8 C2O4).

[0194] Example 4

[0195] The difference from Example 1 is that the ratio of the amount of hydroxide ions in the alkaline solution to the sum of the amounts of Fe and Mn elements in the metal salt solution in S1 is 2:1, resulting in a first slurry with a pH of 9.470.

[0196] The first slurry includes intermediate products with properties shown in Table 1-4:

[0197] Table 1-4

[0198]

[0199] Example 5

[0200] The difference from Example 1 is that the ratio of the amount of hydroxide ions in the alkaline solution in S1 to the sum of the amounts of Fe and Mn elements in the metal salt solution is 3:1, resulting in a first slurry with a pH of 10.52.

[0201] The first slurry includes intermediate products with properties shown in Table 1-5:

[0202] Table 1-5

[0203]

[0204] Example 6

[0205] The difference from Example 1 is that in S2, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1:1.

[0206] Example 7

[0207] The difference from Example 1 is that in S2, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.05:1.

[0208] Example 8

[0209] The difference from Example 1 is that in S2, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.2:1.

[0210] Example 9

[0211] The difference from Example 1 is that in S2, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.3:1.

[0212] Example 10

[0213] The difference from Example 1 is that in S1, a metal salt solution was used as the base liquid. Stirring was started, and an alkaline solution was added dropwise to the metal salt solution at 15°C for 10 minutes to obtain a first mixture. The first mixture was then reacted at 15°C for 3 minutes under the same conditions to obtain a first slurry with a pH of 9.46. The first slurry includes intermediate products with properties shown in Tables 1-6.

[0214] Table 1-6

[0215]

[0216] Example 11

[0217] The difference from Example 1 is that in S1, a metal salt solution was used as the base liquid. Stirring was started, and an alkaline solution was added dropwise to the metal salt solution at 70°C for 40 minutes to obtain a first mixture. The first mixture was then reacted at 70°C for 20 minutes under the same conditions to obtain a first slurry with a pH of 9.72. The first slurry includes intermediate products with properties shown in Tables 1-7.

[0218] Table 1-7

[0219]

[0220] Example 12

[0221] The difference from Example 1 is that in S2, oxalate source is added dropwise to the first slurry at 15°C for 10 minutes to obtain a second mixture; the second mixture is reacted at 15°C for 10 minutes to obtain a second slurry.

[0222] Example 13

[0223] The difference from Example 1 is that in S2, oxalate source is added dropwise to the first slurry at 70°C for 40 minutes to obtain a second mixture; the second mixture is reacted at 70°C for 50 minutes to obtain a second slurry.

[0224] Example 14

[0225] The difference from Example 1 is that the second slurry was placed in a reaction vessel, heated in a water bath, and kept at 100°C for 150 minutes to obtain an aged slurry. After solid-liquid separation, the aged slurry yielded a first solid material. The first solid material was then rinsed with pure water until the conductivity of the rinsing solution was ≤120 μS / cm, yielding a second solid material. The second solid material was dried at 100°C for 5 hours until the moisture content was <0.5%, yielding the manganese ferric oxalate precursor material Mn. 0.2 Fe 0.8 C2O4.

[0226] Comparative Example 1

[0227] The difference from Example 1 is that the preparation method of the comparative example manganese iron oxalate precursor includes the following steps:

[0228] S1, using a metal salt solution as the base liquid, stirring is started, and an alkaline solution and oxalate source are simultaneously added dropwise to the metal salt solution at 35°C for 20 minutes to obtain a first mixture; the first mixture is reacted at 35°C for 10 minutes to obtain a first slurry with a pH of 2.102; wherein, the ratio of the amount of hydroxide ions in the alkaline solution to the sum of the amounts of Fe and Mn elements in the metal salt solution is 2.5:1.0, and the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.1:1;

[0229] S2, the first slurry is placed in a reaction vessel, and a water bath is turned on for heating. The mixture is kept at 90°C for 90 minutes to obtain an aged slurry. After solid-liquid separation, the aged slurry yields a first solid material. The first solid material is rinsed with pure water. The conductivity of the rinsing solution after rinsing is ≤120μs / cm to obtain a second solid material. The second solid material is dried at 80°C for 3 hours until the moisture content is <0.5% to obtain the manganese ferric oxalate precursor material.

[0230] Comparative Example 2

[0231] The difference from Example 1 is that the preparation method of the comparative example manganese iron oxalate precursor includes the following steps:

[0232] S1, using a metal salt solution as the base liquid, stirring is started, and oxalate source is added dropwise to the metal salt solution at 35°C for 20 minutes to obtain a first mixture; the first mixture is reacted at 35°C for 15 minutes to obtain a first slurry with a pH of 0.32; wherein, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 1.1:1;

[0233] S2, the first slurry is placed in a reaction vessel, and a water bath is turned on for heating. The mixture is kept at 90°C for 90 minutes to obtain an aged slurry. After solid-liquid separation, the aged slurry yields a first solid material. The first solid material is rinsed with pure water. The conductivity of the rinsing solution after rinsing is ≤120μs / cm to obtain a second solid material. The second solid material is dried at 80°C for 3 hours until the moisture content is <0.5% to obtain the manganese ferric oxalate precursor material.

[0234] Comparative Example 3

[0235] The difference from Example 1 is that in S2, the ratio of the amount of oxalate ions in the oxalate source to the sum of the amounts of Fe and Mn elements in the metal salt solution is 0.8:1.

[0236] Comparative Example 4

[0237] The difference from Example 1 is that the second slurry was placed in a reaction vessel, heated in a water bath, and kept at 70°C for 50 minutes to obtain an aged slurry. After solid-liquid separation, the aged slurry yielded a first solid material. The first solid material was rinsed with pure water until the conductivity of the rinsing solution was ≤120 μS / cm, yielding a second solid material. The second solid material was dried at 50°C for 1 hour until the moisture content was <0.5%, yielding the manganese ferric oxalate precursor material Mn. 0.6 Fe 0.4 (OH)2.

[0238] II. Testing Methods

[0239] 1. Size testing of primary particles of manganese oxalate ferric precursor material

[0240] The manganese oxalate ferric precursor materials prepared in the above embodiments and comparative examples were placed under a scanning electron microscope. The length, width, and thickness of 10 to 15 particles were measured and the average value was calculated to obtain the length, width, and thickness of the primary particles of the manganese oxalate ferric precursor material. Figure 6 This is a SEM image showing the length of the primary particles of the manganese iron oxalate precursor material in Example 1 of this application. Figure 7 This is a SEM image showing the width measurement of the primary particles of the manganese iron oxalate precursor material in Example 1 of this application; Figure 8 This is a SEM image showing the thickness measurement of the primary particles of the manganese iron oxalate precursor material in Example 1 of this application.

[0241] 2. Preparation of lithium manganese iron phosphate cathode material

[0242] The manganese iron oxalate precursor materials prepared in the above embodiments and comparative examples were mixed with lithium dihydrogen phosphate at a molar ratio of 1:1.01 and sintered at 680°C for 14 hours to obtain lithium manganese iron phosphate cathode materials.

[0243] 3. Property testing of manganese iron phosphate precursor materials and lithium manganese iron phosphate cathode materials

[0244] Specific surface area: tested using a BET analyzer and nitrogen adsorption method.

[0245] D10, D50, D90, and D100 particle sizes were measured using a laser particle size analyzer via laser diffraction.

[0246] Purity: Tested using potassium permanganate titration.

[0247] Mn and Fe content determination: Fe content was determined by potassium dichromate titration, and Mn content was determined by perchloric acid oxidation titration.

[0248] Compacted density: Tested using a compaction density meter with a test pressure of 3T and a compaction time of 30s.

[0249] Scanning electron microscope images: taken using a ZEISS MERLIN Compact scanning electron microscope.

[0250] 4. Properties testing of the positive electrode sheet

[0251] The lithium manganese iron phosphate cathode material, conductive carbon black and polyvinylidene fluoride (PVDF) prepared in the above embodiments and comparative examples were mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added to form a uniform electrode slurry. The electrode slurry was then uniformly coated on aluminum foil, vacuum dried and cut into circular cathode sheets with a diameter of 15 mm. A lithium metal sheet was used as the counter electrode and assembled into a button cell in an argon-filled glove box.

[0252] The button cell was charged and discharged at 25°C and at a current density of 0.1C, with a charge-discharge range of 0.01~1.5V, and the charge-discharge curves were obtained.

[0253] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0254] Table 2 Performance Tests of Ferric Manganese Oxalate Precursor Materials

[0255]

[0256] Table 3 Performance Tests of Ferric Manganese Oxalate Precursor Materials (Part 2)

[0257]

[0258] Table 4 Performance Tests of Lithium Manganese Iron Phosphate Cathode Material

[0259]

[0260] according to Figure 2 and Figure 3 It is known that the intermediate product has a nanoscale porous structure, according to Figure 4 , Figure 5 , Figure 9 and Figure 10 It is known that the primary particles of the manganese iron oxalate precursor material prepared from the intermediate product have a plate-like structure, resulting in a smaller particle size compared to conventional preparation processes. This leads to a shorter lithium-ion transport path, better charge-discharge performance, and makes it more suitable for preparing high-performance lithium manganese iron phosphate cathode materials. According to... Figure 6 , Figure 7 and Figure 8 The length, width, and thickness of the primary particles of the manganese iron oxalate precursor material in Example 1 can be measured.

[0261] according to Figure 11 and Figure 12 It can be seen that the manganese ferric oxalate precursor material prepared in Example 1 is a pure phase manganese oxalate crystal structure with no impurity diffraction peaks. This indicates that the manganese ferric oxalate prepared in Example 1 is a solid solution material based on the manganese oxalate structure. Fe atoms replace the Mn sites in the crystal structure, resulting in a high-purity manganese ferric oxalate precursor material.

[0262] According to Tables 2, 3 and 4, the D50 particle size of the ferromanganese oxalate precursor material prepared in Example 1 is lower than that of the ferromanganese oxalate precursor material prepared in Comparative Example 1. This indicates that the method provided by the present invention, which uses a hydroxide intermediate generated by co-precipitation and then converts the intermediate into ferromanganese oxalate precursor material, significantly reduces the particle size and primary particle size of the ferromanganese oxalate precursor material.

[0263] As shown in Tables 2, 3, and 4, the lithium iron phosphate cathode materials prepared under the same process conditions using the manganese iron oxalate precursor materials prepared in Examples 1 and Comparative Examples 1 as precursors exhibit significantly improved charging and discharging performance compared to those prepared using the manganese iron oxalate precursor materials in Comparative Example 1.

[0264] Comparing Examples 1-14 with Comparative Examples 1-4, it can be seen that in Examples 1-14, the metal salt solution was first mixed with an alkaline solution and co-precipitated to obtain ferrous manganese hydroxide intermediate. Then, oxalate ions were used to replace hydroxide ions in the intermediate to generate ferrous manganese oxalate. The ferrous manganese oxalate precursor materials prepared in Examples 1-14 have a plate-like structure in their primary particles, with a length of 1000 nm to 1500 nm, a width of 400 nm to 870 nm, and a thickness of 300 nm to 500 nm. The purity of the ferrous manganese oxalate precursor materials is ≥99.2%. In Comparative Example 1, the reaction was carried out by simultaneously adding an alkaline solution and an oxalate source to a metal salt substrate. The primary particle size of the ferromanganese oxalate precursor material was relatively large, resulting in a low specific surface area. In Comparative Example 2, the oxalate source was directly reacted with the metal salt substrate. The purity of the ferromanganese oxalate precursor material was <99.2%. Although Comparative Examples 3 and 4 adopted the method of first co-precipitating ferromanganese hydroxide intermediate and then using oxalate ions to replace hydroxide ions in the intermediate, the purity of the product obtained in Comparative Example 3 decreased due to the low oxalate ratio. It could not be completely converted into ferromanganese oxalate, resulting in a mixture of ferromanganese oxalate and ferric hydroxide / manganese. The purity of the ferromanganese oxalate precursor material was <99.2%. In Comparative Example 4, the aging temperature was too low, resulting in incomplete aging, a decreased reaction rate, and a decrease in the purity of the product obtained. The purity of the ferromanganese oxalate precursor material was <99.2%. Compared to Comparative Examples 1-4, the manganese iron oxalate precursor materials prepared in Examples 1-14 combine the advantages of high purity and high specific surface area. This is beneficial for the lithium iron manganese phosphate cathode materials prepared from these precursor materials to also have a high specific surface area, promoting lithium ion insertion and extraction. This, in turn, helps to improve the actual specific capacity and initial coulombic efficiency of the lithium iron manganese phosphate cathode material. Specifically, it can achieve a 0.1C charging specific capacity ≥153.3 mAh / g, a 0.1C discharging specific capacity ≥151.3 mAh / g, and an initial coulombic efficiency ≥97.48%.

[0265] Furthermore, compared to Example 9, Examples 1-8 further controlled the molar amount of oxalate ions during the preparation process to satisfy the following: the ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron elements in the metal salt solution is (1.0~1.2):1. This further reduced the primary particle size of the manganese iron oxalate precursor material prepared in Examples 1-8, resulting in a further improvement in the 0.1C charging specific capacity of the lithium manganese iron phosphate cathode material prepared from this precursor material. In contrast, Example 9 had an excessively high molar amount of oxalate ions during the preparation process, leading to a decrease in the 0.1C charging specific capacity of the lithium manganese iron phosphate cathode material prepared from this precursor material. Compared to Examples 10-11, Examples 1-8 further controlled the first mixing temperature, first mixing time, first reaction temperature, and first reaction time during the preparation process to meet the following requirements: first mixing temperature of 20℃~60℃, first mixing time of 15min~30min, first reaction temperature of 20℃~60℃, and first reaction time of 5min~15min. The primary particle size of the manganese oxalate ferromanganese precursor material prepared in Examples 1-8 was further reduced, and the particle size of the manganese oxalate ferromanganese precursor material was further optimized. However, in Example 10, the first mixing temperature, first mixing time, first reaction temperature, and first reaction time were all too low, resulting in excessively large D0 and D99 particle sizes in the manganese oxalate ferromanganese precursor material. In Example 11, the first mixing temperature, first mixing time, first reaction temperature, and first reaction time were all too high, resulting in excessively large D0, D50, D90, and D99 particle sizes in the manganese oxalate ferromanganese precursor material.

[0266] Compared to Examples 12-13, Examples 1-8 further controlled the second mixing temperature, second mixing time, second reaction temperature, and second reaction time during the preparation process to meet the following requirements: second mixing temperature 20℃~60℃, second mixing time 15min~30min, second reaction temperature 20℃~60℃, and second reaction time 15min~45min. The primary particle size of the manganese oxalate ferromanganese precursor material prepared in Examples 1-8 was further reduced, resulting in a lower D50 particle size but an increased D90 particle size. In contrast, Example 12 had excessively low second mixing temperature, second mixing time, second reaction temperature, and second reaction time during the preparation process, resulting in an excessively small D10 particle size in the manganese oxalate ferromanganese precursor material. Example 13 had excessively high second mixing temperature, second mixing time, second reaction temperature, and second reaction time during the preparation process, resulting in an excessively small D90 particle size in the manganese oxalate ferromanganese precursor material.

[0267] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A manganese iron oxalate precursor material, characterized in that, The manganese iron oxalate precursor material has a chemical formula of Mn x Fe (1-x) C2O4, 0 < x < 1; The primary particles of the manganese iron oxalate precursor material are in a flaky structure, the length of the primary particles is 1000 nm-1500 nm, the width of the primary particles is 400 nm-870 nm, and the thickness of the primary particles is 300 nm-500 nm; The purity of the manganese iron oxalate precursor material is greater than or equal to 99.2%; The D50 particle size of the manganese iron oxalate precursor material is 4 μm-10 μm; The specific surface area of the manganese iron oxalate precursor material is 1.0 m 2 / g ~ 5.0 m 2 / g.

2. The manganese iron oxalate precursor material of claim 1, wherein, The D0 particle size of the manganese iron oxalate precursor material is 0.35 μm-0.42 μm, the D10 particle size of the manganese iron oxalate precursor material is 1 μm-3 μm, the D90 particle size of the manganese iron oxalate precursor material is 10 μm-25 μm, the D99 particle size of the manganese iron oxalate precursor material is 20 μm-45 μm, and the D100 particle size of the manganese iron oxalate precursor material is 20 μm-60 μm.

3. The manganese iron oxalate precursor material according to claim 1 or 2, characterized in that, The length of the primary particles is 1000 nm-1400 nm, the width of the primary particles is 400 nm-700 nm, and the thickness of the primary particles is 350 nm-450 nm.

4. A method of preparing a manganese iron oxalate precursor material, characterized in that, The method comprises the following steps: The metal salt solution is mixed with the alkaline solution, and is subjected to a first reaction treatment to obtain a first slurry; The first slurry is mixed with an oxalate source, and is subjected to a second reaction treatment to obtain a second slurry; The second slurry is subjected to an aging treatment to obtain the manganese iron oxalate precursor material; The metal salt solution comprises divalent manganese ions and divalent iron ions, the first slurry comprises an intermediate product, the intermediate product has a general formula of Mn x Fe (1-x) (OH)2, 0 < x < 1, and a particle size of primary particles of the intermediate product is 30 nm to 100 nm. The chemical formula of the manganese iron oxalate precursor material is Mn x Fe (1-x) C2O4, 0 < x < 1; The primary particles of the manganese iron oxalate precursor material are in a flaky structure, the length of the primary particles is 1000 nm-1500 nm, the width of the primary particles is 400 nm-870 nm, and the thickness of the primary particles is 300 nm-500 nm; The purity of the manganese iron oxalate precursor material is greater than or equal to 99.2%; The D50 particle size of the manganese iron oxalate precursor material is 4 μm-10 μm; The specific surface area of the manganese iron oxalate precursor material is 1.0 m 2 / g ~ 5.0 m 2 / g; The ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron in the metal salt solution is (1.0-1.3):1; The step of subjecting the second slurry to an aging treatment to obtain the manganese iron oxalate precursor material comprises: The second slurry is subjected to an aging treatment at an aging temperature for an aging time to obtain an aged slurry; The aged slurry is subjected to solid-liquid separation to obtain a first solid material; The first solid material is subjected to a rinsing treatment until the conductivity of the rinsing liquid after rinsing is less than or equal to 120 μs / cm to obtain a second solid material; The second solid material is subjected to an oven-drying treatment at an oven-drying temperature for an oven-drying time to obtain the manganese iron oxalate precursor material; The aging temperature is 80°C-100°C, and the aging time is 60 min-150 min.

5. The method for preparing the manganese iron oxalate precursor material according to claim 4, characterized in that, At least one of the following features is included: (1) The pH value of the first slurry is 9.0-11.0; (2) The ratio of the molar amount of hydroxide ions in the alkaline solution to the total molar amount of manganese and iron in the metal salt solution is (2-3):1; (3) The ratio of the molar amount of oxalate ions in the oxalate source to the total molar amount of manganese and iron in the metal salt solution is (1.0-1.2):1; (4) the divalent iron salt containing the divalent iron ion comprises at least one of ferrous chloride, ferrous nitrate, ferrous sulfate, ferrous acetate; (5) the divalent manganese salt containing the divalent manganese ion comprises at least one of manganous chloride, manganous nitrate, manganous sulfate, manganous acetate; (6) the alkaline solution comprises at least one of sodium hydroxide solution, ammonia water; (7) the oxalate source comprises at least one of oxalic acid, ammonium oxalate, sodium oxalate.

6. The method for preparing the manganese iron oxalate precursor material according to claim 4, characterized in that, At least one of the following features is included: (1) the step of mixing the metal salt solution with the alkaline solution, and obtaining a first slurry through first reaction treatment, comprises: the metal salt solution and the alkaline solution are mixed at a first mixing temperature for a first mixing time to obtain a first mixture; the first mixture is reacted at a first reaction temperature for a first reaction time to obtain the first slurry; wherein the first mixing temperature is 20℃-60℃, the first mixing time is 15min-30min, the first reaction temperature is 20℃-60℃, and the first reaction time is 5min-15min; (2) the step of mixing the first slurry with the oxalate source, and obtaining a second slurry through second reaction treatment, comprises: the first slurry and the oxalate source are mixed at a second mixing temperature for a second mixing time to obtain a second mixture; the second mixture is reacted at a second reaction temperature for a second reaction time to obtain the second slurry; wherein the second mixing temperature is 20℃-60℃, the second mixing time is 15min-30min, the second reaction temperature is 20℃-60℃, and the second reaction time is 15min-45min; (3) the drying temperature is 60℃-80℃, and the drying time is 2h-4h.

7. A lithium iron manganese phosphate cathode material, characterized in that, Prepared from a manganese iron oxalate precursor material, the manganese iron oxalate precursor material is selected from the manganese iron oxalate precursor material of any one of claims 1-3, or the manganese iron oxalate precursor material prepared by the preparation method of any one of claims 4-6.

8. The lithium iron manganese phosphate cathode material of claim 7, wherein, At least one of the following features is included: (1) the compaction density of the lithium iron manganese phosphate positive electrode material is 1.85 g / cm 3 1.9 g / cm 3 ; (2) the 0.1C charge specific capacity of the manganese iron lithium phosphate positive electrode material is ≥150mAh / g, and the 0.1C discharge specific capacity of the manganese iron lithium phosphate positive electrode material is ≥150mAh / g; (3) the first coulombic efficiency of the manganese iron lithium phosphate positive electrode material is ≥97.48%.

9. A positive electrode sheet characterized by comprising: The positive electrode active material includes the manganese iron lithium phosphate positive electrode material of claim 7 or 8.

10. A secondary battery characterized by comprising: The positive electrode active material includes the manganese iron lithium phosphate positive electrode material of claim 7 or 8.

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