Method for preparing lithium manganese iron phosphate through regeneration of waste lithium manganate and lithium manganese iron phosphate

Abstract

The invention provides a method for preparing lithium manganese iron phosphate through regeneration of waste lithium manganate and lithium manganese iron phosphate. The preparation method comprises the following steps: mixing waste lithium manganate, a lithium source, an iron source, a phosphorus source and a carbon source, performing first-stage ball milling, and then adding a solvent for second-stage ball milling; performing vacuum drying and screening on the slurry subjected to second-stage ball milling; carrying out multi-stage high-temperature sintering on the screened material in a nitrogen atmosphere; wherein the waste lithium manganate comprises at least one of a lithium manganate waste material in a lithium manganate process, lithium manganate recovered from a pole piece waste material in a battery manufacturing process and lithium manganate recovered from a pole piece stripping material of a waste battery. The preparation method is simple in process, the production cost is reduced by utilizing the waste lithium manganate, and large-scale commercial application is facilitated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a method for preparing lithium manganese iron phosphate from waste lithium manganate and lithium manganese iron phosphate. BACKGROUND

[0002] As a new type of lithium ion battery cathode material developed on the basis of lithium iron phosphate, lithium manganese iron phosphate has a high potential and potential high energy density, which is of great significance to improve the endurance of lithium ion batteries and meet the growing demand for energy storage.

[0003] In related technologies, the preparation method of lithium manganese iron phosphate has many deficiencies. Common preparation methods such as solvothermal method, high-temperature solid-phase method, sol-gel method and co-precipitation method can realize the preparation of lithium manganese iron phosphate to some extent, but these methods generally have the problem of complex process, which not only increases the operation difficulty in the production process, but also easily leads to the fluctuation of the quality of lithium manganese iron phosphate products. At the same time, the high preparation cost limits the large-scale commercial application of lithium manganese iron phosphate. SUMMARY

[0004] An object of embodiments of the application is to provide a new technical solution for a method for preparing lithium manganese iron phosphate from waste lithium manganate.

[0005] According to a first aspect of embodiments of the application, a method for preparing lithium manganese iron phosphate from waste lithium manganate is provided, comprising:

[0006] mixing waste lithium manganate, a lithium source, an iron source, a phosphorus source and a carbon source, then performing first-stage ball milling, and then adding a solvent to perform second-stage ball milling;

[0007] vacuum drying and sieving the slurry after the second-stage ball milling;

[0008] performing multi-stage high-temperature sintering on the sieved material under a nitrogen atmosphere;

[0009] The waste lithium manganate includes at least one of lithium manganate waste in the lithium manganate process, lithium manganate recovered from the electrode tab waste in the battery manufacturing process, and lithium manganate recovered from the electrode tab stripping of the waste battery.

[0010] Optionally, the lithium source includes one or more of lithium carbonate, lithium fluoride and lithium hydroxide, the iron source includes one or more of iron phosphate, iron oxalate, iron powder and iron oxide, and the phosphorus source includes one or more of ammonium dihydrogen phosphate and lithium dihydrogen phosphate.

[0011] Optionally, the carbon source includes one or more of polyvinyl alcohol, polyethylene glycol and glucose.

[0012] The carbon content in the lithium manganese iron phosphate is 1.0%-4.0%.

[0013] Optionally, the solid content in the slurry after the second stage ball milling is 20%-60%.

[0014] Optionally, the solvent includes one or a combination of both of water and ethanol.

[0015] The solvent in the slurry after the second stage ball milling is 40%-80%.

[0016] Optionally, the rotation speed of the first stage ball milling is 200-600 r / min, and the rotation speed of the second stage ball milling is 200-600 r / min.

[0017] The vacuum drying time is 10-30 h, and the temperature is 60-100℃.

[0018] The screen mesh size of the screening is 50-200 mesh.

[0019] Optionally, the nitrogen gas flow rate of the nitrogen atmosphere is 150-650 mL / min.

[0020] Optionally, the multi-stage high-temperature sintering includes a first stage sintering and a second stage sintering, the sintering temperature of the first stage sintering is 300℃-550℃, and the sintering temperature of the second stage sintering is 600℃-900℃.

[0021] Optionally, the heating rate of the first stage sintering and the second stage sintering is 3-8℃ / min.

[0022] According to a second aspect of the embodiments of the present application, a lithium manganese iron phosphate is provided, which is prepared by the method for preparing the lithium manganese iron phosphate according to the first aspect.

[0023] One technical effect of the present application is that:

[0024] The embodiments of the present application provide a method for preparing lithium manganese iron phosphate by recycling waste lithium manganate, which includes: mixing waste lithium manganate, a lithium source, an iron source, a phosphorus source, and a carbon source, and then performing first stage ball milling, and then adding a solvent to perform second stage ball milling; performing vacuum drying and screening on the slurry after the second stage ball milling; performing multi-stage high-temperature sintering on the screened material under a nitrogen atmosphere; wherein the waste lithium manganate includes at least one of lithium manganate waste in the lithium manganate process, lithium manganate recovered from the electrode sheet waste in the battery manufacturing process, and lithium manganate recovered from the electrode sheet stripping of the waste battery. The above preparation method is simple in process, and the use of waste lithium manganate reduces production cost, which is conducive to large-scale commercial application.

[0025] Other features and advantages of the present application will become apparent from the following detailed description of illustrative embodiments thereof, which proceeds with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0027] Figure 1 A flow chart of a method for preparing lithium manganese iron phosphate by recycling waste lithium manganate is provided for an embodiment of the present application;

[0028] Figure 2 A rate performance chart of the example and control batteries provided for an embodiment of the present application;

[0029] Figure 3 A cycle performance chart of the example and control batteries provided for an embodiment of the present application;

[0030] Figure 4 A normal temperature and high temperature discharge specific capacity chart of the example battery provided for an embodiment of the present application. DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present application will now be described in detail with reference to the figures. It should be noted that the relative arrangement of components and steps, numerical expressions, and numerical values set forth in these embodiments are not limitations on the scope of the present application unless specifically stated otherwise.

[0032] Embodiments of the present application will be described in detail below with reference to the drawings. The embodiments described below by reference to the drawings are exemplary and are used to explain the present application, and should not be understood as limiting the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor fall within the scope of the present application.

[0033] The terms "first", "second" in the description and claims of the present application can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / ", generally means that the front and rear associated objects are in an "or" relationship.

[0034] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0035] In the description of the present application, it needs to be understood that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0036] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further discussed in the subsequent drawings.

[0037] In the related art, the common preparation methods of lithium manganese iron phosphate include solvothermal method, high temperature solid phase method, sol-gel method and co-precipitation method, etc. Although the preparation of lithium manganese iron phosphate can be realized to some extent by these methods, these methods generally have the problem of complex process, which not only increases the operation difficulty in the production process, but also easily leads to the fluctuation of the product quality of lithium manganese iron phosphate. At the same time, the high preparation cost limits the large-scale commercial application of lithium manganese iron phosphate.

[0038] The method for preparing lithium manganese iron phosphate by regenerating waste lithium manganate provided by the embodiments of the present application has simple process, and the use of waste lithium manganate reduces the production cost, and the prepared lithium manganese iron phosphate has stable electrochemical performance, which is beneficial to large-scale commercial application.

[0039] Reference Figure 1 The embodiments of the present application provide a method for preparing lithium manganese iron phosphate by regenerating waste lithium manganate, which comprises:

[0040] S101, mixing waste lithium manganate, lithium source, iron source, phosphorus source and carbon source, then performing first stage ball milling, and then adding solvent to perform second stage ball milling;

[0041] In the above embodiment, the waste lithium manganate provides all manganese sources and part of lithium sources, and the lithium source provides the remaining lithium sources to meet the demand of lithium sources. The content of the waste lithium manganate in the raw materials (waste lithium manganate, lithium source, iron source and phosphorus source) is 24-28 wt%, so as to ensure the cycle stability of the capacity of the prepared lithium manganese iron phosphate.

[0042] In the ball mill tank, the combination of dry ball milling and wet ball milling is sequentially carried out. The dry ball milling in the first stage ball milling uniformly mixes the solid raw materials such as waste lithium manganate, lithium source, iron source, phosphorus source and carbon source, breaks the agglomeration between the particles of the raw materials, reduces the particle size of the raw materials, and increases the contact area between the particles. The wet ball milling in the second stage ball milling promotes the uniform dispersion of the raw materials, ensures that each element is highly uniformly mixed at a microscale, and is beneficial to the formation of lithium manganese iron phosphate material with uniform chemical composition.

[0043] S102, vacuum drying and screening the slurry after the second stage ball milling;

[0044] In the above embodiment, the vacuum drying can quickly remove the solvent in the slurry at a lower temperature, avoiding the decomposition or phase change of the raw materials caused by high temperature. At the same time, the vacuum environment can effectively prevent the introduction of impurities during the solvent evaporation process, ensuring the purity of the product. The material after removing the solvent is easier to be sintered in the subsequent process, which is beneficial to the formation of uniform crystal structure.

[0045] The screening operation can remove particles with too large or too small particle size, ensuring that the particle size distribution of the final product is uniform. Uniform particle size can improve the diffusion rate of lithium ions, reduce electrode polarization, and thus improve the charge-discharge performance and cycle stability of the material.

[0046] S103, multi-stage high-temperature sintering of the screened material under a nitrogen atmosphere;

[0047] The waste lithium manganate includes at least one of lithium manganate waste in the lithium manganate process, lithium manganate recovered from the electrode tab waste in the battery manufacturing process, and lithium manganate recovered from the electrode tab stripping of the waste battery.

[0048] In the above embodiment, nitrogen, as an inert gas, can effectively isolate oxygen during high-temperature sintering to prevent the material from being oxidized. Manganese, iron and other elements in lithium manganese iron phosphate are prone to react with oxygen at high temperature, resulting in a decline in material performance. The protection of the nitrogen atmosphere can ensure the stability of the chemical composition and crystal structure of the material, and improve the purity and electrochemical performance of the product.

[0049] The multi-stage high-temperature sintering process can accurately control the parameters such as temperature, time and atmosphere according to the reaction requirements in different stages. In the early stage of sintering, the relatively low temperature is helpful for the preliminary reaction of raw materials and the preliminary combination of particles; as the temperature rises, the growth and perfection of crystals are promoted; finally, through natural cooling or appropriate cooling process, the internal stress of the material is reduced, and the stability of the crystal is improved. The method for preparing lithium manganese iron phosphate from waste lithium manganate provided in the embodiments can form lithium manganese iron phosphate material with good crystal structure and electrochemical performance, and improve the energy density, cycle life and rate performance of the material.

[0050] In the preparation of traditional lithium manganese iron phosphate, the cost of manganese oxide and other manganese sources accounts for a large proportion. The present application utilizes waste lithium manganate, which has a wide source and covers waste generated in multiple links such as lithium manganate production, battery manufacturing and waste battery treatment. By recycling and reusing these waste lithium manganate, the cost of manganese source is greatly reduced, providing cost advantage for large-scale production.

[0051] Specifically, for example, the waste lithium manganate comes from tailings in the lithium manganate production process. These tailings affect the performance of lithium manganate due to their small particle size, and thus form waste lithium manganate. The waste lithium manganate also comes from lithium manganate obtained by recycling of scrap materials in the battery manufacturing process. The waste lithium manganate can also come from lithium manganate obtained by recycling of positive electrode stripping material after disassembly of the recycled waste battery. This kind of waste lithium manganate does not need complex processes such as sintering and impurity removal, and can be directly crushed after stripping the active material on the pole piece after soaking in NMP solution, for use in the preparation of lithium manganese iron phosphate.

[0052] In one embodiment, the ball milling beads include a plurality of zirconia beads, and the mass of the plurality of zirconia beads is 5-10 times the mass of the ball milling material, so as to effectively break and refine the material particles, improve the ball milling efficiency, make the raw materials more fully mixed and reacted, and facilitate the formation of uniform and fine lithium manganese iron phosphate precursor particles. The volume of the slurry after the second stage of ball milling is not more than 1 / 3 of the ball milling tank, which can provide sufficient movement space for the beads and ensure the smooth progress of the ball milling process, thereby improving the ball milling effect.

[0053] In one embodiment, the lithium manganese iron phosphate prepared by the embodiments can be used as a positive electrode material of a lithium ion battery. For example, the material after multi-stage high-temperature sintering is sieved through a 200-mesh sieve to obtain a lithium manganese iron phosphate positive electrode material using lithium manganate as a manganese source.

[0054] The present embodiment comprises a process of mixing waste lithium manganese oxide, a lithium source, an iron source, a phosphorus source, and a carbon source, subjecting the mixture to a first-stage ball milling process, followed by a second-stage ball milling process by adding a solvent; vacuum drying and screening the slurry after the second-stage ball milling; and sintering the screened material in multiple stages of high-temperature sintering under a nitrogen atmosphere. The waste lithium manganese oxide comprises at least one of lithium manganese oxide waste from the lithium manganese oxide production process, lithium manganese oxide recovered from pole piece waste from battery manufacturing, and lithium manganese oxide recovered from pole piece stripping from waste batteries. The preparation method is simple, utilizes waste lithium manganese oxide, reduces production costs, and the resulting lithium iron manganese phosphate has stable electrochemical properties, making it suitable for large-scale commercial applications.

[0055] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium fluoride, and lithium hydroxide, the iron source includes one or more of iron phosphate, iron oxalate, iron powder, and iron oxide, and the phosphorus source includes one or a combination of ammonium dihydrogen phosphate and lithium dihydrogen phosphate.

[0056] In the above embodiment, the price of lithium carbonate is relatively low. The use of lithium carbonate as a lithium source helps to control the preparation cost of lithium manganese iron phosphate, ensure the stable supply of raw materials, and is suitable for large-scale industrial production. The introduction of lithium fluoride will have a positive effect on the crystal structure and surface properties of the lithium manganese iron phosphate material. The doping of fluorine elements can improve the ionic conductivity of the material and increase the diffusion rate of lithium ions in the material, thereby improving the charge and discharge performance and rate performance of the material. Lithium hydroxide has a high reactivity and can react with other raw materials more quickly during ball milling and sintering, promoting the formation of lithium manganese iron phosphate precursors, helping to shorten the preparation cycle and improve production efficiency.

[0057] During the preparation of lithium iron manganese phosphate, the iron phosphate structure serves as a template, facilitating the formation of a lithium iron manganese phosphate material with a well-defined crystal structure. Furthermore, the iron element in the iron phosphate exists in a stable chemical state, allowing it to participate uniformly during the reaction, ensuring a uniform chemical composition and, in turn, improving the electrochemical performance of the material. Iron oxalate readily reacts chemically with other raw materials during ball milling, and the gases produced by its decomposition promote dispersion and mixing of the raw materials, enhancing the milling process. During the sintering process, the active iron source produced by the decomposition of the iron oxalate rapidly participates in the reaction, contributing to the formation of fine, uniform particles and increasing the specific surface area and reactivity of the material. Iron powder has high reactivity and reacts quickly with lithium and phosphorus sources, shortening the reaction time. Furthermore, its relatively low price reduces raw material costs. Iron oxide is chemically stable and highly pure, making it less susceptible to impurities during the preparation process, thus ensuring the purity and performance of the lithium iron manganese phosphate product. Iron oxide reacts with lithium and phosphorus sources at high temperatures, facilitating the formation of a stable lithium iron manganese phosphate crystal structure.

[0058] Ammonium dihydrogen phosphate can provide the necessary phosphorus element for the synthesis of lithium manganese iron phosphate. During the ball milling and sintering process, the phosphate ions produced by the decomposition of ammonium dihydrogen phosphate react with other raw materials to form the crystal structure of lithium manganese iron phosphate. Lithium dihydrogen phosphate, as a phosphorus source, can also supplement lithium, which is conducive to the uniform distribution of lithium ions in the crystal structure and improves the electrochemical performance of the material. Moreover, using lithium dihydrogen phosphate as a phosphorus source can reduce the amount of lithium source used and simplify the raw material ratio.

[0059] In some embodiments, the carbon source includes one or more of polyvinyl alcohol, polyethylene glycol, and glucose.

[0060] By controlling the mass percentage of the carbon source in the lithium manganese iron phosphate raw materials to be 3%-10%, the carbon content in the finished lithium manganese iron phosphate product is 1.0%-4.0%.

[0061] In the above embodiments, polyvinyl alcohol has good film-forming properties, and during ball milling and subsequent sintering, it can form a uniform carbon film on the surface of lithium manganese iron phosphate particles. This carbon film can effectively isolate the particles from direct contact with the electrolyte, reducing the occurrence of side reactions and improving the cycle stability and coulombic efficiency of the material. At the same time, the carbon film can also enhance the electrical conductivity between particles, promote the transport of lithium ions, and improve the charge and discharge performance of the material. Polyethylene glycol can reduce the friction between particles during ball milling, reducing particle wear and helping to evenly disperse the raw materials. Glucose has a lower cost. During high-temperature sintering, glucose can completely decompose to produce a large amount of carbon, providing sufficient carbon source for lithium manganese iron phosphate.

[0062] The mass percentage of the carbon source in lithium manganese iron phosphate is in the range of 3%-10%, which can fully play the role of the carbon source in improving the electrical conductivity of the material, improving the cycle stability and rate performance, while avoiding problems caused by too high or too low carbon content. For example, too high carbon content may result in a decrease in the tap density of the material, affecting the energy density of the battery; too low carbon content may not provide sufficient electrical conductivity, limiting the electrochemical performance of the material.

[0063] In some embodiments, the solid content in the slurry after the second stage of ball milling is 20%-60%.

[0064] In the above embodiments, the sum of the mass of the waste lithium manganate, the lithium source, the iron source, the phosphorus source and the carbon source in the slurry after the second stage of ball milling accounts for 20%-60% of the total mass of the slurry after the second stage of ball milling. A suitable solid content (such as a solid content of 30%, 40% or 50%) can ensure that the prepared lithium manganese iron phosphate material has good electrochemical performance. Within this range, through the synergistic effect of ball milling and sintering, uniform and fine particles can be formed, the specific surface area and lithium ion diffusion rate of the material are improved, and thus the charge and discharge performance, rate performance and cycle life of the material are improved.

[0065] A solid content lower than 20% causes the contact between the particles in the slurry to be loose, which is not conducive to the diffusion and migration of atoms and ions, and reduces the crystal structure and electrochemical performance of the material. In addition, a solid content higher than 60% makes it difficult for gas to escape from the material during sintering, increasing the sintering defects caused by the residual gas, and affecting the density and uniformity of the sintered product.

[0066] In some embodiments, the solvent includes one or a combination of both of water and ethanol.

[0067] The solvent in the slurry after the second stage of ball milling is 40%-80%.

[0068] In the above embodiments, the water can be pure water, which is the most common solvent, and the use of pure water as a solvent can significantly reduce the raw material cost in the preparation process of lithium manganese iron phosphate. Ethanol has high volatility and can be quickly volatilized during the drying of the slurry after ball milling, thereby shortening the drying time and improving the production efficiency. At the same time, ethanol does not leave impurities in the product after volatilization, which is conducive to ensuring the purity of the lithium manganese iron phosphate product.

[0069] The solvent content in the slurry after the second stage of ball milling is in the range of 40%-80%, which can balance the factors such as the fluidity, solid content and ball milling efficiency of the slurry, and ensure the stability and controllability of the ball milling process. At the same time, a suitable solvent content is conducive to the subsequent drying and sintering processes, and can prepare a lithium manganese iron phosphate material with a good crystal structure, uniform particle distribution and excellent electrochemical performance, thereby improving the quality and consistency of the product.

[0070] In some embodiments, the rotation speed of the first stage of ball milling is 200-600 r / min, and the rotation speed of the second stage of ball milling is 200-600 r / min.

[0071] The vacuum drying time is 10-30 h, and the temperature is 60-100°C.

[0072] The screen mesh size of the screening is 50-200 mesh.

[0073] In the above embodiment, the first stage of ball milling has a rotational speed of 200-600 r / min for 120-360 minutes, and the second stage has a rotational speed of 200-600 r / min for 120-480 minutes. This ensures both ball milling efficiency and product quality. However, a rotational speed that is too low may result in excessively long ball milling times and low production efficiency; a rotational speed that is too high may generate excessive heat, causing changes in raw material properties or equipment overheating.

[0074] In the above embodiment, a drying time of 10-30 hours and a drying temperature of 60-100°C achieve a balance between drying effect and cost. However, a drying time that is too short may result in solvent residue, affecting product quality; a drying time that is too long increases energy consumption and production cycle time, thereby increasing production costs.

[0075] In the above embodiment, the sieve mesh size can be 100 mesh to achieve an optimal balance between product performance and process cost. However, a sieve mesh size that is too fine will increase the difficulty and cost of screening, and may also cause some qualified particles to be screened out, reducing product yield; while a sieve mesh size that is too coarse may not effectively control the particle size of the product, affecting product performance.

[0076] In some embodiments, the nitrogen atmosphere has a nitrogen flow rate of 150-650 mL / min. A nitrogen protective atmosphere can be initially formed around the sintering reaction system. This atmosphere can isolate harmful components in the air, such as oxygen and moisture, and prevent unwanted chemical reactions between the raw materials or intermediates and these components. For example, oxygen may cause oxidation of metal elements in the material, changing the chemical composition and structure of the material, thereby affecting the electrochemical properties of the final product.

[0077] In some embodiments, the multi-stage high-temperature sintering includes a first-stage sintering and a second-stage sintering. The sintering temperature of the first-stage sintering is 300°C-550°C, and the sintering temperature of the second-stage sintering is 600°C-900°C.

[0078] In the above embodiment, the first stage of sintering is performed at a temperature of 300°C to 550°C for 3-6 hours, which allows the organic carbon source to decompose and volatilize. Within this temperature range, the chemical bonds in the organic molecules gradually break, generating small molecules of gas (such as carbon dioxide, water vapor, carbon monoxide, etc.) and residual carbon. These gases escape from the material, preventing the rapid decomposition of the organic matter during the subsequent high-temperature sintering process, which would produce large amounts of gas and cause structural damage, thereby ensuring the density and integrity of the material.

[0079] The sintering temperature of the second stage sintering is 600-900℃, and the holding time is 7-15h, which provides sufficient energy for the growth of lithium manganese iron phosphate crystals. In this temperature range, atoms have higher activity and can migrate and recombine more quickly, allowing the crystals to grow further and improve. The complete crystal structure is conducive to the embedding and extraction of lithium ions in the material, improving the charge and discharge capacity and rate performance of the material. At the same time, high-temperature sintering can also eliminate defects and dislocations in the crystal, improve the order and crystallinity of the crystal, and further improve the electrochemical performance of the material.

[0080] Through the synergistic effect of the first stage and the second stage sintering, lithium manganese iron phosphate material with good crystal structure, uniform element distribution and excellent electrical conductivity can be prepared. The lithium manganese iron phosphate material has high charge and discharge capacity, good rate performance and cycle stability, which can meet the needs of different application scenarios, such as electric vehicles, energy storage devices, etc.

[0081] In some embodiments, the heating rate of the first stage sintering and the second stage sintering is 3-8℃ / min.

[0082] In the above embodiments, the heating rate range of 3-8℃ / min can ensure that the material will not produce defects during sintering due to rapid heating, affecting its electrochemical performance (such as charge and discharge capacity, rate performance, cycle stability, etc.), and can also improve production efficiency to a certain extent and reduce production cost. By reasonably selecting the heating rate, a best balance point between material performance and production efficiency can be found.

[0083] In one embodiment, the lithium manganese iron phosphate is prepared according to the chemical formula LiFe x Mn 1-x PO4, the chemical formula LiFe x Mn 1-x PO4, x can be 0.1, 0.2, 0.3, 0.5, 0.7, 0.8 or 0.9, and the lithium compound, lithium manganate, iron compound and phosphide are weighed and mixed in a ball mill jar. The ball milling time is 120-360min, and the rotation speed is 200-600r / min. Then pure water is added to the ball mill jar, and the same rotation speed is continued for 120-480min. After vacuum drying at 60-100℃, it is sieved with a 100 mesh sieve. Finally, it is held at a temperature of 300-550℃ for 3-6h, and held at a temperature of 600-900℃ for 7-15h, with a heating rate of 5℃ / min. After cooling in the furnace, it is sieved with a 200 mesh sieve to obtain lithium manganese iron phosphate.

[0084] The present application provides a lithium manganese iron phosphate prepared by the above method.

[0085] In the above embodiment, the waste lithium manganate, lithium source, iron source, phosphorus source and carbon source are mixed to perform first stage ball milling, then a solvent is added to perform second stage ball milling; the slurry after the second stage ball milling is vacuum dried and sieved; the sieved material is subjected to multi-stage high-temperature sintering under a nitrogen atmosphere; wherein the waste lithium manganate includes at least one of lithium manganate waste in the lithium manganate process, lithium manganate recovered from the tab waste in the battery manufacturing process, and lithium manganate recovered from the tab stripping of the waste battery. The use of waste lithium manganate reduces the production cost of lithium manganese iron phosphate, the carbon content in the lithium manganese iron phosphate is 1.0%-4.0%, and the prepared lithium manganese iron phosphate has stable electrochemical performance, which is conducive to large-scale commercial application.

[0086] The method for preparing lithium manganese iron phosphate provided by the embodiment of the application is described in detail below through examples and control examples.

[0087] The lithium manganese iron phosphate and the battery of the examples and the control examples are prepared in the following manner:

[0088] Preparation of lithium manganese iron phosphate positive electrode material: lithium compound, lithium manganate, iron compound and phosphorus compound are weighed and ball-mixed, the ball-milling time is 200 min, and the rotation speed is 400 r / min; then pure water is added in the ball-milling tank, and the ball-milling is continued at the same rotation speed for 300 min; after vacuum drying at 80℃, sieving is performed with a 100-mesh sieve; the temperature is kept at 400℃ for 6h, and the temperature is kept at 800℃ for 12h, the temperature rising rate is 5℃ / min; after cooling in the furnace, sieving is performed with a 200-mesh sieve.

[0089] Preparation of the battery: the prepared positive electrode material, acetylene black (AB) and binder (PVDF) are dried in a drying box at 60℃ for 2 hours, then uniformly mixed according to the mass ratio of 8:1:1, and an appropriate amount of N-methyl pyrrolidone (NMP) is added to fully stir into a uniform paste, then the slurry is uniformly coated on an aluminum foil, and finally placed in a 90℃ vacuum drying box for drying for 12h, to obtain a positive electrode tab.

[0090] In an argon-filled hand-packed box, the positive electrode tab, lithium tab, separator (Celgard2325) and electrolyte (1mol / L LiPF6 / EC / DMC / EMC / VC) are assembled into a CR2016 type button cell, and a sealing machine is used for sealing. - 1 LiPF6 / EC / DMC / EMC / VC) is assembled into a CR2016 type button cell, and a sealing machine is used for sealing.

[0091] Rate, cycle test was performed on the battery: after the button cell was placed at room temperature for 12 h, the charge-discharge test was performed by using Shenzhen Xinwei battery test system (CT4008W), the room temperature was 25℃, the charge / discharge cut-off voltage was 2.0-4.5V (first charged to 4.5V, then discharged to 2.0V, and so on), first, the activation was performed at a low rate of 0.2C current density for 5 weeks, and then the cycle performance test was performed at 1C to obtain the capacity retention rate of the material.

[0092] The lithium source of the examples and the control example was lithium carbonate, the examples 1-4 and the control example was 12.1wt%, the example 5 was 12.9wt%, the example 6 was 13.8wt%, the iron source was iron phosphate, 29.2wt%, the phosphorus source was lithium dihydrogen phosphate, 36.2wt% (mass ratio relative to the total mass of raw materials), and the solvent was pure water, and the mass of the pure water was 1.5 times the sum of the mass of the raw materials and the carbon source.

[0093] Table 1 specific parameters of the examples and the control example

[0094]

[0095] Wherein, the waste old lithium manganate 1 was lithium manganate waste in the lithium manganate process, the waste old lithium manganate 2 was lithium manganate recovered from the pole piece waste in the battery manufacturing process, the waste old lithium manganate 3 was lithium manganate recovered from the pole piece stripping of the waste battery, the content of the waste old lithium manganate 1, the waste old lithium manganate 2 and the waste old lithium manganate 3 was the waste old lithium manganate calculated according to the IPC test result of the recovered material (the actual content of lithium manganate in the waste old lithium manganate and the total mass percentage of lithium carbonate, iron phosphate and lithium dihydrogen phosphate was 100%), the PEG was polyethylene glycol, the mass of each polyvinyl alcohol in the carbon source and the PEG was the same, and the mass ratio of the carbon source was the mass ratio relative to the raw materials.

[0096] In combination with Table 1 and Figures 1 to 3 It can be seen that the high-temperature cycle performance and the capacity of the battery provided by the examples of the present application are better than the room temperature; when 3wt% glucose is introduced in the example 2 of the present application, the first week high-temperature (55℃) cycle capacity reaches 151.58mAh / g, and the capacity retention rate after 50 weeks of cycle is 101%, which reflects that the waste old lithium manganate releases more capacity after high-temperature cycle.

[0097] Although some specific embodiments of the present application have been described in detail by examples, those skilled in the art should understand that the above examples are only for illustration, but not for limiting the scope of the present application. Those skilled in the art should understand that the above examples can be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide, characterized in that: include: The waste lithium manganese oxide, lithium source, iron source, phosphorus source and carbon source are mixed and subjected to the first stage ball milling, and then a solvent is added to carry out the second stage ball milling; The slurry after the second stage of ball milling is vacuum dried and sieved; The screened materials are subjected to multi-stage high-temperature sintering in a nitrogen atmosphere; The waste lithium manganese oxide includes at least one of lithium manganese oxide waste in the lithium manganese oxide process, lithium manganese oxide recovered from pole piece waste in the battery manufacturing process, and lithium manganese oxide recovered from pole piece stripping materials of waste batteries.

2. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide according to claim 1, characterized in that: The lithium source includes one or more of lithium carbonate, lithium fluoride and lithium hydroxide, the iron source includes one or more of iron phosphate, iron oxalate, iron powder and iron oxide, and the phosphorus source includes one or a combination of ammonium dihydrogen phosphate and lithium dihydrogen phosphate.

3. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide according to claim 1, characterized in that: The carbon source includes one or more of polyvinyl alcohol, polyethylene glycol and glucose; The carbon content in the lithium manganese iron phosphate is 1.0%-4.0%.

4. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide according to claim 1, characterized in that: The solid content of the slurry after the second stage ball milling is 20%-60%.

5. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide according to claim 1, characterized in that: The solvent includes one or a combination of water and ethanol; The solvent content in the slurry after the second stage ball milling is 40%-80%.

6. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide according to claim 1, characterized in that: The rotation speed of the ball milling in the first stage is 200-600 r / min, and the rotation speed of the ball milling in the second stage is 200-600 r / min; The vacuum drying time is 10-30h and the temperature is 60-100°C; The mesh size of the screening sieve is 50-200 mesh.

7. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide according to claim 1, characterized in that: The nitrogen gas flow rate of the nitrogen atmosphere is 150-650 mL / min.

8. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganese oxide according to claim 1, characterized in that: The multi-stage high-temperature sintering includes a first-stage sintering and a second-stage sintering. The sintering temperature of the first-stage sintering is 300°C-550°C, and the sintering temperature of the second-stage sintering is 600°C-900°C.

9. The method for preparing lithium iron manganese phosphate by regenerating waste lithium manganate according to claim 8, characterized in that: The heating rates of the first-stage sintering and the second-stage sintering are 3-8° C. / min.

10. A lithium manganese iron phosphate, characterized in that: The lithium manganese iron phosphate is prepared by the method for preparing lithium manganese iron phosphate according to any one of claims 1 to 9.

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