Lithium manganese iron phosphate materials and their preparation methods, positive electrode active materials, positive electrode sheets, batteries and electrical equipment

Abstract

This application provides a lithium manganese iron phosphate material and its preparation method, a positive electrode active material, a positive electrode sheet, a battery, and an electrical device, belonging to the field of battery technology. The preparation method of the lithium manganese iron phosphate material includes: sequentially grinding and drying a liquid phase containing a lithium source, a manganese source, an iron source, a phosphorus source, and a carbon source to form granules, and then sintering under an inert atmosphere to form a lithium manganese iron phosphate material with a carbon layer coated on its surface; wherein the carbon source is a non-polar carbon-containing compound. In the preparation method of the lithium manganese iron phosphate material provided in this application, the non-polar carbon-containing compound not only inhibits the agglomeration of the liquid phase containing the lithium source, manganese source, iron source, and phosphorus source, but also simultaneously acts as a carbon source to coat the lithium manganese iron phosphate, thereby simultaneously improving the compaction density, conductivity, and specific capacity of the obtained lithium manganese iron phosphate material, and simultaneously improving the cycle performance and rate performance of the lithium-ion battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a lithium manganese iron phosphate material and its preparation method, a positive electrode active material, a positive electrode sheet, a battery, and an electrical device. Background Technology

[0002] Lithium iron manganese phosphate (LMP) is a commonly used positive electrode active material in lithium-ion batteries, possessing advantages such as a specific capacity close to the theoretical specific capacity, a high voltage plateau, and high energy density. However, LMP also has disadvantages such as low compaction density, low conductivity, and low specific capacity. Furthermore, using LMP as a positive electrode active material can lead to lower cycle performance and lower rate performance in lithium-ion batteries. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a lithium manganese iron phosphate material and its preparation method, a positive electrode active material, a positive electrode sheet, a battery, and an electrical device, so as to simultaneously improve the compaction density, specific capacity, and conductivity of the lithium manganese iron phosphate material, and simultaneously improve the cycle performance and rate performance of the lithium-ion battery prepared using the lithium manganese iron phosphate material.

[0004] In a first aspect, this application provides a method for preparing lithium manganese iron phosphate material, the method comprising: sequentially grinding, drying and sintering a liquid phase containing a lithium source, a manganese source, an iron source, a phosphorus source and a carbon source under an inert atmosphere to form a lithium manganese iron phosphate material with a carbon layer on its surface; wherein the carbon source is a nonpolar carbon-containing compound.

[0005] In the preparation method of lithium manganese iron phosphate material provided in this application, the non-polar carbon-containing compound not only inhibits the agglomeration of the liquid phase containing lithium, manganese, iron, and phosphorus sources, but also simultaneously coats the lithium manganese iron phosphate to form a carbon layer on the surface of the lithium manganese iron phosphate. The liquid phase containing lithium, manganese, iron, phosphorus, and carbon sources is less prone to agglomeration, which facilitates the thorough refinement of particles in the liquid phase during grinding. This, in turn, facilitates the formation of a more uniformly dispersed and finely sized granular system after drying. After sintering under an inert atmosphere, the carbon source can form a more uniform and fully coated carbon layer on the surface of the lithium manganese iron phosphate particles. Furthermore, the obtained lithium manganese iron phosphate material generally exhibits spherical or near-spherical particles with relatively uniform particle dispersion. This not only improves the compaction density, conductivity, and specific capacity of the obtained lithium manganese iron phosphate material, but also enhances the cycle performance and rate performance of lithium-ion batteries made using this lithium manganese iron phosphate material. Furthermore, the preparation method of this application does not require an additional grinding and refining step between the drying and sintering steps. The preparation method is simple, easy to implement, low in cost, and suitable for industrial production.

[0006] In some embodiments, the carbon source is a water-insoluble carbon-containing compound; or / and, the carbon source is a carbon-containing compound that can form hard carbon after sintering; or / and, the non-polar carbon-containing compound includes carbon-containing polymers. Using a water-insoluble carbon-containing compound as the carbon source is beneficial for further suppressing the agglomeration of the liquid phase containing lithium, manganese, iron, and phosphorus sources, thereby further improving the compaction density, specific capacity, and conductivity of the lithium manganese iron phosphate material, and further improving the cycle performance and rate performance of the lithium-ion battery. Using a carbon-containing compound that can form hard carbon after sintering, with the hard carbon layer coating the lithium manganese iron phosphate, is beneficial for further improving the compaction density, specific capacity, and conductivity of the lithium manganese iron phosphate material, and further improving the cycle performance and rate performance of the lithium-ion battery. Using a non-polar carbon-containing compound, including carbon-containing polymers, is beneficial for further improving the compaction density, specific capacity, and conductivity of the lithium manganese iron phosphate material, and further improving the cycle performance and rate performance of the lithium-ion battery.

[0007] In some embodiments, the carbon source includes at least one selected from polyethylene, polypropylene, polystyrene, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, linear starch, amylopectin, cyclodextrin, polyoxymethylene, and polyaniline. The selection of carbon sources from these materials not only suppresses agglomeration in liquid phases containing lithium, manganese, iron, and phosphorus sources, but also ensures that these materials, after sintering under an inert atmosphere, produce hard carbon. This is beneficial for simultaneously improving the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate materials, and further enhancing the cycle performance and rate performance of lithium-ion batteries.

[0008] In some embodiments, the carbon source includes at least one selected from polypropylene, cyclodextrin, polyvinylidene fluoride, polytetrafluoroethylene, and polystyrene. Using a carbon source selected from these substances is beneficial for simultaneously improving the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate materials, and further enhancing the cycle performance and rate performance of lithium-ion batteries.

[0009] In some embodiments, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is ≥1:1. This molar ratio allows the lithium-ion battery to exhibit better cycle performance and rate capability.

[0010] In some embodiments, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is (1 to 1.04):1. This molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is beneficial for further improving the cycle performance and rate performance of lithium-ion batteries.

[0011] In some embodiments, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is >1:1 and ≤1.04:1. This molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is beneficial for further improving the cycle performance and rate performance of lithium-ion batteries.

[0012] In some embodiments, the molar ratio of lithium in the lithium source, manganese in the manganese source, iron in the iron source, and phosphorus in the phosphorus source is (1–1.04):(0.3–0.7):(0.3–0.7):1. This ratio of lithium in the lithium source, manganese in the manganese source, iron in the iron source, and phosphorus in the phosphorus source is beneficial for balancing the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate material. It results in higher compaction density, higher specific capacity, and higher conductivity for the lithium manganese iron phosphate material, and also gives the lithium-ion battery better cycle performance and rate performance.

[0013] In some embodiments, the mass ratio of the carbon source to the total mass of the lithium, manganese, iron, and phosphorus sources is (0.012–0.024):1. A mass ratio of the carbon source to the total mass of the lithium, manganese, iron, and phosphorus sources within this range is beneficial for fully utilizing the performance of the non-polar carbon-containing compound (i.e., the carbon source). This results in lithium manganese iron phosphate materials that are generally spherical or near-spherical particles with relatively uniform particle dispersion. Furthermore, the thickness of the carbon layer coating on the surface of the lithium manganese iron phosphate is within a suitable range, which helps to balance the compaction density, specific capacity, and conductivity of the lithium manganese iron phosphate material. This results in higher compaction density, higher specific capacity, and higher conductivity in the lithium manganese iron phosphate material, and also gives the lithium-ion battery better cycle performance and rate performance.

[0014] In some embodiments, the grinding step includes grinding the liquid phase until the particle size of the solid particles in the liquid phase is 0.1 μm to 0.5 μm. This method allows for sufficient refinement of the particles in the liquid phase during grinding, which is beneficial for forming a more uniformly dispersed and finely sized granular system after drying. This improves the specific capacity and conductivity of lithium manganese iron phosphate material, and also gives the lithium manganese iron phosphate material a higher compaction density. Consequently, lithium-ion batteries prepared using this lithium manganese iron phosphate material exhibit higher cycle performance and higher rate performance.

[0015] In some embodiments, the sintering temperature is 670°C to 760°C. A sintering temperature within this range is beneficial for the raw materials to fully react and form lithium manganese iron phosphate particles during the sintering process under an inert atmosphere, and for the carbon source to be fully converted into a carbon layer. This results in the prepared lithium manganese iron phosphate material having higher compaction density, higher specific capacity, and higher electrical conductivity, leading to lithium-ion batteries prepared using this material exhibiting higher cycle performance and higher rate performance.

[0016] In some embodiments, the sintering time is 8h to 16h. A sintering time within the above range is beneficial for the raw materials to fully react and form lithium manganese iron phosphate particles during the sintering process under an inert atmosphere, and for the carbon source to be fully converted into a carbon layer. This results in the prepared lithium manganese iron phosphate material having higher compaction density, higher specific capacity, and higher conductivity, and thus the lithium-ion battery prepared using this lithium manganese iron phosphate material has higher cycle performance and higher rate performance.

[0017] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium dihydrogen phosphate, and lithium phosphate.

[0018] In some embodiments, the manganese source includes at least one of manganese sulfate, manganese chloride, manganese oxalate, manganese oxide, and manganese acetate.

[0019] In some embodiments, the iron source includes at least one of ferrous oxalate, ferric oxide, ferrous oxide, ferrous sulfate, ferrous acetate, and ferrous chloride.

[0020] In some embodiments, the phosphorus source includes at least one of lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and lithium phosphate.

[0021] In some embodiments, the drying method is spray drying. Spray drying facilitates the more complete conversion of the liquid phase containing lithium, manganese, iron, phosphorus, and carbon sources into a particulate system after drying. This method helps to balance the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate material, resulting in higher compaction density, higher specific capacity, and higher conductivity of the lithium manganese iron phosphate material, and giving the lithium-ion battery better cycle performance and rate performance.

[0022] Secondly, this application provides a lithium manganese iron phosphate material, which is prepared by the method for preparing lithium manganese iron phosphate material as provided in any of the first aspects above.

[0023] The lithium manganese iron phosphate material provided in this application is prepared by the method of preparing lithium manganese iron phosphate material provided in any of the first aspects above. Therefore, the lithium manganese iron phosphate material provided in this application has both high compaction density and high electrical conductivity, and the lithium-ion battery prepared using the lithium manganese iron phosphate material can also have high cycle performance and high rate performance.

[0024] Thirdly, this application provides a positive electrode active material, which includes the lithium manganese iron phosphate material provided in the second aspect above.

[0025] The positive electrode active material provided in this application contains the aforementioned lithium iron phosphate material, which has both high compaction density, high specific capacity, and high conductivity, thus improving the cycle performance and rate performance of lithium-ion batteries.

[0026] Fourthly, this application provides a positive electrode sheet, which includes a positive current collector and a positive active layer covering at least one surface of the positive current collector in the thickness direction; wherein the positive active layer includes the positive active material provided in the third aspect above.

[0027] Fifthly, this application provides a battery, which includes the positive electrode provided in the fourth aspect above.

[0028] Sixthly, this application provides an electrical device, which includes the battery provided in the fifth aspect above.

[0029] 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

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0031] Figure 1 The diagram shows the structural features of a vehicle provided in some embodiments of this application.

[0032] Figure 2 This is an exploded structural diagram of a battery provided in some embodiments of this application.

[0033] Figure 3 The diagram shows the structure of a single battery cell provided in some embodiments of this application.

[0034] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application.

[0035] Figure 5 This is a schematic diagram of the structure of an electrode assembly provided in some embodiments of this application.

[0036] Figure 6 This is a SEM characterization image of the lithium manganese iron phosphate material prepared in Example 1 of this application.

[0037] Figure 7 This is a SEM characterization image of the lithium manganese iron phosphate material prepared in Comparative Example 1 of this application.

[0038] Figure 8 This is a SEM characterization image of the lithium manganese iron phosphate material prepared in Comparative Example 4 of this application.

[0039] Icons: 1000 - Vehicle; 100 - Battery; 10 - Housing; 11 - Storage space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Casing; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 231 - Positive electrode; 232 - Negative electrode; 233 - Separator; 24 - Current collector; 25 - Insulation protection component; 200 - Controller; 300 - Motor. Detailed Implementation

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0047] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0048] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0049] Power batteries can be lithium-ion batteries. During the charging process, lithium ions are released from the positive electrode active material, transported through the electrolyte, pass through the separator, and embed into the negative electrode active layer. Lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMP) are both commonly used positive electrode active materials in lithium-ion batteries. Both LFP and LMP have an olivine structure; compared to LFP, LMP has a similar specific capacity, but its voltage plateau (approximately 3.8V–4.1V) is higher than that of LFP (approximately 3.4V). LMP's theoretical energy density is also 10%–20% higher than that of LFP, and its low-temperature performance is relatively better.

[0050] However, lithium manganese iron phosphate also has some drawbacks. For example, lithium manganese iron phosphate has lower conductivity than lithium iron phosphate, lower compaction density, and relatively lower cycle performance and rate performance of lithium-ion batteries made with lithium manganese iron phosphate.

[0051] Based on the above considerations, in order to simultaneously improve the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate material, and to improve the cycle performance and rate performance of lithium-ion batteries prepared using lithium manganese iron phosphate material, this application designs a method for preparing lithium manganese iron phosphate material. The preparation method includes: sequentially grinding, drying, and sintering a liquid phase containing lithium source, manganese source, iron source, phosphorus source, and carbon source under an inert atmosphere to form lithium manganese iron phosphate material with a carbon layer coated on the surface; wherein, the carbon source is a non-polar carbon-containing compound.

[0052] In the preparation method of lithium manganese iron phosphate material provided in this application, the non-polar carbon-containing compound can not only inhibit the agglomeration of the liquid phase containing lithium source, manganese source, iron source and phosphorus source, but also coat the lithium manganese iron phosphate at the same time to form a carbon layer coated on the surface of lithium manganese iron phosphate.

[0053] During the grinding process of a liquid phase containing lithium, manganese, iron, and phosphorus sources, the presence of non-polar carbon-containing compounds (i.e., carbon sources) makes it less likely for the liquid phase containing lithium, manganese, iron, phosphorus, and carbon sources to agglomerate. This facilitates the thorough refinement of particles in the liquid phase during grinding, resulting in a more uniformly dispersed and finely sized granular system after drying. Consequently, the resulting lithium manganese iron phosphate material generally exhibits spherical or near-spherical particles with relatively uniform particle dispersion.

[0054] During the sintering process under an inert atmosphere, the presence of a carbon source can also coat the lithium manganese iron phosphate particles, forming a more uniform and sufficient carbon layer on the surface of the lithium manganese iron phosphate particles.

[0055] Therefore, the preparation method of lithium manganese iron phosphate material provided in this application can not only improve the compaction density, specific capacity, and conductivity of the obtained lithium manganese iron phosphate material, but also improve the cycle performance and rate performance of lithium-ion batteries prepared using this lithium manganese iron phosphate material. Furthermore, this preparation method does not require an additional grinding and refining step between the drying and sintering steps, making it simple, easy to implement, low-cost, and suitable for industrial production.

[0056] This lithium manganese iron phosphate material is used to prepare positive electrode sheets, which can be assembled into batteries. These batteries can be individual cells, modules, or battery packs, and can be used, but are not limited to, in electrical equipment such as vehicles, ships, or aircraft. The power system of such electrical equipment can be composed using batteries disclosed in this application, which helps to improve the battery's cycle performance and lifespan at higher temperatures.

[0057] This application provides an electrical device that uses a battery as its power source. The electrical device can be a vehicle, mobile phone, portable device, laptop, ship, spacecraft, electric toy, or power tool, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical device.

[0058] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0059] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. A battery 100 is disposed inside the vehicle 1000, and the battery 100 may be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000.

[0060] The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, for the power needs of the vehicle 1000 during startup, navigation and driving.

[0061] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0062] Figure 2 This is an exploded structural diagram of the battery 100 provided in some embodiments of this application. Please refer to... Figure 2 The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10.

[0063] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0064] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20. When the opening side of the second part 13 covers the opening side of the first part 12, a housing 10 with an accommodating space 11 is formed. Of course, as... Figure 2 As shown, the first part 12 can also be a hollow structure with an opening on one side, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0065] In battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed manner to form a whole, which is then housed in the housing 10. Battery cells 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 An example is shown where the battery cell 20 is square.

[0066] In some embodiments, the battery 100 may also include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0067] Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application. Figure 4 Exploded views of a battery cell 20 provided for some embodiments of this application. Please refer to... Figure 3 and Figure 4 The battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is housed within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0068] The shape of the outer casing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the outer casing 21 can be a cuboid structure. Figure 3 and Figure 4 An example is shown where the housing 21 and electrode assembly 23 are square.

[0069] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0070] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0071] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used to electrically connect to the positive and negative electrode tabs of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used to electrically connect to the positive electrode tab of the electrode assembly 23; and the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, used to electrically connect to the negative electrode tab of the electrode assembly 23.

[0072] In some embodiments, such as Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming a single integral structure to maintain the structural stability of the electrode assembly 23. The electrode assembly 23 may be a wound electrode assembly or a stacked electrode assembly; the embodiments of this application are not limited to these.

[0073] Figure 5 For schematic diagrams of the electrode assemblies provided in some embodiments of this application, please refer to [link / reference]. Figure 5 The electrode assembly 23 includes a positive electrode 231, a negative electrode 232, and a separator 233. The separator 233 is disposed between the positive electrode 231 and the negative electrode 232. The electrolyte is located in the installation space and fills the gaps in the electrode assembly 23.

[0074] This application does not impose any particular restrictions on the separator, negative electrode plate, and electrolyte.

[0075] For the separator membrane, the separator membrane can be a PP (polypropylene) porous membrane, a PE (polyethylene) porous membrane, a polyimide porous membrane, or a porous membrane formed by a combination of various polymers.

[0076] For the negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer covering at least one surface of the negative current collector in the thickness direction. This application does not impose any particular limitation on the thickness of the negative current collector and the negative active layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative current collector is 4 μm to 12 μm, and the thickness of the negative active layer on one side of the negative current collector is 30 μm to 130 μm.

[0077] The material of the negative electrode current collector may include aluminum foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc.; wherein, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, and poly(p-phenylene terephthalamide).

[0078] The negative electrode active material in the negative electrode active layer includes graphite, coke, etc., or the negative electrode active material in the negative electrode active layer includes elemental lithium, or an alloy formed by lithium with other metal elements or non-metal elements. Among them, the metal elements include tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), foil (Pt), etc., and the non-metal elements include boron (B), carbon (C), silicon (Si), etc.

[0079] The conductive agent in the negative electrode active layer may include, but is not limited to, carbon materials, metals or conductive polymers. Carbon materials may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, natural graphite, artificial graphite, flake graphite, carbon dots or graphene, etc. Metals may include metal powders or metal fibers such as copper, iron, and aluminum, and conductive polymers may include at least one of polythiophene, polypyrrole, polyaniline, polyphenylene and polyphenylene ethylene.

[0080] The binder in the negative electrode active layer may include, but is not limited to, at least one of the following: polyacrylol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylpyrrolidone, polyethylene, polypropylene, epoxy resin, nylon, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral, waterborne acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na).

[0081] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the aforementioned negative electrode active material, conductive agent, and binder are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0082] The electrolyte may include a sodium salt and a non-aqueous solvent, or a lithium salt and a non-aqueous solvent. The sodium salt may include at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, or Na(CH3)C6H4SO3. This application does not impose any particular limitation on the concentration of the sodium salt in the electrolyte, as long as the purpose of this application is achieved. The lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the aforementioned non-aqueous solvents, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents; the aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds; the aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC); the aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC); the fluorocarbonate compounds may include, but are not limited to, fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, and 1,1,2-trifluoroethylene carbonate. At least one of the following: 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoro-methylethylene carbonate; the above carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valproic acid lactone, or caprolactone; the above ether compounds The substances may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran; the other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0083] For the positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive active layer covering at least one surface of the positive current collector in the thickness direction; the material of the positive current collector may include aluminum foil, aluminum foam, aluminum composite current collector (with a polymer support layer in the middle, and both surfaces of the support layer having aluminum metal layers), nickel foil, nickel foam, etc. The binder in the positive active layer is selected from at least one of vinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer; the dispersant in the positive active layer is selected from polyvinylpyrrolidone, etc.; the conductive agent in the positive active layer is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, graphene, activated carbon, graphite sheets, graphite particles, and mesophase carbon microspheres.

[0084] In this application, the positive electrode active material in the positive electrode active layer includes lithium manganese iron phosphate material. The preparation method of lithium manganese iron phosphate material includes: sequentially grinding, drying and sintering a liquid phase containing lithium source, manganese source, iron source, phosphorus source and carbon source under an inert atmosphere to form lithium manganese iron phosphate material with a carbon layer on the surface; the carbon source is a non-polar carbon-containing compound.

[0085] Lithium, manganese, iron, and phosphorus sources are the raw materials for forming lithium manganese iron phosphate. These sources can be sintered under an inert atmosphere to form lithium manganese iron phosphate. This application does not limit the lithium, manganese, iron, and phosphorus sources used in the formation of lithium manganese iron phosphate.

[0086] "Lithium manganese iron phosphate material with a carbon layer on its surface" refers to a material in which a carbon layer at least partially covers the surface of lithium manganese iron phosphate particles. This can mean that the entire surface of the lithium manganese iron phosphate particles is covered by a carbon layer, or that only a portion of the surface of the lithium manganese iron phosphate particles is covered by a carbon layer.

[0087] "Nonpolar carbon-containing compounds" refers to compounds that contain carbon and are nonpolar molecules.

[0088] In the preparation method of lithium manganese iron phosphate material provided in this application, the non-polar carbon-containing compound not only inhibits the agglomeration of the liquid phase containing lithium, manganese, iron, and phosphorus sources, but also simultaneously coats the lithium manganese iron phosphate to form a carbon layer on the surface of the lithium manganese iron phosphate. The liquid phase containing lithium, manganese, iron, phosphorus, and carbon sources is less prone to agglomeration, which facilitates the thorough refinement of particles in the liquid phase during grinding. This, in turn, facilitates the formation of a more uniformly dispersed and finely sized granular system after drying. After sintering under an inert atmosphere, the carbon source can form a more uniform and fully coated carbon layer on the surface of the lithium manganese iron phosphate particles. Furthermore, the obtained lithium manganese iron phosphate material generally exhibits spherical or near-spherical particles with relatively uniform particle dispersion. This not only improves the compaction density, specific capacity, and conductivity of the obtained lithium manganese iron phosphate material, but also enhances the cycle performance and rate performance of lithium-ion batteries prepared using this lithium manganese iron phosphate material.

[0089] Furthermore, the preparation method of this application does not require an additional grinding and refining step between the drying and sintering steps. The preparation method is simple, easy to implement, low in cost, and suitable for industrial production.

[0090] In some embodiments, the carbon source is a water-insoluble carbon-containing compound. This is beneficial for further suppressing the agglomeration of the liquid phase containing lithium, manganese, iron, and phosphorus sources, thereby further improving the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate materials, and further improving the cycle performance and rate performance of lithium-ion batteries.

[0091] In some embodiments, the carbon source is a carbon-containing compound that can form hard carbon after sintering. Compared to soft carbon, hard carbon has a lower expansion rate and greater stability, which allows lithium-ion batteries to have advantages such as high cycle durability, long charge-discharge cycle life, and better safety performance. It also allows the carbon-coated lithium manganese iron phosphate material to have a stable charge-discharge platform and high charge-discharge capacity and efficiency. Furthermore, compared to soft carbon, hard carbon has more disordered structure, higher defect concentration, higher heteroatom content, larger distance between graphite layers, and a more closed pore structure, which is beneficial for Li... + Ions provide more storage sites and diffusion pathways because the hard carbon layer can achieve a better ion migration rate, thus improving the charge and discharge efficiency of lithium-ion batteries. The carbon source is a carbon-containing compound that can form hard carbon after sintering, which is beneficial to further improve the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate materials, and further improve the cycle performance and rate performance of lithium-ion batteries.

[0092] In some embodiments, the nonpolar carbon-containing compound includes a carbon-containing polymer. The polymeric carbon source allows for the formation of a denser carbon layer after sintering in an inert atmosphere, which is beneficial for further improving the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate materials, and further improving the cycle performance and rate performance of lithium-ion batteries.

[0093] In some embodiments, the carbon source includes at least one selected from polyethylene, polypropylene, polystyrene, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, linear starch, amylopectin, cyclodextrin, polyoxymethylene, and polyaniline. The selection of carbon sources from these materials not only suppresses agglomeration in liquid phases containing lithium, manganese, iron, and phosphorus sources, but also ensures that these materials, after sintering under an inert atmosphere, produce hard carbon. This is beneficial for simultaneously improving the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate materials, and further enhancing the cycle performance and rate performance of lithium-ion batteries.

[0094] Furthermore, in some embodiments, the carbon source includes at least one selected from polypropylene, cyclodextrin, polyvinylidene fluoride, polytetrafluoroethylene, and polystyrene. Selecting the carbon source from these substances is beneficial for simultaneously improving the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate materials, and further enhancing the cycle performance and rate performance of lithium-ion batteries.

[0095] It should be noted that nonpolar carbon sources are not limited to the carbon-containing compounds listed above. For example, nonpolar carbon sources can also include phenolic resins, coal tar, petroleum coke, etc.

[0096] In some embodiments, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is ≥1:1, which can enable the lithium-ion battery to have better cycle performance and rate performance.

[0097] Furthermore, in some embodiments, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is (1–1.04):1. This is beneficial for further improving the cycle performance and rate performance of lithium-ion batteries.

[0098] As an example, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source can be any one of 1:1, 1:1.005, 1:1.01, 1:1.015, 1:1.02, 1:1.025, 1:1.03, 1:1.035 and 1:1.04 or any range between the two.

[0099] In some embodiments, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is >1:1 and ≤1.04:1. This is beneficial for further improving the cycle performance and rate performance of lithium-ion batteries.

[0100] In some embodiments, the molar ratio of lithium in the lithium source, manganese in the manganese source, iron in the iron source, and phosphorus in the phosphorus source is (1–1.04):(0.3–0.7):(0.3–0.7):1. This is beneficial for balancing the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate material, resulting in higher compaction density, higher specific capacity, and higher conductivity, and enabling lithium-ion batteries to have better cycle performance and rate performance.

[0101] As an example, the molar ratio of lithium in the lithium source to phosphorus in the phosphorus source can be any value among 1:1, 1:1.005, 1:1.01, 1:1.015, 1:1.02, 1:1.025, 1:1.03, 1:1.035, and 1:1.04, or a range between any two; the molar ratio of manganese in the manganese source to phosphorus in the phosphorus source can be 0.3:1, 0.35:1, 0.4: 1. Any one of the following ratios, or a range between any two: 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, and 0.7:1; the ratio of the molar amount of iron in the iron source to the molar amount of phosphorus in the phosphorus source can be any one of the following ratios, or a range between any two: 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, and 0.7:1.

[0102] It should be noted that, in some embodiments, the molar ratios of lithium in the lithium source, manganese in the manganese source, iron in the iron source, and phosphorus in the phosphorus source can be adjusted according to actual performance requirements.

[0103] In some embodiments, the mass ratio of the carbon source to the total mass of the lithium, manganese, iron, and phosphorus sources is (0.012–0.024):1. This is beneficial for fully utilizing the performance of the non-polar carbon-containing compound (i.e., the carbon source), resulting in lithium manganese iron phosphate materials that are generally spherical or near-spherical particles with relatively uniform particle dispersion. Furthermore, the thickness of the carbon layer coating on the surface of the lithium manganese iron phosphate is within a suitable range, which helps to balance the compaction density, specific capacity, and conductivity of the lithium manganese iron phosphate material. This results in higher compaction density, higher specific capacity, and higher conductivity, and enables the lithium-ion battery to have better cycle performance and rate performance.

[0104] As an example, the ratio of the mass of the carbon source to the total mass of the lithium, manganese, iron, and phosphorus sources can be any one of 0.012:1, 0.015:1, 0.017:1, 0.02:1, 0.022:1, and 0.024:1, or any range between two of them.

[0105] In some embodiments, the grinding step includes grinding the liquid phase until the particle size of the solid particles in the liquid phase is 0.1 μm to 0.5 μm. This allows for sufficient refinement of the particles in the liquid phase during grinding, which is beneficial for forming a more uniformly dispersed and finely sized granular system after drying. This is beneficial for improving the specific capacity and conductivity of lithium manganese iron phosphate material, and also allows the lithium manganese iron phosphate material to have a higher compaction density. Consequently, lithium-ion batteries prepared using this lithium manganese iron phosphate material exhibit higher cycle performance and higher rate performance.

[0106] As an example, the particle size of the solid particles milled into the liquid phase can be any value among 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.4 μm and 0.5 μm or any range between two.

[0107] As an example, the grinding method can be sanding.

[0108] In some embodiments, the sintering temperature is 670°C to 760°C. This facilitates the full reaction of the raw materials during the sintering process under an inert atmosphere to form lithium manganese iron phosphate particles, and the full conversion of the carbon source into a carbon layer. This results in the prepared lithium manganese iron phosphate material having higher compaction density, higher specific capacity, and higher electrical conductivity. Consequently, lithium-ion batteries prepared using this lithium manganese iron phosphate material exhibit higher cycle performance and higher rate performance.

[0109] As an example, the sintering temperature can be any value among 670°C, 690°C, 700°C, 720°C, 750°C, and 760°C, or a range between any two.

[0110] In some embodiments, the sintering time is 8h to 16h. This is beneficial for the raw materials to fully react and form lithium manganese iron phosphate particles during the sintering process under an inert atmosphere, and for the carbon source to be fully converted into a carbon layer. This results in the prepared lithium manganese iron phosphate material having a higher compaction density, higher specific capacity, and higher electrical conductivity. Consequently, lithium-ion batteries prepared using this lithium manganese iron phosphate material have higher cycle performance and higher rate performance.

[0111] As an example, the sintering time can be any value of 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h and 16h or a range between any two.

[0112] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium dihydrogen phosphate, and lithium phosphate.

[0113] As an example, the lithium source is not limited to the substances mentioned above. For example, the lithium source may also include at least one of lithium nitrate, lithium formate, lithium silicate, lithium sulfate, lithium oxalate, lithium octanoate, lithium citrate, lithium salicylate, lithium orthosilicate, lithium permanganate, lithium trifluoroacetate, lithium acetoacetate, lithium difluorophosphate, lithium hexafluorophosphate, lithium benzoate, lithium metaphosphate, lithium pyruvate, lithium acetate, lithium fluoride, lithium bromide, lithium methoxide, lithium ethanol, lithium oxide, lithium nitride, and lithium sulfide.

[0114] In some embodiments, the manganese source includes at least one of manganese sulfate, manganese chloride, manganese oxalate, manganese oxide, and manganese acetate.

[0115] As an example, the manganese source is not limited to the substances mentioned above. For example, the manganese source may also include at least one of manganese carbonate, manganese fluoride, manganese nitride, manganese bromide, manganese carbide, manganese phosphide, potassium permanganate, potassium manganate, manganese nitrate, manganese phosphate, manganese dihydrogen phosphate, manganese pentacarbonyl, manganese decacarbonyl, manganese acetate, manganese acetylacetone, and manganese pyrophosphate.

[0116] In some embodiments, the iron source includes at least one of ferrous oxalate, ferric oxide, ferrous oxide, ferrous sulfate, ferrous acetate, and ferrous chloride.

[0117] As an example, the iron source is not limited to the substances mentioned above. For example, the iron source may also include at least one of ferric hydroxide, ferric phosphate, ferric carbonate, ferrous nitrate, ferrous sulfide, ferrous phosphate, ferrous iodide, ferrous fluoride, ferrous bromide, ferrous acetylacetone, ferrous gluconate, and ferrous acetate.

[0118] In some embodiments, the phosphorus source includes at least one of lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and lithium phosphate.

[0119] As an example, the phosphorus source is not limited to the substances mentioned above. For example, the phosphorus source may also include at least one of sodium pyrophosphate, sodium phosphite, sodium metaphosphate, sodium tripolyphosphate, sodium hexafluorophosphate, ammonium hypophosphite, ammonium polyphosphate, diammonium hydrogen phosphate, ammonium hexafluorophosphate, potassium hypophosphite, potassium pyrophosphate, tripotassium phosphate, potassium phosphite, potassium metaphosphate, and potassium hexafluorophosphate.

[0120] In some embodiments, the drying method is spray drying. Spray drying facilitates the more complete conversion of the liquid phase containing lithium, manganese, iron, phosphorus, and carbon sources into a particulate system after drying. This method helps to balance the compaction density, specific capacity, and conductivity of lithium manganese iron phosphate material, resulting in higher compaction density, higher specific capacity, and higher conductivity of the lithium manganese iron phosphate material, and giving the lithium-ion battery better cycle performance and rate performance.

[0121] It should be noted that in some embodiments, the drying method is not limited to spray drying. For example, the drying method is selected from freeze drying, drum drying or fluidized bed drying, etc., or the drying method is selected from oven drying.

[0122] In some embodiments, the positive electrode active material in the positive electrode active layer may further include other positive electrode active materials, which may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. The modified compounds of the aforementioned positive electrode active materials may be for doping modification, surface coating modification, or doping and surface coating modification of the positive electrode active material. For example, lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. For example, lithium-containing phosphates with an olivine structure may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate and carbon composites, and their modified compounds. As an example, other positive electrode active materials may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, Prussian white, and Prussian blue.

[0123] It should be noted that this application does not limit the preparation method of other positive electrode active materials in the positive electrode active material layer.

[0124] The aforementioned positive electrode active material can be used to prepare positive electrode sheets. Positive electrode sheets can be prepared according to conventional methods in the art. For example, the aforementioned positive electrode active material, conductive agent, and binder are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and the positive electrode sheet is obtained through processes such as drying and cold pressing.

[0125] The positive electrode sheet can be used to prepare the electrode assembly 23, and the electrode assembly can be used to prepare the battery 100, which can be used as a power source for electrical devices.

[0126] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0127] Experimental Example 1

[0128] (1) Preparation of lithium manganese iron phosphate materials:

[0129] Weigh 130.66g of 75wt% phosphoric acid (i.e., phosphorus source) aqueous solution and add it to a stirred tank. Then add 37.13g of 99.5wt% lithium carbonate (i.e. lithium source) solid to the stirred tank and stir until homogeneous to obtain a phosphorus-lithium source solution.

[0130] 72.31 g of ferrous oxalate (i.e., iron source), 107.93 g of manganese oxalate (i.e., manganese source), and 6.2 g of polyvinylidene fluoride (i.e., carbon source) were added to the lithium phosphate source solution. The solution was then milled until the particle size of the solid particles in the liquid phase was about 0.3 μm to obtain the precursor solution.

[0131] After spray drying the precursor solution, it was sintered at 720°C for 12 hours under nitrogen protection to obtain lithium manganese iron phosphate material.

[0132] The differences in the preparation parameters of lithium manganese iron phosphate materials are detailed in Table 1.

[0133] (2) Preparation of positive electrode sheet:

[0134] Lithium manganese iron phosphate material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 92:2.5:5.5 were mixed, and N-methylpyrrolidone (NMP) solvent was added and stirred until the system was homogeneous. After grinding for 10 minutes, a positive electrode slurry with a solid content of 50 wt% was prepared. The specific parameters of the positive electrode active material are detailed in Table 1.

[0135] The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil (thickness of 6μm) and dried at 85℃ for 4h. After cold pressing, the foil was trimmed and cut into pieces. It was then dried under vacuum at 85℃ for 4h to obtain the positive electrode sheet, wherein the thickness of the positive electrode active material layer on one side was 200μm.

[0136] (3) Preparation of negative electrode sheet:

[0137] A negative electrode active slurry with a solid content of 50 wt% was prepared by mixing graphite, conductive agent Super P and binder polytetrafluoroethylene (PTFE) in a mass ratio of 95:2:3 in the solvent N-methylpyrrolidone (NMP).

[0138] The negative electrode active slurry was coated onto the current collector copper foil (9 μm thick) and dried at 85°C for 4 h, then cold-pressed, trimmed, and cut into sheets. The sheets were then dried under vacuum at 85°C for 4 h to obtain the negative electrode substrate. The thickness of the single-sided negative electrode active material layer was 150 μm.

[0139] (4) Fabrication of coin cells:

[0140] A lithium sheet (500 μm thick) was used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte. The lithium sheet and the positive electrode prepared above were assembled into a coin cell in a coin cell box.

[0141] Table 1. Differences in preparation parameters for lithium manganese iron phosphate materials

[0142]

[0143] In Table 1, the mass percentage of the carbon source refers to the proportion of the mass of the carbon source to the total mass of the lithium, manganese, iron, and phosphorus sources; " / " indicates that there is no corresponding parameter; the difference between Examples 13-16 and Example 1 is only the molar ratio of the lithium source to the phosphorus source, while the molar amounts of the manganese source, the molar amounts of the iron source, and the molar amounts of the phosphorus source in Examples 13-16 are the same as in Example 1; the difference between Example 19 and Example 1 is only the selection of the iron and phosphorus sources, while the molar amounts of the lithium source, the manganese source, the iron source, and the phosphorus source in Example 19 are the same as in Example 1.

[0144] Testing the performance of lithium manganese iron phosphate materials and coin cells:

[0145] (1) Test of volume average particle size Dv50 of solid particles in precursor solution

[0146] Equipment Model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer; Reference Standard Procedure: GB / T19077-2016 / ISO 13320:2009; Specific Test Procedure: Take an appropriate amount of the precursor solution sample (the sample concentration should be 8-12% opacity), add 20mL of deionized water, and simultaneously incubate for 5 minutes (53KHz / 120W) to ensure complete dispersion of the precursor solution sample. Then, measure the precursor solution sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0147] (2) Morphological characterization of lithium manganese iron phosphate materials

[0148] The lithium manganese iron phosphate material samples were tested using a ZEISS Sigma 300 scanning electron microscope. The morphology of the lithium manganese iron phosphate material samples was observed and SEM images were taken in accordance with the standard JY / T010-1996.

[0149] (3) 3-ton compaction density test of lithium manganese iron phosphate material

[0150] Weigh 1.0000±0.0500g of the lithium manganese iron phosphate material sample to be tested and place it in the test mold (CARVER#3619 (13mm). Then place the lithium manganese iron phosphate material sample in the test equipment, which is Sansi Zongheng UTM7305, with a test tonnage of 3.0 tons, a pressure increase rate of 10mm / min, a pressure increase holding time of 30s, a pressure release rate of 30mm / min, and a pressure release holding time of 10s. Measure its compaction density when depressurized. The formula for calculating compaction density is: Compaction density = Mass of lithium manganese iron phosphate material / (Force-bearing area of ​​lithium manganese iron phosphate material × Thickness of lithium manganese iron phosphate material).

[0151] (4) Resistivity testing of lithium manganese iron phosphate materials

[0152] The four-probe method was used to test the volume resistivity of lithium manganese iron phosphate powder under 4 MPa pressure. The test method included: adding the lithium manganese iron phosphate material to be tested into the sample stage, applying a pressure of 4 MPa to the lithium manganese iron phosphate material to be tested through a press, and reading the volume resistivity of the lithium manganese iron phosphate material under 4 MPa pressure through a resistivity meter after the pressure stabilized.

[0153] (5) Specific capacity test of lithium manganese iron phosphate materials

[0154] At 25℃, coin cells assembled from lithium manganese iron phosphate material were charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V to a current of 0.01C, rested for 5 minutes, and then discharged at 0.1C to 2.0V. The resulting discharge capacity was recorded as c1. This cycle was repeated a second time, and the resulting capacity was recorded as c2. Three parallel samples of the coin cells were prepared, and the average value of c2 from the three parallel samples was recorded as the average discharge capacity c0. The specific capacity of lithium manganese iron phosphate material was calculated as c0 / M, where M was the average mass of the lithium manganese iron phosphate material.

[0155] (6) Cycle performance test of button cells

[0156] At 25°C, the coin cell battery was first charged to 4.3V with a constant current of 0.1C, then charged to 0.01C with a constant voltage of 4.3V, left to rest for 5 minutes, and then discharged to 2.0V with 0.1C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The coin cell battery was subjected to 100 charge-discharge cycles in the above manner, and the discharge capacity of the 100th cycle was measured. The capacity retention rate of the coin cell battery after the cycles was calculated using the following formula.

[0157] The capacity retention rate (%) of a button cell after 100 cycles = [discharge capacity of the 100th cycle / discharge capacity of the 1st cycle] × 100%.

[0158] (7) Rate performance test of button cells

[0159] At 25℃, the coin cell was first charged to 4.3V with a constant current of 0.1C, then charged to 0.01C with a constant voltage of 4.3V, left to rest for 5 minutes, and then discharged to 2.0V with 0.1C. This constitutes one charge-discharge cycle. The same process was repeated with different charge-discharge currents of 0.1C, 0.33C, 1C, 2C, and 5C, with each current cycle repeated 10 times and the discharge capacity recorded.

[0160] 1C discharge capacity retention rate (%) = (average 1C delithiation capacity / average 0.1C delithiation capacity) × 100%;

[0161] The performance of lithium manganese iron phosphate material and coin cell battery is shown in Table 2:

[0162] Table 2 Performance of Lithium Manganese Iron Phosphate Materials and Button Batteries

[0163]

[0164]

[0165] Figure 6 This is a SEM characterization image of the lithium manganese iron phosphate material prepared in Example 1 of this application. Figure 7 This is a SEM characterization image of the lithium manganese iron phosphate material prepared in Comparative Example 1 of this application. Figure 8 This is a SEM characterization image of the lithium manganese iron phosphate material prepared in Comparative Example 4 of this application.

[0166] from Figures 6 to 8 It can be seen that the lithium manganese iron phosphate material prepared in Example 1 of this application is generally spherical or near-spherical particles, and the particles are relatively uniformly dispersed with a particle size of approximately 0.1 μm to 0.5 μm; while the lithium manganese iron phosphate materials prepared in Comparative Examples 1 and 4 are in an agglomerated state. This indicates that using a non-polar carbon-containing compound as a carbon source can suppress the agglomeration of lithium manganese iron phosphate material during the preparation process, which is beneficial to obtaining lithium manganese iron phosphate material with uniformly dispersed particles.

[0167] As shown in Table 2, the compaction density and specific capacity of the lithium manganese iron phosphate materials prepared in Examples 1-19 are higher than those prepared in Comparative Examples 1-4. The powder resistivity of the lithium manganese iron phosphate materials prepared in Examples 1-19 is lower than that prepared in Comparative Examples 1-4. Furthermore, the cycle performance and rate performance of the coin cells corresponding to the lithium manganese iron phosphate materials prepared in Examples 1-19 are higher than those corresponding to the coin cells prepared in Comparative Examples 1-4. This indicates that using non-polar carbon-containing compounds as a carbon source can improve the compaction density, specific capacity, and electronic conductivity of lithium manganese iron phosphate materials, and can also improve the cycle performance and rate performance of lithium-ion batteries.

[0168] As can be seen from Examples 1-5, the carbon sources in Examples 1-3 are all polymeric carbon sources and become hard carbon after sintering, while the coal tar in Example 4 and the petroleum coke in Example 5 both become hard carbon after sintering. The compaction density and specific capacity of the lithium manganese iron phosphate materials prepared in Examples 1-3 are higher than those prepared in Examples 4-5. The powder resistivity of the lithium manganese iron phosphate materials prepared in Examples 1-3 is lower than that prepared in Examples 4-5. Furthermore, the cycle performance and rate performance of the coin cells corresponding to the lithium manganese iron phosphate materials prepared in Examples 1-3 are higher than those corresponding to the coin cells prepared in Examples 4-5. This indicates that when the carbon source is a non-polar carbon source, the carbon source becomes hard carbon after sintering, which is beneficial to further improve the compaction density, specific capacity, and electronic conductivity of the lithium manganese iron phosphate material, and also beneficial to further improve the cycle performance and rate performance of the lithium-ion battery.

[0169] As can be seen from Examples 1 and 6-9, the "proportion of the mass of the carbon source to the total mass of the lithium source, manganese source, iron source and phosphorus source" can further affect the compaction density, specific capacity and electronic conductivity of lithium manganese iron phosphate material, as well as the cycle performance and rate performance of lithium-ion batteries. When the "proportion of the mass of the carbon source to the total mass of the lithium source, manganese source, iron source and phosphorus source" is 1.2% to 2.4%, the compaction density, specific capacity and electronic conductivity of lithium manganese iron phosphate material are relatively high, and the cycle performance and rate performance of lithium-ion batteries are also relatively high.

[0170] As can be seen from Examples 1 and 10-12, the volume average particle size Dv50 of the solid particles in the precursor solution can further affect the specific capacity and electronic conductivity of lithium manganese iron phosphate material. When the volume average particle size Dv50 of the solid particles in the precursor solution is between 0.1 μm and 0.5 μm, the specific capacity and electronic conductivity of lithium manganese iron phosphate material can be further improved.

[0171] As can be seen from Examples 1 and 13-16, the molar ratio of lithium source to phosphorus source can further affect the cycle performance and rate performance of lithium-ion battery. When the molar ratio of lithium element in lithium source to phosphorus element in phosphorus source is (1-1.04):1, the cycle performance and rate performance of lithium-ion battery can be further improved.

[0172] As can be seen from Examples 1 and 17-18, the sintering temperature and time can further affect the compaction density, specific capacity, and electronic conductivity of lithium manganese iron oxide materials, as well as the cycle performance and rate performance of lithium-ion batteries.

[0173] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for preparing a lithium iron manganese phosphate material, characterized in that, The application relates to a preparation method of a lithium manganese iron phosphate material. The liquid in the liquid phase is water, and the carbon source is a carbon-containing compound insoluble in water. The carbon-containing compound insoluble in water is a carbon-containing compound capable of forming hard carbon after sintering.

2. The production method according to claim 1, characterized by, The carbon source comprises at least one of polyethylene, polypropylene, polystyrene, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, straight-chain amylose, branched-chain amylose, polyformaldehyde and polyaniline. The carbon source comprises at least one of polypropylene, polyvinylidene fluoride, polytetrafluoroethylene and polystyrene.

3. The production method according to claim 1 or 2, characterized by, The molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is greater than 1:

1.

4. The production method according to claim 3, characterized by, The molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is (1-1.04):

1.

5. The production method according to claim 1 or 2, characterized by, The molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is greater than 1:1 and less than or equal to 1.04:

1.

6. The production method according to claim 5, characterized by, The molar ratio of the molar amount of lithium in the lithium source, the molar amount of manganese in the manganese source, the molar amount of iron in the iron source and the molar amount of phosphorus in the phosphorus source is (1-1.04):(0.3-0.7):(0.3-0.7):

1.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the carbon source to the total mass of the lithium source, the manganese source, the iron source and the phosphorus source is (0.012-0.024):

1.

8. The preparation method according to claim 5, characterized in that, The sintering temperature is 670 DEG C-760 DEG C.

9. The production method according to claim 1 or 2, characterized by, The sintering time is 8h-16h.

10. The production method according to claim 1 or 2, characterized by, The lithium source comprises at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium dihydrogen phosphate and lithium phosphate.

11. The method of claim 10, wherein, The manganese source comprises at least one of manganese sulfate, manganese chloride, manganese oxalate, manganese oxide and manganese acetate.

12. The production method according to claim 1 or 2, characterized by, The iron source comprises at least one of ferrous oxalate, iron oxide, ferrous oxide, ferrous sulfate, ferrous acetate and ferrous chloride. The phosphorus source comprises at least one of lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate and lithium phosphate. The drying mode is spray drying. The lithium manganese iron phosphate material is prepared by the preparation method of the lithium manganese iron phosphate material in any one of claims 1-13.

13. The production method according to claim 1 or 2, characterized by, The lithium manganese iron phosphate material is in the shape of spherical particles or quasi-spherical particles.

14. A lithium iron manganese phosphate material, characterized in that, The lithium manganese iron phosphate material has a particle size of 0.1-0.5 microns.

15. The lithium iron manganese phosphate material of claim 14, wherein, The lithium manganese iron phosphate material has a powder volume resistivity of 21-78 ohm-m under a pressure of 4MPa. The lithium manganese iron phosphate material has a specific capacity of 147-158 mAh / g.

16. The lithium iron manganese phosphate material of claim 14 or 15, wherein, The 3-ton compaction density of the lithium iron manganese phosphate material is 2.17 g / cm 3 2.45 g / cm 3 ; The positive active material comprises the lithium manganese iron phosphate material in any one of claims 14-16. ​ 17. A positive electrode active material, characterized by, ​ 18. A positive electrode sheet characterized by comprising: The positive electrode tab comprises a positive electrode current collector and a positive electrode active layer covering at least one surface of the positive electrode current collector in the thickness direction; wherein the positive electrode active layer comprises the positive electrode active material of claim 17.

19. A battery, characterized by The battery comprises the positive electrode tab of claim 18.

20. An electrical device, comprising: The electric device comprises the battery of claim 19.

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