Lithium manganese iron phosphate material and preparation method thereof, positive active material, positive pole piece, battery and electric equipment

Abstract

The invention provides a lithium manganese iron phosphate material and a preparation method thereof, a positive active material, a positive pole piece, a battery and electric equipment, and belongs to the technical field of batteries. The preparation method of the lithium manganese iron phosphate material comprises the following steps: 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 particles, and sintering in an inert atmosphere to form the lithium manganese iron phosphate material coated with a carbon layer on the surface, wherein the carbon source is a non-polar carbon-containing compound. In the preparation method of the lithium manganese iron phosphate material provided by the invention, the non-polar carbon-containing compound not only can inhibit the agglomeration phenomenon of a liquid phase containing a lithium source, a manganese source, an iron source and a phosphorus source, but also can be used as a carbon source to coat the lithium manganese iron phosphate at the same time; the compaction density, the conductivity and the specific capacity of the prepared lithium manganese iron phosphate material can be improved at the same time, and the cycle performance and the rate capability of a lithium ion battery are improved at the same time.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a lithium manganese iron phosphate material and a preparation method thereof, a positive electrode active material, a positive electrode sheet, a battery and an electrical device. Background Art

[0002] Lithium iron manganese phosphate is a commonly used positive electrode active material in lithium-ion batteries. It has the advantages of gram capacity close to the theoretical specific capacity, high voltage platform and high energy density. However, lithium iron manganese phosphate also has the disadvantages of low compaction density, low conductivity and low specific capacity. Using lithium iron manganese phosphate as a positive electrode active material will also lead to low cycle performance and low rate performance of lithium-ion batteries. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present application provides a lithium iron manganese phosphate material and a preparation method thereof, a positive electrode active material, a positive electrode plate, a battery and an electrical device, so as to simultaneously improve the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material, and simultaneously improve the cycle performance and rate performance of a lithium-ion battery prepared using the lithium iron manganese phosphate material.

[0004] In a first aspect, the present application provides a method for preparing a lithium iron manganese phosphate material, the preparation method comprising: grinding, drying and sintering a liquid phase containing a lithium source, a manganese source, an iron source, a phosphorus source and a carbon source in an inert atmosphere in sequence to form a lithium iron manganese phosphate material having a surface coated with a carbon layer; wherein the carbon source is a non-polar carbon-containing compound.

[0005] In the preparation method of the lithium iron manganese phosphate material provided by the present application, the non-polar carbon-containing compound can not only inhibit the agglomeration of the liquid phase containing the lithium source, manganese source, iron source and phosphorus source, but also the non-polar carbon-containing compound can simultaneously coat the lithium iron manganese phosphate to form a carbon layer coated on the surface of the lithium iron manganese phosphate. The liquid phase containing the lithium source, manganese source, iron source, phosphorus source and carbon source is not easy to agglomerate, which is conducive to the full refinement of the particles in the liquid phase during the grinding of the liquid phase, and then it is conducive to forming a granular system with a relatively uniform dispersion and a refined particle size after drying, and then after sintering under an inert atmosphere, the carbon source can form a relatively uniform and fully coated carbon layer on the surface of the lithium iron manganese phosphate particles, and the obtained lithium iron manganese phosphate material is generally spherical or quasi-spherical particles, and the particles are relatively evenly dispersed, which can not only improve the compaction density, conductivity and specific capacity of the obtained lithium iron manganese phosphate material, but also improve the cycle performance and rate performance of the lithium ion battery prepared using the lithium iron manganese phosphate material. In addition, the preparation method of the present application does not require an additional grinding and refining step between the drying and sintering steps. The preparation method is simple and easy, low in cost, and suitable for industrial production.

[0006] In some embodiments, the carbon source is a carbon-containing compound that is insoluble in water; 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 a carbon-containing polymer compound. The carbon source is a carbon-containing compound that is insoluble in water, which is beneficial to further inhibit the agglomeration of the liquid phase containing the lithium source, manganese source, iron source and phosphorus source, and thus is beneficial to further improve the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material at the same time, and further improve the cycle performance and rate performance of the lithium ion battery. The carbon source is a carbon-containing compound that can form hard carbon after sintering, and the hard carbon layer coats the lithium iron manganese phosphate, which is beneficial to further improve the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material at the same time, and further improve the cycle performance and rate performance of the lithium ion battery. The non-polar carbon-containing compound includes a carbon-containing polymer compound, which is beneficial to further improve the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material at the same time, and further improve the cycle performance and rate performance of the lithium ion battery.

[0007] In some embodiments, the carbon source includes at least one of polyethylene, polypropylene, polystyrene, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, amylose, amylopectin, cyclodextrin, polyoxymethylene and polyaniline. The carbon source is selected from the above substances, which can not only inhibit the agglomeration of the liquid phase containing lithium source, manganese source, iron source and phosphorus source, but also the above substances are hard carbon after sintering under an inert atmosphere, which is conducive to further improving the compaction density, specific capacity and conductivity of lithium manganese iron phosphate materials at the same time, and further improving the cycle performance and rate performance of lithium ion batteries.

[0008] In some embodiments, the carbon source includes at least one of polypropylene, cyclodextrin, polyvinylidene fluoride, polytetrafluoroethylene and polystyrene. The carbon source is selected from the above substances, which is conducive to further improving the compaction density, specific capacity and conductivity of the lithium manganese iron phosphate material at the same time, and further improving the cycle performance and rate performance of the lithium ion battery.

[0009] In some embodiments, the molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is ≥ 1: 1. The molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source under the above ratio can make the lithium-ion battery have better cycle performance and rate performance.

[0010] In some embodiments, the molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is (1-1.04): 1. The molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source under the above ratio is conducive to further improving the cycle performance and rate performance of the lithium ion battery.

[0011] In some embodiments, 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. The molar ratio of lithium in the lithium source to phosphorus in the phosphorus source is beneficial to further improve the cycle performance and rate performance of the lithium ion battery under the above ratio.

[0012] In some embodiments, the 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. 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 under the above ratio is conducive to taking into account the compaction density, specific capacity, and conductivity of the lithium iron manganese phosphate material, so that the compaction density, specific capacity, and conductivity of the lithium iron manganese phosphate material are higher, and the lithium ion battery has better cycle performance and rate performance.

[0013] In some embodiments, the ratio of the mass of the carbon source to the total mass of the lithium source, manganese source, iron source and phosphorus source is (0.012-0.024): 1. The ratio of the mass of the carbon source to the total mass of the lithium source, manganese source, iron source and phosphorus source within the above range is conducive to giving full play to the performance of the non-polar carbon-containing compound (i.e., the carbon source), so that the prepared lithium iron manganese phosphate material generally presents spherical or quasi-spherical particles, the particles are more evenly dispersed, and the thickness of the carbon layer coated on the surface of the lithium iron manganese phosphate is within a more appropriate range, which is conducive to taking into account the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material, so that the lithium iron manganese phosphate material has a higher compaction density, higher specific capacity and higher conductivity, and the lithium ion battery has 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. The above method can achieve sufficient refinement of the particles in the liquid phase during the grinding of the liquid phase, which is conducive to forming a granular system with relatively uniform dispersion and refined particle size after drying, which is conducive to improving the specific capacity and conductivity of the lithium iron manganese phosphate material, and can also make the lithium iron manganese phosphate material have a higher compaction density, so that the lithium ion battery prepared using the lithium iron manganese phosphate material has higher cycle performance and higher rate performance.

[0015] In some embodiments, the sintering temperature is 670° C. to 760° C. The sintering temperature within the above range is conducive to the sufficient reaction of the raw materials to form lithium iron manganese phosphate particles during the sintering process under an inert atmosphere, and the carbon source is fully converted into a carbon layer, so that the prepared lithium iron manganese phosphate material has a higher compaction density, a higher specific capacity and a higher conductivity, so that the lithium ion battery prepared using the lithium iron manganese phosphate material has a higher cycle performance and a higher rate performance.

[0016] In some embodiments, the sintering time is 8 hours to 16 hours. The sintering time within the above range is conducive to the sufficient reaction of the raw materials to form lithium iron manganese phosphate particles during the sintering process under an inert atmosphere, and the carbon source is fully converted into a carbon layer, so that the prepared lithium iron manganese phosphate material has a higher compaction density, a higher specific capacity and a higher conductivity, so that the lithium ion battery prepared using the lithium iron manganese phosphate material has a higher cycle performance and a 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. The spray drying method is conducive to the liquid phase containing the lithium source, manganese source, iron source, phosphorus source and carbon source being more fully converted into a granular system after drying, which is conducive to taking into account the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material, so that the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material are higher, and the lithium ion battery has better cycle performance and rate performance.

[0022] In a second aspect, the present application provides a lithium iron manganese phosphate material, which is prepared by the preparation method of the lithium iron manganese phosphate material provided in any one of the first aspects above.

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

[0024] In a third aspect, the present application provides a positive electrode active material, which includes the lithium manganese iron phosphate material provided in the second aspect.

[0025] The positive electrode active material provided in the present application can improve the cycle performance and rate performance of lithium-ion batteries because it contains the above-mentioned lithium iron manganese phosphate material with higher compaction density, higher specific capacity and higher conductivity.

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

[0027] In a fifth aspect, the present application provides a battery, the battery comprising the positive electrode plate provided in the fourth aspect above.

[0028] In a sixth aspect, the present application provides an electrical device, the electrical device comprising the battery provided in the fifth aspect above.

[0029] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0031] Figure 1 A schematic diagram of the structure of a vehicle provided for some embodiments of the present application.

[0032] Figure 2 Schematic diagram of the exploded structure of a battery provided for some embodiments of the present application.

[0033] Figure 3 A schematic diagram of the structure of a battery cell provided in some embodiments of the present application.

[0034] Figure 4 An exploded view of a battery cell provided for some embodiments of the present application.

[0035] Figure 5 A schematic diagram of the structure of an electrode assembly provided in some embodiments of the present application.

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

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

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

[0039] Icons: 1000-vehicle; 100-battery; 10-casing; 11-accommodating space; 12-first part; 13-second part; 20-battery cell; 21-casing; 211-opening; 22-end cover assembly; 221-end cover; 222-electrode terminal; 23-electrode assembly; 231-positive electrode plate; 232-negative electrode plate; 233-separation membrane; 24-current collecting member; 25-insulating protection member; 200-controller; 300-motor. DETAILED DESCRIPTION

[0040] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0042] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0043] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0044] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0045] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0046] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0047] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0048] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0049] The power battery can be a lithium-ion battery. During the charging process of the lithium-ion battery, lithium ions are released from the positive electrode active material, transmitted through the electrolyte, passed through the isolation membrane, and embedded in the negative electrode active layer. Lithium iron phosphate and lithium iron manganese phosphate are both commonly used positive electrode active materials in lithium-ion batteries. Lithium iron phosphate and lithium iron manganese phosphate also have olivine structures; compared with lithium iron phosphate, the specific capacity of lithium manganese iron phosphate is similar to that of lithium iron phosphate, and the voltage platform of lithium manganese iron phosphate (about 3.8V~4.1V) is higher than the voltage platform of lithium iron phosphate (about 3.4V), and the theoretical energy density of lithium manganese iron phosphate is also 10%~20% higher than that of lithium iron phosphate, and the low temperature performance of lithium manganese iron phosphate is relatively better.

[0050] However, lithium iron manganese phosphate also has some defects. For example, lithium iron manganese phosphate is inferior to lithium iron phosphate in terms of electrical conductivity, the compaction density of lithium iron manganese phosphate is low, and the cycle performance and rate performance of lithium-ion batteries prepared with lithium iron manganese phosphate are relatively low.

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

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

[0053] In the process of grinding the liquid phase containing lithium source, manganese source, iron source and phosphorus source, the presence of non-polar carbon-containing compounds (i.e., carbon source) can make the liquid phase containing lithium source, manganese source, iron source, phosphorus source and carbon source less likely to agglomerate, which is beneficial to achieve sufficient refinement of the particles in the liquid phase during the grinding of the liquid phase, so that after drying, a granular system with relatively uniform dispersion and refined particle size is formed, which is beneficial to the obtained lithium manganese iron phosphate material generally presenting spherical or quasi-spherical particles and 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, so as to form a relatively uniform and fully coated carbon layer on the surface of the lithium manganese iron phosphate particles.

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

[0056] The lithium manganese iron phosphate material is used to prepare the positive electrode sheet, and the positive electrode sheet can be assembled into a battery. The battery can be a battery cell, a module, a battery pack, etc. The battery can be used in, but not limited to, electrical equipment such as vehicles, ships or aircraft. The battery disclosed in this application can be used to form a power supply system for the electrical equipment, which is conducive to improving the cycle performance and service life of the battery at higher temperatures.

[0057] The embodiment of the present application provides an electric device that uses a battery as a power source. The electric device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, and the like; the spacecraft includes an airplane, a rocket, a space shuttle, and a spacecraft, and the like; the electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the like; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and an electric tool for railways, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, and the like. The embodiment of the present application does not impose any special restrictions on the above-mentioned electric devices.

[0058] For the convenience of description, the following embodiments are described by taking the electric device as a vehicle as an example.

[0059] Please refer to Figure 1 , Figure 1 The schematic diagram of the structure of the vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 is provided with a battery 100 inside, and the battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000, for example, the battery 100 can be used as an operating power source of the vehicle 1000.

[0060] The vehicle 1000 may further include a controller 200 and a motor 300 , wherein the controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, to meet the power requirements of starting, navigating, and driving the vehicle 1000 .

[0061] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a 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 a schematic diagram of the exploded structure of the battery 100 provided in some embodiments of the present application. Figure 2 The battery 100 includes a housing 10 and a battery cell 20 , and the battery cell 20 is accommodated in the housing 10 .

[0063] The box body 10 is used to provide a storage space 11 for the battery cell 20. In some embodiments, the box body 10 may include a first portion 12 and a second portion 13, and the first portion 12 and the second portion 13 cover each other to define the storage space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a sealing member (not shown in the figure), and the sealing member can be a sealing ring, a sealant, etc.

[0064] The first part 12 and the second part 13 can be in various shapes, such as a cuboid, a cylinder, etc. The first part 12 can be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20. The opening side of the second part 13 covers the opening side of the first part 12, thereby forming a box body 10 with a receiving space 11. Of course, if Figure 2 As shown, the first part 12 may be a hollow structure with one side open, and the second part 13 may be a plate-like structure. The second part 13 covers the open side of the first part 12 to form a box body 10 with an accommodating space 11.

[0065] In the battery 100, there can be one or more battery cells 20. If there are more than one battery cell 20, the battery cells 20 can be connected in series, in parallel or in a mixed connection. A mixed connection means that the battery cells 20 are connected in series and in parallel. The battery cells 20 can be directly connected in series, in parallel or in a mixed connection, and then the whole formed by the battery cells 20 can be accommodated in the box 10; of course, the battery cells 20 can be connected in series, in parallel or in a mixed connection to form a battery module, and then the battery modules can be connected in series, in parallel or in a mixed connection to form a whole, and then accommodated in the box 10. The battery cell 20 can be cylindrical, flat, rectangular or in other shapes. Figure 2 The example shows that the battery cell 20 is in a square shape.

[0066] In some embodiments, the battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or mixed connection of the 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 the present application. Figure 4 This is an exploded view of a battery cell 20 provided in some embodiments of the present application. 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 accommodated in the housing 21 , and the end cap assembly 22 is used to cover the opening 211 .

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

[0069] The shell 21 may be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0070] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a closed installation space (not shown), and the installation space is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte. The end cap assembly 22 is a component for outputting the electrical energy of the electrode assembly 23. The electrode terminal 222 in the end cap assembly 22 is used to be electrically connected to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

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

[0072] In some embodiments, Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the periphery of the electrode assembly 23, and 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 a tape bonded to the periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 is arranged around the periphery of the multiple electrode assemblies 23, and the multiple electrode assemblies 23 are formed into an integral structure to maintain the stability of the electrode assembly 23 structure. Among them, the electrode assembly 23 can be a wound electrode assembly or a laminated electrode assembly, and the embodiments of the present application are not limited thereto.

[0073] Figure 5 For a schematic diagram of the structure of the electrode assembly provided in some embodiments of the present application, please refer to Figure 5 The electrode assembly 23 includes a positive electrode sheet 231, a negative electrode sheet 232 and a separator 233, the separator 233 is arranged between the positive electrode sheet 231 and the negative electrode sheet 232, the electrolyte is located in the installation space and filled in the gap of the electrode assembly 23.

[0074] The present application has no particular restrictions on the separator, the negative electrode plate and the electrolyte.

[0075] As for the isolation membrane, the isolation membrane may be a PP (polypropylene) porous membrane, a PE (polyethylene) porous membrane, a polyimide porous membrane, and a porous membrane formed by a composite of multiple polymers.

[0076] For the negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer covering at least one surface of the negative electrode current collector in the thickness direction; the present application has no particular restrictions on the thickness of the negative electrode current collector and the negative electrode active layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the negative electrode active layer on a single side of the negative electrode 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 covered with a conductive metal, etc.; wherein the conductive metal includes but is not limited to copper, nickel or titanium, and the material of the polymer substrate includes but is not limited to at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene naphthalate 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 lithium alone, an alloy formed by lithium and other metal elements or non-metal elements, wherein the metal elements include tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), platinum (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, etc. The carbon material 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. The metal may include metal powder or metal fibers of copper, iron, aluminum, etc. The conductive polymer 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 polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl pyrrolidone, polyethylene, polypropylene, epoxy resin, nylon, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral, aqueous acrylic resin, carboxymethyl cellulose (CMC) or sodium carboxymethyl cellulose (CMC-Na), etc.

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

[0082] For the electrolyte, the electrolyte includes a sodium salt and a non-aqueous solvent, or the electrolyte includes a lithium salt and a non-aqueous solvent; wherein the sodium salt may include NaPF 6 、NaClO 4 、NaBCl 4 、NaSO 3 CF 3 or Na(CH 3 )C 6 H 4 SO 3 At least one of the following; the present application has no particular limitation on the concentration of the sodium salt in the electrolyte, as long as the purpose of the present application can be achieved. The lithium salt may include LiPF 6 , LiBF 4 、LiAsF 6 、LiClO 4 、LiB(C 6 H 5 ) 4 、LiCH 3 SO 3 、LiCF 3 SO 3 、LiN(SO 2 CF 3 ) 2 、LiC(SO 2 CF 3 ) 3 , Li 2 SiF 6, lithium bis(oxalatoborate) (LiBOB) or lithium difluoroborate; the present application has no particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no particular limitation on the above-mentioned non-aqueous solvent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents; the above-mentioned carbonate compounds may include but are not limited to at least one of chain carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds; the above-mentioned 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 above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC); the fluorinated carbonate compounds may include but are not limited to fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate , 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 trifluoromethylethylene carbonate; the above-mentioned carboxylic acid ester compound may include but is 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, valerolactone or caprolactone; the above-mentioned ether compound may include but is 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, valerolactone or caprolactone; The organic solvent may include but is 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 may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, 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 (a current collector with a polymer support layer in the middle and aluminum metal layers on both surfaces of the support layer), 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, carboxymethyl cellulose sodium salt, styrene-butadiene rubber, polyurethane, ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer; the dispersant in the positive active layer is selected from polyvinyl pyrrolidone, 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 flakes, graphite particles and mesophase carbon microspheres.

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

[0085] Among them, the lithium source, manganese source, iron source and phosphorus source are raw materials for forming lithium iron manganese phosphate, and the lithium source, manganese source, iron source and phosphorus source can be sintered in an inert atmosphere to form lithium iron manganese phosphate. This application does not limit the lithium source, manganese source, iron source and phosphorus source for forming lithium iron manganese phosphate.

[0086] “Lithium manganese iron phosphate material coated with a carbon layer on the surface” means that the carbon layer at least partially coats the surface of the lithium manganese iron phosphate particles. The surface of the lithium manganese iron phosphate particles may be completely covered with the carbon layer, or only a part of the surface of the lithium manganese iron phosphate particles may be covered with the carbon layer.

[0087] “Non-polar carbon-containing compound” means that the compound contains carbon element and is a non-polar molecule.

[0088] In the preparation method of the lithium iron manganese phosphate material provided by the present application, the non-polar carbon-containing compound can not only inhibit the agglomeration of the liquid phase containing the lithium source, manganese source, iron source and phosphorus source, but also the non-polar carbon-containing compound can simultaneously coat the lithium iron manganese phosphate to form a carbon layer coated on the surface of the lithium iron manganese phosphate. The liquid phase containing the lithium source, manganese source, iron source, phosphorus source and carbon source is not easy to agglomerate, which is conducive to the full refinement of the particles in the liquid phase during the grinding of the liquid phase, and then it is conducive to forming a granular system with a relatively uniform dispersion and a refined particle size after drying, and then after sintering under an inert atmosphere, the carbon source can form a relatively uniform and fully coated carbon layer on the surface of the lithium iron manganese phosphate particles, and the prepared lithium iron manganese phosphate material is generally spherical or quasi-spherical particles, and the particles are dispersed more evenly, which can not only improve the compaction density, specific capacity and conductivity of the prepared lithium iron manganese phosphate material, but also improve the cycle performance and rate performance of the lithium ion battery prepared by the lithium iron manganese phosphate material.

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

[0090] In some embodiments, the carbon source is a water-insoluble carbon-containing compound, which is beneficial to further inhibit the agglomeration of the liquid phase containing the lithium source, manganese source, iron source and phosphorus source, 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.

[0091] In some embodiments, the carbon source is a carbon-containing compound that can form hard carbon after sintering. Compared with soft carbon, hard carbon has a small expansion rate and is stable, which can make lithium-ion batteries have the advantages of high cycle durability, long charge and discharge cycle life, and better safety performance. It can make the prepared carbon layer-coated lithium manganese iron phosphate material have a stable charge and discharge platform, and the charge and discharge capacity is large and efficient. In addition, compared with soft carbon, hard carbon has more disordered structure, higher defect concentration, higher heteroatom content, larger distance between graphite layers, and more closed pore structure, which is conducive to Li + Ions provide more storage points and diffusion pathways, because the hard carbon layer can obtain a better ion migration rate, 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 iron manganese phosphate materials at the same time, and further improve the cycle performance and rate performance of lithium-ion batteries.

[0092] In some embodiments, the non-polar carbon-containing compound includes a carbon-containing polymer compound. The polymer carbon source can form a more compact carbon layer after sintering in an inert atmosphere, which is beneficial to further improve the compaction density, specific capacity and conductivity of the lithium manganese iron phosphate material at the same time, and further improve the cycle performance and rate performance of the lithium ion battery.

[0093] In some embodiments, the carbon source includes at least one of polyethylene, polypropylene, polystyrene, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, amylose, amylopectin, cyclodextrin, polyoxymethylene and polyaniline. The carbon source is selected from the above substances, which can not only inhibit the agglomeration of the liquid phase containing lithium source, manganese source, iron source and phosphorus source, but also the above substances are hard carbon after sintering under an inert atmosphere, which is conducive to further improving the compaction density, specific capacity and conductivity of lithium manganese iron phosphate materials at the same time, and further improving the cycle performance and rate performance of lithium ion batteries.

[0094] Furthermore, in some embodiments, the carbon source includes at least one of polypropylene, cyclodextrin, polyvinylidene fluoride, polytetrafluoroethylene and polystyrene. The carbon source is selected from the above substances, which is conducive to further improving the compaction density, specific capacity and conductivity of the lithium manganese iron phosphate material at the same time, and further improving the cycle performance and rate performance of the lithium ion battery.

[0095] It should be noted that the non-polar carbon source is not limited to the carbon-containing compounds listed above. For example, the non-polar carbon source may also include phenolic resin, 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; this 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 to further improve the cycle performance and rate performance of the lithium ion battery.

[0098] 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 of them.

[0099] In some embodiments, 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. This is beneficial for further improving the cycle performance and rate performance of the lithium ion battery.

[0100] In some embodiments, the 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. This is beneficial to take into account the compaction density, specific capacity, and conductivity of the lithium iron manganese phosphate material, so that the compaction density, specific capacity, and conductivity of the lithium iron manganese phosphate material are higher, and the lithium ion battery has better cycle performance and rate performance.

[0101] As an example, the ratio of the molar amount of lithium in the lithium source to the molar amount of phosphorus in the phosphorus source can be 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 two values; the ratio of the molar amount of manganese in the manganese source to the molar amount of phosphorus in the phosphorus source can be 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, or a range between any two of them; the ratio of the molar amount of the iron element in the iron source to the molar amount of the phosphorus element in the phosphorus source can be 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, or a range between any two of them.

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

[0103] In some embodiments, the ratio of the mass of the carbon source to the total mass of the lithium source, manganese source, iron source and phosphorus source is (0.012-0.024): 1. This is conducive to giving full play to the performance of the non-polar carbon-containing compound (i.e., the carbon source), so that the prepared lithium iron manganese phosphate material is generally spherical or quasi-spherical particles, the particles are more evenly dispersed, and the thickness of the carbon layer coated on the surface of the lithium iron manganese phosphate is within a more appropriate range, which is conducive to taking into account the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material, so that the lithium iron manganese phosphate material has a higher compaction density, higher specific capacity and higher conductivity, and the lithium ion battery has 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 source, manganese source, iron source and phosphorus source can be any value among 0.012:1, 0.015:1, 0.017:1, 0.02:1, 0.022:1 and 0.024:1 or a range value between any 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 can make the particles in the liquid phase fully refined during the grinding of the liquid phase, which is conducive to forming a granular system with relatively uniform dispersion and refined particle size after drying, which is conducive to improving the specific capacity and conductivity of the lithium manganese iron phosphate material, and can also make the lithium manganese iron phosphate material have a higher compaction density, so that the lithium ion battery prepared using the lithium manganese iron phosphate material has higher cycle performance and higher rate performance.

[0106] As an example, the particle size of the solid particles ground 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 value therebetween.

[0107] As an example, the grinding method may be sand grinding.

[0108] In some embodiments, the sintering temperature is 670° C. to 760° C. This is conducive to the full reaction of the raw materials to form lithium iron manganese phosphate particles during the sintering process under an inert atmosphere, and the carbon source is fully converted into a carbon layer, so that the prepared lithium iron manganese phosphate material has a higher compaction density, a higher specific capacity and a higher conductivity, so that the lithium ion battery prepared using the lithium iron manganese phosphate material has a higher cycle performance and a higher rate performance.

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

[0110] In some embodiments, the sintering time is 8 hours to 16 hours. This is conducive to the full reaction of the raw materials to form lithium iron manganese phosphate particles during the sintering process under an inert atmosphere, and the carbon source is fully converted into a carbon layer, so that the prepared lithium iron manganese phosphate material has a higher compaction density, a higher specific capacity and a higher conductivity, so that the lithium ion battery prepared using the lithium iron manganese phosphate material has a higher cycle performance and a 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 any range therebetween.

[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 above substances. 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 ethoxide, 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 above substances. 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 acetylacetonate 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] By way of example, the iron source is not limited to the above substances. For example, the iron source may also include at least one of ferric hydroxide, ferric phosphate, ferrous carbonate, ferrous nitrate, ferrous sulfide, ferrous phosphate, ferrous iodide, ferrous fluoride, ferrous bromide, ferrous acetylacetonate, 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 above substances. 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. The spray drying method is conducive to the liquid phase containing the lithium source, manganese source, iron source, phosphorus source and carbon source being more fully converted into a granular system after drying, which is conducive to taking into account the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material, so that the compaction density, specific capacity and conductivity of the lithium iron manganese phosphate material are higher, and the lithium ion battery has 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 to form particles, 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 also include other positive electrode active materials, and other positive electrode active materials may include one or more of lithium transition metal oxides, lithium phosphates with olivine structures, and their respective modified compounds. The modified compounds of the above-mentioned positive electrode active materials may be doping modification, surface coating modification, or doping and surface coating modification of the positive electrode active material. For example, the lithium transition metal oxide 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, the lithium phosphate containing olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, a composite material of lithium manganese iron phosphate and carbon, 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 the present application does not limit the preparation method of other positive electrode active materials in the positive electrode active material layer.

[0124] The above-mentioned positive electrode active materials can be used to prepare positive electrode sheets. The positive electrode sheets can be prepared according to conventional methods in the art. For example, the positive electrode active materials, conductive agents and binders described above are dispersed in a solvent, and the solvent can be N-methylpyrrolidone (NMP) or deionized water to form a uniform positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet is obtained through drying, cold pressing and other processes.

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

[0126] Next, one or more embodiments are described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0127] Experimental Example 1

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

[0129] Weigh 130.66 g of 75 wt % phosphoric acid (i.e. phosphorus source) aqueous solution and add it into a stirring tank, add 37.13 g of 99.5 wt % lithium carbonate (i.e. lithium source) solid into the stirring tank, and stir evenly 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 phosphorus lithium source solution, and the mixture was sand-milled until the particle size of the solid particles in the liquid phase was about 0.3 μm to obtain a precursor solution.

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

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

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

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

[0135] The positive electrode slurry is evenly coated on both sides of the positive electrode collector aluminum foil (thickness of 6 μm) and dried at 85°C for 4 hours, then cold pressed, and then trimmed and cut into pieces, and dried at 85°C under vacuum conditions for 4 hours to obtain a positive electrode sheet, wherein the thickness of the single-side positive electrode active material layer is 200 μm.

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

[0137] Graphite, conductive agent Super P and binder polytetrafluoroethylene (PTFE) in a mass ratio of 95:2:3 were mixed in a solvent N-methylpyrrolidone (NMP) to prepare a negative electrode active slurry with a solid content of 50 wt%.

[0138] The negative electrode active slurry is coated on the current collector copper foil (thickness is 9 μm) and dried at 85°C for 4 hours, then cold pressed, and then trimmed and cut into pieces, and dried at 85°C under vacuum conditions for 4 hours to obtain a negative electrode sheet substrate; wherein the thickness of the single-sided negative electrode active material layer is 150 μm.

[0139] (4) Preparation of button cells:

[0140] A lithium sheet (500 μm thick) was used as the negative electrode, and 1 mol / L LiPF 6A solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 is used as an electrolyte, which is assembled into a button battery in a button box together with the positive electrode sheet prepared above.

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

[0142]

[0143] In Table 1, the mass proportion of the carbon source refers to: the proportion of the mass of the carbon source to the total mass of the lithium source, manganese source, iron source and phosphorus source; " / " means that there is no corresponding parameter; the difference between Examples 13 to 16 and Example 1 is only the different molar ratios of the lithium source and the phosphorus source, and the ratios of the molar amount of the manganese source, the molar amount of the iron source to the molar amount of the phosphorus source in Examples 13 to 16 are the same as those in Example 1; the difference between Example 19 and Example 1 is only the different selection of the iron source and the phosphorus source, and the ratios of the molar amount of the lithium source, the molar amount of the manganese source, the molar amount of the iron source to the molar amount of the phosphorus source in Example 19 are the same as those in Example 1.

[0144] Testing the performance of lithium manganese iron phosphate materials and button batteries:

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

[0146] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009; specific test process: take an appropriate amount of precursor solution sample (the sample concentration is guaranteed to be 8-12% shading), add 20mL deionized water, and simultaneously ultraviolet for 5min (53KHz / 120W) to ensure that the precursor solution sample is completely dispersed, and then measure the precursor solution sample according to 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, and then tested in accordance with the standard JY / T010-1996. The morphology of the lithium manganese iron phosphate material samples was observed and SEM photos were taken.

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

[0150] Weigh 1.0000±0.0500g of the lithium iron manganese phosphate material sample to be tested and place it in a test mold (CARVER#3619 (13mm), and then place the lithium iron manganese phosphate material sample in the test equipment. The test equipment 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 relief rate of 30mm / min, and a pressure relief holding time of 10s. During the pressure relief, the compaction density is measured, and the calculation formula of the compaction density is: compaction density = mass of lithium iron manganese phosphate material / (stress area of ​​lithium iron manganese phosphate material × thickness of lithium iron manganese phosphate material).

[0151] (4) Resistivity test of lithium manganese iron phosphate material

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

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

[0154] At 25°C, the button cell assembled from the corresponding manganese iron phosphate material was charged to 4.3V at a constant current of 0.1C, then charged to a current of 0.01C at a constant voltage of 4.3V, left for 5 minutes, and then discharged to 2.0V at 0.1C. The resulting discharge capacity was recorded as c1, and the capacity obtained after repeating the cycle for the second time was recorded as c2. Three parallel samples of button cells were prepared, and the average c2 of the three parallel samples was recorded as the average discharge capacity c0. The specific capacity of the manganese iron phosphate material = c0 / M, where M is the average mass of the manganese iron phosphate material.

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

[0156] At 25°C, the button cell is first charged to 4.3V at a constant current of 0.1C, then charged to a current of 0.01C at a constant voltage of 4.3V, left for 5 minutes, and then discharged to 2.0V at 0.1C. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The button cell is subjected to a 100-cycle charge and discharge test in the above manner, and the discharge capacity of the 100th cycle is detected, and the capacity retention rate of the button cell after the cycle is calculated by the following formula.

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

[0158] (7) Rate energy test of button cell

[0159] At 25°C, first charge the button cell to 4.3V at a constant current of 0.1C, then charge at a constant voltage of 4.3V to a current of 0.01C, leave for 5 minutes, and then discharge at 0.1C to 2.0V. This is a charge-discharge cycle. Use the same process to change the charge and discharge currents, charge and discharge with currents of 0.1C, 0.33C, 1C, 2C, and 5C, and cycle 10 times for each current, and record the discharge capacity.

[0160] 1C discharge capacity retention rate (%) = (1C de-lithiation capacity average value / 0.1C de-lithiation capacity average value) × 100%;

[0161] Among them, the performance of lithium manganese iron phosphate material and button battery is shown in Table 2:

[0162] Table 2 Performance of lithium manganese iron phosphate material and button battery

[0163]

[0164]

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

[0166] from Figures 6 to 8 It can be seen that the lithium iron manganese phosphate material prepared in Example 1 of the present application is generally spherical or quasi-spherical particles, and the particles are relatively evenly dispersed, and the particle size is roughly between 0.1μm and 0.5μm; while the lithium iron manganese phosphate material particles prepared in Comparative Examples 1 and 4 are in agglomerated state; indicating that the use of non-polar carbon-containing compounds as carbon sources can inhibit the agglomeration of lithium iron manganese phosphate materials during the preparation process, which is conducive to obtaining lithium iron manganese phosphate materials with evenly dispersed particles.

[0167] It can be seen from Table 2 that the compacted density and specific capacity of the lithium iron manganese phosphate materials prepared in Examples 1 to 19 are higher than those of the lithium iron manganese phosphate materials prepared in Comparative Examples 1 to 4, the powder resistivity of the lithium iron manganese phosphate materials prepared in Examples 1 to 19 is lower than that of the lithium iron manganese phosphate materials prepared in Comparative Examples 1 to 4, and the cycle performance and rate performance of the button batteries corresponding to the lithium iron manganese phosphate materials prepared in Examples 1 to 19 are higher than those of the button batteries corresponding to the lithium iron manganese phosphate materials prepared in Comparative Examples 1 to 4; indicating that the use of non-polar carbon-containing compounds as carbon sources can improve the compacted density, specific capacity and electronic conductivity of the lithium iron manganese phosphate material, and can also improve the cycle performance and rate performance of lithium-ion batteries.

[0168] It can be seen from Examples 1 to 5 that the carbon sources of Examples 1 to 3 are all polymer carbon sources and are hard carbon after sintering, while the coal tar of Example 4 and the petroleum coke of Example 5 are both hard carbon after sintering; the compacted density and specific capacity of the lithium iron manganese phosphate materials prepared in Examples 1 to 3 are higher than those of the lithium iron manganese phosphate materials prepared in Examples 4 to 5, the powder resistivity of the lithium iron manganese phosphate materials prepared in Examples 1 to 3 is lower than that of the lithium iron manganese phosphate materials prepared in Examples 4 to 5, and the cycle performance and rate performance of the button batteries corresponding to the lithium iron manganese phosphate materials prepared in Examples 1 to 3 are higher than those of the button batteries corresponding to the lithium iron manganese phosphate materials prepared in Examples 4 to 5; this indicates that: when the carbon source is a non-polar carbon source, the carbon source is hard carbon after sintering, which is beneficial to further improve the compacted density, specific capacity and electronic conductivity of the lithium iron manganese phosphate material, and is also beneficial to further improve the cycle performance and rate performance of lithium-ion batteries.

[0169] It can be seen from Example 1 and Examples 6 to 9 that "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 the lithium iron manganese phosphate material, as well as the cycle performance and rate performance of the lithium ion battery; 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 the lithium iron manganese phosphate material can be high, and the cycle performance and rate performance of the lithium ion battery are high.

[0170] It can be seen from Examples 1 and 10 to 12 that the volume average particle size Dv50 of the solid particles in the precursor solution can further affect the specific capacity and electronic conductivity of the lithium iron manganese 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 the lithium iron manganese phosphate material can be further improved.

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

[0172] It can be seen from Example 1 and Examples 17 to 18 that the sintering temperature and time can further affect the compaction density, specific capacity and electronic conductivity of the lithium iron manganese oxide material, as well as the cycle performance and rate performance of the lithium ion battery.

[0173] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

Claims

1. A method for preparing lithium manganese iron phosphate material, characterized in that: include: The liquid phase containing the lithium source, the manganese source, the iron source, the phosphorus source and the carbon source is sequentially ground, dried and sintered under an inert atmosphere to form a lithium manganese iron phosphate material with a carbon layer coated on the surface; Wherein, the carbon source is a non-polar carbon-containing compound.

2. The preparation method according to claim 1, characterized in that: 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 a carbon-containing polymer compound.

3. The preparation method according to claim 1 or 2, characterized in that: The carbon source comprises at least one of polyethylene, polypropylene, polystyrene, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, amylose, amylopectin, cyclodextrin, polyoxymethylene and polyaniline; Optionally, the carbon source includes at least one of polypropylene, cyclodextrin, polyvinylidene fluoride, polytetrafluoroethylene and polystyrene.

4. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is ≥1:1; Optionally, the molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is (1-1.04):1; Optionally, the molar ratio of the lithium element in the lithium source to the phosphorus element in the phosphorus source is >1:1 and ≤1.04:

1.

5. The preparation method according to claim 4, characterized in that: The ratio of the molar amount of lithium element in the lithium source, the molar amount of manganese element in the manganese source, the molar amount of iron element in the iron source and the molar amount of phosphorus element in the phosphorus source is (1-1.04):(0.3-0.7):(0.3-0.7):

1.

6. The preparation method according to claim 1 or 2, characterized in that: The ratio of the mass 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.

7. The preparation method according to claim 1 or 2, characterized in that: 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.

8. The preparation method according to claim 1 or 2, characterized in that: The sintering temperature is 670°C to 760°C; Optionally, the sintering time is 8 hours to 16 hours.

9. The preparation method according to claim 1 or 2, characterized in that: The lithium source includes at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium dihydrogen phosphate and lithium phosphate; Or / and, the manganese source includes at least one of manganese sulfate, manganese chloride, manganese oxalate, manganese oxide and manganese acetate; Or / and, the iron source comprises at least one of ferrous oxalate, ferric oxide, ferrous oxide, ferrous sulfate, ferrous acetate and ferrous chloride; Or / and, the phosphorus source includes at least one of lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate and lithium phosphate.

10. The preparation method according to claim 1 or 2, characterized in that: The drying method is spray drying.

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

12. A positive electrode active material, characterized in that: The positive electrode active material includes the lithium manganese iron phosphate material as claimed in claim 11.

13. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode collector and a positive electrode active layer covering at least one surface of the positive electrode collector in a thickness direction; wherein the positive electrode active layer includes the positive electrode active material according to claim 12.

14. A battery, characterized in that: The battery comprises the positive electrode sheet according to claim 13.

15. An electrical equipment, characterized in that: The electrical device comprises the battery according to claim 14.

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