Lithium manganese iron phosphate positive electrode active material, positive electrode sheet, battery, battery pack, and electrical equipment

Abstract

The present invention provides a lithium iron manganese phosphate positive electrode active material, a positive electrode sheet, a battery, a battery pack, and an electrical device. The lithium iron manganese phosphate positive electrode active material satisfies the following conditions: 0.2·D≤#imgabs0#≤0.8·D, where D is the Dv50 of the lithium iron manganese phosphate positive electrode active material (unit: μm), n1 is the molar amount of manganese in the lithium iron manganese phosphate positive electrode active material (unit: mol), n2 is the molar amount of iron in the lithium iron manganese phosphate positive electrode active material (unit: mol), and A is the particle size of the primary particles of the lithium iron manganese phosphate positive electrode active material (unit: μm). The voltage platforms in different regions of the lithium iron manganese phosphate positive electrode active material exhibit consistent performance, thereby improving the material's capacity and cycle life.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and in particular to a lithium iron manganese phosphate positive electrode active material, and in particular to a lithium iron manganese phosphate positive electrode active material, a positive electrode sheet, a battery, a battery pack, and an electrical device. Background Art

[0002] As one of the current mainstream battery positive electrode materials, lithium iron phosphate material has the advantages of good safety performance, long cycle life and low cost. However, due to its low discharge voltage platform, its energy density is low, which further limits its wide application.

[0003] At present, the main way to improve the discharge voltage platform of lithium iron phosphate materials includes doping manganese elements into lithium iron phosphate materials. Since the radius of manganese atoms is close to that of iron atoms, they can be better integrated into the lattice structure of lithium iron phosphate. By melting iron and manganese to form lithium iron manganese phosphate materials, the voltage platform of lithium iron phosphate materials can be improved. However, while the introduction of manganese elements can improve the voltage platform of the material, it will also lead to a decrease in the cycle stability of the lithium iron manganese phosphate material. Summary of the Invention

[0004] The present invention provides a lithium iron manganese phosphate positive electrode active material, which can improve the cycle life of lithium iron manganese phosphate batteries.

[0005] The present invention also provides a positive electrode sheet. Since the positive electrode sheet includes the above-mentioned lithium manganese iron phosphate positive electrode active material, the positive electrode sheet has the advantage of good cycle stability.

[0006] The present invention also provides a battery. Since the battery includes the positive electrode sheet, the battery has a long cycle life.

[0007] The present invention also provides a battery pack, which includes the battery and has a long cycle life.

[0008] The present invention also provides an electrical device. Since the electrical device includes the battery or battery pack, it has the advantage of a long service life.

[0009] A first aspect of the present invention provides a lithium manganese iron phosphate positive electrode active material, wherein the lithium manganese iron phosphate positive electrode active material satisfies the following formula 1:

[0010] 0.2·D≤ ≤0.8·D Formula 1,

[0011] Wherein, D is the Dv50 of the lithium iron manganese phosphate positive electrode active material, unit: μm, n1 is the molar amount of manganese element in the lithium iron manganese phosphate positive electrode active material, unit: mol, n2 is the molar amount of iron element in the lithium iron manganese phosphate positive electrode active material, unit: mol, and A is the particle size of the primary particles of the lithium iron manganese phosphate positive electrode active material, unit: μm.

[0012] Optionally, the lithium manganese iron phosphate positive electrode active material satisfies:

[0013] 1.5μm <D<2.0μm;

[0014] and / or, 1.2 μm ≤ A ≤ 2.5 μm;

[0015] and / or, 0.3 ≤ ≤0.6.

[0016] Optionally, the molecular formula of the lithium manganese iron phosphate positive electrode active material is: Li2Fe x Mn y M z PO4; wherein, the M includes at least one of Cr, Zr, Mg, and Co, 0<x<1, 0<y<1, 0≤z<1, and satisfies x+y+z=1.

[0017] Optionally, 0.2<y<0.6.

[0018] A second aspect of the present invention provides a method for preparing the above lithium manganese iron phosphate positive electrode active material, comprising the following steps:

[0019] Sintering a primary material comprising a manganese source, an iron source, a lithium source, and a phosphorus source to obtain a secondary material, and crushing the secondary material to obtain the lithium manganese iron phosphate positive electrode active material;

[0020] Wherein, the iron source includes ferric oxide, and the primary material satisfies the following formula 2:

[0021] 0.2·d≤ 0.8·d Equation 2;

[0022] Wherein, d is the Dv50 of the ferric oxide, unit: μm, n3 is the molar amount of manganese in the manganese source, unit: mol, n4 is the molar amount of iron in the iron source, unit: mol, and B is the particle size of the ferric oxide, unit: μm.

[0023] Optionally, the primary material meets the following requirements:

[0024] 1.5μm <d<2.0μm;

[0025] and / or, 1.2 μm ≤ B ≤ 2.5 μm;

[0026] and / or, 0.3 ≤ ≤0.6.

[0027] Optionally, the manganese source is selected from one or more of manganese chloride, manganese nitrate, manganese acetate, manganese sulfate, and manganese carbonate;

[0028] And / or, the lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium phosphate;

[0029] And / or, the phosphorus source is selected from potassium dihydrogen phosphate and / or ammonium dihydrogen phosphate.

[0030] Optionally, the sintering treatment includes: performing a heat preservation treatment at 600-800° C. in a protective atmosphere.

[0031] A third aspect of the present invention provides a positive electrode sheet comprising the lithium manganese iron phosphate positive electrode active material as described in the first aspect or the lithium manganese iron phosphate positive electrode active material prepared by the preparation method described in the second aspect.

[0032] A fourth aspect of the present invention provides a battery comprising the positive electrode sheet as described in the third aspect above.

[0033] A fifth aspect of the present invention provides a battery pack comprising at least two batteries as described in the fourth aspect above.

[0034] A sixth aspect of the present invention provides an electrical device comprising the battery as described in the fourth aspect or the battery pack as described in the fifth aspect.

[0035] The lithium manganese iron phosphate positive electrode active material provided by the present invention ensures the consistency of the voltage platform performance of the lithium manganese iron phosphate positive electrode active material in different regions by limiting its Dv50, the ratio of the molar content of the Mn element to the total molar amount of the Mn element and the Fe element, and the relationship between the primary particle size, so that the lithium manganese iron phosphate active material participates in the reaction, reduces the loss of invalid capacity, and thus improves the cycle stability of the battery. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0037] Lithium manganese iron phosphate positive electrode active materials have a higher voltage platform than lithium iron phosphate positive electrode active materials, but the cycle stability is relatively low. The present invention finds that this is mainly due to the high manganese content and particle size distribution in the positive electrode active material, which leads to different and unbalanced voltage platforms in different regions of the active material. Therefore, by controlling the relationship between the Mn element, Fe element and the particle size of the lithium manganese iron phosphate positive electrode active material, the above problem can be alleviated. To this end, the present invention provides the following solutions:

[0038] In a first aspect, the present invention provides a lithium manganese iron phosphate positive electrode active material, wherein the lithium manganese iron phosphate positive electrode active material satisfies the following formula 1:

[0039] 0.2·D≤ ≤0.8·D Formula 1,

[0040] Wherein, D is the Dv50 of the lithium iron manganese phosphate positive electrode active material, unit: μm, n1 is the molar amount of manganese element in the lithium iron manganese phosphate positive electrode active material, unit: mol, n2 is the molar amount of iron element in the lithium iron manganese phosphate positive electrode active material, unit: mol, and A is the particle size of the primary particles of the lithium iron manganese phosphate positive electrode active material, unit: μm.

[0041] The lithium manganese iron phosphate positive electrode active material of the present invention can improve the cycle stability of the battery. The main reasons include: the present invention solves the problem of different and unbalanced voltage platforms of different lithium manganese iron phosphate particles by limiting the Dv50 of the lithium manganese iron phosphate positive electrode active material, the ratio of the molar content of the Mn element to the total molar amount of the Mn element and the Fe element, and the proportional relationship between the primary particle sizes. In detail, on the one hand, the particle size and manganese content of the lithium manganese iron phosphate material jointly affect the material voltage platform. When other conditions are equal, the larger the particle size, the lower the voltage platform, and the higher the manganese content, the higher the material voltage platform. If a particle has a small particle size and a high manganese content, the material voltage platform will be relatively high. Similarly, if a particle has a large particle size and a low manganese content, the material voltage platform will be relatively low. In this way, during the charge and discharge process, using the same charge and discharge method will cause some particles to charge and discharge normally, while other particles will be overcharged / over-discharged, causing the overall cycle performance of the material to deteriorate. Since the above formula 1 establishes a suitable matching relationship between the primary particles and the manganese content of the lithium iron manganese phosphate positive electrode active material, and balances the two factors of the effect of particle size on the voltage platform and the effect of manganese content on the voltage platform, the voltage platforms of different particles are kept as consistent as possible, thereby avoiding overcharge / over-discharge of some materials and thus avoiding deterioration of cycle performance; on the other hand, since the Jahn-Teller effect of manganese may cause lattice distortion of the lithium iron manganese phosphate positive electrode active material, the above formula 1 makes the manganese distribution and the median particle size of the lithium iron manganese phosphate positive electrode active material closely related, which can relieve local stress, thereby avoiding the problem of different voltage platform performance of the lithium iron manganese phosphate positive electrode active material due to lattice distortion.

[0042] For the above reasons, the particle voltage platform of the lithium manganese iron phosphate positive active material of the present invention is relatively consistent in different regions, so that the battery assembled therefrom can have both high capacity and high cycle stability, and its overall performance is better.

[0043] In some embodiments, the lithium manganese iron phosphate positive electrode active material satisfies:

[0044] 1.5μm <D<2.0μm。

[0045] In the above-described embodiment, by further limiting the numerical range of D, the lithium manganese iron phosphate positive electrode active material is more balancedly optimized in terms of capacity performance and cycle life, while providing a clear parameter window for industrial production.

[0046] In some embodiments, the lithium manganese iron phosphate positive electrode active material further satisfies:

[0047] 1.2μm≤A≤2.5μm.

[0048] In the above-described embodiment, by further limiting the numerical range of A, the capacity and cycle life of the lithium manganese iron phosphate positive electrode active material are further improved, while providing a clear parameter window for industrial production.

[0049] In some embodiments, the lithium manganese iron phosphate positive electrode active material further satisfies:

[0050] 0.3≤ ≤0.6.

[0051] The above embodiment is further defined by The numerical range of the lithium manganese iron phosphate positive electrode active material further improves the capacity and cycle life, and provides a clear parameter window for industrial production.

[0052] Exemplarily, the D is any one of 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, etc., or a range consisting of both, the A is any one of 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, etc., or a range consisting of both, the It is any one of 0.3, 0.4, 0.5, 0.6, etc., or a range consisting of two of them.

[0053] Generally speaking, lithium iron phosphate cathode materials are microscopically spherical or quasi-spherical particles, each composed of a stack of numerous irregularly shaped small particles. These irregular small particles are called "primary particles," while the spherical particles formed by stacking these primary particles are called secondary particles. In other words, lithium iron phosphate cathode materials, in their natural state, primarily consist of secondary particles formed by stacking primary particles. The Dv50 of the lithium iron phosphate cathode active material represents the particle size on the cumulative curve of the lithium iron phosphate cathode active material when the volumetric penetration percentage is 50%.

[0054] In some embodiments, a method for testing the Dv50 of a lithium iron manganese phosphate positive electrode active material includes: using a Malvern Mastersizer 3000 to perform analysis by wet dispersion-laser derivatization, specifically weighing 0.20±0.01 g of a lithium iron manganese phosphate positive electrode active material sample into a 100 mL beaker, adding 3 mL of a surfactant dropwise, adding deionized water to 20.0±0.1 mL, sealing the beaker with a sealing film, and placing the sample in an ultrasonic machine (40 KHz / 210 W, output power 70%) for 5 minutes of ultrasonication, with a laser intensity of 70-90% and a detector light energy of <100. Testing is started when the shading reaches 5-15%, thereby obtaining a cumulative distribution curve of the lithium iron manganese phosphate positive electrode active material.

[0055] In some embodiments, n1 and n2 are tested for element content by ICP (Inductively Coupled Plasma).

[0056] A refers to the particle size of any primary particle of the lithium manganese iron phosphate positive electrode active material; in some embodiments, A can be tested by a scanning electron microscope, and the specific testing method includes the following steps: placing the material under a scanning electron microscope, and measuring the farthest distance between two points on the edge of any particle, which is the particle size of the primary particle.

[0057] In some embodiments, the molecular formula of the lithium manganese iron phosphate positive electrode active material is: Li2Fe x Mn y M z PO4; wherein, the M includes at least one of Cr, Zr, Mg, and Co, 0<x<1, 0<y<1, 0≤z<1, and satisfies x+y+z=1.

[0058] The above-described embodiment further optimizes the chemical composition of the lithium manganese iron phosphate positive electrode active material, and further regulates the electronic structure, lattice stability and ion transport kinetics of the secondary particles at the atomic scale.

[0059] Illustratively, x is any value of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc., or a range consisting of both; y is any value of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc., or a range consisting of both; z is any value of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc., or a range consisting of both.

[0060] In some embodiments, 0.2<y<0.6.

[0061] The above-described embodiment can further ensure the cycle life and capacity of the lithium manganese iron phosphate positive electrode active material by regulating the value of y.

[0062] In a second aspect, the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode active material, comprising the following steps:

[0063] Sintering a primary material comprising a manganese source, an iron source, a lithium source, and a phosphorus source to obtain a secondary material, and crushing the secondary material to obtain the lithium manganese iron phosphate positive electrode active material;

[0064] Wherein, the iron source includes ferric oxide, and the primary material satisfies the following formula 2:

[0065] 0.2·d≤ ≤0.8·d Equation 2;

[0066] Wherein, d is the Dv50 of the ferric oxide, unit: μm, n3 is the molar amount of manganese in the manganese source, unit: mol, n4 is the molar amount of iron in the iron source, unit: mol, and B is the particle size of the ferric oxide, unit: μm.

[0067] The above preparation method can prepare the lithium manganese iron phosphate positive electrode active material of the above-mentioned first aspect. The main reason is that: the above preparation method introduces ferric oxide as an iron source, and ferric oxide serves as a template. By constraining the relationship between the Dv50 of ferric oxide, the measured particle size B and the manganese element / iron element ratio in the primary material, it can ensure that the diffusion rates of manganese and iron elements during the sintering process are matched, thereby obtaining a lithium manganese iron phosphate positive electrode active material that satisfies Formula 1.

[0068] The test method of d can refer to the test method of Dv50 of lithium manganese iron phosphate positive electrode active material.

[0069] B refers to the measured particle size of any particle of ferric oxide; in some embodiments, the testing method of B is: testing through a scanning electron microscope, and the specific testing method includes the following steps: placing the material under a scanning electron microscope, and measuring the farthest distance between two points on the edge of any particle, which is the particle size of the particle.

[0070] In some embodiments, n3 and n4 are tested for elemental content by ICP (inductively coupled plasma).

[0071] In some embodiments, the primary material satisfies:

[0072] 1.5μm <d<2.0μm。

[0073] In some embodiments, the primary material satisfies:

[0074] 1.2μm≤B≤2.5μm.

[0075] In some embodiments, the primary material satisfies:

[0076] 0.3≤ ≤0.6.

[0077] The above embodiment further limits the range of at least one key parameter of the primary material, thereby avoiding the common problems of component segregation and particle size loss in the traditional preparation process of lithium manganese iron phosphate positive active material, and can also improve the local capacity of the material and enhance the structural stability.

[0078] Exemplarily, the d is any one of 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, etc., or a range consisting of both, the B is any one of 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, etc., or a range consisting of both, the It is any one of 0.3, 0.4, 0.5, 0.6, etc., or a range consisting of two of them.

[0079] In some embodiments, the manganese source is selected from one or more of manganese chloride, manganese nitrate, manganese acetate, manganese sulfate, and manganese carbonate.

[0080] In some embodiments, the lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium phosphate.

[0081] In some embodiments, the phosphorus source is selected from potassium dihydrogen phosphate and / or ammonium dihydrogen phosphate.

[0082] Among them, the iron source, manganese source, lithium source and phosphorus source mentioned above have high stability, and the raw materials are easy to obtain and suitable for large-scale production. Moreover, the preferred combination of the above raw materials can prepare high-energy, long-life or high-rate phosphorus-manganese-iron-lithium positive electrode active materials.

[0083] In some embodiments, the sintering treatment includes: performing a heat preservation treatment at 600-800° C. in a protective atmosphere.

[0084] The above embodiment limits the sintering temperature to 600-800° C. This temperature range can ensure a complete reaction and is more conducive to forming a pure-phase lithium manganese iron phosphate positive electrode active material.

[0085] The above embodiment performs sintering in a protective atmosphere, which can avoid the influence of impurity phases, so that the prepared lithium manganese iron phosphate positive electrode active material has both energy density and cycle stability.

[0086] The protective atmosphere includes but is not limited to nitrogen, argon, etc.

[0087] The sintering treatment time may be 7-10 hours, specifically including but not limited to 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0088] Illustratively, the temperature of the sintering treatment is any value among 600°C, 620°C, 650°C, 670°C, 700°C, 720°C, 750°C, 770°C, 800°C, etc., or a range consisting of any two of the values.

[0089] In some embodiments, the primary material is prepared by a method comprising the following steps:

[0090] The manganese source, the iron source, the lithium source, the phosphorus source and a solvent are mixed to obtain a mixed material, and the mixed material is dried to obtain the primary material.

[0091] The present invention provides for mixing and drying of a mixture of a manganese source, an iron source, a lithium source, a phosphorus source and a solvent, thereby optimizing the mixing uniformity, particle fineness and physical state of the raw materials, thereby laying the foundation for subsequent sintering reactions.

[0092] Exemplarily, the mixing treatment is specifically grinding, stirring and other treatment methods, and the temperature of the drying treatment can be any value between 20-100°C, more specifically any value between 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc., or a range consisting of any two of them.

[0093] In a third aspect, the present invention provides a positive electrode sheet comprising the lithium manganese iron phosphate positive electrode active material described in the second aspect.

[0094] In a specific embodiment, the above-mentioned positive electrode sheet includes a current collector and a positive electrode active material layer located on at least one surface of the current collector, the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder, and the positive electrode active material includes the lithium manganese iron phosphate positive electrode active material described in the first aspect; the material of the above-mentioned current collector is not specifically limited in the present invention, for example, it can be selected from any one or more of aluminum, nickel, titanium, stainless steel, etc.; the above-mentioned conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0095] In a fourth aspect, the present invention provides a battery comprising the positive electrode sheet described in the third aspect.

[0096] In some embodiments, the battery further includes a negative electrode sheet and a separator.

[0097] As for the composition and material of the positive electrode sheet, negative electrode sheet and separator of the battery, the present invention does not specifically limit them. Exemplarily, the above-mentioned negative electrode sheet includes a current collector and a negative electrode active material layer located on at least one surface of the current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder. The negative electrode active material includes one or more of graphite, hard carbon, soft carbon, silicon-based negative electrode, titanium-based material, nitride, tinide, and metallic lithium. The negative electrode current collector can be a conventional negative electrode current collector in the art, for example, including copper foil, etc. The above-mentioned conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0098] In some embodiments, the negative electrode active material layer further includes a dispersant, and the dispersant can be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium lauryl sulfate.

[0099] The battery of the present invention can be manufactured according to conventional methods in the field. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked in sequence, and then assembled into a battery cell through a winding process or a stacking process. Then, after packaging and baking, the electrolyte is injected, and the battery is manufactured after processes such as hot pressing.

[0100] For example, the present invention does not impose any particular restrictions on the material of the separator. Any known porous structure separator with electrochemical and chemical stability can be selected. For example, it can be at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be single-layer or multi-layer.

[0101] The battery also includes an electrolyte. In some embodiments, an electrolyte comprising an organic solvent and an electrolyte salt is selected. The organic solvent, serving as a medium for transporting ions during the electrochemical reaction, may be any organic solvent known in the art for battery electrolytes, such as one or more of fluorocarbonates, fluorocarboxylates, non-fluorocarbonates, fluorocarbonates, non-fluorocarboxylates, fluorocarboxylates, fluoroethers, non-fluoroethers, and tetrahydrofuran. The electrolyte salt, serving as a source of ions, may be any electrolyte salt known in the art for battery electrolytes, such as one or more of lithium hexafluorophosphate, bistrifluoromethylsulfonyl imide, and lithium bis(fluorosulfonyl)imide.

[0102] In a fifth aspect, the present invention provides a battery pack comprising at least two batteries as described in the fourth aspect above.

[0103] Generally, a battery pack includes at least two of the above-mentioned batteries, which are connected as single cells to form a battery pack. The batteries can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods.

[0104] In a sixth aspect, the present invention provides an electrical device comprising the battery described in the fourth aspect or the battery pack described in the fifth aspect.

[0105] It should be noted that the above-mentioned electrical equipment can be any conventional equipment that requires electricity, such as but not limited to computers, electric cars, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0106] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0107] The technical solutions of the present invention are further illustrated below with reference to specific examples. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are by weight. All reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment. The instruments used in the examples are commercially available.

[0108] Example 1

[0109] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y PO4; 0.29≤y≤0.31, x=1-y, the lithium manganese iron phosphate positive electrode active material satisfies the following formula 1:

[0110] 0.2·D≤ ≤0.8·D Formula 1,

[0111] Where D is 1.6μm, 0.29≤ ≤0.31, A is 1.2-2.3μm.

[0112] The preparation method thereof comprises the following steps:

[0113] Manganese chloride, ferric oxide particles, lithium acetate and ammonium dihydrogen phosphate are taken in a molar ratio of 0.3:0.35:2:1, and are ground with a first dispersion of ethanol solvent to obtain a slurry. The slurry is vacuum dried at 70°C for 5 hours to obtain a primary material. The dry powder material is heated from room temperature to 750°C at a heating rate of 5°C / min in a nitrogen atmosphere and kept warm for 8 hours to obtain a secondary material. The secondary material is ball milled for 7 hours to obtain a lithium manganese iron phosphate positive electrode active material.

[0114] Among them, the ferric oxide particles in the raw material satisfy the following formula 2:

[0115] 0.2·d≤ ≤0.8·d Equation 2;

[0116] Where d is 1.6 μm, 0.29≤ ≤0.31, B is 1.2-2.3μm.

[0117] Example 2

[0118] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y PO4, 0.39≤y≤0.42, x=1-y; the parameters of the lithium manganese iron phosphate positive electrode active material are shown in Table 1.

[0119] The preparation method comprises the following steps: manganese chloride, ferric oxide particles, lithium acetate and ammonium dihydrogen phosphate are taken in a molar ratio of 0.4:0.3:2:1, and ground with a first dispersion liquid of ethanol solvent to obtain a slurry; the slurry is vacuum dried at 80°C for 6 hours to obtain a primary material (parameters refer to Table 1); the dry powder material is heated from room temperature to 650°C at a heating rate of 5°C / min in a nitrogen atmosphere, and kept warm for 9 hours to obtain a secondary material; the secondary material is ball-milled for 6.5 hours to obtain a lithium manganese iron phosphate positive electrode active material.

[0120] Example 3

[0121] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y PO4, 0.48≤y≤0.51, x=1-y; the parameters of the lithium manganese iron phosphate positive electrode active material are shown in Table 1.

[0122] The preparation method comprises the following steps: manganese chloride, ferric oxide particles, lithium acetate and ammonium dihydrogen phosphate are taken in a molar ratio of 0.5:0.25:2:1, and ground with a first dispersion liquid of ethanol solvent to obtain a slurry; the slurry is vacuum dried at 80°C for 7 hours to obtain a primary material (parameters refer to Table 1); the dry powder material is heated from room temperature to 700°C at a heating rate of 5°C / min in a nitrogen atmosphere, and kept warm for 8 hours to obtain a secondary material; the secondary material is ball-milled for 6 hours to obtain a lithium manganese iron phosphate positive electrode active material.

[0123] Example 4

[0124] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y PO4, 0.59≤y≤0.61, x=1-y; the parameters of the lithium manganese iron phosphate positive electrode active material are shown in Table 1.

[0125] The preparation method comprises the following steps: manganese chloride, ferric oxide particles, lithium acetate and ammonium dihydrogen phosphate are taken in a molar ratio of 0.6:0.2:2:1, and ground with a first dispersion liquid of ethanol solvent to obtain a slurry; the slurry is vacuum dried at 80°C for 7 hours to obtain a primary material (parameters refer to Table 1); the dry powder material is heated from room temperature to 700°C at a heating rate of 5°C / min in a nitrogen atmosphere, and kept warm for 9 hours to obtain a secondary material; the secondary material is ball-milled for 6.5 hours to obtain a lithium manganese iron phosphate positive electrode active material.

[0126] Example 5

[0127] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y Mg 0.2 PO4, 0.38≤y≤0.41, x=0.8-y; the parameters of the lithium manganese iron phosphate positive electrode active material are shown in Table 1.

[0128] The preparation method comprises the following steps: manganese chloride, ferric oxide particles, magnesium chloride, lithium acetate and ammonium dihydrogen phosphate are taken in a molar ratio of 0.4:0.2:0.2:2:1, and ground with a first dispersion liquid of ethanol solvent to obtain a slurry; the slurry is vacuum dried at 80°C for 7 hours to obtain a primary material (parameters refer to Table 1); the dry powder material is heated from room temperature to 700°C at a heating rate of 5°C / min in a nitrogen atmosphere, and kept warm for 9 hours to obtain a secondary material; the secondary material is ball milled for 6.5 hours to obtain a lithium manganese iron phosphate positive electrode active material.

[0129] Example 6

[0130] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y Cr 0.2 PO4, 0.38≤y≤0.41, x=0.8-y; the parameters of the lithium manganese iron phosphate positive electrode active material are shown in Table 1.

[0131] The preparation method comprises the following steps: manganese chloride, ferric oxide particles, chromium trichloride, lithium acetate and ammonium dihydrogen phosphate are taken in a molar ratio of 0.4:0.2:0.2:2:1, and ground with a first dispersion liquid of ethanol solvent to obtain a slurry; the slurry is vacuum dried at 80°C for 7 hours to obtain a primary material (parameters refer to Table 1); the dry powder material is heated from room temperature to 700°C at a heating rate of 5°C / min in a nitrogen atmosphere, and kept warm for 9 hours to obtain a secondary material; the secondary material is ball-milled for 6.5 hours to obtain a lithium manganese iron phosphate positive electrode active material.

[0132] Example 7

[0133] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y Co 0.2 PO4, 0.38≤y≤0.41, x=0.8-y; the parameters of the lithium manganese iron phosphate positive electrode active material are shown in Table 1.

[0134] The preparation method comprises the following steps: manganese chloride, ferric oxide particles, cobalt chloride, lithium acetate and ammonium dihydrogen phosphate are taken in a molar ratio of 0.4:0.2:0.2:2:1, and ground with a first dispersion liquid of ethanol solvent to obtain a slurry; the slurry is vacuum dried at 80°C for 7 hours to obtain a primary material (parameters refer to Table 1); the dry powder material is heated from room temperature to 700°C at a heating rate of 5°C / min in a nitrogen atmosphere, and kept warm for 9 hours to obtain a secondary material; the secondary material is ball-milled for 6.5 hours to obtain a lithium manganese iron phosphate positive electrode active material.

[0135] Comparative Example 1

[0136] This example provides a lithium manganese iron phosphate positive electrode active material, and its preparation method is basically the same as that of Example 1. The difference from the above Example 1 is that the primary material does not satisfy Formula 2. See Table 1 for details.

[0137] Comparative Example 2

[0138] This example provides a lithium manganese iron phosphate positive electrode active material, and the preparation method is basically the same as that of Example 1. The difference from the above Example 1 is that the primary material does not satisfy Formula 2. See Table 1 for details.

[0139] Comparative Example 3

[0140] This example provides a lithium manganese iron phosphate positive electrode active material, the molecular formula of which is: Li2Fe x Mn y PO4, 0.58≤y≤0.61, x=1-y. The preparation method is basically the same as that of Example 4, except that ferric oxide is replaced with ferric chloride, and manganese chloride, ferric oxide particles, lithium acetate, and ammonium dihydrogen phosphate are taken in a molar ratio of 0.6:0.4:2:1.

[0141] Test example

[0142] Assembling a battery using the above-mentioned lithium manganese iron phosphate positive electrode active material includes the following processes:

[0143] The lithium manganese iron phosphate positive electrode material, conductive agent acetylene black, and binder PVDF obtained in the embodiment and comparative example were mixed at a mass ratio of 90:5:5, and organic solvent N-methylpyrrolidone (NMP) was added to a solvent content of 70wt%. After mixing and slurrying, the mixture was stirred at about 80g / m 2 The surface density is coated on one side on 13μm aluminum foil (the coating thickness of the slurry is 40-45μm), dried in a blower dryer at 80℃ for 4h, and rolled into a thickness of 0.053mm using an MSK-2150 electric roller machine. Then, a positive electrode sheet with a diameter of 14mm is made using an SZ-50 desktop punching machine.

[0144] The negative electrode uses a metallic lithium sheet; the separator is a polyethylene porous membrane; the solvent in the electrolyte is a solution composed of EC, DMC and EMC in a mass ratio of 1:1:1, the solute is LiPF6, and the concentration of LiPF6 is 1.0 mol / L; the 2023 button battery is assembled in a glove box.

[0145] Test Case

[0146] Test the following performance of lithium-ion batteries:

[0147] (1) Battery capacity test: At 25°C, charge at a constant current rate of 0.1C to a voltage of 4.3V, then charge at a constant voltage of 4.3V to a current of less than or equal to 0.05C, then let it stand for 5 minutes, and then discharge at a constant current rate of 0.1C to a voltage of 2.2V. The discharge capacity at this time is the initial capacity of the battery;

[0148] (2) Battery cycle performance test: At 25°C, charge at a constant current rate of 1C to a voltage of 4.3V, then charge at a constant voltage of 4.3V to a current of less than or equal to 0.05C, then let it stand for 5 minutes, and then discharge at a constant current rate of 1C to a voltage of 2.2V. The discharge capacity at this time is the initial capacity of the battery 1C cycle. Test the capacity after 50 cycles of 1C cycle, and the capacity after 100 cycles / initial capacity 100% = 1C 100-cycle retention rate.

[0149] The above test results are summarized in Table 1.

[0150] Table 1:

[0151]

[0152] As can be seen from Table 1, compared with the comparative example, the lithium manganese iron phosphate positive electrode material of the embodiment is used as a positive electrode sheet and applied to a battery, which can significantly improve the cycle performance.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium manganese iron phosphate positive electrode active material, characterized in that: The lithium manganese iron phosphate positive electrode active material satisfies the following formula 1: 0.2·D≤ ≤0.8·D Formula 1, Wherein, D is the Dv50 of the lithium iron manganese phosphate positive electrode active material, unit: μm, n1 is the molar amount of manganese element in the lithium iron manganese phosphate positive electrode active material, unit: mol, n2 is the molar amount of iron element in the lithium iron manganese phosphate positive electrode active material, unit: mol, A is the particle size of any primary particle of the lithium iron manganese phosphate positive electrode active material, unit: μm; The lithium manganese iron phosphate positive electrode active material meets the following requirements: 1.5μm <D<2.0μm; and, 1.2 μm ≤ A ≤ 2.5 μm; and, 0.3≤ ≤0.

6.

2. A method for preparing the lithium manganese iron phosphate positive electrode active material according to claim 1, characterized in that: The following steps are involved: Sintering a primary material comprising a manganese source, an iron source, a lithium source, and a phosphorus source to obtain a secondary material, and crushing the secondary material to obtain the lithium manganese iron phosphate positive electrode active material; Wherein, the iron source includes ferric oxide, and the primary material satisfies the following formula 2: 0.2·d≤ ≤0.8·d Equation 2; Wherein, d is the Dv50 of the ferric oxide, unit: μm, n3 is the molar amount of manganese in the manganese source, unit: mol, n4 is the molar amount of iron in the iron source, unit: mol, B is the measured particle size of any particle of the ferric oxide, unit: μm; The primary material meets the following requirements: 1.5μm <d<2.0μm; and, 1.2μm≤B≤2.5μm; and, 0.3≤ ≤0.

6.

3. The preparation method according to claim 2, characterized in that: The manganese source is selected from one or more of manganese chloride, manganese nitrate, manganese acetate, manganese sulfate, and manganese carbonate; And / or, the lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium phosphate; And / or, the phosphorus source is selected from potassium dihydrogen phosphate and / or ammonium dihydrogen phosphate.

4. The preparation method according to claim 2, characterized in that The sintering process includes: performing heat preservation treatment at 600-800° C. in a protective atmosphere.

5. A positive electrode sheet, characterized in that: The invention comprises the lithium manganese iron phosphate positive electrode active material according to claim 1 or the lithium manganese iron phosphate positive electrode active material obtained by the preparation method according to any one of claims 2 to 4.

6. A battery, characterized in that: Including the positive electrode sheet according to claim 5.

7. A battery pack, characterized in that: Comprising at least two batteries according to claim 6.

8. An electrical device, characterized in that: Comprising the battery according to claim 6 or the battery pack according to claim 7.

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