Lithium manganese iron phosphate composite material, preparation method thereof, positive plate and battery
By combining large and small-sized lithium manganese iron phosphate particles and coating them with a carbon layer, the problem of low compaction density of lithium manganese iron phosphate materials was solved, achieving a balance between high compaction density and electrochemical performance, and improving energy density and activity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN RONBAY SKYLAND TECHNOLOGY CO LTD
- Filing Date
- 2026-01-13
- Publication Date
- 2026-05-05
AI Technical Summary
Existing lithium manganese iron phosphate materials suffer from low compaction density and difficulty in achieving both electrochemical performance, resulting in a lack of advantage in energy density.
By preparing a composite of large and small-sized lithium manganese iron phosphate particles and coating their surfaces with a carbon layer, and by combining different valence states of manganese sources to regulate particle growth rate and size, the particle packing structure is optimized, the compaction density is improved, and good electrochemical performance is maintained.
This achieves a balance between high solid density and electrochemical performance, improving the energy density and electrochemical activity of lithium manganese iron phosphate materials.
Smart Images
Figure CN121983537A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, and in particular to a lithium manganese iron phosphate composite material, its preparation method, positive electrode sheet, and battery. Background Technology
[0002] With the increasing emphasis on safety in the new energy industry, lithium iron phosphate (LFP) materials and their batteries are being widely used and expanded. Currently, LFP materials have reached their limits in terms of both compaction density and specific capacity, resulting in maximum energy density. However, continuous technological breakthroughs necessitate the development of materials with even higher and safer energy density for optimization. Lithium manganese iron phosphate (LFP) is a derivative of LFP, incorporating manganese at the iron position within the LFP system. The manganese contributes to a higher voltage plateau, potentially leading to even higher energy density.
[0003] Currently, lithium manganese iron phosphate (LFP) materials, due to the presence of manganese, have a higher voltage plateau, approximately 12.5% higher than lithium iron phosphate (LFP). However, LFP materials suffer from a relatively low compaction density. The powder compaction density of LFP materials can reach 2.65 g / cm³. 3 The powder compaction density of lithium manganese iron phosphate material is only 2.30 g / cm³. 3 The compaction density is reduced by about 13.0%, so compared with lithium manganese iron phosphate materials, it has no advantage in terms of energy density.
[0004] In existing technologies, it is difficult to synergistically improve high density and electrochemical performance. Simply pursuing particle densification may lead to an extension of ion diffusion paths, affecting rate performance; while excessive particle refinement will reduce packing density, making it difficult to meet energy density requirements.
[0005] Therefore, developing a lithium manganese iron phosphate material that combines high solid density and electrochemical performance is an urgent technical problem to be solved. Summary of the Invention
[0006] This application provides a lithium manganese iron phosphate composite material, its preparation method, positive electrode sheet, and battery, which can obtain a lithium manganese iron phosphate material with both high solid density and good electrochemical performance.
[0007] In a first aspect, this application provides a lithium manganese iron phosphate composite material, comprising lithium manganese iron phosphate particles and a carbon layer coated on at least a portion of the surface of the lithium manganese iron phosphate particles, wherein the lithium manganese iron phosphate particles comprise a first lithium manganese iron phosphate particle and a second lithium manganese iron phosphate particle.
[0008] The primary particle size of the first lithium manganese iron phosphate particle satisfies: 800nm ≤ D V 50≤1500nm, D V99≤2500nm;
[0009] The primary particle size of the second lithium manganese iron phosphate particle satisfies: 50nm ≤ D V 50≤150nm, D V 99≤300nm.
[0010] In one possible implementation, the first lithium manganese iron phosphate particles and the second lithium manganese iron phosphate particles are prepared by mixing the first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor.
[0011] The manganese source in the first lithium manganese iron phosphate precursor includes at least one of manganese carbonate, manganese oxalate, and manganese ammonium phosphate.
[0012] The manganese source in the second lithium manganese iron phosphate precursor includes at least one of manganese tetroxide, manganese dioxide, manganese phosphate, and manganese trioxide.
[0013] In one possible implementation, the molar ratio of Li / P in the first lithium manganese iron phosphate particles is 1.02~1.05, and the molar ratio of Mn / Fe is 0.15~0.65.
[0014] and / or;
[0015] In the second lithium manganese iron phosphate particles, the molar ratio of Li / P is 1.05~1.10, and the molar ratio of Mn / Fe is 1.2~4.0.
[0016] In one possible implementation, the first lithium manganese iron phosphate particle also includes the M1 element;
[0017] M1 elements include at least Ti;
[0018] And / or; element M1 also includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y;
[0019] And / or; in the first lithium manganese iron phosphate particles, the mass percentage of M1 is 0.3%-0.8%;
[0020] And / or; in the first lithium manganese iron phosphate particles, the mass percentage of Ti element is 0.3%~0.5%;
[0021] And / or; in the first lithium manganese iron phosphate particles, the molar ratio of (Mn+Fe+M1) / P is 0.96~0.975.
[0022] In one possible implementation, the second lithium manganese iron phosphate particle also includes the M2 element;
[0023] The M2 element includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y.
[0024] And / or; in the second lithium manganese iron phosphate particles, the mass percentage of M2 is 0.1%-0.3%;
[0025] And / or; in the second lithium manganese iron phosphate particles, the molar ratio of (Mn+Fe+M2) / P is 0.975~1.00.
[0026] In one possible implementation, the specific surface area of the primary particles of the first lithium manganese iron phosphate particle is 13-16 m². 2 / g; The specific surface area of the primary particles of lithium manganese iron phosphate granules is 17-25 m². 2 / g;
[0027] and / or;
[0028] The mass ratio of the first lithium manganese iron phosphate particle to the second lithium manganese iron phosphate particle is (0.1-1):1.
[0029] Secondly, this application provides a method for preparing a lithium manganese iron phosphate composite material, the method comprising:
[0030] S1: Mix, grind, spray dry, and sinter manganese source, iron source, phosphorus source, lithium salt and carbon source to obtain the first lithium manganese iron phosphate precursor; wherein, the manganese source includes at least one of manganese carbonate, manganese oxalate and manganese ammonium phosphate.
[0031] S2: Mix, grind, spray dry, and sinter manganese source, iron source, phosphorus source, lithium salt and carbon source to obtain the second lithium manganese iron phosphate precursor; wherein, the manganese source includes at least one of manganese tetroxide, manganese dioxide, manganese phosphate and manganese trioxide;
[0032] S3: The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor are dispersed in an organic solvent and then ground, filtered, and dried to obtain a mixture; the mixture is then sintered to obtain the lithium manganese iron phosphate composite material.
[0033] In one possible implementation, in step S1, before mixing and grinding, an M1 source is added; the M1 source includes a compound containing the element M1; the element M1 includes at least Ti.
[0034] And / or; element M1 also includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y;
[0035] and / or;
[0036] In step S2, before mixing and grinding, an M2 source is added; the M2 source includes compounds containing the M2 element; the M2 element includes one or more of the elements Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y.
[0037] and / or;
[0038] In step S1, the sintering temperature is 780-820℃ and the sintering time is 8-10h;
[0039] and / or;
[0040] In step S2, the sintering temperature is 700-780℃ and the sintering time is 6-10h;
[0041] and / or;
[0042] In step S3, the organic solvent includes at least one of ethanol, ethylene glycol, methanol, glycerol, and acetone;
[0043] and / or;
[0044] In step S3, the sintering temperature is 680-750℃ and the sintering time is 3-6 hours.
[0045] and / or;
[0046] In step S3, grinding is performed until the particles reach D V 50 represents 0.5-1.0 μm.
[0047] Thirdly, this application provides a positive electrode sheet, which includes the above-mentioned lithium manganese iron phosphate composite material.
[0048] Fourthly, this application provides a battery comprising the aforementioned positive electrode plate.
[0049] This application provides a lithium manganese iron phosphate composite material, its preparation method, a positive electrode sheet, and a battery. The composite material is made by combining large-diameter first lithium manganese iron phosphate particles and small-diameter second lithium manganese iron phosphate particles, and the D-values of the first and second lithium manganese iron phosphate particles are defined. V 50 and D V 99. D of lithium iron phosphate granules V 50 and D V The small difference in particle size (99) indicates that the first lithium manganese iron phosphate particles have good particle size uniformity; simultaneously, the D value of the second lithium manganese iron phosphate particles... V 50 and D VThe particle size difference is also relatively small, indicating good particle size uniformity of the second lithium manganese iron phosphate particles. By combining first and second lithium manganese iron phosphate particles with good particle size uniformity, the larger first lithium manganese iron phosphate particles are beneficial for increasing compaction density, while the smaller second lithium manganese iron phosphate particles can enhance electrochemical activity. This combination optimizes the particle packing structure of the lithium manganese iron phosphate composite material, improving the compaction density of the material from a physical perspective, while the cathode material maintains good electrochemical performance; thus achieving a balance between high compaction density and excellent electrochemical performance in the cathode material. Attached Figure Description
[0050] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.
[0051] Figure 1 SEM image of the lithium manganese iron phosphate composite material of Example 3 provided in this application.
[0052] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concepts of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation
[0053] To enable those skilled in the art to better understand the present invention, this application will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the invention and are not intended to limit its scope. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.
[0054] In a first aspect, this application provides a lithium manganese iron phosphate composite material, comprising lithium manganese iron phosphate particles and a carbon layer coated on at least a portion of the surface of the lithium manganese iron phosphate particles, wherein the lithium manganese iron phosphate particles include first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles.
[0055] The primary particle size of the first lithium manganese iron phosphate particles satisfies: 800nm ≤ D V 50≤1500nm, D V 99≤2500nm;
[0056] The primary particle size of the second lithium manganese iron phosphate particles satisfies: 50nm ≤ D V 50≤150nm, D V 99≤300nm.
[0057] This application employs a compounding method using large-diameter first lithium manganese iron phosphate (LMFP) particles and small-diameter second LFP particles. The large-diameter LFP particles improve the compaction density, while the small-diameter second LFP particles enhance electrochemical reactivity. By compounding these large-diameter LFP particles with small-diameter second LFP particles, the small-diameter second LFP particles are dispersed among multiple large-diameter LFP particles, optimizing the particle packing structure of the LFP composite material and physically improving the compaction density. Simultaneously, the cathode material maintains good electrochemical performance. Therefore, the technical solution of this application simultaneously achieves both high compaction density and excellent electrochemical performance in the cathode material.
[0058] In addition, this application also specifies the primary particle size D of the first lithium manganese iron phosphate particles. V 50 is 800-1500nm, D V 99 ≤ 2500 nm; the primary particle size of the lithium manganese iron phosphate particles satisfies: 50 nm ≤ D V 50≤150nm, D V 99 ≤ 300 nm. D V 50. The first and second lithium manganese iron phosphate particles within the aforementioned particle size range, when compounded, can maximize the optimization of the particle packing structure of the lithium manganese iron phosphate composite material. If the D of the first lithium manganese iron phosphate particles... V A wavelength greater than 1500 nm will result in insufficient active sites in the first lithium manganese iron phosphate particles, affecting electrochemical performance. If the D2 of the second lithium manganese iron phosphate particles is greater than 1500 nm, it will lead to insufficient active sites, affecting electrochemical performance. V If the particle size is less than 50nm, it will affect the final compaction density.
[0059] Secondly, the D of lithium iron phosphate particles V 50 and D V The small difference in particle size (99) indicates that the first lithium manganese iron phosphate particles have good particle size uniformity; meanwhile, the second lithium manganese iron phosphate particles have a relatively small D... V 50 and D V The particle size difference is also relatively small, indicating that the second lithium manganese iron phosphate particles have good particle size uniformity. The first and second lithium manganese iron phosphate particles with good particle size uniformity can better optimize the particle packing structure, further improve the compaction density, and at the same time maintain good electrochemical performance.
[0060] It is understandable that the primary particle size D of the lithium manganese iron phosphate particles is... V50 represents 800-1500nm, such as 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, or any combination of two of the above values.
[0061] It is understandable that the primary particle size D of the lithium manganese iron phosphate particles is... V 50 represents 50-150nm, such as 50nm, 70nm, 100nm, 120nm, 150nm, or any range of two of the above values.
[0062] In one possible implementation, the primary particle size D of the first lithium manganese iron phosphate particle... V 99 is 1500-2500nm.
[0063] In one possible implementation, the primary particle size of the second lithium manganese iron phosphate particle satisfies: 100nm ≤ D V 99≤300nm.
[0064] In one possible implementation, the first lithium manganese iron phosphate particles and the second lithium manganese iron phosphate particles are prepared by mixing the first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor.
[0065] The manganese source in the first lithium manganese iron phosphate precursor includes at least one of manganese carbonate, manganese oxalate and manganese ammonium phosphate.
[0066] The manganese source in the second lithium manganese iron phosphate precursor includes at least one of manganese tetroxide, manganese dioxide, manganese phosphate, and manganese trioxide.
[0067] The lithium manganese iron phosphate composite material provided in this application uses manganese sources with different valence states in the first and second lithium manganese iron phosphate particles. By controlling the difference in the valence state of manganese, the grain growth rate and size of the first and second lithium manganese iron phosphate particles are controlled, thereby achieving particle size differentiation between the first and second lithium manganese iron phosphate particles. This lays the foundation for the subsequent compounding of the first and second lithium manganese iron phosphate particles.
[0068] Specifically, the first lithium manganese iron phosphate precursor uses a +2 valent manganese source, leveraging its characteristic of "no lattice volume change" during solid-solid diffusion to avoid lattice distortion hindering particle growth and facilitate the formation of dense, large particles. The second lithium manganese iron phosphate precursor uses a +3 and / or +4 valent manganese source, utilizing its characteristic of "valence state change causing lattice distortion" during redox reactions to suppress excessive particle growth and achieve precise particle refinement.
[0069] In one possible implementation, the molar ratio of Li / P in the first lithium manganese iron phosphate particles is 1.02~1.05, and the molar ratio of Mn / Fe is 0.15~0.65.
[0070] and / or;
[0071] In the lithium iron phosphate granules, the Li / P molar ratio is 1.05~1.10, and the Mn / Fe molar ratio is 1.2~4.0.
[0072] It is understandable that the Li / P molar ratio in the lithium manganese iron phosphate particles is 1.02 to 1.05, such as 1.02, 1.03, 1.04, 1.05 or any two of the above values.
[0073] It is understandable that the molar ratio of Mn / Fe in the first lithium manganese iron phosphate particles is 0.15~0.65, for example, 0.15, 0.2, 0.25, 0.3, 0.33, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65 or any two of the above values.
[0074] It is understandable that the Li / P molar ratio in the lithium manganese iron phosphate particles is 1.05~1.10, such as 1.05, 1.06, 1.07, 1.08, 1.09, 1.10 or any two of the above values.
[0075] It is understandable that the molar ratio of Mn / Fe in the lithium manganese iron phosphate particles is 1.2 to 4.0, for example, 1.2, 1.5, 1.7, 2.0, 2.3, 2.5, 2.7, 3.0, 3.3, 3.5, 3.7, 4.0 or any two of the above values.
[0076] This application controls the molar ratio of Mn / Fe in the first lithium manganese iron phosphate particle to be less than that in the second lithium manganese iron phosphate particle, thereby promoting a larger particle size in the first lithium manganese iron phosphate particle than in the second lithium manganese iron phosphate particle. This achieves a specific particle packing structure for the first and second lithium manganese iron phosphate particles.
[0077] This application controls the Li / P molar ratio in the first and second lithium manganese iron phosphate particles, mainly because the Li element has a particle-refining effect; secondly, the Li / P ratio is within the above range, which can ensure the material's capacity is fully utilized.
[0078] In one possible implementation, the first lithium manganese iron phosphate particles also include the M1 element;
[0079] M1 elements include at least Ti;
[0080] And / or; element M1 also includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y;
[0081] And / or; in the lithium manganese iron phosphate granules, M1 accounts for 0.3%-0.8% by mass;
[0082] And / or; the mass percentage of Ti element in the lithium manganese iron phosphate particles is 0.3%~0.5%;
[0083] And / or; in the first lithium manganese iron phosphate particles, the molar ratio of (Mn+Fe+M1) / P is 0.96~0.975.
[0084] It should be noted that when the first lithium manganese iron phosphate particles are coated with a carbon layer, the statement in this application that "the mass percentage of M1 in the first lithium manganese iron phosphate particles is 0.3%-0.8%" refers to the mass percentage of M1 after removing the carbon coating layer (i.e., the carbon coating layer is not included in the total mass of the first lithium manganese iron phosphate particles when calculating the mass percentage of M1). Similarly, the statement in this application that "the mass percentage of Ti element in the first lithium manganese iron phosphate particles is 0.3%~0.5%" refers to the mass percentage of Ti element after removing the carbon coating layer (i.e., the carbon coating layer is not included in the total mass of the first lithium manganese iron phosphate particles when calculating the mass percentage of Ti element).
[0085] This application incorporates Ti doping into lithium manganese iron phosphate (LFP) particles. The doped Ti forms Ti-O bonds, which have higher bond energies than Fe-O and Mn-O bonds. This doping suppresses the grain growth rate of the LFP particles, ensuring efficient packing and thus improving compaction density. Furthermore, Ti doping prevents excessively large LFP particles from resulting in insufficient active sites.
[0086] Secondly, Ti element is doped into the first lithium manganese iron phosphate particles. 4+ The charge compensation effect can stabilize Mn 2+ To avoid the valence state of Mn during high-temperature sintering 2+ Oxidized to Mn 3+ / Mn 4+ This leads to a sudden change in lattice volume. That is, the addition of Ti can ensure that there is no lattice distortion in the solid-solid diffusion process of lithium manganese iron phosphate particles, and further promote the formation of large-diameter lithium manganese iron phosphate particles.
[0087] Furthermore, the M1 element also includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y. Doping with Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y can further improve the electrochemical performance of the cathode material.
[0088] It is understandable that the mass percentage of M1 in the lithium manganese iron phosphate particles is 0.3%-0.8%, for example: 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or any two of the above values.
[0089] It is understandable that the mass percentage of Ti element in the lithium manganese iron phosphate particles is 0.3%-0.5%, for example: 0.3%, 0.4%, 0.5% or any two of the above values.
[0090] It is understandable that the molar ratio of (Mn+Fe+M1) / P in the first lithium manganese iron phosphate particles is 0.96~0.975, for example, 0.96, 0.965, 0.97, 0.975, or any combination of two of the above values. Specifically, controlling the molar ratio of metals and phosphorus can further affect the formation of the first lithium manganese iron phosphate particles and thus the capacity utilization of the cathode material.
[0091] In one possible implementation, the second lithium manganese iron phosphate particles also include the M2 element;
[0092] The M2 element includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y.
[0093] And / or; in the lithium manganese iron phosphate particles, the mass percentage of M2 is 0.1%-0.3%;
[0094] And / or; in the second lithium manganese iron phosphate particles, the molar ratio of (Mn+Fe+M2) / P is 0.975~1.00.
[0095] In this application, doping with M2 element can further improve the electrochemical performance of the cathode material.
[0096] It is understandable that the mass percentage of M2 in lithium manganese iron phosphate particles is 0.1%-0.3%, for example: 0.1%, 0.2%, 0.3% or any two of the above values.
[0097] It should be noted that when the second lithium manganese iron phosphate particles are coated with a carbon layer, the statement in this application that "the mass percentage of M2 in the second lithium manganese iron phosphate particles is 0.1%-0.3%" means that after removing the carbon coating layer from the second lithium manganese iron phosphate particles, the mass percentage of M2 is 0.1%-0.3% (that is, when calculating the mass percentage of M2, the carbon coating layer is not included in the total mass of the second lithium manganese iron phosphate particles).
[0098] It is understandable that the molar ratio of (Mn+Fe+M2) / P in the lithium manganese iron phosphate particles is 0.975~1.00, for example, 0.975, 0.98, 0.985, 0.99, 0.995, 1.00 or any two of the above values.
[0099] In one possible implementation, the primary particle surface area of the first lithium manganese iron phosphate particles is 13-16 m². 2 / g; The specific surface area of the primary particles of lithium manganese iron phosphate granules is 17-25m². 2 / g;
[0100] and / or;
[0101] The mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is (0.1-1):1.
[0102] This application defines the specific surface area of the primary particles of the first and second lithium manganese iron phosphate particles. When the first and second lithium manganese iron phosphate particles within the above specific surface area range are compounded, the particle packing structure of the lithium manganese iron phosphate composite material can be optimized to the greatest extent, the compaction density can be improved, and good electrochemical performance can be maintained.
[0103] Secondly, this application also defines the mass ratio of the first lithium manganese iron phosphate particles and the second lithium manganese iron phosphate particles. The mass ratio within the above range, combined with the specific surface area within the above range, further optimizes the particle packing structure, improves the compaction density of the cathode material, and maintains good electrochemical performance.
[0104] It is understandable that the specific surface area of primary lithium manganese iron phosphate particles is 13-16 m². 2 / g, for example, 13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g or a range consisting of any two of the above values.
[0105] It is understandable that the specific surface area of the primary particles of lithium manganese iron phosphate granules is 17-25 m². 2 / g, for example, 17m 2 / g、18m2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g、25m 2 / g or a range consisting of any two of the above values.
[0106] It is understood that the mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is ≤1:1, such as 0.35:1, 0.4:1, 0.45:1, 0.5:1, 1:1 or any range of two of the above values.
[0107] In one possible implementation, the carbon layer accounts for 1.2% to 2.0% of the mass of the lithium manganese iron phosphate composite material.
[0108] It is understandable that the carbon layer accounts for 1.2% to 2.0% of the mass of the lithium manganese iron phosphate composite material, for example, 1.2%, 1.4%, 1.6%, 1.8%, 1.0%, 1.2%, or any two of the above values.
[0109] Secondly, this application provides a method for preparing a lithium manganese iron phosphate composite material, comprising:
[0110] S1: Manganese source, iron source, phosphorus source, lithium salt and carbon source are mixed, ground, spray dried and sintered to obtain the first lithium manganese iron phosphate precursor; wherein, the manganese source includes at least one of manganese carbonate, manganese oxalate and manganese ammonium phosphate.
[0111] S2: Manganese source, iron source, phosphorus source, lithium salt and carbon source are mixed, ground, spray dried and sintered to obtain the second lithium manganese iron phosphate precursor; wherein, the manganese source includes at least one of manganese tetroxide, manganese dioxide, manganese phosphate and manganese trioxide;
[0112] S3: The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor are dispersed in an organic solvent and then ground, filtered, and dried to obtain a mixture; the mixture is then sintered to obtain a lithium manganese iron phosphate composite material.
[0113] The first and second lithium manganese iron phosphate precursors provided in this application use manganese sources with different valence states. By controlling the difference in the valence state of manganese, the grain growth rate and size of the first and second lithium manganese iron phosphate particles are controlled, thereby achieving particle size differentiation between the first and second lithium manganese iron phosphate particles and laying the foundation for subsequent compounding of the first and second lithium manganese iron phosphate particles.
[0114] Specifically, the first lithium manganese iron phosphate precursor uses a +2 valent manganese source, leveraging its characteristic of "no lattice volume change" during solid-solid diffusion to avoid lattice distortion hindering particle growth and facilitate the formation of dense, large particles. The second lithium manganese iron phosphate precursor uses a +3 and / or +4 valent manganese source, utilizing its characteristic of "valence state change causing lattice distortion" during redox reactions to suppress excessive particle growth and achieve precise particle refinement.
[0115] This application utilizes mechanical grinding during the mixing of the first and second lithium manganese iron phosphate precursors. This allows the smaller particles of the second lithium manganese iron phosphate precursor to fill the voids formed between the larger particles of the first lithium manganese iron phosphate precursor before sintering, further optimizing the particle packing structure and improving the material compaction density from a physical perspective.
[0116] Secondly, this application utilizes the carbonization reaction of organic solvents during sintering to form a carbon layer coating on the particle surface, thereby modifying the particle surface morphology, which improves the interfacial contact between particles and enhances the electronic conductivity and structural integrity of the material.
[0117] In one possible implementation, the iron source in steps S1 and S2 independently includes at least one of ferrous carbonate, ferric phosphate, ferric hydrogen phosphate, ferrous oxalate, and ferrous acetate.
[0118] In one possible implementation, the phosphorus source in steps S1 and S2 independently includes at least one of phosphoric acid, iron phosphate, lithium dihydrogen phosphate, lithium trihydrogen phosphate, and ammonium dihydrogen phosphate.
[0119] In one possible implementation, the lithium salts in steps S1 and S2 each independently include at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium acetate, lithium oxalate, and lithium citrate.
[0120] In one possible implementation, the carbon source in steps S1 and S2 independently includes at least one of ethylene glycol, glucose, sucrose, polyethylene glycol, polyvinyl alcohol, citric acid, hydroxypropyl β-cyclodextrin, polyvinylpyrrolidone, acrylic resin, polyvinylidene fluoride, polystyrene, and polypropylene.
[0121] In one possible implementation, in step S1, before mixing and grinding, an M1 source is added; the M1 source includes a compound containing the element M1; the element M1 includes at least Ti.
[0122] And / or; element M1 also includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y;
[0123] and / or;
[0124] In step S2, before mixing and grinding, an M2 source is added; the M2 source includes compounds containing the M2 element; the M2 element includes one or more of the elements Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y.
[0125] and / or;
[0126] In step S1, the sintering temperature is 780-820℃ and the sintering time is 8-10h;
[0127] and / or;
[0128] In step S2, the sintering temperature is 700-780℃ and the sintering time is 6-10h;
[0129] and / or;
[0130] In step S3, the organic solvent includes at least one of ethanol, ethylene glycol, methanol, glycerol, and acetone;
[0131] and / or;
[0132] In step S3, the sintering temperature is 680-750℃ and the sintering time is 3-6 hours;
[0133] and / or;
[0134] In step S3, grinding is performed until the particles reach D V 50 represents 0.5-1.0 μm.
[0135] It is understood that in step S1, the sintering temperature is 780-820℃, such as 780℃, 790℃, 800℃, 810℃, 820℃ or any range of two of the above values.
[0136] It is understandable that in step S1, the sintering time is 8-10h, such as 8h, 9h, 10h or any two of the above values.
[0137] It is understood that in step S2, the sintering temperature is 700-780℃, such as 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃ or any range of two of the above values.
[0138] It is understandable that in step S2, the sintering time is 6-10h, such as 6h, 7h, 8h, 9h, 10h or any range of two of the above values.
[0139] It is understood that in step S3, the sintering temperature is 680-750℃, such as 680℃, 700℃, 720℃, 740℃, 750℃ or any range of two of the above values.
[0140] It is understandable that in step S3, the sintering time is 3-6 hours, such as 3 hours, 4 hours, 5 hours, 6 hours or any range of two of the above values.
[0141] It is understandable that in step S3, grinding to the particle size D V 50 represents 0.5-1.0 μm, such as 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 1.0 μm, or any combination of two of the above values.
[0142] Thirdly, this application provides a positive electrode sheet, which includes the aforementioned lithium manganese iron phosphate composite material.
[0143] The positive electrode sheet of this application specifically includes a positive current collector and a positive active layer formed of lithium manganese iron phosphate composite material disposed on the surface of the positive current collector.
[0144] In the specific preparation of the positive electrode sheet, for example, the lithium manganese iron phosphate composite material applied for can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and cutting, the positive electrode sheet is obtained.
[0145] In one specific embodiment, the positive electrode active layer comprises, by weight percentage, 70-99 wt% of lithium manganese iron phosphate composite material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; more specifically, it comprises 80-98 wt% of lithium manganese iron phosphate composite material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.
[0146] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.
[0147] Fourthly, this application provides a battery including the aforementioned positive electrode.
[0148] It is conceivable that, in addition to the aforementioned positive electrode, the battery of this application also includes a negative electrode, an electrolyte, and a separator.
[0149] This application does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).
[0150] This application does not strictly limit the choice of electrolyte, which may include one or more solvents commonly used in lithium-ion battery electrolytes, as well as lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).
[0151] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.
[0152] In battery manufacturing, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare battery, which is then packaged into a pre-stamped aluminum-plastic film bag or steel casing. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete battery manufacturing.
[0153] Example 1
[0154] The lithium manganese iron phosphate composite material provided in this embodiment includes lithium manganese iron phosphate particles and a carbon layer coated on at least part of the surface of the lithium manganese iron phosphate particles. The carbon layer accounts for 1.60% of the mass of the lithium manganese iron phosphate composite material. The lithium manganese iron phosphate particles include first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles.
[0155] Primary particle size of lithium manganese iron phosphate particles: D V 50 represents 1000nm, D V 99 is 1500nm; the primary particle size of the second lithium manganese iron phosphate particles: D V 50 refers to 50nm, D V99 represents 100nm.
[0156] The first lithium iron phosphate (LFP) particles are doped with Ti, with a Li / P molar ratio of 1.03, a Mn / Fe molar ratio of 0.25, and a (Mn+Fe+Ti) / P molar ratio of 0.975. The Ti mass doping content is 0.3%. The specific surface area of the first LFP particles is 16 m². 2 / g.
[0157] The lithium iron phosphate (LFP) particles are doped with Mg, with a Li / P molar ratio of 1.07, a Mn / Fe molar ratio of 4, and a (Mn+Fe+Mg) / P molar ratio of 0.995; the Mg mass doping content is 0.155%; the specific surface area of the LFP particles is 25 m². 2 / g.
[0158] In the lithium manganese iron phosphate composite material, the mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 1:1.
[0159] The obtained lithium manganese iron phosphate composite material was prepared by the following method:
[0160] 1) Preparation of lithium manganese iron phosphate precursor:
[0161] Choose a mixture of manganese carbonate, iron phosphate, lithium carbonate, lithium dihydrogen phosphate, carbon source, and titanium dioxide;
[0162] The molar ratio of manganese to iron is 1:4 (the molar ratio of Mn / Fe is 0.25); the carbon source is selected from glucose and polyethylene glycol 8000 (mass ratio of 2:1). The amount of carbon source added is controlled to make the mass ratio of carbon in the first lithium manganese iron phosphate precursor 1.2%, the Li / P molar ratio 1.03, the molar ratio of (Mn+Fe+Ti) / P 0.975, and the Ti doping amount accounts for 0.3% of the mass ratio of the first lithium manganese iron phosphate precursor.
[0163] All the above raw materials were dispersed in deionized water and ground (to a particle size of about 0.35 μm), spray-dried at 300°C, and sintered in a box furnace at 800°C for 10 h under nitrogen protection to obtain the first lithium manganese iron phosphate precursor.
[0164] 2) Preparation of lithium manganese iron phosphate precursor:
[0165] Choose a mixture of manganese dioxide, iron phosphate, lithium carbonate, lithium dihydrogen phosphate, carbon source, and magnesium hydroxide;
[0166] The manganese-iron molar ratio is 8:2 (Mn / Fe molar ratio is 4.0). The carbon source is selected from glucose and polyethylene glycol 8000 (mass ratio is 2:1). The amount of carbon source added is controlled to ensure that the mass ratio of carbon in the lithium manganese iron phosphate precursor is 1.5%. The Li / P molar ratio is designed to be 1.07, and the molar ratio of (Mn+Fe+Mg) / P is 0.995. The Mg doping content accounts for 0.155% of the mass ratio of the lithium manganese iron phosphate precursor.
[0167] All raw materials were dispersed in deionized water and ground (to a particle size of about 0.20 μm), spray-dried at 300°C, and sintered in a box furnace at 720°C for 10 h under nitrogen protection to obtain the second lithium manganese iron phosphate precursor.
[0168] The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor were ground to particle size D in an ethanol system at a mass ratio of 1:1. V After the particle size of 50 is reduced to 0.80 μm, the material is filtered, dried, and finally sintered in a box furnace at 700 °C for 4 h under nitrogen protection to obtain a lithium manganese iron phosphate composite material.
[0169] The compacted density of the 3T powder of the lithium manganese iron phosphate composite material in this embodiment can reach 2.48 g / cm³. 3 0.1C discharge capacity is 155mAh / g.
[0170] Example 2
[0171] The lithium manganese iron phosphate composite material provided in this embodiment includes lithium manganese iron phosphate particles and a carbon layer coated on at least part of the surface of the lithium manganese iron phosphate particles. The carbon layer accounts for 1.45% of the mass of the lithium manganese iron phosphate composite material. The lithium manganese iron phosphate particles include first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles.
[0172] Primary particle size of lithium manganese iron phosphate particles: D V 50 is 800nm, D V 99 represents 2000 nm; the primary particle size of the second lithium manganese iron phosphate particles: D V 50 represents 100nm, D V 99 represents 150nm.
[0173] The first lithium iron phosphate (LFP) particles are doped with Ti, with a Li / P molar ratio of 1.02, a Mn / Fe molar ratio of 0.25, and a (Mn+Fe+Ti) / P molar ratio of 0.972. The Ti mass doping content is 0.46%. The specific surface area of the first LFP particles is 15 m². 2 / g.
[0174] The lithium iron phosphate (LFP) particles are doped with Ni, with a Li / P molar ratio of 1.05, a Mn / Fe molar ratio of 1.85, and a (Mn+Fe+Ni) / P molar ratio of 0.998; the Ni mass doping content is 0.1%; and the specific surface area of the LFP particles is 19 m². 2 / g.
[0175] In the lithium manganese iron phosphate composite material, the mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 0.5:1.
[0176] The obtained lithium manganese iron phosphate composite material was prepared by the following method:
[0177] 1) Preparation of lithium manganese iron phosphate precursor:
[0178] Choose a mixture of manganese oxalate, iron phosphate, lithium carbonate, lithium dihydrogen phosphate, carbon source, and titanium dioxide;
[0179] The molar ratio of manganese to iron is 1:4 (the molar ratio of Mn / Fe is 0.25); the carbon source is selected from sucrose and polyethylene glycol 8000 (mass ratio of 3:2). The amount of carbon source added is controlled to ensure that the mass ratio of carbon in the lithium manganese iron phosphate precursor is 1.1%, the molar ratio of Li / P is 1.02, the molar ratio of (Mn+Fe+Ti) / P is 0.972, and the Ti doping amount accounts for 0.46% of the mass ratio of the lithium manganese iron phosphate.
[0180] All the above raw materials were dispersed in deionized water and then ground to a particle size of D. V The 50 was controlled at 0.38 μm, spray dried, the spray temperature was set at 280℃, and sintered in a box furnace at 780℃ for 9 hours under nitrogen protection to obtain the first lithium manganese iron phosphate precursor.
[0181] 2) Preparation of lithium manganese iron phosphate precursor:
[0182] Choose a mixture of manganese trioxide, iron phosphate, lithium carbonate, lithium dihydrogen phosphate, carbon source, and nickel hydroxide;
[0183] The manganese-iron molar ratio is 6.5:3.5 (Mn / Fe molar ratio is 1.85). The carbon source is selected from glucose and polyethylene glycol 8000 (mass ratio is 2:1). The amount of carbon source added is controlled to ensure that the mass ratio of carbon in the lithium manganese iron phosphate precursor is 1.4%. The Li / P molar ratio is designed to be 1.05, and the molar ratio of (Mn+Fe+Ni) / P is 0.998. The Ni doping content accounts for 0.1% of the mass ratio of the lithium manganese iron phosphate precursor.
[0184] All raw materials were dispersed in deionized water and ground to a particle size of 0.25 μm. They were then spray-dried at a spray temperature of 270 °C and sintered in a box furnace at 700 °C for 8 hours under nitrogen protection to obtain the second lithium manganese iron phosphate precursor.
[0185] The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor were ground in a glycerol system at a mass ratio of 0.5:1. V After the particle size of 50 is reduced to 0.85 μm, the material is filtered, dried, and finally sintered in a box furnace at 680 °C for 3 h under nitrogen protection to obtain a lithium manganese iron phosphate composite material.
[0186] Example 3
[0187] The lithium manganese iron phosphate composite material provided in this embodiment includes lithium manganese iron phosphate particles and a carbon layer coated on at least a portion of the surface of the lithium manganese iron phosphate particles. The carbon layer accounts for 1.65% of the mass of the lithium manganese iron phosphate composite material. The lithium manganese iron phosphate particles include first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles.
[0188] Primary particle size of lithium manganese iron phosphate particles: D V 50 is 1500nm, D V 99 is 2500nm; the primary particle size of the second lithium manganese iron phosphate particles: D V 50 is 150nm, D V 99 represents 300nm.
[0189] The first type of lithium iron phosphate (LFP) particles are doped with Ti and Mg elements; the Li / P molar ratio is 1.05, the Mn / Fe molar ratio is 0.33, and the (Mn+Fe+Ti+Mg) / P molar ratio is 0.975; the mass doping amounts of Ti and Mg are 0.46% and 0.078%, respectively; the specific surface area of the first type of LFP particles is 13.8 m². 2 / g.
[0190] The lithium iron phosphate (LFP) particles are doped with Co, with a Li / P molar ratio of 1.10, a Mn / Fe molar ratio of 1.50, and a (Mn+Fe+Co) / P molar ratio of 0.988; the Co mass doping content is 0.187%; and the specific surface area of the LFP particles is 17 m². 2 / g.
[0191] In the lithium manganese iron phosphate composite material, the mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 0.4:1.
[0192] The obtained lithium manganese iron phosphate composite material was prepared by the following method:
[0193] 1) Preparation of lithium manganese iron phosphate precursor:
[0194] Select a mixture of manganese oxalate, iron phosphate, lithium carbonate, lithium dihydrogen phosphate, carbon source, titanium dioxide, and magnesium hydroxide;
[0195] The molar ratio of manganese to iron is 1:3 (the molar ratio of Mn / Fe is 0.33); the carbon source is selected from glucose and polyethylene glycol 6000 (mass ratio of 1:1). The amount of carbon source added is controlled to ensure that the mass ratio of carbon in the first lithium manganese iron phosphate precursor is 1.25%, the Li / P molar ratio is 1.05, the molar ratio of (Mn+Fe+Ti+Mg) / P is 0.975, and the doping amounts of Ti and magnesium account for 0.46% and 0.078% of the mass ratio of the first lithium manganese iron phosphate precursor, respectively.
[0196] All the above raw materials were dispersed in deionized water and then ground to a particle size of D. V The 50 was controlled at 0.30 μm, spray-dried at 280℃, and sintered in a box furnace at 820℃ for 8 hours under nitrogen protection to obtain the first lithium manganese iron phosphate precursor.
[0197] 2) Preparation of lithium manganese iron phosphate precursor:
[0198] Choose a mixture of manganese tetroxide, iron phosphate, lithium carbonate, lithium dihydrogen phosphate, carbon source, and cobalt hydroxide;
[0199] The manganese-iron molar ratio is 3:2 (Mn / Fe molar ratio is 1.5). The carbon source is selected from glucose and polyethylene glycol 8000 (mass ratio is 2:1). The amount of carbon source added is controlled to ensure that the mass ratio of carbon in the lithium manganese iron phosphate precursor is 1.5%. The Li / P molar ratio is designed to be 1.10, and the molar ratio of (Mn+Fe+Co) / P is 0.988. The Co doping content accounts for 0.187% of the mass ratio of the lithium manganese iron phosphate.
[0200] All raw materials were dispersed in deionized water and ground to a particle size of D. V The 50 was controlled at 0.30 μm, spray-dried at 250℃, and sintered in a box furnace at 780℃ for 6 hours under nitrogen protection to obtain the second lithium manganese iron phosphate precursor.
[0201] The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor were ground in a glycerol system at a mass ratio of 0.4:1. V After the 50 μm is reduced to 1.0 μm, it is filtered by pressure, dried, and finally sintered in a box furnace at 750 °C for 6 h under nitrogen protection to obtain lithium manganese iron phosphate composite material.
[0202] Figure 1The image shown is a SEM image of the lithium manganese iron phosphate composite material of Example 3. It can be seen that the first and second lithium manganese iron phosphate particles in the lithium manganese iron phosphate composite material of this example are evenly dispersed.
[0203] Example 4
[0204] This embodiment is basically the same as Embodiment 1, with the only difference being:
[0205] In the preparation of the first lithium manganese iron phosphate precursor, no Ti doping is added.
[0206] Example 5
[0207] This embodiment is basically the same as Embodiment 1, with the only difference being:
[0208] In the preparation of the lithium manganese iron phosphate precursor, magnesium hydroxide is replaced with titanium dioxide.
[0209] Example 6
[0210] This embodiment is basically the same as Embodiment 1, with the only difference being:
[0211] The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor were mixed in an ethanol system at a mass ratio of 1:1, filtered under pressure, dried, and finally sintered in a box furnace at 700°C for 4 hours under nitrogen protection to obtain the lithium manganese iron phosphate composite material. That is, in this embodiment, the first lithium manganese iron phosphate and the second lithium manganese iron phosphate were not ground during mixing.
[0212] Example 7
[0213] This embodiment is basically the same as Embodiment 1, with the only difference being:
[0214] The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor were ground in a glycerol system at a mass ratio of 1:1. V 50 is 0.3μm.
[0215] Comparative Example 1
[0216] This comparative example is basically the same as Example 1, except for the following:
[0217] Replace the manganese source used in the first lithium manganese iron phosphate precursor with manganese tetroxide;
[0218] Primary particle size of lithium manganese iron phosphate particles: D V 50 is 150 nm, D V 99 is 300 nm; the specific surface area of the lithium manganese iron phosphate particles is 18.5 m². 2 / g.
[0219] Comparative Example 2
[0220] This comparative example is basically the same as Example 1, except for the following:
[0221] Replace the manganese source used in the second lithium manganese iron phosphate precursor with manganese carbonate;
[0222] Primary particle size of lithium iron phosphate particles: D V 50 is 400 nm, D V 99 is 600 nm; the specific surface area of lithium manganese iron phosphate particles is 15 m². 2 / g.
[0223] Comparative Example 3
[0224] This comparative example is basically the same as Example 1, except that:
[0225] In the preparation of the first lithium manganese iron phosphate precursor, the sintering temperature is 750℃;
[0226] Primary particle size of lithium manganese iron phosphate particles: D V 50 is 500 nm, D V 99 represents 900 nm; the specific surface area of the first lithium manganese iron phosphate particle is 17.6 m². 2 / g.
[0227] Comparative Example 4
[0228] This comparative example is basically the same as Example 1, except that:
[0229] In the preparation of the lithium iron manganese phosphate precursor, the sintering temperature is 800℃.
[0230] Primary particle size of lithium iron phosphate particles: D V 50 is 300nm, D V 99 is 500 nm; the specific surface area of lithium manganese iron phosphate particles is 16 m². 2 / g.
[0231] Test example:
[0232] Primary particle size test of first / second lithium manganese iron phosphate particles:
[0233] Primary particle size measurement: 10kx electron microscope images were taken using a ZEISS Sigma 300 scanning electron microscope. The primary particle size was obtained by averaging the long side of 100 first / second lithium manganese iron phosphate particles using Nano Measurer 1.2 software.
[0234] BET test of primary particles of first lithium iron phosphate / second lithium iron phosphate:
[0235] The specific surface area of particles was tested by static N2 adsorption using a F-Sorb 2400CE surface area analyzer.
[0236] ICP testing of first / second lithium manganese iron phosphate particles: Li element and doping elements were calibrated using inductively coupled plasma atomic emission spectrometry. The contents of Mn, Fe, and P elements were determined by potassium dichromate titration and quinomolybdate-limonene gravimetric method, respectively. Then, the molecular weights of different elements were calculated.
[0237] Compacted density: The compacted density of the lithium manganese iron phosphate composite materials obtained in the above examples and comparative examples was measured using a Sansi compaction density meter. 1 mg was weighed and placed in a 13 mm diameter disc mold, and the pressure was maintained at 29.4 KN for 30 seconds before the data on the device was read.
[0238] Electrical performance testing:
[0239] The lithium manganese iron phosphate composite materials obtained in the above examples and comparative examples were assembled into batteries according to the following method, and the batteries were subjected to 0.1C discharge capacity testing.
[0240] 0.1C (1C=150mAh / g) rate performance test: Under normal temperature (25℃) conditions, the coin cells of the examples and comparative examples were charged to 4.35V at a constant current of 0.1C, and then charged to 0.02C at a constant voltage of 4.35V. The coin cells were then left to stand for 5 minutes to stabilize the chemical state. Then they were discharged to 2.5V at a constant current of 0.1C. The above charge and discharge process was repeated twice, and the average value of the discharge capacity obtained from the two tests was recorded. The test results are shown in Table 1.
[0241] Battery assembly method:
[0242] Polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone to prepare a PVDF solution with a concentration of 0.2 g / L. The components of lithium manganese iron phosphate composite material, conductive carbon black, and PVDF were weighed according to a mass ratio of 92:5:3, mixed, and stirred into a slurry. The slurry was then uniformly coated onto aluminum foil, dried at 80°C for 30 min, cut into circular positive electrode sheets, and dried in a vacuum oven at 120°C for 8 h. The positive electrode sheets (with an areal density of 70 g / m²) were then dried in an argon atmosphere glove box with a water content of <1 ppm and an oxygen content of <1 ppm. 2 A button cell is assembled using a 2025-type button cell casing, a negative electrode Li metal disc, a 1 mol / L lithium cobalt oxide electrolyte (the solvent is ethylene carbonate), and a negative electrode Li metal disc.
[0243] The test results are shown in Table 1.
[0244] Table 1
[0245]
[0246] Based on the test results of Examples 1-3 and Comparative Examples 1-4, it can be seen that this application achieves its goal by compounding large-particle-size first lithium manganese iron phosphate particles and small-particle-size second lithium manganese iron phosphate particles, and by limiting the D of the first and second lithium manganese iron phosphate particles. V 50 and D V 99. Large-diameter lithium manganese iron phosphate (LMP) particles are beneficial for increasing compaction density, while small-diameter LMP particles can enhance electrochemical reactivity. By compounding large-diameter LMP particles and small-diameter LMP particles, the small-diameter LMP particles can be dispersed among multiple large-diameter LMP particles, optimizing the particle packing structure of the LMP composite material. This physically improves the compaction density of the material while maintaining good electrochemical performance. Therefore, the technical solution of this application simultaneously achieves both high compaction density and excellent electrochemical performance in the cathode material.
[0247] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.
Claims
1. A lithium manganese iron phosphate composite material, characterized in that, It includes lithium manganese iron phosphate particles and a carbon layer coated on at least a portion of the surface of the lithium manganese iron phosphate particles, wherein the lithium manganese iron phosphate particles include first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles. The primary particle size of the first lithium manganese iron phosphate particle satisfies: 800nm ≤ D V 50≤1500nm, D V 99≤2500nm; The primary particle size of the second lithium manganese iron phosphate particle satisfies: 50nm ≤ D V 50≤150nm, D V 99≤300nm.
2. The lithium manganese iron phosphate composite material according to claim 1, characterized in that, The first lithium iron phosphate particles and the second lithium iron phosphate particles are prepared by mixing the first lithium iron phosphate precursor and the second lithium iron phosphate precursor. The manganese source in the first lithium manganese iron phosphate precursor includes at least one of manganese carbonate, manganese oxalate, and manganese ammonium phosphate. The manganese source in the second lithium manganese iron phosphate precursor includes at least one of manganese tetroxide, manganese dioxide, manganese phosphate, and manganese trioxide.
3. The lithium manganese iron phosphate composite material according to claim 1, characterized in that, In the first lithium manganese iron phosphate particles, the molar ratio of Li / P is 1.02~1.05, and the molar ratio of Mn / Fe is 0.15~0.65; and / or; In the second lithium manganese iron phosphate particles, the molar ratio of Li / P is 1.05~1.10, and the molar ratio of Mn / Fe is 1.2~4.
0.
4. The lithium manganese iron phosphate composite material according to claim 1, characterized in that, The first lithium manganese iron phosphate particle also includes the M1 element; M1 elements must include at least Ti; And / or; element M1 also includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y; And / or; in the first lithium manganese iron phosphate particles, the mass percentage of M1 is 0.3%-0.8%; And / or; in the first lithium manganese iron phosphate particles, the mass percentage of Ti element is 0.3%~0.5%; And / or; in the first lithium manganese iron phosphate particles, the molar ratio of (Mn+Fe+M1) / P is 0.96~0.
975.
5. The lithium manganese iron phosphate composite material according to claim 1 or 4, characterized in that, The second lithium manganese iron phosphate particle also includes the M2 element; The M2 element includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y. And / or; in the second lithium manganese iron phosphate particles, the mass percentage of M2 is 0.1%-0.3%; And / or; in the second lithium manganese iron phosphate particles, the molar ratio of (Mn+Fe+M2) / P is 0.975~1.
00.
6. The lithium manganese iron phosphate composite material according to claim 1, characterized in that, The specific surface area of the primary particles of the first lithium manganese iron phosphate particle is 13-16 m². 2 / g; The specific surface area of the primary particles of lithium manganese iron phosphate granules is 17-25m². 2 / g; and / or; The mass ratio of the first lithium manganese iron phosphate particle to the second lithium manganese iron phosphate particle is (0.1-1):
1.
7. A method for preparing a lithium manganese iron phosphate composite material according to any one of claims 1-6, characterized in that, The method includes: S1: Mix, grind, spray dry, and sinter manganese source, iron source, phosphorus source, lithium salt and carbon source to obtain the first lithium manganese iron phosphate precursor; wherein, the manganese source includes at least one of manganese carbonate, manganese oxalate and manganese ammonium phosphate. S2: Mix, grind, spray dry, and sinter manganese source, iron source, phosphorus source, lithium salt and carbon source to obtain the second lithium manganese iron phosphate precursor; wherein, the manganese source includes at least one of manganese tetroxide, manganese dioxide, manganese phosphate and manganese trioxide; S3: The first lithium manganese iron phosphate precursor and the second lithium manganese iron phosphate precursor are dispersed in an organic solvent and then ground, filtered, and dried to obtain a mixture; the mixture is then sintered to obtain the lithium manganese iron phosphate composite material.
8. The preparation method according to claim 7, characterized in that, In step S1, before mixing and grinding, an M1 source is added; the M1 source includes compounds containing the M1 element; the M1 element includes at least Ti. And / or; element M1 also includes one or more of the following elements: Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y; and / or; In step S2, before mixing and grinding, an M2 source is added; the M2 source includes compounds containing the M2 element; the M2 element includes one or more of the elements Mg, Ni, Co, Nb, Cr, La, Sb, Te, Sr, W, In, and Y. and / or; In step S1, the sintering temperature is 780-820℃ and the sintering time is 8-10h; and / or; In step S2, the sintering temperature is 700-780℃ and the sintering time is 6-10h; and / or; In step S3, the organic solvent includes at least one of ethanol, ethylene glycol, methanol, glycerol, and acetone; and / or; In step S3, the sintering temperature is 680-750℃ and the sintering time is 3-6 hours. and / or; In step S3, grinding is performed until the particles reach D V 50 represents 0.5-1.0 μm.
9. A positive electrode plate, characterized in that, The positive electrode comprises lithium manganese iron phosphate composite material according to any one of claims 1-6.
10. A battery, characterized in that, The battery includes the positive electrode according to claim 9.