Positive electrode material and its manufacturing method, positive electrode plate and secondary battery

Abstract

The present disclosure provides a positive electrode material and a manufacturing method thereof, a positive electrode plate, and a secondary battery. The positive electrode material includes an inner core and a first carbon layer, the first carbon layer being a multi-carbon interlocking layer, the multi-carbon interlocking layer including a main skeletal carbon and modified carbon, the main skeletal carbon bonded to the surface of the inner core, and the modified carbon interlocking into the main skeletal carbon. The multi-carbon interlocking layer coats the inner core, the multi-carbon interlocking layer including a main skeletal carbon and modified carbon, the main skeletal carbon bonded to the surface of the inner core, and the modified carbon interlocking into the main skeletal carbon. This suppresses pore formation and reduces the porosity of the multi-carbon interlocking layer compared to conventional in-situ carbon coatings. Reducing the pore structure of the multi-carbon interlocking layer shortens the time it takes for the solvent to infiltrate the pores during slurry preparation, reduces the volume of solvent required to infiltrate the pores, suppresses the generation of bubbles in the slurry, and makes it easier to obtain a slurry with excellent rheology and good uniformity, thereby suppressing a series of problems caused by bubbles and improving the energy density of the electrode plate per unit area.

Description

[Technical Field]

[0001] This disclosure claims priority to a Chinese patent application filed with the China Patent Office on August 18, 2023, bearing application number 202311049485.9 and entitled "Positive electrode material and manufacturing method thereof, positive electrode plate and secondary battery." This disclosure further claims priority to a Chinese patent application filed with the China Patent Office on August 18, 2023, bearing application number 202311049489.7 and entitled "Carbon-coated positive electrode material and manufacturing method thereof, positive electrode plate and secondary battery." The entire contents of which are incorporated by reference into this disclosure. The present disclosure relates to the technical field of lithium ion battery positive electrode materials, and more specifically to a positive electrode material and a manufacturing method thereof, a positive electrode plate, and a secondary battery. [Background technology]

[0002] In a macro-environment where global environmental pollution is becoming increasingly severe and energy is becoming scarce, the shift to renewable new energy sources is becoming increasingly urgent. Lithium-ion batteries boast advantages such as high energy density, high safety, no memory effect, and long cycle life, making them the mainstream of the global new energy vehicle market in recent years. The cathode material is one of the key components that determines the performance of lithium-ion batteries. Lithium manganese iron phosphate cathode material, an upgraded version of lithium iron phosphate, boasts approximately 20% higher energy density, better low-temperature performance, and is lower cost and safer than ternary cathode materials. However, like lithium iron phosphate, it suffers from a drawback: low electronic conductivity. To address this issue, optimization of synthesis methods, such as nanosizing and carbon coating, have been used to improve the performance of lithium manganese iron phosphate.

[0003] Because lithium manganese iron phosphate has lower electronic conductivity than lithium iron phosphate, it must be prepared into finer nanoparticles to fully demonstrate its performance. Furthermore, because the in-situ carbon coating layer itself is porous, the specific surface area of ​​the nano-sized lithium manganese iron phosphate particles produced during the process is higher. However, when the carbon content and pH are similar, the nano-sized lithium manganese iron phosphate particles are more difficult to process using an all-electric slurry. This is mainly due to the generation of many bubbles in the slurry, which tend to burst after sieving. During the coating process, many small bubbles adhere to the electrode plate, which burst after drying, leaving dents or forming voids. This leads to uneven electrode thickness and causes fine cracks, peeling, powder shedding, and other phenomena on the electrode plate, which affect the yield rate of the electrode plate and ultimately deteriorate the battery capacity, internal resistance, cycle life, and safety, seriously affecting the all-electric performance evaluation of the lithium manganese iron phosphate. If the viscosity is reduced by increasing the amount of binder and solvent to reduce the solid content, or if the degassing is performed by extending the time of low-speed vacuum stirring, the degassing effect is poor, resulting in increased economic and time costs. Summary of the Invention [Problem to be solved by the invention]

[0004] The purpose of the present disclosure is to overcome the above-mentioned problems of the prior art and provide a positive electrode material and a manufacturing method thereof, a positive electrode plate, and a secondary battery, thereby solving the problem in the prior art that conventional nano-lithium manganese iron phosphate particles are difficult to process by full electric slurry, resulting in poor battery capacity, internal resistance, cycle life, safety, etc. [Means for solving the problem]

[0005] To achieve the above objectives, the present disclosure adopts the following technical solutions:

[0006] A first aspect provides a positive electrode material, the positive electrode material comprising an inner core and a first carbon layer, the first carbon layer being a multi-carbon interlocking layer, the multi-carbon interlocking layer comprising a main skeletal carbon and a modified carbon, the main skeletal carbon being bonded to a surface of the inner core, and the modified carbon being interlocked and growing within the main skeletal carbon.

[0007] Preferably, the carbon in the main skeleton is bonded to the surface of the inner core in the form of stacked carbon plates, and / or The carbons in the modified carbons are interdigitated into the main backbone carbons to form carbon plates, and / or The mass content of the main skeletal carbon in the multi-carbon interlocking layer is 80 to 90%, and the mass content of the modifying carbon in the multi-carbon interlocking layer is 10 to 20%.

[0008] Preferably, the length of the carbon platelets in the main backbone carbon is greater than the length of the carbon platelets in the modified carbon, and the length of the carbon platelets in the modified carbon is less than 2 nm; and / or The pore volume of the multilayer carbon interlocking layer is 0.070 cm 3 / g and / or The thickness of the multi-layer carbon interlocking layer is less than 10 nm, and / or First carbon layer I G / I D The value is 0.75 to 1.5.

[0009] Preferably, the multi-carbon interlocking layer comprises a carbon element and a first non-carbon element; The first non-carbon element includes at least one of N, S, P, and Li.

[0010] The mass content of the carbon element in the first carbon layer is 97% to 98.5%, and the mass content of the first non-carbon element in the first carbon layer is 1.5% to 3%.

[0011] Preferably, the positive electrode material further comprises a second carbon layer, the second carbon layer being an outer carbon layer, the outer carbon layer being coated on the outer surface of the multi-carbon interlocking layer.

[0012] Preferably, the pore volume of the outer carbon layer is 0.020 cm 3 / g and / or The thickness of the outer carbon layer is less than 1.5 nm, and the thickness of the outer carbon layer is less than the thickness of the multi-carbon interlocking layer.

[0013] Preferably, the degree of graphitization of the second carbon layer is higher than the degree of graphitization of the first carbon layer.

[0014] Preferably, the long-range disorder of the carbon structure in the first carbon layer is higher than the long-range disorder of the carbon structure in the second carbon layer.

[0015] Preferably, most of the carbon structures in the first carbon layer are long carbon plate structures, which are deposited on the surface of the inner core, and most of the carbon structures in the second carbon layer are short carbon plate structures, which are deposited discontinuously and anisotropically on the surface of the first carbon layer, and the size of the long carbon plate structures is larger than the size of the short carbon plate structures.

[0016] Preferably, the second carbon layer comprises a carbon element and a second non-carbon element; the second non-carbon element comprises at least one of N, P and Li elements; and / or The mass content of the carbon element in the second carbon layer is 98% to 99%, and the mass content of the second non-carbon element in the second carbon layer is 1% to 2%.

[0017] Preferably, the second carbon layer I G / I D The value is 1.0 to 1.9.

[0018] Preferably, the inner core contains phosphorus, and a portion of the phosphorus in the inner core and a portion of the carbon in the multi-carbon interlocking layer form CP bonds and / or COP bonds.

[0019] Preferably, the bond formation rate of CP bonds and COP bonds is 0.5% to 1.15%.

[0020] Preferably, the core is a lithium-containing phosphate-based positive electrode active material core, and / or The particle diameter of the inner core is less than 400 nm.

[0021] Preferably, the total pore volume of the positive electrode material is 0.04 cm 3 / g~0.10cm 3 / g, and / or The specific surface area of ​​the positive electrode material is 12.0 m 2 / g~17.0m 2 / g, and / or Cathode Material I G / I D The value is 0.8 to 1.25.

[0022] A second aspect provides a method for producing the above-mentioned positive electrode material.

[0023] The method for producing the positive electrode material is as follows: providing an inner core precursor material and performing a first sintering on the inner core precursor material in an inert atmosphere to obtain an inner core; mixing the inner core with a first carbon source and a carbon source solvent to obtain a mixed material; and a step of subjecting the mixed material to a second sintering in an inert atmosphere to obtain a positive electrode material, in which an atomized second carbon source is introduced during the second sintering process, the first carbon source is cleaved in situ to form main skeletal carbon which is deposited on the surface of the inner core, the second carbon source is cleaved in situ and / or vapor-grown to form modified carbon, and the modified carbon is entangled and interdigitated into the main skeletal carbon to form a first carbon layer which is a multi-carbon interdigitated layer.

[0024] Preferably, the inner core precursor material is a lithium iron manganese phosphate precursor, and the method for producing the lithium iron manganese phosphate precursor comprises: The method includes the step of mixing and reacting a lithium source, an iron source, a phosphorus source, a manganese source, a precursor solvent, and a co-solvent in appropriate proportions to obtain a lithium iron manganese phosphate precursor.

[0025] Preferably, the pH of the mixed solution obtained by mixing the lithium source, iron source, phosphorus source, manganese source, precursor solvent, and co-solvent is 5.0 to 7.5.

[0026] Preferably, the first carbon source comprises at least one of hydroxypropylated phosphate cross-linked starch, glucose, fructose, sucrose, lactose, stevia, xylose, maltose, starch, cellulose, chitin, D-glucosamine, glucosamine sulfate, fructose phosphate, glucose-6-phosphate, N-acetylglucosamine, peptidoglycan, polyacrylate, polyethylene glycol, citric acid, malic acid, propylene, polypropylene glycol, polypropylene, polyacrylamide, lithium polyacrylate, polyvinyl alcohol, cyclodextrin, polyvinyl butyral, polystyrene, graphite, and / or The second carbon source includes at least two of methanol, ethanol, ethyl acetate, polyethylene glycol, acetone, butanone, ethyl ether, acetic acid, oxalic acid, polypropylene glycol, aniline, benzylamine, pyrazine, ammonium citrate, ammonium formate, ammonium acetate, formamide, acetamide, propionamide, butyramide, monoisopropanolamine, N,N-dimethylethanolamine, dimethylethanolamine, and triethylenediamine.

[0027] Preferably, at least one of the first carbon source and the second carbon source contains a carbon element and a first non-carbon element, the first non-carbon element contains at least one of N, S, P, and Li, the mass content of the carbon element in the total mass of the first carbon source and the second carbon source is 97% to 98.5%, and the mass content of the first non-carbon element in the total mass of the first carbon source and the second carbon source is 1.5% to 3%.

[0028] Preferably, the positive electrode material further comprises a second carbon layer, which is an outer carbon layer, and after forming the multiple carbon interlocking layers: The second carbon source is completely cleaved, followed by introducing an atomized second carbon source, which forms an outer carbon layer on the surface of the multi-carbon interlocking layer by in situ cleavage and / or vapor deposition.

[0029] Preferably, the production method satisfies at least one of the following conditions (1) to (4):

[0030] (1) The temperature of the first sintering is 350℃~660℃,

[0031] (2) The temperature of the second sintering is 650℃~855℃,

[0032] (3) The gas flow rate of the atomizing gas of the second carbon source is 10 mL / min to 120 mL / min;

[0033] (4) The second carbon source includes a carbon element and a second non-carbon element, and the second non-carbon element includes at least one of N, P, and Li, and the mass content of the carbon element in the second carbon source is 98% to 99%, and the mass content of the second non-carbon element in the second carbon source is 1% to 2%.

[0034] A third aspect provides a positive electrode plate manufactured using the above positive electrode material or a positive electrode material manufactured by the above method for manufacturing a positive electrode material.

[0035] A fourth aspect provides a secondary battery including the positive electrode plate. [Effects of the Invention]

[0036] The cathode material according to the present disclosure coats an inner core of a cathode active material with a multi-carbon interlocking layer, the multi-carbon interlocking layer comprising a main skeletal carbon and modified carbon, the main skeletal carbon being bonded to the surface of the inner core, and the modified carbon interlocking with the main skeletal carbon, thereby suppressing pore formation and making the porosity of the multi-carbon interlocking layer lower than that of conventional in-situ carbon coating layers. Reducing the pore structure of the multi-carbon interlocking layer shortens the time it takes for the solvent to infiltrate the pores during slurry preparation, reducing the volume of solvent required to infiltrate the pores, suppressing the generation of bubbles in the slurry, making it easier to obtain a slurry with excellent rheology and good uniformity, preventing a series of problems caused by bubbles, and improving the energy density of the electrode plate per unit area.

[0037] According to the method for producing a positive electrode material disclosed herein, by performing a second high-temperature sintering step and introducing an atomized second carbon source, the first carbon source undergoes in-situ cleavage at high temperature to form a main skeletal carbon, and the second carbon source undergoes in-situ cleavage and / or vapor growth to form modified carbon. The modified carbon interlocks with and intercalates into the main skeletal carbon, forming a multi-carbon interlocking layer, which effectively suppresses pore formation and results in a multi-carbon interlocking layer with low porosity, contributing to improving the electronic conductivity of the positive electrode material.

[0038] The positive electrode plate according to the present disclosure is manufactured using the above-mentioned positive electrode material, which includes an inner core and a multi-carbon interlocking layer. The multi-carbon interlocking layer has low porosity, making it difficult for bubbles to be generated during the slurry production process, thereby avoiding the problem of bubbles being generated during the slurry sieving process, the electrode plate coating process, and the electrode plate drying process. This prevents the problems of uneven electrode plate thickness, cracking, peeling, and powder falling caused by depressions or hollow cores formed by the bursting of bubbles, and effectively improves the yield rate of positive electrode plates.

[0039] The secondary battery according to the present disclosure includes the positive electrode plate, which effectively improves the problems of uneven thickness, cracking, peeling, and powder falling, and improves the capacity, internal resistance, cycle life, and safety of the secondary battery. [Brief explanation of the drawings]

[0040] The invention will now be further described with reference to the following figures and examples. [Figure 1] 1 is a flowchart of a method for manufacturing a cathode material according to an embodiment of the present disclosure. [Figure 2] 1 is a flowchart of a method for producing a positive electrode material according to Example 1 of the present disclosure. [Figure 3] FIG. 2 is a diagram comparing the structures of the positive electrode material according to Example 1 of the present disclosure and the positive electrode material of Comparative Example 1. [Figure 4] FIG. 2 is a TEM image of a positive electrode material according to Example 1 of the present disclosure. [Figure 5] FIG. 2 is an SEM image of a positive electrode material according to Example 1 of the present disclosure. [Figure 6] FIG. 2 is a pore size distribution diagram of the positive electrode material according to Example 1 of the present disclosure and the positive electrode material of Comparative Example 1. [Figure 7] FIG. 1 is a structural schematic diagram of a positive electrode material according to an embodiment of the present disclosure. [Figure 8] 10 is a TEM photograph of a positive electrode material according to Example 7 of the present disclosure. [Figure 9] 10 is an SEM photograph of a positive electrode material according to Example 7 of the present disclosure. [Figure 10] FIG. 10 is a Raman spectroscopic analysis diagram of a positive electrode material according to Example 7 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0041] In order to clarify the technical problems, solutions, and advantages of the present disclosure, the present disclosure will be described in more detail below with reference to the drawings and examples. Note that the specific examples described herein are merely for the purpose of illustrating the present disclosure and are not intended to limit the present disclosure.

[0042] The disclosed embodiments provide a positive electrode material, which includes an inner core and a first carbon layer, the first carbon layer being a multi-carbon interlocking layer, the multi-carbon interlocking layer including a main skeletal carbon and a modified carbon, the main skeletal carbon being bonded to the surface of the inner core, and the modified carbon being interlocked and growing into the main skeletal carbon.

[0043] The cathode material according to the present disclosure has a multi-carbon interlocking layer (first carbon layer) coating the cathode active material core. The multi-carbon interlocking layer includes a main skeletal carbon and a modified carbon. The main skeletal carbon is bonded to the surface of the core, and the modified carbon grows by interlocking with the main skeletal carbon, thereby suppressing pore formation and reducing the porosity of the multi-carbon interlocking layer compared to conventional in-situ carbon coating layers. Reducing the pore structure of the multi-carbon interlocking layer shortens the time it takes for the solvent to infiltrate the pores during slurry preparation, reducing the volume of solvent required to infiltrate the pores. This reduces the generation of bubbles in the slurry, making it easier to obtain a slurry with excellent rheology and good uniformity. This reduces the problems caused by bubbles and improves the energy density of the electrode plate per unit area.

[0044] In some embodiments, the main backbone carbon is formed by high-temperature in-situ cleavage using a first carbon source, and the carbon in the main backbone carbon forms layered carbon plates and is bonded to the surface of the inner core; the modified carbon is formed by in-situ cleavage and / or vapor deposition using a second carbon source, and the modified carbon is intertwined and intercalated into the main backbone carbon, and the carbon in the modified carbon forms carbon plates, and the first carbon source and the second carbon source are different, and the carbon chain of the first carbon source is longer than that of the second carbon source. The first carbon source and the second carbon source are simultaneously cleaved and intertwined with each other, and the throwing power of the second carbon source during in-situ cleavage and / or vapor deposition results in an overall pore structure of the multi-carbon intertwining layer that is smaller than that of an in-situ carbon coating alone.

[0045] Because in situ cleavage and / or vapor growth are random, the carbon structure arrangement of the modified carbon has a certain randomness, and is often deposited discontinuously and anisotropically.In the carbon structure of the main backbone carbon, the carbon plates generated by the first carbon source through high-temperature in situ cleavage are long and are deposited parallel to the surface of the inner core, playing the role of introduction and support for the modified carbon.The modified carbon formed through in situ cleavage and / or vapor growth can be well coated on the surface of the inner core through the main backbone carbon, and the final intertwined multi-carbon interlocking layer can completely cover the inner core, resulting in a carbon coating layer of uniform thickness, which makes the surface of the multi-carbon interlocking layer smooth and prevents the occurrence of pores.

[0046] In addition, the carbon plates of the main backbone carbon are longer than the carbon plates of the modified carbon, which is advantageous for forming a support structure and covering the inner core, while the carbon plates of the modified carbon are shorter, which is advantageous for forming interdigitated structures. In some embodiments, the carbon plates of the modified carbon have a length of less than 2 nm.

[0047] In the disclosed embodiment, the pore volume of the multi-carbon interlocking layer is 0.07 cm 3 / g, with a typical value of 0.04 cm 3 / g~0.06cm 3 / g, and the pore volume of the conventional in-situ carbon coating layer is 0.12-0.20 cm 3 / g, and the specific surface area is smaller than that of a conventional in-situ carbon coating layer, which can shorten the time it takes for the solvent to infiltrate the pores.

[0048] In the disclosed embodiments, a typical value refers to an average or normal value of a certain performance of a product, and refers to a representative parameter that can express the characteristics of a population (or the characteristics of a certain subset).

[0049] In some embodiments, the mass content of the main skeletal carbon in the multi-carbon interlocking layer is 80%-90%, and the mass content of the modified carbon in the multi-carbon interlocking layer is 10%-20%. Alternatively, in some embodiments, the mass content of the main skeletal carbon in the multi-carbon interlocking layer is 82%-91%, and the mass content of the modified carbon in the multi-carbon interlocking layer is 9-18%. The low occupancy of the short-structure modified carbon provides the effect of similar particle level blending, which is advantageous for more densely stacked multi-carbon interlocking layers. The main thickness of the multi-carbon interlocking layer is provided by the main skeletal carbon, and the modified carbon is a secondary modification.

[0050] In some embodiments, the main skeletal carbon of the multi-carbon interlocking layer is deposited parallel to the surface of the inner core without gaps, forming a tight coating, reducing the probability of shedding and increasing the stability of the positive electrode material.

[0051] In some embodiments, the multi-carbon interlocking layer includes carbon and an interlocking non-carbon element (first non-carbon element), the interlocking non-carbon element including at least one of N, S, P, and Li, the mass content of the carbon element in the multi-carbon interlocking layer is 97%-98.5%, and the mass content of the interlocking non-carbon element in the multi-carbon interlocking layer is 1.5%-3%. Preferably, a small amount of the non-carbon element is uniformly distributed in the multi-carbon interlocking layer. The introduction of a small amount of the non-carbon element into the multi-carbon interlocking layer can improve the degree of graphitization of the residual carbon layer to some extent, and sp 2 The increase in carbon is beneficial for improving the electronic conductivity of the positive electrode material.

[0052] In some embodiments, the positive electrode active material inner core is a lithium-containing phosphate-based inner core, and some of the carbon in the multi-carbon interlocking layer and some of the phosphorus in the inner core form C—P and C—P bonds, resulting in surface contact between the multi-carbon interlocking layer and the inner core, forming a seamless coating. The bond energies of the C—P and C—P bonds are stronger than the van der Waals bonds formed at the contact surface, which is beneficial to improving the bonding strength and stability between the multi-carbon interlocking layer and the inner core, and reducing the probability of peeling off of the multi-carbon interlocking layer and the outer carbon layer during processing slurry and battery cycle use.

[0053] When the multi-carbon interlocking layer is formed by the interlocking of the main backbone carbon formed by in situ cleavage of the first carbon source at high temperature and the modified carbon formed by in situ cleavage and / or vapor phase growth of the second carbon source, the probability of the carbon in the multi-carbon interlocking layer forming C—P and C—P bonds with the phosphorus in the core reaches 0.5% to 1.15%, resulting in a strong bond between the multi-carbon interlocking layer and the core, high stability, and resistance to peeling and falling off.

[0054] Due to the strong bonding strength between the multi-carbon interlocking layer and the inner core, the degree of delamination of the multi-carbon interlocking layer is as low as 0.8% in some examples.

[0055] The definition of bond formation probability in the examples of the present disclosure means that in the process of producing a precursor such as lithium manganese iron phosphate, a C-H bond or a C-O bond in the solvent carbon source and a P-H bond or a P-O-H bond in the phosphorus source undergo a coupling reaction under the action of a catalyst to form a C-P bond or a C-P bond, which may also exist after sintering.

[0056] The lithium-containing phosphate-based inner core may be, for example, a lithium manganese phosphate inner core, a lithium iron phosphate inner core, or a lithium iron manganese phosphate inner core. In some embodiments, the inner core is selected from an olivine-structured lithium iron manganese phosphate inner core, and the positive electrode material is a carbon-coated lithium iron manganese phosphate positive electrode material.

[0057] In some embodiments, the particle size of the inner cores is smaller than 400 nm, most of the inner cores are 80 nm to 300 nm, and the inner cores with particle sizes of 80 nm to 300 nm account for 70% to 80% of the total number of inner core particles. In some embodiments, the particle size of the inner cores is smaller than 400 nm, most of the inner cores are 50 nm to 300 nm, and the inner cores with particle sizes of 50 nm to 300 nm account for 70% to 80% of the total number of inner core particles, thereby producing a nano-level lithium manganese iron phosphate positive electrode material.

[0058] In some embodiments, the positive electrode material further includes a second carbon layer, which is an outer carbon layer coated on the outer surface of the multi-carbon interlocking layer. The outer carbon layer can cooperate with the multi-carbon interlocking layer to improve the electronic conductivity of the positive electrode material, and when the inner core contains manganese, can inhibit manganese elution from the inner core, thereby improving the cycle life of the positive electrode material.

[0059] In some embodiments, the outer carbon layer (second carbon layer) is formed on the outer surface of the multi-carbon interlocking layer by high-temperature in-situ cleavage and / or vapor deposition using a second carbon source, and is formed from the inner core outward, and is the second layer in the carbon coating layer of the positive electrode material, and there is no macroscopic gap between the outer carbon layer and the multi-carbon interlocking layer.

[0060] When the multi-carbon interlocking layer contains carbon formed by high-temperature cleavage of the first and second carbon sources, the carbon plate structure in the single carbon layer and the carbon plate structure formed by cleavage of the first carbon source in the multi-carbon interlocking layer form a C-C bond when they are in point or line contact, and a van der Waals bond when they are in surface contact with the carbon plate structure in the outer carbon layer and the carbon plate structure formed by cleavage of the first carbon source in the multi-carbon interlocking layer. Meanwhile, the cognate carbon in the outer carbon layer and the multi-carbon interlocking layer are bonded by C-C bonds, further forming a "pinning structure" that improves the bonding strength between the multi-carbon interlocking layer and the outer carbon layer.

[0061] In some embodiments, the thickness of the multi-carbon interlocking layer is less than 10 nm, typically 3 nm to 6 nm, typically 2.8 nm to 5.8 nm, etc.; the thickness of the outer carbon layer is less than 1.5 nm, typically 0.65 nm to 1.0 nm, and the thickness of the outer carbon layer is equal to or less than the thickness of the multi-carbon interlocking layer, which is a thin carbon layer in the carbon coating layer, similar to a "membrane layer structure." The thick multi-carbon interlocking layer is beneficial to the stability of the entire carbon skeleton, making it less susceptible to breakdown during processing or battery cycling; the thin outer carbon layer minimizes the overall carbon layer thickness, providing a filling and modifying effect on the multi-carbon interlocking layer, which is advantageous for Li + This is advantageous for shortening the transmission path.

[0062] The overall thickness of the carbon coating is thin, and the small molecular carbon structures cleaved by the second carbon source are continuously deposited. The pore volume of the carbon coating is 0.020 cm 3 / g, with typical values ​​of 0.010-0.014 cm 3 / g. The reduction in the pore volume of the outer carbon layer is beneficial for reducing the specific surface area of ​​the positive electrode material and reducing the formation of bubble nuclei caused by the solvent infiltrating into the positive electrode material during slurry manufacturing. Furthermore, the reduction in the pore structure reduces contact between the positive electrode material and the electrolyte, inhibiting interfacial reactions between the positive electrode material and the electrolyte, which is beneficial for reducing erosion of the positive electrode material by the electrolyte.

[0063] In some embodiments, the pore volume of the outer carbon layer is smaller than the pore volume of the multi-carbon interlocking layer, and both ends of the pores of the outer carbon layer are connected to the pores of the multi-carbon interlocking layer and the outside of the outer carbon layer, respectively. The pores of the multi-carbon interlocking layer have a certain resistance to the infiltration of air into the solution, which increases the resistance of the solution to enter the pores of the outer carbon layer and further reduces the possibility of the solvent infiltrating into the positive electrode material and generating bubbles during slurry manufacturing.

[0064] In some embodiments, the total pore volume of the positive electrode material is less than or equal to 0.04 cm 3 / g~0.10cm 3 / g.

[0065] The carbon structure in the overcoat carbon layer is often short carbon plates, and because in situ cleavage and / or vapor phase growth are random, the carbon structure arrangement in the overcoat carbon layer also has a certain randomness, and the carbon structure is often deposited discontinuously and anisotropically.

[0066] When the multi-carbon interlocking layer is deposited tightly on the surface of the inner core, for example, the degree of adhesion between the inner core and the multi-carbon interlocking layer, and the degree of adhesion between the multi-carbon interlocking layer and the outer carbon layer are uniform, or some of the carbon in the multi-carbon interlocking layer and some of the phosphorus in the inner core form C—P bonds and C—P bonds, and the carbon plate structure of the multi-carbon interlocking layer and the carbon plate structure of the outer carbon layer form C—C bonds and / or van der Waals bonds, etc., which further increase the electron conduction rate and improve the electrochemical performance of the positive electrode material.

[0067] The pore volume of the positive electrode material is lower than that of the conventional in-situ carbon coating layer, and the specific surface area of ​​the positive electrode material is also lower than that of the conventional in-situ carbon coating layer. In some embodiments of the present disclosure, the specific surface area of ​​the positive electrode material is 12 m 2 / g~17.0m 2 / g, and the specific surface area of ​​the positive electrode material is too small, e.g., 12 m 2 If the carbon content is below 1 / g, the carbon coating may be uneven due to the small carbon content, and the specific surface area of ​​the cathode material may be too large, e.g., 17 m 2 If the specific surface area is higher than 12 m / g, it will be difficult to disperse the slurry during the slurry production process, which may cause aggregation problems and affect the electrical performance. 2 / g~17.0m 2 When the porosity is in the range of / g, the agglomeration of the particles is reduced, which is advantageous for dispersing the active material and uniformly coating the conductive agent during processing.

[0068] The specific surface area of ​​the embodiments of the present disclosure refers to the total area of ​​a material per unit mass, and is expressed in m 2 / m 3 or m 2 / g, which usually refers to the specific surface area of ​​solid materials, such as powders, fibers, particles, plates, and blocks. The calculation method is area / volume or area / mass.

[0069] In some embodiments, the degree of graphitization of the second carbon layer 13 is greater than the degree of graphitization of the first carbon layer 12, as shown in FIG.

[0070] In the carbon-coated cathode material 10 according to the embodiment of the present disclosure, the second carbon layer 13 and the first carbon layer 12 cooperate to transport electrons. When the degree of graphitization of the second carbon layer 13 is higher than that of the first carbon layer 12, the electron transfer resistance of the second carbon layer 13 is smaller than that of the first carbon layer 12, which is advantageous for the inner core 11 to transfer electrons outward, thereby increasing the electron conduction rate and improving the electrical performance of the cathode material 10.

[0071] When the core contains manganese, the multilayer carbon structure is advantageous in suppressing the elution of manganese in the core and improving the cycle life of the positive electrode material.

[0072] In some embodiments, most of the carbon structures in the second carbon layer are short carbon plates. When the second carbon layer is formed by in situ cleavage and / or vapor deposition, the arrangement of the carbon structures in the second carbon layer is random due to the randomness of the in situ cleavage and / or vapor deposition, and the carbon structures are deposited discontinuously and anisotropically. The long-range disorder of the carbon structure in the second carbon layer is lower than that of the carbon structure in the first carbon layer, but because vapor deposition corresponds to gaseous mass transfer at the atomic level, the short-range order of the carbon structure in the second carbon layer is higher, i.e., the degree of graphitization is higher. G / I D In some embodiments, the degree of graphitization of the second carbon layer is expressed as I G / I D The value is 1.0 to 1.9, and typically 1.2 to 1.6. In some embodiments, the I G / I D The value is 0.8 to 1.25.

[0073] Therefore, the degree of graphitization of the first carbon layer is higher than that of the in-situ carbon coating using only the first carbon source, and I G / ID If we express the degree of graphitization of the first carbon layer as I, the degree of graphitization of the first carbon layer is 0.75 to 1.5, and the typical value is 0.8 to 1.1. G / I D The value is the I G / I D The degree of graphitization of the first carbon layer is advantageous for the inner core to transfer electrons to the outside, and the improvement of the degree of graphitization of the second carbon layer is advantageous for increasing the electron conduction rate between the carbon-coated positive electrode material particles and for transferring electrons from the inner core to the second carbon layer via the first carbon layer, both of which are advantageous for improving the electrochemical performance of the carbon-coated positive electrode material.

[0074] In some embodiments, most of the carbon structures in the first carbon layer are long carbon plate structures, which are deposited and bonded to the surface of the inner core. Most of the carbon structures in the second carbon layer are short carbon plate structures, which are discontinuously and anisotropically deposited and coated on the surface of the first carbon layer, with the long carbon plate structures being larger in size than the short carbon plate structures. In some embodiments, when the first carbon layer is formed by high-temperature in-situ cleavage of a first carbon source and the second carbon layer is formed by in-situ cleavage and / or vapor phase growth, the organic carbon chains of the first carbon source are generally longer than the organic carbon chains of the second carbon source, and the size of the carbon plates in the carbon structure of the resulting first carbon layer is larger than the size of the carbon plates in the carbon structure of the second carbon layer. This is advantageous for the first carbon layer to uniformly coat the outer surface of the inner core and also provides a foundation for the growth structure of the carbon structure of the second carbon layer, thereby providing support for the carbon structure of the second carbon layer.

[0075] In some embodiments, the second carbon layer includes a carbon element and a second non-carbon element (envelope non-carbon element), and the mass content of the carbon element in the second carbon layer is 98% to 99%. The second non-carbon element includes at least one of N, P, and Li, and N can be selected. The mass content of the second carbon element in the second carbon layer is 1% to 2%. The introduction of a small amount of the non-carbon element into the second carbon layer can improve the degree of graphitization of the residual carbon layer to some extent, and sp 2The increase in carbon is beneficial for improving the electronic conductivity of the positive electrode material.

[0076] The first carbon layer may be a single carbon layer or may be formed by an appropriate process using multiple carbon sources. The first carbon layer and the second carbon layer have different degrees of graphitization, and the degree of graphitization of the second carbon layer is higher than that of the first carbon layer, so that the electrons in the core tend to move outward.

[0077] The disclosed embodiment further provides a method for manufacturing the above-mentioned cathode material, the method including the following steps:

[0078] In S1, an inner core precursor material is prepared, and the inner core precursor material is subjected to a first sintering in an inert atmosphere to obtain the inner core.

[0079] The inner core is obtained by high temperature sintering, and the material is prepared in the next step.

[0080] In some embodiments, the inner core precursor material is crushed and ball milled to obtain inner core particles of appropriate particle size and clean surface prior to the first sintering.

[0081] In some embodiments, the inner core precursor material can be shaped using a drum vacuum ball mill, and the shaping time can be 15 to 60 minutes, and the carbon interlocking layer can be tightly coated on the inner core, which can be used to manufacture positive electrode materials and positive electrode plates. The protective atmosphere of the vacuum ball mill can be at least one of hydrogen gas, nitrogen gas, and argon gas.

[0082] In some embodiments, the inert atmosphere during the first sintering is either nitrogen gas or argon gas.

[0083] In some embodiments, the temperature of the first sintering is 350°C to 650°C, and the sintering time can be selected according to the actual situation, for example, 2 hours to 10 hours.

[0084] In some embodiments, the temperature of the first sintering is 355°C to 660°C, and the sintering time can be selected according to the actual situation, for example, 2 hours to 8 hours.

[0085] In some embodiments, when the inner core is a lithium iron manganese phosphate inner core, the corresponding inner core precursor material is a lithium iron manganese phosphate precursor.

[0086] In some embodiments, a method for preparing a lithium iron manganese phosphate precursor comprises the following steps.

[0087] A lithium source, an iron source, a manganese source, a phosphorus source, a precursor solvent, and a co-solvent are mixed and reacted in appropriate proportions to obtain a lithium manganese iron phosphate precursor.

[0088] In some embodiments, the lithium source, iron source, manganese source, and phosphorus source are set in an elemental molar ratio of Li:(Fe+Mn):P (0.90-1.10):(0.90-1.10):(0.90-1.10), where the iron source and manganese source have an Fe:Mn molar ratio of 1:(0-10), such as 1:0, 1:0.1, 1:0.5, 1:0.75, 1:1, 1:2, 1:3, 1:5, 1:7, 1:8, or 1:10. The proportions of precursor solvent and co-solvent are added based on the mass ratio of the total mass of the lithium source, iron source, manganese source, and phosphoric acid, and the proportion of precursor solvent may be 150%-500%. The mass proportion of the co-solvent may not exceed 5%, or in some embodiments, the proportion of precursor solvent may be 200%-600%. The mass proportion of the co-solvent may not exceed 6%.

[0089] In certain embodiments, the lithium source comprises at least one of lithium carbonate, lithium sulfate, lithium phosphate, and lithium dihydrogen phosphate.

[0090] In certain embodiments, the manganese source comprises at least one of manganese sulfate, manganese carbonate, manganese acetate, manganese nitrate, manganese chloride, manganese oxide, and manganese hydroxide.

[0091] In certain embodiments, the iron source comprises at least one of iron chloride, iron carbonate, iron acetate, ferrous acetate, and iron phosphate.

[0092] In some embodiments, the phosphorus source comprises at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, red phosphorus, white phosphorus, diphosphorus pentoxide, diphosphorus trioxide, ammonium phosphate, and iron phosphate.

[0093] In some embodiments, the precursor solvent comprises at least one of water, methanol, ethanol, ethylene glycol, glycerin, polyethylene glycol, dimethyl sulfoxide, hexadecyltrimethylammonium salicylate, and the like.

[0094] In some embodiments, the co-solvent may be at least one of nitric acid, phosphoric acid, ammonium dihydrogen phosphate, acetic acid, oxalic acid, citric acid, ascorbic acid (catalyst), and polyvinylpyrrolidone (anti-agglomerating agent). The co-solvent may at least one of dissolve each component material, disperse and mix the slurry, facilitate the catalytic reaction process, adjust the pH of the reaction system, and participate in the formation of the lithium manganese iron phosphate material precursor.

[0095] In some embodiments, the pH of the mixture of the lithium source, iron source, phosphorus source, manganese source, precursor solvent, and co-solvent is 5.0 to 7.5. By adjusting the morphology of the inner core precursor material and the amount of residual alkali after sintering of the inner core precursor material, it is possible to prevent the pH from being too high, which can cause gelation during processing and affect the processing performance evaluation of the positive electrode material.

[0096] The reaction of the lithium source, iron source, phosphorus source, manganese source, precursor solvent and co-solvent includes any of a liquid phase hydrothermal reaction, a co-precipitation reaction and a sol-gel reaction.

[0097] In S2, the inner core, the first carbon source, and the carbon source solvent are mixed to obtain a mixed material.

[0098] After the inner core is mixed with the first carbon source and the carbon source solvent, the first carbon source infiltrates the surface of the inner core. During the second sintering, the carbon structures generated by high-temperature in-situ cleavage can adhere to the surface of the inner core, and some of the carbon structures can form chemical bonds with the phosphorus elements in the inner core.

[0099] The mass ratio between the inner core and the first carbon source may be 1:(4 to 16), and the mass ratio between the inner core and the carbon source solvent may be 1:(0.5 to 10). Alternatively, the mass ratio between the inner core and the first carbon source may be 1:(4 to 18), and the mass ratio between the inner core and the carbon source solvent may be 1:(0.4 to 12). The carbon source solvent is mainly used to dissolve and / or disperse the first carbon source to form a mixed liquid with the first carbon source, providing a solution environment for the inner core and allowing the mixed liquid to uniformly infiltrate the surface of the inner core, thereby preparing to form a first carbon layer of uniform thickness in the inner core.

[0100] In some embodiments, the first carbon source comprises at least one of hydroxypropylated phosphate cross-linked starch, glucose, fructose, sucrose, lactose, stevia, xylose, maltose, starch, cellulose, chitin, D-glucosamine, aminoglucose sulfate, fructose phosphate, glucose-6-phosphate, N-acetylglucosamine, peptidoglycan, polyacrylate, polyethylene glycol, citric acid, malic acid, propylene, polypropylene glycol, polypropylene, polyacrylamide, lithium polyacrylate, polyvinyl alcohol, cyclodextrin, polyvinyl butyral, polystyrene, and graphite.

[0101] In some embodiments, the inner core comprises elemental phosphorus, and a portion of the phosphorus in the inner core and a portion of the carbon in the multi-carbon interlocking layer form C—P and / or C—P bonds, and the first carbon source comprises a sugar compound, for example, at least one of glucose, fructose, and sucrose.

[0102] In some embodiments, the first carbon source comprises a carbon element and a first non-carbon element, the first non-carbon element comprising at least one of N, S, P, and Li, the mass content of the carbon element in the first carbon source is 96% to 98%, and the mass content of the first non-carbon element in the first carbon source is 2% to 4%.

[0103] In some embodiments, the carbon source solvent comprises at least one of water, glycerol, ethanol, ethylene glycol, isopropanol, polyethylene glycol, ethyl acetate, and ethyl acetate.

[0104] In step S3, the mixed material is subjected to a second sintering in an inert atmosphere. During the sintering process, an atomized second carbon source is introduced. The first carbon source is cleaved in situ to form a main skeletal carbon, which is deposited on the surface of the core material. The second carbon source is cleaved in situ and / or vapor-grown to form modified carbon, which interlocks with the main skeletal carbon to form a multi-carbon interlocking layer, thereby obtaining a positive electrode material.

[0105] In the second sintering process, the first carbon source and the second carbon source are simultaneously cleaved at high temperature, and the carbon structure generated after the cleavage of the first carbon source is deposited parallel to the surface of the inner core to form the main skeletal carbon. The carbon structure generated after the cleavage of the second carbon source forms modified carbon through in situ cleavage and / or vapor phase growth, and the modified carbon interdigitates with the main skeletal carbon, forming a multi-carbon interdigitated layer with the modified carbon.

[0106] The second carbon source includes at least two of methanol, ethanol, ethyl acetate, polyethylene glycol, acetone, butanone, ethyl ether, acetic acid, oxalic acid, polypropylene glycol, aniline, benzylamine, pyrazine, ammonium citrate, ammonium formate, ammonium acetate, formamide, acetamide, propionamide, butyramide, monoisopropanolamine, N,N-dimethylethanolamine, dimethylethanolamine, and triethylenediamine.

[0107] Generally, the first carbon source is a polymeric organic material, and the second carbon source is a molecular organic material. Alternatively, the carbon chain of the first carbon source is longer than that of the second carbon source. In this way, the carbon plates of the main skeletal carbon formed are long and can be deposited parallel to the surface of the inner core, while the carbon plates of the modified carbon are short, for example, the maximum length of the carbon plates of the modified carbon is less than 2 nm, and can be intertwined and interdigitated with the main skeletal carbon.

[0108] In some embodiments, the second carbon source comprises carbon and a first non-carbon element, and the first non-carbon element comprises at least one of N, S, P, and Li, and may be N. In some embodiments, the first non-carbon element in the first carbon source and the first non-carbon element in the second carbon source may independently be at least one of N, S, P, and Li. That is, in some embodiments, the first non-carbon element in the first carbon source and the first non-carbon element in the second carbon source may be the same or different. The first non-carbon element N can be introduced from at least one of aniline, benzylamine, pyrazine, ammonium citrate, ammonium formate, ammonium acetate, formamide, acetamide, propionamide, butanamide, monoisopropanolamine, N,N-dimethylethanolamine, dimethylethanolamine, and triethylenediamine. The mass content of carbon in the second carbon source is 98% to 99%, and the mass content of the first non-carbon element in the second carbon source is 1% to 2%.

[0109] In some embodiments, at least one of the first carbon source and the second carbon source comprises a carbon element and a first non-carbon element, the first non-carbon element comprising at least one of N, S, P, and Li, the mass content of the carbon element in the total mass of the first carbon source and the second carbon source is 97% to 98.5%, and the mass content of the first non-carbon element in the total mass of the first carbon source and the second carbon source is 1.5% to 3%.

[0110] In certain embodiments, the inert atmosphere of the second sintering includes at least one of hydrogen gas, nitrogen gas, and argon gas.

[0111] In some embodiments, the temperature of the second sintering may be 650°C to 850°C, and the sintering time may be selected according to the actual situation, for example, 4 hours to 10 hours.

[0112] In some embodiments, the temperature of the second sintering may be 660°C to 855°C, and the sintering time may be selected according to the actual situation, for example, 4 hours to 12 hours.

[0113] The amount of the second carbon source added is controlled by the introduction time and gas flow rate of the atomization gas, and may be 4 to 10 hours, for example, 4, 5, 6, 7, 8, 9, or 10 hours, etc. The gas flow rate of the second carbon source atomization gas may be 10 mL / min to 110 mL / min, and preferably 40 mL / min to 80 mL / min.

[0114] According to the manufacturing method of the positive electrode material of the present disclosure, the first carbon source is cleaved in situ at high temperature after the second high-temperature sintering and the introduction of the atomized second carbon source to form the main skeletal carbon, and the second carbon source is cleaved in situ and / or vapor-grown to form modified carbon. The modified carbon is intertwined and intercalated into the main skeletal carbon to form a first carbon layer. The first carbon layer is a multi-carbon intercalation layer, which effectively suppresses pore formation and results in a multi-carbon intercalation layer with low porosity. The multi-carbon intercalation layer has a high degree of graphitization, which contributes to improving the electronic conductivity of the positive electrode material.

[0115] In some embodiments, the positive electrode material further comprises a second carbon layer, which is an outer carbon layer, and after forming the multi-carbon interlocking layer, further comprises the following step S4, as shown in FIG.

[0116] In S4, the second carbon source is completely cleaved, and then atomized second carbon source is introduced. The second carbon source forms an outer carbon layer (second carbon layer) on the surface of the multi-carbon interlocking layer by in situ cleavage and / or vapor deposition, thereby obtaining a positive electrode material.

[0117] In some embodiments, after the cleavage of the second carbon source is completed, the multi-carbon interlocking layer is substantially formed, and the second sintering temperature is maintained while the atomized second carbon source is subsequently introduced. The second carbon source is deposited on the surface of the multi-carbon interlocking layer by in situ cleavage and / or vapor deposition to form an outer carbon layer. The formed outer carbon layer has a high degree of graphitization and can improve the electronic conductivity of the positive electrode material.

[0118] In some embodiments, when the first carbon layer is formed by high-temperature in-situ cleavage of the first carbon source and in-situ cleavage and / or vapor deposition of the second carbon source, the second carbon source used in the first carbon layer and the second carbon source used in the second carbon layer are the same, and the second carbon source can be continuously introduced during the production process, avoiding the cumbersome operation of multiple replacement of the atomized second carbon source, simplifying the process, and improving process efficiency.

[0119] In specific embodiments, the atomized second carbon source subsequently introduced in step S4 may be the same as or different from the atomized second carbon source subsequently introduced in step S3. That is, in some embodiments, the atomized second carbon source subsequently introduced in step S4 includes at least two of methanol, ethanol, ethyl acetate, polyethylene glycol, acetone, butanone, ethyl ether, acetic acid, oxalic acid, polypropylene glycol, aniline, benzylamine, pyrazine, ammonium citrate, ammonium formate, ammonium acetate, formamide, acetamide, propionamide, butyramide, monoisopropanolamine, N,N-dimethylethanolamine, dimethylethanolamine, and triethylenediamine.

[0120] In specific embodiments, the temperature in step S4 and the temperature in the second sintering in step S3 may be the same or different. That is, in some embodiments, the temperature at which the atomized second carbon source is subsequently introduced in step S4 for in situ cleavage and / or vapor deposition may include the temperature of the second sintering, 650°C to 855°C.

[0121] The reaction time in step S4 can be estimated based on the amount of the second carbon source added, and the thickness of the outer carbon layer can be controlled by subsequently controlling the flow rate and introduction time of the atomized second carbon source.

[0122] In step S4, the amount of the second carbon source added is controlled by the introduction time and gas flow rate of the atomization gas, and may be 4 to 12 hours, for example, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours. The gas flow rate of the second carbon source atomization gas may be 10 mL / min to 110 mL / min, which is the gas flow rate of the second carbon source atomization gas in step S3, or may be 15 mL / min to 120 mL / min, for example, 15 mL / min, 30 mL / min, 45 mL / min, 60 mL / min, 80 mL / min, 85 mL / min, 90 mL / min, 100 mL / min, or 120 mL / min, and is preferably 45 mL / min to 90 mL / min.

[0123] In some embodiments, in step S4, the atomized second carbon source introduced includes a carbon element and a second non-carbon element, and the second non-carbon element includes at least one of N, P, and Li elements, the mass content of the carbon element in the second carbon source is 98% to 99%, and the mass content of the second non-carbon element in the second carbon source is 1% to 2%.

[0124] The second carbon source forms a second carbon layer on the surface of the first carbon layer by in situ cleavage and / or vapor deposition, resulting in two different carbon layer structures. Here, vapor deposition corresponds to gaseous mass transfer at the atomic level, so the short-range order of the carbon structure in the second carbon layer is higher, i.e., the degree of graphitization is higher, and a difference in the degree of graphitization occurs between the first and second carbon layers, allowing the inner core to guide the direction of electron migration and improve the electron conduction rate of the cathode material. The preparation method is simple and controllable, and has good prospects for industrial application.

[0125] The disclosed embodiments further provide a positive electrode plate made from the above-mentioned positive electrode material, which includes an inner core, multiple carbon interlocking layers, and an outer carbon covering layer. The multiple carbon interlocking layers and the outer carbon covering layer have low porosity, so that no or few bubbles are generated during the slurry preparation process, thereby avoiding the problems of bubbles being generated during the slurry sieving process, the electrode plate coating process, and the electrode plate drying process. This avoids the problems of uneven electrode plate thickness, cracking, peeling, and powder falling caused by dents or hollow cores formed by the bursting of bubbles, and effectively improves the yield rate of positive electrode plates.

[0126] The presently disclosed embodiment further provides a secondary battery including the above-mentioned positive electrode plate, which is free from problems of uneven thickness, cracking, peeling, and powder falling off, and improves the capacity, internal resistance, cycle life, and safety of the secondary battery.

[0127] A number of examples will be described below.

[0128] Example 1 As shown in FIG. 3 , the cathode material of this embodiment comprises an inner core 11, a multi-carbon interlocking layer 12, and an outer carbon coating layer 13. The multi-carbon interlocking layer 12 comprises a main skeletal carbon and modified carbon. The main skeletal carbon is deposited on the surface of the inner core 11, the modified carbon is interlocked with the main skeletal carbon, and the outer carbon coating layer 13 is coated on the surface of the multi-carbon interlocking layer 12.

[0129] Here, the mass content of the main skeletal carbon in the multi-carbon interlocking layer 12 is 85%, the mass content of the modified carbon in the multi-carbon interlocking layer is 15%, and the pore volume of the multi-carbon interlocking layer 12 is 0.0495 cm 3 / g, and the pore volume of the outer carbon layer 13 is 0.0122 cm 3 / g, and the total pore volume is 0.0472 cm 3 / g, the thickness of the carbon interlocking layer 12 is 3.14 nm, the thickness of the outer carbon layer 13 is 0.86 nm, the particle diameter of the core 11 is 52 nm to 368 nm, and the specific surface area of ​​the positive electrode material is 14.16 m 2 / g.

[0130] As shown in FIG. 2, the method for producing the positive electrode material of this embodiment includes the following steps.

[0131] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and water (precursor solvent) and oxalic acid (co-solvent) were mixed in amounts of 350% and 2.5% of the total mass of the raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0132] In S2, the inner core precursor material was subjected to the first sintering at a temperature of 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0133] In S3, the inner core is mixed with glucose and fructose phosphate ester (first carbon source) and water (carbon source solvent) to obtain a mixed material. The mass ratio of the inner core to the first carbon source is 1:10, and the mass ratio of the inner core to water is 1:4. The mass ratio of fructose phosphate ester in the first carbon source is 4%, and the non-carbon element in the first carbon source is P.

[0134] In S4, the mixed material was subjected to the second sintering at 700°C for 6 hours. Atomized ethanol, polyethylene glycol, and N,N-dimethylethanolamine (second carbon source) were introduced in a mass ratio of 3:6:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 60 mL / min. The introduction time was 6 hours. A multi-carbon interlocking layer was formed on the surface of the inner core.

[0135] In step S5, the second sintering temperature was maintained, and atomized ethanol, polyethylene glycol, and N,N-dimethylethanolamine (second carbon source) were introduced. The gas flow rate of the atomized second carbon source was 60 mL / min, and the introduction time was 2 h. A carbon coating layer was formed on the surface of the multi-carbon interlocking layer, and a positive electrode material was obtained.

[0136] As shown in FIG. 4, the transmission electron microscope (TEM) image of the obtained cathode material shows that the thickness of the carbon interlocking layer and the outer carbon layer is uniform.

[0137] As shown in FIG. 5, the scanning electron microscope (SEM) image of the obtained positive electrode material shows that the positive electrode material particles are relatively round and have a relatively low specific surface area, which is advantageous for processing.

[0138] <Example 2> The positive electrode material according to this example has almost the same structure as that of Example 1, with the following differences: the mass content of the main skeletal carbon in the multi-carbon interlocking layer is 90%, the mass content of the modified carbon in the multi-carbon interlocking layer is 10%, and the pore volume of the multi-carbon interlocking layer is 0.0687 cm 3 / g, and the pore volume of the outer carbon layer is 0.0184 cm 3 / g, and the total pore volume is 0.0725 cm 3 / g, the thickness of the carbon interlocking layer is 4.28 nm, the thickness of the outer carbon layer is 0.98 nm, the particle diameter of the inner core is 43 nm to 322 nm, and the specific surface area of ​​the positive electrode material is 16.35 m 2 / g.

[0139] The method for manufacturing the positive electrode material according to this embodiment includes the following steps.

[0140] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and water and oxalic acid were mixed in amounts of 350% and 2.5% of the total mass of the raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0141] In S2, the inner core precursor material was subjected to the first sintering at a temperature of 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0142] In step S3, the inner core, sucrose, chitin (first carbon source), and water were mixed to obtain a mixed material. The mass ratio of the inner core to the first carbon source was 1:14, the mass ratio of the inner core to water was 1:4, the mass ratio of chitin in the first carbon source was 4%, and the non-carbon element in the first carbon source was N.

[0143] In step S4, the mixed material was subjected to a second sintering at 750°C for 6 hours. Atomized acetic acid, polypropylene glycol, and benzylamine (second carbon source) were introduced in a mass ratio of 3:6:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 80 mL / min. The introduction time was 6 hours, and a multi-carbon interlocking layer was formed on the surface of the inner core.

[0144] In step S5, the second sintering temperature was maintained, and atomized acetic acid, polypropylene glycol, and benzylamine (second carbon source) were introduced. The gas flow rate of the atomized second carbon source was 70 mL / min, and the introduction time was 2 h. A carbon coating layer was formed on the surface of the multi-carbon interlocking layer, and a positive electrode material was obtained.

[0145] Example 3 The positive electrode material according to this example has almost the same structure as that of Example 1, with the following differences: the mass content of the main skeletal carbon in the multi-carbon interlocking layer is 90%, the mass content of the modified carbon in the multi-carbon interlocking layer is 10%, and the pore volume of the multi-carbon interlocking layer is 0.0724 cm 3 / g, and the pore volume of the outer carbon layer is 0.0125 cm 3 / g, and the total pore volume is 0.0681 cm 3 / g, the thickness of the carbon interlocking layer is 3.65 nm, the thickness of the outer carbon layer is 0.8 nm, the particle diameter of the inner core is 45 nm to 316 nm, and the specific surface area of ​​the positive electrode material is 15.87 m 2 / g.

[0146] The method for producing the positive electrode material of this example includes the following steps.

[0147] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and water and oxalic acid were mixed in amounts of 350% and 2.5% of the total mass of the raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0148] In S2, the lithium manganese iron phosphate material precursor was first sintered at 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0149] In S3, the inner core, glucose and fructose phosphate (first carbon source), and water were mixed to obtain a mixed material. The mass ratio of the inner core to the first carbon source was 1:14, the mass ratio of the inner core to water was 1:4, the mass ratio of fructose phosphate in the first carbon source was 4%, and the non-carbon element in the first carbon source was P.

[0150] In step S4, the mixed material was subjected to a second sintering at 750°C for 6 hours. Atomized ethanol, polyethylene glycol, and N,N-dimethylethanolamine (second carbon source) were introduced in a mass ratio of 3:6:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 60 mL / min. The introduction time was 6 hours, and a multi-carbon interlocking layer was formed on the surface of the inner core.

[0151] In step S5, the second sintering temperature was maintained, and atomized ethanol, polyethylene glycol, and N,N-dimethylethanolamine (second carbon source) were introduced. The gas flow rate of the atomized second carbon source was 80 mL / min, and the introduction time was 2 h. A carbon coating layer was formed on the surface of the multi-carbon interlocking layer, and a positive electrode material was obtained.

[0152] Example 4 The positive electrode material according to this example has almost the same structure as that of Example 1, with the following differences: the mass content of the main skeletal carbon in the multi-carbon interlocking layer is 85%, the mass content of the modified carbon in the multi-carbon interlocking layer is 15%, and the pore volume of the multi-carbon interlocking layer is 0.0513 cm 3 / g, and the pore volume of the outer carbon layer is 0.0267 cm 3 / g, and the total pore volume is 0.0604 cm 3 / g, the thickness of the carbon interlocking layer is 3.22 nm, the thickness of the outer carbon layer is 1.26 nm, the particle diameter of the inner core is 60 nm to 350 nm, and the specific surface area of ​​the positive electrode material is 15.28 m 2 / g.

[0153] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0154] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and water and oxalic acid were mixed in amounts of 350% and 2.5% of the mass of the raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0155] In S2, the inner core precursor material was subjected to the first sintering at a temperature of 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0156] In S3, the inner core, glucose and fructose phosphate (first carbon source), and water were mixed to obtain a mixed material. The mass ratio of the inner core to the first carbon source was 1:10, the mass ratio of the inner core to water was 1:4, the mass ratio of fructose phosphate in the first carbon source was 4%, and the non-carbon element in the first carbon source was P.

[0157] In step S4, the mixed material was subjected to a second sintering at 750°C for 6 hours. Atomized ethanol, polyethylene glycol, and N,N-dimethylethanolamine (second carbon source) were introduced in a mass ratio of 3:6:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 60 mL / min. The introduction time was 6 hours, and a multi-carbon interlocking layer was formed on the surface of the inner core.

[0158] In step S5, the second sintering temperature was maintained, and atomized ethanol, polyethylene glycol, and N,N-dimethylethanolamine (second carbon source) were introduced. The gas flow rate of the atomized second carbon source was 80 mL / min, and the introduction time was 2 h. A carbon coating layer was formed on the surface of the multi-carbon interlocking layer, and a positive electrode material was obtained.

[0159] <Example 5> The positive electrode material according to this example has almost the same structure as that of Example 1, with the following differences: the mass content of the main skeletal carbon in the multi-carbon interlocking layer is 85%, the mass content of the modified carbon in the multi-carbon interlocking layer is 15%, and the pore volume of the multi-carbon interlocking layer is 0.0506 cm 3 / g, and the pore volume of the outer carbon layer is 0.0131 cm 3 / g, and the total pore volume is 0.0490 cm 3 / g, the thickness of the carbon interlocking layer is 3.20 nm, the thickness of the outer carbon layer is 0.90 nm, the particle diameter of the inner core is 54 nm to 355 nm, and the specific surface area of ​​the positive electrode material is 14.52 m 2 / g.

[0160] The method for producing the positive electrode material of this example includes the following steps.

[0161] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and water and oxalic acid were mixed in amounts of 350% and 2.5% of the total mass of the raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0162] In S2, the inner core precursor material was subjected to the first sintering at a temperature of 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0163] In S3, the inner core, glucose (first carbon source), and water were mixed to obtain a mixed material. The mass ratio of the inner core to the first carbon source was 1:10, and the mass ratio of the inner core to water was 1:4.

[0164] In step S4, the mixed material was subjected to the second sintering at 700°C for 6 hours. Atomized ethanol and polyethylene glycol (second carbon source) were introduced at a mass ratio of 3:7, the gas flow rate of the atomized second carbon source was 60 mL / min, and the introduction time was 6 hours, forming a multi-carbon interlocking layer on the surface of the inner core.

[0165] In step S5, the second sintering temperature was maintained, and atomized ethanol and polyethylene glycol (second carbon source) were introduced. The gas flow rate of the atomized second carbon source was 60 mL / min, and the introduction time was 2 h. A carbon coating layer was formed on the surface of the multi-carbon interlocking layer, and a positive electrode material was obtained.

[0166] Example 6 The positive electrode material of this example has almost the same structure as that of Example 1, with the following differences: the mass content of the main skeletal carbon in the multi-carbon interlocking layer is 85%, the mass content of the modified carbon in the multi-carbon interlocking layer is 15%, and the pore volume of the multi-carbon interlocking layer is 0.0498 cm 3 / g, and the total pore volume is 0.0498 cm 3 / g, the thickness of the carbon interlocking layer is 3.06 nm, there is no outer carbon layer, the particle diameter of the core is 62 nm to 384 nm, and the specific surface area of ​​the positive electrode material is 14.76 m 2 / g.

[0167] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0168] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in a molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in a molar ratio of Fe:Mn=1:1.5, and water and oxalic acid were mixed in amounts of 350% and 2.5% of the total mass of the raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0169] In S2, the inner core precursor material was subjected to the first sintering at a temperature of 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0170] In S3, the inner core, glucose and fructose phosphate (first carbon source), and water were mixed to obtain a mixed material. The mass ratio of the inner core to the first carbon source was 1:10, the mass ratio of the inner core to water was 1:4, the mass ratio of fructose phosphate in the first carbon source was 4%, and the non-carbon element in the first carbon source was P.

[0171] In step S4, the mixed material was subjected to the second sintering at 700°C for 8 hours. Atomized ethanol, polyethylene glycol, and N,N-dimethylethanolamine (second carbon source) were introduced in a mass ratio of 3:6:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 60 mL / min. The introduction time was 6 hours. A multi-carbon interlocking layer was formed on the surface of the inner core.

[0172] Example 7 The positive electrode material according to this embodiment includes a core (i.e., inner core), a first carbon layer, and a second carbon layer, the first carbon layer being bonded to the surface of the core, and the second carbon layer being coated on the surface of the first carbon layer, and the second carbon layer having a higher degree of graphitization than the first carbon layer. Here, the thickness of the first carbon layer is 3.26 nm, the thickness of the second carbon layer is 0.90 nm, the particle diameter of the core is 54 nm to 376 nm, and the I of the first carbon layer G / I D The value is 1.05, and the I G / I D The value is 1.14.

[0173] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0174] In S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where iron phosphate and manganese acetate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid were mixed in amounts of 400% and 3.0% of the mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0175] In S2, the core precursor material was subjected to a first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the core.

[0176] In S3, the core part was mixed with lactose and hydroxypropylated phosphate-crosslinked starch as the first carbon source and water as the carbon source solvent to obtain a mixed material. The mass ratio of the core part to the first carbon source was 1:12, and the mass ratio of the core part to the carbon source solvent was 1:5. The mass proportion of hydroxypropylated phosphate-crosslinked starch in the first carbon source was 5%, and the non-carbon element in the first carbon source was P.

[0177] In S4, the mixed material was subjected to a second sintering at 720°C for 7 hours. The atomized second carbon source, butanone, polyethylene glycol, and ammonium formate, were introduced in a mass ratio of 3.2:5.8:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 65 mL / min. The introduction time was 7 hours, and a first carbon layer was formed on the surface of the core.

[0178] In step S5, the second sintering temperature was maintained, and the atomized second carbon source butanone, polyethylene glycol, and ammonium formate were introduced. The gas flow rate of the atomized second carbon source was 65 mL / min, and the introduction time was 2.5 h. A second carbon layer was formed on the surface of the first carbon layer, resulting in the production of a positive electrode material.

[0179] Example 8 The positive electrode material according to this embodiment includes a core (i.e., inner core), a first carbon layer, and a second carbon layer, the first carbon layer being bonded to the surface of the core, and the second carbon layer being coated on the surface of the first carbon layer, and the second carbon layer having a higher degree of graphitization than the first carbon layer. Here, the thickness of the first carbon layer is 4.12 nm, the thickness of the second carbon layer is 0.97 nm, the particle diameter of the core is 40 nm to 342 nm, and the I of the first carbon layer G / I D The value is 0.90, and the I G / I D The value is 1.12, and the degree of graphitization of the positive electrode material is 0.97.

[0180] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0181] In S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where iron phosphate and manganese acetate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid were mixed in amounts of 400% and 3.0% of the mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0182] In S2, the core precursor material was subjected to a first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the core.

[0183] In S3, the core was mixed with fructose and D-glucosamine as the first carbon source and water as the carbon source solvent to obtain a mixed material. The mass ratio of the core to the first carbon source was 1:16, and the mass ratio of the core to the carbon source solvent was 1:5. The mass ratio of D-glucosamine in the first carbon source was 5%, and the non-carbon element in the first carbon source was N.

[0184] In S4, the mixed material was subjected to a second sintering at 670°C for 7 hours. The atomized second carbon source, methanol, polypropylene glycol, and aniline, was introduced in a mass ratio of 3.2:5.8:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 95 mL / min. The introduction time was 7 hours, and a first carbon layer was formed on the surface of the core.

[0185] In step S5, the second sintering temperature was maintained, and the atomized second carbon source, methanol, polypropylene glycol, and aniline, was introduced. The gas flow rate of the atomized second carbon source was 95 mL / min, and the introduction time was 2.5 h. A second carbon layer was formed on the surface of the first carbon layer, and a positive electrode material was obtained.

[0186] Example 9 The positive electrode material according to this embodiment includes a core (i.e., inner core), a first carbon layer, and a second carbon layer, the first carbon layer being bonded to the surface of the core, and the second carbon layer being coated on the surface of the first carbon layer, and the second carbon layer having a higher degree of graphitization than the first carbon layer. Here, the thickness of the first carbon layer is 3.42 nm, the thickness of the second carbon layer is 0.86 nm, the particle diameter of the core is 78 nm to 546 nm, and the I of the first carbon layer G / I D The value is 1.10, and the I G / I DThe value is 1.38. The first carbon layer includes a carbon element and a first non-carbon element, the first non-carbon element includes a P element, the mass content of the carbon element in the first carbon layer is 98.48%, and the mass content of the first non-carbon element in the first carbon layer is 1.52.

[0187] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0188] In S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where iron phosphate and manganese acetate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid were mixed in amounts of 400% and 3.0% of the mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0189] In S2, the core precursor material was subjected to a first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the core.

[0190] In S3, the core part was mixed with lactose and hydroxypropylated phosphate-crosslinked starch as the first carbon source and water as the carbon source solvent to obtain a mixed material. The mass ratio of the core part to the first carbon source was 1:16, and the mass ratio of the core part to the carbon source solvent was 1:5. The mass ratio of hydroxypropylated phosphate-crosslinked starch in the first carbon source was 5%, and the non-carbon element in the first carbon source was P.

[0191] In S4, the mixed material was subjected to a second sintering at 800°C for 7 hours, and the atomized second carbon source, butanone, polyethylene glycol, and ammonium formate, was introduced in a mass ratio of 3.2:5.8:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 95 mL / min. The introduction time was 7 hours, and a first carbon layer was formed on the surface of the core.

[0192] In step S5, the second sintering temperature was maintained, and the atomized second carbon source butanone, polyethylene glycol, and ammonium formate were introduced. The gas flow rate of the atomized second carbon source was 95 mL / min, and the introduction time was 2.5 h. A second carbon layer was formed on the surface of the first carbon layer, resulting in a positive electrode material.

[0193] Example 10 The positive electrode material of this example includes a core (i.e., inner core), a first carbon layer, and a second carbon layer. The thickness of the first carbon layer is 3.08 nm, the thickness of the second carbon layer is 0.77 nm, the particle diameter of the core is 60 nm to 454 nm, and the particle diameter of the first carbon layer is 1. G / I D The value is 0.94, and the I G / I D The value is 1.14, and the degree of graphitization of the positive electrode material is 1.02.

[0194] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0195] In S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where iron phosphate and manganese acetate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid were mixed in amounts of 400% and 3.0% of the mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0196] In S2, the core precursor material was subjected to a first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the core.

[0197] In S3, the core part was mixed with lactose and hydroxypropylated phosphate-crosslinked starch as the first carbon source and water as the carbon source solvent to obtain a mixed material. The mass ratio of the core part to the first carbon source was 1:8, and the mass ratio of the core part to the carbon source solvent was 1:5. The mass ratio of hydroxypropylated phosphate-crosslinked starch in the first carbon source was 5%, and the non-carbon element in the first carbon source was P.

[0198] In S4, the mixed material was subjected to a second sintering at 670°C for 7 hours. The atomized second carbon source, butanone, polyethylene glycol, and ammonium formate, were introduced in a mass ratio of 3.2:5.8:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 35 mL / min. The introduction time was 7 hours, and a first carbon layer was formed on the surface of the core.

[0199] In step S5, the second sintering temperature was maintained, and the atomized second carbon source butanone, polyethylene glycol, and ammonium formate were introduced. The gas flow rate of the atomized second carbon source was 35 mL / min, and the introduction time was 2.5 h. A second carbon layer was formed on the surface of the first carbon layer, resulting in a positive electrode material.

[0200] Example 11 The positive electrode material of this example includes a core (i.e., inner core), a first carbon layer, and a second carbon layer, the second carbon layer being coated on the surface of the first carbon layer, and the second carbon layer having a higher degree of graphitization than the first carbon layer. Here, the thickness of the first carbon layer is 3.32 nm, the thickness of the second carbon layer is 0.92 nm, the particle diameter of the core is 58 nm to 365 nm, and the I of the first carbon layer is 0.92 nm. G / I D The value is 1.01, and the I G / I D The value is 1.23, and the degree of graphitization of the positive electrode material is 1.08.

[0201] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0202] In S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where iron phosphate and manganese acetate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid were mixed in amounts of 400% and 3.0% of the mass of the above-mentioned raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0203] In S2, the core precursor material was subjected to a first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the core.

[0204] In S3, the core was mixed with lactose as the first carbon source and water as the carbon source solvent to obtain a mixed material. The mass ratio of the core to the first carbon source was 1:12, and the mass ratio of the core to the carbon source solvent was 1:5.

[0205] In S4, the mixed material was subjected to a second sintering at 720°C for 7 hours, and the atomized second carbon source butanone and polyethylene glycol were introduced in a mass ratio of 3.2:6.8, the gas flow rate of the atomized second carbon source was 65 mL / min, and the introduction time was 7 hours, forming a first carbon layer on the surface of the core.

[0206] In step S5, the second sintering temperature was maintained, and the atomized second carbon source, butanone and polyethylene glycol, was introduced. The gas flow rate of the atomized second carbon source was 65 mL / min, and the introduction time was 2.5 h. A second carbon layer was formed on the surface of the first carbon layer, and a positive electrode material was obtained.

[0207] Example 12 The positive electrode material of this example comprises an inner core (core), a multi-carbon interlocking layer (first carbon layer), and an outer carbon layer (second carbon layer). The first carbon layer comprises main skeletal carbon and modified carbon. The main skeletal carbon is deposited on the surface of the inner core, and the modified carbon is interlocked with the main skeletal carbon. The second carbon layer coats the surface of the first carbon layer, and the degree of graphitization of the second carbon layer is higher than that of the first carbon layer. Here, the thickness of the first carbon layer is 3.20 nm, the thickness of the second carbon layer is 0.90 nm, the particle diameter of the inner core is 50 nm to 372 nm, and the I of the first carbon layer G / I D The value is 1.06, and the I G / I D The value is 1.32, and the I G / I D The value is 1.13.

[0208] The method for producing the positive electrode material according to this embodiment includes the following steps.

[0209] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and water (precursor solvent) and oxalic acid (co-solvent) were mixed in amounts of 350% and 2.5% of the total mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0210] In S2, the inner core precursor material was subjected to the first sintering at a temperature of 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0211] In S3, the inner core was mixed with glucose and fructose phosphate ester (first carbon source) and water (carbon source solvent) to obtain a mixed material. The mass ratio of the inner core to the first carbon source was 1:10, and the mass ratio of the inner core to water was 1:4. The mass proportion of fructose phosphate ester in the first carbon source was 4%, and the non-carbon element in the first carbon source was P.

[0212] In S4, the mixed material was subjected to a second sintering at 720°C for 7 hours. The atomized second carbon source, butanone, polyethylene glycol, and ammonium formate, were introduced in a mass ratio of 3.2:5.8:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 65 mL / min. The introduction time was 7 hours, and a first carbon layer was formed on the surface of the core.

[0213] In step S5, the temperature of the second sintering was maintained, and the atomized second carbon source butanone, polyethylene glycol, and ammonium formate were introduced. The gas flow rate of the atomized second carbon source was 65 mL / min, and the introduction time was 2.5 h. A second carbon layer was formed on the surface of the first carbon layer, resulting in a positive electrode material.

[0214] <Comparative Example 1> As shown in FIG. 3, the positive electrode material according to this comparative example includes an inner core 21 and a carbon coating layer 22 coated on the surface of the inner core 21. The total pore volume of the carbon coating layer 22 is 0.137 cm. 3 / g, the thickness is 3.10 nm, the particle diameter of the inner core 21 is 64 nm to 395 nm, and the specific surface area of ​​the positive electrode material is 17.85 m 2 / g.

[0215] The method for producing the positive electrode material according to this comparative example includes the following steps.

[0216] In S1, lithium carbonate, ferrous acetate, ammonium dihydrogen phosphate, and manganese carbonate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the ferrous acetate and manganese carbonate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and water and oxalic acid were mixed in amounts of 350% and 2.5% of the total mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained.

[0217] In S2, the inner core precursor material was subjected to the first sintering at a temperature of 400°C in a nitrogen atmosphere for 6 hours to obtain the inner core.

[0218] In S3, the inner core, glucose, fructose phosphate ester (first carbon source), and water were mixed to obtain a mixed material. The mass ratio of the inner core to the first carbon source was 1:10, and the mass ratio of the inner core to water was 1:4. The mass proportion of fructose phosphate ester in the first carbon source was 4%, and the non-carbon element in the first carbon source was P.

[0219] In S4, the mixed material was subjected to a second sintering at 700°C for 6 hours to obtain a positive electrode material.

[0220] <Comparative Example 2> The positive electrode material according to this comparative example includes a core portion and a first carbon layer, and the first carbon layer is deposited on the surface of the core portion. Here, the thickness of the first carbon layer is 3.25 nm, the particle diameter of the core portion is 62 nm to 408 nm, and the I of the first carbon layer G / I D The value is 1.05, and the I G / I D The value is 1.04.

[0221] The method for producing the positive electrode material according to this comparative example includes the following steps.

[0222] In S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where iron phosphate and manganese acetate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid were mixed in amounts of 400% and 3.0% of the mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained. In S2, the core precursor material was subjected to the first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the inner core. In S3, the core part is mixed with lactose and hydroxypropylated phosphate cross-linked starch as the first carbon source and water as the carbon source solvent to obtain a mixed material, in which the mass ratio of the core part to the first carbon source is 1:12, the mass ratio of the core part to the carbon source solvent is 1:5, the mass proportion of hydroxypropylated phosphate cross-linked starch in the first carbon source is 5%, and the non-carbon element in the first carbon source is P. In S4, the mixed material was subjected to a second sintering at 720°C for 9.5 hours. The atomized second carbon source butanone, polyethylene glycol, and ammonium formate were introduced in a mass ratio of 3.2:5.8:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 65 mL / min. The introduction time was 7 hours. A first carbon layer was formed on the surface of the core.

[0223] <Comparative Example 3> This comparative example provides a positive electrode material including a core portion, a first carbon layer deposited on the surface of the core portion, and a second carbon layer coated on the surface of the first carbon layer, the second carbon layer having a higher degree of graphitization than the first carbon layer. Here, the thickness of the first carbon layer is 3.12 nm, the particle diameter of the core portion is 65 nm to 465 nm, and the I of the positive electrode material. G / I D The value is 0.69.

[0224] The method for producing the positive electrode material according to this comparative example includes the following steps.

[0225] In S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate were mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where the iron phosphate and manganese acetate were mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid were mixed in amounts of 400% and 3.0% of the mass of the above raw materials, respectively. The pH of the mixed solution was 6.0, and after reaction, a lithium manganese iron phosphate material precursor was obtained. In S2, the core precursor material was subjected to the first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the inner core. In S3, the core part is mixed with lactose and hydroxypropylated phosphate cross-linked starch as the first carbon source and water as the carbon source solvent to obtain a mixed material, in which the mass ratio of the core part to the first carbon source is 1:15, the mass ratio of the core part to the carbon source solvent is 1:5, the mass proportion of hydroxypropylated phosphate cross-linked starch in the first carbon source is 5%, and the non-carbon element in the first carbon source is P. In S4, the mixed material was subjected to a second sintering at 720°C for 9.5 hours to obtain a positive electrode material.

[0226] <Comparative Example 4> This comparative example provides a cathode material including a core portion, a first carbon layer deposited on the surface of the core portion, and a second carbon layer coated on the surface of the first carbon layer, the second carbon layer having a higher degree of graphitization than the first carbon layer. Here, the thickness of the first carbon layer is 3.17 nm, the thickness of the second carbon layer is 1.05 nm, the particle diameter of the core portion is 52 nm to 403 nm, and the I of the first carbon layer G / I D The value is 1.08, and the I G / I D The value is 1.02, and the I G / I D The value is 1.05.

[0227] The method for producing the positive electrode material according to this comparative example includes the following steps.

[0228] In step S1, lithium carbonate, iron phosphate, ammonium dihydrogen phosphate, and manganese acetate are mixed in an elemental molar ratio of Li:(Fe+Mn):P=1:1:1, where iron phosphate and manganese acetate are mixed in an elemental molar ratio of Fe:Mn=1:1.5, and the precursor solvent water and co-solvent citric acid are mixed in amounts of 400% and 3.0% of the mass of the above raw materials, respectively. The pH of the mixed solution is 6.0, and after reaction, a lithium manganese iron phosphate material precursor is obtained. In S2, the core precursor material was subjected to the first sintering at 420°C in a nitrogen atmosphere for 5.5 hours to obtain the inner core. In S3, the core part was mixed with lactose and hydroxypropylated phosphate-crosslinked starch as the first carbon source and water as the carbon source solvent to obtain a mixed material. The mass ratio of the core part to the first carbon source was 1:12, and the mass ratio of the core part to the carbon source solvent was 1:5. The mass proportion of hydroxypropylated phosphate-crosslinked starch in the first carbon source was 5%, and the non-carbon element in the first carbon source was P. In S4, the mixed material was subjected to a second sintering at 720°C for 7 hours, and the atomized second carbon source butanone, polyethylene glycol, and ammonium formate were introduced in a mass ratio of 3.2:5.8:1. The non-carbon element in the second carbon source was N. The gas flow rate of the atomized second carbon source was 65 mL / min, and the introduction time was 7 hours. A first carbon layer was formed on the surface of the core. In step S5, the second sintering temperature was lowered to 670°C, and the atomized second carbon source, butanone and polyethylene glycol, was introduced in a mass ratio of 6:4. The gas flow rate of the atomized second carbon source was 65 mL / min, and the introduction time was 4 hours. A second carbon layer was formed on the surface of the first carbon layer, and a positive electrode material was obtained.

[0229] [Performance test experiment] (Testing methods for cathode materials) 1. Carbon layer thickness The carbon layer of the positive electrode material was photographed using a transmission electron microscope (TEM), and the thickness of the carbon layer was measured using Image J software. The test results for the carbon layer thickness of Examples 1 to 6 and Comparative Example 1 are shown in Table 1, and the test results for the carbon layer thickness of Examples 7 to 12 and Comparative Examples 2 to 4 are shown in Table 2. The TEM photograph of the positive electrode material of Example 7 is shown in Figure 8.

[0230] 2.Inner core particle size The carbon layer of the positive electrode material was photographed using a scanning electron microscope (SEM), and the primary particle diameter of the particles was measured using Image J software. The results of Examples 1 to 6 and Comparative Example 1 are shown in Table 1, the results of Examples 7 to 12 and Comparative Examples 2 to 4 are shown in Table 2, and an SEM photograph of the core (inner core) of Example 7 is shown in Figure 9.

[0231] 3. Pore volume of the carbon layer The pore volume of the carbon layer of the positive electrode material was measured by static nitrogen gas adsorption. 2-3 g of sample was taken and placed in a U-shaped sample tube. After heating and degassing under vacuum, the tube was placed in liquid nitrogen, and nitrogen gas was adsorbed by the powder surface. The adsorption pressure and the volume of gas adsorbed on the surface of the material were measured to obtain data such as pore volume and pore size distribution. The pore volume and pore size distribution diagrams of the positive electrode material of Example 1 and the positive electrode material of Comparative Example 1 are shown in FIG. 6. Specifically, the measurement results of the pore volume and pore size of the positive electrode materials of Examples 1-6 and Comparative Example 1 are shown in Table 1.

[0232] 4.Specific surface area The test was carried out by static nitrogen gas adsorption. 2-3 g of the sample was placed in a U-shaped sample tube, heated and degassed under vacuum, and then placed in liquid nitrogen. Nitrogen gas was adsorbed by the powder surface, and the specific surface area of ​​the sample was determined by measuring the adsorption pressure and the volume of gas adsorbed on the material surface. The test results for the positive electrode materials of Examples 1 to 6 and Comparative Example 1 are shown in Table 1.

[0233] 5.Powder resistivity The powder resistivity of the positive electrode materials was tested using an automatic powder resistivity tester. The sample mass was 0.5000g to 0.5050g, the test pressure was 8MPa, and the dwell time was 5s. The powder resistivity can reflect the external conductivity of the material and, in turn, the electron transport ability and coating uniformity of the carbon coating layer of the positive electrode material. The test results for Examples 7 to 12 and Comparative Examples 2 to 4 are shown in Table 2.

[0234] 6. Carbon content The carbon content of the positive electrode material was tested using a carbon-sulfur analyzer. The sample mass was about 0.1 g and the co-solvent was 1.5 g. The test results for Examples 7 to 12 and Comparative Examples 2 to 4 are shown in Table 2.

[0235] 7. Degree of graphitization The carbon spectrum of the carbon layer of the positive electrode material (including the first carbon layer and the total carbon layer of the positive electrode material, and the second carbon layer was collected separately on a ceramic plate and then tested) was measured using a Raman spectrophotometer. The scanning range was 3500 cm. -1 ~100cm-1 The laser wavelength is 532 nm. Raman scattering is very sensitive to the offset symmetry in the carbon structure, so carbon materials with graphite structures exhibit two characteristic peaks in the Raman spectrum: the D (Defect) peak and the G (Graphite) peak. Here, the D peak is located at 1350 cm -1 The G peak is close to 1580 cm, which indicates a defective graphite layer structure. -1 The D peak and G peak are both sp 2 After peak fitting to the Raman spectra of the tested cathode materials using Peakit software, sp 2 Heterogenized carbon peak and disordered structure sp 3 The hetero carbon peak can be separated, and I G / I D The degree of graphitization of the carbon material is expressed by

[0000] , and a larger value indicates a higher degree of graphitization. The Raman spectroscopic fitting analysis diagram of the core portion of Example 7 is shown in Figure 10, and the Raman spectroscopic analysis results of the positive electrode materials of Examples 7 to 12 and Comparative Examples 2 to 4 are shown in Table 2.

[0236] (Secondary battery assembly and charge / discharge capacity test method) 1. Positive electrode plate NMP: manganese iron lithium phosphate cathode material: Super P: PVDF were mixed in a mass ratio of 100:93:2:3 to prepare a cathode slurry. The mixing method was ball milling, the ball milling time was 120 min, and the rotation speed was 30 Hz. After homogenization, coating, drying, and cutting, each cathode plate was prepared. The cathode plate was baked in a vacuum oven at 100°C for 12 hours until it reached a constant weight.

[0237] 2. Negative electrode plate A metallic lithium plate was used.

[0238] 3. Separator A polyethylene (PE) separator was used.

[0239] 4. Electrolyte The electrolyte was a 1 mol / L LiPF6 solution, and the solvent consisted of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1:1.

[0240] 5. Secondary battery assembly The lithium plate, separator, positive electrode plate, gasket, elastic plate, and positive electrode case were laminated in that order at the center of the negative electrode case, and an appropriate amount of electrolyte was dropped onto the separator to moisten it. After assembly was complete, the battery was sealed using a button battery sealing machine to obtain a coin cell, which was then left to stand for 12 hours before being placed in a frame and subjected to an electrochemical performance test.

[0241] 6. Cathode Slurry Testing Method The battery was tested at a temperature of 25°C ± 2°C and humidity of <2%RH according to the operating procedure of the battery charge / discharge measuring instrument, and the 0.1C discharge specific capacity data of the simulated battery was tested. The results are shown in Tables 1 and 2.

[0242] 7. Observation of Slurry Bubbles in the Preparation Method of All-Electrode Positive Slurry The positive electrode slurry was prepared using a vacuum mixer and homogenized wet. After the slurry preparation was completed, the bubble state in the slurry was recorded using an image capture method, and the results are shown in Table 1. Table 1 includes the physicochemical parameters of the positive electrode material, the charge / discharge capacity, and the bubble state in the prepared slurry for each example.

[0243] [Table 1] As can be seen from the data in Table 1, the phosphate positive electrode material prepared in Example 1 of the present disclosure not only ensured the best 0.1C charge / discharge capacity, but also had the lowest specific surface area and total pore volume, and the prepared positive electrode slurry was bubble-free, an effect of the modified filling effect of the small-pore-volume modified carbon obtained by in situ cleavage and / or vapor deposition. In Example 2, after changing the type, amount, and sintering conditions of the first and second carbon sources, the prepared positive electrode material had an increased specific surface area and pore volume, decreased electrical performance, and a small number of bubbles appeared in the prepared positive electrode slurry compared to Example 1.

[0244] When the amounts of the first carbon source in step S3 and the second carbon source in step S5 were changed to produce the cathode materials of Examples 3 and 4, the thicknesses of the multi-carbon interlocking layer and the outer carbon layer increased accordingly, and the specific surface area and total pore volume also increased, resulting in a slight decrease in electrical performance. However, only the slurry produced using the cathode material of Example 3 contained bubbles, while the slurry produced using Example 4 was bubble-free. Furthermore, the particle morphology and electrical properties of the cathode material of Example 4 were better than those of Example 3. This indicates that the modified carbon formed by in situ cleavage and / or vapor growth of the second carbon source has a less porous structure and better electronic conductivity.

[0245] The carbon-rich interlocking layer and the outer carbon layer of the positive electrode material of Example 5 did not contain non-carbon elements. The pore volume and specific surface area of ​​the positive electrode material were both slightly larger than those of Example 1, but the electrical performance was slightly inferior. The introduction of non-carbon elements into the carbon layer could make the carbon layer more dense and improve the electronic conductivity of the positive electrode material, which may be related to the increased degree of graphitization of the carbon layer.

[0246] The carbon layer of the positive electrode material in Example 6 only contains multiple carbon interlocking layers, and the total pore volume is small. The resulting slurry is similarly bubble-free, but the electrical properties are poor. Therefore, the carbon coating layer has the effect of enhancing the electronic conductivity of the positive electrode material, which is related to the high degree of graphitization and the further modification effect on the surface of the multiple carbon interlocking layers of the particles.

[0247] The cathode material of Comparative Example 1 was only subjected to in-situ carbon coating, and therefore had the poorest overall performance, and the prepared cathode slurry also contained many bubbles. Comparison of the particle shape characteristics, electrical properties, and slurry bubble conditions of the cathode materials of the Examples and Comparative Examples shows that the cathode material having a multi-carbon interlocking intermediate layer and an outer carbon layer prepared in the disclosed Examples can reduce the porosity of the carbon layer, effectively reducing the specific surface area of ​​the material and improving the electrical performance of the material, ultimately eliminating or improving the bubbles in the slurry.

[0248] [Table 2] Table 2 shows the physicochemical parameters and the degree of graphitization of the carbon layer of the positive electrode materials of Examples 7 to 12 and Comparative Examples 2 to 4. Combining the data in Table 2 and Table 1, it can be seen that the phosphate positive electrode material prepared in Example 7 of the present disclosure has an appropriate carbon content, and the first carbon layer, the second carbon layer, and all of the carbon coating layers of the positive electrode material all have a high degree of graphitization, low electrical resistivity, a small primary particle size range, the highest 0.1C charge / discharge clump capacity, and the best overall performance.

[0249] With reference to Example 7, the changes in physicochemical indexes, degree of graphitization and electrical properties of the positive electrode materials of other Examples are compared and analyzed.

[0250] In Example 8, the types of the first and second carbon sources used in steps S3 to S5 were changed, the amount of carbon source was increased, and the second sintering temperature was reduced. Consequently, the carbon content of the positive electrode material increased, the degree of graphitization of the carbon layer decreased, the resistivity increased, and the primary particle size was minimized, but the electrical properties decreased. This indicates that if the carbon content is too high and the carbon layer is too thick, it becomes more difficult for lithium ions to be released from the positive electrode material. Lowering the sintering temperature reduces the degree of graphitization of the carbon layer, which is detrimental to electron conduction between the carbon layers. The amounts of the first and second carbon sources used in steps S3 to S5 were increased, and the second sintering temperature was raised to prepare the positive electrode material of Example 9. The carbon content increased, the degree of graphitization of the carbon layer was the highest, and the electrical resistivity was the lowest, but the electrical properties were the poorest. This was mainly because the particle size of the primary particles of the positive electrode material was significantly increased after the sintering temperature was increased, which increased the diffusion distance of lithium ions within the crystals and worsened the material kinetics. The positive electrode material of Example 10 was produced by reducing the amounts of the first and second carbon sources used in steps S3 to S5 and lowering the second sintering temperature, resulting in a lower carbon content, a thinner carbon layer, a lower degree of graphitization, an increased electrical resistivity, and reduced electrical performance. This is because the amount of carbon source used was too small, making it difficult to form a good carbon-coated conductive network, and because the lower temperature made it difficult to form a more graphite layer structure in the carbon layer, both of which reduced electrical performance. Neither the first nor the second carbon layer of the positive electrode material of Example 11 contained non-carbon elements, and although the carbon content and thickness of the carbon layers were similar to those of Example 7, the degree of graphitization of both carbon layers was reduced, the resistivity was correspondingly increased, and the electrical properties were deteriorated. This indicates that the non-carbon elements contained in the first and second carbon sources are beneficial to the formation of a more complete graphite layer structure in the carbon layers. In Example 12, the type of the first carbon source was changed in steps S1 to S3, the amount of the first carbon source used was reduced, and the first sintering temperature was lowered. As a result, the carbon content of the positive electrode material decreased, the carbon layer thickness decreased, the degree of graphitization decreased slightly, and the electrical resistivity increased. However, all of these results were similar to those of Example 7, and the electrical properties were good. This shows that when the amount of carbon source used and the sintering temperature are close to those of Example 7, a positive electrode material with good electrical properties can still be obtained even if the type of carbon source is changed.

[0251] The cathode material of Comparative Example 2 has only a first carbon layer outside the core (inner core), but no second carbon layer, which reduces the carbon content and thickness of the carbon layer, reduces the degree of graphitization of the carbon layer, increases resistivity, and reduces electrical performance. The second carbon layer, as a carbon layer with a higher degree of graphitization, effectively improves the electronic conductivity of the entire cathode material and inhibits crystal growth to some extent during the sintering process, thereby improving the dynamic performance of the cathode material.

[0252] The positive electrode material of Comparative Example 3, which only performed in situ coating, had the poorest degree of graphitization and electrical performance of its carbon layer. The positive electrode material of Comparative Example 4, which coated the second carbon layer by adjusting the proportion of the second carbon source, lowering the sintering temperature, and eliminating non-carbon elements in the second carbon layer, resulted in a lower degree of graphitization of the second carbon layer than the first carbon layer, resulting in electrical performance lower than that of Example 7 and similar to that of Comparative Example 2. The graphitization of the carbon layers exhibits a spatial distribution trend in which the degree of graphitization increases in a gradient from the first carbon layer to the second carbon layer (from the inside to the outside), which is beneficial for optimizing the external electronic conductivity of the positive electrode material particles. However, if the graphitization of the carbon layers exhibits a spatial distribution trend in which the degree of graphitization increases in a gradient from the outside to the inside, it resembles a situation in which a low-conductivity carbon layer is coated on a high-conductivity carbon layer, which inhibits surface electron transport in the positive electrode material and reduces electrical performance.

[0253] As described above, the positive electrode material manufactured in the embodiments of the present disclosure includes a core (inner core), a first carbon layer bonded to the surface of the core, and a second carbon layer coated on the surface of the first carbon layer, and the second carbon layer has a higher degree of graphitization than the first carbon layer, which is advantageous in improving the surface electron transport ability of the positive electrode material, reducing the powder resistivity, and improving the electrical properties of the positive electrode material.

[0254] The above are merely preferred embodiments of the present disclosure, and do not limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present disclosure should be included within the protection scope of the present disclosure. [Explanation of symbols]

[0255] 11 Inner core of Example 1 12 Example 1 multi-carbon interlocking layer 13 Outer carbon layer 21 Core of Comparative Example 1 22 Carbon coating layer of Comparative Example 1 10. Cathode materials 11 inner core 12 First carbon layer 13 Second carbon layer

Claims

1. an inner core and a first carbon layer; the first carbon layer is a multi-carbon interlocking layer; The multi-carbon interlocking layer comprises a main skeletal carbon and a modified carbon; the main body skeletal carbon is bonded to the surface of the inner core; The modified carbon grows by interdigitation with the main skeletal carbon. Positive electrode material.

2. The carbon in the main skeleton forms stacked carbon plates bonded to the surface of the inner core, and / or The carbons in the modified carbons are interdigitated into the main backbone carbons to form carbon plates, and / or The mass content of the main skeletal carbon in the multi-carbon interlocking layer is 80% to 90%, and the mass content of the modified carbon in the multi-carbon interlocking layer is 10% to 20%. The positive electrode material according to claim 1 .

3. The length of the carbon plates in the main backbone carbon is greater than the length of the carbon plates in the modified carbon, and the length of the carbon plates in the modified carbon is less than 2 nm; and / or The pore volume of the carbon interlocking layer is 0.070 cm ３ / g and / or the thickness of the carbon interlocking layer is less than 10 nm; and / or I of the first carbon layer Ｇ / I Ｄ The value of is between 0.75 and 1.

5. The positive electrode material according to claim 1 .

4. the multi-carbon interlocking layer comprises a carbon element and a first non-carbon element; the first non-carbon element includes at least one of N, S, P, and Li; a mass content of the carbon element in the first carbon layer is 97% to 98.5%, and a mass content of the first non-carbon element in the first carbon layer is 1.5% to 3%; The positive electrode material according to claim 1 .

5. The positive electrode material further comprises a second carbon layer, the second carbon layer being an outer carbon layer, and the outer carbon layer is coated on the outer surface of the multi-carbon interlocking layer. The positive electrode material according to claim 1 .

6. The pore volume of the outer carbon layer is 0.020 cm ３ / g and / or The thickness of the outer carbon layer is less than 1.5 nm, and the thickness of the outer carbon layer is less than the thickness of the multi-carbon interlocking layer. The positive electrode material according to claim 5 .

7. the degree of graphitization of the second carbon layer is higher than the degree of graphitization of the first carbon layer; The positive electrode material according to claim 5 .

8. a long-range disorder of the carbon structure in the first carbon layer is higher than a long-range disorder of the carbon structure in the second carbon layer; The positive electrode material according to claim 5 .

9. Most of the carbon structures in the first carbon layer are long carbon plate structures, and the long carbon plate structures are deposited on the surface of the inner core; Most of the carbon structures of the second carbon layer are short carbon plate structures, which are discontinuously and anisotropically deposited on the surface of the first carbon layer, and the size of the long carbon plate structures is larger than the size of the short carbon plate structures. The positive electrode material according to claim 5 .

10. the second carbon layer includes a carbon element and a second non-carbon element; the second non-carbon element comprises at least one of N, P, and Li; and / or the mass content of the carbon element in the second carbon layer is 98% to 99%, and the mass content of the second non-carbon element in the second carbon layer is 1% to 2%; The positive electrode material according to claim 5 .

11. I of the second carbon layer Ｇ / I Ｄ The value is between 1.0 and 1.

9. The positive electrode material according to claim 5 .

12. The inner core contains phosphorus, and a portion of the phosphorus in the inner core and a portion of the carbon in the multi-carbon interlocking layer form a C-P bond and / or a C-O-P bond. The positive electrode material according to claim 1 .

13. The bond formation rate of the C—P bond and the C—O—P bond is 0.5% to 1.15%. The positive electrode material according to claim 12.

14. The core is a lithium-containing phosphate-based positive electrode active material core, and / or The particle size of the inner core is less than 400 nm; The positive electrode material according to claim 1 .

15. The total pore volume of the positive electrode material is 0.04 cm ３ / g to 0.10 cm ３ / g, and / or The specific surface area of ​​the positive electrode material is 12.0 m ２ / g to 17.0m ２ / g, and / or I of the positive electrode material Ｇ / I Ｄ The value is between 0.8 and 1.

25. The positive electrode material according to claim 1 .

16. A method for producing the cathode material according to claim 1, comprising: providing an inner core precursor material and performing a first sintering on the inner core precursor material in an inert atmosphere to obtain an inner core; mixing the inner core with a first carbon source and a carbon source solvent to obtain a mixed material; and performing a second sintering of the mixed material in an inert atmosphere to obtain the positive electrode material, wherein an atomized second carbon source is introduced during the second sintering process, the first carbon source is cleaved in situ to form a main skeletal carbon which is deposited on the surface of the inner core, the second carbon source is cleaved in situ and / or vapor-phase grown to form modified carbon, and the modified carbon is entangled and interdigitated into the main skeletal carbon to form a first carbon layer which is a multi-carbon interdigitated layer. A method for producing positive electrode materials.

17. the inner core precursor material is a lithium iron manganese phosphate precursor; The method for producing the lithium manganese iron phosphate precursor includes: mixing and reacting a lithium source, an iron source, a phosphorus source, a manganese source, a precursor solvent, and a co-solvent in appropriate proportions to obtain a lithium iron manganese phosphate precursor; The method for producing the cathode material according to claim 16.

18. the pH of the mixed solution obtained by mixing the lithium source, the iron source, the phosphorus source, the manganese source, the precursor solvent, and the co-solvent is 5.0 to 7.5; The method for producing the cathode material according to claim 17.

19. the first carbon source comprises at least one of hydroxypropylated phosphate cross-linked starch, glucose, fructose, sucrose, lactose, stevia, xylose, maltose, starch, cellulose, chitin, D-glucosamine, glucosamine sulfate, fructose phosphate, glucose-6-phosphate, N-acetylglucosamine, peptidoglycan, polyacrylate, polyethylene glycol, citric acid, malic acid, propylene, polypropylene glycol, polypropylene, polyacrylamide, lithium polyacrylate, polyvinyl alcohol, cyclodextrin, polyvinyl butyral, polystyrene, and graphite; and / or the second carbon source comprises at least two of methanol, ethanol, ethyl acetate, polyethylene glycol, acetone, butanone, ethyl ether, acetic acid, oxalic acid, polypropylene glycol, aniline, benzylamine, pyrazine, ammonium citrate, ammonium formate, ammonium acetate, formamide, acetamide, propionamide, butyramide, monoisopropanolamine, N,N-dimethylethanolamine, dimethylethanolamine, and triethylenediamine; The method for producing the cathode material according to claim 16.

20. at least one of the first carbon source and the second carbon source contains a carbon element and a first non-carbon element, the first non-carbon element contains at least one of N, S, P, and Li, the mass content of the carbon element in the total mass of the first carbon source and the second carbon source is 97% to 98.5%, and the mass content of the first non-carbon element in the total mass of the first carbon source and the second carbon source is 1.5% to 3%; The method for producing the cathode material according to claim 16.

21. The positive electrode material further includes a second carbon layer, which is an outer carbon layer. After forming the multiple carbon interlocking layers, the method for manufacturing the positive electrode material includes: The second carbon source is completely cleaved, and then the atomized second carbon source is introduced, and the second carbon source forms an outer carbon layer on the surface of the multi-carbon interlocking layer by in-situ cleavage and / or vapor deposition. The method for producing the cathode material according to claim 16.

22. The method for producing a positive electrode material satisfies at least one of the following conditions (1) to (4): (1) The temperature of the first sintering is 350°C to 660°C; (2) The temperature of the second sintering is 650°C to 855°C; (3) the gas flow rate of the atomizing gas of the second carbon source is 10 mL / min to 120 mL / min; (4) The second carbon source includes a carbon element and a second non-carbon element, and the second non-carbon element includes at least one of N, P, and Li elements. The mass content of the carbon element in the second carbon source is 98% to 99%. The mass content of the second non-carbon element in the second carbon source is 1% to 2%. The method for producing the cathode material according to claim 16.

23. The positive electrode material according to any one of claims 1 to 15, or the positive electrode material produced by the method for producing the positive electrode material according to any one of claims 16 to 22. Positive electrode plate.

24. A secondary battery comprising the positive electrode plate according to claim 23.

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