Cathode material and method for preparing the same, lithium-ion battery

Abstract

The present invention provides a positive electrode material and a method for preparing the same, as well as a lithium-ion battery. The positive electrode material is made of Li, Fe, Mn, and PO4. - The cathode material comprises a core layer containing ions and doped element A, and a shell layer whose surface is covered to the outer surface of the core layer, and which contains first and second carbon particles, wherein doped element A contains at least one element from Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, the difference in distance between the highest and lowest points on a single surface of the cathode material is 1 nm or less, and the surface roughness of the cathode material is 0.8 μm to 1.6 μm. Two carbon coating processes ensure high capacity and high compressibility of the cathode material, while significantly reducing manganese elution, thereby ensuring the cycle discharge efficiency of the cathode material.

Description

[Technical Field]

[0001] This application relates to the field of lithium battery technology, and more specifically to positive electrode materials, methods for preparing the same, and lithium-ion batteries. [Background technology]

[0002] With the rapid development of electronic products, the demand for portable and reusable secondary batteries is increasing day by day. Meanwhile, among the existing types of secondary batteries, olivine-type cathode materials have many advantages and therefore have great potential for applications in lithium-ion power batteries.

[0003] However, inherent drawbacks of olivine structure phosphate compounds themselves, such as low electronic conductivity and slow one-dimensional lithium ion diffusion rates, seriously affect the electrochemical performance of manganese iron lithium phosphate materials and hinder their further large-scale applications. Energy To improve density, the proportion of manganese is usually increased. However, as the manganese content increases, manganese leaching during the material's cycling process becomes unavoidable. Currently, carbon coating is commonly used to mitigate the problem of manganese leaching during material cycling, improving not only cycling performance but also the material's conductivity.

[0004] However, conventional solid-phase dry carbon coating processes cannot uniformly and evenly coat the material surface with a single layer of carbon material. A carbon coating with an uneven and rough surface not only fails to improve the manganese leaching problem but can also affect the conductivity of the material. [Overview of the project] [Problems that the invention aims to solve]

[0005] This application aims to solve at least one of the above technical problems. [Means for solving the problem]

[0006] Therefore, the first objective of this application is to provide a positive electrode material.

[0007] A second object of this application is to provide a method for preparing a positive electrode material.

[0008] The third object of this application is to provide a lithium-ion battery.

[0009] To achieve the first objective of this application, this application provides a cathode material, the cathode material being Li, Fe, Mn, PO4 - The cathode material comprises a core layer containing ions and doped element A, and a shell layer whose surface is covered on the outer surface of the core layer and which contains first carbon particles and second carbon particles, wherein doped element A contains at least one element from Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, the difference in distance between the highest and lowest points on a single surface of the cathode material is 1 nm or less, and the surface roughness of the cathode material is 0.8 μm to 1.6 μm.

[0010] Compared to conventional technologies, the technical effects obtained by adopting this technical solution are as follows: The core layer consists of Li, Fe, Mn, and PO4. - By incorporating ions and doped element A, and doping lithium iron phosphate with manganese, substituting some of the Fe element, a manganese-iron-lithium phosphate material can be prepared. This increases the voltage and energy density per unit mass, while maintaining relatively good voltage compatibility with current lithium-ion batteries and reducing the difficulty of mutual substitution.

[0011] Furthermore, the doping element A includes at least one element among Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. By doping the lithium iron phosphate with the element A, not only can each element in the core layer be harmonized, but the cathode material can also be modified to enhance the performance of the cathode material. The doping element A can cause defects in the Li site or M site in the manganese iron phosphate lattice, create vacancies in the material lattice, or change the interatomic bond length, which is advantageous for the movement of Li ions in the lattice and can improve the electrochemical performance.

[0012] The shell layer is such that at least a part of the surface is coated on the outer surface of the core layer and consists of the C element. As the proportion of manganese increases, it becomes inevitable to cause the elution of manganese during the cycling process of the material. core layer By coating carbon particles on the surface, the elution of manganese can be reduced. However, it is impossible to uniformly and consistently coat a layer of carbon material on the surface of the material. The uneven and rough carbon coating on the surface cannot only not improve the problem of manganese elution but may also affect the conductivity of the material. The difference in distance between the highest point and the lowest point on the single surface of the cathode material of the present application is 1 nm or less, and the surface roughness of the cathode material is 0.8 μm - 1.6 μm. By adjusting the surface unevenness, the shell layer on the surface of the cathode material is evenly coated, thereby improving the problem of manganese elution and further enhancing the conductivity of the material.

[0013] In one technical solution of the present application, the average diameter of the first carbon particles is 1 μm - 5 μm, and / or the average diameter of the second carbon particles is 0.5 μm - 1 μm.

[0014] Compared with the prior art, the technical effects obtained by adopting this technical solution are as follows. The average diameter of the first carbon particles is 1 μm - 5 μm, and the average diameter of the second carbon particles is 0.5 μm - 1 μm. The cathode material is coated twice with carbon particles of different particle diameters through the interparticle pores, and the first carbon coating layer teeth gap difference Yes , In the gaps of the first carbon coating layerIntroduce the second carbon particles to achieve a uniform and flat coating, and obtain a cathode material with a high carbon coating rate and a flat coating.

[0015] In one technical solution of the present application, the components of the cathode material are shown in Formula (I), Li 1+a Fe 1-x-y Mn x A y (PO 4-b )·C b It is Formula (I), and the ranges of the values of a, x, y, and b are -0.1 ≤ a ≤ 0.4, 0.5 ≤ x ≤ 0.7, 0.005 ≤ y ≤ 0.05, and 0 < b ≤ 0.3, respectively.

[0016] Compared with the prior art, the technical effects obtained by adopting this technical solution are as follows. Using Li, Fe, and PO4 as the matrix of the core layer, the prepared cathode material has better conductivity, high theoretical capacity and conductivity, a simple synthesis process, can realize large-scale production and research popularization, and by adjusting the ratio of different molecules, Li ions are required for insertion and extraction in the cathode material. By adding manganese and substituting part of the Fe element to prepare the lithium iron manganese phosphate material, the voltage can be increased, the energy density per unit mass can be enhanced, the material structure can be stabilized, a sudden change in volume can be prevented, and the battery life can be improved. However, just adding manganese, the crystal structure still generates strain after cycling many times, and the battery life still cannot be optimized. Therefore, the crystal structure is further stabilized by the doping element A, and by coating carbon particles on the outer surface of the core layer, the elution of manganese due to the increase in the amount of manganese can be prevented, and each performance of the cathode material can be further improved. Also, by controlling the ratio of the doping element A and the element C to be coated, the coating effect and the conductive performance are balanced, and the prepared material is not only uniformly coated but also excellent in conductivity.

[0017] In one technical solution of the present application, the specific surface area of the cathode material is 10m 2 / g - 25m 2 ​​The weight is / g, and / or the core layer diameter is 200nm-400nm, and / or the shell layer thickness is 1nm-5nm.

[0018] Compared to conventional technology, the technical effects obtained by adopting this technical solution are as follows: The specific surface area of ​​the positive electrode material is 10 m². 2 / g-25m 2 When the value is / g, the cycle discharge efficiency of the positive electrode material is highest at this time. The shell layer thickness is 1nm-5nm, and the core layer diameter is 200nm-400nm. By adjusting the thickness of the core and shell, Li + During charging, lithium is easily released from the positive electrode and absorbed into the negative electrode via the electrolyte. At the same time, compensatory electron charges are supplied to the negative electrode via an external circuit, ensuring a balance of charges between the positive and negative electrodes. Conversely, during discharge, lithium... + It is released from the negative electrode and absorbed into the positive electrode via the electrolyte, and at the same time, it is advantageous due to the infiltration of doped element A.

[0019] In one technical solution of the present invention, the brightness of the positive electrode material is 0-25, and / or the chroma of the positive electrode material is 0-3.6.

[0020] Compared to conventional technology, the technical effects obtained by adopting this technical solution are as follows: The brightness of the positive electrode material is 0-25, and the chroma of the positive electrode material is 0-3.6. In some cases, brightness and saturation The analysis revealed that the overall condition of the carbon coating on the prepared manganese iron lithium cathode material could be effectively assessed. A carbon layer of appropriate thickness and with a uniform surface not only improves the conductivity of the material but also prevents particle contact and suppresses particle growth, allowing for the production of a cathode material on the nanometer scale.

[0021] In one technical solution of the present invention, the positive electrode material is in the range of 2.0V-4.3V, its initial discharge gram capacity at 0.1C is 160mAh / g or more, and / or the volume specific energy density of the positive electrode material is 80mAh / cm³. 3 The above results, and / or the cycle retention rate of the positive electrode material after 200 cycles, reach 95.62%.

[0022] Compared to conventional technologies, the technical effects obtained by adopting this technical solution are as follows: Initial discharge gram capacity refers to the amount of energy that a battery can release in its first charge-discharge cycle. Since the initial discharge gram capacity directly affects the battery's lifespan and performance, it is one of the important indicators of battery quality. The positive electrode material according to this application is in the range of 2.0V-4.3V, and its initial discharge gram capacity at 0.1C is 160mAh / g or more. The cycle retention rate of the positive electrode material after 200 cycles reaches 95.62%. Volume specific energy density is the ratio between the energy possessed by a certain energy and its volume. It can reflect the volume consumed during battery use and is one of the important indicators of battery mass. The volume specific energy density of the positive electrode material according to this application is 80mAh / cm³. 3 As described above, the positive electrode material of this invention has a high cycle capacity retention rate and a low DC internal resistance increase rate, resulting in superior performance, a long service life, and economic efficiency.

[0023] In one technical solution of the present application, the preparation method is: S100 involves mixing a dopant containing a Li source, a Mn source, a Fe source, a P source, and doping element A, sequentially performing preheating, grinding, and drying treatments, and then performing a primary sintering treatment under a reducing atmosphere to obtain a first cathode material. S200 involves performing a secondary sintering treatment on the first cathode material and the first carbon particles in a reducing atmosphere to obtain the second cathode material. S300 includes a process in which a second positive electrode material, second carbon particles, and a binder are sequentially added and pre-mixed, and a tertiary sintering process is performed under a reducing atmosphere to obtain the positive electrode material. Here, the average diameter of the first carbon particle is 1 μm-5 μm. The average diameter of the second carbon particle is 0.5 μm–1 μm.

[0024] Compared to conventional technology, the technical advantages obtained by adopting this technical solution are as follows: By primary sintering in step S100, a core layer, which is the first positive electrode material, can be obtained. Contains doped element A Dopan toThe synergistic effect of the additives adjusts the interior of the core layer and enhances the performance of the cathode material. In step S200, secondary sintering is performed, coating the surface of the core layer with element C. However, the surface coated in the first layer is uneven and has irregularities, which not only fails to improve the manganese leaching problem but also affects the conductivity of the material. Therefore, the average diameter of the first carbon particles is 1 μm-5 μm, and the average diameter of the second carbon particles is 0.5 μm-1 μm. The cathode material is coated twice with carbon particles of different particle sizes in the interparticle pores, and the first carbon coating layer... There is a gap Distance Having , In the gaps of the first carbon coating layer By introducing a second set of carbon particles, a uniform and flat coating is achieved, resulting in a cathode material with a high carbon coating rate and a flat coating. This ensures high capacity and high compressibility of the cathode material through two carbon coating processes, while significantly reducing manganese leaching and ensuring the cycle discharge efficiency of the cathode material.

[0025] In one technical solution of the present invention, in S100, the molar ratio of the Li source, Mn source + Fe source, P source, and dopant is (1.01-1.04):(0.98-1):1:(0.05-0.1), and / or in S200, the molar ratio of the first positive electrode material to the first carbon particles is 100:(0.5-1), and / or in S300, the molar ratio of the second positive electrode material to the second carbon particles and binder is 100:(0.5-0.8):(0.2-0.5).

[0026] Compared to conventional technologies, the technical effects obtained by adopting this technical solution are as follows: By adjusting the molar ratio of Li source, Mn source, Fe source, P source, and dopant, the performance of the cathode material can be improved. The carbon content after tertiary sintering is lower than in the case of secondary sintering. Although the surface of the cathode material after primary sintering is completely coated, the surface has irregularities. Secondary coating is performed by tertiary sintering, resulting in a more complete coating of the surface, and ultimately preparing an olivine-type cathode material with a uniform and flat carbon coating.

[0027] In one technical solution of the present invention, the grinding process is carried out by sequentially performing ball milling and sand milling, and when the median particle size of the mixed material after ball milling is 1 μm or less, the process moves to sand milling, and the diameter of the medium in the ball milling process is 0.8 μm or less, and / or the diameter of the medium in the sand milling process is 0.3 μm or less.

[0028] Compared to conventional technologies, the technical effects obtained by adopting this technical solution are as follows: After preheating treatment, grinding treatment is performed, first with ball milling, where the diameter of the medium in the ball milling treatment is 0.8 μm or less, and after reducing the median particle size of the mixed material to 1 μm or less, the process moves to sand milling, where the diameter of the medium in the sand milling treatment is 0.3 μm or less, first rapidly grinding the mixed material with a ball mill, and then performing sand milling, making it suitable for industrial production and reducing costs.

[0029] In one technical solution of the present invention, in S100, the median particle size of the particulate material after grinding is 6 μm or less, and / or in S100, the median particle size of the particulate material after drying is 4 μm or less, and / or in S200, the average particle size of the first carbon particles is 1 μm-5 μm, and / or in S200, the powder compression density of the first carbon particles at a pressure of 2T is 3.00 g / cm³. 3 -3.20 g / cm³ 3 In and / or S300, the binder comprises one or more of the following: polyvinylidene fluoride, polyamide, polyimide, polyacrylic acid, polyvinyl alcohol, and styrene-butadiene rubber.

[0030] Compared to conventional technologies, the technical advantages obtained by adopting this technical solution are as follows: By constantly adjusting the particle size, the median particle size of the particulate matter after grinding is 6 μm or less, the median particle size of the particulate matter after drying is 4 μm or less, and primary carbon coating is also achieved. Particle Particle size is secondary carbon coated particleBy increasing the particle size beyond the specified limit, the thickness of the cathode material is controlled to remain within an optimal range, and the powder compression density of the first carbon particles at a 2T pressure is 3.00 g / cm³. 3 -3.20 g / cm³ 3 Therefore, a positive electrode material with a good particle normal distribution can increase the battery's discharge capacity, reduce internal resistance, decrease polarization loss, extend the battery's cycle life, and improve the utilization rate of lithium-ion batteries. If the compressed density is too high or too low, it is unfavorable for the intercalation and release of lithium ions.

[0031] In one technical solution of the present invention, in S100, the temperature of the preheating treatment is 50°C-100°C, and / or in S100, the time of the preheating treatment is 0.1h-1h, and / or in S100, the temperature of the primary sintering treatment is 500°C-800°C, and / or in S100, the time of the primary sintering treatment is 8h-14h, and / or in S200, the temperature of the secondary sintering treatment is 500°C-800°C, and / or in S200, the time of the secondary sintering treatment is 6h-12h, and / or in S300, the time of the premixing treatment is 1h-1.5h, and / or in S300, the temperature of the tertiary sintering treatment is 500°C-800°C, and / or in S300, the time of the tertiary sintering treatment is 6h-12h.

[0032] Compared to conventional technologies, the technical effects obtained by adopting this technical solution are as follows: By controlling the reaction temperature, time, and heating rate, the construction of core and shell layer materials is realized. Specifically, a first cathode material is obtained by sintering using specific process parameters through a stepwise sintering process. First, a preheating treatment is performed, in which a mixture of Li source, Mn source, Fe source, P source, and dopant is thermally decomposed into a precursor at a low temperature during the preheating stage, and the sintering time is controlled to 0.1h-1h. Next, primary sintering is performed to sufficiently decompose and synthesize the raw materials to form a nickel-cobalt-manganese-lithium compound. The sintering temperature is raised to 500-800°C at a rate of 1°C / min-4°C / min for 8h-14h. Furthermore, secondary heating sintering is performed to coat the first cathode material with carbon elements, with a secondary sintering time of 6h-12h. Finally, the second cathode material is uniformly coated. again The material is sintered, its form is modified, and the time and temperature are the same as during secondary sintering.

[0033] This application further provides a lithium-ion battery comprising a cathode material of any of the above-described technical solutions. Therefore, it has all the beneficial effects of any of the above-described technical solutions, which will not be repeated herein. [Effects of the Invention]

[0034] By adopting the technical solution of this invention, the following technical effects can be achieved. (1) The present invention involves coating the cathode material twice with interparticle pores of carbon particles of different particle sizes, with the first carbon coating layer teeth Gap difference Yes The second coating allows the small carbon particles to enter the gaps on the surface of the cathode material, thereby filling the gaps and achieving a uniform and flat coating of the cathode material. This results in a cathode material with a high carbon coating rate, ensuring high capacity and high compressibility of the cathode material, while significantly reducing manganese leaching and ensuring the cycle discharge efficiency of the cathode material. (2) The carbon-coated positive electrode material and the method for preparing the same according to the present invention have a simple process, and the manufactured carbon-coated positive electrode material can maintain a high electrical capacity and has good discharge performance. [Brief explanation of the drawing]

[0035] To more clearly explain the technical solutions of the embodiments of this application, the drawings to be used in describing the embodiments will be briefly described below. Naturally, the drawings described below are only those of the embodiments, and those skilled in the art can obtain other drawings based on these without any creative work. [Figure 1] This is an SEM image of the second cathode material after secondary sintering according to the embodiment of the present invention. [Figure 2] This is an SEM image of the cathode material after tertiary sintering according to the embodiment of the present invention. [Figure 3] This is an SEM image of the cathode material in a comparative example of the present invention. [Figure 4] This is a schematic diagram showing the second positive electrode material after secondary sintering according to the embodiment of the present application, after tertiary sintering coating. [Modes for carrying out the invention]

[0036] To further clarify the above-mentioned objectives, features, and advantages of the present application, the technical solutions in the embodiments of the present application are described clearly and completely, and of course, the embodiments described are not all embodiments but only a selection of embodiments of the present application. All other embodiments that a person skilled in the art could obtain without creative work based on the embodiments of the present application are all within the scope of the present application.

[0037] Olivine-type cathode materials have great potential in applications of lithium-ion power batteries due to their many advantages. However, inherent drawbacks of olivine-structured phosphate compounds themselves, such as low electronic conductivity and a one-dimensional, slow lithium-ion diffusion rate, seriously affect the electrochemical performance of manganese iron lithium phosphate materials, hindering further large-scale applications. To improve capacity density, the manganese content is usually increased, but as the manganese content increases, manganese leaching during the material's cycle becomes unavoidable.

[0038] Currently, carbon coating is commonly used to mitigate the problem of manganese leaching during material cycling, improving not only cycling performance but also the conductivity of the material. However, conventional solid-phase dry carbon coating processes cannot uniformly and evenly coat the material surface with a single layer of carbon material. A carbon coating with an uneven and irregular surface not only fails to improve the manganese leaching problem but can also affect the conductivity of the material.

[0039] Therefore, the embodiments of the present application provide a method for preparing a positive electrode material, the prepared positive electrode material, and a battery prepared using the positive electrode material, wherein a two-step carbon coating process ensures high capacity and high compressibility of the positive electrode material, while significantly reducing manganese leaching, thereby ensuring the cycle discharge efficiency of the positive electrode material.

[0040] Specifically, a dopant containing a Li source, Mn source, Fe source, P source, and dope element A is mixed, and preheating, pulverization, and drying treatments are performed sequentially, followed by a primary sintering treatment in a reducing atmosphere to obtain the first cathode material.

[0041] Preferably, the Li source includes one or more of lithium dihydrogen phosphate, lithium carbonate, and lithium hydroxide; the Mn source includes one or more of manganese carbonate and trimanganese tetroxide; the Fe source includes one or more of iron hydroxide, iron phosphate, and triiron tetroxide; the P source includes one or more of iron phosphate and magnesium phosphate; and the dopant includes one or more of magnesium oxide and magnesium carbonate. The materials are mixed with deionized water, preheated, and thermally decomposed into precursors.

[0042] Preferably, the molar ratio of the Li source, Mn source + Fe source, P source, and dopant is (1.01-1.04):(0.98-1):1:(0.05-0.1), with Mn source being preferred, and the molar ratio of the Fe source being 1:(0.66-2). A stirring kettle can be used for preheating, with a rotation speed of 500. rpm -1500 rpmThe temperature is 120°C-180°C, the duration is 0.1h-1h, and the reducing atmosphere is preferably nitrogen gas or argon.

[0043] Furthermore, the precursor is subjected to a grinding process, which involves sequentially performing ball milling and sand milling. A high-energy ball mill machine can be used for the ball milling process, the diameter of the medium used in the ball milling process is 0.8 μm or less, the ball milling time in the high-energy ball mill machine is 1-3 hours, and the rotational speed of the ball mill is 1000 rpm-3000 rpm.

[0044] Preferably, when the median particle size of the ball-milled mixed material becomes 1 μm or less, the process moves to sand milling, employing a two-stage grinding process suitable for industrial production and cost reduction. Preferably, a high-energy sand mill can be used for sand milling, the diameter of the medium in sand milling is 0.3 μm or less, and the sand milling time in the high-energy sand mill is 2-5 hours. Sandmill The processing speed is 1000 rpm to 3000 rpm, and the median particle size of the mixed particulate matter is 6 μm or less, which is convenient for subsequent steps.

[0045] Furthermore, for the drying process, a centrifugal spray dryer can be selected, with an intake air temperature of 200°C-500°C, an exhaust air temperature of 100°C-300°C, and a spray disc rotation speed of 15,000 rpm-30,000 rpm. rpm The supply rate is 40 L·h. -1 Thus, the median particle size of the particulate material is 4 μm or less, and the first positive electrode material is obtained by primary sintering treatment under a reducing atmosphere. obtain As a result, primary sintering becomes more uniform, the doping elements penetrate the core layer better, and primary sintering is performed at a rate of 1°C / min-4°C / min, heating up to 500°C-650°C, taking 8-12 hours.

[0046] Specifically, the first positive electrode material and the first carbon particles are subjected to secondary sintering in a reducing atmosphere to obtain the second positive electrode material, and the surface of the core layer is coated with element C by secondary sintering, and the first carbon Particle The content is 0.9% of the positive electrode material, and secondary sintering is performed by raising the temperature to 600°C-700°C at a rate of 1°C / min-4°C / min, with a secondary sintering time of 6h-10h.

[0047] Furthermore, because the surface of the primary coating is uneven and has irregularities, which not only fails to improve the manganese leaching problem but can also affect the conductivity of the material, the second cathode material, second carbon particles, and binder are added sequentially and mixed for 1h-1.5h, and after the secondary carbon particles have sufficiently filled the gaps, the tertiary sintering, which is the secondary coating, is performed, and the second carbon Particle The content is 0.6% of the positive electrode material, and the tertiary sintering is performed by raising the temperature to 650°C-750°C at a rate of 1°C / min-4°C / min. three The next sintering time is 6h-10h, and the second positive electrode material is uniformly coated. again The sintering process, modification method, time, and temperature are the same as for secondary sintering. Test method for brightness and saturation: L represents brightness, a and b represent chromaticity, and the color difference value △E = [(△L)] 2 +△a) 2 +(triangle b) 2 ] 1 / 2 The chromaticity value of the sample is measured using a spectrophotometer, the material is placed in close contact with the probe of the colorimeter, the long axis of the lens is perpendicular to the measurement surface of the sample, and the light source of the probe is flashed three times in a row. probe I released it and recorded the value.

[0048] [First Embodiment] S100 and elements Li:Mn:Fe:P were mixed in a molar ratio of 1.04:0.6:0.4:1, deionized water was added, and the mixture was uniformly mixed in a stirring vessel. The mixture was preheated and ground at a heating temperature of 120°C, a rotation speed of 1000 rpm, and a time of 0.5 hours. The mixture was then dried in a centrifugal spray dryer with an intake temperature of 220°C, an exhaust temperature of 100°C, a spray disc rotation speed of 30000 rpm, and a supply rate of 40 L / h. A primary sintering treatment was then performed at a temperature of 650°C under a nitrogen atmosphere for 10 hours to obtain the first cathode material. The grinding process begins with a high-energy ball mill, where the ball milling medium is zirconium beads with a diameter of 0.8 μm, the rotation speed is 1500 rpm, and the processing time is 2 hours. Once the median particle size D50 of the particulate material reaches 1 μm, the process is moved to a high-energy sand mill, where the zirconium beads have a diameter of 0.3 μm and the sand milling time is 3 hours. As shown in Figure 1, S200, the first positive electrode material and the first carbon particles are mixed in a molar ratio of 100:0.9, and a secondary sintering treatment is performed for 8 hours at a temperature of 680°C under a nitrogen atmosphere to obtain the second positive electrode material. The average diameter of the first carbon particles is in the range of 1 μm to 5 μm, and the powder compression density of the first carbon particles is 3.00 g / cm³. 3 -3.20 g / cm³ 3 And, S300, as shown in Figure 2, second cathode material, second carbon particles, Polyvinylidene fluoride ( PVDF ) The following are added sequentially and mixed for 1 hour in a molar ratio of 100:0.6:0.3, and a tertiary sintering treatment is performed for 8 hours at a temperature of 700°C under a nitrogen atmosphere to obtain the cathode material. The average diameter of the second carbon particle is in the range of 0.5 μm to 1 μm.

[0049] [Second Example] This embodiment provides a lithium-ion battery and a method for preparing the same. The preparation method is the same as in Example 1, with the difference being the selection and molar ratio of each component, which are specifically shown in Table 1.

[0050] [Table 1]

[0051] [Third embodiment] This embodiment provides a lithium-ion battery and a method for preparing the same. The preparation method is the same as in Example 1, with the difference being the selection of doping elements and binders for each component, which are specifically shown in Table 2.

[0052] [Table 2]

[0053] [Fourth embodiment] This embodiment provides a lithium-ion battery and a method for preparing the same. The preparation method is the same as in Example 1, with the difference being that each process parameter is different, as specifically shown in Table 3.

[0054] [Table 3]

[0055] [Comparative Example 1] This embodiment provides a lithium-ion battery and a method for preparing the same, the preparation method being the same as in Example 1, the difference being that in S200, the first positive electrode material and the first carbon particles are mixed in a molar ratio of 100:1.8, the average diameter of the first carbon particles is in the range of 1.2 μm to 5.2 μm, and the powder compression density of the first carbon particles is 3.50 g / cm³. 3 -3.80g / cm 3 That is the case.

[0056] [Second Comparative Example] This embodiment provides a lithium-ion battery and a method for preparing the same, the preparation method being the same as in Example 1, as shown in Figure 3, the difference being that in S200, the first positive electrode material and other metal sources are mixed in a molar ratio of 100:0.2.

[0057] [Third Comparative Example] This embodiment provides a lithium-ion battery and a method for preparing the same, the preparation method being the same as in Example 1, with the differences being: S300 The second set of carbon particles has an average diameter in the range of 1.1 μm to 1.5 μm.

[0058] [Fourth Comparative Example] This embodiment provides a lithium-ion battery and a method for preparing the same, the preparation method being the same as in Example 1, the difference being that no binder is added in S300.

[0059] For the above Examples 1-4 and Comparative Examples 1-4, a person skilled in the art measured the positive electrode material by the following method, and the specific data is shown in Table 4. Within the range of 2.0V-4.3V, the initial discharge gram capacity at 0.1C was measured. Assembled battery cells were charged and discharged in a blue battery device at a test temperature of 25±1℃, a test voltage of 2.0V-4.3V, and 0.1C / 0.1C. The charge cutoff current was 0.05C. Cycle retention rate after 200 cycles: All batteries used are Xinwei CT3008-5V3A-A1, and under conditions of 0°C, cycle voltage of 2V-4V, and cutoff current of 20mA at a constant voltage, the battery withstood 200 cycles. Brightness and Saturation: L represents brightness, a and b represent chromaticity, and the color difference value △E = [(△L)] 2 +△a) 2 +(triangle b) 2 ] 1 / 2 The chromaticity value of the sample was measured using a spectrophotometer. The material was placed in close contact with the probe of the colorimeter, the long axis of the lens was positioned perpendicular to the measurement surface of the sample, the probe light source was flashed three times in a row, and then released. The numerical value was recorded.

[0060] The difference in distance between the highest and lowest points on a single surface: shown in the TEM image. Surface roughness: The instrument is a surface roughness measuring instrument. The stylus of the measuring instrument contacts the surface to be measured perpendicularly to the workpiece guided by a constant-speed driver, and moves laterally along the surface of the workpiece. The movement of the stylus can effectively display the surface contour, and minute changes during the movement of the stylus are converted into electrical signals via a sensor. After calculation processing, the surface roughness value is displayed on the screen.

[0061] [Table 4]

[0062] Example 1- 4 The positive electrode material was fabricated into a battery, and measurements showed that within the range of 2.0V-4.3V, its initial discharge gram capacity at 0.1C was 154mAh / g, and after 200 cycles, its cycle retention rate reached 95.62%.

[0063] As can be seen from Example 1 and Comparative Example 2, the first cathode material is coated with a single layer of porous carbon, which effectively suppresses the growth of the first cathode material particles. By adding a new carbon layer, the carbon of the second layer can fill the voids in the first layer. A double carbon layer consisting of an inner carbon layer and an outer carbon layer is advantageous in improving the conductivity of the material and enhancing its electrochemical performance.

[0064] This limits the particle size of carbon twice, and by compressing it, Carbon layer The carbon can be uniformly coated onto the surface of the cathode material. As shown in Figure 4, the coating is inevitably not uniform after the first carbon coating. Therefore, a second coating of smaller carbon particles is applied to fill the gaps on the surface of the cathode material, thereby obtaining a cathode material with a high carbon coating rate. Finally, the carbon coating on the surface of the cathode material is flattened by high-speed mixing and polishing, and an olivine-type cathode material with a uniform and flat carbon coating is prepared. This demonstrates that the high capacity and high compressibility of the cathode material are ensured through the two carbon coating processes, while significantly reducing manganese elution, thereby ensuring the cycle discharge efficiency of the cathode material.

[0065] Finally, it should be noted that the above embodiments are not limitations, but merely serve to illustrate the technical solutions of the present application. While the present application has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical means described in the above embodiments or substitute some of their technical features, and these modifications or substitutions should be understood not to cause the essence of the corresponding technical means to deviate from the spirit and scope of the technical means of the embodiments of the present application. [Cross-reference of related applications]

[0066] This application claims priority to the Chinese patent application filed with the China National Patent Office on October 16, 2023, with application number 202311329054.8 and title "Cathode material and method for preparing the same, lithium-ion battery," all of which are incorporated herein by reference.

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