Positive electrode material and preparation method thereof, lithium ion battery and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a positive electrode material and a preparation method thereof, a lithium ion battery and a power utilization device, the positive electrode material comprises a composition as shown in the formula 1, in the formula 1 of LiaFebMc (PO4) dQe, 0.95 < = a < = 1.10, 0.7 < = b < = 1, 0 < = c < = 0.5, 0.95 < = d < = 1.10, 0 < = e < = 0.05, M comprises at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B and Na, and Q comprises at least one of Si, S, F, Cl, Br and I. L10 is more than or equal to 80nm and less than or equal to 200nm; 150 nm < = L50 < = 500 nm; 400 nm < = L90 < = 1000 nm; 1lt; slt; 2. The positive electrode material meets the conditions, and the compaction density and the electrochemical specific capacity of the positive electrode material are relatively good.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and specifically relates to a cathode material, a preparation method thereof, a lithium-ion battery, and an electrical device. Background Art

[0002] In recent years, with the introduction of policies to support the development of new energy vehicles and energy storage industries in various countries around the world, the market share of lithium iron phosphate (LFP) has been continuously expanding due to its advantages such as high safety, long life, and low cost. However, with the continuous development of policies and the market, the existing lithium iron phosphate (with a generally compacted density of about 2.5 g / cm 3 ) can no longer meet the higher requirements for the cruising range of new energy vehicles and the energy efficiency of energy storage systems. Therefore, the development of high-compaction lithium iron phosphate has become one of the current hot topics.

[0003] Currently, some researchers achieve this by using the method of sand grinding particle size grading. This method mainly grinds raw materials to different particle sizes and then mixes them in a certain proportion to achieve the grading effect. However, because the temperatures for the full reaction of large and small particles are different, when the large particles reach the appropriate temperature, the small particles are overburned, resulting in melting and growth between the small particles, leading to ineffective improvement of the grading effect and the compacted density. Moreover, the preparation process is long and complex, which is not conducive to large-scale production. At the same time, the increase in the compacted density may also have a negative impact on the electrochemical performance of the battery. Therefore, how to improve the compacted density of LFP while ensuring the existing electrochemical performance has received continuous attention from those skilled in the art. Summary of the Invention

[0004] This application aims to at least solve one of the technical problems in the related art to some extent. For this reason, this application proposes a cathode material with better electrochemical performance and a high compacted density.

[0005] In the first aspect of this application, a cathode material is provided. According to an embodiment of this application, the cathode material includes the composition shown in Formula 1, Li a Fe b M c (PO4) d Q e Formula 1 In Formula 1, 0.95 ≤ a ≤ 1.10, 0.7 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0.95 ≤ d ≤ 1.10, 0 ≤ e≤0.05, M includes at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, Na; Q includes at least one of Si, S, F, Cl, Br, I; The positive electrode material satisfies: 80nm ≤ L 10 ≤ 200nm; 150nm ≤ L 50 ≤ 500nm; 400nm ≤ L 90 ≤ 1000nm; 1 < S < 2; Wherein, L 10 , L 50 , L 90 are the sub - grain sizes corresponding to the cumulative volume percentages of the sub - grain sizes Ln of the positive electrode material reaching 10%, 50% and 90% respectively, and S is the skewness coefficient of the sub - grain size sample of the positive electrode material obtained by the third - order moment method.

[0006] The positive electrode material of the present application satisfies the above conditions, and both its tap density and electrochemical specific capacity are better, thereby effectively improving the energy density and electrochemical performance of the lithium - ion battery using this positive electrode material.

[0007] According to the embodiments of the present application, the positive electrode material satisfies at least one of the following conditions: 100nm ≤ L 10 ≤ 180nm; 200nm ≤ L 50 ≤ 400nm; 500nm ≤ L 90 ≤ 900nm; 1.2 < S < 1.9.

[0008] According to the embodiments of the present application, 1.3 ≤ (L 90 - L 10 ) / L 50 ≤ 2.2; preferably 1.5 ≤ (L 90 - L 10 ) / L 50 ≤ 2.0.

[0009] According to the embodiments of the present application, the kurtosis coefficient K of the sub - grain size of the positive electrode material obtained by the fourth - order moment method satisfies: 4 < K < 8; preferably 4.5 < K < 7.5.

[0010] According to the embodiments of the present application, the sub - grain size distribution curve of the positive electrode material includes only one peak.

[0011] According to an embodiment of the present application, the unit cell volume of the positive electrode material is 287.0 Å 3 ~293.0 Å 3 , preferably 288.000 Å 3 ~292.000 Å 3 .

[0012] According to an embodiment of the present application, based on the total weight of the positive electrode material, the carbon content in the positive electrode material is 0.7 wt% to 2 wt%, preferably 1 wt% to 1.5 wt%.

[0013] According to an embodiment of the present application, the tap density of the positive electrode material is 2.6 g / cm 3 ~2.9 g / cm 3 .

[0014] In a second aspect of the present application, a method for preparing the positive electrode material described above is provided. According to an embodiment of the present application, the method includes spray-drying a first mixture to obtain a spray-dried material; subjecting the spray-dried material to a first sintering to obtain a lithium iron phosphate precursor; and subjecting a second mixture containing the lithium iron phosphate precursor to a second sintering to obtain the positive electrode material, wherein the first mixture includes iron phosphate, a lithium source, and a carbon source; the first mixture includes the iron phosphate, the lithium source, the carbon source, and an M 1 source; the first mixture includes the iron phosphate, the lithium source, the carbon source, and the M 1 source and a Q 1 source; or the first mixture includes the iron phosphate, the lithium source, the carbon source, and the Q 1 source. The second mixture includes the lithium iron phosphate precursor and an M 2 source; the second mixture includes the lithium iron phosphate precursor, the M 2 source and a Q 2 source; or the lithium iron phosphate precursor and the Q 2 source. The M in the M 1 source and the M in the M 1 element and the M in the M 2 source each independently include at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, Na; the Q in the Q 2 element and the Q in the Q 1 source and the Q in the Q 1 element and the Q in the Q 2 source each independently include at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, Na; the Q in the Q 2Each element independently includes at least one of Si, S, F, Cl, Br, and I. The preparation process of the cathode material provided by this application is simple, with relatively low cost, suitable for industrialization. The preparation process only requires one grinding and one crushing, and high-compact products can be obtained through dry coating, which is suitable for large-scale production.

[0015] According to an embodiment of this application, the iron phosphate satisfies at least one of the following conditions: The molar ratio of iron to phosphorus Fe / P of the iron phosphate is 0.95 to 0.98; The particle size D of the iron phosphate 50 is 4 μm to 20 μm; The specific surface area BET of the iron phosphate is 6 m 2 / g to 12 m 2 / g.

[0016] According to an embodiment of this application, the method satisfies at least one of the following conditions: The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium nitrate; The M 1 source includes at least one of oxides, hydroxides, carbonates, halides, silicates, and sulfates of the M 1 element; The M 2 source includes at least one of oxides, hydroxides, carbonates, halides, silicates, and sulfates of the M 2 element; The Q 1 source includes at least one of sulfates, silicates, and halides of Li and / or M 1 ; The Q 2 source includes at least one of sulfates, silicates, and halides of Li and / or M 2 ; The carbon source includes at least one of glucose, sucrose, and organic polymers.

[0017] According to an embodiment of this application, the spray drying of the first mixture includes: Mixing the first mixture with a solvent to obtain a dispersion; Grinding the dispersion to obtain a grinding slurry; Performing the spray drying on the grinding slurry to obtain the spray-dried material.

[0018] According to an embodiment of this application, the method satisfies at least one of the following conditions: The solvent includes deionized water; The solid content of the dispersion is ≥ 35%; The particle size of the polishing slurry satisfies: D 50 is 0.1 μm to 0.6 μm, preferably 0.25 μm to 0.5 μm.

[0019] According to an embodiment of the present application, the method satisfies at least one of the following conditions: The sintering temperature of the primary sintering is 700 °C to 850 °C; The sintering time of the primary sintering is 6 h to 16 h; The sintering temperature of the secondary sintering is 650 °C to 800 °C; The sintering time of the secondary sintering is 4 h to 20 h.

[0020] A third aspect of the present application provides a lithium-ion battery, including the positive electrode material described in the first aspect of the present application or the positive electrode material prepared by the method of the second aspect. Thus, the lithium-ion battery has a relatively high energy density, excellent electrochemical performance, and excellent cycle stability.

[0021] A fourth aspect of the present application provides an electrical device, including the lithium-ion battery described in the third aspect of the present application. The electrical device has all the features and advantages of the aforementioned lithium-ion battery, which will not be elaborated herein one by one. Description of the Drawings

[0022] Figure 1 is a scanning electron microscope photograph of the primary crushed material III in Example 1 of the present application.

[0023] Figure 2 is a scanning electron microscope photograph of the finished product of the lithium iron phosphate positive electrode material in Example 1 of the present application.

[0024] Figure 3 is the sub-grain size distribution curve of the positive electrode materials in Example 1 and Comparative Example 1 of the present application. Detailed Embodiments

[0025] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation to the present application.

[0026] The present application is based on the inventor's discovery and recognition of the following facts and problems: With the higher requirements of electric vehicles for endurance and energy storage systems for energy efficiency, how to improve the tap density of the cathode material has become one of the important research directions at present. However, the current particle size grading method, on the one hand, cannot maximize the tap density, and on the other hand, the preparation process is long and complex, which is not conducive to large-scale production, and may also have a negative impact on its electrochemical performance. The inventors of this application have found through research that the microscopic morphology of the lithium iron phosphate cathode material is closely related to its capacity and tap density. By adjusting a certain process, an LFP material with a specific microscopic morphology is prepared, which exhibits a high tap density, and the battery prepared therefrom has a high energy density.

[0027] In view of this, this application overcomes the problems in the related art that it is difficult to have both high tap density and good electrochemical performance of lithium iron phosphate, and the preparation process of high-tap-density samples is complex, and provides a lithium iron phosphate cathode material with high tap density and high electrochemical performance, a preparation method thereof, a lithium ion battery and an electrical device.

[0028] In the first aspect of this application, a cathode material is provided. According to the embodiments of this application, the cathode material comprises the composition shown in Formula 1, Li a Fe b M c (PO4) d Q e Formula 1 In Formula 1, 0.95 ≤ a ≤ 1.10, 0.7 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0.95 ≤ d ≤ 1.10, 0 ≤ e ≤ 0.05, M comprises at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, Na, and Q comprises at least one of F, Cl, Br, I, Si, S; The cathode material satisfies: 80nm ≤ L 10 ≤ 200nm; 150nm ≤ L 50 ≤ 500nm; 400nm ≤ L 90 ≤ 1000nm; 1 < S < 2; Wherein, L 10 、L 50 、L 90are the sub-grain sizes corresponding to when the volume cumulative percentages of the sub-grains of the positive electrode material reach 10%, 50%, and 90% respectively, and S is the skewness coefficient of the sub-grain size sample of the positive electrode material obtained by using the third-order moment method.

[0029] The positive electrode material of this application meets the above conditions, and its tap density and electrochemical specific capacity are both better, thereby effectively improving the energy density and electrochemical performance of the lithium-ion battery using this positive electrode material.

[0030] It should be noted that the sub-grain size Ln of the positive electrode material is obtained by powder X-ray diffraction measurement using CuKα rays, and the powder X-ray diffraction pattern is statistically sized by the Fundamental Parameter method fitting algorithm. Among them, L 50 As a physical quantity representing the median of the quantity distribution, it can represent the size of the sub-grain. The smaller the sub-grain size, the shorter the migration path of lithium ions in the positive electrode material and the relatively higher the diffusion rate, that is, the better the kinetic performance of the positive electrode material. However, too small a sub-grain size will result in a lower tap density of the positive electrode material. This application controls the L 10 、L 50 、L 90 within the above range, so that the positive electrode material can achieve a relatively high tap density and also has better kinetic performance.

[0031] In some embodiments, L 10 can specifically be 100 nm to 180 nm, for example, it can be 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, etc.; L 50 can specifically be 200 nm to 400 nm, for example, it can be 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc.; L 50 can specifically be 500 nm to 900 nm, for example, it can be 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, and so on.

[0032] The moment method is a method based on the concept of moments (moments of inertia) in statistics and probability theory for analyzing and processing data. The moment method has a wide range of applications in statistics, mainly used to describe the characteristics of data distributions. The skewness coefficient (or skewness factor) S of the sub-grain size of the cathode material obtained by calculating using the moment method can be used as a characteristic number to measure the deviation of the sub-grain size distribution from the normal distribution, and is used to measure the uniformity of the sub-grain size of the cathode material. The skewness coefficient S measures the symmetry of the data distribution through the third central moment. The skewness coefficient formula is: Skewness coefficient S = E[(X - μ) 3 / σ 3 ; where E[(X - μ) 3 is the third central moment, X is the sub-grain size of each particle, μ is the average value, and σ is the standard deviation. A skewness coefficient S of 0 indicates a symmetric distribution; a skewness coefficient S greater than 0 indicates a positive skewness; a skewness coefficient S less than 0 indicates a negative skewness. By controlling the skewness coefficient S of the cathode material within the above range in this application, a cathode material with a moderate sub-grain size can be obtained, enabling it to have a high tap density and electrochemical performance.

[0033] In some embodiments, the skewness coefficient S can specifically be 1.2 to 1.9. For example, it can be 1.01, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.99, and so on. Within the above range, a cathode material with a moderate sub-grain size can be obtained, further improving the tap density and electrochemical performance of the cathode material.

[0034] According to the embodiments of this application, the sub-grain size distribution K 90 of the cathode material satisfies: 1.3 ≤ K 90 =(L 90 -L 10 ) / L 50 ≤ 2.2. In some specific embodiments, 1.5 ≤ K 90 =(L 90 -L 10 ) / L 50 ≤ 2.0. As an example, (L 90 -L 10 ) / L 50 can specifically be 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, and so on. Thus, the tap density and electrochemical performance of the cathode material can be further improved.

[0035] K 90 can reflect the degree of uniformity of the sub-grain size distribution. When K 90 is too large or too small, the uniformity of the sub-grain size distribution of the cathode material deteriorates, and the tap density of the cathode material will decrease. K 90If the requirements are not met, the tap density and electrochemical performance of the positive electrode material will decrease.

[0036] According to an embodiment of the present application, the kurtosis coefficient K of the sub-grain size of the positive electrode material obtained by using the fourth-order moment method satisfies: 4 < K < 8; in some specific embodiments, 4.5 < K < 7.5. As an example, K can specifically be 4.1, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 7.9, and so on.

[0037] Calculating the kurtosis coefficient of the sub-grain size of the positive electrode material by using the moment method as a characteristic number for measuring the deviation of the sub-grain size distribution from the normal distribution can be used to measure the sharpness of the sub-grain size distribution of the positive electrode material. The formula for the kurtosis coefficient (or kurtosis coefficient) K is: Kurtosis coefficient = E[(X - μ) 4 / σ 4 , where E[(X - μ) 4 is the fourth-order central moment, X is the sub-grain size of each particle, μ is the average value, and σ is the standard deviation. A kurtosis coefficient of 3 indicates a normal peak in the distribution; greater than 3 indicates a sharp peak; less than 3 indicates a flat peak. By controlling the kurtosis coefficient of the positive electrode material within the above range in the present application, the tap density and electrochemical performance of the positive electrode material can be further improved.

[0038] According to an embodiment of the present application, the sub-grain size distribution curve of the positive electrode material includes only one peak. Thus, the preparation of the positive electrode material is simpler, without the complex operation of grading multiple positive electrode materials with different particle sizes, and the obtained positive electrode material has a higher tap density.

[0039] According to an embodiment of the present application, the unit cell volume of the positive electrode material is 287.0 Å 3 ~293.0 Å 3 , specifically it can be 288.000 Å 3 ~292.000 Å 3 , for example, it can be 287.0 Å 3 , 288.0 Å 3 , 289.0 Å 3 , 290.0 Å 3 , 291.0 Å 3 , 292.0 Å 3 , 293.0 Å 3 and so on. Within the above unit cell volume range, the positive electrode material can be packed more closely, and thus a higher tap density can be obtained.

[0040] According to an embodiment of the present application, based on the total weight of the positive electrode material, the carbon content in the positive electrode material is 0.7 wt% to 2 wt%, specifically it can be 1 wt% to 1.5 wt%, for example it can be 0.7 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, etc. When the carbon content is within the above range, it is beneficial to obtain a positive electrode material with a suitable morphology, which is conducive to improving the tap density of the positive electrode material. At the same time, it can effectively improve the electrical conductivity of the positive electrode material, thereby improving the electrochemical performance of the positive electrode material. It should be noted that the carbon in the positive electrode material is mainly coated on the surface and exists in the positive electrode material in the form of a carbon coating layer.

[0041] According to an embodiment of the present application, the tap density of the positive electrode material is 2.6 g / cm 3 ~2.9 g / cm 3 , specifically it can be 2.6 g / cm 3 , 2.62 g / cm 3 , 2.64 g / cm 3 , 2.66 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.74 g / cm 3 , 2.76 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 , 2.82 g / cm 3 , 2.84 g / cm 3 , 2.86 g / cm 3 , 2.88 g / cm 3 , 2.90 g / cm 3 etc. Within the above tap density range, the service performance of the lithium-ion battery using this positive electrode material can be effectively improved.

[0042] In the second aspect of the present application, a method for preparing the above-mentioned positive electrode material is provided. According to an embodiment of the present application, the method includes the following steps: S10: Spray-dry the first mixture to obtain a spray-dried material.

[0043] In this step, the first mixture can be obtained by mixing iron phosphate, a lithium source, an optional M 1 source, an optional Q 1 source and a carbon source. Mix iron phosphate, a lithium source, an optional M 1 source, an optional Q 1There is no particular limitation on the specific manner of mixing the source and the carbon source, nor is there any special requirement for the feeding order, which can be flexibly selected according to actual needs. As an example, a mixer or the like can be used to mix iron phosphate, a lithium source, an optional M 1 source, and an optional Q 1 source with the carbon source.

[0044] It should be noted that the optional M 1 source means that the raw material used in this step can have an M 1 source, or it can have no M 1 source; similarly, the optional Q 1 source means that the raw material used in this step can have a Q 1 source, or it can have no Q 1 source. As an example, in this step, iron phosphate, a lithium source, and a carbon source can be mixed, iron phosphate, a lithium source, an M 1 source, and a carbon source can be mixed, iron phosphate, a lithium source, an M 1 source, a Q 1 source, and a carbon source can be mixed, or iron phosphate, a lithium source, a Q 1 source, and a carbon source can be mixed.

[0045] In some embodiments, iron phosphate, a lithium source, an optional M 1 source, an optional Q 1 source, and a carbon source can be weighed and proportioned according to the stoichiometric ratio of Li, Fe, M, P, and Q in General Formula 1. The addition amount of the carbon source satisfies that the mass percentage of carbon content in the target prepared cathode material is 0.7 wt% to 2.0 wt%.

[0046] It should be noted that the M 1 source is one of the sources of the M element in Formula 1. The M 1 element in the M 1 source and the M 2 element in the M 2 source in the subsequent step together constitute the M element in Formula 1. Similarly, the Q 1 source is one of the sources of the Q element in Formula 1. The Q 1 element in the Q 1 source and the Q 2 element in the Q 2 source in the subsequent step together constitute the Q element in Formula 1. In addition, the M 1 element in the M 1 source and the Q 1 element in the Q 1 source can be provided by the same substance, that is, the M 1 source and the Q 1 source can be the same substance. For example, sodium sulfate can provide both the Na element (M 1 element) and the S element (Q1 element); Similarly, M 2 source and Q 2 source can also be the same substance.

[0047] In some embodiments, spray-drying the first mixture includes: mixing the first mixture with a solvent to obtain a dispersion; grinding the dispersion to obtain a ground slurry; and subjecting the ground slurry to the spray-drying to obtain the spray-dried material.

[0048] In some embodiments, the type of the solvent and the solid content of the dispersion are not particularly limited, as long as they can be sufficiently dispersed and do not chemically react with iron phosphate, lithium source, optional M 1 source, optional Q 1 source and carbon source. For production cost considerations, the solvent in the present application can be deionized water, and the solid content of the dispersion is ≥ 35% (specifically, such as 35%, 40%, 45%, 50%, 55%, 60%, etc.).

[0049] According to an embodiment of the present application, the particle size of the ground slurry satisfies: D 50 is 0.1 μm to 0.6 μm, specifically, it can be 0.25 μm to 0.5 μm. For example, the D of the ground slurry 50 specifically can be 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, etc. Satisfying the above particle size range is beneficial to obtaining a cathode material with an appropriate sub-grain size and particle size range, and thus is beneficial to improving the tap density of the cathode material.

[0050] According to an embodiment of the present application, the iron-to-phosphorus molar ratio Fe / P of the iron phosphate is 0.95 to 0.98, specifically, such as 0.95, 0.955, 0.96, 0.965, 0.97, 0.975, 0.98, etc. Satisfying the above Fe / P range is beneficial to obtaining a cathode material with an appropriate microscopic morphology, and thus is beneficial to improving the tap density of the cathode material.

[0051] According to an embodiment of the present application, the particle size D of the iron phosphate 50 is 4 μm to 20 μm, specifically, such as 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, etc. Satisfying the above particle size D 50 range is beneficial to obtaining a cathode material with an appropriate microscopic morphology, and thus is beneficial to improving the tap density of the cathode material.

[0052] According to an embodiment of the present application, the specific surface area BET of the iron phosphate is 6 m 2 / g to 12 m 2 / g, specifically such as 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g and so on. Meeting the above BET range is conducive to obtaining a cathode material with a suitable microstructure, and thus conducive to improving the tap density of the cathode material.

[0053] According to an embodiment of the present application, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium nitrate. Thus, it can fully participate in the reaction with iron phosphate to obtain a cathode material with higher quality.

[0054] According to an embodiment of the present application, the M 1 source includes at least one of oxides, hydroxides, carbonates, halides, silicates, and sulfates of the M 1 element. The M 1 element includes at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, and Na. In some embodiments, the M 1 element can be doped into the lattice of the cathode material, which is conducive to improving the electrochemical performance of the cathode material.

[0055] According to an embodiment of the present application, the Q 1 element in the Q 1 source includes at least one of Si, S, F, Cl, Br, and I. The Q 1 source can include at least one of sulfates, silicates, and halides of Li and / or M 1 . In some embodiments, the Q 1 element can be doped into the lattice of the cathode material, which is conducive to improving the electrochemical performance of the cathode material.

[0056] It can be understood that the Q 1 source can include at least one of sulfates, silicates, and halides of Li and / or M 1 means that the Q 1 source can include at least one of lithium sulfate, lithium silicate, lithium halide, sulfate of M 1 , silicate of M 1 , and halide of M 1 .

[0057] According to an embodiment of the present application, the carbon source includes at least one of glucose, sucrose, and organic polymers. Thus, a better carbon coating layer can be formed on the surface of the cathode material, thereby improving the conductivity of the cathode material and facilitating the improvement of the tap density of the cathode material.

[0058] According to an embodiment of the present application, the specific operation mode and parameters of spray drying are not particularly limited and can be referred to conventional techniques. It can be understood that the particle size, morphology, etc. of the spray-dried material can be adjusted by appropriately adjusting the spray-drying parameters.

[0059] S20: Subject the spray-dried material to a first sintering to obtain a lithium iron phosphate precursor.

[0060] In this step, lithium iron phosphate can be formed by reacting iron phosphate with a lithium source through the first sintering. M 1 in the source M 1 element, Q 1 in the source Q 1 element can be doped into the crystal structure of lithium iron phosphate, and the carbon source can form a carbon coating layer on the surface of lithium iron phosphate.

[0061] According to an embodiment of the present application, the sintering temperature of the first sintering is 700 °C to 850 °C, specifically such as 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C, 760 °C, 770 °C, 780 °C, 790 °C, 800 °C, 810 °C, 820 °C, 830 °C, 840 °C, 850 °C, etc. Within the above temperature range, it is beneficial to obtain a cathode material with a suitable microstructure, thereby improving the tap density and electrochemical performance of the cathode material.

[0062] According to an embodiment of the present application, the sintering time of the first sintering is 6 h to 16 h, specifically such as 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc. The above time range can ensure that the reaction is fully completed and will not cause waste of time.

[0063] According to an embodiment of the present application, after the first sintering is completed, the product of the first sintering can be subjected to a crushing treatment. Thereby, the agglomerated particles in the product of the first sintering can be dissociated to obtain a cathode material with a suitable particle size.

[0064] According to an embodiment of the present application, the crushing equipment that can be used is not particularly limited as long as it can break the agglomerated lithium iron phosphate. Considering the production and manufacturing costs, the crushing equipment can be at least one of a mechanical mill and a jet mill.

[0065] S30: Subject the second mixture containing the lithium iron phosphate precursor to a second sintering to obtain the cathode material.

[0066] In this step, the second mixture can be obtained by mixing the lithium iron phosphate precursor, optional M 2 source and optional Q 2 source. Mixing the lithium iron phosphate precursor, optional M 2 source and optional Q 2 source can be carried out by dry coating. In some embodiments, the equipment for dry coating is not particularly limited as long as it can uniformly mix the lithium iron phosphate, optional M 2 source and optional Q 2 source. Considering the production and manufacturing costs, the dry coating equipment can be at least one of a high-speed mixer and a plowshare mixer.

[0067] It should be noted that the optional M 2 source in this text means that the raw material used in this step can have M 2 source or can have no M 2 source; similarly, the optional Q 2 source means that the raw material used in this step can have Q 2 source or can have no Q 2 source. As an example, in this step, the lithium iron phosphate precursor can be directly used, the lithium iron phosphate precursor can be mixed with M 2 source, the lithium iron phosphate precursor, M 2 source and Q 2 source can be mixed, or the lithium iron phosphate precursor can be mixed with Q 2 source.

[0068] According to an embodiment of the present application, the M 2 source includes at least one of oxides, hydroxides, carbonates, halides, silicates, and sulfates of M 2 element. The M 2 element includes at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, and Na. Specifically, the M 2 source can form a coating layer on the surface of the lithium iron phosphate precursor, adjust the microstructure of the cathode material, and thus facilitate improving the tap density of the cathode material.

[0069] According to an embodiment of the present application, the Q 2 element in the Q 2 source includes at least one of Si, S, F, Cl, Br, and I. The Q 2 source can include at least one of sulfates, silicates, and halides of Li and M 2 . In some embodiments, the Q 2 element can be doped into the lattice of the cathode material, and thus facilitate improving the electrochemical performance of the cathode material.

[0070] It is understandable that Q 2 The source may include at least one of sulfates, silicates, and halides of Li and / or M 2 At least one of the sulfates, silicates, and halides of M refers to Q 2 The source may include sulfates of Li, silicates of Li, halides of Li, M 2 sulfates of M 2 silicates of M 2 at least one of halides of M

[0071] According to an embodiment of the present application, the sintering temperature of the secondary sintering is 650°C to 800°C, specifically such as 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C, etc. Within the above temperature range, it is beneficial for the cathode material to obtain a suitable microstructure, thereby improving the energy density and electrochemical performance of the cathode material.

[0072] According to an embodiment of the present application, the sintering time of the secondary sintering is 4h to 20h, specifically such as 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, etc. Within the above time range, the reaction can proceed fully and time will not be wasted.

[0073] The preparation method process flow of the cathode material of the present application is simple, suitable for application in large-scale industrial production, and the obtained cathode material has a high tap density, good electrochemical performance, and excellent cycle stability.

[0074] The third aspect of the present application proposes a lithium-ion battery, including the cathode material described in the first aspect of the present application or the cathode material prepared by the method of the second aspect. Thus, the lithium-ion battery has a high energy density, excellent electrochemical performance, and excellent cycle stability.

[0075] It is understandable that there is no particular limitation on the specific type of the lithium-ion battery, which can be a primary battery or a secondary battery; the shape of the lithium-ion battery can be a cylindrical battery, a square battery, or any other arbitrary-shaped battery, etc., and classified by outer packaging, the lithium-ion battery can be a hard-shell battery, a soft-pack battery, etc.

[0076] Generally, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Among them, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding or stacking process, and the electrode assembly and the electrolyte can be accommodated in an outer packaging. During the charge and discharge process of the lithium-ion battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0077] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode current collector may include a metal foil. For example, the metal foil may be an aluminum foil. The positive electrode active material may include the positive electrode material of the first aspect of the present application or the positive electrode material prepared by the method described in the second aspect of the present application. The conductive agent may include acetylene black, single-walled carbon nanotubes, and conventional materials in the art. The binder may be polyvinylidene fluoride (PVDF) and conventional materials in the art.

[0078] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material, a thickening agent, a conductive agent, and a binder. Among them, the negative electrode current collector may be a metal foil. For example, the metal foil may be a copper foil. The negative electrode active material may include artificial graphite, natural graphite, silicon-containing carbon-based composite materials, lithium-containing metal composite materials, lithium metal materials, and common negative electrode active materials in the art. The thickening agent may be sodium carboxymethyl cellulose (CMC-Na) and conventional materials in the art. The conductive agent may be acetylene black and conventional materials in the art. The binder may be styrene-butadiene rubber and conventional materials in the art.

[0079] In some embodiments, the separator may be a separator well-known in the art that can be used in a lithium-ion battery and is stable to the electrolyte used, such as a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene composite separator, etc.

[0080] A fourth aspect of the present application proposes an electrical device including the lithium-ion battery described in the third aspect of the present application. This electrical device has all the features and advantages of the aforementioned lithium-ion battery, which will not be elaborated herein one by one.

[0081] In some embodiments, the electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but not limited thereto.

[0082] The embodiments of the present application will be described in detail below.

[0083] Example 1 Step S1: Weigh and mix lithium carbonate, iron phosphate, titanium oxide 1, titanium oxide 4, vanadium oxide, and phosphoric acid according to the molar ratio of Li, Fe, Ti1, Ti4, V, and P being 1.050:0.97:0.01:0.01:0.01:1.030. Titanium oxide 1 is used in Step S1, and titanium oxide 4 is used in Step S4. The carbon source glucose accounts for 8.0% of the theoretical yield of lithium iron phosphate. Add it to deionized water as the solvent, control the solid content at 40 wt%, and grind it with a ball mill (rotation speed of 2000 rpm). Stop when it reaches 0.4 μm to obtain the first ground material I; 50 Stop when it reaches 0.4 μm to obtain the first ground material I; Step S2: Spray-dry the first ground material I obtained in Step S1 using a disk atomization dryer (inlet temperature set at 225 ± °C, outlet temperature controlled at 100 ± 5 °C) to obtain the first spray-dried material. Heat this dried material to 800 °C at a heating rate of 2 °C / min in an N2 atmosphere, hold for 8 h, and then cool with the furnace to obtain the first sintered material II; Step S3: Crush the first sintered material II obtained in Step S2 using a jet mill. 50 Stop when it reaches 1.3 μm to obtain the first crushed material III. The scanning electron microscope photo is shown in Figure 1 ; Step S4: Mix the first crushed material III obtained in Step S3 with titanium oxide 4 to obtain a homogeneous mixture IV.

[0084] Step S5: Heat the homogeneous mixture IV obtained in Step S4 to 730 °C at a heating rate of 2 °C / min in an N2 atmosphere, hold for 8 h, and then cool with the furnace to obtain the lithium iron phosphate cathode material. The scanning electron microscope photo is shown in Figure 2 。

[0085] Example 2: According to the method of Example 1, the difference is that in Step S1, the molar ratio of Li, Fe, Ti1, Ti4, V, and P is 1.050:0.97:0.01:0.01:0.01:1.000, and the rest are the same, to obtain the lithium iron phosphate cathode material.

[0086] Example 3: According to the method of Example 1, the difference is that in Step S1, the molar ratio of Li, Fe, Ti1, Ti4, V, and P is 1.050:0.97:0.01:0.01:0.01:1.080, and the rest are the same, to obtain the lithium iron phosphate cathode material.

[0087] Examples 4 - 21 According to the method of Example 1, the specific differences are shown in Table 1.

[0088] Comparative Example 1: According to the method of Example 1, except that in step S1, the molar ratio of Li, Fe, Ti1, Ti4, V, and P is 1.050:0.97:0.01:0.01:0.01:0.920, and the rest are the same, the lithium iron phosphate cathode material is obtained.

[0089] Comparative Example 2: According to the method of Example 1, except that in step S2, the dried material is heated to 400 °C at a heating rate of 2 °C / min in an N2 atmosphere and held for 6 h, and the rest are the same, the lithium iron phosphate cathode material is obtained.

[0090] Table 1: Preparation parameters

[0091] Performance detection: 1. Unit cell volume: Tested by a Rigaku rotating anode diffractometer Smartlab 9KW, in the range of 10° to 80°, voltage 40 kV, current 200 mA, step 0.02°, scanning time 2° / min. The test results are refined and calculated by the WPPF method of SmartLab Studio II software to obtain the unit cell volume.

[0092] 2. Subgrain size and subgrain size distribution: Subgrain size L 10 、L 50 、L 90 : Tested by a Rigaku rotating anode diffractometer Smartlab 9KW, in the range of 10° to 80°, voltage 40 kV, current 200 mA, step 0.02°, scanning time 2° / min. The test results are statistically calculated for the subgrain size using the WPPF subgrain size distribution function of SmartLab Studio II software according to the Fundamental Parameter method (FP method). The subgrain size distribution curves of the cathode materials in Example 1 and Comparative Example 1 are shown in Figure 3 .

[0093] 3. Compaction density: Measured by a Sansi Zongheng (UTM7305) compaction density tester. Weigh 1 ± 0.01 g of the sample and select a pressure of 3 T for testing.

[0094] 4. Carbon content: Measured by a Beijing Wanlianda CS-901B high-frequency infrared carbon-sulfur analyzer. Weigh 0.2 ± 0.05 g of the sample for testing.

[0095] 5. D 50: 1) Malvern 3000-LV particle size analyzer; 2) Dispersant: water; 3) Light obscuration: 10% - 15%; 4) Refractive index: 1.74; 5) Test cycle: 2 times.

[0096] 6. Initial charge-discharge specific capacity at 0.1C: The electrochemical performance of the R2025 coin cell was tested using a Shenzhen Neware battery test system. The test conditions for the initial charge-discharge capacity were: 25°C, charge and discharge at 0.1C, voltage range 2.5V - 4.2V, and the constant voltage cut-off current for charging was 0.05C. The battery preparation process is as follows: Preparation of the electrode sheet: The positive electrode material, conductive agent SuperP, and polyvinylidene fluoride (PVDF) were fully mixed in a mass ratio of 96.5:1.5:2 with an appropriate amount of N-methylpyrrolidone (NMP) to form a homogeneous slurry. The slurry was coated on aluminum foil and dried at 120°C for 12 h, and then the electrode sheet was compacted to 2.5 g / cm 3 , and then stamped into a positive electrode sheet with a diameter of 12 mm.

[0097] Battery assembly: In a glove box filled with argon with a water content and oxygen content both less than 5 ppm, the positive electrode sheet, separator, negative electrode sheet, and electrolyte were assembled into an R2025 coin cell and then left standing for 6 h. Among them, the negative electrode sheet used a lithium metal sheet with a diameter of 15.6 mm and a thickness of 0.45 mm; the separator used a 25 μm polypropylene microporous membrane (Celgard 2325); the electrolyte used an equal-volume mixture of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0098] Table 2: Test results

[0099] From the above test results, it can be seen that when the sub-grain size of the positive electrode material is controlled to satisfy 80nm ≤ L 10 ≤ 200nm; 150nm ≤ L 50 ≤ 500nm; 400nm ≤ L 90 ≤ 1000nm; 1 < S < 2, the compaction density of the positive electrode material is relatively high, and at the same time, the charge-discharge specific capacity of the lithium-ion battery using this positive electrode material remains at a relatively high level.

[0100] In the description of the present application, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0101] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A cathode material, characterized in that, Comprising the composition shown in Formula 1, Li a Fe b M c (PO4) d Q e Formula 1 In Formula 1, 0.95 ≤ a ≤ 1.10, 0.7 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0.95 ≤ d ≤ 1.10, 0 ≤ e ≤ 0.05, M includes at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, Na; Q includes at least one of Si, S, F, Cl, Br, I; The positive electrode material satisfies: 80nm ≤ L 10 ≤ 200nm; 150nm ≤ L 50 ≤ 500nm; 400nm ≤ L 90 ≤ 1000nm; 1<S<2； wherein, L 10 , L 50 , L 90 are the sub-grain sizes corresponding to when the volume cumulative percentages of the sub-grain sizes Ln of the positive electrode material reach 10%, 50% and 90% respectively, and S is the skewness coefficient of the sub-grain size sample of the positive electrode material obtained by using the third-order moment method.

2. The cathode material according to claim 1, characterized in that, The positive electrode material satisfies at least one of the following conditions: 100nm ≤ L 10 ≤ 180nm; 200nm ≤ L 50 ≤ 400nm; 500nm ≤ L 90 ≤ 900nm; 1.2<S<1.9。 3. The cathode material according to claim 1, characterized in that, 1.3 ≤ (L 90 - L 10 ) / L 50 ≤ 2.2 4. The cathode material according to claim 3, characterized in that, 1.5 ≤ (L 90 - L 10 ) / L 50 ≤ 2.0 5. The cathode material according to claim 1, characterized in that, The kurtosis coefficient K of the sub-grain size of the positive electrode material obtained by the fourth-order moment method satisfies: 4 < K < 8.

6. The cathode material according to claim 5, characterized in that, 4.5<K<7.5。 7. The cathode material according to claim 1, characterized in that, The sub-grain size distribution curve of the positive electrode material includes only one peak.

8. The cathode material according to claim 1, characterized in that, The unit cell volume of the positive electrode material is 287.0 Å 3 ~293.0 Å 3 .

9. The cathode material according to claim 8, characterized in that, The unit cell volume of the positive electrode material is 288.000 Å 3 ~292.000 Å 3 .

10. The cathode material according to claim 1, characterized in that, Based on the total weight of the positive electrode material, the carbon content in the positive electrode material is 0.7 wt% to 2 wt%.

11. The cathode material according to claim 10, wherein Based on the total weight of the positive electrode material, the carbon content in the positive electrode material is 1 wt% to 1.5 wt%.

12. The cathode material according to claim 1, characterized in that, The tap density of the positive electrode material is 2.6 g / cm 3 ~2.9 g / cm 3 .

13. A method for preparing the cathode material according to any one of claims 1 to 12, characterized in that, Comprising: Spray-drying the first mixture to obtain a spray-dried material; Performing primary sintering on the spray-dried material to obtain a lithium iron phosphate precursor; Performing secondary sintering on the second mixture containing the lithium iron phosphate precursor to obtain the positive electrode material; Among them, the first mixture includes iron phosphate, a lithium source, and a carbon source; the first mixture includes the iron phosphate, the lithium source, the carbon source, and M 1 source; the first mixture includes the iron phosphate, the lithium source, the carbon source, and the M 1 source and Q 1 source; or the first mixture includes the iron phosphate, the lithium source, the carbon source, and the Q 1 source; The second mixture includes the lithium iron phosphate precursor and M 2 source; the second mixture includes the lithium iron phosphate precursor, the M 2 source and Q 2 source; or the second mixture includes the lithium iron phosphate precursor and the Q 2 source; The M 1 elements in the M 1 source and the M 2 elements in the M 2 source each independently include at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, Na; The Q 1 element in the Q 1 source and the Q 2 element in the Q 2 source each independently includes at least one of Si, S, F, Cl, Br, and I.

14. The method according to claim 13, wherein The iron phosphate satisfies at least one of the following conditions: The iron-to-phosphorus molar ratio Fe / P of the iron phosphate is 0.95 to 0.98; The particle size D of the iron phosphate 50 is 4 μm to 20 μm; The BET specific surface area of the iron phosphate is 6 m 2 / g to 12 m 2 / g.

15. The method according to claim 13, characterized in that, Satisfying at least one of the following conditions: The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium nitrate; The said M 1 source includes at least one of oxides, hydroxides, carbonates, halides, silicates, and sulfates of M 1 elements; The said M 2 source includes at least one of oxides, hydroxides, carbonates, halides, silicates and sulfates of M 2 element; Said Q 1 source includes at least one of sulfates, silicates, and halides of Li and / or M 1 ; Said Q 2 source includes at least one of sulfates, silicates, and halides of Li and / or M 2 ; The carbon source includes at least one of glucose, sucrose, and organic polymers.

16. The method according to claim 13, wherein The spray-drying of the first mixture includes: Mixing the first mixture with a solvent to obtain a dispersion; Grinding the dispersion to obtain a ground slurry; Performing the spray-drying on the ground slurry to obtain the spray-dried material.

17. The method according to claim 16, characterized in that, Satisfying at least one of the following conditions: The solvent includes deionized water; The solid content of the dispersion ≥ 35%; The particle size of the grinding slurry satisfies: D 50 is 0.1 μm to 0.6 μm.

18. The method according to claim 13, wherein Satisfying at least one of the following conditions: The sintering temperature of the primary sintering is 700°C to 850°C; The sintering time of the primary sintering is 6 h to 16 h; The sintering temperature of the secondary sintering is 650°C to 800°C; The sintering time of the secondary sintering is 4 h to 20 h.

19. A lithium-ion battery, characterized in that, Comprising the positive electrode material according to any one of claims 1 to 12.

20. An electrical device, characterized in that, Comprising the lithium ion battery according to claim 19.

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