A positive electrode material, a positive electrode sheet, a lithium ion battery, and an electric device

Abstract

This application provides a positive electrode material, a positive electrode sheet, a lithium-ion battery, and an electrical device, relating to the field of lithium-ion batteries. The raw materials for the positive electrode material include a first active material, a second active material, and a third active material: the mass ratio of the first active material, the second active material, and the third active material is 40-85:5-45:5-15; the first active material includes a layered positive electrode material; the second active material includes an olivine-type lithium iron phosphate positive electrode material; and the third active material includes a spinel-type positive electrode material. The positive electrode material satisfies the following relationship: = 2.6-3.0 g / cm³ 3 By adding the first and second active materials, the cathode material achieves a high compaction density. The third active material, as a spinel-structured cathode material, has a 3D fast lithium-ion transport channel. Its addition compensates for the insufficient rate performance of the second active material, providing the cathode with high rate performance and low-temperature charge-discharge performance.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a positive electrode material, a positive electrode sheet, a lithium-ion battery, and an electrical device. Background Technology

[0002] Since its commercialization in 1991, lithium-ion batteries have been widely used in many fields due to their excellent performance, becoming an important part of modern battery technology. With the rapid development of modern technology, the demand for lithium-ion batteries in the 3C field, electric vehicles, two-wheeled electric vehicles, energy storage, drones and other fields is increasing day by day, which has also put forward higher requirements for the energy density, lifespan and safety of lithium-ion batteries.

[0003] In lithium-ion batteries, the performance of the cathode material has a significant impact on the battery's capacity, lifespan, and safety. Currently, the mainstream cathode materials on the market include layered cathode materials (lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, and doped / modified materials based on them), olivine-type cathode materials (lithium iron phosphate, lithium manganese iron phosphate, and doped / modified materials based on them), and spinel-type cathode materials (lithium manganese oxide, lithium nickel manganese oxide, and doped / modified materials based on them). Layered cathode materials have a specific capacity between 170-270 mAh / g, which can meet high capacity requirements. However, while increasing the specific capacity, it also poses challenges to safety performance. For example, the exothermic peak temperature of high-nickel ternary materials in DSC tests is around 220 degrees Celsius, and the high peak value inevitably affects the overall safety performance of the battery. Olivine-type cathode materials, such as lithium iron phosphate, are widely used in the market due to their good safety and long cycle life. However, in commercial applications, the small particle size results in low compaction density, leading to low energy density and a narrow range of applications. Spinel-type cathode materials, such as lithium manganese oxide, are inexpensive, and their 3D ion channels give them excellent low-temperature performance. However, their poor cycle life and high-temperature performance limit their application range.

[0004] The use of a single cathode material can no longer meet the growing and diversified demands for lithium-ion batteries. How to balance the energy density, lifespan, and safety performance of lithium-ion batteries is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this application is to provide a positive electrode material, a positive electrode sheet, a lithium-ion battery, and an electrical device to solve the above-mentioned problems.

[0006] To achieve the above objectives, the first aspect of this application provides a cathode material, the raw materials of which include a first active material, a second active material and a third active material: the mass ratio of the first active material, the second active material and the third active material is 40-85: 5-45: 5-15; The first active material includes a layered cathode material; The second active material includes olivine-type lithium iron phosphate cathode material; The third active material includes a spinel-type cathode material; The cathode material satisfies the following relationship: =2.6-3.0 g / cm 3 Wherein, C is the theoretical capacity of the battery prepared from the positive electrode material; α is the mass fraction percentage of the first active material in the positive electrode material; β is the mass fraction percentage of the second active material in the positive electrode material; γ is the mass fraction percentage of the third active material in the positive electrode material; λ is the theoretical mass percentage of the positive electrode material in the positive electrode sheet prepared from the positive electrode material; S is the theoretical area of ​​the positive electrode material coated in the positive electrode sheet prepared from the positive electrode material; and d is the theoretical thickness of the positive electrode sheet prepared from the positive electrode material.

[0007] Optionally, the positive electrode material satisfies at least one of the following conditions: (1) The molecular formula of the first active substance is Li x Ni Y Co Z M 1-Y-Z O2, wherein X≥1, 0≤Y<0.98, 0≤Z<0.3, and M includes one or more of Mg, Al, Ti, Ca, Sr, Cr, Ba, and Mn; (2) The D50 of the first active substance is greater than 2 μm.

[0008] Optionally, the positive electrode material satisfies at least one of the following conditions: (1) The molecular formula of the second active substance is LiMn a Fe b P 1-a-b QO4, wherein 0≤a<1, 0<b<1, and P includes one or more of Co, Ni, Al, Mg, Zn, Ti, Ca, Sr, Cr, and Ba; (2) The D50 of the second active substance is <2μm.

[0009] Optionally, the positive electrode material satisfies at least one of the following conditions: (1) The molecular formula of the third active substance is Li1+h K i Mn j O k K includes one or more of Ni, Co, V, Fe, Ti, Mg, Al, Zn, Ti, Ca, Sr, Cr, Ba and P, and h, i, j, k satisfy the relation: (i×u)+(j×t)=2k-(1+h), where 1≤u, t≤4; (2) The D50 of the third active substance is 2-7 μm.

[0010] Optionally, the positive electrode material satisfies at least one of the following conditions: (1) The C is 2000-60000mAh; (2) The λ is 95-97.5%; (3) The value of S is 350-6500cm 2 ; (4) The value of d is 0.014-0.019 cm.

[0011] A second aspect of this application provides a positive electrode sheet, including a current collector and a positive electrode material layer disposed on the surface of the current collector; The positive electrode material layer includes the positive electrode material, conductive agent, dispersant, and binder.

[0012] In the preparation of the positive electrode sheet, the positive electrode active material is obtained through the following steps: the first active material and the second active material are mixed and loaded into a planetary ball mill with a ball-to-material ratio of 5:1. The mixture is dry-milled at 300 rpm for 1 hour to obtain the mixed positive electrode material. Then, the third active material is added and mixed evenly to obtain the positive electrode active material.

[0013] Optionally, the method for preparing the positive electrode material includes: The first active material and the second active material are mixed to obtain a mixed positive electrode material. The mixed positive electrode material and the third active material are mixed to obtain a positive electrode material.

[0014] The positive electrode sheet satisfies at least one of the following conditions: (1) The conductive agent includes one or more of carbon black, graphene, carbon nanotubes, Ketjen black and carbon fiber; (2) The adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, styrene-butadiene rubber, polyacrylonitrile, polyimide, polyacrylic acid, polyacrylate, polyolefin, sodium carboxymethyl cellulose and sodium alginate; (3) The dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyester substances; (4) The mass ratio of the positive electrode material, the conductive agent, the dispersant, and the binder is 90. 98:1 5:0.1-0.5:1 5.

[0015] A third aspect of this application provides a lithium-ion battery, including the aforementioned positive electrode.

[0016] A fourth aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0017] Compared with the prior art, the beneficial effects of this application include: The cathode material provided in this application comprises a first active material, which serves as the main component of the cathode active material and provides high energy density and / or long cycle life for lithium-ion batteries. The second active material is a lithium iron phosphate material with a stable olivine structure, exhibiting long cycle life and high thermal stability. By controlling the D50 particle size of the second active material, the first and second active materials are adsorbed together through Coulomb forces. The second active material coats the first active material, effectively suppressing the flammability and runaway problem of the first active material and improving the thermal stability of the blended material. Furthermore, by controlling the particle size of the first and second active materials, the cathode material containing both active materials has a high compaction density, offering the advantages of both high energy density and high safety compared to batteries with a single cathode material. The third active material, a spinel-structured cathode material, possesses a 3D fast lithium-ion transport channel. Its addition compensates for the insufficient rate performance of the second active material, providing the cathode with high rate performance and low-temperature charge-discharge performance.

[0018] The positive electrode provided in this application has many advantages such as high energy density, long cycle life, and high safety, which can meet the needs of lithium-ion batteries in various fields.

[0019] The lithium-ion battery and electrical device provided in this application have excellent electrochemical performance and high energy density. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0021] Figure 1 SEM image of the cathode material provided in Example 7; Figure 2 SEM image of the positive electrode sheet provided in Example 7; Figure 3Comparison chart of cycle performance of batteries provided for Example 7, Comparative Example 4 and Comparative Example 5. Detailed Implementation

[0022] First, the solution provided in this application will be explained in more detail as follows: The first aspect of this application provides a cathode material, the raw materials of which include a first active material, a second active material and a third active material: the mass ratio of the first active material, the second active material and the third active material is 40-85: 5-45: 5-15; Optionally, the mass ratio of the first active substance, the second active substance, and the third active substance can be any value between (40:5:5), (50:5:5), (60:5:5), (70:5:5), (80:5:5), (85:5:5), (40:25:5), (40:45:5), (40:5:10), (40:5:15), or 40-85:5-45:5-15. The first active material includes a layered cathode material; The second active material includes olivine-type lithium iron phosphate cathode material; The third active material includes a spinel-type cathode material; The cathode material satisfies the following relationship: =2.6-3.0 g / cm 3 Wherein, C is the theoretical capacity of the battery prepared from the positive electrode material; α is the mass fraction percentage of the first active material in the positive electrode material; β is the mass fraction percentage of the second active material in the positive electrode material; γ is the mass fraction percentage of the third active material in the positive electrode material; λ is the theoretical mass percentage of the positive electrode material in the positive electrode sheet prepared from the positive electrode material; S is the theoretical area of ​​the positive electrode material coated in the positive electrode sheet prepared from the positive electrode material; and d is the theoretical thickness of the positive electrode sheet prepared from the positive electrode material.

[0023] It is important to note that existing cathode materials often employ only a single material or rely solely on experience for simple mixing, failing to achieve the combined advantages of high capacity, long lifespan, and high safety in lithium-ion batteries. The cathode material described in this application comprises three active materials. By rationally selecting the first, second, and third active materials and controlling the proportion of each active material in the cathode material, and combining this with the theoretical area S of the cathode material coated on the cathode sheet, the theoretical capacity C of the battery prepared from the cathode material, the specific capacity of the active materials, the theoretical thickness d of the cathode sheet prepared from the cathode material, and the theoretical mass percentage λ of the cathode material in the cathode sheet, the above formula is constructed. The parameters in the formula are some basic parameters required for battery preparation, and the parameters are interconnected to satisfy a value range of 2.6-3.0 g / cm³. 3 When the value is less than 2.6 g / cm³, the resulting positive electrode exhibits excellent performance. 3 At that time, the resulting lithium battery had a low energy density and a narrow range of applications. If the value range is greater than 3.0 g / cm³... 3 At this stage, the resulting lithium-ion batteries have relatively low safety, are prone to heat generation and oxygen release, and have a high probability of thermal runaway under mechanical abuse. In some embodiments, the positive electrode material satisfies at least one of the following conditions: (1) The molecular formula of the first active substance is Li x Ni Y Co Z M 1-Y-Z O2, wherein X≥1, 0≤Y<0.98, 0≤Z<0.3, and M includes one or more of Mg, Al, Ti, Ca, Sr, Cr, Ba, and Mn; Optionally, X can be any value of 1, 1.1, 1.2, 1.3, 1.4, 1.5 or ≥1, Y can be any value of 0, 0.5, 0.97 or greater than or equal to 0 and less than 0.98, and Z can be any value of 0, 0.1, 0.2, 0.29 or greater than or equal to 0 and less than 0.3; (2) The D50 of the first active substance is greater than 2 μm.

[0024] Optionally, the D50 of the first active substance can be any value of 2.1 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm or >2 μm.

[0025] In some embodiments, the cathode material satisfies at least one of the following conditions: (1) The molecular formula of the second active substance is LiMn a Fe b P 1-a-bQO4, wherein 0≤a<1, 0<b<1, and P includes one or more of Co, Ni, Al, Mg, Zn, Ti, Ca, Sr, Cr, and Ba; Optionally, a can be 0, 0.5, 0.99, or any value greater than or equal to 0 and less than 1, and b can be 0.1, 0.5, 0.9, or any value greater than 0 and less than 1; (2) The D50 of the second active substance is <2μm.

[0026] Optionally, the D50 of the second active substance can be any value of 0.1 μm, 1 μm, 1.5 μm, 1.99 μm or <2 μm.

[0027] In some embodiments, the cathode material satisfies at least one of the following conditions: (1) The molecular formula of the third active substance is Li 1+h K i Mn j O k K includes one or more of Ni, Co, V, Fe, Ti, Mg, Al, Zn, Ti, Ca, Sr, Cr, Ba and P, and h, i, j, k satisfy the relation: (i×u)+(j×t)=2k-(1+h), where 1≤u, t≤4; Optionally, u can be any value of 1.1, 1.5, 2 or ≥1, and t can be any value of 1, 2, 3, 4 or ≤4; (2) The D50 of the third active substance is 2-7 μm.

[0028] Optionally, the D50 of the third active substance can be any value between 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 2-7 μm.

[0029] In some embodiments, the cathode material satisfies at least one of the following conditions: (1) The C is 2000-60000mAh; Optionally, C can be any value between 2000 mAh, 5000 mAh, 10000 mAh, 20000 mAh, 30000 mAh, 40000 mAh, 50000 mAh, 600000 mAh or 2000-60000 mAh; (2) The λ is 95-97.5%; Optionally, λ can be any value between 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, or 95-97.5%. (3) The value of S is 350-6500cm 2; Alternatively, S can be 350 cm 2 1000 cm 2 5000 cm 2 6500 cm 2 Or 350-6500 cm 2 Any value between; (4) The value of d is 0.014-0.019 cm.

[0030] Optionally, d can be any value between 0.014cm, 0.015cm, 0.016cm, 0.017cm, 0.018cm, 0.019cm, or 0.014-0.019cm.

[0031] A second aspect of this application provides a positive electrode sheet, including a current collector and a positive electrode material layer disposed on the surface of the current collector; The positive electrode material layer includes the positive electrode material, conductive agent, dispersant, and binder.

[0032] In some embodiments, the method for preparing the positive electrode material includes: The first active material and the second active material are mixed to obtain a mixed positive electrode material. The mixed positive electrode material and the third active material are mixed to obtain a positive electrode material.

[0033] Specifically, the preparation method of the cathode material includes: mixing the first active material and the second active material and loading them into a planetary ball mill with a ball-to-material ratio of 5:1, and dry ball milling at 300 rpm for 1 hour to obtain a mixed cathode material, and then adding the third active material and mixing them evenly to obtain the cathode material.

[0034] The positive electrode sheet satisfies at least one of the following conditions: (1) The conductive agent includes one or more of carbon black, graphene, carbon nanotubes, Ketjen black and carbon fiber; (2) The adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, styrene-butadiene rubber, polyacrylonitrile, polyimide, polyacrylic acid, polyacrylate, polyolefin, sodium carboxymethyl cellulose and sodium alginate; (3) The dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyester substances; It should be noted that dispersants mainly achieve uniform dispersion of particles in solution by reducing the interaction forces between particles, thus preventing particle aggregation and sedimentation. (4) The mass ratio of the positive electrode material, the conductive agent, the dispersant, and the binder is 90. 98:1 5:0.1-0.5:1 5.

[0035] Optionally, the mass ratio of the positive electrode material, conductive agent, dispersant, and binder can be (90:5:0.1:4.9), (95:1:0.1:3.9), (97:1:0.5:1.5), or 90... 98:1 5:0.1-0.5:1 Any value between 5 and 6.

[0036] A third aspect of this application provides a lithium-ion battery, including the aforementioned positive electrode.

[0037] It should be noted that lithium-ion batteries include, but are not limited to, at least one of pouch batteries, prismatic lithium-ion batteries, and cylindrical lithium-ion batteries.

[0038] A fourth aspect of this application provides an electrical device including the aforementioned lithium-ion battery.

[0039] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0040] Example 1 The first aspect of this embodiment provides a positive electrode material and its preparation method, wherein the raw materials, based on a total mass of 100%, include: 50% primary active ingredient, 40% secondary active ingredient, and 10% tertiary active ingredient; The first active material is a layered cathode material with the molecular formula LiNi. 0.6 Co 0.2 Mn 0.2 The first active material is O2, with a Dv50 of 10.84 μm; the second active material is an olivine-type cathode material with the molecular formula LiFePO4 and a Dv50 of 1.03 μm; the third active material is a spinel-type cathode material with the molecular formula LiMn2O4.

[0041] The first and second active materials are mixed and loaded into a planetary ball mill with a ball-to-material ratio of 5:1. The mixture is dry-milled at 300 rpm for 1 hour to obtain a mixed cathode material. Then, the third active material is added and mixed evenly to obtain the cathode material.

[0042] The second aspect of this embodiment provides a positive electrode sheet and its preparation method, the specific preparation steps of which are as follows: The above-mentioned positive electrode material, conductive carbon black, dispersant polyacrylate, and binder PVDF were uniformly dispersed in N at a mass ratio of 97:1.5:0.5:1.5. A uniform slurry was obtained in methylpyrrolidone. Subsequently, the positive electrode slurry was uniformly coated on both surfaces of an aluminum foil, and then dried and rolled sequentially to finally produce the positive electrode sheet.

[0043] The third aspect of this embodiment provides a battery and its preparation method, with the specific preparation steps as follows: Negative electrode preparation: Negative electrode active material (graphite), binder SBR, thickener CMC and conductive carbon black are dispersed in deionized water at a mass ratio of 96:1.5:1:1.5 to obtain a uniform negative electrode slurry with a solid content of 50%. The negative electrode slurry is uniformly coated on both surfaces of copper foil, and after drying and rolling, a negative electrode sheet is obtained. Battery preparation: The positive and negative electrode sheets prepared above are processed through steps such as slitting, sheet making, winding, packaging, baking, liquid injection, formation and capacity testing to obtain a lithium-ion secondary battery.

[0044] Example 2 The difference from Example 1 is that the mass ratio of the first active substance, the second active substance, and the third active substance is 6:3.5:0.5.

[0045] Example 3 The difference from Example 1 is that the mass ratio of the first active substance, the second active substance, and the third active substance is 4:4.5:1.5.

[0046] Example 4 The difference from Example 1 is that the structural formula of the first active substance is LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0047] Example 5 The difference from Example 4 is that the mass ratio of the first active substance, the second active substance, and the third active substance is 6:3.5:0.5.

[0048] Example 6 The difference from Example 4 is that the mass ratio of the first active substance, the second active substance, and the third active substance is 4:4.5:1.5.

[0049] Example 7 The difference from Example 4 is that the structural formula of the first active substance is Li. 1.2 Ni 0.54 Co 0.13 Mn 0.13 O2.

[0050] SEM images of the cathode material prepared in this embodiment are shown below. Figure 1 As shown.

[0051] SEM image of the positive electrode sheet prepared in this embodiment is shown below. Figure 2 As shown.

[0052] Example 8 The difference from Example 7 is that the mass ratio of the first active substance, the second active substance, and the third active substance is 6:3.5:0.5.

[0053] Example 9 The difference from Example 7 is that the mass ratio of the first active substance, the second active substance, and the third active substance is 4:4.5:1.5.

[0054] Example 10 The difference from Example 1 is that the structural formula of the second active substance is LiMn. 0.4 Fe 0.6 PO4.

[0055] Example 11 The difference from Example 10 is that the structural formula of the first active substance is LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0056] Example 12 The difference from Example 10 is that the structural formula of the first active substance is Li. 1.2 Ni 0.54 Co 0.13 Mn 0.13 O2. Comparative Example 1 The difference from Example 1 is that the positive electrode material is only the second active material, LiFePO4.

[0057] Comparative Example 2 The difference from Example 1 is that the cathode material is only the first active material LiNi. 0.6 Co 0.2 Mn 0.2 O2.

[0058] Comparative Example 3 The difference from Example 1 is that the positive electrode material is only the third active material, LiMn2O4.

[0059] Comparative Example 4 The difference from Example 1 is that the mass ratio of the first active substance, the second active substance, and the third active substance is 3.5:4.5:2.

[0060] Comparative Example 5 The difference from Example 1 is that the first active substance is Li. 1.2 Ni 0.54 Co 0.13 Mn 0.13 The mass ratio of the first active substance, the second active substance, and the third active substance in O2 is 3.5:4.5:2.

[0061] The above embodiments and comparative examples are applied according to the formula: The test was conducted, and the results are shown in Table 1.

[0062] Table 1 Formula Test Results

[0063] The batteries obtained in the above examples and comparative examples were subjected to electrochemical performance tests, and the test results are shown in Table 2.

[0064] The cycle performance of the batteries provided in Example 7, Comparative Example 4, and Comparative Example 5 is compared to that of the batteries provided in Example 5. Figure 3 As shown.

[0065] Table 2 Performance Tests

[0066] analyze: As shown in Table 1, the calculation results of Examples 1-12, when substituted into the formula, satisfy the formula value range of 2.6-3.0 g / cm³. 3 The energy density, 45-degree cycling and nail penetration safety test results of the prepared lithium batteries are shown in Table 2. The energy density of the examples can reach more than 190Wh / KG, the cycling at 45 degrees can reach more than 800 cycles, the capacity retention rate of Example 7 reaches 80% up to 1780 cycles, and the nail penetration test also achieves a pass rate of more than 6 / 10.

[0067] The calculation results of comparative examples 1-5, when substituted into the formula, do not meet the requirement of a value range of 2.6-3.0 g / cm³. 3 Comparative Examples 1 and 2 used only a single active material. Although they passed the needle penetration safety test 10 / 10, their energy density was low and their high-temperature cycling performance was poor. Comparative Example 2 used only NCM622, which had a higher energy density, but its high-temperature cycling performance was poor and its safety was also insufficient. Comparative Examples 4 and 5 used three active materials, but Comparative Example 4 had a lower energy density and its high-temperature cycling performance was not excellent. Comparative Example 5 also had too low an energy density. The batteries made by Comparative Examples 1-5 could not simultaneously achieve excellent performance in terms of energy density, high-temperature cycling, and safety.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0069] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A positive electrode material, characterized in that, Its raw materials include a first active substance, a second active substance, and a third active substance: the mass ratio of the first active substance, the second active substance, and the third active substance is 40-85: 5-45: 5-15; The first active material includes a layered cathode material; The second active material includes olivine-type lithium iron phosphate cathode material; The third active material includes a spinel-type cathode material; The cathode material satisfies the following relationship: =2.6-3.0 g / cm 3 Wherein, C is the theoretical capacity of the battery prepared from the positive electrode material; α is the mass fraction percentage of the first active material in the positive electrode material; β is the mass fraction percentage of the second active material in the positive electrode material; γ is the mass fraction percentage of the third active material in the positive electrode material; λ is the theoretical mass percentage of the positive electrode material in the positive electrode sheet prepared from the positive electrode material; S is the theoretical area of ​​the positive electrode material coated in the positive electrode sheet prepared from the positive electrode material; and d is the theoretical thickness of the positive electrode sheet prepared from the positive electrode material.

2. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The molecular formula of the first active substance is Li x Ni Y Co Z M 1-Y-Z O2, wherein X≥1, 0≤Y<0.98, 0≤Z<0.3, and M includes one or more of Mg, Al, Ti, Ca, Sr, Cr, Ba, and Mn; (2) The D50 of the first active substance is greater than 2 μm.

3. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The molecular formula of the second active substance is LiMn a Fe b P 1-a-b QO4, wherein 0≤a<1, 0<b<1, and P includes one or more of Co, Ni, Al, Mg, Zn, Ti, Ca, Sr, Cr, and Ba; (2) The D50 of the second active substance is <2μm.

4. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The molecular formula of the third active substance is Li 1+h K i Mn j O k K includes one or more of Ni, Co, V, Fe, Ti, Mg, Al, Zn, Ti, Ca, Sr, Cr, Ba and P, and h, i, j, k satisfy the relation: (i×u)+(j×t)=2k-(1+h), where 1≤u, t≤4; (2) The D50 of the third active substance is 2-7 μm.

5. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The C is 2000-60000mAh; (2) The λ is 95-97.5%; (3) The value of S is 350-6500cm 2 ; (4) The value of d is 0.014-0.019 cm.

6. A positive electrode sheet, characterized in that, It includes a current collector and a positive electrode material layer disposed on the surface of the current collector; The positive electrode material layer comprises the positive electrode material, conductive agent, dispersant, and binder as described in any one of claims 1-5.

7. The positive electrode sheet according to claim 6, characterized in that, The method for preparing the cathode material includes: The first active material and the second active material are mixed to obtain a mixed positive electrode material. The mixed positive electrode material and the third active material are mixed to obtain a positive electrode material.

8. The positive electrode sheet according to claim 6, characterized in that, At least one of the following conditions must be met: (1) The conductive agent includes one or more of carbon black, graphene, carbon nanotubes, Ketjen black and carbon fiber; (2) The adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, styrene-butadiene rubber, polyacrylonitrile, polyimide, polyacrylic acid, polyacrylate, polyolefin, sodium carboxymethyl cellulose and sodium alginate; (3) The dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyester substances; (4) The mass ratio of the positive electrode material, the conductive agent, the dispersant, and the binder is 90. 98:1 5:0.1-0.5:1 5.

9. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 6-8.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

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