Positive electrode material and preparation method therefor, positive electrode sheet, and battery

Abstract

The present application provides a positive electrode material and a preparation method therefor, a positive electrode sheet, and a battery. The positive electrode material comprises a positive electrode active material, and the positive electrode active material comprises a ternary monocrystal material and lithium iron manganese phosphate. The lattice spacing of crystals of the ternary monocrystal material a1=b1, the lattice spacing a1 ranges from 2.7Å to 3.0Å, and a lattice spacing c1 ranges from 13.5Å to 15.0Å. The lattice spacing of crystals of lithium iron manganese phosphate a2=b2, the lattice spacing a2 ranges from 6.1Å to 6.4Å, and a lattice spacing c2 ranges from 4.6Å to 5.0Å.

Description

Positive electrode materials and their preparation methods, positive electrode sheets and batteries

[0001] This application claims priority to Chinese Patent Application No. 202411442037.X, filed on October 15, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a positive electrode material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0003] As a crucial component of lithium-ion batteries, the choice of cathode material directly impacts battery performance. Different cathode materials possess varying advantages and disadvantages due to their structural characteristics. Currently, to balance energy density and safety, a novel approach is emerging: combining ternary materials (NCM) with lithium manganese iron phosphate (LMFP) to integrate the strengths of both materials, compensate for their weaknesses, and achieve higher energy density and safer performance. Invention Overview

[0004] However, ternary materials (NCM) have drawbacks such as poor stability and lithium manganese iron phosphate (LMFP) materials have insufficient conductivity, which seriously affect their application in scenarios with special requirements such as long battery life and fast charging.

[0005] This application provides a positive electrode material and its preparation method, a positive electrode sheet, and a battery, which can improve the stability and conductivity of the electrode material and enhance the charging and discharging efficiency of the battery.

[0006] In a first aspect, this application provides a cathode material, including a cathode active material, which comprises a ternary single-crystal material and lithium iron manganese phosphate; the ternary single-crystal material has a lattice spacing of a1 in a first direction, a lattice spacing of b1 in a second direction, and a lattice spacing of c1 in a third direction, wherein a1 = b1, a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å; the lithium iron manganese phosphate has a lattice spacing of a2 in a first direction, a lattice spacing of b2 in a second direction, and a lattice spacing of c2 in a third direction, wherein a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å;

[0007] The first direction intersects the second direction, and both the first and second directions are perpendicular to the third direction.

[0008] Secondly, this application also provides a method for preparing a cathode material, comprising:

[0009] A ternary single-crystal material is obtained by sintering a mixed nickel-cobalt-manganese hydroxide precursor, a lithium source, and additives. The ternary single-crystal material has a lattice spacing of a1 in the first direction, b1 in the second direction, and c1 in the third direction, where a1 = b1, a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å. The first and second directions intersect, and both the first and second directions are perpendicular to the third direction.

[0010] A mixture of lithium manganese iron phosphate precursor, a phosphorus-manganese mixture, and an alkaline solution is sintered to obtain lithium iron manganese phosphate. The lattice spacing of the lithium iron manganese phosphate crystals is a2 in the first direction, b2 in the second direction, and c2 in the third direction, where a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å.

[0011] The positive electrode active material is mixed with a conductive agent and a binder to obtain the positive electrode material.

[0012] Thirdly, this application also provides a positive electrode sheet, including a positive current collector and a positive electrode material as described in the first aspect coated on the positive current collector.

[0013] Fourthly, this application also provides a battery, including a positive electrode as described in the third aspect. Beneficial effects

[0014] This application provides a cathode material and its preparation method, a cathode electrode sheet, and a battery. The cathode material provided in this application includes a cathode active material, which includes a ternary single crystal material and lithium iron manganese phosphate. The ternary single crystal material has a lattice spacing of a1 in a first direction, b1 in a second direction, and c1 in a third direction, where a1 = b1, a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å. The lithium iron manganese phosphate crystal has a lattice spacing of a2 in a first direction, b2 in a second direction, and c2 in a third direction, where a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å. The positive electrode active material of this application is formed by mixing ternary single crystal material and lithium iron manganese phosphate, and the lattice spacing of the two is controlled within the above-mentioned range, so that the positive electrode material has a suitable lattice spacing, which helps to accommodate more ions, enhance the stability and conductivity of the positive electrode material, and thus improve the charging and discharging efficiency of the battery. Attached Figure Description

[0015] Figure 1 is a schematic diagram of the crystal structure of a ternary single crystal material provided in an embodiment of this application;

[0016] Figure 2 is a schematic diagram of the crystal structure of lithium iron manganese phosphate provided in an embodiment of this application;

[0017] Figure 3 is a flowchart of a method for preparing a cathode material according to an embodiment of this application. Embodiments of the present invention

[0018] According to a first aspect of this application, a cathode material is provided, comprising a cathode active material, which includes a ternary single-crystal material (NCM) and lithium iron manganese phosphate (LMFP). The ternary single-crystal material has a lattice spacing of a1 in a first direction, b1 in a second direction, and c1 in a third direction, where a1 = b1, a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å. The lithium iron manganese phosphate has a lattice spacing of a2 in a first direction, b2 in a second direction, and c2 in a third direction, where a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å. The first and second directions intersect, and both the first and second directions are perpendicular to the third direction.

[0019] Both ternary single-crystal materials and lithium iron manganese phosphate belong to the hexagonal crystal system. The characteristic symmetry of the hexagonal crystal system determines that the basis vectors corresponding to the hexagonal crystal cell are as follows: the two secondary axes (a, b) are both perpendicular to the principal axis (c), the magnitudes of the two secondary axis basis vectors are equal, and the included angle between the secondary axes is 120°. That is, its cell parameters have the relationship a=b≠c, α=β=90°, γ=120°.

[0020] Please refer to Figures 1 and 2. Figure 1 is a schematic diagram of the crystal structure of a ternary single-crystal material provided in an embodiment of this application, and Figure 2 is a schematic diagram of the crystal structure of lithium iron manganese phosphate provided in an embodiment of this application. In the embodiments of this application, the crystal structure has a first direction a, a second direction b, and a third direction c, where the first and second directions are both perpendicular to the third direction. Wherein, a1 represents the lattice spacing of the ternary single-crystal material in the a direction, b1 represents the lattice spacing of the ternary single-crystal material in the b direction, and c1 represents the lattice spacing of the ternary single-crystal material in the c direction (perpendicular to the bottom surface direction), a1=b1≠c1; a2 represents the lattice spacing of the lithium iron manganese phosphate crystal in the a direction, b2 represents the lattice spacing of the lithium iron manganese phosphate crystal in the b direction, and c2 represents the lattice spacing of the lithium iron manganese phosphate crystal in the c direction (perpendicular to the bottom surface direction), a2=b2≠c2.

[0021] During the charging and discharging process of lithium-ion batteries, lithium ions continuously insert and extract. The performance of electrode materials is crucial for the free and stable insertion and extraction of lithium ions. Among these, the lattice size of the electrode material is an important parameter for measuring this capability. An excessively large lattice weakens the interatomic bonding forces, making the material more susceptible to deformation under external impact and affecting its stability. Conversely, an excessively small lattice reduces the distance between atoms, increasing electron scattering, increasing resistance to ion diffusion, and decreasing conductivity. This leads to increased electrode polarization and a reduction in battery charging and discharging efficiency.

[0022] This application uses a mixture of ternary single-crystal materials and lithium iron manganese phosphate as the cathode material. While improving the energy density and safety performance of the battery, it also improves the problems of poor stability of ternary single-crystal materials and insufficient conductivity of lithium iron manganese phosphate by controlling the lattice spacing of ternary single-crystal materials and lithium iron manganese phosphate within the above-mentioned range.

[0023] The ternary single-crystal material and lithium iron manganese phosphate of this application have suitable lattice spacing, which helps the electrode material to accommodate more ions and enhance the stability of the structure. In addition, the suitable lattice spacing reduces the diffusion resistance of electrons and ions, increases the conductivity, improves the electrochemical performance of the cathode material, enhances the stability and conductivity of the cathode material, and thus helps to improve the charging and discharging efficiency of the battery.

[0024] In the cathode active material provided in this application, the mass percentage of ternary single-crystal material is M1, ranging from 10% to 40%; the mass percentage of lithium iron manganese phosphate is M2, ranging from 60% to 90%. For example, the proportions of ternary single-crystal material and lithium iron manganese phosphate in the cathode active material can be, but are not limited to: the mass percentage of ternary single-crystal material in the cathode active material can be 10%, and the mass percentage of lithium iron manganese phosphate can be 90%; or the mass percentage of ternary single-crystal material in the cathode active material can be 20%, and the mass percentage of lithium iron manganese phosphate can be 80%; or the mass percentage of ternary single-crystal material in the cathode active material can be 30%, and the mass percentage of lithium iron manganese phosphate can be 70%; or the mass percentage of ternary single-crystal material in the cathode active material can be 40%, and the mass percentage of lithium iron manganese phosphate can be 60%. In positive electrode active materials, when the content of ternary single crystal material is too low or the content of lithium iron manganese phosphate is too high, the conductivity of the battery will be too low, the rate performance will be insufficient, and the kinetics will not be improved to enhance fast charging performance. When the content of ternary single crystal material is too high or the content of lithium iron manganese phosphate is too low, the stability of the positive electrode material will be insufficient, and problems such as battery thermal runaway will easily occur.

[0025] In this application, the mass percentages M1 of the ternary single crystal material and M2 of lithium iron manganese phosphate are related to the lattice spacings a1 and c1 of the ternary single crystal material and a2 and c2 of the lithium iron manganese phosphate. The ratios of M1, M2, a1, a2, c1, and c2 are as follows: Proportional relationship The calculated value is in the range of 32 to 34, which makes the ternary single crystal material and lithium iron manganese phosphate in the positive electrode active material have a suitable mass ratio and a suitable lattice size, so that the material has high conductivity and stability, while also having high energy density and safety performance, thus making the battery have high charge and discharge efficiency.

[0026] In this application, the cathode material also includes a conductive agent and a binder. The conductive agent is used to improve the conductivity of the cathode material, and the binder is used to increase the adhesion of the cathode material. In the cathode material, with the total mass of the cathode material as 100%, the mass percentage of the cathode active material ranges from 94.5% to 97%, the mass percentage of the conductive agent ranges from 1.5% to 3%, and the mass percentage of the binder ranges from 1.5% to 2.5%. When the content of each component of the cathode material is within the above ranges, it exhibits superior electrochemical performance.

[0027] The conductive agent can be one or more of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, etc., and the binder can be one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), etc., but is not limited to.

[0028] According to a second aspect of this application, a method for preparing a cathode material is provided. Referring to Figure 3, the method for preparing the cathode material includes:

[0029] A ternary single-crystal material is obtained by sintering a mixed nickel-cobalt-manganese hydroxide precursor, a lithium source, and additives. The ternary single-crystal material has a lattice spacing of a1 in the first direction, b1 in the second direction, and c1 in the third direction, where a1 = b1, a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å. The first and second directions intersect, and both the first and second directions are perpendicular to the third direction.

[0030] A mixture of lithium manganese iron phosphate precursor, a phosphorus-manganese mixture, and an alkaline solution is sintered to obtain lithium iron manganese phosphate. The lattice spacing of the lithium iron manganese phosphate crystals is a2 in the first direction, b2 in the second direction, and c2 in the third direction, where a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å.

[0031] By mixing ternary single-crystal materials and lithium iron manganese phosphate, a positive electrode active material is obtained;

[0032] The positive electrode active material is mixed with a conductive agent and a binder to obtain the positive electrode material.

[0033] In some embodiments, the method for preparing the cathode material includes the following steps:

[0034] S1. Preparation of ternary single-crystal materials

[0035] A ternary single crystal sintering material is obtained by mixing a nickel-cobalt-manganese hydroxide precursor, a lithium source, and a first additive.

[0036] Then, the ternary single crystal sintering material is mixed with the second additive and sintered a second time to obtain the ternary single crystal material. The ternary single crystal material has a lattice spacing of a1 in the first direction, b1 in the second direction, and c1 in the third direction, where a1 = b1, a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å.

[0037] The lithium source can be one or more of lithium hydroxide, lithium nitrate, lithium acetate, etc., but is not limited to.

[0038] The first additive may be one or more of the following, but not limited to: strontium carbonate, aluminum oxide, zirconium hydroxide, zirconium dioxide, lithium nitrate, magnesium dioxide, niobium oxide, yttrium oxide, aluminum phosphate, or tungsten trioxide.

[0039] The second additive may be one or more of the following, but not limited to, metal fluorides, lithium compounds, silicates, phosphates, or oxides.

[0040] The temperature range for the first sintering is 750~900℃, and the sintering time is 20~30h; the temperature range for the second sintering is 400~500℃, and the sintering time is 3~10h.

[0041] The process after the second sintering includes the following steps: roller crushing, jaw crushing, pulverizing and sieving, to obtain ternary single crystal material.

[0042] S2, Preparation of lithium manganese iron phosphate

[0043] In a liquid-phase system, a lithium iron manganese phosphate precursor, a phosphorus-manganese mixture, and an alkaline solution are mixed, dried, and sintered under an inert gas atmosphere to obtain lithium iron manganese phosphate. The lithium iron manganese phosphate crystal has a lattice spacing of a2 in the first direction, b2 in the second direction, and [missing information - likely a value] in the third direction. a2 = b2, the range of a2 is 6.1 Å ~ 6.4 Å, and the range of c2 is 4.6 Å ~ 5.0 Å.

[0044] The drying step includes obtaining the lithium iron manganese phosphate precursor by spray drying.

[0045] The sintering temperature range is 750~800℃ and the sintering time is 10~15h in an inert gas atmosphere.

[0046] The lithium iron manganese phosphate obtained after sintering in an inert gas atmosphere is carbon-coated lithium iron manganese phosphate.

[0047] S3. Preparation of positive electrode active material

[0048] The ternary single crystal material obtained in step S1 and the lithium iron manganese phosphate obtained in step S2 are mixed to obtain the positive electrode active material.

[0049] The ternary single-crystal material has a mass percentage of M1, ranging from 10% to 40%; lithium iron manganese phosphate has a mass percentage of M2, ranging from 60% to 90%. The ratio of M1, M2, a1, a2, c1, and c2 is as follows: .

[0050] S4. Preparation of cathode materials

[0051] The positive electrode active material obtained in step S3 is dispersed and mixed with the conductive agent and binder in a solvent to obtain the positive electrode material.

[0052] According to a third aspect of this application, a positive electrode sheet is provided, comprising a positive current collector and a positive electrode material as described in the first aspect coated on the positive current collector.

[0053] In this application, the material of the positive electrode current collector can be a metal, such as aluminum or copper, but is not limited thereto. The positive electrode sheet is formed by coating a mixture slurry of the positive electrode material as in the first aspect onto the surface of the positive electrode current collector, and then drying and rolling it.

[0054] The positive electrode current collector can be a sheet-like structure with two opposing surfaces. At least one side of the positive electrode current collector is coated with a positive electrode material; for example, the positive electrode material can be coated on one surface of the positive electrode current collector, or it can be coated on both opposing surfaces. The areal density of the single side coated with the positive electrode material is 210 g / m³. 2 ~230 g / m 2 When the areal density is within the above-mentioned range, the battery has good range. When the areal density is too low, the battery capacity is too small, resulting in insufficient range; when the areal density is too high, there are problems with dynamics and the manufacturing cost increases.

[0055] According to a fourth aspect of this application, a battery is provided, the battery including a battery casing and an electrolyte, a negative electrode, a separator and a positive electrode as described in the third aspect, located within the battery casing.

[0056] The battery casing has a receiving cavity, in which the negative electrode, separator, and positive electrode are sequentially stacked, and the electrolyte is contained within the receiving cavity. The battery casing can be made of metal, such as steel or aluminum.

[0057] The negative electrode sheet includes a negative current collector and a negative electrode material coated on the negative current collector. The negative electrode material may include graphite, conductive agent, binder, etc. The negative electrode sheet is formed by coating a mixture of negative electrode materials into the surface of the negative current collector, and then drying and rolling it.

[0058] The following specific embodiments illustrate the cathode material and battery of this application.

[0059] 1. Battery manufacturing methods

[0060] S1. Preparation of ternary single-crystal materials:

[0061] S11, mixed nickel-cobalt-manganese hydroxide precursor (NCM622), lithium hydroxide and strontium carbonate were sintered for the first time at 800℃ for 24 hours to obtain ternary single crystal sintered material;

[0062] S12. The ternary single crystal sinter obtained in step S11 is mixed with Mn3O4 and sintered for a second time at 450℃ for 6 hours. Then, it is crushed and sieved by roller crushing, jaw crushing, and sieving to obtain ternary single crystal material. The lattice spacing of the ternary single crystal material in the first direction is a1, the lattice spacing in the second direction is b1, and the lattice spacing in the third direction is c1. a1=b1, the range of a1 is 2.7 Å ~ 3.0 Å, and the range of c1 is 13.5 Å ~ 15.0 Å.

[0063] S2, Preparation of lithium manganese iron phosphate:

[0064] S21. In a liquid phase system, a lithium iron phosphate precursor, a phosphorus-manganese mixture and an alkaline solution are mixed and spray-dried to obtain a lithium iron phosphate precursor.

[0065] S22. Under an Ar protective atmosphere, the lithium iron manganese phosphate precursor obtained in step S21 is sintered at a temperature of 700°C to obtain lithium iron manganese phosphate. The lithium iron manganese phosphate is carbon-coated lithium iron manganese phosphate. The lattice spacing of the lithium iron manganese phosphate crystal in the first direction is a2, the lattice spacing in the second direction is b2, and the lattice spacing in the third direction is c2, where a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å.

[0066] S3. Preparation of positive electrode active material:

[0067] The ternary single-crystal material obtained in step S1 and the lithium iron manganese phosphate obtained in step S2 are mixed to obtain a positive electrode active material. The ternary single-crystal material has a mass percentage of M1, ranging from 10% to 40%; the lithium iron manganese phosphate has a mass percentage of M2, ranging from 60% to 90%. The ratio of M1, M2, a1, a2, c1, and c2 is as follows: .

[0068] S4. Preparation of the positive electrode sheet:

[0069] The positive electrode active material, conductive agent, and binder obtained in step S3 are dispersed in N-methylpyrrolidone (NMP) and mixed. The mixture is stirred until homogeneous to obtain a positive electrode slurry. This slurry is then coated onto a positive electrode current collector, and the positive electrode sheet is obtained through drying and cold pressing. The positive electrode current collector is double-sided coated, with a single-sided areal density of 210 g / m³. 2 ~230 g / m 2 The conductive agents include conductive carbon black (SP) and carbon nanotubes (CNTs), and the binder includes polyvinylidene fluoride (PVDF). The mass ratio of the positive electrode active material, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride is 96.5:0.9:0.6:2.

[0070] S5. Preparation of the negative electrode sheet:

[0071] The negative electrode material, conductive agent, and binder are dispersed in a solvent and stirred evenly to obtain a slurry. This slurry is then coated onto the negative electrode current collector and processed through drying and cold pressing to obtain the negative electrode sheet. The negative electrode material is graphite, the conductive agent includes conductive carbon black (SP), and the binder includes sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). The mass ratio of the negative electrode material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber is 95.5:2:0.5:2.

[0072] S6. Battery fabrication:

[0073] After vacuum drying, the positive electrode, separator, and negative electrode are assembled and then cut, die-cut, and slit before being placed inside the battery casing. Electrolyte is then injected under high temperature and negative pressure to assemble a square aluminum-cased battery.

[0074] Batteries of Example 1 and Comparative Examples 1 to 6 were prepared using the battery preparation method described above. The preparation methods for the positive electrode, negative electrode, and batteries of Example 1 and Comparative Examples 1 to 6 were the same; the difference lay in the lattice spacing and mass percentage of the ternary single-crystal material and lithium iron manganese phosphate in the positive electrode active material.

[0075] Example 1: The lattice spacing a1 of the ternary single crystal material in the positive electrode is 2.8 Å and c1 is 14 Å; the lattice spacing a2 of lithium iron manganese phosphate is 6.3 Å and c2 is 4.8 Å; the mass percentage of the ternary single crystal material in the positive electrode active material is 20%, and the mass percentage of lithium iron manganese phosphate is 80%.

[0076] Comparative Example 1: The lattice spacing a1 of the ternary single crystal material in the positive electrode sheet is 2.5 Å and c1 is 13.3 Å; the lattice spacing a2 of lithium iron manganese phosphate is 6.3 Å and c2 is 4.8 Å; the mass percentage of the ternary single crystal material in the positive electrode active material is 20% and the mass percentage of lithium iron manganese phosphate is 80%.

[0077] Comparative Example 2: The lattice spacing a1 of the ternary single crystal material in the positive electrode sheet is 3.3 Å and c1 is 15.2 Å; the lattice spacing a2 of lithium iron manganese phosphate is 6.3 Å and c2 is 4.8 Å; the mass percentage of the ternary single crystal material in the positive electrode active material is 20% and the mass percentage of lithium iron manganese phosphate is 80%.

[0078] Comparative Example 3: The lattice spacing a1 of the ternary single crystal material in the positive electrode sheet is 2.8 Å and c1 is 14 Å; the lattice spacing a2 of lithium iron manganese phosphate is 5.8 Å and c2 is 4.3 Å; the mass percentage of the ternary single crystal material in the positive electrode active material is 20%, and the mass percentage of lithium iron manganese phosphate is 80%.

[0079] Comparative Example 4: The lattice spacing a1 of the ternary single crystal material in the positive electrode sheet is 2.8 Å and c1 is 14 Å; the lattice spacing a2 of lithium iron manganese phosphate is 6.7 Å and c2 is 5.1 Å; the mass percentage of the ternary single crystal material in the positive electrode active material is 20% and the mass percentage of lithium iron manganese phosphate is 80%.

[0080] Comparative Example 5: The lattice spacing a1 of the ternary single crystal material in the positive electrode sheet is 2.8 Å and c1 is 14 Å; the lattice spacing a2 of lithium iron manganese phosphate is 6.3 Å and c2 is 4.8 Å; the mass percentage of the ternary single crystal material in the positive electrode active material is 5%, and the mass percentage of lithium iron manganese phosphate is 95%.

[0081] Comparative Example 6: The lattice spacing a1 of the ternary single crystal material in the positive electrode sheet is 2.8 Å and c1 is 14 Å; the lattice spacing a2 of lithium iron manganese phosphate is 6.3 Å and c2 is 4.8 Å; the mass percentage of the ternary single crystal material in the positive electrode active material is 45%, and the mass percentage of lithium iron manganese phosphate is 55%.

[0082] 2. Methods for determining lattice spacing

[0083] The lattice spacing of the aforementioned ternary single-crystal materials and lithium iron manganese phosphate was determined by X-ray diffraction (XRD). The steps for determining the lattice spacing by X-ray diffraction (XRD) include:

[0084] 1) Sample preparation: Grind the sample into uniform fine particles;

[0085] 2) Test procedure: Place the sample in a suitable position on the sample stage using a specific glass slide, then set the wavelength of the X-rays (usually using a copper Cu target), the scanning range (to cover as many angles as possible where diffraction peaks may appear, based on the understanding of the material), and the scanning speed; record the test results.

[0086] 3) Data Processing: Based on the diffraction pattern obtained from the test, identify each diffraction peak and apply the Bragg equation. (where d is the lattice spacing) Given the wavelength and diffraction angle, η is the diffraction order, and λ is the X-ray wavelength, calculate the interplanar spacing d for a specific diffraction peak (usually higher angle peaks are more accurately calculated) and its corresponding diffraction order (first-order diffraction η=1 is commonly used for simple crystal structures).

[0087] It should be noted that, as shown in Figures 1-2, both ternary single-crystal materials and lithium iron manganese phosphate belong to the hexagonal crystal system. Within the hexagonal crystal system, the following relationships exist: a = b ≠ c, α = β = 90°, γ = 120°. Here, a and b represent the in-plane spacing of the lattice, and c represents the interlayer spacing. For (hkl) crystal planes, such as (100) and (001), the relationship between the interplanar spacing d and the lattice parameters is l / d. 2 =4 / 3(h 2 +hk+k 2 / a 2 )+l 2 / c 2 The values ​​of a, b, and c can be obtained through measurement and calculation.

[0088] The lattice spacings a1 and c1 of the ternary single crystal material and a2 and c2 of lithium iron manganese phosphate in this application were determined by the above-mentioned X-ray diffraction (XRD) method. The measurement results are shown in Table 1.

[0089] 3. Battery performance testing

[0090] 1) Ratio performance test:

[0091] Example 1 and Comparative Examples 1 to 6 were calibrated at 25°C with a capacity of 1C. After being fully charged, they were discharged at a rate of 2C, and their discharge capacity retention rates were tested. The test results are shown in Table 1.

[0092] 2) Cyclic performance test:

[0093] After resting at 25°C for 1 hour, Examples 1 and Comparative Examples 1 to 6 were charged to 4.2V with a constant current and voltage of 1C and a cutoff current of 0.05C. Then, they were rested for 30 minutes and placed at 2.5V with a constant current of 1C. After 500 cycles, the stability of the materials was evaluated by the cycle capacity retention rate. The test results are shown in Table 1.

[0094] 3) Thermal stability test:

[0095] The cells of Example 1 and Comparative Examples 1 to 6 were charged to 100% SOC, then overcharged with a 1C current to trigger thermal runaway. Charging was then stopped, and the cells were observed for 1 hour. The test results are shown in Table 1.

[0096] Table 1

[0097]

[0098] The proportions in Table 1 represent The calculated value.

[0099] Data from Examples 1 and Comparative Examples 1-4 show that the NCM lattice spacing and LMFP lattice spacing in Example 1 are within the range of the aforementioned lattice spacings in this application. However, the NCM lattice spacing and / or LMFP lattice spacing in Comparative Examples 1-4 are not within the aforementioned range. Compared to Example 1, the NCM lattice spacing in Comparative Example 1 is smaller, the NCM lattice spacing in Comparative Example 2 is larger, the LMFP lattice spacing in Comparative Example 3 is smaller, and the LMFP lattice spacing in Comparative Example 4 is larger. Data from the rate performance and cycle performance of Comparative Examples 1-4 show that when the lattice spacing of Comparative Examples 1-4 is not within the aforementioned range, the electrochemical performance deteriorates. This is because when the lattice spacing of the positive electrode active material increases, the diffusion resistance of ions and electrons decreases, and the rate performance improves. However, the interatomic bonding force weakens, the material stability deteriorates, and the cycle performance is affected.

[0100] Data from Example 1 and Comparative Examples 5-6 show that when the mass percentages of NCM and LMFP are outside the ranges specified in this application, the overall performance of the lithium-ion battery cannot reach its optimal level. When the NCM content is too low, the battery's rate performance will be insufficient; when the NCM content is too high, large lattices dominate, leading to insufficient stability of the cathode material and a higher risk of thermal runaway.

[0101] Therefore, when the positive electrode active material includes ternary single crystal material and lithium iron manganese phosphate, and the lattice spacing a1 of the ternary single crystal material in the first direction ranges from 2.7 Å to 3.0 Å, and the lattice spacing c1 in the third direction ranges from 13.5 Å to 15.0 Å, and the lattice spacing a2 of the lithium iron manganese phosphate crystal in the first direction ranges from 6.1 Å to 6.4 Å, and the lattice spacing c2 in the third direction ranges from 4.6 Å to 5.0 Å, the stability and conductivity of the positive electrode material can be effectively improved, thereby enhancing the charge and discharge efficiency of the battery.

Claims

1. A cathode material, comprising a cathode active material, wherein the cathode active material comprises a ternary single crystal material and lithium iron manganese phosphate; The crystal of the ternary single crystal material has a lattice spacing of a1 in a first direction, a lattice spacing of b1 in a second direction, and a lattice spacing of c1 in a third direction, wherein a1=b1, where a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å. The lattice spacing of the lithium iron manganese phosphate crystal in the first direction is a2, the lattice spacing in the second direction is b2, and the lattice spacing in the third direction is c2, wherein a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å. Wherein, the first direction intersects the second direction, and both the first direction and the second direction are perpendicular to the third direction.

2. The positive electrode material of claim 1, wherein, In the positive electrode active material, the mass percentage of the ternary single crystal material is M1, and the range of M1 is 10% to 40%. The mass percentage of the lithium iron manganese phosphate is M2, and the range of M2 is 60% to 90%.

3. The cathode material of claim 2, wherein, The ratio of M1, M2, a1, a2, c1 and c2 is: .

4. The positive electrode material according to any one of claims 1 to 3, wherein The positive electrode material also includes a conductive agent and a binder; In the positive electrode material, the mass percentage of the positive electrode active material ranges from 94.5% to 97%, the mass percentage of the conductive agent ranges from 1.5% to 3%, and the mass percentage of the binder ranges from 1.5% to 2.5%.

5. The cathode material according to any one of claims 1 to 3, wherein, The lithium iron manganese phosphate is carbon-coated lithium iron manganese phosphate.

6. A method for preparing a cathode material, comprising: A ternary single-crystal material is obtained by sintering a mixed nickel-cobalt-manganese hydroxide precursor, a lithium source, and additives. The ternary single-crystal material has a lattice spacing of a1 in a first direction, b1 in a second direction, and c1 in a third direction, where a1 = b1, a1 ranges from 2.7 Å to 3.0 Å, and c1 ranges from 13.5 Å to 15.0 Å. The first direction intersects the second direction, and both the first and second directions are perpendicular to the third direction. A mixture of lithium iron manganese phosphate precursor, a phosphorus-manganese mixture, and an alkaline solution is sintered to obtain lithium iron manganese phosphate. The lattice spacing of the lithium iron manganese phosphate crystals is a2 in the first direction, b2 in the second direction, and c2 in the third direction. a2 = b2, a2 ​​ranges from 6.1 Å to 6.4 Å, and c2 ranges from 4.6 Å to 5.0 Å. The ternary single crystal material and the lithium iron manganese phosphate are mixed to obtain the positive electrode active material; The positive electrode active material is mixed with a conductive agent and a binder to obtain the positive electrode material.

7. The method of producing a cathode material according to claim 6, wherein The steps of sintering the mixed nickel-cobalt-manganese hydroxide precursor, lithium source, and additives to obtain ternary single crystal materials include: A ternary single crystal sintering material is obtained by mixing a nickel-cobalt-manganese hydroxide precursor, a lithium source, and a first additive. Then the ternary single crystal sintering material is mixed with the second additive and sintered a second time to obtain the ternary single crystal material. The step of sintering the mixed lithium manganese iron phosphate precursor, the phosphorus-manganese mixture, and the alkaline solution to obtain lithium iron manganese phosphate includes: In a liquid phase system, a lithium iron manganese phosphate precursor, a manganese-phosphorus mixed solution and an alkali solution are mixed, dried and sintered in an inert gas atmosphere to obtain a lithium iron manganese phosphate, which is a carbon-coated lithium iron manganese phosphate.

8. A positive electrode sheet comprising a positive electrode current collector and the positive electrode material as claimed in any one of claims 1 to 5 coated on the positive electrode current collector.

9. The cathode sheet of claim 8, wherein, At least one side of the positive electrode current collector is coated with the positive electrode material, and the single-sided areal density of the positive electrode material coating is 210 g / m 2 230 g / m 2 .

10. A battery comprising the positive electrode sheet as claimed in any one of claims 8 to 9.

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