Positive electrode material, positive electrode sheet, secondary battery and electronic device

Abstract

Provided in the present application are a positive electrode material, a positive electrode sheet, a secondary battery and an electronic device. The positive electrode material comprises lithium manganese iron phosphate. In a scanning electron microscope image of the lithium manganese iron phosphate with an amplification factor of 10,000 within a range of 10 μm × 8 μm, the total number of primary particles of the lithium manganese iron phosphate is N, the number of primary particles of the lithium manganese iron phosphate having a particle size of Φ1 nm is N1, and the number of primary particles of the lithium manganese iron phosphate having a particle size of Φ2 nm is N2, wherein N≥200; 50<Φ1≤100, and 10%≤N1 / N≤30%; and 100<Φ2≤150, and 15%≤N2 / N≤35%. The positive electrode material satisfies the above-mentioned characteristics, and the processing performance, dynamic performance and cycle performance of the positive electrode material can be improved.

Description

Positive electrode materials, positive electrode sheets, secondary batteries and electronic devices

[0001] This application claims priority to Chinese Patent Application No. 202411570308.X, filed on November 5, 2024, entitled "Positive Electrode Material, Positive Electrode Sheet, Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a positive electrode material, a positive electrode sheet, a secondary battery, and an electronic device. Background Technology

[0003] To address the severe global energy crisis, environmental pollution, climate change, and the development of a low-carbon economy, the research and application of electric vehicles, large-scale power supplies, and energy storage technologies have become inevitable. Lithium iron phosphate (LFP) batteries, as a crucial component, offer advantages such as long lifespan, safety, and affordability; however, LFP batteries suffer from relatively low energy density.

[0004] Lithium manganese iron phosphate (LFP) incorporates a certain proportion of manganese (Mn) into lithium iron phosphate, which increases its average voltage and energy density. However, LFP suffers from the Jan Taylor effect, resulting in poor kinetic and cycle performance. Summary of the Invention

[0005] The purpose of this application is to provide a positive electrode material, a positive electrode sheet, a secondary battery, and an electronic device to improve the processing performance, kinetic performance, and cycle performance of the positive electrode material. The specific technical solution is as follows:

[0006] The first aspect of this application provides a cathode material comprising lithium manganese iron phosphate. In a scanning electron microscope (SEM) image of lithium manganese iron phosphate at a magnification of 10000x within a range of 10μm × 8μm, the total number of primary particles of lithium manganese iron phosphate is N, the number of primary particles with a particle size of Φ1nm is N1, and the number of primary particles with a particle size of Φ2nm is N2. N ≥ 200; 50 < Φ1 ≤ 100, 10% ≤ N1 / N ≤ 30%; 100 < Φ2 ≤ 150, 15% ≤ N2 / N ≤ 35%. The cathode material satisfies the above characteristics, which can improve the processing performance, kinetic performance, and cycle performance of the cathode material. Applying the above cathode material to a secondary battery can enable the secondary battery to have better processing performance, kinetic performance, and cycle performance.

[0007] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ3nm is N3, Φ3≤50, and 0≤N3 / N≤10%. When the ratio of the number of primary particles N3 of lithium manganese iron phosphate with a particle size of Φ3≤50 to the total number N of primary particles of lithium manganese iron phosphate is within the range of this application, lithium manganese iron phosphate satisfies the above particle size distribution. The smaller particle size of lithium manganese iron phosphate can further improve the kinetic performance of the cathode material, such as rate performance or low-temperature discharge performance, while further reducing the kinetic performance decay of the cathode material during cycling.

[0008] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ4nm is N4, where 150 < Φ4 ≤ 250, and 20% ≤ N4 / N ≤ 40%. When the ratio of the number of primary particles N4 of lithium manganese iron phosphate with a particle size of Φ4 satisfying 150 < Φ4 ≤ 250 to the total number N of primary particles of lithium manganese iron phosphate is within the range of this application, lithium manganese iron phosphate satisfies the above particle size distribution. Lithium manganese iron phosphate has a certain number of medium-sized and large-sized particles, which can further improve the processing performance of the cathode material, for example, increase the compaction density of the cathode material.

[0009] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ5nm is N5, where 250 < Φ5 ≤ 350, and 5% ≤ N5 / N ≤ 15%. When the ratio of the number of primary particles N5 of lithium manganese iron phosphate with a particle size of Φ5 satisfying 250 < Φ5 ≤ 350 to the total number N of primary particles of lithium manganese iron phosphate is within the range of this application, lithium manganese iron phosphate satisfies the above particle size distribution. Lithium manganese iron phosphate has a certain number of medium-sized and large-sized particles, which can further improve the processing performance of the cathode material, for example, increase the compaction density of the cathode material.

[0010] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ6nm is N6, where 350<Φ6≤500 and 1%≤N6 / N≤5%. When the ratio of the number of primary particles N6 of lithium manganese iron phosphate with a particle size of Φ6 satisfying 350<Φ6≤500 to the total number N of primary particles of lithium manganese iron phosphate is within the range of this application, lithium manganese iron phosphate satisfies the above particle size distribution. Lithium manganese iron phosphate has a certain number of larger particle sizes, which can further improve the processing performance of the cathode material, for example, increase the compaction density of the cathode material.

[0011] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ7nm is N7, where Φ7>500 and 0≤N7 / N≤5%. When the ratio of the number of primary particles N7 of lithium manganese iron phosphate with a particle size of Φ7>500 to the total number N of primary particles of lithium manganese iron phosphate is within the range of this application, lithium manganese iron phosphate satisfies the above particle size distribution. Lithium manganese iron phosphate has a certain number of larger particle sizes, which can further improve the processing performance of the cathode material, for example, increase the compaction density of the cathode material.

[0012] In one or more embodiments of this application, the average particle size of lithium manganese iron phosphate is D nm, where 50 ≤ D ≤ 200. By controlling the average particle size of lithium manganese iron phosphate within the scope of this application, lithium manganese iron phosphate includes particles with smaller diameters, as well as particles with medium and larger diameters. The smaller diameter particles in lithium manganese iron phosphate can improve the kinetic performance of the cathode material, such as rate performance or low-temperature discharge performance, while effectively reducing the kinetic performance degradation of the cathode material during cycling. Furthermore, the presence of a certain number of medium and larger diameter particles in lithium manganese iron phosphate can improve the processing performance of the cathode material, such as increasing the compaction density of the cathode material.

[0013] In one or more embodiments of this application, based on the mass of lithium manganese iron phosphate, the mass percentage of carbon in lithium manganese iron phosphate is Wc%, 1.0≤Wc≤2.5, preferably 1.3≤Wc≤2.0; more preferably 1.5≤Wc≤1.8. By adjusting the mass percentage of carbon in lithium manganese iron phosphate within the scope of this application, the electronic conductivity of lithium manganese iron phosphate can be further improved, thereby further improving the kinetic performance and cycle performance of the cathode material.

[0014] In one or more embodiments of this application, the specific surface area of ​​lithium manganese iron phosphate is SSA m². 2 / g, 12≤SSA≤35; preferably, 14≤SSA≤20. By controlling the specific surface area of ​​lithium manganese iron phosphate within the scope of this application, lithium manganese iron phosphate has a suitable specific surface area and a suitable particle size distribution. Lithium manganese iron phosphate includes particles of smaller diameter, as well as particles of medium and larger diameter. The smaller diameter particles in lithium manganese iron phosphate can improve the kinetic performance of the cathode material, such as rate performance or low-temperature discharge performance, while effectively reducing the kinetic performance degradation of the cathode material during cycling. Furthermore, the presence of a certain number of medium and larger diameter particles in lithium manganese iron phosphate can improve the processing performance of the cathode material, such as increasing the compaction density of the cathode material.

[0015] In one or more embodiments of this application, the resistivity of lithium manganese iron phosphate powder is ρΩ·cm, 10≤ρ≤300, preferably 10≤ρ≤100. By adjusting the resistivity of lithium manganese iron phosphate powder within the range of this application, the resistivity of lithium manganese iron phosphate powder is relatively small, and the electronic conductivity of lithium manganese iron phosphate is good, which can further improve the kinetic performance and cycle performance of the cathode material.

[0016] In one or more embodiments of this application, the chemical formula of lithium manganese iron phosphate is Li x Mn y Fe 1-y-z M z PO4, 1.0≤x≤1.1, 0.5≤y≤0.8, 0≤z≤0.02, M includes at least one of Mg, Ti, Nb, V, Ni, or Co. Using the above-mentioned lithium iron manganese phosphate (LFP), which has a high energy density and satisfies the above-mentioned particle size distribution (including small, medium, and large particles), enables the cathode material to have good processing performance, kinetic performance, and cycle performance. Applying this cathode material to secondary batteries can result in secondary batteries with good processing performance, kinetic performance, cycle performance, and high energy density.

[0017] A second aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, wherein the positive electrode material layer includes the positive electrode material in any of the foregoing embodiments. Therefore, applying the positive electrode sheet to a secondary battery enables the secondary battery to have better processing performance, kinetic performance, and cycle performance.

[0018] A third aspect of this application provides a secondary battery, which includes the positive electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by this application has better processing performance, kinetic performance, and cycle performance.

[0019] A fourth aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has better processing performance, kinetic performance, and cycle performance.

[0020] The beneficial effects of this application are:

[0021] This application provides a cathode material, a cathode electrode sheet, a secondary battery, and an electronic device. The cathode material includes lithium manganese iron phosphate (LFP). In a scanning electron microscope (SEM) image of LFP at 10000x magnification within a 10μm × 8μm range, the total number of primary LFP particles is N, the number of primary LFP particles with a diameter of Φ1nm is N1, and the number of primary LFP particles with a diameter of Φ2nm is N2. N ≥ 200; 50 < Φ1 ≤ 100, 10% ≤ N1 / N ≤ 30%; 100 < Φ2 ≤ 150, 15% ≤ N2 / N ≤ 35%. The cathode material satisfies the above characteristics, which can improve the processing performance, kinetic performance, and cycle performance of the cathode material.

[0022] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0024] Figure 1 is a scanning electron microscope image of the positive electrode material of Embodiment 1-1 of this application. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that the following explanation uses lithium-ion batteries as an example of secondary batteries to illustrate this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0027] The first aspect of this application provides a cathode material comprising lithium manganese iron phosphate. In a scanning electron microscope image of lithium manganese iron phosphate at a magnification of 10000x and within a range of 10μm × 8μm, the total number of primary particles of lithium manganese iron phosphate is N, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ1nm is N1, and the number of primary particles of lithium manganese iron phosphate with a particle size of Φ2nm is N2. N≥200; 50<Φ1≤100, 10%≤N1 / N≤30%; 100<Φ2≤150, 15%≤N2 / N≤35%. For example, the value of N can be 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 500, 700, 900, 1000, 1300, 1500, 1700, 1900, 2000, or a range of any two of the above values; Φ1 can be 51, 53, 55, 57, 59, 60, 63, 65, 67, 70, 73, 75, 77, 80, 83, 85, 87, 90, 93, 95, 97, 100, or a range of any two of the above values; N1 / N can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or a range of any two of the above values; Φ2 can be 101, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, or a range of any two of the above values; N2 / N can be 15%, 17%, 19%, 20%, 21%, 23%, 25%, 27%, 29%, 30%, 31%, 33%, 35%, or a range of any two of the above values.

[0028] The inventors have discovered that the cathode material includes lithium manganese iron phosphate (LFP). Within the scope of this application, the ratio of the number N1 of primary LFP particles with a particle size Φ1 satisfying 50 < Φ1 ≤ 100 to the total number N of primary LFP particles, and the ratio of the number N2 of primary LFP particles with a particle size Φ2 satisfying 100 < Φ2 ≤ 150 to the total number N of primary LFP particles, satisfy the aforementioned particle size distribution. Smaller particles in the LFP can improve the kinetic performance of the cathode material, such as rate performance or low-temperature discharge performance, while effectively reducing the kinetic performance degradation of the cathode material during cycling. Furthermore, the presence of a certain number of medium and large-sized particles in the LFP can improve the processing performance of the cathode material, such as increasing the compaction density. Therefore, the cathode material satisfies the above characteristics, improving its processing performance, kinetic performance, and cycle performance. Applying this cathode material to a secondary battery can result in a secondary battery with better processing performance, kinetic performance, and cycle performance.

[0029] In one or more embodiments of this application, the cathode material includes lithium manganese iron phosphate. In a scanning electron microscope image of lithium manganese iron phosphate at a magnification of 10000x and within a range of 10μm × 8μm, the total number of primary particles of lithium manganese iron phosphate is N, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ1nm is N1, and the number of primary particles of lithium manganese iron phosphate with a particle size of Φ2nm is N2, where 200≤N≤2000; 50<Φ1≤100, 10%≤N1 / N≤30%; 100<Φ2≤150, 15%≤N2 / N≤35%.

[0030] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ3nm is N3, where Φ3≤50 and 0≤N3 / N≤10%. Exemplarily, Φ3 can be 1, 3, 5, 7, 9, 10, 11, 13, 15, 17, 19, 20, 21, 23, 25, 27, 29, 30, 31, 33, 35, 37, 39, 40, 41, 43, 45, 47, 49, 50, or a range consisting of any two of the above values; N3 / N can be 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values. Within the scope of this application, the ratio of the number N3 of primary lithium manganese iron phosphate particles with a particle size Φ3 ≤ 50 to the total number N of primary lithium manganese iron phosphate particles satisfies the above particle size distribution. The smaller particle size in lithium manganese iron phosphate can further improve the kinetic performance of the cathode material, such as rate performance or low-temperature discharge performance, while further reducing the kinetic performance decay of the cathode material during cycling.

[0031] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ4nm is N4, where 150 < Φ4 ≤ 250, and 20% ≤ N4 / N ≤ 40%. Exemplarily, Φ4 can be 151, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, or a range consisting of any two of the above values; N4 / N can be 20%, 21%, 23%, 25%, 27%, 29%, 30%, 31%, 33%, 35%, 37%, 39%, 40%, or a range consisting of any two of the above values. When the ratio of the number N4 of primary lithium manganese iron phosphate particles with a particle size Φ4 satisfying 150<Φ4≤250 to the total number N of primary lithium manganese iron phosphate particles is within the range of this application, lithium manganese iron phosphate satisfies the above particle size distribution. Lithium manganese iron phosphate has a certain number of medium and large particle sizes, which can further improve the processing performance of the cathode material, such as increasing the compaction density of the cathode material.

[0032] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ5nm is N5, where 250 < Φ5 ≤ 350, and 5% ≤ N5 / N ≤ 15%. Exemplarily, Φ5 can be 251, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, 350, or a range consisting of any two of the above values; N5 / N can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of the above values. When the ratio of the number N5 of primary lithium manganese iron phosphate particles with a particle size Φ5 satisfying 250<Φ5≤350 to the total number N of primary lithium manganese iron phosphate particles is within the range of this application, lithium manganese iron phosphate satisfies the above particle size distribution. Lithium manganese iron phosphate has a certain number of medium and large particle sizes, which can further improve the processing performance of the cathode material, such as increasing the compaction density of the cathode material.

[0033] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ6 nm is N6, where 350 < Φ6 ≤ 500, and 1% ≤ N6 / N ≤ 5%. Exemplarily, Φ6 can be 351, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, or any combination of two of the above values; N6 / N can be 1%, 2%, 3%, 4%, 5%, or any combination of two of the above values. When the ratio of the number of primary particles N6 of lithium manganese iron phosphate with a particle size of Φ6 (350 < Φ6 ≤ 500) to the total number N of primary particles of lithium manganese iron phosphate is within the range of this application, the lithium manganese iron phosphate satisfies the above particle size distribution. Lithium manganese iron phosphate has a certain number of larger particle sizes, which can further improve the processing performance of the cathode material, for example, increasing the compaction density of the cathode material.

[0034] In one or more embodiments of this application, the number of primary particles of lithium manganese iron phosphate with a particle size of Φ7nm is N7, where Φ7 > 500, and 0 ≤ N7 / N ≤ 5%. For example, Φ7 can be 501, 505, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, or a range of any two of the above values; N7 / N can be 0, 1%, 2%, 3%, 4%, 5%, or a range of any two of the above values. When the ratio of the number of primary particles N7 of lithium manganese iron phosphate with a particle size of Φ7 > 500 to the total number N of primary particles of lithium manganese iron phosphate is within the range of this application, the lithium manganese iron phosphate satisfies the above particle size distribution. The lithium manganese iron phosphate has a certain number of larger particle sizes, which can further improve the processing performance of the cathode material, for example, increasing the compaction density of the cathode material.

[0035] In one or more embodiments of this application, the average particle size of lithium manganese iron phosphate is D nm, where 50 ≤ D ≤ 200. Exemplarily, D can be 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or a range of any two of the above values. The particle size distribution of lithium manganese iron phosphate affects its average particle size. By controlling the average particle size of lithium manganese iron phosphate within the scope of this application, lithium manganese iron phosphate includes particles with smaller diameters, as well as particles with medium and larger diameters. The smaller diameter particles in lithium manganese iron phosphate can improve the kinetic performance of the cathode material, such as rate performance or low-temperature discharge performance, while effectively reducing the kinetic performance degradation of the cathode material during cycling. Furthermore, lithium manganese iron phosphate having a certain number of medium and larger diameter particles can improve the processing performance of the cathode material, such as increasing the compaction density of the cathode material.

[0036] In one or more embodiments of this application, based on the mass of lithium manganese iron phosphate, the mass percentage of carbon in the lithium manganese iron phosphate is Wc%, 1.0≤Wc≤2.5, preferably 1.3≤Wc≤2.0; more preferably 1.5≤Wc≤1.8. Exemplarily, Wc can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or a range consisting of any two of the above values. By adjusting the mass percentage of carbon in the lithium manganese iron phosphate within the range of this application, the electronic conductivity of the lithium manganese iron phosphate can be further improved, thereby further improving the kinetic performance and cycle performance of the cathode material.

[0037] In one or more embodiments of this application, the specific surface area of ​​lithium manganese iron phosphate is SSA m². 2 / g, 12≤SSA≤35; preferably, 14≤SSA≤20. Exemplarily, SSA can be 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, or a range of any two of the above values. By controlling the specific surface area of ​​lithium manganese iron phosphate within the scope of this application, lithium manganese iron phosphate has a suitable specific surface area and a suitable particle size distribution. Lithium manganese iron phosphate includes particles of smaller diameter, as well as particles of medium and larger diameter. The smaller diameter particles in lithium manganese iron phosphate can improve the kinetic performance of the cathode material, such as rate performance or low-temperature discharge performance, while effectively reducing the kinetic performance degradation of the cathode material during cycling. Furthermore, the presence of a certain number of medium and larger diameter particles in lithium manganese iron phosphate can improve the processing performance of the cathode material, such as increasing the compaction density of the cathode material.

[0038] In one or more embodiments of this application, the powder resistivity of lithium manganese iron phosphate is ρΩ·cm, 10≤ρ≤300, preferably 10≤ρ≤100. Exemplarily, ρ can be 10, 30, 50, 70, 90, 100, 110, 130, 150, 170, 190, 200, 210, 230, 250, 270, 290, 300, or a range of any two of the above values. By adjusting the powder resistivity of lithium manganese iron phosphate within the range of this application, the powder resistivity of lithium manganese iron phosphate is relatively small, and the electronic conductivity of lithium manganese iron phosphate is good, which can further improve the kinetic performance and cycle performance of the cathode material.

[0039] In one or more embodiments of this application, the chemical formula of lithium manganese iron phosphate is Li x Mn y Fe 1-y-z M zPO4, 1.0≤x≤1.1, 0.5≤y≤0.8, 0≤z≤0.02, M includes at least one of Mg, Ti, Nb, V, Ni or Co. For example, x can be 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1 or any range of any two of the above values; y can be 0.5, 0.53, 0.55, 0.57, 0.6, 0.63, 0.65, 0.67, 0.7, 0.73, 0.75, 0.77, 0.8 or any range of any two of the above values; z can be 0, 0.003, 0.005, 0.007, 0.009, 0.01, 0.013, 0.015, 0.017, 0.019, 0.02 or any range of any two of the above values. The selection of lithium iron manganese phosphate (LMP) provides a high energy density and satisfies the aforementioned particle size distribution, which includes particles of smaller, medium, and larger sizes. This allows the cathode material to exhibit good processing performance, kinetic performance, and cycle performance. Applying this cathode material to secondary batteries enables the secondary batteries to possess good processing performance, kinetic performance, cycle performance, and high energy density.

[0040] This application does not impose any particular limitation on the preparation method of the cathode material. Exemplarily, the preparation method of the cathode material may include, but is not limited to, the following steps: adding manganese source, iron source, lithium source, and phosphorus source to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution to obtain particles with a particle size of [missing information]. The first precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The second precursor solution is prepared by mixing the first and second precursor solutions, followed by spray granulation, sintering, cooling, and air jet milling to obtain the cathode material. When glucose is added, it reacts with the precursor during heating, causing Mn... 3+ / Fe 3+ Restored to Mn 2+ / Fe 2+ The process involves the formation of LiFeMnPO4; furthermore, the addition of glucose can form a carbon coating layer, improving the electronic conductivity of the cathode material. The aforementioned precursors refer to manganese, iron, lithium, and phosphorus sources. The cathode material includes lithium iron manganese phosphate.

[0041] For example, the preparation method of the cathode material may include, but is not limited to, the following steps: adding manganese source, iron source, lithium source, and phosphorus source to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution to obtain particles with a particle size of [missing information]. The first precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The second precursor solution; manganese source, iron source, lithium source, and phosphorus source are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The third precursor solution; the first precursor solution, the second precursor solution and the third precursor solution are mixed, then spray granulated, sintered and cooled, and then pulverized by airflow to obtain the cathode material.

[0042] For example, the preparation method of the cathode material may include, but is not limited to, the following steps: adding manganese source, iron source, lithium source, and phosphorus source to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution to obtain particles with a particle size of [missing information]. The first precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The second precursor solution; manganese source, iron source, lithium source, and phosphorus source are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The third precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The fourth precursor solution; the first precursor solution, the second precursor solution, the third precursor solution and the fourth precursor solution are mixed, then spray granulated, sintered and cooled, and then pulverized by airflow to obtain the cathode material.

[0043] For example, the preparation method of the cathode material may include, but is not limited to, the following steps: adding manganese source, iron source, lithium source, and phosphorus source to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution to obtain particles with a particle size of [missing information]. The first precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The second precursor solution; manganese source, iron source, lithium source, and phosphorus source are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The third precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The fourth precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The fifth precursor solution; the first, second, third, fourth and fifth precursor solutions are mixed, then spray granulated, sintered and cooled, and then pulverized by airflow to obtain the cathode material.

[0044] For example, the preparation method of the cathode material may include, but is not limited to, the following steps: adding manganese source, iron source, lithium source, and phosphorus source to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution to obtain particles with a particle size of [missing information]. The first precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The second precursor solution; manganese source, iron source, lithium source, and phosphorus source are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The third precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The fourth precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The fifth precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The sixth precursor solution; the first, second, third, fourth, fifth and sixth precursor solutions are mixed, then spray granulated, sintered and cooled, and then pulverized by airflow to obtain the cathode material.

[0045] For example, the preparation method of the cathode material may include, but is not limited to, the following steps: adding manganese source, iron source, lithium source, and phosphorus source to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution to obtain particles with a particle size of [missing information]. The first precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The second precursor solution; manganese source, iron source, lithium source, and phosphorus source are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The third precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The fourth precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The fifth precursor solution; manganese, iron, lithium, and phosphorus sources are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The sixth precursor solution; manganese, iron, lithium, and phosphorus sources were added to water in a certain molar ratio, and glucose was added to obtain an intermediate solution. The intermediate solution was mixed and ground to obtain particles with a particle size of [missing information]. The seventh precursor solution; the first, second, third, fourth, fifth, sixth and seventh precursor solutions are mixed, then spray granulated, sintered and cooled, and then pulverized by airflow to obtain the cathode material.

[0046] This application does not impose any particular restriction on the manganese source, as long as it achieves the purpose of this application. For example, the manganese source may include, but is not limited to, Mn3O4. This application does not impose any particular restriction on the iron source, as long as it achieves the purpose of this application. For example, the iron source may include, but is not limited to, FePO4. This application does not impose any particular restriction on the lithium source, as long as it achieves the purpose of this application. For example, the lithium source may include, but is not limited to, Li2CO3. This application does not impose any particular restriction on the phosphorus source, as long as it achieves the purpose of this application. For example, the phosphorus source may include, but is not limited to, LiH2PO4. This application does not impose any particular restriction on the mass ratio of glucose to lithium manganese iron phosphate, as long as it achieves the purpose of this application. For example, the mass ratio of glucose to lithium manganese iron phosphate may be (0.1:1) to (0.25:1). This application does not impose any particular restriction on the solid content of the intermediate solution, as long as it achieves the purpose of this application. For example, the solid content of the intermediate solution may be 20wt% to 35wt%. In this application, the particle size in the first precursor solution or the second precursor solution can be controlled by adjusting the grinding time of the mixing and grinding. This application does not impose any particular restrictions on sintering temperature or sintering time, as long as the purpose of this application can be achieved. For example, the sintering temperature can be 600℃ to 800℃, and the sintering time can be 6h to 20h.

[0047] This application does not impose any particular limitations on the methods for controlling the ratio of the number N1 of primary lithium manganese iron phosphate particles with a particle size Φ1 satisfying 50 < Φ1 ≤ 100 to the total number N of primary lithium manganese iron phosphate particles, and the ratio of the number N2 of primary lithium manganese iron phosphate particles with a particle size Φ2 satisfying 100 < Φ2 ≤ 150 to the total number N of primary lithium manganese iron phosphate particles, as long as the purpose of this application can be achieved. For example, the ratio of the number N1 of primary lithium manganese iron phosphate particles with a particle size Φ1 satisfying 50 < Φ1 ≤ 100 to the total number N of primary lithium manganese iron phosphate particles, and the ratio of the number N2 of primary lithium manganese iron phosphate particles with a particle size Φ2 satisfying 100 < Φ2 ≤ 150 to the total number N of primary lithium manganese iron phosphate particles, can be controlled by adjusting the mass ratio of the first precursor solution and the second precursor solution.

[0048] This application does not impose any particular limitation on the method for controlling the ratio of the number N3 of primary lithium manganese iron phosphate particles with a particle size Φ3 satisfying Φ3≤50 to the total number N of primary lithium manganese iron phosphate particles, as long as the objective of this application can be achieved. For example, the ratio of the number N3 of primary lithium manganese iron phosphate particles with a particle size Φ3 satisfying Φ3≤50 to the total number N of primary lithium manganese iron phosphate particles can be controlled by adjusting the mass ratio of the first precursor solution, the second precursor solution, and the third precursor solution.

[0049] This application does not impose any particular limitation on the method for controlling the ratio of the number N4 of primary lithium manganese iron phosphate particles with a particle size Φ4 satisfying 150 < Φ4 ≤ 250 to the total number N of primary lithium manganese iron phosphate particles, as long as the objective of this application can be achieved. For example, the ratio of the number N4 of primary lithium manganese iron phosphate particles with a particle size Φ4 satisfying 150 < Φ4 ≤ 250 to the total number N of primary lithium manganese iron phosphate particles can be controlled by adjusting the mass ratio of the first precursor solution, the second precursor solution, the third precursor solution, and the fourth precursor solution.

[0050] This application does not impose any particular limitation on the method for controlling the ratio of the number N5 of primary lithium manganese iron phosphate particles with a particle size Φ5 satisfying 250 < Φ5 ≤ 350 to the total number N of primary lithium manganese iron phosphate particles, as long as the objective of this application can be achieved. For example, the ratio of the number N5 of primary lithium manganese iron phosphate particles with a particle size Φ5 satisfying 250 < Φ5 ≤ 350 to the total number N of primary lithium manganese iron phosphate particles can be controlled by adjusting the mass ratio of the mixture of the first precursor solution, the second precursor solution, the third precursor solution, the fourth precursor solution, and the fifth precursor solution.

[0051] This application does not impose any particular limitation on the method for controlling the ratio of the number N6 of primary lithium manganese iron phosphate particles with a particle size Φ6 satisfying 350 < Φ6 ≤ 500 to the total number N of primary lithium manganese iron phosphate particles, as long as the objective of this application can be achieved. For example, the ratio of the number N6 of primary lithium manganese iron phosphate particles with a particle size Φ6 satisfying 350 < Φ6 ≤ 500 to the total number N of primary lithium manganese iron phosphate particles can be controlled by adjusting the mass ratio of the mixture of the first precursor solution, the second precursor solution, the third precursor solution, the fourth precursor solution, the fifth precursor solution, and the sixth precursor solution.

[0052] This application does not impose any particular limitation on the method for adjusting the ratio of the number N7 of primary lithium manganese iron phosphate particles with a particle size Φ7 satisfying Φ7 > 500 to the total number N of primary lithium manganese iron phosphate particles, as long as the objective of this application can be achieved. For example, the ratio of the number N7 of primary lithium manganese iron phosphate particles with a particle size Φ7 satisfying Φ7 > 500 to the total number N of primary lithium manganese iron phosphate particles can be adjusted by controlling the mass ratio of the mixture of the first precursor solution, the second precursor solution, the third precursor solution, the fourth precursor solution, the fifth precursor solution, the sixth precursor solution, and the seventh precursor solution.

[0053] This application does not impose any particular limitation on the method for controlling the average particle size of lithium manganese iron phosphate, as long as it achieves the purpose of this application. For example, the average particle size of lithium manganese iron phosphate can be controlled by adjusting the mass ratio of the first precursor solution and the second precursor solution.

[0054] This application does not impose any particular limitation on the method for controlling the mass percentage of carbon in lithium manganese iron phosphate, as long as it achieves the purpose of this application. For example, the mass percentage of carbon in lithium manganese iron phosphate can be controlled by adjusting the mass ratio of glucose to lithium manganese iron phosphate.

[0055] In this application, it is understood that adding a dopant precursor to the reactants to prepare a cathode material including lithium manganese iron phosphate, wherein the lithium manganese iron phosphate contains a dopant element M. Exemplarily, the preparation method of the cathode material may include, but is not limited to, the following steps: adding a manganese source, an iron source, a lithium source, a phosphorus source, and the dopant precursor to water in a certain molar ratio, adding glucose to obtain an intermediate solution, mixing and grinding the intermediate solution to obtain particles with a particle size of [missing information]. The first precursor solution; manganese source, iron source, lithium source, phosphorus source, and dopant element precursor are added to water in a certain molar ratio, glucose is added to obtain an intermediate solution, the intermediate solution is mixed and ground to obtain particles with a particle size of The second precursor solution; the first precursor solution and the second precursor solution are mixed, then spray granulated, sintered, cooled, and pulverized by airflow to obtain the cathode material.

[0056] This application does not impose any particular limitation on the precursor of the doped element, as long as it can achieve the purpose of this application. For example, the precursor of the doped element may include, but is not limited to, oxides, hydroxides, or sulfates of the doped element. For example, oxides of the doped element may include, but are not limited to, MgO, TiO2, Nb2O5, V2O5, NiO, or CoO; hydroxides of the doped element may include, but are not limited to, Mg(OH)2; and sulfates of the doped element may include, but are not limited to, MgSO4 or CoSO4.

[0057] In this application, Dv50 represents the particle size that, measured from the smallest particle size, reaches 50% of the volumetric particle size in the particle size distribution of the material on a volumetric basis.

[0058] The second aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, which includes the positive electrode material in any of the foregoing embodiments. Therefore, applying the positive electrode sheet to a secondary battery can enable the secondary battery to have better processing performance, kinetic performance, and cycle performance. The aforementioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its own thickness direction, or it can be disposed on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or a part of the positive current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0059] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0060] The positive electrode material layer of this application also includes a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitations on the positive electrode conductive agent and positive electrode binder in the positive electrode material layer, as long as they can achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black. The aforementioned carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The positive electrode binder may include at least one of the following: polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, lithium polyacrylate, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0061] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be from 6 μm to 25 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer can be from 25 μm to 250 μm.

[0062] Optionally, the positive electrode may further include a conductive layer, which is located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned positive electrode conductive agents and positive electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0063] A third aspect of this application provides a secondary battery, which includes the positive electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by this application has better processing performance, kinetic performance, and cycle performance.

[0064] In this application, the secondary battery further includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0065] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors.

[0066] The negative electrode material layer of this application includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO₂, etc. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 The negative electrode material layer of this application includes at least one of the following: Li-Al alloy or metallic lithium. The negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. This application does not impose any particular limitation on the negative electrode binder and negative electrode conductive agent in the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the negative electrode binder can be at least one of the aforementioned positive electrode binders, and the negative electrode conductive agent can be at least one of the aforementioned positive electrode conductive agents. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application can be achieved.

[0067] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 20 μm. This application also does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the single-sided negative electrode material layer can be from 30 μm to 250 μm.

[0068] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and they can be at least one of the aforementioned negative electrode conductive agents and negative electrode binders. This application does not impose any particular limitation on the mass ratio of the conductive agent and binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0069] In this application, the secondary battery also includes an electrolyte. The electrolyte includes a lithium salt. This application does not particularly limit the type of lithium salt; lithium salts known in the art can be used. Exemplarily, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). This application does not particularly limit the mass percentage of lithium salt in the electrolyte, as long as the purpose of this application is achieved. The electrolyte also includes a non-aqueous organic solvent. This application does not particularly limit the non-aqueous organic solvent, as long as the purpose of this application is achieved. For example, the non-aqueous organic solvent may contain at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of 1,3-propanesulfonyl lactone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters.This application does not impose any particular limitation on the mass percentage of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application can be achieved.

[0070] In this application, the secondary battery also includes a separator. The separator is used to separate the positive electrode and the negative electrode, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0071] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a diaphragm binder. This application does not particularly limit the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the aforementioned diaphragm binder, and may include at least one of the aforementioned negative electrode binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0072] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0073] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

[0074] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and pre-lithiated negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and pre-lithiated negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0075] A fourth aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has better processing performance, kinetic performance, and cycle performance.

[0076] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0077] Example

[0078] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0079] Test methods and equipment:

[0080] Scanning electron microscopy test:

[0081] The cathode material was characterized using a Philips XL-30 field emission scanning electron microscope (SEM). The test conditions were: accelerating voltage of 10 kV, grating of 10 spots, working distance of 10 mm, and magnification of 10,000. The resulting SEM images of the cathode material were obtained. In the scanning electron microscope images of the cathode material at a magnification of 10000x and within a range of 10μm×8μm, the cathode material with a total number of primary particles of N was selected. The number of primary particles N1 of the cathode material with a particle size Φ1 satisfying 50<Φ1≤100 was counted, the number of primary particles N2 of the cathode material with a particle size Φ2 satisfying 100<Φ2≤150 was counted, the number of primary particles N3 of the cathode material with a particle size Φ3 satisfying Φ3≤50 was counted, the number of primary particles N4 of the cathode material with a particle size Φ4 satisfying 150<Φ4≤250 was counted, the number of primary particles N5 of the cathode material with a particle size Φ5 satisfying 250<Φ5≤350 was counted, the number of primary particles N6 of the cathode material with a particle size Φ6 satisfying 350<Φ6≤500 was counted, and the number of primary particles N7 of the cathode material with a particle size Φ7>500 was counted.

[0082] The method for calculating the average particle size of cathode materials is as follows: In a scanning electron microscope image of cathode materials with a magnification of 10000x and a range of 10μm×8μm, select cathode materials with a total number of N particles. The sum of the particle sizes of N cathode materials divided by N is the average particle size of the cathode material.

[0083] Carbon element mass percentage test:

[0084] For cathode material powder, the mass percentage of carbon in the cathode material powder is directly tested using a carbon-sulfur analyzer (model DK-606).

[0085] For the prepared positive electrode sheet or the positive electrode sheet removed from the lithium-ion battery, the electrode sheet of the coated area is cut into sheets, ultrasonically vibrated in an N-methylpyrrolidone (NMP) bath at 100℃ for 48 hours, the current collector is removed, the remaining material is ground for 1 hour, washed and filtered 3 times to remove the gel, and the remaining solid material is dried at 100℃ for 8 hours. The resulting powder is then tested for the mass percentage of carbon element using a carbon-sulfur analyzer (model DK-606).

[0086] Specific surface area test:

[0087] According to the national standard "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), the specific surface area of ​​the cathode material was tested by nitrogen adsorption using a specific surface area analyzer (model TristarⅡ3020M).

[0088] Powder resistivity test:

[0089] The resistivity of the cathode material powder was tested using a resistivity meter (Suzhou Jingge Electronics, model ST-2255A). 5g of cathode material powder was taken and pressed into a sheet using an electronic press. The press maintained a constant pressure of 5000kg for 20s to obtain a cathode material sample. The sample was then placed between the electrodes of the resistivity meter for testing, and the resistance r was measured. The resistance was then calculated using the following formula:

[0090] ρ = r × s / l;

[0091] Where ρ is the powder resistivity; r is the measured resistance of the cathode material sample (in Ω); l is the measured thickness of the cathode material sample (in cm); and s is the bottom area of ​​the cathode material sample (in cm²). 2 ).

[0092] Cathode material compaction density test:

[0093] Weigh 1.0g of the positive electrode material sample and place it in the test mold (CARVER#3619 (13mm)). Then place the positive electrode material sample in the test equipment, which is Sansi Zongheng UTM7305. The test pressure is 3T, the pressurization displacement rate is 10mm / min, the pressurization holding time is 30s, the depressurization displacement rate is 30mm / min, and the depressurization holding time is 10s.

[0094] The formula for calculating compaction density is: Compaction density = Sample mass / (Sample stress area × Sample thickness).

[0095] DC Impedance (DCR) Test:

[0096] At 25℃, the lithium-ion battery is charged to 4.3V at a constant current of 0.1C, then charged to 0.025C at a constant voltage of 4.3V, and left to stand for 10 minutes. Then it is discharged at a constant current of 0.1C for 5 hours (at which point the lithium-ion battery is at 50% state of charge). Then it is discharged at a constant current of 1C for 1 second. The voltage before the 1C constant current discharge is V0, the voltage after the 1C constant current discharge is V1, and the current of the 1C constant current discharge is A. Calculate the DC impedance R corresponding to the 50% state of charge (SOC) of the lithium-ion battery as (V0-V1) / A.

[0097] The lower the DC impedance at 50% state of charge (SOC) of a lithium-ion battery, the better its dynamic performance.

[0098] Low-temperature discharge performance test:

[0099] At 25°C, the lithium-ion battery was charged at a constant current of 0.3C to 4.3V, then charged at a constant voltage of 4.3V to 0.025C, left to stand for 10 minutes, and then discharged at a constant current of 0.3C to 2.5V. The discharge capacity was recorded as C0. Then, the lithium-ion battery was charged at a constant current of 0.3C to 4.3V, then charged at a constant voltage of 4.3V to 0.025C. After that, the lithium-ion battery was placed in a -20°C constant temperature chamber for 4 hours, and then discharged at a constant current of 0.3C to 2.5V. The discharge capacity was recorded as C1.

[0100] -20℃ capacity retention rate (%) = C1 / C0 × 100%.

[0101] Cyclic performance test:

[0102] The lithium-ion battery was subjected to its first charge and discharge cycle at 45℃. The specific steps were as follows: the lithium-ion battery was charged at a constant current of 0.5C to 4.3V, then charged at a constant voltage of 4.3V to 0.025C, allowed to stand for 10 minutes, and then discharged at a constant current of 0.5C to 2.5V. The discharge capacity of the lithium-ion battery was measured as C2. The ratio of discharge energy to discharge capacity during the above discharge process was the initial equalization voltage. This constituted one charge-discharge cycle. The above steps were repeated for 500 charge-discharge cycles (cls). The discharge capacity of the lithium-ion battery in the 500th cycle was measured as C3. The ratio of discharge energy to discharge capacity during the 500th discharge cycle was the equalization voltage of the 500th cycle. The equalization voltage drop = equalization voltage of the 500th cycle - initial equalization voltage. The unit of discharge energy is mWh, and the unit of discharge capacity is Ah.

[0103] 500-cycle capacity retention rate (%) = C3 / C2 × 100%.

[0104] A higher capacity retention rate and a smaller average voltage drop after 500 cycles indicate better stability of the cathode material and better cycle performance of the lithium-ion battery.

[0105] Example 1-1

[0106] <Preparation of cathode materials>

[0107] The Li source was designed using manganese Mn3O4, iron FePO4, lithium Li2CO3, phosphorus LiH2PO4, and MgO in the molar ratio corresponding to this example. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The first precursor solution is 300 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used in the molar ratio corresponding to this example to design Li… 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The second precursor solution is at 350 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used in the molar ratio corresponding to this example to design Li… 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The fourth precursor solution is at 500 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used in the molar ratio corresponding to this example to design Li… 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The fifth precursor solution was prepared at 800 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO were used to design Li in the molar ratio corresponding to this example. 1.05 Mn 0.5 Fe 0.49Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The sixth precursor solution has a wavelength of 1000 nm. The first, second, fourth, fifth, and sixth precursor solutions were mixed at a mass ratio of 1.53:8.52:39.54:39.25:11.16, then spray-granulated and sintered under a nitrogen atmosphere at 700℃ for 8 hours. After cooling, the mixture was pulverized using an air jet mill to obtain the cathode material. The cathode material includes lithium manganese iron phosphate, whose chemical formula is Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 PO4. The precursor for Mg doping is MgO.

[0108] <Preparation of the positive electrode>

[0109] The above-mentioned positive electrode material, positive electrode conductive agent Super P, and positive electrode binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.7:0.8:2.5. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 60 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The sheet was dried under vacuum at 90°C for 1 hour, and then cold-pressed, cut, and slit to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm. The coating weight of the positive electrode material layer was 180 g / m², and the compaction density during the cold pressing process was 2.3 g / cm³. 3 .

[0110] <Preparation of Negative Electrode Sheets>

[0111] Artificial graphite (negative electrode active material), Super P (negative electrode conductive agent), and lithium polyacrylate (PAA-Li) (negative electrode binder) were mixed in a weight ratio of 97.3:1.5:1.2. Deionized water was added as a solvent, and the mixture was stirred until homogeneous to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector and dried at 110 °C to obtain a negative electrode sheet with a single-sided coating of negative electrode material. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. The sheet was dried under vacuum at 110 °C for 1 hour, and then cold-pressed, cut, and slit to obtain a negative electrode sheet with a size of 78 mm × 875 mm. The particle size Dv50 of the artificial graphite (negative electrode active material) was 14 μm; the coating weight of the negative electrode material layer was 84 g / m²; and the compaction density during the cold pressing process was 1.6 g / cm³. 3 .

[0112] <Preparation of Electrolyte>

[0113] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a mass ratio of EC:EMC:DEC = 30:50:20 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, with the remainder being the base solvent.

[0114] <Preparation of the diaphragm>

[0115] A diaphragm binder PVDF and inorganic granular alumina were mixed at a mass ratio of 1:2, and NMP was added as a solvent to prepare an inorganic layer slurry with a solid content of 12 wt%. The mixture was stirred until homogeneous and then uniformly coated onto one surface of a 15 μm thick polyethylene substrate. The substrate was then dried at 85°C for 4 hours to obtain a diaphragm with a single-sided inorganic layer coating thickness of 3 μm. Next, PVDF was added to NMP solvent and stirred until homogeneous, preparing a polymer layer slurry with a solid content of 25 wt%. This polymer layer slurry was then uniformly coated onto the surface of the inorganic layer, with a coating weight of 1.5 mg / 1540.25 mm². 2 Then, it is dried at 85℃ for 4 hours. Finally, a polymer layer slurry is uniformly coated on the other surface of the polyethylene substrate. The coating weight of the polymer layer slurry is 1.5 mg / 1540.25 mm. 2 Then, it is dried at 85°C for 4 hours to obtain a diaphragm with an inorganic layer and a polymer layer on one side and only a polymer layer on the other side.

[0116] <Preparation of Lithium-ion Batteries>

[0117] The positive electrode, separator, negative electrode, and separator prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a separator. The electrode assembly is then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. Electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation (charged at a constant current of 0.02C to 3.3V, then charged at a constant current of 0.3C to 4.3V), degassing, edge trimming, and capacity processing to obtain the lithium-ion battery.

[0118] Examples 1-2

[0119] Except for the preparation of the cathode material according to the following method, the rest is the same as in Example 1-1.

[0120] <Preparation of cathode materials>

[0121] The Li source was designed using manganese Mn3O4, iron FePO4, lithium Li2CO3, phosphorus LiH2PO4, and MgO in the molar ratio corresponding to this example. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The first precursor solution is 300 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used in the molar ratio corresponding to this example to design Li… 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The second precursor solution is at 350 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used in the molar ratio corresponding to this example to design Li… 1.05 Mn 0.5 Fe 0.49 Mg0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The third precursor solution is at 250 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used to design Li in the molar ratio corresponding to this example. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The fourth precursor solution is at 500 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used in the molar ratio corresponding to this example to design Li… 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The fifth precursor solution was prepared at 800 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO were used to design Li in the molar ratio corresponding to this example. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The sixth precursor solution is at 1000 nm. Manganese source Mn3O4, iron source FePO4, lithium source Li2CO3, phosphorus source LiH2PO4, and MgO are used to design Li in the molar ratio corresponding to this example. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 The molar ratio of PO4 to water is added, then glucose is added, and glucose reacts with Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 A PO4 mass ratio of 0.16:1 was used to obtain an intermediate solution with a solid content of 30 wt%. The intermediate solution was then mixed and ground to obtain the particle size distribution. The seventh precursor solution has a wavelength of 1500 nm. The first, second, third, fourth, fifth, sixth, and seventh precursor solutions were mixed in a mass ratio of 0.24:1.66:0.01:18.10:22.91:21.72:35.36, then spray-granulated and sintered under a nitrogen atmosphere at 700℃ for 8 hours. After cooling, the cathode material was obtained by air jet milling. The cathode material includes lithium manganese iron phosphate, whose chemical formula is Li. 1.05 Mn 0.5 Fe 0.49 Mg 0.01 PO4. The precursor for Mg doping is MgO.

[0122] Examples 1-3

[0123] Except for adjusting the mass ratio of the first, second, third, fourth, fifth, sixth, and seventh precursor solutions to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, N6 / N, and N7 / N as shown in Table 1, the rest is the same as in Examples 1-2.

[0124] Examples 1-4 to Examples 1-8

[0125] Except for adjusting the mass ratio of the first precursor solution, second precursor solution, third precursor solution, fourth precursor solution, fifth precursor solution, and sixth precursor solution to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, and N6 / N as shown in Table 1, the rest is the same as in Example 1-1.

[0126] Examples 1-9 to Examples 1-11

[0127] Except for adjusting the mass ratio of the first, second, third, fourth, fifth, sixth, and seventh precursor solutions to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, N6 / N, and N7 / N as shown in Table 1, the rest is the same as in Examples 1-2.

[0128] Examples 1-12 to Examples 1-17

[0129] Except for adjusting the mass ratio of the first precursor solution, second precursor solution, third precursor solution, fourth precursor solution, fifth precursor solution, and sixth precursor solution to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, and N6 / N as shown in Table 1, the rest is the same as in Example 1-1.

[0130] Examples 1-18 to Examples 1-20

[0131] Except for adjusting the mass ratio of the first, second, third, fourth, fifth, sixth, and seventh precursor solutions to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, N6 / N, and N7 / N as shown in Table 1, the rest is the same as in Examples 1-2.

[0132] Examples 1-21

[0133] Except for adjusting the mass ratio of the first precursor solution, second precursor solution, third precursor solution, fourth precursor solution, fifth precursor solution, and sixth precursor solution to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, and N6 / N as shown in Table 1, the rest is the same as in Example 1-1.

[0134] Examples 1-22

[0135] Except for adjusting the mass ratio of the first, second, third, fourth, fifth, sixth, and seventh precursor solutions to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, N6 / N, and N7 / N as shown in Table 1, the rest is the same as in Examples 1-2.

[0136] Examples 2-1 to 2-6

[0137] Except for adjusting the mass ratio of glucose to lithium manganese iron phosphate to achieve the mass percentage of carbon in lithium manganese iron phosphate as shown in Table 3, the rest is the same as in Examples 1-1.

[0138] Examples 2-7 to 2-8

[0139] Except for the fact that no doped precursor is added in the <Preparation of Cathode Material> and the chemical formula of lithium manganese iron phosphate is as shown in Table 3 by adjusting the molar ratio of manganese source, iron source, lithium source and phosphorus source, the rest is the same as in Example 1-1.

[0140] Examples 2-9

[0141] Except for the fact that the chemical formula of lithium manganese iron phosphate is obtained by adjusting the molar ratio of manganese source, iron source, lithium source, phosphorus source and MgO in the <Preparation of Cathode Material>, as shown in Table 3, the rest is the same as in Example 1-1.

[0142] Example 2-10

[0143] Except for the use of TiO2 as the precursor for doping elements in the <Preparation of Cathode Materials> and the adjustment of the molar ratio of manganese source, iron source, lithium source, phosphorus source and precursor for doping elements to make the chemical formula of lithium manganese iron phosphate as shown in Table 3, the rest is the same as in Example 1-1.

[0144] Example 2-11

[0145] Except for the use of Nb2O5 as the dopant precursor in the <Preparation of Cathode Material> and the adjustment of the molar ratio of manganese source, iron source, lithium source, phosphorus source and dopant precursor to make the chemical formula of lithium manganese iron phosphate as shown in Table 3, the rest is the same as in Example 1-1.

[0146] Comparative Examples 1 to 4

[0147] Except for adjusting the mass ratio of the first, second, third, fourth, fifth, sixth, and seventh precursor solutions to achieve N1 / N, N2 / N, N3 / N, N4 / N, N5 / N, N6 / N, and N7 / N as shown in Table 1, the rest is the same as in Example 1-1.

[0148] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0149] Table 2

[0150] Note: (1) In Table 2, in Comparative Example 2, “DC impedance R corresponding to 50% state of charge (SOC) of lithium-ion battery” is “cannot be processed”, “-20℃ capacity retention rate” is “cannot be processed”, “500-cycle capacity retention rate” is “cannot be processed”, and “equal voltage drop” is “cannot be processed”, indicating that lithium-ion batteries cannot be processed and lithium-ion batteries have no corresponding performance.

[0151] As can be seen from Examples 1-1 to 1-22 and Comparative Examples 1 to 4, when the cathode material includes lithium manganese iron phosphate, and the ratio of the number N1 of primary lithium manganese iron phosphate particles with a particle size Φ1 satisfying 50 < Φ1 ≤ 100 to the total number N of primary lithium manganese iron phosphate particles, and the ratio of the number N2 of primary lithium manganese iron phosphate particles with a particle size Φ2 satisfying 100 < Φ2 ≤ 150 to the total number N of primary lithium manganese iron phosphate particles are within the scope of this application, the cathode material has a high compaction density, and the prepared lithium-ion battery has a low DC resistance, a high capacity retention rate at -20℃, a high capacity retention rate after 500 cycles, and a low voltage drop, indicating that the processing performance, kinetic performance, and cycle performance of the cathode material can be improved. In Comparative Examples 1 to 4, the ratio of the number N1 of primary lithium manganese iron phosphate particles with a particle size Φ1 satisfying 50 < Φ1 ≤ 100 to the total number N of primary lithium manganese iron phosphate particles, and / or the ratio of the number N2 of primary lithium manganese iron phosphate particles with a particle size Φ2 satisfying 100 < Φ2 ≤ 150 to the total number N of primary lithium manganese iron phosphate particles, is not within the scope of this application. The cathode material has a low compaction density, and the prepared lithium-ion battery has a high DC resistance, a low capacity retention rate at -20℃, a low capacity retention rate after 500 cycles, and a high average voltage drop, indicating that the cathode material has poor processing performance, kinetic performance, and cycle performance.

[0152] The average particle size of lithium manganese iron phosphate typically affects the kinetic and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-22, the lithium-ion batteries prepared with an average particle size of lithium manganese iron phosphate within the scope of this application exhibit lower DC resistance, higher capacity retention at -20°C, higher capacity retention after 500 cycles, and lower voltage drop, indicating that the processing performance, kinetic performance, and cycle performance of the cathode material can be improved.

[0153] The specific surface area of ​​lithium manganese iron phosphate typically affects the kinetic and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-22, the lithium-ion batteries prepared with lithium manganese iron phosphate within the scope of this application exhibit lower DC resistance, higher capacity retention at -20°C, higher capacity retention after 500 cycles, and lower voltage drop, indicating that it can improve the processing performance, kinetic performance, and cycle performance of the cathode material.

[0154] The resistivity of lithium manganese iron phosphate powder typically affects the kinetic and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-22, the lithium-ion batteries prepared with lithium manganese iron phosphate powder resistivity within the scope of this application exhibit lower DC impedance, higher capacity retention at -20°C, higher capacity retention after 500 cycles, and lower voltage drop, indicating that it can improve the processing performance, kinetic performance, and cycle performance of the cathode material.

[0155] As can be seen from Figure 1, the morphology of the cathode material in Example 1-1 is granular.

[0156] Table 3

[0157] The mass percentage of carbon in lithium manganese iron phosphate typically affects the kinetic and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-6, the lithium-ion batteries prepared with a carbon mass percentage within the scope of this application exhibit lower DC impedance, higher capacity retention at -20°C, higher capacity retention after 500 cycles, and lower voltage drop, indicating that the processing performance, kinetic performance, and cycle performance of the cathode material can be improved.

[0158] As can be seen from Examples 1-1, 2-7 to 2-11, the lithium-ion battery prepared with the chemical formula of lithium manganese iron phosphate within the scope of this application has lower DC impedance, higher capacity retention at -20°C, higher capacity retention after 500 cycles, and lower average voltage drop, indicating that it can improve the processing performance, kinetic performance and cycle performance of the cathode material.

[0159] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0160] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0161] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A cathode material, said cathode material comprising lithium manganese iron phosphate, characterized in that, In the scanning electron microscope image of the lithium manganese iron phosphate at a magnification of 10000x and within the range of 10μm×8μm, the total number of primary particles of the lithium manganese iron phosphate is N, the number of primary particles of the lithium manganese iron phosphate with a particle size of Φ1nm is N1, the number of primary particles of the lithium manganese iron phosphate with a particle size of Φ2nm is N2, and N≥200. 50<Φ1≤100,10%≤N1 / N≤30%; 100<Φ2≤150, 15%≤N2 / N≤35%.

2. The cathode material according to claim 1, characterized in that, The number of primary particles of the lithium manganese iron phosphate with a particle size of Φ3nm is N3, where Φ3≤50 and 0≤N3 / N≤10%.

3. The cathode material according to claim 1, characterized in that, The number of primary particles of the lithium manganese iron phosphate with a particle size of Φ4nm is N4, 150<Φ4≤250, 20%≤N4 / N≤40%.

4. The cathode material according to claim 1, characterized in that, The number of primary particles of the lithium manganese iron phosphate with a particle size of Φ5nm is N5, where 250 < Φ5 ≤ 350, and 5% ≤ N5 / N ≤ 15%.

5. The positive electrode material according to claim 1, characterized in that, The number of primary particles of the lithium manganese iron phosphate with a particle size of Φ6nm is N6, 350<Φ6≤500, 1%≤N6 / N≤5%.

6. The cathode material according to claim 1, characterized in that, The number of primary particles of the lithium manganese iron phosphate with a particle size of Φ7nm is N7, where Φ7>500 and 0≤N7 / N≤5%.

7. The cathode material according to any one of claims 1 to 6, characterized in that, The average particle size of the lithium manganese iron phosphate is D nm, where 50 ≤ D ≤ 200.

8. The positive electrode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) Based on the mass of the lithium manganese iron phosphate, the mass percentage of carbon in the lithium manganese iron phosphate is Wc%, 1.0≤Wc≤2.5; (2) The specific surface area of ​​the lithium manganese iron phosphate is SSA m. 2 / g, 12≤SSA≤35; (3) The resistivity of the lithium manganese iron phosphate powder is ρΩ·cm, 10≤ρ≤300.

9. The positive electrode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) Based on the mass of the lithium manganese iron phosphate, the mass percentage of carbon in the lithium manganese iron phosphate is Wc%, 1.3≤Wc≤2.0; (2) The specific surface area of ​​the lithium manganese iron phosphate is SSA m. 2 / g, 14≤SSA≤20; (3) The resistivity of the lithium manganese iron phosphate powder is ρΩ·cm, 10≤ρ≤100.

10. The cathode material according to claim 1, characterized in that, Based on the mass of the lithium manganese iron phosphate, the mass percentage of carbon in the lithium manganese iron phosphate is Wc%, 1.5≤Wc≤1.

8.

11. The cathode material according to claim 1, characterized in that, The chemical formula of the lithium manganese iron phosphate is Li x Mn y Fe 1-y-z M z PO4, 1.0≤x≤1.1, 0.5≤y≤0.8, 0≤z≤0.02, M includes at least one of Mg, Ti, Nb, V, Ni or Co.

12. A positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer comprising the positive electrode material according to any one of claims 1 to 11.

13. A secondary battery, the secondary battery comprising the positive electrode sheet as described in claim 12.

14. An electronic device comprising the secondary battery of claim 13.

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