Positive electrode material, secondary battery, and electric device

Abstract

Disclosed in the present application are a positive electrode material, a secondary battery, and an electric device. The positive electrode material exhibits a non-uniform distribution of manganese and iron, which can promote the transformation of a metastable phase thereof into a more stable crystal structure, thereby avoiding Mn dissolution during the cycle process and effectively prolonging the cycle life of a battery. Moreover, the non-uniform particle size distribution of the positive electrode material, in cooperation with large and small particles, can effectively increase the compaction density and the reactive specific surface area of the positive electrode, thereby improving the capacity and charge-discharge rate.

Description

Positive electrode materials, secondary batteries and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese invention patent application CN202411850811.0, filed on December 13, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a positive electrode material, a secondary battery, and an electrical device. Background Technology

[0004] The cathode material of a secondary battery is a key factor determining its performance. Currently, traditional cathode materials (such as LiFePO4) have low theoretical capacity and poor conductivity, affecting the fast-charge cycle life of secondary batteries. Therefore, developing cathode materials with higher cycle performance has become an urgent technical challenge.

[0005] In recent years, researchers have effectively increased the charge / discharge plateau voltage (e.g., from 3.4V to 4.1V) by replacing some of the iron in lithium iron phosphate with manganese, resulting in lithium manganese iron phosphate cathodes. This allows lithium manganese iron phosphate cathode materials to combine the high safety and low cost of lithium iron phosphate with the high power of ternary materials. The resurgence of low-cost lithium iron phosphate cathodes has spurred research into the application of lithium manganese iron phosphate materials, which are considered to have the potential to replace lithium iron phosphate cathodes as the next generation of cathode materials for large-scale applications, possessing a broad market prospect. Summary of the Invention

[0006] This application provides a positive electrode material, a secondary battery, and an electrical device, wherein the positive electrode material has excellent cycle stability.

[0007] The first aspect of this application provides a cathode material, including lithium iron manganese oxide;

[0008] The positive electrode material satisfies: 0.5 ≤ μ, σ 2 ≥0.05;

[0009] Where μ is the expected value of the normal distribution curve of the manganese-iron ratio in the cathode material;

[0010] σ 2 denoted as the variance of the normal distribution curve of the manganese-iron ratio in the cathode material.

[0011] In some embodiments, the average manganese-iron ratio of the cathode material is 0.25 to 4.

[0012] In some embodiments, the particle size distribution curve of the cathode material includes a first peak and a second peak; the first peak is located between 100 and 300 nm, and the second peak is located between 300 and 800 nm.

[0013] In some implementations, the peak area of ​​the first peak is S1, and the peak area of ​​the second peak is S2, satisfying: 1≤S1 / S2≤4.

[0014] In some implementations, 0.5 ≤ S1 / (S1+S2) ≤ 0.8.

[0015] In some implementations, 0.2 ≤ S2 / (S1+S2) ≤ 0.5.

[0016] In some implementations, 0.9 ≤ μ ≤ 2.

[0017] In some implementations, 1.1 ≤ μ ≤ 1.5.

[0018] In some implementations, 0.05 ≤ σ 2 ≤0.2.

[0019] In some implementations, 0.1 ≤ σ 2 ≤0.15.

[0020] In some implementations, the first peak is located between 240 and 270 nm, and the second peak is located between 420 and 440 nm.

[0021] In some implementations, 1.2 ≤ S1 / S2 ≤ 1.5.

[0022] In some embodiments, a coating layer disposed on the outer surface of the lithium iron manganese oxide is also included, the coating layer comprising at least one of a carbon-based material, a metal oxide, and an ionic conductor.

[0023] In some embodiments, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon;

[0024] In some embodiments, the metal oxide includes at least one of aluminum oxide, magnesium oxide, titanium dioxide, lanthanum oxide, zirconium dioxide, antimony trioxide, antimony pentoxide, vanadium trioxide, and zinc oxide.

[0025] In some embodiments, the ion conductor includes at least one of LLZO, LLTO, LATP, sulfide solid electrolytes, and polymer ion conductors;

[0026] In some embodiments, the thickness of the coating layer is 1–100 nm;

[0027] In some embodiments, the mass of the coating layer accounts for 0.5-5% of the total mass of the positive electrode material.

[0028] In some embodiments, the lithium manganese iron oxide includes a compound with the molecular formula Li x Mn y Fe 1-y M z PO4, where 0.9 ≤ x ≤ 1.1, 0 < y < 1, 0 ≤ z ≤ 0.05, and M includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr.

[0029] The second aspect of the present application provides a secondary battery, including a positive electrode plate, and the positive electrode plate contains the positive electrode material described above.

[0030] The third aspect of the present application provides an electrical device, including the secondary battery described above.

[0031] The beneficial effect of the present application is that in the positive electrode material of the present application, the manganese and iron elements show a non-uniform distribution, which can promote the transformation of its metastable phase into a more stable crystal structure, avoid the dissolution of Mn during cycling, and at the same time avoid the separation of Mn and Fe elements. Furthermore, it effectively avoids the transformation of Mn and Fe into relatively aggregated two phases, effectively improves the reaction active specific surface of the positive electrode material, and improves the cycle life of the secondary battery. Description of the Drawings

[0032] Figure 1 is a particle size distribution curve graph of Example 1 and Comparative Example 1.

[0033] Figure 2 is a graph of the distribution and variance of manganese and iron elements and the ratio of manganese and iron elements in Example 1.

[0034] Figure 3 is a graph of the distribution and variance of manganese and iron elements and the ratio of manganese and iron elements in Comparative Example 1. Specific Embodiments

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0036] In the present application, for the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, as well as an open technical solution including the listed features.

[0037] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0038] The inventors of this application have discovered that structural stability needs to be considered when designing lithium manganese iron phosphate cathodes. During cycling, the metastable phase leads to the dissolution of Mn, which reduces cycle life. Due to the inconsistency in the kinetics of the Fe and Mn plateaus during charge and discharge, after long-term cycling, the initially uniformly distributed Mn and Fe elements will gradually separate and transform into two relatively aggregated phases, thus resulting in a decrease in cycle life.

[0039] Therefore, embodiments of this application provide a cathode material, including lithium iron manganese oxide;

[0040] The positive electrode material satisfies: 0.5 ≤ μ, σ 2 ≥0.05;

[0041] Where μ is the expected value of the normal distribution curve of the manganese-iron ratio in the cathode material;

[0042] σ 2 denoted as the variance of the normal distribution curve of the manganese-iron ratio in the cathode material.

[0043] The inventors of this application have discovered that when μ and σ in the normal distribution curve of the manganese-iron ratio in the cathode material... 2 When the value meets the above range, the manganese and iron elements in the cathode material exhibit a non-uniform distribution. This non-uniform distribution of manganese and iron elements can promote the transformation of the metastable phase into a stable crystal structure, avoid Mn dissolution during cycling, and prevent the separation of Mn and Fe elements. This effectively prevents Mn and Fe from transforming into two relatively aggregated phases, effectively improving the reactive surface area of ​​the cathode material and increasing the cycle life of the secondary battery.

[0044] The manganese-iron ratio mentioned in this application refers to the molar ratio.

[0045] The method for obtaining the normal distribution curve of the manganese-iron element ratio described in this application is as follows: the horizontal axis of the manganese-iron element distribution intensity curve of the cathode material is divided into n parts, the manganese-iron element ratio of each point is calculated, and a normal distribution curve of the manganese-iron element ratio is constructed for the values ​​of the manganese-iron element ratio of the n points, where n is a positive integer ≥ 4.

[0046] In some implementations, taking n=16 as an example, the abscissa of the manganese-iron element distribution intensity curve of the positive electrode material is divided into 16 parts. The manganese-iron element ratio corresponding to the abscissa of each point is calculated. A normal distribution curve of the manganese-iron element ratio is constructed for the values ​​of the manganese-iron element ratio at the 16 points, thereby obtaining μ (expected value) and σ. 2 Value (variance).

[0047] The manganese-iron element distribution intensity curve mentioned in this application can be obtained using conventional techniques in the art. The following is an exemplary method for obtaining the manganese-iron element distribution intensity curve: The target cathode material is scanned and collected using the EDS energy dispersive spectroscopy of an EDS elemental distribution analyzer to obtain the Mn / Fe element distribution map. This map is then converted to a grayscale (e.g., 8-bit grayscale value) mode using image processing software, and subsequently (e.g., using contour graphics functions) converted into a manganese-iron element distribution intensity curve.

[0048] For example, the image processing software could be ImageJ.

[0049] In some implementations, 0.5 ≤ μ ≤ 2. In some implementations, 0.9 ≤ μ ≤ 2, for example, it can be 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or a range of any two of these values.

[0050] In some of these implementations, 1.1 ≤ μ ≤ 1.5.

[0051] In some implementations, 0.05 ≤ σ 2 ≤0.2, for example, can be 0.05, 0.06, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, or a range of any two values ​​therein. When the σ in the normal distribution curve of the manganese-iron ratio in the cathode material... 2 When the values ​​meet the above range, the manganese and iron elements in the cathode material exhibit a non-uniform distribution, which can promote the transformation of the metastable phase into a stable crystal structure, avoid Mn dissolution during cycling, and prevent the separation of Mn and Fe elements. This effectively prevents Mn and Fe from transforming into two relatively aggregated phases, effectively improving the reactive surface area of ​​the cathode material and increasing the cycle life of the secondary battery.

[0052] In some implementations, 0.1 ≤ σ 2 ≤0.15. When the σ value in the normal distribution curve of the manganese-iron ratio in the cathode material is... 2 When the value meets the above range, the impedance can be further reduced, and the cycle performance of the secondary battery can be improved.

[0053] In some embodiments, the average manganese-iron ratio of the cathode material is 0.25 to 4, for example, it can be a range of 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.1, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.2, 3.4, 3.5, 3.6, 3.8, 4 or any two of these values. By controlling the average manganese-iron ratio of the cathode material within this range, it is possible to further promote the transformation of the metastable phase into a stable crystal structure, avoid Mn dissolution during cycling, improve the structural stability of the cathode material, reduce the attenuation caused by volume expansion and contraction during cycling, improve the conductivity of the cathode material, avoid the structural damage of the cathode material during charging and discharging, and effectively improve the cycle performance of the secondary battery.

[0054] In some embodiments, the average manganese-iron ratio of the cathode material is 1 to 2.

[0055] In some embodiments, the particle size distribution curve of the cathode material includes a first peak and a second peak; the first peak is located between 100 and 300 nm, for example, it can be 100 nm, 120 nm, 140 nm, 150 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 250 nm, 260 nm, 280 nm, 300 nm or any two of these values.

[0056] In some embodiments, the second peak is located between 300 and 800 nm, for example, it can be a range of 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, 520 nm, 550 nm, 580 nm, 600 nm, 620 nm, 650 nm, 680 nm, 700 nm, 720 nm, 750 nm, 780 nm, 800 nm or any two of these values.

[0057] In some implementations, the first peak is located between 240 and 270 nm, and / or the second peak is located between 420 and 440 nm.

[0058] It should be noted that the position of a peak refers to the x-coordinate value (i.e., particle size) of the highest point (maximum point) corresponding to the peak. The ordinal numbers "first" and "second" on the particle size distribution curve described herein are used only to distinguish different particle size intervals and do not impose any restrictions on the order of appearance, relative importance, or number of peaks. In addition to the first and second peaks, the particle size distribution curve of the cathode material may also include one or more other peaks. In some embodiments, the "first peak" or "second peak" itself may be a peak cluster composed of multiple adjacent or closely located sub-peaks. In this case, the peak positions of all sub-peaks are located within the aforementioned specific interval, and their peak area refers to the sum of the peak areas of the entire peak cluster.

[0059] The particle size distribution curve of the cathode material described in this application contains at least two peaks. The cathode material has a wide and uneven particle size distribution range, which can reduce porosity, increase the compaction density of the cathode sheet, improve the stability of the cathode material during the pressing process, and effectively improve the cycle performance of the secondary battery. At the same time, it is beneficial to increase the specific surface area of ​​the cathode material, increase the contact area with the conductive agent and electrolyte, effectively improve the conductivity of the cathode sheet, increase the reactive specific surface area of ​​the cathode, and improve the ohmic internal resistance (Rs) and electrochemical transfer internal resistance (Rct). The reduction of Rs and Rct can effectively increase the output power of the battery, and at the same time, it can widen the current boundary during fast charging, effectively improving the cycle performance of the secondary battery.

[0060] In this application, the particle size distribution curve can be obtained by laser diffraction testing; typically, the particle size distribution curve is plotted with particle size on the horizontal axis; exemplarily, the percentage content is plotted on the vertical axis; after plotting the corresponding points according to the percentage content of each particle size, the points of the percentage content of each particle size form a smooth frequency curve with undulating waves.

[0061] In some embodiments, the particle size distribution curve is obtained by laser diffraction of particle size distribution according to GB / T 19077-2016. Specifically, in some embodiments, 0.1g to 0.13g of the positive electrode active material sample to be tested is weighed into a 50mL beaker, 5g of anhydrous ethanol is added, a stir bar of about 2.5mm is placed in the beaker, and then sealed with plastic wrap. After ultrasonic treatment for 5 minutes, the sample is transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples are taken from each batch of product for testing. For example, a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd. can be used for testing to obtain the particle size distribution curve.

[0062] In some embodiments, the peak area of ​​the first peak is S1, and the peak area of ​​the second peak is S2, satisfying: 1≤S1 / S2≤4. For example, it can be a range of 1, 1.5, 2, 2.5, 3, 3.5, 4, or any two of these values. By controlling the ratio of S1 / S2 within the above range, the particle pores of the cathode material are maximized, effectively improving the compaction density and specific capacity of the cathode material, increasing the wettability of the electrolyte to the secondary particles, effectively reducing interfacial side reactions, reducing gas production in the secondary battery, improving the diffusion path of lithium ions, and further improving the cycle performance of the secondary battery.

[0063] In some implementations, 1.2 ≤ S1 / S2 ≤ 1.5.

[0064] In some embodiments, 0.5 ≤ S1 / (S1+S2) ≤ 0.8, for example, it can be a range of 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8 or any two of these values. By controlling S1 / (S1+S2) within this range, the diffusion distance of lithium ions in the cathode material can be effectively reduced, the lithium ion insertion / extraction rate can be improved, the contact area with the electrolyte can be increased, the electrochemical reactivity of the secondary battery can be improved, and thus the cycle performance of the secondary battery can be improved.

[0065] In some embodiments, 0.2≤S2 / (S1+S2)≤0.5, for example, it can be a range of 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or any two of these values. By controlling S2 / (S1+S2) within this range, the compaction density of the positive electrode sheet can be further improved, the stability of the positive electrode material during the pressing process can be improved, and the cycle performance of the secondary battery can be effectively improved.

[0066] In some embodiments, a coating layer is further provided on the outer surface of the lithium iron manganese oxide, the coating layer comprising at least one of a carbon-based material, a metal oxide, and an ionic conductor.

[0067] In some embodiments, when a carbon-based material is used as the coating layer, it can be obtained using a carbon coating method. In some embodiments, for carbon coating, a hydrothermal method can be used, in which the obtained lithium iron manganese oxide and carbon source are co-dissolved in water and stirred, and the resulting solid is sintered to achieve carbon coating of the cathode material.

[0068] In some embodiments, the sintering temperature is 800–900°C, for example, it can be 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, or any combination of two values ​​therein. While satisfying the various limitations of this application on the cathode material, those skilled in the art can also select other suitable sintering temperatures.

[0069] In some embodiments, when a carbon-based material is used as the coating layer, the carbon source includes at least one of sucrose, glucose, citric acid, polyethylene glycol, and soluble starch.

[0070] In some embodiments, when a carbon-based material is used as the coating layer, the mass of the carbon source added (or the total mass of the carbon source added if added multiple times) is 1 to 10 wt% of the total mass of the cathode powder.

[0071] In some embodiments, when a carbon-based material is used as the coating layer, the mass of the carbon source added (or the total mass of the carbon source added if added multiple times) is 1 to 5 wt% of the total mass of the cathode powder.

[0072] In some embodiments, when a carbon-based material is used as the coating layer, the mass of the carbon source added (or the total mass of the carbon source added if added multiple times) is 5 to 10 wt% of the total mass of the cathode powder.

[0073] In some implementations, metal oxide coating is typically achieved using vapor deposition (CVD). In this method, lithium iron manganese oxide is placed in a tube furnace, and a corresponding metal source gas is introduced along with oxygen during a high-temperature process, causing the powder surface to be coated with the corresponding metal oxide.

[0074] In some embodiments, for ionic conductors, a hydrothermal coating method is used, in which lithium iron manganese oxide is mixed with the coating precursor in water while undergoing a hydrolysis-condensation reaction, followed by high-temperature sintering and solidification to obtain the corresponding ionic conductor coated with lithium iron manganese oxide.

[0075] In some embodiments, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0076] In some embodiments, the metal oxide includes at least one selected from aluminum oxide, magnesium oxide, titanium dioxide, lanthanum oxide, zirconium dioxide, antimony trioxide, antimony pentoxide, vanadium trioxide, and zinc oxide.

[0077] In some embodiments, the ion conductor includes at least one of LLZO (lithium lanthanum zirconium oxide), LLTO (lithium lanthanum titanium oxide), LATP (lithium titanium aluminum phosphate), sulfide solid electrolyte, and polymer ion conductor.

[0078] In some embodiments, the sulfide solid electrolyte includes at least one of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 , Li2S-P2S5, LiSiPSCl, Li7P3S 11 , Li 5.5 PS 4.5 C l1.5 , Li 10 SnP2S 12 .

[0079] In some embodiments, the polymer ion conductor includes at least one of PEO-based solid polymers and polycarbonate.

[0080] In some embodiments, the thickness of the coating layer is 1 to 100 nm, for example, it can be 1 nm, 2 nm, 5 nm, 6 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a range composed of any two of these values.

[0081] In some embodiments, the mass of the coating layer accounts for 0.5 to 5% of the total mass of the positive electrode material, for example, it can be 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range composed of any two of these values.

[0082] In some embodiments, the lithium manganese iron oxide includes a compound with the molecular formula Li x Mn y Fe 1-y M z PO4, where 0.9 ≤ x ≤ 1.1, 0 < y < 1, 0 ≤ z ≤ 0.05, and M includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr.

[0083] In some embodiments, the mentioned M element can be incorporated into the lithium manganese iron oxide by doping and / or surface coating.

[0084] Some embodiments of the present application provide a method for preparing a positive electrode material, including the following steps:

[0085] (1) According to the stoichiometric ratio, iron source, manganese source, phosphorus source, lithium source, and dopant containing element M are added to the battery powder mixer, and then mixed with pure water as a solvent. During the mixing and stirring process, a complexing agent is added to adjust the pH to 8-9.5, and the amount of complexing agent (e.g., ammonia) added is adjusted by a flow meter to control the pH of the mixed solution to 10.2-10.5, so that the pH continuously increases from low to high throughout the mixing process. Finally, the target mixed precipitate is obtained by co-precipitation.

[0086] (2) The mixed precipitate in step (1) is placed in an inert atmosphere and calcined to obtain calcined powder. The calcined powder is then crushed and sieved to remove iron to obtain the positive electrode material.

[0087] In some embodiments, the Li:Fe:P:M molar ratio in the lithium source, iron source, phosphorus source, and dopant containing element M in step (1) is (1.0~1.1):(0.4~1.0):1:(0~0.03).

[0088] This application does not impose any special restrictions on the lithium source; commonly used lithium sources in this application can be used.

[0089] In some embodiments, the manganese source includes at least one of manganese carbonate, manganese acetate, manganese phosphate, manganese phosphate, manganese dioxide, manganese tetroxide, manganese sulfate, manganese nitrate, manganese oxalate, manganese sulfate, manganese nitrate, and manganese acetate.

[0090] In some embodiments, the iron source includes at least one of ferric phosphate, ferric oxide, ferrous sulfate, ferric sulfate, ferrous nitrate, ferrous chloride, ferric acetate, and ferrous acetate.

[0091] In some embodiments, the phosphorus source includes at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, iron phosphate, manganese phosphate, and manganese phosphate.

[0092] In some embodiments, the dopant containing element M includes at least one of oxides, nitrates, sulfates, chlorides, and acetates containing element M.

[0093] The element M includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, and Cr.

[0094] In some embodiments, the complexing agent used in the co-precipitation method of step 1 includes one or more of the following: ammonia solution, citric acid, ethylenediaminetetraacetic acid (EDTA), disodium EDTA, tetrasodium EDTA, sodium gluconate, and sodium alginate. Adjusting the pH of the solution is intended to enhance the complexing ability of the complexing agent.

[0095] In some embodiments, the molar ratio of the lithium source to the iron source and the manganese source, respectively, based on Li and Fe+Mn, is (1.0~1.05):1.

[0096] In some embodiments, a carbon-based material-coated cathode material can also be obtained by adding a carbon source and a mixed precipitate and calcining in step (2). In some embodiments, the carbon source accounts for 5 to 10 wt% of the total amount of the lithium source, calcined powder, and carbon source (i.e., the total mass of the cathode powder), for example, it can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any two of these values.

[0097] In some embodiments, step (1) is performed in a mixer, using a special variable pH process for mixing. By utilizing Fe... 2+ and Mn 2+ The difference in pH value during precipitation is used to control the Mn / Fe ratio of the coprecipitate. Initially, a complexing agent is used to set the pH of the solution to 8-9.5 (e.g., 8.1-8.4). At this point, the iron, manganese, phosphorus, lithium sources, and dopants are mixed and stirred. Since the pH value at this stage is already close to that of Fe... 2+ The threshold for complete precipitation of Mn 2+ Since precipitation had just begun, the Fe content in the precursor was higher than that of Mn. During the subsequent stirring process, the amount of complexing agent introduced was controlled by a flow meter to adjust the pH value, achieving a gradual increase in pH throughout the mixing process until it reached a range of 10.2–10.5, at which point Mn... 2+ It also reaches the threshold for complete precipitation. Therefore, the proportion of Mn in the precursor gradually increases during the entire mixed precipitation process, eventually resulting in an uneven distribution of the Mn / Fe ratio in the precursor.

[0098] In some embodiments, the flow rate of the complexing agent (e.g., ammonia solution) is 1 to 5 L / h, for example, it can be 1 L / h, 2 L / h, 3 L / h, 4 L / h, 5 L / h or any two of these values.

[0099] In some embodiments, the volume concentration of the complexing agent (e.g., an aqueous ammonia solution) is 2% to 40%, for example, it can be a range of 2%, 4%, 5%, 6%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or any two of these values.

[0100] In some embodiments, the calcination temperature in step (2) is 500 to 800°C, for example, it can be 500°C, 520°C, 540°C, 550°C, 560°C, 580°C, 600°C, 620°C, 640°C, 650°C, 660°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C or any two of these values.

[0101] In some embodiments, step (2) involves two-step calcination: first, calcination at 500–600°C for 1–4 hours, and then calcination at 700–800°C for 1–4 hours.

[0102] In some embodiments, the calcination time in step (2) is 1 to 4 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any two of these values. It is understood that this refers to a single-step calcination process with a calcination time of 1 to 4 hours; or a two-step calcination process with each step having a calcination time within the range of 1 to 4 hours.

[0103] While meeting the various limitations on the cathode material in this application, those skilled in the art can also select other suitable calcination times and temperatures.

[0104] Some embodiments of this application provide a secondary battery including a positive electrode sheet, the positive electrode sheet comprising the positive electrode material described above.

[0105] In some embodiments, the positive electrode 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 including the positive electrode material described above.

[0106] In this application, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In some embodiments, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0107] In this application, there are no particular limitations on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, its form includes, but is not limited to, metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, its form may include, but is not limited to, carbon plate, carbon film, carbon cylinder, etc.

[0108] In some embodiments, the positive electrode material layer also includes a conductive agent and a binder.

[0109] In some embodiments, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0110] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0111] In some embodiments, the negative electrode active material may be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloys and metallic lithium.

[0112] In some embodiments, the negative electrode active material layer also includes a conductive agent and a binder.

[0113] There are no restrictions on the types of conductive agents mentioned in this application; any known conductive agent may be used.

[0114] In some embodiments, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0115] There are no restrictions on the type of binder mentioned in this application; any known positive electrode binder may be used.

[0116] In some embodiments, the binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenation, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, and sodium carboxymethyl cellulose.

[0117] In some embodiments, in the secondary battery mentioned in this application, a separator is typically provided between the positive and negative electrodes to prevent short circuits. There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0118] In some embodiments, the diaphragm comprises a porous sheet-like or nonwoven material with excellent liquid retention properties. Materials for resin or glass fiber diaphragms include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone.

[0119] In some embodiments, the polyolefin is polyethylene or polypropylene.

[0120] In some embodiments, the polyolefin is polypropylene. The materials of the diaphragm described above can be used alone or in any combination.

[0121] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0122] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. In some embodiments, the outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. In some embodiments, the material of the soft pack can be plastic, and non-limiting examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0123] The type of electrolyte is not specifically limited. In some embodiments, the electrolyte includes an electrolyte salt and an organic solvent; the specific types of electrolyte salt and organic solvent are not specifically limited and can be selected according to actual needs. In some embodiments, the electrolyte may also include additives, and the type of additives is not particularly limited. In some embodiments, the additives may be film-forming additives for the positive and / or negative electrodes, or additives that can improve certain battery performance, such as additives that improve the high or low temperature performance of the battery.

[0124] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0125] Some embodiments of this application provide an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0126] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0127] The present application is further illustrated below with specific embodiments:

[0128] Example 1

[0129] A method for preparing a secondary battery includes the following steps:

[0130] (1) Preparation of the positive electrode sheet:

[0131] 1. A method for preparing the cathode material, comprising the following steps: First, 9.5 kg of iron phosphate, 2.8 kg of lithium hydroxide, 8.9 kg of lithium dihydrogen phosphate, 8.6 kg of manganese carbonate, and 0.11 kg of titanium dioxide are added to a battery powder mixer, and mixed with 30 L of pure water. At this point, the manganese-iron ratio is approximately 1.18. The initial pH of the solution is adjusted to 8.2 using ammonia as a complexing agent. Simultaneously, during the initial 1 hour of stirring, ammonia (25% concentration) is added as a complexing agent, and the ammonia injection rate is maintained at 5 L / H using a liquid flow meter, gradually increasing the pH of the mixed solution to 10.2. This achieves a variable pH (gradually rising from 8.2 to 10.2) mixing and stirring process in the first half, followed by another 1 hour of mixing and stirring until precipitation is complete. The precipitate in the solution was filtered out and pre-sintered at 500°C for 2 hours under a nitrogen protective atmosphere to obtain the precursor. After being allowed to stand and return to room temperature, it was finely ground and then sintered at 700°C for 2 hours. After being crushed and sieved to remove iron, the positive electrode material was obtained.

[0132] 2. Preparation of the positive electrode sheet: The prepared positive electrode material, acetylene black conductive agent, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 90:5:5, using N-methyl-2-pyrrolidone (NMP) as a solvent to obtain a positive electrode slurry. The slurry is then coated onto aluminum foil using an extrusion coating method, dried in an oven at 80°C, and finally rolled using a roller press to obtain the positive electrode sheet.

[0133] (2) Preparation of negative electrode sheet: Graphite was selected as the negative electrode active material, and it was mixed with acetylene black conductive agent and CSM / SBR in a mass ratio of 90:5:5. Water was used as the solvent to obtain a negative electrode slurry. The slurry was coated onto copper foil by extrusion coating, dried in an oven at 80°C, and then rolled using a roller press to obtain the negative electrode sheet.

[0134] (3) Separator: 20μm PP / PE composite separator with 10μm PVDF modified coating on the surface.

[0135] (4) Preparation of electrolyte: Ethyl carbonate and diethyl carbonate are mixed in a 1:1 ratio, and then 1M LiPF6 solution is added. After stirring and mixing evenly, it is used as the electrolyte for lithium-ion batteries.

[0136] (5) Preparation of secondary batteries:

[0137] The positive electrode, negative electrode, and separator prepared above are wound in a predetermined order to prepare a bare cell. The bare cell is placed in an outer packaging aluminum-plastic film, baked to remove moisture, injected with electrolyte, and vacuum sealed to prepare a secondary battery.

[0138] Examples 2-5, Comparative Example 2

[0139] The difference between Examples 2-5 and Comparative Example 2 and Example 1 is that the preparation methods of the positive electrode materials are different. Examples 2-5 change the variance of the manganese-iron ratio by changing the pH value change pattern.

[0140] Example 2

[0141] The entire preparation process was consistent with Example 1, except for the difference in the pH adjustment pattern caused by adding ammonia. Specifically, the initial pH of the solution was adjusted to 9.5 using an ammonia complexing agent. Simultaneously, during the initial 1-hour stirring process, 25% ammonia was added as a complexing agent, and the ammonia injection rate was maintained at 2 L / H using a flow meter, gradually increasing the pH of the mixed solution to 10.2. This resulted in a first half of a pH-variable (gradually rising from 9.5 to 10.2) mixing and stirring process, followed by another 1 hour of mixing and stirring until precipitation was complete.

[0142] Example 3

[0143] The entire preparation process was consistent with Example 1, except for the difference in the pH adjustment pattern caused by adding ammonia. Specifically, the initial pH of the solution was adjusted to 8.5 using ammonia as a complexing agent. Simultaneously, 25% ammonia was added as a complexing agent during the initial 1-hour stirring process, with the ammonia injection rate maintained at 4 L / H using a flow meter. This gradually increased the pH of the mixed solution to 10.2. This resulted in a first half of a pH-variable (gradually rising from 8.5 to 10.2) mixing and stirring process, followed by another 1-hour of mixing and stirring until precipitation was complete.

[0144] Example 4

[0145] The entire preparation process was consistent with Example 1, except for the difference in the pH adjustment mechanism caused by adding ammonia. Specifically, the initial pH of the solution was adjusted to 8 using ammonia as a complexing agent. Simultaneously, 25% ammonia was added as a complexing agent during 2 hours of stirring. The ammonia injection rate was maintained at 2 L / H using a flow meter, gradually increasing the pH of the mixed solution to 10.2. This resulted in a variable pH (gradually rising from 8 to 10.2) mixing process until complete precipitation.

[0146] Example 5

[0147] The entire preparation process was consistent with Example 1, except for the difference in the pH adjustment mechanism caused by adding ammonia. Specifically, the initial pH of the solution was adjusted to 8 using ammonia as a complexing agent. Simultaneously, 25% ammonia was added as a complexing agent during 4 hours of stirring. The ammonia injection rate was maintained at 1 L / H using a flow meter, gradually increasing the pH of the mixed solution to 10.2. This resulted in a variable pH (slowly rising from 8 to 10.2) mixing process until complete precipitation.

[0148] Comparative Example 2

[0149] The entire preparation process remained the same as in Example 1, except for changing the initial ratio of iron and manganese sources. Specifically, 12 kg of iron phosphate, 2.8 kg of lithium hydroxide, 8.9 kg of lithium dihydrogen phosphate, 3.7 kg of manganese carbonate, and 0.11 kg of titanium dioxide were added to a battery powder mixer and mixed with 30 L of pure water. At this point, the manganese-to-iron ratio was approximately 0.4.

[0150] Examples 6-9

[0151] The difference between Examples 6-9 and Example 1 is that the preparation methods of the positive electrode materials are different. Examples 6-9 change the amount of manganese source and iron source added, thereby changing the expected value of the manganese-iron element ratio.

[0152] Example 6

[0153] The entire preparation process remained the same as in Example 1, except for changing the initial ratio of iron and manganese sources. Specifically, 11 kg of iron phosphate, 2.8 kg of lithium hydroxide, 8.9 kg of lithium dihydrogen phosphate, 7.5 kg of manganese carbonate, and 0.11 kg of titanium dioxide were added to a battery powder mixer and mixed with 30 L of pure water. At this point, the manganese-iron ratio was approximately 0.9.

[0154] Example 7

[0155] The entire preparation process remained the same as in Example 1, except for changing the initial ratio of iron and manganese sources. Specifically, 9.2 kg of iron phosphate, 2.8 kg of lithium hydroxide, 9.2 kg of lithium dihydrogen phosphate, 8.8 kg of manganese carbonate, and 0.11 kg of titanium dioxide were added to a battery powder mixer, and mixed with 30 L of pure water. At this point, the manganese-iron ratio was approximately 1.3.

[0156] Example 8

[0157] The entire preparation process remained the same as in Example 1, except for changing the initial ratio of iron and manganese sources. Specifically, 8.3 kg of iron phosphate, 2.8 kg of lithium hydroxide, 9.6 kg of lithium dihydrogen phosphate, 9.5 kg of manganese carbonate, and 0.11 kg of titanium dioxide were added to a battery powder mixer and mixed with 30 L of pure water. At this point, the manganese-iron ratio was approximately 1.5.

[0158] Example 9

[0159] The entire preparation process remained the same as in Example 1, except for changing the initial ratio of iron and manganese sources. Specifically, 7 kg of iron phosphate, 2.8 kg of lithium hydroxide, 8.9 kg of lithium dihydrogen phosphate, 11 kg of manganese carbonate, and 0.11 kg of titanium dioxide were added to a battery powder mixer, and mixed with 30 L of pure water. At this point, the manganese-iron ratio was approximately 2.

[0160] Examples 10-15

[0161] The difference between Examples 10-15 and Example 1 is that the preparation methods of the cathode materials are different. Examples 10-15 change the position of the first and second peaks, as well as S1 and S2, by changing the temperature and time during the sintering process and the crushing and sieving steps.

[0162] Example 10

[0163] Except for changing the temperature and time during sintering, the entire preparation process remained the same as in Example 1. The precipitate in the solution was filtered out and pre-sintered at 500°C for 2.25 h in a nitrogen protective atmosphere to obtain the precursor. After being allowed to stand and return to room temperature, it was finely ground and then sintered at 700°C for 2 h. After being crushed and sieved to remove iron, the cathode material was obtained.

[0164] Example 11

[0165] The entire preparation process remained the same as in Example 1, except for changes in the temperature and time during sintering. The precipitate in the solution was filtered out and pre-sintered at 500°C for 1.75 h in a nitrogen protective atmosphere to obtain the precursor. After being allowed to stand and return to room temperature, it was finely ground and then sintered at 700°C for 2 h. After being crushed and sieved to remove iron, the cathode material was obtained.

[0166] Example 12

[0167] The entire preparation process remained the same as in Example 1, except for changes in the temperature and time during sintering. The precipitate in the solution was filtered out and pre-sintered at 500°C for 3 hours under a nitrogen protective atmosphere to obtain the precursor. After being allowed to stand and return to room temperature, it was finely ground and then sintered at 700°C for 1 hour. After being crushed and sieved to remove iron, the cathode material was obtained.

[0168] Example 13

[0169] The entire preparation process remained the same as in Example 1, except for changes in the temperature and time during sintering. The precipitate in the solution was filtered out and pre-sintered at 400°C for 2 hours under a nitrogen protective atmosphere to obtain the precursor. After being allowed to stand and return to room temperature, it was finely ground and then sintered at 600°C for 2 hours. After pulverization and iron removal by sieving, the cathode material was obtained.

[0170] Example 14

[0171] The entire preparation process remained the same as in Example 1, except for changes in the temperature and time during sintering. The precipitate in the solution was filtered out and pre-sintered at 500°C for 2.25 h in a nitrogen protective atmosphere to obtain the precursor. After being allowed to stand and return to room temperature, it was finely ground and then sintered at 800°C for 2 h. After pulverizing and sieving to remove iron, the cathode material was obtained.

[0172] Example 15

[0173] The entire preparation process remained the same as in Example 1, except for changes in the temperature and time during sintering. The precipitate in the solution was filtered out and pre-sintered at 600°C for 2.25 h in a nitrogen protective atmosphere to obtain the precursor. After being allowed to stand and return to room temperature, it was finely ground and then sintered at 900°C for 2 h. After pulverizing and sieving to remove iron, the cathode material was obtained.

[0174] Examples 16-19

[0175] The difference between Examples 16-19 and Example 1 is that, based on Example 1, Examples 16-19 form a carbon coating layer on the surface of the cathode material.

[0176] The specific method is as follows: the positive electrode material of Example 1 is mixed evenly with anhydrous glucose in water, filtered, dried, and then sintered to coat the surface of the positive electrode material with carbon material.

[0177] The coating layer shown in Table 1 was obtained by controlling the amount of anhydrous glucose added and the sintering parameters.

[0178] Example 16

[0179] 10 kg of positive electrode powder material obtained in Example 1 was mixed with 0.1 kg of anhydrous glucose and 70 kg of pure water in a sand mill. The powder was then calcined at 700°C for 9 hours in a nitrogen atmosphere. After crushing and screening, a positive electrode material with carbon coating on the surface was obtained.

[0180] Example 17

[0181] 10 kg of positive electrode powder material obtained in Example 1 was mixed with 0.2 kg of anhydrous glucose and 70 kg of pure water in a sand mill. The powder was then calcined at 700°C for 9 hours in a nitrogen atmosphere. After crushing and screening, a positive electrode material with carbon coating on the surface was obtained.

[0182] Example 18

[0183] 10 kg of positive electrode powder material obtained in Example 1 was mixed with 1.4 kg of anhydrous glucose and 70 kg of pure water in a sand mill. The powder was then calcined at 700°C for 9 hours in a nitrogen atmosphere. After crushing and screening, a positive electrode material with carbon coating on the surface was obtained.

[0184] Example 19

[0185] 10 kg of positive electrode powder material obtained in Example 1 was mixed with 1.8 kg of anhydrous glucose and 70 kg of pure water in a sand mill. The powder was then calcined at 700°C for 9 hours in a nitrogen atmosphere. After crushing and screening, a positive electrode material with carbon coating on the surface was obtained.

[0186] Comparative Example 1

[0187] A method for preparing a positive electrode material includes the following steps:

[0188] 9.67 kg of ferric nitrate, 10.74 kg of manganese nitrate, and 19.21 kg of citric acid were dissolved in pure water. The pH of the mixed solution was adjusted to 10.5. The mixture was sealed and heated and stirred at 70°C for 12 hours. The powder was then calcined at 250°C for 2 hours, cooled, and ground. The powder was then calcined at 450°C for 2 hours in a nitrogen atmosphere. After grinding, all the powder, 7.61 kg of lithium carbonate, 11.50 kg of ammonium dihydrogen phosphate, 1.34 kg of sucrose, and 70 kg of pure water were mixed evenly and then sand-milled. The powder was then calcined at 700°C for 9 hours in a nitrogen atmosphere, and then pulverized and sieved to obtain the cathode material.

[0189] Test Example 1

[0190] The particle size distribution curves of the cathode materials in the examples and comparative examples were obtained by laser diffraction. The specific positions of the diffraction peaks are shown in Table 1.

[0191] The particle size distribution curves of Example 1 and Comparative Example 1 are shown in Figure 1. As can be seen from Figure 1, the cathode material described in this application (non-uniform distribution in the figure) has a wider particle size distribution range and exhibits two typical particle size distribution ranges (200-270 nm, 360-470 nm), while Comparative Example 1 (uniform distribution in the figure) shows a different particle size distribution.

[0192] The particle size distribution range is relatively concentrated (240–420 nm). This result indicates that we have successfully prepared cathode materials with similar average particle sizes but significantly different particle size distribution trends.

[0193] Test Example 2

[0194] The abscissa of the manganese-iron element distribution intensity curves of the cathode materials in the examples and comparative examples was divided into 16 parts. The manganese-iron element ratio corresponding to the abscissa of each point was calculated. A normal distribution curve of the manganese-iron element ratio was constructed for the values ​​of the manganese-iron element ratio at the 16 points, thereby obtaining μ (expected value) and σ. 2 Value (variance).

[0195] The distribution maps, variances, and Mn / Fe ratios of Example 1 and Comparative Example 1 are shown in Figures 2 and 3, respectively. Besides the non-uniform distribution in particle size, the non-uniform distribution of Mn / Fe atom occupancy within the particles was also verified using transmission electron microscopy combined with image recognition methods. As shown in Figure 2, microscopic characterization of the prepared lithium manganese iron phosphate particles yields the corresponding Mn / Fe element distribution mapping map. Combined with image processing methods, the Mn / Fe element ratio in different regions within the particles can be quantitatively analyzed. The obtained Mn / Fe element distribution mapping map is approximately divided into 16 equal parts to obtain the Mn / Fe ratio value Xn (n = 1, 2…16) for each sample size. A normal distribution curve X ~ N(μ, σ) is constructed by organizing the statistical data of the 16 Mn / Fe ratios. 2 As shown in Figure 2, statistical results for samples with uneven elemental distribution within the particles revealed a mean Mn / Fe ratio of 1.171, with a variance σ0. 2 =0.118, with the overall ratio ranging from 0.9 to 1.41, indicating a relatively dispersed distribution. In contrast, as shown in Figure 3, the elements within the particles are uniformly distributed. Statistical results reveal that the average Mn / Fe ratio is 1.186, with a variance σ... 2 =0.038, the overall ratio ranges from 1.12 to 1.28, and the distribution range is concentrated.

[0196] Table 1 Parameter Table

[0197] Performance testing

[0198] 1. Loop testing:

[0199] a. Place the secondary battery in a 25℃ test chamber and let it stand for half an hour until the temperature is uniform;

[0200] b. Charge to 4.35V using a 0.33C rate current, then maintain a constant voltage until the current decreases to a 0.05C rate current;

[0201] c. Let it stand for half an hour;

[0202] d. Discharge to 2.5V with a 0.33C rate current and read the discharge capacity Cn (n = 1, 2, 3...);

[0203] e. Let it stand for half an hour;

[0204] f. Perform 400 cycles of the cyclic test, calculate the ratio of the discharge capacity Cn per cycle to the discharge capacity C1 of the first cycle, and obtain the cycle capacity retention rate.

[0205] 2. DCR internal resistance test

[0206] a. Charge to 4.35V using a 0.33C rate current, then maintain a constant voltage until the current decreases to a 0.05C rate current;

[0207] b. Let it stand for half an hour;

[0208] c. Discharge to 50% SOC using a 0.33C rate current;

[0209] d. Let it stand for half an hour;

[0210] e. Discharge at 3C rate for 30s, record the current and voltage during the discharge process, read the voltage V1 before discharge, the voltage V2 after 30s of discharge, and the discharge current A0, and test the corresponding DCR = V1 - V2 / A0.

[0211] Table 2 Performance Test Results

[0212] As can be seen from Table 2, the cathode material described in this application can significantly improve the cycle life of secondary batteries and reduce DCR.

[0213] Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that this application achieves its effect by controlling: 0.5 ≤ μ, σ 2 ≥0.05; significantly improved the cycle life of secondary batteries and reduced DCR.

[0214] As can be seen from the comparison of Examples 1 to 5, this application controls 0.1≤σ 2 ≤0.15, further improving the cycle life of the secondary battery and reducing DCR.

[0215] Comparing Examples 1, 6-9, it can be seen that this application further improves the cycle life of the secondary battery and reduces the DCR by controlling 1.17≤μ≤1.5.

[0216] Comparing Examples 1, 10-12, it can be seen that this application further improves the cycle life of the secondary battery and reduces the DCR by controlling 1.2≤S1 / S2≤1.5.

[0217] Comparing Examples 1 and 13-15, it can be seen that by controlling the first peak of the positive electrode material in the particle size distribution curve to be between 240 and 270 nm and the second peak to be between 420 and 440 nm, this application further improves the cycle life of the secondary battery and reduces the DCR.

[0218] Comparing Examples 1 and 16-19, it can be seen that this application further improves the cycle life of the secondary battery and reduces the DCR by coating the surface of the positive electrode material with a coating layer.

[0219] Furthermore, based on improving the cycle life and reducing the DCR of the secondary battery by using a coating layer, the thickness of the coating layer and the mass ratio of the coating layer to the total mass of the cathode material can be optimized to further improve the performance of the secondary battery.

[0220] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A cathode material, comprising lithium iron manganese oxide; The positive electrode material satisfies: 0.5 ≤ μ, σ 2 ≥0.05; in, μ is the expected value of the normal distribution curve of the manganese-iron ratio in the cathode material; σ 2 denoted as the variance of the normal distribution curve of the manganese-iron ratio in the cathode material.

2. The cathode material according to claim 1, wherein, The average manganese-iron ratio of the cathode material is 0.25 to 4.

3. The cathode material according to claim 1, wherein, The particle size distribution curve of the cathode material includes a first peak and a second peak; the first peak is located between 100 and 300 nm, and the second peak is located between 300 and 800 nm.

4. The cathode material according to claim 1, wherein, The peak area of ​​the first peak is S1, and the peak area of ​​the second peak is S2, satisfying: 1≤S1 / S2≤4.

5. The cathode material according to claim 1, wherein, 0.9≤μ≤2.

6. The cathode material according to claim 1, wherein, 0.05≤σ 2 ≤0.2。 7. The cathode material according to claim 3, wherein, The first peak is located between 240 and 270 nm, and the second peak is located between 420 and 440 nm.

8. The cathode material according to claim 4, wherein, 1.2≤S1 / S2≤1.

5.

9. The cathode material according to any one of claims 1-8, wherein, It also includes a coating layer disposed on the outer surface of the lithium iron manganese oxide, the coating layer comprising at least one of a carbon-based material, a metal oxide, and an ionic conductor.

10. The cathode material according to claim 9, wherein, The carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

11. The cathode material according to claim 9, wherein, The metal oxide includes at least one of aluminum oxide, magnesium oxide, titanium dioxide, lanthanum oxide, zirconium dioxide, antimony trioxide, antimony pentoxide, vanadium trioxide, and zinc oxide.

12. The cathode material according to claim 9, wherein, The ionic conductor includes at least one of LLZO, LLTO, LATP, sulfide solid electrolytes, and polymer ionic conductors.

13. The cathode material according to claim 9, wherein, The thickness of the coating layer is 1–100 nm.

14. The cathode material according to claim 9, wherein, The mass of the coating layer accounts for 0.5% to 5% of the total mass of the cathode material.

15. The cathode material according to any one of claims 1-8, wherein, The manganese iron lithium oxide includes a compound with the molecular formula Li x Mn y Fe 1-y M z PO4, wherein 0.9 ≤ x ≤ 1.1, 0 < y < 1, 0 ≤ z ≤ 0.05, and M includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, and Cr.

16. A secondary battery, comprising a positive electrode sheet, said positive electrode sheet comprising the positive electrode material according to any one of claims 1 to 15.

17. An electrical device comprising the secondary battery of claim 16.

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