Positive electrode active material, battery and electrical device

Abstract

This application discloses a positive electrode active material, a battery, and an electrical device. The positive electrode active material includes a first manganese iron lithium oxide and a second manganese iron lithium oxide. The molar percentage of Mn in the first manganese iron lithium oxide is n1%, and the molar percentage of Mn in the second manganese iron lithium oxide is n2%, satisfying n1>n2, and 70≤n1≤95, 60≤n2≤80. By mixing a manganese iron lithium oxide with a lower manganese content, the effect of Mn ion dissolution on the high-temperature cyclability and storage stability of the battery can be reduced, thereby improving the high-temperature cyclability and storage stability of a battery having a single manganese iron lithium oxide component without significantly reducing the overall gram capacity of the positive electrode active material.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode active material, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries are green, high-energy rechargeable batteries with advantages such as high voltage, high energy density, good cycle performance, low self-discharge, no memory effect, and a wide operating range. They have good application prospects in electric vehicles. During the charge and discharge process of lithium-ion batteries, the specific capacity of the positive electrode material determines the energy density of the lithium-ion battery, and thus the range of the electric vehicle. As one of the positive electrode materials, lithium iron manganese phosphate material has a higher specific capacity and energy density than lithium iron phosphate material, and its safety performance is better than that of nickel-cobalt-manganese ternary materials. In order to further improve its specific capacity and energy density, its manganese content needs to be further increased. However, simply increasing the manganese content will lead to a decrease in its high-temperature cycle performance and high-temperature storage performance, and reduce the stability of the lithium iron manganese phosphate material. Summary of the Invention

[0003] The present application provides a positive electrode active material, a battery and an electrical device, which solve the problem that simply increasing the manganese content of a single lithium manganese iron phosphate material leads to a decrease in its high-temperature cycle performance and high-temperature storage performance.

[0004] In a first aspect, the present application provides a positive electrode active material, the positive electrode active material comprising a first manganese iron lithium oxide and a second manganese iron lithium oxide;

[0005] The molar percentage of Mn in the first manganese iron lithium oxide is n1%, and the molar percentage of Mn in the second manganese iron lithium oxide is n2%, satisfying n1>n2, and 70≤n1≤95, 60≤n2≤80.

[0006] Optionally, in some embodiments of the present application, the first manganese iron lithium oxide comprises a general formula of Li a1 Mn n1 / 100 Fe 1-n1 / 100 Me 1-a1 PO4 compound, the second manganese iron lithium oxide includes a general formula Li a2 Mn n2 / 100 Fe 1-n2 / 100 Me 1- a2 A compound of PO4, wherein 0.95≤a1≤1, 0.95≤a2≤1, and Me includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, or Cr.

[0007] Optionally, the molar percentage of Mn in the first manganese iron lithium oxide is n1%, the molar percentage of Mn in the second manganese iron lithium oxide is n2%, and n1-n2≥10.

[0008] Optionally, in some embodiments of the present application, the chemical formula of the first manganese iron lithium oxide includes LiMn 0.9 Fe 0.1 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.8 Fe 0.2 PO4、LiMn 0.7 Fe 0.3 PO4 or LiMn 0.6 Fe 0.4 Any of PO4.

[0009] Alternatively, in some other embodiments of the present application, the chemical formula of the first manganese iron lithium oxide includes LiMn 0.8 Fe 0.2 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.7 Fe 0.3 PO4 or LiMn 0.6 Fe 0.4 Any of PO4.

[0010] Alternatively, in some other embodiments of the present application, the chemical formula of the first manganese iron lithium oxide includes LiMn 0.7 Fe 0.3 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.6 Fe 0.4 PO4.

[0011] Optionally, in some embodiments of the present application, the chemical formula of the first manganese iron lithium oxide may include Li 0.96 Mn 0.7 Fe 0.3 Mg 0.03 W 0.01 PO4, Li 0.96 Mn 0.7 Fe 0.3 Sr 0.04 PO4, Li 0.96 Mn 0.7 Fe 0.3 Zr 0.04 PO4, Li 0.96 Mn 0.7 Fe 0.3 Ti 0.04 PO4, Li 0.96 Mn 0.7 Fe 0.3 V 0.04PO4 or Li 0.96 Mn 0.7 Fe 0.3 Ti 0.04 Any of PO4.

[0012] Optionally, in some embodiments of the present application, the chemical formula of the second manganese iron lithium oxide may include Li 0.96 Mn 0.6 Fe 0.4 Mg 0.03 W 0.01 PO4, Li 0.96 Mn 0.6 Fe 0.4 Sr 0.04 PO4, Li 0.96 Mn 0.6 Fe 0.4 Zr 0.04 PO4, Li 0.96 Mn 0.6 Fe 0.4 Ti 0.04 PO4, Li 0.96 Mn 0.6 Fe 0.4 V 0.04 PO4 or Li 0.96 Mn 0.6 Fe 0.4 Ti 0.04 Any of PO4.

[0013] Optionally, in some embodiments of the present application, the mass ratio of the first manganese iron lithium oxide to the second manganese iron lithium oxide is (1-1.5):1.

[0014] Optionally, the D of the first manganese iron lithium oxide is n 50 is D1, D of the second manganese iron lithium oxide n 50 is D2, which satisfies: D1>D2. n 50 represents the particle size at which the cumulative number distribution percentage of a sample reaches 50%.

[0015] Optionally, in some embodiments of the present application, the D of the first manganese iron lithium oxide is n 50 is D1, D of the second manganese iron lithium oxide n 50 is D2, D1 and D2 satisfy D1 = (1.9 to 2.6) × D2. Alternatively, D1 = (2.06 to 2.46) × D2.

[0016] Optionally, in some embodiments of the present application, the D of the first manganese iron lithium oxide is n50 can be 3.25 to 3.64 μm. Optionally, in some embodiments of the present application, the D n 50 is 1.32~1.72μm.

[0017] An embodiment of the present application provides a battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material of any of the above embodiments.

[0018] Optionally, in some embodiments of the present application, the battery satisfies at least one of the following characteristics:

[0019] (1) The energy density of the battery is 208.5-210.0Wh / kg;

[0020] (2) The platform voltage of the battery is 3.66~3.70V;

[0021] (3) The battery's capacity retention rate after 500 cycles at 45°C 1C / 1C is 93.05% to 94.20%;

[0022] (4) The capacity attenuation rate of the battery after 30 days of storage at 60°C is 3.29% to 3.64%;

[0023] (5) The compaction density of the positive electrode is 2.19-2.30 g / cm 3 ;

[0024] (6) The 0.1C discharge capacity of the positive electrode active material is 144.5 to 146.0 mAh / g.

[0025] An embodiment of the present application provides an electrical device, which includes a battery according to any one of the above embodiments, and the battery serves as a power supply for the electrical device.

[0026] Due to the adoption of the above technical solution, the embodiments of the present application have at least the following technical effects:

[0027] In the embodiment of the present application, two manganese iron lithium oxides with different Mn contents are mixed to prepare the positive electrode active material. The molar percentage of Mn in the first manganese iron lithium oxide is n1%, and the molar percentage of Mn in the second manganese iron lithium oxide is n2%, satisfying n1>n2, and 70≤n1≤95, 60≤n2≤80. By mixing the manganese iron lithium oxide with a lower manganese content, the effect of Mn ion dissolution on the high-temperature cyclability and storage stability of the battery can be reduced, thereby improving the high-temperature cyclability and storage stability of the battery with a single manganese iron lithium oxide component without significantly reducing the overall gram capacity of the positive electrode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 This is a schematic diagram of the mixed state of the first manganese iron lithium oxide and the second manganese iron lithium oxide in Example 1 of the present application. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. It should be noted that the description order of the following embodiments is not intended to limit the preferred order of the embodiments.

[0031] In this specification, a numerical range expressed using “to” means a range including the numerical values ​​described before and after “to” as the minimum value and the maximum value, respectively.

[0032] The inventors of this application discovered in their research that, in order to improve the electrochemical performance of lithium manganese iron phosphate materials, the molar percentage of Mn in the lithium manganese iron phosphate material can be increased, thereby improving the platform voltage and energy density of the battery made therefrom. However, the Mn content cannot be increased to a very high value because this would lead to a decrease in the high-temperature cycling performance and storage performance of the lithium manganese iron phosphate material, thereby reducing the stability of the battery. Therefore, in order to solve the above technical problems, the inventors of this application proposed the following technical solution.

[0033] The present invention provides a positive electrode active material. The positive electrode active material includes a first manganese iron lithium oxide and a second manganese iron lithium oxide;

[0034] In an embodiment of the present application, the molar percentage of Mn in the first manganese iron lithium oxide is n1%, and the molar percentage of Mn in the second manganese iron lithium oxide is n2%, satisfying n1>n2, and 70≤n1≤95, 60≤n2≤80.

[0035] In the embodiment of the present application, the first manganese iron lithium oxide comprises a general formula of Li a1 Mn n1 / 100 Fe 1-n1 / 100 Me 1-a1 PO4 compound, the second manganese iron lithium oxide includes a general formula Lia2 Mn n2 / 100 Fe 1-n2 / 100 Me 1-a2 PO4, wherein 0.95≤a1≤1, 0.95≤a2≤1, and Me includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, or Cr. For example, when the metal element Me is present, the chemical formula of the first manganese iron lithium oxide includes Li 0.96 Mn 0.7 Fe 0.3 Mg 0.03 W 0.01 PO4, Li 0.96 Mn 0.7 Fe 0.3 Sr 0.04 PO4, Li 0.96 Mn 0.7 Fe 0.3 Zr 0.04 PO4, Li 0.96 Mn 0.7 Fe 0.3 Ti 0.04 PO4, Li 0.96 Mn 0.7 Fe 0.3 V 0.04 PO4 or Li 0.96 Mn 0.7 Fe 0.3 Ti 0.04 PO4, etc. The chemical formula of the second manganese iron lithium oxide includes Li 0.96 Mn 0.6 Fe 0.4 Mg 0.03 W 0.01 PO4, Li 0.96 Mn 0.6 Fe 0.4 Sr 0.04 PO4, Li 0.96 Mn 0.6 Fe 0.4 Zr 0.04 PO4, Li 0.96 Mn 0.6 Fe 0.4 Ti 0.04 PO4, Li 0.96 Mn 0.6 Fe 0.4 V 0.04 PO4 or Li 0.96 Mn 0.6 Fe 0.4 Ti 0.04 PO4, etc.

[0036] In some other embodiments of the present application, when the metal element Me is absent, the first manganese iron lithium oxide comprises a chemical formula of LiMn 0.9 Fe 0.1 PO4、LiMn 0.8 Fe 0.2 PO4 or LiMn 0.7 Fe 0.3 PO4 compound, the second manganese iron lithium oxide includes a chemical formula LiMn 0.8 Fe 0.2 PO4、LiMn 0.7 Fe 0.3 PO4 or LiMn 0.6 Fe 0.4 PO4 compounds.

[0037] In some embodiments, the chemical formula of the first manganese iron lithium oxide includes LiMn 0.9 Fe 0.1 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.8 Fe 0.2 PO4、LiMn 0.7 Fe 0.3 PO4 or LiMn 0.6 Fe 0.4 For example, the first manganese iron lithium oxide is LiMn 0.9 Fe 0.1 PO4, the second manganese iron lithium oxide is LiMn 0.8 Fe 0.2 PO4, which ensures that the content of Mn in the first manganese iron lithium oxide is greater than the content of Mn in the second manganese iron lithium oxide. For another example, the first manganese iron lithium oxide is LiMn 0.9 Fe 0.1 PO4, the second manganese iron lithium oxide is LiMn 0.7 Fe 0.3 PO4. Alternatively, the first manganese iron lithium oxide is LiMn 0.9 Fe 0.1 PO4, the second manganese iron lithium oxide is LiMn 0.6 Fe 0.4 PO4.

[0038] In other embodiments, the chemical formula of the first lithium iron manganese oxide includes LiMn 0.8 Fe 0.2 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.7 Fe 0.3 PO4 or LiMn 0.6 Fe 0.4For example, the chemical formula of the first manganese iron lithium oxide includes LiMn 0.8 Fe 0.2 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.7 Fe 0.3 PO4. For another example, the chemical formula of the first manganese iron lithium oxide includes LiMn 0.8 Fe 0.2 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.6 Fe 0.4 PO4.

[0039] In some other embodiments, the chemical formula of the first manganese iron lithium oxide includes LiMn 0.7 Fe 0.3 PO4, the chemical formula of the second manganese iron lithium oxide includes LiMn 0.6 Fe 0.4 PO4. However, the chemical formulas of the first manganese iron lithium oxide and the second manganese iron lithium oxide are not both LiMn 0.7 Fe 0.3 PO4, nor LiMn 0.6 Fe 0.4 PO4. This is because the Mn content in the first manganese iron lithium oxide and the second manganese iron lithium oxide cannot be the same.

[0040] Optionally, in some embodiments of the present application, the mass ratio of the first manganese iron lithium oxide to the second manganese iron lithium oxide may be (1-1.5):1, or (1.1-1.4):1, or (1.2-1.3):1. Adjusting the mass ratio of the first manganese iron lithium oxide to the second manganese iron lithium oxide within the above range can achieve a balance in gram capacity or compacted density after mixing, thereby achieving better results.

[0041] Optionally, in some embodiments of the present application, the D of the first manganese iron lithium oxide is n 50 is D1, D of the second manganese iron lithium oxide n50 is D2, satisfying: D1>D2, and the molar percentage of Mn in the first manganese iron lithium oxide (n1%) is greater than the molar percentage of Mn in the second manganese iron lithium oxide (n2%). Although the gram capacity of the second manganese iron lithium oxide is low, through the adjustment of the particle size distribution of the first manganese iron lithium oxide and the second manganese iron lithium oxide, the second manganese iron lithium oxide with smaller particle size and smaller gram capacity can be filled in the gaps between the first manganese iron lithium oxide with larger particle size and larger gram capacity. This can ensure that the overall discharge gram capacity of the positive electrode active material mixed with the first manganese iron lithium oxide and the second manganese iron lithium oxide does not decrease after rolling, and can maintain the compaction density within the required range. If the first manganese iron lithium oxide and the second manganese iron lithium oxide with the same particle size are rolled in pursuit of a higher compaction density, the structure of the manganese oxide octahedron of the two particles will collapse, resulting in manganese dissolution and side reactions with the electrolyte, resulting in excessively rapid attenuation of the high temperature cycle and storage capacity of the battery, which is not conducive to obtaining a positive electrode active material and battery with balanced performance.

[0042] In addition, the molar percentage of Mn in the first manganese iron lithium oxide is higher, which is manifested in that the Mn / Fe ratio of the first manganese iron lithium oxide is greater than that of the second manganese iron lithium oxide. Therefore, if the compaction density of the first manganese iron lithium oxide is simply increased, then at a higher compaction density, the Mn content of the first manganese iron lithium oxide will be 2+ and Mn 4+ The dissolution probability of the second manganese iron lithium oxide is higher than that of the second manganese iron lithium oxide, which will cause side reactions between Mn ions and the electrolyte, so the second manganese iron lithium oxide is added to the first manganese iron lithium oxide. n 50 is less than the D of the first manganese iron lithium oxide n 50, then the second manganese iron lithium oxide with a smaller particle size can be incorporated into the gaps between the first manganese iron lithium oxide. When the positive electrode active material contacts the electrolyte, the second manganese iron lithium oxide can reduce the contact area between the first manganese iron lithium oxide and the electrolyte, delaying or inhibiting the dissolution of Mn ions in the first manganese iron lithium oxide, thereby reducing the probability of side reactions caused by the dissolution of Mn ions and reducing the impact of Mn ion dissolution on the high-temperature cycling performance and storage stability of the battery.

[0043] Therefore, the present embodiment effectively improves the high-temperature cycling performance of lithium manganese iron phosphate batteries by mixing two types of lithium manganese iron oxide particles with different particle sizes and different Mn contents, reducing their capacity decay during high-temperature storage. Furthermore, the present embodiment obtains the positive electrode active material through a mixing operation, which is simple to operate and does not introduce other elements, eliminating the risk of reduced battery energy density due to the introduction of other elements.

[0044] Optionally, in some embodiments of the present application, the D of the first manganese iron lithium oxide is n 50 is D1, D of the second manganese iron lithium oxide n 50 is D2, and D1 and D2 satisfy D1 = (1.9 to 2.6) × D2. The relationship between D1 and D2 can also satisfy D1 = (2.0 to 2.5) × D2 or D1 = (2.06 to 2.46) × D2.

[0045] Optionally, in some embodiments of the present application, the D of the first manganese iron lithium oxide is n 50(D1) is 3.25 to 3.64 μm, and may be 3.27 to 3.60 μm, 3.32 to 3.58 μm, 3.36 to 3.55 μm, 3.42 to 3.50 μm, or 3.44 to 3.47 μm.

[0046] Optionally, in some embodiments of the present application, the D of the second manganese iron lithium oxide is n 50(D2) can be 1.32 to 1.72 μm, 1.36 to 1.70 μm, 1.40 to 1.65 μm, 1.42 to 1.62 μm, 1.47 to 1.60 μm, or 1.50 to 1.55 μm.

[0047] The present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material of any of the above embodiments.

[0048] The battery in the embodiment of the present application satisfies at least one of the following characteristics:

[0049] (1) The energy density of the battery is 208.5-210.0Wh / kg;

[0050] (2) The platform voltage of the battery is 3.66~3.70V;

[0051] (3) The battery's capacity retention rate after 500 cycles at 45°C 1C / 1C is 93.05% to 94.20%;

[0052] (4) The capacity attenuation rate of the battery after 30 days of storage at 60°C is 3.29% to 3.64%;

[0053] (5) The compaction density of the positive electrode is 2.19-2.30 g / cm 3 ;

[0054] (6) The 0.1C gram capacity of the positive electrode active material is 144.5 to 146.0 mAh / g.

[0055] The present application also provides an electrical device comprising the battery of any of the above embodiments, the battery serving as a power source for the electrical device. The electrical devices include, but are not limited to, backup power supplies, motors, electric vehicles, electric motorcycles, power-assisted bicycles, bicycles, power tools, and large household batteries.

[0056] The technical solution of this application is described below with reference to specific embodiments.

[0057] Example 1

[0058] This embodiment provides a method for preparing a positive electrode active material, which includes the following steps:

[0059] D n 50 is 3.34μm (D1) of the first manganese iron lithium oxide (LiMn 0.7 Fe 0.3 PO4) and D n 50 is 1.61μm (D2) of the second manganese iron lithium oxide (LiMn 0.6 Fe 0.4 PO4) in a mass ratio of 1:1, and mixed evenly to obtain a positive electrode active material.

[0060] The mixed state of the first manganese iron lithium oxide 101 and the second manganese iron lithium oxide 102 in this embodiment is as follows Figure 1 shown.

[0061] This embodiment also provides a method for preparing a positive electrode sheet, which includes the following steps:

[0062] The above-mentioned positive electrode active material, conductive agent (conductive carbon black), and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 97:1.8:1.2, and then mixed with a solvent (1-methyl-2-pyrrolidone, NMP) under vacuum stirring to obtain a positive electrode slurry. The positive electrode slurry was sieved to remove impurities and then evenly coated on both surfaces of the positive electrode current collector (aluminum foil). After drying at room temperature, the slurry was transferred to an oven for baking. After roller pressing (cold pressing), slitting, and cutting, the positive electrode sheet was produced.

[0063] The positive electrode slurry is coated on the positive electrode current collector and baked to form the positive electrode active material layer. The thickness of the positive electrode sheet is 200 μm, and the compaction density of the positive electrode sheet is 2.30 g / cm 3 The thickness of the positive electrode current collector is 10 μm.

[0064] This embodiment also provides a method for preparing a battery, which includes the following steps:

[0065] The positive electrode sheet, separator, and negative electrode sheet are stacked in order (one positive electrode sheet, one separator, and one negative electrode sheet), with the separator positioned between the positive and negative electrodes. This process is wound to produce a bare cell. After drying, the bare cell is added with electrolyte. The battery is then vacuum packaged, allowed to stand, formed, and then capacity divided.

[0066] The preparation method of the negative electrode sheet includes: mixing the negative electrode active material graphite, the conductive agent CNT, the thickener CMC, and the binder SBR in a mass ratio of 96.5:0.8:0.9:1.8, adding a solvent (deionized water) and vacuum stirring until the system is uniform to obtain a negative electrode slurry, which is then evenly coated on the upper and lower surfaces of the negative electrode current collector (copper foil), dried at room temperature, and then transferred to an oven for further drying, cold pressed, and cut to obtain a negative electrode sheet. The compacted density of the negative electrode sheet is 1.7g / cm 3 .

[0067] The electrolyte includes lithium hexafluorophosphate (LiPF6) and an organic solvent. The mass percentage of lithium hexafluorophosphate is 12 wt % based on the total mass of the electrolyte. The organic solvent is a mixture of EC, EMC, and DEC in a mass ratio of 20:30:30.

[0068] The separator is a polyethylene film with a thickness of 9 to 18 μm.

[0069] The ratios of the various examples and comparative examples of this application are shown in Table 1. The mass ratio of the first manganese iron lithium oxide to the first manganese iron lithium oxide is denoted as M1 / M2. The test methods used are as follows. The test results of the various examples and comparative examples are shown in Table 2.

[0070] 1. The compaction density test of the positive electrode in the battery. The test method includes measuring the thickness of the positive electrode after cold pressing, subtracting the thickness of the foil used, and dividing it by the actual coating area density. The result is the compaction density.

[0071] 2. 0.1C discharge gram capacity test of the positive electrode active material in the battery, the test method includes: assembling the positive electrode sheet and the lithium negative electrode into a button battery, using 1C constant current constant voltage charging to the charging cut-off voltage, switching to constant current charging until the current drops to 0.05C and stopping, standing for 30 minutes, using 0.1C constant current constant voltage discharge to the discharge cut-off voltage, switching to constant voltage discharge until the current drops to 0.05C, recording the discharge capacity, repeating the above steps three times, taking the average of the three discharge capacities, and recording it as the 0.1C discharge capacity of the positive electrode active material.

[0072] 3. 45°C 1C / 1C cycle 500 cycle capacity retention rate (%) test of the battery, the test method includes: placing the battery in a 45°C environment, standing for 60 minutes, using a 1C constant voltage charge to the charge cut-off voltage, switching to constant current charging until the current drops to 0.05C and stopping, standing for 10 minutes, and discharging at a 1C constant current rate to the discharge cut-off voltage. The above steps are repeated 500 times, and the discharge capacity at the first cycle and the discharge capacity at the 500th cycle are recorded, and the capacity retention rate is calculated.

[0073] 4. The battery is tested for capacity attenuation rate (%) after 30 days of storage at 60°C. The test method includes: placing the battery in a 60°C environment, charging the battery at a constant current rate of 1C to the charge cut-off voltage, then switching to constant voltage charging until the current drops to 0.05C, discharging the battery at a constant current rate of 1C to the discharge cut-off voltage, and recording the discharge capacity; charging the battery at a constant current rate of 1C to the charge cut-off voltage, then switching to constant voltage charging until the current drops to 0.05C, and after storing the battery at 60°C for 30 days, discharging the battery at a constant current rate of 1C to the discharge cut-off voltage, and recording the discharge capacity.

[0074] 5. Battery platform voltage test, the test method includes: charging the battery at a constant current rate of 0.33C to the charge cut-off voltage, switching to constant voltage charging until the current drops to 0.05C and stopping, standing for 10 minutes, and discharging at a constant current rate of 0.33C to the discharge cut-off voltage, recording the discharge energy and discharge capacity, where platform voltage = discharge energy ÷ discharge capacity. The charge cut-off voltage is between 4.3V and 4.4V, and the discharge cut-off voltage is 2.5V. The battery contains the positive electrode active materials described in various embodiments and comparative examples of this application.

[0075] 6. Battery energy density test: The test method includes: charging the battery at a constant current rate of 0.33C to the charge cutoff voltage, switching to constant voltage charging until the current drops to 0.05C, stopping, standing for 10 minutes, and discharging at a constant current rate of 0.33C to the discharge cutoff voltage. The discharge energy is recorded. Battery energy density = discharge energy ÷ battery mass.

[0076] Example 2 to Example 8

[0077] The above embodiment and comparative example provide a positive electrode active material and a battery. The difference between the above embodiment and comparative example and embodiment 1 is that the first manganese iron lithium oxide and the second manganese iron lithium oxide have different sizes, and the rest are the same as embodiment 1.

[0078] In Examples 2 to 5, the sizes of the first manganese iron lithium oxide and the second manganese iron lithium oxide are different from those in Example 1, but the D n 50(D1) is in the range of 3.25 to 3.64 μm, and the D n50(D2) is within the range of 1.32-1.72 μm. The experimental data in Table 2 show that as long as the particle size distribution of both particles is within this range, good results are achieved. A particle size ratio of 2.06 achieves a good balance of various properties, demonstrating high 0.1C discharge capacity per gram, high energy density, and good high-temperature cycling and storage stability. However, a particle size ratio above or below 2.06 reduces the compaction density and degrades the aforementioned properties.

[0079] In Example 6, the particle size of the first manganese iron lithium oxide was reduced compared to Example 1, and in Example 7, the particle size of the second manganese iron lithium oxide was increased compared to Example 1. The results in Table 2 show that if the particle size requirements for the first manganese iron lithium oxide and the second manganese iron lithium oxide are not met, the compaction density, platform voltage, and energy density will decrease. Although high-temperature cycling and storage stability will also be moderately reduced, they still meet basic usage requirements.

[0080] In Example 8, the particle size of the first manganese iron lithium oxide was reduced, while the particle size of the second manganese iron lithium oxide was increased compared to Example 1. The results in Table 2 show that this resulted in a moderate decrease in high-temperature cycling and storage stability, but still met basic usage requirements.

[0081] Examples 9 to 13, Comparative Examples 1 to 2

[0082] The above embodiments and comparative examples provide a positive electrode active material and a battery. The difference between the above embodiments 9, 11 and 13 and embodiment 1 is that the added mass ratio of the first manganese iron lithium oxide and the second manganese iron lithium oxide is different, and the rest is the same as embodiment 1. Embodiment 10 and embodiment 12 change the particle size and ratio of the first manganese iron lithium oxide and the second manganese iron lithium oxide relative to the embodiment. It can be seen from the experimental results in Table 2 that when the ratio is 1.4:1, the compaction density, 0.1C gram capacity, and energy density are all high, and the high temperature cycle and storage stability are good. When the ratio is lower or higher than 1.4:1, the compaction density is reduced, but as long as the ratio is (1 to 1.5):1, the requirements of various performance balances can be met.

[0083] Comparative Example 1, compared to Example 1, only the first manganese iron lithium oxide was added, without the second manganese iron lithium oxide. Comparative Example 2, compared to Example 1, only the second manganese iron lithium oxide was added, without the first manganese iron lithium oxide. The results in Table 2 show that the addition of only the first manganese iron lithium oxide significantly reduces high-temperature cycling and storage stability, while the addition of only the second manganese iron lithium oxide significantly reduces the 0.1C discharge capacity per gram and energy density.

[0084] Example 14 to Example 18

[0085] The above embodiments provide a positive electrode active material and a battery. The difference between the above embodiments 14 to 18 and embodiment 1 is that the composition, particle size distribution and addition mass ratio of the first manganese iron lithium oxide and the second manganese iron lithium oxide are adjusted. According to the results in Table 2, the above embodiments have achieved a balance of high battery compaction density, 0.1C discharge gram capacity, high energy density, high temperature cycle and storage stability. This result proves that as long as the Mn content in the first manganese iron lithium oxide is greater than the Mn content in the second manganese iron lithium oxide, and the D n 50 is greater than the D of the second manganese iron lithium oxide n 50, both can achieve good technical results.

[0086] Example 19 to Example 21

[0087] The above embodiment provides a positive electrode active material and battery. The difference between the above embodiment and Example 1 lies in the different compositions of the first and second manganese-iron lithium oxides. The manganese-iron lithium oxides of Example 1 contain no other metal elements besides manganese, iron, and lithium, while Examples 19 through 21 contain other metal elements in addition to manganese, iron, and lithium. The experimental results in Table 2 indicate that the addition of other metal elements does not significantly reduce the battery's high-temperature cycling and storage stability.

[0088] Table 1

[0089]

[0090]

[0091] Table 2

[0092]

[0093]

[0094] The above is a detailed introduction to the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the idea of ​​the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material includes a first manganese iron lithium oxide and a second manganese iron lithium oxide, and the positive electrode active material is obtained by mixing the first manganese iron lithium oxide and the second manganese iron lithium oxide; The mass ratio of the first manganese iron lithium oxide to the second manganese iron lithium oxide is (1-1.5):1; The first manganese iron lithium oxide D n 50 is D1, D of the second manganese iron lithium oxide n 50 is D2, D1 and D2 satisfy D1=(1.9-2.6)×D2, the D of the first manganese iron lithium oxide n 50 is 3.25 to 3.64 μm, and the D n 50 is 1.32~1.72μm; The molar percentage of Mn in the first manganese iron lithium oxide is n1%, and the molar percentage of Mn in the second manganese iron lithium oxide is n2%, satisfying n1>n2, and 70≤n1≤95, 60≤n2≤80.

2. The positive electrode active material according to claim 1, characterized in that The first manganese iron lithium oxide comprises a general formula of Li a1 Mn n1 / 100 Fe 1-n1 / 100 Me 1-a1 PO4 compound, the second manganese iron lithium oxide includes a general formula Li a2 Mn n2 / 100 Fe 1-n2 / 100 Me 1-a2 A compound of PO4, wherein 0.95≤a1≤1, 0.95≤a2≤1, and Me includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, or Cr.

3. The positive electrode active material according to claim 1, characterized in that n1-n2≥10.

4. The positive electrode active material according to claim 1, characterized in that D1=(2.06~2.46)×D2.

5. A battery comprising a positive electrode, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material according to any one of claims 1 to 4.

6. The battery according to claim 5, characterized in that The battery satisfies at least one of the following characteristics: (1) The energy density of the battery is 208.5 to 210.0 Wh / kg; (2) The platform voltage of the battery is 3.66 to 3.70 V; (3) The capacity retention rate of the battery after 500 cycles at 45°C 1C / 1C is 93.05% to 94.20%; (4) The capacity attenuation rate of the battery after storage at 60°C for 30 days is 3.29% to 3.64%; (5) The compaction density of the positive electrode sheet is 2.19-2.30 g / cm 3 ; (6) The 0.1C discharge capacity of the positive electrode active material is 144.5 to 146.0 mAh / g.

7. An electrical device, characterized in that: The device comprises the battery as claimed in claim 5 or 6, wherein the battery serves as a power supply for the electrical device.

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