Positive electrode material, method for preparing same, positive electrode sheet, battery, and electrical device

Abstract

The present application relates to a positive electrode material, a preparation method thereof, a positive electrode sheet, a battery and an electrical device. The positive electrode material includes a positive electrode active material and a coating layer located on at least a part of the surface of the positive electrode active material. The positive electrode active material includes a material with the chemical formula Li<subgt;a< / subgt;Fe<subgt;1‑b< / subgt>M<subgt;b< / subgt>PO<subgt;4< / subgt> and a C material. The coating layer includes a material with the chemical formula Li<subgt;m< / subgt>Fe<subgt;1‑n< / subgt>M’<subgt;n< / subgt>PO<subgt;4< / subgt>‑CN, where 0.95 ≤ a ≤ 1.1, 0.4 ≤ b ≤ 0.9, 0.95 ≤ m ≤ 1.1, 0.4 ≤ n ≤ 0.9, and M and M’ independently include other transition metal elements except Fe. This positive electrode material has a high specific capacity and good cycling performance. Applying this positive electrode material to a battery can enable the battery to have both a high energy density and good cycling performance.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular to a cathode material, a preparation method thereof, a cathode electrode sheet, a battery and an electrical device. Background Art

[0002] The lithium iron phosphate material has good safety and cycle performance, but its specific capacity is low. When it is used as a cathode material in a battery, the energy density of the battery is low. In order to improve the energy density of the battery, introducing transition metal elements into the lithium iron phosphate material is a relatively effective method. For example, lithium manganese iron phosphate obtained by introducing manganese element into the lithium iron phosphate material can exhibit a higher specific capacity than lithium iron phosphate, and thus can improve the energy density of the battery. However, after introducing transition metal elements into the lithium iron phosphate material, the cycle performance of the material is low, resulting in a decrease in the cycle performance of the battery. Summary of the Invention

[0003] Based on this, it is necessary to provide a cathode material based on lithium iron phosphate, a preparation method thereof, as well as a cathode electrode sheet, a battery and an electrical device including the cathode material. The cathode material can take into account a relatively high specific capacity and good cycle performance, and thus can enable the battery to have a relatively high energy density and good cycle performance.

[0004] A cathode material includes a cathode active material and a coating layer located on at least a part of the surface of the cathode active material. The cathode active material includes a material with the chemical formula Li a Fe 1-b M b PO4 and a C material, and the coating layer includes a material with the chemical formula Li m Fe 1-n M’ n PO4-CN, where 0.95 ≤ a ≤ 1.1, 0.4 ≤ b ≤ 0.9, 0.95 ≤ m ≤ 1.1, 0.4 ≤ n ≤ 0.9, and M and M’ independently include other transition metal elements except Fe.

[0005] In the above cathode material, by coating the cathode active material including the chemical formula Li a Fe 1-b M b PO4, the dissolution of the transition metal element M in the cathode active material can be reduced, the service life of the cathode material can be extended, and thus the cycle performance of the cathode active material can be extended. At the same time, in the above cathode material, the introduction of the transition metal element can improve the specific capacity of the cathode material. Therefore, the above cathode material has a relatively high specific capacity and good cycle performance. Applying the cathode material to a battery can enable the battery to take into account a relatively high energy density and good cycle performance.

[0006] In some embodiments, the coating layer includes a flaky coating and a particulate coating. The flaky coating includes a material with the chemical formula Li m Fe 1-n M’ n PO4-CN, and the particulate coating includes the C material.

[0007] In some embodiments, the flaky coating and the particulate coating are distributed at intervals on the surface of the positive electrode active material.

[0008] In some embodiments, the particulate coating is distributed on the surface of the positive electrode active material, part of the flaky coating is connected to the surface of the particulate coating, and part of the flaky coating is connected to the surface of the positive electrode active material.

[0009] In some embodiments, the thickness of the flaky coating is 2 nm to 5 nm.

[0010] In some embodiments, the length of the flaky coating ≥ 100 nm.

[0011] In some embodiments, the particle size of the particulate coating is 10 nm to 100 nm.

[0012] In some embodiments, in the positive electrode material, the mass percentage of N element in the positive electrode material is 0.005% to 0.5%.

[0013] In some embodiments, in the positive electrode material, the mass percentage of C element in the positive electrode material is 1% to 2%.

[0014] In some embodiments, M and M’ independently include at least one of Mg, Al, Ca, Ti, Mn, Co, Ni, Cu, Zn, Zr, Nb, and Mo.

[0015] A method for preparing the positive electrode material includes the following steps:

[0016] Mix the positive electrode active material, a carbon source, a lithium source, an M’ source, a phosphorus source, and a Prussian blue material in a solvent to obtain a slurry. The Prussian blue material includes a material with the chemical formula M’ x Fe 4-x [Fe(CN)6]3, where 0 ≤ x ≤ 4;

[0017] Perform spray drying on the slurry to obtain a precursor;

[0018] Under the atmosphere of a protective gas, perform a calcination treatment on the precursor.

[0019] In some embodiments, the molar percentage of Fe in the Prussian blue material to Li in the slurry is 0.3% to 5%.

[0020] In some embodiments, the carbon source includes at least one of glucose, sucrose, citric acid, starch, and polyethylene glycol.

[0021] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium triphosphate, and lithium oxalate.

[0022] In some embodiments, the M' source includes an oxide of M'.

[0023] In some embodiments, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, lithium triphosphate, and lithium dihydrogen phosphate.

[0024] In some embodiments, the outlet air temperature controlled by spray drying is 90°C to 110°C; the temperature of the calcination treatment is 600°C to 750°C; the time of the calcination treatment is 6 h to 20 h.

[0025] A positive electrode plate includes a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector, and the positive electrode active layer contains the positive electrode material or the positive electrode material prepared by the preparation method.

[0026] A battery includes the positive electrode plate.

[0027] In some embodiments, the total dissolution amount of Fe and the other transition metal elements in the battery is 25 ppm to 55 ppm.

[0028] An electrical device includes the battery. Description of the Drawings

[0029] Figure 1 It is a scanning electron microscope (SEM) image of the positive electrode material in Example 1 of the present application.

[0030] Figure 2 It is an SEM image of the positive electrode material in Example 1 at another scale.

[0031] Figure 3 It is an X-ray photoelectron spectroscopy (XPS) image of the positive electrode material in Example 1.

[0032] Figure 4 It is a fitting spectrum of the N element in the positive electrode material in Example 1.

[0033] Figure 5 It is a fitting spectrum of the Fe element in the positive electrode material in Example 1.

[0034] Figure 6 The fitting spectrum of Li and C elements in the positive electrode material in Example 1.

[0035] Figure 7 The X-ray diffraction (XRD) pattern of the positive electrode material in Example 1. Detailed implementation manners

[0036] To make the above objects, features, and advantages of the present application more obvious and understandable, the following provides a detailed description of the specific implementation manners of the present application. Many specific details are set forth in the following description to fully understand the present application. However, the present application can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0037] In the present application, unless otherwise clearly defined and limited, terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0038] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present application, "a plurality" means at least two, such as two, three, etc., unless otherwise clearly specifically defined.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0040] One embodiment of the present application provides a positive electrode material. The positive electrode material includes a positive electrode active material and a coating layer located on at least a part of the surface of the positive electrode active material. The positive electrode active material includes a material with the chemical formula Li a Fe 1-b M b PO4, and the coating layer includes a material with the chemical formula Li m Fe1-n M’ n Materials of PO4-CN and C material, where 0.95 ≤ a ≤ 1.1, 0.4 ≤ b ≤ 0.9, 0.95 ≤ m ≤ 1.1, 0.4 ≤ n ≤ 0.9, and M and M’ independently include transition metal elements other than Fe. In the positive electrode material of this embodiment, by coating the positive electrode active material including the material with the chemical formula Li a Fe 1-b M b PO4, the dissolution of the transition metal element M in the positive electrode active material can be reduced, the service life of the positive electrode material can be extended, and further the cycle performance of the positive electrode active material can be extended. At the same time, in the positive electrode material of this embodiment, the introduction of the transition metal element can improve the specific capacity of the positive electrode material. Therefore, the positive electrode material of this embodiment has a relatively high specific capacity and good cycle performance. Applying this positive electrode material to a battery can enable the battery to have both a relatively high energy density and good cycle performance.

[0041] Optionally, in Li a Fe 1-b M b PO4, a can be, but is not limited to, 0.95, 0.98, 1, 1.05, 1.1, and any value within the numerical range formed by any two of these values. b can be, but is not limited to, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and any value within the numerical range formed by any two of these values.

[0042] Optionally, in Li m Fe 1-n M’ n PO4-CN, m can be, but is not limited to, 0.95, 0.98, 1, 1.05, 1.1, and any value within the numerical range formed by any two of these values. n can be, but is not limited to, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and any value within the numerical range formed by any two of these values. It can be understood that Li m Fe 1-n M’ n PO4-CN means that -CN is connected to Li m Fe 1-n M’ n PO4.

[0043] In some embodiments, as some optional examples of M and M’, M and M’ independently include at least one of Mg, Al, Ca, Ti, Mn, Co, Ni, Cu, Zn, Zr, Nb, and Mo. That is, M includes at least one of Mg, Al, Ca, Ti, Mn, Co, Ni, Cu, Zn, Zr, Nb, and Mo. M’ includes at least one of Mg, Al, Ca, Ti, Mn, Co, Ni, Cu, Zn, Zr, Nb, and Mo.

[0044] In some embodiments, in the cathode material, M and M’ are the same, which can keep the coating layer and the cathode active material highly consistent in elemental composition in the cathode material, making the coating layer and the cathode active material better matched and more fully showing the contribution effect on the specific capacity and cycling performance of the cathode material. Further, in the cathode material, M and M’ are the same, a and m are the same, and b and n are the same, which can further promote the matching of the coating layer and the cathode active material and further improve the specific capacity and cycling performance of the cathode material.

[0045] In some embodiments, the coating layer includes flaky coating materials and particulate coating materials. The flaky coating materials include a material with the chemical formula Li m Fe 1-n M’ n PO4-CN. The particulate coating materials include the C material. The coexistence of the flaky coating materials and the particulate coating materials can make the coating layer exhibit a better coating effect and further promote the improvement of the specific capacity and cycling performance of the cathode material. The material with the chemical formula Li m Fe 1-n M’ n PO4-CN as the flaky coating materials can further inhibit the dissolution of transition metal elements in the cathode active material, and further improve the cycling performance of the cathode material and keep the cathode material with a high specific capacity. Further, the material with the chemical formula Li m Fe 1-n M’ n PO4-CN contains a cyano group (-CN), and the flaky coating materials can bind to the cathode active material and / or the particulate coating materials through the cyano group.

[0046] In some embodiments, the sheet-like coating and the particulate coating are distributed at intervals on the surface of the positive electrode active material. It can be understood that the sheet-like coating and the particulate coating being distributed at intervals on the surface of the positive electrode active material means that there are gaps between the sheet-like coatings on the surface of the positive electrode active material, and the particulate coatings are located in the gaps between adjacent sheet-like coatings. At the same time, there are gaps between the particulate coatings, and the sheet-like coatings are located between adjacent particulate coatings. When the sheet-like coating and the particulate coating are distributed at intervals on the surface of the positive electrode active material, the sheet-like coating and the particulate coating can better play their roles and synergistically promote the further improvement of the cycling performance and specific capacity of the positive electrode material.

[0047] In some embodiments, the particulate coating is distributed on the surface of the positive electrode active material, and some of the sheet-like coatings are connected to the surface of the particulate coating, and some of the sheet-like coatings are connected to the surface of the positive electrode active material.

[0048] In some embodiments, the thickness of the sheet-like coating is 2 nm to 5 nm. For example, the thickness of the sheet-like coating can be, but is not limited to, 2 nm, 3 nm, 4 nm, 5 nm, and any value within the numerical range formed by any two of these values.

[0049] In some embodiments, the length of the sheet-like coating is ≥ 100 nm. For example, the length of the sheet-like coating can be, but is not limited to, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 400 nm, 700 nm, and any value within the numerical range formed by any two of these values. Optionally, the length of the sheet-like coating is 100 nm to 1000 nm.

[0050] In some embodiments, the particle size of the particulate coating is 10 nm to 100 nm. For example, the particle size of the particulate coating can be, but is not limited to, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, and any value within the numerical range formed by any two of these values.

[0051] In some embodiments, in the positive electrode material, the mass percentage of N element in the positive electrode material is 0.005% to 0.5%. For example, the mass percentage of N element in the positive electrode material can be, but is not limited to, 0.005%, 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, and any value within the numerical range formed by any two of these values.

[0052] In some embodiments, the mass percentage of the C element in the positive electrode material is 1% to 2%. Alternatively, the mass percentage of the C element in the positive electrode material can be, but is not limited to, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, and any value in a range consisting of any two of these values.

[0053] It can be understood that, in the positive electrode material, a portion of the N element is used to form a cyano group, and a portion of the C element is used to form a cyano group.

[0054] In some embodiments, the cathode material includes spherical secondary particles.

[0055] Another embodiment of the present application provides a method for preparing the above-mentioned positive electrode material. The method for preparing the positive electrode material comprises the following steps:

[0056] The positive electrode active material, carbon source, lithium source, M' source, phosphorus source and Prussian blue material are mixed in a solvent to obtain a slurry. The Prussian blue material includes a chemical formula of M' x Fe 4-x [Fe(CN)6]3 materials, where 0≤x≤4;

[0057] The slurry is spray-dried to obtain a precursor;

[0058] The precursor is calcined under a protective gas atmosphere.

[0059] In the preparation method of this embodiment, based on the coating of the positive electrode active material with the Prussian blue material, during the preparation process, a lithium source, an M' source, and a phosphorus source are introduced to obtain a slurry, and then the slurry is spray-dried and calcined to generate a Li-ion battery having a chemical formula of Li-ion battery on the surface of the positive electrode active material. m Fe 1-n M' n The coating layer of PO4-CN material enables the obtained positive electrode material to have both higher gram capacity and better cycle performance.

[0060] In some embodiments, the molar percentage of Fe in the Prussian blue material to Li in the slurry is 0.3% to 5%. When the molar percentage of Fe in the Prussian blue material to Li in the slurry is within this range, the total dissolution amount of Fe and other transition metal elements can be further reduced. Optionally, the molar percentage of Fe in the Prussian blue material to Li in the slurry can be, but is not limited to, 0.3%, 0.4%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, and any value within the numerical range formed by any two of these values. Further optionally, the molar percentage of Fe in the Prussian blue material to Li in the slurry is 0.3% to 0.5%.

[0061] In some embodiments, when mixing the cathode active material, carbon source, lithium source, M' source, phosphorus source, and Prussian blue material in a solvent, the lithium source, M' source, and phosphorus source can be first mixed in the solvent to obtain a first mixed solution, and then the first mixed solution is added to a second mixed solution including the carbon source and the cathode active material to obtain a third mixed solution. Then the Prussian blue material is added to the third mixed solution. It can be understood that during the mixing process, the mixed solution is stirred to promote mixing. Optionally, the temperature of the stirring is 25°C, the time of the stirring is 0.5 h, and the frequency of the stirring is 20 Hz. Further, after adding the Prussian blue material to the third mixed solution, the obtained mixed solution is ball-milled to further promote mixing. Optionally, the temperature of the ball-milling is 25°C, the time of the ball-milling is 4 h, and the rotation speed of the ball-milling is 200 r / min.

[0062] In some embodiments, when mixing the cathode active material, carbon source, lithium source, M' source, phosphorus source, and Prussian blue material in a solvent, the solvent used is deionized water.

[0063] In some embodiments, the carbon source includes at least one of glucose, sucrose, citric acid, starch, and polyethylene glycol. The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium triphosphate, and lithium oxalate. The M' source includes an oxide of M'. The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, lithium triphosphate, and lithium dihydrogen phosphate.

[0064] In some embodiments, the temperature of spray drying is 90°C to 110°C. The temperature of the calcination treatment is 600°C to 750°C. The time of the calcination treatment is 6 h to 20 h. Optionally, the temperature of spray drying can be, but is not limited to, 90°C, 95°C, 100°C, 105°C, 110°C, and any value within the numerical range formed by any two of these values. The temperature of the calcination treatment is 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, and any value within the numerical range formed by any two of these values. The time of the calcination treatment is 6 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h, and any value within the numerical range formed by any two of these values.

[0065] Another embodiment of the present application provides a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector, and the positive electrode active layer contains the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method.

[0066] Another embodiment of the present application provides a battery. The battery includes the above-mentioned positive electrode plate.

[0067] In some embodiments, the total dissolution amount of Fe and other transition metal elements in the battery is 25 ppm to 55 ppm. For example, the total dissolution amount of Fe and other transition metal elements in the battery is 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm, and any value within the numerical range formed by any two of these values.

[0068] Another embodiment of the present application provides an electrical device. The electrical device includes the above-mentioned battery.

[0069] Example 1

[0070] The preparation method of the positive electrode material in this example includes:

[0071] S101: Mix lithium carbonate, manganese tetroxide, and phosphoric acid in deionized water to obtain a first mixed solution.

[0072] S102: Add the first mixed solution to a second mixed solution including a carbon source PEG-2000 and glucose (Glu) and a positive electrode active material LiFe 0.4 Mn 0.6 PO4 to obtain a third mixed solution.

[0073] S103: Add the Prussian blue material Fe4[Fe(CN)6]3 to the third mixed solution, stir and mix to obtain a slurry. Among them, the molar percentage of Fe in the Prussian blue material to Li in the slurry is 0.5%. The temperature of stirring and mixing is 25 °C, the time of stirring and mixing is 0.5 h, and the frequency of stirring and mixing is 20 Hz.

[0074] S104: Ball-mill the slurry obtained in S103. The temperature of ball-milling and mixing is 25 °C, the time of ball-milling and mixing is 4 h, and the rotation speed of ball-milling and mixing is 200 r / min.

[0075] S105: Spray-dry the slurry to obtain a precursor. The temperature of spray-drying is 110 °C.

[0076] S106: Under a nitrogen atmosphere, calcine the precursor. The temperature of calcination is 600 °C, and the time of calcination is 20 h.

[0077] S107: After the calcination treatment, cool it naturally to obtain the positive electrode material in this embodiment.

[0078] Compared with Example 1, the differences between Examples 2-5 and Comparative Examples 1-2 are shown in Table 1.

[0079] Table 1

[0080]

[0081] Figure 1 is the SEM image of the positive electrode material in Example 1. It can be Figure 1 seen that the positive electrode material is spherical secondary particles.

[0082] Figure 2 is the SEM image of the positive electrode material in Example 1 under another scale. It can be Figure 2 seen that the coating layer of the positive electrode material includes flaky coatings and granular coatings. Among them, the length of the flaky coatings is between 100 nm and 1000 nm, and the particle size of the granular coatings is within 100 nm.

[0083] Figure 3 is the XPS total spectrum of the positive electrode material in Example 1.

[0084] Figure 4 is the N1s fitting spectrum of the positive electrode material in Example 1. The binding energy is 400.87 eV, which is consistent with the corresponding peak position of C-NH2, indicating the presence of a C-N bond structure in the positive electrode material.

[0085] Figure 5It is the fitting spectrum of the Fe element in the cathode material in Example 1. The peaks near 711 eV and 725 eV respectively correspond to Fe2p3 / 2 and Fe2p1 / 2, both of which show blue shifts, indicating that Fe atoms form coordination bonds Fe-C≡N-Fe with C atoms and N atoms respectively, forming an interface with high electronic conductivity and high ionic conductivity between the cathode active material and the coating layer, inducing the rapid movement of electrons and the rapid deintercalation and intercalation of ions in the cathode material, and obtaining a cathode material with high electronic conductivity and high ionic conductivity.

[0086] Figure 6 For Li and CO3 in the cathode material in Example 1 2- In the spectrum, fitting the peaks can obtain 54.84 eV and 55.67 eV, corresponding to the Li1s and CO3 2- peak positions respectively.

[0087] Figure 7 It is the XRD spectrum of the cathode material in Example 1, corresponding to the lithium iron phosphate structure, without obvious impurity peaks, indicating a relatively high purity of the material and no obvious impurity phases.

[0088] The specific capacities and battery cycling performances of the cathode materials in the examples and comparative examples were tested.

[0089] The test methods are as follows:

[0090] 1. Making coin cells: Using a 2032 standard battery case for production, the cathode ratio is cathode material: SP: PVDF = 9:0.5:0.5, the pole piece compaction density is 2.0 g / cm 3 , the active material loading is 6 mg, and the anode material is a Li sheet.

[0091] 2. The specific capacity of the coin cell was tested according to the theoretical capacity of 150 mAh / g, 0.1 C, and 2.5 V to 4.5 V.

[0092] 3. The cycling retention rate of the coin cell: The voltage window is 2.5 V to 4.3 V, 100 charge-discharge cycles under 1 C condition. The average value of the capacities of the first three cycles is taken as the initial specific capacity, and the average value of the capacities of the last three cycles is taken as the final specific capacity. The cycling retention rate is the final specific capacity / initial specific capacity × 100%.

[0093] 4. The test method for Mn+Fe dissolution: After discharging the battery to 2.0 V and disassembling it after 100 cycles, the anode material was taken, and the contents of Mn and Fe in it were detected by ICP-OES and added up.

[0094] The coating layer in Comparative Example 1 is a carbon coating layer, and the coating layer in Comparative Example 2 is a Prussian blue coating layer. Compared with Comparative Examples 1-2, the batteries in Examples 1-5 can better balance a relatively high energy density and a relatively high cycling retention rate. It shows that the coating layer includes a chemical formula of Lim Fe 1-n M’ n The materials of PO4-CN and C materials can improve the energy density and cycling performance of the cathode material.

[0095] It can be seen from Examples 1 to 3 that when the molar percentage of Fe in the Prussian blue material in the slurry is within a suitable range, it can promote the reduction of the dissolution amount of Mn+Fe in the battery.

[0096] It can be seen from Examples 2, 4 to 5 that the cathode active material includes a material with the chemical formula Li a Fe 1-b M b PO4, the battery can obtain a higher energy density and better cycling performance.

[0097] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0098] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application.

Claims

1. A cathode material, characterized in that, Comprising a positive electrode active material and a coating layer located on at least a part of the surface of the positive electrode active material, the positive electrode active material comprises a material with the chemical formula Li a Fe 1-b M b PO4, the coating layer comprises a material with the chemical formula Li m Fe 1-n M’ n PO4-CN and a C material, wherein, 0.95 ≤ a ≤ 1.1, 0.4 ≤ b ≤ 0.9, 0.95 ≤ m ≤ 1.1, 0.4 ≤ n ≤ 0.9, M and M’ independently comprise other transition metal elements except Fe; the coating layer comprises flaky coatings and particulate coatings, the flaky coatings comprise a material with the chemical formula Li m Fe 1-n M’ n PO4-CN, Li m Fe 1- n M’ n PO4-CN represents that a cyano group is connected to Li m Fe 1-n M’ n PO4, and the particulate coatings comprise the C material.

2. The cathode material according to claim 1, wherein The sheet-like coating and the particulate coating are distributed at intervals on the surface of the positive electrode active material.

3. The cathode material according to claim 1, wherein The particulate coating is distributed on the surface of the positive electrode active material, part of the sheet-like coating is connected to the surface of the particulate coating, and part of the sheet-like coating is connected to the surface of the positive electrode active material.

4. The cathode material according to claim 1, characterized in that, The coating layer satisfies at least one of the following characteristics: (1) The thickness of the sheet-like coating is 2 nm to 5 nm; (2) The length of the sheet-like coating is ≥ 100 nm; (3) The particle size of the particulate coating is 10 nm to 100 nm.

5. The cathode material according to any one of claims 1 to 4, characterized in that, The positive electrode material satisfies at least one of the following characteristics: (1) In the positive electrode material, the mass percentage of N element in the positive electrode material is 0.005% to 0.5%; (2) In the positive electrode material, the mass percentage of C element in the positive electrode material is 1% to 2%; (3) M and M' independently include at least one of Ti, Mn, Co, Ni, Cu, Zn, Zr, Nb, and Mo.

6. The cathode material according to any one of claims 1 to 4, characterized in that, The positive electrode material satisfies at least one of the following characteristics: (1) M and M' are the same; (2) a and m are the same; (3) b and n are the same.

7. A method for preparing the cathode material according to any one of claims 1 to 6, characterized in that, It includes the following steps: Mix the positive electrode active material, carbon source, lithium source, M' source, phosphorus source, and Prussian blue material in a solvent to obtain a slurry. The Prussian blue material includes a material with the chemical formula M' x Fe 4-x [Fe(CN)6]3, where 0 ≤ x ≤ 4; Spray-dry the slurry to obtain a precursor; Under the atmosphere of a protective gas, perform a calcination treatment on the precursor.

8. The preparation method of the cathode material according to claim 7, characterized in that, In the Prussian blue material, the molar percentage of Fe in the slurry to Li is 0.3% to 5%.

9. The method for preparing the cathode material according to any one of claims 7 to 8, characterized in that, The carbon source includes at least one of glucose, sucrose, citric acid, starch, and polyethylene glycol; and / or, The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium triphosphate, and lithium oxalate; and / or, The M' source includes an oxide of M'; and / or, The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, lithium triphosphate, and lithium dihydrogen phosphate.

10. The method for preparing a cathode material according to any one of claims 7 to 8, characterized in that, The outlet air temperature controlled by the spray drying is 90 °C to 110 °C; the temperature of the calcination treatment is 600 °C to 750 °C; the time of the calcination treatment is 6 h to 20 h.

11. A positive electrode sheet, characterized in that, It includes a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector, and the positive electrode active layer contains the positive electrode material described in any one of claims 1 to 6 or the positive electrode material prepared by the preparation method described in any one of claims 7 to 10.

12. A battery, characterized in that, It includes the positive electrode tab described in claim 11.

13. The battery according to claim 12, characterized in that, The total dissolution amount of Fe and the other transition metal elements in the battery is 25 ppm to 55 ppm.

14. An electrical device, characterized in that, It includes the battery described in any one of claims 12 to 13.

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