Positive electrode active material and preparation method thereof, lithium ion battery and electric equipment

Abstract

The embodiment of the invention provides a positive electrode active material and a preparation method thereof, a lithium ion battery and electric equipment, and belongs to the technical field of positive electrode active material manufacturing. The positive electrode active material is of a core-shell structure, a core material comprises lithium manganese iron phosphate, a shell material comprises a carbon material, the compaction density of the positive electrode active material is 2.26-2.49 g / cm < 3 >, the disorder degree of the positive electrode active material is 3.0-14%, the positive electrode active material has high compaction density and low disorder degree, and the positive electrode active material can be applied to the field of lithium ion batteries. Therefore, the corresponding battery has relatively excellent energy density and rate capability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of positive electrode active material manufacturing, in particular to a positive electrode active material, a preparation method thereof, a lithium ion battery and an electric device. BACKGROUND

[0002] Lithium ion batteries have advantages of high energy density and high rate life, and are widely used in the fields of portable electronic devices and new energy vehicles. Among them, lithium iron phosphate is a traditional positive electrode material, which has advantages of low cost, good rate performance and high safety; however, it has problems of low energy density and voltage platform, which is difficult to meet the increasing demand for high energy density.

[0003] Therefore, the skilled person has developed a lithium manganese iron phosphate positive electrode active material (LiMn x Fe y PO4), which has higher energy density than lithium iron phosphate, which can effectively improve the energy density of lithium iron phosphate; however, the existing lithium manganese iron phosphate positive electrode active material has problems of poor rate performance of the corresponding battery in the specific application process, which limits the promotion and application of this type of positive electrode active material. SUMMARY

[0004] The purpose of the present application is to provide a positive electrode active material, a preparation method thereof, a lithium ion battery and an electric device, which have high tap density and low disorder degree, so as to have excellent energy density and rate performance of the corresponding battery.

[0005] The embodiments of the present application are implemented as follows:

[0006] In a first aspect, the present application provides a positive electrode active material, which is a core-shell structure, the inner core material includes lithium manganese iron phosphate, and the shell material includes carbon material, wherein the tap density of the positive electrode active material is 2.26-2.49 g / cm 3 , and the disorder degree of the positive electrode active material is 3.0-14%.

[0007] In the above technical solution, in a first aspect, the positive electrode active material is a core-shell structure, specifically, the inner core contains lithium manganese iron phosphate and the shell contains carbon material, which can effectively reduce the probability of interface side reactions caused by direct contact between lithium manganese iron phosphate and electrolyte, thereby effectively improving the rate performance and cycle performance of the corresponding battery; in a second aspect, the high tap density of the positive electrode active material means that more active substances can be contained in the same volume, so that the corresponding battery has excellent energy density, and at the same time, the low disorder degree of the positive electrode active material broadens the Li +The diffusion channel on the (010) crystal surface makes the material have excellent ionic conductivity, and meanwhile, Li + The diffusion resistance on the (010) crystal surface is reduced, which helps to reduce polarization, enables the corresponding battery to have excellent rate performance and helps to improve the energy density of the corresponding battery. Therefore, the battery prepared by using the positive electrode active material can have high energy density and high rate performance.

[0008] In some optional embodiments, the compaction density of the positive electrode active material is 2.45-2.49 g / cm 3 The disorder degree of the positive electrode active material is 3.0-10%.

[0009] In the above technical solution, the compaction density of the positive electrode active material is higher and the disorder degree is lower, which helps to better improve the energy density and rate performance of the corresponding battery.

[0010] In some optional embodiments, the disorder degree of the positive electrode active material is 3.0-4.3%.

[0011] In the above technical solution, the upper limit of the disorder degree of the positive electrode active material is only 4.3%, which can more effectively improve the rate performance and energy density of the corresponding battery.

[0012] In some optional embodiments, the mass ratio of the carbon material in the positive electrode active material is 1.2-1.8%.

[0013] In the above technical solution, the above mass ratio makes the shell have a suitable thickness, which can make the positive electrode active material have a more suitable electronic conductivity while taking into account the coating effect.

[0014] In some optional embodiments, the chemical formula of the lithium manganese iron phosphate is: Li a Fe 1-x-y Mn x M y PO4; wherein 1.0≤a≤1.04, 0.2≤x≤0.8, 0≤y≤0.007, and M is selected from at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y.

[0015] The lithium manganese iron phosphate has the above chemical formula, so that it has the following characteristics: (1) the ratio of the molar amount of Li element to the sum of the molar amount of the remaining metal elements in the lithium manganese iron phosphate is limited in the above range, so that the material has relatively suitable structural stability and relatively high energy density; (2) the molar ratio of Mn element and Fe element in the lithium manganese iron phosphate has a relatively large adjustable range, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the application; (3) when y is not 0, it indicates that the lithium manganese iron phosphate further includes a doping element M, and element doping helps to improve the stability, capacity or ionic conductivity of the material, thereby making the corresponding battery have more ideal comprehensive electrical performance; further, the molar proportion of the doping element is limited in the above range, which can achieve a good modification effect while taking into account the performance of the material itself.

[0016] In some optional embodiments, the positive electrode active material is subjected to XPS test and peak fitting is performed on the C1 S The results show that the graphitization degree of the carbon material is 74-96%.

[0017] In the above technical solution, the carbon material in the positive electrode active material has a relatively high graphitization degree, so that the positive electrode active material has relatively excellent electronic conductivity.

[0018] In some optional embodiments, the content of S element in the positive electrode active material is 15-136 ppm.

[0019] In the above technical solution, the content of S element in the positive electrode active material is relatively low, so that the material has relatively excellent thermal stability, which helps to improve the problem that the corresponding battery is prone to produce gas during operation under high temperature conditions (for example, 45°C or 60°C).

[0020] In some optional embodiments, the Li ion diffusion coefficient of the positive electrode active material is (0.72-9.7) x 10 -12 cm 2 / S.

[0021] In the above technical solution, the Li ion diffusion coefficient of the positive electrode active material is relatively high, so that the corresponding battery has relatively excellent rate performance and energy density.

[0022] In some optional embodiments, the BET of the positive electrode active material is 11.4-14.27 m 2 / g.

[0023] In the above technical solution, the suitable BET makes the positive electrode active material have a relatively ideal lithium ion diffusion channel, so that the corresponding battery has a relatively ideal rate performance.

[0024] In a second aspect, the embodiments of the present application provide a preparation method of a positive electrode active material, comprising the following steps:

[0025] S1adding a lithium source, a manganese source, an iron source, a phosphorus source, an acidic cosolvent and an organic carbon source into water to mix, to obtain a first mixture; performing heat treatment to form a gel-like carbon-containing lithium iron manganese phosphate precursor; S2performing first tabletting treatment on the precursor to obtain a first tablet; S3performing sintering treatment on the first tablet to obtain the positive electrode active material, wherein during the sintering process, the air pressure in at least part of the time is negative pressure.

[0026] In the above technical solution, in step S1: the carbon-containing precursor is prepared by a sol-gel method first, wherein the addition of the acidic cosolvent can make the various metal raw materials fully dissolved and uniformly dispersed, and can also adjust the pH of the mixed system, thereby helping to promote the formation of the gel; the addition of the organic carbon source can act as a chelating agent before the formation of the precursor, achieving uniform distribution of the metal elements by complexing with various metal ions, and after the formation of the precursor, the carbon source is located on the surface of the precursor, and after subsequent sintering, a carbon material coating layer can be formed; in step S2: the tabletting treatment on the precursor can effectively improve the compaction density of the material to improve the energy density of the corresponding battery; in step S3: the air pressure in at least part of the time during the sintering process is negative pressure, and the negative pressure condition can inhibit the mixing of Mn / Fe atoms in the crystal lattice (i.e., reduce the disorder degree of the positive electrode active material), improve the compaction density of the material, reduce the S residue in the material, improve the graphitization degree of the carbon material, and reduce the BET of the material. That is, according to the above process, a lithium manganese iron phosphate positive electrode active material with high compaction density, low disorder degree, low S residue, high graphitization degree, and small BET can be prepared, so that the corresponding battery has excellent energy density and rate performance.

[0027] In some optional embodiments, the negative pressure is -0.02 to -0.5 MPa.

[0028] In the above technical solution, the negative pressure is within the above range, and a lithium manganese iron phosphate positive electrode active material with high compaction density, low disorder degree, low S residue, high graphitization degree, and small BET can be prepared, so that the corresponding battery has excellent energy density and rate performance.

[0029] In some optional embodiments, the sintering treatment comprises sequentially performing temperature rising treatment at a first air pressure and first sintering treatment at a second air pressure; the temperature rising treatment has a temperature of 300 to 500°C, and the first air pressure is -0.1 to -0.5 MPa; or / and, the first sintering treatment has a temperature of 550 to 700°C, a time of 6 to 10 h, and the second air pressure is -0.02 to -0.1 MPa.

[0030] In the above technical solution, the sintering process is carried out in two steps. First, heating to 300–500°C under negative pressure helps to effectively reduce the residual sulfur (S) content and decrease the material's BET (Best Equivalent Tolerance). Simultaneously, it effectively suppresses the mixing of Mn / Fe atoms within the crystal lattice. Second, performing a first sintering process at 550–700°C under the same negative pressure promotes carbon atom rearrangement, thereby increasing the graphitization degree of the carbon material. This also helps to increase the material's compaction density and effectively suppresses the mixing of Mn / Fe atoms within the crystal lattice. Therefore, by following this process, a lithium manganese iron phosphate cathode active material can be prepared that simultaneously possesses higher compaction density, lower disorder, lower residual sulfur, higher graphitization degree, and lower BET, resulting in batteries with superior energy density and rate performance.

[0031] In some alternative implementations, the heating process is carried out in a first atmosphere, which may include an inert atmosphere and a reducing atmosphere.

[0032] In the above technical solution, the first atmosphere includes an inert atmosphere and a reducing atmosphere. On the one hand, the presence of the reducing atmosphere can reduce the residual sulfur element in the material to volatile H2S and remove it, thereby preparing a positive electrode active material with lower residual sulfur content. On the other hand, the presence of the reducing atmosphere can suppress the presence of manganese (Mn) in the material. 3+ The generation of [something] reduces the occurrence of lattice distortion, thereby preparing a positive electrode active material with higher structural stability.

[0033] In some alternative implementations, the reducing atmosphere accounts for 1 to 10% of the volume of the first atmosphere.

[0034] In the above technical solution, the volume percentage of the reducing atmosphere in the first atmosphere is limited to the aforementioned range, which can effectively remove S element and effectively suppress Mn while providing a suitable inert atmosphere. 3+ generate.

[0035] In some alternative embodiments, the acidic co-solvent is selected from at least one of nitric acid, sulfuric acid, and perchloric acid.

[0036] Among the above technical solutions, there are many applicable types of acidic co-solvents, which can provide a variety of feasible solutions, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0037] In some alternative embodiments, the molar ratio of the anions in the acidic cosolvent to the organic carbon source in the first mixture is (10–16):1.

[0038] In the above technical solution, the molar ratio of acid radical ions in the acidic co-solvent to the organic carbon source is limited to the above range. Before the precursor is formed, an appropriate amount of organic carbon source can act as a chelating agent to make the distribution of various metal elements more uniform. After the precursor is formed, an appropriate amount of organic carbon source can be distributed more completely and uniformly on the surface of the precursor in order to obtain a carbon material shell with better coating integrity and more uniform thickness.

[0039] In some alternative embodiments, the density of the first sheet is 0.4–0.6 cm³. 3 / g.

[0040] In the above technical solution, the first tableting process is carried out according to the above standards, which can better protect the material while increasing the compaction density of the material.

[0041] In some alternative embodiments, the acidic co-solvent is selected from nitric acid, and the organic carbon source contains reducing groups.

[0042] In the above technical solution, nitrate has oxidizing properties. By selecting an organic carbon source with reducing groups, nitric acid and organic carbon source can react exothermically during the preparation of the precursor by the sol-gel method, thereby promoting the reaction process and enabling the precursor to be prepared more efficiently by the sol-gel method.

[0043] In some alternative embodiments, the reducing group is selected from at least one of hydroxyl and carboxyl groups.

[0044] In the above technical solution, the organic carbon source with the aforementioned reducing group can react with nitrate ions relatively easily and completely, so as to obtain the precursor more efficiently by the sol-gel method.

[0045] In some alternative embodiments, after the first sintering treatment, the first sheet is further subjected to a crushing treatment and a second pressing treatment in sequence; or, after the first sintering treatment, the first sheet is further subjected to a crushing treatment and a second sintering treatment in sequence, wherein the third gas pressure during the second sintering treatment is -0.02 to -0.5 MPa.

[0046] In the above technical solution, adding a second pressing treatment after the first sintering treatment helps to further improve the compaction density of the material; adding a second sintering treatment after the first sintering treatment helps to further reduce the disorder of the material, further increase the graphitization degree of the carbon material, and the compaction density of the material.

[0047] Thirdly, embodiments of this application provide a lithium-ion battery, including the positive electrode active material provided in the first aspect embodiment or the positive electrode active material prepared by the preparation method provided in the second aspect embodiment.

[0048] In the above technical solution, the positive electrode active material contained in the lithium-ion battery has both high compaction density and low disorder, so that the lithium-ion battery has excellent rate performance.

[0049] Fourthly, embodiments of this application provide an electrical device including a lithium-ion battery as provided in the third aspect embodiment. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 A process flow diagram of the preparation method of the positive electrode active material provided in the embodiments of this application;

[0052] Figure 2 The SEM-EDS results for the positive electrode active material provided in Example 12 of this application;

[0053] Figure 3 This is a TEM image of the positive electrode active material provided in Example 3 of this application;

[0054] Figure 4 The refined fitting curve of the XRD pattern of the positive electrode active material provided in Example 3 of this application. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0056] It should be noted that the terms "and / or" in this application, such as "feature 1 and / or feature 2", all refer to the three cases of "feature 1" alone, "feature 2" alone, and "feature 1" plus "feature 2".

[0057] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0058] In existing technologies, current lithium manganese iron phosphate (LFP) cathode active materials suffer from poor rate performance in corresponding batteries. The inventors have discovered that the cathode active materials prepared using current processes have high disorder, and this material disorder is one of the main reasons affecting the rate performance of LFP cathode active materials in corresponding batteries. Specifically, high disorder leads to... + The narrow diffusion channels on the (010) crystal plane result in poor ionic conductivity of the material. Meanwhile, Li... + The high diffusion resistance on the (010) crystal plane can lead to severe battery polarization, ultimately resulting in poor rate performance. At the same time, it should be noted that poor ion transport performance can also cause a simultaneous decrease in battery energy density.

[0059] Further research by the inventors revealed that by integrating the gel pressing process and the negative pressure sintering process, a positive electrode active material with both high solid density and low disorder can be prepared, so that the corresponding battery has both high solid density and low disorder.

[0060] The following provides a detailed description of the positive electrode active material, its preparation method, lithium-ion battery, and electrical equipment according to embodiments of this application.

[0061] In a first aspect, embodiments of this application provide a positive electrode active material with a core-shell structure. The core material includes lithium manganese iron phosphate, and the outer shell material includes carbon material. The compaction density of the positive electrode active material is 2.26–2.49 g / cm³. 3 (For example, but not limited to, a compaction density of 2.26 g / cm³) 3 2.29 g / cm 3 2.37 g / cm 3 2.38g / cm 3 2.40 g / cm 3 2.42 g / cm 3 2.45g / cm 3 and 2.49 g / cm 3 The disorder of the positive electrode active material is 3.0% to 14% (e.g., but not limited to any one of the following values ​​or a range between any two): 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 5%, 7%, 9%, 10%, 12%, and 14%.

[0062] It should be noted that disorder refers to the degree of mixed arrangement of Mn atoms and Fe atoms in the crystal lattice of the positive electrode active material. Specifically, it is the sum of the proportion of Mn atoms occupying Li sites and the proportion of Fe atoms occupying Mn sites. It can be obtained by fine-fitting the material after XRD testing using the Rietveld method.

[0063] In this application, firstly, the positive electrode active material has a core-shell structure. Specifically, the core contains lithium manganese iron phosphate, and the shell contains carbon material. By coating the lithium manganese iron phosphate with carbon material, the probability of interfacial side reactions caused by direct contact between the lithium manganese iron phosphate and the electrolyte can be effectively reduced, thereby effectively improving the rate performance and cycle performance of the corresponding battery. Secondly, the high compaction density of the positive electrode active material means that more active material can be accommodated in the same volume, so that the corresponding battery has a superior energy density. At the same time, the low disorder of the positive electrode active material broadens the Li... + The diffusion channels on the (010) crystal plane give the material excellent ionic conductivity. Meanwhile, Li... + The reduced diffusion resistance on the (010) crystal plane helps to reduce polarization, enabling the corresponding battery to have superior rate performance and also helping to improve the energy density of the battery. Therefore, the battery prepared using this positive electrode active material can achieve both high energy density and high rate performance.

[0064] As an example, the compaction density of the positive electrode active material is 2.45–2.49 g / cm³. 3 (For example, but not limited to, a compaction density of 2.45 g / cm³) 3 2.46 g / cm 3 2.47 g / cm 3 2.48 g / cm 3 and 2.49 g / cm 3 The disorder of the positive electrode active material is 3.0% to 10% (e.g., but not limited to any one of the following values ​​or a range between any two): 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 5%, 6%, 8%, 9% and 10%).

[0065] In this embodiment, the positive electrode active material has a higher compaction density and lower disorder, which helps to better improve the energy density and rate performance of the corresponding battery.

[0066] As an example, the disorder of the positive electrode active material is 3.0% to 4.3%, for example, but not limited to any one of 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, and 4.3%, or any range between two of them.

[0067] In this embodiment, the upper limit of disorder of the positive electrode active material is only 4.3%, which can more effectively improve the rate performance and energy density of the corresponding battery.

[0068] As an example, the mass percentage of carbon material in the positive electrode active material is 1.2% to 1.8%, for example, but not limited to any one of 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7% and 1.8% or any range between two.

[0069] In this embodiment, the aforementioned mass ratio is used to ensure that the outer shell has a suitable thickness, which can achieve a suitable electronic conductivity of the positive electrode active material while taking into account the coating effect.

[0070] As an example, the thickness of the casing is 3 to 10 nm, for example, but not limited to any one of 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm and 10 nm, or any range between two of them.

[0071] As an example, the chemical formula of lithium manganese iron phosphate is: Li a Fe 1-x-y Mn x M y PO4; wherein 1.0≤a≤1.04, 0.2≤x≤0.8, 0≤y≤0.007, and M is selected from at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y.

[0072] It should be noted that when y is 0, it means that lithium manganese iron phosphate does not contain doping elements, and when y is not 0, it means that lithium manganese iron phosphate contains doping elements.

[0073] Lithium manganese iron phosphate has the above chemical formula, which gives it the following characteristics: (1) The molar ratio of Li to the total amount of other metal elements in lithium manganese iron phosphate is limited to the above range, so that the material has both suitable structural stability and high energy density; (2) The molar ratio of Mn to Fe in lithium manganese iron phosphate has a large adjustable range, which can provide more feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application; (3) When y is not 0, it indicates that lithium manganese iron phosphate also includes doping element M. Element doping helps to improve the stability, capacity or ionic conductivity of the material, thereby making the corresponding battery have more ideal comprehensive electrical performance; furthermore, limiting the molar ratio of doping elements to the above range can achieve better modification effect while taking into account the performance of the material itself.

[0074] As an example, 'a' includes, but is not limited to, any one of the point values ​​of 1.0, 1.01, 1.02, 1.03, and 1.04, or any range of values ​​between any two.

[0075] As an example, x includes, but is not limited to, any one of the point values ​​of 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8, or any range of values ​​between any two.

[0076] As an example, y includes, but is not limited to, any one of the point values ​​or any range of values ​​between 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006 and 0.007.

[0077] As an example, the positive electrode active material was subjected to XPS testing and C1 S Peak fitting of the spectrum showed that the degree of graphitization of the carbon material was 74-96%, for example, but not limited to any one of the graphitization values ​​of 74%, 78%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, and 96%, or any range between two values.

[0078] It should be noted that when using XPS to test the graphitization degree of carbon materials, the sp_s of carbon atoms can be obtained. 2 Hybridization and sp 3 The respective proportions of hybridization, of which sp 2 Hybridization consists of a mixture of one s orbital and two p orbitals to form three hybrid orbitals, arranged in a planar triangle (bond angle 120°), sp 3 Hybridization occurs when one s orbital and three p orbitals combine to form four hybrid orbitals, exhibiting a tetrahedral structure (bond angles approximately 109.5°); furthermore, in XPS measurements, the sp orbitals of the carbon atom...2 Hybridization (binding energy approximately 284.5 eV) represents the graphitization characteristic, while the sp of carbon atoms... 3 Hybridization (binding energy approximately 285.5 eV) corresponds to amorphous or defective structures; a graphitization degree passing the sp requirement is sufficient. 2 / (sp 2 +sp 3 ) was calculated.

[0079] In this embodiment, the carbon material in the positive electrode active material has a high degree of graphitization, so that the positive electrode active material has a superior electronic conductivity.

[0080] As an example, the degree of graphitization of carbon materials is 78 to 96%, for example, but not limited to any one of the following points or any range between two: 78%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, and 96%.

[0081] As an example, the degree of graphitization of carbon materials is 90 to 96%, for example, but not limited to any one of 90%, 91%, 92%, 93%, 94%, 95% and 96% or any range between two.

[0082] In this embodiment, the graphitization degree of the carbon material in the positive electrode active material is as high as 90% or more, so that the positive electrode active material has a more superior electronic conductivity.

[0083] As an example, the sulfur content in the positive electrode active material is 15 to 136 ppm, for example, but not limited to any one of the following values ​​or any range between two: 15 ppm, 16 ppm, 17 ppm, 18 ppm, 19 ppm, 20 ppm, 50 ppm, 51 ppm, 100 ppm, 124 ppm, 130 ppm and 136 ppm.

[0084] In this embodiment, the sulfur content in the positive electrode active material is low, so that the material has better thermal stability, which helps to improve the problem of gas generation in the corresponding battery during operation at high temperatures (e.g., 45°C or 60°C).

[0085] As an example, the sulfur content in the positive electrode active material is 15 to 51 ppm, for example, but not limited to any one of 15 ppm, 16 ppm, 17 ppm, 18 ppm, 19 ppm, 20 ppm, 30 ppm, 40 ppm and 51 ppm or any range between two of them.

[0086] As an example, the sulfur content in the positive electrode active material is 15 to 18 ppm, for example, but not limited to any one of 15 ppm, 15.5 ppm, 16 ppm, 16.5 ppm, 17 ppm, 17.5 ppm and 18 ppm or any range between two of them.

[0087] In this embodiment, the sulfur content in the positive electrode active material is as low as 18 ppm, so that the material has better thermal stability and helps to better improve the problem of gas generation during the operation of the corresponding battery at high temperature conditions (e.g., 45°C or 60°C).

[0088] As an example, the Li ion diffusion coefficient of the positive electrode active material is (0.72–9.7) × 10⁻⁶. -12 cm 2 / S, for example, but not limited to, a Li ion diffusion coefficient of 0.72 × 10⁻⁶. -12 cm 2 / S, 0.83×10 -12 cm 2 / S、5×10 -12 cm 2 / S、6×10 - 12 cm 2 / S、7×10 -12 cm 2 / S, 7.4×10 -12 cm 2 / S、7.7×10 -12 cm 2 / S, 7.8×10 -12 cm 2 / S, 8.4×10 -12 cm 2 / S、8.6×10 -12 cm 2 / S, 9.5×10 -12 cm 2 / S、9.6×10 -12 cm 2 / S and 9.7×10 -12 cm 2 Any point value in / S or any range value between the two.

[0089] In this embodiment, the positive electrode active material has a high Li ion diffusion coefficient, which enables the corresponding battery to have excellent rate performance and energy density.

[0090] As an example, the Li ion diffusion coefficient of the positive electrode active material is (0.83–9.7) × 10⁻⁶. -12 cm2 / S, for example, but not limited to, a Li ion diffusion coefficient of 0.83 × 10⁻⁶. -12 cm 2 / S、5×10 -12 cm 2 / S、6×10 -12 cm 2 / S、7×10 - 12 cm 2 / S, 7.4×10 -12 cm 2 / S、7.7×10 -12 cm 2 / S, 7.8×10 -12 cm 2 / S, 8.4×10 -12 cm 2 / S、8.6×10 - 12 cm 2 / S, 9.5×10 -12 cm 2 / S、9.6×10 -12 cm 2 / S and 9.7×10 -12 cm 2 Any point value in / S or any range value between the two.

[0091] As an example, the Li ion diffusion coefficient of the positive electrode active material is (7.4–9.7) × 10⁻⁶. -12 cm 2 / S, for example, but not limited to, a Li ion diffusion coefficient of 7.4 × 10⁻⁶. -12 cm 2 / S、7.7×10 -12 cm 2 / S, 7.8×10 -12 cm 2 / S、8.0×10 - 12 cm 2 / S, 8.4×10 -12 cm 2 / S、8.6×10 -12 cm 2 / S、9.0×10 -12 cm 2 / S、9.3×10 -12 cm 2 / S, 9.5×10 - 12 cm 2 / S、9.6×10 -12 cm2 / S and 9.7×10 -12 cm 2 Any point value in / S or any range value between the two.

[0092] In this embodiment, the Li ion diffusion coefficient of the positive electrode active material is as high as (7.4~9.7)×10⁻⁶. -12 cm 2 / S, so that the corresponding battery has better rate performance and energy density.

[0093] As an example, the BET of primary particles in positive electrode active materials is 11.4–14.27 μm. 2 / gm 2 / g, for example, but not limited to BET of 11.4m 2 / g, 11.6m 2 / g, 13.3m 2 / g, 13.5m 2 / g, 14.0m 2 / g, 14.25m 2 / g, 14.26m 2 / g and 14.27m 2 Any point value in / g or any range value between the two.

[0094] In this embodiment, a suitable BET is used to enable the positive electrode active material to have a more ideal lithium-ion diffusion channel, so that the corresponding battery has a more ideal rate performance.

[0095] It should be noted that for processes or steps in positive electrode active materials that are not specifically described or limited, they can be set according to conventional choices in the field.

[0096] Secondly, embodiments of this application provide a method for preparing a positive electrode active material, comprising the following steps:

[0097] S1. A lithium source, manganese source, iron source, phosphorus source, acidic co-solvent, and organic carbon source are added to water and mixed to obtain a first mixture; the mixture is then heated to form a gel-like carbon-containing lithium iron manganese phosphate precursor; S2. The precursor is subjected to a first pressing treatment to obtain a first sheet; S3. The first sheet is sintered to obtain a positive electrode active material, wherein the gas pressure is negative for at least a portion of the time during the sintering process.

[0098] In this application, in step S1: a carbon-containing precursor is first prepared by the sol-gel method. The addition of an acidic co-solvent allows various metal raw materials to be fully dissolved and uniformly dispersed, and also adjusts the pH of the mixed system, thereby helping to promote gel formation. The addition of an organic carbon source can act as a chelating agent before the precursor is formed, achieving uniform distribution of metal elements by complexing with various metal ions. After the precursor is formed, the carbon source is located on the surface of the precursor, and can form a carbon material coating layer after subsequent sintering. In step S2: by pressing the precursor, the compaction density of the material can be effectively improved, thereby increasing the energy density of the corresponding battery. In step S3: the gas pressure is negative for at least part of the sintering process. The negative pressure condition can suppress the mixing of Mn / Fe atoms in the lattice (i.e., reduce the disorder of the positive electrode active material), increase the compaction density of the material, reduce the residual S in the material, increase the graphitization degree of the carbon material, and reduce the BET of the material. By following the above process, a lithium iron phosphate cathode active material can be prepared that simultaneously possesses high compaction density, low disorder, low sulfur residue, high graphitization degree, and low BET, so that the corresponding battery has both excellent energy density and rate performance.

[0099] As an example, during the sintering process, the negative pressure is -0.02 to -0.5 MPa (e.g., but not limited to any one of -0.02 MPa, -0.01 MPa, -0.1 MPa, -0.2 MPa, -0.3 MPa, -0.4 MPa and -0.5 MPa or any range between two).

[0100] In this embodiment, when the negative pressure is within the above range, it is possible to prepare a lithium iron phosphate cathode active material that simultaneously has high compaction density, low disorder, low S residual content, high graphitization degree, and small BET, so that the corresponding battery has both excellent energy density and rate performance.

[0101] As an example, the sintering process includes sequentially performing a heating process under a first pressure and a first sintering process under a second pressure; the heating temperature is 300–500°C (e.g., but not limited to any one of 300°C, 350°C, 400°C, 450°C, and 500°C, or a range between any two), and the first pressure is -0.1–-0.5 MPa (e.g., but not limited to any one of -0.1 MPa, -0.2 MPa, -0.3 MPa, -0.4 MPa, and -0.5 MPa, or a range between any two); and / or the first sintering process… The temperature is 550–700°C (e.g., but not limited to any one of 550°C, 600°C, 650°C, and 700°C, or any range between any two), the first sintering treatment time is 6–10 h (e.g., but not limited to any one of 6 h, 7 h, 8 h, 9 h, and 10 h, or any range between any two), and the second pressure is -0.02–-0.1 MPa (e.g., but not limited to any one of -0.02 MPa, -0.04 MPa, -0.06 MPa, -0.08 MPa, and -0.1 MPa, or any range between any two).

[0102] In this embodiment, the sintering process is carried out in two steps. First, heating to 300–500°C under the aforementioned negative pressure helps to effectively reduce the residual sulfur content and the material's BET (Best Equivalent Tolerance). Simultaneously, it effectively suppresses the mixing of Mn / Fe atoms within the crystal lattice. Second, performing a first sintering process at 550–700°C under the same negative pressure promotes carbon atom rearrangement, thereby increasing the graphitization degree of the carbon material. This also helps to increase the material's compaction density and effectively suppresses the mixing of Mn / Fe atoms within the crystal lattice. Therefore, by following the above process, a lithium manganese iron phosphate cathode active material can be prepared that simultaneously possesses higher compaction density, lower disorder, lower residual sulfur content, higher graphitization degree, and lower BET, resulting in batteries with superior energy density and rate performance.

[0103] It should be noted that "or / and" means that the relevant process parameters of the heating treatment and the relevant process parameters of the first sintering treatment can be limited separately or simultaneously. It can be understood that when the relevant parameters of the two stages are limited at the same time, the prepared positive electrode active material has more ideal physicochemical properties.

[0104] As an example, the heating process is carried out in a first atmosphere, which includes an inert atmosphere and a reducing atmosphere.

[0105] In this embodiment, the first atmosphere includes an inert atmosphere and a reducing atmosphere. The presence of the reducing atmosphere can reduce the residual sulfur element in the material to volatile H2S and remove it, thereby preparing a positive electrode active material with lower residual sulfur content. At the same time, the presence of the reducing atmosphere can also suppress the presence of Mn in the material. 3+ The generation of [something] reduces the occurrence of lattice distortion, thereby preparing a positive electrode active material with higher structural stability.

[0106] As an example, the reducing atmosphere has a volume percentage of 1 to 10% in the first atmosphere, such as, but not limited to, any one of the volume percentages of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%, or a range between any two.

[0107] In this embodiment, the volume percentage of the reducing atmosphere in the first atmosphere is limited to the aforementioned range, which enables the effective removal of S element and effective suppression of Mn while providing a suitable inert atmosphere. 3+ generate.

[0108] It should be noted that the type of inert atmosphere is not limited, for example, it can be at least one of nitrogen and argon.

[0109] It should be noted that the type of reducing atmosphere is not limited; for example, it can be at least one of hydrogen and carbon monoxide.

[0110] It should be noted that the first sintering process is carried out under an inert atmosphere, wherein the inert atmosphere is selected from at least one of nitrogen and argon.

[0111] As an example, in the step of heating the first sheet to 300-500°C, the heating rate is 3-5°C / min, for example, but not limited to any one of 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min and 5°C / min or any range between two of the heating rates.

[0112] In this embodiment, limiting the heating rate in the above steps to a suitable range helps to better reduce the residual S content and effectively reduce the BET of the material. At the same time, it can also better suppress the mixing of Mn / Fe atoms in the crystal lattice.

[0113] It should be noted that the first sintering process also includes two stages: the heating stage, in which the temperature of the first sheet is raised from 300-500℃ to 550-700℃, and the heat-holding sintering stage, in which the temperature is maintained at 550-700℃.

[0114] It should be noted that the gas pressure conditions during the heating and holding sintering stages of the first sintering process are both -0.02 to -0.1 MPa, which are within the range of the second gas pressure.

[0115] As an example, the heating stage in the first sintering process includes heating the first sheet to 550–700°C, wherein the heating rate is 3–5°C / min, for example, but not limited to any one of 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min and 5°C / min or a range between any two.

[0116] In this embodiment, limiting the heating rate in the above steps to a suitable range helps to promote carbon atom rearrangement, thereby increasing the graphitization degree of carbon materials. At the same time, it helps to increase the compaction density of the material. In addition, it can also better suppress the mixing of Mn / Fe atoms in the crystal lattice.

[0117] As an example, in step S1, the temperature of the heat treatment is 40 to 70°C (e.g., but not limited to any one of 40°C, 50°C, 60°C, and 70°C, or a range between any two).

[0118] In this embodiment, carbon-containing lithium iron manganese phosphate precursors can be prepared relatively efficiently by the sol-gel method under the above temperature conditions.

[0119] It should be noted that the specific types of lithium, manganese, iron, and phosphorus sources are not limited and can be selected and set according to the conventional methods in this field.

[0120] As an example, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium dihydrogen phosphate, and lithium oxalate.

[0121] As an example, the iron source is selected from at least one of ferric nitrate, ferric oxide, ferrous nitrate, and ferric oxalate.

[0122] As an example, the manganese source is selected from at least one of manganese monoxide, manganese trioxide, manganese tetroxide, manganese pentoxide, manganese carbonate, manganese oxalate, and manganese nitrate.

[0123] As an example, the phosphorus source is selected from at least one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, ammonium phosphate, and monoammonium phosphate.

[0124] It should be noted that when the raw material contains two or more target elements, the raw material can be understood as a common source of raw material elements for multiple target elements: for example, when the raw material is lithium dihydrogen phosphate, it can simultaneously serve as part of the lithium source and phosphorus source.

[0125] As an example, in the first mixture, the ratio of the sum of the masses of lithium, manganese, iron and phosphorus sources to the mass of water is (8 to 12):1, for example, but not limited to any one of the ratios of 8:1, 9:1, 10:1, 11:1 and 12:1 or any range between any two.

[0126] In this embodiment, limiting the ratio of the sum of the masses of lithium source, manganese source, iron source and phosphorus source to the mass of water within the above-mentioned range helps the various raw materials to dissolve quickly and disperse evenly in water.

[0127] As an example, in the first mixture, the molar ratio of Mn to Fe is 1:(0.25 to 4), for example, but not limited to any one of the molar ratios of 1:0.25, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 and 1:4, or any range between the two.

[0128] In this embodiment, the molar ratio of Mn and Fe elements in lithium manganese iron phosphate has a large adjustable range, which can provide a variety of possible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0129] As an example, the first mixture also includes a compound containing element M, wherein element M is selected from at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y.

[0130] In this embodiment, the first mixture also includes a compound containing element M. Element doping helps to improve the stability, capacity, or ionic conductivity of the material, thereby giving the corresponding battery a more ideal overall electrical performance.

[0131] As an example, the compound type containing element M is selected from at least one of the weak acid salts and oxides of the corresponding metal element.

[0132] In this embodiment, the compounds of the above type can be well dissolved and dispersed in the first mixture.

[0133] As an example, in the first mixture, the molar percentage of element M in the metal elements other than Li is 0.05% to 0.7%, for example, but not limited to, any one of 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, and 0.7%, or a range between any two.

[0134] In this embodiment, limiting the molar percentage of dopant elements within the aforementioned range allows for better modification effects while maintaining the material's inherent properties.

[0135] As an example, in the first mixture, the molar ratio of Li to the sum of the other metal elements is (1.0 to 1.04):1, for example, but not limited to any one of the molar ratios of 1:1, 1.01:1, 1.02:1, 1.03:1 and 1.04:1 or any range between two of them.

[0136] In this embodiment, the molar ratio of Li element to the total amount of other metal elements in the first mixture is limited to the above-mentioned range so that the prepared material has both suitable structural stability and high energy density.

[0137] It should be noted that, in order to better control the amount of acidic co-solvent added, the state of the first mixture can be used as a reference.

[0138] As an example, the first mixture is a clear and transparent solution.

[0139] It should be noted that a clear and transparent state means that there are no visible suspended particles or turbidity in the first mixture, and it has good light transmittance and uniformity.

[0140] In this embodiment, when the first mixture is a clear and transparent solution, it indicates that the various raw materials in the first mixture have been fully dissolved and uniformly dispersed with the assistance of an acidic co-solvent, which helps to finally prepare a positive electrode active material with high compaction and low disorder.

[0141] In addition to setting the amount of acidic cosolvent added based on the state of the first mixture, the amount of acidic cosolvent added can also be quantitatively calculated based on the principle of charge balance.

[0142] As an example, in the first mixture, the sum of the valence molar amounts of the cations of all metal elements is m1, and the sum of the valence molar amounts of the anions in the acidic co-solvent is m2. The ratio of the lower limit values ​​of m1 to m2 is 1.05:1, that is, the lower limit of the amount of acidic co-solvent added can be set according to this standard.

[0143] It should be noted that "valence molar mass" refers to the product of the valence of an ion and its molar mass. For example, if the raw material contains 0.2 mol of Fe... 2+ Then the corresponding molar mass of its valence state is 0.2 × 2 = 0.4 mol (i.e., containing 0.4 mol of positive charge); correspondingly, the "sum of molar masses of valence states" refers to the sum of the molar masses of the valence states of the same type of ions (e.g., multiple metal cations), for example, the raw material contains 0.2 mol of Fe. 2+and 0.3 mol Mn 2+ Then the sum of the molar amounts of the corresponding metal cations in their valence states is (0.2×2)+(0.3×2)=1.0mol (that is, a total of 1.0mol of positive charge). Correspondingly, the total amount of negative charge of the anions also needs to be 1.0mol in order for the cations and anions to achieve charge balance.

[0144] In this embodiment, the ratio of m1 to m2 is limited to the above range so that the first mixture contains an appropriate amount of acidic co-solvent, thereby helping various metal raw materials to dissolve quickly and disperse evenly.

[0145] As an example, the acidic co-solvent is selected from at least one of nitric acid, sulfuric acid, and perchloric acid.

[0146] In this embodiment, a wide variety of acidic co-solvents are applicable, providing numerous feasible solutions, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0147] In some alternative implementations, the acidic co-solvent is selected from nitric acid.

[0148] In this embodiment, nitric acid is selected as a co-solvent, which has the advantages of good solubilizing effect and less likelihood of introducing impurity elements (such as S).

[0149] As an example, the mass fraction of nitric acid is 50 to 70%, for example, but not limited to any one of the mass fractions of 50%, 55%, 60%, 65% and 70% or any range between two.

[0150] In this embodiment, nitric acid within the above concentration range is used, which has the advantage of better solubilizing effect.

[0151] As an example, in the first mixture, the molar ratio of the anion ions in the acidic cosolvent to the organic carbon source is (10–16):1, for example, but not limited to any one of the ratios of 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, and 16:1, or any range between the two.

[0152] In this embodiment, the molar ratio of acid radical ions in the acidic co-solvent to the organic carbon source is limited to the above range. Before the precursor is formed, an appropriate amount of organic carbon source can act as a chelating agent to make the distribution of various metal elements more uniform. After the precursor is formed, an appropriate amount of organic carbon source can be distributed more completely and uniformly on the surface of the precursor in order to obtain a carbon material shell with better coating integrity and more uniform thickness.

[0153] As an example, the first sheet has a thickness of 0.4–0.6 cm. 3 / g (e.g., but not limited to, a density of 0.4cm³) 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, 0.55cm 3 / g and 0.6cm 3 (any point value in / g or any range value between the two).

[0154] It should be noted that the compaction density of the first sheet in step S3 is the same as that of the first sheet in step S2.

[0155] In this embodiment, the first tableting process is carried out according to the above standards, which can better protect the material while increasing the compaction density of the material.

[0156] As an example, the acidic co-solvent is selected from nitric acid, and the organic carbon source contains reducing groups.

[0157] In this embodiment, nitrate ions have oxidizing properties. By selecting an organic carbon source with reducing groups, nitric acid and the organic carbon source can react exothermically during the preparation of the precursor by the sol-gel method, which helps to promote the decomposition of nitrate ions and the escape of water vapor, thereby obtaining the precursor more efficiently by the sol-gel method.

[0158] As an example, the reducing group is selected from at least one of hydroxyl and carboxyl groups.

[0159] In this embodiment, the organic carbon source having the aforementioned reducing groups can react with nitrate ions more easily and completely, so as to obtain the precursor more efficiently by the sol-gel method.

[0160] It should be noted that there are no restrictions on the types of organic carbon sources with reducing groups, and they can be selected and set in accordance with the conventional methods in this field.

[0161] As an example, the organic carbon source is selected from at least one of glucose, sucrose, citric acid, oxalic acid, acetic acid, glycine, tartaric acid, malic acid, malonic acid, polyvinyl alcohol, and ascorbic acid.

[0162] In this embodiment, a wide variety of organic carbon sources with reducing groups are applicable, providing a large number of feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0163] As an example, after the first sintering process, the first sheet is further subjected to a crushing process and a second pressing process in sequence; or, after the first sintering process, the first sheet is further subjected to a crushing process and a second sintering process in sequence, wherein the third gas pressure during the second sintering process is -0.02 to -0.5 MPa (e.g., but not limited to any one of -0.02 MPa, -0.01 MPa, -0.1 MPa, -0.2 MPa, -0.3 MPa, -0.4 MPa and -0.5 MPa or any range between two of the gas pressures).

[0164] It should be noted that the second sintering process is carried out under an inert atmosphere, wherein the inert atmosphere is selected from at least one of nitrogen and argon.

[0165] In this embodiment, adding a second pressing treatment after the first sintering treatment helps to further improve the compaction density of the material; adding a second sintering treatment after the first sintering treatment helps to further reduce the disorder of the material, further increase the graphitization degree of the carbon material, and the compaction density of the material.

[0166] It should be noted that after the first sintering treatment, either a second tableting treatment or only the second sintering treatment can be performed as an optimization method.

[0167] As an example, in the second tableting step, a density of 0.2–0.3 cm³ is obtained. 3 / g (e.g., but not limited to, a density of 0.2cm³) 3 / g, 0.4cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g and 0.3cm 3 The second sheet (any point value in / g or any range value between the two).

[0168] In this embodiment, the second tableting process is carried out according to the above standards, which can better protect the material while increasing the compaction density of the material.

[0169] As an example, in the second sintering process, the processing temperature is 500–600°C (e.g., but not limited to any one of 500°C, 520°C, 540°C, 560°C, 580°C, and 600°C, or a range between any two), and the processing time is 3–5 h (e.g., but not limited to any one of 3 h, 4 h, and 5 h, or a range between any two).

[0170] In this embodiment, the second sintering process is carried out at the above-mentioned temperature and duration, which helps to further reduce the disorder of the material, further increase the graphitization degree of the carbon material, and increase the compaction density of the material.

[0171] In other possible implementations, after the first sintering treatment, the first sheet is further subjected to a crushing treatment, a second pressing treatment, and a second sintering treatment in sequence, wherein the third gas pressure during the second sintering treatment is -0.02 to -0.5 MPa (e.g., but not limited to any one of -0.02 MPa, -0.01 MPa, -0.1 MPa, -0.2 MPa, -0.3 MPa, -0.4 MPa, and -0.5 MPa, or a range between any two).

[0172] In this embodiment, a second pressing process and a second sintering process are added after the first sintering process. The second pressing process helps to further improve the compaction density of the material, and the second sintering process helps to further reduce the disorder of the material, further increase the graphitization degree of the carbon material, and further improve the compaction density of the material.

[0173] It should be noted that for processes or steps in the preparation of positive electrode active materials that are not specifically described or limited, they can be set according to the conventional selection in this field.

[0174] Understandably, after the positive electrode active material is finally prepared, a crushing process is still required to obtain positive electrode active material particles with a suitable particle size.

[0175] As an example, this application provides a process flow diagram illustrating a method for preparing a positive electrode active material; for details, please refer to... Figure 1 .

[0176] Thirdly, embodiments of this application provide a lithium-ion battery, including the positive electrode active material provided in the first aspect embodiment or the positive electrode active material prepared by the preparation method provided in the second aspect embodiment.

[0177] In this application, the positive electrode active material contained in the lithium-ion battery has both high compaction density and low disorder, so that the lithium-ion battery has superior rate performance.

[0178] Fourthly, embodiments of this application provide an electrical device including a lithium-ion battery as provided in the third aspect embodiment.

[0179] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0180] Example 1

[0181] This application provides a method for preparing a positive electrode active material, including the following steps:

[0182] S1. Lithium nitrate, manganese oxalate, ferrous oxalate, ammonium dihydrogen phosphate, 50% nitric acid (co-solvent), and sucrose (organic carbon source) are added to water and mixed. The molar ratio of lithium nitrate, manganese oxalate, ferrous oxalate, and ammonium dihydrogen phosphate is Li:Mn:Fe:P = 1.02:0.58:0.42:1. The standard for the amount of nitric acid added is that the ratio of the sum of the valence molar amounts of nitrate ions (m1) in the nitric acid to the sum of the valence molar amounts of various metal elements (m2) is 1.05:1, and the molar ratio of nitrate ions to the carbon source is 12:1, resulting in a clear and transparent first mixture. Then, the first mixture is stirred at 50°C to allow the metal ions to complex and form a gel, thus obtaining a carbon-containing lithium iron manganese phosphate precursor.

[0183] S2 was used to perform the first tableting process on the precursor, resulting in a tablet with a density of 0.5 cm³. 3 / g of the first sheet.

[0184] S3 firstly, the first sheet is subjected to a first heating treatment under a first atmosphere (by volume percentage: 5% H2 + 95% N2) and a first pressure. Specifically, the temperature is increased to 400℃ at a rate of 4℃ / min, and the first pressure is maintained at -0.2MPa during the first heating process. Then, a sintering treatment is performed under a second pressure. Specifically, the first sheet is heated to 650℃ at a rate of 4℃ / min under a nitrogen atmosphere and subjected to a first heat preservation sintering treatment for 8 hours, while the second pressure is maintained at 0MPa. Finally, after crushing, the positive electrode active material is obtained. The chemical formula of lithium manganese iron phosphate in the positive electrode active material is Li. 1.02 Fe 0.42 Mn 0.58 PO4.

[0185] Example 2

[0186] This application provides a method for preparing a positive electrode active material, which differs from Example 1 only in that: in S3, the first gas pressure is maintained at 0 MPa and the second gas pressure is maintained at -0.05 MPa.

[0187] Example 3

[0188] This application provides a method for preparing a positive electrode active material, which differs from Example 1 only in that: in S3, the first gas pressure is maintained at -0.2MPa and the second gas pressure is maintained at -0.05MPa.

[0189] Example 4

[0190] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in step S2, the density of the first sheet is 0.6 cm³. 3 / g.

[0191] Example 5

[0192] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in step S1, the molar ratio of nitrate ions to carbon source is 15:1.

[0193] Example 6

[0194] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in S3, the first gas pressure is maintained at -0.4MPa.

[0195] Example 7

[0196] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in S3, the second gas pressure is maintained at -0.1 MPa.

[0197] Example 8

[0198] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: after step 3, step S4 is added. Step S4 specifically involves sequentially crushing the first sheet, performing a second pressing process, and then a second sintering process. In the second pressing process, a material with a density of 0.25 cm³ is obtained. 3 / g of the second sheet; in the second sintering process, the temperature is raised to 600℃ at a rate of 5℃ / min under a nitrogen atmosphere and a second heat preservation sintering process is carried out for 4h, wherein the third pressure is maintained at -0.4MPa during the second heat preservation sintering process.

[0199] Example 9

[0200] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: after step 3, step S4 is added: step S4 specifically involves: sequentially crushing the first sheet and performing a second heat preservation sintering treatment, wherein, in the second sintering treatment step, the temperature is raised to 600°C at a rate of 5°C / min under a nitrogen atmosphere and a second heat preservation sintering treatment is performed for 4 hours, wherein, during the second heat preservation sintering process, the third gas pressure is maintained at -0.4MPa.

[0201] Example 10

[0202] This application provides a method for preparing a positive electrode active material, which differs from Example 9 only in that: after step 3, step S4 is added; step S4 specifically involves: sequentially crushing and pressing the first sheet into a second sheet, wherein the second pressing step yields a material with a density of 0.25 cm³. 3 / g of the second sheet.

[0203] Example 11

[0204] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that the first atmosphere contains only N2 and no H2.

[0205] Example 12

[0206] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in step S1, MgO compound is added to the first mixture, wherein the molar percentage of Mg element in the first mixture other than Li is 0.2%, and the chemical formula of lithium manganese iron phosphate in the positive electrode active material is Li 1.02 Fe 0.42 Mn 0.58 Mg 0.002 PO4.

[0207] Example 13

[0208] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in step S1, the H2 content in the first atmosphere is 7%.

[0209] Example 14

[0210] This application provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in step S1, sulfuric acid with a mass fraction of 50% is used as a co-solvent.

[0211] Comparative Example 1

[0212] This comparative example provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in S3, the first gas pressure is maintained at 0 MPa and the second gas pressure is maintained at 0 MPa.

[0213] Comparative Example 2

[0214] This comparative example provides a method for preparing a positive electrode active material, which differs from Example 3 only in that: in step S2, the first tableting process is not performed.

[0215] Comparative Example 3

[0216] This comparative example provides a method for preparing a positive electrode active material, which differs from Example 3 only in that nitric acid (an acidic co-solvent) is not added in step S1.

[0217] To better understand the parameter differences between the above embodiments and comparative examples, the important parameters in the above embodiments and comparative examples are summarized and explained in the form of a table, as shown in Table 1.

[0218] Table 1

[0219]

[0220]

[0221] It should be noted that “—” in Table 1 indicates that the component was not present or the step was not performed, and therefore there is no corresponding parameter value.

[0222] Test case

[0223] (1) Morphology and composition testing of positive electrode active material

[0224] Test methods: The positive electrode active materials prepared in Examples 3 and 12 were used as samples. The elemental composition of the sample in Example 12 was tested by scanning electron microscopy combined with EDS scanning, and the TEM image of the sample in Example 3 was tested by transmission electron microscopy.

[0225] See Figure 2 and Figure 3 It can be seen that the positive electrode active material has a core-shell structure, in which the lighter-colored edge is a carbon material layer, and the darker-colored interior is lithium manganese iron phosphate.

[0226] (2) Performance testing of positive electrode active materials:

[0227] The testing method used the positive electrode active materials prepared in Examples 1-14 and Comparative Examples 1-3 as samples, and then tested the carbon material mass ratio, disorder, compaction density, S content, graphitization degree, BET of primary particles, and Li content of each sample. + The diffusion coefficient was calculated, and the test results were then summarized in Table 2.

[0228] The testing steps for the carbon material mass percentage are as follows:

[0229] A carbon-sulfur analyzer was used to test the positive electrode active material to obtain the mass content of the carbon coating layer in the positive electrode active material.

[0230] The test steps for disorder are as follows:

[0231] The sample was sieved, filled, and sealed using a neutron diffraction refinement method, and the neutron wavelength was set. The detection range 2θ was set to 10–90°, and (311) superlattice diffraction peaks were collected to accurately distinguish the occupancy information of Mn and Fe atoms. The structure was refined and fitted using the Rietveld method in GSAS software. The crystal structure model was set to the Pbnm space group, and the peak width and shape parameters were refined using the pseudo-Voigt function. The occupancy rate of Mn atoms at Li sites (Occ-Mn) was refined. Li ), refine the occupancy of Fe atoms at Mn sites (Occ-Fe), Mn This yields the atomic occupancy parameters and atomic position information of Mn and Fe, based on the formula D = (Occ - Mn). Li +Occ-Fe Mn The Mn / Fe site disorder degree was calculated by multiplying the result by 100%. Simultaneously, the weighted profile factor Rwp (<10%) and the expectation factor R were used to calculate the site disorder. p and goodness of fit χ² 2 (0.8~1.2) To determine the reliability of the refinement results, where, Figure 4 This is the XRD refinement result diagram corresponding to the positive electrode active material in Example 3 of this application.

[0232] The test steps for compaction density are as follows:

[0233] The positive electrode active material was tested using a powder compaction density meter, with a test pressure of 220 MPa and a holding time of 15 s.

[0234] The testing steps for sulfur content are as follows:

[0235] The sulfur content of the positive electrode active material was tested using inductively coupled plasma atomic emission spectrometry (ICP).

[0236] The testing steps for graphitization degree are as follows:

[0237] Peak fitting of the C1s spectrum was performed using XPS, employing a Gaussian-Lorentzian mixing function, primarily targeting sp... 2 -C(284.5eV), sp 3 The -C (285.2 eV) bonds are subjected to peak fitting, and the peak areas of each are directly obtained. The degree of graphitization can then be calculated using the formula: Graphitization degree = sp 2 / (sp 2 +sp 3 ).

[0238] The BET test procedure for a single particle is as follows:

[0239] Take 5g of sample and put it into a long tube with a bulb. First, vacuum it at 200℃ for 2 hours, and then introduce N2 for gas adsorption. The amount of adsorbate molecules (N2) adsorbed by the positive electrode material sample is determined according to the pressure or weight change before and after adsorption, so as to obtain the specific surface area.

[0240] Among them, Li + The steps for testing the diffusion coefficient are as follows:

[0241] The positive electrode active material was assembled into a coin cell with lithium metal as the negative electrode. Then, the diffusion coefficient of the material was tested by the GITT method. The specific test steps were as follows: (1) The assembled coin cell was charged and discharged twice at 0.1C to fully wet the electrode material and form a stable SEI film; (2) It was charged at a constant current of 0.1C, and a current pulse was applied every 10 minutes, followed by a 30-minute pause until the voltage returned to steady state; this process was repeated until the charging cutoff voltage was 4.3V, and the voltage transient response curve during each pulse was recorded; (3) It was discharged under the same conditions (0.1C), and a 30-minute pause was applied after every 10 minutes of discharge until the discharge cutoff voltage was 2.0V, and the voltage relaxation data was recorded synchronously; (4) According to Fick's second law, the Li+ diffusion coefficient was calculated by using the voltage change (ΔEs and ΔEt) and the pulse time (t) through the formula, where the calculation formula is as follows:

[0242]

[0243] Where τ is the relaxation time, m B V M M B S and S represent the active material mass, molar volume, molar mass, and electrode area, respectively.

[0244] Table 2

[0245]

[0246]

[0247] (3) Electrical property testing of materials

[0248] Test method: The positive electrode active materials prepared in Examples 1-14 and Comparative Examples 1-3 were assembled into coin cells, and then charge-discharge tests were performed in the Blue Battery Test System. The test voltage was 2.5V-4.3V, the cutoff current was 0.05C, 0.1C charge-discharge for 2 cycles (activation), 0.33C charge-discharge for 1 cycle, 1C charge-discharge for 1 cycle, and 1C charge-3C discharge for 1 cycle, where 1C = 150mAh / g. The energy density and the 1C and 3C rates were recorded, and the test results are summarized in Table 3.

[0249] The battery assembly steps are as follows: active materials, conductive carbon black, and PVDF binder are slurried at a mass ratio of 90:5:5, coated on aluminum foil, and vacuum dried at 120°C for 12 hours; the battery is assembled in an argon glove box, with lithium sheet as the counter electrode. The electrolyte includes lithium salt, solvent, and additives. The lithium salt is lithium hexafluorophosphate (LiPF6) with a concentration of 1 mol / L. The solvent is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. The additives are vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in a volume ratio of 1:1.

[0250] Table 3

[0251]

[0252] Referring to Tables 2 and 3, the test results of Examples 1-14 and Comparative Examples 1-2 show that the positive electrode active material prepared by combining gel pressing process with micro negative pressure sintering process has both high compaction density and low disorder, so that the corresponding battery has both excellent energy density and rate performance.

[0253] As can be seen from the test results of Examples 3 and 8-10, after the first sintering treatment, the addition of a second pressing treatment and a second sintering treatment can produce a positive electrode active material with higher compaction and lower disorder, thereby enabling the corresponding battery to have both superior energy density and rate performance.

[0254] The test results of Examples 3 and 12 show that when the first inert atmosphere contains hydrogen, the positive electrode active material prepared has advantages such as lower residual sulfur and lower disorder compared to the one without hydrogen, so that the corresponding battery has better rate performance and energy density.

[0255] As can be seen from the test results of Example 3 and Comparative Example 3, in the process of preparing carbon-containing lithium manganese iron phosphate precursor by sol-gel method, the addition of acidic co-solvent can effectively improve the compaction density of positive electrode active material and effectively reduce the disorder of positive electrode active material compared with the absence of acidic co-solvent, so that the corresponding battery has both better energy density and rate performance.

[0256] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material has a core-shell structure, with the core material comprising lithium manganese iron phosphate and the outer shell material comprising carbon materials. The compaction density of the positive electrode active material is 2.26–2.49 g / cm³. 3 The disorder degree of the positive electrode active material is 3.0-14%.

2. The positive electrode active material according to claim 1, characterized in that, The compaction density of the positive electrode active material is 2.45–2.49 g / cm³. 3 The disorder degree of the positive electrode active material is 3.0-10%; Optionally, the disorder degree of the positive electrode active material is 3.0 to 4.3%.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The carbon material accounts for 1.2% to 1.8% of the mass of the positive electrode active material.

4. The positive electrode active material according to claim 1 or 2, characterized in that, The chemical formula of the lithium manganese iron phosphate is: Li a Fe 1-x-y Mn x M y PO4; wherein, 1.0≤a≤1.04, 0.2≤x≤0.8, 0≤y≤0.007, and M is selected from at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y; Optionally, 0.0005≤y≤0.

007.

5. The positive electrode active material according to claim 1 or 2, characterized in that, XPS tests were performed on the positive electrode active material and C1 was analyzed. S Peak fitting of the spectrum showed that the degree of graphitization of the carbon material was 74-96%. Or / and, the sulfur content in the positive electrode active material is 15 to 136 ppm; Or / and, the Li ion diffusion coefficient of the positive electrode active material is (0.72~9.7)×10 -12 cm 2 / S; Or / and, the BET of the positive electrode active material is 11.4–14.27m. 2 / g.

6. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: S1 involves adding lithium source, manganese source, iron source, phosphorus source, acidic cosolvent, and organic carbon source to water and mixing them to obtain a first mixture; then heating the mixture to form a gel-like carbon-containing lithium iron manganese phosphate precursor. S2 performs a first compression process on the precursor to obtain a first sheet; S3 performs sintering treatment on the first sheet to obtain a positive electrode active material, wherein the gas pressure is negative for at least a portion of the time during the sintering process.

7. The preparation method according to claim 6, characterized in that, The negative pressure is -0.02 to -0.5 MPa.

8. The preparation method according to claim 6, characterized in that, The sintering process includes sequentially heating under a first pressure and performing a first sintering process under a second pressure. The heating treatment temperature is 300-500℃, and the first gas pressure is -0.1--0.5MPa; or / and, the first sintering treatment temperature is 550-700℃, the first sintering treatment time is 6-10h, and the second gas pressure is -0.02--0.1MPa.

9. The preparation method according to claim 8, characterized in that, The heating process is carried out under a first atmosphere, which includes an inert atmosphere and a reducing atmosphere; Optionally, the reducing atmosphere accounts for 1 to 10% of the volume of the first atmosphere.

10. The preparation method according to any one of claims 6 to 9, characterized in that, The acidic co-solvent is selected from at least one of nitric acid, sulfuric acid, and perchloric acid; Or / and, in the first mixture, the molar ratio of the anion ions in the acidic cosolvent to the organic carbon source is (10-16):1; Or / and, the density of the first sheet is 0.4 to 0.6 cm³. 3 / g.

11. The preparation method according to claim 10, characterized in that, The acidic co-solvent is selected from nitric acid, and the organic carbon source contains reducing groups; Optionally, the reducing group is selected from at least one of hydroxyl and carboxyl groups.

12. The preparation method according to claim 8, characterized in that, After the first sintering process, the process also includes sequentially crushing the first sheet and performing a second pressing process. Alternatively, after the first sintering treatment, the first sheet may be subjected to a crushing treatment and a second sintering treatment in sequence, wherein the third gas pressure during the second sintering treatment is -0.02 to -0.5 MPa.

13. A lithium-ion battery, characterized in that, It includes the positive electrode active material as described in any one of claims 1 to 5 or the positive electrode active material prepared by the preparation method described in any one of claims 6 to 12.

14. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 13.

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