Lithium iron phosphate positive electrode active material, positive electrode plate, lithium secondary battery, and electrical device

Abstract

The present application provides a lithium iron phosphate positive electrode active material, a positive electrode plate, a lithium secondary battery, and an electrical device. The positive electrode active material comprises a lithium iron phosphate base material, the molar ratio of elemental Sn in the lithium iron phosphate base material being 5-15%, and the molar ratio of elemental Ni in the lithium iron phosphate base material being 20-30%. The powder resistivity of the positive electrode active material at 8 MPa is less than or equal to 30Ω·cm. The lithium iron phosphate positive electrode active material provided by the present application is characterized by high capacity per gram, and batteries prepared therefrom exhibit both good energy density and cycling performance.

Description

Lithium iron phosphate positive electrode active material, positive electrode sheet, lithium secondary battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202410256785.2 “Lithium iron phosphate positive electrode active material, positive electrode sheet, lithium secondary battery and electrical device” filed on March 6, 2024, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a lithium iron phosphate positive electrode active material, a positive electrode sheet, a lithium secondary battery, and an electrical device. Background Art

[0004] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion batteries have achieved significant development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0005] As a lithium-ion battery cathode material, LiFePO4 has rapidly become a global research hotspot due to its abundant resources, low price, environmental friendliness, and stable voltage in its two-phase reaction. Because lithium iron phosphate (LFP) has a lower specific capacity than ternary materials, recent research has focused on improving its capacity. However, focusing solely on improving LFP's capacity inevitably compromises other battery properties, such as cycling and processing performance.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problem, and its purpose is to provide a lithium iron phosphate positive electrode active material with high gram capacity, and the battery prepared therefrom can have good energy density, cycle performance and processing performance.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a lithium iron phosphate positive electrode active material, the positive electrode active material includes a lithium iron phosphate substrate, the molar ratio of the Sn element in the lithium iron phosphate substrate is 5%-15%, and the molar ratio of the Ni element in the lithium iron phosphate substrate is 20%-30%; the powder resistivity of the positive electrode active material at 8MPa is ≤30Ω·cm.

[0009] Introducing Sn and Ni within the aforementioned content range into the lithium iron phosphate substrate significantly increases the specific capacity of the positive electrode active material. Furthermore, the surface of the lithium iron phosphate substrate is coated with a complete and dense carbon coating, resulting in a low powder resistivity of the positive electrode active material. Therefore, batteries fabricated using the positive electrode active material disclosed herein can achieve both good energy density and cycle performance.

[0010] In any embodiment, the lithium iron phosphate substrate has the formula Li a Fe b P c O d Sn x Ni y Q q , wherein Q includes at least one of V, Ti, Cu, Cr, Zn, Pb, Ca, Co, Sr, and Nb, 0.99≤a≤1, 0.545≤b≤0.9, 0.99≤c≤1, 3.9≤d≤4, 0.05≤x≤0.15, 0.20≤y≤0.30, and 0≤q≤0.008.

[0011] After introducing Sn and Ni elements into the lithium iron phosphate matrix, further introducing at least one of the elements V, Ti, Cu, Cr, Zn, Pb, Ca, Co, Sr, Nb, etc. can further increase the gram capacity of the positive electrode active material, thereby making the prepared battery have better energy density.

[0012] In any embodiment, the molar ratio of Sn element in the lithium iron phosphate substrate is 7.5%-12.5%, and the molar ratio of Ni element in the lithium iron phosphate substrate is 22.5%-27.5%.

[0013] In any embodiment, 0.075≤x≤0.125, 0.225≤y≤0.275.

[0014] In any embodiment, the positive electrode active material has a powder resistivity of ≤20 Ω·cm at 8 MPa.

[0015] When the contents of Sn and Ni elements and the powder resistivity are controlled within the above ranges, both the energy density and the cycle performance of the battery can be improved.

[0016] In any embodiment, the molar ratio of the Ti element in the lithium iron phosphate matrix is ​​0.1%-0.5%, and the molar ratio of the V element in the lithium iron phosphate matrix is ​​0.1%-0.3%.

[0017] In any embodiment, the lithium iron phosphate substrate has the formula Li a Fe b P c O d Snx Ni y Ti z V n , where 0.99≤a≤1, 0.545≤b≤0.9, 0.99≤c≤1, 3.9≤d≤4, 0.05≤x≤0.15, 0.20≤y≤0.30, 0.001≤z≤0.005, 0.001≤n≤0.003.

[0018] In any embodiment, the molar ratio of the Ti element in the lithium iron phosphate matrix is ​​0.2%-0.4%, and the molar ratio of the V element in the lithium iron phosphate matrix is ​​0.15%-0.25%.

[0019] In any embodiment, 0.002≤z≤0.004, 0.0015≤n≤0.0025.

[0020] After introducing Sn and Ni elements into the lithium iron phosphate matrix, further introducing at least one of V and Ti elements can further increase the gram capacity of the positive electrode active material, thereby making the prepared battery have better energy density.

[0021] In any embodiment, the positive electrode active material further comprises carbon, and the carbon content of the positive electrode active material is 1.28%-1.35% based on the total weight of the positive electrode active material. In any embodiment, the carbon content of the positive electrode active material is 1.30%-1.34% based on the median weight of the positive electrode active material. In any embodiment, the carbon content of the positive electrode active material is 1.31%-1.33% based on the median weight of the positive electrode active material.

[0022] In any embodiment, the positive electrode active material includes a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate substrate.

[0023] The lithium iron phosphate substrate has a complete, thin and dense carbon coating layer on at least part of its surface, which builds a complete conductive network in the positive electrode active material, thus making a good contribution to the energy density and cycle performance of the battery.

[0024] In any embodiment, the iron characteristic peak intensity of the positive electrode active material is Fe and carbon characteristic peak intensity I c The ratio satisfies I Fe / I c ≤0.023, lithium characteristic peak intensity I of positive electrode active material Li and carbon characteristic peak intensity I c The ratio satisfies I Li / I c ≤0.013, where the iron characteristic peak intensity I FeThe peak position is at 706.7±0.5eV, and the lithium characteristic peak intensity I Li The peak position is at 54.9±0.5eV, and the carbon characteristic peak intensity is I c The peak position is at 285.0±0.5eV

[0025] In any embodiment, the iron characteristic peak intensity of the positive electrode active material is Fe and carbon characteristic peak intensity I c The ratio satisfies I Fe / I c ≤0.015, lithium characteristic peak intensity I of positive electrode active material Li and carbon characteristic peak intensity I c The ratio satisfies I Li / I c ≤0.010, where the iron characteristic peak intensity I Fe The peak position is at 706.7±0.5eV, and the lithium characteristic peak intensity I Li The peak position is at 54.9±0.5eV, and the carbon characteristic peak intensity is I c The peak position is at 285.0±0.5eV.

[0026] When the ratio of the iron characteristic peak intensity, lithium characteristic peak intensity and carbon characteristic peak intensity of the positive electrode active material is within the above range, the carbon coating layer on the surface of the lithium iron phosphate substrate has better integrity, which can make the battery have better cycle performance.

[0027] In any embodiment, the iron dissolution rate of the positive electrode active material is ≤5.5 mg / L, wherein the iron dissolution rate is the iron ion concentration of the positive electrode active material after standing in 0.008 mol / L hydrochloric acid at 25° C. for 2 hours.

[0028] In any embodiment, the iron dissolution rate of the positive electrode active material is ≤4 mg / L, wherein the iron dissolution rate is the iron ion concentration of the positive electrode active material after standing in 0.008 mol / L hydrochloric acid at 25° C. for 2 hours.

[0029] When the iron dissolution rate of the positive electrode active material is within the above range, the carbon coating layer on the surface of the lithium iron phosphate substrate has good integrity, which can slow down the damage of the acid to the lithium iron phosphate substrate, and enable the battery to have better cycle performance and storage life.

[0030] In any embodiment, the true BET value of the positive electrode active material ranges from 8.9 to 15.312 m 2 / g, the apparent BET value range of the positive electrode active material is 9.428-16.994m 2 / g.

[0031] In any embodiment, the true BET value of the positive electrode active material is in the range of 10-14m2 / g, the apparent BET value of the positive electrode active material ranges from 11 to 15 m 2 / g.

[0032] The lithium iron phosphate substrate having the above characteristics has a dense carbon coating layer and a lower overall BET, which can enable the battery to have better energy density and cycle performance.

[0033] In any embodiment, the degree of graphitization of the positive electrode active material is ≤1.039.

[0034] In any embodiment, the degree of graphitization of the positive electrode active material is ≤1.01.

[0035] The positive electrode active material with the above characteristics has a carbon coating layer on the surface of the lithium iron phosphate substrate with a high degree of graphitization, which can make the battery have better energy density and cycle performance.

[0036] In any embodiment, the volume average particle size D50 of the positive electrode active material is 0.7-1.52 μm. In any embodiment, the volume average particle size D50 of the positive electrode active material is 0.9-1.5 μm. In any embodiment, the volume average particle size D50 of the positive electrode active material is 1.1-1.3 μm.

[0037] In any embodiment, the powder compaction density of the positive electrode active material at 22.6 MPa is 2.21-2.73 g / cm 3 In any embodiment, the powder compaction density of the positive electrode active material at 22.6 MPa is 2.45-2.65 g / cm 3 In any embodiment, the powder compaction density of the positive electrode active material at 22.6 MPa is 2.5-2.6 g / cm 3 .

[0038] When the D50 and powder compaction density of the positive electrode active material are within the above ranges, the prepared battery can have better energy density and cycle performance.

[0039] The second aspect of the present application provides a positive electrode plate, characterized in that it includes a positive electrode collector and a positive electrode active material arranged on at least one surface of the positive electrode collector, wherein the positive electrode active material is the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application.

[0040] In any embodiment, the dehydration efficiency of the positive electrode sheet is 6.6-9.8 ppm / min. In any embodiment, the dehydration efficiency of the positive electrode sheet is 8-9 ppm / min.

[0041] In any embodiment, the compaction density of the positive electrode sheet is not less than 2.23 g / cm 3 .

[0042] Since a certain proportion of Sn and Ni elements are introduced into the lithium iron phosphate substrate, the carbon coating layer on its surface can be more complete and dense. Therefore, the prepared positive electrode sheet has the characteristics of high compaction density and easy dehydration, which can enable the lithium-ion battery to have excellent energy density, cycle performance and processing performance, and can significantly improve the battery production efficiency and reduce the battery production cost.

[0043] The third aspect of the present application provides a lithium secondary battery, characterized in that it includes the positive electrode sheet described in the third aspect of the present application.

[0044] A fourth aspect of the present application provides an electrical device comprising the lithium secondary battery described in the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0046] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0047] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0048] FIG4 is a spectrum of a Raman spectrometer used to characterize the degree of graphitization in an embodiment of the present application, wherein the corresponding peak intensities are respectively recorded as D2, D1, D3 and G, and the degree of graphitization is D1 / G.

[0049] Description of reference numerals:

[0050] 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0051] Hereinafter, embodiments of the lithium iron phosphate positive electrode active material, the positive electrode sheet containing the positive electrode active material, the secondary battery, the electric device and the method for manufacturing the same of the present application will be described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0052] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0056] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0057] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0058] Because lithium iron phosphate has a lower gram capacity than ternary materials, improving its capacity has been a major research and development focus in recent years. However, focusing solely on improving lithium iron phosphate's capacity inevitably compromises other battery properties, such as cycling performance and processing performance. The lithium iron phosphate cathode active material provided in this application has a high gram capacity, and batteries prepared therefrom can achieve excellent energy density, cycling performance, and processing performance.

[0059] [Positive electrode active material]

[0060] In order to achieve the above-mentioned purpose, the present application provides a lithium iron phosphate positive electrode active material, which includes a lithium iron phosphate substrate, the molar ratio of the Sn element in the lithium iron phosphate substrate is 5%-15%, and the molar ratio of the Ni element in the lithium iron phosphate substrate is 20%-30%; the powder resistivity of the positive electrode active material at 8MPa is ≤30Ω·cm.

[0061] In some embodiments, the lithium iron phosphate substrate contains Sn. In some embodiments, the molar ratio of Sn in the lithium iron phosphate substrate is 5%-15%, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or other values ​​not listed in the range of 5%-15%. In some non-limiting embodiments, the molar ratio of Sn in the lithium iron phosphate substrate is 5%, 7.5%, 10%, 12.5%, or 15%.

[0062] In some embodiments, the lithium iron phosphate substrate contains nickel. In some embodiments, the molar ratio of the nickel element in the lithium iron phosphate substrate is 20%-30%, such as 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or other values ​​not listed in the range of 20%-30%. In some non-limiting embodiments, the molar ratio of the nickel element in the lithium iron phosphate substrate is 20%, 22.5%, 25%, 27.5%, or 30%.

[0063] In some embodiments, the powder resistivity of the positive electrode active material at 8 MPa is ≤ 30 ohm·cm (Ω·cm), such as 1 Ω·cm, 5 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm, etc., or other unlisted values ​​within the range of ≤ 30 Ω·cm. In some non-limiting embodiments, the powder resistivity of the positive electrode active material at 8 MPa is 16.8 Ω·cm, 24.7 Ω·cm, 18.8 Ω·cm, 11.4 Ω·cm, 9.6 Ω·cm, 8.5 Ω·cm, 13.5 Ω·cm, 23.7 Ω·cm, 27.8 Ω·cm, 15.3 Ω·cm, 16.2 Ω·cm, 20.3 Ω·cm, 28.9 Ω·cm, 13.4 Ω·cm, 15.3 Ω·cm, 17.9 Ω·cm, 19.5 Ω·cm, 19.8 Ω·cm, 11.2 Ω·cm, 16.5 Ω·cm, and 9.8 Ω·cm.

[0064] As used herein, "powder resistivity" describes the electrical conductivity of a powder material, typically referring to the resistance per unit length or area, expressed in ohm-meters (Ω·m). It is measured using a powder resistivity tester (ST2722) according to standard GB / T 30835-2014.

[0065] Introducing Sn and Ni within the aforementioned content range into the lithium iron phosphate substrate significantly increases the specific capacity of the positive electrode active material. Furthermore, the surface of the lithium iron phosphate substrate is coated with a complete and dense carbon coating, resulting in a low powder resistivity of the positive electrode active material. Therefore, batteries fabricated using the positive electrode active material disclosed herein can achieve both good energy density and cycle performance.

[0066] In some embodiments, the lithium iron phosphate substrate further contains one, two, or more of the elements V, Ti, Cu, Cr, Zn, Pb, Ca, Co, Sr, and Nb.

[0067] In some embodiments, the molar percentage of the elements V, Ti, Cu, Cr, Zn, Pb, Ca, Co, Sr, and Nb in the lithium iron phosphate matrix is ​​0%-0.8%, for example, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., or other values ​​not listed in the range of 0%-0.8%.

[0068] In some embodiments, the lithium iron phosphate substrate has the formula Li a Fe b P c O d Sn x Ni y Qq , wherein Q includes at least one of V, Ti, Cu, Cr, Zn, Pb, Ca, Co, Sr, and Nb, 0.99≤a≤1, 0.545≤b≤0.9, 0.99≤c≤1, 3.9≤d≤4, 0.05≤x≤0.15, 0.20≤y≤0.30, and 0≤q≤0.008.

[0069] When used in this article, "having a molecular formula" is not limited to the substance represented by the molecular formula, but also includes other substances formed after further doping modification and / or coating modification on the basis of the molecular formula, which is not limited here. The use of "having a molecular formula" is only for the convenience of description and is not intended to limit this application. It can be understood that new materials or new substances obtained by appropriate modification on the basis of the listed positive active materials are also within the scope of positive active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive active material, and a non-limiting example is coating modification.

[0070] In the enumeration of positive electrode active materials in this application, unless otherwise specified, the Li content refers to the initial state of the material. When the positive electrode active material is applied to the positive electrode sheet in the battery system, the Li content in the positive electrode active material contained in the positive electrode sheet will usually change after charge and discharge cycles. The Li content can be measured by atomic molar content, but is not limited to this. Regarding "the Li content refers to the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry.

[0071] In the list of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the atomic molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by atomic molar content, but is not limited to this.

[0072] In some embodiments, the molecular formula Li a Fe b P c O d Sn x Ni y Q q The numerical range of x is 0.05≤x≤0.15, such as 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, etc., or other unlisted numerical values ​​within the range of 0.05≤x≤0.15. In some non-limiting embodiments, the molecular formula Li a Fe b P c O d Sn x Ni y Q qThe value range of x is 0.05, 0.075, 0.10, 0.125, and 0.15.

[0073] In some embodiments, the molecular formula Li a Fe b P c O d Sn x Ni y Q q The numerical range of y is 0.20≤y≤0.30, such as 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, etc., or other unlisted numerical values ​​within the range of 0.20≤y≤0.30. In some non-limiting embodiments, the molecular formula Li a Fe b P c O d Sn x Ni y Q q The numerical range of y is 0.2, 0.225, 0.25, 0.275, and 0.30.

[0074] After introducing Sn and Ni elements into the lithium iron phosphate matrix, further introducing at least one of the elements V, Ti, Cu, Cr, Zn, Pb, Ca, Co, Sr, Nb, etc. can further increase the gram capacity of the positive electrode active material, thereby making the prepared battery have better energy density.

[0075] In some embodiments, the molar ratio of Sn element in the lithium iron phosphate substrate is 7.5%-12.5%, and the molar ratio of Ni element in the lithium iron phosphate substrate is 22.5%-27.5%.

[0076] Correspondingly, the molecular formula Li a Fe b P c O d Sn x Ni y Q q In the equation (a), 0.075≤x≤0.125, 0.225≤y≤0.275.

[0077] Introducing Sn and Ni elements within the above ranges, especially Sn and Ni elements within the above preferred ranges, into the lithium iron phosphate substrate can significantly increase the gram capacity of the positive electrode active material, thereby enabling the prepared battery to have better energy density.

[0078] In some embodiments, the lithium iron phosphate substrate further contains Ti and V elements.

[0079] In some embodiments, the lithium iron phosphate substrate has the formula Li a Fe b P c O d Sn x Ni y Ti z V n , where 0.99≤a≤1, 0.545≤b≤0.9, 0.99≤c≤1, 3.9≤d≤4, 0.05≤x≤0.15, 0.20≤y≤0.30, 0.001≤z≤0.005, 0.001≤n≤0.003.

[0080] In some embodiments, the molar percentage of Ti in the lithium iron phosphate matrix is ​​0.1%-0.5%, such as 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or other values ​​not listed in the range of 0.1%-0.5%. In some non-limiting embodiments, the molar percentage of Ti in the lithium iron phosphate matrix is ​​0.1%, 0.2%, 0.3%, 0.4%, or 0.5%.

[0081] Correspondingly, the molecular formula Li a Fe b P c O d Sn x Ni y Ti z V n The numerical range of z is 0.001≤z≤0.005, such as 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045, 0.005, etc., or other unlisted numerical values ​​within the range of 0.001≤z≤0.005. In some non-limiting embodiments, the molecular formula Li a Fe b P c O d Sn x Ni y Ti z V n The numerical range of z is 0.001, 0.002, 0.003, 0.004, and 0.005.

[0082] In some embodiments, the molar percentage of the V element in the lithium iron phosphate matrix is ​​0.1%-0.3%, such as 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or other values ​​not listed in the range of 0.1%-0.3%. In some non-limiting embodiments, the molar percentage of the V element in the lithium iron phosphate matrix is ​​0.1%, 0.15%, 0.2%, 0.25%, or 0.3%.

[0083] Correspondingly, the molecular formula Li a Fe b P c O d Sn x Ni y Ti z V n The numerical range of n is 0.001≤n≤0.003, such as 0.001, 0.0015, 0.002, 0.0025, 0.003, etc., or other unlisted numerical values ​​within the range of 0.001≤n≤0.003. In some non-limiting embodiments, the molecular formula Li a Fe b P c O d Sn x Ni y Ti z V n The numerical range of n is 0.001, 0.0015, 0.002, 0.0025, and 0.003.

[0084] In some embodiments, the molar ratio of the Ti element in the lithium iron phosphate substrate is 0.2%-0.4%, and the molar ratio of the V element in the lithium iron phosphate substrate is 0.15%-0.25%.

[0085] Correspondingly, the molecular formula Li a Fe b P c O d Sn x Ni y Ti z V n In the medium, 0.002≤z≤0.004, 0.0015≤n≤0.0025.

[0086] After introducing Sn and Ni elements into the lithium iron phosphate matrix, further introducing at least one of V and Ti elements can further increase the gram capacity of the positive electrode active material, thereby making the prepared battery have better energy density.

[0087] In some embodiments, the positive electrode active material further includes carbon element. Calculated based on the total weight of the positive electrode active material, the carbon content of the positive electrode active material is 1.28%-1.35%, for example, 1.28%, 1.29%, 1.30%, 1.31%, 1.32%, 1.33%, 1.34, 1.35%, etc., or other unlisted values ​​within the range of 1.28%-1.35%.

[0088] In some embodiments, the carbon content of the positive electrode active material is 1.30%-1.34% based on the total weight of the positive electrode active material.

[0089] In some embodiments, the carbon content of the positive electrode active material is 1.31%-1.33% based on the total weight of the positive electrode active material.

[0090] As used in this article, “carbon content” is determined using a carbon-sulfur analyzer in accordance with GB / T 20123-2006 / ISO 15350:2000.

[0091] In some embodiments, the positive electrode active material includes a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate substrate.

[0092] As used herein, "carbon coating layer" refers to the portion coated on the lithium iron phosphate substrate, which may but does not necessarily completely coat the lithium iron phosphate substrate. The term "carbon coating layer" is used only for ease of description and is not intended to limit this application.

[0093] The surface of the lithium iron phosphate substrate has a complete, thin and dense carbon coating layer, which builds a complete conductive network in the positive electrode active material, thus making a good contribution to the energy density and cycle performance of the battery.

[0094] In some embodiments, the positive electrode active material has a powder resistivity of ≤30 ohm·cm at 8 MPa.

[0095] In some embodiments, the positive electrode active material has a powder resistivity of ≤28.9 Ω·cm at 8 megapascals (MPa).

[0096] In some embodiments, the powder resistivity of the positive electrode active material at 8 MPa is ≤20 Ω·cm.

[0097] Powder resistivity, particle size distribution, and bulk density are all related to the conductivity of the carbon coating. Under the conditions of similar particle size distribution and bulk density, powder resistivity can characterize the conductive effect of the carbon coating and also reflect the degree of graphitization of the carbon coating.

[0098] The positive electrode active material has the above characteristics, and the carbon coating layer on the surface of the lithium iron phosphate substrate makes the positive electrode active material have better powder resistivity, which can make the battery have better energy density and cycle performance.

[0099] In some embodiments, the iron characteristic peak intensity of the positive electrode active material is Fe and carbon characteristic peak intensity I c The ratio satisfies I Fe / I c ≤0.023, such as 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.020, 0.021, 0.022, 0.023, etc., or other unlisted values ​​within the range of ≤0.023; in some embodiments, the lithium characteristic peak intensity I Li and carbon characteristic peak intensity I c The ratio satisfies I Li / I c ≤0.013, such as 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, etc., or other values ​​not listed in the range of ≤0.013; wherein, the iron characteristic peak intensity I Fe The peak position is at 706.7±0.5eV, and the lithium characteristic peak intensity I Li The peak position is at 54.9±0.5eV, and the carbon characteristic peak intensity is I c The peak position is at 285.0±0.5eV.

[0100] In some embodiments, the iron characteristic peak intensity of the positive electrode active material is Fe and carbon characteristic peak intensity I c The ratio satisfies I Fe / I c ≤0.015, lithium characteristic peak intensity I of positive electrode active material Li and carbon characteristic peak intensity I c The ratio satisfies I Li / I c≤0.010. X-ray electron spectrometers can determine the chemical composition of samples by measuring characteristic peak intensities based on the measured electron binding energy. Due to the barrier effect of the carbon coating, the characteristic peak intensity of the coated lithium iron phosphate substrate is relatively low. Therefore, the integrity of the carbon coating on the surface of the lithium iron phosphate particles can be characterized by calculating the ratio of the iron characteristic peak intensity (706.7±0.5eV), the lithium characteristic peak intensity (54.9±0.5eV), and the carbon characteristic peak intensity (285.0±0.5eV).

[0101] When the ratio of the iron characteristic peak intensity, lithium characteristic peak intensity and carbon characteristic peak intensity of the positive electrode active material is within the above range, the carbon coating layer on the surface of the lithium iron phosphate substrate has better integrity, which can make the battery have better cycle performance.

[0102] In some embodiments, the iron dissolution rate of the positive electrode active material is ≤5.5 mg / L, for example, 0.1 mg / L, 0.5 mg / L, 1.0 mg / L, 1.5 mg / L, 2.0 mg / L, 2.5 mg / L, 3.0 mg / L, 3.5 mg / L, 4.0 mg / L, 4.5 mg / L, 5.0 mg / L, 5.5 mg / L, etc., or other unlisted values ​​within the range of ≤5.5 mg / L; wherein the iron dissolution rate is the iron ion concentration of the positive electrode active material after standing in 0.008 mol / L (mol / L) hydrochloric acid at 25°C for 2 hours.

[0103] In some embodiments, the iron dissolution rate of the positive electrode active material is ≤ 5 mg / L.

[0104] In some embodiments, the iron dissolution rate of the positive electrode active material is ≤ 4 mg / L.

[0105] Lithium iron phosphate substrates are soluble in dilute hydrochloric acid. Due to the barrier effect of the carbon coating, the coated lithium iron phosphate substrate comes into contact with dilute hydrochloric acid more slowly, resulting in a lower dissolution rate. Therefore, under the same experimental conditions (0.008 mol / L hydrochloric acid concentration, 25°C temperature, and 2 hours of standing time), the concentration of Fe ions dissolved in hydrochloric acid can be used to characterize the integrity of the carbon coating on the lithium iron phosphate substrate.

[0106] When the iron dissolution rate of the positive electrode active material is within the above range, the carbon coating layer on the surface of the lithium iron phosphate substrate has good integrity, which can slow down the damage of the acid to the lithium iron phosphate substrate, and enable the battery to have better cycle performance and storage life.

[0107] As used herein, "specific surface area" refers to the total surface area per unit mass of a material. The apparent BET is the sum of the specific surface areas provided by the lithium iron phosphate substrate and the carbon coating, i.e., the total specific surface area of ​​the lithium iron phosphate cathode material, while the true BET is the specific surface area of ​​the lithium iron phosphate substrate.

[0108] Since the carbon coating layer on the surface of the lithium iron phosphate substrate has microporous and mesoporous structures, lithium iron phosphate substrate particles with the same size will have different BET values ​​due to differences in the density of their surface carbon coating layers.

[0109] In some embodiments, the true BET value of the positive electrode active material ranges from 8.9 to 15.312 m 2 / g, for example 8.9m 2 / g, 9.0m 2 / g, 10.0m 2 / g, 11.0m 2 / g, 12.0m 2 / g, 13.0m 2 / g, 14.0m 2 / g, 15.0m 2 / g, 15.312m 2 / g, etc., or 8.9-15.312m 2 In some embodiments, the apparent BET value of the positive electrode active material ranges from 9.428 to 16.994 m 2 / g, for example 9.428m 2 / g, 9.5m 2 / g, 10.0m 2 / g, 11.0m 2 / g, 12.0m 2 / g, 13.0m 2 / g, 14.0m 2 / g, 15.0m 2 / g, 16.0 m 2 / g、16.994m 2 / g, etc., or 9.428-16.994m 2 / Other values ​​not listed in the g range.

[0110] In some embodiments, the true BET value of the positive electrode active material is in the range of 10-14 m 2 / g, the apparent BET value of the positive electrode active material ranges from 11 to 15 m 2 / g.

[0111] The lithium iron phosphate substrate having the above characteristics has a dense carbon coating layer and a lower overall BET, which can enable the battery to have better energy density and cycle performance.

[0112] In some embodiments, the graphitization degree of the positive electrode active material is ≤1.039, such as 0.970, 0.980, 0.990, 1.000, 1.010, 1.020, 1.030, 1.039, etc., or other unlisted values ​​within the range of ≤1.039.

[0113] In some embodiments, the degree of graphitization of the positive electrode active material is ≤1.01.

[0114] In some embodiments, the degree of graphitization of the positive electrode active material is ≤1.

[0115] As used herein, the "degree of graphitization" of a positive electrode active material refers to the degree of graphitization of the carbon component. It reflects the integrity of the graphite crystal structure in the carbon-coated lithium iron phosphate of this application, particularly in the carbon coating layer, and specifically the regularity of the arrangement of carbon atoms within the graphite structure. The degree of graphitization of the carbon layer on the LFP surface can be characterized using a Raman spectrometer to measure the spectrum curve. After peak fitting and separation, the D1 / G peak intensity ratio can be used to characterize the degree of graphitization of the carbon layer.

[0116] In some embodiments, the volume average particle size D50 of the positive electrode active material is 0.7-1.52 μm, for example, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1.0 μm, 1.05 μm, 1.10 μm, 1.15 μm, 1.20 μm, 1.25 μm, 1.30 μm, 1.35 μm, 1.40 μm, 1.45 μm, 1.50 μm, 1.52 μm, etc., or other unlisted values ​​within the range of 0.7-1.52 μm.

[0117] In some embodiments, the volume average particle size D50 of the positive electrode active material is 0.9-1.5 μm.

[0118] In some embodiments, the volume average particle size D50 of the positive electrode active material is 1.1-1.3 μm.

[0119] As used herein, "volume average particle size D50" refers to the particle size at which the cumulative volume distribution percentage reaches 50%, calculated from the smallest particle size. This value can be determined using a Malvern MasterSizer 2000 laser particle size analyzer, in accordance with GB / T19077-2016 / ISO 13320:2009.

[0120] In some embodiments, the powder compaction density of the positive electrode active material at 22.6 MPa is 2.21-2.73 g / cm 3 , for example 2.21 g / cm 3 , 2.25g / cm 3, 2.3g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 , 2.45g / cm 3 , 2.5g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3 , 2.65g / cm 3 , 2.7g / cm 3 , 2.73g / cm 3 etc., or 2.21-2.73g / cm 3 Other values ​​not listed within the range.

[0121] In some embodiments, the powder compaction density of the positive electrode active material at 22.6 MPa is 2.45-2.65 g / cm 3 .

[0122] In some embodiments, the cathode active material has a powder compaction density of 2.5-2.6 g / cm at 22.6 MPa. 3 .

[0123] As used herein, "compacted density" is defined as: compacted density = surface density / (thickness of the electrode after rolling - thickness of the current collector). The determination method can refer to GB / T24533-2009.

[0124] In some embodiments, the positive electrode active material has a gram capacity of 155-165 mAh / g.

[0125] In some embodiments, the positive electrode active material has a gram capacity of 157-163 mAh / g.

[0126] In some embodiments, the gram capacity of the positive electrode active material is 159-162 mAh / g.

[0127] As used herein, the "gram capacity" of a positive electrode active material refers to the ratio of the amount of electricity that the positive electrode active material can release to its mass.

[0128] When the D50, powder compaction density and gram capacity of the positive electrode active material are within the above ranges, the prepared battery can have better energy density and cycle performance.

[0129] [Positive electrode]

[0130] The present application also provides a positive electrode plate, characterized in that it includes a positive electrode current collector and a positive electrode active material arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the positive electrode active material of the present application or the positive electrode active material prepared by the method described in the second aspect of the present application.

[0131] In some embodiments, the dehydration efficiency of the positive electrode sheet is 6.6-9.8 ppm / min, for example, 6.6 ppm / min, 7 ppm / min, 7.5 ppm / min, 8 ppm / min, 8.5 ppm / min, 9 ppm / min, 9.5 ppm / min, 9.8 ppm / min, etc., or other unlisted values ​​within the range of 6.6-9.8 ppm / min.

[0132] In some embodiments, the dehydration efficiency of the positive electrode sheet is 8-9 ppm / min.

[0133] In some embodiments, the compaction density of the positive electrode sheet is not less than 2.23 g / cm 3 , for example 2.23 g / cm 3 , 2.25g / cm 3 , 2.3g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 , 2.45g / cm 3 , 2.5g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3 , 2.65g / cm 3 , 2.7g / cm 3 , 2.72g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3.0g / cm 3 etc., or not less than 2.23g / cm 3 Other values ​​not listed within the range.

[0134] Excessive water content in the electrode will, on the one hand, lead to problems such as easy detachment of the positive electrode film layer in the electrode, unstable structure and chemical properties, and ultimately affect the battery cycle performance; on the other hand, it will also increase the risk of defective products in the battery preparation process, which not only increases costs but also seriously affects battery production efficiency.

[0135] Since a certain proportion of Sn and Ni elements are introduced into the lithium iron phosphate substrate, the carbon coating layer on its surface can be more complete and dense. Therefore, the prepared positive electrode sheet has the characteristics of high compaction density and easy dehydration, which can enable the lithium-ion battery to have excellent energy density, cycle performance and processing performance, and can significantly improve the battery production efficiency and reduce the battery production cost.

[0136] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0137] In some embodiments, the positive electrode plate may further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0138] In some embodiments, the positive electrode plate may further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0139] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0140] [Negative electrode]

[0141] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0142] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0143] In some embodiments, the compaction density of the negative electrode sheet is not less than 1.4 g / cm 3 .

[0144] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0145] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0146] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0147] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0148] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0149] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0150] [Electrolytes]

[0151] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. This application has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0152] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0153] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0154] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0155] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0156] [Isolation film]

[0157] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0158] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0159] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0160] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0161] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0162] [Lithium secondary battery]

[0163] The present application also provides a lithium secondary battery, characterized in that it includes the positive electrode sheet described in the present application.

[0164] The present application has no particular limitation on the shape of the lithium secondary battery, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0165] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0166] [Electrical devices]

[0167] In addition, the present application also provides an electrical device, which includes the lithium secondary battery provided in the present application. The lithium secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0168] As the power-consuming device, a lithium secondary battery can be selected according to its usage requirements.

[0169] Figure 3 shows an example of an electric device. This device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of lithium secondary batteries, a battery pack or battery module can be used.

[0170] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a lithium secondary battery as a power source.

[0171] Example

[0172] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0173] 1. Preparation method

[0174] Example 1

[0175] 1. Preparation of lithium iron phosphate positive electrode active material

[0176] (1) Preparation of core material: Using iron phosphate, lithium carbonate, tin oxide, nickel oxide, titanium oxide, vanadium oxide, carbon source and carbon coating additive as raw materials, the finished product molecular formula is LiFe 0.645 Ni 0.25 Sn 0.1 Ti 0.003 V 0.002 The carbon source is a mixture of glucose, sucrose and a highly graphitizable carbon source, wherein the highly graphitizable carbon source refers to a polymer carbon source with a molecular weight of more than 2000 and containing at least one characteristic functional group, benzene ring or carboxyl group. During the high-temperature sintering process, it is easy to decompose to form a graphite-like structure. The coating additive refers to a material that can catalyze the graphitization of the carbon layer, such as ferrocene, ferric nitrate, and iron oxide.

[0177] The raw materials are sequentially added to solvent water for wet grinding to obtain a mixed slurry. The resulting slurry is spray-dried, and the dried product is then placed in a roller hearth furnace and sintered in an airtight atmosphere at 500°C for 28 hours. The product is then naturally cooled to a temperature below 80°C before being discharged to obtain a calcined material. The calcined material is then crushed, screened, and demagnetized to obtain a core material. The prepared core material has a carbon content of 0.3% to 0.35% and a Dv50 of 0.5 to 0.55 μm.

[0178] (2) Carbon Coating: The core material was placed in a roller hearth furnace and sintered under a nitrogen atmosphere. Acetone solution was sprayed into the sintering furnace and sintered at a constant temperature of 770°C for 10 hours, with a total sintering time of 24 hours. The material was discharged after natural cooling to a temperature of less than 80°C. It was further pulverized using a jet mill to obtain the lithium iron phosphate positive electrode active material.

[0179] 2. Preparation of positive electrode sheet

[0180] The lithium iron phosphate positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black were mixed in a mass ratio of 96.5:2.0:1.5, and then N-methylpyrrolidone (NMP) solvent was added to form a uniform positive electrode slurry. The slurry was coated on a carbon-coated aluminum foil with a thickness of 13 μm and a coating surface density of 26 mg / cm 2 After drying, cold pressing and cutting, the positive electrode sheet is obtained.

[0181] 3. Preparation of negative electrode sheet

[0182] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the binder styrene butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on a copper foil with a thickness of 8 μm; after drying, the negative electrode sheet is obtained by cold pressing and slitting.

[0183] 4. Preparation of electrolyte

[0184] The solvents EC and DMC were mixed in a mass ratio of 30:70. After complete dissolution, LiPF6 was added, followed by VC and FEC. After mixing evenly, an electrolyte solution with a LiPF6 concentration of 1 mol / L and a mass content of VC and FEC of 3% was obtained.

[0185] 5. Isolation film

[0186] A 12μm thick polypropylene isolation film was selected.

[0187] 6. Preparation of lithium-ion batteries

[0188] The electrode is placed in a high-temperature oven at 110°C and baked for 7 hours to remove moisture from the electrode. The positive electrode, isolation film, and negative electrode are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role. After winding into a square bare battery cell, it is filled with aluminum-plastic film, injected with the corresponding non-aqueous electrolyte, and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a lithium-ion battery is obtained.

[0189] Examples 2 to 21

[0190] The secondary batteries of Examples 2-21 were prepared similarly to Example 1, except that the type and content of the doping elements in the lithium iron phosphate substrate, as well as the D50, carbon content, powder compaction density, and BET of the positive electrode active material, were adjusted. The different preparation parameters are detailed in Tables 1, 2, and 3. The chemical formulas of the different lithium iron phosphate substrates in Tables 1-3 can be used to calculate the types and mass percentages of the different elements in the lithium iron phosphate substrates.

[0191] Comparative Examples 1 to 6

[0192] The secondary batteries of Comparative Examples 1 to 6 were prepared similarly to Example 1, except that the type or content of the doping element in the lithium iron phosphate substrate was adjusted, or the parameters of the carbon coating layer were adjusted. The different preparation parameters are detailed in Tables 1, 2, and 3.

[0193] 2. Performance Testing

[0194] 1. Test methods for parameters related to positive electrode active materials

[0195] (1) Test method for iron characteristic peak intensity, lithium characteristic peak intensity, and carbon characteristic peak intensity

[0196] X-ray photoelectron spectroscopy (X-ray photoelectron spectroscopy) was used for all tests. All tests were performed on an Axis Supra / Supra+ X-ray photoelectron spectrometer according to the GB / T19500-2004 standard. The peak heights and concentrations of Fe, Li, and C were output using ESCApe software.

[0197] (2) Test method for average particle size D

[0198] The average particle size D was measured using an X-ray powder diffractometer (X'pert PRO, USA). The detailed test process is as follows:

[0199] 1) Measure the measured width (Bm) of the sample to be tested. Set the instrument scan rate to 2 degrees / minute and obtain the XRD spectrum of the sample to be tested. Use JADE software to subtract the Cu Kα2 background to obtain the Bm of each diffraction peak.

[0200] 2) Instrument broadening Bs measurement.

[0201] Use a standard sample with the same material as the sample to be tested and a grain size of 5 to 20 μm, and measure the XRD spectrum of the standard sample under the same experimental conditions as the sample to be tested, and obtain Bs from the spectrum.

[0202] 3) Calculate the half-width (B). B = Bm - Bs. (Note: If the calculated unit of B is degrees, it must be converted to radians.)

[0203] 4) Calculation of average particle size D. Using the Scherrer formula D = Kλ / Bcosθ, where K is 0.89, θ is the diffraction angle, and λ = 0.154056 nm, and substituting B, we can obtain the grain thickness D' in the normal direction of the crystal plane represented by a single diffraction peak. Calculate D' for each of the diffraction peaks and take the average value to obtain the average particle size D.

[0204] (3) Test method for powder compaction density

[0205] 1g of lithium iron phosphate cathode active material from each of the Examples and Comparative Examples was weighed and placed into a cylindrical mold with a circular hole having a cross-sectional area of ​​S. A pressure of 3t was applied to the powder in the mold and maintained for 30 seconds. The powder thickness was recorded as t. The compacted density ρ of the lithium iron phosphate cathode active material for each of the Examples and Comparative Examples can be calculated using the following formula: ρ = m / (S × t).

[0206] (4) Carbon content test method

[0207] The positive electrode active materials in all the above embodiments and comparative examples were burned in a high-frequency induction furnace and then tested for carbon content using an infrared absorption method. The specific testing process was based on the standard GB / T20123-2006 / ISO 15350:2000 "Determination of total carbon and sulfur content of steel - Infrared absorption method after high-frequency induction furnace combustion". The carbon and sulfur analyzer was used for convenient determination, such as the Dekai HCS infrared carbon and sulfur analyzer.

[0208] (5) Test methods for true specific surface area and apparent specific surface area

[0209] The specific surface area parameters were tested using a 3Flex specific surface area analyzer from Micromeritics, USA. The total surface area of ​​the particle body, micropores, mesopores, and macropores, BET, was obtained by T-Plot fitting, which is the apparent specific surface area.

[0210] True specific surface area = apparent specific surface area - BET1 - BET2. BET1 is the specific surface area of ​​pores with a pore size of 100 nm to 2.0 nm, as determined using the T-Plot method. BET2 is the specific surface area of ​​mesopores and macropores, measured using a PCA-MP003 mercury porosimeter according to GB / T 21650.1-2008.

[0211] (6) Test method for iron dissolution rate

[0212] 5 g of lithium iron phosphate positive electrode active material was weighed, 100 ml of 0.008 mol / L dilute hydrochloric acid was added, and after standing for 2 h, 1 ml of the filtrate was vacuum filtered and the volume was adjusted to 50 ml. The Fe ion concentration in the filtrate was tested by ICP-OES.

[0213] (7) Test method for powder resistivity

[0214] The powder resistivity of the positive electrode active material was tested using a powder resistivity tester (ST2722) in accordance with standard GB / T 30835-2014.

[0215] (8) Test method for volume average particle size Dv50

[0216] The volume average particle size Dv50 refers to the standard process: GB / T19077-2016 / ISO 13320:2009, and is measured using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. The specific test process is as follows: take an appropriate amount of lithium iron phosphate positive electrode active material, add 20 ml of deionized water (the sample concentration ensures 8-12% shading), and ultrasonically disperse for 5 minutes (53KHz / 120W) to ensure that the sample is completely dispersed. Then, the samples of the embodiment and the comparative example are measured according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0217] (9) Test method for graphitization degree

[0218] The degree of graphitization was characterized using a Raman spectrometer (InVia Qontor (Reflex)) with a light source wavelength of 532 nm. The spectrum was intercepted from 750-2000 cm⁻¹ and fitted with the following Gaussian function after background subtraction. Ai, vi, and wi are the peak intensity, peak position, and peak width, respectively. The two peaks corresponding to the carbon coating can be fitted with four peaks, with the corresponding peak intensities recorded as D2, D1, D3, and G, respectively. The degree of graphitization is then calculated as D1 / G.

[0219] However, since the test spot size of the Raman spectrometer is 0.5~1μm, which is slightly smaller than a single LFP particle, it has a certain degree of randomness. To this end, the surface scanning Raman spectrum can be used to continuously and evenly scan 100 points in a 50*50μm area to simultaneously generate an I in the XY spatial direction. D / I G Depth map to improve the uniformity and representativeness of the test.

[0220] 2. Test method for parameters related to positive electrode

[0221] (1) Test method for dehydration efficiency

[0222] The lithium iron phosphate positive electrode active material of the embodiment and the comparative example, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed in a mass ratio of 96.5:2.0:1.5, and an appropriate amount of N-methylpyrrolidone (NMP) solvent was added and stirred thoroughly to form a uniform positive electrode slurry; the slurry was coated on a carbon-coated aluminum foil with a thickness of 13 μm of the positive electrode current collector, and the coating surface density was 26 mg / cm 2, followed by drying and cold pressing, and then slitting for standby use to obtain the positive electrode. The electrode dish is placed in a humidity environment with a water content of 50%, and allowed to absorb water for 24 hours until it is close to saturation. A punching device is used to punch out small discs with a diameter of 1.4 cm, which are cut into small pieces of about 0.5 cm × 0.5 cm. The pieces are placed in a moisture tester and the water content is tested to be Appm. The remaining electrode is then placed in a vacuum oven. This process is sealed with a plastic bag to prevent the electrode from absorbing and dehydrating water. After drying at 110°C for 7 hours, small discs are punched out and cut into pieces. The water content is tested to be B ppm, and the material dehydration rate W = (AB) / 420ppm / min.

[0223] (2) Test method for compaction density

[0224] The pole pieces of the embodiment and comparative example were cut into 1000mm long membranes, and the pole pieces were rolled under a certain pressure. Due to the ductility of the aluminum foil, the membrane length was 1006mm. Then 1540.25mm was punched out on the membrane. 2 The weight M and thickness L of the small disc are measured. The pure aluminum foil is punched into 1540.25mm 2 The empty aluminum foil mass M0 is weighed, and the corresponding positive electrode sheet compaction density of all embodiments and all comparative examples can be calculated by the following formula: PD = (M-M0) / 1.54025 / 2 / L.

[0225] 3. Battery performance test method

[0226] (1) Test method for gram capacity

[0227] The positive electrode active material of Example 1, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed in a weight ratio of 90:5:5, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred thoroughly to form a uniform positive electrode slurry. The slurry is coated on an aluminum foil with a thickness of 1 μm for the positive electrode current collector, and then dried and cold pressed. It is then punched into small discs with a diameter of 14 mm for use as positive electrode sheets. A lithium sheet is used as the negative electrode, and a 12 μm thick polypropylene isolation membrane and the electrolyte in the embodiment are used to assemble a button-type half-cell. The button-type half-cell is charged and discharged at rates of 0.1C and 1C, respectively, and the gram capacity at different rates is recorded. The test process of the comparative example and other embodiments is the same as above.

[0228] (2) Energy density test method

[0229] All lithium-ion batteries from the examples and comparative examples were placed in a 25°C oven, left to rest for 2 hours, and then subjected to charge and discharge tests. The charge and discharge cycle was as follows: 1C constant-current charging to 3.65V, then constant-voltage charging until the charging current fell below 0.05C, followed by a 5-minute pause; then 1C constant-current discharge to 2.0V, followed by a 5-minute pause. This represents a single charge and discharge cycle. Cell mass energy density (Wh / kg) = energy discharged during the third discharge divided by the mass of the lithium iron phosphate active material in the battery.

[0230] (3) Cyclic performance test method

[0231] All lithium-ion batteries from the examples and comparative examples were placed in a 60°C oven and allowed to rest for 2 hours before undergoing charge and discharge testing. One charge-discharge cycle was as follows: 1C constant-current charging to 3.65V, followed by constant-voltage charging until the charge current fell below 0.05C, followed by a 5-minute pause; then 1C constant-current discharge to 2.5V, followed by a 5-minute pause. This constituted one charge-discharge cycle for the battery, which was repeated until the battery capacity decayed to 80% of its initial value. The number of cycles was recorded.

[0232] 3. Analysis of test results of various embodiments and comparative examples

[0233] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Tables 2 to 4 below.

[0234] Table 1 Preparation parameters

[0235] Table 2 Preparation or performance parameters

[0236] Table 3 Preparation or performance parameters

[0237] Table 4 Performance parameters

[0238] The lithium iron phosphate substrates in Examples 1 to 21 are all added with Sn and Ni elements, and the surface of the lithium iron phosphate substrate has a complete and dense carbon coating layer (when the powder resistivity is controlled at 8 MPa ≤ 30 Ω·cm). The positive electrode active materials prepared therefrom have a high gram capacity, the prepared positive electrode sheets have good dehydration performance, and the prepared lithium secondary batteries have both excellent energy density and cycle performance.

[0239] In Comparative Example 1, the lithium iron phosphate substrate does not contain Sn and Ni elements, but contains Mn element.

[0240] From the comparison between Comparative Example 1 and Examples 1 to 21, it can be seen that the addition of Sn and Ni to the lithium iron phosphate substrate can effectively increase the gram capacity of the positive electrode active material and improve the energy density and cycle performance of the lithium secondary battery; while the addition of other elements other than Sn and Ni (such as Mn) cannot increase the gram capacity of the positive electrode active material, nor can it improve the energy density and cycle performance of the lithium secondary battery.

[0241] In Comparative Examples 2-3, one of the two elements Sn and Ni is added to the lithium iron phosphate substrate: in Comparative Example 2, only Sn is added to the lithium iron phosphate substrate, and in Comparative Example 3, only Ni is added to the lithium iron phosphate substrate.

[0242] From the comparison of Comparative Examples 2 to 3 with Examples 1 to 21, it can be seen that, compared with adding only one of Sn and Ni, adding both Sn and Ni elements to the lithium iron phosphate substrate can effectively increase the gram capacity of the positive electrode active material and improve the energy density and cycle performance of the lithium secondary battery; while when only one of Sn and Ni is added, the improvement in battery performance is limited.

[0243] As shown in Examples 1-9, controlling the molar ratio of Sn in the lithium iron phosphate substrate to 5% to 15% and the molar ratio of Ni to 20% to 30% can result in a higher specific capacity of the positive electrode active material and better energy density and cycle performance for the lithium secondary battery. The battery's overall performance is optimal when the molar ratio of Sn is 10% and the molar ratio of Ni is 25%.

[0244] In the lithium iron phosphate substrate of Comparative Example 4, the molar proportion of the Sn element is 20%, which exceeds the range of 5% to 15%; in the lithium iron phosphate substrate of Comparative Example 5, the molar proportion of the Ni element is 35%, which exceeds the range of 20% to 30%.

[0245] From the comparison of Comparative Examples 4 to 5 with Examples 1 to 21, it can be seen that only when the contents of Sn and Ni in the lithium iron phosphate substrate are controlled within a certain range can the gram capacity of the positive electrode active material be effectively increased, and the energy density and cycle performance of the lithium secondary battery be improved; and when the molar proportion of the Sn element exceeds the range of 5% to 15%, or the molar proportion of the Ni element exceeds the range of 20% to 30%, the improvement in battery performance is small.

[0246] As can be seen from Examples 1 and 10 to 13, after Sn and Ni are added to the lithium iron phosphate substrate, V and Ti are further introduced, which can further improve the gram capacity of the positive electrode active material and further enhance the energy density and cycle performance of the lithium secondary battery.

[0247] At the same time, it can be seen from Examples 1 and 10 to 13 that the molar ratio of the Ti element in the lithium iron phosphate substrate needs to be controlled within the range of 0.1% to 0.5%, and the molar ratio of the V element in the lithium iron phosphate substrate needs to be controlled within the range of 0.1% to 0.3%. The positive electrode active materials prepared therefrom have a high gram capacity, and the prepared lithium secondary batteries have excellent energy density and cycle performance.

[0248] As can be seen from Examples 1 to 21, the carbon content of the positive electrode active material is controlled within the range of 1.28%-1.35%, the D50 is within the range of 0.7-1.52 μm, and the powder compaction density is within the range of 2.21-2.73 g / cm 3 Within the range, the positive electrode active materials prepared therefrom have a high gram capacity, and the prepared lithium secondary batteries have excellent energy density and cycle performance.

[0249] It can be seen from Examples 1 to 21 that when the powder resistivity of the positive electrode active material is controlled to be ≤30Ω·cm at 8 MPa, it indicates that the carbon coating layer on the surface of the lithium iron phosphate substrate is relatively complete and dense, the positive electrode active materials prepared therefrom all have a high gram capacity, the prepared positive electrode sheets have good dehydration performance, and the prepared lithium secondary batteries all have excellent energy density and cycle performance.

[0250] In the positive electrode active material of Comparative Example 6, the integrity and density of the carbon coating layer are relatively poor. For example, the powder resistivity thereof is 103.7 Ω·cm at 8 MPa, which exceeds the range of 28.9 Ω·cm.

[0251] From the comparison between Comparative Example 6 and Examples 1 to 21, it can be seen that the energy density and cycle performance of the lithium secondary battery can be effectively improved only when Sn and Ni are added to the lithium iron phosphate substrate and its surface is also coated with a complete and dense carbon coating layer; when Sn and Ni are added to the lithium iron phosphate substrate, but the integrity and density of the carbon coating layer coated on its surface are poor (for example, the powder resistivity is high, the iron dissolution rate is too fast, and the electrode dehydration efficiency is too high), the improvement in battery performance is small.

[0252] From Examples 1 to 21, it can be seen that the iron characteristic peak intensity I Fe and carbon characteristic peak intensity I c The ratio satisfies I Fe / I c ≤0.023, or control the lithium characteristic peak intensity I of the positive electrode active material Li and carbon characteristic peak intensity I c The ratio satisfies I Li / I c≤0.013, or control the iron dissolution rate of the positive electrode active material to ≤5.5mg / L, or control the true BET value of the positive electrode active material to be between 8.9-15.312m 2 / g range, or control the apparent BET value between 9.428-16.994m 2 / g range, or when the graphitization degree of the positive electrode active material is controlled to be ≤1.039, it indicates that the integrity and density of the carbon coating layer are good, so the prepared positive electrode sheet has good dehydration performance, and the prepared lithium secondary batteries have excellent energy density and cycle performance.

[0253] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included within the technical scope of the present application. In addition, without departing from the scope of the present application, any other modifications that can be imagined by those skilled in the art to the embodiments, or any other methods constructed by combining some of the constituent elements in the embodiments are also included within the scope of the present application.

Claims

1. A lithium iron phosphate positive electrode active material, characterized in that The positive electrode active material includes a lithium iron phosphate substrate, wherein the molar ratio of Sn element in the lithium iron phosphate substrate is 5%-15%, and the molar ratio of Ni element in the lithium iron phosphate substrate is 20%-30%; The powder resistivity of the positive electrode active material at 8 MPa is ≤30Ω·cm.

2. The positive electrode active material according to claim 1, characterized in that The lithium iron phosphate substrate has a molecular formula of Li a Fe b P c O d Sn x Ni y Q q , wherein Q includes at least one of V, Ti, Cu, Cr, Zn, Pb, Ca, Co, Sr, and Nb, 0.99≤a≤1, 0.545≤b≤0.9, 0.99≤c≤1, 3.9≤d≤4, 0.05≤x≤0.15, 0.20≤y≤0.30, and 0≤q≤0.

008.

3. The positive electrode active material according to claim 1 or 2, characterized in that The molar ratio of Sn element in the lithium iron phosphate substrate is 7.5%-12.5%, and the molar ratio of Ni element in the lithium iron phosphate substrate is 22.5%-27.5%.

4. The positive electrode active material according to claim 2, characterized in that Among them, 0.075≤x≤0.125, 0.225≤y≤0.

275.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The powder resistivity of the positive electrode active material at 8 MPa is ≤20Ω·cm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The molar ratio of the Ti element in the lithium iron phosphate substrate is 0.1%-0.5%, and the molar ratio of the V element in the lithium iron phosphate substrate is 0.1%-0.3%.

7. The positive electrode active material according to claim 6, characterized in that The lithium iron phosphate substrate has a molecular formula of Li a Fe b P c O d Sn x Ni y Ti z V n , where 0.99≤a≤1, 0.545≤b≤0.9, 0.99≤c≤1, 3.9≤d≤4, 0.05≤x≤0.15, 0.20≤y≤0.30, 0.001≤z≤0.005, 0.001≤n≤0.

003.

8. The positive electrode active material according to claim 6 or 7, characterized in that The molar ratio of the Ti element in the lithium iron phosphate substrate is 0.2%-0.4%, and the molar ratio of the V element in the lithium iron phosphate substrate is 0.15%-0.25%.

9. The positive electrode active material according to claim 7, characterized in that Among them, 0.002≤z≤0.004, 0.0015≤n≤0.0025.

10. The positive electrode active material according to any one of claims 1 to 9, characterized in that The positive electrode active material further includes carbon element. Calculated based on the total weight of the positive electrode active material, the carbon content of the positive electrode active material is 1.28%-1.35%.

11. The positive electrode active material according to claim 10, characterized in that The positive electrode active material includes a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate substrate.

12. The positive electrode active material according to any one of claims 1 to 11, characterized in that The positive electrode active material satisfies at least one of the following groups (1) to (4): (1) The iron characteristic peak intensity I of the positive electrode active material Fe and carbon characteristic peak intensity I c The ratio satisfies I Fe / I c ≤0.023, the lithium characteristic peak intensity I of the positive electrode active material Li and carbon characteristic peak intensity I c The ratio satisfies I Li / I c ≤0.013, wherein the iron characteristic peak intensity I Fe The peak position is at 706.7±0.5eV, and the lithium characteristic peak intensity I Li The peak position is at 54.9±0.5eV, and the carbon characteristic peak intensity I c The peak position is at 285.0±0.5eV; (2) The iron dissolution rate of the positive electrode active material is ≤5.5 mg / L, wherein the iron dissolution rate is the iron ion concentration of the positive electrode active material after standing in 0.008 mol / L hydrochloric acid at 25°C for 2 hours; (3) The true BET value of the positive electrode active material is in the range of 8.9-15.312 m 2 / g, the apparent BET value range of the positive electrode active material is 9.428-16.994m 2 / g; (4) The graphitization degree of the positive electrode active material is ≤1.

039.

13. The positive electrode active material according to any one of claims 1 to 11, characterized in that The positive electrode active material satisfies at least one of the following groups (1) to (4): (1) The iron characteristic peak intensity I of the positive electrode active material Fe and carbon characteristic peak intensity I c The ratio satisfies I Fe / I c ≤0.015, the lithium characteristic peak intensity I of the positive electrode active material Li and carbon characteristic peak intensity I c The ratio satisfies I Li / I c ≤0.010, wherein the iron characteristic peak intensity I Fe The peak position is at 706.7±0.5eV, and the lithium characteristic peak intensity I Li The peak position is at 54.9±0.5eV, and the carbon characteristic peak intensity I c The peak position is at 285.0±0.5eV; (2) The iron dissolution rate of the positive electrode active material is ≤4 mg / L, wherein the iron dissolution rate is the iron ion concentration of the positive electrode active material after standing in 0.008 mol / L hydrochloric acid at 25°C for 2 hours; (3) The true BET value of the positive electrode active material is in the range of 10-14m 2 / g, the apparent BET value range of the positive electrode active material is 11-15m 2 / g; (4) The graphitization degree of the positive electrode active material is ≤1.

01.

14. The positive electrode active material according to any one of claims 1 to 13, characterized in that The volume average particle size D50 of the positive electrode active material is 0.7-1.52 μm.

15. The positive electrode active material according to any one of claims 1 to 13, characterized in that The volume average particle size D50 of the positive electrode active material is 1.1-1.3 μm.

16. The positive electrode active material according to any one of claims 1 to 13, characterized in that The powder compaction density of the positive electrode active material at 22.6 MPa is 2.21-2.73 g / cm 3 .

17. The positive electrode active material according to any one of claims 1 to 13, characterized in that The powder compaction density of the positive electrode active material at 22.6 MPa is 2.5-2.6 g / cm 3 .

18. A positive electrode plate, characterized in that: The invention comprises a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the positive electrode active material according to any one of claims 1 to 17.

19. The positive electrode sheet according to claim 18, characterized in that: The dehydration efficiency of the positive electrode sheet is 6.6-9.8 ppm / min.

20. The positive electrode sheet according to claim 18, characterized in that: The dehydration efficiency of the positive electrode sheet is 8-9 ppm / min.

21. The positive electrode sheet according to claim 18, characterized in that: The compaction density of the positive electrode sheet is not less than 2.23g / cm 3 .

22. A lithium secondary battery, characterized in that: The positive electrode sheet comprises the positive electrode sheet according to any one of claims 18 to 21.

23. An electrical device, characterized in that: A lithium secondary battery comprising the lithium secondary battery according to claim 22.

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