Positive electrode active material, method for manufacturing the same, positive electrode sheet, secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a mixed positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. The positive electrode active material comprises a first positive electrode active material and a second positive electrode active material; wherein the first positive electrode active material comprises a compound LiNi b Co d Mn e M f O2, and the second positive electrode active material comprises a compound Li a A x Mn 1‑y B y P 1‑z C z O 4‑n D n The application improves the cycle capacity retention rate of the secondary battery, prolongs the cycle life of the secondary battery and improves the safety of the secondary battery by mixing the first positive electrode active material and the second positive electrode active material.

Description

[0001] This application is a divisional application of patent application 202280012894.9 filed on July 15, 2022, entitled "Positive electrode active material and preparation method thereof, positive electrode sheet, secondary battery, battery module, battery pack and power device". Technical Field

[0002] This application relates to the field of secondary battery technology, and in particular to a positive electrode active material and its preparation method, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0003] In recent years, with the increasingly widespread application of rechargeable batteries, they have been widely used in energy storage power 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 many other fields. Due to the significant development of rechargeable batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance. As an existing positive electrode active material for rechargeable batteries, lithium manganese phosphate is prone to Li / Mn antisite defects during charge and discharge, resulting in severe manganese dissolution, which affects the specific capacity of the rechargeable battery and leads to poor safety and cycle performance. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material, a method for preparing the positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device, so as to solve the problems of low cycle capacity retention, short cycle life, and low safety of secondary batteries made using existing positive electrode active materials.

[0005] To achieve the above objectives, a first aspect of this application provides a positive electrode active material, comprising a first positive electrode active material and a second positive electrode active material; wherein...

[0006] The first positive electrode active material contains the compound LiNi. b Co d Mn e M f O2, wherein b is selected from the range of 0.314-0.970, d is selected from the range of 0-0.320, optionally from the range of 0.047-0.320, e is selected from the range of 0.006-0.390, and the sum of b, d, e and f is 1 and f is greater than 0, M is selected from one or more elements selected from Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y, optionally M is Mg and / or Al;

[0007] The second positive electrode active material contains the compound Li.a A x Mn 1-y B y P 1-z C z O 4-n D n a is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, A is selected from one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W, B is selected from one or more elements of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C is selected from one or more elements of B (boron), S, Si and N, and D is selected from one or more elements of S, F, Cl and Br.

[0008] Consequently, the applicant unexpectedly discovered that by simultaneously doping specific elements in specific amounts at the Li, Mn, P, and O sites of the compound LiMnPO4 to obtain a second positive electrode active material, significantly improved rate performance can be achieved. Simultaneously, the dissolution of Mn and Mn-site dopants is significantly reduced, resulting in significantly improved cycle performance and / or high-temperature stability. Furthermore, the specific capacity and compaction density of the material are also increased, and interfacial side reactions are reduced. However, the second positive electrode active material only has a one-dimensional lithium-ion transport channel, while the first positive electrode active material is a layered transition metal oxide with a two-dimensional lithium-ion transport channel. Therefore, this application utilizes a mixture of the first and second positive electrode active materials, allowing the advantages of both materials to complement each other, thereby improving the cycle capacity retention rate of the secondary battery, extending its cycle life, and enhancing its safety.

[0009] Unless otherwise stated, the chemical formula Li a A x Mn 1-y B y P 1-z C z O 4-n D n In this context, when A comprises two or more elements, the aforementioned limitation on the range of x values ​​applies not only to the stoichiometric coefficient of each element representing A, but also to the sum of the stoichiometric coefficients of all elements representing A. For example, when A comprises two or more elements A1, A2…An, the stoichiometric coefficients x1, x2…xn of each of A1, A2…An must each fall within the range of x values ​​defined in this application, and the sum of x1, x2…xn must also fall within this range. Similarly, for the case where B, C, and D comprise two or more elements, the limitation on the range of stoichiometric coefficients of B, C, and D in this application also has the aforementioned meaning. Similarly, for the chemical formula LiNi…b Co d Mn e M f When M in O2 consists of two or more elements, the limitation on the numerical range of the stoichiometric coefficient of M in this application also has the above meaning.

[0010] In any embodiment, the mass of the first positive electrode active material is m1, the mass of the second positive electrode active material is m2, and the value of m1 / (m1+m2) is 2%-55%, optionally 3%-50%. Thus, the mass percentage of the first positive electrode active material in the two positive electrode active materials is within the above range, which can improve the overall stability and safety of the positive electrode active material.

[0011] In any embodiment, the value of b×m1 / (m1+m2) is 0.017-0.457, and can be selected as 0.025-0.415. This can further improve the overall stability and safety of the positive electrode active material.

[0012] In any embodiment, the first positive electrode active material is a single crystal or quasi-single crystal material, and the particle size D of the first positive electrode active material is... v 50 represents less than or equal to 5.8 μm, and can be selected from 2.3 to 5.8 μm, or even from 2.3 to 4.3 μm.

[0013] The particle size of the first positive electrode active material, which is a single crystal or quasi-single crystal, is within the above range, which can optimize the electrochemical reaction area, further reduce and suppress the interfacial side reactions of the positive electrode during the cycling process of the secondary battery, reduce the cycle decay rate of the secondary battery, and extend the cycle life of the secondary battery.

[0014] In any embodiment, when the first positive electrode active material is a single crystal or quasi-single crystal material, d is selected from the range of 0.05-0.320, and may be selected from the range of 0.05-0.282; and / or,

[0015] b is greater than 0.314 and less than 0.97, and can be selected from the range of 0.55-0.869.

[0016] When the first positive electrode active material is a single crystal or quasi-single crystal material, d and b within the above range are beneficial to further improve the conductivity and rate performance of the positive electrode active material, further improve the cycle capacity retention rate of the secondary battery, and further extend the cycle life of the secondary battery.

[0017] In any embodiment, when the first positive electrode active material is a polycrystalline material, the particle size D of the first positive electrode active material is... v 50 is 3.5–13.5 μm; and / or,

[0018] The BET specific surface area of ​​the first positive electrode active material is less than or equal to 1.32 m².2 / g, which can be selected as 0.28-1.32m 2 / g; and / or,

[0019] The compaction density of the first positive electrode active material under 3T pressure is greater than or equal to 2.92 g / cm³. 3 The selectable value is 2.92-3.31 g / cm³. 3 .

[0020] The particle size, specific surface area, and compaction density of the polycrystalline first cathode active material are kept within the above range to further improve the rate performance of the cathode active material, further reduce and suppress the interfacial side reactions of the cathode during the cycle of the secondary battery, reduce the cycle decay rate of the secondary battery, and extend the cycle life of the secondary battery.

[0021] In any embodiment, the first positive electrode active material further comprises lithium carbonate and / or lithium hydroxide;

[0022] Optionally, based on the mass of the first positive electrode active material, the mass content of lithium carbonate is less than or equal to 1%, and / or the mass content of lithium hydroxide is less than or equal to 1%.

[0023] Residual water molecules introduced by the second positive electrode active material may react with the electrolyte to produce HF. HF can easily damage the positive electrode active material itself or the SEI film on the negative electrode, thus affecting the cycle life of the secondary battery. The lithium carbonate and / or lithium hydroxide further contained in the first positive electrode active material of this application can neutralize HF, reducing or inhibiting the destructive effect of HF on the positive electrode active material or the SEI film of the negative electrode, thereby further improving the cycle life of the secondary battery.

[0024] In any embodiment, in the second positive electrode active material, A is selected from any one of Zn, Al, Na, K, Mg, Nb, Mo and W; B is selected from at least two of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C is selected from any one of B (boron), S, Si and N; and D is selected from any one of S, F, Cl and Br.

[0025] Optionally, A is Mg or Nb, and / or,

[0026] B is selected from at least two elements chosen from Fe, Ti, V, Co, and Mg, and may also be selected from Fe and one or more elements chosen from Ti, V, Co, and Mg, and / or

[0027] C is S, and / or,

[0028] D is F.

[0029] By selecting doping elements at the Li sites within the aforementioned range, the lattice change rate during the lithium removal process can be further reduced, thereby further improving the rate performance of the secondary battery. Similarly, by selecting doping elements at the Mn sites within the aforementioned range, electronic conductivity can be further increased and the lattice change rate further reduced, thereby enhancing the rate performance and specific capacity of the secondary battery. Furthermore, by selecting doping elements at the P sites within the aforementioned range, the rate performance of the secondary battery can be further improved. Finally, by selecting doping elements at the O sites within the aforementioned range, interfacial side reactions can be further mitigated, improving the high-temperature performance of the secondary battery.

[0030] In any embodiment, in the second positive electrode active material, x is selected from the range of 0.001 to 0.005; and / or,

[0031] y is selected from the range of 0.01 to 0.5, and may optionally be selected from the range of 0.25 to 0.5; and / or,

[0032] z is selected from the range of 0.001 to 0.005; and / or,

[0033] n is selected from the range of 0.001 to 0.005.

[0034] By selecting the y-value within the above range, the specific capacity and rate performance of the material can be further improved. By selecting the x-value within the above range, the kinetic performance of the material can be further improved. By selecting the z-value within the above range, the rate performance of the secondary battery can be further improved. By selecting the n-value within the above range, the high-temperature performance of the secondary battery can be further improved.

[0035] In any embodiment, the value of (1-y):y is selected from the range of 1 to 4, and optionally from the range of 1.5 to 3, and the value of a:x is selected from the range of 9 to 1100, and optionally from the range of 190-998. Thus, the energy density and cycle performance of the positive electrode active material can be further improved.

[0036] In any embodiment, the lattice change rate of the second positive electrode active material before and after complete lithium insertion / extraction is less than 8%, and optionally less than 4%. By reducing the lattice change rate, Li ion transport becomes easier, i.e., Li ions have stronger migration ability in the material, which is beneficial for improving the rate performance of the secondary battery. The lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD).

[0037] In any embodiment, the Li / Mn antisite defect concentration of the second positive electrode active material is less than 2%, and optionally less than 0.5%. The so-called Li / Mn antisite defect refers to the presence of Li in the LiMnPO4 lattice. + With Mn 2+The positions of Li and Mn are interchanged. The Li / Mn antisite defect concentration refers to the concentration of Li / Mn antisite defects in the positive electrode active material. 2+ Interchangeable Li + Zhan Li + Percentage of the total. Mn of the inversion defect. 2+ It will hinder Li + The transport of Li / Mn antisite defects, by reducing the concentration of Li / Mn antisite defects, is beneficial to improving the specific capacity and rate performance of the positive electrode active material. The concentration of Li / Mn antisite defects can be measured by methods known in the art, such as XRD.

[0038] In any embodiment, the surface oxygen valence state of the second positive electrode active material is below -1.82, optionally between -1.89 and -1.98. By reducing the surface oxygen valence state, interfacial side reactions between the positive electrode active material and the electrolyte can be mitigated, thereby improving the cycle performance and high-temperature stability of the secondary battery. The surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).

[0039] In any embodiment, the compaction density of the second positive electrode active material at 3T is 2.0 g / cm³. 3 The above can be selected as 2.2g / cm. 3 The higher the compaction density, the greater the weight of active material per unit volume. Therefore, increasing the compaction density is beneficial for improving the volumetric energy density of the battery cell. Compaction density can be measured according to GB / T 24533-2009.

[0040] In any embodiment, the second positive electrode active material further comprises carbon, which is coated on the compound Li. a A x Mn 1-y B y P 1- z C z O 4-n D n The surface of the electrode can be improved, thereby enhancing the conductivity of the positive electrode active material.

[0041] A second aspect of this application also provides a method for preparing a positive electrode active material, comprising the following steps:

[0042] Provide a first positive electrode active material and a second positive electrode active material;

[0043] Simply mix the first positive electrode active material and the second positive electrode active material;

[0044] The first positive electrode active material contains the compound LiNi. b Co d Mn e M fO2, the second positive electrode active material contains the compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n , wherein a, b, d, e, f, x, y, z, n, M, A, B, C and D are defined as described in the first aspect of this application;

[0045] Optionally, the first positive electrode active material further comprises lithium carbonate and / or lithium hydroxide;

[0046] Optionally, the second positive electrode active material further comprises compounds coated with Li a A x Mn 1-y B y P 1-z C z O 4-n D n Carbon on the surface.

[0047] Therefore, by using a mixture of the first positive electrode active material and the second positive electrode active material, the advantages of the two materials complement each other, thereby improving the cycle capacity retention rate of the secondary battery, extending the cycle life of the secondary battery, and improving the safety of the secondary battery.

[0048] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application. Optionally, the content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, and more preferably 95-99.5% by weight, based on the total weight of the positive electrode film layer.

[0049] The fourth aspect of this application provides a secondary battery, including the positive electrode active material of the first aspect of this application, or the positive electrode active material prepared according to the method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.

[0050] The fifth aspect of this application provides a battery module, including the secondary battery of the fourth aspect of this application.

[0051] A sixth aspect of this application provides a battery pack that includes the battery module of the fifth aspect of this application.

[0052] A seventh aspect of this application provides an electrical device comprising at least one selected from the fourth aspect of this application, the fifth aspect of this application, and the sixth aspect of this application. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0054] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0055] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0056] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0057] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0058] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0059] Figure 7 This is a SEM image of the first positive electrode active material prepared by preparation example A10 of this application.

[0060] Figure 8 This is a SEM image of the first positive electrode active material prepared in Preparation Example A15 of this application.

[0061] Explanation of reference numerals in the attached figures:

[0062] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0063] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, positive electrode sheet, secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0064] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0067] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0068] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0069] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0070] [Rechargeable Battery]

[0071] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0072] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0073] [Positive electrode active material]

[0074] One embodiment of this application provides a positive electrode active material, comprising a first positive electrode active material and a second positive electrode active material; wherein...

[0075] The first positive electrode active material contains the compound LiNi. b Co d Mn e M f O2, wherein b is selected from the range of 0.314-0.970, optionally from the range of 0.65-0.97, d is selected from the range of 0-0.320, optionally from the range of 0.047-0.320 or from the range of 0.005-0.188, e is selected from the range of 0.006-0.390, optionally from the range of 0.006-0.102, and the sum of b, d, e and f is 1 and f is greater than 0, and M is selected from one or more elements selected from Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y;

[0076] The second positive electrode active material contains the compound Li. a A x Mn 1-y B y P 1-z C z O 4-n D na is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, A is selected from one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W, optionally Mg and / or Mo, B is selected from one or more elements of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally V, Fe and Co, C is selected from one or more elements of B (boron), S, Si and N, optionally S, Si and N, D is selected from one or more elements of S, F, Cl and Br, optionally F.

[0077] The first cathode active material is a layered transition metal oxide with two-dimensional lithium-ion transport channels; the second cathode active material has only one-dimensional lithium-ion transport channels. Using them together, their complementary advantages improve the overall electrochemical performance. The initial coulombic efficiency of the first cathode active material is typically lower than that of the second. After the secondary battery is used in combination, it still contains a significant amount of reversible lithium ions after the negative electrode film in the chemical system is consumed, thus improving the cycle capacity retention rate, extending the cycle life, and enhancing the safety of the secondary battery.

[0078] Furthermore, although the mechanism is not yet clear, the applicant unexpectedly discovered that the second positive electrode active material of this application is obtained by elemental doping of the compound LiMnPO4, wherein A, B, C, and D are the elements doped at the Li, Mn, P, and O sites of the compound LiMnPO4, respectively. Not wanting to be confined to theory, the inventors of this application discovered that the performance improvement of lithium manganese phosphate is related to reducing the lattice change rate of lithium manganese phosphate during lithium insertion / extraction and reducing surface activity. Reducing the lattice change rate can reduce the difference in lattice constants between the two phases at the grain boundary, reduce interfacial stress, and enhance Li... +The ability to transport substances at the interface improves the rate performance of the positive electrode active material. However, high surface activity can easily lead to severe interfacial side reactions, exacerbating gas generation, electrolyte consumption, and interface damage, thus affecting the cycle performance of the secondary battery. In this application, lattice change rate is reduced through Li and Mn doping. Mn doping also effectively reduces surface activity, thereby suppressing Mn dissolution and interfacial side reactions between the positive electrode active material and the electrolyte. P-site doping accelerates the change rate of Mn-O bond length, lowering the small polaron migration barrier of the material, which is beneficial to electronic conductivity. O-site doping has a good effect on reducing interfacial side reactions. P-site and O-site doping also affect the dissolution of Mn from antisite defects and the kinetic properties. Therefore, doping reduces the concentration of antisite defects in the material, improves the kinetic properties and specific capacity of the material, and can also change the particle morphology, thereby increasing the compaction density. The applicant unexpectedly discovered that by simultaneously doping specific elements at specific amounts at the Li, Mn, P, and O sites of the compound LiMnPO4, it is possible to obtain significantly improved rate performance, while significantly reducing the dissolution of Mn and Mn-site dopants, resulting in significantly improved cycle performance and / or high-temperature stability, and also improving the specific capacity and compaction density of the material.

[0079] In some embodiments, M is Mg and / or Al. Doping the first positive electrode active material with Al can improve the structural and thermal stability of the material and enhance its cycle performance. Doping the first positive electrode active material with Mg can lead to an increase or decrease in the valence state of transition metal ions, thereby generating holes or electrons, changing the band structure of the material, increasing the intrinsic electronic conductivity of the material, and improving the cycle performance of the secondary battery. Co-doping of Mg and Al into the lattice of the host material can synergistically stabilize the material structure, improve the mixing degree of cations in the material, suppress oxygen evolution, and further improve the cycle performance and thermal stability of the secondary battery.

[0080] Unless otherwise stated, the chemical formula Li a A x Mn 1-y B y P 1-z C z O 4-n D nIn this context, when A comprises two or more elements, the aforementioned limitation on the range of x values ​​applies not only to the stoichiometric coefficient of each element representing A, but also to the sum of the stoichiometric coefficients of all elements representing A. For example, when A comprises two or more elements A1, A2…An, the stoichiometric coefficients x1, x2…xn of each of A1, A2…An must each fall within the range of x values ​​defined in this application, and the sum of x1, x2…xn must also fall within this range. Similarly, for the case where B, C, and D comprise two or more elements, the limitation on the range of stoichiometric coefficients of B, C, and D in this application also has the aforementioned meaning. Similarly, for the chemical formula LiNi… b Co d Mn e M f When M in O2 consists of two or more elements, the limitation on the numerical range of the stoichiometric coefficient of M in this application also has the above meaning.

[0081] In some implementations, the compound LiNi b Co d Mn e M f O2 and Li a A x Mn 1-y B y P 1-z C z O 4-n D n Both remain electrically neutral.

[0082] In some embodiments, the mass of the first positive electrode active material is m1, the mass of the second positive electrode active material is m2, and the value of m1 / (m1+m2) is 2%-55%, optionally 3%-50%. Thus, the mass percentage of the first positive electrode active material in the two positive electrode active materials is within the above range, which can improve the overall stability and safety of the positive electrode active material.

[0083] In some embodiments, the value of b×m1 / (m1+m2) is 0.017-0.457, and can be selected as 0.025-0.415. This can further improve the overall stability and safety of the positive electrode active material.

[0084] In some embodiments, the first positive electrode active material is a single crystal or quasi-single crystal material, and the particle size D of the first positive electrode active material is... v 50 represents less than or equal to 5.8 μm, and can be selected from 2.3 to 5.8 μm, or even from 2.3 to 4.3 μm.

[0085] The particle size of the first positive electrode active material, which is a single crystal or quasi-single crystal, is within the above range, which can optimize the electrochemical reaction area, further reduce and suppress the interfacial side reactions of the positive electrode during the cycling process of the secondary battery, reduce the cycle decay rate of the secondary battery, and extend the cycle life of the secondary battery.

[0086] In some embodiments, the first positive electrode active material is a single crystal or quasi-single crystal material, and the BET specific surface area of ​​the first positive electrode active material is less than or equal to 1.15 m². 2 / g, which can be selected as 0.45-1.15m 2 / g; and / or,

[0087] The compaction density of the first positive electrode active material under 3T pressure is greater than or equal to 3.11 g / cm³. 3 The selectable value is 3.11-3.4 g / cm³. 3 .

[0088] In some embodiments, when the first positive electrode active material is a single crystal or quasi-single crystal material, d is selected from the range of 0.05-0.320, and may be selected from the range of 0.05-0.282; and / or,

[0089] b is greater than 0.314 and less than 0.97, and can be selected from the range of 0.55-0.869.

[0090] When the first positive electrode active material is a single crystal or quasi-single crystal material, d and b within the above range are beneficial to further improve the conductivity and rate performance of the positive electrode active material, further improve the cycle capacity retention rate of the secondary battery, and further extend the cycle life of the secondary battery.

[0091] In some embodiments, when the first positive electrode active material is a polycrystalline material, the particle size D of the first positive electrode active material is... v 50 is 3.5–13.5 μm; and / or,

[0092] The BET specific surface area of ​​the first positive electrode active material is less than or equal to 1.32 m². 2 / g, which can be selected as 0.28-1.32m 2 / g; and / or,

[0093] The compaction density of the first positive electrode active material under 3T pressure is greater than or equal to 2.92 g / cm³. 3 The selectable value is 2.92-3.31 g / cm³. 3 .

[0094] The particle size, specific surface area, and compaction density of the polycrystalline first cathode active material are kept within the above range to further improve the rate performance of the cathode active material, further reduce and suppress the interfacial side reactions of the cathode during the cycle of the secondary battery, reduce the cycle decay rate of the secondary battery, and extend the cycle life of the secondary battery.

[0095] In some embodiments, the first positive electrode active material further comprises lithium carbonate and / or lithium hydroxide;

[0096] Optionally, based on the mass of the first positive electrode active material, the mass content of lithium carbonate is less than or equal to 1%, and / or the mass content of lithium hydroxide is less than or equal to 1%.

[0097] Residual water molecules introduced by the second positive electrode active material may react with the electrolyte to produce HF. HF can easily damage the positive electrode active material itself or the SEI film on the negative electrode, thus affecting the cycle life of the secondary battery. The lithium carbonate and / or lithium hydroxide further contained in the first positive electrode active material of this application can neutralize HF, reducing or inhibiting the destructive effect of HF on the positive electrode active material or the SEI film of the negative electrode, thereby further improving the cycle life of the secondary battery.

[0098] In some embodiments, in the second positive electrode active material, A is selected from any one of Zn, Al, Na, K, Mg, Nb, Mo and W; B is selected from at least two of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C is selected from any one of B (boron), S, Si and N; and D is selected from any one of S, F, Cl and Br.

[0099] Optionally, A is Mg or Nb, and / or,

[0100] B is selected from at least two elements chosen from Fe, Ti, V, Co, and Mg, and may also be selected from Fe and one or more elements chosen from Ti, V, Co, and Mg, and / or

[0101] C is S, and / or,

[0102] D is F.

[0103] By selecting doping elements at the Li sites within the aforementioned range, the lattice change rate during the lithium removal process can be further reduced, thereby further improving the rate performance of the secondary battery. Similarly, by selecting doping elements at the Mn sites within the aforementioned range, electronic conductivity can be further increased and the lattice change rate further reduced, thereby enhancing the rate performance and specific capacity of the secondary battery. Furthermore, by selecting doping elements at the P sites within the aforementioned range, the rate performance of the secondary battery can be further improved. Finally, by selecting doping elements at the O sites within the aforementioned range, interfacial side reactions can be further mitigated, improving the high-temperature performance of the secondary battery.

[0104] In some embodiments, x in the second positive electrode active material is selected from the range of 0.001 to 0.005; and / or,

[0105] y is selected from the range of 0.01 to 0.5, and may optionally be selected from the range of 0.25 to 0.5; and / or,

[0106] z is selected from the range of 0.001 to 0.005; and / or,

[0107] n is selected from the range of 0.001 to 0.005.

[0108] By selecting the y-value within the above range, the specific capacity and rate performance of the material can be further improved. By selecting the x-value within the above range, the kinetic performance of the material can be further improved. By selecting the z-value within the above range, the rate performance of the secondary battery can be further improved. By selecting the n-value within the above range, the high-temperature performance of the secondary battery can be further improved.

[0109] In some embodiments, the value of (1-y):y is selected from the range of 1 to 4, and optionally from the range of 1.5 to 3, and the value of a:x is selected from the range of 9 to 1100, and optionally from the range of 190-998. Thus, the energy density and cycle performance of the positive electrode active material can be further improved.

[0110] In some embodiments, the lattice change rate of the second positive electrode active material before and after complete lithium insertion / extraction is less than 8%, optionally less than 4%. Reducing the lattice change rate facilitates Li-ion transport, meaning that Li-ions have greater migration ability within the material, which is beneficial for improving the rate performance of the secondary battery. The lattice change rate can be measured using methods known in the art, such as X-ray diffraction (XRD).

[0111] In some embodiments, the Li / Mn antisite defect concentration of the second positive electrode active material is less than 2%, and optionally less than 0.5%. The so-called Li / Mn antisite defect refers to the presence of Li in the LiMnPO4 lattice. + With Mn 2+The positions of Li and Mn are interchanged. The Li / Mn antisite defect concentration refers to the concentration of Li / Mn antisite defects in the positive electrode active material. 2+ Interchangeable Li + Zhan Li + Percentage of the total. Mn of the inversion defect. 2+ It will hinder Li + The transport of Li / Mn antisite defects, by reducing the concentration of Li / Mn antisite defects, is beneficial to improving the specific capacity and rate performance of the positive electrode active material. The concentration of Li / Mn antisite defects can be measured by methods known in the art, such as XRD.

[0112] In some embodiments, the surface oxygen valence state of the second positive electrode active material is below -1.82, optionally between -1.89 and -1.98. By reducing the surface oxygen valence state, interfacial side reactions between the positive electrode active material and the electrolyte can be mitigated, thereby improving the cycle performance and high-temperature stability of the secondary battery. The surface oxygen valence state can be measured by methods known in the art, such as electron energy loss spectroscopy (EELS).

[0113] In some embodiments, the compaction density of the second positive electrode active material at 3T is 2.0 g / cm³. 3 The above can be selected as 2.2g / cm. 3 The higher the compaction density, the greater the weight of active material per unit volume. Therefore, increasing the compaction density is beneficial for improving the volumetric energy density of the battery cell. Compaction density can be measured according to GB / T 24533-2009.

[0114] In some embodiments, the second positive electrode active material further comprises carbon, which is coated on the compound Li a A x Mn 1-y B y P 1- z C z O 4-n D n The surface of the electrode can be improved, thereby enhancing the conductivity of the positive electrode active material.

[0115] In some implementations, b can be, for example, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0116] In some implementations, d can be, for example, 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3.

[0117] In some implementations, e can be, for example, 0.01, 0.02, 0.05, 0.1, 0.15, 0.2, 0.26, 0.3, or 0.35.

[0118] [Methods for preparing positive electrode active materials]

[0119] One embodiment of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0120] Provide a first positive electrode active material and a second positive electrode active material;

[0121] Simply mix the first positive electrode active material and the second positive electrode active material;

[0122] The first positive electrode active material contains the compound LiNi. b Co d Mn e M f O2, the second positive electrode active material contains the compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n The definitions of a, b, d, e, f, x, y, z, n, M, A, B, C, and D are as described in [Positive Electrode Active Materials].

[0123] Optionally, the first positive electrode active material further comprises lithium carbonate and / or lithium hydroxide;

[0124] Optionally, the second positive electrode active material further comprises compounds coated with Li a A x Mn 1-y B y P 1-z C z O 4-n D n Carbon on the surface.

[0125] Therefore, by using a mixture of the first positive electrode active material and the second positive electrode active material, the advantages of the two materials complement each other, thereby improving the cycle capacity retention rate of the secondary battery, extending the cycle life of the secondary battery, and improving the safety of the secondary battery.

[0126] In some embodiments, the first positive electrode active material is prepared by the following steps:

[0127] Step 1): React Ni salt, Co salt, and Mn salt with alkali in a solvent, separate the solid and liquid phases, and collect the solid phase.

[0128] Step 2): Mix the solid material, lithium source and source of element M, ball mill, sinter, and cool to obtain the first positive electrode active material;

[0129] Optionally, in step 2), the cooled first positive electrode active material is crushed and sieved, or the cooled first positive electrode active material is crushed, sintered again, broken, and sieved.

[0130] In some embodiments, step 1) is carried out at a pH of 9-13, or alternatively at a pH of 9-12 or 10-13.

[0131] In some embodiments, in step 1), the reaction temperature is 40°C-80°C, for example 50°C, 55°C, or 60°C.

[0132] In some implementations, the reaction time in step 1) is 8-70 hours, for example, 20 hours, 55 hours, 60 hours, or 65 hours.

[0133] In some embodiments, in step 1), the reaction is carried out at a rotational speed of 150-1000 r / min, for example 300 r / min or 500 r / min.

[0134] In some implementations, in step 1), solid-liquid separation is filtration.

[0135] In some embodiments, the solid phase is washed and dried before step 2); optionally, it is vacuum dried at 100°C-140°C for 12-48 hours, for example, vacuum dried at 120°C for 24 hours.

[0136] In some implementations, in step 2), the rotational speed of the ball mill is 200-500 r / s, for example 300 r / s or 500 r / s.

[0137] In some implementations, in step 2), the ball milling time is 1-5 hours, for example 2, 3, or 4 hours.

[0138] In some embodiments, step 2) involves sintering in an air atmosphere; alternatively, sintering is performed in an air atmosphere at 0.1-0.4 MPa.

[0139] In some embodiments, in step 2), the sintering procedure is as follows: pre-sintering is performed by heating to 750℃-950℃ and holding for 12-20 hours, with a heating rate of 1℃ / min; optionally, the temperature is then lowered to 600℃ and held for 8 hours at the same rate for sintering; after sintering, the temperature is lowered to 300℃ at a rate of 1℃ / min.

[0140] In some embodiments, in step 2), the re-sintering procedure is as follows: heat to 400°C at a heating rate of 20°C / min and hold for 20 hours for sintering, and then cool down to 300°C at a rate of 1°C / min after sintering.

[0141] In some embodiments, step 2) involves using an air jet mill for pulverization; optionally, the rotational speed of the air jet mill is 2500-3500 r / min, for example, 3000 r / min; optionally, the airflow rate of the air jet mill is 400-600 m³ / min. 3 / h, for example 500m 3 / h.

[0142] In some implementations, step 2) involves sieving the material through a 450-550 mesh (e.g., 500 mesh) filter.

[0143] In some embodiments, the second positive electrode active material is prepared by the following steps:

[0144] Step (1): Mix the manganese source, the source of element B, the acid, and an optional solvent to obtain a mixture;

[0145] Step (2): Mix the mixture with a lithium source, a phosphorus source, a source of element A, a source of element C and a source of element D, an optional carbon source and an optional solvent, dry and sinter to obtain a mixture containing Li. m A x Mn 1-y B y P 1-z C z O 4-n D n The core material. The definitions of A to D are as described above.

[0146] In some embodiments, step (1) is performed at 60°C-120°C, or optionally at 70°C-120°C (e.g., about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C); and / or, in step (1), mixing is performed by stirring at a speed of 200-800 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm), optionally for 1-9 hours (more preferably 3-7 hours, e.g., about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours or about 9 hours).

[0147] In some embodiments, in step (2), the mixing is carried out for 8-15 hours (e.g., about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, or about 15 hours), optionally at a temperature of 20-120°C, optionally at 40-120°C (e.g., about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C).

[0148] When the temperature and time during the preparation process are within the above range, the resulting second positive electrode active material has fewer lattice defects, which helps to suppress manganese dissolution, reduce interfacial side reactions between the positive electrode active material and the electrolyte, and thus improve the cycle performance and safety performance of the secondary battery.

[0149] In some embodiments, in step (2), mixing is performed at a pH of 3.5-6, optionally at a pH of 4-6, and more preferably at a pH of 4-5. It should be noted that the pH can be adjusted in this application using methods commonly used in the art, for example, by adding an acid or a base.

[0150] In some embodiments, optionally, in step (2), the molar ratio of the mixture or manganese salt particles doped with element B to the lithium source and phosphorus source is 1:0.4-2.1:0.1-2.1, optionally about 1:0.4-0.5:0.1-1.

[0151] In some embodiments, in step (2), sintering is performed at 600-900°C for 4-10 hours; optionally, sintering can be performed at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C or about 900°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, sintering is performed under an inert gas or a mixture of inert gas and hydrogen atmosphere; more preferably, the protective atmosphere is a mixture of 70-90 vol% nitrogen and 10-30 vol% hydrogen; the sintering temperature and sintering time can be within any range of the above values, which can improve crystallinity, reduce the formation of impurity phases, maintain a certain particle size, thereby improving the specific capacity and compaction density of the positive electrode active material, and improving the overall performance of the secondary battery, including rate performance.

[0152] In some alternative embodiments, the mixture obtained in step (1) is filtered, dried, and ground to obtain element B-doped manganese salt particles with a particle size Dv50 of 50-200 nm. The element B-doped manganese salt particles are used in step (2) to mix with lithium source, phosphorus source, source of element A, source of element C and source of element D and optional solvent.

[0153] In some alternative implementations, in step (2), drying is performed using a spray drying device.

[0154] In some alternative implementations, in step (2), grinding is performed simultaneously with mixing.

[0155] The preparation method of this application does not have any particular restrictions on the source of materials. The source of a certain element may include one or more of the element's elemental form, sulfate, halide, nitrate, phosphate, oxalate, carbonate, oxide and hydroxide, provided that the source can achieve the purpose of the preparation method of this application.

[0156] In some embodiments, the source of element A is selected from one or more of the following: elemental form, oxide, phosphate, oxalate, carbonate, and sulfate; and / or,

[0157] The source of element B is one or more selected from elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of element B; and / or,

[0158] The source of element C is one or more selected from sulfates, borates, nitrates, and silicates of element C; and / or,

[0159] The source of element D is one or more selected from element D in its simple form and ammonium salt.

[0160] In some embodiments, the source of element M is one or more selected from elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide of element M.

[0161] The amount of source added for each of elements A, B, C, D, and M depends on the target doping amount, and the ratio of the amount of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0162] In this application, the manganese source can be any manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the manganese source can be one or more selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0163] In this application, the acid may be one or more organic acids selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, siliceous acid, and organic acids such as oxalic acid. In some embodiments, the acid is a dilute organic acid with a concentration of 60% by weight or less.

[0164] In this application, the lithium source may be any lithium-containing material known in the art that can be used to prepare lithium manganese phosphate. As an example, the lithium source may be one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0165] In this application, the phosphorus source may be any phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the phosphorus source may be one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0166] In this application, as an example, the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0167] [Positive electrode plate]

[0168] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the positive active material described above or the positive active material prepared by the method described above.

[0169] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0170] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0171] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0172] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0173] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0174] [Negative electrode plate]

[0175] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0176] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0177] 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 material substrate and a metal layer formed on at least one surface of the polymer material substrate. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0178] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0179] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, 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).

[0180] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0181] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0182] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0183] [Electrolytes]

[0184] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0185] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0186] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0187] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0188] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0189] [Isolation membrane]

[0190] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0191] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0192] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0193] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0194] 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. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0195] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0196] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0197] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0198] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0199] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0200] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0201] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0202] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0203] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0204] Figure 6 This is an example of an electrical device. The device could 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 the secondary battery for this device, a battery pack or battery module can be used.

[0205] [Example]

[0206] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0207] Preparation of the first positive electrode active material

[0208] Preparation Example A3: LiNi 0.55 Co 0.113 Mn 0.277 Al 0.04 Mg 0.02 O2 (similar to single crystal)

[0209] (1) Prepare a mixed solution by adding water to NiSO4, CoSO4 and MnSO4 in a molar ratio of 0.55:0.113:0.277, wherein the concentration of NiSO4 in the mixed solution is 2 mol / L; prepare a 5 mol / L NaOH solution;

[0210] (2) 50L of mixed solution was introduced into the reaction vessel, and then 50L of NaOH solution and an appropriate amount of 0.5mol / L ammonia solution were introduced into the reaction vessel to make the pH value in the reaction vessel 9.0-12.0, the reaction temperature 40℃-80℃, and the reaction was carried out for 60h under stirring conditions at a stirring speed of 300-1000r / min. After completion, the precipitate was filtered out and washed. The washed precipitate was vacuum dried at 120℃ for 24h to obtain the precursor.

[0211] (3) Li2CO3, precursor, Al2O3 and MgO were mixed, wherein the molar ratio of Li2CO3 (based on the molar amount of Li), precursor (based on the total molar amount of Ni, Co and Mn in the mixed solution), Al2O3 (based on the molar amount of Al) to MgO was 1.05:0.94:0.04:0.02. After mixing, the mixture was placed in a ball mill jar and ball-milled at 300 r / s for 2 h. Then, it was placed in a box furnace and pre-fired at 950 °C for 12 h under an air atmosphere of 0.2 MPa, with a heating rate of 1 °C / min. Then, it was sintered at 600 °C for 8 h at a rate of 1 °C / min. After sintering, it was cooled to 300 °C at a rate of 1 °C / min and then allowed to cool naturally to room temperature. Finally, it was passed through an air jet mill at a speed of 3000 r / min and a 500 m... 3 The material is pulverized at an airflow rate of / h for 0.5h, and then sieved through a 500-mesh filter to obtain the first positive electrode active material.

[0212] Preparation Example A16: LiNi 0.83 Co 0.114 Mn 0.006 Al 0.04 Mg 0.01 O2 (polycrystalline)

[0213] (1) Prepare a mixed solution by adding water to NiSO4, CoSO4 and MnSO4 in a molar ratio of 0.83:0.114:0.006, wherein the concentration of NiSO4 in the mixed solution is 2 mol / L; prepare a 6 mol / L NaOH solution;

[0214] (2) Pass 50L of mixed solution into the reaction vessel, then pass 50L of NaOH solution and an appropriate amount of 0.5mol / L ammonia solution into the reaction vessel to make the pH value in the reaction vessel 10-13, the reaction temperature 40℃-80℃, and react for 8-20 hours under stirring conditions at a stirring speed of 150-300r / min. After completion, filter out the precipitate and wash it. The washed precipitate is vacuum dried at 120℃ for 24 hours to obtain the precursor.

[0215] (3) Mix LiOH, precursor, Al2O3 and MgO, wherein the molar ratio of LiOH, precursor (based on the total molar amount of Ni, Co and Mn in the mixed solution), Al2O3 (based on the molar amount of Al) to MgO is 1.05:0.95:0.04:0.01. After mixing, place the mixture in a ball mill jar and ball mill at 500 r / s for 2 h. Then place the mixture in a chamber furnace and heat it to 750℃ under an air atmosphere of 0.2 MPa. Pre-fired at 20℃ / min for 20 hours, then sintered at 1℃ / min to 300℃, and allowed to cool naturally to room temperature. The mixture was then crushed at 2000 rpm for 5 hours. Next, the mixture was heated to 400℃ at 20℃ / min and held for 20 hours for sintering. After sintering, it was cooled to 300℃ at 1℃ / min and allowed to cool naturally to room temperature. Finally, it was passed through an air jet mill at 3000 rpm and 500 m³ / min. 3 The material is crushed at an air volume of / h for 0.5h, and then sieved through a 400-mesh filter to obtain the first positive electrode active material.

[0216] Preparation Examples A1, A2, A4 to A15, A17 to A22 and Comparative Preparation Example A1

[0217] The first positive electrode active materials of preparation examples A1, A2, A4 to A11, A22 and comparative preparation example A1 were prepared using a method similar to that of preparation example A3. The differences in preparation are shown in Table 1, and the rest are the same as those in preparation example A3.

[0218] Preparation Examples A12 to A15 and A17 to A21 were prepared using a method similar to that used in Preparation Example A16. The differences in the preparation are shown in Table 1, and the rest are the same as those used in Preparation Example A16.

[0219]

[0220]

[0221]

[0222]

[0223]

[0224]

[0225]

[0226]

[0227]

[0228] Preparation of the second positive electrode active material

[0229] Preparation Example B1

[0230] Preparation of doped manganese oxalate: 1.3 mol MnSO4·H2O and 0.7 mol FeSO4·H2O were thoroughly mixed in a mixer for 6 hours; the mixture was transferred to a reaction vessel, 10 L of deionized water and 2 mol oxalic acid dihydrate were added, and the mixture was heated to 80 °C, then stirred at 600 rpm for 6 hours until the reaction was terminated (no more bubbles were generated), resulting in a suspension of Fe-doped manganese oxalate; the suspension was filtered, the filter cake was dried at 120 °C, and ground to obtain a particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0231] Preparation of doped lithium manganese phosphate: 1 mol of Fe-doped manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.005 mol of sucrose were added to 20 L of deionized water. The mixture was then transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying and granulation. The drying temperature was set at 250℃, and the granules were dried for 4 hours to obtain particles. Under a nitrogen (90% v / v) + hydrogen (10% v / v) protective atmosphere, the particles were sintered at 700℃ for 10 hours to obtain the second positive electrode active material, carbon-coated Li. 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 The elemental content of positive electrode active materials can be detected using inductively coupled plasma atomic emission spectroscopy (ICP).

[0232] Preparation Example B2

[0233] Except for changing the amount of high-purity Li2CO3 to 0.4885 mol, replacing Mo(SO4)3 with an equimolar amount of MgSO4, changing the amount of FeSO4·H2O to 0.68 mol, adding 0.02 mol of Ti(SO4)2 when preparing doped manganese oxalate, and replacing H4SiO4 with an equimolar amount of HNO3, everything else is the same as in preparation example B1.

[0234] Preparation Example B3

[0235] Except for changing the amount of high-purity Li2CO3 to 0.496 mol, replacing Mo(SO4)3 with an equimolar amount of W(SO4)3, and replacing H4SiO4 with an equimolar amount of H2SO4, the preparation method is the same as in Preparation Example B1.

[0236] Preparation Example B4

[0237] Except for changing the amount of high-purity Li2CO3 to 0.4985 mol, replacing 0.001 mol of Mo(SO4)3 with 0.0005 mol of Al2(SO4)3 and NH4HF2 with an equimolar amount of NH4HCl2, the preparation method is the same as in Preparation Example B1.

[0238] Preparation Example B5

[0239] Except for changing 0.7 mol FeSO4·H2O to 0.69 mol, adding 0.01 mol VCl2 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.4965 mol, replacing 0.001 mol Mo(SO4)3 with 0.0005 mol Nb2(SO4)5 and H4SiO4 with an equimolar amount of H2SO4, everything else is the same as in preparation example B1.

[0240] Preparation Example B6

[0241] Except for changing the amount of FeSO4·H2O to 0.68 mol, adding 0.01 mol of VCl2 and 0.01 mol of MgSO4 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.4965 mol, replacing 0.001 mol of Mo(SO4)3 with 0.0005 mol of Nb2(SO4)5 and H4SiO4 with an equimolar amount of H2SO4, everything else is the same as in preparation example B1.

[0242] Preparation Example B7

[0243] Except for replacing MgSO4 with an equimolar amount of CoSO4, the preparation method is the same as in Preparation Example B6.

[0244] Preparation Example B8

[0245] Except for replacing MgSO4 with an equimolar amount of NiSO4, the preparation method is the same as in Preparation Example B6.

[0246] Preparation Example B9

[0247] Except for changing the amount of FeSO4·H2O to 0.698 mol, adding 0.002 mol of Ti(SO4)2 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.4955 mol, replacing 0.001 mol of Mo(SO4)3 with 0.0005 mol of Nb2(SO4)5, replacing H4SiO4 with an equimolar amount of H2SO4, and replacing NH4HF2 with an equimolar amount of NH4HCl2, everything else is the same as in preparation example B1.

[0248] Preparation Example B10

[0249] Except for changing the amount of FeSO4·H2O to 0.68 mol, adding 0.01 mol of VCl2 and 0.01 mol of MgSO4 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.4975 mol, replacing 0.001 mol of Mo(SO4)3 with 0.0005 mol of Nb2(SO4)5 and NH4HF2 with an equimolar amount of NH4HBr2, everything else is the same as in preparation example B1.

[0250] Preparation Example B11

[0251] Except for changing the amount of FeSO4·H2O to 0.69 mol, adding 0.01 mol of VCl2 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.499 mol, replacing Mo(SO4)3 with an equimolar amount of MgSO4 and NH4HF2 with an equimolar amount of NH4HBr2, everything else is the same as in preparation example B1.

[0252] Preparation Example B12

[0253] Except for changing the amount of MnSO4·H2O to 1.36 mol, the amount of FeSO4·H2O to 0.6 mol, adding 0.04 mol of VCl2 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.4985 mol, replacing Mo(SO4)3 with an equimolar amount of MgSO4 and H4SiO4 with an equimolar amount of HNO3, everything else is the same as in preparation example B1.

[0254] Preparation Example B13

[0255] Except for changing the amount of MnSO4·H2O to 1.16 mol and the amount of FeSO4·H2O to 0.8 mol, the preparation method is the same as in Example B12.

[0256] Preparation Example B14

[0257] Except for changing the amount of MnSO4·H2O to 1.3 mol and the amount of VCl2 to 0.1 mol, the preparation method is the same as in Example B12.

[0258] Preparation Example B15

[0259] Except for changing the amount of MnSO4·H2O to 1.2 mol, adding 0.1 mol of VCl2 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.494 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4 and H4SiO4 with an equimolar amount of H2SO4, everything else is the same as in preparation example B1.

[0260] Preparation Example B16

[0261] Except for changing the amount of MnSO4·H2O to 1.2 mol, adding 0.1 mol of VCl2 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.467 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4, replacing 0.001 mol of H4SiO4 with 0.005 mol of H2SO4, and replacing 1.175 mol of 85% phosphoric acid with 1.171 mol of 85% phosphoric acid, everything else is the same as in preparation example B1.

[0262] Preparation Example B17

[0263] Except for changing the amount of MnSO4·H2O to 1.2 mol, adding 0.1 mol of VCl2 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.492 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4, replacing H4SiO4 with an equimolar amount of H2SO4, and changing 0.0005 mol of NH4HF2 to 0.0025 mol, everything else is the same as in preparation example B1.

[0264] Preparation Example B18

[0265] Except for changing the amount of FeSO4·H2O to 0.5 mol, adding 0.1 mol of VCl2 and 0.1 mol of CoSO4 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.492 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4, replacing H4SiO4 with an equimolar amount of H2SO4, and changing 0.0005 mol of NH4HF2 to 0.0025 mol, everything else is the same as in preparation example B1.

[0266] Preparation Example B19

[0267] Except for changing the amount of FeSO4·H2O to 0.4 mol and the amount of CoSO4 from 0.1 mol to 0.2 mol, the preparation method is the same as in Preparation Example B18.

[0268] Preparation Example B20

[0269] Except for changing the amount of MnSO4·H2O to 1.5 mol, FeSO4·H2O to 0.1 mol, and CoSO4 to 0.3 mol, the preparation method is the same as in Preparation Example B18.

[0270] Preparation Example B21

[0271] Except for replacing 0.1 mol of CoSO4 with 0.1 mol of NiSO4, the preparation method is the same as in Preparation Example B18.

[0272] Preparation Example B22

[0273] Except for changing the amount of MnSO4·H2O to 1.5 mol, the amount of FeSO4·H2O to 0.2 mol, and replacing 0.1 mol of CoSO4 with 0.2 mol of NiSO4, the preparation method is the same as in Example B18.

[0274] Preparation Example B23

[0275] Except for changing the amount of MnSO4·H2O to 1.4 mol, FeSO4·H2O to 0.3 mol, and CoSO4 to 0.2 mol, the preparation method is the same as in Preparation Example B18.

[0276] Preparation Example B24

[0277] Except for changing 1.3 mol of MnSO4·H2O to 1.2 mol, 0.7 mol of FeSO4·H2O to 0.5 mol, adding 0.1 mol of VCl2 and 0.2 mol of CoSO4 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.497 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4, replacing H4SiO4 with an equimolar amount of H2SO4, and changing 0.0005 mol of NH4HF2 to 0.0025 mol, everything else is the same as in preparation example B1.

[0278] Preparation Example B25

[0279] Except for changing the amount of MnSO4·H2O to 1.0 mol, FeSO4·H2O to 0.7 mol, and CoSO4 to 0.2 mol, the preparation method is the same as in Preparation Example B18.

[0280] Preparation Example B26

[0281] Except for changing the amount of MnSO4·H2O to 1.4 mol, the amount of FeSO4·H2O to 0.3 mol, adding 0.1 mol of VCl2 and 0.2 mol of CoSO4 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.4825 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4, changing the amount of H4SiO4 to 0.1 mol, changing the amount of phosphoric acid to 0.9 mol, and changing the amount of NH4HF2 to 0.04 mol, everything else is the same as in preparation example B1.

[0282] Preparation Example B27

[0283] Except for changing the amount of MnSO4·H2O to 1.4 mol, the amount of FeSO4·H2O to 0.3 mol, adding 0.1 mol of VCl2 and 0.2 mol of CoSO4 when preparing doped manganese oxalate, changing the amount of Li2CO3 to 0.485 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4, changing the amount of H4SiO4 to 0.08 mol, changing the amount of phosphoric acid to 0.92 mol, and changing the amount of NH4HF2 to 0.05 mol, everything else is the same as in preparation example B1.

[0284] Preparation Examples B28-B41

[0285] The positive electrode active material was prepared in the same manner as in Preparation Example B1, but the stirring speed, temperature, grinding and stirring time in the sand mill, sintering temperature and sintering time were changed when preparing the doped manganese oxalate, as shown in Table 2 below.

[0286] Table 2 shows the stirring speed, temperature, grinding and stirring time in the sand mill, sintering temperature, and sintering time during the preparation of doped manganese oxalate in Examples B28-B41.

[0287]

[0288]

[0289] Preparation Examples B42-B54

[0290] The positive electrode active material was prepared in the same manner as in Preparation Example B1, but the sources of lithium, manganese, phosphorus, and doping elements A, B, C, and D were changed, as shown in Table 3 below. The composition of the obtained positive electrode active material was the same as that in Preparation Example B1, i.e., all were Li. 0.994 Mo 0.001 Mn 0.65 Fe0.35 P 0.999 Si 0.001 O 3.999 F 0.001 .

[0291] Table 3 shows the sources of lithium, manganese, phosphorus, and doping elements A, B, C, and D in preparation examples B42-B54.

[0292]

[0293]

[0294] Preparation Example B55

[0295] (1) Preparation of doped manganese oxalate

[0296] 1.2 mol MnSO4·H2O and 0.79 mol FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was then transferred to a reaction vessel, and 10 L of deionized water, 2 mol oxalic acid dihydrate, and 0.01 mol VCl2 were added. The mixture was heated to 80 °C and then stirred at 600 rpm for 6 hours until the reaction was terminated (no more bubbles were generated), yielding a suspension of Fe-doped manganese oxalate. The suspension was filtered, and the filter cake was dried at 120 °C and ground to obtain a particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0297] (2) Preparation of doped lithium manganese phosphate

[0298] 1 mol of Fe-doped manganese oxalate particles, 0.45 mol of lithium carbonate, 0.05 mol of MgSO4, an 85% phosphoric acid aqueous solution containing 0.9 mol of phosphoric acid, 0.1 mol of H4SiO4, 0.05 mol of NH4HF2, and 0.005 mol of sucrose were added to 20 L of deionized water. The mixture was then transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250℃, and the granules were dried for 4 hours to obtain particles. The particles were sintered at 700℃ for 10 hours under a nitrogen (90% v / v) + hydrogen (10% v / v) protective atmosphere to obtain the positive electrode active material. Inductively coupled plasma atomic emission spectrometry (ICP) was used to detect the elemental content, yielding the chemical formula Li. 0.9 Mg 0.05 Mn 0.6 Fe 0.395 V 0.00 5P 0.9 Si 0.1 O 3.9 F 0.1 .

[0299] Preparation Example B56

[0300] Except for step (2), where lithium carbonate is 0.55 mol, MgSO4 is 0.001 mol, and NH4HF2 is 0.001 mol, the rest is the same as in preparation example B55; thus, the positive electrode active material Li is obtained. 1.1 Mg 0.001 Mn 0.6 Fe 0.395 V 0.005 P 0.9 Si 0.1 O 3.998 F 0.002 .

[0301] Preparation Example B57

[0302] Except for step (2), in which MgSO4 is 0.1 mol, the 85% phosphoric acid aqueous solution contains 0.95 mol of phosphoric acid, H4SiO4 is 0.05 mol, and NH4HF2 is 0.025 mol, the rest is the same as in preparation example B55; thus, the positive electrode active material Li is obtained. 0.9 Mg 0.1 Mn 0.6 Fe 0.395 V 0.005 P 0.95 Si 0.05 O 3.95 F 0.05 .

[0303] Preparation Example B58

[0304] Except for step (1) where MnSO4·H2O is 1.998 mol, FeSO4·H2O is 0.002 mol, and VCl2 is not used; and except for step (2) where lithium carbonate is 0.475 mol, the 85% phosphoric acid aqueous solution contains 0.96 mol phosphoric acid, H4SiO4 is 0.04 mol, and NH4HF2 is 0.01 mol; the rest is the same as in preparation example B55; thus, the positive electrode active material Li is obtained. 0.95 Mg 0.05 Mn 0.999 Fe 0.001 P 0.96 Si 0.04 O 3.99 F 0.01 .

[0305] Preparation Example B59

[0306] Except for step (1) where MnSO4·H2O is 1.98 mol, FeSO4·H2O is 0.02 mol, and VCl2 is not used; and except for step (2) where lithium carbonate is 0.475 mol, the 85% phosphoric acid aqueous solution contains 0.96 mol phosphoric acid, H4SiO4 is 0.04 mol, and NH4HF2 is 0.01 mol; the rest is the same as in preparation example B55; thus, the positive electrode active material Li is obtained. 0.95 Mg 0.05 Mn 0.9 9Fe 0.01 P 0.96 Si 0.04 O 3.99 F 0.01 .

[0307] Preparation Example B60

[0308] Except for step (1) where MnSO4·H2O is 1.6 mol, FeSO4·H2O is 0.4 mol, and VCl2 is not used; and except for step (2) where lithium carbonate is 0.475 mol, the 85% phosphoric acid aqueous solution contains 0.96 mol phosphoric acid, H4SiO4 is 0.04 mol, and NH4HF2 is 0.01 mol; the rest is the same as in preparation example B55; thus, the positive electrode active material Li is obtained. 0.95 Mg 0.05 Mn 0. 8Fe 0.2 P 0.96 Si 0.04 O 3.99 F 0.01 .

[0309] Comparative preparation example B1

[0310] Preparation of manganese oxalate: 1 mol of MnSO4·H2O was added to a reaction vessel, along with 10 L of deionized water and 1 mol of oxalic acid dihydrate (calculated as oxalic acid). The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no more bubbles were generated), yielding a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and subsequently ground to obtain the median particle size Dv. 50 Manganese oxalate particles with a diameter of 50-200 nm.

[0311] Preparation of lithium manganese phosphate: 1 mol of the above-mentioned manganese oxalate particles, 0.5 mol of lithium carbonate, an 85% phosphoric acid aqueous solution containing 1 mol of phosphoric acid, and 0.005 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250℃, and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700℃ for 10 hours to obtain carbon-coated LiMnPO4.

[0312] Comparative preparation example B2

[0313] Except that in Comparative Example 1, 1 mol of MnSO4·H2O was replaced with 0.85 mol of MnSO4·H2O and 0.15 mol of FeSO4·H2O, and the mixture was added to a mixer and thoroughly mixed for 6 hours before being added to the reactor, the preparation was otherwise the same as in Comparative Preparation Example B1.

[0314] Comparative preparation example B3

[0315] Except for changing the amount of MnSO4·H2O to 1.9 mol, replacing 0.7 mol of FeSO4·H2O with 0.1 mol of ZnSO4, changing the amount of Li2CO3 to 0.495 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of MgSO4, changing the amount of phosphoric acid to 1 mol, and not adding H4SiO4 and NH4HF2, everything else is the same as in preparation example B1.

[0316] Comparative preparation example B4

[0317] Except for changing the amount of MnSO4·H2O to 1.2 mol, FeSO4·H2O to 0.8 mol, Li2CO3 to 0.45 mol, replacing 0.001 mol of Mo(SO4)3 with 0.005 mol of Nb2(SO4)5, replacing 0.999 mol of phosphoric acid with 1 mol, replacing 0.0005 mol of NH4HF2 with 0.025 mol, and not adding H4SiO4, everything else is the same as in preparation example B1.

[0318] Comparative preparation example B5

[0319] Except for changing the amount of MnSO4·H2O to 1.4 mol, the amount of FeSO4·H2O to 0.6 mol, the amount of Li2CO3 to 0.38 mol, and replacing 0.001 mol of Mo(SO4)3 with 0.12 mol of MgSO4, everything else is the same as in preparation example B1.

[0320] Comparative preparation example B6

[0321] Except for changing the amount of MnSO4·H2O to 0.8 mol, replacing 0.7 mol of FeSO4·H2O with 1.2 mol of ZnSO4, changing the amount of Li2CO3 to 0.499 mol, and replacing 0.001 mol of Mo(SO4)3 with 0.001 mol of MgSO4, everything else is the same as in preparation example B1.

[0322] Comparative preparation example B7

[0323] Except for changing the amount of MnSO4·H2O to 1.4 mol, FeSO4·H2O to 0.6 mol, Li2CO3 to 0.534 mol, replacing 0.001 mol of Mo(SO4)3 with 0.001 mol of MgSO4, changing the amount of phosphoric acid to 0.88 mol, H4SiO4 to 0.12 mol, and NH4HF2 to 0.025 mol, everything else is the same as in preparation example B1.

[0324] Comparative preparation example B8

[0325] Except for changing the amount of MnSO4·H2O to 1.2 mol, FeSO4·H2O to 0.8 mol, Li2CO3 to 0.474 mol, replacing 0.001 mol of Mo(SO4)3 with 0.001 mol of MgSO4, changing the amount of phosphoric acid to 0.93 mol, H4SiO4 to 0.07 mol, and NH4HF2 to 0.06 mol, everything else is the same as in Preparation Example B1.

[0326] Preparation of hybrid positive electrode active materials

[0327] Examples 1 to 43 and Comparative Example 1

[0328] The first positive electrode active material and the second positive electrode material are stirred and mixed in a mixing tank. The mass of the first positive electrode material is m1, the mass of the second positive electrode material is m2, and the mass of the mixed positive electrode active material is m1+m2.

[0329] The parameters for each embodiment and comparative example are shown in Table 4.

[0330] Table 4 Parameters of Examples 1 to 43 and Comparative Example 1

[0331]

[0332]

[0333]

[0334] Preparation of full cells

[0335] The positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed evenly in an N-methylpyrrolidone solvent system at a weight ratio of 92:2.5:5.5. The mixture was then coated onto aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet. The coating amount was 0.4 g / cm³. 2 The compacted density is 2.4 g / cm³. 3 .

[0336] Artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in deionized water at a weight ratio of 90:5:2:2:1. The mixture was then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 1.7 g / cm³. 3 .

[0337] Using a porous polyethylene (PE) polymer film as a separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound up. The bare cell is placed in an outer package, injected with the same electrolyte as used in the preparation of the coin cell, and sealed to obtain a full battery (hereinafter also referred to as "full battery").

[0338] Preparation of button cells

[0339] The positive electrode active material, polyvinylidene fluoride (PVDF), and acetylene black were added to N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0340] Lithium foil was used as the negative electrode, and 1 mol / L LiPF6 was dissolved in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 to form an electrolyte. The electrolyte was then assembled with the positive electrode prepared above in a coin cell to form a coin cell (hereinafter also referred to as "coin cell").

[0341] The aforementioned positive electrode active material can be a first positive electrode active material, a second positive electrode active material, or a mixed positive electrode active material.

[0342] Material property testing

[0343] 1. Determination of the chemical formula of positive electrode active material

[0344] High spatial resolution characterization of the internal microstructure and surface structure of the positive electrode active material was performed using spherical aberration electron microscopy (ACSTEM), and the chemical formula of the positive electrode active material was obtained by combining it with three-dimensional reconstruction technology.

[0345] 2. Methods for measuring lattice change rate

[0346] Under a constant temperature environment of 25℃, the positive electrode active material sample was placed in an XRD (model Bruker D8 Discover) and tested at 1° / min. The test data were then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of each aspect of the unit cell, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0347] The positive electrode active material was prepared into a coin cell according to the "Preparation of Coin Cell" procedure described above, and the coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. The positive electrode sheet was then removed from the coin cell and immersed in DMC for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500 nm were screened out. Samples were taken, and the lattice constant v1 was calculated in the same manner as for the fresh samples tested above. The lattice change rate before and after complete lithium insertion / extraction is shown in the table, with (v0-v1) / v0×100% representing the lattice change rate before and after complete lithium insertion / extraction.

[0348] 3. Method for measuring the concentration of Li / Mn antisite defects

[0349] The XRD results obtained from the "lattice change rate measurement method" are compared with the PDF (Powder Diffraction File) card of the standard crystal to determine the Li / Mn antisite defect concentration. Specifically, the XRD results obtained from the "lattice change rate measurement method" are imported into the General Structure Analysis System (GSAS) software to automatically obtain refined results, which include the occupancy of different atoms. The Li / Mn antisite defect concentration is then obtained by reading the refined results.

[0350] 4. Methods for measuring surface oxygen valence state

[0351] A 5g sample of positive electrode active material was prepared into a coin cell according to the "Preparation of Coin Cell" procedure described above. The coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. The positive electrode sheet was then removed from the coin cell and immersed in DMC for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500nm were screened out. The obtained particles were measured using electron energy loss spectroscopy (EELS, using a Talos F200S instrument) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the elements. Based on the density of states and energy level distribution, the number of occupied electrons was calculated by integrating the valence band density of states data, thereby deducing the valence state of surface oxygen after charging.

[0352] 5. Compacted density measurement method

[0353] Take 5g of positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm, USA). Then place the mold on a compaction density instrument. Apply a pressure of 3T to the positive electrode active material and read the thickness of the powder under pressure (thickness after depressurization) on the instrument. Calculate the compaction density using ρ = m / v.

[0354] 6. Method for measuring the amount of Mn (and Mn-doped Fe) dissolved after cycling

[0355] The positive electrode active material sample was prepared into a full cell according to the above "Preparation of Full Cell".

[0356] A full battery, having been cycled at 45°C until its capacity decayed to 80%, was discharged at a 0.1C rate to a cutoff voltage of 2.0V. The battery was then disassembled, the negative electrode was removed, and 30 unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2 The discs were tested using an Agilent ICP-OES730 inductively coupled plasma emission spectrometry (ICP). The amounts of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn were calculated based on the ICP results, thus determining the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0357] 7. Method for measuring the initial specific capacity of button cells

[0358] At 2.5–4.3V, the button cell is charged at 0.1C to 4.3V, then charged at 4.3V at a constant voltage until the current is less than or equal to 0.05mA. After resting for 5 minutes, it is discharged at 0.1C to 2.0V. The discharge capacity at this point is the initial specific capacity, denoted as D0.

[0359] 8.3C Charging Constant Current Ratio Measurement Method

[0360] Under a constant temperature of 25℃, a fresh full battery is allowed to stand for 5 minutes, then discharged at 1 / 3C to 2.5V. After standing for 5 minutes, it is charged at 1 / 3C to 4.3V, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After standing for 5 minutes, the charge capacity at this point is recorded as C0. The battery is then discharged at 1 / 3C to 2.5V, allowed to stand for 5 minutes, and then charged at 3C to 4.3V. After standing for 5 minutes, the charge capacity at this point is recorded as C1. The constant current ratio for 3C charging is C1 / C0 × 100%.

[0361] The higher the constant current ratio during 3C charging, the better the battery's rate performance.

[0362] 9. Full battery 45℃ cycle performance test

[0363] Under constant temperature conditions of 45℃, the full battery was charged at 1C to 4.3V within a range of 2.5V to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. This charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed at this point was recorded.

[0364] 10. Full battery gas expansion test at 60°C

[0365] Full cells at 100% State of Charge (SOC) were stored at 60°C. The open-circuit voltage (OCV) and internal resistance (IMP) of the cells were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. Every 48 hours of storage, the full cells were removed, allowed to stand for 1 hour, and then the OCV and IMP were measured. After cooling to room temperature, the cell volume was measured using the displacement method. The displacement method involves first measuring the cell's weight (F1) separately using a balance with automatic unit conversion, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the process, measure the weight F2 of the battery cell at this moment, and the buoyancy F of the battery cell. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The cell volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0366] Based on the OCV and IMP test results, the battery in this embodiment maintained a state of charge (SOC) of over 99% throughout the entire experiment until the end of storage.

[0367] After 30 days of storage, the cell volume was measured, and the percentage increase in cell volume after storage was calculated relative to the cell volume before storage.

[0368] In addition, measure the residual capacity of the battery cell. Charge the full battery at 1C to 4.3V within the range of 2.5V to 4.3V, then charge it at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this point as the residual capacity of the battery cell.

[0369] 11. Specific Surface Area (BET) Measurement Method

[0370] According to GB / T 19587-2004, the specific surface area of ​​the positive electrode active material was tested using a TRISTAR II 3020 specific surface area and porosity analyzer (McMed Instruments, Inc., USA). Before testing, the positive electrode active material was dried in a vacuum oven at 200℃ for ≥2h, and the required sample amount was >20g.

[0371] 12. Particle size Dv50 test

[0372] Referring to GB / T19077-2016, the particle size Dv50 of the positive electrode active material was determined using a Mastersizer 3000 laser diffractometer (Malvin Panaco). Deionized water was used as the solvent, and the positive electrode active material was ultrasonically treated for 5 minutes before the test.

[0373] 13. ICP testing (Inductively Coupled Plasma Emission Spectrometry)

[0374] Referring to EPA6010D-2014, the elemental content was determined using an iCAP 7400 inductively coupled plasma atomic emission spectrometer, with aqua regia as the solvent.

[0375] Formula for calculating element content in powders: Element content (mass%) = 100% × element mass / sample mass;

[0376] The formula for calculating the element content of electrodes is: Element content (mass%) = 100% × element mass / (sample mass - current collector mass).

[0377] 14. Content determination of Li₂CO₃ and LiOH (free lithium potentiometric titration test)

[0378] Referring to GB / T 9736-2008, the test was conducted using a 905 potentiometric titrator. After sampling, the sample was immediately vacuum-sealed in an aluminum-plastic film bag. The minimum sample amount for a single test was ≥30g.

[0379] 15. Crystal type testing

[0380] Unless otherwise specified, in this application, the terms "single crystal / quasi-single crystal particle", "quasi-single crystal particle", "single crystal particle", "single crystal material particle" or similar expressions have a substantially similar meaning, referring to a single particle (i.e., a primary particle) and / or agglomerated particles, wherein the agglomerated particles are formed by the agglomeration of no more than 100 (particularly about 5 to 50) primary particles with an average particle size in the range of 50 nm to 10000 nm.

[0381] Unless otherwise specified, in this application, the terms "secondary particles" and "polycrystalline material particles" generally have similar meanings, referring to particles formed by the agglomeration of more than 100 primary particles with an average particle size in the range of 50-800 nm.

[0382] Scanning electron microscopy (SEM) was used to test the positive electrode active material. The sample and magnification were adjusted to ensure more than 10 aggregated particles were visible in the field of view. The number of primary particles constituting each aggregate was measured, and the length of each primary particle was recorded as its diameter. The primary particle diameters of each aggregate were sorted from largest to smallest. One-tenth of the largest and smallest particle diameters were removed, and the average of the remaining diameters was taken as the average diameter of the primary particles in that aggregate. If the number of primary particles and the average diameter of 50% or more (including 50%) of the aggregates met the definition of "polycrystalline material particles," the positive electrode active material was determined to be a polycrystalline material; otherwise, it was determined to be a monocrystalline or near-monocrystalline material.

[0383] The SEM images of the first positive electrode active materials prepared in Preparation Example A10 and Preparation Example A15 are shown below. Figure 7-8 As shown.

[0384] 16. Hot Box Safety Test

[0385] The test referenced the "Heating" section of the safety testing in GB 38031-2020, and explored the upper limit boundaries, optimizing the test conditions as follows:

[0386] ①Preparation:

[0387] Test conditions: Prepare an explosion-proof oven that can heat the circuit connection points; the test cells are fresh bare cells (cycle count ≤ 10 times); temperature sensing wires are attached around the cells and on the terminals for temperature monitoring; and a temperature recording device is also provided.

[0388] Cell treatment before testing: Constant current and constant voltage charging is performed using a 0.33C rate current until the cell is fully charged to the nominal voltage (e.g., 4.3V in this invention).

[0389] ② Test procedure: Place the sample in a high-temperature chamber, and raise the temperature from room temperature to 100℃ at a rate of 5℃ / min, and maintain it for 2 hours; then raise the temperature at a rate of 5℃ / min, and maintain it for 30 minutes every 5℃, until the cell runs out of control (runout criteria: voltage drops by ≥50% within 1 minute, cell temperature rises by ≥50% within 1 minute) or heats to 200℃, then stop heating.

[0390] ③ Data processing: Based on the above conditions, find the failure point and obtain the corresponding heat preservation temperature and heat preservation time, which are recorded as: time@temperature, such as 21min@150℃.

[0391] ④ Result Benchmarking:

[0392] Samples that undergo testing for a longer period of time are safer; samples that undergo testing for a longer period of time can be: samples with the same failure point temperature but longer testing time; samples with the same failure point time but higher temperature; samples with different failure point temperatures and times but higher temperature.

[0393]

[0394]

[0395]

[0396]

[0397]

[0398]

[0399]

[0400]

[0401]

[0402]

[0403]

[0404]

[0405]

[0406]

[0407]

[0408] As shown in Table 12:

[0409] Comparing Examples 1-43 with Comparative Example 1, it can be seen that, compared with the secondary battery prepared in Comparative Example 1, the secondary battery prepared by mixing the first positive electrode active material and the second positive electrode active material of this application has a higher cycle capacity retention rate and a longer cycle life; furthermore, the secondary batteries prepared by mixing positive electrode active materials in Examples 1, 3-7, 9, 12-13, 23-25, and 28 of this application have better safety than the secondary battery prepared in Comparative Example 1.

[0410] Comparing Examples 16 and 23-29, it can be seen that the secondary battery prepared with the mass relationship m1 / (m1+m2) of the first positive electrode active material and the second positive electrode active material in this application being between 3% and 50% has a further improved cycle capacity retention rate and a further extended cycle life.

[0411] The first positive electrode active material and the second positive electrode active material of this application are b*m 1 / The secondary battery with m1+m2 less than or equal to 0.457 exhibits high cycle capacity retention, long cycle life, and high safety. Comparing Examples 16 and Examples 23-29, it can be seen that the mass relationship b×m1 / (m1+m2) between the first and second positive electrode active materials in this application is within the range of 0.025-0.415, further improving the cycle capacity retention, extending the cycle life, and enhancing the safety of the secondary battery.

[0412] Comparing Examples 1-11 and 22, it can be seen that when the first positive electrode active material of this application is a quasi-single crystal, the D of the first positive electrode active material is... v Secondary batteries fabricated with a particle size of 50 μm or less exhibit high cycle capacity retention, long cycle life, and high safety; furthermore, the D of the first positive electrode active material... v With a particle size of 4.3 μm or less, the secondary batteries made from these particles have higher cycle capacity retention and longer cycle life.

[0413] Comparing Examples 12-21, it can be seen that when the first positive electrode active material of this application is polycrystalline, the D of the first positive electrode active material is... v 50 particles with a diameter of 3.5–13.5 μm and a BET specific surface area less than or equal to 1.32 m² 2 / g and a compacted density at 3T pressure greater than or equal to 2.92g / cm³ 3 The resulting secondary batteries have higher cycle capacity retention and longer cycle life.

[0414] Comparing Examples 1-8, 10-11, and 22, it can be seen that when the first positive electrode active material of this application is a near-single crystal, the first positive electrode active material LiNi b Co d Mn e M fSecondary batteries made with d values ​​of 0.047-0.320 in O2 have higher cycle capacity retention and longer cycle life.

[0415] The first positive electrode active material of this application is LiNi b Co d Mn e M f The b value in O2 is selected from the range of 0.314-0.970. The secondary battery made with this value has a high cycle capacity retention rate, long cycle life, and high safety. Comparing Examples 1-11 and 22, it can be seen that when the first positive electrode active material is a single crystal or quasi-single crystal material, the secondary battery made with a b value greater than 0.314 and less than 0.97 (excluding the values ​​of 0.314 and 0.97) has a higher cycle capacity retention rate and a longer cycle life.

[0416] Comparing Examples 10 and 22, it can be seen that the secondary battery made with a lithium carbonate mass content of less than or equal to 1% and a lithium hydroxide mass content of less than or equal to 1% in the first positive electrode active material of this application has a higher cycle capacity retention rate, a longer cycle life, and higher safety.

[0417] Comparing Table 5 and Table 12, we can see that:

[0418] Compared with secondary batteries made of the first positive electrode active material, the secondary batteries made of the mixed positive electrode active material containing the corresponding first positive electrode active material of this application have higher safety; compared with secondary batteries made using the first positive electrode active materials of preparation examples A14-A17 and A19-A21, the secondary batteries made of the mixed positive electrode active material containing the corresponding first positive electrode active material of this application have higher cycle capacity retention and longer cycle life.

[0419] Comparing Tables 7, 9, 10, 11 and Table 12, we can see that:

[0420] Compared with secondary batteries made using the second positive electrode active materials of preparation examples B1, B14, B16, B25, B26, B27, B31, B47, and B55-B60, the secondary batteries made with the mixed positive electrode active materials containing the corresponding second positive electrode active materials of this application have higher cycle capacity retention and longer cycle life.

[0421] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, comprising a first positive electrode active material and a second positive electrode active material; wherein, The first positive electrode active material contains the compound LiNi b Co d Mn e M f O2, wherein b is selected from the range of 0.314-0.970, e is selected from the range of 0.006-0.390, and the sum of b, d, e and f is 1 and f is greater than 0, and M is selected from one or more elements selected from Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y; The second positive electrode active material contains the compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n The a is selected from the range of 0.9 to 1.1, the x is selected from the range of 0.001 to 0.1, the y is selected from the range of 0.001 to 0.5, the z is selected from the range of 0.001 to 0.1, the n is selected from the range of 0.001 to 0.1, the A is selected from one or more elements of Zn, Al, Na, K, Mg, Nb, Mo, and W, the B is selected from one or more elements of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge, the C is selected from one or more elements of B, S, Si, and N, and the D is selected from one or more elements of S, F, Cl, and Br. When the first positive electrode active material is a polycrystalline material, d is selected from 0.095-0.320; when the first positive electrode active material is a single crystal or quasi-single crystal material, d is selected from 0.048 to 0.

320.

2. The positive electrode active material according to claim 1, wherein, The mass of the first positive electrode active material is m1, the mass of the second positive electrode active material is m2, and the value of m1 / (m1+m2) is 2%-55%.

3. The positive electrode active material according to claim 2, wherein, The value of m1 / (m1+m2) is 3%-50%.

4. The positive electrode active material according to claim 2, wherein, The value of b×m1 / (m1+m2) is 0.017-0.

457.

5. The positive electrode active material according to claim 4, wherein, The value of b×m1 / (m1+m2) is 0.025-0.

415.

6. The positive electrode active material according to any one of claims 1 to 5, wherein, The first positive electrode active material is a single crystal or quasi-single crystal material, and the particle size D of the first positive electrode active material is... v 50 means less than or equal to 5.8 μm.

7. The positive electrode active material according to claim 6, wherein, The particle size D of the first positive electrode active material v 50 is 2.3-5.8μm.

8. The positive electrode active material according to claim 7, wherein, The particle size D of the first positive electrode active material v 50 is 2.3-4.3μm.

9. The positive electrode active material according to any one of claims 1 to 8, wherein, When the first positive electrode active material is a single crystal or quasi-single crystal material The d is selected from the range of 0.048-0.282; and / or, The value of b is greater than 0.314 and less than 0.

97.

10. The positive electrode active material according to claim 9, wherein, The value of b is selected from the range of 0.55 to 0.

869.

11. The positive electrode active material according to any one of claims 1 to 10, wherein, When the first positive electrode active material is a polycrystalline material, the particle size D of the first positive electrode active material is... v 50 is 3.0~13.5μm; and / or, The BET specific surface area of ​​the first positive electrode active material is less than or equal to 1.73 m². 2 / g; and / or, The compaction density of the first positive electrode active material under 3T pressure is greater than or equal to 2.90 g / cm³. 3 .

12. The positive electrode active material according to claim 11, wherein, When the first positive electrode active material is a polycrystalline material, the particle size D of the first positive electrode active material is... v 50 is 3.5~13.5μm; and / or, The BET specific surface area of ​​the first positive electrode active material is less than or equal to 1.32 m². 2 / g; and / or, The compaction density of the first positive electrode active material under 3T pressure is greater than or equal to 2.92 g / cm³. 3 .

13. The positive electrode active material according to claim 12, wherein, The BET specific surface area of ​​the first positive electrode active material is 0.28-1.32 m². 2 / g; and / or, The compaction density of the first positive electrode active material under 3T pressure is 2.92-3.31 g / cm³. 3 .

14. The positive electrode active material according to any one of claims 1 to 13, wherein, The first positive electrode active material further comprises lithium carbonate and / or lithium hydroxide.

15. The positive electrode active material according to claim 14, wherein, Based on the mass of the first positive electrode active material, the mass content of lithium carbonate is less than or equal to 1.05%, and / or the mass content of lithium hydroxide is less than or equal to 1.02%.

16. The positive electrode active material according to claim 15, wherein, Based on the mass of the first positive electrode active material, the mass content of lithium carbonate is less than or equal to 1%, and / or the mass content of lithium hydroxide is less than or equal to 1%.

17. The positive electrode active material according to any one of claims 1 to 16, wherein, M is Mg and / or Al.

18. The positive electrode active material according to any one of claims 1 to 17, wherein, A is selected from any one of Zn, Al, Na, K, Mg, Nb, Mo and W; B is selected from at least two of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C is selected from any one of B, S, Si and N; and D is selected from any one of S, F, Cl and Br.

19. The positive electrode active material according to claim 18, wherein, The A is Mg or Nb, and / or, The element B is selected from at least two elements chosen from Fe, Ti, V, Co, and Mg, and / or, The C is S, and / or, The D is F.

20. The positive electrode active material according to claim 19, wherein, The B is Fe and one or more elements selected from Ti, V, Co and Mg.

21. The positive electrode active material according to any one of claims 1 to 20, wherein, The x is selected from the range of 0.001 to 0.005; and / or, The value of y is selected from the range of 0.01 to 0.5; and / or, The z is selected from the range of 0.001 to 0.005; and / or, The value of n is selected from the range of 0.001 to 0.

005.

22. The positive electrode active material according to claim 21, wherein, The value of y is selected from the range of 0.25 to 0.

5.

23. The positive electrode active material according to any one of claims 1 to 22, wherein, (1-y): The value of y is selected from the range of 1 to 4, and the value of a:x is selected from the range of 9 to 1100.

24. The positive electrode active material according to claim 23, wherein, (1-y): The value of y is selected from the range of 1.5 to 3, and the value of a:x is selected from the range of 190 to 998.

25. The positive electrode active material according to any one of claims 1 to 10, wherein, The lattice change rate of the second positive electrode active material before and after complete lithium insertion / extraction is less than 8%.

26. The positive electrode active material according to claim 25, wherein, The lattice change rate of the second positive electrode active material before and after complete lithium insertion / extraction is less than 4%.

27. The positive electrode active material according to any one of claims 1 to 26, wherein, The concentration of Li / Mn antisite defects in the second positive electrode active material is below 2%.

28. The positive electrode active material according to claim 27, wherein, The concentration of Li / Mn antisite defects in the second positive electrode active material is below 0.5%.

29. The positive electrode active material according to any one of claims 1 to 28, wherein, The surface oxygen valence state of the second positive electrode active material is below -1.

82.

30. The positive electrode active material according to claim 29, wherein, The surface oxygen valence state of the second positive electrode active material is -1.89 to -1.

98.

31. The positive electrode active material according to any one of claims 1 to 30, wherein, The compaction density of the second positive electrode active material at 3T is 2.0 g / cm³. 3 above.

32. The positive electrode active material according to claim 31, wherein, The compaction density of the second positive electrode active material at 3T is 2.2 g / cm³. 3 above.

33. The positive electrode active material according to any one of claims 1 to 32, wherein, The second positive electrode active material also contains carbon, which is coated with the compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n The surface.

34. A method for preparing a positive electrode active material according to any one of claims 1-33, comprising the following steps: Provide a first positive electrode active material and a second positive electrode active material; The first positive electrode active material and the second positive electrode active material are mixed.

35. A positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising the positive electrode active material according to any one of claims 1 to 33 or the positive electrode active material prepared by the method of claim 34.

36. The positive electrode sheet according to claim 35, wherein, The content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, based on the total weight of the positive electrode film layer.

37. The positive electrode sheet according to claim 36, wherein, The content of the positive electrode active material in the positive electrode film is 95-99.5% by weight, based on the total weight of the positive electrode film.

38. A secondary battery comprising the positive electrode active material according to any one of claims 1 to 33, or the positive electrode active material prepared by the method according to claim 34, or the positive electrode sheet according to any one of claims 35 to 37.

39. A battery module comprising the secondary battery of claim 38.

40. A battery pack comprising the battery module of claim 39.

41. An electrical device comprising at least one selected from the secondary battery of claim 38, the battery module of claim 39, and the battery pack of claim 40.

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