Secondary battery and preparation method therefor, and electric device

Abstract

Provided in the present application are a secondary battery and a preparation method therefor, and an electric device. The secondary battery comprises a positive electrode sheet. The positive electrode sheet comprises a positive electrode active material, which comprises a substrate and a carbon coating layer located on a surface of the substrate. The substrate has a general structural formula of Lim1A1a1Fex1Mny1M1b1Pz1Q1c1On1N1d1, wherein 0.8≤m1≤1.2, 0≤x1<0.5, 0.5<y1≤1, 0.9≤x1+y1≤1, 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, and 0≤d1≤0.1; A1 comprises Al, Na, K or Mg; M1 comprises Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V or Ti; Q1 comprises B, S, Si or N; and N1 comprises S, F, Cl or Br. According to the particle size distribution of primary particles in the positive electrode active material, primary particles having a primary particle size of 50 nm to 180 nm in the positive electrode active material account for an amount less than or equal to 10%; and the number of the primary particles of the positive electrode active material having a primary particle size of greater than or equal to 1200 nm in an area of 250 μm2 of the longitudinal section of the positive electrode sheet is less than or equal to 15.

Description

Secondary battery, preparation method thereof, and power utilization device

[0001] Cross-reference to related applications

[0002] This application refers to Chinese Patent Application No. 202411035617.7, filed on July 30, 2024, entitled “Secondary battery, preparation method thereof, and power utilization device”, which is incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a preparation method thereof, and a power utilization device. BACKGROUND

[0004] Secondary batteries have the advantages of high energy density, high working voltage, low self-discharge rate, small volume, and light weight, and have a wide range of applications.

[0005] At present, with the rapid development of electric vehicles and mobile electronic devices, people have increasingly high requirements for the cycle performance of secondary batteries. How to improve the cycle performance of the battery is a scientific and technical problem that needs to be solved in the current application field of secondary batteries. SUMMARY

[0006] The present application aims to at least solve one of the technical problems in the background art. To this end, one object of the present application is to provide a secondary battery having excellent cycle capacity retention rate and long service life.

[0007] A first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a substrate and a carbon coating layer on the surface of the substrate, the substrate having a general structure of Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 ,

[0008] wherein 0.8≤m1≤1.2, 0≤x1<0.5, 0.5<y1≤1, 0.9≤x1+y1≤1,

[0009] 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1;

[0010] A1 includes one or more of Al, Na, K, Mg, M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1 includes one or more of B, S, Si, N, and N1 includes one or more of S, F, Cl, and Br;

[0011] The primary particles of the positive electrode active material with a primary particle size of 50 nm-180 nm have a particle size distribution in the positive electrode active material of less than or equal to 10%.

[0012] The primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm have a particle size distribution in the positive electrode active material of less than or equal to 10%. 2 The number of particles in the region is less than or equal to 15.

[0013] On the one hand, controlling the particle size distribution of the primary particles with a primary particle size of 50 nm-180 nm in the positive electrode active material powder within a suitable range helps to reduce or slow down the cycle life attenuation of the primary particles with a small particle size in the positive electrode active material, slow down the rate of side reactions of the primary particles with a small particle size with the electrolyte, reduce the likelihood of manganese dissolution in the positive electrode active material, and thus improve the cycle life of the positive electrode active material and extend the service life of the battery. On the other hand, since the primary particles with a primary particle size of greater than or equal to 1200 nm are prone to particle breakage or pulverization during the cycle of the positive electrode active material, the mechanical integrity of the positive electrode active material particles is reduced, thereby causing loss of active material. The present application controls the number of primary particles with a primary particle size of greater than or equal to 1200 nm in the longitudinal cross-section of the positive electrode active material within a suitable range, which helps to improve the chemical and mechanical stability of the positive electrode active material and improve the electrochemical performance, improve the cycle stability of the positive electrode active material, and extend the service life of the battery.

[0014] In some embodiments, the primary particles of the positive electrode active material with a primary particle size of 50 nm-180 nm have a particle size distribution in the positive electrode active material of 3%-8.5%.

[0015] In some embodiments, the primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm have a particle size distribution in the longitudinal cross-section of the positive electrode active material of 2-12. 2 The number of particles in the region is less than or equal to 15.

[0016] In some embodiments, the primary particles of the positive electrode active material with a primary particle size of greater than 180 nm and less than 1200 nm have a particle size distribution index of less than or equal to 0.45, and optionally 0.3-0.36.

[0017] The particle size distribution index of the primary particles with a particle size greater than 180 nm and less than 1200 nm is within a suitable range, the material has excellent particle size consistency, so that the discharge behavior of each particle during battery cycling tends to be consistent, the possibility of overcharging and overdischarging during charging and discharging of each particle is reduced, which is beneficial to ensuring the structural stability of the positive active material and improving the cycle performance of the battery.

[0018] In some embodiments, the positive active material satisfies at least one of (a1)-(f1):

[0019] (a1) the (Dv90-Dv10) / Dv50 of the positive active material is 1-3;

[0020] (b1) the Dv50 of the positive active material is 0.35 μm-1.5 μm;

[0021] (c1) the Dv10 of the positive active material is 0.1 μm-0.4 μm;

[0022] (d1) the Dv90 of the positive active material is 2.5 μm-6 μm;

[0023] (e1) the mass content of the carbon coating layer is 1%-3% based on the mass of the positive active material;

[0024] (f1) the thickness of the carbon coating layer is 2 nm-10 nm.

[0025] In some embodiments, 0.3≤x1<0.5, 0.5<y1≤0.7.

[0026] The content of iron and manganese in the positive active material is within a suitable range, which can reduce the possibility of side reactions between the material and the electrolyte and the occurrence of manganese dissolution, improve the cycle stability of the material, and improve the cycle performance of the battery.

[0027] In some embodiments, the mass content of the M1 element is 1000 ppm-6000 ppm based on the mass of the positive active material, which can be optionally 1500 ppm-5000 ppm.

[0028] The mass content of the M1 element in the positive active material within a suitable range helps to improve the structural stability of the positive active material and improve the cycle performance of the battery.

[0029] The second aspect of the present application provides a preparation method of a secondary battery, comprising the following steps:

[0030] Compaction granulation: raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, and a forming aid are compacted and granulated to obtain compacted and formed particles, and the raw materials can optionally further include one or more of an A1 source, an M1 source, a Q1 source, and an N1 source.

[0031] sintering: filling and compacting the shaped particles, sintering the compacted shaped particles to obtain a primary product;

[0032] crushing: crushing the primary product to obtain a positive electrode active material;

[0033] coating: coating at least one side of the current collector with a positive electrode slurry containing the positive electrode active material to obtain a positive electrode sheet;

[0034] assembly: assembling an electrode assembly including the positive electrode sheet, the negative electrode sheet, and the electrolyte into a secondary battery;

[0035] wherein the positive electrode active material includes a substrate and a carbon coating layer on the surface of the substrate, the substrate has a general structure of Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 ,

[0036] wherein 0.8≤m1≤1.2, 0≤x1<0.5, 0.5<y1≤1, 0.9≤x1+y1≤1,

[0037] 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1;

[0038] wherein A1 includes one or more of Al, Na, K, Mg, M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1 includes one or more of B, S, Si, N, and N1 includes one or more of S, F, Cl, Br;

[0039] The particle size distribution of the primary particles of the positive electrode active material with a primary particle size of 50nm-180nm in the positive electrode active material is less than or equal to 10%;

[0040] The number of primary particles of the positive electrode active material with a primary particle size greater than or equal to 1200nm in the 250μm 2 region of the longitudinal section of the positive electrode sheet is less than or equal to 15.

[0041] Controlling the particle size distribution of the primary particles with a primary particle size of 50nm-180nm and the number of primary particles with a primary particle size greater than or equal to 1200nm in the positive electrode active material helps to reduce the impact of small primary particles and large primary particles on the cycle performance of the battery, and a secondary battery with long cycle life is obtained.

[0042] In some embodiments, the average particle size of the compacted granules in the compacting granulation step is 3 mm-30 mm.

[0043] The compacted granules are within a suitable range, which helps to improve the uniformity of different raw materials inside the granules, facilitates the obtaining of a uniformly granular material, reduces the proportion of small and large particle size particles in the material, or improves the particle size distribution, and improves the cycle stability of the material. At the same time, the pores between the particles are beneficial to the removal of reducing gas generated by the decomposition of the carbon source during preparation, and the uniformity of carbon at different positions of the sintering device (such as the sagger) is improved. At the same time, the carbon source precursor after compaction will not flow significantly at high temperatures, causing stratification at the height.

[0044] In some embodiments, the compacted density of the compacted granules is 1.0 g / cm 3 -3.0 g / cm 3 .

[0045] The compacted density of the compacted granules is controlled within a suitable range, which helps to improve the sagger loading amount during preparation, thereby improving the sintering capacity, and a suitable compacted density is beneficial to the compaction molding process, the uniformity of the particle size, and the uniformity of the carbon layer distribution, and reduces the number of large and small particle size particles in the material.

[0046] In some embodiments, the preparation method comprises: filling the compacted granules to a filling height of 5 cm-30 cm, and sintering the compacted granules to obtain a primary product.

[0047] The filling height of the compacted granules during sintering is within a suitable range, which helps to timely discharge reducing gas generated by the decomposition of the carbon source during sintering, accelerates heat transfer while avoiding uneven decomposition of the carbon source in the compacted granules at different positions in the sintering device, and can improve the consistency of particle growth, which is beneficial to obtaining a positive electrode active material with fewer small and large particle size particles. At the same time, it can also take into account a certain production capacity, which is beneficial to industrial production.

[0048] In some embodiments, the sintering temperature in the sintering step is 600°C-800°C; and / or, the isothermal sintering time in the sintering step is 2h-12h.

[0049] Controlling the sintering temperature and / or the sintering time within a suitable range allows the compacted granules to be fully sintered, so that the positive electrode active material has excellent structural parameters.

[0050] In some embodiments, the compacting granulation step specifically comprises:

[0051] The raw materials are ground to obtain a slurry; the slurry is dried and then compacted and granulated to obtain compacted and shaped particles.

[0052] Firstly, grinding treatment is performed to reduce the particle size of large particles in the raw materials, thereby reducing the content of large particles in the raw materials, which helps to reduce the number of large primary particles in the positive electrode active material, and reduces the particle size of different raw materials, which helps to obtain primary particles of nanoscale with more uniform particle size. Meanwhile, the uniformity of the mixture of different raw materials is improved, which helps to improve the uniformity of the prepared positive electrode active material particles. The drying treatment makes the particles of the raw materials have appropriate pores, which helps to discharge the reducing gas generated by the decomposition of the carbon source in the sintering process. In addition, the raw materials contain a shaping aid, which helps to improve the particle size distribution concentration of the raw materials and improve the consistency of particle growth, thereby obtaining a positive electrode active material with fewer small and large particles.

[0053] In some embodiments, the compacting and granulating step specifically comprises:

[0054] (1-1) uniformly mixing initial reactants containing a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source, and then performing pre-sintering treatment to obtain an initial product, wherein the initial reactants optionally further comprise one or more of an Al source, an M1 source, a Q1 source and an N1 source;

[0055] (1-2) mixing and grinding intermediate reactants containing the initial product, the carbon source and the shaping aid to obtain an intermediate product;

[0056] (2) compacting and granulating the intermediate product to obtain compacted and shaped particles,

[0057] In step (1-1), the mass content of the carbon source is 2%-5%, based on the total mass of the initial reactants.

[0058] A small amount of carbon source in the pre-sintering process can play a reducing role, so that the initial reactants can be fully mixed and reacted, improving the uniformity and completeness of the reaction, and making the particle size of the initial product have excellent uniformity. In addition, the pre-sintering treatment allows the small particles in the initial reactants to pre-react, which helps to improve the particle size uniformity of the product. Meanwhile, the intermediate reactants containing the initial product, the carbon source and the shaping aid are further ground, which refines the large particles and helps to reduce the content of large particles in the product, further improving the particle size uniformity of the material, and providing a material basis for subsequent preparation of a positive electrode active material with excellent particle size uniformity.

[0059] In summary, the pre-sintering treatment can improve the particle size uniformity of the initial reactants, so that the intermediate product subjected to compacting and granulation has excellent particle size uniformity, which helps to improve the uniformity of the primary particle size of the positive electrode active material.

[0060] In some embodiments, the Dv50 of the intermediate product is 0.25 μm-1.05 μm, and the Dv50 of the positive active material is 0.10 μm-0.40 μm. V 10 is 0.10 μm-0.40 μm.

[0061] Controlling the Dv50 and D V 10 within a suitable range is conducive to controlling the particle size uniformity of the positive active material, and can improve the structural stability of the positive active material and the cycle performance of the battery.

[0062] The third aspect of the present application provides a power consumption device comprising the secondary battery prepared by the preparation method of the first aspect or the second aspect of the present application.

[0063] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented in accordance with the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0064] In the drawings, like reference numerals designate like or similar parts throughout the several views, and that the drawings are not necessarily to scale. It should be understood that the drawings are only intended to depict some embodiments of the application and should not be considered as limiting the scope of the application.

[0065] FIG. 1 is a schematic diagram of the statistical classification rule of primary particles in the transmission electron microscope image of particles according to the present application;

[0066] FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0067] FIG. 3 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 2;

[0068] FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present application;

[0069] FIG. 5 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0070] FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5;

[0071] FIG. 7 is a schematic diagram of a power consumption device using the secondary battery according to an embodiment of the present application as a power source.

[0072] BRIEF DESCRIPTION OF DRAWINGS: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0073] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0074] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0075] In this paper, the reference to "embodiments" means that the specific features, structures or properties described in conjunction with the embodiments can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily refer to the same embodiment, nor is it mutually exclusive or alternative to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0076] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents a "or" relationship between the front and rear associated objects.

[0077] "RANGES" disclosed herein are defined by both a lower and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., 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, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, 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 contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" indicates a shorthand way of describing all real combinations of the numbers a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand way of describing these numerical combinations. In addition, when a parameter is stated to be an integer > 2, it is equivalent to state that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all steps of the methods of the present application can be performed in any order, and preferably are performed in the order specified. For example, the method comprises steps (a) and (b) indicates that the method can comprise steps (a) and (b) performed in the order specified, or the method can comprise steps (b) and (a) performed in the order specified. For example, the method can further comprise step (c) indicates that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b), and (c), or the method can comprise steps (a), (c), and (b), or the method can comprise steps (c), (a), and (b), etc.

[0079] Unless otherwise specified, the terms "comprise" and "comprising" as used herein are open-ended and also include the more restrictive terms "consist of and "consisting of." For example, the terms "comprise" and "comprising" can mean that the method can further comprise or consist of other components not listed.

[0080] The positive active material is one of the decisive factors of the performance of the secondary battery. At present, the common positive active materials mainly include lithium cobaltate, lithium manganate, nickel-cobalt-manganese ternary material and lithium iron phosphate, etc. These materials have advantages and disadvantages respectively. For example, lithium cobaltate has high energy density and voltage platform, but high cost and poor safety; lithium manganate has low cost and good safety, but low energy density and voltage platform; nickel-cobalt-manganese ternary material combines the advantages of the former two, but the cost is still high. Lithium iron phosphate has the advantages of low cost, high safety and long life, etc., and can better meet the requirements of the new energy vehicle market for high safety and low cost of lithium ion batteries. However, lithium iron phosphate also has some disadvantages, such as low compaction density and low discharge capacity, which limit its application in high energy density batteries. Lithium manganese iron phosphate, as a new type of material developed from lithium iron phosphate, combines the advantages of manganese and iron, has two voltage platforms at 4.1V and 3.4V respectively, and can provide a certain platform capacity, which is expected to improve the disadvantages of lithium iron phosphate material. However, in the current research and application process, the trivalent manganese ions in lithium manganese iron phosphate will be converted into tetravalent manganese ions due to the Jahn-Teller effect, the high-reactivity tetravalent manganese ions are easy to react with the electrolyte to convert into divalent manganese ions, the divalent manganese ions will further dissolve in the electrolyte and be reduced and precipitated on the negative electrode, which will damage the SEI film and cause more active lithium to be consumed in the process of repairing the SEI film, thereby affecting the cycle life of the battery. Therefore, how to improve the cycle performance of the lithium manganese iron phosphate battery system has become a key point of research.

[0081] Based on this, the application provides a kind of secondary battery, including positive pole piece, negative pole piece and electrolyte,

[0082] The positive pole piece includes positive pole current collector and positive pole film layer arranged on at least one side of the positive pole current collector, the positive pole film layer includes positive active material, the positive active material includes substrate and carbon coating layer on the surface of the substrate, the substrate has structural general formula Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 ,

[0083] 0.8≤m1≤1.2, 0≤x1<0.5, 0.5<y1≤1, 0.9≤x1+y1≤1,

[0084] 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1;

[0085] A1 includes one or more of Al, Na, K, Mg, M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1 includes one or more of B, S, Si, N, and N1 includes one or more of S, F, Cl, Br;

[0086] Primary particles of the positive electrode active material having a primary particle size of 50 nm to 180 nm have a particle size distribution in the positive electrode active material of 10% or less;

[0087] Primary particles of the positive electrode active material having a primary particle size of 50 nm to 180 nm have a particle size distribution in the positive electrode active material of 10% or less; 2 The number of particles in the region is 15 or less.

[0088] In some embodiments, m1 can be 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, 1.17, 1.2, or a value in a range between any two of the foregoing.

[0089] In some embodiments, x1 can be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.49, or a value in a range between any two of the foregoing.

[0090] In some embodiments, y1 can be 0.51, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or a value in a range between any two of the foregoing.

[0091] In some embodiments, x1+y1 can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or a value in a range between any two of the foregoing.

[0092] In some embodiments, z1 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, or a value in a range between any two of the foregoing.

[0093] In some embodiments, n1 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, or a value in a range between any two of the foregoing.

[0094] In some embodiments, a1, b1, c1, each independently, can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value in a range between any two of the above values.

[0095] The selection of the appropriate doping element M1 can improve the lattice change rate of the material during the lithium extraction process, improve the structural stability of the material, reduce the dissolution of manganese, and reduce the oxygen activity on the surface of the particles, thereby improving the specific capacity of the material, improving the energy density of the battery, and reducing the interface side reaction between the material and the electrolyte during use, thereby improving the cycle performance and storage performance of the material.

[0096] The selection of the appropriate doping element Q1 can help to change the difficulty of the Mn-O bond length change, thereby improving the electronic conductivity and reducing the lithium ion migration barrier, promoting the migration of lithium ions, and improving the rate performance of the secondary battery.

[0097] The appropriate element doping A1 can also improve the lattice change rate of the material and maintain the battery capacity of the material.

[0098] The doping element N1 can help to improve the interface side reaction between the material and the electrolyte, reduce the interface activity, thereby improving the cycle performance of the positive electrode active material, etc. In addition, by doping at the O position, the performance of the material in resisting acid corrosion such as HF can be improved, thereby improving the cycle performance and storage life of the material.

[0099] In some embodiments, the particle size distribution of the primary particles of the positive electrode active material with a primary particle size of 50-180 nm in the positive electrode active material can be selected to be less than or equal to 10%, less than or equal to 9.5%, less than or equal to 9%, less than or equal to 8.5%, less than or equal to 8%, less than or equal to 7%, less than or equal to 6%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, or less than or equal to 1%, or the particle size distribution of the primary particles of the positive electrode active material with a primary particle size of 50-180 nm in the positive electrode active material can be selected to be 0.1-10%, 0.5-10%, 1-10%, 0.1-8%, 0.1-6%, 0.1-4%, 0.1-3%, 0.1-2%, 0.1-1%, 0.3-5%, 0.8-3%, or 0.1-1.5%.

[0100] In this document, the term "primary particle size" refers to the particle size of the primary particles.

[0101] Primary particles refer to the single particles that can be distinguished after the transmission electron microscopy (TEM) images of the particles are recognized by general professional software (for example, spectrum see; Avizo 3D) and / or are recognized by manual recognition or manual aided calibration. Specifically, in order to determine the primary particles, the particles contained in the positive electrode film layer are subjected to enrichment and / or dispersion treatment, and then the particles are imaged under the transmission electron microscope. The imaged picture can be directly subjected to particle recognition by software (according to parameters such as gray scale and / or contrast / brightness), and the single particles that can be distinguished after the recognition are primary particles. The imaged picture can also be directly subjected to manual recognition, and the single particles that can be distinguished after the recognition are primary particles. The imaged picture can also be directly subjected to software recognition combined with manual aided calibration recognition, and the single particles that can be distinguished after the recognition are primary particles. More specifically, the particles in the transmission electron microscope field of view form particles with clear boundaries that can be clearly distinguished from each other, and the single particles can be directly recognized by software recognition or manual recognition. However, some particles may be adhered and stacked to a certain extent in the transmission electron microscope field of view after the dispersion treatment. For the adhered and stacked particles, the single particles that can be distinguished after the recognition by software (according to parameters such as gray scale / contrast / brightness) are counted as primary particles. More accurately, for the particles that are adhered and stacked to a certain extent in the transmission electron microscope field of view, the single particles that can be distinguished after the recognition by software according to parameters such as gray scale / contrast / brightness are manually calibrated according to certain rules by manual aided calibration, and the single particles that can be distinguished after the calibration are counted as primary particles. If the manual calibration results are not uniform, the results obtained by 3 persons or 5 persons or 7 persons who are unaware of each other and separately calibrate the same imaging results according to the rules exemplified below are counted as the number of primary particles. FIG. 1 is a schematic diagram of the statistical distinguishing rules of the primary particles in the transmission electron microscopy images of the particles, wherein FIG. 1-a is an original transmission electron microscopy image, FIG. 1-b is a software recognition image of the image, and FIG. 1-c is an example of software recognition and / or manual recognition of the independent particles, adhered particles and stacked particles in FIG. 1-a. The particle 1 and the particle 2 in FIG. 1-c are independent particles that can be distinguished, and are primary particle 1 and primary particle 2, respectively. The particle 3 and the particle 4 in FIG. 1-c are adhered, and the particle 5, the particle 6 and the particle 7 are adhered. After the software recognition or the manual recognition, the primary particle 3, the primary particle 4, the primary particle 5, the primary particle 6 and the primary particle 7 are determined. The particles 8 and 9 that are stacked together are finally determined as the primary particle 8 and the primary particle 9, instead of being determined as one particle. FIG. 1-d is another example of software recognition and / or manual recognition of the particles that are stacked in FIG. 1-a. The particles 10-14 that are stacked together are finally determined as the primary particle 10, 11, 12, 13 and the primary particle 14, instead of being determined as one particle.In selecting the transmission electron microscope field of view, the number of stacked particles in the selected field of view accounts for less than 20% of the total number of particles (the total number of independent particles, adhered particles and stacked particles), more preferably the number of stacked particles in the selected field of view accounts for less than 15% of the total number of particles (the total number of independent particles, adhered particles and stacked particles), and further more preferably the number of stacked particles in the selected field of view accounts for less than 10% of the total number of particles (the total number of independent particles, adhered particles and stacked particles).

[0102] The term "particle size distribution" refers to the percentage of particles in a certain particle size or a certain particle size range in the total number of powder particles.

[0103] The particle size distribution of the primary particles of the positive electrode active material with a primary particle size of 50 nm-180 nm in the positive electrode active material can be tested by any method known in the art. Specifically, the battery is disassembled to obtain a positive electrode sheet, the positive electrode film layer of the positive electrode sheet is peeled off, the positive electrode film layer is washed with acetone to remove the binder and dispersant in the positive electrode film layer, and the like, and then filtered, dried and treated to obtain a powder. 0.05 g of the uniformly mixed powder is dissolved in 40 ml of anhydrous ethanol, then an appropriate amount of dispersant is added, and stirred uniformly to obtain a suspension. 2 ml of the suspension and 2 ml of anhydrous ethanol are mixed and then ultrasonically treated for 5 min at a power of 480 W to obtain a uniformly dispersed suspension. An appropriate amount of the middle layer of the suspension is taken for transmission electron microscope testing, and the projected area of each primary particle in the transmission electron microscope image is counted according to the definition of the primary particle, i.e. the cross-sectional area S of the primary particle, the equivalent circle diameter of the primary particle is obtained by the equivalent circle method, the primary particles with a primary particle size of less than 50 nm are not counted in the statistical range (i.e. the primary particles with a primary particle size of 50 nm or more are effective particles, and at least 500 effective particles are tested), the number of primary particles with a primary particle size of 50 nm-180 nm is denoted as M, the number of effective particles counted is N, and the particle size distribution of the primary particles with a primary particle size of 50 nm-180 nm in the positive electrode active material is M / N*100%. During testing, 10 statistical regions can be randomly selected for testing, and then the average value is taken.

[0104] In the positive electrode active material provided by the present application, the particle size distribution of the primary particles with a primary particle size of 50 nm-180 nm in the positive electrode active material powder is within a suitable range, which slows down the rate of side reactions between small primary particles and electrolyte, reduces the possibility of manganese dissolution in the positive electrode active material, helps to reduce or slow down the cycle life attenuation of small primary particles in the positive electrode active material, and further improves the cycle life of the positive electrode active material and prolongs the service life of the battery.

[0105] In some embodiments, the particle size distribution of primary particles with a primary particle size of 50-180 nm in the positive electrode active material is 3-8.5%.

[0106] In some embodiments, the particle size distribution of primary particles with a primary particle size of 50-180 nm in the positive electrode active material can be 3%, 4%, 5%, 6%, 7%, 8%, 8.5%, or a value in a range defined by any two of the above values.

[0107] Controlling the particle size distribution of primary particles with a primary particle size of 50-180 nm in the positive electrode active material powder to be 3-8.5% can further reduce the possibility of side reactions between small particle size materials and electrolyte, reduce the possibility of manganese dissolution during the cycle process, improve the cycle performance of the battery, and prolong the service life of the battery.

[0108] In some embodiments, the number of primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm in the 250 μm 2 region of the longitudinal section of the positive electrode tab is less than or equal to 15.

[0109] In some embodiments, the number of primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm in the 250 μm 2 region of the longitudinal section of the positive electrode tab can be 2-12.

[0110] In some embodiments, the number of primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm in the 250 μm 2 region of the longitudinal section can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a value in a range defined by any two of the above values.

[0111] The number of primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm in the 250 μm 2 region of the longitudinal section of the positive electrode tab can be tested by any method known in the art. For example, the battery is disassembled to obtain the positive electrode tab, the argon ion beam is used to cut the tab perpendicular to the large surface of the positive electrode tab to expose the entire longitudinal section, the entire longitudinal section is tested by scanning electron microscopy to obtain a scanning electron microscopy image of the longitudinal section of the positive electrode tab, and a 250 μm 2 region is randomly selected, and the number of primary particles with a primary particle size of greater than or equal to 1200 nm in the region is counted by the equivalent circle method. Ten test regions can be randomly selected during testing, and the average value is obtained, i.e., the number of primary particles with a primary particle size of greater than or equal to 1200 nm in the 250 μm 2 region of the longitudinal section.

[0112] Primary particles with a diameter greater than or equal to 1200 nm are also referred to as "large-diameter primary particles." During cycling, the positive electrode active material undergoes repeated expansion and contraction deformation. Large-diameter primary particles develop intergranular cracks due to this deformation, leading to severe pulverization. This significantly reduces the mechanical integrity of the primary particles and the material, exacerbates electrolyte penetration, intensifies manganese dissolution, and affects battery cycle performance. Simultaneously, the presence of intergranular cracks also causes electrical contact failure, exacerbating capacity polarization loss. Correspondingly, the continuous formation of new electrode / electrolyte interfaces leads to a sharp deterioration in the chemical-mechanical properties of the positive electrode active material during long-term cycling. Furthermore, the longer migration path of lithium ions within large-diameter primary particles affects lithium ion transport performance and overall battery cycle performance.

[0113] Controlling the number of primary particles with a diameter greater than or equal to 1200 nm within a suitable range can effectively prevent particle breakage, alleviate surface degradation, and suppress intergranular cracking, thereby enhancing chemical-mechanical stability and improving electrochemical performance. Interface degradation and overall mechanical disintegration effects are suppressed, and enhanced chemical-mechanical stability can improve the cycle stability of the cathode active material, thus improving the battery's cycle performance. Simultaneously, controlling the number of large-diameter primary particles within a suitable range can also reduce the impact of large-diameter primary particles on lithium-ion transport performance, improve the material's conductivity, and enhance the battery's rate performance and cycle performance.

[0114] In some embodiments, the particle size distribution index of the primary particles of the positive electrode active material with a primary particle size greater than 180 nm and less than 1200 nm is less than or equal to 0.45.

[0115] In some embodiments, the particle size distribution index of the primary particles of the positive electrode active material with a primary particle size greater than 180 nm and less than 1200 nm can be selected as 0.3-0.36.

[0116] In some embodiments, the particle size distribution index of the primary particles of the positive electrode active material with a primary particle size greater than 180 nm and less than 1200 nm can be selected as 0.2, 0.25, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, or a value within a range consisting of any two of the above values.

[0117] The particle size distribution index has the meaning known in the art and can be measured by methods and instruments known in the art. The particle size distribution index is an important parameter for measuring the uniformity of particle size, the lower the particle size distribution index, the smaller the particle size deviation value, and the higher the uniformity of particle size. As an example, the test method is as follows: referring to the test method of the particle size distribution of the primary particles with a primary particle size of 50 nm-180 nm in the positive electrode active material, the primary particles with a primary particle size greater than 180 nm and less than 1200 nm are measured, defined as the first type of particles, and the primary particle size of each first type of particle is measured,

[0118] The particle size distribution index PDI of the primary particles with a primary particle size greater than 180 nm and less than 1200 nm is the standard deviation σ of the particle size divided by the average particle size

[0119] wherein σ is the standard deviation of the particle size, x i is the particle size value of the first type of particles, is the average particle size of the first type of particles, and n is the total number of particles of the first type of particles, and the average particle size is the particle size value of the total first type of particles divided by the number of particles of the total first type of particles,

[0120] The primary particles with a primary particle size greater than 1800 nm and less than 1200 nm have excellent particle size consistency, so that the discharge behavior of each particle tends to be consistent during battery cycling, and the possibility of overcharging and overdischarging during charging and discharging of each particle is reduced, which is beneficial to ensuring the structural stability of the positive electrode active material, improving the normal temperature cycle performance and high temperature cycle performance of the battery, and prolonging the service life of the battery.

[0121] In some embodiments, the (Dv90-Dv10) / Dv50 of the positive electrode active material is 1-3, optionally 2.9, 2.8, 2.6, 2.5, 2.4, 2.3, 2.2, 1.4, 1.5, 1.2, 1, or a value within a range defined by any two of the above values.

[0122] The particle size distribution of the material can be tested by any method known in the art, and the volume distribution particle size Dv10, Dv50, Dv90 of the material has the meaning known in the art, which respectively represents the particle size corresponding to the cumulative volume distribution percentage of 10%, 50%, and 90% of the material, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured by a laser particle size analyzer according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The test instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0123] The (Dv90-Dv10) / Dv50 particle size distribution of the positive electrode active material is in a suitable range, which helps to improve the particle size uniformity of the positive electrode active material and further improve the cycle performance.

[0124] In some embodiments, the Dv50 of the positive electrode active material is 0.35 μm-1.5 μm.

[0125] In some embodiments, the Dv50 of the positive electrode active material can be selected from 0.35 μm, 0.45 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or any value in the range.

[0126] In some embodiments, the Dv10 of the positive electrode active material is 0.1 μm-0.4 μm.

[0127] In some embodiments, the Dv10 of the positive electrode active material can be selected from 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, or any value in the range.

[0128] In some embodiments, the Dv90 of the positive electrode active material is 2.5 μm-6 μm.

[0129] In some embodiments, the Dv90 of the positive electrode active material can be selected from 2.5 μm, 3.0 μm, 3.5 μm, 4 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, or any value in the range.

[0130] The particle size of the positive electrode active material is in a suitable range, which improves the structural stability and cycle stability of the material during charging and discharging, and also helps to reduce the polarization degree of the material during charging and discharging, helps to make the current density on the surface of the material more uniform, thereby fully exerting the capacity of the positive electrode active material and improving the cycle performance.

[0131] In some embodiments, the mass content of the carbon coating layer is 1%-3% based on the mass of the positive electrode active material.

[0132] In some embodiments, the mass content of the carbon coating layer can be selected from 1%, 1.5%, 2.0%, 2.5%, 3%, or any value in the range based on the mass of the positive electrode active material.

[0133] The mass content of the carbon coating layer is tested by any method known in the art, for example as follows: turn on all power switches of the carbon-sulfur analyzer, press the "zero" button, open the oxygen valve of the carbon-sulfur analyzer, adjust the oxygen pressure to 0.02-0.04 MPa. Turn on the "front oxygen" and "rear control", and adjust the flow meter to about 100 L / h. Add silicon molybdenum powder (0.3 g), weighed sample (250 mg), tin particles (0.3 g), and pure iron (1 g) into the crucible in sequence, and close the crucible. Click the "test" button to start the test, and the test result is automatically displayed after the test is completed. Record the result as the content of the carbon coating layer.

[0134] In some embodiments, the thickness of the carbon coating layer is 2-10 nm. In some embodiments, the thickness of the carbon coating layer can be selected as 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any value in the range.

[0135] The thickness of the carbon coating layer can be tested by the following method: a thin slice of about 100 nm in thickness is cut from the middle of a single particle of the positive electrode active material by FIB, and then the slice is subjected to TEM test to obtain a TEM test original picture, and the original picture is saved in the format (xx.dm3). The original picture obtained by the above TEM test is opened in the Digital Micrograph software, the carbon coating layer is identified by the lattice spacing and the included angle information, and the thickness of the carbon coating layer is measured. The thickness at three positions of the selected particle is measured, and the average value is taken.

[0136] The mass content or thickness of the carbon coating layer in the positive electrode active material in a suitable range can improve the conductivity of the positive electrode active material, enhance the electron transmission between particles, promote the migration of lithium ions, and improve the cycle performance of the battery, without affecting the specific capacity of the positive electrode active material due to excessive carbon content.

[0137] In some embodiments, 0.3≤x1<0.5, and 0.5

[0138] In some embodiments, x1may be selected as 0.3, 0.32, 0.34, 0.35, 0.38, 0.4, 0.42, 0.44, 0.48, 0.49, or any value in the range.

[0139] In some embodiments, y1may be selected as 0.51, 0.55, 0.58, 0.60, 0.62, 0.64, 0.0.68, 0.7, or any value in the range.

[0140] The base body containing manganese and iron in a suitable molar content is conducive to reducing the possibility of manganese dissolution of the positive electrode active material, improving the cycle stability of the material, and prolonging the service life of the battery. Meanwhile, the material has a suitable molar ratio of manganese and iron, and the material has a high gram capacity, which provides a material basis for preparing a high-energy-density battery.

[0141] In some embodiments, the mass content of the M1 element is selected from 1000 ppm-6000 ppm, optionally 1000 ppm-5500 ppm, 1000 ppm-5000 ppm, 1500 ppm-6000 ppm, 1500 ppm-5000 ppm, 2000 ppm-6000 ppm, 2500 ppm-6000 ppm, or 2000 ppm-5500 ppm, or any value in the range, based on the mass of the positive electrode active material.

[0142] The test method of the mass content of the M1 element can be tested by a method known in the art, for example, determined by reference to the EPA 6010D-2014 standard; specifically, an ICP-OES (elemental analysis-inductively coupled plasma emission spectrometry) test can be used, in which the sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization, and further, the gaseous atoms to be tested are ionized and excited in a strong magnetic field, and then restored to the ground state from the excited state; the energy released in the above process is recorded as different characteristic spectral lines, and the element quantitative analysis is carried out.

[0143] In some embodiments, the M1 includes Ti. In some embodiments, the M1 includes V. In some embodiments, the M1 includes Mg. In some embodiments, the M1 includes Nb.

[0144] By introducing divalent or multivalent M1 cations, lithium ions are deintercalated in the base body of the olivine structure composed of cations including M1 and anions including phosphoric acid, which helps to improve the structural stability of the positive electrode active material and improve the cycle stability of the battery.

[0145] The application also provides a preparation method of a secondary battery, including the following steps:

[0146] Compaction granulation: the raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, and a forming aid are compacted and granulated to obtain compacted and formed particles, and optionally, the raw materials further include one or more of an A1 source, an M1 source, a Q1 source, and an N1 source;

[0147] Sintering: the compacted and formed particles are filled and sintered to obtain a primary product;

[0148] Crushing: the primary product is crushed to obtain the positive electrode active material;

[0149] coating: coating a cathode slurry containing the cathode active material on at least one side of the current collector to form a cathode electrode sheet;

[0150] assembly: assembling an electrode assembly including the cathode electrode sheet, an anode electrode sheet, and an electrolyte into a secondary battery;

[0151] wherein the cathode active material includes a substrate and a carbon coating layer on the surface of the substrate, the substrate has a general structure of Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 ,

[0152] wherein 0.8≤m1≤1.2, 0≤x1<0.5, 0.5<x1≤1, 0.9≤x1+y1≤1,

[0153] 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1;

[0154] wherein A1 includes one or more of Al, Na, K, Mg, M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1 includes one or more of B, S, Si, N, and N1 includes one or more of S, F, Cl, Br;

[0155] the particle size distribution of primary particles of the cathode active material with a primary particle size of 50nm-180nm in the cathode active material is less than or equal to 10%;

[0156] the number of primary particles of the cathode active material with a primary particle size of greater than or equal to 1200nm in the 250μm 2 region of the longitudinal cross section of the cathode electrode sheet is less than or equal to 15.

[0157] Controlling the particle size distribution of primary particles with a primary particle size of 50nm-180nm and the number of primary particles with a primary particle size of greater than or equal to 1200nm in the cathode active material in the cathode electrode sheet helps to reduce the impact of small primary particles and large primary particles on the cycle performance of the battery, and obtain a secondary battery with long cycle life.

[0158] In some embodiments, the raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, and a forming aid are compacted and granulated to obtain compacted and formed particles, and the raw materials optionally further include one or more of an Al source, an M1 source, a Q1 source, and an N1 source.

[0159] Generally, the compacted and formed particles are a group of actual particles with different sizes and shapes. Compared with a group of imaginary particles with uniform spherical particles, if the total length of the particle size of the actual particles is the same as that of the spherical particles, the diameter of the spherical particles is the average particle size of the actual particles (compacted and formed particles). For spherical particles, the spherical diameter is the particle size of the particles, but in fact, there are no real spherical particles, and the shape of the actual particles is very complex. For convenience, the equivalent particle size is used to describe the particle size (size of the particles) or average particle size of irregular particles. It can be understood that when the physical properties or physical behavior of a particle is most similar to that of a homogeneous sphere with a certain diameter, the diameter (or combination) of the sphere is taken as the equivalent particle size of the measured particle.

[0160] The method for measuring the average particle size can use the commonly used particle size measuring method or instrument in the art, including but not limited to a laser particle size analyzer and an ultrasonic particle size analyzer. The average particle size can be a linear average diameter, an area average diameter, a volume average diameter, a weight average diameter, or a specific surface average diameter. In this application, the average particle size refers to the volume average diameter. When the equivalent particle size is used to describe the particle size, the average particle size in this application can also be the volume equivalent diameter.

[0161] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium oxide, lithium chloride, lithium nitrate, and lithium sulfate, and optionally, the lithium source includes lithium carbonate.

[0162] In some embodiments, the iron source includes at least one of iron phosphate, ferrous hydroxide, ferrous nitrate, ferrous phosphate, ferrous pyrophosphate, ferrous carbonate, ferrous chloride, ferrous oxalate, ferric chloride, ferric hydroxide, ferric nitrate, ferric citrate, and diiron trioxide, and optionally, the iron source includes diiron trioxide.

[0163] In some embodiments, the manganese source includes at least one of manganese dioxide, dimanganese trioxide, trimanganese tetraoxide, manganese oxalate, manganese acetate, and manganese nitrate.

[0164] In some embodiments, the phosphorus source includes at least one of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, iron phosphate, lithium dihydrogen phosphate, and lithium phosphate, and optionally, the phosphorus source includes ammonium dihydrogen phosphate.

[0165] In some embodiments, the carbon source comprises at least one of sucrose, glucose, citric acid, fructose, lactose, porous graphene, activated carbon, activated carbon fiber, mesoporous carbon, carbon nanotube, carbon molecular sieve, pitch, and polyethylene glycol, optionally, the carbon source comprises sucrose.

[0166] In some embodiments, the Al source is selected from at least one of oxides, hydroxides, oxalates, acetates, chlorides, nitrates, or phosphates of Al, Na, K, Mg elements.

[0167] In some embodiments, the M1 source is selected from at least one of oxides, hydroxides, oxalates, acetates, chlorides, nitrates, or phosphates of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti elements, optionally, the M1 source comprises one or more of titanium dioxide, vanadium pentoxide, niobium pentoxide.

[0168] In some embodiments, the Q1 source comprises one or more of silicic acid, metasilicic acid, silicon tetrachloride, silicon dioxide, tetraethyl orthosilicate, elemental boron, boric acid, diboron trioxide, boron nitride, trimethyl borate, sodium tetraphenylborate, boron trichloride, ethylenediamine, melamine, benzylamine, acetonitrile, ammoniated sucrose, pyrrole, aniline, acrylonitrile, polyimide acid, nitrogen-containing heterocyclic compounds, sulfur powder, sulfuric acid, sulfurous acid, ammonium sulfate, thiophene, thiazole, thiourea, dimethyl sulfoxide, thioacetamide, mercaptans.

[0169] In some embodiments, the N1 source comprises any one or more of sulfur powder, sulfuric acid, sulfurous acid, ammonium sulfate, thiophene, thiazole, thiourea, dimethyl sulfoxide, thioacetamide, mercaptans, hydrofluoric acid, ammonium fluoride, fluorine-containing organic compounds selected from one or more of fluorinated alkanes, fluorinated alkenes, fluorinated aromatic hydrocarbons, fluorinated carboxylic acids.

[0170] The forming aid is selected from a high molecular substance that can be dissolved or dispersed in water or alcohol, in some embodiments, the forming aid comprises at least one of polyacrylate, starch, phenol formaldehyde resin, polyurethane, melamine resin, polyethylene, stearic acid, PVC, polyacrylonitrile, natural rubber, styrene butadiene rubber, cis-butadiene rubber, optionally, the forming aid comprises starch.

[0171] The forming aid can further improve the integrity of the compacted particles during sintering, enhance the mechanical stability of the compacted particles during sintering, and avoid structural collapse of the particles during sintering.

[0172] In some embodiments, the raw materials including the lithium source, the iron source, the manganese source, the phosphorus source, the carbon source and the forming aid are ground; optionally, the raw materials are ground to a Dv50 of 0.3-1.5 μm, 0.3-1.0 μm, 0.3-0.8 μm, 0.35-0.6 μm, or 0.35-0.9 μm. The raw materials can be ground using a grinding device, such as a ball mill, a sand mill, or a mechanical mill.

[0173] In some embodiments, water, an alcohol solvent, or a mixture of both can be added to the raw materials and mixed uniformly, and then the raw materials are ground. The alcohol solvent includes, but is not limited to, methanol, ethanol, ethylene glycol, and can be one or more different alcohol solvents mixed together.

[0174] In some embodiments, the forming aid in the raw materials can be dissolved or dispersed in water, an alcohol solvent, or a mixture of both, and mixed with other components in the raw materials as the solvent or solution is added.

[0175] After the grinding process, the particle size of the large particles present in the raw materials is reduced, and the content of the large particles in the raw materials is reduced, which helps to reduce the particle size distribution of the large primary particles in the prepared positive electrode active material; the particle sizes of different raw materials are reduced, which helps to obtain primary particles of a more uniform size at the nanometer level. At the same time, the uniformity of the mixture of different raw materials is improved, which helps to improve the uniformity of different components in the prepared positive electrode active material.

[0176] In some embodiments, the ground raw materials are subjected to a drying process, and optionally, the ground raw materials are subjected to a spray drying process. In some embodiments, the particle size Dv50 of the microspheres formed by spray drying is 5-50 μm, optionally, 5-40 μm, 8-30 μm, 10-25 μm, or 10-20 μm.

[0177] The raw materials subjected to the spray drying process are in the form of spherical particles with good flowability, and the particles of the raw materials have suitable pores, which helps to discharge the reducing gas generated by the decomposition of the carbon source during the sintering process.

[0178] In some embodiments, the raw materials subjected to the spray drying process are compacted and granulated.

[0179] In some embodiments, the raw materials are compacted and granulated to obtain compacted and formed particles with an average particle size of 3 mm-30 mm, optionally, 5 mm-25 mm, 5 mm-20 mm, 5 mm-15 mm, 10 mm-15 mm, 10 mm-20 mm, or 10 mm-25 mm. The average particle size can also be selected from any value in the range of 7.5 mm, 12.5 mm, 17.5 mm, 22.5 mm, or 27.5 mm, or any range between any two values.

[0180] The particle size of the compacted granules is within a suitable range, which helps to improve the uniformity of different raw materials inside the granules, and the pores between the granules are conducive to the removal of reducing gases generated by the decomposition of the carbon source during preparation.

[0181] In some embodiments, the compacted density of the compacted granules obtained by compaction granulation is 1.0 g / cm 3 The above, the optional 1.2-3.0 g / cm 3 In some embodiments, the compacted density of the compacted granules can be selected from any value in the range of 1.0 g / cm 3 , 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 , 1.8 g / cm 3 , 2.0 g / cm 3 , 2.2 g / cm 3 , 2.4 g / cm 3 , 2.6 g / cm 3 , 2.8 g / cm 3 , 3.0 g / cm 3 or a range between any two values.

[0182] The compacted density of the compacted granules is controlled within a suitable range, which helps to improve the loading capacity during preparation, thereby improving the sintering capacity.

[0183] In some embodiments, the preparation method comprises: filling the compacted granules to a filling height of 5 cm-30 cm, and sintering the compacted granules to obtain a primary product. Optionally, the filling height is 8 cm-30 cm, 8 cm-20 cm, 5 cm-25 cm, 5 cm-20 cm, 10 cm-30 cm, 10 cm-25 cm, or 10 cm-20 cm.

[0184] The filling height of the compacted granules is within a suitable range, which helps to timely remove reducing gases and other gaseous non-desired substances during sintering, accelerates heat transfer while avoiding uneven decomposition of the carbon source in the compacted granules at different positions in the sintering device, and improves the consistency of granule growth while taking into account the capacity.

[0185] In some embodiments, after the compacted granules are filled, the porosity between the granules is 5%-20%, and the porosity is selected from 5%-15%, 10%-20%, 10%-15%, 8%-20%, 12%-20%, or 8%-17%.

[0186] In some embodiments, the sintering of the compacted granules is performed in an inert gas atmosphere, which can include one or more of nitrogen, carbon dioxide, helium, and optionally, the inert gas is selected from nitrogen.

[0187] In some embodiments, the sintering of the compacted granules is performed at a sintering temperature in the range of 600-800°C, and optionally, the sintering temperature is selected from 650-800°C, 680-800°C, 700-800°C, 600-780°C, 600-750°C, 620-800°C, or 640-720°C.

[0188] In some embodiments, the sintering of the compacted granules is performed at a sintering temperature in the range of 600-800°C for 2-12 hours, and optionally, the sintering is performed at the sintering temperature for 2-10 hours, 4-12 hours, 2-10 hours, 4-8 hours, 6-12 hours, 6-10 hours, or 6-8 hours.

[0189] In some embodiments, the temperature ramping rate during the sintering is controlled to be in the range of 1-5°C / min to the sintering temperature, and optionally, the temperature ramping rate is selected from 2-5°C / min, 3-5°C / min, 2-4°C / min, or 2-3°C / min; or, the temperature ramping rate is selected from 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, or a range between any two of the recited values.

[0190] In the preparation method provided herein, the raw material mixture is subjected to compacted granulation treatment before sintering, which is beneficial for the reduction gas generated from the decomposition of the carbon source during the sintering process to be timely discharged, avoiding uneven decomposition of the carbon source at different positions of the sintering device; at the same time, the compacted granules at different positions of the sintering device are uniformly heated. After sintering, the carbon content in the surface layer, the middle part, and the bottom of the granules tends to be at a consistent level, and the carbon content tends to be consistent, which is beneficial for the growth of the raw material granules during the sintering and reduction process to be substantially uniform, and the carbon content uniformity of the primary granular nanomaterial is improved, which is beneficial for improving the particle size uniformity of the material.

[0191] In some embodiments, the preparation method includes: crushing the primary product obtained after sintering to have a Dv50 in the range of 0.35-1.5 μm, and optionally, the crushing is performed to have a Dv50 selected from 0.5-1.5 μm, 0.8-1.5 μm, 0.7-1.5 μm, 1-1.5 μm, 0.45-1.3 μm, 0.45-1.0 μm, 0.5-1.0 μm, 0.6-1.5 μm, or 0.7-1.5 μm.

[0192] The particle size of the primary product is crushed to a suitable range, which helps to reduce the polarization degree of the material in the charging and discharging process, improve the stability of the material, and thus fully exert the capacity of the positive electrode active material and improve the cycle performance.

[0193] In some embodiments, the preparation method comprises: crushing the primary product to have a particle size distribution satisfying (Dv90-Dv10) / Dv50 being 1-3, optionally, being less than or equal to 2.9, 2.8, 2.6, 2.5, 2.4, 2.3, 2.2, 2, 1.8, 1.4, 1.2 or 1. Optionally, the primary product is crushed to have a particle size distribution satisfying 1≤(Dv90-Dv10) / Dv50≤3.

[0194] The particle size distribution of the positive electrode active material is in a suitable range, which helps to improve the particle size uniformity of the positive electrode active material and further improve the cycle performance.

[0195] In some embodiments, the preparation method does not comprise multiple compaction granulations.

[0196] The preparation method provided in the present application has a simple process flow, high reproducibility and relatively low cost, and is beneficial to industrial batch production.

[0197] In some embodiments, the preparation method comprises:

[0198] The raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source and a forming aid are mixed with water, alcohol or a mixed solvent, ground, dried and compacted to form compacted particles, and optionally the raw materials further include one or more of an Al source, an M1 source, a Q1 source and an N1 source;

[0199] The compacted particles are filled, sintered and crushed to obtain the positive electrode active material.

[0200] In some embodiments, the preparation method comprises:

[0201] The raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source and a forming aid are mixed with water, alcohol or a mixed solvent, ground, dried and compacted to form compacted particles having an average particle size controlled in a range of 3 mm-30 mm; and optionally the raw materials further include one or more of an Al source, an M1 source, a Q1 source and an N1 source;

[0202] The compacted particles are filled to a filling height of 5 cm-30 cm and a porosity of 5%-20% and sintered.

[0203] The primary product obtained by sintering is crushed to have Dv50 being 0.35 μm-1.5 μm and / or 1≤(Dv90-Dv10) / Dv50≤3, to obtain the positive electrode active material.

[0204] In some embodiments, the preparation method comprises:

[0205] Compaction granulation: grinding raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a forming aid, and a solvent to obtain a slurry; drying the slurry and then performing compaction granulation to obtain compaction-formed particles, and optionally the raw materials further include one or more of an Al source, an M1 source, a Q1 source, and an N1 source;

[0206] Sintering: filling the compaction-formed particles and sintering the compaction-formed particles to obtain a primary product;

[0207] Crushing: crushing the primary product to obtain a positive electrode active material.

[0208] In some embodiments, the preparation method comprises:

[0209] Mixing raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, and a forming aid with water, alcohol, or a mixed solvent, grinding, drying, and compaction forming to obtain compaction-formed particles; filling the compaction-formed particles, sintering, and crushing to obtain a positive electrode active material, and optionally the raw materials further include one or more of an Al source, an M1 source, a Q1 source, and an N1 source;

[0210] The forming aid includes at least one of polyacrylate, starch, phenolic resin, polyurethane, melamine resin, polyethylene, stearic acid, PVC, polyacrylonitrile, natural rubber, styrene butadiene rubber, and cis-butadiene rubber.

[0211] In some embodiments, the compaction granulation step specifically comprises:

[0212] (1-1) uniformly mixing initial reactants including a lithium source, an iron source, a manganese source, a phosphorus source, and a carbon source, and then performing pre-sintering treatment to obtain an initial product, and optionally the initial reactants further include one or more of an Al source, an M1 source, a Q1 source, and an N1 source;

[0213] (1-2) mixing and grinding intermediate reactants including the initial product, a carbon source, and a forming aid to obtain an intermediate product;

[0214] (2) compaction granulating the intermediate product to obtain compaction-formed particles,

[0215] In some embodiments, the mass content of the carbon source in step (1-1) is 2% to 5%, based on the total mass of the initial reactants.

[0216] In some embodiments, the mass content of the carbon source in step (1-1) is optionally any value in 2%, 3%, 4%, 5%, or a range between any two values.

[0217] The small amount of carbon source in the pre-sintering process can play a reducing role, so that the initial reactants can be fully mixed and reacted, improving the uniformity and completeness of the reaction, and making the particle size of the initial product have excellent uniformity. In addition, the pre-sintering treatment makes the small particles in the initial reactants pre-react, which is beneficial to improve the particle size uniformity of the product. At the same time, the intermediate reactants containing the initial product, the carbon source and the forming aid are further ground, which refines the large particles and is beneficial to reduce the content of large particle size particles in the product, further improving the particle size uniformity of the material, and providing a material basis for subsequent preparation of the positive electrode active material with excellent particle size uniformity.

[0218] In summary, the pre-sintering treatment can improve the particle size uniformity of the initial reactants, so that the intermediate product prepared by compaction granulation has excellent particle size uniformity, which is helpful to improve the uniformity of different components in the prepared positive electrode active material.

[0219] In some embodiments, the preparation method comprises:

[0220] (1-1) uniformly mixing the initial reactants containing a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source, and then performing a pre-sintering treatment to obtain an initial product, and optionally the initial reactants further comprise one or more of an Al source, an M1 source, a Q1 source and an N1 source;

[0221] (1-2) mixing and grinding the intermediate reactants containing the initial product, the carbon source and the forming aid to obtain an intermediate product;

[0222] (2) compacting and granulating the intermediate product to obtain compacted and granulated particles;

[0223] (3) filling the compacted and granulated particles, sintering, and crushing to obtain a positive electrode active material,

[0224] wherein the mass content of the carbon source in step (1-1) is 2%-5%, based on the total mass of the initial reactants,

[0225] The forming aid includes at least one of polyacrylate, starch, phenolic resin, polyurethane, melamine resin, polyethylene, stearic acid, PVC, polyacrylonitrile, natural rubber, styrene butadiene rubber, and cis-butadiene rubber.

[0226] In some embodiments, the Dv50 of the intermediate product is 0.25-1.05 pm, and the Dv10 of the intermediate product is 0.10-0.40 pm. V 10 is 0.10-0.40 pm.

[0227] In some embodiments, the Dv50 of the intermediate product can be selected as any value in 0.25 pm, 0.45 pm, 0.55 pm, 0.65 pm, 0.75 pm, 0.85 pm, 0.95 pm, 1.05 pm, or a range between any two values.

[0228] In some embodiments, the Dv50 of the intermediate product can be selected as any value in 0.25 pm, 0.45 pm, 0.55 pm, 0.65 pm, 0.75 pm, 0.85 pm, 0.95 pm, 1.05 pm, or a range between any two values. V 10 can be selected as any value in 0.10 pm, 0.15 pm, 0.20 pm, 0.25 pm, 0.30 pm, 0.35 pm, 0.40 pm, or a range between any two values.

[0229] Controlling the Dv50 and D V 10 of the intermediate product within a suitable range is beneficial to control the mass content of small particles of the positive electrode active material, further improve the particle size uniformity of the positive electrode active material, and improve the structural stability of the positive electrode active material, and improve the cycle performance of the battery.

[0230] Positive electrode sheet

[0231] The positive electrode sheet of the present application comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector. For example, the positive electrode current collector has two surfaces opposite in the thickness direction of itself, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0232] The positive electrode film layer is usually formed by coating a positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto. The types and contents of the conductive agent and the binder are not particularly limited and can be selected according to actual needs. As an example, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylic ester resin. As an example, the conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.

[0233] In the secondary battery of the present application, the positive current collector can be a metal foil or a composite current collector. As an example of the metal foil, the positive current collector can be an aluminum foil. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can be selected from one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer can be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, and the like.

[0234] Negative electrode sheet

[0235] In some embodiments, the negative electrode sheet includes a negative current collector and a negative film layer disposed on at least one surface of the negative current collector, the negative film layer including a negative active material.

[0236] In the secondary battery of the present application, the negative film layer generally includes a negative active material, an optional binder, an optional conductive agent, and other optional additives.

[0237] In some embodiments, the negative active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, a silicon-based material, and a tin-based material.

[0238] The negative film layer is generally formed by coating a negative slurry on a negative current collector, drying, and cold-pressing. The negative slurry is generally formed by dispersing a negative active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP), deionized water, or the like, but is not limited thereto. The type and content of the conductive agent and the binder are not particularly limited and can be selected as desired. As an example, the conductive agent can include one or more of super conductive carbon, carbon black (e.g., acetylene black, ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As an example, the binder can include one or more of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethylacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). The other optional additives can include a thickening agent (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor material, and the like.

[0239] In the secondary battery of the present application, the negative film layer can be disposed on one side of the negative current collector or on both sides of the negative current collector. For example, the negative current collector has two opposite sides in the thickness direction thereof, and the negative film layer is disposed on either one or both of the opposite sides of the negative current collector.

[0240] In the secondary battery of the present application, the type of the negative current collector is not particularly limited and can be selected as desired.

[0241] In the secondary battery of the present application, the negative current collector can be a metal foil or a composite current collector. As an example of the metal foil, the negative current collector can be a copper foil. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can be selected from one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0242] It should be noted that each parameter (e.g., thickness, compacted density, etc.) of the negative film layer given in the present application refers to the parameter of the negative film layer on one side of the negative current collector. When the negative film layer is provided on both sides of the negative current collector, the parameter of the negative film layer on any one side thereof satisfying the present application is considered to fall within the scope of protection of the present application. Further, the range of the thickness, compacted density, etc. of the negative film layer described in the present application refers to the parameter of the negative film layer after being cold-pressed and compacted and used for assembling the battery.

[0243] In addition, in the secondary battery of the present application, the negative electrode sheet does not exclude other additional functional layers other than the negative film layer. For example, in some embodiments, the negative electrode sheet described in the present application can further include a conductive primer layer (e.g., composed of a conductive agent and a binder) provided between the negative current collector and the negative film layer. In some other embodiments, the negative electrode sheet described in the present application further includes a protective layer covering the surface of the negative film layer.

[0244] [Electrolyte]

[0245] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not particularly limited in the present application and can be selected as desired. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0246] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0247] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0248] In some embodiments, the solvent can 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, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butanedisulfone, methyl ethyl sulfone, and diethyl sulfone.

[0249] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0250] In the secondary battery of the present application, the type of the separator is not particularly limited, and any known porous separator having good chemical stability and mechanical stability can be used.

[0251] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0252] In some embodiments, the outer package of the secondary battery can be a hard shell such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0253] The shape of the battery of the present application is not particularly limited, and can be cylindrical, square, or any other shape. For example, FIG. 2 is a secondary battery 5 of a square structure as an example.

[0254] In some embodiments, referring to FIG. 3, the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be wound or stacked to form an electrode assembly 52. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte solution is impregnated in the electrode assembly 52. The number of the electrode assembly 52 contained in the secondary battery 5 can be one or more, and can be selected by those skilled in the art according to the specific actual needs.

[0255] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0256] FIG. 4 is a battery module 4 as an example. Referring to FIG. 4, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, the plurality of secondary batteries 5 can also be arranged in any other manner. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0257] Optionally, the battery module 4 can also include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0258] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0259] FIGS. 5 and 6 are a battery pack 1 as an example. Referring to FIGS. 5 and 6, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0260] Electric device

[0261] The application also provides an electric device, which includes at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power source of the electric device, or can be used as an energy storage unit of the electric device. The electric device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0262] As the electric device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0263] FIG. 7 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electric device for the secondary battery, a battery pack or a battery module can be used.

[0264] As another example, the device can be a mobile phone, a tablet, a notebook computer, etc. The device generally requires thinning, and a secondary battery can be used as a power source.

[0265] Finally, it should be noted that the above embodiments are merely used to illustrate the technical solutions of the present application, rather than limit the same; even though the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered in the scope of the claims and the specification of the present application. In particular, as long as there is no conflict, each technical feature mentioned in the embodiments can be combined in any manner. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0266] Embodiment

[0267] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are intended to explain the present application only, and should not be understood as limiting the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0268] I. Preparation of the battery

[0269] Example 1

[0270] Lithium carbonate, diiron trioxide, ammonium dihydrogen phosphate and trimanganese tetraoxide were weighed respectively, so that the molar ratio of Li:Fe:Mn:P elements was 1.01:0.4:0.6:1.02. After mixing with water, a slurry was obtained, and sucrose with a mass fraction of 8% in the total solid raw materials and starch with a mass fraction of 1% in the total solid raw materials were added. The solid content in the slurry was 40%.

[0271] The uniformly mixed slurry was ground in a ball mill to a Dv50 of about 0.4 μm, and spray dried (the negative pressure of the high-speed spray dryer was -650 to -200 pa, the inlet temperature was 300 to 360°C, and the outlet temperature was 100 to 140°C). The powder obtained by spray drying was compacted and granulated by a granulator, and the average particle size was about 10 mm, and the compacted density of the granules was 1.2 g / cm 3The granulated reactants were loaded into a graphite crucible with a loading depth of 12 cm. The crucible loaded with the reactants was placed in a kiln for sintering, with a heating rate of 3°C / min, a holding temperature of 720°C, and a holding time of 10 hours. After cooling, the material was pulverized by air jet milling or mechanical milling to a Dv50 of about 1.1 pm, to obtain a positive electrode active material LiFe 0.4 Mn 0.6 PO4 / C.

[0272] 2) Preparation of the positive electrode sheet

[0273] A 2.0 wt% polyvinylidene fluoride binder was fully dissolved in N-methyl pyrrolidone (NMP), and then 1.0 wt% Super P, 0.5 wt% carbon nanotubes, and 96.5 wt% of the above positive electrode active material were stirred and mixed uniformly to obtain a positive electrode slurry. The slurry was uniformly coated on the surface of the current collector aluminum foil, and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet was subjected to rolling and punching to obtain a positive electrode sheet with a compacted density of 2.35 g / cm 3 .

[0274] 3) Preparation of the negative electrode sheet

[0275] The active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickening agent carboxymethyl cellulose sodium (CMC-Na) were dissolved in deionized water according to a weight ratio of 96.7:1.3:0.8:1.2, and the mixture was uniformly prepared into a negative electrode slurry. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil one or more times, and then subjected to drying, cold pressing, and slitting to obtain a negative electrode sheet.

[0276] 4) Electrolyte

[0277] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), organic solvents ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were uniformly mixed according to a volume ratio of 3:7, and LiPF6 lithium salt was dissolved in the organic solvents to prepare a solution with a mass content of 12.5%, to obtain an electrolyte.

[0278] 5) Separation film

[0279] A polypropylene film was used as the separation film.

[0280] 6) Preparation of the battery

[0281] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive and negative electrode sheets to serve as a separator, and then wound to obtain an electrode assembly; the electrode assembly is placed in a battery case, dried, and then injected with an electrolyte, and then sequentially subjected to processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like, to obtain the lithium battery product of Example 1.

[0282] Example 2 is prepared in a similar manner to Example 1, but the preparation process of the positive active material is adjusted, as follows:

[0283] (1) Lithium carbonate, diiron trioxide, ammonium dihydrogen phosphate, and trimanganese tetroxide are weighed out separately, such that the molar ratio of Li:Fe:Mn:P is 1.01:0.40:0.6:1.02. After mixing with water, a slurry is obtained, and sucrose is added to the slurry at a mass fraction of 2.5% of the total mass of the solid materials. The solid content of the slurry is 40%. The uniformly mixed slurry is ground in a ball mill to a Dv50 of about 0.4 μm, and spray dried (the negative pressure of a high-speed spray dryer is -320 pa, the inlet temperature is 320°C, and the outlet temperature is 110°C). The dried material is loaded into a graphite crucible and sintered in a kiln, with the heating rate controlled at 5°C / min and the holding temperature controlled at 660°C for 6 hours.

[0284] (2) After the material is cooled, it is ground by mechanical milling. The ground material, sucrose, and starch are mixed with water to obtain a slurry, in which the mass fraction of sucrose is 5.5% and the mass fraction of starch is 1%, based on the total mass of the solid materials in the slurry. The slurry (i.e., the intermediate product in Table 1) is ground in a ball mill to a Dv50 of 0.4 μm and a Dv10 of 0.12 μm, and spray dried (the negative pressure of a high-speed spray dryer is -320 pa, the inlet temperature is 320°C, and the outlet temperature is 110°C).

[0285] (3) The dried powder is compacted and granulated to an average particle size of about 10 mm, and the compacted density of the granules is 1.2 g / cm 3 .

[0286] Sintering: The granulated reactants are loaded into a graphite crucible, and the loading depth of the material is 12 cm. The crucible with the loaded material is placed in a kiln for sintering, with the heating rate controlled at 3°C / min and the holding temperature controlled at 720°C for 10 hours.

[0287] Crushing: After the material is cooled, it is ground by air milling or mechanical milling to a Dv50 of 1 μm to obtain the positive active material LiFe 0.4 Mn 0.60 PO4 / C

[0288] Example 3 is similar to the preparation method of Example 2, but the types of raw materials are adjusted. Specifically, lithium carbonate, diiron trioxide, ammonium dihydrogen phosphate, trimanganese tetraoxide and titanium dioxide are weighed respectively, so that the molar ratio of Li:Fe:Mn:Ti:P elements is 1.01:0.4:0.59:0.005:1.02, and the other conditions are the same as those in Example 2.

[0289] Example 4 is similar to the preparation method of Example 3, and the specific preparation parameters are referred to Table 1.

[0290] Example 5 is similar to the preparation method of Example 2, and the titanium dioxide is replaced by niobium pentoxide, wherein the mass ratio of Li:Fe:Mn:Nb:P elements is 1.01:0.4:0.59:0.005:1.02.

[0291] Examples 6-8 are similar to the preparation method of Example 3, and the specific preparation parameters are referred to Table 1.

[0292] Examples 9-11 are similar to the preparation method of Example 3, and the molar ratio of manganese source and iron source and the preparation parameters are adjusted. The specific preparation parameters are shown in Table 1, and the mass ratio of manganese source and iron source is as follows:

[0293] Example 9: lithium carbonate, diiron trioxide, ammonium dihydrogen phosphate, trimanganese tetraoxide and titanium dioxide are weighed respectively, so that the mass ratio of Li:Fe:Mn:Ti:P elements is 1.01:0.2:0.79:0.005:1.01.

[0294] Example 10: lithium carbonate, diiron trioxide, ammonium dihydrogen phosphate, manganese dioxide and titanium dioxide are weighed respectively, so that the mass ratio of Li:Fe:Mn:Ti:P elements is 1.01:0.3:0.69:0.005:1.01.

[0295] Example 11: lithium carbonate, diiron trioxide, ammonium dihydrogen phosphate, manganese dioxide and titanium dioxide are weighed respectively, so that the mass ratio of Li:Fe:Mn:Ti:P elements is 1.01:0.48:0.51:0.005:1.0.

[0296] Comparative Example 1

[0297] The battery of Comparative Example 1 is similar to the preparation method of the battery of Example 1, and the specific preparation method is as follows:

[0298] Lithium carbonate, diiron trioxide, ammonium dihydrogen phosphate and trimanganese tetraoxide are weighed respectively, so that the mass ratio of Li:Fe:Mn:P elements is 1.01:0.4:0.6:1.02. After being mixed with water, a slurry is obtained, and sucrose with a mass fraction of 8% in the total solid raw materials is added. The solid content in the slurry is 40%.

[0299] The slurry with uniform mixture is ground by a ball mill to a Dv50 of about 0.4 μm, and is spray dried (the negative pressure of a high-speed spray dryer is -650 to -200 pa, the inlet temperature is 300 to 360 °C, and the outlet temperature is 100 to 140 °C). The powder obtained by spray drying is sintered in a kiln, the heating rate is controlled to be 3 °C / min, the holding temperature is controlled to be 720 °C, and the holding time is 10 hours. After the material is cooled, the material is crushed by an air jet mill or a mechanical mill to a Dv50 of about 1.1 μm, and a positive electrode active material LiFe 0.4 Mn 0.6 PO4 / C.

[0300] II. Performance test

[0301] 5. Battery performance test

[0302] 1) 60 °C cycle number test

[0303] The battery is placed in a 60 °C oven environment and left for 2 h until the battery temperature is 60 °C; then the battery is discharged at 1 / 3 C constant current to 2.0 V; after standing for 5 min, the battery is charged to a voltage of 4.1 V at 1 C constant current, and then charged to a current of 0.05 C at 4.1 V constant voltage, and after standing for 2 min, the battery is discharged at 1 C constant current to a voltage of 2.0 V, which is one charge and discharge cycle process. The discharge capacity of this time is the discharge capacity of the first cycle. The battery is subjected to multiple cycle charge and discharge tests according to the above method until the discharge capacity of the secondary battery decays to 80%, and the cycle number of the battery is recorded.

[0304] III. Analysis of test results of each embodiment and comparative example

[0305] Table 1

[0306] Table 2

[0307] The positive electrode sheet in the secondary battery in Examples 1-11 includes a current collector and a positive electrode film layer located on at least one side of the current collector, and the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a substrate and a carbon coating layer located on the surface of the substrate, and the substrate includes LiFe 0.4 Mn 0.6 PO4, LiFe 0.4 Mn 0.59 Ti 0.005 PO4, LiFe 0.4 Mn 0.59 Nb 0.005 PO4, LiFe 0.2 Mn 0.79 Ti 0.005 PO4, LiFe0.3 Mn 0.69 Ti 0.005 PO4, LiFe 0.48 Mn 0.51 Ti 0.005 PO4, the primary particles of the positive electrode active material with a primary particle size of 50 nm-180 nm have a particle size distribution in the positive electrode active material of less than or equal to 10%; the primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm have a particle size distribution in the 250 μm 2 region of the longitudinal cross section of the positive electrode tab of less than or equal to 15 particles.

[0308] Examples 1-11 compared with Comparative Example 1, the particle size distribution of the primary particles of the positive electrode active material with a primary particle size of 50 nm-180 nm in the positive electrode active material is controlled to be less than or equal to 10%, the primary particles of the positive electrode active material with a primary particle size of greater than or equal to 1200 nm have a particle size distribution in the 250 μm 2 region of the longitudinal cross section of the positive electrode tab of less than or equal to 15 particles, the high-temperature cycle number of the battery can be increased, and the service life of the battery can be prolonged.

[0309] As can be seen from the comparison of Example 2 and Example 1, the particle size distribution index of the primary particles of the positive electrode active material with a primary particle size of greater than 180 nm and less than 1200 nm is less than or equal to 0.45, which can further increase the high-temperature cycle number of the battery and improve the cycle performance of the battery. As can be seen from the comparison of Examples 7-8 and Examples 3, 4, and 6, the particle size distribution index of the primary particles of the positive electrode active material with a primary particle size of greater than 180 nm and less than 1200 nm is less than or equal to 0.36, which can further increase the high-temperature cycle number of the battery and improve the cycle performance of the battery.

[0310] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The positive electrode active material includes a positive electrode tab, a negative electrode tab, and an electrolyte, The positive electrode tab includes a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including a substrate and a carbon coating layer on a surface of the substrate, the substrate having a general structure of Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 , 0.8≤m1≤1.2, 0≤x1<0.5, 0.5<y1≤1, 0.9≤x1+y1≤1, 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1; A1 includes one or more of Al, Na, K, and Mg, M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti, Q1 includes one or more of B, S, Si, and N, and N1 includes one or more of S, F, Cl, and Br; The particle size distribution of primary particles of the positive electrode active material with a primary particle size of 50 nm-180 nm in the positive electrode active material is less than or equal to 10%; Primary particles of the positive electrode active material having a primary particle diameter of 1200 nm or more exist in a range of 250 μm from the surface of the positive electrode tab in the longitudinal cross section of the positive electrode tab 2 The number of particles in the region is 15 or less.

2. The secondary battery according to claim 1, characterized by The particle size distribution of primary particles of the positive electrode active material with a primary particle size of 50 nm-180 nm in the positive electrode active material is 3%-8.5%.

3. The secondary battery according to claim 1 or 2, characterized by The primary particles of the positive electrode active material having a primary particle diameter of 1200 nm or more are 2 or more in the number of particles in the longitudinal cross section of 250 μm 2 The number of particles in the region is 2-12.

4. The secondary battery according to any one of claims 1 to 3, characterized by, The particle size distribution index of primary particles of the positive electrode active material with a primary particle size greater than 180 nm and less than 1200 nm is less than or equal to 0.

45.

5. The secondary battery according to any one of claims 1 to 3, characterized by The particle size distribution index of primary particles of the positive electrode active material with a primary particle size greater than 180 nm and less than 1200 nm is 0.3-0.

36.

6. The secondary battery according to any one of claims 1 to 5, characterized by The positive electrode active material satisfies at least one of (a1)-(f1): (a1) The (Dv90-Dv10) / Dv50 of the positive electrode active material is 1-3; (b1) The Dv50 of the positive electrode active material is 0.35 μm-1.5 μm; (c1) The Dv10 of the positive electrode active material is 0.1 μm-0.4 μm; (d1) The Dv90 of the positive electrode active material is 2.5 μm-6 μm; (e1) The mass content of the carbon coating layer is 1%-3% based on the mass of the positive electrode active material; (f1) The thickness of the carbon coating layer is 2 nm-10 nm.

7. The secondary battery according to any one of claims 1 to 6, characterized by 0.3≤x1<0.5, 0.5<y1≤0.

7.

8. The secondary battery according to any one of claims 1 to 7, characterized by, The mass content of the M1 element is 1000 ppm-6000 ppm based on the mass of the positive electrode active material.

9. A method for producing a secondary battery, characterized by, The method includes the following steps: Compaction granulation: raw materials including a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, and a forming aid are compacted and granulated to obtain compacted and formed particles, and the raw materials can optionally further include one or more of an A1 source, an M1 source, a Q1 source, and an N1 source; Sintering: the compacted and formed particles are filled and sintered to obtain a primary product; Crushing: the primary product is crushed to obtain the positive electrode active material; Coating: a positive electrode slurry containing the positive electrode active material is coated on at least one side of a current collector to obtain a positive electrode tab; Assembling: an electrode assembly including the positive electrode tab, a negative electrode tab, and an electrolyte is assembled into a secondary battery; The positive electrode active material comprises a substrate and a carbon coating layer on the surface of the substrate, the substrate has a general structure of Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 , 0.8≤m1≤1.2, 0≤x1<0.5, 0.5<y1≤1, 0.9≤x1+y1≤1, 0.95≤z1≤1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1; wherein A1 comprises one or more of Al, Na, K, Mg, M1 comprises one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1 comprises one or more of B, S, Si, N, and N1 comprises one or more of S, F, Cl, Br; The primary particles of the positive electrode active material having a primary particle size of 50 nm-180 nm have a particle size distribution in the positive electrode active material of less than or equal to 10%; Primary particles of the positive electrode active material having a primary particle size of 1200 nm or more exist in a longitudinal cross-section of the positive electrode tab at a density of 1 particle or more per 250 μm2 2 The number of particles in the region is 15 or less.

10. The method of claim 9, wherein, The average particle size of the compacted and formed particles in the compacting and granulating step is 3 mm-30 mm.

11. The production method according to claim 9 or 10, characterized by, The compacted density of the compacted formed particles is 1.0 g / cm 3 - 3.0 g / cm 3 .

12. The production method according to any one of claims 9 to 11, characterized by, The sintering step specifically comprises filling the compacted and formed particles to a filling height of 5 cm-30 cm, and sintering the compacted and formed particles to obtain a primary product.

13. The production method according to any one of claims 9 to 12, characterized by, The sintering temperature in the sintering step is 600°C-800°C; and / or, the isothermal sintering time in the sintering step is 2 h-12 h.

14. The production method according to any one of claims 9 to 13, characterized by, The compacting and granulating step specifically comprises: The raw materials are ground to obtain a slurry, and the slurry is dried and then compacted and granulated to obtain the compacted and formed particles.

15. The production method according to any one of claims 9 to 13, characterized by, The compacting and granulating step specifically comprises: (1-1) uniformly mixing initial reactants comprising a lithium source, an iron source, a manganese source, a phosphorus source, and a carbon source, and then performing a pre-sintering treatment to obtain an initial product, and optionally, the initial reactants further comprise one or more of an A1 source, an M1 source, a Q1 source, and an N1 source; (1-2) mixing and grinding intermediate reactants comprising the initial product, a carbon source, and a forming aid to obtain an intermediate product; (2) compacting and granulating the intermediate product to obtain compacted and formed particles, wherein the mass content of the carbon source in the step (1-1) is 2%-5%, based on the total mass of the initial reactants.

16. The method of claim 15, wherein, The Dv50 of the intermediate product is 0.25 μm to 1.05 μm, and the Dv10 of the intermediate product is 0.10 μm to 0.40 μm. V 10 is 0.10 μm to 0.40 μm.

17. An electrical device, comprising: The secondary battery of any one of claims 1-8 or prepared by the preparation method of any one of claims 9-16.

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