Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material; the positive electrode active material comprises a lithium-containing transition metal oxide; a particle of the lithium-containing transition metal oxide comprises an inner region and a surface layer region at least partially surrounding the inner region; the surface layer region comprises a first surface layer region and a second surface layer region; the second surface layer region is located between the first surface layer region and the inner region; the first surface layer region and the second surface layer region each comprise a first phase structure and a second phase structure; the first phase structure comprises a layered phase structure; the second phase structure comprises at least one of a spinel phase structure and a rock salt phase structure; the first surface layer region comprises a rock salt phase structure and a layered phase structure; and the second surface layer region comprises a spinel phase structure and a layered phase structure. The secondary battery has excellent cycle performance.

Description

Secondary battery and power consuming device

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410767576.4, filed on June 14, 2024, entitled “Secondary battery and power consuming device”, which is incorporated by reference in its entirety into this application. TECHNICAL FIELD

[0003] The present application relates to a secondary battery and a power consuming 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 are widely used in the field of consumer electronics.

[0005] 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 to be solved in the current application field of secondary batteries.

[0006] SUMMARY

[0007] The present application is made in view of the above-mentioned problems, and aims to provide a secondary battery and a power consuming device, which have excellent cycle performance and long service life.

[0008] A first aspect of the present application provides a secondary battery, comprising:

[0009] a positive electrode tab, a negative electrode tab, and an electrolyte,

[0010] The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing transition metal oxide,

[0011] The particles of the lithium-containing transition metal oxide include an inner region and a surface layer region at least partially surrounding the inner region,

[0012] The surface layer region includes a first surface layer region and a second surface layer region, the second surface layer region is located between the first surface layer region and the inner region, and the first surface layer region and the second surface layer region both contain a first phase structure and a second phase structure,

[0013] The first phase structure includes a layered phase structure, and the second phase structure includes at least one of a spinel phase structure and a rock salt phase structure,

[0014] The first surface layer region includes a rock salt phase structure and a layered phase structure, and the second surface layer region includes a spinel phase structure and a layered phase structure.

[0015] The first phase structure containing a layered phase structure and the second phase structure containing a spinel phase structure or a rock salt phase structure in the surface layer region, on the one hand, reduces the possibility of side reactions of the positive electrode active material with the electrolyte by using the second phase structure of the non-electrochemically active spinel phase structure or the rock salt phase structure, improves the structural stability of the positive electrode active material, improves the cycle performance of the battery, and on the other hand, the layered phase structure in the first phase structure can provide a channel for the deintercalation of lithium ions on the surface of the material, so that the positive electrode active material has a high lithium ion migration speed, which is conducive to the exertion of the specific capacity of the positive electrode active material, reduces the loss of active lithium during the cycle process, improves the cycle performance of the battery, and prolongs the service life of the battery. In addition, the first surface layer region close to the surface of the particle includes a rock salt phase structure and a layered phase structure, the rock salt phase structure has relatively more excellent stability, the effect of improving the structural stability and thermal stability is more obvious, and at the same time, the layered phase structure in the first surface layer region can provide a path for the deintercalation of lithium ions and accelerate the diffusion of lithium ions, thereby improving the cycle performance and kinetic performance of the battery; the second surface layer region close to the internal region includes a spinel phase structure and a layered phase structure, the spinel phase structure has good structural stability and high lithium ion transmission speed, which improves the structural stability of the material and also makes the material have excellent lithium ion transmission performance, and the cycle stability and rate performance of the battery are taken into account, and at the same time, the second surface layer region including the layered phase structure is conducive to providing more lithium ion transmission channels and storage sites, thereby improving the kinetic performance and cycle performance of the battery.

[0016] In any embodiment, the first surface layer region refers to a region extending from the surface of the lithium-containing transition metal oxide particle to the interior of the particle by a distance of 10 nm.

[0017] The area of the first surface layer region is controlled within a suitable range, so that the rock salt phase in the first surface layer region can achieve the purpose of improving the structural stability and thermal stability, and at the same time, the material has good lithium ion transmission performance, thereby improving the cycle performance of the battery.

[0018] In any embodiment, the second surface layer region refers to a region extending from the surface of the lithium-containing transition metal oxide particle to the interior of the particle by a distance of 10 nm to a distance of 60 nm.

[0019] The area of the second surface layer region is controlled within a suitable range, so that the spinel phase structure in the second surface layer region can realize a smooth transition from the first surface layer region to the internal region, improve the lattice adaptability of the whole material, improve the structural stability of the material, and at the same time, it is also conducive to comprehensively improving the structural stability of the material and the transmission speed of lithium ions, thereby improving the cycle performance of the battery.

[0020] In any embodiment, the internal region includes a layered phase structure.

[0021] The internal region comprises a layered phase structure, the material has multiple lithium ion deintercalation paths, the material has excellent lithium ion diffusion speed, which is beneficial to the development of the material's capacity and improves the cycle capacity retention rate and energy density of the battery.

[0022] In any embodiment, the area ratio of the rock salt phase structure in the first surface layer region is 60%-80% based on the total area of the rock salt phase structure and the layered phase structure in the first surface layer region, and / or the area ratio of the layered phase structure in the first surface layer region is 20%-40%.

[0023] In any embodiment, the area ratio of the rock salt phase structure in the first surface layer region is 65%-75% based on the total area of the rock salt phase structure and the layered phase structure in the first surface layer region, and / or the area ratio of the layered phase structure in the first surface layer region is 25%-35%.

[0024] Controlling the area ratio of the rock salt phase structure and the layered phase structure in the first surface layer region within a suitable range achieves the purpose of improving the structural stability and thermal stability of the material, while also making the material have good lithium ion transmission performance, and comprehensively improving the cycle performance of the battery.

[0025] In any embodiment, the mass content of nickel element is 50%-80% based on the total moles of metal elements other than Li in the first surface layer region.

[0026] In any embodiment, the area ratio of the spinel phase structure in the second surface layer region is 50%-90% based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region, and / or the area ratio of the layered phase structure in the second surface layer region is 10%-50%.

[0027] In any embodiment, the area ratio of the spinel phase structure in the second surface layer region is 60%-80% based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region, and / or the area ratio of the layered phase structure in the second surface layer region is 20%-40%.

[0028] Controlling the area ratio of the spinel phase structure and the layered phase structure in the second surface layer region within a suitable range improves the structural stability and lattice adaptability of the material, while also making the material have excellent lithium ion performance and lithium ion storage sites, and comprehensively improving the cycle performance of the battery.

[0029] In any embodiment, the mole content of cobalt element is 60%-90% based on the total moles of metal elements other than Li in the second surface layer region.

[0030] In any embodiment, the molar content of nickel element in the lithium-containing transition metal oxide is greater than or equal to 60% based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

[0031] In any embodiment, the molar content of nickel element in the lithium-containing transition metal oxide is greater than or equal to 80% based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

[0032] In any embodiment, the molar content of nickel element in the lithium-containing transition metal oxide is greater than or equal to 90% based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

[0033] In any embodiment, the lithium-containing transition metal oxide further comprises a modifying element, and the modifying element comprises one or more of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K.

[0034] The lithium-containing transition metal oxide comprising the modifying element of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, or K can further improve the cycle stability of the material and improve the cycle stability of the battery.

[0035] In any embodiment, the mass content of the modifying element is less than or equal to 3000 ppm based on the mass of the lithium-containing transition metal oxide.

[0036] The mass content of the modifying element is within a suitable range, which can improve the cycle stability of the material, increase the discharge capacity of the material, and comprehensively improve the cycle performance and energy density of the battery.

[0037] In any embodiment, the lithium-containing transition metal oxide comprises Li a1 Ni x1 Co y1 Mn 1-x1- y1 M1 w1 O 2-b1 , Li a2 Ni x2 Co y2 Al 1-x2-y2 M2 w2 O 2-b2 , any one of;

[0038] wherein 0.8≤a1≤1.2, 0.6≤x1≤1, 0≤y1≤0.4, -0.1≤b1≤0.1,

[0039] 0≤w1≤0.1;

[0040] 0.8≤a2≤1.2, 0.6≤x2≤1, 0≤y2≤0.4, -0.1≤b2≤0.1, 0≤w2≤0.1,

[0041] M1 includes at least one element among Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K,

[0042] M2 includes at least one element among Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K.

[0043] In any embodiment, the lithium-containing transition metal oxide includes Li a1 Ni x1 Co y1 Mn 1-x1- y1 M1 w1 O 2-b1 , Li a2 Ni x2 Co y2 Al 1-x2-y2 M2 w2 O 2-b2 , and any one of them;

[0044] wherein 0.8≤a1≤1.2, 0.8≤x1≤1, 0≤y1≤0.2, -0.1≤b1≤0.1,

[0045] 0≤w1≤0.1;

[0046] 0.8≤a2≤1.2, 0.8≤x2≤1, 0≤y2≤0.2, -0.1≤b2≤0.1, 0≤w2≤0.1,

[0047] M1 includes at least one element among Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K,

[0048] M2 includes at least one element among Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K.

[0049] A second aspect of the present application provides an electric device including the secondary battery of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0050] FIG. 1 is a schematic view of a cross-sectional image of a particle of a lithium-containing transition metal oxide of the present application;

[0051] FIG. 2 is a schematic view of an embodiment of a secondary battery of the present application;

[0052] FIG. 3 is an exploded schematic view of an embodiment of a secondary battery of the present application;

[0053] FIG. 4 is a schematic view of an embodiment of a battery module of the present application;

[0054] FIG. 5 is a schematic view of an embodiment of a battery pack of the present application;

[0055] FIG. 6 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 5;

[0056] FIG. 7 is a schematic view of an embodiment of an electric device including a secondary battery of the present application as a power source.

[0057] In the drawings, the drawings are not necessarily drawn to scale. Reference signs are explained as follows:

[0058] 1 battery pack, 2 upper case, 3 lower case, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 cover plate, 100 particle of lithium-containing transition metal oxide, 101 inner region, 102 surface layer region, 1021 second surface layer region, 1022 first surface layer region. DETAILED DESCRIPTION

[0059] Hereinafter, embodiments of a secondary battery and an electric device of the present application are specifically disclosed while appropriately referring to the drawings. However, there are cases where unnecessary detailed explanations are omitted. For example, there are cases where detailed explanations of matters that are already well known, repeated explanations of actually identical structures are omitted. This is to avoid the following explanations from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following explanations are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0060] The ranges disclosed herein are intended to be "open" ranges, i.e., the end values are not included in the range. For example, if a range is listed as 60-120 and 80-110, it is intended that 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is 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" means a range of any combination of the numbers between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0062] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0063] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0064] Unless otherwise specified, "including" and "comprising" mentioned in the present application means open-ended, which can also be closed. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0065] If not specifically stated, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0066] High capacity, low cost lithium-containing transition metal oxides are likely to be widely used as positive active materials for high specific energy lithium ion batteries. However, this series of materials is prone to side reactions with electrolyte during the cycle process, resulting in a decrease in cycle capacity, which is not conducive to its large-scale practical application. Since the reaction of the material with the electrolyte occurs in the surface structure of the material, a large amount of research work is focused on improving the unstable surface structure of lithium-containing transition metal oxides. In the prior art, the structure stability of the material is improved by setting a rock salt phase or a spinel phase in the surface structure of the lithium-containing transition metal oxide, thereby improving the cycle performance of the battery. However, the rock salt phase or the spinel phase itself has poor electrochemical activity, and the surface structure is all rock salt phase or spinel phase structure, resulting in a large resistance of lithium ions to be extracted and inserted from the surface of the material, which will affect the energy density and the play of the electrochemical performance of the material, resulting in the loss of active lithium, and thus the purpose of improving the cycle performance of the battery cannot be achieved.

[0067] [Secondary battery]

[0068] Based on this, the application provides a secondary battery, comprising:

[0069] A positive electrode sheet, a negative electrode sheet, and an electrolyte,

[0070] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium-containing transition metal oxide,

[0071] The particle of the lithium-containing transition metal oxide comprises an internal region and a surface layer region at least partially surrounding the internal region,

[0072] The surface layer region comprises a first surface layer region and a second surface layer region, the second surface layer region is located between the first surface layer region and the internal region, and the first surface layer region and the second surface layer region both contain a first phase structure and a second phase structure,

[0073] The first phase structure comprises a layered phase structure, and the second phase structure comprises at least one of a spinel phase structure and a rock salt phase structure,

[0074] The first surface layer region includes a rock salt phase structure and a layered phase structure, and the second surface layer region includes a spinel phase structure and a layered phase structure.

[0075] FIG. 1 is a schematic diagram of a cross-sectional image of a particle of a lithium-containing transition metal oxide according to the present application. As shown in FIG. 1, the particle of the lithium-containing transition metal oxide 100 includes an inner region 101 and a surface layer region 102 at least partially surrounding the inner region 101, the surface layer region 102 including a first surface layer region 1022 and a second surface layer region 1021 between the first surface layer region 1022 and the inner region 101.

[0076] In the present context, the term "spinel phase structure" refers to a crystal structure in which oxygen ions are arranged in a cubic close packing, and cations are filled in one-eighth of the tetrahedral voids and one-half of the octahedral voids, and the space group is Fd-3m.

[0077] In the present context, the term "rock salt phase structure" refers to a sodium chloride type structure, a crystal structure of a class of AB type ionic compounds represented by sodium chloride, belonging to a cubic crystal system, a face-centered cubic lattice, and the space group is Fm-3m.

[0078] In the present context, the term "layered phase structure" refers to a crystal structure in which oxygen ions (O 2- ) are arranged in a cubic close packing to form a spatial framework, and lithium ions (Li + ) and cobalt ions (Co 3+ ) are each located in an alternating octahedral position of the oxygen ion cubic close packing framework, having an alpha-sodium ferrite type layered structure, and the crystal structure thus formed has a space group of R-3m.

[0079] The phase structure in the first surface layer region and the second surface layer region can be tested by methods and known devices known in the art. For example, a battery is disassembled to obtain a positive electrode sheet, the positive electrode film layer is peeled off from the current collector, and then dissolved in N-methyl pyrrolidone solvent. After the binder, dispersant, etc. in the positive electrode film layer are dissolved in the solvent, filtration and drying are performed to obtain a sample powder. The sample powder is cut by focused ion beam (FIB) to obtain a sample thin sheet with a thickness of 20 nm, and then the surface of the sample thin sheet is tested by HR-TEM to obtain an HR-TEM original picture. The phase structure of the particle in the original picture is calibrated by Fourier transform (FFT), as follows. A particle is randomly selected from the original picture, and the diffraction pattern of the region extending 100 nm from the surface of the particle to the interior of the particle is obtained by FFT. The distance from the diffraction spot to the center of the diffraction pattern is measured, and the reciprocal is the interplanar spacing of the corresponding crystal plane. According to the differences in interplanar spacing of the three phase structures, the interplanar spacing of the rock salt phase structure is 4.1 A, the interplanar spacing of the layered phase structure is 4.7 A, and the interplanar spacing of the spinel phase structure is 4.8 A. (Emmett) is the interplanar spacing of the (003) crystal plane of the layered phase structure, the interplanar spacing is (220) crystal plane of the spinel phase structure, the interplanar spacing is (002) crystal plane of the rock salt phase, that is, three phase structures can be determined, and then the phase distribution structure diagram of the region extending 100 nm from the surface of the particle to the interior of the particle is obtained. According to the distribution difference of the three phase structures, the demarcation line between the first surface layer region, the second surface layer region and the internal region can be distinguished, and then the phase structure in the first surface layer region and the second surface layer region can be determined.

[0080] In this paper, according to the phase distribution structure diagram of the region extending 100 nm from the surface of the particle to the interior of the particle, the demarcation line between the first surface layer region, the second surface layer region and the internal region can be distinguished, and then the first surface layer region, the second surface layer region and the internal region can be determined.

[0081] The first surface layer region and the second surface layer region simultaneously include the first phase structure containing the layered phase structure and the second phase structure containing the spinel phase structure or the rock salt phase structure. On the one hand, the second phase structure of the spinel phase structure or the rock salt phase structure with non-electrochemical activity reduces the possibility of side reaction between the positive active material and the electrolyte, improves the structural stability of the positive active material, improves the cycle performance of the battery, and on the other hand, the layered phase structure in the first phase structure can provide a channel for lithium ion deintercalation on the surface of the material, so that the positive active material has a high lithium ion migration speed, and also provides a sufficient number of lithium ion storage sites, which is beneficial to the development of the gram capacity of the positive active material, reduces the loss of active lithium in the cycle process, improves the cycle performance of the battery, and prolongs the service life of the battery. In addition, the first surface layer region close to the surface of the particle includes the rock salt phase structure and the layered phase structure, and the rock salt phase structure has relatively more excellent stability, and the effect of improving the structural stability and thermal stability can be more obvious. At the same time, the layered phase structure in the first surface layer region can provide a path for lithium ion deintercalation, accelerate lithium ion diffusion, provide a certain amount of lithium ion storage sites, improve the gram capacity and kinetic performance of the material, and comprehensively improve the cycle performance of the battery. The second surface layer region close to the internal region includes the spinel phase structure and the layered phase structure, and the spinel phase structure has good structural stability and high lithium ion transmission speed, which improves the structural stability of the material while making the material have excellent lithium ion transmission performance. The battery has good cycle stability and rate performance, and at the same time, the second surface layer region including the layered phase structure is also beneficial to accelerate lithium ion diffusion, provide a certain amount of lithium ion storage sites, and is beneficial to the development of the gram capacity of the material and the improvement of the cycle performance of the battery.

[0082] Compared with the first surface layer region and the second surface layer region containing a single first phase structure or a second phase structure, the first surface layer region and the second surface layer region of the application both contain a mixed phase structure, which can improve the cycle stability of the material while also considering the lithium ion transmission path and storage site of the material, and comprehensively improve the cycle performance of the battery.

[0083] Compared with the first surface layer region containing a layered phase structure and a rock salt phase structure, the second surface layer region contains a layered phase structure and a rock salt phase structure, i.e., the second phase structure of the second surface layer region close to the internal region is a rock salt phase structure. The application sets a spinel phase structure with good structural stability and excellent lithium ion transmission performance in the second surface layer region close to the internal region, which can reduce the possibility of side reactions between the second surface layer region and the electrolyte, improve the transmission speed of active ions of the material, improve the rate performance of the material, and improve the cycle performance and rate performance of the material.

[0084] Compared with the first surface layer region containing a layered phase structure and a spinel phase structure, the second surface layer region contains a layered phase structure and a spinel phase structure, i.e., the second phase structure of the first surface layer region close to the particle surface is a spinel phase structure. The application sets a rock salt phase structure with excellent structural stability and thermal stability in the first surface layer region close to the particle surface, which is more effective in reducing side reactions between the particle surface and the electrolyte, and is conducive to improving the structural stability of the material and improving the cycle performance of the battery.

[0085] Compared with the first surface layer region containing a layered phase structure and a spinel phase structure, the second surface layer region contains a layered phase structure and a rock salt phase structure, i.e., the second phase structure of the first surface layer region close to the particle surface is a spinel phase structure, and the second phase structure close to the internal region is a rock salt phase structure. The application selects a rock salt phase structure with more excellent structural stability in the first surface layer region close to the particle surface, and selects a spinel phase structure with certain structural stability and excellent lithium ion transmission performance in the second surface layer region close to the internal region, which can reduce the possibility of side reactions between the material and the electrolyte, improve the ion transmission performance of the material, improve the lattice matching of the material, and improve the cycle performance of the material.

[0086] In some embodiments, the internal region, the first surface layer region, and the second surface layer region comprise the same lithium-containing transition metal oxide.

[0087] In some embodiments, the internal region, the first surface layer region, and the second surface layer region are the same lithium-containing transition metal oxide.

[0088] In some embodiments, the internal region, the first surface layer region, and the second surface layer region comprise lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0089] In some embodiments, the inner region, the first surface layer region, and the second surface layer region are lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0090] In this context, the inner region, the first surface layer region, and the second surface layer region comprise the same lithium-containing transition metal oxide, such as lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, and the rock salt phase structure, the layered phase structure, and the spinel phase structure therein are different phase structures of the lithium nickel cobalt manganese oxide or the lithium nickel cobalt aluminum oxide.

[0091] In some embodiments, the first surface layer region refers to a region extending from the surface of the particles of the lithium-containing transition metal oxide to a distance of 10 nm inside the particles.

[0092] The test method of the phase structure in the first surface layer region and the second surface layer region described above can distinguish the boundary between the first surface layer region, the second surface layer region, and the inner region, i.e., the location region of the first surface layer region and the second surface layer region can be tested.

[0093] Controlling the area of the first surface layer region within a suitable range enables the rock salt phase in the first surface layer region to achieve the purpose of improving the structural stability and thermal stability, and at the same time enables the material to have good lithium ion transmission performance, thereby comprehensively improving the cycle performance of the battery.

[0094] In some embodiments, the second surface layer region refers to a region extending from the surface of the particles of the lithium-containing transition metal oxide to a distance of 10 nm to a distance of 60 nm inside the particles.

[0095] Controlling the area of the second surface layer region within a suitable range enables the spinel phase structure in the second surface layer region to achieve a smooth transition from the first surface layer region to the inner region, improves the overall lattice adaptability of the material, improves the structural stability of the material, and at the same time is also conducive to comprehensively improving the structural stability of the material and the transmission speed of lithium ions, thereby being conducive to improving the cycle performance of the battery.

[0096] In some embodiments, the inner region comprises a layered phase structure.

[0097] The phase structure of the inner region can be tested with reference to the aforementioned test method of the phase structure in the first surface layer region and the second surface layer region.

[0098] The inner region comprises a layered phase structure, the material has multiple lithium ion deintercalation paths, the material has excellent lithium ion diffusion speed, is conducive to the exertion of the material's capacity, and improves the cycle capacity retention rate and energy density of the battery.

[0099] In some embodiments, the first surface layer region comprises rock salt phase structure and layered phase structure, the second surface layer region comprises spinel phase structure and layered phase structure, and the inner region comprises layered phase structure.

[0100] The second surface layer region comprising spinel phase structure and layered phase structure is arranged between the inner region and the first surface layer region, and the spinel phase structure contained therein can act as a transition phase between the rock salt phase in the first surface layer region and the layered phase structure in the inner region, improving the lattice matching of the material and being conducive to improving the structural stability of the material and the cycle performance of the battery.

[0101] In some embodiments, the area ratio of the rock salt phase structure in the first surface layer region is 60%-80%, and in some embodiments, 65%-75%, based on the total area of the rock salt phase structure and the layered phase structure in the first surface layer region. In some embodiments, the area ratio of the rock salt phase structure can be 60%, 65%, 70%, 75%, 80% or any numerical range between any two of them, based on the total area of the rock salt phase structure and the layered phase structure in the first surface layer region.

[0102] Referring to the test method of the phase structure in the first surface layer region and the second surface layer region described above, the phase structure distribution of the first surface layer region and the second surface layer region obtained according to the foregoing method is calculated using ImageJ software to obtain the area ratio of different phase structures in the first surface layer region and the second surface layer region.

[0103] Controlling the area ratio of the rock salt phase structure and the layered phase structure in the first surface layer region within a suitable range achieves the purpose of improving the structural stability and thermal stability of the material, while also making the material have good lithium ion transmission performance, thereby comprehensively improving the cycle performance of the battery.

[0104] In some embodiments, the molar content of nickel element is 50%-80%, based on the total number of moles of metal elements other than Li in the first surface layer region. In some embodiments, the molar content of nickel element can be 50%, 60%, 65%, 70%, 75%, 80% or any numerical range between any two of them, based on the total number of moles of metal elements other than Li in the first surface layer region.

[0105] The test method of the molar content of nickel element in the first surface layer region can be tested by a method known in the art. As an example, the battery is disassembled, the positive electrode sheet is obtained, the positive electrode sheet is cut into a sample of appropriate size (5 mm*5 mm) and is attached to a sample disc, the sample is placed into an XPS sample chamber, after vacuumizing, the sample is sent into an analysis chamber, a 0.5 keV-5 keV Ar ion source is used as a depth analysis ion gun, the spot size is 50 μm-400 μm, then the depth profiling parameters are set for testing, after sputtering to a certain depth (according to the specific region of the first surface layer region determined in the foregoing, an example is sputtering to 10 nm from the surface), narrow scan analysis of nickel element is performed, and the molar content of nickel element is obtained by calculating the peak area of C1s.

[0106] The molar content of nickel element in the first surface layer region is within a suitable range, which is beneficial to forming a suitable area ratio of rock salt phase in the first surface layer region, so as to achieve the purpose of considering the stability of the material and the transmission performance of lithium ions, and comprehensively improving the cycle performance of the battery.

[0107] In some embodiments, the area ratio of the spinel phase structure is 50%-90%, and in some examples, 60%-80%, based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region. In some embodiments, the area ratio of the spinel phase structure can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any numerical range between any two of them, based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region.

[0108] In some embodiments, the area ratio of the layered phase structure in the second surface layer region is 10%-50%, and in some examples, 20%-40%, based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region. In some embodiments, the area ratio of the layered phase structure in the second surface layer region can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any numerical range between any two of them, based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region.

[0109] Controlling the area ratio of the spinel phase structure and the layered phase structure in the second surface layer region within a suitable range can improve the structural stability and lattice matching of the material, and also make the material have excellent lithium ion performance and lithium ion storage sites, thereby comprehensively improving the cycle performance of the battery.

[0110] In some embodiments, the molar content of cobalt element is 60%-90% based on the total moles of metal elements other than Li in the second surface layer region. In some embodiments, the molar content of cobalt element can be 60%, 65%, 70%, 75%, 80%, 85%, 90% or any numerical range between any two of them, based on the total moles of metal elements other than Li in the second surface layer region.

[0111] The test method of the molar content of cobalt element in the second surface layer region can be tested by a method known in the art. For example, reference can be made to the test method of the molar content of nickel element in the first surface layer region, and the positions of the first surface layer region and the second surface layer region determined according to the aforementioned test method, for example, the first surface layer region is a region extending from the surface of the particle to the interior of the particle by a distance of 10 nm, and the second surface layer region is a region extending from the surface of the particle to the interior of the particle by a distance of 10 nm to 60 nm. First, the element analysis data of the first surface layer region is obtained by sputtering 10 nm from the surface, and then the element analysis data of the second surface layer region is obtained by continuing to sputter to 60 nm from the interior of the particle, and the molar content of cobalt element in the second surface layer region is obtained.

[0112] The molar content of cobalt element in the second surface layer region is within a suitable range, which is beneficial to forming a suitable area ratio of spinel phase structure in the second surface layer region, so as to achieve the purpose of taking into account the stability of the material and the transmission speed of lithium ions, and comprehensively improving the cycle performance of the battery.

[0113] In some embodiments, the total area ratio of the rock salt phase structure and the layered phase structure in the first surface layer region is greater than or equal to 98% based on the total area of the phase structure in the first surface layer region.

[0114] In some embodiments, the total area ratio of the rock salt phase structure and the layered phase structure in the first surface layer region can be 98%, 99%, 99.5%, 100% or any numerical range between any two of them, based on the total area of the phase structure in the first surface layer region.

[0115] The determination method of the total area ratio of the rock salt phase structure and the layered phase structure is referred to the aforementioned test method of the area ratio of the rock salt phase structure.

[0116] The total area ratio of the rock salt phase structure and the layered phase structure in the first surface layer region is within a suitable range, so that the first surface layer region has a suitable area ratio of rock salt phase structure and layered phase structure, so that the rock salt phase structure and the layered phase structure in the first surface layer region can maximize the structural advantages of each other, so as to achieve the purpose of improving the cycle performance of the battery.

[0117] In some embodiments, the total area ratio of the spinel phase structure and the layered phase structure in the second surface layer region is greater than or equal to 98% based on the total area of the phase structure in the second surface layer region.

[0118] In some embodiments, the total area ratio of the spinel phase structure and the layered phase structure in the second surface layer region can be 98%, 99%, 99.5%, 100%, or any numerical range between any two of them, based on the total area of the phase structure in the second surface layer region.

[0119] The total area ratio of the spinel phase structure and the layered phase structure in the second surface layer region is within a suitable range, so that the spinel phase structure and the layered phase structure in the second surface layer region have a suitable area ratio, so that the spinel phase structure and the layered phase structure in the second surface layer region can maximize their respective structural advantages, achieving the purpose of improving the cycle performance of the battery.

[0120] In some embodiments, the molar content of nickel element in the lithium-containing transition metal oxide can be greater than or equal to 60%, in some embodiments greater than or equal to 80%, and in some embodiments greater than or equal to 90%, based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

[0121] In some embodiments, the molar content of nickel element in the lithium-containing transition metal oxide can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or any numerical range between any two of them, based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

[0122] The test method for the molar content of nickel element in the lithium-containing transition metal oxide can be tested by a method known in the art, as an example, reference is made to the EPA 6010D-2014 standard for determination; specifically, the battery is disassembled to obtain the positive electrode sheet, and the positive electrode film layer is peeled off from the current collector, then it is dissolved in N-methyl pyrrolidone solvent, after the binder, dispersant, etc. in the positive electrode film layer are dissolved in the solvent, filtration and drying are carried out to obtain the test sample, which can be tested by ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry). The test sample is first dissolved into a liquid with a strong acid, and then the liquid is introduced into the ICP light source by atomization, and further the gaseous atoms are ionized and excited in a strong magnetic field after the excited state returns to the ground state. Energy is released and recorded as different characteristic spectral lines during the above process for elemental quantitative analysis.

[0123] In order to improve the energy density of the battery, a high-nickel lithium-containing transition metal oxide is generally used, however, the increase of nickel content will exacerbate the side reaction between the material and the electrolyte, resulting in a decrease in the cycle capacity of the battery.

[0124] This application improves the structural stability of the material by simultaneously including a first phase structure containing a layered phase structure and a second phase structure containing a spinel phase structure or a layered phase structure in the first and second surface regions of the lithium-containing transition metal oxide, thereby also enabling the material to have a certain lithium-ion transport path and comprehensively improving the cycle performance of the battery.

[0125] In some embodiments, the positive electrode active material further includes modifying elements, which include any one or more of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K.

[0126] The types of modified elements were determined by referring to the above-mentioned test method for the molar content of nickel.

[0127] The positive electrode active material includes modifying elements such as Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb or K, which can further improve the cycle stability of the material and improve the cycle stability of the battery.

[0128] In some embodiments, based on the mass of the lithium-containing transition metal oxide, the mass content of the modifying element is less than or equal to 3000 ppm.

[0129] In some embodiments, based on the mass of the lithium-containing transition metal oxide, the mass content of the modified element can be 10 ppm, 50 ppm, 100 ppm, 200 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, or any value between the two.

[0130] The mass content of the modified elements was determined by referring to the above-mentioned test method for the molar content of nickel.

[0131] When the mass content of the modified elements is within a suitable range, it can improve the cycle stability of the material while also increasing the specific capacity, thereby comprehensively improving the cycle performance and energy density of the battery.

[0132] In some embodiments, the positive electrode active material includes Li a1 Ni x1 Co y1 Mn 1-x1- y1 M1 w1 O 2-b1 Li a2 Ni x2 Co y2 Al 1-x2-y2 M2 w2 O 2-b2 Any one of them;

[0133] wherein 0.8≤a1≤1.2, 0.6≤x1≤1, 0≤y1≤0.4, -0.1≤b1≤0.1, 0≤w1≤0.1;

[0134] 0.8≤a2≤1.2, 0.6≤x2≤1, 0≤y2≤0.4, -0.1≤b2≤0.1, 0≤w2≤0.1,

[0135] M1 comprises at least one element of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K,

[0136] M2 comprises at least one element of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K.

[0137] In any embodiment, the positive active material comprises Li a1 Ni x1 Co y1 Mn 1-x1- y1 M1 w1 O 2-b1 , Li a2 Ni x2 Co y2 Al 1-x2-y2 M2 w2 O 2-b2 ; and any combination thereof.

[0138] wherein 0.8≤a1≤1.2, 0.8≤x1≤1, 0≤y1≤0.2, -0.1≤b1≤0.1, 0≤w1≤0.1;

[0139] 0.8≤a2≤1.2, 0.8≤x2≤1, 0≤y2≤0.2, -0.1≤b2≤0.1, 0≤w2≤0.1,

[0140] M1 comprises at least one element of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K,

[0141] M2 comprises at least one element of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, K.

[0142] In some embodiments, a1 can be 0.8, 0.9, 1.0, 1.1, 1.2, or any numerical range between any two of them.

[0143] In some embodiments, x1 can be 0.6, 0.7, 0.8, 0.9, 1.0, or any numerical range between any two of them.

[0144] In some embodiments, y1 can be 0, 0.1, 0.2, 0.3, 0.4, or any numerical range between any two of them.

[0145] In some embodiments, b1 can be -0.1, 0, 0.1, or any numerical range between any two of them.

[0146] In some embodiments, w1 can be 0, 0.05, 0.1, or any numerical range between any two of them.

[0147] In some embodiments, a2 can be 0.8, 0.9, 1.0, 1.1, 1.2, or any numerical range between any two of them.

[0148] In some embodiments, x2 can be 0.6, 0.7, 0.8, 0.9, 1.0, or any numerical range between any two of them.

[0149] In some embodiments, y2 can be 0, 0.1, 0.2, 0.3, 0.4, or any numerical range between any two of them.

[0150] In some embodiments, b2 can be -0.1, 0, 0.1, or any numerical range between any two of them.

[0151] In some embodiments, w2 can be 0, 0.05, 0.1, or any numerical range between any two of them.

[0152] The confirmation of the chemical formula of the positive active material can adopt any method and any test equipment in the art, for example: specifically, disassemble the battery, obtain the positive electrode sheet, peel the positive film layer from the current collector, dissolve it in N-methyl pyrrolidone solvent, after the binder, dispersant, etc. in the positive film layer are dissolved in the solvent, filter and dry to obtain the sample to be tested, digest with HF, and add ICP-OES instrument to detect the contents of Li, Ni, Co, Mn, Al, M1, M2 elements, obtain the specific element content molar ratio, and obtain the specific chemical composition.

[0153] In some embodiments, a preparation method of a lithium-containing transition metal oxide is provided:

[0154] Step S0: providing a precursor, the chemical composition of which is Ni x1 Co y1 Mn 1-x1-y1 (OH)2or Ni x2 Co y2 Al 1-x2-y2 (OH)2, wherein 0.6≤x1≤1, 0≤y1≤0.4, 0.6≤x2≤1, 0≤y2≤0.4;

[0155] Step S1: performing first sintering on first raw materials containing a lithium source and a precursor to obtain an initial product;

[0156] Step S2: performing second sintering treatment on second raw materials containing the initial product and a cobalt source to obtain a secondary product;

[0157] Step S3: stirring the secondary product with a weakly acidic additive solution, and drying the intermediate product;

[0158] Step S4: performing third sintering treatment on the intermediate product to obtain a lithium-containing transition metal oxide,

[0159] The particles of the lithium-containing transition metal oxide include an inner region and a surface layer region at least partially surrounding the inner region,

[0160] The surface layer region includes a first surface layer region and a second surface layer region, the second surface layer region being located between the first surface layer region and the inner region, and the first surface layer region and the second surface layer region both containing a first phase structure and a second phase structure,

[0161] The first phase structure includes a layered phase structure, and the second phase structure includes at least one of a spinel phase structure and a rock salt phase structure,

[0162] The first surface layer region includes a layered phase structure and a rock salt phase structure, and the second surface layer region includes a layered phase structure and a spinel phase structure.

[0163] In some embodiments, the ratio of the number of moles of cobalt in the cobalt source to the total number of moles of Ni, Co, and Mn in the precursor is 0.005:0.995-0.025:0.975.

[0164] In some embodiments, the temperature of the second sintering treatment is 400-650°C.

[0165] In some embodiments, the time of the second sintering treatment is 4-10h.

[0166] In some embodiments, the first raw materials further include one or more of a Zr source, an Al source, a B source, a Mg source, a Ti source, a W source, a Mo source, a Nb source, a Ta source, a Sr source, a Sb source, and a K source.

[0167] In some embodiments, the molar content of the weakly acidic additive in the weakly acidic additive solution is 0.05-0.2mol / L.

[0168] In some embodiments, the time of the stirring treatment in step S3 is 1-10min.

[0169] In some embodiments, the weakly acidic additive includes one or more of malic acid, maleic acid, benzoic acid, and the like.

[0170] In some embodiments, the sintering time of the third sintering is 6h-12h.

[0171] In some embodiments, the sintering temperature of the third sintering is 200℃-450℃.

[0172] In some embodiments, a method for preparing a lithium-containing transition metal oxide is provided:

[0173] Step S0: providing a precursor with a chemical composition of Ni x1 Co y1 Mn 1-x1-y1 (OH)2or Ni x2 Co y2 Al 1-x2-y2 (OH)2, wherein 0.6≤x1≤1, 0≤y1≤0.4, 0.6≤x2≤1, 0≤y2≤0.4;

[0174] Step S1: performing first sintering on first raw materials containing a lithium source and the precursor to obtain an initial product;

[0175] Step S2: performing second sintering on second raw materials containing the initial product and a cobalt source to obtain a lithium-containing transition metal oxide,

[0176] wherein the particles of the lithium-containing transition metal oxide include an inner region and a surface layer region at least partially surrounding the inner region,

[0177] the surface layer region includes a first surface layer region and a second surface layer region, the second surface layer region is located between the first surface layer region and the inner region, and the first surface layer region and the second surface layer region both contain a first phase structure and a second phase structure,

[0178] wherein the first phase structure includes a layered phase structure, and the second phase structure includes a spinel phase structure.

[0179] In some embodiments, a method for preparing a lithium-containing transition metal oxide is provided:

[0180] Step S0: providing a precursor with a chemical composition of Ni x1 Co y1 Mn 1-x1-y1 (OH)2or Ni x2 Co y2 Al 1-x2-y2 (OH)2, wherein 0.6≤x1≤1, 0≤y1≤0.4, 0.6≤x2≤1, 0≤y2≤0.4;

[0181] Step S1: performing first sintering on first raw materials containing lithium source and precursors to obtain initial product;

[0182] Step S2: stirring the initial product with weak acid additive solution, and drying the intermediate product;

[0183] Step S3: performing third sintering treatment on the intermediate product to obtain lithium-containing transition metal oxide.

[0184] The particle of the lithium-containing transition metal oxide includes an inner region and a surface layer region at least partially surrounding the inner region,

[0185] The surface layer region includes a first surface layer region and a second surface layer region, the second surface layer region being located between the first surface layer region and the inner region, and the first surface layer region and the second surface layer region both containing a first phase structure and a second phase structure,

[0186] The first phase structure includes a layered phase structure, and the second phase structure includes a rock salt phase structure.

[0187] In some embodiments, a preparation method of lithium-containing transition metal oxide is provided:

[0188] Step S0: providing precursors with chemical composition of Ni x1 Co y1 Mn 1-x1-y1 (OH)2or Ni x2 Co y2 Al 1-x2-y2 (OH)2, wherein 0.6≤x1≤1, 0≤y1≤0.4, 0.6≤x2≤1, 0≤y2≤0.4;

[0189] Step S1: performing first sintering on first raw materials containing lithium source and precursors to obtain first product;

[0190] Step S2: stirring the initial product with weak acid additive solution, and drying the second product;

[0191] Step S3: performing second sintering treatment on the second product to obtain third product;

[0192] Step S4: performing third sintering treatment on second raw materials containing third product and cobalt source to obtain lithium-containing transition metal oxide,

[0193] The particle of the lithium-containing transition metal oxide includes an inner region and a surface layer region at least partially surrounding the inner region,

[0194] The surface layer region includes a first surface layer region and a second surface layer region, the second surface layer region being located between the first surface layer region and the inner region, the first surface layer region and the second surface layer region each comprising a first phase structure and a second phase structure,

[0195] wherein the first phase structure comprises a layered phase structure, and the second phase structure comprises at least one of a spinel phase structure, a rock salt phase structure,

[0196] wherein the first surface layer region comprises a layered phase structure and a spinel phase structure, and the second surface layer region comprises a layered phase structure and a rock salt phase structure.

[0197] [Positive electrode sheet]

[0198] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including a lithium-containing transition metal oxide.

[0199] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0200] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0201] In some embodiments, the positive electrode active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0202] In some embodiments, the positive electrode active material layer can further include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0203] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode current collector to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0204] [Positive electrode sheet]

[0205] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer optionally disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0206] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0207] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. As a metal foil, for example, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, or the like) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), or the like).

[0208] In some embodiments, the negative electrode active material can employ a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, or the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0209] In some embodiments, the negative electrode film layer can further include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0210] In some embodiments, the negative electrode film layer can further include a conductive agent. The conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0211] In some embodiments, the negative electrode film layer can further include other additives, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0212] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0213] [Electrolyte]

[0214] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid-state.

[0215] In some embodiments, the electrolyte is an electrolyte solution.

[0216] In some embodiments, the electrolyte includes a lithium salt.

[0217] In some embodiments, the electrolyte includes an organic solvent.

[0218] In some embodiments, the lithium salt can be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, lithium tetrafluoro oxalate phosphate.

[0219] In some embodiments, the organic 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0220] In some embodiments, the electrolyte solution can further 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 properties 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.

[0221] [Separator]

[0222] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0223] 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 layers can be the same or different, and are not particularly limited. In some embodiments, the separator can also have one or more coating layers.

[0224] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly by a stacking process or a rolling process.

[0225] [Outer package]

[0226] In some embodiments, the secondary battery can comprise an outer package for packaging the positive electrode sheet, the negative electrode sheet, and the electrolyte. As an example, the positive electrode sheet, the negative electrode sheet, and the separator can be stacked or rolled to form a stacked structure battery cell or a rolled structure battery cell, and the battery cell is packaged in the outer package; the electrolyte is the electrolyte described in the first aspect of the present application, and the electrolyte is impregnated in the battery cell. The number of battery cells in the secondary battery can be one or several, which can be adjusted according to the needs.

[0227] In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly by a stacking process or a rolling process. The outer package can be used to package the above-mentioned electrode assembly and the electrolyte.

[0228] In some embodiments, the outer package of the secondary battery can be a soft package, such as a pouch. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. 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 shape of the secondary battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, FIG. 2 is a battery cell 5 in a square structure as an example.

[0229] 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 side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be wound or stacked to form an electrode assembly 52. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific actual needs.

[0230] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells 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.

[0231] FIG. 4 is a battery module 4 as an example. Referring to FIG. 4, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0232] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0233] 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.

[0234] 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 receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0235] In addition, the application also provides a power consuming device, which includes the secondary battery provided by the application. The secondary battery can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming 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.

[0236] As the electric device, a battery cell, a battery module, or a battery pack can be selected according to the use requirement thereof.

[0237] 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. To meet the requirement of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

[0238] As another example of the device, a mobile phone, a tablet, a notebook computer, etc. can be used. The device generally requires thinness, and a secondary battery can be used as a power source.

[0239] Embodiments

[0240] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application only, and are not to be understood as a limitation of 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.

[0241] I. Preparation method

[0242] Embodiment 1

[0243] 1) Preparation of positive active material

[0244] Step SO: A mixed salt solution with a concentration of 2 moles / liter (mol / L) was prepared by using nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of Ni:Co:Mn = 92:7:1. A 4 mol / L NaOH solution was used as an alkali precipitant, and 2 mol / L ammonia was used as a complexing agent;

[0245] In a 100 L reaction kettle, 20 liters (L) of deionized water were added, and a certain amount of NaOH solution was added to make the pH in the reaction kettle 11 to obtain a reaction bottom solution;

[0246] Under a nitrogen protective atmosphere, the reaction bottom solution was heated to 55°C, and the mixed salt solution, the alkali solution, and the ammonia solution were added to the reaction bottom solution in parallel flow under a stirring speed of 600 revolutions per minute (rpm). The flow rate of the mixed salt solution, the alkali solution, and the ammonia solution was controlled to make the pH of the reaction solution 11. After the reaction reached the target particle size Dv50 (9.5 micrometers (μm)), the pumping was stopped, and the reaction solution was left to stand for 24 h to obtain an aging slurry containing a precursor material, which was washed and dried to obtain the precursor material;

[0247] Step S1: LiOH H2O and the precursor material described above are mixed uniformly at a molar ratio of 1.05:1, and then sintered at 750°C for 15h in a box furnace under a pure oxygen atmosphere, and then crushed and sieved to obtain an initial product;

[0248] Step S2: The initial product obtained above is mixed with cobalt hydroxide, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.02:0.98, and sintering is performed under an oxygen atmosphere, with a sintering temperature of 600°C and a sintering time of 8h, to obtain a secondary product;

[0249] Step S3: A certain amount of malic acid is dissolved in 5L of pure water and stirred to obtain an acid solution with a concentration of 0.1mol / L. 5kg of the intermediate product obtained above is added to the acid solution and stirred for 2min, then filtered and dried to obtain an intermediate product, which is sintered at 400°C for 6h in an oxygen atmosphere to obtain a positive electrode active material.

[0250] 2) Positive electrode sheet

[0251] The positive electrode active material, polyvinylidene fluoride, and conductive carbon black are mixed at a mass ratio of 94:3:3, then N-methyl pyrrolidone (NMP) is added, stirred for 2h, then stirred in a homogenizer at 1200 revolutions per minute (r / min) until uniformly mixed, then uniformly coated on both sides of a 13-micron-thick aluminum foil current collector, and after coating, dried in a drying oven at 120°C, cold-pressed, and cut to obtain a positive electrode sheet.

[0252] 3) Negative electrode sheet

[0253] Artificial graphite, hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickening agent sodium carboxymethyl cellulose (CMC) are mixed at a weight ratio of 90:5:2:2:1, deionized water is added, and stirred uniformly in a stirrer, then the slurry is coated on both sides of an 8μm-thick copper foil, dried in a 120°C oven, cold-pressed, and cut to obtain a negative electrode sheet.

[0254] 4) Electrolyte

[0255] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1 to obtain an organic solvent, then lithium hexafluorophosphate (LiPF6) is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1mol / L.

[0256] 5) Separation film

[0257] A polyethylene film with a thickness of 13μm is used as the separation film.

[0258] 6) Preparation of secondary battery

[0259] 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 play a role of isolation, and then wound to obtain a bare battery cell. The bare battery cell is welded with tabs, and is put into an aluminum case. An electrolyte is injected, and the steps of standing, formation, and capacity are performed to prepare a secondary battery.

[0260] Example 2

[0261] Compared with Example 1, the preparation method of the positive active material is adjusted in Example 2, as follows:

[0262] Step S0: A mixed salt solution with a concentration of 2 mol / L is prepared by using nickel sulfate, cobalt sulfate, and manganese sulfate according to a molar ratio of Ni:Co:Mn = 92:7:1. A 4 mol / L NaOH solution is used as an alkali precipitant, and a 2 mol / L ammonia solution is used as a complexing agent;

[0263] In a 100 L reaction kettle, 20 L of deionized water is added, and a certain amount of NaOH solution is added to make the pH of the reaction kettle 11 to obtain a reaction bottom solution;

[0264] Under a nitrogen protective atmosphere, the reaction bottom solution is heated to 55°C, and the mixed salt solution, the alkali solution, and the ammonia solution are added to the reaction bottom solution under a 600 rpm stirring speed. The flow rates of the mixed salt solution, the alkali solution, and the ammonia solution are controlled to make the pH of the reaction solution 11. After the reaction reaches the target particle size Dv50 (9.5 μm), the pumping is stopped. The reaction solution is left to stand for 24 h to obtain an aging slurry containing a precursor material, and the precursor material is obtained after washing and drying;

[0265] Step S1: Lithium hydroxide monohydrate (LiOH·H2O) is uniformly mixed with the above-mentioned precursor material and niobium pentoxide (Nb2O5, in terms of the molar number of Nb element) according to a molar ratio of 1.05:1:0.002. Then, under a pure oxygen atmosphere, the mixture is sintered in a box furnace at 750°C for 15 h. After crushing and sieving, an initial product is obtained;

[0266] Step S2: The above-mentioned initial product is mixed with cobalt hydroxide. The molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.02:0.98. Sintering is performed under an oxygen atmosphere, and the sintering temperature is 600°C and the sintering time is 8 h to obtain a secondary product.

[0267] Step S3: A certain amount of malic acid is dissolved in 5 L of pure water and stirred to obtain an acid solution of 0.1 mol / L. The 5 kg of intermediate product obtained above is added to the acid solution and stirred for 2 min, and then filtered and dried to obtain an intermediate product. The intermediate product is sintered at 400°C for 6 h in an oxygen atmosphere to obtain the positive electrode active material.

[0268] Example 3

[0269] Compared with Example 1, the preparation method of the positive electrode active material is adjusted in Example 3 as follows.

[0270] Step S0: A mixed salt solution with a concentration of 2 mol / L is prepared by using nickel sulfate, cobalt sulfate, and manganese sulfate according to a molar ratio of Ni:Co:Mn = 80:10:10. A 4 mol / L NaOH solution is used as an alkali precipitant, and a 2 mol / L ammonia solution is used as a complexing agent.

[0271] In a 100 L reaction kettle, 20 L of deionized water is added, and a certain amount of NaOH solution is added to make the pH of the reaction kettle 11 to obtain a reaction bottom solution.

[0272] Under a nitrogen protective atmosphere, the reaction bottom solution is heated to 55°C, and the mixed salt solution, the alkali solution, and the ammonia solution are added to the reaction bottom solution in parallel flow at a stirring speed of 600 rpm. The flow rates of the mixed salt solution, the alkali solution, and the ammonia solution are controlled to make the pH of the reaction solution 11. After the reaction reaches the target particle size Dv50 (9.5 μm), the pumping is stopped, and the reaction solution is allowed to stand for 24 h to obtain an aging slurry containing a precursor material. After washing and drying, the precursor material is obtained.

[0273] Step S1: LiOH·H2O is uniformly mixed with the precursor material according to a molar ratio of 1.05:1, and then sintered at 780°C for 15 h in a box furnace under a pure oxygen atmosphere. After crushing and sieving, the initial product is obtained.

[0274] Step S2: The initial product obtained above is mixed with cobalt hydroxide, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.02:0.98. Sintering is performed under an oxygen atmosphere at a sintering temperature of 600°C for 8 h to obtain a secondary product.

[0275] Step S3: A certain amount of malic acid is dissolved in 5 L of pure water and stirred to obtain an acid solution of 0.1 mol / L. The 5 kg of intermediate product obtained above is added to the acid solution and stirred for 2 min, and then filtered and dried to obtain an intermediate product. The intermediate product is sintered at 400°C for 6 h in an oxygen atmosphere to obtain the positive electrode active material.

[0276] Examples 4-7

[0277] Compared with Example 1, Examples 4-7 adjust the area ratio of the rock salt phase structure in the first surface layer region by adjusting step S3 in the preparation method of the positive electrode active material, as follows:

[0278] Example 4: A certain amount of malic acid is dissolved in 5L of pure water and stirred to obtain an acid solution of 0.1 mol / L. The 5kg of intermediate product obtained above is added to the acid solution and stirred for 1.5min, then filtered and dried to obtain an intermediate product. The positive electrode active material is obtained by sintering the intermediate product at 400°C for 6h in an oxygen atmosphere.

[0279] Example 5: A certain amount of malic acid is dissolved in 5L of pure water and stirred to obtain an acid solution of 0.1 mol / L. The 5kg of intermediate product obtained above is added to the acid solution and stirred for 2.5min, then filtered and dried to obtain an intermediate product. The positive electrode active material is obtained by sintering the intermediate product at 400°C for 6h in an oxygen atmosphere.

[0280] Example 6: A certain amount of malic acid is dissolved in 5L of pure water and stirred to obtain an acid solution of 0.1 mol / L. The 5kg of intermediate product obtained above is added to the acid solution and stirred for 2min, then filtered and dried to obtain an intermediate product. The positive electrode active material is obtained by sintering the intermediate product at 450°C for 6h in an oxygen atmosphere.

[0281] Example 7: A certain amount of malic acid is dissolved in 5L of pure water and stirred to obtain an acid solution of 0.1 mol / L. The 5kg of intermediate product obtained above is added to the acid solution and stirred for 2.5min, then filtered and dried to obtain an intermediate product. The positive electrode active material is obtained by sintering the intermediate product at 450°C for 6h in an oxygen atmosphere.

[0282] Examples 8-11

[0283] Compared with Example 1, Examples 8-11 adjust the area ratio of the spinel phase structure in the second surface layer region by adjusting step S2 in the preparation method of the positive electrode active material, as follows:

[0284] Example 8: The initial product obtained above is mixed with cobalt hydroxide, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.01:0.99. Sintering is performed in an oxygen atmosphere, with a sintering temperature of 600°C and a sintering time of 8h, to obtain a secondary product.

[0285] Example 9: The initial product obtained above is mixed with cobalt hydroxide, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.02:0.98. Sintering is performed in an oxygen atmosphere, with a sintering temperature of 620°C and a sintering time of 8h, to obtain a secondary product.

[0286] Example 10: The initial product obtained above is mixed with cobalt hydroxide, wherein the ratio of the molar amount of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.025:0.975, and sintering is performed in an oxygen atmosphere, with a sintering temperature of 600°C and a sintering time of 8h, to obtain a secondary product.

[0287] Example 11: The initial product obtained above is mixed with cobalt hydroxide, wherein the ratio of the molar amount of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.025:0.975, and sintering is performed in an oxygen atmosphere, with a sintering temperature of 650°C and a sintering time of 8h, to obtain a secondary product.

[0288] Example 12

[0289] Compared with Example 1, the preparation method of the positive electrode active material in Example 12 is adjusted as follows:

[0290] Step S1: LiOH·H2O and the precursor material in Example 1 are mixed uniformly according to a molar ratio of 1.05:1, and then sintering is performed in a pure oxygen atmosphere in a box furnace at 750°C for 15h, and the initial product is obtained after crushing and sieving;

[0291] Step S2: The initial product obtained above is mixed with cobalt hydroxide, wherein the ratio of the molar amount of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor is 0.02:0.98, and sintering is performed in an oxygen atmosphere, with a sintering temperature of 600°C and a sintering time of 12h, to obtain an intermediate product;

[0292] Step S3: A certain amount of malic acid is dissolved in 5L of pure water and stirred to obtain an acid solution of 0.1mol / L, 5kg of the intermediate product obtained above is added to the acid solution and stirred for 5min, then filtered and dried, and sintered in an oxygen atmosphere at 400°C for 8h to obtain a positive electrode active material.

[0293] Example 13

[0294] Compared with Example 1, the preparation method of the positive electrode active material in Example 13 is adjusted as follows:

[0295] Step S1: LiOH·H2O and the precursor material in Example 1 are mixed uniformly according to a molar ratio of 1.05:1, and then sintering is performed in a pure oxygen atmosphere in a box furnace at 750°C for 15h, and the initial product is obtained after crushing and sieving;

[0296] Step S2: the initial product obtained above is mixed with cobalt hydroxide, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total amount of Ni, Co, and Mn elements in the precursor is 0.02:0.98, and sintering is performed in an oxygen atmosphere, with a sintering temperature of 580°C and a sintering time of 7h, to obtain a secondary product;

[0297] Step S3: a certain amount of malic acid is dissolved in 5L of pure water and stirred to obtain an acid solution of 0.1mol / L, 5kg of the intermediate product obtained above is added to the acid solution and stirred for 2min, then filtered and dried to obtain an intermediate product, which is sintered in an oxygen atmosphere at 400°C for 6h to obtain a positive electrode active material.

[0298] Comparative Example 1

[0299] Compared with Example 1, the preparation method of the positive electrode active material in Comparative Example 1 is adjusted as follows:

[0300] Step S0: a mixed salt solution with a concentration of 2mol / L is prepared by using nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of Ni:Co:Mn=92:7:1, a 4mol / L NaOH solution is used as the alkali precipitant, and 2mol / L ammonia water is used as the complexing agent;

[0301] In a 100L reaction kettle, 20L of deionized water is added, and a certain amount of NaOH solution is added to make the pH of the reaction kettle 11 to obtain a reaction bottom solution;

[0302] Under a nitrogen protective atmosphere, the reaction bottom solution is heated to 55°C, and the mixed salt solution, the alkali solution, and the ammonia water solution are added to the reaction bottom solution under a 600rpm stirring speed, the flow rate of the mixed salt solution, the alkali solution, and the ammonia water solution is controlled to make the pH of the reaction solution 11, and after the reaction reaches the target particle size Dv50(9.5μm), the pumping is stopped, the reaction solution is left to stand for 24h to obtain an aging slurry containing the precursor material, and the precursor material is obtained after washing and drying;

[0303] Step S1: LiOH·H2O is mixed with the precursor material according to the molar ratio 1.05:1, and then sintered in a pure oxygen atmosphere in a box furnace at 750°C for 15h, and the positive electrode active material is obtained after crushing and sieving.

[0304] Comparative Example 2

[0305] Compared with Example 1, the preparation method of the positive electrode active material in Comparative Example 2 is adjusted as follows:

[0306] Step S1: LiOH H2O and the precursor material prepared in Example 1 were mixed uniformly according to a molar ratio of 1.05:1, and then sintered at 750°C for 15h in a box furnace under a pure oxygen atmosphere, and the initial product was obtained after crushing and sieving;

[0307] Step S2: A certain amount of malic acid was dissolved in 5L pure water and stirred to obtain an acid solution of 0.1 mol / L, and then 5kg of the intermediate product was added into the acid solution and stirred for 12min, and then filtered and dried, and then sintered at 400°C for 6h under an oxygen atmosphere to obtain the positive electrode active material.

[0308] Comparative Example 3

[0309] Compared with Example 1, the preparation method of the positive electrode active material in Comparative Example 3 was adjusted, and the specific method was as follows:

[0310] Step S1: LiOH H2O and the precursor material prepared in Example 1 were mixed uniformly according to a molar ratio of 1.05:1, and then sintered at 750°C for 15h in a box furnace under a pure oxygen atmosphere, and the initial product was obtained after crushing and sieving;

[0311] Step S2: The initial product and cobalt hydroxide were mixed, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co and Mn in the precursor was 0.02:0.98, and sintering was carried out under an oxygen atmosphere, the sintering temperature was 660°C, and the sintering time was 12h, to obtain the positive electrode active material.

[0312] Comparative Example 4

[0313] Compared with Example 1, the preparation method of the positive electrode active material in Comparative Example 4 was adjusted, and the specific method was as follows:

[0314] Step S1: LiOH H2O and the precursor material prepared in Example 1 were mixed uniformly according to a molar ratio of 1.05:1, and then sintered at 750°C for 15h in a box furnace under a pure oxygen atmosphere, and the initial product was obtained after crushing and sieving;

[0315] Step S2: The initial product and cobalt hydroxide were mixed, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co and Mn in the precursor was 0.03:0.97, and sintering was carried out under an oxygen atmosphere, the sintering temperature was 600°C, and the sintering time was 12h, to obtain the secondary product.

[0316] Step S3: A certain amount of malic acid was dissolved in 5 L of pure water and stirred to obtain an acid solution of 0.2 mol / L. The 5 kg of intermediate product obtained above was added to the acid solution and stirred for 10 min, then filtered and dried to obtain an intermediate product. The intermediate product was sintered in an oxygen atmosphere at 450°C for 10 h to obtain the positive electrode active material.

[0317] Comparative Example 5

[0318] Comparative Example 5 adjusts the preparation method of the positive electrode active material compared with Example 1, as follows:

[0319] Step S1: LiOH H2O and the precursor material prepared in Example 1 were mixed uniformly according to a molar ratio of 1.05:1, then sintered in a box furnace under pure oxygen atmosphere at 750°C for 15 h, and then crushed and sieved to obtain an initial product;

[0320] Step S2: A certain amount of malic acid was dissolved in 5 L of pure water and stirred to obtain an acid solution of 0.1 mol / L. The 5 kg of intermediate product obtained above was added to the acid solution and stirred for 10 min, then filtered and dried, and sintered in an oxygen atmosphere at 500°C for 6 h to obtain the positive electrode active material.

[0321] Comparative Example 6

[0322] Comparative Example 6 adjusts the preparation method of the positive electrode active material compared with Example 1, as follows:

[0323] Step S1: LiOH H2O and the precursor material prepared in Example 1 were mixed uniformly according to a molar ratio of 1.05:1, then sintered in a box furnace under pure oxygen atmosphere at 750°C for 15 h, and then crushed and sieved to obtain an initial product;

[0324] Step S2: The initial product obtained above was mixed with cobalt hydroxide, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total molar amount of Ni, Co, and Mn elements in the precursor was 0.02:0.98. Sintering was performed under an oxygen atmosphere, with a sintering temperature of 650°C and a sintering time of 8 h, to obtain the positive electrode active material.

[0325] Comparative Example 7

[0326] Comparative Example 7 adjusts the preparation method of the positive electrode active material compared with Example 1, as follows:

[0327] Step S1: LiOH H2O and the precursor material in Example 1 were mixed uniformly according to a molar ratio of 1.05:1, then sintered in a box furnace under pure oxygen atmosphere at 750°C for 15 h, and then crushed and sieved to obtain an initial product;

[0328] Step S2: a certain amount of malic acid was dissolved in 5L pure water and stirred to obtain an acid solution of 0.1 mol / L, and then the 5kg initial product obtained above was added to the acid solution and stirred for 10min, and then filtered and dried, and then sintered in an oxygen atmosphere at 500℃ for 6h to obtain an intermediate product;

[0329] Step S3: the intermediate product obtained above was mixed with cobalt hydroxide, wherein the molar ratio of cobalt in the added cobalt hydroxide to the total amount of Ni, Co and Mn elements in the precursor was 0.005:0.995, and then sintered in an oxygen atmosphere, the sintering temperature was 550℃, and the sintering time was 8h to obtain the positive electrode active material.

[0330] II. Test method

[0331] 1. Cycle capacity retention rate of secondary battery

[0332] At 25℃, the secondary battery was charged at 1C to a voltage of 4.25V, and then charged at 4.25V until the current was ≤0.05mA, and then rested for 5min, and then discharged at 1C to a voltage of 2.8V, which was the first charge / discharge cycle of the battery, and the discharge capacity of this cycle was recorded as the discharge capacity of the first cycle (C0); the above steps were repeated for the same battery, and the discharge capacity of the battery after 500 cycles (C1), and the capacity retention rate after 500 cycles = C1 / C0x100%.

[0333] III. Analysis of test results of each example and comparative example

[0334] The positive electrode active materials and secondary batteries of each example and comparative example were prepared according to the above method, and each parameter was measured, and the results are shown in the following table.

[0335] Table 1

[0336] Table 2

[0337] As can be seen from the above table, the secondary battery in Examples 1-13 of the present application comprises: a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material comprises a lithium-containing transition metal oxide, the particles of the lithium-containing transition metal oxide comprise an inner region and a surface layer region at least partially surrounding the inner region, the surface layer region comprises a first surface layer region and a second surface layer region, the second surface layer region is located between the first surface layer region and the inner region, and the first surface layer region and the second surface layer region each contain a first phase structure and a second phase structure, wherein the first phase structure comprises a layered phase structure, and the second phase structure comprises at least one of a spinel phase structure and a rock salt phase structure, wherein the first surface layer region comprises a rock salt phase structure and a layered phase structure, and the second surface layer region comprises a spinel phase structure and a layered phase structure.

[0338] As can be seen from the comparison between Examples 1-13 and Comparative Example 1, the first surface layer region and the second surface layer region comprising the second phase structure of the spinel phase structure or the rock salt phase structure can improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0339] As can be seen from the comparison between Examples 1-13 and Comparative Examples 2-4, the first surface layer region and the second surface layer region containing the layered phase structure can improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0340] As can be seen from the comparison between Examples 1-13 and Comparative Examples 6-7, the first surface layer region comprising the rock salt phase structure and the layered phase structure can further improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0341] As can be seen from the comparison between Examples 1-13 and Examples 5 and 7, the second surface layer region comprising the spinel phase structure and the layered phase structure can further improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0342] As can be seen from the comparison between Examples 1-11 and Example 12, the first surface layer region refers to a region extending 10 nanometers (nm) from the surface of the particles of the positive electrode active material to the interior of the particles, which can further improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0343] As can be seen from the comparison between Examples 1-11 and Example 13, the second surface layer region refers to a region extending from 10 nm to 60 nm from the surface of the particles of the positive electrode active material to the interior of the particles, which can further improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0344] It can be seen from Examples 1, 4-7 that the area ratio of the rock salt phase structure is 60%-80% and the area ratio of the layered phase structure in the first surface layer region is 20%-40% based on the total area of the rock salt phase structure and the layered phase structure in the first surface layer region, the battery has a high cycle capacity retention rate, and the battery has excellent cycle performance. It can be seen from the comparison of Examples 1, 5-6 and Examples 4, 7 that the area ratio of the rock salt phase structure is 65%-75% and the area ratio of the layered phase structure in the first surface layer region is 25%-35% based on the total area of the rock salt phase structure and the layered phase structure in the first surface layer region, which can further improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0345] It can be seen from Examples 1, 8-11 that the area ratio of the spinel phase structure is 50%-90% and the area ratio of the layered phase structure in the second surface layer region is 10%-50% based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region, the battery has a high cycle capacity retention rate, and the battery has excellent cycle performance. It can be seen from the comparison of Examples 1, 9-10 and Examples 8, 11 that the area ratio of the spinel phase structure is 60%-80% and the area ratio of the layered phase structure in the second surface layer region is 20%-40% based on the total area of the spinel phase structure and the layered phase structure in the second surface layer region, which can further improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0346] It can be seen from the comparison of Example 2 and Example 1 that the positive active material further includes any one or more modification elements of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K, which can further improve the cycle capacity retention rate of the battery and improve the cycle performance of the battery.

[0347] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution 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 of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The positive electrode tab, the negative electrode tab, and the electrolyte, The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including a lithium-containing transition metal oxide, The particle of the lithium-containing transition metal oxide includes an inner region and a surface layer region at least partially surrounding the inner region, The surface layer region includes a first surface layer region and a second surface layer region, the second surface layer region being located between the first surface layer region and the inner region, and the first surface layer region and the second surface layer region each containing a first phase structure and a second phase structure, The first phase structure includes a layered phase structure, and the second phase structure includes at least one of a spinel phase structure and a rock salt phase structure, The first surface layer region includes a rock salt phase structure and a layered phase structure, and the second surface layer region includes a spinel phase structure and a layered phase structure. The first surface layer region refers to a region extending 10 nm from the surface of the particle of the lithium-containing transition metal oxide to the interior of the particle.

2. The secondary battery according to claim 1, characterized by The second surface layer region refers to a region extending from the surface of the particle of the lithium-containing transition metal oxide to a position extending 10 nm to a position extending 60 nm to the interior of the particle.

3. The secondary battery according to claim 1 or 2, characterized by The inner region includes a layered phase structure.

4. The secondary battery according to any one of claims 1 to 3, characterized by, The area ratio of the rock salt phase structure to the total area of the rock salt phase structure and the layered phase structure in the first surface layer region is 60%-80%, and / or the area ratio of the layered phase structure in the first surface layer region is 20%-40%.

5. The secondary battery according to any one of claims 1 to 4, characterized by The area ratio of the rock salt phase structure to the total area of the rock salt phase structure and the layered phase structure in the first surface layer region is 65%-75%, and / or the area ratio of the layered phase structure in the first surface layer region is 25%-35%.

6. The secondary battery according to any one of claims 1 to 5, characterized by The molar content of nickel element based on the total number of moles of metal elements other than Li in the first surface layer region is 50%-80%.

7. The secondary battery according to any one of claims 1 to 6, characterized by, The area ratio of the spinel phase structure to the total area of the spinel phase structure and the layered phase structure in the second surface layer region is 50%-90%, and / or the area ratio of the layered phase structure in the second surface layer region is 10%-50%.

8. The secondary battery according to any one of claims 1 to 7, characterized by, The area ratio of the spinel phase structure to the total area of the spinel phase structure and the layered phase structure in the second surface layer region is 60%-80%, and / or the area ratio of the layered phase structure in the second surface layer region is 20%-40%.

9. The secondary battery according to any one of claims 1 to 8, characterized by, The molar content of cobalt element based on the total number of moles of metal elements other than Li in the second surface layer region is 60%-90%.

10. The secondary battery according to any one of claims 1 to 9, characterized by The molar content of nickel element in the lithium-containing transition metal oxide is greater than or equal to 60% based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

11. The secondary battery according to any one of claims 1 to 10, characterized by The molar content of nickel element in the lithium-containing transition metal oxide is greater than or equal to 80% based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

12. The secondary battery according to any one of claims 1 to 11, characterized by ​ 13. The secondary battery according to any one of claims 1 to 12, characterized by The molar content of the nickel element in the lithium-containing transition metal oxide is greater than or equal to 90% based on the molar amount of metal elements other than Li in the lithium-containing transition metal oxide.

14. The secondary battery according to any one of claims 1 to 13, characterized by The lithium-containing transition metal oxide further comprises a modifying element, and the modifying element comprises one or more of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K.

15. The secondary battery according to claim 14, characterized by The mass content of the modifying element is less than or equal to 3000 ppm based on the mass of the lithium-containing transition metal oxide.

16. The secondary battery according to any one of claims 1 to 15, characterized by The lithium-containing transition metal oxide includes Li a1 Ni x1 Co y1 Mn 1-x1-y1 M1 w1 O 2-b1 , Li a2 Ni x2 Co y2 Al 1-x2-y2 M2 w2 O 2-b2 any one of 0.8≤a1≤1.2, 0.6≤x1≤1, 0≤y1≤0.4, -0.1≤b1≤0.1, 0≤w1≤0.1; 0.8≤a2≤1.2, 0.6≤x2≤1, 0≤y2≤0.4, -0.1≤b2≤0.1, 0≤w2≤0.1, M1 comprises at least one element of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K, M2 comprises at least one element of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K.

17. The secondary battery according to any one of claims 1 to 16, characterized by Li a1 Ni x1 Co y1 Mn 1-x1-y1 M1 w1 O 2-b1 , Li a2 Ni x2 Co y2 Al 1-x2-y2 M2 w2 O 2-b2 any one of 0.8≤a1≤1.2, 0.8≤x1≤1, 0≤y1≤0.2, -0.1≤b1≤0.1, 0≤w1≤0.1; 0.8≤a2≤1.2, 0.8≤x2≤1, 0≤y2≤0.2, -0.1≤b2≤0.1, 0≤w2≤0.1, M1 comprises at least one element of Zr, Al, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K, M2 comprises at least one element of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K.

18. An electrical device, comprising: The secondary battery comprises the secondary battery according to any one of claims 1 to 17.

Images