Lithium-ion secondary battery, positive electrode active material, method for producing same, and electric device

Abstract

The application provides a lithium ion secondary battery, a positive electrode active material, a preparation method of the positive electrode active material and an electric device. The lithium ion secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active layer, and a positive electrode active material of the positive electrode active layer comprises primary particles of a lithium-containing transition metal oxide. Transition metal elements of the lithium-containing transition metal oxide comprise nickel elements and cobalt elements. The percentage of the molar amount of the nickel elements in the total molar amount of the transition metal elements is 50% to 75%. The average particle size of the primary particles is 1.5 microns to 2.6 microns. The mass concentration of the cobalt elements on the surface of the primary particles is 4.4% to 6.5%. The lithium ion secondary battery can have good cycle performance and high power performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to lithium-ion secondary batteries, positive electrode active materials, their preparation methods, and electrical devices. Background Technology

[0002] In recent years, lithium-ion rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the continuous expansion of the application range of lithium-ion rechargeable batteries, correspondingly higher requirements are being placed on battery performance. For example, the balance between cycle performance and power performance of lithium-ion rechargeable batteries needs further improvement. Summary of the Invention

[0003] The first aspect of this application provides a lithium-ion secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode active layer, the positive electrode active material of the positive electrode active layer including primary particles containing lithium transition metal oxide, the transition metal elements of the lithium transition metal oxide including nickel and cobalt, the molar amount of nickel accounting for 50% to 75% of the total molar amount of the transition metal elements, the average particle size of the primary particles being 1.5 μm to 2.6 μm, and the mass concentration of cobalt on the surface of the primary particles being 4.4% to 6.5%.

[0004] With the expanding applications of lithium-ion rechargeable batteries, improving energy density has become a crucial requirement for enhancing battery performance. For lithium-ion rechargeable batteries, including those containing lithium transition metal oxides, increasing the nickel content in the lithium transition metal oxide and raising the battery's operating voltage are beneficial for improving energy density. However, increasing the nickel content in the lithium transition metal oxide increases gas production during cycling, affecting battery safety. In the aforementioned lithium-ion rechargeable batteries, the molar percentage of nickel in the lithium transition metal oxide accounts for 50%–75% of the total molar percentage of transition metal elements, resulting in higher energy density and better safety. In this case, correspondingly increasing the battery's operating voltage is beneficial for improving energy density. However, increasing the battery's operating voltage exacerbates side reactions at the interface of the positive electrode active material particles, worsening the battery's cycle performance. Selecting primary particles with an average particle size of 1.5 μm or larger can reduce side reactions at the particle interface and improve battery cycle performance. Meanwhile, if the average particle size of the primary particles is too large, the lithium-ion insertion / extraction will be uneven, and the uneven internal stress of the particles during charging and discharging will easily lead to particle cracking. Selecting primary particles with an average particle size of less than 2.6 μm can reduce the risk of particle cracking during battery cycling, thereby maintaining good cycle performance. However, if the average particle size of the primary particles is large, the lithium-ion diffusion path becomes longer, and the diffusion efficiency decreases, which will limit the power performance of the battery. At this time, the mass concentration of cobalt on the surface of the primary particles is 4.4%~6.5%, which can accelerate the lithium-ion transport on the particle surface and reduce the risk of excessive cobalt dissolution from the positive electrode, which would worsen the battery cycle performance, thereby improving the power performance of the battery. Therefore, the above-mentioned lithium-ion secondary battery can achieve both good cycle performance and high power performance.

[0005] In some embodiments, in scanning electron microscopy (SEM) images of more than 2000 primary particles, the total number of aggregated particles with a particle size greater than 5 μm in the positive electrode active material is less than or equal to 9. In this case, the positive electrode active material is uniformly dispersed, allowing cobalt to be more fully coated on the surface of the primary particles, which is beneficial for further improving the battery's power performance.

[0006] In some embodiments, the half-width at half-maximum (WHM) of the primary particle size distribution curve is 1.5 μm to 2.5 μm. A smaller WHM in the primary particle size distribution curve indicates a more uniform particle size distribution, which can reduce the content of tiny primary particles in the cathode material, further reduce side reactions on the surface of the cathode active material, and further improve the cycle performance of the battery under high-voltage conditions.

[0007] In some embodiments, the mass concentration of cobalt inside the primary particles is 1.5% to 4.4%. Within this range, the intrinsic electronic conductivity of the primary particles is high, while the ohmic impedance and charge transport impedance are reduced. At the same time, the cobalt inside can stabilize the layered structure, suppress harmful phase transitions, reduce lattice distortion, reduce phase transition impedance, and improve the lithium-ion diffusion rate, thereby improving the power performance of the battery.

[0008] In some embodiments, the lithium-containing transition metal oxide accounts for 90% to 100% of the mass percentage of the positive electrode active material.

[0009] In some embodiments, the charging cutoff voltage of the lithium-ion secondary battery is 4.3V to 4.5V.

[0010] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0011] A positive electrode active material precursor and a lithium source are mixed to obtain a preliminary mixture. The positive electrode active material precursor includes a transition metal element, including nickel, and the molar amount of nickel accounts for 50% to 75% of the total molar amount of the transition metal element.

[0012] The initial mixture is subjected to a first sintering and a first crushing in sequence. The product of the first crushing is mixed with a cobalt-containing additive, which includes one or more of cobalt hydroxyl oxide, cobalt monoxide, and cobalt tetroxide. Then, a second sintering and a second crushing are performed in sequence, followed by a third sintering to prepare the positive electrode active material. The temperature of the first sintering is 900℃~990℃, the temperature of the second sintering is 700℃~800℃, and the temperature of the third sintering is 300℃~600℃.

[0013] In some embodiments, the cobalt-containing additive accounts for 0.5% to 2.5% of the mass percentage of the product from the first crushing.

[0014] In some embodiments, the first sintering time is 7h to 18h.

[0015] In some embodiments, the second sintering time is 4h to 14h.

[0016] In some embodiments, the third sintering time is 3h to 12h.

[0017] A third aspect of this application provides a positive electrode active material comprising primary particles containing lithium transition metal oxide, wherein the transition metal element of the lithium transition metal oxide includes nickel and cobalt, the molar amount of nickel accounts for 50% to 75% of the total molar amount of the transition metal element, the average particle size of the primary particles is 1.5 μm to 2.6 μm, and the mass concentration of cobalt on the surface of the primary particles is 4.4% to 6.5%.

[0018] The fourth aspect of this application provides an electrical device including the lithium-ion secondary battery of the first aspect. Attached Figure Description

[0019] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0020] Figure 1 This is a schematic diagram of a lithium-ion secondary battery according to one embodiment of this application.

[0021] Figure 2 for Figure 1 An exploded view of a lithium-ion secondary battery according to an embodiment of this application is shown.

[0022] Figure 3 This is a schematic diagram of an electrical device that uses a lithium-ion secondary battery as a power source according to an embodiment of this application.

[0023] Figure 4 This is a SEM image of the positive electrode active material precursor in Example 1 of this application.

[0024] Figure 5 This is a scan of the EPMA surface of the positive electrode active material in Example 1 of this application.

[0025] Figure 6 This is a particle size distribution curve of the primary particles in the positive electrode active material in Example 1 of this application.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1. Lithium-ion secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0028] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0031] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0033] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0034] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0035] In this application, unless otherwise stated, “A, such as B” means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0036] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0037] In this application, unless otherwise specified, "lithium-ion secondary battery" refers to a basic unit capable of converting chemical energy into electrical energy, and more generally includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, lithium ions repeatedly insert and extract between the positive and negative electrode.

[0038] With the expanding applications of lithium-ion rechargeable batteries, increasing energy density has become a crucial requirement for improving battery performance. For lithium-ion rechargeable batteries, including those containing lithium transition metal oxides, increasing the nickel content in the lithium transition metal oxide and raising the battery's operating voltage are beneficial for improving energy density. However, increasing the nickel content in the lithium transition metal oxide increases gas production during battery cycling, potentially affecting battery safety.

[0039] The nickel molar percentage in lithium-containing transition metal oxides is 50%–75% of the total molar percentage of transition metals, which can give the battery high energy density and good safety. However, as the battery operating voltage increases, side reactions at the interface of the positive electrode active material particles are aggravated, deteriorating the battery's cycle performance.

[0040] Using primary particles with a larger average particle size is an effective way to improve the cycle performance of batteries. However, when the average particle size of primary particles is larger, the diffusion path of lithium ions becomes longer, and the diffusion efficiency decreases, which will limit the power performance of the battery.

[0041] The inventors of this application discovered during their research on batteries that increasing the cobalt content on the surface of lithium-containing transition metal oxides (LMOs) can improve battery power performance. However, increasing the surface cobalt content may lead to excessive cobalt leaching from the positive electrode, thereby compromising the structural stability of the LMO and deteriorating the battery's cycle performance. The inventors found that for LMOs, the average particle size of the primary particles and the cobalt content on their surface have a synergistic effect in improving both cycle and power performance. Adapting these two factors can potentially enable batteries to achieve a balance between good cycle and power performance.

[0042] In response, one embodiment of this application provides a lithium-ion secondary battery. The lithium-ion secondary battery includes a positive electrode sheet, which includes a positive active layer. The positive active material of the positive active layer comprises primary particles containing lithium transition metal oxides. The transition metal elements in the lithium transition metal oxides include nickel and cobalt. The molar percentage of nickel in the total molar percentage of the transition metal elements is 50% to 75%. The average particle size of the primary particles is 1.5 μm to 2.6 μm, and the mass concentration of cobalt on the surface of the primary particles is 4.4% to 6.5%.

[0043] In this embodiment of the lithium-ion secondary battery, primary particles with an average particle size of 1.5 μm or larger are selected. Using primary particles with a larger average particle size reduces side reactions at the particle interface and improves the battery's cycle performance. However, if the average particle size of the primary particles is too large, uneven lithium-ion insertion / extraction can occur, and uneven internal stress during charging and discharging can easily lead to particle cracking. Selecting primary particles with an average particle size of less than 2.6 μm reduces the risk of cracking during battery cycling, thus maintaining good cycle performance. However, with a larger average particle size, the lithium-ion diffusion path becomes longer, reducing diffusion efficiency and limiting the battery's power performance. In this case, the mass concentration of cobalt on the surface of the primary particles is 4.4% to 6.5%, which accelerates lithium-ion transport on the particle surface and reduces the risk of excessive cobalt dissolution from the positive electrode, thus improving the battery's power performance. Therefore, the above-mentioned lithium-ion secondary battery can achieve both good cycle performance and high power performance.

[0044] In some embodiments of this application, the primary particle surface refers to the region of the primary particle with a thickness of less than 0.5 μm along its outer-to-inner direction.

[0045] In some embodiments of this application, high voltage refers to a voltage of 4.3V or higher. For example, high voltage can be 4.3V, 4.4V, 4.42V, 4.45V, 4.48V, 4.5V, etc.

[0046] In some embodiments, the charging cutoff voltage of the lithium-ion secondary battery is 4.3V to 4.5V. Optionally, the charging cutoff voltage of the lithium-ion secondary battery can be 4.3V, 4.4V, 4.42V, 4.45V, 4.48V, 4.5V, etc.

[0047] It is understood that lithium-containing transition metal oxides include lithium, transition metal elements, and oxygen, with the transition metal elements including nickel and cobalt. Optionally, the percentage of nickel molar amount in the total molar amount of the transition metal elements can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, or any value within the range of any two of the above values. Further, optionally, the molar amount of nickel in the total molar amount of the transition metal elements is 65% to 70%.

[0048] Furthermore, in lithium-containing transition metal oxides, the transition metal element typically also includes manganese. In their research on lithium-containing transition metal oxides, the inventors discovered that excessively high cobalt content on the surface of these oxides not only leads to excessive cobalt leaching from the cathode but also catalyzes manganese leaching, further deteriorating battery cycle performance. However, in some embodiments of this application, the mass concentration of cobalt on the primary particle surface is less than or equal to 6.5%, effectively suppressing cobalt and manganese leaching and promoting improved battery cycle performance.

[0049] It is understood that in this application, primary particles refer to the basic unit of the positive electrode active material particles. Primary particles can typically consist of one or no more than five individual particles. Due to the fewer grain boundaries in primary particles, they can maintain a relatively stable structure under high voltage, which is beneficial for improving the cycle performance of the battery at high operating voltages.

[0050] Optionally, the average particle size of the primary particles in the positive electrode active material in this application can be 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.6 μm, or any value within the range of any two of the above values.

[0051] In this application, the average particle size of primary particles refers to the average particle size of primary particles in a lithium-ion secondary battery under full discharge conditions.

[0052] In this application, the average particle size of the primary particles can be tested using the following method: A positive electrode active material powder sample is laid and adhered to a conductive adhesive, and a scanning electron microscope (SEM) is used to obtain an SEM image of the positive electrode active material powder sample. The scanning electron microscope can be a ZEISS Sigma 300, JEOL scanning electron microscope, or AxiaChemi SEM scanning electron microscope. SEM testing can refer to JY / T(001)-1996. The number of primary particles in the SEM image of the positive electrode active material powder sample is more than 2000. It is understood that the scanning electron microscope can automatically identify the number of primary particles during the testing. Ten images are selected at 1000x magnification, and the LIBMAS lithium-ion battery material microscopic intelligent analysis system is used to analyze the test images to obtain the average particle size of the primary particles. The particle size of the primary particle is taken as the maximum diameter of the primary particle in each two-dimensional direction in the SEM image.

[0053] It is understandable that the statistical range of the average particle size of primary particles in positive electrode active materials includes the particle size of non-agglomerated primary particles as well as the particle size of primary particles in agglomerated particles.

[0054] In this application, the positive electrode active material in a lithium-ion secondary battery can be extracted by disassembling the battery, removing the positive electrode sheet, and using methods such as solvent washing, ultrasonic dispersion, centrifugation, and fractional sedimentation to extract the positive electrode active material from the positive electrode active layer of the positive electrode sheet, followed by drying to obtain a powder sample. Alternatively, the powder material extracted from the positive electrode active layer can be sintered to remove organic components, thereby obtaining a positive electrode active material powder sample.

[0055] Optionally, the positive electrode active material powder sample can be obtained by the following method: fully fill the lithium-ion secondary battery, disassemble the battery, remove the positive electrode sheet, soak and clean it with a solvent such as dimethyl carbonate to remove residual electrolyte; scrape off the powder material of the positive electrode active layer, soak the powder material extracted from the positive electrode active layer with a solvent such as N-methylpyrrolidone to dissolve organic components such as binders in the solvent, wash and filter, collect the solid phase, and then use density difference to centrifuge to separate the relatively low-density conductive agent from the suspension, collect the centrifuged precipitate to obtain the positive electrode active material powder sample.

[0056] In this application, the mass concentration of cobalt on the surface of primary particles can be tested using the following method: A positive electrode active material powder sample is prepared into an electron microscopy sample by resin embedding and ion polishing. Before testing, it undergoes carbon spraying to increase the material's conductivity. Particles with good flatness and polishing are selected for electron probe microanalysis (EPMA). The elemental intensity is collected when the screen scale is adjusted to 2 μm. Ten images of different locations in the sample are selected, and the average mass concentration of cobalt at these ten locations is used as the test result. The final result shows that the mass concentration of cobalt on the surface of the primary particles ranges from 4.4% to 6.5%.

[0057] In some embodiments of this application, when the mass concentration of cobalt on the surface of the primary particles is less than 4.4%, the kinetic improvement of lithium-containing transition metal oxides is insufficient, and the power is not significantly improved. When the mass concentration of cobalt on the surface of the primary particles is greater than 6.5%, the amount of cobalt dissolved from the positive electrode increases, and manganese is dissolved simultaneously. At this time, the structural stability of the positive electrode is destroyed, the oxidation of the electrolyte is intensified, and the SEI film is destroyed when metal ions are transferred to the negative electrode for deposition, resulting in a significant deterioration in battery cycle performance.

[0058] Optionally, the mass concentration of cobalt on the surface of the primary particles can be 4.4%, 4.6%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, or any value within the range of any two of the above values.

[0059] In some embodiments, the mass concentration of cobalt inside the primary particles is 1.5% to 4.4%. Within this range, the intrinsic electronic conductivity of the primary particles is high, while the ohmic impedance and charge transport impedance are reduced. At the same time, the cobalt inside can stabilize the layered structure, suppress harmful phase transitions, reduce lattice distortion, reduce phase transition impedance, and improve the lithium-ion diffusion rate, thereby improving the power performance of the battery.

[0060] Optionally, the mass concentration of cobalt inside the primary particle can be 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.4%, or any value within the range of any two of the above values.

[0061] In this application, the mass concentration of cobalt within the primary particles can be tested using the following method: A positive electrode active material powder sample is prepared into an electron microscopy sample by resin embedding and ion polishing. Before testing, it undergoes carbon spraying to increase the material's conductivity. Particles with good flatness and polishing are selected for electron probe microanalysis (EPMA). The image is adjusted to a scale bar of 2 μm, and elemental intensities are collected. Ten images from different locations within the sample are selected, and the average mass concentration of cobalt at these ten locations is used as the test result. The final result shows that the mass concentration of cobalt within the primary particles ranges from 1.5% to 4.4%.

[0062] In some embodiments, in scanning electron microscopy (SEM) images of more than 2000 primary particles of the positive electrode active material, the total number of aggregated particles with a particle size of 5 μm or larger is less than or equal to 9. In this case, the positive electrode active material is uniformly dispersed, allowing cobalt to be more fully coated on the surface of the primary particles, which is beneficial for further improving the power performance of the battery. Optionally, in SEM images of more than 2000 primary particles of the positive electrode active material, the total number of aggregated particles with a particle size of 5 μm or larger is less than or equal to 5, 4, 3, 2, or 1.

[0063] Furthermore, during battery cycling, volume changes in the positive electrode active material particles lead to increased shear stress between particles, causing microcracks and potentially inhibiting battery cycle performance. In this case, when the total number of agglomerated particles with a diameter greater than 5 μm in the positive electrode active material is less than or equal to 9, the particles are uniformly dispersed with fewer agglomerated particles. This reduces interparticle forces, lowers the shear stress caused by particle volume changes, reduces the risk of microcracks, and further improves battery cycle performance. Simultaneously, uniform dispersion of the positive electrode active material can increase the lithium-ion diffusion rate, further improving battery power performance.

[0064] In this application, the total number of agglomerated particles with a particle size greater than 5 μm in the positive electrode active material can be tested by the following method: A positive electrode active material powder sample is laid and adhered to a conductive adhesive, and a scanning electron microscope (SEM) is used to obtain an SEM image of the positive electrode active material powder sample. The scanning electron microscope can be a ZEISS Sigma 300, JEOL scanning electron microscope, or Axia Chemi SEM. SEM testing can refer to JY / T(001)-1996. The number of particles in a single SEM image of the positive electrode active material powder sample is greater than 2000. Ten images are selected at 1000x magnification, and the LIBMAS lithium-ion battery material microscopic intelligent analysis system is used to analyze the test images to obtain the average total number of agglomerated particles with a particle size greater than 5 μm in the positive electrode active material.

[0065] In some embodiments, the half-width at half-maximum (WHM) of the primary particle size distribution curve is 1.5 μm to 2.5 μm. In these embodiments, the smaller WHM in the primary particle size distribution curve indicates a more uniform particle size distribution, which can reduce the content of tiny primary particles in the cathode material, further reduce side reactions on the surface of the cathode active material, and further improve the cycle performance of the battery under high voltage conditions.

[0066] In this application, the half-peak width (WHM) of the primary particle size distribution curve in the positive electrode active material corresponds to the half-peak width (WHM) of the main peak. Unless otherwise specified, the main peak refers to a peak whose percentage of the integrated area under the peak relative to the sum of the integrated areas of the curve exceeds 50%, and can be further selected as a peak whose percentage of the integrated area under the peak relative to the sum of the integrated areas of the curve is 80% to 100%. When the particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve, that single peak is the main peak.

[0067] In some embodiments, the particle size distribution curve of the primary particles in the positive electrode active material is a single-peak curve.

[0068] Furthermore, the half-width at half-maximum (HWHM) refers to the width between the two particle size boundaries corresponding to half the peak height of the distribution curve. This HWHM reflects the concentration of the primary particle size distribution. The smaller the HWHM value, the narrower the primary particle size distribution, the better the particle size uniformity, and the more concentrated the particle size distribution. Conversely, the larger the HWHM value, the wider the primary particle size distribution, the greater the particle size difference, and the more particles deviating from the average particle size, with a higher proportion of both smaller and larger primary particles.

[0069] Optionally, the particle size distribution curve of primary particles in the positive electrode active material can be tested using the following method: A positive electrode active material powder sample is laid and adhered to a conductive adhesive, and a scanning electron microscope (SEM) is used to obtain an SEM image of the positive electrode active material powder sample. The scanning electron microscope can be a ZEISS Sigma 300, JEOL scanning electron microscope, or Axia Chemi SEM. SEM testing can refer to JY / T(001)-1996. The number of primary particles in the SEM image of the positive electrode active material powder sample should be more than 2000. Ten images are selected at 1000x magnification, and the LIBMAS lithium-ion battery material microscopic intelligent analysis system is used to analyze the test images to obtain the particle size of the primary particles. The obtained particle size data of the primary particles is used to plot a histogram in Minitab, which includes a fitted curve. The fitted curve is used as the particle size distribution curve of the primary particles. It can be understood that the half-maximum width (WHM) of the primary particle size distribution curve can be obtained from the obtained particle size distribution curve of the primary particles.

[0070] It is understood that, in this application, the statistical range of the particle size distribution curve of primary particles in the positive electrode active material includes the particle size of non-agglomerated primary particles as well as the particle size of primary particles in agglomerated particles.

[0071] Optionally, the half-width at half-maximum (WHM) of the primary particle size distribution curve is 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, or any value within the range of any two of the above values.

[0072] In some embodiments, the lithium-containing transition metal oxide includes one or more of lithium nickel cobalt-based oxides and their modifications.

[0073] It is understandable that lithium nickel cobalt-based oxides refer to lithium-containing transition metal oxides that include lithium, nickel, cobalt, and oxygen. It is also understandable that lithium nickel cobalt-based oxides are lithium-containing transition metal oxides, wherein the transition metal elements include at least nickel and cobalt.

[0074] Unless otherwise stated, lithium nickel cobalt-based oxides have a layered structure.

[0075] In some embodiments, the modified material includes a lithium nickel cobalt-based oxide and a dopant element doped into the lithium nickel cobalt-based oxide. Introducing a dopant element into the lithium nickel cobalt-based oxide is beneficial to improving the stability of the lithium nickel cobalt-based oxide, and further improving the cycle performance of the battery at high voltage. Optionally, the dopant element includes one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn, and Sb.

[0076] In some embodiments, the modified material includes a lithium nickel cobalt-based oxide and a coating layer covering at least a portion of the surface of the lithium nickel cobalt-based oxide. Introducing a coating layer onto at least a portion of the surface of the lithium nickel cobalt-based oxide is beneficial for improving the stability of the lithium nickel cobalt-based oxide, further improving the cycle performance of the battery at high voltages. Optionally, the coating layer contains a coating element, including one or more of Co, Al, Ti, Mg, Zr, Y, Li, W, Na, and Nb.

[0077] Alternatively, lithium nickel cobalt-based oxides may include lithium nickel cobalt manganese-based oxides.

[0078] Further optionally, the lithium nickel cobalt-based oxide modifier includes a lithium nickel cobalt manganese-based modifier. The lithium nickel cobalt manganese-based modifier comprises a lithium nickel cobalt manganese-based oxide and a dopant element doped into the lithium nickel cobalt manganese-based oxide. The dopant element may include one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn, and Sb.

[0079] Further optionally, the lithium nickel cobalt manganese-based modified material includes a lithium nickel cobalt manganese-based oxide and a coating layer covering at least a portion of the surface of the lithium nickel cobalt manganese-based oxide. The coating layer contains a coating element, which may include one or more of Co, Al, Ti, Mg, Zr, Y, Li, W, Na, and Nb.

[0080] It is understandable that the nickel content in lithium-containing transition metal oxides represents the percentage of the molar amount of nickel in the lithium-containing transition metal oxide relative to the total molar amount of the transition metal elements.

[0081] Optionally, in the lithium-containing transition metal oxide, the percentage of nickel molar amount to the total molar amount of the transition metal elements can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, or any value within the range of any two of the above values. More preferably, the molar amount of nickel molar amount to the total molar amount of the transition metal elements is 65% to 70%.

[0082] In some embodiments, the chemical formula of the lithium transition metal oxide is Li. x (Ni a Co b Mn c ) 1-d M d O 2-y A yWherein, 0.2≤x≤1.2, 0.5≤a≤0.75, 0≤b≤0.4, 0≤c≤0.4, a+b+c=1, 0≤d<1, 0≤y<2, M includes one or more of Al, Ti, Mg, Zr, Sr, Y, W, La, Na, Fe, Cu, Zn, Sb and Nb, and A includes one or more of N, P, S and halogen elements.

[0083] Understandably, 'a' is typically used to represent the nickel content in lithium-containing transition metal oxides. A larger 'a' indicates a higher nickel content, while a smaller 'a' indicates a lower nickel content. As some possible examples of 'a', 'a' can be 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, or any value within the range of any two of the above values.

[0084] Understandably, 'b' is typically used to represent the cobalt content in lithium-containing transition metal oxides. A larger 'b' indicates a higher cobalt content, while a smaller 'b' indicates a lower cobalt content. As some possible examples of 'b', it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or any value within the range of any two of the above values.

[0085] Understandably, 'c' is typically used to represent the manganese content in lithium-containing transition metal oxides. A larger 'c' indicates a higher manganese content, while a smaller 'c' indicates a lower manganese content. As some possible examples of 'c', it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or any value within the range of any two of the above values.

[0086] Understandably, d is typically used to represent the content of element M in lithium-containing transition metal oxides. A larger d indicates a higher content of element M, while a smaller d indicates a lower content of element M. As some possible examples of d, d can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and any value within the range of any two of the above values.

[0087] Understandably, x is typically used to represent the lithium content in lithium-containing transition metal oxides. A larger x indicates a higher lithium content, while a smaller x indicates a lower lithium content. As some possible examples of x, x can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, and any value within the range of any two of the above values.

[0088] Understandably, y is typically used to represent the content of element A in lithium-containing transition metal oxides. A larger y indicates a higher content of element A, while a smaller y indicates a lower content of element A. As some possible examples of y, y can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, and any value within the range of any two of the above values. Optionally, 0 ≤ y ≤ 0.05.

[0089] It is understandable that A includes one or more of N, P, S and halogen elements, where halogen elements can be F, Cl, Br, etc.

[0090] Optionally, lithium nickel-based oxides include LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.6 Co 0.13 Mn 0.27 O2, LiNi 0.63 Co 0.1 Mn 0.27 O2, LiNi 0.65 Co 0.07 Mn0.28 O2, LiNi 0.65 Co 0.1 Mn 0.25 O2, LiNi 0.65 Co 0.12 Mn 0.23 O2, LiNi 0.68 Co 0.08 Mn 0.24 O2, LiNi 0.68 Co 0.1 Mn 0.22 O2, LiNi 0.68 Co 0.12 Mn 0.2 O2, LiNi 0.69 Co 0.12 Mn 0.19 O2, LiNi 0.70 Co 0.05 Mn 0.25 O2, LiNi 0.70 Co 0.10 Mn 0.20 O2, etc.

[0091] In some embodiments, the lithium-containing transition metal oxide accounts for 90% to 100% of the mass percentage of the positive electrode active material. Optionally, the lithium-containing transition metal oxide accounts for 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, and any value within the range of any two of the above values.

[0092] In some embodiments, the lithium-containing transition metal oxide accounts for 85.5% to 98.5% of the mass percentage of the positive electrode active layer. Optionally, the lithium-containing transition metal oxide accounts for 85.5%, 86%, 88%, 90%, 92%, 95%, 98%, 98.5%, and any value within the range of any two of the above values.

[0093] In some embodiments, the positive electrode active material may further include one or more of the following materials: lithium cobalt oxide, lithium manganese oxide, lithium manganese cobalt oxide, and modified compounds thereof. Non-limiting examples of lithium cobalt oxide may include LiCoO2. Non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.

[0094] In some embodiments, the positive electrode active material further includes a lithium phosphate with an olivine structure. The lithium phosphate with an olivine structure exhibits good cycle stability, which is beneficial for improving battery cycle performance. Optionally, the lithium phosphate with an olivine structure accounts for less than or equal to 10% of the mass of the positive electrode active material. For example, the mass percentage of the lithium phosphate with an olivine structure in the positive electrode active material can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0, or any value within the range of any two of the above values.

[0095] Optionally, lithium-containing phosphates may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. Lithium-containing phosphates may also include one or more of lithium manganese phosphate and lithium manganese phosphate and carbon composites.

[0096] In some embodiments, the positive electrode active layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Optionally, the binder accounts for 0.7% to 3% of the mass percentage of the positive electrode active layer. For example, the binder percentage of the positive electrode active layer may be 0.7%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any value within the range of any two of the above values.

[0097] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Optionally, the conductive agent accounts for 0.8% to 2% of the mass percentage of the positive electrode active layer. For example, the mass percentage of the conductive agent in the positive electrode active layer may be 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0098] In some embodiments, the positive electrode sheet further includes a positive current collector. The positive active layer is located on at least one surface of the positive current collector.

[0099] Optionally, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0100] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector.

[0101] In some embodiments, the lithium-ion secondary battery further includes a negative electrode sheet, which includes a negative electrode active layer, and the negative electrode active material of the negative electrode active layer includes one or more of carbon-based materials and silicon-based materials.

[0102] Optionally, carbon-based materials include one or more of graphite, soft carbon, and hard carbon. It is understood that graphite includes one or more of synthetic graphite and natural graphite.

[0103] Optionally, the silicon-based material may include one or more of elemental silicon, silicon oxides, and silicon-carbon composites.

[0104] Optionally, the negative electrode active material may also include negative electrode active materials known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: tin-based materials and lithium titanate, etc. Optionally, the tin-based material may include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0105] Optionally, the negative electrode active material accounts for 91% to 98% of the mass of the negative electrode active layer. For example, the mass percentage of the negative electrode active material in the negative electrode active layer can be 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or any value within the range of any two of the above values.

[0106] In some embodiments, the negative electrode active layer may optionally include a binder. The binder may include one or more 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). Optionally, the binder accounts for 1% to 5% of the mass percentage of the negative electrode active layer. Optionally, the binder's mass percentage of the negative electrode active layer may be 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the above values.

[0107] In some embodiments, the negative electrode active layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Optionally, the conductive agent accounts for 0.2% to 2% of the mass percentage of the negative electrode active layer. Optionally, the conductive agent accounts for 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0108] In some embodiments, the negative electrode active layer may optionally include other additives, such as a thickener. The thickener may be sodium carboxymethyl cellulose (CMC-Na). Optionally, the thickener accounts for 0.8% to 2% of the mass of the negative electrode active layer. Optionally, the mass percentage of the thickener in the negative electrode active layer may be 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0109] In some embodiments, the negative electrode sheet further includes a negative current collector. The negative active layer is located on at least one surface of the negative current collector.

[0110] Optionally, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0111] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent to form a negative electrode slurry. Optionally, a non-limiting example of a solvent is deionized water. The negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet is obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0112] In some embodiments, the lithium-ion secondary battery also includes an electrolyte. The electrolyte serves to conduct ions between the positive and negative electrode plates.

[0113] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0114] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0115] In some embodiments, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate, fluoroethylene carbonate (FEC), 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.

[0116] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0117] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoromethyl ethylene carbonate (TFPC).

[0118] It is understood that lithium-ion secondary batteries also include a separator. The separator is located between the positive electrode and the negative electrode. This application does not impose any particular restriction on the type of separator; any well-known porous separator with good chemical and mechanical stability can be selected.

[0119] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0120] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0121] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0122] In some embodiments, the outer packaging of the lithium-ion secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion secondary battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0123] This application does not impose any particular limitation on the shape of the lithium-ion secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured lithium-ion secondary battery 1.

[0124] In some implementations, refer to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The lithium-ion secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0125] In some implementations, the lithium-ion secondary battery can be a single battery cell, a battery module, or a battery pack.

[0126] The battery module includes at least one lithium-ion secondary battery. The battery module may contain one or more lithium-ion secondary batteries, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0127] In a battery module, multiple lithium-ion secondary batteries can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion secondary batteries can be secured using fasteners.

[0128] Optionally, the battery module may also include a housing with a receiving space in which multiple lithium-ion secondary batteries are housed.

[0129] In some embodiments, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0130] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0131] In addition, this application also provides an electrical device, which includes the lithium-ion secondary battery provided in this application. The battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0132] As an electrical device, lithium-ion rechargeable batteries can be selected according to its usage requirements.

[0133] Figure 3 Here is an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack or battery module can be used.

[0134] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0135] Another embodiment of this application provides a method for preparing a positive electrode active material. The method for preparing the positive electrode active material includes the following steps:

[0136] The positive electrode active material precursor and the lithium source are mixed to obtain a preliminary mixture. The positive electrode active material precursor includes transition metal elements, including nickel, and the molar amount of nickel accounts for 50% to 75% of the total molar amount of the transition metal elements.

[0137] The initial mixture is subjected to a first sintering and a first crushing in sequence. The product of the first crushing is mixed with a cobalt-containing additive, which includes one or more of cobalt hydroxyl oxide, cobalt monoxide, and cobalt tetroxide. Then, a second sintering and a second crushing are performed in sequence, followed by a third sintering to prepare the positive electrode active material. The temperature of the first sintering is 900℃~990℃, the temperature of the second sintering is 700℃~800℃, and the temperature of the third sintering is 300℃~600℃.

[0138] It is understood that the positive electrode active material obtained by this preparation method also meets the relevant characteristics of the positive electrode active material in lithium-ion secondary batteries mentioned above, which will not be repeated here. In some embodiments, the mass percentage of the cobalt-containing additive in the product of the first crushing is 0.5% to 2.5%. Optionally, the mass percentage of the cobalt-containing additive in the product of the first crushing can be 0.5%, 1%, 1.5%, 2%, 2.5%, or any value within the range of any two of the above values.

[0139] In some embodiments, the temperature for the first sintering is 900°C to 990°C. Optionally, the temperature for the first sintering can be 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, or any value within the range of any two of the above values.

[0140] In some implementations, the first sintering time is 7h to 18h. For example, the first sintering time can be 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, or any value within the range of any two of the above values.

[0141] In some embodiments, the temperature of the second sintering is 700°C to 800°C. Optionally, the temperature of the second sintering can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or any value within the range of any two of the above values.

[0142] In some embodiments, the second sintering time is 4h to 14h. Optionally, the second sintering time can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, or any value within the range of any two of the above values.

[0143] In some embodiments, the temperature of the third sintering is 300°C to 600°C. Optionally, the temperature of the third sintering can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, or any value within the range of any two of the above values.

[0144] In some embodiments, the third sintering time is 3h to 12h. Optionally, the third sintering time can be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any value within the range of any two of the above values.

[0145] In some embodiments, the initial mixture also includes raw materials containing dopant elements. In this case, dopant elements can be introduced into the positive electrode active material to improve its structural stability.

[0146] Optionally, the doping element includes one or more of Al, Ti, Co, Mg, Zr, Sr, Y, Li, W, La, Na, Fe, Cu, Zn, and Sb.

[0147] Further optionally, the raw materials containing doped elements include one or more of oxides, hydroxides, sulfates, carbonates, nitrates, and phosphates containing doped elements.

[0148] In some embodiments, the preparation method of the positive electrode active material further includes, before the second sintering: mixing the product from the first crushing with a first coating agent.

[0149] The first coating agent may contain a first coating element, which includes one or more of Al, Ti, Mg, Zr, Y, Li, W, and Nb.

[0150] Optionally, the first coating agent includes one or more of oxides, hydroxides, sulfates, carbonates, nitrates, and phosphates containing the first coating element.

[0151] Optionally, the preparation method of the positive electrode active material further includes, before the third sintering, mixing the product from the second crushing with a second coating agent. This introduces coating elements onto the surface of the positive electrode active material particles, improving the structural stability of the positive electrode active material.

[0152] Optionally, the second coating agent contains a second coating element, which includes one or more of Al, Ti, Zr, Li, W, Na, and Nb.

[0153] Optionally, the second coating agent includes one or more of oxides, hydroxides, carbonates, and phosphates containing the second coating element.

[0154] In some implementations, a co-precipitation method is used to prepare the precursor of the positive electrode active material.

[0155] Optionally, taking lithium nickel cobalt manganese-based oxide as an example, the preparation of the positive electrode active material precursor includes: obtaining a metal salt solution by mixing nickel salt, cobalt salt, and manganese salt. Then, pure water is added to a reaction vessel, and nitrogen gas is used to control the temperature inside the reaction vessel to 60℃~70℃. Ammonia water is added to adjust the pH value inside the reaction vessel to 11.2~11.8. Then, the metal salt solution is added to carry out a co-precipitation reaction to obtain positive electrode active material precursor particles.

[0156] Optionally, the temperature inside the reactor can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, or any value within the range of any two of the above values.

[0157] Optionally, the pH value inside the reactor can be 112, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, or any value within the range of any two of the above values.

[0158] Optionally, the concentration of ammonia water is 2 g / L to 8 g / L. For example, the concentration of ammonia water can be 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, or any value within the range of any two of the above values.

[0159] Optionally, the pH value inside the reactor can be adjusted using a sodium hydroxide solution.

[0160] Optionally, the nickel salt, cobalt salt, and manganese salt are nickel sulfate, cobalt sulfate, and manganese sulfate, respectively.

[0161] Optionally, in the metal salt solution, the sum of the molar concentrations of nickel ions, cobalt ions, and manganese ions is 1.4 mol / L to 1.8 mol / L. For example, in the metal salt solution, the sum of the molar concentrations of nickel ions, cobalt ions, and manganese ions can be 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, or any value within the range of any two of the above values.

[0162] Another embodiment of this application provides a positive electrode active material. The positive electrode active material comprises primary particles containing a lithium transition metal oxide. The transition metal element in the lithium transition metal oxide includes nickel and cobalt. The molar amount of nickel accounts for 50% to 75% of the total molar amount of the transition metal elements. The average particle size of the primary particles is 1.5 μm to 2.6 μm, and the mass concentration of cobalt on the surface of the primary particles is 4.4% to 6.5%.

[0163] Optionally, the positive electrode active material includes the positive electrode active material prepared by the above-described method for preparing positive electrode active materials.

[0164] Optionally, the positive electrode active material includes the positive electrode active material defined in the above-mentioned lithium-ion secondary battery.

[0165] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0166] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0167] Example 1

[0168] (1) Precursor of positive electrode active material

[0169] Nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in a molar ratio of 0.7:0.1:0.2 to obtain a sulfate solution with a total molar concentration of nickel, cobalt, and manganese ions of 1.6 mol / L. Pure water was then added to a reactor, nitrogen gas was introduced, and the reaction temperature was controlled at 65°C. Ammonia solution with a concentration of 4 g / L was added, and sodium hydroxide solution was introduced to adjust the pH of the reactor to 11.4. Simultaneously, the sodium hydroxide solution and the sulfate solution were introduced to carry out a co-precipitation reaction. During the feeding process, the environment inside the reactor was kept constant. The clear liquid in the reactor was filtered out using a microporous filter to maintain a constant liquid level. Feeding continued, and the material in the reactor was continuously concentrated, with particles continuously growing until the particle size reached 3.6 μm. After feeding was completed, the precursor of the positive electrode active material (Ni) was obtained. 0.7 Co 0.1 Mn 0.2 )OH2.

[0170] (2) Positive electrode active material

[0171] The positive electrode active material precursor and LiOH·H2O were thoroughly mixed at a mass ratio of 949.2:450.3, and then subjected to a first sintering at 935℃ under pure oxygen conditions for 12 hours. The resulting product was then subjected to a first air jet milling treatment, with an inlet pressure of 0.35 MPa and a feeding frequency of 35 Hz, to obtain a first fragment. The first fragment was mixed with 18.7 g of cobalt hydroxyl oxide. A second sintering was then performed at 770℃ under pure oxygen conditions for 8 hours. The resulting product was then subjected to a second air jet milling treatment, with an inlet pressure of 0.35 MPa and a feeding frequency of 35 Hz, to obtain a second fragment. The second fragment was mixed with a coating agent. Finally, a third sintering was performed at 500℃ under pure oxygen conditions for 6 hours, to prepare the positive electrode active material LiNi. 0.68 Co 0.12 Mn 0.2 O2.

[0172] SEM image of the positive electrode active material as follows Figure 4 As shown. By Figure 4 It can be seen that the average particle size of the primary particles in the positive electrode active material is 2.2 μm, and the total number of aggregated particles with a particle size of more than 5 μm is 1.

[0173] EPMA surface scan of the positive electrode active material is shown below. Figure 5 As shown. By Figure 5 It can be seen that the mass concentration of cobalt on the surface of the primary particles is 5.6%, while the mass concentration of cobalt inside the primary particles is 4%.

[0174] The particle size distribution curve of primary particles in the positive electrode active material is as follows: Figure 6 As shown, by Figure 6 It can be seen that the half-peak width is 2 μm in the particle size distribution curve of the primary particles.

[0175] (3) Positive electrode plate

[0176] The above-mentioned positive electrode active material, super-P, CNT, and PVDF were mixed in a mass ratio of 96:1.5:0.5:2 and dispersed in the solvent N-methylpyrrolidone to obtain a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil with a thickness of 13 μm, dried, and cold-pressed to obtain a positive electrode sheet. The compacted density of the positive electrode sheet was 3.45 g / cm³. 3 .

[0177] (4) Negative electrode plate

[0178] Artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in a deionized water solvent system at a mass ratio of 95:2:2:1 to obtain a negative electrode slurry. The negative electrode slurry was coated onto copper foil, dried, and cold-pressed to obtain a negative electrode sheet. The compacted density of the negative electrode sheet was 1.7 g / cm³. 3 .

[0179] (5) Separating membrane

[0180] A PE separator with a thickness of 7μm.

[0181] (6) Electrolyte

[0182] Lithium salt LiPF6 was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 35:65 and mixed thoroughly to obtain an electrolyte. The molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0183] (7) Lithium-ion secondary battery

[0184] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The cells are then wound to obtain a bare battery cell. The bare battery cell is placed in outer packaging, injected with electrolyte, and undergoes processes such as encapsulation, electrolyte injection, formation, and venting to obtain a lithium-ion secondary battery.

[0185] Examples 2 to 10, Comparative Examples 1 to 4

[0186] By adjusting the sintering temperature, time, pulverization intensity, and amount of cobalt hydroxyoxide in the preparation method of the positive electrode active material, the positive electrode active materials of Examples 2 to 10 and Comparative Examples 1 to 4 were obtained. The differences between Examples 2 to 10 and Comparative Examples 1 to 4 and Example 1 are shown in Table 1.

[0187] Test case

[0188] (1) The cycle performance of the lithium-ion secondary batteries obtained in the examples and comparative examples was tested. The test method was as follows: at 45°C, the lithium-ion secondary battery was charged at a constant current of 1C to 4.4V, then charged at a constant voltage of 4.4V to the cutoff current of 0.05C, rested for 10 minutes, and then discharged at a constant current of 1C to 2.8V, and rested for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this time was recorded as C0. This charge-discharge cycle process was repeated for the same battery, and the discharge capacity Cn of the 1st cycle, 2nd cycle, ... nth cycle was recorded. The cycle capacity retention rate of the battery after 200 cycles was recorded as P200 = C200 / C0 × 100%. The results are shown in Table 1.

[0189] (2) The DC internal resistance of the lithium-ion secondary batteries obtained in the examples and comparative examples was tested. The test method was as follows: the lithium-ion secondary batteries were charged at a constant current rate of 0.33C to 4.4V in a constant temperature environment of 25℃, then charged at a constant voltage of 4.4V until the current dropped to 0.05C, and then discharged at a constant current rate of 0.33C to 2.8V to obtain the first discharge capacity. Then the state of charge (SOC) of the battery was adjusted to 20% and placed in a constant temperature chamber at -25℃, and discharged at a rate of 4C for 30s. The voltage difference before and after discharge divided by the current density is the DC internal resistance of the battery at that SOC. The results are shown in Table 1. It can be understood that the power performance of lithium-ion secondary batteries is related to the DC internal resistance of the battery. Generally, the higher the DC internal resistance, the worse the power performance of the battery.

[0190] Table 1

[0191]

[0192] In Table 1, the total number of aggregated particles represents the total number of aggregated particles with a diameter greater than 5 μm in the positive electrode active material. The half-width at half-maximum (WHM) of the primary particle distribution represents the half-maximum width of the particle size distribution curve of the primary particles.

[0193] As can be seen from Table 1, when the average particle size of the primary particles and the mass concentration of cobalt on the surface of the primary particles are within a suitable range, lithium-ion secondary batteries can achieve both good power performance and good cycle performance.

[0194] For example, as can be seen from Examples 1 to 4, Example 10, and Comparative Examples 1 to 2, when the average particle size of the primary particles is 1.5 μm to 2.6 μm, the battery can achieve both good power performance and good cycle performance. However, when the average particle size of the primary particles is too large or too small, the battery cannot achieve both good power performance and good cycle performance.

[0195] For example, as can be seen from Examples 5 to 6 and Comparative Examples 3 to 4, when the mass concentration of cobalt on the surface of the primary particles is 4.4% to 6.5%, the battery can achieve both good power performance and good cycle performance. However, when the mass concentration of cobalt on the surface of the primary particles is too high or too low, the battery cannot achieve both good power performance and good cycle performance.

[0196] Furthermore, as can be seen from Examples 1 and 7 to 9, when the total number of agglomerated particles with a particle size of 5 μm or larger in the positive electrode active material is less than or equal to 5, the battery can better balance good power performance and good cycle performance.

[0197] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0198] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A lithium-ion secondary battery, characterized in that, It includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active layer, the positive electrode active material of the positive electrode active layer includes primary particles containing lithium transition metal oxide, the primary particles are particles composed of no more than 5 single particles; The transition metal elements in the lithium-containing transition metal oxide include nickel and cobalt, and the molar amount of nickel accounts for 50% to 75% of the total molar amount of the transition metal elements. The average particle size of the primary particles is 1.5 μm to 2.6 μm, and the average particle size of the primary particles represents the average particle size of the primary particles when the lithium-ion secondary battery is fully discharged. The mass concentration of cobalt on the surface of the primary particles is 4.4% to 6.5%; the surface of the primary particles refers to the area of ​​the primary particles with a thickness of less than 0.5 μm along the direction from the outside to the inside; the mass concentration of cobalt on the surface of the primary particles refers to the mass concentration of cobalt on the surface of the primary particles when the lithium-ion secondary battery is fully discharged; the mass concentration of cobalt on the surface of the primary particles is tested using EPMA. In the scanning electron microscope image of more than 2000 primary particles of the positive electrode active material, the total number of aggregated particles with a particle size of more than 5 μm in the positive electrode active material is less than or equal to 9.

2. The lithium-ion secondary battery according to claim 1, characterized in that, Nickel accounts for 65% to 70% of the total molar amount of transition metals.

3. The lithium-ion secondary battery according to claim 1, characterized in that, The particle size distribution curve of the primary particles has a half-peak width of 1.5 μm to 2.5 μm.

4. The lithium-ion secondary battery according to claim 1, characterized in that, The mass concentration of cobalt inside the primary particles is 1.5% to 4.4%.

5. The lithium-ion secondary battery according to claim 1, characterized in that, The lithium-containing transition metal oxide accounts for 90% to 100% of the mass percentage of the positive electrode active material.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that, The charging cutoff voltage of the lithium-ion secondary battery is 4.3V~4.5V.

7. A method for preparing a positive electrode active material, wherein the positive electrode active material is the positive electrode active material in the lithium-ion secondary battery according to any one of claims 1 to 6, characterized in that, Includes the following steps: A positive electrode active material precursor and a lithium source are mixed to obtain a preliminary mixture. The positive electrode active material precursor includes a transition metal element, including nickel, and the molar amount of nickel accounts for 50% to 75% of the total molar amount of the transition metal element. The initial mixture is subjected to a first sintering and a first crushing in sequence. The product of the first crushing is mixed with a cobalt-containing additive, which includes one or more of cobalt hydroxyl oxide, cobalt monoxide, and cobalt tetroxide. Then, a second sintering and a second crushing are performed in sequence, followed by a third sintering to prepare the positive electrode active material. The temperature of the first sintering is 900℃~990℃, the temperature of the second sintering is 700℃~800℃, and the temperature of the third sintering is 300℃~600℃.

8. The method for preparing the positive electrode active material according to claim 7, characterized in that, It meets one or more of the following characteristics: (1) The cobalt-containing additive accounts for 0.5% to 2.5% of the mass percentage of the product from the first crushing; (2) The first sintering time is 7h~18h; (3) The second sintering time is 4h~14h; (4) The third sintering time is 3h~12h.

9. A positive electrode active material, characterized in that, The positive electrode active material includes primary particles containing lithium transition metal oxides, wherein the primary particles are composed of no more than 5 individual particles. The transition metal elements in the lithium-containing transition metal oxide include nickel and cobalt, with the molar amount of nickel accounting for 50% to 75% of the total molar amount of the transition metal elements. The average particle size of the primary particles is 1.5 μm to 2.6 μm, where the average particle size represents the average particle size of the primary particles under full discharge conditions of the lithium-ion secondary battery. The lithium-ion secondary battery includes a positive electrode sheet, which includes a positive active layer, and the positive active layer includes the positive active material. The mass concentration of cobalt on the surface of the primary particles is 4.4% to 6.5%; the surface of the primary particles refers to the area of ​​the primary particles with a thickness of less than 0.5 μm along the direction from the outside to the inside; the mass concentration of cobalt on the surface of the primary particles refers to the mass concentration of cobalt on the surface of the primary particles when the lithium-ion secondary battery is fully discharged; the mass concentration of cobalt on the surface of the primary particles is tested using EPMA.

10. An electrical device, characterized in that, The lithium-ion secondary battery includes any one of claims 1 to 6.

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