Positive electrode active material precursor and preparation method and application thereof

Abstract

The invention provides a positive electrode active material precursor and a preparation method and application thereof, the precursor has a chemical composition of NiaCobMnc (OH) 2, 0.1 < = a < = 0.5, 0 < = b < = 0.5, and 0.5 < = c < = 0.9; the positive electrode active material precursor comprises secondary particles agglomerated by a plurality of crystal whiskers, the crystal whiskers comprise a plurality of first crystal whiskers, and the length-diameter ratio of the first crystal whiskers is 1.3-4.5; wherein the first crystal whiskers comprise cross-linked crystal whiskers, and the cross-linked crystal whiskers are connected with at least five first crystal whiskers. The precursor provided by the invention is helpful for obtaining a high-manganese positive electrode active material with a stable structure, so that the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode active material precursor and a preparation method and application thereof. Background Art

[0002] Secondary batteries, as energy storage devices that can be repeatedly charged and discharged, have become an important component of the modern energy system. In the consumer electronics field, secondary batteries are widely used in portable electronic devices such as smartphones, laptops, and tablets, providing them with efficient and stable power supply. In the transportation field, lithium-ion batteries have become the main power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs) due to their high energy density and long cycle life, and have gradually expanded to application scenarios such as electric ships and rail transit. As the global energy structure shifts towards a low-carbon economy, the market demand for secondary batteries continues to grow, and the requirements for their energy density, safety, and cost-effectiveness are also increasing.

[0003] Among the many lithium-ion battery cathode materials, nickel-cobalt-manganese ternary materials have become the mainstream choice for power batteries due to their high energy density, good cycle stability and moderate cost. Compared with traditional lithium cobalt oxide and lithium iron phosphate, ternary materials can achieve a balance between energy density and safety by adjusting the ratio of nickel, cobalt and manganese. Among them, high manganese ternary materials (such as NCM523, NCM433, etc.) show unique advantages due to the introduction of manganese elements. Manganese resources are abundant and low in price, which can significantly reduce material costs; at the same time, Mn 4+ The stable electronic structure can effectively inhibit lattice oxygen precipitation and improve the safety of the material.

[0004] Although high manganese ternary materials have many advantages, they often exhibit lower-than-expected cycle performance and storage performance during the charging and discharging process, which greatly limits the application and promotion of this material. Summary of the Invention

[0005] The present application provides a positive electrode active material precursor having a high manganese content. By controlling the morphology and structure of its primary particles, it is helpful to obtain a high manganese positive electrode active material with a stable structure.

[0006] The present application provides a method for preparing a positive electrode active material precursor, which is used to prepare the positive electrode active material precursor.

[0007] The present application provides a positive electrode active material, which is a high-manganese binary / ternary material and has excellent structural stability.

[0008] The present application provides a positive electrode sheet, which includes the above-mentioned positive electrode active material, thereby helping to improve the first coulombic efficiency and cycle stability of the battery.

[0009] The present application provides a battery having the advantages of high gram capacity and long cycle life.

[0010] The present application provides a positive electrode active material precursor having Ni a Co b Mn c The chemical composition of (OH)2, wherein 0.1≤a≤0.5, 0≤b≤0.5, 0.5≤c≤0.9;

[0011] The positive electrode active material precursor includes secondary particles formed by agglomeration of multiple whiskers, the whiskers include multiple first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5; wherein, the first whiskers include cross-linked whiskers, and the cross-linked whiskers are connected to at least 5 first whiskers.

[0012] The positive electrode active material precursor as described above, wherein the ratio of the number of the cross-linked whiskers to the number of the first whiskers is not less than 50%.

[0013] The positive electrode active material precursor as described above, wherein the length of the first whisker is 1000 nm ≤ ≤ 4000 nm, and the thickness is ≥ 500 nm.

[0014] In the positive electrode active material precursor as described above, the whiskers further include second whiskers, and the thickness of the second whiskers is ≤100 nm and the length is ≤2000 nm.

[0015] In the positive electrode active material precursor as described above, among the at least five first whiskers connected to the cross-linked whiskers, at most three first whiskers have an angle of ≤30° with the cross-linked whiskers.

[0016] The positive electrode active material precursor as described above, wherein the first whiskers further include anisotropic whiskers, the anisotropic whiskers are connected to N first whiskers, and among the N first whiskers, at most M first whiskers have an angle ≤30° with the anisotropic whiskers, N≥3, M≤3.

[0017] The positive electrode active material precursor as described above, wherein among the M first whiskers, X first whiskers are connected through the anisotropic whiskers, and X≤M.

[0018] The positive electrode active material precursor as described above, wherein the D50 of the secondary particles is 8-16 μm and the tap density is 1.2-2.1 g / cm 3 , the specific surface area is 5~25㎡ / g.

[0019] The present application provides a method for preparing a positive electrode active material precursor as described in any one of the above, comprising the following steps:

[0020] 1) Adding a metal salt solution and a precipitant solution to the reaction base liquid at 50-70° C. to perform a first coprecipitation reaction, controlling the pH of the reaction system to 11.2-11.8 and the complexing agent to 0, until the median particle size D1 of the secondary particles reaches 2.0 μm, thereby obtaining a first coprecipitation product system;

[0021] 2) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the first coprecipitation product system to perform a second coprecipitation reaction, and controlling the pH of the reaction system to be 10.9-11.5 until the median particle size of the secondary particles is D2, thereby obtaining a second coprecipitation product system;

[0022] 3) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the second coprecipitation product system to perform a third coprecipitation reaction, and controlling the pH of the reaction system to be 10.6-11.2, until the median particle size of the secondary particles reaches D3, thereby obtaining a third coprecipitation product system;

[0023] 4) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the third coprecipitation product system to perform a fourth coprecipitation reaction, and controlling the pH of the reaction system to be 10.3-10.9, until the median particle size of the secondary particles reaches a preset value D0, thereby obtaining the positive electrode active material precursor;

[0024] D2=1 / 3D0, D3=1 / 2D0, and C 络 ≤3C 盐 , C 络 is the concentration of the complexing agent in the reaction system of step 2) to step 4), C 盐 is the concentration of the metal salt solution.

[0025] The preparation method as described above, wherein the rotation speed V1 of step 1) is 700-900 rpm, the rotation speed V2 of step 2) is 70%-80% of V1, the rotation speed V3 of step 3) is 70%-80% of V2, and the rotation speed of step 4) is 70%-80% of V3; and / or,

[0026] The solid content of the reaction system of the fourth coprecipitation reaction is greater than the solid content of the reaction systems of the first coprecipitation reaction, the second coprecipitation reaction and the third coprecipitation reaction.

[0027] The present application provides a positive electrode active material having Li x Ni a Co b Mn c The chemical composition of O2, where 0.9≤x≤1.1, 0.1≤a≤0.5, 0≤b≤0.5, 0.5≤c≤0.9;

[0028] The positive electrode active material includes secondary particles formed by agglomerating multiple whiskers, wherein the whiskers include multiple first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5; wherein the first whiskers include cross-linked whiskers, and the cross-linked whiskers are connected to at least 5 first whiskers.

[0029] The present application provides a positive electrode sheet, comprising the positive electrode active material described above.

[0030] The present application provides a battery, comprising the positive electrode sheet described above.

[0031] The present application provides a positive electrode active material precursor having a high manganese content. By regulating the aspect ratio of the precursor primary particles and constructing a cross-linked structure between the primary particles, the sintering behavior and microstructure of the material can be significantly improved, and the mechanical strength of the secondary particles can be significantly improved, so that the precursor material can obtain a high-manganese binary / ternary positive electrode active material with higher structural stability during the sintering process with a lithium source, thereby improving the cycle performance, storage performance and first efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a scanning electron microscope image of the positive electrode active material precursor of Example 1 of the present application at a magnification of 1000;

[0033] Figure 2 is a scanning electron microscope image of the positive electrode active material precursor of Example 1 of the present application at a magnification of 5000;

[0034] Figure 3 is a scanning electron microscope image of the positive electrode active material precursor of Example 1 of the present application at a magnification of 10,000;

[0035] Figure 4 : This is a cross-sectional electron micrograph of the positive electrode active material precursor of Example 1 of the present application at a magnification of 9000;

[0036] Figure 5 is a scanning electron microscope image of the positive electrode active material precursor of Example 2 of the present application at a magnification of 1000;

[0037] Figure 6 10,000 times the scanning electron microscope image of the positive electrode active material precursor of Example 2 of the present application;

[0038] Figure 7 : This is a cross-sectional electron micrograph of the positive electrode active material precursor of Example 2 of the present application at a magnification of 6000;

[0039] Figure 8 1000 times the scanning electron microscope image of the positive electrode active material precursor of Comparative Example 1 of the present application;

[0040] Figure 9 10,000 times the scanning electron microscope image of the positive electrode active material precursor of Comparative Example 1 of the present application;

[0041] Figure 10 This is a cross-sectional electron micrograph of the positive electrode active material precursor of Comparative Example 1 of the present application at a magnification of 8000;

[0042] Figure 11 is a scanning electron microscope image of the positive electrode active material of Example 1 of the present application at a magnification of 10,000;

[0043] Figure 12 1 is a scanning electron microscope image of the positive electrode active material of Example 2 of the present application at a magnification of 10,000. DETAILED DESCRIPTION

[0044] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] In order to improve the structural stability of high manganese binary / ternary positive electrode active materials during the cycle process, the inventors studied the morphology of high manganese binary / ternary positive electrode active material precursors. The inventors speculate that during the charge and discharge process of the battery, the repeated insertion and extraction of lithium ions will cause the lattice volume to change, thereby generating anisotropic stress inside the particles and causing cracks, and the more single the crack extension direction and the faster the extension speed, the worse the structural stability of the positive electrode active material. Therefore, the inventors took the inhibition of crack generation and the control of crack extension as the starting point of the research, in order to improve the structural stability of the high manganese binary / ternary positive electrode active material prepared from the high manganese binary / ternary positive electrode active material precursor.

[0046] Based on this, the first aspect of the present application provides a positive electrode active material precursor having Ni a Co b Mn c The chemical composition of (OH)2 is as follows: 0.1≤a≤0.5, 0≤b≤0.5, 0.5≤c≤0.9;

[0047] The positive electrode active material precursor includes secondary particles formed by agglomeration of multiple whiskers, the whiskers include multiple first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5; wherein, the first whiskers include cross-linked whiskers, and the cross-linked whiskers are connected to at least 5 first whiskers.

[0048] In detail, when b is 0, the cathode active material precursor of the present application is a nickel-manganese binary precursor with a high manganese content; when b>0, the cathode active material precursor of the present application is a nickel-cobalt-manganese ternary precursor with a high manganese content.

[0049] The cathode active material precursor of the present application includes secondary particles formed by agglomeration of multiple whiskers, and the whiskers are primary particles. Among them, the whiskers in the present application include multiple first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5. It can be understood that when the ratio of the length to the thickness of the whiskers is 1.3-4.5, the whiskers are the first whiskers mentioned in the present application.

[0050] In the positive electrode active material precursor of the present application, at least part of the first whiskers are cross-linked whiskers. It should be explained that in the present application, when a first whisker is taken as the main body, at least 5 first whiskers are connected to the first whisker as the main body (the two have an angle greater than 0° and less than 180°), then the first whisker as the main body is called a cross-linked whisker. In the present application, the number of first whiskers connected to the cross-linked whisker is at least 5, for example, it can be 5, 6, 7, 8 or more. As to whether the first whisker connected to the cross-linked whisker is a cross-linked whisker, the present application does not make a specific limitation. It can be a cross-linked whisker or not, as long as it has an aspect ratio of 1.3-4.5.

[0051] The positive electrode active material precursor of the present application can obtain a positive electrode active material with excellent structural stability. The main reason is that: on the one hand, during the sintering process of the positive electrode active material, the coordinated optimization of the cross-linked structure and the aspect ratio parameters of the precursor primary particles plays a decisive role in the stability of the final crystal structure. Specifically, the cross-linked whiskers introduce a suitable cross-linked structure into the precursor, so that a three-dimensional interlocking complex topological morphology is formed between the primary particles, which fundamentally changes the way stress is transferred and cracks propagate, so that the cracks will encounter the obstruction of the first whiskers with a suitable aspect ratio of different orientations during the propagation process, and are forced to change direction or even terminate. This cross-linked structure with a mechanical interlocking effect can make the crack propagation path more tortuous and significantly delay the fracture process. At the same time, the primary particles with the above-mentioned aspect ratio have isotropic volume change characteristics, which evenly disperse the volume strain in the cycle process to the entire interior of the particles, avoiding lattice rupture caused by local stress concentration in the primary particles. The synergistic effect of the two is particularly prominent in high-pressure cycles. The cross-linked network disperses the phase change stress through multi-point support, while the primary particles with appropriate aspect ratio reduce the stress accumulation at the grain boundaries by reducing the degree of lattice distortion, thereby significantly improving the structural stability of the positive electrode active material obtained by sintering the precursor.

[0052] On the other hand, in terms of interface stability, the synergistic effect of the cross-linked whiskers and the special aspect ratio in the positive electrode active material precursor can reduce the direct contact between the electrolyte and the positive electrode active material, significantly inhibiting the interface side reactions. Specifically, the cross-linked network composed of the cross-linked whiskers in the precursor can form a continuous barrier in the positive electrode active material, effectively blocking the permeation channel of the electrolyte, thereby reducing the contact opportunity between the electrolyte and the transition metal ions in the positive electrode active ions. At the same time, the first whiskers with the above aspect ratio also help to reduce the specific surface area of the positive electrode active material, reduce the contact area between the positive electrode active material and the electrolyte, and further reduce the interfacial reaction activity.

[0053] Therefore, the synergistic optimization of the cross-linked whiskers and the first whiskers with an appropriate aspect ratio in the cathode active material precursor of the present application provides a feasible technical path for constructing a cathode active material with high stability and long life.

[0054] In a specific embodiment, in the positive electrode active material precursor of the present application, the ratio of the number of cross-linked whiskers to the first whiskers is not less than 50%.

[0055] Specifically, each secondary particle contained cross-linked whiskers. Five secondary particles were examined under a scanning electron microscope (SEM) (5000x magnification). In the SEM image, the number of cross-linked whiskers in each secondary particle and the number of first whiskers in that image were counted. The ratio of these two values was the cross-linked whisker to first whisker ratio for that secondary particle. The average of the cross-linked whisker to first whisker ratios for the five secondary particles was used to obtain the cross-linked whisker to first whisker ratio.

[0056] The present application further ensures the degree of cross-linking of the first whiskers in each secondary particle by controlling the proportion of the cross-linked whiskers in the first whiskers, thereby further increasing the tortuosity of the crack propagation path, and ultimately reducing the cracking probability of the positive electrode active material, significantly inhibiting the dissolution of transition metal ions and the occurrence of interfacial side reactions, and improving the cycle performance of the battery.

[0057] Furthermore, when the length of the first whisker is 1000nm≤4000nm and the thickness is ≥500nm, the shrinkage anisotropy of the sintering can be further reduced when the positive electrode active material precursor is sintered with the lithium source, which not only effectively improves the phase change stress dispersion efficiency of the positive electrode active material, but also further improves the tortuosity of the crack propagation path, thereby enabling the positive electrode active material to maintain higher structural stability during the process of lithium ion insertion and extraction.

[0058] In addition to the first whiskers, the cathode active precursor material of the present application also includes second whiskers. Specifically, among the whiskers that make up the secondary particles of the present application, whiskers with a thickness of ≤100nm and a length of ≤2000nm are all secondary whiskers. Second whiskers of this size help provide better structural support for the first whiskers, thereby making the stress in the system more dispersed, which is conducive to further enhancing the structural stability of the cathode active material after sintering.

[0059] Furthermore, among the at least five first whiskers connected to the cross-linked whisker, at most three first whiskers have an angle of ≤30° with the cross-linked whisker.

[0060] As mentioned above, the cross-linked structure formed by the cross-linked whiskers has a significant barrier effect on crack extension. Therefore, in order to further increase the complexity of the cross-linked structure, when at most 3 of the at least 5 first whiskers connected to the cross-linked whiskers have an angle of ≤30° with the cross-linked whiskers, the complexity of the cross-linked structure is higher. The complex cross-linked structure can enhance the stress dispersion and load-bearing capacity within the material, effectively regulate the stress state of the material, reduce the risk of structural damage to the material due to crack extension, and have a more significant effect on improving the structural stability of the positive electrode active material.

[0061] In a specific embodiment, in the cathode active material precursor of the present application, the first whiskers further include anisotropic whiskers. The anisotropic whiskers are connected to N first whiskers, and among the N first whiskers, at most M first whiskers have an angle of ≤30° with the anisotropic whiskers, where N≥3 and M≤3;

[0062] Specifically, when a first whisker is taken as the main body, the first whisker as the main body is connected to at least three first whiskers respectively, and among these at least three first whiskers, at most three first whiskers have an angle of no more than 30° with the first whisker as the main body, then the first whisker as the main body is the anisotropic whisker described in this application.

[0063] The inventors discovered that when anisotropic whiskers are introduced into the cathode active material precursor, they spontaneously construct a more complex three-dimensional stress network. This network enhances stress dispersion and load-bearing capacity within the material, effectively regulating the material's stress state. Crucially, it significantly increases resistance to crack propagation, making it difficult for cracks to continue to propagate within the material, thereby reducing the risk of structural damage caused by crack propagation.

[0064] Furthermore, when X of the M first whiskers connected to the anisotropic whiskers are through-connected to the anisotropic whiskers, the crack propagation resistance is more significantly improved. The through-connection referred to in this application means that the X first whiskers pass through the interior of the anisotropic whiskers.

[0065] It should be pointed out that when N≥5, the anisotropic whiskers are also the cross-linked whiskers mentioned above in this application; similarly, when the aforementioned cross-linked whiskers have at most three first whiskers connected to them and the angle between them is ≤30°, the cross-linked whiskers can also be called the anisotropic whiskers mentioned above in this application.

[0066] In addition, in the cathode active material precursor of the present application, primary particles aggregate with each other in a radial arrangement to form secondary particles. This orderly arrangement helps to form more lithium ion insertion and extraction channels.

[0067] It should be noted that the angle mentioned in this application refers to the minimum angle between two connected whiskers.

[0068] In a specific embodiment, the secondary particles in the present application have a D50 of 8 to 16 μm, a tap density TD of 1.2 to 2.1, and a specific surface area BET of 5 to 25 m2 / g.

[0069] In the cathode active material precursor described in this application, the D50, tap density, and specific surface area of the secondary particles are limited to the aforementioned ranges, establishing a stable system with multi-scale constraints. This system, through the optimized balance of physical structure and chemical properties, jointly ensures the long-term cycling stability of the cathode active material prepared from this cathode active material precursor.

[0070] D50 and tap density play a key role in ensuring particle structural integrity. This D50 ensures uniform densification and shrinkage of secondary particles during sintering, preventing oversintering of undersized particles and residual porosity in oversized particles. Simultaneously, optimized tap density ensures ideal particle packing, forming a continuous network with appropriate porosity. This balance provides the positive electrode active material with excellent mechanical strength and lithium-ion transport pathways.

[0071] In terms of surface stability control, the specific surface area determines the degree of contact between the material and the electrolyte and needs to be inversely balanced with the D50. Although a smaller specific surface area can reduce the number of active sites for side reactions, it must be combined with an appropriate D50 to ensure a sufficient reaction interface. In this application, a D50 of 8-16μm and a specific surface area of 5-25㎡ / g are used to achieve a balance between suppressing side reactions and maintaining reaction kinetics.

[0072] A second aspect of the present application provides a method for preparing a positive electrode active material precursor, comprising the following steps:

[0073] 1) Adding a metal salt solution and a precipitant solution to the reaction base liquid at 50-70° C. to perform a first coprecipitation reaction, controlling the pH of the reaction system to 11.2-11.8 and the complexing agent to 0, until the median particle size D1 of the secondary particles reaches 2.0 μm, thereby obtaining a first coprecipitation product system;

[0074] 2) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the first coprecipitation product system to perform a second coprecipitation reaction, and controlling the pH of the reaction system to be 10.9-11.5 until the median particle size of the secondary particles is D2, thereby obtaining a second coprecipitation product system;

[0075] 3) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the second coprecipitation product system to perform a third coprecipitation reaction, and controlling the pH of the reaction system to be 10.6-11.2, until the median particle size of the secondary particles reaches D3, thereby obtaining a third coprecipitation product system;

[0076] 4) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the third coprecipitation product system to perform a fourth coprecipitation reaction, and controlling the pH of the reaction system to be 10.3-10.9, until the median particle size of the secondary particles reaches a preset value D0, thereby obtaining the positive electrode active material precursor;

[0077] D2=1 / 3D0, D3=1 / 2D0, and C 络 ≤3C 盐 , C 络为 The concentration of the complexing agent in the reaction system of step 2) to step 4) is the concentration of the metal salt solution.

[0078] In detail, at the beginning of the preparation, the preparation of the metal salt solution, the precipitant solution, the complexing agent solution, and the reaction base liquid can be completed first. Among them, the metal salt solution refers to an aqueous solution including at least nickel salt and manganese salt. Furthermore, when b>0, the metal salt solution also includes cobalt salt. The present application does not limit the anion of the metal salt, for example, it can be a soluble salt such as sulfate, nitrate, acetate, etc.; the precipitant solution is used to precipitate the metal ions in the metal salt solution, which can generally be an aqueous sodium hydroxide solution; the complexing agent solution can be, for example, an ammonia solution. The present application does not specifically limit the concentration of the above solution, which can be a conventional concentration in the art.

[0079] In step 1), at 50-70°C, at the beginning of the reaction, a metal salt solution and a precipitant solution are introduced into the reaction base solution including the precipitant solution at a certain rate, causing a first coprecipitation reaction. During the reaction, the pH of the system is controlled to be 11.2-11.8 by controlling the introduction rate of the precipitant solution. During the first coprecipitation reaction, the metal salt and the precipitant react to form a metal hydroxide precipitate. This first coprecipitation reaction is the nucleation stage of the positive electrode active material precursor of the present application. It should be noted that in step 1), the complexing agent solution introduced in the present application is 0, that is, no complexing agent solution is introduced. The aforementioned pH value and the absence of a complexing agent are not only conducive to obtaining the first whiskers of the size of the present application, but also can reduce the stacking order of the first whiskers, making the staggered stacking of the first whiskers more compact, thereby allowing more first whiskers to present an interlaced structure, which is conducive to the formation of the cross-linked whiskers and anisotropic whiskers of the present application. When the median particle size D1 of the secondary particles in the system is 2.0 μm, the first coprecipitation system is obtained.

[0080] Subsequently, in step 2), a metal salt solution, a precipitant solution, and a complexing agent solution are introduced into the first coprecipitation system to conduct a second coprecipitation reaction. During the reaction, the pH of the system is controlled to 10.9-11.5 by controlling the rate at which the precipitant solution is introduced. During the second coprecipitation reaction, the introduction of the complexing agent promotes the precipitation of the salt solution on the original secondary particles, forming a densely packed whisker. This results in a sample with a higher tap density and a smaller specific surface area. When the median particle size D2 of the secondary particles in the system is 1 / 3 D0, a second coprecipitation system is obtained.

[0081] The metal salt solution, precipitant solution, and complexing agent solution are continuously introduced into the second coprecipitation system to conduct a third coprecipitation reaction, and the pH of the reaction system is controlled to be 10.6-11.2 by controlling the introduction rate of the precipitant solution until the median particle size of the secondary particles is D3, thereby obtaining a third coprecipitation product system. Finally, the metal salt solution, precipitant solution, and complexing agent solution are introduced into the third coprecipitation product system, and the pH of the reaction system is controlled to be 10.3-10.9 by controlling the introduction rate of the precipitant solution until the median particle size of the secondary particles is a preset value D0, thereby obtaining a positive electrode active material precursor.

[0082] It is important to note that in the reaction systems of steps 2) through 4), the concentration of the complexing agent in the reaction system must be controlled so that it does not exceed three times the concentration of the metal salt solution. For example, when the concentration of the metal salt solution introduced into the system is 1.5 mol / L, the complexing agent concentration in the reaction system should be controlled within the range of 0 < x < 4.5 g / L.

[0083] Furthermore, in the reaction systems of steps 2) to 4), the concentration of the complexing agent in each reaction system may be the same, partially the same, or completely different. For example, after controlling the concentration of the complexing agent in the reaction system of step 2) to not exceed three times the concentration of the metal salt solution, the flow rate of the complexing agent can be adjusted in steps 3) and 4) to maintain the same concentration of the complexing agent in the system as in step 2). Alternatively, after controlling the concentration of the complexing agent in the reaction system of step 2) to not exceed three times the concentration of the metal salt solution, the flow rate of the complexing agent can be adjusted so that the concentration of the complexing agent in the reaction systems of steps 3) and 4) is independently higher than the concentration of the complexing agent in step 2), but still not more than three times the concentration of the metal salt solution.

[0084] It can be understood that in step 4), when the median particle size of the secondary particles reaches the preset value D0, the current reaction system needs to be post-processed including aging, washing, and drying to obtain the positive electrode active material precursor of the present application.

[0085] In addition, during the above reaction process, it is necessary to continuously introduce inert gas (such as nitrogen, argon, etc.) into the system for protection.

[0086] Furthermore, the inventors discovered that the stirring speed during the reaction preparation process has a certain degree of influence on the number of cross-linked and anisotropic whiskers in the positive electrode active material precursor. When the speed V1 in step 1) is 700-900 rpm, the speed V2 in step 2) is 70%-80% of V1, the speed V3 in step 3) is 70%-80% of V2, and the speed in step 4) is 70%-80% of V3, the number of cross-linked and anisotropic whiskers in the positive electrode active material precursor can be increased.

[0087] In addition, the solid content of the reaction system of the fourth coprecipitation reaction can be made greater than the solid content of the reaction systems of the first coprecipitation reaction, the second coprecipitation reaction, and the third coprecipitation reaction, respectively, thereby increasing the degree of crosslinking between the primary particles.

[0088] The third aspect of the present application also provides a positive electrode active material, which has Li x Ni a Co b Mn c The chemical composition of O2, where 0.9≤x≤1.1, 0.1≤a≤0.5, 0≤b≤0.5, 0.5≤c≤0.9;

[0089] The positive electrode active material includes secondary particles formed by agglomerating multiple whiskers, wherein the whiskers include multiple first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5; wherein the first whiskers include cross-linked whiskers, and the cross-linked whiskers are connected to at least 5 first whiskers.

[0090] It is understood that the positive electrode active material has the same morphological characteristics as the aforementioned positive electrode active material precursor, with the only difference being that the positive electrode active material is a lithium-intercalating compound of the aforementioned positive electrode active material precursor. Therefore, the positive electrode active material has excellent cycle stability and specific capacity.

[0091] The positive electrode active material of the present application is prepared from the positive electrode active material precursor of the first aspect, or prepared from the positive electrode active material precursor obtained by the preparation method of the second aspect. Specifically, the positive electrode active material precursor of the first aspect or the second aspect is mixed with an active metal source and calcined.

[0092] The active metal source may be, for example, lithium hydroxide or a lithium salt, wherein the lithium salt may be one or more of common lithium sulfate, lithium nitrate, lithium chloride, lithium hypochlorite, lithium perchlorate, lithium carbonate, and lithium acetate.

[0093] During the preparation of the positive electrode active material, parameters such as the molar ratio of the positive electrode active material precursor to the active metal source and the calcination temperature can be selected from conventional parameters in the art and are not specifically limited in this application. In one specific embodiment, the molar ratio of the positive electrode precursor to the active metal source is (1:1.05) to (1:1.3).

[0094] The fourth aspect of the present application provides a positive electrode sheet comprising the positive electrode active material described in the third aspect. Therefore, the positive electrode sheet can not only ensure the gram capacity of the battery, but also greatly improve the cycle performance of the battery.

[0095] Specifically, the positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active layer including a positive electrode active material and disposed on at least one surface of the positive electrode current collector.

[0096] When preparing the positive electrode sheet, for example, the positive electrode active material of the present application can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is evenly coated on the positive electrode current collector, and the positive electrode sheet is obtained after drying, rolling, and slitting. In one embodiment, the positive electrode active layer comprises, by weight percentage, 70-99 wt% of the positive electrode active material, 0.5-15 wt% of the conductive agent, and 0.5-15 wt% of the binder. Furthermore, the positive electrode active layer comprises 80-98 wt% of the positive electrode active material, 1-10 wt% of the conductive agent, and 1-10 wt% of the binder.

[0097] Among them, the material of the positive electrode current collector can be at least one of aluminum foil and nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, and polyurethane.

[0098] The fourth aspect of the present application further provides a battery comprising the above-mentioned positive electrode sheet. The battery provided in the present application has advantages corresponding to the above-mentioned positive electrode active material, which will not be described in detail here.

[0099] In this application, unless otherwise specified, the processes involved, such as coating, drying, and rolling, are all conventional operations in the art, and the equipment used may be conventional equipment in the art, without particular limitation.

[0100] Generally speaking, a battery includes an electrolyte, a cell, and a casing that encapsulates the cell. The electrolyte is injected into the cell within the casing, and the cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrodes. The cell can be a laminated cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked in an alternating pattern. Alternatively, the cell can be a wound cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked and then wound.

[0101] Specifically, the negative electrode sheet includes a negative electrode collector and a negative electrode active layer located on at least one side surface of the negative electrode collector. Specifically, the negative electrode active layer can be provided on one side surface of the negative electrode collector, or the negative electrode active layer can be provided on both sides of the negative electrode collector in the thickness direction.

[0102] Specifically, the negative electrode active layer may include a negative electrode active material, a conductive agent and a binder, all of which may be conventional materials in the art. For example, the negative electrode active material may include one or more of natural graphite, artificial graphite, petroleum coke, and silicon-carbon materials; the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fibers; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0103] The embodiments of the present application may use a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes copper foil.

[0104] In the embodiments of the present application, the negative electrode sheet can be prepared by conventional methods in the art, such as a coating method. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. The slurry is then coated on the surface of the negative electrode current collector. After drying and roller pressing, the negative electrode sheet is prepared. The coating, drying, and roller pressing steps involved are conventional operations for preparing negative electrode sheets using a coating method and are not particularly limited thereto.

[0105] The electrolyte of the embodiment of the present application can be a conventional electrolyte in the field. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent, an additive and an electrolyte salt. The organic solvent includes, for example, one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC), the additive includes, for example, fluoroethylene carbonate (FEC), the additive includes, for example, vinylene carbonate (VC), the electrolyte salt may include a lithium salt, and the lithium salt includes, for example, lithium hexafluorophosphate (LiPF6), etc., but is not limited thereto.

[0106] In the embodiments of the present application, a separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent contact and short circuit between the positive and negative electrode sheets. Conventional separators in the art can be used in the embodiments of the present application, without particular limitation. For example, the separator material can be made from one or more of high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0107] In the embodiment of the present application, conventional shell materials in the art may be used to encapsulate the battery cell. The shell may include, for example, a soft packaging material such as an aluminum-plastic film, but is not limited thereto.

[0108] In the embodiments of the present application, components such as positive electrode sheets, separators, and negative electrode sheets can be assembled into a battery by conventional methods in the art. For example, the positive electrode sheets, separators, and negative electrode sheets can be stacked in an alternating manner to produce a laminated battery cell (or wound into a wound battery cell); the battery cell can then be placed in a shell (outer packaging), and after conventional processes such as liquid injection (i.e., injecting electrolyte) and packaging, the battery can be produced.

[0109] Hereinafter, the cathode active material precursor of the present application will be described in detail through specific examples.

[0110] Example 1

[0111] The method for preparing the positive electrode active material precursor of this embodiment includes the following steps:

[0112] 1) Prepare a mixed metal salt solution of nickel salt and manganese salt (the molar ratio of nickel ion to manganese ion is 25:75) with a concentration of 2.0 mol / L; prepare a sodium hydroxide solution with a concentration of 11 mol / L;

[0113] Under nitrogen protection, deionized water and sodium hydroxide solution were added to the reactor as reaction base liquids, the reactor was heated to a constant temperature of 60°C, and the mixed metal salt solution and sodium hydroxide solution were injected into the reactor for co-precipitation reaction. The flow rate of the mixed metal salt solution was 2 L / h, and the pH of the reaction process was controlled to be approximately 11.3. The stirring rate was 800 rpm.

[0114] 2) When the median particle size D1 of the secondary particles in the system is 2.0 μm, the flow rate of the mixed metal salt solution is adjusted to 4 L / h and the stirring rate is adjusted to 650 rpm. The pH of the system is controlled to 10.9-11.1 by adjusting the flow rate of sodium hydroxide. At the same time, ammonia solution is introduced into the system to gradually increase the ammonia value in the system to 3.0 g / L.

[0115] 3) When the median particle size D2 of the secondary particles in the system is 1 / 3 D0, the flow rate of the mixed metal salt solution is adjusted to 6 L / h and the stirring rate is adjusted to 500 rpm. The pH of the system is controlled to 10.6-10.9 by adjusting the flow rate of sodium hydroxide. Ammonia solution is continued to be introduced into the system to maintain the ammonia value in the system at 3.0 g / L.

[0116] 4) When the median particle size D3 of the precursor in the system is 1 / 2D0, the concentration device is turned on, the flow rate of the mixed metal salt solution is maintained at 6 L / h, the stirring rate is maintained at 350 rpm, and the pH of the system is controlled at 10.3-10.6 by adjusting the flow rate of sodium hydroxide. Ammonia solution is continued to be introduced into the system to maintain the ammonia value in the system at 3 g / L;

[0117] When the median particle size of the precursor in the system reaches the target median particle size D0, the reaction is stopped;

[0118] The reaction solution was aged, washed and dried to obtain the positive electrode active material precursor Ni 0.25 Mn 0.75 (OH)2.

[0119] Example 2

[0120] The steps of this embodiment are basically the same as those of embodiment 1, except that the ammonia value in the control system in steps 2), 3) and 4) is 1 g / L.

[0121] Example 3

[0122] The steps of this embodiment are basically the same as those of embodiment 1, except that the reaction temperature is controlled at 65°C.

[0123] Example 4

[0124] The steps of this embodiment are basically the same as those of embodiment 1, except that the molar ratio of nickel ions to manganese ions in the mixed metal salt solution is 20:80. 0.20 Mn 0.80 (OH)2.

[0125] Example 5

[0126] The steps of this embodiment are basically the same as those of embodiment 1, except that the molar ratio of nickel ions to manganese ions in the mixed metal salt solution is 50:50. 0.50 Mn 0.50 (OH)2.

[0127] Example 6

[0128] The steps of this embodiment are basically the same as those of embodiment 1, except that in step 1), a mixed metal salt solution of nickel salt, cobalt salt and manganese salt (the molar ratio of nickel ion, cobalt ion and manganese ion is 20:5:75) is prepared with a concentration of 2.0 mol / L. The positive electrode active material precursor of this embodiment is Ni 0.20 Co 0.05 Mn 0.75 (OH)2.

[0129] Example 7

[0130] The steps of this embodiment are basically the same as those of embodiment 1, except that the rotation speed in steps 1) to 4) is maintained at 800 rpm.

[0131] Comparative Example 1

[0132] The steps of this comparative example are basically the same as those of Example 1, except that ammonia water is introduced in step 1), and the concentration of the complexing agent in the reaction system in steps 1) to 4) is 8 g / L.

[0133] Comparative Example 2

[0134] The steps of this comparative example are basically the same as those of Example 1, except that ammonia water is introduced in step 1), and the complexing agent concentration of the reaction system in steps 1) to 4) is 3 g / L.

[0135] Comparative Example 3

[0136] The steps of this comparative example are basically the same as those of Example 1, except that in step 3), the ammonia value of the reaction system is 5 g / L, and in step 4), ammonia water is continued to be introduced to make the ammonia value in the reaction system 8 g / L.

[0137] Test example

[0138] The relevant parameters of the positive electrode active material precursors in the examples and comparative examples were tested, and the results are shown in Table 1.

[0139] Among them, the tap density is measured by a tap density meter, the specific surface area is measured by a nitrogen adsorption static volume method, and the particle size is measured by a particle size tester;

[0140] Other parameters were obtained through SEM observations. Specifically, n is the number of first whiskers connected to the cross-linked whiskers; w is the ratio of the number of cross-linked whiskers to the number of first whiskers; M is the number of first whiskers connected to the anisotropic whiskers with an angle ≤30°; and X is the number of first whiskers that are through-connected to the anisotropic whiskers among the M first whiskers.

[0141] Figure 1 is a scanning electron microscope image of the positive electrode active material precursor of Example 1 of the present application at 1000 magnification, Figure 2 is a scanning electron microscope image of the positive electrode active material precursor of Example 1 of the present application at a magnification of 5000. Figure 3 is a scanning electron microscope image of the positive electrode active material precursor of Example 1 of the present application at a magnification of 10,000. Figure 4 The cross-sectional electron microscope image of the positive electrode active material precursor of Example 1 of the present application is taken at a magnification of 9000. Figure 3 It can be seen that in this view, the present application includes a cross-linked whisker (whisker No. 1 in the figure) connected to 6 first whiskers (whisker No. 2-7 in the figure), and the angle between two first whiskers (No. 3 and No. 5) and the cross-linked whisker is ≤30°. Figure 4 It can be seen that the primary particles agglomerate with each other in a radioactive manner.

[0142] Figure 5 is a scanning electron microscope image of the positive electrode active material precursor of Example 2 of the present application at 1000 magnification, Figure 6 is a scanning electron microscope image of the positive electrode active material precursor of Example 2 of the present application at a magnification of 10,000. Figure 7 The cross-sectional electron microscope image of the positive electrode active material precursor of Example 2 of the present application at a magnification of 6000 is shown. Figure 6 It can be seen that in this view, the present application includes cross-linked whiskers and anisotropic whiskers, and includes cross-linked whiskers connected to 5 first whiskers, and the angle between the three first whiskers and the cross-linked whiskers is ≤30°. Figure 7 It can be seen that the primary particles agglomerate with each other in a radioactive manner.

[0143] Figure 8 is a scanning electron microscope image of the positive electrode active material precursor of Comparative Example 1 of the present application at a magnification of 1000. Figure 9 is a scanning electron microscope image of the positive electrode active material precursor of Comparative Example 1 of the present application at a magnification of 10,000. Figure 10 This is a cross-sectional electron microscope image of the positive electrode active material precursor of Comparative Example 1 of the present application at a magnification of 8000.

[0144] Table 1 Parameters of positive electrode active material precursors in Examples and Comparative Examples

[0145]

[0146] Test Example 2

[0147] The positive electrode active material precursors of the examples and comparative examples were mixed with a lithium source and sintered at 850° C. for 10 h to obtain the positive electrode active material of the present application.

[0148] Figure 11 This is a scanning electron microscope image of the positive electrode active material of Example 1 of the present application; Figure 12 This is a scanning electron microscope image of the positive electrode active material of Example 2 of the present application; Figure 11 and 12 It can be seen that the positive electrode active material of the present application has the same morphology as the positive electrode active material precursor.

[0149] The positive electrode active materials corresponding to the examples and comparative examples were prepared into positive electrode sheets, and button batteries were assembled with negative electrode sheets, electrolytes, and separators according to the following method. Specifically, each positive electrode active material was mixed with conductive carbon black (SP) and PVDF in a weight ratio of 80%: 10%: 10%, and a positive electrode slurry was obtained by dispersion. The slurry was coated on an aluminum foil current collector and rolled to obtain a positive electrode sheet. The positive electrode sheet was then punched into a small disc with a diameter of 12 mm using a film mold. After drying and weighing, a button battery was assembled in a glove box under an Ar protective atmosphere using a 2025 button battery shell, a Li metal disc as the negative electrode, and a conventional high-voltage lithium cobalt oxide electrolyte.

[0150] The following tests were performed on the lithium-ion battery, and the results are shown in Table 2:

[0151] 1) First discharge capacity and first efficiency

[0152] After each battery was left standing at 25°C for 4 hours, the first charge and discharge capacity test was carried out. The test conditions were: charging at 0.1C to 4.95V, constant voltage charging to 1C cutoff, leaving it standing for 3 minutes, and then discharging at 0.1C to 3.5V. The first charge capacity (C0) and the first discharge capacity (D0) were recorded respectively, and the first coulombic efficiency was calculated according to D0 / C0.

[0153] 2) Capacity retention rate

[0154] 28-Day Storage Capacity Retention: After the soft-pack battery is fully formed, the air pocket is removed and the battery is sealed. The initial capacity after formation is measured. Charge the battery to 4.95V and store it for 28 days. The ratio of the remaining battery capacity to the initial capacity is the storage capacity retention rate.

[0155] Cycle retention rate: At 25°C, charge the battery to 4.95 V at a constant current at a charge rate of 1 C, then discharge it to 3.5 V at a discharge rate of 1 C. Repeat this charge and discharge cycle 200 times, and measure the discharge capacity Q1 at the first cycle and the discharge capacity Q at the 200th cycle. 200 .

[0156] Cycle retention rate Q=Q 200 / Q1×100%.

[0157] Table 2 Electrical performance parameters of lithium-ion batteries

[0158]

[0159] It can be seen from Table 1 and Table 2 that the positive electrode active material precursor of the present application helps to obtain a high manganese positive electrode active material with a stable structure, thereby improving the cycle performance and storage performance of the battery.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode active material precursor, characterized in that: Ni a Co b Mn c The chemical composition of (OH)2, wherein 0.1≤a≤0.5, 0≤b≤0.5, 0.5≤c≤0.9; The positive electrode active material precursor includes secondary particles formed by agglomeration of multiple whiskers, the whiskers include multiple first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5; wherein, the first whiskers include cross-linked whiskers, and the cross-linked whiskers are connected to at least 5 first whiskers.

2. The positive electrode active material precursor according to claim 1, characterized in that The ratio of the number of the cross-linked whiskers to the number of the first whiskers is not less than 50%.

3. The positive electrode active material precursor according to claim 1, characterized in that The first whisker has a length of 1000 nm ≤ 4000 nm and a thickness of 500 nm or more.

4. The positive electrode active material precursor according to claim 1, characterized in that The whiskers further include second whiskers, wherein the thickness of the second whiskers is less than or equal to 100 nm and the length is less than or equal to 2000 nm.

5. The positive electrode active material precursor according to any one of claims 1 to 4, characterized in that: Among the at least five first whiskers connected to the cross-linked whiskers, at most three first whiskers have an angle of ≤30° with the cross-linked whiskers.

6. The positive electrode active material precursor according to any one of claims 1 to 4, characterized in that: The first whiskers further include anisotropic whiskers, which are connected to N first whiskers. Among the N first whiskers, at most M first whiskers have an angle ≤30° with the anisotropic whiskers, where N≥3 and M≤3.

7. The positive electrode active material precursor according to claim 6, characterized in that: Among the M first whiskers, X first whiskers are through-connected to the anisotropic whiskers, and X≤M.

8. The positive electrode active material precursor according to any one of claims 1 to 4, characterized in that: The secondary particles have a D50 of 8-16 μm and a tap density of 1.2-2.1 g / cm 3 , the specific surface area is 5~25㎡ / g.

9. A method for preparing a cathode active material precursor according to any one of claims 1 to 8, characterized in that: The following steps are involved: 1) Adding a metal salt solution and a precipitant solution to the reaction base liquid at 50-70° C. to perform a first coprecipitation reaction, controlling the pH of the reaction system to 11.2-11.8 and the complexing agent to 0, until the median particle size D1 of the secondary particles reaches 2.0 μm, thereby obtaining a first coprecipitation product system; 2) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the first coprecipitation product system to perform a second coprecipitation reaction, and controlling the pH of the reaction system to be 10.9-11.5 until the median particle size of the secondary particles is D2, thereby obtaining a second coprecipitation product system; 3) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the second coprecipitation product system to perform a third coprecipitation reaction, and controlling the pH of the reaction system to be 10.6-11.2, until the median particle size of the secondary particles reaches D3, thereby obtaining a third coprecipitation product system; 4) introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the third coprecipitation product system to perform a fourth coprecipitation reaction, and controlling the pH of the reaction system to be 10.3-10.9, until the median particle size of the secondary particles reaches a preset value D0, thereby obtaining the positive electrode active material precursor; D2=1 / 3D0, D3=1 / 2D0, and C 络 ≤3C 盐 , C 络 is the concentration of the complexing agent in the reaction system of step 2) to step 4), C 盐 is the concentration of the metal salt solution.

10. The preparation method according to claim 9, characterized in that The rotation speed V1 of step 1) is 700-900 rpm, the rotation speed V2 of step 2) is 70%-80% of V1, the rotation speed V3 of step 3) is 70%-80% of V2, and the rotation speed of step 4) is 70%-80% of V3; and / or, The solid content of the reaction system of the fourth coprecipitation reaction is greater than the solid content of the reaction systems of the first coprecipitation reaction, the second coprecipitation reaction and the third coprecipitation reaction.

11. A positive electrode active material, characterized in that: With Li x Ni a Co b Mn c The chemical composition of O2, where 0.9≤x≤1.1, 0.1≤a≤0.5, 0≤b≤0.5, 0.5≤c≤0.9; The positive electrode active material includes secondary particles formed by agglomerating multiple whiskers, wherein the whiskers include multiple first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5; wherein the first whiskers include cross-linked whiskers, and the cross-linked whiskers are connected to at least 5 first whiskers.

12. A positive electrode sheet, characterized in that: The positive electrode active material according to claim 11 is included.

13. A battery, characterized in that: Including the positive electrode sheet according to claim 12.

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