A positive electrode active material precursor, a preparation method therefor, and use thereof

Abstract

The application provides a positive electrode active material precursor and a preparation method and application thereof. The precursor has a chemical composition of Li a Co b Mn c (OH)2, wherein 0.1<=a<=0.5, 0<=b<=0.5, and 0.5<=c<=0.9; the positive electrode active material precursor comprises secondary particles formed by aggregation of a plurality of whiskers, the whiskers comprise a plurality of first whiskers, and the first whiskers have an aspect ratio of 1.3-4.5; wherein the first whiskers comprise crosslinked whiskers, and the crosslinked whiskers are connected with at least 5 first whiskers. The precursor provided by the application is helpful to obtain a high-manganese positive electrode active material with a stable structure, thereby improving the cycle performance of a battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode active material precursor and a preparation method and application thereof. BACKGROUND

[0002] As energy storage devices that can be repeatedly charged and discharged, secondary batteries have become an important part of modern energy systems. In the consumer electronics field, secondary batteries are widely used in smartphones, laptops, tablets and other portable electronic devices, providing efficient and stable power supply. In the field of transportation, lithium-ion batteries, with their high energy density and long cycle life, have become the main power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs), and are gradually expanding to electric ships and rail transportation applications. With the global energy structure shifting towards low carbonization, 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 cobaltate 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.) exhibit unique advantages due to the introduction of manganese. Manganese is abundant and low in price, which can significantly reduce material costs; at the same time, the stable electronic structure of Mn 4+ can effectively inhibit the precipitation of lattice oxygen, improving the safety of the material.

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

[0005] The present application provides a positive electrode active material precursor with a high manganese content composition, which helps to obtain a high manganese positive electrode active material with stable structure by controlling the morphology and structure of its primary particles.

[0006] The present application provides a preparation method of a positive electrode active material precursor, which is used to prepare the above-mentioned positive electrode active material precursor.

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

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

[0009] The application provides a battery with high gravimetric capacity and long cycle life.

[0010] The application provides a positive electrode active material precursor with a chemical composition of Li a Co b Mn c (OH)2, wherein 0.1≤a≤0.5, 0≤b≤0.5, and 0.5≤c≤0.9.

[0011] The positive electrode active material precursor comprises secondary particles formed by agglomeration of a plurality of whiskers, the whiskers comprising a plurality of first whiskers, the first whiskers having an aspect ratio of 1.3-4.5; wherein the first whiskers comprise crosslinked whiskers, the crosslinked whiskers being connected to at least 5 first whiskers.

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

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

[0014] The positive electrode active material precursor as described above, wherein the whiskers further comprise second whiskers, the second whiskers having a thickness of ≤100 nm and a length of ≤2000 nm.

[0015] The positive electrode active material precursor as described above, wherein, of the at least 5 first whiskers connected to the crosslinked whiskers, at most 3 first whiskers have an angle of ≤30° with the crosslinked whiskers.

[0016] The positive electrode active material precursor as described above, wherein the first whiskers further comprise hetero-directional whiskers, the hetero-directional whiskers being connected to N first whiskers, of the N first whiskers, at most M first whiskers have an angle of ≤30° with the hetero-directional whiskers, N≥3, and M≤3.

[0017] The positive electrode active material precursor as described above, wherein, of the M first whiskers, X first whiskers are connected to the hetero-directional whiskers in a penetrating manner, X≤M.

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

[0019] The application provides a preparation method of the positive electrode active material precursor as described above, comprising the following steps:

[0020] 1) introducing a metal salt solution, a precipitant solution into the reaction solution at 50-70℃, carrying out a first co-precipitation reaction, and controlling the pH of the reaction system to be 11.2-11.8, the complexing agent to be 0, until the median particle size D1 of the secondary particles is 2.0 μm, to obtain a first co-precipitation product system;

[0021] 2) introducing a metal salt solution, a precipitant solution and a complexing agent solution into the first co-precipitation product system to carry out a second co-precipitation 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, to obtain a second co-precipitation product system;

[0022] 3) introducing a metal salt solution, a precipitant solution and a complexing agent solution into the second co-precipitation product system to carry out a third co-precipitation reaction, and controlling the pH of the reaction system to be 10.6-11.2, until the median particle size of the secondary particles is D3, to obtain a third co-precipitation product system;

[0023] 4) introducing a metal salt solution, a precipitant solution and a complexing agent solution into the third co-precipitation product system to carry out a fourth co-precipitation reaction, and controlling the pH of the reaction system to be 10.3-10.9, until the median particle size of the secondary particles is a preset value D0, to obtain 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), and 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% V1, the rotation speed V3 of step 3) is 70%-80% V2, and the rotation speed of step 4) is 70%-80% V3; and / or,

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

[0027] The present application provides a positive electrode active material having a chemical composition of Li x Ni a Co b Mn c O2, wherein 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 comprises secondary particles agglomerated by a plurality of whiskers, the whiskers comprise a plurality of first whiskers, and an aspect ratio of the first whiskers is 1.3-4.5; wherein the first whiskers comprise crosslinked whiskers, and the crosslinked whiskers are connected to at least 5 first whiskers.

[0029] The application provides a positive electrode sheet comprising the positive electrode active material.

[0030] The application provides a battery comprising the positive electrode sheet.

[0031] The application provides a positive electrode active material precursor with a high manganese content. By adjusting the aspect ratio of primary particles of the precursor and constructing a crosslinked 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 in the sintering process with a lithium source, thereby facilitating the improvement of the cycle performance, storage performance and initial efficiency of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A scanning electron microscope image of the positive electrode active material precursor of the application example 1 at 1000 times;

[0033] Figure 2 A scanning electron microscope image of the positive electrode active material precursor of the application example 1 at 5000 times;

[0034] Figure 3 A scanning electron microscope image of the positive electrode active material precursor of the application example 1 at 10000 times;

[0035] Figure 4 A cross-sectional electron microscope image of the positive electrode active material precursor of the application example 1 at 9000 times;

[0036] Figure 5 A scanning electron microscope image of the positive electrode active material precursor of the application example 2 at 1000 times;

[0037] Figure 6 A scanning electron microscope image of the positive electrode active material precursor of the application example 2 at 10000 times;

[0038] Figure 7 A cross-sectional electron microscope image of the positive electrode active material precursor of the application example 2 at 6000 times;

[0039] Figure 8 A scanning electron microscope image of the positive electrode active material precursor of the application comparative example 1 at 1000 times;

[0040] Figure 9 A scanning electron microscope image of the positive electrode active material precursor of the application comparative example 1 at 10000 times;

[0041] Figure 10 A cross-section electron microscope image of the positive electrode active material precursor of the application comparative example 1 at 8000 times;

[0042] Figure 11 A scanning electron microscope image of the positive electrode active material of the application example 1 at 10000 times;

[0043] Figure 12 A scanning electron microscope image of the positive electrode active material of the application example 2 at 10000 times. DETAILED DESCRIPTION

[0044] In order to make the objects, technical solutions and advantages of the application clearer, the following will combine the embodiments of the application to make a clear and complete description of the technical solutions in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the application.

[0045] In order to improve the structural stability of high-manganese binary / ternary positive electrode active material in the cycle process, the inventors have studied the morphology of the high-manganese binary / ternary positive electrode active material precursor. The inventors speculate that in the process of battery charging and discharging, the repeated extraction and insertion of lithium ions will cause the change of lattice volume, thus generating cracks in the particle interior due to anisotropic stress, and the more single the extension direction of the crack and the faster the extension speed, the worse the structural stability of the positive electrode active material. Therefore, the inventors take the suppression of crack generation and the control of crack propagation as the breakthrough 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 application provides a positive electrode active material precursor with a chemical composition of Ni a Co b Mn c (OH)2, wherein 0.1≤a≤0.5, 0≤b≤0.5, and 0.5≤c≤0.9.

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

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

[0049] The positive electrode active material precursor of the present application comprises secondary particles agglomerated by a plurality of whiskers, and the whisker is a primary particle. Among them, the whisker in the present application comprises a plurality of first whiskers, and the aspect ratio of the first whisker is 1.3-4.5. It can be understood that when the ratio of the length to the thickness of the whisker is 1.3-4.5, the whisker is the first whisker mentioned in the present application.

[0050] In the positive electrode active material precursor of the present application, at least part of the first whisker is a cross-linked whisker. It needs to be explained that in the present application, when a certain first whisker is taken as the main body, at least 5 first whiskers are connected with the first whisker as the main body (the two have an angle greater than 0° and less than 180°), and the first whisker as the main body is called a cross-linked whisker. In the present application, the number of first whiskers connected with the cross-linked whisker is at least 5, for example, it can be 5, 6, 7, 8 or more. Whether the first whisker connected with the cross-linked whisker is a cross-linked whisker is not specifically limited in the present application, which 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 reason mainly lies in that: on the one hand, in the sintering process of the positive electrode active material, the synergistic optimization of the cross-linked structure and the aspect ratio parameter of the precursor primary particle has a decisive role on the stability of the final crystal structure. Specifically, the cross-linked whisker introduces a suitable cross-linked structure into the precursor, making the primary particles form a three-dimensional interlocking complex topological morphology, fundamentally changing the way of stress transfer and crack propagation, so that the crack will encounter different orientation first whiskers with suitable aspect ratio in the propagation process, and be forced to change direction or even stop. This cross-linked structure with mechanical interlocking effect can make the tortuosity of the crack propagation path higher, significantly delay the fracture process. At the same time, the primary particles with the above aspect ratio disperse the volume strain in the cycle process to the whole particle interior through the isotropic volume change characteristics, avoiding the lattice rupture caused by local stress concentration of the primary particle. The synergistic effect of the two is particularly prominent in high-pressure cycling, and the cross-linked network disperses the phase transition stress through multi-point support, while the primary particle with appropriate aspect ratio reduces the stress accumulation at the grain boundary by reducing the lattice distortion degree, thereby having a significant improvement effect on the structural stability of the positive electrode active material sintered from the precursor.

[0052] On the other hand, in terms of interface stability, the synergistic effect of the crosslinked whiskers and the special aspect ratio of the first whiskers in the positive electrode active material precursor can reduce the direct contact between the electrolyte and the positive electrode active material, and significantly inhibit the interface side reaction. Specifically, the crosslinked network formed by the crosslinked whiskers in the precursor can form a continuous barrier in the positive electrode active material, effectively blocking the penetration 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 whisker with the above aspect ratio also helps to reduce the specific surface area of the positive electrode active material, reducing the contact area between the positive electrode active material and the electrolyte, and further reducing the interface reaction activity.

[0053] Therefore, in the positive electrode active material precursor of the present application, the synergistic optimization of the crosslinked whiskers and the first whiskers with appropriate aspect ratio provides a feasible technical path for constructing positive electrode active materials with high stability and long service life.

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

[0055] In detail, each secondary particle includes crosslinked whiskers, and 5 secondary particles are subjected to SEM detection (magnification is 5000x). In the SEM view, the number of crosslinked whiskers in each secondary particle in the view and the number of first whiskers in the view are counted, and the ratio of the two is the number ratio of the crosslinked whiskers to the first whiskers of the secondary particle. The number ratio of the crosslinked whiskers to the first whiskers of 5 secondary particles is summed and averaged, and the obtained value is the number ratio of the crosslinked whiskers to the first whiskers.

[0056] By controlling the number ratio of the crosslinked whiskers to the first whiskers, the present application further ensures the crosslinking degree of the first whiskers in each secondary particle, thereby further improving the tortuosity of the crack propagation path, ultimately reducing the cracking probability of the positive electrode active material, significantly inhibiting the occurrence of transition metal ion dissolution and interface side reaction, and improving the cycle performance of the battery.

[0057] Further, when the length of the first whisker is 1000nm≤length≤4000nm and the thickness is ≥500nm, the anisotropy of the shrinkage of the sintering of the positive electrode active material precursor and the lithium source can be further reduced, not only effectively improving the phase change stress dispersion efficiency of the positive electrode active material, but also further improving the tortuosity of the crack propagation path, thereby maintaining higher structural stability of the positive electrode active material during lithium ion deintercalation.

[0058] In addition, in the positive electrode active precursor material of the application, in addition to the first whisker, a second whisker is also included. Specifically, in the whisker constituting the secondary particle of the application, the whisker with a thickness of ≤100 nm and a length of ≤2000 nm is a secondary whisker. The second whisker with the above size helps to provide better structural support for the first whisker, so that the stress in the system is more dispersed, which is conducive to further enhancing the structural stability of the sintered positive electrode active material.

[0059] Further, in the at least 5 first whiskers connected with the cross-linked whisker, at most 3 first whiskers have an angle ≤30° with the cross-linked whisker.

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

[0061] In a specific embodiment, the positive electrode active material precursor of the application further includes a heterotropic whisker. The heterotropic whisker is connected with N first whiskers, and in the N first whiskers, at most M first whiskers have an angle ≤30° with the heterotropic whisker, N≥3, M≤3.

[0062] Specifically, when a certain first whisker is taken as the main body, the first whisker as the main body has a connection relationship with at least 3 first whiskers, and in the at least 3 first whiskers, at most 3 first whiskers have an angle not higher than 30° with the first whisker as the main body, the first whisker as the main body is the heterotropic whisker of the application.

[0063] The inventors have found through research that after introducing the heterotropic whisker into the positive electrode active material precursor, these whiskers will spontaneously build a more complex three-dimensional stress network. This network can enhance the stress dispersion and bearing capacity inside the material, effectively adjust the stress state of the material. What is particularly key is that it significantly improves the resistance to crack propagation, making it difficult for cracks to continue to spread in the material, thereby reducing the risk of structural damage of the material due to crack propagation.

[0064] Further, when X first whiskers are connected with the heterotropic whisker in the M first whiskers connected with the heterotropic whisker, the resistance to crack propagation will be more obvious. The penetration connection referred to in the application means that the X first whiskers pass through the inside of the heterotropic whisker.

[0065] It should be noted that when N≥5, the heterotropic whisker is also the crosslinked whisker as described above; similarly, when there are at most three first whiskers connected to the crosslinked whisker and the included angle is ≤30°, the crosslinked whisker can also be referred to as the heterotropic whisker as described above.

[0066] In addition, in the positive electrode active material precursor of the application, primary particles are aggregated with each other in a radial arrangement to form secondary particles, and such an ordered arrangement helps to form more lithium ion deintercalation channels.

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

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

[0069] In the positive electrode active material precursor of the application, the D50, tap density and specific surface area of the secondary particles are limited in the above ranges, thereby constructing a stable system with multiple scales and mutual constraints. Through the balance optimization of physical structure and chemical properties, this system collectively guarantees the long-cycle stability of the positive electrode active material prepared from the positive electrode active material precursor.

[0070] In the construction of particle structural integrity, D50 and tap density play a core role. The above D50 allows the secondary particles to shrink uniformly and densely during sintering, avoiding excessive sintering of too small particles and preventing internal pore residues of too large particles. At the same time, the optimized tap density ensures that the particles reach an ideal stacking state, forming a through network structure with appropriate porosity. This balance endows the positive electrode active material with good mechanical strength and lithium ion transmission channels.

[0071] In terms of surface stability regulation, the specific surface area determines the contact degree of the material with the electrolyte, and needs to form an inverse balance with D50. Although a smaller specific surface area can reduce the active sites of side reactions, it needs to be matched with appropriate D50 to ensure sufficient reaction interface, and the D50 of 8-16 μm and the specific surface area of 5-25 m2 / g of 5-25 m2 / g in the application achieve a balance between inhibiting side reactions and maintaining reaction kinetics.

[0072] The second aspect of the application provides a preparation method of a positive electrode active material precursor, comprising the following steps:

[0073] 1) introducing metal salt solution, precipitant solution into the reaction bottom solution to carry out the first coprecipitation reaction at 50-70℃, and controlling the pH of the reaction system to be 11.2-11.8, the complexing agent to be 0, until the median particle size D1 of the secondary particles is 2.0 μm, to obtain the first coprecipitation product system;

[0074] 2) introducing metal salt solution, precipitant solution and complexing agent solution into the first coprecipitation product system to carry out the 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, to obtain the second coprecipitation product system;

[0075] 3) introducing metal salt solution, precipitant solution and complexing agent solution into the second coprecipitation product system to carry out the 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 is D3, to obtain the third coprecipitation product system;

[0076] 4) introducing metal salt solution, precipitant solution and complexing agent solution into the third coprecipitation product system to carry out the 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 is the preset value D0, to obtain 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 C, and the concentration of the metal salt solution is C.

[0078] In detail, at the beginning of preparation, the preparation of the metal salt solution, the precipitant solution and the complexing agent solution, and the reaction bottom solution can be completed first. The metal salt solution refers to an aqueous solution including at least nickel salt and manganese salt, and further, when b>0, the metal salt solution further includes cobalt salt. The 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 for precipitating metal ions in the metal salt solution, which can be generally sodium hydroxide aqueous solution; the complexing agent solution can be ammonia water solution, for example. The application does not specifically limit the concentration of the above-mentioned solutions, which can be the conventional concentration in the art.

[0079] In step 1), at 50-70°C, the metal salt solution and the precipitant solution are introduced into the reaction solution including the precipitant solution at a certain speed at the beginning of the reaction, and a first co-precipitation reaction occurs. During the reaction, the pH of the system is controlled to be 11.2-11.8 by controlling the introduction speed of the precipitant solution. During the first co-precipitation reaction, the metal salt and the precipitant react to form a metal hydroxide precipitate, and the first co-precipitation reaction is the nucleation stage of the positive electrode active material precursor of the present application. It should be pointed out that in step 1), the complexing agent solution introduced by the present application is 0, that is, no complexing agent solution is introduced. In the above pH value and the environment without complexing agent, not only is it beneficial to obtain the first whisker of the size of the present application, but also the stacking order of the first whisker can be reduced, so that the staggered stacking of the first whisker is more compact, so that more first whiskers present a staggered structure, which is beneficial to the occurrence of the cross-linked whisker and the heterodirectional whisker of the present application. When the median particle size D1 of the secondary particles in the system is 2.0 μm, the first co-precipitation system is obtained.

[0080] Subsequently, in step 2), the metal salt solution, the precipitant solution and the complexing agent solution are introduced into the first co-precipitation system to carry out a second co-precipitation reaction. During the reaction, the pH of the system is controlled to be 10.9-11.5 by controlling the introduction speed of the precipitant solution. During the second co-precipitation reaction, the introduction of the complexing agent promotes the precipitation of the salt solution on the original secondary particles, forming a tightly packed whisker, so that the prepared sample has a large tap density and a small specific surface area. When the median particle size D2 of the secondary particles in the system is 1 / 3D0, the second co-precipitation system is obtained.

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

[0082] It should be noted that in the reaction system of step 2) to step 4), the concentration of the complexing agent in the reaction system needs to be controlled, so that the concentration of the complexing agent is not more than 3 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 concentration of the complexing agent in the reaction system needs to be controlled in the range of 0

[0083] Further, the concentration of the complexing agent in each of the reaction systems of steps 2) to 4) can be the same, partially the same, or all different. For example, after controlling the concentration of the complexing agent in the reaction system of step 2) to be no more than 3 times the concentration of the metal salt solution, the concentration of the complexing agent in the reaction systems of steps 3) and 4) can be kept the same as that in step 2) by adjusting the flow rate of the complexing agent; or, after controlling the concentration of the complexing agent in the reaction system of step 2) to be no more than 3 times the concentration of the metal salt solution, the concentration of the complexing agent in the reaction systems of steps 3) and 4) can be made to be higher than that in step 2) respectively by adjusting the flow rate of the complexing agent, but still no more than 3 times the concentration of the metal salt solution.

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

[0085] In addition, in the process of the above reaction, inert gas (such as nitrogen, argon, etc.) needs to be continuously introduced into the system for protection.

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

[0087] In addition, the solid content of the reaction system of the fourth co-precipitation reaction can also be made to be greater than the solid content of the reaction systems of the first co-precipitation reaction, the second co-precipitation reaction, and the third co-precipitation reaction respectively, so as to improve the cross-linking degree between the primary particles.

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

[0089] The positive electrode active material comprises secondary particles formed by agglomeration of a plurality of whiskers, and the whiskers comprise a plurality of first whiskers, and the aspect ratio of the first whiskers is 1.3-4.5; wherein the first whiskers comprise cross-linked whiskers, and the cross-linked whiskers are connected to at least 5 first whiskers.

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

[0091] The positive electrode active material of the present application is prepared from the positive electrode active material precursor of the aforementioned first aspect, or the positive electrode active material precursor obtained by the preparation method of the aforementioned second aspect. Specifically, it is obtained by mixing the positive electrode active material precursor of the aforementioned first aspect or second aspect and an active metal source and then performing calcination treatment.

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

[0093] In the process of preparing the positive electrode active material, the molar ratio of the positive electrode active material precursor and the active metal source, the calcination temperature and other parameters can be selected as conventional parameters in the art, and the present application does not make special limitations. In one specific embodiment, the molar ratio of the positive electrode precursor and the active metal source is (1:1.05)~(1:1.3).

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

[0095] Specifically, the positive electrode sheet of the present application specifically comprises a positive electrode current collector and a positive electrode active layer comprising the positive electrode active material arranged on at least one surface of the positive electrode current collector.

[0096] Specifically, in the preparation of 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-methyl pyrrolidone (NMP) solvent, and fully stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and then dried, rolled and cut to obtain the positive electrode sheet. In one specific embodiment, the positive electrode active layer comprises 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, further comprising 80-98 wt% of the positive electrode active material, 1-10 wt% of the conductive agent, and 1-10 wt% of the binder.

[0097] The material of the positive electrode current collector can be at least one of an aluminum foil and a nickel foil; the conductive agent can be at least one of carbon black, acetylene black, graphene, ketjen black, and carbon fiber; and the binder can be at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, an oxirane-containing polymer, polyvinylpyrrolidone, and polyurethane.

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

[0099] In the present application, unless otherwise specified, the coating, drying, rolling and other processes involved are conventional operations in the art, and the equipment used can be conventional equipment in the art, which will not be particularly limited.

[0100] Generally, a battery comprises an electrolyte, a battery cell, and a shell encapsulating the battery cell, the electrolyte is injected into the battery cell in the shell, and the battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The battery cell can be a laminated battery cell, i.e., the battery cell is formed by interleaving and stacking the positive electrode sheet, the separator and the negative electrode sheet; or the battery cell can also be a wound battery cell, i.e., the battery cell is formed by stacking and winding the positive electrode sheet, the separator and the negative electrode sheet.

[0101] Specifically, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer on at least one side surface of the negative electrode current collector. Specifically, the negative electrode active layer can be arranged on one side surface of the negative electrode current collector, or the negative electrode active layer can be arranged on both side surfaces of the negative electrode current collector in the thickness direction.

[0102] Specifically, the negative electrode active layer can comprise a negative electrode active material, a conductive agent and a binder, which can all be conventional materials in the art. For example, the negative electrode active material can comprise one or more of natural graphite, artificial graphite, petroleum coke, silicon-carbon material, the conductive agent can comprise one or more of conductive carbon black, carbon nanotube (CNT), acetylene black, graphene, ketjen black, and carbon fiber; and the binder can comprise one or more of sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0103] The negative electrode current collector used in the embodiments of the present application can be conventional in the art, for example, the negative electrode current collector comprises a copper foil.

[0104] In the embodiments of the present application, the negative electrode sheet can be prepared by conventional methods in the art, for example, by a coating method. Specifically, the negative electrode active material, the conductive agent, the binder and other components used to form the negative electrode active layer can be dispersed in a solvent, for example, water, to prepare a negative electrode slurry, which is then coated on the surface of the negative electrode current collector, and then subjected to drying, rolling and other processes to obtain the negative electrode sheet. The coating, drying, rolling and other processes are conventional operations for preparing the negative electrode sheet by the coating method, and are not particularly limited.

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

[0106] In the embodiments of the present application, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from being in contact and short-circuited. The separator in the embodiments of the present application can be a conventional separator in the art, and is not particularly limited. For example, the separator material can be a separator prepared 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 embodiments of the present application, the battery cell can be packaged by using a conventional casing material in the art, for example, an aluminum plastic film or other soft packaging material, but is not limited thereto.

[0108] The positive electrode sheet, the separator and the negative electrode sheet and other components can be assembled into a battery by conventional methods in the art. For example, the positive electrode sheet, the separator and the negative electrode sheet can be arranged in an interleaved and stacked manner to obtain a jelly-roll type battery cell (or a wound type battery cell). Then, the battery cell is placed in a casing (an outer package), and then subjected to conventional processes such as liquid injection (i.e., electrolyte injection) and packaging to obtain the battery.

[0109] In the following, the positive electrode active material precursor in the embodiments of the present application is described in detail through specific examples.

[0110] Example 1

[0111] The preparation method of the positive electrode active material precursor in the embodiments includes the following steps:

[0112] 1) A mixed metal salt solution of nickel salt and manganese salt (the molar ratio of nickel ions to manganese ions is 25:75) is prepared, and the concentration is 2.0 mol / L. A sodium hydroxide solution with a concentration of 11 mol / L is prepared.

[0113] Under the protection of nitrogen, deionized water and sodium hydroxide solution were added into a reaction kettle as a reaction bottom solution, the reaction kettle was heated to a constant temperature of 60℃, and the mixed metal salt solution and the sodium hydroxide solution were injected into the reaction kettle 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 at about 11.3, and the stirring rate was 800 rpm;

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

[0115] 3) when the median particle size D2 of the secondary particles in the system was 1 / 3D0, the flow rate of the mixed metal salt solution was adjusted to 6 L / h, the stirring rate was 500 rpm, and the pH of the system was controlled at 10.6-10.9 by adjusting the flow rate of sodium hydroxide, and at the same time, the ammonia water solution was continuously introduced into the system, so that the ammonia value in the system was maintained at 3.0 g / L;

[0116] 4) when the median particle size D3 of the precursor in the system was 1 / 2D0, the concentration device was started, the flow rate of the mixed metal salt solution was maintained at 6 L / h, the stirring rate was 350 rpm, and the pH of the system was controlled at 10.3-10.6 by adjusting the flow rate of sodium hydroxide, and at the same time, the ammonia water solution was continuously introduced into the system, and the ammonia value in the system was maintained at 3 g / L;

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

[0118] The reaction liquid 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 example and example 1 are basically the same, the difference is that the ammonia value in the system is controlled at 1 g / L in steps 2), 3) and 4).

[0121] Example 3

[0122] The steps of this example and example 1 are basically the same, the difference is that the reaction temperature is controlled at 65℃.

[0123] Example 4

[0124] The steps of the present example are basically consistent with those of Example 1, except that the molar ratio of nickel ions to manganese ions in the mixed metal salt solution is 20:80. The positive electrode active material precursor of the present example is Ni 0.20 Mn 0.80 (OH)2.

[0125] Example 5

[0126] The steps of the present example are basically consistent with those of Example 1, except that the molar ratio of nickel ions to manganese ions in the mixed metal salt solution is 50:50. The positive electrode active material precursor of the present example is Ni 0.50 Mn 0.50 (OH)2.

[0127] Example 6

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

[0129] Example 7

[0130] The steps of the present example are basically consistent with those of Example 1, except that the rotation speed in Steps 1) to 4) is kept at 800 rpm.

[0131] Comparative Example 1

[0132] The steps of the present comparative example are basically consistent with those of Example 1, except that ammonia water is passed in Step 1), and the complexing agent concentration of the reaction system in Steps 1) to 4) is 8 g / L.

[0133] Comparative Example 2

[0134] The steps of the present comparative example are basically consistent with those of Example 1, except that ammonia water is passed 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 the present comparative example are basically consistent with those of Example 1, except that the ammonia value of the reaction system in Step 3) is 5 g / L, ammonia water is continuously passed in Step 4) and the ammonia value in the reaction system is 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 was measured by a tap density meter, the specific surface area was measured by nitrogen adsorption static volume method, and the particle size was measured by a particle size analyzer.

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

[0141] Figure 1 The image shown is a scanning electron microscope (SEM) image of the positive electrode active material precursor of Example 1 of this application at 1000x magnification. Figure 2 This is a scanning electron microscope image of the positive electrode active material precursor of Example 1 of this application at 5000x magnification. Figure 3 The image shown is a scanning electron microscope (SEM) image of the positive electrode active material precursor of Example 1 of this application at 10,000x magnification. Figure 4 This is a cross-sectional electron microscope image of the positive electrode active material precursor of Example 1 of this application, magnified at 9000x. Figure 3 As can be seen in this view, this application includes a cross-linked whisker (whisker 1 in the figure) connected to six first whiskers (whiskers 2-7 in the figure), and the angle between two of the first whiskers (whiskers 3 and 5) and the cross-linked whisker is ≤30°. Figure 4 It can be seen that particles aggregate together radioactively.

[0142] Figure 5 The image shown is a scanning electron microscope (SEM) image of the positive electrode active material precursor of Example 2 of this application at 1000x magnification. Figure 6 This is a scanning electron microscope image of the positive electrode active material precursor of Example 2 of this application at 10000x magnification. Figure 7 This is a cross-sectional electron microscope image of the positive electrode active material precursor of Example 2 of this application, magnified at 6000x. Figure 6 As can be seen in this view, the present application includes cross-linked whiskers and anisotropic whiskers, and includes cross-linked whiskers connected to five first whiskers, wherein the angle between three of the first whiskers and the cross-linked whiskers is ≤30°. Figure 7 It can be seen that particles aggregate together radioactively.

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

[0144] Table 1. Relevant parameters of the positive electrode active material precursors in the Examples and Comparative Examples.

[0145]

[0146] Experimental 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 hours to obtain the positive electrode active material of this application.

[0148] Figure 11 This is a scanning electron microscope image of the positive electrode active material of Example 1 of this application; Figure 12 This is a scanning electron microscope (SEM) image of the positive electrode active material of Example 2 of this application; by Figure 11 and 12 It is known that the positive electrode active material of this 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, which were then assembled with negative electrode sheets, electrolytes, and separators to obtain coin cells. Specifically, each positive electrode active material was mixed with conductive carbon black (SP) and PVDF in a weight ratio of 80%:10%:10%, and dispersed to obtain a positive electrode slurry. The slurry was coated onto an aluminum foil current collector and rolled to obtain a positive electrode sheet. The positive electrode sheet was then punched into small discs with a diameter of 12 mm using a film die. After drying and weighing, the discs were assembled into coin cells using a 2025 coin cell case, a Li metal disc as the negative electrode, and a conventional high-voltage lithium cobalt oxide electrolyte in a glove box under an Ar protective atmosphere.

[0150] The lithium-ion batteries were tested as follows, and the results are shown in Table 2:

[0151] 1) Initial discharge capacity and first effect

[0152] After each battery was left to stand at 25°C for 4 hours, its first charge-discharge capacity was tested. The test conditions were: 0.1C charging to 4.95V, constant voltage charging to 1C cutoff, standing for 3 minutes, and then 0.1C discharging 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 package full cell was formed, the gas bag was cut off and sealed, and the initial capacity after formation was tested. After charging to 4.95V, the remaining capacity of the battery was tested after 28 days of storage, and the ratio of the remaining battery capacity to the initial capacity was the storage capacity retention.

[0155] Cycle retention: at 25℃, charge to 4.95V at 1C charge rate, then discharge to 3.5V at 1C discharge rate, repeat 200 times of such charge-discharge cycle, measure the discharge capacity Q1 at the first cycle and the discharge capacity Q200 at the 200th cycle 200 .

[0156] Cycle retention Q = Q 200 / Q1x100%.

[0157] Table 2: Table of electrical performance parameters of lithium ion batteries

[0158]

[0159] From Table 1 and Table 2, it can be seen that the positive active material precursor of the application is helpful to obtain high-manganese positive active material with 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, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate 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, Having Ni a Co b Mn c The chemical composition of (OH)2, wherein 0.1≤a≤0.5, 0≤b≤0.5, and 0.5≤c≤0.9; The positive electrode active material precursor includes secondary particles formed by the aggregation of 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; the length of the first whiskers is 1000nm≤length≤4000nm, and the thickness is ≥500nm; The whisker also includes a second whisker, the second whisker having a thickness ≤100nm and a length ≤2000nm; Of the at least five first whiskers connected to the cross-linked whiskers, at most three first whiskers have an angle ≤30° with the cross-linked whiskers.

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

3. The positive electrode active material precursor according to any one of claims 1-2, characterized in that, The first whisker also includes 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, N≥3, and M≤3.

4. The positive electrode active material precursor according to claim 3, characterized in that, Of the M first whiskers, X first whiskers are connected to the anisotropic whiskers through each other, where X≤M.

5. The positive electrode active material precursor according to any one of claims 1-2, characterized in that, The secondary particles have a D50 of 8–16 μm and a tap density of 1.2–2.1 g / cm³. 3 The specific surface area is 5~25㎡ / g.

6. A method for preparing a positive electrode active material precursor according to any one of claims 1-5, characterized in that, Includes the following steps: 1) At 50-70℃, a metal salt solution and a precipitant solution are introduced into the reaction base liquid to carry out the first coprecipitation reaction, and the pH of the reaction system is controlled at 11.2-11.8 and the complexing agent is 0, until the median particle size D1 of the secondary particles is 2.0μm, and the first coprecipitation product system is obtained. 2) A metal salt solution, a precipitant solution, and a complexing agent solution are introduced into the first coprecipitate product system to carry out a second coprecipitation reaction, and the pH of the reaction system is controlled at 10.9-11.5 until the median particle size of the secondary particles is D2, thus obtaining the second coprecipitate product system; 3) A metal salt solution, a precipitant solution, and a complexing agent solution are introduced into the second coprecipitate product system to carry out a third coprecipitation reaction, and the pH of the reaction system is controlled at 10.6-11.2 until the median particle size of the secondary particles is D3, thus obtaining the third coprecipitate product system; 4) A fourth coprecipitation reaction is carried out by introducing a metal salt solution, a precipitant solution, and a complexing agent solution into the third coprecipitation product system, and the pH of the reaction system is controlled at 10.3-10.9 until the median particle size of the secondary particles is the preset value D0, thereby obtaining the positive electrode active material precursor. D2 = 1 / 3D0, D3 = 1 / 2D0, and C 络 ≤3C 盐 C 络 C represents the concentration of the complexing agent in the reaction system from steps 2) to 4). 盐 This represents the concentration of the metal salt solution.

7. The preparation method according to claim 6, characterized in that, The rotational speed V1 in step 1) is 700-900 rpm, the rotational speed V2 in step 2) is 70%-80% of V1, the rotational speed V3 in step 3) is 70%-80% of V2, and the rotational speed in step 4) is 70%-80% of V3; and / or, The solid content of the reaction system for the fourth coprecipitation reaction is greater than that of the reaction systems for the first, second, and third coprecipitations.

8. A positive electrode active material, characterized in that, Having Li x Ni a Co b Mn c The chemical composition of O2, wherein 0.9≤x≤1.1, 0.1≤a≤0.5, 0≤b≤0.5, and 0.5≤c≤0.9; The positive electrode active material comprises secondary particles formed by the aggregation of 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; the length of the first whiskers is 1000nm≤length≤4000nm, and the thickness is ≥500nm; The whisker also includes a second whisker, the second whisker having a thickness ≤100nm and a length ≤2000nm; Of the at least five first whiskers connected to the cross-linked whiskers, at most three first whiskers have an angle ≤30° with the cross-linked whiskers.

9. A positive electrode plate, characterized in that, Includes the positive electrode active material as described in claim 8.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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