Nickel-manganese binary precursor as well as preparation method and application thereof

Abstract

The invention provides a nickel-manganese binary precursor and a preparation method and application thereof. The nickel-manganese binary precursor comprises an inner core and a shell stacked on the outer surface of the inner core, the shell is formed by stacking a plurality of strip-shaped structures and a plurality of block-shaped structures in a staggered mode, the length-width ratio of the strip-shaped structures is (4-8): 1, and the size range of the block-shaped structures in any direction is 220-840 nm. A plurality of strip-shaped structures and a plurality of block-shaped structures in the nickel-manganese binary precursor are staggered and stacked, so that the lithium salt or the additive can quickly enter the inner core through the shell, and the element distribution uniformity is improved; the blocky structure increases the structural stability of the nickel-manganese binary precursor, and is beneficial to reducing the risk of structural cracking or particle crushing of the nickel-manganese binary precursor, thereby being beneficial to preparing the nickel-manganese binary positive electrode material with high specific capacity and high stability.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a nickel-manganese binary precursor, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles and power tools, higher demands are being placed on the energy density and cost control of lithium-ion batteries. In traditional ternary cathode materials, cobalt is expensive and scarce, leading to high battery costs. Cobalt-free nickel-manganese-based binary cathode materials have become a research hotspot due to their high safety and low cost advantages.

[0003] However, cobalt-free cathode materials suffer from problems such as low conductivity, poor structural stability, poor rate performance, and rapid cycle degradation. Therefore, how to improve the structural and cycle stability of nickel-manganese-based binary cathode materials while reducing costs has become a key technical challenge that urgently needs to be overcome in the current lithium-ion battery field. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, this application provides a nickel-manganese binary precursor.

[0005] In addition, embodiments of this application also provide a method for preparing a nickel-manganese binary precursor, a nickel-manganese binary cathode material, and an electrochemical device.

[0006] In a first aspect, embodiments of this application provide a nickel-manganese binary precursor, which includes a core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacking of multiple strip structures and multiple block structures. The aspect ratio of the strip structures is (4~8):1, and the size range of the block structures in any direction is 220nm~840nm.

[0007] Based on the first aspect, in some possible embodiments, in the nickel-manganese binary precursor, the ratio of the number of strip structures to the number of block structures is (2.5~3.5):1.

[0008] Based on the first aspect, in some possible embodiments, the size range of the strip structure along any direction is 60nm~690nm.

[0009] Based on the first aspect, in some possible embodiments, the length of the strip structure ranges from 410nm to 690nm, and the width of the strip structure ranges from 50nm to 170nm.

[0010] Based on the first aspect, in some possible embodiments, the aspect ratio of the block structure is (1.5~2.3):1; and / or the length of the block structure ranges from 500nm to 840nm, and the width of the block structure ranges from 220nm to 470nm.

[0011] Secondly, this application provides a method for preparing a nickel-manganese binary precursor, the method comprising: mixing a metal salt solution containing manganese salt and nickel salt, an ammonia solution, and a precipitant to form a reaction system, wherein the reaction system reacts under alkaline conditions to form a core; maintaining the ammonia concentration of the reaction system, decreasing the pH of the reaction system, and continuing the reaction to form multiple staggered stacked strip structures on the surface of the core; and maintaining the pH of the reaction system, increasing the ammonia concentration of the reaction system, and continuing the reaction to allow some of the strip structures to continue growing into block structures, thereby obtaining the nickel-manganese binary precursor, wherein the nickel-manganese binary precursor includes the core and a shell stacked on the outer surface of the core, the shell being formed by staggered stacking of multiple strip structures and multiple block structures, the aspect ratio of the strip structures being (4~8):1, and the size range of the block structures in any direction being 220nm~840nm.

[0012] Thirdly, embodiments of this application also provide a nickel-manganese binary cathode material, which is obtained using the aforementioned nickel-manganese binary precursor.

[0013] Based on the third aspect, in some possible embodiments, the nickel-manganese binary cathode material includes a core layer and an outer shell layer stacked on the outer surface of the core layer. The outer shell layer is formed by alternating stacking of multiple first structures and multiple second structures, wherein the aspect ratio of the first structure is (4~8):1, and the size range of the second structure along any direction is 315nm~980nm.

[0014] Fourthly, embodiments of this application also provide an electrochemical device, the electrochemical device including a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material being the aforementioned nickel-manganese binary positive electrode material.

[0015] Compared to existing technologies, the nickel-manganese binary precursor provided in this application has a shell, which is formed by the alternating stacking of multiple strip-shaped structures and multiple block-shaped structures. In this alternating stacked shell, certain pores are formed between adjacent strip-shaped or block-shaped structures. Furthermore, due to the specific aspect ratio of the strip-shaped structures, the number of pores in the shell is increased. During the sintering of this nickel-manganese binary precursor to prepare the cathode material, these pores facilitate the rapid entry of lithium salts or additives through the shell into the core, thereby improving the uniformity of mixing and element distribution. Simultaneously, the larger size of the block-shaped structures in the alternating stacked shell increases the structural stability of the nickel-manganese binary precursor, reducing the risk of structural cracking or particle breakage. Therefore, the nickel-manganese binary precursor provided in this application has the structural advantages of facilitating rapid and uniform mixing and high structural stability, which is beneficial for producing nickel-manganese binary cathode materials with both high specific capacity and high stability. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the preparation method of the nickel-manganese binary precursor provided in an embodiment of this application.

[0017] Figure 2 These are scanning electron microscope (SEM) images of the nickel-manganese binary precursor and the nickel-manganese binary cathode material in Example 1 of this application. Figure 2 Figure (a) is a scanning electron microscope image of the nickel-manganese binary precursor in Example 1 at a magnification of 20k. Figure 2 Figure (b) is a cross-sectional scanning electron microscope image of the nickel-manganese binary precursor of Example 1 at a magnification of 40k. Figure 2 Figure (c) is a scanning electron microscope image of the nickel-manganese binary cathode material in Example 1 at a magnification of 8k. Figure 2 Figure (d) is a cross-sectional scanning electron microscope image of the nickel-manganese binary cathode material in Example 1 at a magnification of 20k.

[0018] Figure 3 These are scanning electron microscope (SEM) images of the nickel-manganese binary precursor and the nickel-manganese binary cathode material in Comparative Example 1 of this application. Figure 3 Figure (a) in the figure is a scanning electron microscope image of the nickel-manganese binary precursor of Comparative Example 1 at a magnification of 20k. Figure 3 Figure (b) is a cross-sectional scanning electron microscope image of the nickel-manganese binary precursor in Comparative Example 1 at a magnification of 40k. Figure 3 Figure (c) in the diagram is a scanning electron microscope image of the nickel-manganese binary cathode material in Comparative Example 1 at a magnification of 8k.

[0019] Figure 4 These are scanning electron microscope (SEM) images of the nickel-manganese binary precursor and the nickel-manganese binary cathode material in Comparative Example 2 of this application. Figure 4Figure (a) in the figure is a scanning electron microscope image of the nickel-manganese binary precursor of Comparative Example 2 at a magnification of 20k. Figure 4 Figure (b) is a cross-sectional scanning electron microscope image of the nickel-manganese binary precursor of Comparative Example 2 at a magnification of 40k. Figure 4 Figure (c) in the diagram is a scanning electron microscope image of the nickel-manganese binary cathode material in Comparative Example 2 at a magnification of 8k. Detailed Implementation

[0020] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0021] The inventors of this application have discovered that nickel-manganese binary precursors are the core "semi-finished products" for synthesizing nickel-manganese binary cathode materials, and their metal element ratios, particle size, and morphology affect the performance of the final cathode material. However, existing nickel-manganese binary precursors have the following drawbacks: manganese easily hinders electron transport within the cathode material, directly affecting the battery's rate performance, and is commonly modified by external coating or doping; during charge and discharge, manganese ions easily dissolve into the electrolyte, and the cathode material's crystal lattice is prone to distortion, leading to decreased structural stability and a faster battery cycle decay rate than ternary precursors; nickel and manganese have similar hydrolysis pH values, and uneven composition is easily generated during co-precipitation, affecting the consistency of the final cathode material's performance, requiring precise control of reaction parameters (such as temperature and stirring speed).

[0022] Therefore, this application provides a novel nickel-manganese binary precursor, which includes a core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacking of multiple strip structures and multiple block structures. The aspect ratio of the strip structures is (4~8):1, and the size range of the block structures in any direction is 220nm~840nm.

[0023] The outer shell is formed by the staggered stacking of multiple strip-like and block-like structures. These structures are not simply arranged in parallel, but rather overlap and intersect at different angles, resembling a randomly stacked pile of firewood or a bird's nest. This stacking method results in a porous yet robust shell with a three-dimensional network structure. Furthermore, the strip-like structures have the aforementioned suitable aspect ratio, while the block-like structures have the aforementioned large dimensions. This facilitates the formation of abundant gaps and channels between the strip-like and block-like structures, creating a channel network that allows direct access from the outside of the particle to its interior. In the preparation of cathode materials from sintered nickel-manganese binary precursors, this significantly promotes the rapid and uniform penetration of lithium salts and additives into the nickel-manganese binary precursor particles, achieving more uniform bulk phase mixing or doping. The nickel-manganese binary precursor exhibits high reactivity, solving the problems of hindered lithium-ion and electron transport and poor bulk phase uniformity in the precursor, thereby improving the electrical performance and bulk phase uniformity of the cobalt-free nickel-manganese binary cathode material. Meanwhile, the larger block structure itself has higher structural strength, and the interlocking of the block structure and the strip structure can also increase the structural stability of the nickel-manganese binary precursor, effectively reducing the risk of structural cracking or particle breakage of the nickel-manganese binary precursor.

[0024] The aspect ratio of the strip structure is (4~8):1, which is beneficial for forming abundant voids and channels on the core surface, providing a fast and low-resistance diffusion path for lithium ions or dopants from the surface of the nickel-manganese binary precursor particles directly to the core. When the aspect ratio is too low (below 4:1), the resulting stacked pores will be too few or too short, which is not conducive to uniform mixing; when the aspect ratio is too high (above 8:1), the strip structure will be too weak and prone to breakage during synthesis and battery cycling. The aspect ratio of the strip structure can be exemplarily 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, or any value within the range of any two of the above values. The aspect ratio of the strip structure can further be (5~7):1.

[0025] In some embodiments, the size range of the strip structure in any direction can be 60nm to 690nm. The overall size of the strip structure is smaller than that of the block structure, which is beneficial for further forming through-hole channels in the shell. The size range of the strip structure in any direction can, for example, be 60nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 690nm, or any value within the range of any two of the above values. The size range of the strip structure in any direction can further be 100nm to 500nm.

[0026] Specifically, the length of the strip structure can range from 410nm to 690nm, and can be, for example, 410nm, 430nm, 450nm, 500nm, 550nm, 600nm, 650nm, 690nm, or any value within the range of any two of the above values. The width of the strip structure can range from 50nm to 170nm, and can be, for example, 50nm, 80nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, or any value within the range of any two of the above values.

[0027] The bulk structure's dimensions range from 220 nm to 840 nm in any direction, meaning it has a suitablely large size, making it less prone to breakage. This increases the structural stability of the nickel-manganese binary precursor and reduces the risk of structural cracking or particle breakage. Simultaneously, this size prevents the outer shell from becoming too dense, which could hinder the entry of lithium ions or other elements into the nickel-manganese binary precursor. If the bulk structure is too small (less than 220 nm), its strength is low, making it prone to breakage and reducing the structural stability of the nickel-manganese binary precursor. Conversely, if the bulk structure is too large (greater than 840 nm), the outer shell becomes too dense, making it difficult to uniformly mix the nickel-manganese binary precursor when used in cathode material preparation. The size range of the bulk structure in any direction can, for example, be 220nm, 240nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 840nm, or any value within the range of any two of the above values. The size range of the bulk structure in any direction can further be 300nm to 700nm.

[0028] Specifically, the length of the block structure can range from 500nm to 840nm, and can be, for example, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 840nm, or any value within the range of any two of the above values. The width of the block structure can range from 220nm to 470nm, and can be, for example, 220nm, 250nm, 300nm, 350nm, 400nm, 450nm, 470nm, or any value within the range of any two of the above values.

[0029] In some embodiments, the aspect ratio of the block structure can be (1.5~2.3):1. By further limiting the aspect ratio of the block structure within this range, the length and width dimensions of the block structure are closer, which further improves the stability and structural strength of the block structure, thereby improving the structural stability of the nickel-manganese binary precursor.

[0030] In nickel-manganese binary precursors, the ratio of strip-like structures to block-like structures can be (2.5~3.5):1, which is beneficial for improving the structural stability and strength of the nickel-manganese binary precursor while allowing lithium ions or other elements to rapidly penetrate its core. This ratio can be exemplarily 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, or any value within the range of any two of the above values. A further variation of this ratio is (2.8~3.2):1.

[0031] In some embodiments, the core has a porous structure that is interconnected with the pores of the outer shell, forming a channel network extending from the outside of the particle to its interior. This greatly facilitates the rapid and uniform penetration of lithium salts or additives into the particle during the preparation of cathode materials.

[0032] In some embodiments, the ratio of the core diameter to the shell thickness can be (2.5~4.0):1. The core provides the primary specific capacity, while the shell provides diffusion channels for lithium ions or other elements and mechanical strength. Adjusting the aforementioned size ratio is beneficial for the nickel-manganese binary precursor to achieve a balance of high capacity, reactivity, rate performance, and structural stability. This ratio can exemplarily be 2.5:1, 2.75:1, 3.0:1, 3.25:1, 3.5:1, 3.75:1, 4.0:1, or any value within the range of any two of the above values. Further, this ratio can be (3~3.5):1.

[0033] Specifically, the diameter of the core can be 1.0 μm to 1.6 μm, and exemplaryly it can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, or any value within the range of any two of the above values. The thickness of the outer shell can be 350 nm to 450 nm, and exemplaryly it can be 350 nm, 375 nm, 400 nm, 425 nm, 450 nm, or any value within the range of any two of the above values.

[0034] In some embodiments, the median particle size D50 of the nickel-manganese binary precursor can be 3.3 μm to 3.7 μm, and exemplaryly can be 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, or any value within the range of any two of the above values.

[0035] Please see Figure 1 As shown, this application provides a method for preparing the aforementioned nickel-manganese binary precursor, specifically including the following steps: Step S1 involves mixing a metal salt solution containing manganese and nickel salts, an ammonia solution, and a precipitant to form a reaction system. This reaction system reacts under alkaline conditions to form a core.

[0036] Specifically, the formation process of the aforementioned reaction system includes the following steps: Step S11: Prepare the reaction solution, which includes a metal salt solution, an ammonia solution, and a precipitant: Dissolve nickel sulfate and manganese sulfate in deionized water to prepare a metal salt solution with a total nickel and manganese metal ion concentration of approximately 130 g / L, wherein the molar ratio of nickel to manganese can be (0.01-0.99):(0.01-0.99); the precipitant used is, for example, a sodium hydroxide solution with a concentration of approximately 429 g / L; the concentration of the ammonia solution used is approximately 110 g / L.

[0037] Step S12: Add deionized water to the sealed reactor and purge with submerged nitrogen gas (flow rate approximately 2.0 m³ / s). 3 (Continue to pass through the ammonia solution for about 2 hours), and start stirring. Add ammonia solution and precipitant in sequence to obtain the reaction base liquid.

[0038] Step S13: The above metal salt solution, ammonia solution and precipitant are added to the reaction substrate and mixed to carry out precipitation reaction to form the core.

[0039] During the nucleus formation stage, maintaining the ammonia concentration in the reaction system at 2.5 g / L to 3.5 g / L and the pH at 11.8 to 11.9 is beneficial for promoting the rapid formation of small-diameter crystal nuclei and further forming a denser nucleus. At the same time, the nucleus has a porous structure, which is conducive to lithium salt permeation.

[0040] In some embodiments, the reaction phase can last from 3.5 h to 4.5 h, which is beneficial for forming nuclei of the target particle size. The time can be exemplarily 3.5 h, 3.75 h, 4 h, 4.25 h, 4.5 h, or any value within the range of any two of the above values.

[0041] In some embodiments, nitrogen gas is continuously introduced during this reaction stage, with a submerged flow rate of approximately 2.0 m³. 3 The nitrogen flow rate at the liquid level is approximately 2.0 m³ / h. 3 / h, which helps to eliminate oxygen interference and reduce the oxidation of manganese ions.

[0042] Step S2: Maintain the ammonia concentration in the reaction system, reduce the pH of the first slurry reaction system, and continue the reaction to form multiple staggered strip structures on the surface of the core.

[0043] Specifically, in this step, the ammonia concentration in the reaction system remains constant. By adjusting the pH value of the reaction system, multiple primary particles with strip-like structures are formed on the surface of the core. pH adjustment involves gradually decreasing the pH of the reaction system while maintaining alkaline conditions. For example, the pH can be adjusted until it stabilizes at 10.9–11.0, and the reaction continues for 28–36 hours, at which point this stage of the reaction ends. During this stage, the lower pH value is conducive to the formation of primary particles with strip-like structures, and allows these structures to deposit on the surface of the core.

[0044] In this step, the pH decrease rate can be (0.12~0.18) / 6h, meaning the pH decreases by approximately 0.12~0.18 every 6 hours, reaching 10.9~11.0 after about 36 hours. This slow pH decrease facilitates better and more uniform deposition of the strip-like structures on the core surface, reducing their aggregation and thus improving the sphericity and morphology of the nickel-manganese binary precursor. Furthermore, controlling the pH every 6 hours simplifies the production process and improves operational convenience. The pH decrease rate can, for example, be any value within the range of any two of the above values: 0.12 / 6h, 0.13 / 6h, 0.14 / 6h, 0.15 / 6h, 0.16 / 6h, 0.17 / 6h, or 0.18 / 6h. A further possible pH decrease rate is (0.13~0.17) / 6h.

[0045] Furthermore, the pH decrease rate can be 0.02 / h to 0.03 / h, which facilitates more precise control of the reaction pH. The pH decrease rate can, for example, be any value within the range of any two of the above values: 0.02 / h, 0.021 / h, 0.022 / h, 0.023 / h, 0.024 / h, 0.025 / h, 0.026 / h, 0.027 / h, 0.028 / h, 0.029 / h, or 0.03 / h. The pH decrease rate can further be 0.022 / h to 0.028 / h.

[0046] Step S3: Maintain the pH of the reaction system, increase the ammonia concentration of the reaction system, and continue the reaction so that some of the strip structures continue to grow into block structures, thereby obtaining a nickel-manganese binary precursor. The nickel-manganese binary precursor includes a core and a shell stacked on the outer surface of the core. The shell is formed by multiple strip structures and multiple block structures stacked alternately. The aspect ratio of the strip structures is (4~8):1, and the size range of the block structures in any direction is 220nm~840nm.

[0047] Specifically, in this step, the pH of the reaction system remains constant. By controlling the ammonia concentration, some of the strip-like structures continue to grow into block-like structures. The ammonia concentration is controlled by gradually increasing it until it reaches 11.5 g / L to 12.5 g / L, and then continuing the reaction until the particles reach the target particle size of the nickel-manganese binary precursor, at which point the reaction is complete. During this reaction stage, the lower pH and higher ammonia content result in low supersaturation of the precipitate, making it difficult for new primary particles to grow. Instead, the precipitate adsorbs onto the existing strip-like primary particles, thus allowing some of the original strip-like structures to continue growing and forming block-like structures.

[0048] After the ammonia concentration increases at a constant rate, the final ammonia concentration in the reaction system is 11.5 g / L to 12.5 g / L. For example, it can be 11.5 g / L, 11.6 g / L, 11.7 g / L, 11.8 g / L, 11.9 g / L, 12.0 g / L, 12.1 g / L, 12.2 g / L, 12.3 g / L, 12.4 g / L, 12.5 g / L, or any value within the range of any two of the above values.

[0049] In this step, the rate of increase in ammonia concentration can be 0.15 g·L⁻¹. -1 ·h -1 ~0.25 g·L -1 ·h -1 After approximately 40-50 hours, the ammonia concentration reaches 11.5 g / L to 12.5 g / L, which is beneficial for some strip-like structures to continue growing into blocky structures and reduces particle agglomeration, thereby improving the sphericity and morphology of the nickel-manganese binary precursor. The rate of increase in ammonia concentration can, for example, be 0.15 g / L. -1 ·h -1 0.16 g·L -1 ·h -1 0.17 g·L -1 ·h -1 0.18 g·L -1 ·h -1 0.19 g·L -1 ·h -1 0.20 g·L -1 ·h -1 0.21 g·L-1 ·h -1 0.22 g·L -1 ·h -1 0.23 g·L -1 ·h -1 0.24 g·L -1 ·h -1 0.25 g·L -1 ·h -1 Any value within the range formed by any two of the above values. The rate of increase in ammonia concentration can further be 0.18 g·L⁻¹. -1 ·h -1 ~0.22g·L -1 ·h -1 .

[0050] In some embodiments, the ratio of strip structures to block structures can be (2.5~3.5):1. This ratio is affected by the final pH, final ammonia concentration, and reaction time in steps S2 and S3. Within the above ratio range, it is beneficial to improve the structural stability and structural strength of the nickel-manganese binary precursor while rapidly penetrating lithium ions or other elements into the core of the precursor. This ratio can exemplarily be 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, or any value within the range of any two of the above values. Further, this ratio can be (2.8~3.2):1.

[0051] In some embodiments, the target particle size of the nickel-manganese binary precursor, i.e. the median particle size D50 of the nickel-manganese binary precursor, can be 3.3 μm to 3.7 μm, and can be, for example, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm or any value within the range of any two of the above values.

[0052] In some embodiments, after the reaction continues until the particles reach the target particle size of the nickel-manganese binary precursor, the preparation method may further include aging, washing, drying, sieving and demagnetizing the slurry to obtain the nickel-manganese binary precursor.

[0053] Compared with existing technologies, the preparation method of the nickel-manganese binary precursor in this application has the following advantages: 1. By adjusting the pH value of the reaction system, multiple strip-shaped structures are formed on the surface of the core, which is beneficial for lithium salt or additives to quickly enter the core through the shell when preparing cathode materials from nickel-manganese binary precursors, thereby improving the mixing uniformity of nickel-manganese binary precursors.

[0054] 2. By adjusting the ammonia concentration in the reaction system, some strip-like structures on the core surface continue to grow to form block-like structures, thereby increasing the structural stability of the nickel-manganese binary precursor and helping to reduce the risk of structural cracking or particle breakage of the nickel-manganese binary precursor.

[0055] 3. By adjusting the pH, ammonia concentration, and reaction time at each reaction stage, the ratio of strip-like to block-like structures in the shell is controlled, thereby further balancing the mixing uniformity and structural stability of the nickel-manganese binary precursor.

[0056] 4. This preparation method requires no new equipment or raw materials, is simple in process, easy to operate, and is conducive to the large-scale production of nickel-manganese binary precursors.

[0057] This application provides a nickel-manganese binary cathode material, which is obtained using the aforementioned nickel-manganese binary precursor.

[0058] Compared to existing technologies, this nickel-manganese binary cathode material is prepared using the aforementioned nickel-manganese binary precursor. The preparation method includes, but is not limited to, the traditional high-temperature solid-state method, in which the nickel-manganese binary precursor is uniformly mixed with a lithium source or additives, and then heat-treated at high temperature to allow lithium elements to diffuse into the precursor's crystal lattice. Since the nickel-manganese binary precursor has an outer shell formed by multiple strip structures and multiple block structures stacked alternately, lithium salts or additives can quickly enter the core through the outer shell, improving the uniformity of element distribution and thus improving the capacity and cycle performance of the nickel-manganese binary cathode material. At the same time, the block structure increases the structural stability of the nickel-manganese binary precursor, thereby improving the structural stability of the nickel-manganese binary cathode material. As a result, the prepared nickel-manganese binary cathode material has both high specific capacity and high stability.

[0059] From a microstructural perspective, this nickel-manganese binary cathode material inherits from the nickel-manganese binary precursor. The nickel-manganese binary cathode material includes a core layer and an outer shell layer stacked on the outer surface of the core layer. The outer shell layer is formed by multiple first structures and multiple second structures stacked alternately. In the nickel-manganese binary cathode material, the core layer inherits the core of the nickel-manganese binary precursor, and the outer shell layer inherits the outer shell of the nickel-manganese binary precursor. The aspect ratio of the first structure is (4~8):1. The first structure inherits the aspect ratio of the strip structure in the nickel-manganese binary precursor. The size range of the second structure in any direction is 315nm~980nm. The size of the strip block structure in the nickel-manganese binary precursor increases during the lithiation sintering process to form the second structure in the nickel-manganese binary cathode material.

[0060] This application also provides an electrochemical device (e.g., a secondary battery) comprising a positive electrode plate, the positive electrode plate comprising a positive electrode material, wherein the positive electrode material is the aforementioned nickel-manganese binary positive electrode material. Compared with the prior art, the electrochemical device provided in this application has good structural stability and cycle performance, as well as a lower cost.

[0061] Typically, an electrochemical device may also include a negative electrode, a separator, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing ions to pass through.

[0062] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer comprising the ternary positive electrode material. The positive current collector can be aluminum foil or carbon-coated aluminum foil. The positive electrode film layer may also contain a binder, such as polyvinylidene fluoride (PVDF). The positive electrode film layer also contains a conductive agent, such as at least one selected from superconducting carbon, acetylene black, carbon black, carbon nanotubes, and graphene.

[0063] In some embodiments, the negative electrode may be a lithium sheet.

[0064] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative current collector may be a metal current collector, such as copper foil. The negative electrode film layer may contain a negative electrode active material. Negative electrode active materials are well known in the art, and this application does not particularly limit them. The negative electrode active material may be selected from at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, and lithium titanate, etc.

[0065] In some embodiments, the negative electrode film layer may further include a binder. The binder used for the negative electrode is, for example, at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylamide, and carboxymethyl cellulose. In some embodiments, the negative electrode film may also contain a conductive agent, such as one or more of the following materials: superconducting carbon, acetylene black, carbon black, graphene, carbon nanotubes, etc.

[0066] The electrolyte can be selected based on existing lithium battery specifications. Generally, the electrolyte contains an organic solvent and an electrolyte lithium salt. The electrolyte salt includes, but is not limited to: lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, and bis(fluorosulfonyl)imide. Organic solvents include, but are not limited to: ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, methyl acetate, propyl acetate, methyl propionate, and ethyl propionate.

[0067] This application does not impose any particular restrictions on the type of diaphragm; various porous diaphragms well-known in the art can be selected. The material of the diaphragm can be, for example, polyethylene, polypropylene, or polyvinylidene fluoride.

[0068] The electrochemical device of the present invention may be in the form of a single battery cell, a battery module, or a battery pack.

[0069] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of the application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically described are all conventional commercially available products or publicly disclosed.

[0070] Example 1 Step S1: Add 120L of anhydrous brine to the sealed reactor, and purge with submerged nitrogen gas for 2 hours at a flow rate of 2.0m³. 3 The mixture was stirred at 35 Hz and the temperature was controlled at 60℃. Ammonia solution and sodium hydroxide solution were added sequentially to the reactor to obtain a bottom liquid with an ammonia concentration of 0.18 mol / L and a pH of 11.86. The nitrogen flow rate was adjusted to 1.5 m below the liquid level. 3 / h, 1.5m above the liquid 3 At a rate of 1 h, a metal salt solution, sodium hydroxide solution, and ammonia solution are simultaneously added to the reactor to form a reaction system. The reaction is carried out for 4 h to form a core. During this period, the pH of the reaction system is maintained at 11.86, the ammonia concentration is 3.0 g / L, the temperature is 60 °C, and an inert gas is continuously introduced. The metal salt solution is prepared by dissolving nickel sulfate and manganese sulfate in deionized water. The total metal ion concentration of the metal salt solution is 130 g / L, and the molar ratio of nickel to manganese is (0.01~0.99):(0.01-0.99). The concentration of the sodium hydroxide solution used is 429 g / L, and the concentration of the ammonia solution used is 110 g / L.

[0071] Step S2: Maintain the ammonia concentration of the reaction system at 3.0 g / L, and gradually decrease the pH of the reaction system at a rate of 0.15 / 6 h until the pH stabilizes at 10.96. Continue the reaction for 32 h to form multiple interlaced stacked strip structures on the surface of the core.

[0072] Step S3: Maintain the pH of the reaction system at 10.96, and use approximately 0.25 g·L⁻¹ -1 ·h -1 The ammonia concentration in the reaction system was gradually increased to 12.5 g / L, and the reaction continued until the median particle size D50 of the nickel-manganese binary precursor was 3.3 μm to 3.7 μm, so that some strip structures could continue to grow into block structures. After the reaction was completed, the machine was stopped for 30 to 60 minutes. After the particle size was retested and found to be normal, the slurry that had completed the reaction in the reactor was placed in an aging tank for aging. The slurry in the aging tank was then pumped into a washing device and alkali washed with a sodium hydroxide solution with a concentration of 429 g / L. Then, it was washed multiple times with water without brine until the total dissolved solids (TDS) was <25. The washed binary nickel-manganese precursor wet material was placed in a 110℃ oven for drying, and then sieved and demagnetized to obtain the nickel-manganese binary precursor material.

[0073] The nickel-manganese binary precursor includes a core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacks of multiple strip structures and multiple block structures. The aspect ratio of the strip structures is (4~8):1, and the size of the block structures ranges from 220nm to 840nm in any direction. The ratio of the number of strip structures to the number of block structures is (2.5~3.5):1.

[0074] Example 2: The difference from Example 1 is that in step S2, the ammonia concentration of the reaction system is maintained at 3.0 g / L, and the pH of the reaction system is gradually decreased at a rate of approximately 0.15 g / L over 6 hours until the pH stabilizes at 11.0, and the reaction continues for 32 hours; in step S3, the pH of the reaction system is maintained at 10.96, and the pH is gradually decreased at a rate of approximately 0.25 g / L over 6 hours. -1 ·h -1 The ammonia concentration in the reaction system was gradually increased to 11.5 g / L. The preparation methods for the remaining nickel-manganese binary precursors were basically the same as in Example 1.

[0075] The nickel-manganese binary precursor includes a core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacks of multiple strip structures and multiple block structures. The aspect ratio of the strip structures is (4~8):1, and the size of the block structures ranges from 220nm to 840nm in any direction. The ratio of the number of strip structures to the number of block structures is (2.5~3.5):1.

[0076] Example 3: The difference from Example 1 is as follows: In step S2, the ammonia concentration of the reaction system is maintained at 3.0 g / L, and the pH of the reaction system is gradually decreased at a rate of approximately 0.15 g / L over 6 hours until the pH stabilizes at 10.9, and the reaction continues for 32 hours; In step S3, the pH of the reaction system is maintained at 10.9, and the pH is gradually decreased at a rate of approximately 0.25 g / L over 6 hours. -1 ·h -1The ammonia concentration in the reaction system was gradually increased to 11.5 g / L. The preparation methods for the remaining nickel-manganese binary precursors were basically the same as in Example 1.

[0077] The nickel-manganese binary precursor includes a core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacks of multiple strip structures and multiple block structures. The aspect ratio of the strip structures is (4~8):1, and the dimensions of the block structures in any direction range from 220nm to 840nm. The ratio of the number of strip structures to block structures is (2.5~3.5):1.

[0078] Comparative Example 1: The difference from Example 1 is as follows: In step S2, the ammonia concentration of the reaction system is maintained at 3.0 g / L, and the pH of the reaction system is gradually decreased at a rate of approximately 0.15 g / L over 6 hours until the pH stabilizes at 11.1, and the reaction continues for 32 hours; In step S3, the pH of the reaction system is maintained at 11.1, and the pH is gradually decreased at a rate of approximately 0.16 g / L over 6 hours. -1 ·h -1 The ammonia concentration in the reaction system was gradually increased to 8 g / L~9 g / L. The preparation methods for the remaining nickel-manganese binary precursors were basically the same as in Example 1.

[0079] The nickel-manganese binary precursor includes a core and a shell stacked on the outer surface of the core. The shell is formed by multiple strip structures stacked alternately. The aspect ratio of the strip structures is (4~8):1. The size of the strip structures in any direction ranges from 50nm to 690nm. The length of the strip structures ranges from 410nm to 690nm. The width of the strip structures ranges from 50nm to 170nm.

[0080] Comparative Example 2 The difference from Example 1 is as follows: In step S2, the ammonia concentration of the reaction system is maintained at 3.0 g / L, and the pH of the reaction system is gradually decreased at a rate of approximately 0.15 g / L over 6 hours until the pH stabilizes at 10.7-10.8, and the reaction continues for 32 hours; In step S3, the pH of the reaction system is maintained at 10.7-10.8, and the pH is gradually decreased at a rate of approximately 0.25 g / L over 6 hours. -1 ·h -1 The ammonia concentration in the reaction system was gradually increased to 13.6~14.5 g / L. The preparation methods for the remaining nickel-manganese binary precursors were basically the same as in Example 1.

[0081] The nickel-manganese binary precursor includes a core and a shell stacked on the outer surface of the core. The shell is formed by multiple block structures stacked alternately. The aspect ratio of the block structures is (1.5~2.3):1. The size of the block structures in any direction ranges from 220nm to 840nm. The length of the block structures ranges from 500nm to 840nm. The width of the block structures ranges from 220nm to 470nm.

[0082] The nickel-manganese binary precursors obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to the following tests.

[0083] 1. Scanning electron microscopy (SEM) test: A JSM-IT210 scanning electron microscope was used. This model of instrument has high-resolution imaging capabilities and can clearly observe the microscopic morphology and structural features of materials.

[0084] 2. Particle size test: The median particle size D50 was measured using a Malvern 3000 particle size analyzer after internal ultrasonic dispersion for 5 minutes.

[0085] 3. Microscopic testing of material surface: Scanning electron microscopy (SEM) was used to scan the nickel-manganese binary precursor to obtain SEM images with a magnification of 20K. Multiple SEM images were randomly selected, and complete single nickel-manganese binary precursor particles were randomly selected from each selected SEM image. The approximate central area of ​​the particle was delineated using a 2μm scale as the measurement area. Using Nano Measurer software, 50 primary particles (strip-like or block-like structures) were randomly selected from the measurement area, and the size of the particles along any direction was measured. The maximum size was the length of the particle, and the maximum width perpendicular to the maximum size was the width of the particle. The aspect ratio was calculated as length / width. The range of size, length, width, and aspect ratio along any direction for the strip-like and block-like structures tested above were statistically analyzed.

[0086] Scanning electron microscopy (SEM) was used to scan the nickel-manganese binary precursor to obtain SEM images with a magnification of 20K. Multiple SEM images were randomly selected, and complete single nickel-manganese binary precursor particles were randomly selected from each selected SEM image. The approximate central region of the particle was delineated using a 2μm scale as the measurement area. The number of strip-like structures and block-like structures in the measurement area was counted. The ratio of the number of strip-like structures to the number of block-like structures was calculated as: number of strip-like structures / number of block-like structures.

[0087] Material cross-sectional microscopic testing: Scanning electron microscopy (SEM) was used to scan the nickel-manganese binary precursor to obtain cross-sectional SEM images with a magnification of 20K. Multiple SEM images were randomly selected, and complete single nickel-manganese binary precursor particles were randomly selected from each selected SEM image. Using Nano Measurer software, the average diameter of the nickel-manganese binary precursor core (average of 10 measurements) and the average thickness of the shell (average of 10 measurements) were calculated as the diameter. The diameter range of the core and the thickness range of the shell were then statistically analyzed.

[0088] 4. Chemical performance testing: The nickel-manganese binary precursor described above was mixed with a lithium source and calcined to obtain a nickel-manganese binary cathode material. The nickel-manganese binary cathode material, conductive agent SP, and binder PVDF were mixed uniformly at a mass ratio of 90:5:5, and then prepared into a coin cell.

[0089] Specific capacity test: Constant current charge-discharge test was performed using the LAND battery testing system. The test operating voltage range was 2.8V~4.5V, the temperature was 25℃, the charge-discharge rate was +1C / -1C, the CV cutoff current was 0.01C, and the initial discharge capacity of the battery was tested.

[0090] High-temperature cycle performance test: At 45℃, the button cell battery is subjected to 0.1C / 0.1C charge-discharge cycles, with an operating voltage range of 2.8V-4.5V and a CV cutoff current of 0.01C. The cycle retention rate after 100 cycles is tested. The capacity retention rate = discharge capacity of the 100th cycle / discharge capacity of the 1st cycle × 100%.

[0091] The test results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1 and 2. Figures 2 to 4 As shown.

[0092] Table 1 The above results indicate that: Depend on Figure 2 It can be seen that the nickel-manganese binary precursors in Example 1 all include a core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacks of multiple strip structures and multiple block structures. Furthermore, the strip structures and block structures in Examples 1-3 all satisfy the following conditions: the aspect ratio of the strip structures is (4~8):1, and the size range of the block structures in any direction is 220nm~840nm. Figure 3 and Figure 4 It can be seen that the shell of the nickel-manganese binary precursor in Comparative Example 1 is formed by the alternating stacking of block structures, while the shell of the nickel-manganese binary precursor in Comparative Example 2 is formed by the alternating stacking of strip structures. The shells of Comparative Examples 1 and 2 are formed by the stacking of single-structure particles.

[0093] As shown in Table 1, the nickel-manganese binary precursors in Examples 1-3 have an outer shell formed by the interlacing of multiple strip-shaped and multiple block-shaped structures. This facilitates the rapid penetration of lithium salts or additives into the core through the outer shell, improving the uniformity of the mixture and thus the uniformity of elemental distribution in the nickel-manganese binary cathode material. It also improves the structural stability of the nickel-manganese binary precursors, thereby improving the structural stability of the nickel-manganese binary cathode material. As a result, the batteries prepared with the nickel-manganese binary precursors in Examples 1-3 have good capacity and cycle performance. The initial discharge capacity of the batteries corresponding to Examples 1-3 is as high as 230.8 mAh / g or above, and the capacity retention rate after 100 cycles is also 88.5% or above.

[0094] Compared to Comparative Example 1, the lithium salt in Comparative Example 1 is not easy to enter the core because the outer shell is a large block structure and cannot be uniformly mixed with the nickel-manganese binary precursor, thus reducing the capacity performance of the battery in Comparative Example 1.

[0095] Compared to Comparative Example 2, the nickel-manganese binary precursor has poor structural stability due to the elongated strip structure of the outer shell, which reduces the cycle performance of the battery in Comparative Example 2.

[0096] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A nickel-manganese binary precursor, characterized in that, The nickel-manganese binary precursor includes a core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacking of multiple strip structures and multiple block structures. The aspect ratio of the strip structures is (4~8):1, and the size range of the block structures in any direction is 220nm~840nm.

2. The nickel-manganese binary precursor as described in claim 1, characterized in that, The ratio of the number of strip structures to the number of block structures is (2.5~3.5):

1.

3. The nickel-manganese binary precursor as described in claim 1, characterized in that, The dimensions of the strip structure range from 60nm to 690nm in any direction.

4. The nickel-manganese binary precursor as described in claim 3, characterized in that, The length of the strip structure ranges from 410nm to 690nm, and the width of the strip structure ranges from 60nm to 170nm.

5. The nickel-manganese binary precursor as described in claim 1, characterized in that, The aspect ratio of the block structure is (1.5~2.3):1; and / or The length of the block structure ranges from 500nm to 840nm, and the width of the block structure ranges from 220nm to 470nm.

6. A method for preparing a nickel-manganese binary precursor, characterized in that, The preparation method includes: A reaction system is formed by mixing a metal salt solution containing manganese and nickel salts, an ammonia solution, and a precipitant. The reaction system reacts under alkaline conditions to form a core. Maintaining the ammonia concentration in the reaction system, decreasing the pH of the reaction system, and continuing the reaction to form multiple interlocking, stacked strip-like structures on the surface of the core; and The pH of the reaction system is maintained, the ammonia concentration of the reaction system is increased, and the reaction continues so that some of the strip structures continue to grow into block structures, thereby obtaining the nickel-manganese binary precursor. The nickel-manganese binary precursor includes the core and a shell stacked on the outer surface of the core. The shell is formed by alternating stacking of multiple strip structures and multiple block structures. The aspect ratio of the strip structures is (4~8):1, and the size range of the block structures in any direction is 220nm~840nm.

7. The method for preparing the nickel-manganese binary precursor as described in claim 6, characterized in that, In the step of forming the core, the pH of the reaction system is 11.8 to 11.9, and the ammonia concentration of the reaction system is 2.5 g / L to 3.5 g / L; In the step of forming the strip-shaped structure, the ammonia concentration of the reaction system is 2.5 g / L to 3.5 g / L, and the pH of the reaction system is 10.9 to 11.0; In the step of forming the block structure, the ammonia concentration of the reaction system is 11.5 g / L to 12.5 g / L, and the pH of the reaction system is 10.9 to 11.

0.

8. A nickel-manganese binary cathode material, characterized in that, The nickel-manganese binary cathode material is made from the nickel-manganese binary precursor as described in any one of claims 1 to 5, or from the nickel-manganese binary precursor prepared by the method described in any one of claims 6 to 7.

9. The nickel-manganese binary cathode material as described in claim 8, characterized in that, The nickel-manganese binary cathode material includes a core layer and an outer shell layer stacked on the outer surface of the core layer. The outer shell layer is formed by alternating stacking of multiple first structures and multiple second structures. The aspect ratio of the first structure is (4~8):1, and the size range of the second structure along any direction is 315nm~980nm.

10. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode plate, the positive electrode plate includes a positive electrode material, and the positive electrode material is a nickel-manganese binary positive electrode material as described in any one of claims 8 to 9.

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