Positive electrode material for lithium ion batteries and method for producing the same

Abstract

This invention provides a cathode material for lithium-ion batteries, having the following general formula I: Li 1+a Ni x Co y Mn z M c M' d O 2‑ b A b General Formula I, where -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤c≤0.01, 0≤d≤0.01, x+y+z+c+d=1, and 0≤b≤0.05; M and M' are different from each other and are each independently selected from at least one of La, Cr, Mo, Ca, Fe, Ti, Zn, Y, Zr, W, Nb, V, Mg, B, Al, Sr, Ba, Ta, and A is selected from at least one of F, Cl, Br, I, S, and the number N of micrograin boundaries in the primary particles of the cathode material is 10.5~14.5, where N is calculated by Formula I: N=D S / D X Formula I, where D S The average size of the primary particles was measured using a cross-sectional SEM image of the cathode material, and D... X The value is the average crystallite size in the primary particles of the cathode material, obtained by XRD testing and Scherrer equation calculation. This invention also provides a method for preparing the cathode material.

Description

Technical Field

[0001] This invention relates to a positive electrode material for lithium-ion batteries and a method for preparing the same. Background Technology

[0002] In the current context, new energy vehicles and energy conservation and emission reduction have become top priorities for the automotive industry, driving the transformation of traditional internal combustion engine vehicles to more environmentally friendly new energy electric vehicles. Among electric vehicles, lithium-ion batteries, as a promising, efficient, and environmentally friendly power source, have received widespread attention.

[0003] Layered ternary materials are one of the mainstream choices for cathode materials in lithium-ion batteries. Compared with components such as anode and electrolyte, cathode materials have low capacity, high proportion, and high cost, thus becoming a key factor restricting the overall performance of lithium-ion batteries.

[0004] The capacity, rate capability, and lifetime of layered ternary materials can be improved by adjusting particle size, structural morphology, doping, and coating modification. Patent application CN111106344 A uses a magnesium aluminum phosphate composite as a raw material, coating the surface of the cathode material using solid-phase, liquid-phase, and gas-phase methods. After heat treatment, a composite cathode material is obtained, consisting of cathode material, a doped layer, and a coating layer from the inside out. During the reheating process, a small amount of lithium ions enters the coating layer, improving its ionic conductivity. Simultaneously, some metals from the coating layer enter the cathode surface, stabilizing the material structure, thus obtaining a high-capacity cathode material with superior overall performance. Patent application CN111217407 A improves the material's crystallinity and reduces the residual alkali content on the surface by pre-calcining the precursor and lithium-containing compound separately before mixing and sintering. This inhibits surface side reactions, thereby enhancing the cathode material's capacity and cycle stability.

[0005] To meet the ever-growing demands of electric vehicles for longer driving range and faster charging, it is still necessary to continuously improve the rate performance, capacity, and cycle life of lithium-ion batteries. Improving the performance of layered ternary materials is a key aspect of this. Summary of the Invention

[0006] To this end, on the one hand, this disclosure provides a cathode material for lithium-ion batteries, which has the following general formula I: Li 1+a Ni x Co y Mn z M c M' d O 2-b A b General Formula I, Where -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤c≤0.01, 0≤d≤0.01 and x+y+z+c+d=1, and 0≤b≤0.05; M and M' are distinct from each other and are each independently selected from at least one of La, Cr, Mo, Ca, Fe, Ti, Zn, Y, Zr, W, Nb, V, Mg, B, Al, Sr, Ba, and Ta. A is selected from at least one of F, Cl, Br, I, and S, and The number of grain boundaries N in the primary particles of the cathode material is approximately 10.5 to approximately 14.5, where N is calculated using formula I: N=D S / D X Formula I, Among them, D S The average size of the primary particles was measured using a cross-sectional SEM image of the cathode material, and D... X The average size of the microcrystals in the primary particles of the cathode material is obtained by XRD testing and Scherrer's formula.

[0007] According to the present invention, by including a controllable specific number of micrograin boundaries in the primary particles of the cathode material, a path for rapid diffusion of lithium ions in the bulk phase is provided, thereby improving the lithium ion diffusion coefficient and achieving excellent rate performance and capacity utilization. At the same time, the crystallinity of the primary particles is taken into account, avoiding the generation of microcracks inside the particles, especially in the primary particles, during the battery charge / discharge cycle, thereby improving the cycle life of the cathode material and the lithium-ion battery.

[0008] On the other hand, the present invention also provides a method for preparing a cathode material according to the present invention, which includes the following steps: Step i)-1: Mix a first aqueous solution containing nickel, cobalt, and manganese salts, a second aqueous solution containing a sodium-based alkaline compound and / or a potassium-based alkaline compound, and ammonia. Adjust the pH of the resulting mixed aqueous solution to approximately 9 to approximately 12 to induce a co-precipitation reaction to form crystals. Step i)-2 When the crystal grows to its median grain size D 50 When the particle size is approximately 2 to approximately 5 μm, the second pH value of the mixed aqueous solution is adjusted to approximately 9 to approximately 12, wherein the second pH value is greater than the first pH value and the difference is between approximately 0.1 and approximately 1.0, allowing the crystals to continue growing to their median particle size D. 50 The size is approximately 9 to 20 μm, from which the precursor is obtained; and Step ii) The precursor, lithium source, and first additive containing element M are mixed and sintered at a constant temperature of 650~900°C for approximately 4~20 hours. The mixture is then allowed to cool naturally to room temperature. After crushing, sieving, and iron removal, the first cathode material Li is obtained. 1+a Ni x Co y Mn z M c O2, and optionally Step iii) Mixing the first cathode material Li 1+a Ni x Co y Mn z M c O2 and a second additive containing elements M' and / or A are subjected to isothermal sintering at a temperature of approximately 200 to approximately 700°C for approximately 3 to approximately 10 hours to obtain the second cathode material Li. 1+a Ni x Co y Mn z M c M' d O 2-b A b .

[0009] The preparation method according to the present invention is controllable, simple, and easy to operate. By controlling the pH value of the nucleation process and crystal growth process of the precursor, the primary fiber morphology and crystallinity of the precursor can be controlled in a simple manner, thereby controlling the number of micrograin boundaries in the primary particles of the cathode material. Moreover, by selecting the type and controlling the amount of doping elements that have the effect of regulating micrograin boundary growth, combined with controlling the sintering temperature, the crystallinity and the number of micrograin boundaries of the cathode material can be controlled.

[0010] Lithium-ion batteries containing the cathode material according to the present invention can be used in electric vehicles (such as automobiles), regional power stations, and portable devices.

[0011] Various other features, aspects, and advantages of the invention will become more apparent from the following accompanying drawings. These drawings are not drawn to scale and are intended to illustrate various structures and positional relationships, and should not be construed as limiting. Attached Figure Description

[0012] Figure 1 This is a scanning electron microscope (SEM) image of the cathode material prepared in Example 1.

[0013] Figure 2 This is a cross-sectional SEM image of the cathode material prepared in Example 1.

[0014] Figure 3The image shows the XRD pattern of the cathode material prepared in Example 1.

[0015] Figure 4 This is a schematic diagram illustrating the method for calculating the angle of repose. Detailed Implementation

[0016] Unless otherwise defined, all technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains. In case of any inconsistency, the definitions provided herein shall prevail.

[0017] Unless otherwise stated, the ranges of values ​​listed in this article are intended to include the endpoints of the range, and all values ​​within that range and all subranges.

[0018] The materials, contents, methods, equipment, figures and examples in this article are exemplary and should not be construed as limiting unless otherwise stated.

[0019] As used herein, the terms “comprising,” “including,” and “having” all mean that other components or other steps that do not affect the final effect may be included. These terms encompass the meanings of “composed of” and “substantially composed of.” Products and methods according to the invention may comprise or include the essential technical features described in this disclosure, as well as additional and / or optional components, ingredients, steps, or other limiting features described herein; or may consist of the essential technical features described in this disclosure, as well as additional and / or optional components, ingredients, steps, or other limiting features described herein; or may consist substantially of the essential technical features described in this disclosure, as well as additional and / or optional components, ingredients, steps, or other limiting features described herein.

[0020] Unless otherwise expressly stated, all materials and reagents used in this disclosure are commercially available.

[0021] Unless otherwise indicated or there is an obvious contradiction, the operations described herein can be performed at room temperature and normal pressure.

[0022] Unless otherwise indicated or clearly contradictory, the method steps in this disclosure may be performed in any suitable order.

[0023] As used herein, the term “about” means that the value it defines may have a deviation within a range of ±10% of that value. For example, the term “about 300 nm” means a range of “300 ± 30 nm”.

[0024] Examples of this disclosure will be described in detail below.

[0025] [Cathode Material] According to this disclosure, a positive electrode material for lithium-ion batteries is provided, which has the following general formula I: Li 1+a Ni x Co y Mn z M c M' d O 2-b A b General Formula I, Where -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤c≤0.01, 0≤d≤0.01 and x+y+z+c+d=1, and 0≤b≤0.05; M and M' are different from each other and are each independently selected from at least one of La, Cr, Mo, Ca, Fe, Ti, Zn, Y, Zr, W, Nb, V, Mg, B, Al, Sr, Ba, Ta, and A is selected from at least one of F, Cl, Br, I, S, and The number N of micrograin boundaries in the primary particles of the cathode material is approximately 10.5 to approximately 14.5, where N is calculated using formula I: N=D S / D X Formula I, Among them, D S D represents the average size of the primary particles obtained by measuring cross-sectional SEM images of the cathode material. X The average size of the microcrystals in the primary particles of the cathode material is obtained by XRD testing and Scherrer's formula.

[0026] In some instances, when d and b in general formula I are 0, the cathode material has the following general formula II: Li 1+a Ni x Co y Mn z M c O2, General Formula II, Where a, x, y, z, c, M, M' and A are as defined above for general formula I.

[0027] The capacity and rate performance of layered ternary materials are limited by the lithium-ion diffusion capability. Besides interlayer diffusion and solid-liquid interface exchange, lithium-ion diffusion at defect sites such as grain boundaries is often neglected. The cathode material of this invention retains a certain number of microcrystals within the primary particles and forms grain boundaries between them. This number of grain boundaries helps to increase the diffusion rate of lithium-ions in the bulk phase, thereby improving the capacity and rate performance of the cathode material. Simultaneously, it maintains good crystallinity, avoiding the risk of primary particle breakage during repeated charge / discharge processes, thus ensuring the cycle life of the cathode material.

[0028] The cathode material exhibits a structural characteristic of primary particles agglomerating into secondary particles. Primary particles refer to relatively intact single particles with clear boundaries from the surrounding cathode material. Secondary particles are larger cathode material spheres formed by the stacking of multiple primary particles, which do not separate under external force. The interior of the primary particles is not a perfect single-crystal structure, but rather composed of multiple tightly bonded microcrystalline regions with short-range ordered crystal structures. The boundaries between these microcrystalline regions are defined as grain boundaries, which cannot be clearly identified by external observation methods such as scanning electron microscopy.

[0029] The number of grain boundaries is evaluated using Formula I: N = D S / D X Formula I.

[0030] In some instances, D S The wavelength is approximately 300 to approximately 600 nm, preferably approximately 400 to approximately 550 nm, more preferably approximately 450 to approximately 550 nm, and D S It was obtained by measuring the cross-section of the cathode material using SEM images.

[0031] In some instances, D X The nm value is approximately 30 to approximately 60 nm, preferably approximately 40 to approximately 50 nm, more preferably approximately 40 to approximately 45 nm, and D X The result is obtained by calculation using Formula II: Dx=(D (003) +D (104) ) / 2 Formula II, Among them, D (003) D represents the crystal thickness along the normal to the (003) crystal plane represented by a single (003) peak. (104) This represents the crystal thickness of the (104) crystal plane normal represented by a single (104) peak, and D (003) and D (104) Each was calculated using the Scherrer formula: D=Kλ / (β·cosθ) Scherrer's formula in, K is Sherry's constant, 0.89. λ is the X-ray wavelength of 1.54056 Å. β represents the diffraction peak D in the XRD pattern. (003) Or D (104) The half-height width, and θ represents the diffraction peak D in the XRD pattern. (003) Or D (104)The Buglar diffraction angles are approximately 18.5 to 19.5° for the (003) peak and approximately 44.0 to 45.0° for the (104) peak.

[0032] In some instances, the median particle size D of the secondary particles of the cathode material is... 50 It is approximately 9 to approximately 20 μm, and D 50 The results were obtained by measuring with a laser particle size analyzer and calculating based on volume distribution.

[0033] Median particle size D 50 This refers to the particle size value corresponding to a 50% volumetric distribution percentage of particles. For example, the median particle size D of secondary particles. 50 The value is 9μm, meaning that secondary particles larger than 9μm account for 50% of the volume, and particles smaller than 9μm also account for 50% of the volume.

[0034] In some instances, the ratio of the compaction density (PD) to the tap density (TD) of the cathode material measured at 20 kN conforms to 1.1 ≤ PD / TD ≤ 1.3. A PD / TD ratio within this range ensures that the cathode material is sufficiently dense, which is beneficial for processing high-compact-density lithium-ion battery electrodes and improving volumetric energy density. Simultaneously, suitable porosity facilitates electrolyte wetting of the cathode material, resulting in excellent capacity and rate performance for the lithium-ion battery.

[0035] In some instances, the angle of repose α of the cathode material is ≤ 50°, preferably about 30 to about 45°, and the angle of repose α is measured according to GB / T 6609.24-2004, the test method for angle of repose of alumina powder. Within this range, the angle of repose α gives the cathode material good flowability, which is beneficial for processability in actual production.

[0036] [Preparation methods for cathode materials] The present invention also provides a method for a cathode material for lithium-ion batteries, comprising the following steps: Step i)-1: Mix a first aqueous solution containing nickel, cobalt, and manganese salts, a second aqueous solution containing a sodium-based alkaline compound and / or a potassium-based alkaline compound, and ammonia. Adjust the pH of the resulting mixed aqueous solution to approximately 9 to approximately 12 to induce a co-precipitation reaction to form crystals. Step i)-2 When the crystal grows to its median grain size D 50 When the particle size is approximately 2 to approximately 5 μm, the second pH value of the mixed aqueous solution is adjusted to approximately 9 to approximately 12, wherein the second pH value is greater than the first pH value and the difference is between approximately 0.1 and approximately 1.0, allowing the crystals to continue growing to their median particle size D. 50 The size is approximately 9 to 20 μm, from which the precursor is obtained; and Step ii) The precursor, lithium source, and additives containing element M are mixed, and the resulting mixture is sintered at a constant temperature of 650~900°C for about 4~20 hours. The mixture is then allowed to cool naturally (preferably to room temperature), crushed, sieved, and iron-removed to obtain the first cathode material Li. 1+a Ni x Co y Mn z M c O2, and optionally Step iii) Mixing the first cathode material Li 1+a Ni x Co y Mn z M c O2 and a second additive containing elements M' and / or A are subjected to isothermal sintering at a temperature of approximately 200 to approximately 700°C for approximately 3 to approximately 10 hours to obtain the second cathode material Li. 1+a Ni x Co y Mn z M c M' d O 2-b A b .

[0037] As mentioned above, the preparation method according to the present invention is controllable and simple. By jointly adjusting the pH value of the nucleation process and crystal growth process of the precursor with a sodium / potassium alkaline compound and ammonia, the primary fiber morphology and crystallinity of the precursor can be controlled, thereby controlling the number of micrograin boundaries in the primary particles of the cathode material. Moreover, by selecting and controlling the amount of doping elements with micrograin boundary growth regulation function, combined with controlling the sintering temperature, the crystallinity and the number of micrograin boundaries of the cathode material can be controlled.

[0038] In some instances, the first pH value is about 10.5 to about 11.2, and the second pH value is about 11.2 to about 11.8.

[0039] In some instances, in step i)-1, the nickel salt, cobalt salt, and manganese salt are each independently selected from sulfates, nitrates, acetates, and combinations thereof, preferably all of the nickel salt, cobalt salt, and manganese salt are sulfates, all of the nickel salt, and all of the cobalt salt, and all of the manganese salt are acetates.

[0040] In some instances, in step i)-1, nickel salt, cobalt salt, and manganese salt are prepared according to the general formula of the first cathode material, Li. 1+ a Ni x Co y Mn z M c O 2-bThe molar ratio of nickel, cobalt, and manganese is mixed.

[0041] In some instances, in step i)-1, the concentration of the first aqueous solution is 1-3 mol / L, the concentration of the second aqueous solution as a precipitant is 2-12 mol / L, and the concentration of ammonia water as a complexing agent is 2-10 mol / L.

[0042] In some instances, in step i)-1, the sodium-containing basic compound and / or the potassium-containing basic compound are each independently selected from sodium or potassium hydroxides, carbonates, bicarbonates, oxalates, and combinations thereof.

[0043] In some instances, in step i)-1, the coprecipitation reaction is carried out in the presence of an inert gas. In some instances, the inert gas is nitrogen.

[0044] In some instances, in step i)-1, the reaction system temperature for the coprecipitation reaction is constant, preferably 50~80℃.

[0045] In some instances, the coprecipitation reaction time in step i)-1 is 40 to 100 hours.

[0046] In some instances, in step i)-1, the coprecipitation reaction is carried out under stirring.

[0047] In some instances, crystal growth is carried out under stirring in steps i)-2.

[0048] In some instances, in steps i)-2, after the coprecipitation reaction is completed, one or more of the following operations are performed: aging, separation, washing, and drying, thereby obtaining the precursor.

[0049] In some instances, in step ii), the lithium source is selected from lithium carbonate, lithium hydroxide, and combinations thereof, preferably lithium hydroxide.

[0050] In some instances, in step ii), the first additive containing element M is selected from oxides, hydroxides, halides, sulfides, phosphates, borates, and combinations thereof of element M, preferably tungsten trioxide, molybdenum trioxide, niobium pentoxide, lanthanum trioxide, and tantalum pentoxide, or combinations thereof.

[0051] In some instances, in step ii), the precursor, lithium source, and first additive containing element M are mixed uniformly in a high-speed mixer.

[0052] In some instances, in step ii), isothermal sintering is performed in an oxygen furnace.

[0053] In some instances, in step ii), after the sintered mixture has cooled to room temperature, it is crushed, sieved, and iron removed to obtain the cathode material Li. 1+a Ni x Co y Mn z M c O2.

[0054] In some instances, in step iii), the second additive containing element M' and / or A is selected from oxides, hydroxides, halides, sulfides, phosphates, borates, and combinations thereof of element M' and / or A, preferably alumina and / or lithium fluoride.

[0055] In some instances, in step iii), the first cathode material Li is mixed in a high-speed mixer. 1+a Ni x Co y Mn z M c O2 and a second additive containing elements M' and / or A are mixed evenly.

[0056] In some instances, the second additive containing elements M' and / or A may be a mixture of compounds each containing element M' and compounds containing element A, or it may be a compound containing both elements M' and A.

[0057] In some instances, in step iii), isothermal sintering is carried out in an oxygen furnace.

[0058] In some instances, in step iii), the material coating methods include dry coating, coating after washing and drying, and wet in-situ coating.

[0059] Example Example 1 Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in pure water at a molar ratio of 83:11:6 to obtain a first aqueous solution with a concentration of 2 mol / L. An 8 mol / L sodium hydroxide solution was prepared as a second aqueous solution to be used as a precipitant, and a 6 mol / L ammonia solution was prepared as a complexing agent solution.

[0060] Add a mixed aqueous solution of sodium hydroxide and ammonia to the reactor, adjust the pH to 10.9, purge with nitrogen for protection, and control the reaction system temperature at 60℃. Add the first aqueous solution, sodium hydroxide solution, and ammonia to the reactor through the inlet pipes, maintain the stirring speed at 500 rpm, control the inlet flow rate of the first aqueous solution at 200 mL / h, and adjust the flow rates of sodium hydroxide solution and ammonia to keep the pH of the reaction system stable at 10.9±0.05.

[0061] The particle size D of the nuclei in the reaction system 50 After the particles grew to 3.0 μm, the pH of the solution was adjusted to 11.2 ± 0.05, the flow rate of the first aqueous solution was adjusted to 500 mL / h, the stirring speed was increased to 700 rpm, and the reaction temperature was kept constant. The reaction proceeded until the average particle size D in the solution reached a certain value. 50 After growing to 14 μm, the material was aged for 1 h, then separated, washed, and dried to obtain the precursor material Ni. 0.83 Co 0.11 Mn 0.06 (OH)2; The aforementioned precursor, lithium hydroxide, and tungsten trioxide were weighed separately in a molar ratio of 1:1.03:0.002, and then mixed evenly in a mixer. The mixture was then sintered at a constant temperature in an oxygen furnace with an oxygen concentration greater than 95%, a heating rate of 5℃ / min, a sintering temperature of 800℃, and a sintering time of 12 h. After natural cooling to room temperature, the mixture was crushed, sieved, and iron removed to obtain the cathode material 1:Li. 1.03 Ni 0.828 Co 0.110 Mn 0.060 W 0.002 O2.

[0062] Figure 1 This is a SEM image of the cathode material prepared in Example 1.

[0063] Examples 2-5 and Comparative Examples 1-6 The cathode material was prepared according to the method of Example 1, with the material composition and specific process conditions as shown in Table 1. Examples 2-5 and Comparative Examples 1-6 were carried out respectively to prepare cathode materials 2 to 5 and cathode materials D1 to D6.

[0064] In Example 2, the first additive is niobium pentoxide.

[0065] In Example 3, the first additive was molybdenum trioxide.

[0066] In Example 4, the first additive was lanthanum trioxide and the second additive was aluminum oxide.

[0067] In Example 5, the first additive is tantalum pentoxide and the second additive is lithium fluoride.

[0068] Table 1. Adjustment Table of Process Parameters for Preparation

[0069] [Cathode Material Performance Testing] The cathode materials prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to the following tests, and the test results are recorded in Table 2.

[0070] DS It was measured by SEM images of the cross-section of the cathode material after it was cut open. Figure 2 This is a SEM image of a cross-section of the cathode material prepared in Example 1.

[0071] D X The result is obtained by calculation using Formula II: (D (003) +D (104) ) / 2 Formula II, Among them, D (003) D represents the crystal thickness along the normal to the (003) crystal plane represented by a single (003) peak. (104) This represents the crystal thickness of the (104) crystal plane normal represented by a single (104) peak, and D (003) and D (104) Each was calculated using Formula III: D=Kλ / (β·cosθ) Formula III, in, K is Sherry's constant, 0.89. λ is the X-ray wavelength of 1.54056 Å. β represents the diffraction peak D in the XRD pattern. (003) Or D (104) The half-height width, and θ represents the diffraction peak D in the XRD pattern. (003) Or D (104) The Buglar diffraction angles are as follows: the 2θ range of the (003) peak is 18.5~19.5°, and the 2θ range of the (104) peak is 44.0~45.0°.

[0072] Figure 3 The image shows the XRD pattern of the cathode material prepared in Example 1.

[0073] Median particle size D 50 The results were obtained by measuring with a laser particle size analyzer and calculating based on volume distribution.

[0074] The angle of repose was measured according to GB / T 6609.24-2004, "Test Method for Angle of Repose of Alumina Powder". The measuring device included: a glass funnel (3 mm inner diameter of the discharge port); a glass base plate (cleaned surface, horizontally placed below the funnel); a funnel fixing bracket (sturdy structure, keeping the funnel centerline perpendicular to the horizontal plane); and a height positioner (to determine the height from the funnel discharge port to the glass base plate surface; 60 mm was used in this invention). During the test, 15 g of positive electrode material was added to the glass discharge funnel at a uniform rate, controlling the feeding speed to avoid clogging the discharge port. After feeding, the diameter d and height h of the bottom circle of the cone formed by the powder were measured. The angle of repose α of the powder material was obtained according to the inverse trigonometric function α = arctan(2h / d). Figure 4 As shown.

[0075] [Preparation of button cells] The positive electrode materials, conductive carbon black and polyvinylidene fluoride (PVDF) prepared in Examples 1-5 and Comparative Examples 1-6 were weighed and mixed in a mass ratio of 95%:2.5%:2.5%. N-methylpyrrolidone (NMP) was added and stirred to form a uniform slurry. The slurry was coated on aluminum foil, leveled, dried and then rolled flat. It was then pressed into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm under a pressure of 100 MPa. The sheet was then placed in a vacuum oven and dried at 120°C for 12 h.

[0076] The coin cell assembly process was carried out in an Ar-protected glove box, where the water and oxygen contents were both less than 5 ppm. The electrode obtained above was used as the positive electrode, and a 17 mm diameter, 1 mm thick Li metal sheet was used as the negative electrode. A 25 μm thick polyethylene porous membrane was used as the separator, and a 1:1 volume ratio mixture of ethylene carbonate (EC) and diethylene carbonate (DEC) containing 1 mol / L LiPF6 was used as the electrolyte. A coin cell case (model 2025) was used as the battery case. After assembly, an unactivated half-cell was obtained.

[0077] [Performance Evaluation of Button Cell Batteries] After the button cell is assembled, it is left to stand for 2 hours until its open circuit voltage stabilizes. Then, it is charged with a constant current of 0.1C (1C=200 mA / g) to the cutoff voltage of 4.3 V. Then, it is charged with a constant voltage for 30 minutes, and then discharged with a constant current of 0.1C to the cutoff voltage of 3.0 V. Then, the same charge / discharge cycle is repeated once. The battery at this time is considered an activated battery.

[0078] Rate performance test method: Using the activated batteries described above, under room temperature conditions, charge / discharge tests were conducted at current densities of 0.1C, 0.2C, 0.33C, 0.5C, 1C, and 2C in the voltage range of 3.0~4.3V. The rate performance was evaluated by comparing the capacity values ​​at different rates with the retention rate at 0.1C. The results are shown in Table 3.

[0079] Cyclic performance test method: Using activated batteries, 80 cycles were performed at a current density of 1C within a voltage range of 3.0~4.3 V under high temperature (50℃) conditions. The cycle performance was evaluated by its capacity retention rate. The results are shown in Table 3.

[0080] [Lithium-ion diffusion coefficient test] To explain the performance improvement of the characteristic material described in this invention, the lithium-ion diffusion coefficient of the powder material was tested using the EIS test method: The previously prepared unactivated half-cell was taken, allowed to stand for 2 hours, and then charged at a constant current of 0.1C to a cutoff voltage of 4.3 V. This was followed by constant voltage charging for 30 minutes, and then constant current discharge at 0.1C to a cutoff voltage of 3.0 V. Subsequently, it was charged again at a constant current of 0.1C to a cutoff voltage of 4.3 V. The fully charged half-cell was then removed, and EIS testing was performed in the frequency range of 100 kHz to 0.01 Hz with an amplitude of 10 mV. According to the formula: Z re = R s + R ct + σω -1 / 2 ,as well as ω = 2πf, Z can be obtained re With ω -1 / 2 The slope of the fitted line, i.e., σ; Among them, Z re R is the real part of the impedance spectrum obtained from the test. s R is the resistance of the solution. ct ω is the charge transfer resistor, f is the angular frequency, f is the test frequency, and σ is the Warburg factor. Then, according to the formula for calculating the lithium-ion diffusion coefficient: D Li + =R 2 T 2 / (2A 2 n 4 F 4 C 2 σ 2 ) The bulk Li phase of the material was calculated. +Diffusion coefficient; where R is the ideal gas constant, T is the absolute temperature, A is the cross-sectional area of ​​the electrode, n is the number of electrons transferred, F is the Faraday constant, and C is the lithium ion concentration in the electrode.

[0081] The physicochemical parameters of the cathode materials of Examples 1-5 and Comparative Examples 1-6 are shown in Table 2.

[0082] Table 2 Physicochemical parameters of cathode materials

[0083] *Note: In Comparative Example 1, the introduction of 2 mol% W reduces the molar ratios of Ni, Co, and Mn. Taking Ni as an example, after introducing 2 mol% W, the molar ratio of Ni in the molecular formula... The ratio will decrease to 0.83 / (1+0.02)=0.814.

[0084] As can be seen from Tables 1 and 2, in Examples 1-5 of the present invention, by controlling the pH of the reaction system during the precursor crystal growth process, selecting doping elements with micrograin boundary growth control effects and their amounts, and controlling the sintering temperature, the obtained cathode material has a micrograin boundary number N in the range of 10.5 to 14.5 and an excellent lithium diffusion coefficient.

[0085] In Comparative Example 1, when the amount of additive elements that regulate the growth of microcrystal boundaries is too large, the size of the microcrystals becomes significantly smaller due to the obstruction of growth and fusion, the number of internal microcrystal boundaries becomes too large, the overall crystallinity of the cathode material deteriorates, and the lithium diffusion coefficient decreases.

[0086] In Comparative Example 2, when no additive elements that regulate the growth of microcrystal boundaries are added, it is beneficial for the microcrystals to fuse and grow together, thereby eliminating microcrystal boundaries. As a result, the number of microcrystal boundaries is too small, and the lithium diffusion coefficient is significantly reduced.

[0087] In Comparative Example 3, when the pH is too high in the second stage of the precursor synthesis process, the crystallinity of the precursor will deteriorate. During the sintering process, the primary particles of the cathode material are more likely to grow, and the microcrystal size does not change much. As a result, the internal microcrystal boundaries increase, and the poor crystallinity of the precursor will continue to the cathode material, leading to a smaller lithium diffusion coefficient.

[0088] In Comparative Example 4, when the pH of the second stage in the precursor synthesis process is lower than that of the first stage, the crystallinity of the precursor is better, the primary particles of the cathode material are less likely to grow during the sintering process and their size is smaller, the microcrystal size does not change much, thus reducing the internal microcrystal boundaries and significantly reducing the lithium diffusion coefficient.

[0089] In Comparative Example 5, when the sintering temperature is too low, the intercrystalline fusion growth inside the cathode material is insufficient, the size is significantly smaller, the microcrystal boundaries increase, but the overall crystallinity of the cathode material is poor, and the lithium diffusion coefficient is greatly reduced.

[0090] In Comparative Example 6, the sintering temperature was too high, resulting in excessive fusion and growth between microcrystals inside the cathode material, leading to a significantly larger size, reduced microcrystal boundaries, and a decreased lithium diffusion coefficient.

[0091] The performance parameters of the cathode materials of Examples 1-5 and Comparative Examples 1-6 are shown in Table 3.

[0092] Table 3 Performance parameters of cathode materials

[0093] As can be seen from Table 3 above, the cathode materials of Examples 1-5 of the present invention exhibit excellent capacity, rate retention and cycle retention.

[0094] Compared to Example 1, the cathode materials of Comparative Examples 1-6 generally exhibited reduced capacity at 0.1C. Comparative Example 5, due to its excessively low sintering temperature, suffered from insufficient growth and crystallization of the cathode material, resulting in its inability to achieve its full capacity potential. Furthermore, it can be observed that when the number of micrograin boundaries in the cathode material is too high, the rate retention rate decreases, and the cycle retention rate deteriorates significantly. This is mainly because excessive micrograin boundaries within the primary particles easily lead to breakage during cycling. Conversely, when the number of micrograin boundaries N is relatively small, the rate performance deteriorates significantly, consistent with the aforementioned conclusions. This indicates that controlling the number of micrograin boundaries N in the cathode material within the range of 10.5 to 14.5 is beneficial for simultaneously achieving high rate performance and long cycle life.

Claims

1. A cathode material for lithium-ion batteries, having the following general formula I: Li 1+a Ni x Co y Mn z M c M' d O 2-b A b General formula I, Where -0.05≤a≤0.3, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2, 0≤c≤0.01, 0≤d≤0.01, x+y+z+c+d=1, and 0≤b≤0.05; M and M' are distinct from each other and are each independently selected from at least one of La, Cr, Mo, Ca, Fe, Ti, Zn, Y, Zr, W, Nb, V, Mg, B, Al, Sr, Ba, and Ta. A is selected from at least one of F, Cl, Br, I, and S, and The number N of micrograin boundaries in the primary particles of the cathode material is 10.9~14.5, where, N is calculated using formula I: N = D S / D X Formula I Among them, D S D represents the average size of the primary particles obtained by measuring cross-sectional SEM images of the cathode material. S The wavelength is 300~600 nm, and D X D represents the average size of the crystallites in the primary particles of the cathode material, calculated using XRD and the Scherrer equation. X The wavelength is 30~60 nm. Among them, D X The result is obtained by calculation using Formula II: Dx=(D (003) +D (104) ) / 2 formula II, Among them, D (003) D represents the crystal thickness along the normal to the (003) crystal plane represented by a single (003) peak. (104) This represents the crystal thickness of the (104) crystal plane normal represented by a single (104) peak, and D (003) and D (104) Each was calculated using the Scherrer formula: D = Kλ / (β·cosθ) Scherrer's formula in, K is Sherry's constant, 0.

89. λ is the X-ray wavelength of 1.54056 Å. β represents the diffraction peak D in the XRD pattern. (003) Or D (104) The half-height width, and θ represents the diffraction peak D in the XRD pattern. (003) Or D (104) The Buglar diffraction angles are such that the 2θ range of the (003) peak is 18.5~19.5°, and the 2θ range of the (104) peak is 44.0~45.0°.

2. The cathode material according to claim 1, wherein, D S The wavelength is 400~550 nm.

3. The cathode material according to claim 1 or 2, wherein, The median particle size D of the secondary particles of the cathode material 50 The value is 9~20μm.

4. The cathode material according to claim 1 or 2, wherein, The ratio of the compaction density PD to the tapped density TD of the cathode material measured at 20 kN conforms to 1.1 ≤ PD / TD ≤ 1.

3.

5. The cathode material according to claim 1 or 2, wherein, The angle of repose α of the positive electrode material is ≤ 50°.

6. A method for preparing the cathode material according to any one of claims 1-5, comprising the following steps: Step i)-1: Mix a first aqueous solution containing nickel, cobalt, and manganese salts, a second aqueous solution containing a sodium-based alkaline compound and / or a potassium-based alkaline compound, and ammonia. Adjust the pH of the resulting mixed aqueous solution to 9-12 to induce a co-precipitation reaction and form crystals. Step i)-2 When the crystal grows to its median grain size D 50 When the crystal size is 2-5 μm, the second pH value of the mixed aqueous solution is adjusted to 9-12, wherein the second pH value is greater than the first pH value and the difference is between 0.1 and 1.0, so that the crystal continues to grow to 9-20 μm, thereby obtaining the precursor; Step ii) The precursor, lithium source, and additives containing element M are mixed, and the resulting mixture is sintered at a constant temperature of 650~900°C for 4~20 hours. After natural cooling, crushing, sieving, and iron removal, the first cathode material Li is obtained. 1+a Ni x Co y Mn z M c O2, and optionally Step iii) Mixing the first cathode material Li 1+a Ni x Co y Mn z M c O2 and a second additive containing elements M' and / or A are subjected to isothermal sintering at 200~700℃ for 3~10 hours to obtain the second cathode material Li. 1+a Ni x Co y Mn z M c M' d O 2-b A b .

7. The method according to claim 6, wherein, The first pH value is 10.5 to 11.2, and the second pH value is 11.2 to 11.

8.

8. The method according to claim 6 or 7, wherein, In step i)-1, the nickel salt, cobalt salt, and manganese salt are each independently selected from sulfates, nitrates, acetates, and combinations thereof; and / or The sodium-containing basic compound and / or potassium-containing basic compound are each independently selected from sodium and potassium hydroxides, carbonates, bicarbonates, oxalates, and combinations thereof.

9. The method according to claim 6 or 7, wherein, In step ii), the lithium source is selected from lithium carbonate, lithium hydroxide, and combinations thereof; and / or The first additive containing element M is selected from oxides, hydroxides, halides, sulfides, phosphates, borates, and combinations thereof of element M.

10. The method according to claim 6 or 7, wherein, In step iii), the second additive containing element M' is selected from oxides, hydroxides, halides, sulfides, phosphates, borates, and combinations thereof of element M'.

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