Single-crystal multi-element positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application relates to the field of positive electrode material preparation, and discloses a single-crystal multi-element positive electrode material, a preparation method thereof and a lithium ion battery. The ratio of the length of the longest diagonal to the length of the shortest diagonal of a single-crystal particle of the single-crystal multi-element positive electrode material is roundness R, and R>=1; the D 10 , D 50 and D 90 of the single-crystal particle of the single-crystal multi-element positive electrode material satisfy: K 90 =(D 90 -D 10 ) / D 50 , and the product of K 90 and R is 1.20-1.40. The single-crystal multi-element positive electrode material has a more round and regular morphology, the size of the single-crystal particle is uniform, the single-crystal particle has less aggregation and adhesion, the single-crystal multi-element positive electrode material has a high compaction density, good rate performance and excellent cycle performance.

Description

Technical Field

[0001] This invention relates to the field of cathode material preparation, specifically to single-crystal multi-element cathode materials, their preparation methods, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries possess outstanding advantages such as high voltage, high energy density, good cycle performance, low self-discharge, and no memory effect. The cathode material, as a crucial component, plays a decisive role in the battery's capacity, performance, and cost. Nickel-cobalt-manganese ternary cathode materials are among the most popular lithium-ion battery cathode materials, exhibiting high specific capacity and good cycle stability. Based on their particle state, ternary cathode materials are classified into agglomerated and monocrystalline types. Agglomerated ternary cathode materials are prone to breakage during rolling, allowing electrolyte to seep into the broken particles, leading to a series of side effects and posing a significant challenge to the processing technology. Designing the cathode material into a more stable monocrystalline structure can effectively avoid these problems.

[0003] Existing single-crystal cathode materials are limited by the conditions during the preparation process, especially the influence of the sintering atmosphere. This results in single-crystal particles with sharp edges, poor roundness and regularity, or severe adhesion between particles, poor independence, and even a precursor-like morphology. This is because most existing technologies use a single atmosphere (air or oxygen) for sintering. While pure air sintering can reduce processing costs, lithium salts are difficult to melt and penetrate into the particles under air conditions, instead covering the particle surface. During the heating growth stage, this easily leads to the formation of irregular primary particles. During the isothermal fusion stage, the lithium covering the particle surface can fuse the particles, causing them to grow rapidly. The sintered single-crystal particles have sharp edges, poor roundness and regularity. Irregular particles are more prone to breakage during electrode rolling or puncturing the separator during assembly, leading to poor battery cycle performance or even a sharp drop in performance. On the other hand, using pure oxygen sintering not only increases processing costs, but also causes lithium salt to melt into the interior of the particles under an oxygen atmosphere. Although the primary particles formed in the heating section are relatively round and regular, they are difficult to fuse in the isothermal section. This makes it difficult for the particles to grow into single crystals or for the formed crystal particles to stick together severely, have poor independence, or even maintain a precursor-like morphology.

[0004] Therefore, it is crucial to provide a single-crystal cathode material with a rounded morphology, uniform size, low agglomeration and adhesion, and a preparation method suitable for industrial production. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of uneven grain size, easy adhesion between particles, and poor roundness and regularity of single crystal cathode materials in the prior art.

[0006] To achieve the above objectives, the first aspect of the present invention provides a single-crystal multi-element cathode material, wherein the ratio of the longest diagonal length to the shortest diagonal length of the single-crystal particles of the single-crystal multi-element cathode material, as measured by SEM, is defined as the roundness R, and R ≥ 1; the D of the single-crystal particles of the single-crystal multi-element cathode material... 10 D 50 and D 90 Satisfy: K 90 =(D 90 -D 10 ) / D 50 K 90 The product of R is 1.20-1.40.

[0007] A second aspect of the present invention provides a method for preparing a single-crystal multi-element cathode material, the method comprising:

[0008] (1) A mixture containing nickel-cobalt-manganese precursor and lithium source is subjected to a first sintering, and the resulting product is crushed to obtain a single-crystal cathode material process product.

[0009] (2) The single-crystal cathode material is subjected to a second sintering to obtain a single-crystal multi-element cathode material;

[0010] The first sintering includes a heating stage I and a isothermal stage I, which are performed sequentially. The heating stage I is carried out in an oxygen atmosphere, and the isothermal stage I is carried out in an air atmosphere.

[0011] The temperature of the second sintering is not higher than the temperature of the first sintering.

[0012] The third aspect of the present invention provides a single-crystal multi-element cathode material prepared by the preparation method described in the second aspect.

[0013] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery contains the monocrystalline multi-element cathode material described in the first or third aspect.

[0014] Through the above technical solution, the preparation method provided by the present invention starts from the perspective of optimizing the sintering process. In the first sintering process, an oxygen atmosphere is used in the heating stage and an air atmosphere is used in the isothermal stage to optimize the single crystal morphology. Combined with the second sintering, the single crystal multi-element cathode material obtained meets specific roundness and uniformity. Its single crystal particles have a more rounded and regular morphology, uniform size, less agglomeration, and less adhesion. This enables it to have a higher compaction density during the electrode manufacturing process and is less prone to breakage and detachment during processing and battery cycling, thereby improving the energy density, rate performance, and cycle stability of the battery.

[0015] In addition, monocrystalline cathode materials outperform non-monocrystalline cathode materials in terms of cycle life, rate performance, stability, safety, and processability. Attached Figure Description

[0016] Figure 1 This is a SEM image of the single-crystal multi-element cathode material prepared in Example 1 of this invention;

[0017] Figure 2 This is a SEM image of the single-crystal multi-element cathode material prepared in Example 2 of this invention;

[0018] Figure 3 This is a SEM image of the single-crystal multi-element cathode material prepared in Example 3 of this invention;

[0019] Figure 4 This is a SEM image of the single-crystal multi-element cathode material prepared in Comparative Example 1 of this invention;

[0020] Figure 5 This is a SEM image of the single-crystal multi-element cathode material prepared in Comparative Example 2 of this invention;

[0021] Figure 6 This is a SEM image of the single-crystal multi-element cathode material prepared in Comparative Example 3 of this invention;

[0022] Figure 7 This is a SEM image of the single-crystal multi-element cathode material prepared in Comparative Example 4 of this invention. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] In this invention, unless otherwise specified, "first" and "second" do not represent a sequence or limit the materials or operations, but are only used to distinguish between the materials or operations. For example, "first" and "second" in "first sintering" and "second sintering" are only used to distinguish them to indicate that they are not the same sintering operation.

[0025] Unless otherwise specified, the room temperature referred to in this invention is 25±2℃.

[0026] The first aspect of this invention provides a single-crystal multi-element cathode material, wherein the roundness R of the single-crystal particles of the single-crystal material is defined as the ratio of the length of the longest diagonal to the length of the shortest diagonal as measured by SEM, and R ≥ 1; the D of the single-crystal particles of the single-crystal multi-element cathode material is... 10 D 50 and D 90 Satisfy: K 90 =(D 90 -D 10 ) / D 50 K 90 The product of R is 1.20-1.40.

[0027] For single-crystal cathode materials, the quality of their single-crystal structure directly affects their electrochemical performance. During the research process, the inventors of this invention discovered that single-crystal multi-element cathode materials that meet the above-mentioned specific parameter requirements have a round and regular morphology, uniform particle size, and less agglomeration and adhesion. This allows the cathode material to have a higher compaction density during electrode fabrication and is less prone to breakage and detachment during processing and battery cycling, thereby improving the energy density and cycle stability of the battery.

[0028] According to some embodiments of the present invention, the roundness R is defined as the ratio of the longest diagonal length to the shortest diagonal length of the single-crystal particles of the single-crystal cathode material as measured by SEM, and R ≥ 1. The closer the R value is to 1, the closer the lengths of the longest and shortest diagonals of the single-crystal particles are, indicating that the morphology of the material is more rounded and regular. Rounded and regular single-crystal particles are beneficial to preventing the cathode material from breaking during the electrode rolling process and to preventing irregular edges of the cathode material from piercing the separator during battery assembly, which is beneficial to improving the safety and cycle performance of the battery. In the present invention, R is the statistical result obtained by randomly selecting 300 single-crystal particles as a sample from the SEM image.

[0029] According to some embodiments of the present invention, preferably, R is 1-1.2. The single-crystal particles of the single-crystal multi-element cathode material using the above preferred embodiments have a more rounded and regular morphology, which is beneficial to further improving the safety performance and cycle performance of the battery.

[0030] According to some embodiments of the present invention, the particle size corresponding to 10% of the volume distribution of the single-crystal particles of the single-crystal type multi-element cathode material obtained by particle size testing is defined as D. 10 The particle size corresponding to 50% volume distribution is D. 50 The particle size corresponding to 90% volume distribution is D. 90 The uniformity of the single-crystal multi-element cathode material is defined as K. 90 And K 90 =(D 90 -D10 ) / D 50 K 90 The product of R is 1.20-1.40.

[0031] According to some embodiments of the present invention, preferably, K 90 The product of R is 1.25-1.35. The single-crystal multi-element cathode material using the above preferred embodiment has high capacity and cycle retention, and is also beneficial for further improving the compaction density of the cathode material.

[0032] According to some embodiments of the present invention, preferably, the particle size D of the single-crystal multi-element cathode material is... 10 It is 1.5-2.5μm.

[0033] According to some embodiments of the present invention, preferably, the particle size D of the single-crystal multi-element cathode material is... 50 It is 3-5μm.

[0034] According to some embodiments of the present invention, preferably, the particle size D of the single-crystal multi-element cathode material is... 90 It is 6-8μm.

[0035] In this invention, the particle size test is performed using a Marvern Hydro 2000mu laser particle size analyzer.

[0036] According to some embodiments of the present invention, K 90 The smaller the value of K, the better the uniformity of the single crystal particles; 90 The larger the value of K, the worse the uniformity of the single crystal particles. Preferably, K... 90 The value is 1.18-1.25, preferably 1.20-1.22. The single-crystal multi-element cathode material using the above preferred embodiment has better uniformity of single-crystal particles, which is beneficial for increasing the gradation and improving the compaction density of the material.

[0037] According to some embodiments of the present invention, preferably, the single-crystal multi-element cathode material has the structure shown in Formula I:

[0038] Li 1+a (Ni x Co y Mn z G b M c O 2-d Formula I;

[0039] In the formula, -0.05≤a≤0.3, 0≤b≤0.05, 0≤c≤0.05, 0.5≤x<1, 0<y<0.5, 0<z<0.5; the value of d ensures that the number of positive and negative charges are equal; G is one or more of Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, B, Mg, Co, F and Y; M is one or more of Sr, F, B, Al, Nb, Co, Mn, Mo, W, Si, Mg, Ti and Zr.

[0040] More preferably, in the formula, 0≤a≤0.2, 0.0001≤b≤0.005, 0.0001≤c≤0.005, 0.5≤x≤0.95, 0.01≤y≤0.4, and 0.01≤z≤0.4.

[0041] More preferably, in the formula, G is one or more of Ti, W, Zr, Sr, Si, Al, B and F; and / or, M is one or more of Sr, F, B, Al, W, Si and Ti.

[0042] The above-described preferred embodiments are beneficial for further improving the energy density, rate performance, and cycle stability of the battery.

[0043] According to some embodiments of the present invention, in Formula I, if both G and M are cations, then d = 0; if both G and M are anions, then d = b + c; if G is an anion and M is a cation, then d = b; if M is an anion and G is a cation, then d = c.

[0044] According to some embodiments of the present invention, preferably, the agglomeration rate B of the single-crystal multi-element cathode material is defined as follows: n is the number of agglomerated single-crystal particles among any 300 single-crystal particles of the single-crystal multi-element cathode material measured by SEM, where B = n / 300*100%, and B is 0-3.0%, preferably 0.8-2.4%. A larger agglomeration rate B indicates a lower degree of single crystallization of the cathode material, and vice versa. Under high voltage or during long cycles, the cathode material particles that are adhered together are prone to detachment or breakage, leading to battery failure. Generally, the smaller the agglomeration rate B, the better the cycle performance. The single-crystal multi-element cathode material using the above preferred embodiments has a low agglomeration rate, high degree of single crystallization, and less adhesion, making it less prone to detachment or breakage under high voltage or during long cycles, which is beneficial for further improving the energy density, rate performance, and cycle stability of the battery.

[0045] According to some embodiments of the present invention, preferably, the average of the longest and shortest diagonal lengths of any 300 single-crystal particles of the single-crystal multi-element cathode material measured by SEM is defined as the grain size P. 50And P 50 The micrometer size is 1.5-3.0 μm, preferably 2.0-2.4 μm. P 50 If the value of P is too large, it will increase the transport distance of lithium ions inside the cathode material, affecting the capacity performance; 50 If the value is too small, it will lead to material agglomeration, or even prevent the formation of single-crystal materials, affecting the cycle performance of the material. Using the single-crystal multi-element cathode material of the above-described preferred embodiment is beneficial for further improving the capacity and cycle performance of the single-crystal multi-element cathode material.

[0046] In this invention, the single-crystal multi-element cathode material is prepared using a two-stage sintering process. In the first sintering process, an oxygen atmosphere is used in the heating stage and an air atmosphere is used in the isothermal stage. This makes the single-crystal particles more rounded and regular in shape, more uniform in size, less agglomeration and adhesion, and higher in compaction density, which is beneficial to improving the energy density, rate performance and cycle stability of the battery.

[0047] A second aspect of the present invention provides a method for preparing a single-crystal multi-element cathode material, the method comprising:

[0048] (1) A mixture containing nickel-cobalt-manganese precursor and lithium source is subjected to a first sintering, and the resulting product is crushed to obtain a single-crystal cathode material process product.

[0049] (2) The single-crystal cathode material is subjected to a second sintering to obtain a single-crystal multi-element cathode material;

[0050] The first sintering includes a heating stage I and a isothermal stage I, which are performed sequentially. The heating stage I is carried out in an oxygen atmosphere, and the isothermal stage I is carried out in an air atmosphere.

[0051] The temperature of the second sintering is not higher than the temperature of the first sintering.

[0052] Most existing methods for preparing single-crystal cathode materials employ sintering in a single atmosphere (air or oxygen), resulting in single-crystal particles with sharp edges, poor roundness and regularity, or severe adhesion and poor independence between particles, sometimes even retaining a precursor-like morphology. However, the inventors of this invention discovered during their research that the solid-state reaction of the nickel-cobalt-manganese precursor mixture with the lithium source consists of two stages: growth and fusion. The growth stage is a low-temperature heating phase, where the lithium source melts and penetrates into the precursor particles, undergoing an initial reaction that allows the fibers constituting the precursor to grow and become fuller, forming fine primary particles. The fusion stage is a high-temperature isothermal phase, where the lithium source further reacts with the fine primary particles, fusing them into larger particles. By using an oxygen atmosphere during the heating and nucleation stage of the reaction between the nickel-cobalt-manganese precursor and the lithium source (heating stage I of the first sintering), the primary particles formed by the fibers are made fuller and rounder. During the growth stage of the isothermal sintering (isothermal stage I of the first sintering), an air atmosphere is used to make it easier for the single crystal particles to fuse and form large single crystal particles. Further secondary sintering (second sintering) makes the finished cathode material particles more rounded and regular. The resulting single-crystal multi-element cathode material has a rounded and regular morphology, uniform particle size, less agglomeration and adhesion, and features high compaction density, good rate performance and excellent cycle performance.

[0053] According to some embodiments of the present invention, in step (1), the nickel-cobalt-manganese precursor can be any nickel-cobalt-manganese precursor known in the art suitable for preparing cathode materials, and there are no particular limitations, as they can all achieve the inventive purpose of the present invention to a certain extent. Preferably, the nickel-cobalt-manganese precursor is selected from oxides and / or hydroxides containing nickel, cobalt, and manganese.

[0054] According to some embodiments of the present invention, in step (1), the lithium source can be any lithium source known in the art suitable for preparing cathode materials, and there are no particular limitations thereto, all of which can achieve the inventive purpose of the present invention to a certain extent. Preferably, the lithium source is selected from lithium carbonate and / or lithium hydroxide.

[0055] According to some embodiments of the present invention, preferably, in step (1), the amount of lithium source used, according to stoichiometry, satisfies: 1.02≤[n(Li)] / [n(Ni)+n(Co)+n(Mn)]≤1.06.

[0056] According to some embodiments of the present invention, preferably, in step (1), the mixed raw materials further include additives, wherein the additives are selected from compounds containing G, preferably at least one of oxides, hydroxides, carbonates and fluorides containing G, more preferably at least one of zirconium oxide, strontium carbonate, strontium hydroxide, silicon dioxide, aluminum oxide, aluminum hydroxide, tungsten trioxide, titanium oxide, aluminum fluoride and boron oxide. Wherein, G can be selected as described above, and will not be repeated here. In the present invention, the additives facilitate the formation of single crystals in the material, reduce internal resistance, and improve the cycling stability of the material.

[0057] According to some embodiments of the present invention, preferably, in step (1), the amount of the additive, calculated in terms of element G, satisfies the following stoichiometric ratio: 0.0001≤[n(G)] / [n(Ni)+n(Co)+n(Mn)]≤0.005.

[0058] According to some embodiments of the present invention, in step (1), the heating stage I is carried out in an oxygen atmosphere. By using an oxygen atmosphere in the heating nucleation stage of the reaction between the nickel cobalt manganese precursor and the lithium source (i.e., the heating stage I of the first sintering), the primary particles formed by the fiber can be made fuller and rounder.

[0059] According to some embodiments of the present invention, preferably, in step (1), the conditions of the heating stage I further include: the heating time is 2-10 hours, preferably 6-8 hours. In the heating stage I, the temperature is raised to the constant temperature of the constant temperature stage I by the above-mentioned heating time.

[0060] According to some embodiments of the present invention, in step (1), the isothermal stage I is carried out in an air atmosphere. By using an air atmosphere in the growth stage of isothermal sintering (the isothermal stage I of the first sintering), it is possible to more easily fuse single crystal particles to form large single crystal particles.

[0061] According to some embodiments of the present invention, preferably, in step (1), the conditions of the constant temperature stage I further include: the constant temperature is 600-1100℃, preferably 900-1000℃; the constant temperature time is 6-12h, preferably 8-10h.

[0062] According to some embodiments of the present invention, preferably, in step (1), the median particle size D of the nickel-cobalt-manganese precursor is... 50 It is 3-5μm.

[0063] According to some embodiments of the present invention, preferably, in step (1), the median particle size D′ of the single-crystal cathode material process product is... 50 It is 3-5μm.

[0064] According to some embodiments of the present invention, preferably, in step (1), the median particle size D of the nickel-cobalt-manganese precursor is... 50 The median particle size D′ of the single-crystal cathode material process product 50 Satisfaction Equation II:

[0065] |(D 50 -D′ 50 ) / D 50 | <5% Formula II.

[0066] Using the above preferred embodiment is beneficial for obtaining the particle size D of single crystal particles. 10 D 50 D 90 and uniformity K 90 Single-crystal multi-element cathode materials that meet the above requirements.

[0067] According to some embodiments of the present invention, in step (1), the median particle size D′ of the obtained single-crystal cathode material is reduced by combining the first sintering with the crushing process. 50 The above requirements are met. There are no particular restrictions on the equipment used for the crushing process, as long as the median particle size D′ can be obtained. 50 Any single-crystal cathode material that meets the above requirements is acceptable. Preferably, the equipment used for the crushing process is selected from at least one of a soybean milk maker, jaw crusher, double roller mill, colloid mill, mechanical mill, and air jet mill.

[0068] According to some embodiments of the present invention, preferably, in step (2), the single-crystal cathode material is first mixed with a coating agent, and then the resulting mixture is subjected to the second sintering; the coating agent is selected from compounds containing M, preferably at least one of oxides, hydroxides, carbonates and fluorides containing M, more preferably at least one of strontium carbonate, strontium hydroxide, silicon dioxide, aluminum oxide, aluminum hydroxide, tungsten trioxide, titanium oxide, aluminum fluoride and boron oxide. M can be selected as described above, and will not be repeated here. In the present invention, the coating agent helps to reduce free lithium and improve the cycle stability of the material under high temperature and high voltage conditions.

[0069] According to some embodiments of the present invention, preferably, in step (2), the amount of the coating agent, calculated based on element M according to the stoichiometric ratio, satisfies: 0.0001≤[n(M)] / [n(Ni)+n(Co)+n(Mn)]≤0.005.

[0070] According to some embodiments of the present invention, the amounts of the nickel-cobalt-manganese precursor, the lithium source, the additive, and the coating agent are such that in the obtained single-crystal multi-element cathode material, n(Li):n(Ni):n(Co):n(Mn):n(G):n(M) = (1+a):x:y:z:b:c, where the values ​​of a, b, c, x, y, and z can be defined and selected with reference to the above, and will not be repeated here.

[0071] According to some embodiments of the present invention, preferably, in step (2), the second sintering is carried out in an air atmosphere.

[0072] According to some embodiments of the present invention, preferably, in step (2), the second sintering includes a heating stage II and a isothermal stage II performed sequentially.

[0073] According to some embodiments of the present invention, preferably, in step (2), the conditions of the heating stage II further include: the heating time is 2-10h, preferably 4-7h.

[0074] According to some embodiments of the present invention, preferably, in step (2), the conditions of the constant temperature stage II further include: the constant temperature is 500-900℃, preferably 600-800℃; the constant temperature time is 6-12h, preferably 8-10h.

[0075] According to some embodiments of the present invention, preferably, ΔP is defined as the grain size change value of the single-crystal multi-element cathode material, in μm; ΔT is the temperature change value under the same sintering step, in °C; and Δt is the time change value under the same sintering step, in h, and the three satisfy: ΔP=ωΔT+γΔt, where ω=0.02μm / ℃ and γ=0.1μm / h. For example, when the isothermal temperature of the first sintering isothermal stage I is T1℃ and the isothermal time is t1h, the grain size P of the obtained single-crystal multi-element cathode material is... 50 The grain size P of the obtained single-crystal multi-element cathode material is P1μm; when the isothermal temperature of the first sintering stage I is T2℃ and the isothermal time is t2h, the grain size P is P1μm. 50 If P2μm, then ΔT is the absolute value of the difference between T1 and T2 (i.e., |T1-T2|℃), Δt is the absolute value of the difference between t1 and t2 (i.e., |t1-t2|h), ΔP is the absolute value of the difference between P1 and P2 (i.e., |P1-P2|μm), and ΔP=ωΔT+γΔt.

[0076] The third aspect of the present invention provides a single-crystal multi-element cathode material prepared by the preparation method described in the second aspect.

[0077] According to some embodiments of the present invention, the single-crystal multi-element cathode material is the same as or similar to the single-crystal multi-element cathode material described in the first aspect of the present invention, and will not be described again here.

[0078] A fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery contains the monocrystalline multi-element cathode material described in the first or third aspect.

[0079] The present invention will be described in detail below through embodiments.

[0080] Unless otherwise specified, all raw materials used in the following examples and comparative examples are commercially available products.

[0081] In the following examples and comparative examples, the relevant parameters were obtained through testing using the following methods:

[0082] (1) Morphology test: The results were obtained using a Hitachi S-4800 scanning electron microscope. Among them, the roundness R, agglomeration rate B and grain size P were measured. 50 All were obtained through SEM image testing;

[0083] (2) Particle size D 10 D 50 D 90 The particle size distribution was obtained using a Marvern Hydro 2000mu laser particle size analyzer.

[0084] (3) Compacted density: obtained by testing with a BT-30 compaction density tester from Baxter Corporation;

[0085] (4) Electrochemical performance testing:

[0086] In the following examples and comparative examples, the electrochemical performance of the monocrystalline multi-element cathode material was tested using a CR2032 coin cell.

[0087] The specific manufacturing process of CR2032 coin cell is as follows:

[0088] Electrode preparation: Monocrystalline multi-element cathode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3 to form a uniform slurry. This slurry was coated onto aluminum foil and dried at 120°C for 12 hours. The foil was then pressed into a cathode sheet with a diameter of 15.8 mm and a thickness of 3.2 mm using a pressure of 100 MPa. The loading of the monocrystalline multi-element cathode material was 15.5 mg / cm³. 2 .

[0089] Battery Assembly: In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into CR2032 coin cells and then left to stand for 6 hours. The negative electrode used a 15.8 mm diameter, 1 mm thick lithium metal sheet; the separator used a 25 μm thick polypropylene microporous membrane (Celgard 2325); and the electrolyte used was a 1 mol / L mixture of equal parts LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0090] Electrochemical performance testing:

[0091] In the following examples and comparative examples, the electrochemical performance of CR2032 coin cells was tested using the Shenzhen Newwell Battery Testing System, with a charge / discharge current density of 100 mA / g at 0.1C.

[0092] The charge / discharge voltage range was controlled between 3.0 and 4.4V. At room temperature, the coin cells were charged and discharged at 0.1C and 0.3C to evaluate the charge / discharge specific capacity of the monocrystalline multi-element cathode material.

[0093] High-temperature cycling performance test: The charge and discharge voltage range was controlled at 3.0-4.4V. At a constant temperature of 60℃, the coin cell was charged and discharged twice at 0.1C and then charged and discharged 80 times at 1C to evaluate the high-temperature cycling capacity retention of the monocrystalline multi-element cathode material.

[0094] Rate performance test: The charge and discharge voltage range was controlled at 3.0-4.4V. At room temperature, the coin cell was charged and discharged twice at 0.1C and then once at 0.3C. The rate performance of the multi-element cathode material was evaluated by the ratio of the initial discharge specific capacity at 0.1C to the discharge specific capacity at 0.3C.

[0095] Example 1

[0096] (1) A mixture containing nickel-cobalt-manganese precursors, lithium source, and additives is subjected to a first sintering process, and the resulting product is crushed to obtain a single-crystal cathode material; wherein:

[0097] The nickel-cobalt-manganese precursor is a hydroxide containing nickel, cobalt and manganese, and its chemical formula is shown in Table 2; the types of lithium source and additives and the amount of each raw material are shown in Table 1; the equipment used for crushing is a soybean milk maker.

[0098] The first sintering process consists of a heating stage I and a isothermal stage I, with specific conditions shown in Table 1.

[0099] Median particle size D of nickel-cobalt-manganese precursors 50 The median particle size D′ of single-crystal cathode material process products 50 See Table 1;

[0100] (2) The single-crystal cathode material is subjected to a second sintering process to obtain a single-crystal multi-element cathode material; wherein:

[0101] The second sintering was carried out in an air atmosphere; the second sintering consisted of a heating stage II and an isothermal stage II, with specific conditions shown in Table 1; the chemical formulas of the products during the reaction are shown in Table 2.

[0102] Example 2

[0103] The method is the same as in Example 1, except that in step (1), the isothermal temperature of the first sintering isothermal stage I and the median particle size D′ of the single-crystal cathode material are different. 50 As shown in Table 1, all other parameters are the same, resulting in a single-crystal multi-element cathode material.

[0104] Example 3

[0105] The method is the same as in Example 1, except that in step (1), the isothermal temperature of the first sintering isothermal stage I and the median particle size D′ of the single-crystal cathode material are different. 50 As shown in Table 1, all other parameters are the same, resulting in a single-crystal multi-element cathode material.

[0106] The remaining embodiments follow the method of Embodiment 1, with the differences shown in Table 1. All other aspects are the same, and single-crystal multi-element cathode materials are obtained respectively.

[0107] Comparative Example 1

[0108] The method of Example 1 is the same except that in step (1), the first sintering is carried out in an air atmosphere, and the rest are the same, so as to obtain a single crystal multi-element cathode material.

[0109] Comparative Example 2

[0110] The method of Example 1 is the same except that in step (1), the first sintering is carried out in an oxygen atmosphere, and the rest are the same, so as to obtain a single crystal multi-element cathode material.

[0111] Comparative Example 3

[0112] The method of Example 2 is the same except that in step (1), the first sintering is carried out in an air atmosphere, and the rest are the same, so as to obtain a single crystal multi-element cathode material.

[0113] Comparative Example 4

[0114] The method of Example 3 is the same except that in step (1), the first sintering is carried out in an oxygen atmosphere, and the rest are the same, so as to obtain a single crystal multi-element cathode material.

[0115] Comparative Example 5

[0116] The method is the same as in Example 3, except that in step (1), the D′ of the obtained single-crystal cathode material is... 50 It is 3.64 μm, |(D 50 -D′ 50 ) / D 50 |=13.3%, all others are the same, resulting in a single-crystal multi-element cathode material, whose uniformity K 90 See Table 3.

[0117] Comparative Example 6

[0118] The method is the same as in Example 3, except that in step (1), the D′ of the obtained single-crystal cathode material is... 50 It is 4.49 μm, |(D 50 -D′ 50 ) / D 50 |=6.9%, all others are the same, resulting in a single-crystal multi-element cathode material, whose uniformity K 90 See Table 3.

[0119] Table 1

[0120]

[0121]

[0122] Note: Dosage 1 That is, the total molar amount of nickel, cobalt and manganese elements in the nickel-cobalt-manganese precursor; the molar amount of lithium elements in the lithium source; and the molar amount of G elements in the additive.

[0123] Dosage 2 This refers to the total molar amount of nickel, cobalt, and manganese elements in the nickel-cobalt-manganese precursor, and the molar amount of M element in the coating agent.

[0124] Table 2

[0125]

[0126] Test Example 1

[0127] The single-crystal multi-element cathode materials obtained in the examples and comparative examples were tested, including agglomeration rate B and particle size D. 10 Particle size D 50 Particle size D 90 Uniformity K 90 The results for the roundness R are shown in Table 3.

[0128] Table 3

[0129] serial number Reunion rate B <![CDATA[D 10 ]]> <![CDATA[D 50 ]]> <![CDATA[D 90 ]]> <![CDATA[K 90 ]]> Roundness R <![CDATA[K 90 *R]]> unit ％ μm μm μm / / / Example 1 1.30 2.11 4.22 7.24 1.22 1.05 1.28 Example 2 2.40 2.01 4.16 7.03 1.21 1.09 1.32 Example 3 0.80 2.37 4.34 7.58 1.20 1.14 1.37 Example 4 1.20 2.04 3.90 6.78 1.22 1.03 1.25 Example 5 1.30 1.93 3.60 6.41 1.24 1.06 1.32 Comparative Example 1 1.40 2.31 4.32 7.83 1.28 1.47 1.88 Comparative Example 2 4.30 1.93 4.09 6.73 1.14 1.21 1.42 Comparative Example 3 2.10 2.01 4.22 7.38 1.27 1.54 1.96 Comparative Example 4 1.80 1.99 4.13 7.37 1.30 1.26 1.64 Comparative Example 5 1.60 1.43 3.74 7.97 1.75 1.06 1.85 Comparative Example 6 1.70 2.22 4.55 6.78 1.00 1.09 1.09

[0130] Test Example 2

[0131] The single-crystal multi-element cathode materials obtained in the examples and comparative examples were tested, including the grain size P. 50 The compaction density and electrochemical performance were tested, and the results are shown in Table 4.

[0132] Table 4

[0133]

[0134]

[0135] Note: Capacity retention rate 3 This is the high-temperature cycling capacity retention rate.

[0136] The present invention provides, by way of example, scanning electron microscope (SEM) images of the single-crystal multi-element cathode materials obtained in Examples 1-3 and Comparative Examples 1-4, as shown in the figures below. Figure 1-7 As shown in the figure. It can be seen from the figure that, compared to the single-crystal multi-element cathode materials obtained in Examples 2-3 ( Figure 2 , 3 ) and the single-crystal multi-element cathode materials obtained in Comparative Examples 1-2 ( Figure 4-5 Compared to the single-crystal multi-element cathode material obtained in Example 1 of this invention, Figure 1 The single crystal particles of the ) are round and regular, with better morphology;

[0137] The single-crystal multi-element cathode material obtained in Example 2 ( Figure 2 The single-crystal multi-element cathode material obtained in Comparative Example 2 () and Comparative Example 2 Figure 5 The grain size P of the single crystal particles 50 The particle size is 1.8 μm. It can be clearly seen from the electron microscope image that some particles still retain the precursor morphology and there is adhesion between the particles. However, compared with the single-crystal multi-element cathode material obtained in Comparative Example 2, the single-crystal multi-element cathode material obtained by oxygen and air sintering process in the first sintering process of the present invention has better particle independence and regularity.

[0138] The single-crystal multi-element cathode material obtained in Example 3 ( Figure 3 ) and the single-crystal multi-element cathode material obtained in Comparative Example 1 ( Figure 4 The grain size P of the single crystal particles 50 The crystal particles are 2.6 μm in size, which are relatively large, have good independence but poor regularity. However, compared with the single-crystal multi-element cathode material obtained in Comparative Example 1, the single-crystal particles of the single-crystal multi-element cathode material obtained in Example 3 of this invention are more rounded.

[0139] The grain size P of the single-crystal particles of the single-crystal cathode material obtained in Example 1 and the single-crystal cathode materials obtained in Comparative Examples 3 and 4 50Both are 2.2 μm, but compared with the single-crystal multi-element cathode materials obtained in Comparative Examples 3 and 4, the single-crystal particles of the single-crystal multi-element cathode material obtained in Example 1 of this invention have better roundness and independence.

[0140] The above results show that the single-crystal multi-element cathode material provided by this invention has a more rounded and regular morphology, and its single-crystal particles are uniform in size, with less agglomeration and adhesion, exhibiting high compaction density, good rate performance, and excellent cycle performance. Specifically:

[0141] Comparing Examples 1-3 with Comparative Examples 1 and 2, it can be seen that when the grain size P of the single crystal particles... 50 When the P0.05 is 2.0-2.4 μm, the overall performance is optimal, with the highest compaction density, the best rate of return and high-temperature cycling retention, and the capacity can be maintained at a high level; when P0.05... 50 When the particle size is <2.0 μm, the compaction density decreases, and the magnification and retention rate deteriorate. However, because the transport path of lithium ions within the particles is shortened after the crystal particles become smaller, the capacity is slightly improved; when P 50 When the compaction density is greater than 2.4 μm, the compaction density also decreases, and the decreasing trend is more pronounced than that of P. 50 The value should be smaller when it is <2.0μm;

[0142] Comparing Example 2 and Comparative Example 2, and Example 3 and Comparative Example 1, it can be seen that under the condition of an air atmosphere throughout the sintering process, after the lithium source melts on the particle surface, the crystal growth direction starts from the outside, so a lower temperature is required for it to grow larger. However, under the condition of an oxygen atmosphere throughout the sintering process, there are more crystals, and they grow from the inside of the particle, requiring a higher temperature to grow larger. Comparing the compaction density and electrochemical performance of the single-crystal multi-element cathode material, it can be seen that the single-crystal particles of the single-crystal multi-element cathode material obtained by the sintering method of oxygen in the heating stage and air in the isothermal stage provided by the present invention have better compaction density and better electrochemical performance.

[0143] Comparing Example 1 with Comparative Examples 3 and 4, it can be seen that the single-crystal multi-element cathode materials prepared by different processes have different properties even if they have the same grain size. The single-crystal multi-element cathode material prepared by a sintering method using oxygen in the heating section and air in the isothermal section has a significantly better compaction density and electrochemical performance than the multi-element cathode material prepared by a single atmosphere.

[0144] Furthermore, the agglomeration rate affects the cycling performance of the material. As shown in the table above, the grain size is directly related to the agglomeration rate; the larger the grain size, the smaller the agglomeration rate, and the better the cycling performance. Simultaneously, the sintering atmosphere also has a certain impact on the agglomeration rate and cycling performance. With comparable grain sizes, the agglomeration rate of the single-crystal particles prepared by the oxygen-air combined sintering method of this invention is significantly lower than that obtained by a single sintering under either a single oxygen or air atmosphere (the agglomeration rate under an oxygen atmosphere is lower than that under an air atmosphere). The corresponding cycling performance of the multi-element cathode material is: oxygen combined with air > oxygen > air. Furthermore, the roundness index also shows that the single-crystal particles of the single-crystal multi-element cathode material obtained by the method provided by this invention are more rounded and regular, and under the same grain size, the roundness of the single-oxygen atmosphere is better than that of the single-air atmosphere.

[0145] As can be seen from Examples 4 and 5, the method provided by the present invention is also applicable to high-nickel products. With the increase of nickel content and the decrease of cobalt content, the roundness and compaction density of the multi-element cathode material can be maintained at a high level, and the capacity in terms of electrochemical performance will be significantly improved, but the rate performance and cycle performance will deteriorate accordingly.

[0146] As can be seen from Examples 1 and Comparative Examples 5 and 6, for multi-element cathode materials with different particle size distributions prepared by the same sintering method, under the condition that their roundness meets the limits defined by this invention, K 90 Too large or too small, resulting in K 90 If the product of R exceeds the range defined in this invention, its compaction density, capacity, and cycle life will all be reduced to varying degrees.

[0147] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A single-crystal multi-element cathode material, characterized in that, The roundness R of the single-crystal particles of the monocrystalline multi-element cathode material is defined as the ratio of the longest diagonal length to the shortest diagonal length as measured by SEM, and R is 1-1.2; the agglomeration rate B of the single-crystal multi-element cathode material is 0-3.0%. Define the particle size corresponding to 10% of the volume distribution of the single-crystal particles in the monocrystalline multi-element cathode material as D, obtained from particle size analysis. 10 The particle size corresponding to 50% volume distribution is D. 50 The particle size corresponding to 90% of the volume distribution is D. 90 The D of the single-crystal particles of the single-crystal type multi-element cathode material 10 D 50 and D 90 Satisfy: K 90 =(D 90 -D 10 ) / D 50 K 90 The product of R and R is 1.20-1.40; The single-crystal multi-element cathode material has the structure shown in Formula I: Li 1+a (Ni x Co y Mn z G b )M c O 2-d Formula I; In the formula, 0.05≤a≤0.3, 0<b≤0.05, 0<c≤0.05, 0.5≤x<1, 0<y<0.5, 0<z<0.5; the value of d ensures that the number of positive and negative charges are equal; G is one or more of Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, B, Mg, Co, F and Y; M is one or more of Sr, F, B, Al, Nb, Co, Mn, Mo, W, Si, Mg, Ti and Zr.

2. The single-crystal multi-element cathode material according to claim 1, wherein, K 90 The product of R and R is 1.25-1.35; And / or, K 90 It is 1.18-1.

25.

3. The single-crystal multi-element cathode material according to claim 2, wherein, K 90 It is 1.20-1.

22.

4. The single-crystal multi-element cathode material according to claim 1, wherein, In the formula, 0≤a≤0.2, 0.0001≤b≤0.005, 0.0001≤c≤0.005, 0.5≤x≤0.95, 0.01≤y≤0.4, 0.01≤z≤0.4; And / or, G is one or more of Ti, W, Zr, Sr, Si, Al, B and F; And / or, M is one or more of Sr, F, B, Al, W, Si and Ti.

5. The single-crystal multi-element cathode material according to claim 1, wherein, B ranges from 0.8% to 2.4%.

6. The single-crystal multi-element cathode material according to any one of claims 1-3, wherein, The average length of the longest diagonal and the shortest diagonal of the single-crystal particles of the monocrystalline multi-element cathode material is the grain size P. 50 And P 50 The thickness ranges from 1.5 to 3.0 μm.

7. The single-crystal multi-element cathode material according to claim 6, wherein, P 50 It is 2.0-2.4μm.

8. A method for preparing a single-crystal multi-element cathode material according to any one of claims 1-7, characterized in that, The preparation method includes: (1) A mixture containing nickel-cobalt-manganese precursor and lithium source is subjected to a first sintering, and the resulting product is crushed to obtain a single-crystal cathode material process product; the mixed raw materials also include additives, which are selected from compounds containing G; (2) First, the single-crystal cathode material is mixed with a coating agent, and then the resulting mixture is subjected to the second sintering to obtain a single-crystal multi-element cathode material; the coating agent is selected from compounds containing M; The first sintering includes a heating stage I and a isothermal stage I, which are carried out sequentially. The heating stage I is carried out in an oxygen atmosphere, and the isothermal stage I is carried out in an air atmosphere. The temperature of the second sintering is not higher than the temperature of the first sintering.

9. The preparation method according to claim 8, wherein, In step (1), the nickel-cobalt-manganese precursor is selected from oxides and / or hydroxides containing nickel, cobalt and manganese; And / or, the lithium source is selected from lithium carbonate and / or lithium hydroxide.

10. The preparation method according to claim 8 or 9, wherein, The compound containing G is at least one of oxides, hydroxides, carbonates, and fluorides containing G.

11. The preparation method according to claim 10, wherein, The compound containing G is at least one of zirconium oxide, strontium carbonate, strontium hydroxide, silicon dioxide, aluminum oxide, aluminum hydroxide, tungsten trioxide, titanium oxide, aluminum fluoride, and boron oxide.

12. The preparation method according to claim 8 or 9, wherein, In step (1), the conditions for the heating stage I also include: the heating time is 2-10h; And / or, the conditions for the isothermal stage I further include: an isothermal temperature of 600-1100℃; and an isothermal time of 6-12h; And / or, the median particle size D of the nickel-cobalt-manganese precursor 50 The median particle size D′ of the single-crystal cathode material process product 50 Satisfaction Equation II: |(D 50 - D' 50 ) / D 50 | < 5% Formula II.

13. The preparation method according to claim 12, wherein, In step (1), the conditions for the heating stage I also include: the heating time is 6-8 hours.

14. The preparation method according to claim 12, wherein, The conditions for the constant temperature stage I also include: the constant temperature is 900-1000℃.

15. The preparation method according to claim 12, wherein, The conditions for the constant temperature stage I also include: the constant temperature time is 8-10 hours.

16. The preparation method according to claim 8 or 9, wherein, The compound containing M is at least one of oxides, hydroxides, carbonates, and fluorides containing M.

17. The preparation method according to claim 16, wherein, The compound containing M is at least one of strontium carbonate, strontium hydroxide, silicon dioxide, aluminum oxide, aluminum hydroxide, tungsten trioxide, titanium oxide, aluminum fluoride, and boron oxide.

18. The preparation method according to claim 8 or 9, wherein, In step (2), the second sintering is carried out in an air atmosphere; And / or, the second sintering includes a heating stage II and a isothermal stage II performed sequentially; And / or, the conditions for the heating stage II also include: a heating time of 2-10 hours; And / or, the conditions for the isothermal stage II also include: an isothermal temperature of 500-900℃; and an isothermal time of 6-12h.

19. The preparation method according to claim 18, wherein, The conditions for the second heating stage also include a heating time of 4-7 hours.

20. The preparation method according to claim 18, wherein, The conditions for the constant temperature stage II also include: a constant temperature of 600-800℃.

21. The preparation method according to claim 18, wherein the conditions of the isothermal stage II further include: The constant temperature time is 8-10 hours.

22. The preparation method according to claim 8 or 9, wherein, definition P represents the grain size variation of the single-crystal multi-element cathode material, in μm. T represents the temperature change during the same sintering step, in °C. t represents the time change value under the same sintering step, in hours, and the three conditions are satisfied as follows: P = T + t, where, =0.02 μm / ℃, =0.1 μm / h.

23. A single-crystal multi-element cathode material prepared by the preparation method according to any one of claims 8-22.

24. A lithium-ion battery, characterized in that, The lithium-ion battery contains the single-crystal multi-element cathode material as described in any one of claims 1-7 or 23.

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