Positive electrode material and manufacturing method thereof, lithium ion battery

Abstract

The present invention relates to the field of lithium-ion batteries, and discloses a positive electrode material, a manufacturing method thereof, and a lithium-ion battery. The micro residual stress measured by XRD of the positive electrode material is 0.01 - 0.15, the average diameter of the positive electrode material measured by SEM electron microscope is D, and the crystal grain diameter measured by XRD is R, where D / R is 1.4 - 2.5. Since the positive electrode material has a micro residual stress within a specific range and a ratio (D / R) of the average diameter to the crystal grain diameter within a specific range, it has significantly improved electrochemical performance and thermal stability.

Description

[Technical Field]

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a cathode material and its manufacturing method, and a lithium ion battery. [Background technology]

[0002] Power batteries are the energy source for electric vehicles, and battery performance is crucial for the performance of new energy vehicles. Cathode materials, as an important component of power batteries, significantly affect battery performance. During the manufacturing process, cathode materials often have excessive residual alkali on their surface, which increases the viscosity of the slurry during the homogenization process and leads to a jelly-like phenomenon, which is detrimental to the battery's fabrication and electrical performance. Cobalt-containing compounds, a commonly used coating agent for cathode materials, can effectively reduce the amount of residual alkali on the surface.

[0003] There are many types of cobalt-containing compounds, such as lithium cobalt oxide, cobalt oxide, and tricobalt tetroxide. Different types of cobalt-containing compounds can improve or worsen the electrical performance of the cathode material. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention aims to provide a cathode material having a specific range of micro residual stress and a specific range of the ratio of average diameter to crystal grain diameter (D / R), thereby exhibiting significantly improved electrochemical performance and thermal stability, a method for producing the same, and a lithium ion battery. [Means for solving the problem]

[0005] In order to achieve the above object, a first aspect of the present invention provides a positive electrode material, wherein the micro residual stress of the positive electrode material measured by XRD is 0.01-0.15; The average diameter of the positive electrode material measured by SEM electron microscopy is D, and the grain diameter measured by XRD is R; D / R is 1.4-2.5.

[0006] A second aspect of the present invention provides a method of making a cathode material, the method comprising: (1) mixing a positive electrode material precursor, a lithium source, and an optional G element-containing additive to obtain a mixture I; (2) first sintering the mixture I under an air or oxygen atmosphere to obtain a cathode material process product II; (3) mixing the cathode material process product II, the cobalt additive, and an optional additive containing an M element to obtain a mixture III; (4) second sintering the mixture III under an air or oxygen atmosphere to obtain the positive electrode material; The peak intensity ratio of the characteristic peak at 38.5° to the characteristic peak at 37.4° of the cobalt additive measured by XRD is 1:1.1-7.5; The isothermal temperature T1 of the first sintering is 1000° C. or less.

[0007] A third aspect of the present invention provides a positive electrode material produced by the above method.

[0008] A fourth aspect of the present invention provides a lithium ion battery comprising the above positive electrode material. [Effects of the Invention]

[0009] According to the above technical solutions, the positive electrode material and the manufacturing method thereof, and the lithium ion battery according to the present invention achieve the following beneficial effects:

[0010] The positive electrode material according to the present invention has a specific range of micro residual stress and a specific range of the ratio of average diameter to grain diameter (D / R), and therefore has significantly improved electrochemical performance and thermal stability.

[0011] In the method for producing a positive electrode material according to the present invention, a positive electrode material is produced using a cobalt additive as a coating agent, which simultaneously contains cobalt oxyhydroxide and cobalt hydroxide and has a specific XRD structure, particle size, and particle size distribution. This makes it possible to compensate for lattice defects in the matrix of the positive electrode material, thereby improving the structural stability and electrochemical performance of the produced positive electrode material.

[0012] Furthermore, by using the cobalt additive of the present invention as a coating agent, the surface of the positive electrode particles can be well coated during the coating mixing process, and there is no occurrence of uneven coating or clumping of the coating agent.

[0013] Furthermore, compared with conventional single cobalt oxyhydroxide or cobalt hydroxide, the use of the cobalt additive of the present invention can significantly improve the electrochemical performance of the positive electrode material, thereby improving the charge / discharge capacity, cycle retention rate and safety performance of the lithium ion battery using the positive electrode material.

[0014] Furthermore, this method involves a simple process and is easy to mass-produce. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is an XRD spectrum diagram of the cobalt additives of Example 2 and Comparative Example 1. [Figure 2] FIG. 2 is an SEM image of the positive electrode material of Example 1. [Figure 3] FIG. 12 is an SEM image of the positive electrode material of Example 12. [Figure 4] FIG. 2 is a DSC spectrum diagram of the positive electrode materials of Example 1, Comparative Example 3, and Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0016] The endpoints of ranges and any value disclosed herein should be understood to be not limited to such exact ranges or values, but to include values ​​close to those ranges or values. In the case of ranges of numerical values, values ​​between the endpoints of each range, between the endpoints of each range and any single point value, and between any single point value can be combined with each other to create one or more new numerical ranges, and these numerical ranges are considered to be specifically disclosed in the specification.

[0017] A first aspect of the present invention provides a positive electrode material, wherein the positive electrode material has a micro-residual stress of 0.01-0.15 as measured by XRD; The average diameter of the positive electrode material measured by SEM electron microscopy is D, and the grain diameter measured by XRD is R; The D / R is characterized by being 1.4-2.5.

[0018] In the present invention, the positive electrode material has a specific range of micro residual stress and a specific range of the ratio of average diameter to grain diameter (D / R), and therefore has excellent electrochemical performance and thermal stability.

[0019] Specifically, in the present invention, when the D / R in the positive electrode material satisfies the range defined in the present invention, the contact interface resistance between the particles of the positive electrode material and the contact area with the electrolyte and the conductive material are kept within a reasonable range, the crystal grains have good crystallinity and size, the diffusion channels of lithium ions are kept smooth, the diffusion distance is shortened, and the reaction rate is further improved, and finally the positive electrode material has low resistance and excellent initial charge / discharge efficiency.

[0020] Furthermore, in the present invention, the cathode material is produced as a finished product by coating and sintering, and the cobalt coating agent can compensate for the internal lattice defects of the cathode material, and does not cause changes in the valence of the nickel and manganese elements in the cathode material, thereby improving the stability of the material. Finally, the cathode material has low micro-residual stress, which indicates that the cathode material has excellent structural stability and is not easily cracked during the manufacturing process.

[0021] In the present invention, the crystal grain diameter R of the positive electrode material is the crystal grain diameter calculated by Reid-Bern analysis of the powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement using CuKα radiation. Software for Reid-Bern analysis includes, but is not limited to, TOPAS, Rietan, JANA, JADE, etc.

[0022] In the present invention, the average particle size D of the positive electrode material is the average diameter of 300 representative particles in a scanning electron microscope photograph.

[0023] In the present invention, the micro-residual stress of the positive electrode material is obtained by X-ray diffraction testing and refinement. The XRD test scanning range is 10°≦2θ≦90°, the scanning speed is 5° / min, and Topas refinement software and Pawley full spectrum fitting method are used.

[0024] Furthermore, the micro residual stress of the positive electrode material measured by XRD was 0.03 It is -0.15.

[0025] Furthermore, the D / R is 1.4-2.

[0026] According to the present invention, the average diameter D of the positive electrode material is 1-3 μm.

[0027] The inventors of the present invention have found through research that a smaller average diameter D of a positive electrode material indicates smaller single-crystal particles of the positive electrode material, while a larger D indicates larger single-crystal particles of the positive electrode material. If the D value is too small, the degree of single crystallization decreases, the single-crystal particles become more closely packed, and single crystallization becomes difficult, approaching a polycrystalline structure. This causes the positive electrode material to crack and pulverize during cycling, resulting in a sharp drop in the capacity cycling curve. If the D value is too high, the number of paths for lithium ion transport within the particles increases, reducing the lithium ion transport capacity and increasing the transport impedance, thereby increasing the battery's internal resistance and reducing capacity. In the present invention, the average diameter of the positive electrode material within the above range prevents the positive electrode material from cracking and pulverizing and ensures that the positive electrode material has low impedance and high charge / discharge capacity.

[0028] Furthermore, the average diameter D of the positive electrode material is 1.5-2 μm.

[0029] According to the present invention, the crystal grain diameter R of the positive electrode material is 700-1200 nm.

[0030] In the present invention, when the crystal grain diameter R of the positive electrode material satisfies the above range, the purity and crystallinity of the crystal grains of the positive electrode material are high, and suitable diffusion channels for lithium ion diffusion can be provided, further reducing the resistance inside the single crystal particles. If the crystal grain diameter R is too large, the diffusion channels for lithium ions during charge and discharge become longer, and the internal resistance of the single crystal particles is likely to increase. If R is too small, the crystallinity and purity of the positive electrode material particles will be low, and they will contain inactive crystalline phases and non-crystalline impurity phases, which will hinder smooth absorption and release of lithium ions and likely increase resistance.

[0031] Furthermore, the crystal grain diameter R of the positive electrode material is 900-1000 nm.

[0032] In the present invention, when the micro residual stress and the crystal grain size of the positive electrode material simultaneously satisfy the ranges defined in the present invention, it can be ensured that the positive electrode material has high charge / discharge capacity and excellent cycle performance.

[0033] According to the present invention, the median diameter D50 of the positive electrode material is 3 - 4.5 μm.

[0034] According to the present invention, the mixed arrangement nickel content of the positive electrode material is 0 - 4 wt%.

[0035] In the present invention, the mixed arrangement nickel content refers to the proportion of Ni in which lithium nickel mixing occurs in the total Ni, and can be measured by XRD finishing. 2+

[0036] In the present invention, since the positive electrode material has a low mixed arrangement nickel content, it has high structural stability, and particularly at high voltages, it can effectively suppress the dissolution and structural destruction of the positive electrode active material particles, improving the chemical stability of the material and resulting in the effect of extending the battery cycle life.

[0037] Furthermore, the mixed arrangement nickel content of the positive electrode material is 0 - 3 wt%.

[0038] In a specific embodiment of the present invention, the positive electrode material is a cobalt-coated positive electrode material.

[0039] According to the present invention, the positive electrode material includes a matrix and a coating layer coated on the matrix. The matrix has a composition shown in Formula I. Li 1+a Ni x Mn y Co z G b O2 Formula I Here, -0.05 ≤ a ≤ 0.1, 0 ≤ b ≤ 0.05, 0.5 ≤ x < 1, 0 < y < 0.5, 0 ≤ z < 0.5, and G is selected from at least one of W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Mg, and Y. The coating layer includes a lithium oxygen compound containing a cobalt element and / or an oxide containing a cobalt element. ​Optionally, the coating layer further includes a lithium oxygen compound containing an M element and / or an oxide containing an M element, and M is selected from at least one of B, Al, Nb, Mn, Mo, W, Si, Mg, Ti, and Zr.

[0040] Furthermore, in Formula I, 0.01 ≦ a ≦ 0.1, 0 ≦ b ≦ 0.005, 0.5 ≦ x < 1, 0 < y < 0.2, 0 ≦ z < 0.3, and G is selected from at least one of W, V, Ta, Zr, Sr, Si, and Y. M is selected from at least one of B, Al, W, Mg, Ti, and Zr.

[0041] In the present invention, in the case of a lithium oxygen compound containing an M element and a lithium oxygen compound containing a cobalt element, in addition to the metal element M and Li, or Co and Li, it contains at least one of Ni, Mn, and G.

[0042] According to the present invention, between the molar amount n'(Co) of the cobalt element in the coating layer, the molar amount n(M) of the M element in the coating layer, and the total molar amount [n(Ni) + n(Co) + n(Mn) + n(G)] of the metal elements other than Li in the matrix, 0.001 ≦ n'(Co):[n(Ni) + n(Co) + n(Mn) + n(G)] ≦ 0.05, 0 ≦ n(M):[n(Ni) + n(Co) + n(Mn) + n(G)] ≦ 0.05 is satisfied.

[0043] In the present invention, when the contents of the coating layer containing a cobalt element and the coating layer containing an M element in the positive electrode material satisfy the above ranges, Li + The migration rate and transport efficiency can be improved, and furthermore, the electrical conductivity of the positive electrode material can be increased, and the manufactured positive electrode material has higher reaction activity and utilization rate.

[0044] Furthermore, between the molar amount n'(Co) of the cobalt element in the coating layer, the molar amount n(M) of the M element in the coating layer, and the total molar amount [n(Ni) + n(Co) + n(Mn) + n(G)] of the metal elements other than Li in the matrix, 0.01≦n'(Co):[n(Ni)+n(Co)+n(Mn)+n(G)]≦0.03, The formula satisfies 0≦n(M):[n(Ni)+n(Co)+n(Mn)+n(G)]≦0.01.

[0045] According to the present invention, the residual alkali content of the positive electrode material is 1000-10000 ppm.

[0046] In the present invention, the surface of the positive electrode material has a low residual alkali content and is coated with cobalt, so that the positive electrode material undergoes small volume changes and heat changes during the reaction process, thereby improving the thermal stability and safety of lithium ion batteries containing the positive electrode material.

[0047] Furthermore, the residual alkali content of the positive electrode material is 1000-6000 ppm.

[0048] In one embodiment of the present invention, when 0.5≦x<0.8, the residual alkali content of the positive electrode material is 1000-3000 ppm, preferably 2000-3000 ppm.

[0049] In one embodiment of the present invention, when 0.8≦x<1, the residual alkali content of the positive electrode material is 4000-6000 ppm, preferably 4000-5000 ppm.

[0050] In the present invention, as long as the cathode material has the characteristics described in the first aspect of the present invention, a lithium ion battery containing the cathode material can have excellent electrochemical performance. Regarding the manufacturing method of the cathode material, any method that can manufacture the cathode material described in the first aspect of the present invention falls within the scope of protection of the present invention.

[0051] In the present invention, in order to further reduce the microstress and the content of mixed-arrangement nickel in the positive electrode material and improve the thermal stability, etc., preferably, a second aspect of the present invention provides a method for producing a positive electrode material, the method comprising: (1) mixing a positive electrode material precursor, a lithium source, and an optional G element-containing additive to obtain a mixture I; (2) first sintering the mixture I under an air or oxygen atmosphere to obtain a cathode material process product II; (3) mixing the cathode material process product II, the cobalt additive, and an optional additive containing an M element to obtain a mixture III; (4) second sintering the mixture III under an air or oxygen atmosphere to obtain the positive electrode material; The peak intensity ratio of the characteristic peak at 38.5° to the characteristic peak at 37.4° of the cobalt additive measured by XRD is 1:1.1-7.5; Here, the isothermal temperature T1 of the first sintering is 1000° C. or less.

[0052] In the method for preparing the positive electrode material according to the present invention, the cobalt additive containing cobalt oxyhydroxide and cobalt hydroxide at the same time is used as a coating agent, which can convert cobalt oxyhydroxide and cobalt hydroxide into each other, and can convert Co according to the change of potential and pH value. 2+ and Co 3+ The cobalt additive achieves ionic dynamic equilibrium and stabilizes the performance of the coating layer under different environments. The cobalt additive has a specific XRD structure, particle size and particle size distribution, and can compensate for lattice defects in the positive electrode material matrix, thereby improving the structural stability and electrochemical performance of the final positive electrode material.

[0053] Specifically, the cobalt additive is combined with the cathode material process product II using a high-temperature solid-state method to obtain a cobalt additive-coated cathode material. At high temperatures, the cobalt hydroxide reduces the residual alkali content on the surface of the cathode material, improving the homogenization efficiency and, at the same time, improving the conductivity of the cathode material. The valence of cobalt in the cobalt oxyhydroxide is +3, which is the same as the average valence of the nickel-cobalt-manganese in the cathode material. This allows it to penetrate well into the material to compensate for lattice defects and not cause any change in the valence of the nickel and manganese elements in the material, playing a role in stabilizing the material and reducing the micro-residual stress in the cathode material.

[0054] In the present invention, by adjusting the content ratio of cobalt oxyhydroxide and cobalt hydroxide, the peak intensity ratio of the 38.5° peak and the 37.4° peak in the XRD of the cobalt additive can be controlled, and when the peak intensity ratio is within a certain range, the addition of the cobalt additive as a coating agent to the positive electrode material can effectively improve the electrochemical performance and thermal stability of the positive electrode material.

[0055] Furthermore, when the cobalt additive of the present invention is used as a coating agent, it can be wrapped around the surface of the positive electrode particles during the coating mixing process, and there is no uneven coating or clumping of the coating agent.

[0056] Furthermore, compared with conventional single cobalt oxyhydroxide or cobalt hydroxide, the use of the cobalt additive of the present invention can significantly improve the electrochemical performance of the positive electrode material, and the charge / discharge capacity, cycle retention rate, and safety performance of lithium ion batteries containing the positive electrode material are all improved.

[0057] In the present invention, controlling the isothermal temperature T1 of the first sintering to satisfy the above range can promote the growth and alignment of the crystal grains of the positive electrode material, reduce grain boundaries and voids, facilitate the spatial transport of electrons / ions, and improve electrochemical performance. At the same time, it can change and optimize the crystalline structure of the material, thereby improving material stability. Furthermore, this method is simple and easy to mass-produce.

[0058] Furthermore, the peak intensity ratio of the characteristic peak at 38.5° to the characteristic peak at 37.4° of the cobalt additive measured by XRD is 1:2-4.5.

[0059] Furthermore, the isothermal temperature T1 of the first sintering is 700-1000°C.

[0060] According to the present invention, the median diameter D of the cobalt additive (Co)50is 0.5-5 μm, and the particle size distribution K of the cobalt additive (Co)90 =(D (Co)90 -D (Co)10 ) / D (Co)50 is 0.8≦K 90 Satisfies ≦2.

[0061] In the present invention, the median diameter D of the cobalt additive (Co)50 and particle size distribution K (Co)90 By controlling the cobalt content within the range defined by the present invention, the resulting cathode material has excellent electrochemical performance, while reducing production costs and enabling mass production. Specifically, if the cobalt additive powder particles are too large, the coating uniformity on the cathode material process product II will be poor, resulting in partial concentration on the surface of the cathode material, partially exposing the cathode material, which will further affect the electrochemical performance of the product. If the powder particles are too small, more precise production equipment will be required, and damage to the equipment will increase rapidly during production, increasing production costs and making it unsuitable for industrial mass production.

[0062] Furthermore, the median diameter D of the cobalt additive (Co)50 is 0.5-3 μm, and the particle size distribution K of the cobalt additive (Co)90 =(D (Co)90 -D (Co)10 ) / D (Co)50 is 1≦K (Co)90 ≦1.8.

[0063] In the present invention, there is no particular limitation on the method for producing the cobalt additive, and the cobalt additive can be produced by a conventional method in this field, as long as the obtained cobalt additive has a specific XRD structure defined in the present invention. Preferably, in the present invention, cobalt oxyhydroxide and cobalt hydroxide are mixed and pulverized to obtain the cobalt additive.

[0064] In the present invention, the mixture of cobalt oxyhydroxide and cobalt hydroxide can be milled by conventional methods in the art, such as by air milling.

[0065] In the present invention, the amounts of cobalt oxyhydroxide and cobalt hydroxide used and the conditions for pulverization are not particularly limited, and the cobalt additive is selected from the group consisting of the peak intensity ratio of the characteristic peak at 38.5° to the characteristic peak at 37.4°, the median diameter D 50 and particle size distribution K 90 It is sufficient to have the following.

[0066] According to the present invention, based on the total weight of the cobalt additive, the content of Co element is 55-75wt%.

[0067] According to the present invention, the isothermal time t1 of the first sintering is not more than 15 hours, preferably 6-12 hours.

[0068] In the present invention, the constant temperature T2 of the second sintering is not particularly limited, and it is sufficient to ensure that 1000° C.≧T1>T2≧300° C. Specifically, the constant temperature T2 is 300-800° C., preferably 300-700° C.

[0069] In the present invention, the constant temperature time t2 of the second sintering is not particularly limited, and it is sufficient to ensure that 15 h ≥ t1 > t2 ≥ 5 h is satisfied. Specifically, the constant temperature time t2 is 6 to 12 h, preferably 6 to 10 h.

[0070] According to the present invention, the total molar amount [n(Ni)+n(Mn)+n(Co)] of metal elements in the precursor of the positive electrode material, the molar amount n(Li) of Li element in the lithium source, and the molar amount n(G) of G element in the G element-containing additive are used in amounts of 0.95≦n(Li) / [n(Ni)+n(Mn)+n(Co)]≦1.1, The condition satisfies 0≦n(G) / [n(Ni)+n(Mn)+n(Co)]≦0.05.

[0071] Furthermore, the total molar amount of metal elements in the precursor of the positive electrode material [n(Ni)+n(Mn)+n(Co)], the molar amount n(Li) of Li element in the lithium source, and the molar amount n(G) of G element in the G element-containing additive are used in amounts of 1≦n(Li) / [n(Ni)+n(Mn)+n(Co)]≦1.1, The condition satisfies 0.0005≦n(G) / [n(Ni)+n(Mn)+n(Co)]≦0.03.

[0072] In the present invention, the precursor of the positive electrode material is selected from nickel cobalt manganese oxide and / or nickel cobalt manganese hydroxide.

[0073] In the present invention, the type of lithium source is not particularly limited, and may be a conventional lithium source in this field, such as lithium carbonate and / or lithium hydroxide.

[0074] In the present invention, the type of G element-containing additive is not particularly limited, and may be a conventional compound in this field capable of providing a G element, such as a G-containing oxide, a G-containing hydroxide, or a G-containing carbonate.

[0075] In the present invention, G is selected from at least one of W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Mg, and Y.

[0076] According to the present invention, the total molar amount of metal elements in the positive electrode material process product II [n(Ni)+n(Co)+n(Mn)+n(G)], the molar amount n'(Co) of cobalt element in the cobalt additive, and the molar amount n(M) of M element in the M element-containing additive are used in amounts of 0.001≦n'(Co) / [n(Ni)+n(Co)+n(Mn)+n(G)]≦0.05, The condition satisfies 0≦n(M) / [n(Ni)+n(Co)+n(Mn)+n(G)]≦0.05.

[0077] Furthermore, the total molar amount of metal elements in the positive electrode material process product II [n(Ni)+n(Co)+n(Mn)+n(G)], the molar amount n'(Co) of cobalt element in the cobalt additive, and the molar amount n(M) of M element in the M element-containing additive are used in amounts of 0.001≦n'(Co)[n(Ni)+n(Co)+n(Mn)+n(G)]≦0.03, The condition satisfies 0≦n(M) / [n(Ni)+n(Co)+n(Mn)+n(G)]≦0.03.

[0078] In the present invention, the type of the M element-containing additive is not particularly limited, and may be a conventional compound in this field capable of providing the M element, such as an M-containing oxide, an M-containing hydroxide, or an M-containing carbonate.

[0079] In the present invention, M is selected from at least one of B, Al, Nb, Mn, Mo, W, Si, Mg, Ti and Zr.

[0080] A third aspect of the present invention provides a positive electrode material produced by the above method.

[0081] A fourth aspect of the present invention provides a lithium ion battery comprising the above positive electrode material.

[0082] The present invention will now be described in detail with reference to examples. (1) Morphology test: Obtained by testing with a scanning electron microscope (Hitachi S-4800 model, Japan), and calculate the average particle size D of the positive electrode material by measuring 300 particles in the electron microscope photograph. (2) Grain size D50, D10, D90: Obtained by Marvern Hydro 3000mu laser grain sizer test. (3) XRD test: The XRD test was conducted by a Smartlab 9KW physical turning target diffractometer, and / or by refinement. The grain diameter R and micro residual stress of the positive electrode material were calculated, and the peak intensity ratio of the characteristic peak at 38.5° and the characteristic peak at 37.4° in the cobalt additive was obtained. The lithium-nickel mixed arrangement value was then calculated. (4) The residual alkali content of the positive electrode material is obtained by testing with a Swiss Metrohm Orby potentiometric titrator. (5) Mass of Co element in total compounds: Measured by inductively coupled plasma (ICP) atomic emission spectroscopy. (6) Electrochemical performance test: In the above examples and comparative examples, the electrochemical performance of the positive electrode materials is tested by a CR2025 button cell battery.

[0083] The specific manufacturing process of CR2025 button battery is as follows:

[0084] Sheet preparation: The positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 95:3:2 to form a uniform slurry. The slurry was then applied to an aluminum foil and dried at 120°C for 12 hours. The aluminum foil was then pressed under a pressure of 100 MPa to form a positive electrode sheet with a diameter of 12 mm and a thickness of 3.2 mm. The loading of the positive electrode material was 15.5 mg / cm. 2 is.

[0085] Battery assembly: The positive electrode sheet, separator, negative electrode sheet, and electrolyte were assembled into a CR2025 button cell battery in a gas glove box filled with argon gas (water and oxygen contents were both less than 5 ppm) and then allowed to stand for 6 hours. The negative electrode sheet was a lithium metal sheet with a diameter of 15.8 mm and a thickness of 1 mm, the separator was a 25 μm thick polypropylene microporous film (Celgard 2325), and the electrolyte was a mixture of equal parts of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0086] Electrochemical performance test: In the following examples and comparative examples, electrochemical performance tests were carried out on CR2025 button batteries using a Shenzhen Nova battery test system. The charge / discharge voltage range was controlled to 2.8-4.5V, and the button batteries were charged / discharged at 0.1C for 2 cycles at a constant temperature of 60°C, followed by charging / discharging at 1C for 80 cycles to evaluate the high-temperature cycle capacity retention of the positive electrode material.

[0087] Thermal Stability Test: The thermal stability of the material was tested by Mettler DSC3+, and the steps were as follows: The battery was charged and discharged twice at 0.2C CC-CV in the voltage range of 3-4.4V, and then charged to 4.4V at 0.2C CC-CV. After charging was completed, the battery was disassembled, and the positive electrode material was scraped off from the electrode piece. 1g of the positive electrode material scraped off from the electrode piece was weighed and subjected to a DSC test to evaluate the thermal stability of the positive electrode material.

[0088] All of the raw materials used in the examples and comparative examples are commercially available products.

[0089] Example 1 S1, cobalt oxyhydroxide and cobalt hydroxide are mixed, and the grinding intensity of the airflow mill is adjusted to D 50 The cobalt additive was obtained with a particle size of 0.96 μm, and the peak intensity ratio of 38.5° and 37.4° in the XRD of the cobalt additive was 1:2. The specific parameters of the cobalt additive are shown in Table 1. S2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, lithium carbonate, and ZrO2 were mixed in a molar ratio of [n(Ni) + n(Co) + n(Mn)]:n(Li):n(Zr) = 1:1.03:0.0002 to obtain mixture I. S3. The mixture I is first sintered in an air atmosphere in a muffle furnace at a constant temperature T1 of 950°C and a constant temperature time t1 of 8 hours. The mixture is then pulverized by an air mill and sieved to obtain a cathode material process product II. S4, the positive electrode material process product II and the cobalt additive and Al2O3 prepared in step (1) are coated and mixed in a molar ratio of [n(Ni) + n(Co) + n(Mn) + n(Zr)]:n(Co):n(Al) = 1:0.02:0.0001 to obtain a uniform mixture III; S5. Secondly, in an air or oxygen atmosphere, the mixture III is sintered at a constant temperature T2 of 700°C for a constant time t2 of 10 hours, and then directly sieved to obtain cathode material A1. Some of the process conditions and the composition of cathode material A1 are listed in Table 2.

[0090] The physicochemical parameters of the positive electrode material A1 were tested and the results are shown in Table 3.

[0091] The positive electrode material A1 was assembled into a CR2025 button cell battery, and the electrochemical performance and thermal stability of the battery were tested, and the results are shown in Table 4.

[0092] Example 2 In step S1, a positive electrode material A2 was produced in the same manner as in Example 1, except that the ratio of cobalt oxyhydroxide and cobalt hydroxide was adjusted so that the peak intensity ratio at 38.5° and 37.4° in the XRD of the cobalt additive was 1:4.

[0093] Example 3 In step S2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2 instead of Ni 0.8 Co 0.1 Mn 0.1 A positive electrode material A3 was produced in the same manner as in Example 1, except that (OH)2 was used.

[0094] Example 4 In step S1, the ratio of cobalt oxyhydroxide and cobalt hydroxide was adjusted so that the peak intensity ratio at 38.5° and 37.4° in the XRD of the cobalt additive was 1:7. A positive electrode material A4 was produced in the same manner as in Example 1.

[0095] Example 5 A positive electrode material A5 was produced in the same manner as in Example 1, except that in step S4, Al2O3 was not added and only cobalt additive was added, so that [n(Ni) + n(Co) + n(Mn) + n(Zr)]:n(Co) = 1:0.02.

[0096] Example 6 In step S2, Ni 0.6 Co 0.2 Mn 0.2 A positive electrode material A6 was produced in the same manner as in Example 1, except that (OH)2, lithium carbonate, Al2O3, and SrCO3 were used in a molar ratio of [n(Ni) + n(Co) + n(Mn)]:n(Li):n(Al):n(Sr) = 1:1.03:0.00015:0.00005.

[0097] Example 7 In step S1, a positive electrode material A7 was produced in the same manner as in Example 1, except that the ratio of cobalt oxyhydroxide and cobalt hydroxide was adjusted so that the peak intensity ratio at 38.5° and 37.4° in the XRD of the cobalt additive was 1:1.4.

[0098] Example 8 In step S4, the positive electrode material process product II, the cobalt additive produced in step S1, and Al2O3 were coated and mixed in a molar ratio of [n(Ni) + n(Co) + n(Mn) + n(Zr)]:n(Co):n(Al) = 1:0.01:0.0001, except that the positive electrode material A8 was produced in the same manner as in Example 1.

[0099] Example 9 In step S4, the positive electrode material process product II, the cobalt additive produced in step S1, and Al2O3 were coated and mixed in a molar ratio of [n(Ni) + n(Co) + n(Mn) + n(Zr)]:n(Co):n(Al) = 1:0.04:0.0001, except that a positive electrode material A9 was produced in the same manner as in Example 1.

[0100] Example 10 In step S3, the mixture I was first sintered to produce a positive electrode material A10 in the same manner as in Example 1, except that the constant temperature T1 was changed to 930° C. and the constant temperature time t1 was changed to 9.5 hours.

[0101] Example 11 In step S3, the mixture I was first sintered to produce a positive electrode material A11 in the same manner as in Example 1, except that the constant temperature T1 was changed to 980° C. and the constant temperature time t1 was changed to 7 hours.

[0102] Example 12 In step S1, the D of the cobalt additive is adjusted by adjusting the grinding intensity of the airflow mill. 50 A positive electrode material D3 was produced in the same manner as in Example 1, except that the thickness was changed to 7.90 μm.

[0103] Example 13 In step S1, the D of the cobalt additive is adjusted by adjusting the grinding intensity of the airflow mill. 50 1.2 μm, K 90 A positive electrode material A13 was produced in the same manner as in Example 1, except that the value of was 2.2.

[0104] Comparative Example 1 In step S1, a positive electrode material D1 was produced in the same manner as in Example 1, except that the ratio of cobalt oxyhydroxide and cobalt hydroxide was adjusted so that the peak intensity ratio at 38.5° and 37.4° in the XRD of the cobalt additive was 1:8.

[0105] Comparative Example 2 In step S1, a positive electrode material D2 was produced in the same manner as in Example 1, except that the ratio of cobalt oxyhydroxide and cobalt hydroxide was adjusted so that the peak intensity ratio at 38.5° and 37.4° in the XRD of the cobalt additive was 1:0.2.

[0106] Comparative Example 3 A positive electrode material D3 was produced in the same manner as in Example 1, except that only cobalt oxyhydroxide was used in step S1.

[0107] Comparative Example 4 A positive electrode material D4 was produced in the same manner as in Example 1, except that only cobalt hydroxide was used in step S1.

[0108] Comparative Example 5 In step S3, a positive electrode material D5 was produced in the same manner as in Example 1, except that the isothermal temperature T1 of the first sintering was set to 1020°C.

[0109] [Table 1]

[0110] [Table 2-1]

[0111] [Table 2-2]

[0112] [Table 2-3]

[0113] [Table 2-4]

[0114] [Table 2-5]

[0115] [Table 2-6]

[0116] [Table 3]

[0117] [Table 4]

[0118] FIG. 1 shows the XRD spectra of the cobalt additives of Example 2 and Comparative Example 1. As can be seen from Tables 1 and 4, the peak intensity ratios at 38.5° and 37.4° in the XRD spectra of the cobalt additives are different, and therefore, when the prepared positive electrode material is used in a lithium ion battery, the electrical performance of the lithium ion battery is significantly different. When the peak intensity ratios at 38.5° and 37.4° in the XRD spectra of the cobalt additives are within the range defined by the present invention, the prepared positive electrode material in a lithium ion battery exhibits high capacity and excellent cycle retention.

[0119] As can be seen from Examples 1, 2, and 7 and Comparative Examples 1 and 2, when the XRD peak intensity ratio of the cobalt additive in Examples 1 and 2 is within the range defined by the present invention, compared to Examples 1 and 2, the peak intensity ratio of the cobalt additive in Example 7 is not within the preferred range of the present invention, and the capacity and cycle retention of the lithium ion battery manufactured using this positive electrode material are both reduced, but are much higher than those of Comparative Examples 1 and 2. When the XRD peak intensity of the cobalt additive in Comparative Examples 1 and 2 is not within the range defined by the present invention, the capacity of the lithium ion battery containing the positive electrode material manufactured in Comparative Examples 1 and 2 is reduced, and the cycle retention at high magnification and high temperature are both reduced.

[0120] As can be seen from Examples 1, 5, 6, 8-11, whether the cathode material contains coating element M, whether the type of doping element G is changed, whether the amount of cobalt additive used is changed, and whether the first sintering conditions are changed all have no effect on the XRD structural characteristics of the cathode material. As long as the cathode material contains a coating layer formed by the cobalt additive defined in the present invention, it is possible to prepare a cathode material with the specific XRD structural characteristics described in the present invention. When this cathode material is used in a lithium ion battery, the electrical performance of the battery is significantly improved compared to conventional techniques.

[0121] FIG. 2 is an SEM image of the positive electrode material of Example 1, and FIG. 3 is an SEM image of the positive electrode material of Example 12. As can be seen from FIGS. 2 and 3, compared with Example 1, the coating condition on the surface of the positive electrode material of Example 12 is significantly worse. The SEM image shows a large amount of cobalt aggregate particles (especially small particles concentrated in the middle part), and some of the surface of the positive electrode material remains exposed even after coating. This indicates that the additive in Comparative Example 3 is difficult to mix uniformly. This is due to the D of the cobalt additive in Example 12. 50 As can be seen from Examples 1, 12, and 13, the K of the cobalt additive is large and the particles are closely attached to each other. 90 The particle size distribution is large and the uniform mixing is difficult under the same conditions. 50 is too large and / or K 90If a product is manufactured using a cobalt additive with too large a cobalt content, the electrical performance of the finished cathode material will be significantly reduced due to uneven mixing.

[0122] The cobalt additive in Comparative Examples 3 and 4 was a single cobalt oxyhydroxide or cobalt hydroxide, and its D 50 is within the range limited by the present invention, and the performance of the finished cathode materials prepared therefrom is inferior to that of the material in Example 1. Figure 4 shows DSC spectra of the cobalt cathode materials of Example 1, Comparative Example 3, and Comparative Example 4. As can be seen from the DSC data in Figure 4, the thermal stability of the cathode material prepared in Example 1 is optimal. The valence of cobalt in the cobalt oxyhydroxide is +3, which is the same as the average valence of the nickel-cobalt-manganese in the cathode material, so it can penetrate into the material to compensate for lattice defects, preventing changes in the valence of the nickel and manganese elements and stabilizing the material. Therefore, the DSC peak values ​​of Example 1 and Comparative Example 3 are higher than that of Comparative Example 4. The higher the temperature corresponding to the peak value, the higher the temperature required for combustion and, ultimately, explosion to occur. That is, the higher the peak value, the better the stability. Compared to single cobalt oxyhydroxide, the cobalt additive prepared by this method further increases the DSC peak value, improving thermal stability and further improving the stability of batteries prepared with this cathode material.

[0123] When the sintering temperature in Comparative Example 5 is too high, the value of D / R increases, which increases the crystalline structure of the positive electrode material, weakens the lithium ion transport ability inside the material, and at the same time, deteriorates the lithium-nickel mixed arrangement inside the material, ultimately deteriorating the capacity and cycle performance of the material.

[0124] As can be seen from the XRD refinement data in Table 3, the Ni in the cathode material according to the present invention 2+The positive electrode material according to the present invention has low microstress, mixed nickel content, and specific XRD structure characteristics, which allows the positive electrode material to have excellent stability.

[0125] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited thereto. Within the technical concept of the present invention, the technical solutions of the present invention may be modified in a number of simple ways, including the combination of each technical feature in any other suitable manner. These simple modifications and combinations are also considered to be the contents disclosed in the present invention, and all fall within the scope of protection of the present invention. Cross-reference to related applications

[0126] This application claims the benefit of Chinese Patent Application No. 202310575361.8, proposed on May 19, 2023, the contents of which are incorporated herein by reference.

Claims

1. A positive electrode material for a lithium ion battery, wherein the micro residual stress of the positive electrode material measured by XRD is 0.01-0.15; the average diameter of the positive electrode material measured by SEM electron microscopy is D, and the grain diameter measured by XRD is R; where D / R is 1.4-2.5, the positive electrode material includes a matrix and a coating layer coated on the matrix, The matrix has the composition shown in Formula I, Li 1+a Ni x Mny Co z G b O 2 Formula I wherein −0.05≦a≦0.1, 0≦b≦0.05, 0.5≦x<1, 0<y<0.5, and 0≦z<0.5; G is selected from at least one of W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Mg, and Y; The positive electrode material, wherein the coating layer contains a lithium oxygen compound containing cobalt element and / or an oxide containing cobalt element.

2. 2. The positive electrode material for a lithium ion battery according to claim 1, wherein the micro residual stress of the positive electrode material measured by XRD is 0.03-0.

15.

3. 3. The cathode material for a lithium ion battery according to claim 1, wherein the average diameter D of the cathode material is 1-3 μm.

4. 2. The positive electrode material for lithium ion batteries according to claim 1, wherein the residual alkali content of the positive electrode material is 1000-10000 ppm.

5. A method for producing a positive electrode material for a lithium ion battery according to claim 1, said method comprising: (1) mixing a cathode material precursor, a lithium source, and an optional additive containing a G element to obtain a mixture I, wherein the G is selected from at least one of W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, Mg, and Y; (2) first sintering the mixture I under an air or oxygen atmosphere to obtain a processed cathode material II; (3) mixing the cathode material process product II, a cobalt additive, and an optional M element-containing additive to obtain a mixture III; (4) second sintering the mixture III under an air or oxygen atmosphere to obtain the positive electrode material; The peak intensity ratio of the characteristic peak at 38.5° to the characteristic peak at 37.4° of the cobalt additive measured by XRD is 1:1.1-7.5; The first sintering isothermal temperature T １ is 1000°C or less.

6. 6. The method according to claim 5, wherein the peak intensity ratio of the characteristic peak at 38.5° to the characteristic peak at 37.4° of the cobalt additive measured by XRD is 1:2-4.

5.

7. 7. The method according to claim 5 or 6, wherein the content of Co element is 55-75 wt% based on the total weight of the cobalt additive.

8. the total molar amount of metal elements in the positive electrode material precursor [n(Ni)+n(Mn)+n(Co)], the molar amount n(Li) of Li element in the lithium source, and the molar amount n(G) of G element in the G element-containing additive are used in amounts satisfying 0.95≦n(Li) / [n(Ni)+n(Mn)+n(Co)]≦1.1; The method according to claim 5, wherein 0≦n(G) / [n(Ni)+n(Mn)+n(Co)]≦0.05 is satisfied.

9. A lithium ion battery comprising the positive electrode material of claim 1.

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