Single-crystal positive electrode material and preparation method therefor, and lithium ion battery

Abstract

A single-crystal positive electrode material and a preparation method therefor, and a lithium ion battery. The single-crystal positive electrode material is a particulate matter, and the particulate matter comprises an inner-layer material and a cladding layer covering the surface of the inner-layer material, wherein the particulate matter comprises a first particle having an average particle size F1 of 1.0-2.0 μm and a second particle having an average particle size F2 of 2.5-6.0 μm, and the average thickness T1 of a cladding layer of the first particle is smaller than the average thickness T2 of a cladding layer of the second particle; the cladding layer comprises a fast ion conductor; the molecular formula of the inner-layer material is: Li1+a[NixCoyMzQb]O2±cAd, wherein 0≤a<0.20, 0.60≤x<1.0, 0<y<0.30, 0<z<0.30, 0≤b<0.20, c≤0.02, 0≤d≤0.05, x+y+z+b=1, M is Mn and / or Al, Q is selected from at least one of Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce and Y, and A is selected from at least one of F, Cl and S.

Description

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

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on October 26, 2023, with application number 202311408941.4 and application name “A single crystal positive electrode material, its preparation method, and lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of secondary battery positive electrode materials, and in particular to a single crystal positive electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0003] With the development of the new energy industry, lithium-ion batteries have also seen significant growth, with their industrial applications becoming increasingly widespread. Lithium-ion batteries are composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. The performance of the positive electrode material crucially influences the rate capability, energy density, and lifespan of lithium-ion batteries.

[0004] Lithium-ion battery cathode materials include single-crystal and polycrystalline cathode materials. Due to the numerous fragile grain boundaries in polycrystalline cathode materials, the anisotropic expansion and contraction of the material during charge and discharge can easily cause significant cracking and differentiation, leading to capacity decay and potential safety hazards.

[0005] For this reason, the proportion of single-crystal cathode materials used is gradually increasing. Compared to polycrystalline cathode materials, single-crystal cathode materials have the characteristic of being relatively small in size, but the compaction performance of small-sized cathode materials is not as good as that of large-sized cathode materials. Increasing the size of single-crystal cathode materials to improve their compaction performance leads to a decrease in electrochemical performance such as capacity. As a result, current single-crystal cathode materials face the problem of balancing compaction performance and capacity performance.

[0006] Summary of the Invention

[0007] The present application provides a single crystal positive electrode material and a preparation method thereof, and a lithium ion battery, to provide a single crystal positive electrode material with excellent compaction performance and capacity density.

[0008] In a first aspect, an embodiment of the present application provides a single crystal positive electrode material, wherein the single crystal positive electrode material is a granular material, the granular material comprises an inner layer material and a coating layer of the inner layer material; the coating layer comprises a fast ion conductor; wherein,

[0009] The particulate matter includes a first particle with an average particle size F1 of 1.0 - 2.0 μm and a second particle with an average particle size F2 of 2.5 - 6.0 μm, and the average thickness T1 of the coating layer of the first particle is less than the average thickness T2 of the coating layer of the second particle;

[0010] The coating layer includes a fast ion conductor, and the molecular formula of the inner layer material is: Li 1+a [Ni x Co y M z Q b O 2±c A d , 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.30, 0 < z < 0.30, 0 ≤ b < 0.20, c ≤ 0.02, 0 ≤ d ≤ 0.05, and x + y + z + b = 1, M is Mn and / or Al, Q is selected from at least one of: Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of: F, Cl, and S.

[0011] In a possible implementation, the fast ion conductor includes a metal lithium compound and / or a non-metal lithium compound.

[0012] In a possible implementation, the single crystal cathode material is obtained by co-sintering a mixture containing a first inner layer material and a second inner layer material; wherein, the residual alkali content on the particle surface of the first inner layer material is lower than the residual alkali content on the particle surface of the second inner layer material.

[0013] In a possible implementation, F2 - F1 ≥ 0.6 μm.

[0014] In a possible implementation, the metal lithium compound includes at least one of: lithium iron phosphate, lithium cobaltate, lithium nickel cobalt manganese oxide, lithium manganate, lithium nickelate, lithium titanate, lithium titanium aluminum phosphate, lithium lanthanum titanate, lithium lanthanum tantalate, lithium germanium aluminum phosphate, lithium lanthanum zirconium oxide, lanthanum zirconium aluminum lithium oxide, niobium-doped lithium lanthanum zirconium oxide, and tantalum-doped lithium lanthanum zirconium oxide; the non-metal lithium compound includes at least one of: boron lithium compound, sulfur lithium compound, and phosphorus lithium compound.

[0015] In a possible implementation, the thickness of the coating layer is 5 - 100 nm.

[0016] In a possible implementation, T1 ≥ 5 nm, and T2 - T1 ≥ 10 nm.

[0017] In a possible implementation, T1 < 20 nm, 10 nm ≤ T2 < 100 nm.

[0018] In a possible implementation, 8 nm ≤ T1 < 15 nm.

[0019] A possible implementation, 20 nm ≤ T2 < 50 nm.

[0020] A possible implementation where m is a preset coefficient, 0.4 ≤ m ≤ 0.6, and B1 and B2 are the specific surface areas of the first particle and the second particle, respectively.

[0021] In a second aspect, an embodiment of the present application provides a method for preparing the single crystal cathode material according to the first aspect and any possible implementation thereof, including:

[0022] Performing coating sintering on a mixture containing a first cathode material and a second cathode material to obtain the single crystal cathode material; where

[0023] The mass ratio between the first cathode material and the second cathode material is 2:3 - 3:2; the average particle size of the first cathode material is 1.0 - 2.0 μm, the average particle size of the second cathode material is 2.5 - 6.0 μm; the difference between the residual alkali content on the surface of the second cathode material and the residual alkali content on the surface of the first cathode material is greater than 500 ppm;

[0024] The molecular formulas of the first cathode material and the second cathode material are Li 1+a [Ni x Co y M z Q b O 2±c A d , 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.​​​​​​​​​​​​​t Q u TM; 0.60 ≤ r < 1.0, 0 < s < 0.30, 0 < t < 0.30, 0 ≤ u < 0.20, M is Mn and / or Al, Q is selected from at least one of: Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and TM is selected from: and / or OH - ;

[0028] The first sintering temperature in the first condition and the second sintering temperature in the second condition are both selected from 750 - 980 °C; the difference between the second lithium doping amount per mole of the second precursor in the second mixture and the first lithium doping amount per mole of the first precursor in the first mixture is 0.005 - 0.1.

[0029] A possible implementation, the molecular formula of the first precursor is [Ni r1 Co s1 M t1 Q' u1 TM1, and the molecular formula of the second precursor is [Ni r2 Co s2 M t2 Q” u2 TM2; 0.60 ≤ r1 < 10,​​​​​​​​​​​​​​​​​​In a third aspect, an embodiment of the present application provides a lithium-ion battery, comprising:

[0035] The single crystal positive electrode material described in the first aspect and any possible embodiment.

[0036] One or more implementations provided in the embodiments of this application have at least the following technical effects:

[0037] First, the present embodiment provides a single crystal positive electrode material having a particle size that is compatible with the coating layer thickness, by using a single crystal positive electrode material containing first particles with an average particle size of 1.0-2.0 μm and second particles with an average particle size of 2.5-6.0 μm, and correspondingly different average coating layer thicknesses. Thus, a single crystal positive electrode material with a high compaction density and high capacity is provided.

[0038] Secondly, in the preparation method of the single crystal positive electrode material provided in the embodiment of the present application, a single crystal positive electrode material with a coating layer thickness adapted to the particle size is prepared in one step by using a first positive electrode material and a second positive electrode material with different residual alkali contents, thereby achieving efficient preparation of a single crystal positive electrode material with high compaction density and high capacity.

[0039] Other features and advantages of the present application will be described in the following description and, in part, will become apparent from the description or may be learned through practice of the present application. The objectives and other advantages of the present application may be achieved and obtained through the structures particularly pointed out in the written description, claims, and drawings. It should be understood that the above general description and the detailed description that follow are merely exemplary and explanatory and do not limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] FIG1 is a SEM schematic diagram of the single crystal positive electrode material in Example 1 provided in the examples of the present application. DETAILED DESCRIPTION

[0042] The technical scheme of the present application will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of the present application's embodiments, rather than all of the embodiments, and are only used to illustrate the present application, and should not be considered as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present application. Those who do not specify specific conditions in the embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified as manufacturers are conventional products that can be purchased commercially.

[0043] In response to the current problem of lack of single crystal positive electrode materials with excellent compaction performance and capacity performance, the embodiment of the present application provides a single crystal positive electrode material, which has better compaction performance because it includes first particles with an average particle size of 1.0-2.0μm and second particles with an average particle size of 2.5-6.0μm. In addition, the single crystal positive electrode material has a coating layer thickness that is basically adapted to the particle size, and the average coating thickness of large particles is greater than the average coating thickness of small particles. Such differentiated coating, on the one hand, promotes a significant increase in the capacity of the single crystal positive electrode material, and on the other hand, it can also avoid a significant decrease in the cycle performance of small particles due to the large coating thickness.

[0044] The following is a detailed description of a single crystal positive electrode material, a preparation method thereof, and a lithium-ion battery provided in the embodiments of the present application. It should be noted that the embodiments described below are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0045] The present application first provides a single crystal positive electrode material that has both good compaction performance and good capacity. Referring to FIG1 , the single crystal positive electrode material is a granular material.

[0046] The particle comprises an inner layer material and a coating layer coated on the surface of the inner layer material.

[0047] The coating layer includes a fast ion conductor. The coating layer may also include an oxide of a metal element other than lithium in the fast ion conductor. For example, if the fast ion conductor is lithium cobalt oxide, the coating layer may also include cobalt hydroxide. The fast ion conductor may include a metal lithium compound and / or a non-metal lithium compound.

[0048] The molecular expression of the inner layer material is: Li 1+a [Ni x Co y M z Q bO 2±c A d , where 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.30, 0 < z < 0.30, 0 ≤ b < 0.20, c ≤ 0.02, 0 ≤ d ≤ 0.05, and x + y + z + b = 1, M is Mn and / or Al, Q is selected from at least one of Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of F, Cl, and S.

[0049] The particulate matter includes first particles with an average particle size of 1.0 - 2.0 μm and second particles with an average particle size of 2.5 - 6.0 μm, thereby ensuring the tap density of the single-crystal cathode particles provided in the embodiments of the present application (the tap density is not less than 3.24 g / cm 3 ).

[0050] Furthermore, the above-mentioned particulate matter is obtained by co-sintering a mixture containing a first inner layer material and a second inner layer material. The mixture also includes a coating agent. The molecular formulas of the first inner layer material and the second inner layer material are Li 1+a [Ni x Co y M z Q b O 2±c A d , where 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.30, 0 < z < 0.30, 0 ≤ b < 0.20, c ≤ 0.02, 0 ≤ d ≤ 0.05, and x + y + z + b = 1, M is Mn and / or Al, Q is selected from at least one of Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of F, Cl, and S.

[0051] The actual purpose of the co-sintering of the above mixture containing the first inner layer material and the second inner layer material is to achieve the coating of the first inner layer material and the second inner layer material. Since the thickness of the coating layer is nanoscale and has little effect on the particle size of the particulate matter, the average particle size of the particulate matter of the first inner layer material is the same as that of the first particles, which is 1.0 - 2.0 μm; the average particle size of the particulate matter of the second inner layer material is the same as that of the second particles, which is 2.5 - 6.0 μm.

[0052] Among them, the residual alkali content on the surface of the first inner layer material is lower than that on the surface of the second inner layer material, so as to form coating layers with different thicknesses during the sintering of the mixture.

[0053] Furthermore, the specific surface area and average particle size of the above first particles and second particles respectively satisfy the following relationship:

[0054] Wherein, m is a preset coefficient, 0.4≤m≤0.6, B1 and B2 are the specific surface areas of the first particle and the second particle respectively.

[0055] In the above relationship, the preset coefficient is consistent with the mass ratio of the inner layer materials (i.e., the first inner layer material and the second inner layer material) mixed during the preparation process. For example, if the mixing ratio of the two positive electrode materials is 1:1, then m is 0.5. For example, if the mixing ratio of the two positive electrode materials is 2:3, then m = 0.4.

[0056] Furthermore, the single-crystal positive electrode material provided in the embodiments of the present application has the characteristic that the coating thickness is substantially compatible with the particle size. The average thickness T1 of the coating layer of the first particles is less than the average thickness T2 of the coating layer of the second particles. This avoids the problem of significantly reduced cycling performance of small-sized particles due to thicker coating layers.

[0057] In the embodiment of the present application, the first particles and the second particles are particles obtained by screening. The screening of the first particles and the second particles is described in detail below:

[0058] First, the target particle sizes of the first and second particles in the particulate matter are determined, and the single crystal positive electrode material particles are tested by a particle size analyzer to obtain the target particle size values ​​of the first and second particles in the single crystal positive electrode material.

[0059] The target particle size is determined by the median particle size D of the particles of the first inner layer material. 50 , the median particle size D of the second inner layer material 50 , and the mass ratio of the first inner layer material and the second inner layer material (i.e., the aforementioned preset coefficient) is determined. That is, the target particle size of the two sizes of inner layer particles in the single crystal positive electrode material obtained by mixing and co-sintering is determined by the mixing ratio of the two sizes of inner layer particles. For example, when the mass ratio of the first inner layer material and the second inner layer material is 1:1, that is, m=0.5, the target particle size of the first particle is D 25 The target particle size of the second particle is D 75 For example, the mass ratio of the first inner layer material to the second inner layer material is 2:3, that is, m=0.4, then the target particle size of the first particle is D 20 , the target particle size of the second particle is D 80 Correspondingly, when the mass ratio of the first inner layer material to the second inner layer material is 3:2, that is, m=0.6, the target particle size of the first particles is D 30 , the target particle size of the second particle is D 70 .

[0060] After determining the target particle size of the first particle and the target particle size of the second particle according to the above method, the target particle size of the above single crystal positive electrode material can be tested using a particle size analyzer. The target particle size value obtained by the test is the target particle size of the first particle and the target particle size of the second particle.

[0061] Select a sieve according to the target particle size and sieve 10g of single crystal positive electrode material to obtain the first particle and the second particle. Continuing with the example of the mass ratio of the first inner layer material to the second inner layer material being 1:1:

[0062] Determine at least two mesh sizes based on the target particle size. First, use the smaller mesh size to sieve the single crystal positive electrode material to obtain the undersize material. Then, use another mesh size sieve to sieve the undersize material, and take the oversize material to obtain the granular material containing particles of the target particle size. For example, first sieve the single crystal positive electrode material particles with a 4500 mesh sieve (particle size of approximately 2.8±0.5μm) to take the undersize material. Then, sieve the undersize material with a 5500 mesh sieve (particle size of approximately 2.3±0.5μm). The oversize material obtained at this time is the first particle.

[0063] Similarly, the single crystal cathode material particles are first screened through an 1800 mesh sieve (particle size of approximately 7.2 ± 0.5 μm), and the undersize particles are taken. The undersize particles are then sieved through a 2200 mesh sieve (particle size of approximately 5.9 ± 0.5 μm), and the oversize particles obtained are the second particles.

[0064] The screening of the first particles and the second particles and the selection of the screen corresponding to the other mixing ratios of the first inner layer material and the second inner layer material are consistent with the above examples and will not be repeated here.

[0065] After screening to obtain the first and second particles, samples can be taken for SEM imaging and measurement. Each of the first and second particles should be sampled at least three times. For each sample, at a magnification of 2000x, the electron microscope lens should be moved to capture at least three observation areas. Within the captured SEM images, the particle sizes of 100 particles are randomly measured and the average value calculated.

[0066] The particle size of each particle is determined by measuring the length of a straight line between the two farthest points on the particle in the image, and the length of a perpendicular line perpendicular to the straight line and passing through the midpoint of the straight line. The average of the lengths of the perpendicular line and the straight line is the particle size. The endpoints of the perpendicular line are the edges of the particle.

[0067] Furthermore, the following describes the measurement of the coating thickness:

[0068] Samples are taken from the first and second particles obtained by screening to prepare TEM images. Then, at a magnification of 20,000x, the lens is moved to randomly photograph and measure the coating thickness of at least 50 particles. The coating thickness of at least 30 particles is thus obtained, and the average value is the average coating thickness of the first or second particle. The coating thickness of each particle is determined by measuring at least three different locations on the same particle and calculating the average value. The measuring tool may be, for example, a Nano Measurer.

[0069] It should be noted that since single-crystal positive electrode materials have the characteristic of being extremely easy to agglomerate, compared with the particle size value directly measured by a particle size analyzer, the average particle size obtained by screening the first particles and the second particles and then measuring them in the embodiment of the present application can more accurately reflect the size distribution of the particles of the single-crystal positive electrode material.

[0070] Moreover, the particle size of the particles has the characteristics of normal distribution or quasi-normal distribution, so the first particles obtained by screening the first particles and the second particles with their respective target particle sizes contain a small amount of sintered products corresponding to the second inner layer material; the second particles also contain a small amount of sintered products corresponding to the first inner layer material.

[0071] Nevertheless, since the vast majority of the particles in the first particles (at least 85% or more) are still single crystal positive electrode materials with a thin coating layer obtained from the first inner layer material with a low surface residual alkali content, and similarly, the vast majority of the second particles (at least 85% or more) are still single crystal positive electrode materials with a thick coating layer obtained from the second inner layer material with a high surface residual alkali content, determining the average thickness of the coating layer of the first and second particles after screening can still relatively accurately reflect the characteristics of the difference in coating layer thickness between the positive electrode material corresponding to the first inner layer material and the positive electrode material corresponding to the second inner layer material in the single crystal positive electrode material, and can relatively accurately reflect the specific circumstances of the difference.

[0072] In some embodiments, a>0, b>0, and c>0.

[0073] In some embodiments, F2-F1≥0.6 μm.

[0074] In some embodiments, 1.0 μm<F2−F1<2.5 μm.

[0075] The above-mentioned metal lithium compounds include at least one of lithium iron phosphate, lithium cobaltate, lithium nickel cobalt manganate, lithium manganate, lithium nickelate, lithium titanate, lithium aluminum titanium phosphate, lithium lanthanum titanate, lithium lanthanum tantalate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lanthanum zirconium aluminum lithium oxide, niobium-doped lithium lanthanum zirconium oxide and tantalum-doped lithium lanthanum zirconium oxide; the non-metallic lithium compounds include at least one of boron lithium compounds, sulfur lithium compounds and phosphorus lithium compounds.

[0076] The doping of a particular element in the aforementioned metal and / or non-metal lithiates indicates that the element is present in trace amounts relative to the other primary elements. For example, niobium-doped lithium lanthanum zirconium oxide indicates that the oxide contains relatively high levels of lithium, lanthanum, and zirconium, while the niobium content is relatively low.

[0077] In some embodiments, the metal lithium compound is composed of at least one of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium nickel oxide, lithium titanate, lithium aluminum titanium phosphate, lithium lanthanum titanate, lithium lanthanum tantalate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lanthanum zirconium aluminum lithium oxide, niobium-doped lithium lanthanum zirconium oxide, and tantalum-doped lithium lanthanum zirconium oxide. The non-metal lithium compound is composed of at least one of a lithium boron compound, a lithium sulfur compound, and a lithium phosphorus compound.

[0078] Furthermore, in the single crystal positive electrode material, the thickness of the coating layer of the particles is 5-100 nm.

[0079] In some embodiments, the average thickness T1 of the coating layer of the first particles is ≥5 nm, and the difference T2 - T1 between the average thickness T2 and T1 of the coating layer of the second particles is ≥10 nm.

[0080] In some embodiments, T1<20 nm, 10 nm≤T2<100 nm.

[0081] In some embodiments, 8 nm ≤ T1 < 15 nm.

[0082] In some embodiments, 20 nm ≤ T2 < 50 nm.

[0083] Furthermore, the following describes a method for preparing the aforementioned single crystal positive electrode material. The method includes at least the following steps:

[0084] The mixture containing the first positive electrode material and the second positive electrode material is coated and sintered to obtain the above-mentioned single crystal positive electrode material.

[0085] The mass ratio of the first positive electrode material to the second positive electrode material in the mixture is 2:3-3:2. The average particle size of the first positive electrode material is 1.0-2.0 μm, and the average particle size of the second positive electrode material is 2.5-6.0 μm.

[0086] The above mixture may also include a coating agent so that the coating layer on the surface of the particles of the single crystal positive electrode material contains a fast ion conductor.

[0087] The average particle sizes of the first and second cathode materials can be obtained through the following two implementation manners:

[0088] (1) Directly obtained by separately testing with a particle size analyzer.

[0089] (2) Obtained by the method described above: sampling to take SEM pictures for measurement.

[0090] Similarly, to avoid inaccurate average particle sizes obtained by the particle size analyzer due to easy agglomeration of the single crystal cathode material, the test manner of the average particle sizes of the first and second cathode materials in the embodiments of the present application is preferably the second one.

[0091] The difference between the residual alkali content on the surface of the second cathode material and the residual alkali content on the surface of the first cathode material is greater than 500 ppm.

[0092] The molecular formulas of the first and second cathode materials are: Li 1+a [Ni x Co y M z Q b O 2±c A d , 0≤a<0.20, 0.60≤x<1.0, 0<y<0.30, 0<z<0.30, 0≤b<0.20, c≤0.02, 0≤d≤0.05, and x + y + z + b = 1, M is Mn and / or Al, Q is selected from at least one of Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of F, Cl, and S.

[0093] Specifically, the sintering temperature of the above coating sintering is selected from: 750 - 980 °C.

[0094] In the embodiments of the present application, by controlling the different residual alkali contents on the surfaces of the first cathode material (i.e., the aforementioned first inner layer material) and the second cathode material (i.e., the aforementioned second inner layer material), the control of the coating layer thickness on the surfaces of the two-sized cathode materials is achieved. The residual alkali on the surface of the first cathode material and the residual alkali on the surface of the second cathode material are mainly composed of Li2CO3 and LiOH.

[0095] The above residual alkali content is the free lithium content obtained by converting the measured Li2CO3 content h1 and LiOH content h2. The conversion method is:

[0096] (h1*2 / 73.88 + h2 / 23.94)*6.941.

[0097] On the surface of the first cathode material, the content of Li2CO3 is 500 - 3000 ppm, and the content of LiOH is 5000 - 10000 ppm. On the surface of the second cathode material, the content of Li2CO3 is 800 - 3500 ppm, and the content of LiOH is 8000 - 18000 ppm.

[0098] Further, an embodiment for preparing the first cathode material and the second cathode material is provided as follows:

[0099] Sinter the first mixture containing the first precursor and the first lithium source under the first condition to obtain the first cathode material. And sinter the second mixture containing the second precursor and the second lithium source under the second condition to obtain the second cathode material.

[0100] Among them, the molecular formulas of the first precursor and the second precursor are [Ni r Co s M t Q u TM, 0.60 ≤ r < 10, 0 < s < 0.30, 0 < t < 0.30, 0 ≤ u < 0.20, 0.60 ≤ r < 10, 0 < s < 0.30, 0 < t < 0.30, 0 ≤ u < 0.20, Q is selected from at least one of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce and Y, and TM is selected from: and / or OH - .

[0101] The above-mentioned first mixture may further include a first dopant. Similarly, the second mixture may also include a second dopant. The amounts of the first dopant and the second dopant may be the same or different.

[0102] The doping elements corresponding to the first dopant and the second dopant may be the same or different. The specific addition amounts and types (i.e., doping elements) are respectively set according to the doping elements in the first precursor and the first cathode material, and the doping elements in the second precursor and the second cathode material.

[0103] In order to make the difference between the residual alkali content on the surface of the second positive electrode material and the residual alkali content on the surface of the first positive electrode material be 500ppm, on the one hand, the first sintering temperature in the above-mentioned first condition and the second sintering temperature in the second condition are both selected from 750-980℃; and the first sintering temperature is less than or equal to the second sintering temperature. The difference between the second sintering temperature and the first sintering temperature is greater than or equal to 20℃. On the other hand, the amount of lithium in the first mixture is lower than the amount of lithium in the second mixture. Since the higher the sintering temperature, the lower the residual alkali content, for embodiments in which the first sintering temperature is lower than the second sintering temperature, the amount of lithium in the preparation of the second positive electrode material should be higher so that the difference between the residual alkali content on the surface of the second positive electrode material and the residual alkali content on the surface of the first positive electrode material is greater than 500ppm. The difference between the amount of the second lithium per mole of the second precursor in the second mixture and the amount of the first lithium per mole of the first precursor in the first mixture is 0.005-0.1.

[0104] The molecular expressions of the first precursor and the second precursor may be the same or different. To achieve an average particle size of 1.0-2.0 μm for the first cathode material and 2.5-6.0 μm for the second cathode material, corresponding control methods include, but are not limited to, the following embodiments:

[0105] (1) For the same precursor, adjust the sintering temperature of each

[0106] The greater the temperature difference between the first sintering temperature and the second sintering temperature, the greater the difference between the average particle size of the first positive electrode material and the average particle size of the second positive electrode material.

[0107] In some embodiments, the first precursor and the second precursor having the same average particle size of not less than 1.0 μm are sintered separately. The nickel content in the first precursor and the second precursor is equal, that is, r1=r2, and the first sintering temperature is lower than the second sintering temperature.

[0108] For example, in order to make the difference between the average particle size of the first positive electrode material and the average particle size of the second positive electrode material be 0.5-4.5 μm, the difference between the average particle size of the second positive electrode material and the average particle size of the first positive electrode material is increased by 0.1 μm for every 4°C increase in temperature difference; or,

[0109] When the difference between the average particle size of the first positive electrode material and the average particle size of the second positive electrode material is greater than 4.5 μm, the difference between the average particle size of the second positive electrode material and the average particle size of the first positive electrode material is adjusted by 0.1 μm for every 2°C increase in the temperature difference. It should be understood that when calculating the temperature difference and the first and second sintering temperatures based on this, the calculated first and second sintering temperatures should also be adaptively adjusted based on parameters such as the lithium content.

[0110] Therefore, the difference between the second sintering temperature and the first sintering temperature is greater than or equal to 20°C. For example, the first precursor and the second precursor have the same average particle size of 3.5 μm. To make the average particle size of the first positive electrode material lower than the average particle size of the second positive electrode material by a difference of 1.5 μm, the second sintering temperature is 50°C higher than the first sintering temperature. In this case, the first sintering temperature can be 870°C, and the second sintering temperature can be 920°C. In this case, the molecular expressions of the first precursor and the second precursor are the same.

[0111] (2) The sintering temperature is similar and the precursor is regulated

[0112] In this embodiment, by regulating the types and / or atomic indices of elements in precursors with equal average particle sizes, the average particle size of the first positive electrode material is 1.0-2.0 μm, and the average particle size of the second positive electrode material is 2.5-6.0 μm.

[0113] Then the molecular expression of the first precursor is [Ni r1 Co s1 M t1 Q' u1 ]TM1, the molecular expression of the second precursor is [Ni r2 Co s2 M t2 Q” u2 ]TM2.

[0114] Among them, 0.60≤r1<10,0 <s1<0.30,0<t1<0.30,0≤u1<0.20。

[0115] 0.60≤r2<10,0 <s2<0.30,0<t2<0.30,0≤u2<0.20

[0116] Q' and Q" are each independently selected from at least one of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce and Y.

[0117] TM1 and TM2 are each independently selected from: and / or OH - .

[0118] Illustratively, under the condition that the second sintering temperature is the same as the first sintering temperature or the temperature difference is not higher than 30°C, the nickel content in the first precursor and the second precursor can be adjusted to be different, and / or the content and / or type of doping elements can be adjusted to be different, so that the average particle size of the first positive electrode material is 1.0-2.0μm, and the average particle size of the second positive electrode material is 2.5-6.0μm. Specifically, the Ni content r1 in the first precursor can be lower than the Ni content r2 in the second precursor, and the difference between r2 and r1 can be reduced by 50°C (the first sintering temperature is greater than the second sintering temperature) for every increase of about 0.1 (for example, 0.05-0.12). By such regulation, the first precursor and the second precursor with different nickel contents can be used to obtain the first positive electrode material and the second positive electrode material at similar sintering temperatures. Or,

[0119] The doping element in the first precursor includes at least one of W, Mo, and Mg, but does not include at least one of Ce, Zr, Sr, and Nb, so as to increase the first sintering temperature. Simultaneously, the doping element in the second precursor includes at least one of Ce, Zr, Sr, and Nb, but does not include at least one of W, Mo, and Mg, so as to reduce the second sintering temperature. The relative molar content of the doping elements in each precursor can also be adjusted accordingly. This regulation allows the first and second precursors, each with different nickel contents, to be sintered at similar temperatures to produce the first and second positive electrode materials.

[0120] In order to further improve the uniformity of the coating layer and make the thickness of the coating layer on each particulate of the single crystal positive electrode material almost equal, in some embodiments, the mixture is first sintered for a short time and at a relatively low temperature so that the residual alkali on the surface of each particulate of the first positive electrode material and the second positive electrode material can be redistributed in the molten state. The residual alkali in the molten state will be more evenly coated on the surface of the particulate. That is, the mixture is sintered at a temperature of 480-520°C for 2-3 hours to obtain an intermediate mixture. Then, the mixture of the intermediate mixture and the coating agent is subjected to the coating sintering to obtain the aforementioned single crystal positive electrode material.

[0121] It should be noted that the subscripts in the molecular expressions in the embodiments of the present application are atomic indices, which are used to indicate the relative molar content of the corresponding atoms in the molecule. For example, the precursor [Ni r Co s M t Q u In ]TM, r, s, t, and u are atomic indices, i.e., r, s, t, and u represent the relative molar contents of Ni, Co, M, and doping element Q in the molecule, respectively. For example, r represents the molar ratio of Ni in the precursor.

[0122] The present invention also provides another method for preparing the above-mentioned single-crystal cathode material, and this method includes: respectively performing coating sintering on the first cathode material and the second cathode material, and mixing the obtained coating sintering products to obtain the single-crystal cathode material; wherein, the mass ratio between the first cathode material and the second cathode material is 2:3 - 3:2; the average particle size of the first cathode material is 1.0 - 2.0 μm, and the average particle size of the second cathode material is 2.5 - 6.0 μm; the difference between the residual alkali content on the surface of the second cathode material and the residual alkali content on the surface of the first cathode material is greater than 500 ppm; the molecular expressions of the first cathode material and the second cathode material are Li 1+a [Ni x Co y M z Q b O 2±c A d , 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.30, 0 < z < 0.30, 0 ≤ b < 0.20, c ≤ 0.02, 0 ≤ d ≤ 0.05, and x + y + z + b = 1, M is Mn and / or Al, Q is selected from at least one of: Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of: F, Cl, and S.

[0123] This method is basically the same as the first preparation method of the single-crystal cathode material provided by the present invention. The difference is that in the first preparation method of the single-crystal cathode material provided by the present invention, coating sintering is performed on the mixture containing the first cathode material and the second cathode material, while in this method, coating sintering is first performed on the first cathode material and the second cathode material respectively, and then the obtained coating sintering products are mixed. This method can also obtain the single-crystal cathode material provided by the present invention.

[0124] Furthermore, the first cathode material and the second cathode material are obtained by the following method: sintering a first mixture containing a first precursor and a first lithium source under first conditions to obtain the first cathode material, and sintering a second mixture containing a second precursor and a second lithium source under second conditions to obtain the second cathode material; wherein, the molecular expressions of the first precursor and the second precursor are [Ni r Co s M t Q u TM; 0.60 ≤ r < 1.0, 0 < s < 0.30, 0 < t < 0.30, 0 ≤ u < 0.20, M is Mn and / or Al, Q is selected from at least one of: Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and TM is selected from: and / or OH- ; The first sintering temperature in the first condition and the second sintering temperature in the second condition are both selected from 750-980°C; the difference between the second lithium coordination amount per mole of the second precursor in the second mixture and the first lithium coordination amount per mole of the first precursor in the first mixture is 0.005-0.1.

[0125] The following is a detailed description through examples and comparative examples.

[0126] (1) Preparation

[0127] Example 1

[0128] S1, the first precursor Ni 0.82 Co 0.1 Mn 0.08 The first lithium source lithium hydroxide and the first dopant SrO are sintered at a first sintering temperature of 875°C for 15 hours with an element molar ratio of Sr:TM=0.02:1 to obtain a first positive electrode material LiNi with an average particle size of 1.51 μm. 0.8 Co 0.1 Mn 0.08 Sr 0.02 O2.

[0129] Here, TM refers to Ni, Co and Mn.

[0130] S2, the second precursor Ni 0.82 Co 0.1 Mn 0.08 The second lithium source lithium hydroxide and the second dopant SrO are sintered at a molar ratio of Sr:TM=0.02:1 at a second sintering temperature of 925°C for 14 hours to obtain a second positive electrode material LiNi with an average particle size of 3.12 μm. 0.8 Co 0.1 Mn 0.08 Sr 0.02 O2.

[0131] S3. Mix the first positive electrode material and the second positive electrode material in a mass ratio of 1:1 and a coating agent Co(OH)2 of 10000 ppm to obtain a first mixture.

[0132] S4. The first mixture is coated and sintered at 670°C for 10 hours to obtain a single crystal positive electrode material. The single crystal positive electrode material has a granular morphology. The coating layer of the granular material is LiCoO2, and the inner layer material is LiNi. 0.8 Co 0.1 Mn 0.08 Sr 0.02 O2.

[0133] Example 2-Example 5

[0134] Compared with Example 1, the main differences between Examples 2 to 5 are the different sintering temperatures and the different residual alkali contents on the surfaces of the first and second positive electrode materials. See Table 1 for details.

[0135] Example 6-Example 10

[0136] Compared with Example 1, the differences between Examples 6 to 10 mainly lie in the different sintering temperatures, coating agents and residual alkali contents, as shown in Table 1.

[0137] Example 11-Example 12

[0138] Compared with Example 1, the differences between Examples 11 and 12 mainly lie in the different sintering temperatures and changes in the first positive electrode material. Accordingly, the surface residual alkali content is also different.

[0139] Example 13

[0140] Compared with Example 1, the mass ratio between the first positive electrode material and the second positive electrode material in Example 13 is 2:3. Please refer to Table 1 for details.

[0141] Example 14

[0142] Compared with Example 1, in Example 14, after step S3 and between step S4, the first mixture is further sintered at 500° C. for 2 h. See Table 1 for details.

[0143] Example 15-Example 16

[0144] Compared with Example 1, the main differences between Example 15-2 are the different sintering temperatures and the different residual alkali contents on the surfaces of the first positive electrode material and the second positive electrode material. See Table 1 for details.

[0145] Example 17-Example 19

[0146] Compared with Example 1, Examples 17-19 have different sintering temperatures, use different coating agents and coating amounts, and have different residual alkali contents on the surfaces of the first and second positive electrode materials. See Table 1 for details.

[0147] Compared with Example 1, the difference of Comparative Example 1 is that the first positive electrode material and the second positive electrode material are coated separately and then mixed. That is, S1-S2 are the same as Example 1.

[0148] S3. Mix the first positive electrode material and the coating agent at 10000 ppm, and perform coating and sintering at 670° C. for 10 h to obtain a first single crystal positive electrode material.

[0149] S4. Mix the second positive electrode material and the coating agent at 10000 ppm, and perform coating and sintering at 670° C. for 10 h to obtain a second single crystal positive electrode material.

[0150] The first single crystal positive electrode material and the second single crystal positive electrode material both contain LiCoO2 in the coating layer and LiNi in the inner layer. 0.8 Co 0.1 Mn 0.08 Sr 0.02 O2 particles.

[0151] S5. The first single crystal positive electrode material and the second single crystal positive electrode material are mixed to obtain a single crystal positive electrode material.

[0152] Comparative Example 2

[0153] Compared with Example 1, Comparative Example 2 is different in that it does not contain the S3-S4 steps.

[0154] The following summarizes the parameters related to the first sintering temperature T1 and first sintering time t1 of the first cathode material, the second sintering temperature T2 and second sintering time t1 of the second cathode material, and the coating sintering temperature T3 and coating time t3 (see Tables 1 and 2). The coating sintering temperature depends primarily on the coating agent. The molecular expression of the inner layer material was analyzed using high-precision EDS, as summarized in Table 3.

[0155] Table 1

[0156] Table 2

[0157] Table 3

[0158] (2) Testing

[0159] The residual alkali content of the first positive electrode material and the second positive electrode material obtained in steps S1 and S2 in the embodiment and the comparative example was tested, and the D of the single crystal positive electrode material obtained in step S4 was tested. 25 and D 75 , compaction density is tested. The following is a detailed description:

[0160] 1. Residual Alkali Test: Weigh 30g of sample (accuracy 0.0001g) and place it in a 100mL beaker. Add 50mL of deionized water, place magnetic beads in the beaker, and seal it with plastic wrap. Place the beaker on a magnetic stirrer and stir for approximately 25 minutes. Remove the beaker and let it sit for 5 minutes. Filter the filtered solution using a glass funnel. The clear solution is the test solution. See Table 3 for the corresponding test data.

[0161] Specifically, 0.1 M HCl was added to the solution to be tested at a rate of 0.5 ml / min to obtain a reference voltage curve by titrating a suitable mixture of LiOH and Li2CO3 dissolved in deionized water at low concentrations. In almost all cases, two distinct plateaus were observed. The upper plateau with the endpoint V1 (in ml) between pH 8 and 9 is the equilibrium OH - / H2O, followed by balancing CO3 2- / HCO 3- The lower platform with end point V2 (in ml) between pH 4 and 6 is HCO 3- / H2CO 3 The inflection point V1 between the first and second plateaus and the inflection point V2 after the second plateau are obtained from the corresponding minimum values ​​of the derivative of the pH curve, dpH / dVol. The second inflection point is generally found near pH 4.7. The results are then expressed as the weight percentages of LiOH and Li2CO3 as shown in the following formulas (a) and (b):

[0162] Li2CO3wt%=73.89 / 1000*(V2-V1) formula (a)

[0163] LiOHwt%=23.95 / 1000*(2V1-V2) formula (b)

[0164] 2. Particle size test: Use a particle size analyzer to test the single crystal cathode material and obtain D 25 and D 75 , and the first particles and the second particles are screened accordingly. The corresponding test data can be found in Table 3.

[0165] 3. Compacted density: Hold the pressure at 3T for 30 seconds to obtain the corresponding compacted density. See Table 4 for the corresponding test data.

[0166] Table 4

[0167] Furthermore, the sieve for screening the first and second particles was determined according to the target particle size values ​​of the first and second particles in Table 4, and the first and second particles in each embodiment and comparative example were obtained by screening according to the following implementation mode:

[0168] Example 1: Single crystal positive electrode particles were first screened through a 4500 mesh sieve (particle size of approximately 2.8±0.5 μm) to obtain the undersize particles. The undersize particles were then screened through a 5500 mesh sieve (particle size of approximately 2.3±0.5 μm) to obtain the oversize particles as the first particles.

[0169] The single crystal positive electrode particles were then screened through an 1800 mesh sieve (particle size of approximately 7.2 ± 0.5 μm), and the undersize particles were taken. The undersize particles were then screened through a 2200 mesh sieve (particle size of approximately 5.9 ± 0.5 μm), and the oversize particles were the second particles.

[0170] Example 2: Single crystal positive electrode particles were first screened through a 4500 mesh sieve (particle size of approximately 2.8 ± 0.5 μm) to obtain the undersize particles. The undersize particles were then screened through a 5500 mesh sieve (particle size of approximately 2.3 ± 0.5 μm) to obtain the oversize particles as the first particles.

[0171] The single crystal positive electrode particles were then screened using a 1500 mesh screen (particle size of approximately 8.7±0.5 μm) to remove the undersize particles, which were then sieved using an 1800 mesh screen (particle size of approximately 7.2±0.5 μm) to obtain the oversize particles, which were the second particles.

[0172] Example 3: Single crystal positive electrode particles were first screened through a 3400 mesh sieve (particle size of approximately 3.8±0.5 μm) to obtain the undersize particles, which were then sieved through a 3900 mesh sieve (particle size of approximately 3.3±0.5 μm) to obtain the oversize particles as the first particles.

[0173] The single crystal positive electrode particles were then screened using a 1100 mesh screen (particle size of approximately 11.8 ± 0.5 μm) to remove the undersize particles, which were then sieved using a 1400 mesh screen (particle size of approximately 9.3 ± 0.5 μm) to obtain the oversize particles, which were the second particles.

[0174] Example 4: The screen selected is the same as that in the aforementioned Example 1.

[0175] Example 5: Single crystal positive electrode particles were first screened through a 3400 mesh sieve (particle size of approximately 3.8 ± 0.5 μm) to obtain the undersize particles. The undersize particles were then sieved through a 3900 mesh sieve (particle size of approximately 3.3 ± 0.5 μm) to obtain the oversize particles as the first particles.

[0176] The single crystal positive electrode particles were then screened through an 1800 mesh sieve (particle size of approximately 7.2 ± 0.5 μm), and the undersize particles were taken. The undersize particles were then screened through a 2200 mesh sieve (particle size of approximately 5.9 ± 0.5 μm), and the oversize particles were the second particles.

[0177] Example 6: Single crystal positive electrode particles were first screened through a 3400 mesh sieve (particle size of approximately 3.8 ± 0.5 μm) to obtain the undersize particles. The undersize particles were then screened through a 3900 mesh sieve (particle size of approximately 3.3 ± 0.5 μm) to obtain the oversize particles as the first particles.

[0178] The single crystal positive electrode particles were then screened using a 1500 mesh screen (particle size of approximately 8.7±0.5 μm) to remove the undersize particles, which were then sieved using an 1800 mesh screen (particle size of approximately 7.2±0.5 μm) to obtain the oversize particles, which were the second particles.

[0179] Example 7: The screen selected is the same as that in the aforementioned Example 1.

[0180] Example 8: Single crystal positive electrode particles were first screened through a 4500 mesh sieve (particle size of approximately 2.8±0.5 μm) to obtain the undersize particles, which were then sieved through a 5500 mesh sieve (particle size of approximately 2.3±0.5 μm) to obtain the oversize particles as the first particles.

[0181] The single crystal positive electrode particles were then screened using a 1500 mesh screen (particle size of approximately 8.7±0.5 μm) to remove the undersize particles, which were then sieved using an 1800 mesh screen (particle size of approximately 7.2±0.5 μm) to obtain the oversize particles, which were the second particles.

[0182] Example 9: The screen selected is the same as that in the aforementioned Example 1.

[0183] Example 10: Single crystal positive electrode particles were first screened through a 3400 mesh sieve (particle size of approximately 3.8±0.5 μm) to obtain the undersize particles, which were then sieved through a 3900 mesh sieve (particle size of approximately 3.3±0.5 μm) to obtain the oversize particles as the first particles.

[0184] The single crystal positive electrode particles were then screened through an 1800 mesh sieve (particle size of approximately 7.2 ± 0.5 μm), and the undersize particles were taken. The undersize particles were then screened through a 2200 mesh sieve (particle size of approximately 5.9 ± 0.5 μm), and the oversize particles were the second particles.

[0185] Example 11-Example 13: The screen selected is the same as that in the aforementioned Example 1.

[0186] Example 14: Single crystal positive electrode particles were first screened through a 3400 mesh sieve (particle size of approximately 3.8 ± 0.5 μm) to obtain the undersize particles, which were then sieved through a 3900 mesh sieve (particle size of approximately 3.3 ± 0.5 μm) to obtain the oversize particles as the first particles.

[0187] The single crystal positive electrode particles were then screened through an 1800 mesh sieve (particle size of approximately 7.2 ± 0.5 μm), and the undersize particles were taken. The undersize particles were then screened through a 2200 mesh sieve (particle size of approximately 5.9 ± 0.5 μm), and the oversize particles were the second particles.

[0188] Example 15-Example 16, Comparative Example 1: The sieve selected is the same as that in the aforementioned Example 1.

[0189] Furthermore, the average particle size, average coating layer thickness, and specific surface area of ​​the first and second particles obtained by screening were tested respectively. The test data obtained by the test are shown in Table 5.

[0190] 1) BET specific surface area: About 5 g of sample is placed in a long tube with a bulb. First, vacuum treatment is performed at 200°C for 2 hours. Then, N2 is passed through the tube for gas adsorption. The amount of adsorbate molecules (N2) adsorbed by the sample is determined based on the pressure or weight change before and after adsorption. The specific surface area B1 of the first particle and the specific surface area B2 of the second particle are obtained.

[0191] 2) Average Particle Size: The number of samples for each of the first and second particles was three. Each sample was tested as follows: SEM images were taken at a magnification of 2000, with three image areas captured. Each sample then generated three SEM images. From each SEM image, 100 particles were randomly selected and their particle size measured. The average particle size of the particles in each sample was calculated, and then the average particle size of the particles in the three samples was calculated to obtain the average particle size of the first and second particles.

[0192] 3) Average coating thickness: Weigh the sample, disperse it, and perform a TEM image. Randomly image and measure the coating thickness of 50 particles, then calculate the average to obtain the average coating thickness T1 of the first particle and the average coating thickness T2 of the second particle.

[0193] According to the test data of the first particle and the second particle, the relationship is calculated The value of .

[0194] Table 5

[0195] To achieve different coating thicknesses on the surfaces of the first and second positive electrode materials, the lithium addition amount can be adjusted so that the difference in residual alkali content between the first and second positive electrode materials corresponds to the difference in average coating thickness. Combining Tables 1-2 and 4-5, it can be seen that, using the same positive electrode material and the same sintering temperature, different lithium addition amounts can achieve different residual alkali content, and accordingly, different average coating thicknesses can be achieved on the first and second particles.

[0196] (3) Preparation and testing of lithium-ion batteries

[0197] To test the electrochemical performance of the positive electrode materials in the examples and comparative examples, the positive electrode materials were installed in lithium-ion button cells to test their capacity. The positive electrode materials were also installed in full cells to test their cycling performance.

[0198] Specifically, at 25°C and atmospheric pressure (0.1 MPa), the positive electrode sheet, lithium sheet, separator and electrolyte were assembled into a button cell in a button cell box. The area of ​​the positive electrode sheet on the side where the positive electrode material is loaded is 1.54 cm 2 , with an area loading of 15 mg / cm 2 .

[0199] The test parameters are: 0.2C rate constant current charging until the voltage is the cut-off voltage (4.25V for series VIII and above, 4.3V for series VII), and then constant voltage charging under the cut-off voltage condition until the current is less than 0.05C. The charging capacity at this time is recorded as the first cycle charging capacity. After that, it is left to stand for 5 minutes, and then discharged at a constant current rate of 0.2C to a voltage of 2.5V. The discharge capacity this time is recorded as the battery's first cycle discharge capacity, which is also the initial capacity.

[0200] Furthermore, the positive electrode material is coated into a pole piece, the negative electrode is made of graphite, and the separator is polyethylene, and the electrolyte (the electrolyte is LiPF6, the solvent is EC / DMC) is used to form a full battery. Among them, the surface area of ​​the positive electrode piece on the side where the positive electrode material is loaded is , and the surface loading is 15mg / cm 2 .

[0201] The test parameters are: under the condition of charge and discharge at a rate of 1C, the battery is cycled and the capacity of each cycle is compared with the capacity of the first cycle to confirm the capacity retention rate; at 45°C, the capacity retention rate is calculated after 300 cycles.

[0202] The above test data are shown in Table 6.

[0203] Table 6

[0204] It can be seen from Table 6 that the cycle performance of the single crystal positive electrode material in the embodiment is significantly improved. Referring to Table 1, the difference in residual alkali content on the surface of the first positive electrode material and the second positive electrode material in Example 3 is similar to the difference in residual alkali content on the surface of the first positive electrode material and the second positive electrode material in Example 5 and Comparative Example 1. Combined with Table 5, it can be seen that the capacity retention rate of Example 3 and Example 5 is higher than that of Comparative Example 1. It can be seen that compared with the method of obtaining single crystal positive electrode materials by coating them separately and then mixing them in Comparative Example 1, the method provided in the embodiment of the present application can avoid the problem of uneven coating caused by coating single crystal particles of similar size in agglomerated state, especially when single crystal particles are extremely easy to agglomerate. This makes the capacity retention rate of Example 3 and Example 5 higher than that of Comparative Example 1.

[0205] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A single crystal positive electrode material, wherein: The single crystal positive electrode material is a particle, and the particle includes an inner layer material and a coating layer of the inner layer material; wherein, The particles include first particles with an average particle size F1 of 1.0-2.0 μm and second particles with an average particle size F2 of 2.5-6.0 μm, and an average thickness T1 of the coating layer of the first particles is less than an average thickness T2 of the coating layer of the second particles; The coating layer includes a fast ion conductor, and the molecular formula of the inner layer material is: Li 1+a [Ni x Co y M z Q b O 2±c A d , where 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.30, 0 < z < 0.30, 0 ≤ b < 0.20, c ≤ 0.02, 0 ≤ d ≤ 0.05, and x + y + z + b = 1, M is Mn and / or Al, Q is selected from at least one of Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of F, Cl, and S.

2. The single crystal positive electrode material according to claim 1, wherein: The single crystal positive electrode material is obtained by co-sintering a mixture containing a first inner layer material and a second inner layer material; wherein the residual alkali content on the surface of particles of the first inner layer material is lower than the residual alkali content on the surface of particles of the second inner layer material.

3. The single crystal positive electrode material according to claim 1, wherein: F2-F1≥0.6μm.

4. The single crystal positive electrode material according to claim 1, wherein: The coating layer has a thickness of 5-100 nm.

5. The single crystal positive electrode material according to any one of claims 1 to 4, wherein: T1≥5nm, and T2-T1≥10nm.

6. The single crystal positive electrode material according to claim 5, wherein: T1<20nm, 10nm≤T2<100nm.

7. The single crystal positive electrode material according to claim 5, wherein: 8nm≤T1<15nm; 20nm≤T2<50nm.

8. The single crystal positive electrode material according to claim 1, wherein: Wherein, m is a preset coefficient, 0.4≤m≤0.6, B1 and B2 are the specific surface areas of the first particle and the second particle respectively.

9. A method for preparing the single crystal positive electrode material according to any one of claims 1 to 8, wherein: include: The mixture containing the first positive electrode material and the second positive electrode material is coated and sintered to obtain the single crystal positive electrode material; wherein, The mass ratio between the first positive electrode material and the second positive electrode material is 2:3-3:2; The average particle size of the first positive electrode material is 1.0-2.0 μm, and the average particle size of the second positive electrode material is 2.5-6.0 μm; the difference between the residual alkali content on the surface of the second positive electrode material and the residual alkali content on the surface of the first positive electrode material is greater than 500 ppm; The molecular formulas of the first and second cathode materials are Li 1+a [Ni x Co y M z Q b O 2±c A d , where 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.30, 0 < z < 0.30, 0 ≤ b < 0.20, c ≤ 0.02, 0 ≤ d ≤ 0.05, and x + y + z + b = 1. M is Mn and / or Al, Q is selected from at least one of Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of F, Cl, and S.

10. The method of claim 9, wherein: The first positive electrode material and the second positive electrode material are obtained by the following method: Sintering a first mixture comprising a first precursor and a first lithium source under a first condition to obtain the first positive electrode material, and sintering a second mixture comprising a second precursor and a second lithium source under a second condition to obtain the second positive electrode material; Among them, the molecular formulas of the first precursor and the second precursor are [Ni r Co s M t Q u TM; 0.60 ≤ r < 1.0, 0 < s < 0.30, 0 < t < 0.30, 0 ≤ u < 0.20, M is Mn and / or Al, Q is selected from at least one of: Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and TM is selected from: and / or OH - ; The first sintering temperature in the first condition and the second sintering temperature in the second condition are both selected from 750-980°C; The difference between the second lithium coordination amount of the second precursor per mole in the second mixture and the first lithium coordination amount of the first precursor per mole in the first mixture is 0.005-0.

1.

11. The method according to claim 9 or 10, wherein: The method of coating and sintering a mixture containing the first positive electrode material and the second positive electrode material to obtain the single crystal positive electrode material comprises: sintering the mixture at a temperature of 480-520° C. for 2-3 hours to obtain an intermediate mixture; The mixture of the intermediate mixture and the coating agent is subjected to the coating sintering to obtain the single crystal positive electrode material.

12. A method for preparing the single crystal positive electrode material according to any one of claims 1 to 8, wherein: include: The first positive electrode material and the second positive electrode material are coated and sintered respectively, and the obtained coated and sintered products are mixed to obtain the single crystal positive electrode material; wherein, The mass ratio between the first positive electrode material and the second positive electrode material is 2:3-3:2; The average particle size of the first positive electrode material is 1.0-2.0 μm, and the average particle size of the second positive electrode material is 2.5-6.0 μm; the difference between the residual alkali content on the surface of the second positive electrode material and the residual alkali content on the surface of the first positive electrode material is greater than 500 ppm; The molecular formulas of the first and second cathode materials are Li 1+a [Ni x Co y M z Q b O 2±c A d , where 0 ≤ a < 0.20, 0.60 ≤ x < 1.0, 0 < y < 0.30, 0 < z < 0.30, 0 ≤ b < 0.20, c ≤ 0.02, 0 ≤ d ≤ 0.05, and x + y + z + b = 1, M is Mn and / or Al, Q is selected from at least one of Zr, Mg, Ti, Te, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is selected from at least one of F, Cl, and S.

13. A lithium ion battery, wherein: include: The single crystal positive electrode material according to any one of claims 1 to 8.

Images