Low-polarization single-crystal ternary positive electrode material prepared by independent fusion and application thereof

Abstract

The invention provides a low-polarization single-crystal ternary positive electrode material prepared by independent fusion and application thereof, the single-crystal ternary positive electrode material has an oil absorption value of OACD and resistivity of rho CD under the compaction density of 3.1-3.8 g / cm < 3 >, the unit of the OACD is g / g, the unit of the rho CD is omega.cm, and the OACD and the rho CD meet the following condition: OACD * rho CD = tau = 50 omega.cm to 720 omega.cm. According to the present invention, the oil absorption value and the resistivity of the single-crystal ternary positive electrode material under the compaction density meet the specific relational expression, such that the lithium ion diffusion rate and the conductivity of the single-crystal ternary positive electrode material have good compatibility so as to improve the cycle stability of the battery, such that the battery has the high cycle capacity retention rate, and the battery performance is improved. And the voltage platform is reduced little, and heat generated during working is little.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a low-polarization single-crystal ternary positive electrode material prepared by independent fusion and its application. Background Art

[0002] Nickel cobalt manganese oxide ternary cathode materials have the advantages of high specific capacity, high discharge voltage, high energy density and good rate performance, which can provide new energy vehicles with longer driving range and faster charging speed, and have become one of the mainstream power battery cathode materials. Compared with secondary spherical ternary cathode materials, single crystal ternary cathode materials have the following advantages due to their special morphology: (1) Excellent cycle performance. The single crystal structure can avoid the accumulation of long-cycle strain and the generation of intergranular cracks; (2) High compaction density. The high compressive strength of the single crystal enables it to withstand large rolling pressure, providing conditions for the preparation of high-density electrode sheets, thereby enabling the preparation of batteries with high volume energy density. These advantages of single crystals are also their disadvantages. Since single crystals have no grain boundaries, although they give them the ability to resist cycle cracking and rolling crushing, they also hinder the diffusion of lithium ions.

[0003] The electrochemical performance of cathode materials is controlled by their lithium ion conductivity and electronic conductivity (ie, electrical conductivity). Generally, the lithium ion conductivity of layered transition metal oxide cathode materials (10 -7 ~10 -8 S / cm range) is usually lower than the electronic conductivity (10 -2 ~10 -3 S / cm), which shows that the intrinsic lithium ion conductivity of lithium nickel cobalt manganese oxide layered transition metal oxide is inherently low. Due to single crystallization, the lithium diffusion in its solid phase is further reduced, which will aggravate the difference between its lithium ion conductivity and electronic conductivity. The difference in conductivity between the two will lead to an intensified polarization effect, resulting in a drop in the voltage platform and capacity decay. It will also cause uneven lithium ion diffusion, resulting in local volume changes and stress concentration, which in turn leads to particle cracking. Furthermore, the increase in internal resistance caused by polarization can lead to thermal runaway, posing a safety risk.

[0004] Based on the above research, it is necessary to provide a single crystal ternary cathode material, the lithium ion diffusion rate and electrical conductivity of the single crystal ternary cathode material have high compatibility, thereby improving the cycle performance of the battery. Summary of the Invention

[0005] The purpose of the present invention is to provide a single crystal ternary positive electrode material and its preparation method and application. The oil absorption value and resistivity of the single crystal ternary positive electrode material at a specific compaction density satisfy a specific relationship, which can make the lithium ion diffusion rate and electrical conductivity of the single crystal ternary positive electrode material have good compatibility, thereby improving the cycle stability of the battery, which is reflected in the battery having a higher cycle capacity retention rate and less voltage platform drop.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a single crystal ternary cathode material, wherein the single crystal ternary cathode material has an average molecular weight of 3.1 g / cm 3 ~3.8g / cm 3 The oil absorption value at compacted density is OA CD , the resistivity is ρ CD , wherein the OA CD The unit is g / g, the ρ CD The unit is Ω·cm, the OA CD and the ρ CD Satisfied: OA CD ×ρ CD =τ=50Ω·cm~720Ω·cm.

[0008] It should be noted that the oil absorption value is tested using a static method, which refers to the maximum mass of oily solvents such as dibutyl phthalate that can be absorbed by the single crystal ternary positive electrode material per unit mass at the compacted density; specifically, the oil absorption value is measured by the following method: the single crystal ternary positive electrode material at the compacted density is weighed (m0), and then dibutyl phthalate is added drop by drop to the surface of the sample, and the dibutyl phthalate is allowed to stand to be slowly absorbed into the interior of the positive electrode material until there is no liquid accumulation on the surface of the sample before the next drop is added. When oil stains are found on the weighing paper at the bottom of the sample, the drop is stopped, and the total amount of drop added, m, is recorded. oil , calculate the oil absorption value OA CD =m oil / m0.

[0009] Since the lithium ion conductivity of ternary cathode materials is usually lower than the electronic conductivity, there is a large difference between the two. In order to solve the problem of low compatibility between the lithium ion diffusion rate and the electrical conductivity of single-crystal ternary cathode materials, the present invention makes the oil absorption value and resistivity of the single-crystal ternary cathode material at a specific compaction density satisfy a specific relationship, which can improve the matching of the lithium ion conductivity and the electronic conductivity of the material, thereby improving the cycle stability of the battery. The specific reasons are as follows:

[0010] Lithium ion diffusion occurs in two ways: solid-phase diffusion within the cathode material crystal lattice and liquid-phase diffusion in the electrolyte. The former is slower and the latter is faster. Electrons diffuse only through solid-phase diffusion, conducting from the cathode material and / or conductive agent through solid-solid contact points. According to the diffusion mechanism, increasing the contact area between the cathode material particles and the electrolyte is an effective way to improve lithium ion conductivity. In addition, since the cathode material accounts for >95% of the cathode film layer of the electrode, the oil absorption value of the powder at the compacted density can reflect the degree of electrolyte wetting of the cathode film layer, that is, the size of the contact area between the cathode material and the electrolyte in the cathode film layer. On the other hand, according to the diffusion mechanism, electronic conductivity (the inverse of resistivity) is related to the solid-solid contact area.

[0011] Therefore, τ = OA CD ×ρ CD It reflects the compatibility between the lithium ion diffusion rate and the conductivity of the positive electrode material, because OA CD It reflects the contact area between the electrolyte and the positive electrode material, ρ CD is the inverse of the electron conductivity, so OA CD ×ρ CD It reflects the matching relationship between lithium ion diffusion and electron conduction at a specific compaction density. CD ×ρ CD When the resistance is 50Ω·cm to 720Ω·cm, the lithium ion diffusion rate and the electrical conductivity of the material have good compatibility. Therefore, the prepared battery has good cycle stability, which is reflected in the battery having a good cycle capacity retention rate, less voltage platform drop, and less heat generation during operation.

[0012] Moreover, since the ionic conductivity of the ternary single crystal cathode material is much lower than the electronic conductivity, the ionic conductivity is the short board that limits the improvement of the electrochemical performance of the cathode material. Therefore, efforts should be made to improve the lithium ion conductivity, that is, to improve the OA CD In addition, OA is usually CD There is a trade-off relationship between the solid-solid contact area and the particle contact area, that is, the more particles contact, the more closed pores, and the OA CD and ρ CD At the same time, the less contact between particles, the more through holes, the larger the exposed surface area, and the OA CD and ρ CD At the same compaction density, the morphology of the cathode material, including particle size, particle size distribution, sphericity and agglomeration structure, will affect the OA CD and ρ CDFor example, agglomeration will reduce the oil absorption value and increase the solid-solid contact area, which is not conducive to improving the lithium ion conductivity, thereby widening the gap between ion conductivity and electronic conductivity. For another example, the higher the sphericity of particles of the same volume, the more regular the arrangement and the denser the stacking, which will easily lead to more closed pores and reduce OA. CD However, when the sphericity is too low, the particles will be crushed during pressing to form more fine particles. If the particle size of the fine particles is too low and / or the number is too large, the closed pores will increase and the solid-solid contact area will increase, which will eventually lead to OA. CD Decreases and increases in electronic conductivity (ρ CD It is not conducive to improving the lithium ion conductivity, and will further increase the gap between ion conductivity and electronic conductivity. It can be seen that the sphericity of the particles should not be too low or too high, the particle size distribution should not be too wide, and the hardness should not be too low. The sphericity, particle size and particle size distribution jointly affect the OA CD and ρ CD , we cannot discuss a single factor alone.

[0013] In summary, since we cannot discuss a single factor, τ=OA CD ×ρ CD Related to the stacking state of the powder after pressing, τ that is too large or too small will make it difficult for the lithium ion diffusion rate to match the conductivity. When the oil absorption value and resistivity of the single crystal ternary cathode material at a specific compaction density meet the OA CD ×ρ CD =τ=50Ω·cm~720Ω·cm, the lithium ion diffusion rate and the electrical conductivity of the positive electrode material have good compatibility, and the prepared battery has good cycle stability.

[0014] It should be noted that the OA of the present invention at a specific compaction density CD and ρ CD The test is carried out by the following method: the powder agglomerates obtained after the compaction density test are subjected to static oil absorption value and resistivity test.

[0015] It should be noted that the OA CD and ρ CD It refers to the oil absorption value and resistivity of single crystal ternary cathode materials at the same compaction density, which is 3.1g / cm 3 ~3.8g / cm 3 (at 200 MPa), for example, 3.1 g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 、3.5g / cm 3 、3.6g / cm 3 、3.7g / cm3 or 3.8g / cm 3 , but not limited to the listed values, other values ​​not listed in the numerical range are also applicable; In addition, the present invention selects 3.1g / cm 3 ~3.8g / cm 3 The oil absorption value and resistivity at the compaction density of 3.2g / cm can reflect the state of the granular positive electrode sheet at this compaction density. The oil absorption value at this compaction density reflects the degree of infiltration of the positive electrode film layer by the electrolyte, that is, reflects the size of the contact area between the positive electrode material and the electrolyte in the positive electrode film layer; preferably, the compaction density is 3.2g / cm 3 ~3.5g / cm 3 .

[0016] The OA CD ×ρ CD =τ=50Ω·cm~720Ω·cm, for example, it can be 50Ω·cm, 100Ω·cm, 150Ω·cm, 200Ω·cm, 250Ω·cm, 300Ω·cm, 350Ω·cm, 400Ω·cm, 450Ω·cm, 500Ω·cm, 550Ω·cm, 600Ω·cm, 650Ω·cm, 700Ω·cm or 720Ω·cm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; preferably, OA CD ×ρ CD =τ=55Ω·cm~610Ω·cm.

[0017] Preferably, the OA CD The test oil sample is dibutyl phthalate.

[0018] Preferably, the OA CD 0.10 g / g to 0.16 g / g, for example, 0.11 g / g, 0.12 g / g, 0.13 g / g, 0.14 g / g, 0.15 g / g or 0.16 g / g, but not limited to the values ​​listed, other values ​​not listed within the numerical range are also applicable; further preferably, OA CD It is 0.12g / g~0.15g / g.

[0019] Preferably, the p CD300Ω·cm~4500Ω·cm, for example, 300Ω·cm, 600Ω·cm, 900Ω·cm, 1200Ω·cm, 1500Ω·cm, 1800Ω·cm, 2100Ω·cm, 2400Ω·cm, 2700Ω·cm, 3000Ω·cm, 3300Ω·cm, 3600Ω·cm, 3900Ω·cm, 4200Ω·cm or 4500Ω·cm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; further preferably, ρ CD It is 400Ω·cm~4300Ω·cm.

[0020] Preferably, the single crystal ternary cathode material is 3.1 g / cm 3 ~3.8g / cm 3 The water absorption value at compacted density is WA CD , WA CD / OA CD Less than or equal to 3, for example, it can be 2.9, 2.5, 2.0, 1.5, 1.3, 1.2, 1.1 or 1, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable. It is more preferably 1.053 to 1.5, wherein the WA CD The unit is g / g.

[0021] It should be noted that the water absorption value is tested using deionized water. The water absorption value refers to the maximum mass of water that a single crystal ternary cathode material can absorb per unit mass at the compacted density. Specifically, the water absorption value is measured by the following method: weigh the single crystal ternary cathode material at the compacted density (m0), then add deionized water dropwise to the surface of the sample, let it stand and allow the deionized water to be slowly absorbed into the cathode material until there is no liquid on the surface of the sample before adding the next drop. When water stains are found on the weighing paper at the bottom of the sample, stop adding the drop, and record the total amount of drop added (m0). w , calculate the water absorption value WA CD =m w / m0.

[0022] Due to the difference in density and polarity between the oil sample (dibutyl phthalate) and deionized water, the wetting degree of the pores in the single crystal ternary cathode material at the compacted density is inconsistent; and the smaller the pore size of the pores in the single crystal ternary cathode material at the compacted density, the worse the wettability of the oil sample with greater density and / or lower polarity, resulting in WA CD / OA CD The larger the ratio; the single crystal ternary cathode material provided by the present invention further satisfies WA at its compaction density CD / OA CDLess than or equal to 3 indicates that the pores contained therein are larger in diameter, which is conducive to the infiltration of the electrolyte, and thus has a better lithium ion conduction rate, and the diffusion rate and conductivity are more compatible.

[0023] In a second aspect, the present invention provides a method for preparing the single crystal ternary cathode material as described in the first aspect, the preparation method comprising the following steps:

[0024] Mixing and sintering the precursor material and the lithium source to obtain the single crystal ternary cathode material;

[0025] The primary particles of the precursor material are in the form of flakes, and an organic dispersant is adsorbed on the surface of the primary particles of the precursor material.

[0026] The present invention controls the morphology of the primary particles in the precursor material to be flaky, and controls the organic dispersant to adhere to the surface of the primary particles through electrostatic adsorption. Since the thermal decomposition temperature of the organic dispersant is relatively high, the fusion of the primary particles can be suppressed during sintering to prepare the positive electrode material, so that the primary particles grow into a single crystal particle, thereby improving the particle size distribution uniformity and sphericity of the single crystal particles, and making the oil absorption value and resistivity of the single crystal ternary positive electrode material at a specific compaction density satisfy a specific relationship.

[0027] Preferably, the thermal decomposition temperature of the organic dispersant is ≥300°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C. Preferably, the temperature at which the organic dispersant is completely decomposed is above 600°C, for example, it can be 600°C, 650°C, 700°C or 750°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the organic dispersant comprises water-soluble polyimide.

[0029] The preferred organic dispersant of the present invention is water-soluble polyimide, which has a high thermal decomposition temperature and can be completely decomposed at about 600° C., which is conducive to obtaining single crystal particles with uniform particle size distribution and high sphericity, thereby helping τ to be within a specific range.

[0030] Preferably, the mass percentage of carbon element in the precursor material is 0.2% to 0.8%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] The mass proportion of the organic dispersant in the precursor material of the present invention will affect the growth of single crystal particles. Testing the carbon content in the precursor material by a carbon-sulfur meter can reflect the content of the organic dispersant contained therein. If the percentage of the carbon element content is too low, that is, the mass proportion of the organic dispersant is too low, the sphericity of the single crystal ternary positive electrode material will decrease and the particle size distribution will be uneven. If the percentage of the carbon element content is too high, that is, the mass proportion of the organic dispersant is too high, the sintering time will be extended, and the diffusion of the lithium source will be hindered, which is not conducive to the full progress of the reaction.

[0032] Preferably, the average flake length of the primary particles of the precursor material is 800nm ​​to 1500nm, for example, it can be 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm or 1500nm, and the coefficient of variation of the flake length is 2% to 30%, for example, it can be 2%, 5%, 10%, 15%, 20%, 25% or 30%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] The average length of the primary particles of the precursor material of the present invention and the coefficient of variation of the length will affect the value of τ, and are preferably within a specific range.

[0034] It should be noted that the primary particles of the precursor material described in the present invention are flake-shaped. In the flake structure, the flake length refers to the maximum Feret diameter obtained by measuring the SEM image using image analysis software, and the flake length variation coefficient refers to the degree of dispersion of the flake length = (standard deviation of flake length / average flake length) × 100%, wherein the number of flakes analyzed is not less than 15.

[0035] Preferably, the BET of the precursor material is 10m 2 / g~20m 2 / g, for example, it can be 10m 2 / g、12m 2 / g、14m 2 / g、16m 2 / g、18m 2 / g or 20m 2 / g, and the particle size D50 is 1.5μm to 8μm, for example, it can be 1.5μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm or 8μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the method for preparing the precursor material comprises the following steps:

[0037] A mixed metal salt solution, a complexing agent solution and a precipitant solution are introduced into the base liquid to carry out a first coprecipitation reaction. After the first coprecipitation reaction is completed, the mixed metal salt solution, the complexing agent solution, the precipitant solution and the organic dispersant solution are continued to be introduced to carry out a second coprecipitation reaction to obtain the precursor material.

[0038] Preferably, the pH of the first coprecipitation reaction is 10 to 12, for example, it can be 10, 10.5, 11, 11.5 or 12, the concentration of the complexing agent is 0.4 mol / L to 0.8 mol / L, for example, it can be 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L or 0.8 mol / L, and the first coprecipitation reaction is terminated after the particle size D50 reaches 1 μm to 6 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, after the first coprecipitation reaction is completed, the flow rate of the mixed metal salt solution is reduced, and while keeping the pH and complexing agent concentration unchanged, the mixed metal salt solution, complexing agent solution, precipitant solution and organic dispersant solution are continued to be introduced to carry out the second coprecipitation reaction.

[0040] Preferably, the pH of the base solution is 10 to 12, for example, 10, 10.5, 11, 11.5 or 12, and the concentration of the complexing agent is 0.4 mol / L to 0.8 mol / L, for example, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L or 0.8 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] Preferably, during the first coprecipitation reaction, the flow rate of the mixed metal salt solution is 6 L / h to 8 L / h, for example, it can be 6 L / h, 6.5 L / h, 7 L / h, 7.5 L / h or 8 L / h, and the stirring speed is 600 rpm to 800 rpm, for example, it can be 600 rpm, 650 rpm, 700 rpm, 750 rpm or 800 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, during the second coprecipitation reaction, the flow rate of the mixed metal salt solution is 2L / h to 4L / h, for example, it can be 2L / h, 2.5L / h, 3L / h, 3.5L / h or 4L / h, and the stirring speed is 300 to 500rpm, for example, it can be 300rpm, 350rpm, 400rpm, 450rpm or 500rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the temperature of the first coprecipitation reaction and the second coprecipitation reaction are independently 30°C to 80°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the total metal ion concentration of the mixed metal salt solution is 1.5 mol / L to 2.5 mol / L, for example, 1.5 mol / L, 2.0 mol / L or 2.5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, in the mixed metal salt solution, the molar ratio of Ni ions, Co ions and Mn ions is (0.3-0.8):(0.1-0.3):(0.1-0.3), for example, it can be 0.8:0.1:0.1, 0.7:0.15:0.15, 0.6:0.2:0.2, 0.5:0.2:0.3 or 0.4:0.3:0.3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the precipitant solution includes potassium hydroxide and / or sodium hydroxide, and the concentration of the precipitant solution is 6 mol / L to 12 mol / L, for example, 6 mol / L, 8 mol / L, 10 mol / L or 12 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] Preferably, the complexing agent solution comprises any one of ammonia water, ammonium nitrate solution, ammonium sulfate solution or ammonium chloride solution, or a combination of at least two thereof, and the concentration of the complexing agent solution is 6 mol / L to 10 mol / L, for example, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the mixing and sintering of the precursor material and the lithium source comprises the following steps:

[0049] (1) wet-mixing and drying the precursor material and a portion of the lithium source to obtain the precursor material;

[0050] (2) performing a first sintering on the precursor material of step (1) to obtain a sintered material;

[0051] (3) Mixing the first sintered material in step (2) with the remaining lithium source and performing a second sintering to obtain the single crystal ternary positive electrode material.

[0052] The present invention improves the uniformity of the mixture by wet mixing the precursor material with the lithium salt, thereby improving the uniformity of the sintering material and making the reaction more sufficient, thereby improving the uniformity and dispersibility of the single crystal ternary positive electrode material. In addition, the present invention adopts a process of two mixing and two-stage sintering to improve the product quality of the single crystal ternary positive electrode material. It should be noted that the present invention divides the lithium source into two parts, one part of which is wet mixed with the precursor material, and the remaining lithium source is mixed with the first sintering material and sintered in the second stage.

[0053] Preferably, the lithium source and the precursor material are mixed in a ratio of (1.05-1.1):1 in a molar ratio of Li ions to the sum of (Ni ions + Co ions + Mn ions), for example, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.0:1 or 1.1:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] Preferably, the lithium source includes any one of lithium hydroxide, lithium acetate, lithium oxalate, lithium nitrate or lithium sulfate, or a combination of at least two thereof.

[0055] Preferably, the first sintered material is first crushed and screened before the second sintering.

[0056] In the present invention, the material obtained by the first sintering is crushed before the second sintering, which is beneficial to improving the sphericity of the single crystal particles and reducing agglomerates.

[0057] Preferably, the heating rate of the second sintering in step (3) is 50°C / min to 80°C / min, for example, it can be 50°C / min, 60°C / min, 70°C / min or 80°C / min, the temperature is 800°C to 1000°C, for example, it can be 800°C, 850°C, 900°C, 950°C or 1000°C, and the time is 2h to 4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0058] Preferably, the second sintering in step (3) is carried out under negative pressure, and the negative pressure is -0.01 MPa to -0.05 MPa, for example, it can be -0.01 MPa, -0.02 MPa, -0.03 MPa, -0.04 MPa or -0.05 MPa, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0059] According to the present invention, the single crystal particles after the crushing of the first sintered material are subjected to a second sintering at a higher temperature. Under the combined action of the interface (solid-gas) tension and the negative pressure, the sphericity of the particles will be improved and the sharp edges will be reduced. At the same time, a higher heating rate is adopted in the second sintering stage, which is beneficial to improving the hardness of the single crystal, thereby helping to improve the cycle performance of the battery.

[0060] Preferably, a coating element compound is also added during the second sintering in step (3).

[0061] Preferably, in step (2), the heating rate of the first sintering is 5°C / min to 10°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, the temperature is 600°C to 800°C, for example, it can be 600°C, 700°C or 800°C, and the time is 4h to 6h, for example, it can be 4h, 5h or 6h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0062] Preferably, a doping element compound is also added during the wet mixing in step (1).

[0063] Preferably, the doping element compound and the coating element compound independently include any one or a combination of at least two of oxides, fluorides, carbonates, hydroxides, nitrides, borides or nitrates.

[0064] In a third aspect, the present invention provides an application of the single crystal ternary cathode material as described in the first aspect, wherein the single crystal ternary cathode material is applied to a lithium ion battery.

[0065] It should be noted that the name of the present invention, i.e., low-polarization single-crystal ternary cathode material prepared by independent fusion, should include the following understandings: independent fusion means that the present invention makes the surface of the hydroxide precursor primary particles adsorbed with an organic dispersant, thereby inhibiting the fusion of the primary particles during sintering, so that the primary particles grow into independent single crystals; independent fusion is only one of the means to obtain the low-polarization single-crystal ternary cathode material defined by the present invention. In addition, the present invention also regulates the morphology of the primary particles of the hydroxide precursor to obtain the defined low-polarization single-crystal ternary cathode material. Positive electrode material, therefore, "independently fused and prepared" does not constitute a limitation on the product of the present invention, and the low-polarization single crystal ternary positive electrode material defined by the present invention obtained by other means also falls within the scope of protection required by the claims of the present invention; in addition, the low-polarization single crystal ternary positive electrode material refers to the single crystal ternary positive electrode material having a low degree of polarization during the charge and discharge cycle, which is manifested as the potential difference △E between the oxidation peak and the reduction peak on the cyclic voltammetry curve has a lower growth rate as the number of cycles increases, and a higher capacity retention rate, which indicates that the single crystal ternary positive electrode material has good cycle performance.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] The present invention improves the matching of the lithium ion conductivity and the electronic conductivity of the material by making the oil absorption value and the resistivity of the single crystal ternary positive electrode material at a specific compaction density satisfy a specific relationship, thereby improving the cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a morphology diagram of the single crystal ternary positive electrode material described in Example 2 of the present invention.

[0069] Figure 2 This is a morphology diagram of the ternary positive electrode material described in Comparative Example 1 of the present invention.

[0070] Figure 3 This is a morphology diagram of the ternary positive electrode material described in Comparative Example 2 of the present invention.

[0071] Figure 4 This is the cyclic voltammetry curve of a battery prepared using the single crystal ternary cathode material described in Example 1 of the present invention.

[0072] Figure 5 This is the cyclic voltammetry curve of a battery prepared using the single crystal ternary cathode material described in Example 3 of the present invention.

[0073] Figure 6 This is the cyclic voltammetry curve of the battery prepared using the ternary cathode material described in Comparative Example 1 of the present invention.

[0074] Figure 7 This is a morphology diagram of the hydroxide precursor described in Example 1 of the present invention. DETAILED DESCRIPTION

[0075] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0076] Example 1

[0077] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0078] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 11 and an ammonia concentration of 0.6 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 6 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 11, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.6 mol / L. After the first precipitation reaction is carried out until the particle size D50 of the product reaches 3.62 μm, the flow rate of the metal salt solution is reduced to 4 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 6 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0079] Among them, the stirring speed of the first precipitation reaction is 700 rpm, the stirring speed of the second precipitation reaction is 500 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 2.5 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 9 mol / L; and the concentration of the ammonia water is 8 mol / L.

[0080] The secondary particle size D50 of the hydroxide precursor is 4.22 μm, and the BET is 13.54 μm. 2 / g, the average length of the primary particles is 802nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 29.6%; the mass percentage of carbon element in the hydroxide precursor is 0.55%;

[0081] (2) adding a portion of lithium hydroxide and a hydroxide precursor into deionized water, stirring to completely dissolve the lithium hydroxide, and then heating to evaporate the solvent to obtain a precursor;

[0082] The lithium hydroxide and the hydroxide precursor are added in a molar ratio of Li / (Ni+Co+Mn)=1.1, and the partial lithium hydroxide refers to 85% of the total lithium hydroxide mass.

[0083] (3) In an oxygen-containing atmosphere, the precursor is placed in a rotary kiln and heated to 800°C at a rate of 5°C / min for 4 hours, and a first sintered product is obtained after air flow crushing;

[0084] (4) The first sintered product is mixed with the remaining lithium hydroxide and placed under -0.05 MPa for a second sintering, wherein the second sintering is carried out in an oxygen-containing atmosphere, and the second sintering refers to heating to 1000°C at a rate of 60°C / min and keeping the temperature for 2 hours, and crushing and screening after sintering to obtain the single crystal ternary positive electrode material.

[0085] The morphology of the hydroxide precursor in this embodiment is as follows Figure 7 shown.

[0086] Example 2

[0087] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0088] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 11 and an ammonia concentration of 0.6 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 7 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 11, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.6 mol / L. After the first precipitation reaction is carried out until the particle size D50 of the product reaches 3.25 μm, the flow rate of the metal salt solution is reduced to 3 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 6 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0089] Among them, the stirring speed of the first precipitation reaction is 700 rpm, the stirring speed of the second precipitation reaction is 400 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 2.0 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 9 mol / L; and the concentration of the ammonia water is 8 mol / L.

[0090] The secondary particle size D50 of the hydroxide precursor is 4.12 μm, and the BET is 11.15 μm. 2 / g, the average length of the primary particles is 1044nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 6.5%; the mass percentage of carbon element in the hydroxide precursor is 0.57%;

[0091] (2) adding a portion of lithium hydroxide and a hydroxide precursor into deionized water, stirring to completely dissolve the lithium hydroxide, and then heating to evaporate the solvent to obtain a precursor;

[0092] The lithium hydroxide and the hydroxide precursor are added in a molar ratio of Li / (Ni+Co+Mn)=1.1, and the partial lithium hydroxide refers to 85% of the total lithium hydroxide mass.

[0093] (3) In an oxygen-containing atmosphere, the precursor is placed in a rotary kiln and heated to 800°C at a rate of 5°C / min for 4 hours, and a first sintered product is obtained after air flow crushing;

[0094] (4) The first sintered product is mixed with the remaining lithium hydroxide and placed under -0.03 MPa for a second sintering. The second sintering is carried out in an oxygen-containing atmosphere, and the second sintering refers to heating to 1000°C at a rate of 60°C / min and keeping the temperature for 1 hour. After sintering, the product is crushed and sieved to obtain the single crystal ternary positive electrode material. The morphology of the single crystal ternary positive electrode material is shown in FIG. Figure 1 shown.

[0095] Example 3

[0096] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0097] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 12 and an ammonia concentration of 0.8 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 7 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 12, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.8 mol / L. After the first precipitation reaction is carried out until the product particle size D50 reaches 4.51 μm, the flow rate of the metal salt solution is reduced to 2 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 8 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0098] Among them, the stirring speed of the first precipitation reaction is 600 rpm, the stirring speed of the second precipitation reaction is 400 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 2.0 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 9 mol / L; and the concentration of the ammonia water is 8 mol / L.

[0099] The secondary particle size D50 of the hydroxide precursor is 5.87 μm, and the BET is 11.24 μm. 2 / g, the average length of the primary particles is 985nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 31.22%; the mass percentage of carbon element in the hydroxide precursor is 0.78%;

[0100] (2) adding a portion of lithium hydroxide and a hydroxide precursor into deionized water, stirring to completely dissolve the lithium hydroxide, and then heating to evaporate the solvent to obtain a precursor;

[0101] The lithium hydroxide and the hydroxide precursor are added in a molar ratio of Li / (Ni+Co+Mn)=1.1, and the partial lithium hydroxide refers to 85% of the total lithium hydroxide mass.

[0102] (3) In an oxygen-containing atmosphere, the precursor is placed in a rotary kiln and heated to 800°C at a rate of 5°C / min for 4 hours, and a first sintered product is obtained after air flow crushing;

[0103] (4) The first sintered product is mixed with the remaining lithium hydroxide and placed under -0.03 MPa for a second sintering, wherein the second sintering is carried out in an oxygen-containing atmosphere, and the second sintering refers to heating to 1000°C at a rate of 60°C / min and keeping the temperature for 1 hour, and crushing and screening after sintering to obtain the single crystal ternary positive electrode material.

[0104] Example 4

[0105] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0106] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 12 and an ammonia concentration of 0.8 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 7 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 12, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.8 mol / L. After the first precipitation reaction is carried out until the particle size D50 of the product reaches 2.24 μm, the flow rate of the metal salt solution is reduced to 2 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 4 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0107] Among them, the stirring speed of the first precipitation reaction is 600 rpm, the stirring speed of the second precipitation reaction is 500 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 1.5 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 9 mol / L; and the concentration of the ammonia water is 8 mol / L.

[0108] The secondary particle size D50 of the hydroxide precursor is 3.17 μm, and the BET is 11.8 μm.2 / g, the average length of the primary particles is 1121nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 24.43%; the mass percentage of carbon element in the hydroxide precursor is 0.22%;

[0109] (2) adding a portion of lithium oxalate and a hydroxide precursor into deionized water, stirring to completely dissolve the lithium oxalate, and then heating to evaporate the solvent to obtain a precursor;

[0110] The lithium oxalate and the hydroxide precursor are added in a molar ratio of Li / (Ni+Co+Mn)=1.1, and the partial lithium oxalate refers to 85% of the total lithium oxalate mass.

[0111] (3) In an oxygen-containing atmosphere, the precursor is placed in a rotary kiln and heated to 800°C at a rate of 10°C / min and calcined for 4 hours, and a first sintered product is obtained after air flow crushing;

[0112] (4) The first sintered product is mixed with the remaining lithium oxalate and placed under -0.05 MPa for a second sintering, wherein the second sintering is carried out in an oxygen-containing atmosphere, and the second sintering refers to heating to 1000°C at a rate of 50°C / min and keeping the temperature for 4 hours. After sintering, the product is crushed and sieved to obtain the single crystal ternary positive electrode material.

[0113] Example 5

[0114] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0115] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 11 and an ammonia concentration of 0.6 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 7 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 11, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.6 mol / L. After the first precipitation reaction is carried out until the particle size D50 of the product reaches 2.74 μm, the flow rate of the metal salt solution is reduced to 2 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 5 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0116] Among them, the stirring speed of the first precipitation reaction is 700 rpm, the stirring speed of the second precipitation reaction is 300 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 2.0 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 9 mol / L; and the concentration of the ammonia water is 8 mol / L.

[0117] The secondary particle size D50 of the hydroxide precursor is 4.88 μm, and the BET is 10.5 μm. 2 / g, the average length of the primary particles is 1445nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 7.02%; the mass percentage of carbon element in the hydroxide precursor is 0.36%;

[0118] (2) adding a portion of lithium oxalate and a hydroxide precursor into deionized water, stirring to completely dissolve the lithium oxalate, and then heating to evaporate the solvent to obtain a precursor;

[0119] The lithium oxalate and the hydroxide precursor are added in a molar ratio of Li / (Ni+Co+Mn)=1.1, and the partial lithium oxalate refers to 85% of the total lithium oxalate mass.

[0120] (3) In an oxygen-containing atmosphere, the precursor is placed in a rotary kiln and heated to 600°C at a rate of 5°C / min and calcined for 6 hours, and a first sintered product is obtained after air flow crushing;

[0121] (4) The first sintered product is mixed with the remaining lithium oxalate and placed under -0.01 MPa for a second sintering, wherein the second sintering is carried out in an oxygen-containing atmosphere, and the second sintering refers to heating to 800°C at a rate of 50°C / min and keeping the temperature for 2 hours, and crushing and screening after sintering to obtain the single crystal ternary positive electrode material.

[0122] Example 6

[0123] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0124] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 12 and an ammonia concentration of 0.8 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 7 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 12, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.8 mol / L. After the first precipitation reaction is carried out until the product particle size D50 reaches 6.38 μm, the flow rate of the metal salt solution is reduced to 4 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 4 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0125] Among them, the stirring speed of the first precipitation reaction is 600 rpm, the stirring speed of the second precipitation reaction is 500 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 1.5 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 9 mol / L; and the concentration of the ammonia water is 8 mol / L.

[0126] The secondary particle size D50 of the hydroxide precursor is 7.55 μm, and the BET is 13.03 μm. 2 / g, the average length of the primary particles is 814nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 26.33%; the mass percentage of carbon element in the hydroxide precursor is 0.22%;

[0127] (2) adding a portion of lithium acetate, aluminum isopropoxide, and a hydroxide precursor into deionized water, stirring to completely dissolve the lithium acetate, and then heating to evaporate the solvent to obtain a precursor;

[0128] The aluminum isopropoxide and the hydroxide precursor are fed in a molar ratio of Al / (Al+Ni+Co+Mn)=0.1, and the lithium acetate, the aluminum isopropoxide and the hydroxide precursor are fed in a molar ratio of Li / (Ni+Co+Mn+Al)=1.1. Part of the lithium acetate refers to 85% of the total lithium acetate mass.

[0129] (3) In an oxygen-containing atmosphere, the precursor is placed in a rotary kiln and heated to 800°C at a rate of 5°C / min for 4 hours, and a first sintered product is obtained after air flow crushing;

[0130] (4) The first sintered product is mixed with the remaining lithium hydroxide and placed under -0.05 MPa for a second sintering, wherein the second sintering is carried out in an oxygen-containing atmosphere, and the second sintering refers to heating to 1000°C at a rate of 80°C / min and keeping the temperature for 2 hours, and crushing and screening after sintering to obtain the single crystal ternary positive electrode material.

[0131] Example 7

[0132] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0133] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 10 and an ammonia concentration of 0.4 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 8 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 10, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.4 mol / L. After the first precipitation reaction is carried out until the particle size D50 of the product reaches 1.98 μm, the flow rate of the metal salt solution is reduced to 4 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 7 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0134] Among them, the stirring speed of the first precipitation reaction is 800 rpm, the stirring speed of the second precipitation reaction is 400 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 2.0 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 6 mol / L; and the concentration of the ammonia water is 7 mol / L.

[0135] The secondary particle size D50 of the hydroxide precursor is 4.12 μm, and the BET is 11.15 μm. 2 / g, the average length of the primary particles is 1044nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 6.5%; the mass percentage of carbon element in the hydroxide precursor is 0.57%;

[0136] Steps (2) to (3) are the same as in Example 2;

[0137] (4) The first sintered product is mixed with the remaining lithium hydroxide and the coating agent titanium dioxide and placed under -0.03 MPa for a second sintering, the second sintering is carried out in an oxygen-containing atmosphere, and the second sintering refers to heating to 1000°C at a rate of 60°C / min and keeping the temperature for 1 hour, and crushing and screening after sintering to obtain the single crystal ternary positive electrode material.

[0138] The amount of titanium dioxide added is 0.3% of the total mass of the first sintered product and the remaining lithium hydroxide.

[0139] Example 8

[0140] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0141] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 11 and an ammonia concentration of 0.6 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 8 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 10, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.6 mol / L. After the first precipitation reaction is carried out until the product particle size D50 reaches 4.75 μm, the flow rate of the metal salt solution is reduced to 2 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 6 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0142] Among them, the stirring speed of the first precipitation reaction is 600 rpm, the stirring speed of the second precipitation reaction is 300 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 2.0 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 6 mol / L; and the concentration of the ammonia water is 6 mol / L.

[0143] The secondary particle size D50 of the hydroxide precursor is 6.22 μm, and the BET is 11.51 μm. 2 / g, the average length of the primary particles is 951nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 3.8%; the mass percentage of carbon element in the hydroxide precursor is 0.55%;

[0144] Steps (2) to (4) are the same as in Example 2.

[0145] Example 9

[0146] This embodiment provides a single crystal ternary cathode material, and a method for preparing the single crystal ternary cathode material includes the following steps:

[0147] (1) A solution having a volume of 1 / 5 of the volume of the reactor, a pH of 11 and an ammonia concentration of 0.6 mol / L is added to the reactor as a reaction base liquid, and then a metal salt solution containing nickel sulfate, cobalt sulfate and manganese sulfate, a sodium hydroxide solution and ammonia water are introduced into the reactor through a metering pump to carry out a first precipitation reaction, wherein the flow rate of the metal salt solution is 7 L / h, the flow rate of the sodium hydroxide solution is controlled so that the pH of the first precipitation reaction is maintained at 11, and the flow rate of the ammonia water is controlled so that the ammonia concentration of the first precipitation reaction is maintained at 0.6 mol / L. After the first precipitation reaction is carried out until the particle size D50 of the product reaches 3.44 μm, the flow rate of the metal salt solution is reduced to 4 L / h, the pH and ammonia concentration remain unchanged, and a 12 wt% water-soluble polyimide aqueous solution is pumped in at a flow rate of 7 L / h, and the second precipitation reaction is continued until the target hydroxide precursor is obtained.

[0148] Among them, the stirring speed of the first precipitation reaction is 700 rpm, the stirring speed of the second precipitation reaction is 400 rpm, and the temperatures of the first precipitation reaction and the second precipitation reaction are both 80°C; the total metal ion concentration of the metal salt solution is 2.0 mol / L, and the molar ratio of Ni ions, Co ions and Mn ions is 0.5:0.2:0.3; the concentration of the sodium hydroxide solution is 12 mol / L; and the concentration of the ammonia water is 10 mol / L.

[0149] The secondary particle size D50 of the hydroxide precursor is 5.05 μm, and the BET is 13.93 μm. 2 / g, the average length of the primary particles is 874nm, and the coefficient of variation of the length (standard deviation / average value)×100% is 17.68%; the mass percentage of carbon element in the hydroxide precursor is 0.72%;

[0150] Steps (2) to (4) are the same as in Example 5.

[0151] Comparative Example 1

[0152] This comparative example provides a ternary positive electrode material, and the preparation method of the ternary positive electrode material comprises the following steps:

[0153] Lithium oxalate, nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a solution and mixed evenly in a molar ratio of Li:Ni:Co:Mn of 1.08:0.5:0.2:0.3. The raw materials were fully mixed by spray drying at 200°C to obtain a solid powder. The solid powder was then ball-milled with flux NaCl to obtain a mixture, wherein the flux NaCl accounted for 5% by mass in the mixture. In an air atmosphere, the mixture was heated to 600°C at 500°C / h and pre-calcined for 4h. The mixture was then heated to 850°C at 500°C / h and sintered for 10h. The mixture was cooled to room temperature, washed and dried, and then passed through a 400-mesh sieve to obtain the ternary positive electrode material. The morphology of the ternary positive electrode material is shown in FIG. Figure 2 shown.

[0154] Comparative Example 2

[0155] This comparative example provides a ternary cathode material, which is the same as Example 2 except that in the preparation method of the ternary cathode material, no water-soluble polyimide aqueous solution is added when preparing the hydroxide precursor in step (1).

[0156] The secondary particle size D50 of the hydroxide precursor is 4.24 μm, and the BET is 13.28 μm. 2 / g, the average length of primary particles was 875 nm, and the coefficient of variation of the length (standard deviation / average value)×100% was 24.35%.

[0157] The morphology of the ternary cathode material obtained in this comparative example is shown in FIG. Figure 3 shown.

[0158] Comparative Example 3

[0159] This comparative example provides a single crystal ternary cathode material. In addition to the preparation method of the single crystal ternary cathode material, the water-soluble polyimide aqueous solution is replaced by an aqueous solution of polyoxyethylene ether (AEO-9) of equal mass concentration (thermal decomposition temperature <300°C). The secondary particle size D50 of the obtained hydroxide precursor is 3.58 μm and the BET is 12.24 μm. 2 / g, the average sheet length of the primary particles is 1022nm, and the coefficient of variation of the sheet length (standard deviation / average value)×100% is 28.77%; except that the mass percentage of carbon element in the hydroxide precursor is 0.18%, the rest are the same as those in Example 4.

[0160] The positive electrode materials obtained in the above embodiments and comparative examples were tested for physical properties and electrochemical performance. The electrochemical performance test was conducted by preparing the positive electrode materials obtained in the above embodiments and comparative examples into button-type batteries in accordance with GB / T37201-2018.

[0161] The test method is as follows:

[0162] (1) Compacted density, ρ CD :The powder resistivity & compaction density instrument of Yuanneng Technology Co., Ltd. was used to measure the compaction density and ρ of the positive electrode material. CD The pressure end point is 200 MPa, the pressure is maintained for 5 seconds, the test sample mass is 2.4000g~2.4100g, and the test results are shown in Table 1; the powder agglomerates obtained after the test are taken out and used as the single crystal ternary positive electrode material at the compacted density to test the oil absorption value in (2) and the water absorption value in (3).

[0163] (2) Static oil absorption value test: Place the powder agglomerates obtained in test (1) on an analytical balance lined with weighing paper and weigh to obtain m0. After returning to zero, use a pipette to add dibutyl phthalate (>99.5% (GC)) drop by drop to the surface of the agglomerates. The amount of each drop is 0.0200 to 0.0250 g. After each drop, let it stand until there is no liquid on the surface of the agglomerates before adding the next drop. Stop adding when oil stains appear on the weighing paper and record the total amount of drop added, m oil Calculate the oil absorption value OA=m oil / m0×100%, 3 groups of each single crystal sample were measured and the average value was taken. The test results are shown in Table 1.

[0164] (3) Water absorption value test: Place the powder agglomerates obtained in test (1) on an analytical balance lined with weighing paper and weigh them to obtain m0. After returning to zero, use a pipette to add deionized water drop by drop to the surface of the agglomerates. The amount of each drop is 0.0100 to 0.0150 g. After each drop, let it stand until there is no liquid on the surface of the agglomerates before adding the next drop. Stop adding when water stains appear on the weighing paper and record the total amount of water added, m. w , calculate the water absorption value WA=m w / m0×100%, 3 groups of each sample were measured and the average value was taken. The test results are shown in Table 1.

[0165] (4) Cyclic voltammetry test: Cyclic voltammetry test was performed on button cells using a CHI660E electrochemical workstation to investigate the cyclic stability of the single crystal ternary cathode material. The test voltage window was 2.7V-4.5V, the test temperature was 25°C, and the scan rate was 0.1mV / s. The redox potential of the assembled button cells was measured during the charge and discharge process of the 3rd, 10th, and 100th cycles, and the potential difference ΔE between the oxidation peak and the reduction peak was calculated. This potential difference can be used to measure the degree of electrochemical polarization. The test results are shown in Table 2. The cyclic voltammetry curve of the battery prepared from the single crystal ternary cathode material described in Example 1 is shown in Table 2. Figure 4 As shown, the cyclic voltammetry curve of the battery prepared by the single crystal ternary cathode material described in Example 3 is as follows Figure 5As shown, the cyclic voltammetry curve of the battery prepared by the ternary cathode material of Comparative Example 1 is as follows Figure 6 shown.

[0166] (5) Cycling Performance Test: The button cell batteries were subjected to cycling performance tests using a Blue Power battery testing system at a test temperature of 25°C. The batteries were activated for three cycles at currents of 0.1C, 0.2C, and 0.5C, respectively. Starting from the fourth cycle, charge and discharge cycles were performed using a current of 1C. The test voltage range was 2.8-4.3V. The capacity retention after the 100th cycle relative to the fourth cycle is shown in Table 2.

[0167] Table 1

[0168]

[0169]

[0170] Table 2

[0171]

[0172]

[0173] From Tables 1 to 2 and Figures 1 to 7 It can be seen that:

[0174] (1) By Figure 1-Figure 3 Combined with Table 1, it can be seen that the single crystal ternary positive electrode material described in Example 2 has a uniform particle size distribution, no agglomerates, and a medium sphericity without excessive edges and corners, while the ternary positive electrode material described in Comparative Example 1 has a larger particle size, a high sphericity, and a wide particle size distribution, so the compaction density is larger, but τ is smaller. Comparative Example 2 has a low sphericity, resulting in less contact between particles, so the compaction density is smaller and τ is larger. Figure 4-Figure 6 Combined with Table 2, it can be seen that the potential difference ΔE between the oxidation peak and the reduction peak after the cycle of Example 1 and Example 3 is lower than that of Comparative Example 1. Figure 7 It can be seen that the primary particles of the precursor material obtained in Example 1 of the present invention have a flake structure, and the flake length is relatively uniform.

[0175] (2) It can be seen from Examples 1-9 and Comparative Examples 1 to 3 that the embodiments provided by the present invention have better cycle stability than the comparative examples, which is manifested in that the potential difference ΔE between the oxidation peak and the reduction peak after the cycle changes little, and the capacity retention rate is high; in addition, in each embodiment, as τ increases, the cycle stability roughly conforms to the law of first increasing and then decreasing (that is, the growth rate of the potential difference ΔE first decreases and then increases with the increase of τ, and the capacity retention rate first increases and then decreases with the increase of τ), thus indicating that maintaining τ within an appropriate range is beneficial to improving the cycle stability of the single crystal ternary positive electrode material. Comparative Example 1 Although OA CD and ρ CDare all within the appropriate range, and ρ CD In the preferred range, the compacted density is also high, but the product τ is lower than 50Ω·cm, making its cycle stability worse than that of the embodiment. This shows that controlling OA CD and ρ CD The product τ of OA is within the scope of the present invention to improve the cycle stability of the positive electrode material. CD or ρ CD The technical effect cannot be achieved. The single crystal ternary cathode material of Comparative Example 2 has a low contact degree under compaction density due to its poor sphericity, so the compaction density is low, ρ CD The final τ is as high as 754Ω·cm, so the measured cycle stability is poor. Comparative Example 3: The organic dispersant in Example 4 is changed from water-soluble polyimide to polyoxyethylene ether. The decomposition temperature of polyoxyethylene ether is low and it is difficult to play the role of inhibiting fusion. Therefore, the sphericity of the obtained single crystal ternary positive electrode material is lower than that of Example 4, making its ρ CD The OA of Comparative Example 3 is higher than 4500Ω·cm, and the variation coefficient of the length of the primary particles is large, which makes the particles of the positive electrode material have a wide distribution. CD to 0.1622 g / g, which ultimately results in τ being higher than 720 Ω·cm, and thus the cycle performance is worse than that of Example 4 (including the increase in the rate of potential difference ΔE with the number of cycles and the lower capacity retention rate). CD / OA CD The τ value is higher than 3, and although the τ value is similar to that of Example 3, the cycle capacity retention rate is lower. The reason is that the single crystal ternary cathode material contains more small pores, which have poor wettability to non-polar organic solvents, which is not conducive to the diffusion and exchange of substances, limiting the Li + The transmission of electrons results in a large difference between the ion diffusion rate and the electron transmission rate.

[0176] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A single crystal ternary cathode material, characterized in that: The single crystal ternary cathode material has a temperature of 3.1 g / cm 3 ~3.8g / cm 3 The oil absorption value at compacted density is OA CD , the resistivity is ρ CD , wherein the OA CD The unit is g / g, the ρ CD The unit is Ω·cm, the OA CD and the ρ CD Satisfied: OA CD ×ρ CD =τ=50Ω·cm~720Ω·cm.

2. The single crystal ternary cathode material according to claim 1, characterized in that: The OA CD The test oil sample is dibutyl phthalate; and / or, the OA CD 0.10g / g~0.16g / g; And / or, the p CD It is 300Ω·cm~4500Ω·cm.

3. The single crystal ternary cathode material according to claim 1 or 2, characterized in that: The single crystal ternary cathode material has a temperature of 3.1 g / cm 3 ~3.8g / cm 3 The water absorption value at compacted density is WA CD , WA CD / OA CD Less than or equal to 3, wherein the WA CD The unit is g / g.

4. A method for preparing a single crystal ternary cathode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: Mixing and sintering the precursor material and the lithium source to obtain the single crystal ternary cathode material; The primary particles of the precursor material are in the form of flakes, and an organic dispersant is adsorbed on the surface of the primary particles of the precursor material.

5. The preparation method according to claim 4, characterized in that The thermal decomposition temperature of the organic dispersant is ≥300°C; and / or, the organic dispersant comprises a water-soluble polyimide; And / or, the mass percentage of carbon element in the precursor material is 0.2% to 0.8%; and / or, the average length of the primary particles of the precursor material is 800 nm to 1500 nm, and the coefficient of variation of the length is 2% to 30%; And / or, the BET of the precursor material is 10m 2 / g~20m 2 / g, and the particle size D50 is 1.5μm to 8μm.

6. The preparation method according to claim 4 or 5, characterized in that The method for preparing the precursor material comprises the following steps: A mixed metal salt solution, a complexing agent solution and a precipitant solution are introduced into the base liquid to carry out a first coprecipitation reaction. After the first coprecipitation reaction is completed, the mixed metal salt solution, the complexing agent solution, the precipitant solution and the organic dispersant solution are continued to be introduced to carry out a second coprecipitation reaction to obtain the precursor material.

7. The preparation method according to claim 6, characterized in that The pH of the first coprecipitation reaction is 10-12, the concentration of the complexing agent is 0.4 mol / L-0.8 mol / L, and the first coprecipitation reaction is terminated after the particle size D50 reaches 1 μm-6 μm; And / or, after the first coprecipitation reaction is completed, the flow rate of the mixed metal salt solution is reduced, and while keeping the pH and complexing agent concentration unchanged, the mixed metal salt solution, complexing agent solution, precipitant solution and organic dispersant solution are continued to be introduced to carry out the second coprecipitation reaction.

8. The preparation method according to claim 4, characterized in that The mixing and sintering of the precursor material and the lithium source comprises the following steps: (1) wet-mixing and drying a precursor material with a portion of a lithium source to obtain a precursor material; (2) performing a first sintering on the precursor material of step (1) to obtain a sintered material; (3) Mixing the first sintered material in step (2) with the remaining lithium source and performing a second sintering to obtain the single crystal ternary positive electrode material.

9. The preparation method according to claim 8, characterized in that Step (3) The second sintering is performed at a heating rate of 50°C / min to 80°C / min, a temperature of 800°C to 1000°C, and a time of 2h to 4h; And / or, the second sintering in step (3) is carried out under negative pressure, wherein the negative pressure is -0.01 MPa to -0.05 MPa; and / or, in step (3), a coating element compound is further added during the second sintering; And / or, in step (2), the first sintering is performed at a heating rate of 5°C / min to 10°C / min, a temperature of 600°C to 800°C, and a time of 4h to 6h; And / or, a doping element compound is also added during the wet mixing in step (1).

10. A use of the single crystal ternary cathode material according to any one of claims 1 to 3, characterized in that: The single crystal ternary cathode material is applied to lithium ion batteries.

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