A positive electrode active material, a method for manufacturing the same, and a battery

Abstract

This invention provides a positive electrode active material, its preparation method, and a battery. The first aspect of this invention provides a positive electrode active material with a chemical composition of Li. x Ni y Co z MnA u B v C w O2, A represents an ionic radius greater than 100*10 ‑12 The element m is B, which is an element with an ionic valence greater than or equal to 4; and the I003 / I104 ratio of the positive electrode active material is n. The cycle retention rate of a battery containing this positive electrode active material after 300 charge-discharge cycles at 45°C and a 1C / 1C rate is m, where n*m ​​> 1.9. The positive electrode active material provided by this invention has good crystal stability and surface stability, and the inclusion of doping elements A and B in the crystal structure helps to improve the particle strength and discharge capacity of the positive electrode active material, thereby improving the overall performance of the lithium-ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to a positive electrode active material and a preparation method and application thereof, and relates to the technical field of secondary batteries. BACKGROUND

[0002] Long cruising range is the primary technical index of new energy passenger cars, and it is an inevitable development trend to continuously improve the energy density of the battery under the premise of ensuring safety. As an important component of the battery, the performance of the positive electrode active material affects the performance of the battery. With the increase of the nickel content in the positive electrode active material, the energy density of the battery is also improved. Therefore, increasing the nickel content in the positive electrode active material is one of the means to improve the energy density of the battery.

[0003] With the increase of the nickel content, the defects of the positive electrode active material are more and more obvious, mainly including high lithium-nickel mixing, unstable surface, low particle strength and the like. Therefore, how to optimize the high-nickel positive electrode active material is a technical problem that the person skilled in the art needs to continuously solve. SUMMARY

[0004] The present application provides a positive electrode active material and a preparation method, which are used for optimizing the high-nickel positive electrode active material to improve the comprehensive performance of the lithium ion battery.

[0005] The present application also provides a lithium ion battery comprising the positive electrode active material.

[0006] The present application provides a positive electrode active material, which has a chemical composition of Li x Ni y Co z MnA u B v C w O2;

[0007] wherein, 0.9≤x≤1.1, 0.6≤y≤1, 0 -12 m, B is an element with an ionic valence greater than or equal to 4 valence, and C is one or more of B, F, P, V, Al, Mg, Y, Nb, Mo, Sb, Ge;

[0008] The I003 / I104 of the positive electrode active material is n, the cycle retention rate of the battery comprising the positive electrode active material after being charged and discharged at 45℃ and 1C / 1C rate and cycled for 300 cycles is m, and n*m>1.9.

[0009] The positive electrode active material as described above, the positive electrode active material comprising first particles and second particles, the particle size of the first particles being 1-5 μm, the particle size of the second particles being 8-12 μm;

[0010] The molar mass percentage of Ni on the surface of the first particles in the total molar mass of Ni, Co and Mn on the surface of the first particles is a1, and the molar mass percentage of Mn in the total molar mass of Ni, Co and Mn on the surface of the first particles is a2;

[0011] The molar mass percentage of Ni on the surface of the second particles in the total molar mass of Ni, Co and Mn on the surface of the second particles is b1, and the molar mass percentage of Mn in the total molar mass of Ni, Co and Mn on the surface of the second particles is b2;

[0012] 0.003%≤b1-a1≤5%, 0.003%≤a2-b2≤5%.

[0013] The positive electrode active material as described above, A is selected from one or more of Sr, Ce, Na; B is selected from one or more of V, Zr, Cr, Mo, Ti, W.

[0014] The second aspect of the present application provides a preparation method of the positive electrode active material as described above, comprising the following steps:

[0015] Mixing a nickel-cobalt-manganese precursor, a lithium source and a dopant to obtain a mixture, and performing a first sintering treatment on the mixture to obtain first particles;

[0016] Obtaining second particles by sequentially crushing, washing with water and drying the first particles;

[0017] Performing a second sintering treatment on the second particles to obtain the positive electrode active material.

[0018] The preparation method as described above, the first sintering treatment is performed in an oxygen atmosphere, the oxygen flux is 500-1500 L / min, the heating rate is 1-5 ℃ / min, the sintering temperature is 700-850 ℃, and the time is 8-12 h.

[0019] The preparation method as described above, the D104 of the first particles is 45-70 nm, the LiCO3 content on the surface of the first particles is 2000-8000 ppm, the LiOH content is 2000-8000 ppm, and the Free Li+ content is 1500-3000 ppm.

[0020] The preparation method as described above, the D50 of the first particles is crushed to 8-13 μm.

[0021] In the preparation method described above, during the water washing process, the mass ratio of deionized water to the first crushed particles is 0.6-1.5, the water washing temperature is 10-30℃, and the water washing time is no more than 30 minutes.

[0022] As described above, the secondary sintering process is carried out in an oxygen or air atmosphere, with a heating rate of 1-5℃ / min, a sintering temperature of 200-700℃, and a time of 8-12h.

[0023] A third aspect of the present invention provides a lithium-ion battery comprising any of the above-described positive electrode active materials.

[0024] The positive electrode active material provided by this invention has good crystal stability and surface stability, and the crystal structure includes doping elements A and B, which helps to improve the particle strength and discharge capacity of the positive electrode active material and improve the overall performance of lithium-ion batteries. Attached Figure Description

[0025] Figure 1 This is a SEM image of the positive electrode active material provided in Example 1 of the present invention;

[0026] Figure 2 The image shows the EDS diagram of the positive electrode active material provided in Example 1 of this invention.

[0027] Figure 3 The XRD pattern of the positive electrode active material provided in Embodiment 1 of the present invention;

[0028] Figure 4 This is a SEM image of the positive electrode active material provided in Example 2 of the present invention;

[0029] Figure 5 This is a SEM image of the positive electrode active material provided in Example 3 of the present invention;

[0030] Figure 6 This is a SEM image of the positive electrode active material provided in Comparative Example 1 of the present invention;

[0031] Figure 7 This is a SEM image of the positive electrode active material provided in Comparative Example 2 of the present invention;

[0032] Figure 8 This is a SEM image of the positive electrode active material provided in Comparative Example 3 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] The first aspect of this invention provides a positive electrode active material, wherein the chemical composition of the positive electrode active material is Li. x Ni y Co z MnA u B v C w O2;

[0035] Where 0.9≤x≤1.1, 0.6≤y≤1, 0<z≤0.4, 0<u≤0.1, 0<v≤0.1, 0≤w≤0.1, and A represents ions with ionic radii greater than 100*10⁻⁶. -12 For the element m, B is an element with an ionic valence greater than or equal to 4, and C is one or more of B, F, P, V, Al, Mg, Y, Nb, Mo, Sb, and Ge.

[0036] The positive electrode active material I003 / I104 is n, and the cycle retention rate of the battery including the positive electrode active material after being charged and discharged at 45°C and 1C / 1C rate for 300 cycles is m, where n*m>1.9.

[0037] The positive electrode active material provided by this invention is a high-nickel ternary positive electrode active material, whose chemical composition is Li. x Ni y Co z MnA u B v C wIn the context of O2, x, y, z, u, v, and w refer to the molar ratios of various elements in the positive electrode active material. For example, x represents the molar ratio of lithium in the positive electrode active material, specifically selected from the range of 0.900, 0.911, 0.915, 0.925, 0.930, 0.935, 0.950, 0.980, 0.995, 1.000, 1.050, 1.085, 1.100, or any combination thereof; y represents the molar ratio of nickel in the positive electrode active material, for example, selected from 0.600, 0.605, 0.612, 0.625, 0.650, 0.685, 0.690, 0.700, 0.705, 0. 0.720, 0.755, 0.800, 0.850, 0.900, 0.905, 0.950, 1.000 or any two of these ranges; z is the molar ratio of cobalt in the positive electrode active material, for example, it can be selected from the range of 0.010, 0.050, 0.080, 0.1, 0.110, 0.150, 0.185, 0.200, 0.201, 0.220, 0.250, 0.285, 0.300, 0.310, 0.320, 0.350, 0.380, 0.400 or any two of these ranges; u, v, w refer to the molar ratios of A, B, and C elements in the positive electrode active material, respectively.

[0038] The positive electrode active material includes primary particles and secondary particles formed by the aggregation of primary particles. Because the ionic radius of dopant element A is relatively large, it does not easily penetrate the crystal structure of the primary particles, but instead accumulates at the grain boundaries. This helps to improve the adhesion between primary particles, thereby increasing the particle strength of the positive electrode active material and reducing the risk of particle cracking. It also helps to reduce the gaps between primary particles, improving the electron conduction efficiency between them and reducing the internal resistance of the battery. In one specific embodiment, dopant element A is one or more of Sr, Ce, and Na.

[0039] Dopant element B is an element with an ionic valence greater than or equal to four. According to the principle of charge conservation, dopant element B helps to induce Ni... 3+ To Ni 2+ The transformation increases the battery's capacity. In one specific embodiment, the doping element B is selected from one or more of V, Zr, Cr, Mo, Ti, and W.

[0040] C can be used as a dopant or coating element, and can be selected as needed, for example, one or more of B, F, P, V, Al, Mg, Y, Nb, Mo, Sb, and Ge.

[0041] This invention uses the product of parameters n and m to characterize the stability of the positive electrode active material. It can be understood that as the stability of the positive electrode active material improves, the cycle retention rate of the battery is better. Specifically, n is I003 / I104 of the positive electrode active material. I003 refers to the peak intensity of the characteristic diffraction peak of the (003) crystal plane obtained by XRD diffraction of the positive electrode active material, and I104 refers to the peak intensity of the characteristic diffraction peak of the (104) crystal plane obtained by XRD diffraction of the positive electrode active material. The ratio of the two peak intensities is denoted as n. At the same time, the cycle retention rate of the battery including the positive electrode active material after being charged and discharged at 45°C and 1C / 1C rate and cycled for 300 times is m. The values ​​of n and m can characterize the stability of the layered structure and the stability of the particle surface of the positive electrode active material, respectively. When n*m>1.9, it indicates that the overall stability of the positive electrode active material is good.

[0042] Furthermore, the I003 / I104 ratio of the positive electrode active material provided by the present invention is greater than or equal to 2.00, and can be specifically selected from 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.50, 3.00, 3.50, 4.00, 5.00, etc.; even further, the I003 / I104 ratio is 2.00-2.40.

[0043] Furthermore, the battery including this positive electrode active material has a cycle retention rate of no less than 85% after being charged and discharged at 45°C and 1C / 1C rate for 300 cycles.

[0044] In one specific embodiment, the positive electrode active material provided by the present invention includes a first particle and a second particle with different particle sizes. The particle size of the first particle is 1-5 μm, and the particle size of the second particle is 8-12 μm. Based on the different activities of Ni and Mn, their molar contents on the surfaces of the first and second particles are also different. Specifically, the percentage of the molar mass of Ni on the surface of the first particle relative to the total molar mass of Ni, Co, and Mn on the surface of the first particle is a1, and the percentage of the molar mass of Mn on the surface of the first particle relative to the total molar mass of Ni, Co, and Mn on the surface of the first particle is a2; the percentage of the molar mass of Ni on the surface of the second particle relative to the total molar mass of Ni, Co, and Mn on the surface of the second particle is b1, and the percentage of the molar mass of Mn on the surface of the second particle relative to the total molar mass of Ni, Co, and Mn on the surface of the second particle is b2; and 0.003% ≤ b1 - a1 ≤ 5%, 0.003% ≤ a2 - b2 ≤ 5%.

[0045] Specifically, b1-a1 represents the difference in the molar content of Ni on the surface of the second particle and the first particle, where b1 is greater than a1, and the difference can be selected from 0.003%, 0.010%, 0.020%, 0.030%, 0.040%, 0.050%, 0.060%, 0.070%, 0.080%, 0.090%, 0.100%, 0.15%, 0.20%, 0.50%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, and 5.00%.

[0046] a2-b2 represents the difference in molar Mn content on the surface of the first and second particles, where a2 is greater than b2, and the difference can be selected from 0.003%, 0.010%, 0.020%, 0.030%, 0.040%, 0.050%, 0.060%, 0.070%, 0.080%, 0.090%, 0.100%, 0.15%, 0.20%, 0.50%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, and 5.00%.

[0047] When the particle size distribution of the positive electrode active material and the molar content of Ni and Mn elements on the surface of the particles are within the above range, it indicates that the positive electrode active material has good stability and particle strength, which helps to improve the cycle stability of the battery.

[0048] A second aspect of the present invention provides a method for preparing any of the above-described positive electrode active materials, comprising the following steps:

[0049] Nickel-cobalt-manganese precursor, lithium source, and dopant are mixed to obtain a mixture, and the mixture is sintered once to obtain the first particle.

[0050] The first particle is sequentially crushed, washed, and dried to obtain the second particle;

[0051] The second particle is subjected to a secondary sintering process to obtain the positive electrode active material.

[0052] In one specific embodiment, the method for preparing the positive electrode active material includes the following steps:

[0053] Step 1: Mix the nickel-cobalt-manganese precursor, lithium source, and dopant to obtain a mixture, and sinter the mixture to obtain the first particle;

[0054] First, the nickel-cobalt-manganese precursor, lithium source, and dopant can be conventional materials in the field. Specifically, the nickel-cobalt-manganese precursor is nickel-cobalt-manganese hydroxide, the lithium source is lithium hydroxide, and the dopant is an oxide or hydroxide of at least elements A and B, such as SrO, CeO, Na2O, NaOH, ZrO2, V2O3, Mo2O3, etc.

[0055] Next, the above raw materials are mixed according to the required mass ratio to obtain a mixture. The mixing process can be carried out in a high-speed mixer. The speed of the high-speed mixer is controlled at 200-600 rpm / min, and the mixing time is 10-30 min.

[0056] Next, the mixture is sintered once. Specifically, the mixture is placed in a sagger and then placed in a high-temperature heating device such as a tube furnace, muffle furnace, box furnace, roller kiln, pusher kiln, or rotary kiln for sintering. The loading amount of the mixture in the sagger is 3-6 kg / sagger. If the loading amount of the mixture in the sagger is too high, it will lead to difficulty in heat conduction and poor sintering consistency. At the same time, if the loading amount is too high, it will be difficult for the water vapor generated during the sintering process to be discharged, which will affect the alkali content of the product.

[0057] During the sintering process, oxygen is introduced into the high-temperature heating equipment at a flow rate of 500-1500 L / min, a heating rate of 1-5℃ / min, a sintering temperature of 700-850℃, and a sintering time of 8-12 h. After sintering, the heating equipment is turned off, and the first particles are obtained after the temperature drops to room temperature.

[0058] The performance of the first particle and the first efficiency of the coin cell including the first particle were tested to determine the degree of sintering. Specifically, the D104 of the first particle is 45-70nm, the LiCO3 content on the surface of the first particle is 2000-8000ppm, the LiOH content is 2000-8000ppm, the Free Li+ content is 1500-3000ppm, the discharge specific capacity of the coin cell including the first particle is 180-195mAh / g, and the first efficiency is above 80%. Here, D104 refers to the crystal plane width of the (104) crystal plane obtained by XRD diffraction.

[0059] Furthermore, the first particle has a D104 density of 52-62 nm, and the surface content of the first particle is 3500-4500 ppm for LiCO3, 4500-5000 ppm for LiOH, and 2000-2200 ppm for Free Li+. The coin cell including the first particle has a discharge specific capacity of 185-192 mAh / g and an initial efficiency of over 83%. When the above conditions are met, it indicates that the first sintering degree meets the requirements, which helps to improve the performance of subsequent positive electrode active materials.

[0060] Step 2: The first particle is crushed, washed, and dried to obtain the second particle;

[0061] First, the first particles obtained in step 1 are crushed to make the particle D50 8-13μm. The dispersibility of the first particles is characterized by D50. If D50 is too small, it indicates that the degree of crushing is too high and the particles are easy to break. If D50 is too high, it indicates that the particles are agglomerated and need to be further crushed.

[0062] Next, the first crushed particles are washed with deionized water to remove residual soluble impurities and reactants on the surface, reduce the amount of residual alkali on the surface of the positive electrode active material, and improve the gas generation performance of the lithium-ion battery. Specifically, the mass ratio of deionized water to the first crushed particles is 0.6-1.5, the water washing temperature is 10-30℃, and the water washing time is no more than 30 minutes.

[0063] Finally, the washed granules are dried to ensure that the moisture content in the dried granules is below 0.5 wt%, thus obtaining the second granules.

[0064] Step 3: Perform a secondary sintering treatment on the second particle to obtain the positive electrode active material.

[0065] The second particle obtained in step 2 is subjected to a secondary sintering treatment. The secondary sintering treatment is carried out in an oxygen or air atmosphere. During the sintering process, the heating rate is controlled at 1-5℃ / min, the sintering temperature is 200-700℃, and the time is 8-12h. After the sintering is completed, the product is collected to obtain the positive electrode active material.

[0066] In addition, after the secondary sintering is completed, it is also necessary to remove the metallic impurities introduced in the process, which are generally iron. Magnetic separation is usually used to remove iron, and those skilled in the art can do so according to conventional operations.

[0067] A third aspect of the present invention provides a lithium-ion battery comprising any of the above-described positive electrode active materials.

[0068] Based on the characteristics of the positive electrode active material in the first aspect, lithium-ion batteries containing this positive electrode material have good overall performance.

[0069] In one specific embodiment, the lithium-ion battery provided by the present invention includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector, and the positive active layer includes the aforementioned positive active material.

[0070] In addition to the positive electrode active material, the positive electrode active layer also includes a conductive agent and a binder. There are no special requirements for the selection of the conductive agent and binder; they can be conventional choices in the field. For example, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, single-walled carbon nanotubes, multi-arm carbon nanotubes, and carbon fibers; the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium polyacrylate (PAALi).

[0071] In the preparation process, the positive electrode active material, conductive agent and binder are first mixed in a certain proportion and dispersed in a solvent, usually NMP, and stirred evenly to obtain a positive electrode active material layer slurry; secondly, the positive electrode active material layer slurry is evenly coated on the positive electrode current collector, usually the surface of aluminum foil, and dried to form a positive electrode active material layer; finally, the positive electrode sheet is obtained by pressing and cutting.

[0072] There are no special requirements for the selection of the negative electrode, separator, and electrolyte; all are conventional choices in this field.

[0073] The technical solution provided by the present invention will be described in detail below with reference to specific embodiments:

[0074] Example 1

[0075] Step 1: Take 20 kg of precursor Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 9.54 kg of lithium hydroxide, 100 g of ZrO2, and 40 g of SrO were mixed in a 60 L high-speed mixer at 500 rpm for 15 min to obtain a mixture.

[0076] The mixture was packed into bowls at a rate of 4 kg / bowl, and heated at a rate of 3℃ / min. When the temperature reached 760℃, it was held for 12 hours. The sintering atmosphere was pure oxygen with an oxygen flow rate of 1000 L / min, and the first particles were obtained.

[0077] Step 2: Crush the first particle to control the D50 to 10.5±1.5μm, then wash it with water at a water-to-material ratio of 1:1 for 2 minutes at a temperature between 15-25℃ and a stirring rod speed of 30 rpm. Then filter and dry it to control the moisture content to below 0.5% to obtain the second particle.

[0078] Step 3: Place the dried second particles in a roller kiln for secondary sintering. The sagger loading is 5.5 kg / sagger, the sintering temperature is 600℃, and the holding time is 8 hours. After screening, iron removal, and packaging, the finished high-nickel ternary cathode active material is obtained.

[0079] The prepared high-nickel ternary cathode active material was observed using a scanning electron microscope. The observation results are as follows: Figure 1 As shown, it can be seen that it consists of two types of particles with different sizes. The molar content of Ni, Mn, and Co on the surface of the two types of particles with different sizes was measured using energy dispersive spectroscopy (EDS). The test sites are shown in [reference needed]. Figure 2 The test results are shown in Table 1. It can be seen that the average Ni content on the surface of the first particle is 81.426%, and the average Ni content on the surface of the second particle is 83.172%, with a difference of 1.746%. The average Mn content on the surface of the first particle is 6.15%, and the average Mn content on the surface of the second particle is 4.31%, with a difference of 1.84%. X-ray diffraction was performed on the high-nickel ternary cathode active material, and the diffraction pattern was obtained as follows: Figure 3 As shown, it can be seen that it contains diffraction peaks of (003) and (104) crystal planes, and the ratio of the peak intensities of the two peaks, I003 / I104, is calculated to be 2.21.

[0080] Table 1. Molar content of Ni, Mn, and Co on the surface of the positive electrode active material provided in Example 1

[0081]

[0082] Example 2

[0083] The method for preparing the positive electrode active material provided in this embodiment includes the following steps:

[0084] Step 1: Take 20 kg of precursor Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 9.54 kg of lithium hydroxide, 100 g of CeO2, and 40 g of SrO were mixed in a 60 L high-speed mixer at 500 rpm for 15 min to obtain a mixture.

[0085] The mixture was packed into bowls at a rate of 4.5 kg / bowl, and heated at a rate of 4℃ / min. When the temperature reached 765℃, it was held for 13 hours. The sintering atmosphere was pure oxygen with an oxygen flow rate of 1200 L / min, and the first particles were obtained.

[0086] Step 2: Crush the first particle to control the D50 to 10±1.5μm, then wash it with water at a water-to-material ratio of 1.2:1 for 5 minutes at a temperature of 15-25℃. Then filter and dry it to control the moisture content to below 0.5% to obtain the second particle.

[0087] Step 3: Place the dried second particles in a roller kiln for secondary sintering. The sagger loading is 6 kg / sagger, the sintering temperature is 550℃, and the holding time is 10 h. After screening, iron removal, and packaging, the finished high-nickel ternary cathode active material is obtained.

[0088] The prepared high-nickel ternary cathode active material was observed using a scanning electron microscope. The observation results are as follows: Figure 4 As shown.

[0089] Example 3

[0090] The method for preparing the positive electrode active material provided in this embodiment includes the following steps:

[0091] Step 1: Take 20 kg of precursor Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 9.54 kg of lithium hydroxide, 70 g of WO2, and 40 g of SrO were mixed in a 60 L high-speed mixer at 500 rpm for 15 min to obtain a mixture.

[0092] The mixture was packed into a pot at a rate of 3 kg / pot, and heated at a rate of 2℃ / min. When the temperature reached 755℃, it was held for 11 hours. The sintering atmosphere was pure oxygen with an oxygen flow rate of 800 L / min, and the first particles were obtained.

[0093] Step 2: Crush the first particle to control the D50 to 10±1.5μm, then wash it with water at a water-to-material ratio of 0.8:1 for 2 minutes at a temperature of 20-35℃. Then filter and dry it to control the moisture content to below 0.5% to obtain the second particle.

[0094] Step 3: Place the dried second particles in a roller kiln for secondary sintering. The sagger loading is 4.5 kg / sagger, the sintering temperature is 500℃, and the holding time is 10 h. After screening, iron removal, and packaging, the finished high-nickel ternary cathode active material is obtained.

[0095] The prepared high-nickel ternary cathode active material was observed using a scanning electron microscope. The observation results are as follows: Figure 5 As shown.

[0096] Comparative Example 1

[0097] The preparation method of the positive electrode active material provided in this comparative example includes the following steps:

[0098] Step 1: Take 20 kg of precursor Ni 0.83 Co 0.12 Mn 0.05(OH)2, 9.54 kg of lithium hydroxide, and 100 g of ZrO2 were mixed in a 60 L high-speed mixer at 500 rpm for 15 min to obtain a mixture.

[0099] The mixture was packed into bowls at a rate of 7 kg / bowl, and heated at a rate of 6 °C / min. When the temperature reached 760 °C, it was held for 12 hours. The sintering atmosphere was pure oxygen with an oxygen flow rate of 1000 L / min, and the first particles were obtained.

[0100] Step 2: Crush the first particle to control the D50 to 10.5±1.5μm, then wash it with water at a water-to-material ratio of 2:1 for 10 minutes at a temperature of 35-45℃. Then filter and dry it to control the moisture content to below 0.5% to obtain the second particle.

[0101] Step 3: Place the dried second particles in a roller kiln for secondary sintering. The sagger loading is 7 kg / sagger, the sintering temperature is 600℃, and the holding time is 8 hours. After screening, iron removal, and packaging, the finished high-nickel ternary cathode active material is obtained.

[0102] The prepared high-nickel ternary cathode active material was observed using a scanning electron microscope. The observation results are as follows: Figure 6 As shown.

[0103] Comparative Example 2

[0104] The preparation method of the positive electrode active material provided in this comparative example includes the following steps:

[0105] Step 1: Take 20 kg of precursor Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 9.54 kg of lithium hydroxide, and 100 g of ZrO2 were mixed in a 60 L high-speed mixer at 500 rpm for 15 min to obtain a mixture.

[0106] The mixture was packed into bowls at a rate of 4 kg / bowl, and heated at a rate of 3℃ / min. When the temperature reached 775℃, it was held for 13 hours. The sintering atmosphere was pure oxygen with an oxygen flow rate of 1000 L / min, and the first particles were obtained.

[0107] Step 2: Crush the first particle to control the D50 to 9±1.5μm, then wash it with water at a 1:1 ratio for 20 minutes at a temperature between 5-15℃. Then filter and dry it to control the moisture content to below 0.5% to obtain the second particle.

[0108] Step 3: Place the dried second particles in a roller kiln for secondary sintering. The sagger loading is 5 kg / sagger, the sintering temperature is 500℃, and the holding time is 8 hours. After screening, iron removal, and packaging, the finished high-nickel ternary cathode active material is obtained.

[0109] The prepared high-nickel ternary cathode active material was observed using a scanning electron microscope. The observation results are as follows: Figure 7 As shown.

[0110] Comparative Example 3

[0111] The preparation method of the positive electrode active material provided in this comparative example includes the following steps:

[0112] Step 1: Take 20 kg of precursor Ni 0.83 Co 0.12 Mn 0.05 (OH)2, 9.54 kg of lithium hydroxide, and 40 g of SrO were mixed in a 60 L high-speed mixer at 500 rpm for 15 min to obtain a mixture.

[0113] The mixture was packed into bowls at a rate of 4 kg / bowl, and heated at a rate of 3℃ / min. When the temperature reached 760℃, it was held for 14 hours. The sintering atmosphere was pure oxygen with an oxygen flow rate of 1000 L / min, and the first particles were obtained.

[0114] Step 2: Crush the first particle to control the D50 to 10.5±1.5μm, then wash it with water at a 1:1 ratio for 5 minutes at a temperature between 15-25℃. Then filter and dry it to control the moisture content to below 0.5% to obtain the second particle.

[0115] Step 3: Place the dried second particles in a roller kiln for secondary sintering. The sagger loading is 5 kg / sagger, the sintering temperature is 500℃, and the holding time is 8 hours. After screening, iron removal, and packaging, the finished high-nickel ternary cathode active material is obtained.

[0116] The prepared high-nickel ternary cathode active material was observed using a scanning electron microscope. The observation results are as follows: Figure 8 As shown.

[0117] Using the same testing method as in Example 1, the nickel and manganese content on the surface of the positive electrode active materials provided in Examples 2-3 and Comparative Examples 1-3 was tested, and the difference in nickel and manganese content on the surface of the first particle and the second particle was calculated. The calculation results are shown in Table 2.

[0118] Table 2 shows the differences in the molar content of nickel and manganese on the surface of the positive electrode active materials provided in Examples 2-3 and Comparative Examples 1-3.

[0119] (b1 - a1 ) % (a2 - b2) % Example 2 1.16 1.03 Example 3 1.32 0.85 Comparative Example 1 2.03 1.54 Comparative Example 2 0.84 0.92 Comparative Example 3 1.22 1.15

[0120] The performance of the first particles prepared in step 1 of Examples 1-3 and Comparative Examples 1-3 was tested. The test methods are as follows, and the test results are shown in Table 3.

[0121] One-burned D104 / I003 / I104: Tested using a Bruker D8A A25 X-ray diffractometer, with Cu as the target material, voltage 40kV, current 40mA, Soller value 2.5, and EVA and TOPAS software used for data processing.

[0122] To determine the content of LiOH, LiCO3, and Free Li+ in the first test particle: Weigh 30g of the first particle to be tested, add 100ml of pure water, stir for 30min, filter using double-layer medium-speed filter paper, transfer 10ml of liquid, use 0.05mol / L HCl as the standard solution, determine the endpoint by potentiometric titration, determine the content of LiCO3 and LiOH, and calculate the content of Free Li+ according to Equation 1.

[0123] Formula 1: Free Li+=6.941*2*Li2CO3 / 73.89+6.941*LiOH / 23.94

[0124] The calcined product, acetylene black, and polyvinylidene fluoride (PVDF) were weighed at a mass ratio of 94:3:3 and dispersed in NMP solvent. The mixture was stirred for 2 hours to prepare the positive electrode active layer slurry. This slurry was then uniformly coated onto the positive electrode current collector aluminum foil, vacuum baked at 80℃, pressed into sheets, and cut into positive electrode sheets with a diameter of 14 mm. Using a 16 mm diameter pure lithium sheet as the negative electrode, a 1 mol / L LiPF6 + DEC / EC (volume ratio 1:1) mixed solution as the electrolyte, and a polyCelgard propylene microporous membrane as the separator, the cells were assembled into coin cells in an argon-filled glove box. The discharge specific capacity and initial charge-discharge efficiency were tested, and the results are shown in Table 3.

[0125] Table 3 shows the performance test results of the calcined products provided in Examples 1-3 and Comparative Examples 1-3.

[0126]

[0127] The particle strength of the positive electrode active materials provided in Examples 1-3 and Comparative Examples 1-3 was tested. The test methods are as follows, and the test results are shown in Table 4.

[0128] Particle strength: Using a Shimadzu DUH-211S instrument under a 500x microscope, a single particle with a secondary particle size distribution of D50±2μm in the cathode material was selected, and pressure was applied using a 50μm flat indenter. The corresponding pressure and stress were recorded to obtain the stress corresponding to particle breakage. More than 10 particles were tested, and the average value was taken.

[0129] The positive electrode active materials provided in Examples 1-3 and Comparative Examples 1-3 were used to prepare lithium-ion batteries. Specifically, the high-nickel positive electrode active materials, acetylene black, and polyvinylidene fluoride (PVDF) provided in Examples 1-3 and Comparative Examples 1-3 were weighed at a mass ratio of 94:3:3, dispersed in NMP solvent, and stirred for 2 hours to prepare a positive electrode active layer slurry. This slurry was then uniformly coated onto the positive electrode current collector aluminum foil, vacuum baked at 80°C, pressed into sheets, and cut into positive electrode sheets with a diameter of 14 mm. A 16 mm diameter pure lithium sheet was used as the negative electrode sheet, a 1 mol / L LiPF6 + DEC / EC (volume ratio 1:1) mixed solution was used as the electrolyte, and a polyCelgard propylene microporous membrane was used as the separator. The batteries were assembled into coin cells in an argon-filled glove box. The initial discharge specific capacity and initial charge-discharge efficiency were tested, and the test results are shown in Table 4.

[0130] The positive electrode active material, conductive carbon black SP, conductive graphite KS-6, and binder PVDF provided in Examples 1-3 and Comparative Examples 1-3 were dispersed in NMP (N-methylpyrrolidone) at a mass ratio of 94.5:2:1:2.5 to prepare a positive electrode active layer slurry. The slurry was then fabricated into a positive electrode sheet through coating and rolling processes. The positive electrode sheet was assembled with a negative electrode (graphite), a separator (polyCelgard propylene microporous membrane), and an electrolyte (1 mol / L LiPF6 + DEC / EC (volume ratio 1:1)) to form a 503048 full cell with a capacity of approximately 800 mAh. The initial DCR, gas generation performance, and capacity retention of the full cell were tested. The test methods are as follows, and the test results are shown in Table 4.

[0131] Initial DCR: Using a Xinwei CT-9004-5V5A-G4 full battery, fully charge at 45℃ with 1C, constant voltage cutoff current of 20mA, and let stand for 5 minutes. Discharge to 50% SOC at 1C according to the battery capacity, let stand for 1 hour, and record the voltage V1. Discharge at 5C for 10 seconds and record the voltage V2. Calculate (V1-V2) / I to obtain the initial DCR.

[0132] Gas production performance: After the battery is fully charged, the battery volume V1 is tested. Then, the fully charged battery is stored at 70°C for 7 days, and the battery volume V2 is tested again. The gas production is (V2-V1) / V1×100%. The volume measurement device is an electronic solid density meter TW-120E.

[0133] Capacity retention: Using the Xinwei test cabinet (CT3008-5V3A-A1), under 45℃ conditions, the cycle voltage is 4.25-3V, the constant voltage cutoff current is 20mA, and the cycle is 300 times at a 1C / 1C charge / discharge rate.

[0134] Table 4. Test results of the positive electrode active materials and batteries provided in Examples 1-3 and Comparative Examples 1-3.

[0135]

[0136] As shown in Table 4, compared with Comparative Examples 1-2, the particle strength and I003 / I104 of the positive electrode active materials provided in Examples 1-3 are significantly improved, which helps to improve the cycle capacity retention rate of lithium-ion batteries and reduce the initial DCR. Compared with Comparative Example 3, the positive electrode active materials provided in Examples 1-3 include dopant element B with a higher ionic valence, which helps to improve the discharge specific capacity of the battery. The content of alkyl LiOH, LiCO3, and Free Li+ on the surface of the first particles provided in Examples 1-3 is reduced, which helps to improve the gas generation performance of lithium-ion batteries.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized in that, The chemical composition of the positive electrode active material is Li x Ni y Co z Mn 1-e- f A u B v C w O2; Where e = u + v + w, f = y + z, and satisfying 0.9 ≤ x ≤ 1.1, 0.6 ≤ y ≤ 1, 0 < z ≤ 0.4, 0 < u ≤ 0.1, 0 < v ≤ 0.1, 0 ≤ w ≤ 0.1, and A is an ionic radius greater than 100. 10 -12 The element m is B, which is an element with an ionic valence greater than or equal to 4, and C is one or more of B, F, P, V, Al, Mg, Y, Nb, Mo, Sb, and Ge. The positive electrode active material has an I003 / I104 ratio of n. The battery containing this positive electrode active material has a cycle retention rate of m after being charged and discharged 300 times at 45°C and a 1C / 1C rate. m > 1.9; The positive electrode active material includes a first particle and a second particle formed by the aggregation of primary particles. The particle size of the first particle is 1-5 μm, and the particle size of the second particle is 8-12 μm. The percentage of the molar mass of Ni on the surface of the first particle to the total molar mass of Ni, Co, and Mn on the surface of the first particle is a1, and the percentage of the molar mass of Mn to the total molar mass of Ni, Co, and Mn on the surface of the first particle is a2. The percentage of the molar mass of Ni on the surface of the second particle to the total molar mass of Ni, Co, and Mn on the surface of the second particle is b1, and the percentage of the molar mass of Mn on the surface of the second particle to the total molar mass of Ni, Co, and Mn is b2. 0.003%≤b1-a1≤5%, 0.003%≤a2-b2≤5%.

2. The positive electrode active material according to claim 1, characterized in that, A is selected from one or more of Sr, Ce, and Na; B is selected from one or more of V, Zr, Cr, Mo, Ti, and W.

3. A method for preparing the positive electrode active material according to claim 1 or 2, characterized in that, Includes the following steps: Nickel-cobalt-manganese precursor, lithium source, and dopant are mixed to obtain a mixture, and the mixture is sintered once to obtain the first particle. The first particle is sequentially crushed, washed, and dried to obtain the second particle; The second particle is subjected to a secondary sintering process to obtain the positive electrode active material.

4. The preparation method according to claim 3, characterized in that, The first sintering process is carried out in an oxygen atmosphere with an oxygen flux of 500-1500 L / min, a heating rate of 1-5 °C / min, a sintering temperature of 700-850 °C, and a time of 8-12 h.

5. The preparation method according to claim 3 or 4, characterized in that, The first particle has a D104 of 45-70 nm, and the surface of the first particle contains 2000-8000 ppm of LiCO3, 2000-8000 ppm of LiOH, and 1500-3000 ppm of Free Li+.

6. The preparation method according to claim 3, characterized in that, The D50 of the first particle was broken down to 8-13 μm.

7. The preparation method according to claim 3, characterized in that, During the washing process, the mass ratio of deionized water to the first crushed particle is 0.6-1.5, the washing temperature is 10-30℃, and the washing time is no more than 30 minutes.

8. The preparation method according to claim 3, characterized in that, The secondary sintering process is carried out in an oxygen or air atmosphere, with a heating rate of 1-5℃ / min, a sintering temperature of 200-700℃, and a time of 8-12h.

9. A lithium-ion battery, characterized in that, Includes the positive electrode active material as described in claim 1 or 2.

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