Nickel-cobalt-manganese ternary precursor having high specific surface area, and preparation and use thereof

Abstract

A nickel-cobalt-manganese ternary precursor having a high specific surface area, and preparation and a use thereof. The preparation comprises the following steps: S1, in an inert atmosphere, introducing in parallel a mixed metal salt solution containing nickel, cobalt and manganese, a strong alkaline solution, and ammonia water into a reaction kettle base solution, and carrying out a nucleation stage reaction in a coprecipitation process to obtain a first slurry containing seed crystals; S2, in the inert atmosphere, reducing the pH value in the first slurry by 1.0-2.0, carrying out stirring, and carrying out a stage I growth reaction to obtain a second slurry containing stage I crystal grains; and S3, in an oxygen-containing atmosphere, reducing the pH value in the second slurry by 0.4-0.6, carrying out stirring, and carrying out a stage II growth reaction to obtain a second slurry containing stage II crystal grains, wherein the stage II crystal grains are the nickel-cobalt-manganese ternary precursor having a high specific surface area, and the D50 of the stage I crystal grains is 1 / 2-4 / 5 of the D50 of the stage II crystal grains. The specific surface area of the nickel-cobalt-manganese ternary precursor is increased, and the structural uniformity of the nickel-cobalt-manganese ternary precursor is maintained.

Description

A high specific surface area nickel-cobalt-manganese ternary precursor and its preparation and application Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a nickel-cobalt-manganese ternary precursor with a high specific surface area, and its preparation and application. Background Art

[0002] Lithium-ion batteries, with their advantages of high energy, long life, no memory effect, and low pollution, are widely used in a variety of fields, including consumer electronics, energy storage, and power batteries. Currently, the main cathode materials used in lithium-ion batteries include lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, and nickel cobalt manganese oxide. The rapid development of the electric vehicle industry in recent years has placed higher demands on the capacity of power batteries. Lithium nickel cobalt manganese oxide ternary cathode materials, due to their higher energy density than lithium iron phosphate and lithium manganese oxide, hold great market prospects and development potential.

[0003] The performance of ternary cathode materials (lithium nickel cobalt manganese oxide) depends largely on the performance of ternary precursors (such as nickel cobalt manganese hydroxide). Wet coprecipitation is a common method for preparing nickel cobalt manganese hydroxide. The prepared nickel cobalt manganese hydroxide is then added with a lithium source and sintered at high temperature to form the lithium nickel cobalt manganese oxide cathode material. The chemical composition, size, morphology, and structure of the nickel cobalt manganese ternary precursor have a direct and crucial impact on the technical indicators of the nickel cobalt manganese ternary cathode material. Currently, the primary grains of nickel cobalt manganese ternary precursors prepared using conventional process parameters are relatively coarse, and the primary grains are also relatively dense, resulting in a small specific surface area of ​​the nickel cobalt manganese ternary precursor, which increases the difficulty of sintering the back-end positive electrode material. The high sintering temperature causes a more serious Li / Ni mixing in the high-nickel ternary cathode material, causing serious performance degradation during subsequent charge and discharge cycles of the battery. In addition, the sintered positive electrode material largely inherits the structural characteristics of the precursor material, namely, coarse and dense primary grains and a small specific surface area. Particles with small specific surface area have very small contact area with the electrolyte, which will reduce the insertion and extraction migration rate of lithium ions and make it difficult to meet the performance requirements of high-power charging and discharging of power batteries.

[0004] Related technicians have increased the specific surface area of ​​precursor materials by oxidation. For example, Chinese patent CN 106684351B adds oxidants (such as potassium permanganate, sodium chlorate and hydrogen peroxide) during the precursor preparation process to obtain a high specific surface area precursor formed by the aggregation of fibrous primary crystals. However, this method uses a large amount of oxidant, which is costly and not economical. It may also introduce additional K + 、Na + and Cl -Impurities such as nitric acid and nitric acid affect the quality of the precursor. Chinese patent CN 115215384A discloses a high nickel precursor with both high specific surface area and high compacted density obtained by controlling ammonia and reaction atmosphere at different reaction stages. However, the air or oxygen atmosphere in the late reaction stage easily leads to excessive oxidation of more Mn to MnOOH or MnO2, resulting in the introduction of a large amount of impurities, leading to serious structural inhomogeneity that affects the performance of subsequent positive electrode materials. Although the above method can improve the specific surface area of ​​the precursor, the introduction of impurities will inevitably cause the inhomogeneity of the precursor structure. That is, in the related art, the nickel-cobalt-manganese ternary precursor has the problem of difficulty in balancing the increase in specific surface area and the maintenance of structural uniformity.

[0005] Therefore, it is necessary to provide a solution for increasing the specific surface area of ​​the nickel-cobalt-manganese ternary precursor and ensuring its structural uniformity while ensuring high tap density.

[0006] Summary of the Invention

[0007] In view of this, the present application provides a nickel-cobalt-manganese ternary precursor with a high specific surface area and its preparation and application, which are used to solve the problem of how to increase the specific surface area of ​​the nickel-cobalt-manganese ternary precursor and maintain its structural uniformity while ensuring a high tap density.

[0008] In order to achieve the above technical objectives, this application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, comprising the following steps:

[0010] S1. Under an inert atmosphere, a mixed metal salt solution containing nickel, cobalt and manganese, a strong alkali solution and aqueous ammonia are passed into the bottom liquid of the reactor in parallel to carry out the nucleation stage reaction of the coprecipitation process, and stirring is maintained to obtain a first slurry containing seed crystals;

[0011] S2. Under an inert atmosphere, the pH value of the first slurry is reduced by 1.0-2.0, and the stirring speed is gradually reduced according to the particle size growth to perform an I-order growth reaction to obtain a second slurry containing I-order grains;

[0012] S3. In an oxygen-containing atmosphere, the pH value of the second slurry is reduced by 0.4-0.6, and stirring is maintained to perform a stage II growth reaction to obtain a second slurry containing stage II grains, wherein the stage II grains are a nickel-cobalt-manganese ternary precursor having a high specific surface area;

[0013] The D50 of the I-order grains is 1 / 2-4 / 5 of the D50 of the II-order grains.

[0014] Preferably, the concentration of aqueous ammonia in steps S1 to S3 remains unchanged.

[0015] Preferably, the stirring speed of step S3 is adjusted by reducing the speed by 20-50 rpm for every 1 μm increase in D50 of the I-order grains; more preferably, the stirring speed of step S3 is adjusted by reducing the speed by 30-40 rpm for every 1 μm increase in D50 of the I-order grains.

[0016] Preferably, the D50 of the II-stage grains is 6-18 μm.

[0017] Preferably, in step S3, the mass proportion of oxygen in the oxygen-containing atmosphere is 2-10%.

[0018] Preferably, in the mixed metal salt solution containing nickel, cobalt and manganese, the molar ratio of the nickel source, the cobalt source and the manganese source is (1-xy):x:y, wherein 0.02≤x+y≤0.67.

[0019] Preferably, in step S1, the temperature of the coprecipitation reaction is 40-80°C.

[0020] Preferably, the rate of pH reduction in step S2 is (0.04-0.1) / h, and the rate of pH reduction in step S3 is (0.1-0.2) / h; the rate of pH reduction in step S3 is greater than the rate of pH reduction in step S2.

[0021] In a second aspect, the present application provides a nickel-cobalt-manganese ternary precursor with a high specific surface area.

[0022] In a third aspect, the present application provides an application of a nickel-cobalt-manganese ternary precursor with a high specific surface area in the preparation of a nickel-cobalt-manganese oxide ternary positive electrode material.

[0023] The beneficial effects of the present application are as follows: In the present application, a precursor is obtained by a coprecipitation method, which includes a nucleation stage and a growth stage, and the growth stage is divided into a first-order growth stage and a second-order growth stage. Nitrogen is introduced into the nucleation stage and the first-order growth stage to ensure a high tap density, and the pH value of the first-order growth stage is lowered compared to the nucleation stage to complete the transition from nucleation to growth, and the rotation speed is gradually reduced, so that the gaps between the primary particles are gradually filled and the secondary particles gradually grow; in the second-order growth stage, the pH value is further reduced, a high rotation speed is maintained, and the reaction atmosphere is converted to an oxygen-containing atmosphere, so that the specific surface area of ​​the first-order grains is increased. At the same time, instead of introducing an oxygen-containing atmosphere immediately after nucleation, an oxygen-containing atmosphere is introduced for oxidation when the D50 of the grains grows to 1 / 2-4 / 5 of the target particle size. This avoids the introduction of an oxygen-containing atmosphere when the particles are small or the introduction of a large amount of oxygen in a short time to cause impurities, thereby improving the structural uniformity of the precursor. In addition, in the II-stage growth stage under an oxygen-containing atmosphere, further lowering the pH and maintaining a higher rotation speed are also beneficial to the refinement of the primary grains, thereby increasing the specific surface area. Ultimately, while ensuring a high tap density, the specific surface area of ​​the nickel-cobalt-manganese ternary precursor is increased while maintaining its structural uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 shows the Ni 0.6 Co 0.2 Mn 0.2 SEM image of (OH)2 precursor;

[0025] Figure 2 shows the Ni 0.6 Co 0.2 Mn 0.2 XRD pattern of (OH)2 precursor;

[0026] Figure 3 shows the Ni 0.6 Co 0.2 Mn 0.2 SEM image of (OH)2 precursor;

[0027] Figure 4 shows the Ni 0.6 Co 0.2 Mn 0.2 SEM image of (OH)2 precursor. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] The present application provides a method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, comprising the following steps:

[0030] S1. Under an inert atmosphere, a mixed metal salt solution containing nickel, cobalt, and manganese, a strong alkaline solution, and aqueous ammonia are simultaneously introduced into the bottom liquid of the reactor to carry out the nucleation stage reaction of the coprecipitation process while maintaining stirring to obtain a first slurry containing seed crystals; the pH of the nucleation stage reaction is 11.4-12.5;

[0031] S2. Under an inert atmosphere, lowering the pH of the first slurry by 1.0-2.0, gradually reducing the stirring speed according to the particle size growth, performing an I-order growth reaction, and obtaining a second slurry containing I-order grains; preferably, in step S2, the pH range is 10.4-11.4, for example, 10.4, 10.6, 10.8, 11, or 11.4; preferably, the pH of the first slurry is lowered by 1.0-1.1;

[0032] S3. In an oxygen-containing atmosphere, lowering the pH of the second slurry by 0.4-0.6 while maintaining stirring to carry out a stage II growth reaction to obtain a second slurry containing stage II grains, wherein the stage II grains are a nickel-cobalt-manganese ternary precursor having a high specific surface area; preferably, in step S3, the pH range is 10-11, for example, 10, 10.2, 10.5, or 11;

[0033] The D50 of the I-order grains is 1 / 2-4 / 5 of the D50 of the II-order grains. Preferably, the D50 of the I-order grains is 2 / 3-4 / 5 of the D50 of the II-order grains.

[0034] The present application achieves the purpose of increasing the specific surface area and structural uniformity of the precursor while maintaining a high tap density by controlling the pH, stirring speed, and reaction atmosphere during the nucleation-I-stage growth-II-stage growth process. The specific mechanism is as follows:

[0035] In this application, a precursor is obtained by a coprecipitation method, which includes a nucleation stage and a growth stage, and the growth stage is divided into a I-stage growth stage and a II-stage growth stage. Nitrogen is introduced into the nucleation stage and the I-stage growth stage to ensure a high tap density, and the pH value of the I-stage growth stage is lowered compared to the nucleation stage to complete the transition from nucleation to growth, and the rotation speed is gradually reduced, so that the gaps between the primary particles are gradually filled and the secondary particles gradually grow; in the II-stage growth stage, the pH value is further reduced, a high rotation speed is maintained, and the reaction atmosphere is converted to an oxygen-containing atmosphere, so that the primary grains of the I-stage grains are refined and the specific surface area of ​​the precursor is increased. At the same time, instead of introducing an oxygen-containing atmosphere immediately after nucleation, an oxygen-containing atmosphere is introduced for oxidation when the D50 of the grains grows to 1 / 2-4 / 5 of the target particle size. This avoids the introduction of an oxygen-containing atmosphere when the particles are small or the introduction of a large amount of oxygen in a short time to cause impurities, thereby improving the uniformity of the precursor. In addition, in the II-stage growth stage under an oxygen-containing atmosphere, further reducing the pH and maintaining a higher rotation speed are also beneficial to the refinement of the primary grains, thereby increasing the specific surface area. Ultimately, under the premise of ensuring a high tap density, the specific surface area of ​​the nickel-cobalt-manganese ternary precursor is increased while maintaining its structural uniformity.

[0036] In some embodiments, in the mixed metal salt solution containing nickel, cobalt and manganese, the nickel source is a nickel soluble salt, including but not limited to nickel sulfate, nickel nitrate, and nickel chloride; the cobalt source is a cobalt soluble salt, including but not limited to cobalt sulfate, cobalt nitrate, and cobalt chloride; the manganese source is a manganese soluble salt, including but not limited to manganese sulfate, manganese nitrate, and manganese chloride; preferably, the nickel source is nickel sulfate, the cobalt source is cobalt sulfate, and the manganese source is manganese sulfate; in step S1, the mass concentration of total metal ions in the mixed solution of the nickel source, cobalt source, and manganese source is 60-120 g / L, for example, 60 g / L, 80 g / L, 100 g / L, 120 g / L, or any value within the above range; the flow rate of the mixed solution is 2-5% V / h, where V is the volume of the reactor.

[0037] The concentration of ammonia water in steps S1 to S3 of this solution remains unchanged. Strong alkali solution includes but is not limited to one or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution. Preferably, the alkali solution is sodium hydroxide solution; the mass fraction of the alkali solution is 20-40%. The mass fraction of ammonia water used in this solution is 12-30%, and the ammonia concentration of the supernatant of the reaction slurry in steps S1 to S3 is maintained relatively constant. In some embodiments, the concentration of ammonia water is 2-12 g / L, for example, the ammonia concentration of the supernatant of the reaction slurry in steps S1-S3 is maintained at one of 2 g / L, 5 g / L, 8 g / L, 10 g / L, and 12 g / L, or maintained at any value within the above range. The entire process of this solution maintains the pH value and ammonia water concentration of each reaction stage constant by adjusting the flow rate of strong alkali solution and ammonia water. The ammonia concentration remains stable throughout the process, avoiding large fluctuations in the ammonia concentration of the system caused by large adjustments to the flow rate of volatile ammonia solution. The product has high consistency and is easy to repeat and mass produce.

[0038] The stirring speed of step S2 is adjusted by reducing the speed by 20-50 rpm for every 1 μm increase in the particle size D50 of the seeded slurry obtained in step S1. The stirring speed of step S3 is maintained after the completion of the first stage growth stage and does not decrease until the reaction is completed. Steps S1 to S3 are all reacted in a stirring environment, wherein the stirring speed of step S1 is 400-800 rpm; after the D50 of the reaction slurry reaches a certain particle size in step S2, the stirring speed is reduced to 250-400 rpm at a certain decreasing rate; the stirring speed of step S3 is maintained at the stirring speed at the end of step S2.

[0039] In this embodiment, the D50 of the II-stage grains is 6-18 μm, and preferably, the D50 of the II-stage grains is 10-15 μm.

[0040] In step S3, in the oxygen-containing atmosphere, the mass proportion of oxygen is 2-10%. The oxygen-containing atmosphere can be air, a mixture of air and inert atmosphere, etc. In the present application, the flow rate of the oxygen-containing atmosphere is 0.5-3V / h, where V is the volume of the reactor.

[0041] In this solution, the molar ratio of nickel source, cobalt source and manganese source is (1-xy):x:y, wherein 0.02≤x+y≤0.67. The general chemical formula of the nickel-cobalt-manganese ternary precursor of this application is Ni 1-x-y Co x Mn y (OH)2, where 0.02≤x+y≤0.67, the chemical formula of the nickel-cobalt-manganese ternary precursor is matched by controlling the molar ratio of the nickel source, cobalt source, and manganese source. For example, the molar ratio of the nickel source, cobalt source, and manganese source is set to 6:2:2 to obtain Ni 0.6 Co0.2 Mn 0.2 (OH)2, the molar ratio of nickel source, cobalt source and manganese source is 8:1:1, corresponding to Ni 0.8 Co 0.1 Mn 0.1 (OH)2, or other ratios that meet the requirements.

[0042] In some embodiments, in step S1, the temperature of the coprecipitation reaction is 40-80°C, and the reaction temperature in steps S1-S3 is kept constant.

[0043] In some embodiments, the rate of pH reduction in step S2 is (0.04-0.1) / h, and the rate of pH reduction in step S3 is (0.1-0.2) / h. In the nucleation-growth stage I, a lower pH reduction rate is adopted and the stirring speed is gradually reduced to increase the tap density; in the growth stage I-growth stage II, a higher pH reduction rate is adopted and a higher stirring speed is maintained to quickly reach the target pH and cooperate with oxidation to refine the primary grains and increase the specific surface area.

[0044] The present application provides a nickel-cobalt-manganese ternary precursor with a high specific surface area. The nickel-cobalt-manganese ternary precursor of the present application has a large specific surface area, a high tap density, and the primary particles are flaky and the secondary particles are loose and porous. When mixed with a lithium source and sintered to prepare a positive electrode material, the reaction activity is higher and it can be sintered at a lower calcination temperature. The obtained positive electrode active material has a lower degree of Li / Ni mixing and a larger specific surface area, which can significantly improve the cycle performance and rate performance of the positive electrode material.

[0045] The present application provides an application of a nickel-cobalt-manganese ternary precursor with a high specific surface area in the preparation of a nickel-cobalt-manganese oxide ternary positive electrode material.

[0046] The present invention is further described below through specific examples.

[0047] Raw material preparation

[0048] Mixed metal salt solution: nickel sulfate, cobalt sulfate, and manganese sulfate are mixed and dissolved in deionized water at a molar ratio of 6:2:2 to prepare a mixed metal salt solution with a total metal ion concentration of 100 g / L.

[0049] Example 1

[0050] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area comprises the following steps:

[0051] S1. Add 20L of pure water to a 100L reactor, add alkali solution and ammonia water to prepare a reaction base solution with a pH of 11.6 and an ammonia concentration of 6g / L, and introduce nitrogen. Add a mixed metal salt solution at a flow rate of 3L / h, and simultaneously add a 30% by mass sodium hydroxide solution and a 15% by mass ammonia solution. Adjust the flow rates of the sodium hydroxide solution and ammonia water to control the pH in the reactor to maintain at 11.6±0.2 and the ammonia concentration to maintain at 6±0.5g / L. Control the stirring speed to 550r / min and the reaction temperature to 60°C. Carry out a coprecipitation reaction and maintain nucleation for 4h to obtain a first slurry containing seed crystals, at which point the D50 is approximately 2μm.

[0052] S2. In the reactor of step S1, nitrogen was continued to be introduced and the feed rate of the sodium hydroxide solution was reduced, the pH value of the first slurry was gradually reduced to 10.6, and the mixture was stirred to carry out the first-order growth reaction to obtain a second slurry containing first-order grains, until the D50 of the first-order grains reached 7 μm; in step S2, the pH value was reduced at a rate of 0.05 / h, and the stirring speed was reduced by 30 rpm for each 1 μm increase, i.e., from 3 μm to 520 rpm, from 4 μm to 490 rpm, from 5 μm to 460 rpm, from 6 μm to 430 rpm, and from 7 μm to 400 rpm;

[0053] S3. In the reactor of step S2, the nitrogen gas introduced is switched to a mixture of air and nitrogen containing 2% oxygen, and the feed flow rate of the sodium hydroxide solution is reduced to reduce the pH value in the second slurry to 10.2, and a II-stage growth reaction is carried out until the D50 of the grains reaches 10 μm, and the feeding is stopped to obtain a second slurry containing II-stage grains. The flow rate of the mixed gas in step S3 is 120 L / h, the rate of pH reduction is 0.15 / h, and the stirring speed is maintained at 400 rpm. The second slurry is subjected to solid-liquid separation, and the solid product is washed and dried to obtain a nickel-cobalt-manganese ternary precursor with a high specific surface area. The nickel-cobalt-manganese ternary precursor is Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor. Figure 1 shows the Ni 0.6 Co 0.2 Mn 0.2 Figure 2 is the SEM image of Ni 0.6 Co 0.2 Mn 0.2 XRD pattern of (OH)2 precursor.

[0054] Example 2

[0055] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, the other contents are the same as those in Example 1, except that the rate of pH reduction in step S2 is 0.1 / h, the rate of stirring speed reduction is 50 rpm / h; and the rate of pH reduction in step S3 is 0.1 / h.

[0056] Example 3

[0057] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, the other contents are the same as those in Example 1, except that the pH value of step S1 is 12.5, the pH value of step S2 is 11.2, and the pH value of step S3 is 10.6.

[0058] Comparative Example 1

[0059] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, the other contents are the same as those in Example 1, except that in step S3, the mixed gas containing 2% oxygen is replaced with nitrogen. 0.6 Co 0.2 Mn 0.2 SEM image of (OH)2 precursor.

[0060] Comparative Example 2

[0061] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, the other contents are the same as those in Example 1, except that the nitrogen gas introduced in step S1 and step S2 is changed to the same mixed gas containing 2% oxygen as in step S3. 0.6 Co 0.2 Mn 0.2 XRD pattern of (OH)2 precursor.

[0062] Comparative Example 3

[0063] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area is the same as in Example 1 except that the nitrogen gas introduced in step S2 is replaced with a mixed gas containing 2% oxygen as in step S3.

[0064] Comparative Example 4

[0065] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area is the same as that in Example 1 except that the pH value in step S3 is maintained the same as the pH value in step S2.

[0066] Comparative Example 5

[0067] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area is the same as that in Example 1 except that the stirring speed in step S3 is maintained at the same reduced speed as in step S2 until the reaction is completed.

[0068] Comparative Example 6

[0069] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area is the same as in Example 1 except that, in step S3, the mixed gas containing 2% oxygen is replaced with nitrogen; in step S3, the pH value is maintained at the same pH value as in step S2.

[0070] Comparative Example 7

[0071] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area is the same as in Example 1, except that in step S3, the mixed gas containing 2% oxygen is replaced with nitrogen; in step S3, the stirring speed is maintained at the same reduced speed as in step S2 until the reaction is completed.

[0072] Comparative Example 8

[0073] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, the other contents of which are the same as those of Example 1, except that step S3 is started when the D50 of the I-stage grains in step S2 reaches 4 μm, and the feeding is stopped until the D50 of the grains reaches 10 μm.

[0074] Comparative Example 9

[0075] A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, the other contents are the same as those in Example 1, except that the pH value in the first slurry is reduced by 0.4, that is, the pH value is reduced to 11.2; the pH value in the second slurry is reduced by 1.0, that is, the pH value is reduced to 10.2.

[0076] Testing and Application

[0077] The precursor materials obtained in the examples and comparative examples were tested for D50, TD, AD, and BET, where:

[0078] D50: represents the particle size at which 50% of particles are found, and is measured using a Malvern 3000 particle size analyzer.

[0079] TD / AD: tap density / apparent density. The larger the value, the higher the density of the precursor and the denser the filling between the particles. It is measured using Shenzhen Sino-Nude JZ-1 tap density meter.

[0080] BET: Specific surface area. The larger the value, the larger the specific surface area and the higher the porosity of the particles. It is measured using Anton Paar Nova 800 specific surface area analyzer.

[0081] Impurity content: It is the percentage of the mass of the impurity phase in the precursor to the total mass. The larger the value, the more impurities there are and the poorer the structural heterogeneity of the precursor. It is measured using a Rigaku MiniFlex600 X-ray diffractometer with a test angle range of 5-90°, a test rate of 2° / min, and a test step size of 0.01°.

[0082] Table 1 Test results

[0083] It can be seen from the data in Table 1 that Examples 1-3 of the present invention all maintain a relatively high tap density (TD>1.85 g / cm 3 ), with a high specific surface area (BET>14m 2 / g) and very low impurity content.

[0084] Compared with Example 1, Comparative Example 1 was protected by nitrogen throughout the process without oxidation. Its tap density was greatly improved, but the specific surface area decreased sharply. Comparison of the SEM photos of the two (Figures 1 and 3) also shows that the primary grains of Comparative Example 1 are relatively coarse and thick, and the particles are very dense. This is mainly because oxidation can destroy the bonding between the precursor layers and inhibit the growth of the primary grains in the thickness direction. The lack of oxidation in Comparative Example 1 causes the primary grains to become coarse and thick, and continuously fill the gaps between the particles to become dense.

[0085] Compared with Example 1, Comparative Example 2 is introduced into an oxygen-containing atmosphere throughout the entire process, and its specific surface area is significantly increased, but the tap density is sharply reduced and the impurity content is significantly increased. This is because the oxidation has a destructive effect on the interlayer bonding of the precursor, which significantly inhibits the growth of the primary grain thickness direction. At the same time, since oxidation is introduced when the particles are very small, it is easy to form impurity phases such as MnOOH or MnO2 (compare Figure 2 and Figure 4, Figure 4 shows the peak of the impurity phase), resulting in serious structural inhomogeneity, which will be detrimental to the electrochemical performance of the positive electrode material. Comparative Example 3 only introduces nitrogen in step S1, and introduces an oxygen-containing mixed gas in steps S2 and S3. Its degree of oxidation is slightly lower than that of Comparative Example 2, so the tap density is slightly higher than that of Comparative Example 2, and the specific surface area is slightly lower than that of Comparative Example 2;

[0086] Compared with Example 1, Comparative Example 4 did not further reduce the pH during the process from growth stage I to growth stage II, and its tap density slightly increased and its specific surface area significantly decreased. This is because in the oxygen-containing atmosphere of growth stage II, the reduction in pH can further reduce the precipitation rate and inhibit the growth of primary grains along the thickness direction. Therefore, the slightly higher pH in growth stage II of Comparative Example 4 appropriately increases the thickness of its primary grains, which is not conducive to the increase in specific surface area.

[0087] Compared with Example 1, in Comparative Example 5, the stirring speed is continuously reduced in the growth stage II, and its tap density increases slightly and the specific surface area decreases significantly. This is because in the oxygen-containing atmosphere of the growth stage II, the lower speed is conducive to the further attachment and growth of the solute on the primary grains, promoting the growth of the primary grains along the thickness direction. Therefore, the tap density of Comparative Example 5 increases slightly and the specific surface area decreases significantly; at the same time, its tap density is slightly lower and the specific surface area is slightly higher than that of Comparative Example 4, indicating that maintaining a higher pH is more likely to increase the tap density and reduce the specific surface area than reducing the speed;

[0088] Compared with Example 1, Comparative Example 6, in which nitrogen was introduced throughout the entire process and the pH was not further lowered during Growth Stage II, exhibited the following tap density: Example 1 < Comparative Example 4 < Comparative Example 6, specific surface area: Comparative Example 6 < Comparative Example 4 < Example 1, and structural uniformity: Example 1 ≈ Comparative Example 4 < Comparative Example 6. This is because the lack of oxygen-containing atmosphere for oxidation during Growth Stage II and the maintenance of a relatively high pH significantly promote the growth of primary grains along the thickness direction. Consequently, Comparative Example 6 exhibits a significantly higher tap density and a significantly lower specific surface area than Example 1.

[0089] Compared with Example 1, Comparative Example 7, in which nitrogen was introduced throughout the entire process while the stirring speed was further reduced during Growth Stage II, exhibited the following tap density: Example 1 < Comparative Example 5 < Comparative Example 7; specific surface area: Comparative Example 7 < Comparative Example 5 < Example 1; and structural uniformity: Example 1 ≈ Comparative Example 5 < Comparative Example 7. This is because no oxygen-containing atmosphere was introduced for oxidation during Growth Stage II and a high pH was maintained. The synergistic effect of these two factors greatly promoted the growth of primary grains along the thickness direction. Therefore, Comparative Example 6 exhibited a significantly higher tap density and a significantly lower specific surface area than Example 1.

[0090] Compared with Example 1, Comparative Example 8 completed the reaction of growth stage I at a lower particle size, and entered the growth stage II reaction and was oxidized by passing an oxygen-containing atmosphere. Its tap density was significantly reduced, the specific surface area was slightly increased, and the structural uniformity was deteriorated. This is because oxidation at a smaller particle size will lead to more severe oxidation, inhibiting the growth of primary grains along the thickness direction, thereby reducing the tap density and increasing the specific surface area, and at the same time causing the appearance of impurities such as MnOOH or MnO2;

[0091] Compared with Example 1, the tap density of Comparative Example 9 is slightly lower and the specific surface area is slightly higher. This is because the growth is carried out at a relatively high pH in Growth Stage I, which is accompanied by the nucleation of appropriate small particles, and its particle size distribution range is wider than that of Example 1. The growth of the primary grains of these particles with smaller particle sizes is further inhibited in Growth Stage II, resulting in a decrease in the overall tap density and a slight increase in the specific surface area.

[0092] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area, characterized in that, it includes the following steps: S1. Under an inert atmosphere, a mixed metal salt solution containing nickel, cobalt, and manganese, a strong alkali solution, and ammonia are introduced into the bottom liquid of the reaction kettle in parallel to carry out the nucleation stage reaction of the coprecipitation process, maintaining stirring to obtain a first slurry containing seeds; S2. Under an inert atmosphere, the pH value in the first slurry is reduced by 1.0 - 2.0 to carry out the first-stage growth reaction to obtain a second slurry containing first-stage grains; S3. Under an oxygen-containing atmosphere, the pH value in the second slurry is reduced by 0.4 - 0.6, maintaining stirring to carry out the second-stage growth reaction to obtain a second slurry containing second-stage grains, and the second-stage grains are the nickel-cobalt-manganese ternary precursor with a high specific surface area; The D50 of the first-stage grains is 1 / 2 - 4 / 5 of the D50 of the second-stage grains.

2. The method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 1, characterized in that, the ammonia concentration in steps S1 - S3 remains unchanged.

3. The method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 1, characterized in that, the stirring speed in step S3 is adjusted at a rate of 20 - 50 rpm for every 1 μm increase in the D50 of the first-stage grains.

4. The method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 1, characterized in that, the D50 of the second-stage grains is 6 - 18 μm.

5. The method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 1, characterized in that, in step S3, in the oxygen-containing atmosphere, the mass ratio of oxygen is 2 - 10%.

6. The method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 1, characterized in that, in the mixed metal salt solution containing nickel, cobalt, and manganese, the molar ratio of the nickel source, cobalt source, and manganese source is (1 - x - y) : x : y, where 0.02 ≤ x + y ≤ 0.

67.

7. The method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 1, characterized in that, in step S1, the temperature of the coprecipitation reaction is 40 - 80°C.

8. The method for preparing a nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 1, characterized in that, in step S2, the rate of pH value reduction is (0.04 - 0.1) / h, and in step S3, the rate of pH value reduction is (0.1 - 0.2) / h.

9. A nickel-cobalt-manganese ternary precursor with a high specific surface area obtained by the preparation method according to any one of claims 1 - 8.

10. An application of the nickel-cobalt-manganese ternary precursor with a high specific surface area according to claim 9 in the preparation of a nickel-cobalt-manganese lithium ternary cathode material.

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