A high-nickel precursor, positive electrode material and preparation method thereof

Abstract

A kind of high nickel precursor, positive electrode material and preparation method thereof, belong to the technical field of lithium ion battery materials, overcome the defect that doping elements are unevenly distributed in the material body when the prior art prepares high nickel precursor. The preparation method of the high nickel precursor of the present invention comprises the following steps: step 1, prepare Al-containing nickel cobalt manganese salt solution, ammonia solution, alkali solution precipitant and ammonia bottom liquid; in the Al-containing nickel cobalt manganese salt solution, the Al / TM atomic ratio is 0.001-0.01, and TM is the sum of the amount of substance of nickel, cobalt and manganese atoms; step 2, add the ammonia bottom liquid to the reactor, and adjust the pH of the ammonia bottom liquid to 10.7-11.7, pump the Al-containing nickel cobalt manganese salt solution, ammonia solution and alkali solution precipitant into the reactor at the same time, stir during the feeding process, and continue stirring reaction after the feeding ends; step 3, solid-liquid separation, washing, drying to obtain a high nickel precursor. The present invention can reduce the generation of particle microcracks and improve the long cycle stability of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery materials, and in particular relates to a high-nickel precursor, a positive electrode material and a preparation method thereof. Background Art

[0002] In order to alleviate the shortage of oil and reduce CO2 emissions, my country is gradually moving towards the era of new energy appliances. With the promotion and popularization of new energy vehicles, lithium-ion power batteries, as their main power source, have also ushered in broad development prospects. At present, the main commercial lithium-ion power battery positive electrode materials include nickel-cobalt-manganese ternary materials LiNi x Co y Mn z (OH)2(0<x+y<1) and lithium iron phosphate material (LiFePO4), due to the low nickel ternary material LiNi x Co y Mn z The energy density of (OH)2(x<0.6) and LiFePO4 materials is low (about 150-160Wh / kg), which is difficult to meet the requirements of electric vehicles for driving range, becoming the main bottleneck in the development of power batteries; and among high-nickel ternary materials (LiNi x Co y Mn z (OH)2, x≥0.6) Since the increase of Ni component can give the material more reversible capacity, the development of high-nickel positive electrode materials with excellent performance has become one of the main development directions of future power lithium battery materials.

[0003] At present, the production of high-nickel positive electrode materials generally adopts the complex co-precipitation method to prepare its polycrystalline spherical precursor, and then prepares the corresponding positive electrode material by mixed lithium sintering. Although the increase in the Ni component content of high-nickel materials increases the reversible capacity, the structural stability and safety of the materials also deteriorate accordingly. During the material preparation and circulation process, it is easy to form unfavorable Li / Ni mixed phase transition, surface residual alkali and lattice anisotropic expansion / expansion caused by stress accumulation, etc., which in turn causes the material to rapidly decay in capacity during cyclic overcharge, increase charge transfer impedance, intensify interface side reactions and serious particle crushing, which brings safety hazards to the long-term use of batteries.

[0004] In order to stabilize the material structure, an effective method is to introduce a small amount of impurity elements into the material to stabilize and strengthen its structure. For example, commonly used doping elements include: Mg, Al, Zr, Nb, Ta, etc. Among them, Al as a doping element can significantly improve the cyclability, rate capability and thermal stability of high-nickel materials, and also has a certain inhibitory effect on surface residual alkali. However, most studies generally introduce doping elements during the precursor lithiation sintering stage, and disperse the doping elements at various sites of the material grains by solid-phase thermal diffusion. Due to the low diffusion efficiency of elements in solid-phase sintering, it is easy to cause uneven distribution of doping elements in the bulk phase of the material, resulting in inconsistent electrochemical behavior between different sites of the material and poor doping effect. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect of uneven distribution of doping elements in the bulk phase of the material when preparing a high-nickel precursor in the prior art, thereby providing a high-nickel precursor, a positive electrode material and a preparation method thereof.

[0006] To this end, the present invention provides the following technical solutions.

[0007] In a first aspect, the present invention provides a method for preparing a high-nickel precursor, comprising the following steps:

[0008] Step 1, preparing an Al-containing nickel-cobalt-manganese salt solution, an ammonia solution, an alkaline solution precipitant and an ammonia solution base solution; in the Al-containing nickel-cobalt-manganese salt solution, the Al / TM atomic ratio is 0.001-0.01, and TM is the sum of the amounts of nickel, cobalt and manganese atoms;

[0009] Step 2, adding an ammonia base liquid into the reactor, and adjusting the pH of the ammonia base liquid to 10.7-11.7, pumping Al-containing nickel-cobalt-manganese salt solution, an ammonia solution, and an alkaline solution precipitant into the reactor at the same time, stirring during the feeding process, and continuing to stir the reaction after the feeding is completed;

[0010] Step 3: solid-liquid separation, washing and drying to obtain a high-nickel precursor.

[0011] Furthermore, at least one of the following conditions is met:

[0012] (1) During the feeding process, the feeding rate of the Al-containing nickel-cobalt-manganese salt solution is in the range of 0.5-2.0 mL / min;

[0013] Preferably 0.5-0.9 mL / min;

[0014] (2) During the feeding process, in order to ensure the coordinated coordination of the complexation reaction and the precipitation reaction, the molar ratio of NH3 in the ammonia solution fed to TM in the Al-containing nickel-cobalt-manganese salt solution per unit time is 1.0-1.4, preferably 1.1-1.3.

[0015] The feed rate of the aqueous ammonia solution is converted according to the ammonia concentration and the NH3:TM feed molar ratio.

[0016] The flow rate of the alkali solution precipitant is used to adjust the pH of the feed solution in the reactor so that it is always constant at the target pH.

[0017] (3) In the Al-containing nickel-cobalt-manganese salt solution, the Al / TM atomic ratio is 0.005-0.01.

[0018] Furthermore, the feed rate of the Al-containing nickel-cobalt-manganese salt solution is 0.8-0.9 mL / min or 0.5-0.6 mL / min.

[0019] During the feeding process, the reaction materials are fully dispersed under stirring and meet again to undergo precipitation and crystallization reaction; in order to maintain the stability of the system supersaturation and allow the crystal-forming ions to deposit evenly, the reaction pH, feeding rate, and feed liquid temperature are maintained constant during this process.

[0020] After the reaction is completed, the precursor precipitate is washed 3-4 times with low concentration alkaline water and pure water to remove the Na + 、NH3、SO4 2- The washed precursor is placed in a vacuum drying oven at 100-120° C. and dried for 12-20 hours to obtain a dry high-nickel precursor powder.

[0021] Furthermore, at least one of the following conditions is met in step 2:

[0022] (1) After adding the ammonia water base liquid into the reaction kettle, the ammonia water base liquid is heated to 45-60° C.;

[0023] (2) ultrasonically dispersing the dissolved oxygen in the Al-containing nickel-cobalt-manganese salt solution, ammonia solution, and alkali solution precipitant before pumping into the reactor;

[0024] (3) The stirring speed during the feeding process is 500-1000 rpm;

[0025] Preferably, the feeding time is controlled within 10-50h;

[0026] (4) After the feeding is completed, stirring and heating are continued for 10-12 hours to allow the reaction to proceed fully and the crystal growth to become more mature;

[0027] Optionally, the stirring speed after the feeding is completed is adjusted to 100-500 rpm.

[0028] Furthermore, step 1 satisfies at least one of the following conditions:

[0029] (1) The TM concentration in the Al-containing nickel-cobalt-manganese salt solution is 1.5-2.5 mol / L;

[0030] The preparation of the Al-containing nickel-cobalt-manganese salt solution includes: taking soluble metal salts of nickel, cobalt, manganese and aluminum and dissolving them quickly with hot water to obtain an Al-containing nickel-cobalt-manganese salt solution of a target concentration; or using Al-containing nickel-cobalt-manganese leaching solution obtained by wet recovery of waste lithium-ion batteries, and adjusting the concentration of each metal element in the leaching solution to meet the material design ratio, and then using it as a metal salt raw material solution, thereby realizing the recycling of metal resources;

[0031] (2) Press Ni x Co y Mn 1-x-y (OH)2 to prepare Al-containing nickel-cobalt-manganese salt solution, wherein 0.6≤x<1, 0<x+y<1;

[0032] (3) The concentration of the ammonia solution is 4.0-5.6 mol / L;

[0033] (4) The concentration of the alkali solution precipitant is 4.0-8.0 mol / L;

[0034] (5) The concentration of the ammonia bottom liquid is 1.0-1.4 mol / L (the ammonia concentration in the bottom liquid (i.e., the ammonia bottom liquid) initially entering the reactor should be the ammonia concentration after the ammonia solution is diluted by the Al-containing nickel-cobalt-manganese salt solution and the alkaline solution precipitant during feeding.

[0035] In step 2, the amount of ammonia bottom liquid added is selected according to the position of the stirring paddle from the bottom of the reactor to ensure that the stirring paddle can hit the ammonia bottom liquid. Optionally, the amount of ammonia bottom liquid added is 1 / 4 to 1 / 2 of the volume of the reactor. After adding the ammonia bottom liquid, preheat it to 45-60°C, and continuously inject protective gas into the reactor to drive out the air. At this time, the pH of the ammonia bottom liquid is generally lower than the reaction set value of 10.7-11.7. Turn on the alkali solution pump to adjust the pH of the ammonia bottom liquid to the reaction set value.

[0036] Furthermore, at least one of the following conditions is met:

[0037] (1) using soluble metal salts of nickel, cobalt, manganese and aluminum to prepare an Al-containing nickel-cobalt-manganese salt solution, wherein the metal salt is one or more of hydrochloride, sulfate, nitrate or acetate;

[0038] (2) The alkaline solution precipitant is selected from one or more of LiOH, NaOH, and KOH.

[0039] In a second aspect, the present invention provides a high-nickel precursor prepared by the above method.

[0040] In a third aspect, the present invention provides a method for preparing a positive electrode material, wherein the high nickel precursor prepared by the above method is subjected to lithium sintering to prepare the positive electrode material.

[0041] Optionally, after sintering, the prepared positive electrode material is ground and sieved (the ambient humidity is controlled below 30%), and then sealed in a vacuum sample bag for storage. Exemplarily, a 200-mesh screen is used for sieving.

[0042] Furthermore, the lithiation sintering comprises: mixing a high nickel precursor with a lithium source and then sintering in an oxygen-enriched and heat-insulated environment;

[0043] Optionally, the lithium source is LiOH·H2O micron-sized powder;

[0044] Exemplarily, heat preservation sintering is carried out in a tubular furnace; the sagger is made of corundum alumina.

[0045] Optionally, the heat preservation sintering is divided into two stages, the first stage is pre-sintering at 450-550°C for 4-6 hours, and the second stage is heat preservation at 700-800°C for 8-16 hours. The higher the Ni content, the lower the temperature during the second heat preservation sintering.

[0046] In a possible design, during the sintering process, the heating rate is 3-5°C / min; and the cooling rate is 3-5°C / min.

[0047] In a fourth aspect, the present invention provides a positive electrode material prepared according to the above method.

[0048] The technical solution of the present invention has the following advantages:

[0049] 1. The preparation method of the high-nickel precursor provided by the present invention comprises the following steps: step 1, preparing an Al-containing nickel-cobalt-manganese salt solution, an ammonia solution, an alkaline solution precipitant and an ammonia base solution; in the Al-containing nickel-cobalt-manganese salt solution, the Al / TM atomic ratio is 0.001-0.01, and TM is the sum of the amounts of nickel, cobalt and manganese atoms; step 2, adding the ammonia base solution into a reactor, and adjusting the pH of the ammonia base solution to 10.7-11.7, pumping the Al-containing nickel-cobalt-manganese salt solution, the ammonia solution and the alkaline solution precipitant into the reactor at the same time, stirring during the feeding process, and continuing to stir the reaction after the feeding is completed; step 3, solid-liquid separation, washing, and drying to obtain a high-nickel precursor.

[0050] The present invention utilizes Al element and other elements to co-precipitate and dope in situ. 3+ It migrates evenly into the interior of the precursor particles, thereby effectively avoiding the uneven distribution of elements caused by solid-phase sintering diffusion, thereby reducing the difference in lattice shrinkage / expansion during the material charging and discharging process caused by uneven doping, reducing the generation of particle microcracks, and improving the long-cycle stability of the material.

[0051] In order to improve the structural instability of high-nickel positive electrode materials and enhance the cyclability, the present invention introduces an appropriate amount of impurity Al into the nickel-cobalt-manganese metal salt solution. 3+, so that it is uniformly doped into the high-nickel spherical precursor during the nickel-cobalt-manganese co-precipitation process, and forms a high-nickel positive electrode material with uniform Al doping after lithium sintering. Al occupies the transition metal position in the material. Since the bond energy of Al-O (512kJ / mol) is higher than other TM-O bonds (Ni-O, 391.6kJ / mol; Co-O, 368kJ / mol; Mn-O, 402kJ / mol), the doping of Al stabilizes the bulk structure of the material and can inhibit the collapse of the layered structure during long cycles;

[0052] In the Al-containing nickel-cobalt-manganese salt solution of the present invention, the Al / TM atomic ratio is 0.001-0.01. By controlling the Al content, the influence of Al on the particle size and uniformity of the precursor is avoided, and the tap density of the precursor is increased, thereby ensuring the energy density of the high-nickel positive electrode material.

[0053] 2. The preparation method of the high nickel precursor provided by the present invention satisfies at least one of the following conditions: (1) During the feeding process, the feeding rate of the Al-containing nickel cobalt manganese salt solution is in the range of 0.5-2.0 mL / min; preferably 0.5-0.9 mL / min; (2) During the feeding process, the molar ratio of NH3 in the ammonia solution to TM in the Al-containing nickel cobalt manganese salt solution is 1.0-1.4; preferably 1.1-1.3 (3) In the Al-containing nickel cobalt manganese salt solution, the Al / TM atomic ratio is 0.005-0.01.

[0054] After aluminum is introduced into the liquid phase, the present invention controls the Al / TM atomic ratio and the NH3:TM ratio and adopts a lower feed rate of the Al-containing nickel-cobalt-manganese salt solution to obtain a product with better particle size consistency, that is, the particle size distribution of the precursor product is narrower. 3+ The solubility product constant K sp (~10 -33 ) is much lower than Ni 2+ 、Co 2+ , Mn 2+ , so Al 3+ The introduction of can increase the reaction supersaturation of the solution system, so that new agglomeration sites are continuously formed in the continuous feeding reaction, thereby inhibiting the continuous growth of primary grains and secondary particles on the original basis, and finally causing the precursor product particle size to shrink and the particle size distribution to be uneven. However, the present invention reduces the number of crystallization ions entering the reaction system per unit time by reducing the reaction feed rate (especially the feed rate range of the Al-containing nickel-cobalt-manganese salt solution is 0.5-0.9mL / min), which can reduce the reaction supersaturation, and to a certain extent can improve the reaction caused by Al. 3+ The introduction of adverse effects on the precursor morphology provides the necessary conditions for further improving the cycle life and energy density of the product.

[0055] 3. In the method for preparing the high-nickel precursor provided by the present invention, the feed rate of the Al-containing nickel-cobalt-manganese salt solution is controlled at 0.5-0.6 mL / min, which can obtain higher cycle performance.

[0056] 4. Pretreatment and sorting of waste lithium batteries often cannot completely separate Al foil from the positive electrode material, resulting in the nickel-cobalt-manganese metal solution obtained during the wet leaching process inevitably containing impurities Al. 3+ In the present invention, the impurity Al 3+ Within a certain concentration range, it does not need to be removed and can be directly used as a doping element to stably strengthen the structure of regenerated positive electrode materials, greatly reducing production costs and realizing the recycling of metal resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0058] Figure 1 This is the SEM image of the high nickel precursor sample of Example 1;

[0059] Figure 2 This is the SEM image of the high nickel precursor sample of Example 2;

[0060] Figure 3 This is the SEM image of the high nickel precursor sample of Example 3;

[0061] Figure 4 This is the SEM image of the high nickel precursor sample of Example 4;

[0062] Figure 5 This is the SEM image of the high nickel precursor sample of Comparative Example 3;

[0063] Figure 6 This is the SEM image of the high nickel precursor sample of Comparative Example 4;

[0064] Figure 7 The SEM images of the positive electrode material samples of (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, and (e) Comparative Example 3;

[0065] Figure 8 The discharge capacity decay curves of Example 1, Example 2, Example 3, Example 4, Comparative Example 1, and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0066] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0067] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0068] Example 1

[0069] This embodiment provides a method for preparing a positive electrode material, wherein the Al / TM atomic ratio is 0.005, comprising the following steps:

[0070] (1) Preparation of high nickel precursor:

[0071] Step 1. Prepare an Al-containing nickel-cobalt-manganese salt solution: accurately weigh soluble NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O salts according to the molar ratio of elements Ni:Co:Mn=0.9:0.05:0.05 and place them in a beaker, then add a certain amount of Al2(SO4)3·18H2O as an Al source, add a certain amount of hot pure water, stir and ultrasonically dissolve, and after cooling to room temperature, transfer to a volumetric flask and make up to volume to obtain an Al-containing nickel-cobalt-manganese salt solution, wherein the total metal concentration of nickel, cobalt and manganese is 2.0 mol / L, and the molar ratio of Al / TM is 0.005.

[0072] Prepare ammonia solution: Use a pipette to accurately measure a certain volume of concentrated ammonia solution into a volumetric flask, and add pure water to make up to a 4.8 mol / L ammonia solution.

[0073] Preparation of alkaline solution precipitant: weigh a certain amount of NaOH into a beaker, add cold pure water and dissolve it by ultrasonic in a cold water bath, then quickly transfer it to a volumetric flask and make up the volume to obtain an alkaline solution precipitant with a concentration of 8.0 mol / L.

[0074] Prepare ammonia base solution: Use a pipette to accurately measure a certain volume of concentrated ammonia water into a volumetric flask, add pure water to make up to the volume to obtain an ammonia base solution with a concentration of 1.2 mol / L. The volume of the ammonia base solution is 1.5 L.

[0075] Step 2: Before the experiment, perform a two-point calibration on the pH meter, add the ammonia base liquid into the reactor, pump circulating water into the reactor interlayer through a water bath to heat the temperature in the reactor, and at the same time, continuously introduce nitrogen into the reactor to exhaust the air (nitrogen is introduced below the liquid surface). After the temperature in the reactor rises to the reaction temperature of 50°C, adjust the pH of the ammonia base liquid to 11.5.

[0076] Preparation process: Use three feeding pumps to pump the three streams of liquid to the end of the feeding port and then stop (to ensure that the three streams of liquid enter the kettle at the same time), set the flow rates of the three feeding pumps, where pump 1 is used to pump the Al-containing nickel-cobalt-manganese salt solution, and its flow rate is controlled at 0.9mL / min, and the feeding time is about 24h; pumps 2 and 3 are used to pump ammonia solution and alkaline solution precipitant, respectively, and their flow rates are set according to the feed rate of the Al-containing nickel-cobalt-manganese salt solution of pump 1, which are 0.45mL / min and 0.7mL / min, respectively.

[0077] After the preparation process is completed, three feed pumps are turned on at the same time and the timing is started. During the reaction, the temperature in the kettle is controlled at 50°C, the pH of the feed liquid is maintained constant at 11.5, and the stirring speed is 600rpm; during the feeding process, the NH3:TM molar ratio must be ensured to be 1.2.

[0078] After the feeding is completed, the heating and stirring are continued for 12 hours at a stirring speed of 600 rpm. Then the precursor liquid is discharged and collected. The precursor is washed with alkaline water and pure water for 4 times and then vacuum filtered. The filter cake is transferred to a vacuum drying oven at 100°C and dried for 24 hours to obtain a high-nickel precursor. After grinding, the high-nickel precursor is placed in a sealed bag for drying and storage. The particle morphology is as follows Figure 1 As shown, the tap density is 1.93g / cm 3 .

[0079] (2) Lithiation and sintering of the high nickel precursor to prepare the positive electrode material:

[0080] The precursor and micron-sized LiOH·H2O were uniformly mixed and ground using ethanol as a dispersant (atomic ratio Li:TM=1.04), and then placed in a sagger and placed in a tube furnace for sintering with oxygen. The heating rate was 3°C / min. The calcination was divided into two stages. The first stage was kept at 500°C for 5h, and the second stage was kept at 700°C for 12h. Then, the precursor was taken out after cooling at 5°C / min and ground through a 200-mesh sieve to obtain Al-doped LiNi 0.9 Co 0.05 Mn 0.05 O2 high nickel cathode material (Al / TM=0.005), its particle morphology is as follows Figure 7 (a) shown.

[0081] Example 2

[0082] This embodiment is substantially the same as Embodiment 1, except that in this embodiment, the Al / TM atomic ratio is 0.01.

[0083] The morphology of the high nickel precursor particles prepared in this example is as follows Figure 2 As shown, the tap density is 1.87g / cm 3 .

[0084] The morphology of the positive electrode material prepared in this embodiment is as follows Figure 7 (b) as shown.

[0085] Example 3

[0086] This embodiment is basically the same as embodiment 2, except that the feed rate of the Al-containing nickel-cobalt-manganese salt solution in this embodiment is 0.5 mL / min (the feed time is correspondingly extended), and the feed rate of ammonia water is also reduced by a corresponding proportion (0.25 mL / min).

[0087] The morphologies of the high nickel precursor and the positive electrode material prepared in this embodiment are as follows: Figure 3 , Figure 7 (c) The tap density of the precursor is 1.94 g / cm 3 Compared with Example 2, the particle size of the sample in Example 3 is slightly increased, and the particle uniformity is significantly improved.

[0088] Example 4

[0089] This embodiment is basically the same as embodiment 3, except that the feed rate of the Al-containing nickel-cobalt-manganese salt solution in this embodiment is 0.7 mL / min, and the feed rate of ammonia water is also adjusted to a corresponding ratio (0.35 mL / min).

[0090] The morphologies of the high nickel precursor and the positive electrode material prepared in this embodiment are as follows: Figure 4 , Figure 7 (d) The tap density of the precursor is 1.90 g / cm 3 Compared with Example 3, the particle size of the high nickel precursor of Example 4 is slightly reduced, and the size uniformity is slightly reduced, but it is better than the sample of Example 2.

[0091] Comparative Example 1

[0092] This comparative example is substantially the same as Example 1, except that no Al is added for doping, ie, Al / TM=0.

[0093] Comparative Example 2

[0094] This comparative example is basically the same as Example 1, except that the nickel-cobalt-manganese salt solution in this comparative example does not contain aluminum, and a certain amount of Al(OH)3 is added during the precursor lithium sintering process for aluminum doping, wherein the atomic ratio Al:TM=0.005.

[0095] Comparative Example 3

[0096] This comparative example is substantially the same as Example 1, except that in this comparative example, the Al / TM atomic ratio is 0.02.

[0097] The morphologies of the high nickel precursor and positive electrode material prepared in this comparative example are as follows: Figure 5 , Figure 7 (e) The tap density of the precursor is 1.69 g / cm 3 Compared with Examples 1 and 2, the particle size of the sample in this comparative example is further reduced, the consistency of the particle morphology is poor, and the low tap density will lead to a decrease in the energy density of the material, which is difficult to meet the needs of commercial power lithium-ion batteries.

[0098] Comparative Example 4

[0099] This comparative example is basically the same as comparative example 3, except that the feed rate of the Al-containing nickel-cobalt-manganese salt solution in this comparative example is 0.5 mL / min, and the feed rate of ammonia water is also reduced by a corresponding proportion (~0.25 mL / min).

[0100] The morphology of the high nickel precursor particles prepared in this comparative example is as follows Figure 6 As shown, the tap density is 1.77g / cm 3 .

[0101] Test example

[0102] The positive electrode materials prepared in Examples 1-4 and Comparative Examples 1 and 2 were mixed with a binder PVDF and an acetylene black conductive agent in a mass ratio of 8:1:1 and ground. Then, an NMP solvent was added and stirred for 3 hours to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum foil and baked at 90°C for 12 hours to obtain a positive electrode sheet. The positive electrode sheet was cut into discs with a diameter of 12 mm by a punching machine. A metal lithium sheet was used as the negative electrode. The button cells were assembled in an argon glove box, and the battery charge and discharge performance test was carried out on a blue electric test system.

[0103] The test system is: at a current density of 1C (1C = 200mAh / g), a temperature of 25°C, a voltage range of 2.8-4.3V, and 100 charge and discharge cycles; the test results are shown in Table 1 and Figure 8 .

[0104] Table 1 Electrical properties of positive electrode materials

[0105]

[0106] It can be seen from Table 1 that the increase in the amount of Al doping in Example 2 compared to Example 1 promotes the material cycle performance.

[0107] Compared with Examples 1 and 2, the cycle performance of Comparative Example 1 is significantly deteriorated, which shows that doping an appropriate amount of Al into the high-nickel positive electrode material by this method can indeed improve the electrochemical stability of the material.

[0108] The capacity retention rate of Example 3 exceeds 100% because the material has not been fully activated at the beginning of the cycle, resulting in a low initial capacity. Compared with Example 2, the feed rate of Example 3 is slowed down, which reduces the Al 3+ The increased supersaturation brought about by the introduction causes the primary grains and secondary particles of the precursor to grow slowly, making the spherical particles more compact, reducing the contact area between the material and the electrolyte, inhibiting interfacial side reactions, and thus promoting the enhancement of the material's cycle performance.

[0109] The feed rate of Example 4 is between that of Examples 2 and 3, and the particle size and tap density of the prepared precursor are also between the two, so that the cyclic stability of the material is also between the two. Therefore, by controlling the feed rate, the particle morphology of the Al-doped precursor can be regulated, thereby affecting the corresponding electrochemical performance.

[0110] The Al content of doping in Comparative Example 3 is relatively high. Compared with Examples 1 and 2, the particle size of Comparative Example 3 is reduced and the morphology uniformity is deteriorated, resulting in a significant decrease in its tap density, which in turn affects the key practical parameters of the material such as the energy density.

[0111] Comparative Example 4 has a high Al content. After reducing the feed rate, the precursor particle size has recovered, and the tap density has increased compared with the product of Comparative Example 3, but it is still lower than that of Examples 1 and 2, and it is difficult to meet the tap density requirements of high-nickel materials. Therefore, the Al / TM atomic ratio in the Al-containing nickel-cobalt-manganese salt solution is limited to 0.001-0.01.

[0112] Although the cycle performance of the solid-phase Al-doped product of Comparative Example 2 is also improved, since the Al element may be unevenly doped in the bulk phase of the material, the Al content on the particle surface is high and the Al content inside is low, resulting in a lack of Al element stabilization effect on the material in the internal region of the particle. Therefore, the cycle performance improvement effect is not as obvious as in-situ co-precipitation Al doping.

[0113] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: The following steps are involved: (1) Preparation of high nickel precursor: Step 1, preparing an Al-containing nickel-cobalt-manganese salt solution: NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O are weighed and placed in a beaker according to the molar ratio of the elements Ni:Co:Mn=0.9:0.05:0.05, and then a certain amount of Al2(SO4)3·18H2O is added as an Al source, and a certain amount of hot pure water is added, stirred and ultrasonically dissolved, and after cooling to room temperature, the solution is transferred to a volumetric flask and fixed to volume to obtain an Al-containing nickel-cobalt-manganese salt solution, wherein the total metal concentration of nickel, cobalt and manganese is 2.0 mol / L, and the molar ratio of Al / TM is 0.01; TM is the sum of the moles of nickel, cobalt and manganese atoms; Prepare ammonia solution: Use a pipette to measure a certain volume of concentrated ammonia solution into a volumetric flask, add pure water to make up to 4.8 mol / L ammonia solution; Preparation of alkali solution precipitant: weigh a certain amount of NaOH into a beaker, add cold pure water and dissolve it by ultrasonic in a cold water bath, then transfer it to a volumetric flask to make up the volume to obtain an alkali solution precipitant with a concentration of 8.0 mol / L; Prepare ammonia base solution: use a pipette to measure a certain volume of concentrated ammonia water into a volumetric flask, add pure water to make up to a concentration of 1.2 mol / L ammonia base solution, the volume of the ammonia base solution is 1.5 L; Step 2: Before the experiment, perform a two-point calibration on the pH meter, add the ammonia water base solution into the reactor, pump circulating water into the reactor interlayer through a water bath to heat the reactor temperature, and at the same time, continue to introduce nitrogen into the reactor to exhaust the air. After the temperature in the reactor rises to the reaction temperature of 50°C, adjust the pH of the ammonia water base solution to 11.5; Preparation process: three feed pumps are used to pump the three streams of liquid to the end of the feed port and then stop, and the flow rates of the three feed pumps are set. Pump 1 is used to pump the Al-containing nickel-cobalt-manganese salt solution, and its flow rate is controlled at 0.5 mL / min. The feeding time is correspondingly extended on the basis of 24 hours; pumps 2 and 3 are used to pump ammonia solution and alkaline solution precipitant, respectively, and their flow rates are set according to the feed rate of the Al-containing nickel-cobalt-manganese salt solution of pump 1, which are 0.25 mL / min and 0.7 mL / min respectively; After the preparation process is completed, three feed pumps are turned on at the same time and the timing is started. During the reaction, the temperature in the reactor is controlled to be 50°C, the pH of the feed liquid is maintained constant at 11.5, and the stirring speed is 600rpm; during the feeding process, the NH3:TM molar ratio must be ensured to be 1.2; After the feeding is completed, the heating and stirring are continued for 12 hours at a stirring speed of 600 rpm; then the precursor liquid is discharged and collected, the precursor is washed with alkaline water and pure water for 4 times and then vacuum filtered, the filter cake is transferred to a vacuum drying oven at 100°C and dried for 24 hours to obtain a high-nickel precursor, and after grinding, the high-nickel precursor is placed in a sealed bag for drying and storage; (2) Lithiation and sintering of high nickel precursor to prepare positive electrode material: The high nickel precursor and micron-sized LiOH·H2O were uniformly mixed and ground with ethanol as a dispersant, and the atomic ratio of Li:TM was 1.

04. Then, the mixture was placed in a sagger and placed in a tube furnace for sintering with oxygen. The heating rate was 3℃ / min. The calcination was divided into two stages. The first stage was kept at 500℃ for 5h, and the second stage was kept at 700℃ for 12h. Then, the mixture was cooled at 5℃ / min and taken out. After grinding through a 200-mesh sieve, Al-doped LiNi 0.9 Co 0.05 Mn 0.05 O2 high nickel positive electrode material.

2. A positive electrode material, characterized in that: Prepared according to the preparation method of claim 1.

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