A medium-high nickel ternary positive electrode material powder and preparation method thereof, and a ternary positive electrode sheet

Abstract

The present application belongs to the field of lithium-ion batteries, and discloses a method for preparing a medium-high nickel ternary positive electrode material powder, wherein a nickel-cobalt-manganese precursor, a lithium source, and a dopant are mixed to obtain a mixed material; the mixed material is sintered, cooled, crushed, and sieved to obtain a sintered powder; the sintered powder is then mixed with a phosphorus source powder and a lanthanum source powder, calcined, cooled, crushed, and sieved to obtain a medium-high nickel ternary positive electrode material powder; the phosphorus source powder and the lanthanum source powder are low-temperature melt-coated to reduce residual lithium while improving the performance of the positive electrode material. In addition, a medium-high nickel ternary positive electrode material powder prepared by the above method and a medium-high nickel ternary positive electrode sheet prepared from the above medium-high nickel ternary positive electrode material powder are also disclosed.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular to a medium-high nickel ternary positive electrode material powder and a preparation method thereof, and a ternary positive electrode sheet. Background Art

[0002] Nickel cobalt manganese oxide positive electrode materials are widely used in power lithium batteries due to their high energy density, long cycle life and high voltage platform. Positive electrode materials account for about 40% of the cost of single cells, and their performance is directly related to the energy density, safety and life of the cells and systems. Surface coating is the main way to modify lithium cobalt manganese oxide positive electrode materials. A uniform and dense coating layer can greatly improve the comprehensive performance of lithium cobalt manganese oxide. The main coating methods currently include wet method, dry method, atomic deposition ALD, chemical deposition CVD, etc. Among them, the most widely used is the coating method of dry mixing + heat treatment with simple process and low cost. Although the dry coating process is simple and easy to industrialize, it cannot form a uniform and continuous coating layer, and its side reaction inhibition effect is not good. Under high voltage and high temperature conditions, it will inevitably lead to increased battery cycle attenuation or even a drop.

[0003] Prior art 1: Chinese patent application 201510365733.X discloses a lithium manganese phosphate-coated nickel cobalt manganese oxide positive electrode material and a preparation method thereof, comprising the steps of dissolving a complexing agent compound, a lithium source compound, a manganese source compound, and a phosphorus source compound in water in sequence to prepare a solution, and adjusting the pH value; then adding lithium nickel cobalt manganese oxide to the above-prepared solution, stirring the obtained solution to evaporate the solution until it becomes viscous, aging, drying, and crushing the solution to obtain a solid powder; and calcining the obtained solid powder, and naturally cooling the temperature to room temperature to obtain a lithium manganese phosphate-coated nickel cobalt manganese oxide positive electrode material.

[0004] In this case, the stable structure of lithium phosphate is used as a coating material to promote the conduction of lithium ions on the surface of lithium nickel cobalt manganese oxide and improve the rate performance. 4 PO in 4 3- It can effectively inhibit the dissolution of electrode materials in the electrolyte, prevent the hydrofluoric acid in the electrolyte from corroding the surface of active materials, and improve safety performance and cycle stability.

[0005] Prior art 2: Chinese patent application 201610462297.2 discloses a method for preparing lanthanum phosphate-coated lithium nickel cobalt manganese oxide, a positive electrode material for a lithium-ion battery. The method comprises adding a ternary precursor, a lithium salt, a lanthanum salt and a phosphate into a high-speed mixer and stirring at 500 to 2000 rpm for 1 to 4 hours; then heating the treated material in an oxygen-containing atmosphere at 750 to 1200°C for 5 to 20 hours and keeping the temperature for 4 to 10 hours. After cooling, lanthanum phosphate-coated lithium nickel cobalt manganese oxide, a positive electrode material for a lithium-ion battery, is obtained.

[0006] During the coating process, LaPO4 The P=O bond in the electrolyte can improve the chemical stability of the material and protect the electrode material from acid corrosion in the electrolyte. The combination of the composite material and lanthanum can improve the thermal stability. In addition, an amorphous LaPO can be formed on the surface of the nickel-cobalt-manganese-lithium ternary positive electrode material. 4 Compound, amorphous LaPO 4 Coating on the surface of nickel-cobalt-lithium manganese oxide ternary positive electrode material can effectively reduce the content of impurity lithium and effectively improve the cycle performance and electrochemical performance of lithium-ion batteries under high voltage.

[0007] The problem that this program needs to solve: How to propose a new preparation method to improve the electrochemical performance of medium- and high-nickel ternary positive electrode materials. Summary of the invention

[0008] The purpose of the present invention is to provide a medium-high nickel ternary positive electrode material powder and a preparation method thereof, by using a dopant to form a shallow coating structure on the ternary positive electrode material, and then adding a phosphorus source and a lanthanum source for calcination and coating, so that a uniform coating layer is formed on the surface of the positive electrode material, under the protection of the two coating structures, the electrochemical performance of the medium-high nickel ternary positive electrode material is improved.

[0009] To achieve the above object, the present application discloses a method for preparing medium-high nickel ternary positive electrode material powder, characterized in that the preparation method comprises the following steps:

[0010] Step 1: Mixing a nickel-cobalt-manganese precursor, a lithium source, and a dopant to obtain a mixed material;

[0011] Step 2: sintering, cooling, crushing and sieving the mixed material to obtain sintered powder;

[0012] Step 3: Mix the sintered powder with the phosphorus source powder and the lanthanum source powder, calcine, cool, crush and sieve to obtain medium-high nickel ternary positive electrode material powder;

[0013] The phosphorus source powder is selected from diammonium phosphate NH 4 H 2 PO 4 、diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 、Lithium dihydrogen phosphate LiH 2 PO 4 、Lithium hydrogen phosphate 2 HPO 4 , sodium dihydrogen phosphate NaH 2 PO 4 and disodium hydrogen phosphate Na 2 HPO 4 At least one of;

[0014] The lanthanum source powder is selected from lanthanum nitrate hexahydrate La (NO 3 ) 3 6H 2 O, Lanthanum nitrate La (NO 3 ) 3 , Lanthanum acetate C 6 H 9 O 6 La and lanthanum isopropoxide (i-PrO) 3 At least one of La.

[0015] Preferably, the mass of phosphorus element in the phosphorus source powder is 1500-5500 ppm of the mass of the sintered powder;

[0016] The mass of lanthanum element in the lanthanum source powder is 1500-5500ppm of the mass of the sintered powder.

[0017] Preferably, the structural formula of the high nickel cobalt manganese precursor in step 1 is Ni x Co y Mn z (OH) 2 , where 0.50≤x≤0.92,0.03≤y≤0.20,0.05≤z≤0.30 and x+y+z=1;

[0018] The lithium source is selected from lithium carbonate Li 2 CO 3 or hydrated lithium hydroxide LiOH·H 2 At least one of O;

[0019] Further preferably, the lithium source is lithium carbonate;

[0020] The Li / Me ratio of the nickel-cobalt-manganese precursor and the lithium source is 1.02 to 1.06.

[0021] Preferably, the dopant is selected from aluminum oxide Al 2 O 3 , lanthanum oxide La 2 O 3 、ZrO 2 、TiO 2 、Tungsten Oxide WO 3 、Niobium oxide Nb 2 O 5 At least one of the above, and the added amount of the dopant is 1000 to 5000 ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source.

[0022] Preferably, the sintering process in step 2 is: firstly increase the temperature to 450-720°C at a rate of 2-4°C / min, and keep warm for 1-5h; then increase the temperature to 720-950°C at a rate of 2-4°C / min, and keep warm for 8-12h.

[0023] Preferably, the mixing operation in step 3 is: putting the sintered powder, phosphorus source powder and lanthanum source powder into a planetary mill and mixing and stirring at a speed of 800 rpm for 1 hour, so that the phosphorus source powder and lanthanum source powder are coated on the surface of the sintered powder.

[0024] Preferably, it is characterized in that, in step 3, the calcination temperature is 300-600° C., and the calcination time is 6-12 min.

[0025] Preferably, the mesh size of the sieve in step 2 and step 3 is 300 meshes.

[0026] In addition, a medium-high nickel ternary positive electrode material powder is also disclosed, which is prepared by the above-mentioned preparation method of the medium-high nickel ternary positive electrode material powder.

[0027] In addition, a medium-high nickel ternary positive electrode sheet is also disclosed, which is prepared by coating the above-mentioned medium-high nickel ternary positive electrode material powder on aluminum foil.

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a medium-high nickel ternary positive electrode material powder and a preparation method thereof, and a medium-high nickel ternary positive electrode sheet, wherein after the dopant added to the medium-high nickel ternary positive electrode material is mixed and sintered, part of the doping element enters the shallow surface structure of the material at high temperature, inhibits the structural phase change of the material under high voltage, slows down the cracking and pulverization of the material, and preliminarily improves the cycle performance of the material, and the other part can form a lithium-containing substance Li on the surface of primary particles inside the ternary positive electrode material and secondary particles formed by the primary particles with the lithium source in the sintering process. x M y O z , M is the metal element in the dopant, which provides a lithium source for the subsequent coating layer. At this time, the addition of lanthanum and phosphorus molten salts, due to La 3+ and PO 4 3- It has strong binding ability, which can combine the lithium-containing substances between the secondary particles and the primary particles and the residual lithium on the surface of the ternary positive electrode material, and form a solid Li on the surface of the primary and secondary particles. 3 La(PO 4 ) 2 The coating layer protects the primary and secondary particles of the material while reducing the amount of residual lithium, thereby improving the electrochemical performance of the ternary positive electrode material. DETAILED DESCRIPTION

[0030] In the description of the present invention, it should be noted that, if the specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0031] Example 1

[0032] Step 1: Ni-Co-Mn precursor Ni 0.6 Co 0.1 Mn 0.3 (OH) 2 , lithium carbonate is first mixed at a ratio of Li / Me=1.04, and then lanthanum oxide having a mass of 3000ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source is added and mixed to obtain a mixed material;

[0033] Step 2: The mixed material is first heated to 580°C at a rate of 3°C / min and kept warm for 3 hours; then heated to 830°C at a rate of 3°C / min and kept warm for 10 hours to complete sintering, cooled to room temperature, crushed, and sieved with a 300-mesh sieve to obtain sintered powder;

[0034] Step 3: Place the sintered powder, lithium dihydrogen phosphate powder with a phosphorus content of 3500ppm by mass of the sintered powder, and lanthanum nitrate powder with a lanthanum content of 3500ppm by mass of the sintered powder into a planetary mill and stir at a speed of 800rpm for 1h to coat the lithium dihydrogen phosphate powder and lanthanum nitrate powder on the surface of the sintered powder. Then calcine at 450°C for 9h, cool, crush, and sieve through a 300-mesh sieve to obtain medium-high nickel ternary positive electrode material powder.

[0035] Example 2

[0036] Step 1: Ni-Co-Mn precursor Ni 0.6 Co 0.1 Mn 0.3 (OH) 2 , lithium carbonate is first mixed at a ratio of Li / Me=1.02, and then lanthanum oxide having a mass of 3000ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source is added and mixed to obtain a mixed material;

[0037] Step 2: The mixed material is first heated to 450°C at a rate of 2°C / min and kept warm for 5 hours; then heated to 720°C at a rate of 2°C / min and kept warm for 12 hours to complete sintering, cooled to room temperature, crushed, and sieved with a 300-mesh sieve to obtain sintered powder;

[0038] Step 3: Place the sintered powder, lithium dihydrogen phosphate powder with a phosphorus content of 3500ppm by mass of the sintered powder, and lanthanum nitrate powder with a lanthanum content of 3500ppm by mass of the sintered powder into a planetary mill and stir at a speed of 800rpm for 1h to coat the lithium dihydrogen phosphate powder and lanthanum nitrate powder on the surface of the sintered powder. Then calcine at 300°C for 12h, cool, crush, and sieve through a 300-mesh sieve to obtain medium-high nickel ternary positive electrode material powder.

[0039] Example 3

[0040] Step 1: Ni-Co-Mn precursor Ni 0.6 Co 0.1 Mn 0.3 (OH) 2 , lithium carbonate is first mixed at a ratio of Li / Me=1.06, and then lanthanum oxide having a mass of 3000ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source is added and mixed to obtain a mixed material;

[0041] Step 2: The mixed material was first heated to 720°C at a rate of 4°C / min and kept warm for 1 hour; then heated to 950°C at a rate of 4°C / min and kept warm for 8 hours to complete sintering, cooled to room temperature, crushed, and sieved with a 300-mesh sieve to obtain sintered powder;

[0042] Step 3: Place the sintered powder, lithium dihydrogen phosphate powder with a phosphorus content of 3500ppm by mass of the sintered powder, and lanthanum nitrate powder with a lanthanum content of 3500ppm by mass of the sintered powder into a planetary mill and stir at a speed of 800rpm for 1h to coat the lithium dihydrogen phosphate powder and lanthanum nitrate powder on the surface of the sintered powder. Then calcine at 600℃ for 6h, cool, crush, and sieve through a 300-mesh sieve to obtain medium-high nickel ternary positive electrode material powder.

[0043] Example 4

[0044] It is basically the same as Example 1, except that the mass of phosphorus element in the phosphorus source powder is 1500ppm of the mass of the sintered powder, and the mass of lanthanum element in the lanthanum source powder is 1500ppm of the mass of the sintered powder.

[0045] Example 5

[0046] It is basically the same as Example 1, except that the mass of phosphorus element in the phosphorus source powder is 5500ppm of the mass of the sintered powder, and the mass of lanthanum element in the lanthanum source powder is 5500ppm of the mass of the sintered powder.

[0047] Example 6

[0048] It is basically the same as Example 1, except that the mass of phosphorus element in the phosphorus source powder is 1000ppm of the mass of the sintered powder, and the mass of lanthanum element in the lanthanum source powder is 1000ppm of the mass of the sintered powder.

[0049] Example 7

[0050] It is basically the same as Example 1, except that the mass of phosphorus element in the phosphorus source powder is 6000ppm of the mass of the sintered powder, and the mass of lanthanum element in the lanthanum source powder is 6000ppm of the mass of the sintered powder.

[0051] Example 8

[0052] The method is basically the same as Example 1, except that the phosphorus source is sodium dihydrogen phosphate.

[0053] Example 9

[0054] The method is basically the same as Example 1, except that the lanthanum source is lanthanum nitrate hexahydrate.

[0055] Example 10

[0056] The method is basically the same as Example 1, except that the mass of lanthanum oxide in step 1 is 1000ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source.

[0057] Embodiment 11

[0058] The method is basically the same as Example 1, except that the mass of lanthanum oxide in step 1 is 5000ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source.

[0059] Example 12

[0060] The method is basically the same as Example 1, except that the mass of lanthanum oxide in step 1 is 500ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source.

[0061] Example 13

[0062] The method is basically the same as Example 1, except that the mass of lanthanum oxide in step 1 is 6000ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source.

[0063] Comparative Example 1

[0064] The method is basically the same as Example 1, except that in step 3, no phosphorus source and lanthanum source are used for coating.

[0065] Comparative Example 2

[0066] The method is basically the same as Example 1, except that in step 3, only lithium dihydrogen phosphate having a phosphorus mass of 3500 ppm based on the mass of the sintered powder is added for calcination.

[0067] Comparative Example 3

[0068] The method is basically the same as Example 1, except that in step 3, only lanthanum nitrate having a mass of 3500 ppm of the lanthanum element based on the mass of the sintered powder is added for calcination.

[0069] Comparative Example 4

[0070] The method is basically the same as Example 1, except that lithium carbonate is used instead of lithium dihydrogen phosphate in step 3.

[0071] Comparative Example 5

[0072] The process is substantially the same as Example 1, except that yttrium nitrate is used instead of the lanthanum nitrate in step 3.

[0073] Comparative Example 6

[0074] The method is basically the same as Example 1, except that lanthanum oxide is not added in step 1.

[0075] Comparative Example 7

[0076] The same as Example 1, except that the nickel-cobalt-manganese precursor in step 1 is Ni 0.4 Co 0.2 Mn 0.4 (OH) 2。

[0077] Comparative Example 8

[0078] It is basically the same as Comparative Example 7, except that in step 3, no phosphorus source and lanthanum source are used for coating.

[0079] Performance Test:

[0080] Titration test for residual lithium

[0081] Weigh 10 g of sample (accurate to 0.01 g) into a beaker and add 100 mL of distilled water.

[0082] Place the clean magnetic rotor in a beaker, seal it with a sealing film, and place it on a magnetic stirrer and stir at a rate of 500 r / min for 15 min.

[0083] After standing, the sample solution was filtered using a vacuum filtration device.

[0084] Use a pipette of corresponding specifications to accurately transfer 1mL to 10mL of the filtrate to be tested into a 100mL beaker, add 50mL of distilled water, and place it on the potentiometric titrator.

[0085] Turn on the automatic potentiometric titrator, adjust the magnetic stirring rate of the automatic potentiometric titrator to prevent bubbles from being generated in the test solution, and titrate with pH value as the ordinate and the volume of hydrochloric acid titration solution consumed as the abscissa. Record the volumes V1 and V2 of the hydrochloric acid titration solution consumed corresponding to the electrode potential jump points EP1 and EP2.

[0086] The results were calculated according to formula 1 and formula 2 to calculate the Li content in the sample. 2 CO 3 , the content of lithium hydroxide, and then calculate the content of free lithium in the sample according to formula 3, formula 4, and formula 5:

[0087] Formula 1: ;

[0088] Formula 2: ;

[0089] Formula 3: ;

[0090] Formula 4: ;

[0091] Formula 5: ;

[0092] Where:

[0093] W X ——Li in the sample 2 CO 3 The mass fraction, in parts per million (ppm);

[0094] W Y ——The mass fraction of lithium hydroxide in the sample, in parts per million (ppm);

[0095] w X ——Li in the sample 2 CO 3 The mass fraction of lithium in the atmosphere, expressed in parts per million (ppm);

[0096] w Y ——The mass fraction of lithium in lithium hydroxide in the sample, in parts per million (ppm);

[0097] w Z ——The total content of free lithium in the sample, in parts per million (ppm);

[0098] V a ——The volume of distilled water used when stirring and leaching the sample, in milliliters (mL);

[0099] V b ——The volume of distilled water used for stirring and leaching the sample after filtration, in milliliters (mL);

[0100] V 1 ——The volume of hydrochloric acid titration solution consumed when titrating to the potential jump point EP1, in milliliters mL;

[0101] V 2 ——The volume of hydrochloric acid titration solution consumed when titrating to the potential jump point EP2, in milliliters mL;

[0102] m ——the mass of the sample weighed, in grams;

[0103] C —— molar concentration of hydrochloric acid titration solution, in moles per liter mol / L;

[0104] 73.88——Li 2 CO 3 The molar mass of a substance is expressed in grams per mole (g / mol);

[0105] 23.94 – The molar mass of lithium hydroxide in grams per mole (g / mol).

[0106] 0.188——Li 2 CO 3 The mass ratio of lithium in

[0107] 0.290 – The mass ratio of lithium in lithium hydroxide.

[0108] Discharge capacity: After the materials are assembled into R2016 button cells, they are tested on the Xinwei battery test cabinet. The thermostat is set to a constant temperature of 25°C, the charge cut-off voltage is set to 4.45V, and the discharge voltage is set to 3.0V. After completing the charge and discharge at a rate of 0.1C, the first-cycle discharge capacity of 0.1C can be obtained.

[0109] Hundred-cycle retention rate: After the materials are assembled into R2016 button batteries, they are tested on the Xinwei battery testing integrated cabinet. The constant temperature box is set to 25°C, the charge cut-off voltage is set to 4.45V, and the discharge cut-off voltage is set to 3.0V. First, set the rate of 0.1C for activation, and then set 1C to cycle for 100 weeks to get the 100-cycle retention rate.

[0110] The performance test is shown in Table 1:

[0111] Table 1

[0112] Group Residual lithium content ppm 0.1C first cycle discharge capacity mAh / g 100-cycle retention rate% Example 1 1162 196.60 95.95 Example 2 1205 195.10 94.12 Example 3 1248 195.21 94.59 Example 4 1583 194.64 93.91 Example 5 1088 194.29 94.22 Example 6 3309 190.37 85.31 Example 7 997 190.21 88.45 Example 8 1335 194.11 93.18 Example 9 1348 193.62 93.53 Example 10 1833 192.78 91.31 Embodiment 11 1797 192.35 90.73 Example 12 2910 189.48 81.42 Example 13 2886 189.51 83.15 Comparative Example 1 4602 188.60 50.74 Comparative Example 2 3688 190.12 67.15 Comparative Example 3 4071 189.33 68.93 Comparative Example 4 2649 190.14 82.34 Comparative Example 5 3136 189.82 80.95 Comparative Example 6 3851 189.35 66.37 Comparative Example 7 2984 190.26 64.28 Comparative Example 8 4354 187.66 51.78

[0113] Conclusion analysis:

[0114] 1. Through Example 1 and Examples 4-7, the performance test results are shown in Table 2:

[0115] Table 2

[0116] Group Residual lithium content ppm 0.1C first cycle discharge capacity mAh / g 100-cycle retention rate% Example 1 1162 196.60 95.95 Example 4 1583 194.64 93.91 Example 5 1088 194.29 94.22 Example 6 3309 190.37 85.31 Example 7 997 190.21 88.45

[0117] Combined with the data in Table 2, it can be seen that when the addition amount of phosphorus source and lanthanum source is 3500ppm of the mass of the sintered powder, the performance of the obtained ternary positive electrode material is the best. As the addition amount increases, more free lithium will be combined during the coating process, so the residual lithium amount will continue to decrease. However, due to excessive phosphorus source and lanthanum source coating, the formed coating layer is too thick, which will also affect the migration of lithium ions in the positive electrode material, resulting in performance degradation; and as the addition amount decreases, not only can the purpose of reducing residual lithium not be achieved, but also imperfect coating will result in decreased performance of the positive electrode material.

[0118] 2. Through Example 1 and Example 8, Comparative Example 4, the performance test results are shown in Table 3:

[0119] Table 3

[0120] Group Residual lithium content ppm 0.1C first cycle discharge capacity mAh / g 100-cycle retention rate% Example 1 1162 196.60 95.95 Example 8 1335 194.11 93.18 Example 9 1348 193.62 93.53 Comparative Example 4 2649 190.14 82.34 Comparative Example 5 3136 189.82 80.95

[0121] It can be seen from the data in Table 3 that when lithium carbonate or yttrium nitrate is used to replace the lithium dihydrogen phosphate or lanthanum nitrate in Example 1, respectively, carbonate or yttrium ions cannot achieve the binding effect of acid radicals and lanthanum ions, and the carbonate structure is unstable and easily decomposed under high temperature and acidic environment. At the same time, since phosphate has a stronger coordination ability than carbonate, it can form a stable coating layer after combining with lanthanum element; and when replaced with yttrium ions having a smaller ionic radius than lanthanum ions, since the electronegativity of yttrium element is higher than that of lanthanum element, the binding ability with phosphate is stronger, so the coating formed by the combination of yttrium ions and phosphate should be more stable than the coating formed by lanthanum ions and phosphate, and the performance is better. However, it can be seen from the data of Comparative Example 5 that the performance improvement effect of yttrium nitrate is worse than that of lanthanum nitrate, which is an unexpected result.

[0122] 3. Through Example 1 and Examples 10-13, the performance test results are shown in Table 4:

[0123] Table 4

[0124] Group Residual lithium content ppm 0.1C first cycle discharge capacity mAh / g 100-cycle retention rate% Example 1 1162 196.60 95.95 Example 10 1833 192.78 91.31 Embodiment 11 1797 192.35 90.73 Example 12 2910 189.48 81.42 Example 13 2886 189.51 83.15

[0125] Combined with the data in Table 4, it can be seen that when the dopant content is lower than 1000ppm, the excessively low doping element content cannot effectively stabilize the bulk structure of the material, and cannot form sufficient LiLaO on the surface of the primary and secondary particles of the material. 2 layer, which affects the subsequent coating effect, so the improvement of material performance is limited.

[0126] When the dopant content is higher than 5000ppm, a portion of the doping elements will be doped into the superficial structure of the material and form a preliminary LiLaO 2 There is still a large amount of residual oxide in the coating layer remaining on the surface of the material, and the residual oxide is an electrochemically inert substance, which affects the performance of the material.

[0127] 4. The performance test results of Example 1, Comparative Examples 1-3 and Comparative Example 6 are shown in Table 5:

[0128] Table 5

[0129] Group Residual lithium content ppm 0.1C first cycle discharge capacity mAh / g 100-cycle retention rate% Example 1 1162 196.60 95.95 Comparative Example 1 4602 188.60 50.74 Comparative Example 2 3688 190.12 67.15 Comparative Example 3 4071 189.33 68.93 Comparative Example 6 3851 189.35 66.37

[0130] Combined with the data in Table 5, it can be seen that compared with Comparative Example 1 in which no phosphorus source and lanthanum source are used for coating, when lanthanum source and phosphorus source are used alone or lanthanum oxide is not added, the improvement in the performance of the positive electrode material is not obvious; on the other hand, in Example 1, when the lanthanum source, phosphorus source and lanthanum oxide are used together, the lanthanum oxide lithium layer formed by lanthanum oxide provides a basis for the coating of the phosphorus source and lanthanum source, making them more firmly coated on the core of the positive electrode material, and the combination of the two can also improve the absorption of free lithium and further reduce the residual lithium content.

[0131] 5. The performance test results of Example 1, Comparative Example 1, and Comparative Examples 7-8 are shown in Table 6:

[0132] Table 6

[0133] Group Residual lithium content ppm 0.1C first cycle discharge capacity mAh / g 100-cycle retention rate% Example 1 1162 196.60 95.95 Comparative Example 1 4602 188.60 50.74 Comparative Example 7 2984 190.26 64.28 Comparative Example 8 4354 187.66 51.78

[0134] Combined with the data in Table 6, it can be seen that when the same doping and coating process in Example 1 is used on the low-nickel ternary positive electrode material, there is a significant difference in the performance improvement effect of the positive electrode material. It can be seen that the doping and coating process of the present application is not suitable for low-nickel ternary positive electrode materials.

[0135] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A method for preparing medium-high nickel ternary positive electrode material powder, characterized in that: The preparation method comprises the following steps: Step 1: Mixing a nickel-cobalt-manganese precursor, a lithium source, and a dopant to obtain a mixed material; Step 2: The mixed material is first heated to 450-720°C at a rate of 2-4°C / min, and kept warm for 1-5 hours; then heated to 720-950°C at a rate of 2-4°C / min, and kept warm for 8-12 hours, and then cooled, crushed, and sieved in sequence to obtain sintered powder; Step 3: Mix the sintered powder with the phosphorus source powder and the lanthanum source powder, calcine at 300-600° C. for 6-12 hours, cool, crush, and sieve to obtain a medium-high nickel ternary positive electrode material powder; The phosphorus source powder is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, dilithium hydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate; The lanthanum source powder is selected from at least one of lanthanum nitrate hexahydrate and lanthanum nitrate; The mass of phosphorus element in the phosphorus source powder is 1500-5500 ppm of the mass of the sintered powder; The mass of lanthanum element in the lanthanum source powder is 1500-5500 ppm of the mass of the sintered powder; The dopant is lanthanum oxide La2O3, and the amount of lanthanum oxide added is 3000ppm of the total mass of the nickel-cobalt-manganese precursor and the lithium source; The structural formula of the high nickel cobalt manganese precursor in step 1 is Ni 0.6 Co 0.1 Mn 0.3 (OH)2; The lithium source is selected from at least one of lithium carbonate Li2CO3 or hydrated lithium hydroxide LiOH·H2O; The Li / Me ratio of Li in the lithium source to Me in the nickel-cobalt-manganese precursor is 1.02 to 1.

06.

2. The method for preparing the medium-high nickel ternary positive electrode material powder according to claim 1, characterized in that: The mesh number of the sieve in step 2 and step 3 is 300 meshes.

3. A medium-high nickel ternary positive electrode material powder, characterized in that: The powder is prepared by the method for preparing the medium-high nickel ternary positive electrode material powder according to claim 1 or 2.

4. A ternary positive electrode sheet, characterized in that: The method is prepared by coating the medium-high nickel ternary positive electrode material powder as claimed in claim 3 on aluminum foil.