Coated ternary cathode material, method for preparing the same, and lithium ion battery

Abstract

The present disclosure provides a coated ternary positive electrode material, its preparation method and a lithium ion battery. The coated ternary positive electrode material includes an aluminum, zirconium and fluorine co-doped ternary positive electrode active material inner core and a coating layer coated on the inner core, the coating layer including zirconium hydrogen phosphate and a boron compound. The coated ternary positive electrode material effectively solves the problem of gas generation and improves safety performance, and has high discharge capacity, high initial efficiency, good cycle stability and safety performance.

Description

Technical Field

[0001] The present disclosure relates to the technical field of new energy, and relates to a coated ternary cathode material, a preparation method thereof, and a lithium-ion battery.

Background Art

[0002] High-nickel ternary cathode materials have attracted attention in the new energy industry in recent years because of their high specific capacity and low raw material costs. Although studies have found that this material generally has some defects, many companies still recommend high-nickel ternary batteries at present. One of the serious problems is that a large amount of gas is generated after manufacturing the battery cells, which affects the safety and cycle service life of the battery. One of the main causes of gas generation is that the reaction activity of the high-nickel cathode material is strong, and oxygen is released during the charge and discharge process or the high-nickel cathode material directly contacts the electrolyte, resulting in instability during the charging process and chemical reactions occurring to generate gas. As the number of cycles increases, cracks occur and gas generation begins to increase significantly.

[0003] To improve the problem of gas generation in batteries, many studies have focused on doping and coating of cathode materials. Doping improves the safety and stability of the material itself, and the stable coating layer reduces the contact reaction between the material and the electrolyte and the dissolution effect of the metal, thereby reducing the gas generation problem of the battery cells. In recent years, various research results on coating have provided many valuable coating methods in this field, and many excellent doping and coating methods have emerged. Conventional high-nickel materials generally utilize doping with zirconium, titanium, aluminum, tungsten, magnesium, scandium, vanadium, calcium, strontium, barium, gallium, indium, etc. to improve the structural stability and conductivity of the material to a certain extent, and by coating the oxides of the above metals, most of the isolation between the material and the electrolyte is realized, and the gas generation amount is significantly reduced. However, there are still certain deficiencies in the conventional coating methods, and the problem of high gas generation in high-nickel materials still exists.

Summary of the Invention

Means for Solving the Problem

[0004] In one embodiment, the present disclosure provides a coated ternary cathode material including a ternary cathode active material internal core co-doped with aluminum, zirconium, and fluorine and a coating layer coated on the surface of the internal core, wherein the coating layer includes zirconium hydrogen phosphate and a boron compound.

[0005] In the coated ternary cathode material according to one embodiment of the present disclosure, by co-doping the ternary cathode material with aluminum, zirconium, and fluorine and synergistically coating with zirconium hydrogen phosphate and a boron compound, the problem of gas generation in the cathode material can be effectively solved, the safety performance can be improved, and furthermore, good conductivity and structural stability of the material can be ensured, and the normal operation of the electrochemical performance can be ensured, having a high discharge capacity, a high initial efficiency, good cycle stability, and safety performance. The technical principle is as follows. First, by doping zirconium and aluminum into the crystal lattice and introducing fluoride ions instead of doping at the oxygen position, the stability of the ternary cathode material (for example, a high-nickel ternary cathode material) itself can be improved, thereby reducing the gas generation amount. Second, due to the synergistic effect of zirconium hydrogen phosphate and the boron compound as the coating, not only the stabilizing effect of the coating layer is ensured, but also the conductivity of the coating layer is improved by zirconium hydrogen phosphate, and the decrease in the electrochemical performance of the material due to the decrease in the conductivity of the material caused by the introduction of boron is avoided. Third, due to the very small volume change of zirconium hydrogen phosphate and the high stability of phosphate ions, the introduction of the coating layer can reduce the degree of damage of the coating layer after multiple cycles and the reaction between the coating layer and the electrolyte, and also play a role in improving the reduction of gas generation.

[0006] In one embodiment, the boron compound is obtained by sintering and converting a boron source as a raw material, and the boron source contains at least one of boric acid and boron oxide. The boron source may be, for example, a single type of boric acid, or a single type of boron oxide, or a mixture of boric acid and boron oxide.

[0007] In one embodiment, a mixture of boric acid and boron oxide is used as the boron source.

[0008] In one embodiment according to the present disclosure, by sintering the boron source to convert it into a boron compound and blending it with zirconium hydrogen phosphate, good coating stability and uniformity of the coating layer can be ensured, good conductivity can be obtained, and good electrochemical performance of the positive electrode material can be ensured.

[0009] In one embodiment, based on the total mass of the internal core, the total mass concentration of the doping elements aluminum, zirconium, and fluorine is 500 ppm to 5000 ppm, for example, 500 ppm, 600 ppm, 650 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1250 ppm, 1500 ppm, 1600 ppm, 1800 ppm, 2000 ppm, 2300 ppm, 2600 ppm, 2800 ppm, 3000 ppm, 3500 ppm, 3700 ppm, 4000 ppm, 4200 ppm, 4500 ppm or 5000 ppm, etc., and the mass concentration of the coating layer is 500 ppm to 5000 ppm, for example, 500 ppm, 600 ppm, 650 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1250 ppm, 1500 ppm, 1600 ppm, 1800 ppm, 2000 ppm, 2300 ppm, 2600 ppm, 2800 ppm, 3000 ppm, 3500 ppm, 3700 ppm, 4000 ppm, 4200 ppm, 4500 ppm or 5000 ppm, etc. The mass ratio of the zirconium hydrogen phosphate in the coating layer is 30% to 85%, for example, 30%, 32.5%, 35%, 40%, 45%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 70%, 72.5%, 75%, 80% or 85%, etc.

[0010] In one embodiment, the present disclosure mixing a dopant containing elements of aluminum, zirconium and fluorine, a ternary cathode material precursor and a lithium source, and performing primary sintering in an oxygen-containing atmosphere to obtain a ternary cathode active material internal core co-doped with aluminum, zirconium and fluorine in step (1); and step (2) of mixing the internal core with an additive containing zirconium hydrogen phosphate and a boron source and performing secondary sintering to obtain the coated ternary cathode material, to provide a method for preparing the coated ternary cathode material.

[0011] In one embodiment according to the present disclosure, the volume content of oxygen in the oxygen-containing atmosphere in step (1) exceeds 80%, for example, 82%, 85%, 90%, 95%, 98%, 99% or 100%, etc.

[0012] In one embodiment according to the present disclosure, the final coating effect can be adjusted and controlled by adjusting the usage amount of the additive.

[0013] In one embodiment according to the present disclosure, a dopant containing elements of aluminum, zirconium and fluorine (for example, a mixture of aluminum fluoride and zirconium fluoride) is used for doping in the lithium compounding process. In the doping process, not only metal zirconium and aluminum are doped into the crystal lattice, but also by introducing fluorine ions instead of doping at the oxygen position, the stability of the ternary material (for example, a high-nickel ternary material) itself is further improved, so that the gas generation amount can be reduced. The coating process is carried out synergistically by introducing zirconium hydrogen phosphate and a boron source, which not only ensures the stabilizing effect of the coating layer, but also improves the conductivity of the coating layer by zirconium hydrogen phosphate, and avoids the decrease in the conductivity and electrochemical performance of the material due to the introduction of boron. Furthermore, due to the very small volume change of zirconium hydrogen phosphate and the high stability of phosphate ions, after coating, the degree of damage caused by multiple cycles of the coating layer can be reduced, and the reaction between the coating layer and the electrolyte can be decreased. The above doping and coating further improve the problem of gas generation of the material.

[0014] The positive electrode material prepared by the method according to an embodiment of the present disclosure can achieve doping and coating with good doping and coating effects and uniformity, effectively solve the problem of gas generation of the positive electrode material, improve the safety performance, and further ensure good conductivity and structural stability of the material, ensure the normal operation of the electrochemical performance, and ensure that there is no abnormality in the detection of electrical performance.

[0015] The method according to an embodiment of the present disclosure is feasible, has good uniformity, is easy to operate, and has the advantage of good coating effect after firing, and can effectively reduce gas generation.

[0016] The specific types and preparation methods of the ternary positive electrode material precursor in the present disclosure are not limited.

[0017] The type of the ternary positive electrode material precursor may be, for example, Ni x Co y Mn z (OH)2, where 0.8 ≦ x < 1, 0 < y < 0.2, 0 < z < 0.2, and x + y + z = 1.

[0018] The preparation method of the ternary positive electrode material precursor may refer to the preparation methods disclosed in the related art, or may be carried out according to the following scheme, for example. (I) Prepare a mixed solution of soluble nickel salt, cobalt salt, and manganese salt with a concentration of 0.5 mol / L to 1.0 mol / L. The concentration mentioned here is the total metal cation concentration in the mixed solution. Prepare a sodium hydroxide solution with a concentration of 5 mol / L to 10 mol / L. Prepare an aqueous ammonia solution with a concentration of 8 mol / L to 12 mol / L. There is no priority order in the preparation of the above various solutions. (II) Add the sodium hydroxide solution and the aqueous ammonia solution to the mixed solution of the soluble nickel salt, cobalt salt, and manganese salt simultaneously, react to synthesize the nickel-cobalt-manganese ternary positive electrode material precursor, and after the synthesis is completed, wash, dehydrate, and dry to obtain the finished product of the ternary positive electrode material precursor.

[0019] In one embodiment, the dopant in step (1) is a mixture of aluminum fluoride and zirconium fluoride, and the mass ratio of the aluminum fluoride to the zirconium fluoride is 1:(0.5 - 5), for example, 1:0.5, 1:1, 1:1.2, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, etc. The temperature of the first sintering in step (1) is 750°C - 980°C, for example, 750°C, 775°C, 800°C, 820°C, 840°C, 850°C, 880°C, 900°C, 925°C, 950°C or 980°C, etc., and the time of the first sintering is 10h - 20h, for example, 10h, 12h, 13h, 15h, 16h, 18h, 19h or 20h, etc.

[0020] In one embodiment, the usage amount of the lithium source is moderately excessive.

[0021]

[0022] In one embodiment, the boron source in step (2) adopts boric acid, the mixing in step (2) is carried out by a wet method, the mixing time is 15min - 45min, the addition amount of zirconium hydrogen phosphate accounts for 0.05% - 0.5% of the internal core mass, and the addition amount of boric acid accounts for 0.05% - 0.3% of the internal core mass.

[0023] In one embodiment, the boron source in step (2) is a mixture of boric acid and boron oxide in any ratio.

[0024] By using a mixture of boric acid and boron oxide as the boron source, the temperature of the secondary sintering can be controlled, so that the coating temperature will not be too high to cause energy waste and lithium precipitation reaction, and the surface of the material will not be overly corroded to form defects when using pure boric acid, thus improving.

[0025] In one embodiment, the moisture content of the material obtained after mixing in step (2) is less than 0.05 wt%, for example, 0.04 wt%, 0.03 wt% or 0.02 wt%, etc.

[0026] In one embodiment, in step (2), during the mixing process, it may be dried, for example, with a Coulter Dryer at 150°C to 200°C (for example, 150°C, 155°C, 165°C, 180°C, 190°C or 200°C, etc.) for 2 hours to 6 hours (for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or 6h, etc.) for initial drying, and dried until the predetermined moisture content is reached while sufficiently mixing the additive and the cathode material to dehydrate.

[0027] In one embodiment, the atmosphere of the secondary sintering in step (2) is an oxygen-containing atmosphere, the temperature of the secondary sintering is 300°C to 700°C, for example, 300°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or 700°C, etc., and the time of the secondary sintering is 2h to 15h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 10h, 12h or 15h, etc. Here, the volume content of oxygen in the oxygen-containing atmosphere exceeds 80%, for example, 82%, 85%, 90%, 95%, 98%, 99% or 100%, etc.

[0028] In one embodiment, the method further includes a washing and dehydration step after step (1) and before step (2). The washing and dehydration involves mixing the ternary cathode active material inner core co-doped with the above-mentioned aluminum, zirconium and fluorine with water, with a liquid-solid ratio of 1:1 to 5:1 (for example, 1:1, 2:1, 3:1, 3.5:1, 4:1 or 5:1, etc.), stirring for 2 minutes to 30 minutes (for example, 2min, 5min, 10min, 15min, 20min, 25min or 30min, etc.) for washing, and then introducing nitrogen gas to dehydrate until the moisture content is less than 5 wt%, for example, 4.5 wt%, 4 wt%, 3 wt%, 2.5 wt%, 2 wt%, 1 wt% or 0.5 wt%, etc.

[0029] In one embodiment, nitrogen gas is introduced to dehydrate until the water content becomes 1 wt% to 5 wt%.

[0030] By performing the above washing and dehydration steps after doping, residual alkali can be removed.

[0031] In one embodiment, the method includes the following steps.

[0032] (i) Synthesis of precursor: According to the molar ratio of the elements of nickel, cobalt and manganese, first, soluble nickel salt, soluble cobalt salt and soluble manganese salt are weighed to prepare a mixed solution of soluble nickel salt, cobalt salt and manganese salt. Here, the molar content of nickel in the precursor is 80% or more. An alkali solution with a concentration of 5 mol / L to 10 mol / L is prepared. The alkali solution includes sodium hydroxide solution and / or potassium hydroxide solution. An aqueous ammonia solution with a concentration of 8 mol / L to 12 mol / L is prepared. There is no priority order for the preparation of the above various solutions. The above alkali solution and aqueous ammonia solution are simultaneously added to the mixed solution of soluble nickel salt, cobalt salt and manganese salt and reacted to synthesize a ternary precursor. After the synthesis is completed, it is washed, dehydrated and dried to obtain a finished precursor.

[0033] (ii) Primary sintering of the positive electrode: Weigh a certain amount of the finished precursor, lithium source and dopant (specifically, a mixture of aluminum fluoride and zirconium fluoride), mix them with a high-speed mixer, and after sufficient mixing, bake at 750 °C for 15 hours in an oxygen atmosphere to obtain a primary sintered material.

[0034] (iii) Washing and dehydration: Put the primary sintered material into a three-way washing machine, add an appropriate amount of pure water, with a liquid-solid ratio of 1:1 to 5:1, stir and wash for 2 minutes to 30 minutes, then introduce nitrogen gas to quickly dehydrate, and after dehydration, confirm that the water content is less than 5%.

[0035] (iv) Introduction of Additives: Add zirconium hydrogen phosphate and a boron source. The addition amounts of zirconium hydrogen phosphate and the boron source respectively account for 0.05% - 0.5% and 0.05% - 0.3% of the washed and dehydrated primary sintered material, and premix for 15 - 45 minutes by the wet method.

[0036] (v) Secondary Mixing: Use a colter dryer to initially dry at 200°C for 4 hours, fully mix the additive and the cathode material, dry and dehydrate, and ensure that the moisture content is less than 0.05% after drying.

[0037] (vi) Secondary Sintering: Weigh a certain amount of the initially dried sample, bake at 400°C for 8 hours in an oxygen atmosphere to obtain the secondary sintered material, i.e., the coated ternary cathode material, specifically a spherical high-nickel ternary doped and coated cathode material.

[0038] This disclosure provides a lithium-ion battery in one embodiment, and the lithium-ion battery includes the above-mentioned coated ternary cathode material.

Embodiments for Carrying Out the Invention

[0039] Hereinafter, the technical solution of this disclosure will be further described by specific embodiments. Those skilled in the art should understand that the following examples are only for helping to understand this disclosure and should not be regarded as specific limitations to this disclosure.

[0040] Example 1 This example provides a coated ternary cathode material, which includes a ternary cathode active material inner core co-doped with aluminum, zirconium, and fluorine and a coating layer coated on the surface of the inner core. The coating layer includes zirconium hydrogen phosphate and a boron compound, and the boron compound is boron oxide and lithium borate. Here, based on the total mass of the inner core, the total mass concentration of aluminum, zirconium, and fluorine is 3000 ppm, the mass concentration of the coating layer is 3500 ppm, and the mass ratio of zirconium hydrogen phosphate in the coating layer is 57%.

[0041] The preparation method of the coated ternary cathode material includes the following steps.

[0042] (i) Synthesis of the precursor: First, soluble nickel salt, soluble cobalt salt, and soluble manganese salt are weighed in a molar ratio of 8:1:1 to prepare a nickel-cobalt-manganese ternary mixed solution A (the total metal cation concentration in the mixed solution A is 0.6 mol / L). Next, 6 mol / L sodium hydroxide solution B and 9 mol / L aqueous ammonia solution C are prepared. Sodium hydroxide solution B and aqueous ammonia solution C are simultaneously added to the nickel-cobalt-manganese ternary mixed solution A and reacted to synthesize a ternary 811 precursor. After the synthesis is completed, it is washed, dehydrated, and dried to obtain a finished precursor D with a particle size D50 of 10 μm.

[0043] (ii) Primary sintering of the cathode: A certain amount of the finished precursor D, lithium hydroxide E, and additives aluminum fluoride F and zirconium fluoride G are weighed and mixed in a high-speed mixer. The molar ratio of the finished precursor D to lithium hydroxide is 1:1.05. The addition amount of aluminum fluoride accounts for 0.1 wt% of the finished precursor D, and the addition amount of zirconium fluoride accounts for 0.2 wt% of the finished precursor D. After thorough mixing, it is calcined at a temperature of 750 °C for 15 hours in an oxygen atmosphere to obtain a primary sintered material H.

[0044] (iii) Washing and dehydration: The primary sintered material H is put into a three-one washing machine, an appropriate amount of pure water is added, the liquid-solid ratio is 2:1, and it is stirred and washed for 10 minutes. Then, nitrogen gas is introduced to quickly dehydrate it. After dehydration, it is confirmed that the water content is less than 5%.

[0045] (iv) Introduction of additives: Zirconium hydrogen phosphate and boric acid are added and pre-mixed by the wet method for 30 minutes. Here, the addition amount of zirconium hydrogen phosphate accounts for 0.2 wt% of the washed and dehydrated primary sintered material H, and the addition amount of boric acid accounts for 0.15 wt% of the washed and dehydrated primary sintered material H.

[0046] (v) Secondary mixing: Use a colter dryer to perform initial drying at 200 °C for 4 hours, sufficiently mix the additive and the cathode material, and dry and dehydrate them. The moisture content after drying is less than 0.05 wt%.

[0047] (vi) Secondary sintering: Weigh a certain amount of the initially dried sample, and sinter it at a temperature of 400 °C for 8 hours in an oxygen atmosphere to obtain the secondary sintered material I, that is, the coated ternary cathode material.

[0048] Example 2 This example provides a coated ternary cathode material, which includes a ternary cathode active material inner core co-doped with aluminum, zirconium, and fluorine and a coating layer coated on the surface of the inner core. The coating layer includes zirconium hydrogen phosphate and a boron compound, and the boron compound is boron oxide and lithium borate. Here, based on the total mass of the inner core, the total mass concentration of aluminum, zirconium, and fluorine is 5000 ppm, the mass concentration of the coating layer is 4000 ppm, and the mass ratio of the zirconium hydrogen phosphate in the coating layer is 75%.

[0049] The preparation method of the above coated ternary cathode material includes the following steps.

[0050] (i) Synthesis of precursor: First, weigh soluble nickel salt, soluble cobalt salt, and soluble manganese salt in a molar ratio of 83:11:6 to prepare a nickel-cobalt-manganese ternary mixed solution A (the total metal cation concentration in the mixed solution A is 0.5 mol / L). Next, prepare an 8 mol / L sodium hydroxide solution B and a 10 mol / L aqueous ammonia solution C. Add the sodium hydroxide solution B and the aqueous ammonia solution C to the nickel-cobalt-manganese ternary mixed solution A simultaneously and react to synthesize a ternary 831106 precursor. After the synthesis is completed, wash, dehydrate, and dry to obtain a finished precursor D with a particle size D50 of 9 μm.

[0051] (ii) Primary sintering of the positive electrode: Weigh a certain amount of the completed precursor D, lithium hydroxide E, and additives aluminum fluoride F and zirconium fluoride G, and mix them in a high-speed mixer. The molar ratio of the completed precursor D to lithium hydroxide is 1:1.05. The addition amount of aluminum fluoride accounts for 0.2 wt% of the completed precursor D, and the addition amount of zirconium fluoride accounts for 0.3 wt% of the completed precursor D. Mix them thoroughly and sinter at a temperature of 780 °C for 10 hours in an oxygen atmosphere to obtain the primary sintered material H.

[0052] (iii) Washing and dehydration: Put the primary sintered material H into a three-tank washing machine, add an appropriate amount of pure water, with a liquid-solid ratio of 2:1, stir and wash for 10 minutes, then introduce nitrogen gas to quickly dehydrate. After dehydration, confirm that the moisture content is less than 5%.

[0053] (iv) Introduction of additives: Add zirconium hydrogen phosphate and boron oxide, and pre-mix them by the wet method for 30 minutes. Here, the addition amount of zirconium hydrogen phosphate accounts for 0.3 wt% of the washed and dehydrated primary sintered material H, and the addition amount of boron oxide accounts for 0.1 wt% of the washed and dehydrated primary sintered material H.

[0054] (v) Secondary mixing: Use a Colter dryer to initially dry at 170 °C for 4 hours, thoroughly mix and dry the additives and the positive electrode material to dehydrate. The moisture after drying is less than 0.05%.

[0055] (vi) Secondary sintering: Weigh a certain amount of the initially dried sample and sinter at a temperature of 500 °C for 7 hours in an oxygen atmosphere to obtain the secondary sintered material I, that is, the coated ternary positive electrode material.

[0056] Example 3 This example provides a coated ternary positive electrode material. The coated ternary positive electrode material includes a ternary positive electrode active material inner core co-doped with aluminum, zirconium, and fluorine and a coating layer coated on the surface of the inner core. The coating layer includes zirconium hydrogen phosphate and a boron compound. The boron compound is boron oxide and lithium borate. Here, based on the total mass of the internal core, the total mass concentration of aluminum, zirconium, and fluorine is 4000 ppm, the mass concentration of the coating layer is 2700 ppm, and the mass ratio of zirconium hydrogen phosphate in the coating layer is 74%.

[0057] The preparation method of the above-coated ternary cathode material includes the following steps.

[0058] (i) Synthesis of the precursor: First, weigh soluble nickel salt, soluble cobalt salt, and soluble manganese salt in a molar ratio of 88:9:3 to prepare a nickel-cobalt-manganese ternary mixed solution A (the total metal cation concentration in the mixed solution A is 0.8 mol / L). Next, prepare a 4 mol / L sodium hydroxide solution B and a 6 mol / L aqueous ammonia solution C. Add the sodium hydroxide solution B and the aqueous ammonia solution C to the nickel-cobalt-manganese ternary mixed solution A simultaneously and react to synthesize a ternary 880903 precursor. After the synthesis is completed, wash, dehydrate, and dry to obtain a finished precursor D with a particle size D50 of 9.5 μm.

[0059] (ii) Primary sintering of the cathode: Weigh a certain amount of the finished precursor D, lithium hydroxide E, and additive aluminum fluoride F and zirconium fluoride G, and mix them with a high-speed mixer. The molar ratio of the finished precursor D to lithium hydroxide is 1:1.04. The addition amount of aluminum fluoride accounts for 0.1 wt% of the finished precursor D, and the addition amount of zirconium fluoride accounts for 0.3 wt% of the finished precursor D. Mix well and sinter at a temperature of 730 °C for 18 hours in an oxygen atmosphere to obtain a primary sintered material H.

[0060] (iii) Washing and dehydration: Put the primary sintered material H into a three-way washing machine, add an appropriate amount of pure water, with a liquid-solid ratio of 2:1, stir and wash for 10 minutes, then introduce nitrogen gas to quickly dehydrate, and after dehydration, confirm that the moisture content is less than 5%.

[0061] (iv) Introduction of additives: Zirconium hydrogen phosphate and boric acid were added and premixed by the wet method for 30 minutes. Here, the addition amount of zirconium hydrogen phosphate accounted for 0.2 wt% of the washed and dehydrated primary sintered material H, and the addition amount of boric acid accounted for 0.07 wt% of the washed and dehydrated primary sintered material H.

[0062] (v) Secondary mixing: Dried at 180 °C for 4 hours with a Colter dryer to thoroughly mix and dry the additive and the cathode material to dehydrate, and the moisture after drying was less than 0.05%.

[0063] (vi) Secondary sintering: A certain amount of the initially dried sample was weighed and fired at a temperature of 350 °C for 6 hours in an oxygen atmosphere to obtain the secondary sintered material I, i.e., the coated ternary cathode material.

[0064] Example 4 The difference from Example 1 is that the addition amount of aluminum fluoride in step (ii) accounted for 0.2 wt% of the precursor finished product D, and the addition amount of zirconium fluoride accounted for 0.1 wt% of the precursor finished product D.

[0065] Example 5 The difference from Example 1 is that in step (iv), boric acid was changed to a mixture of equal amounts of boric acid and boron oxide, and the mass ratio of boric acid to boron oxide was 1:1, and the temperature of secondary sintering was 380 °C.

[0066] Example 6 The difference from Example 1 is that the addition amount of zirconium hydrogen phosphate in step (iv) was changed so that the mass ratio of zirconium hydrogen phosphate in the coating layer was 90%.

[0067] Comparative Example 1 The difference from Example 1 is that zirconium hydrogen phosphate was not added in step (iv).

[0068] Comparative Example 2 The difference from Example 1 is that boric acid was not added in step (iv).

[0069] Comparative Example 3 The difference from Example 1 is that aluminum fluoride and zirconium fluoride are not added in step (ii).

[0070] Test part: Using the positive electrode materials prepared in each example and comparative example, a positive electrode sheet was prepared and assembled into a full electric soft pack for an electrochemical performance test. Here, the negative electrode active material is graphite, and the results are as shown in Table 1. Specifically, it is as follows.

[0071] Discharge capacity test: Under the condition of 25 °C, the charge rate is 0.33C and the discharge rate is 0.33C.

[0072] Gas generation test: Under the condition of 45 °C, the charge rate is 0.5C and the discharge rate is 1C. After 600 cycles, the gas generation amount was tested using the battery cell volume change test method after gas generation.

[0073]

Table 1

[0074] From the comparison between Example 1 and Example 4, it was found that when the mass ratio of the dopants aluminum fluoride and zirconium fluoride is within the range of 1:(0.5 - 5), good electrochemical performance can be obtained in both cases.

[0075] From the comparison between Example 1 and Example 5, it was found that by selecting a mixture of boric acid and boron oxide as the boron source, the temperature of the secondary sintering can be adjusted, and good electrochemical performance can be obtained at a low secondary sintering temperature.

[0076] From the comparison between Example 1 and Example 6 and Comparative Example 2, it was found that when the content of zirconium hydrogen phosphate is too high and the content of the boron compound is low, the coating effect deteriorates, and it cannot effectively play a role in improving conductivity and stability, and gas generation increases.

[0077] From the comparison between Example 1 and Comparative Example 1, it was found that when the coating layer does not contain zirconium hydrogen phosphate, it affects the conductivity and coating stability of the positive electrode material, leading to a decrease in the initial efficiency of the capacity and an increase in gas generation.

Claims

1. It includes a ternary cathode active material internal core co-doped with aluminum, zirconium, and fluorine, and a coating layer coated on the surface of the internal core. The coating layer includes zirconium hydrogen phosphate and a boron compound. The ternary cathode active material internal core is a lithium composite oxide of a ternary system of Ni-Co-Mn, and the ratio of Ni to the total of Ni, Co, and Mn is 0.8 or more and less than 1. Based on the total mass of the internal core, the total mass concentration of the doping elements aluminum, zirconium, and fluorine is 500 ppm to 5000 ppm, and the mass concentration of the coating layer is 500 ppm to 5000 ppm. A coated ternary cathode material, wherein the mass ratio of the zirconium hydrogen phosphate in the coating layer is 30% to 85%.

2. The boron compound is converted by sintering the boron source of the raw material, and the boron source includes at least one of boric acid and boron oxide. The coated ternary cathode material according to claim 1.

3. A method for preparing the coated ternary cathode material according to claim 1 or 2, Step (1) of mixing a dopant containing elements of aluminum, zirconium, and fluorine, a ternary cathode material precursor, and a lithium source, and performing primary sintering in an oxygen-containing atmosphere to obtain a ternary cathode active material internal core co-doped with aluminum, zirconium, and fluorine; Step (2) of mixing the internal core with an additive containing zirconium hydrogen phosphate and a boron source and performing secondary sintering to obtain the coated ternary cathode material.

4. The dopant in step (1) is a mixture of aluminum fluoride and zirconium fluoride, and the mass ratio of the aluminum fluoride to the zirconium fluoride is 1:(0.5 to 5). The temperature of the primary sintering in step (1) is 750°C to 980°C, and the time of the primary sintering is 10 h to 20 h. The method according to claim 3.

5. The boron source in step (2) is a mixture of boric acid and boron oxide in an arbitrary ratio. The method according to claim 3.

6. The moisture of the material obtained after mixing in step (2) is less than 0.05 wt%. The method according to claim 3.

7. The atmosphere of the secondary sintering in step (2) is an oxygen-containing atmosphere, the temperature of the secondary sintering is 300°C to 700°C, and the time of the secondary sintering is 2 h to 15 h. The method according to claim 3.

8. After step (1) and before step (2), it further includes a washing and dehydration step, wherein the washing and dehydration is to mix the ternary cathode active material internal core co-doped with the above-mentioned aluminum, zirconium and fluorine with water, with a liquid-solid ratio of 1:1 to 5:1, stir and wash for 2 minutes to 30 minutes, and then introduce nitrogen gas to dehydrate until the moisture content is less than 5 wt%, according to the method of claim 3.

9. A lithium-ion battery comprising the coated ternary cathode material according to claim 1 or 2.

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