A high-nickel ternary positive electrode material for lithium battery, preparation method and lithium battery

Abstract

The present invention provides a high-nickel ternary positive electrode material for a lithium battery, a preparation method, and a lithium battery. The high-nickel ternary positive electrode material for a lithium battery has a core-shell structure, including an inner core and an outer shell coated on the surface of the inner core, wherein the outer shell has a double coating layer structure, comprising, from the inside out, a first coating layer and a second coating layer. The inner core is lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, the first coating layer is an olivine-type solid solution lithium manganese iron phosphate, and the second coating layer is an olivine-structured lithium iron phosphate. The present invention effectively reduces interfacial side reactions between the surface of the high-nickel ternary material and the electrolyte by constructing a first coating layer of lithium iron manganese phosphate and a second coating layer of lithium iron phosphate on the surface of the high-nickel ternary positive electrode material, effectively suppressing the precipitation of transition metal ions in the high-nickel ternary material, and fully utilizing the synergistic effect of the double coating layers, thereby ensuring the capacity of the high-nickel ternary material and significantly improving the cycle performance and thermal stability of the high-nickel ternary material.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and more specifically relates to a high-nickel ternary positive electrode material for lithium batteries, a preparation method and an application thereof. Background Art

[0002] Compared with lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide, layered NCM or NCA composite ternary positive electrode materials have the advantages of low cost, high discharge capacity, good cycle performance and good thermal stability. It is a material with great development prospects and has been widely used in electric vehicles, 3C digital and power tools and other fields. Among them, high nickel ternary positive electrode materials (Nimol% ≥ 0.8) have the advantage of significantly high energy density and have become the most competitive positive electrode material for lithium batteries, but with the increase of Ni content, it will bring a series of adverse problems. For example: with the increase of Ni content, the residual alkali (mainly lithium hydroxide and lithium carbonate) on the surface of the material is also higher, and excessive residual alkali will not only affect the processing performance of the material, but also affect the safety performance of the material; in the high delithiation state, Ni 2+ / Ni 3+ It will be converted into Ni, which is more oxidizing. 4+ It will accelerate the decomposition of the electrolyte, thus affecting the safety and cycle performance of the material; in addition, Mn 4+ The dissolution and precipitation of nickel ions at the negative electrode continuously damage the SEI film, continuously consuming the electrolyte, and also affecting the safety performance of high-nickel ternary materials. To address the problems of high-nickel ternary materials, the main strategies include doping modification, surface coating modification, and synthesis of concentration gradient materials. Among them, surface coating modification can significantly improve the side reactions between the positive electrode material and the electrolyte, thereby improving the material's cycle performance and thermal stability.

[0003] Compared with layered oxides represented by high-nickel ternary materials, the polyanions of polyanion-based cathode materials can support and stabilize the lattice structure of the material, and generally have higher chemical stability, thermal stability and safety.

[0004] This approach utilizes polyanionic cathode materials to coat high-nickel ternary materials, which has the advantage of improving the cycling stability and safety of high-nickel ternary materials. Common polyanionic cathode materials include LFP, LFMP, and lithium vanadium phosphate, but the toxicity of vanadium limits the large-scale application of lithium vanadium phosphate. Invention patent CN 201410011342.3, NCM523 ternary materials are dry-milled with LFP to produce LFP-coated NCM523 ternary materials. Invention patent CN 201710711402.6, LFMP and NCA ternary materials are mechanically mixed at high speeds by adding a binder to produce LMFP-coated NCA materials. Both of the above patents are single-factor LFP or LFMP coatings, and both are to first synthesize LFP or LFMP and then simply mechanically mix it with the ternary material. The main problems with this coating process are: 1) Single LFP coating will affect the low-temperature performance and capacity of the high-nickel ternary material, and single LFMP coating will not improve the cyclic stability and thermal stability of the high-nickel ternary material sufficiently; 2) The coating is carried out by mechanically mixing LFP or LFMP with the ternary material. The coating agent is easily separated from the base material, and the coating effect is not ideal. Invention patent CN201510897636.5 prepares the LFMP-coated ternary material by adding the ternary material to the LFMP precursor slurry and then vacuum drying it. The dried material is then sintered to improve the coating uniformity. However, the above patents only coat a single LFP or LFMP on the surface. The mechanism for reducing the residual alkali on the surface is mainly based on the neutralization reaction between the weak acidity of LFP or LFMP and the residual alkali on the surface, but its effect in reducing the residual alkali is limited. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the problems of poor surface stability and interface stability with the electrolyte of high-nickel ternary positive electrode materials, and to reduce the surface residual alkali, thereby improving the cycle performance and safety performance of high-nickel ternary materials. To this end, the present invention provides a high-nickel ternary positive electrode material for lithium batteries.

[0006] Another object of the present invention is to provide a method for preparing the high-nickel ternary positive electrode material.

[0007] Another object of the present invention is to provide an application of the high-nickel ternary positive electrode material in lithium batteries.

[0008] In order to achieve the above object of the invention, the technical solution adopted by the present invention is as follows:

[0009] A high-nickel ternary positive electrode material for a lithium battery, the high-nickel ternary positive electrode material having a core-shell structure, comprising an inner core and a first coating layer and a second coating layer sequentially coated on the surface of the inner core from the inside out; the inner core is lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, the first coating layer is lithium manganese iron phosphate with an olivine structure, and the second coating layer is lithium iron phosphate with an olivine structure; preferably, the inner core is Zr-doped lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0010] On the other hand, a method for preparing the aforementioned high-nickel ternary positive electrode material for lithium batteries comprises the following steps:

[0011] (1) Weighing a precursor and a lithium source in a ratio such that the total molar amount of nickel, cobalt, manganese or nickel, cobalt, aluminum in the precursor and the molar ratio of lithium in the lithium source is 1:Me, and mixing the precursor, the lithium source and an optional nano-zirconia powder in a ball mill for 3 to 5 hours to obtain a uniform mixture; preferably, weighing the nano-zirconia so that the mass of zirconium in the nano-zirconia powder accounts for 0.3% of the total mass of nickel, cobalt, manganese or nickel, cobalt, aluminum in the precursor;

[0012] (2) sintering the mixture of step (1) at a temperature of 1-5°C / min to T°C, maintaining the temperature for t hours, crushing and sieving the material after sintering to obtain a core of a high-nickel ternary positive electrode material, which is optionally Zr-doped lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, wherein the surface of the core contains LiOH with a mass fraction a of the core and Li2CO3 with a mass fraction b of the core;

[0013] (3) weighing the crushed and sieved material from step (2) and the iron source, phosphorus source, and manganese source in a certain proportion and mixing them in a ball mill for 3 to 5 hours to obtain a mixed material;

[0014] (4) Sintering the mixture in step (3), raising the temperature to T1°C at 1-5°C / min, and keeping it warm for t1 hour to obtain a first coating layer; then continuing to raise the temperature to T2°C at 1-5°C / min, and keeping it warm for t2 hours to obtain a second coating layer; the sintered material is directly sieved to obtain the final high-nickel ternary positive electrode material for lithium batteries.

[0015] In a specific embodiment, the molecular formula of the precursor in step (1) is [Ni x Co y M 1-x-y ](OH)2, wherein M=Mn and / or Al, 0.6≤x<1, 0<y<0.4; preferably, the lithium source is at least any one of lithium carbonate, lithium hydroxide or lithium acetate.

[0016] In a specific embodiment, the value range of Me in step (1) is 1.01≤Me≤1.08; preferably, 1.03≤Me≤1.06.

[0017] In a specific embodiment, the chemical formula of the core in step (2) is Li[Ni x Co y M 1-x-y ]O2, an α-NaFeO2 phase crystal structure, wherein M = Mn and / or Al, 0.6≤x<1, 0<y<0.4; wherein:

[0018] 0.6%≤a≤1.2%; preferably, 0.8%≤a≤1.0%;

[0019] 0.3%≤b≤1.0%; preferably, 0.5%≤b≤0.8%.

[0020] In a specific embodiment, in step (2) or step (4): the temperature T is in the range of 500°C ≤ T ≤ 1000°C; preferably 700°C ≤ T ≤ 900°C;

[0021] The range of temperature T1 is: 500°C ≤ T1 ≤ 800°C; preferably 600°C ≤ T1 ≤ 700°C;

[0022] The range of temperature T2 is: 500°C ≤ T2 ≤ 800°C; preferably 700°C ≤ T2 ≤ 800°C;

[0023] and 50℃≤T2-T1≤150℃;

[0024] The range of the holding time t is: 8h≤t≤20h; preferably 10h≤t≤15h;

[0025] The range of the holding time t1 is: 5h≤t1≤15h; preferably 8h≤t1≤12h;

[0026] The range of the insulation time t2 is: 5h≤t2≤15h; preferably 8h≤t2≤12h.

[0027] In a specific embodiment, the chemical formula of the first coating layer in step (4) is LiMn x Fe 1-x PO4, the second coating layer has the general chemical formula of LiFePO4, both of which have an olivine structure, wherein: 0.3≤x≤0.9; more preferably, 0.5≤x≤0.7.

[0028] In a specific embodiment, the iron source in step (3) is selected from at least one of ferrous oxalate, ferrous acetate, ferric phosphate, and ferric oxide, preferably ferrous oxalate; the phosphorus source is selected from at least one of ammonium hydrogen phosphate, diammonium dihydrogen phosphate, and ammonium phosphate, preferably diammonium dihydrogen phosphate; and the manganese source is selected from one or both of manganese oxide and manganese carbonate, preferably manganese oxide. For example, the relationship between the mass of the iron source, phosphorus source, and manganese source, respectively, and the lithium hydroxide content a and lithium carbonate content b in step (2) is:

[0029] m(FeC2O4)=[(0.8~5.6)*(0.3a)+8*(0.2b)] / 0.39;

[0030] m(NH4H2PO4)=[4.5*(0.3a)+4.5*(0.2b)] / 0.27;

[0031] m(MnO)=[(7.0~2.5)*(0.3a)] / 0.77;

[0032] Preferably, m(FeC2O4)=[(2.5-4.0)*(0.3a)+8*(0.2b)] / 0.39;

[0033] Preferably, m(MnO)=[(5.5-4.0)*(0.3a)] / 0.77.

[0034] In a specific embodiment, the sintering in step (2) is carried out in an oxygen atmosphere with an oxygen concentration of ≥90%; and the sintering in step (4) is carried out in a nitrogen atmosphere with a nitrogen concentration of ≥90%.

[0035] On the other hand, a lithium battery includes a positive electrode, a negative electrode, an electrolyte and a separator, wherein the positive electrode includes a positive electrode collector and a positive electrode slurry coated on the surface of the positive electrode collector, wherein the positive electrode slurry includes the aforementioned high-nickel ternary positive electrode material or the high-nickel ternary positive electrode material prepared by the aforementioned preparation method.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention simultaneously coats LFP and LFMP on the surface of the high-nickel ternary material, which can take into account the respective advantages of LFP and LFMP. During the coating, the residual alkali on the surface is used as the raw material for forming LFP or LFMP. That is, the residual alkali on the surface is no longer treated as an impurity, but as a lithium source for forming a coating layer, which significantly reduces the residual alkali on the surface and improves the cycle stability and thermal stability of the material, which has a very positive significance for the high-nickel ternary material.

[0038] The present invention forms the first LFMP coating layer and the second LFP coating layer on the surface of the high nickel ternary material by secondary high temperature solid phase sintering. The LFP in the outermost layer can suppress the high nickel ternary material in the core and the Mn of the LFMP. 4+ The LFMP and LFP coatings formed are more uniform and not easy to fall off from the surface of the material.

[0039] The present invention uses LFMP and LFP composite coating to greatly improve the interface stability of high-nickel ternary materials without reducing capacity, thereby improving the cycle performance and thermal stability of the material.

[0040] The method of the present invention can also control the amount of residual alkali formed on the surface by adjusting the lithiation ratio, thereby regulating the thickness of the surface coating layer; this method is simple, reliable, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the XRD pattern of the high-nickel ternary positive electrode material prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0042] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0043] A high-nickel ternary positive electrode material, the preparation method of which is as follows:

[0044] (1) The precursor and the lithium source are weighed according to the molar ratio of the total molar amount of nickel, cobalt, manganese or nickel, cobalt, and aluminum in the precursor to the lithium element in the lithium source of 1:Me. Zirconium oxide is weighed according to the mass of zirconium in zirconium oxide accounting for 0.3% of the total mass of nickel, cobalt, manganese or nickel, cobalt, and aluminum in the precursor. The precursor, lithium source, and zirconium oxide are mixed in a ball mill for 5 hours to obtain a uniform mixture.

[0045] Among them, the molecular formula of the precursor [Ni x Co y M 1-x-y ](OH)2, wherein M=Mn or / and Al, 0.6≤x<1, 0<y<0.4; the lithium source is any one of lithium carbonate, lithium hydroxide or lithium acetate. The molar ratio of the total molar amount of nickel-cobalt-manganese or nickel-cobalt-aluminum in the precursor to the lithium element in the lithium source is 1:(1.01-1.08), for example, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, etc., preferably 1:(1.03-1.06).

[0046] In this step, the ball milling and mixing in the ball mill is a conventional method in the art, for example, the ball mill speed is 1000-1300 rpm, the ball milling time is 3-5 hours, etc.

[0047] It should be noted that zirconium oxide is added in step (1), and the Zr-doped core lithium nickel cobalt manganate or lithium nickel cobalt aluminum oxide is prepared in the subsequent steps. It will be understood by those skilled in the art that the core-shell structure of the present invention has no restrictions on whether it is doped or not, and for example, other elements can be doped. In another embodiment, the core of the present invention is not doped with Zr, that is, zirconium oxide is not required in step 1, and the core prepared in the subsequent steps is lithium nickel cobalt manganate or lithium nickel cobalt aluminum oxide.

[0048] (2) The mixture of step (1) is sintered in an atmosphere box furnace, and the temperature is raised to T°C at 3°C / min, and the temperature is maintained at th. After sintering, the material is crushed and sieved to obtain the core of the high-nickel ternary positive electrode material, that is, Zr-doped lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, and the surface of the core contains LiOH with a mass fraction a of the core and Li2CO3 with a mass fraction b of the core.

[0049] Wherein, sintering is carried out in an oxygen atmosphere, for example, the oxygen volume concentration is ≥90%; the sintering temperature T ranges from 500°C ≤ T ≤ 1000°C; for example, including but not limited to 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, preferably 700°C ≤ T ≤ 900°C; the sintering holding time t is: 8h ≤ t ≤ 20h, for example, including but not limited to 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, preferably 10h ≤ t ≤ 15h. After sintering, the material is crushed and sieved, for example, through a 400-mesh sieve, to obtain the target D 50 The powder with a particle size of 10 to 12 μm is the core of the high nickel ternary positive electrode material. The chemical formula of the core is Li[Ni x Co y M 1-x-y ]O2, an α-NaFeO2 phase crystal structure, wherein M = Mn and / or Al, 0.6 ≤ x < 1, 0 < y < 0.4; wherein the surface residual alkali content a of the inner core and the content b of Li2CO3 are: 0.6% ≤ a ≤ 1.2%; preferably 0.8% ≤ a ≤ 1.0%; 0.3% ≤ b ≤ 1.0%; and preferably 0.5% ≤ b ≤ 0.8%. In the present invention, even if Zr doping is performed, the Zr doping amount is relatively low, at only the ppm level, and is generally not shown in the aforementioned general chemical formula of the inner core.

[0050] (3) The crushed and sieved material of step (2) (i.e., the core of the crushed and sieved high-nickel ternary positive electrode material) and ferrous oxalate, diammonium dihydrogen phosphate, and manganese oxide are weighed in a certain proportion and mixed in a ball mill for 5 hours to obtain a mixture.

[0051] The relationship between the mass of ferrous oxalate, diammonium dihydrogen phosphate and manganese oxide and the lithium hydroxide content a and lithium carbonate content b in step (2) is:

[0052] m(FeC2O4)=[(0.8~5.6)*(0.3a)+8*(0.2b)] / 0.39;

[0053] m(NH4H2PO4)=[4.5*(0.3a)+4.5*(0.2b)] / 0.27;

[0054] m(MnO)=[(7.0~2.5)*(0.3a)] / 0.77;

[0055] Preferably, m(FeC2O4)=[(2.5-4.0)*(0.3a)+8*(0.2b)] / 0.39;

[0056] m(MnO)=[(5.5~4.0)*(0.3a)] / 0.77.

[0057] In the above content relationship formula, the denominator in the relationship formula needs to be adjusted according to the mass proportion of iron, phosphorus, and manganese in the specific iron, phosphorus, and manganese sources. For example, the denominator in the formula only needs to be changed to the mass fraction of iron, phosphorus, and manganese in the corresponding iron, phosphorus, and manganese sources. For example, if the iron source is changed from ferrous oxalate to ferric phosphate, the 0.39 in the Fe source formula should be changed to 0.37. The same principle applies to the relationship formulas for phosphorus and manganese sources.

[0058] Specifically, the lithium hydroxide content a and the lithium carbonate content b in step (2) can be obtained by acid-base titration, for example, the detection method is potentiometric titration.

[0059] In this step, the ball milling and mixing in the ball mill is a conventional method in the art, for example, the ball mill speed is 1000-1300 rpm, the ball milling time is 3-5 hours, etc.

[0060] (4) The mixed material in step (3) is sintered in an atmosphere box furnace, increasing the temperature to T1°C at 3°C / min and holding the temperature for t1h to obtain a first coating layer; then the temperature is further increased to T2°C at 3°C / min and held for t2h to obtain a second coating layer. The sintered material is directly sieved to obtain the final product.

[0061] Wherein, sintering is carried out in a nitrogen atmosphere, for example, a nitrogen volume concentration ≥ 90%. A secondary sintering process is adopted to form a first coating layer and a second coating layer respectively. Wherein, the range of the primary sintering temperature T1 is: 500℃≤T1≤800℃, for example, including but not limited to 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, preferably 600℃≤T1≤700℃; the range of the primary sintering holding time t1 is: 5h≤t1≤15h, for example, including but not limited to 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, preferably 8h≤t1≤12h. The range of the secondary sintering temperature T2 is: 500℃≤T2≤800℃, for example, including but not limited to 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, preferably 700℃≤T2≤800℃; the range of the secondary sintering holding time t2 is: 5h≤t2≤15h, for example, including but not limited to 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, preferably 8h≤t2≤12h.

[0062] In the present invention, the sintering temperature difference of the secondary sintering is controlled to form the first coating layer and the second coating layer, specifically satisfying 50℃≤T2-T1≤150℃. For example, the temperature difference between the two sinterings is 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc., but is not limited to this.

[0063] Among them, the chemical formula of the first coating layer is LiMn x Fe 1-x PO4, 0.3≤x≤0.9; preferably, 0.5≤x≤0.7; the general chemical formula of the second coating layer is LiFePO4, both of which have an olivine structure.

[0064] The high-nickel ternary positive electrode material prepared by the above method is a core-shell structure, including an inner core and a first coating layer and a second coating layer sequentially coated on the surface of the inner core from the inside to the outside; the inner core is lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, the first coating layer is lithium manganese iron phosphate with an olivine structure, and the second coating layer is lithium iron phosphate with an olivine structure.

[0065] The high-nickel ternary cathode material prepared above can be used in lithium batteries, for example, a lithium battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode comprises a positive electrode current collector and a positive electrode slurry coated on the surface of the positive electrode current collector, wherein the positive electrode slurry comprises the high-nickel ternary cathode material described above or the high-nickel ternary cathode material prepared by the above preparation method. The preparation method of the lithium battery can refer to the existing technology, the key being that the cathode material is the core-shell structure high-nickel ternary cathode material of the present invention.

[0066] The present invention has found through research that high nickel ternary materials have high residual alkali and strong oxidizing properties in high delithiation state. 4+ Accelerate the decomposition of electrolyte, Mn 4+ The dissolution and precipitation of the electrolyte will continue to damage the SEI film at the negative electrode. These problems will greatly affect the cycle performance and thermal stability of high nickel ternary materials. The above problems are highly related to the surface stability of high nickel ternary materials and the interface stability between the ternary materials and the electrolyte. Therefore, improving the surface and interface stability is of great significance to improving the cycle performance and safety performance of high nickel ternary materials.

[0067] The surface and interface stability of the material can be improved by surface coating modification. LFP is a typical polyanion compound. The polyanion can support and stabilize the lattice structure of the material. Generally, the chemical stability, thermal stability and safety are relatively high, but its capacity is low and its low-temperature performance is poor. LFMP, as an "upgraded version" of LFP, takes into account the advantages of LFP and makes up for the shortcomings such as low energy density and poor low-temperature performance. However, its Jahn-Teller effect causes the precipitation of Mn, which becomes a pain point of this material. Therefore, the composite coating of LFP and LFMP can take into account the respective advantages of the two. It will not significantly reduce the capacity and low-temperature performance of the high-nickel ternary material, but can also significantly improve its cycle performance and safety performance. The present invention uses the residual alkali on the surface of the high-nickel ternary material as a lithium source, and synthesizes the LFMP first coating layer and the LFP second coating layer on its surface by high-temperature solid-phase sintering. It can give full play to the synergistic effect of LFMP and LFP, and utilize the residual alkali on the surface as a lithium source, greatly reducing the surface residual alkali. Without affecting the gram capacity, it greatly improves the cycle stability and thermal stability of the high-nickel ternary material.

[0068] The present invention is further explained below with reference to more specific examples, but is not intended to be limiting in any way.

[0069] Preparation Example 1

[0070] The precursor (Ni 0.88 Co 0.10 Al 0.02 After the mixture of )(OH)2 and lithium hydroxide monohydrate was uniformly mixed in a molar ratio of 1.03:1, and the Zr element accounted for 0.3% of the mass of nickel, cobalt, and aluminum in the precursor, the mixture was transferred to an atmosphere box furnace, and the mixture was sintered at 500°C for 2h in an oxygen atmosphere at 3°C / min, and then sintered at 750°C for 12h to obtain the Zr-doped positive electrode active material Li(Ni 0.88 Co 0.10 Al 0.02 )O2, denoted as NCA-1, was measured to contain about 0.8% of LiOH and about 0.5% of Li2CO3 on its surface, which accounted for about 0.8% of the core mass.

[0071] Preparation Example 2

[0072] The precursor (Ni 0.88 Co 0.10 Al 0.02 After the mixture of )(OH)2 and lithium hydroxide monohydrate was uniformly mixed in a molar ratio of 1.01:1, and the Zr element accounted for 0.3% of the mass of nickel, cobalt, and aluminum in the precursor, the mixture was transferred to an atmosphere box furnace, and the mixture was sintered at 500°C for 2h in an oxygen atmosphere at 3°C / min, and then sintered at 750°C for 12h to obtain the Zr-doped positive electrode active material Li(Ni 0.88 Co 0.10 Al 0.02 )O2, denoted as NCA-2, was measured to contain about 0.6% of LiOH and about 0.3% of Li2CO3 on its surface, which accounted for about 0.6% of the core mass.

[0073] Example 1

[0074] 100g of the positive electrode active material NCA-1 from Preparation Example 1, 2.424g of ferrous oxalate, 2.133g of manganese oxide, and 5.399g of ammonium dihydrogen phosphate were ball-milled for 5 hours to uniformly mix. The mixture was then transferred to an atmospheric box furnace and sintered at 3°C / min to 650°C for 10 hours under a nitrogen atmosphere. The temperature was then raised to 730°C for another 10 hours. This resulted in LFMP- and LFP-coated NCA-1. The molar ratio of Mn:Fe in the LFMP was 9:1.

[0075] Example 2

[0076] The precursor (Ni 0.88 Co 0.10 Al 0.02 )(OH)2 and lithium hydroxide monohydrate were weighed and mixed uniformly in a molar ratio of 1.04:1, transferred to an atmosphere box furnace, and sintered at 500°C in an oxygen atmosphere at 3°C / min for 2h, and then continued to heat up to 750°C and sinter for 12h to obtain the positive electrode active material Li(Ni 0.88 Co 0.10 Al 0.02 )O2, and it was measured that its surface contained about 1.0% of LiOH and about 0.8% of Li2CO3, which accounted for the mass of the core.

[0077] 100g of the above-mentioned cathode active material, 3.383g of ferrous oxalate, 1.659g of manganese oxide, and 5.399g of ammonium dihydrogen phosphate were ball-milled for 5 hours to achieve uniform mixing. The mixture was then transferred to an atmospheric box furnace and sintered at 650°C at 3°C / min under a nitrogen atmosphere for 10 hours. The temperature was then raised to 730°C for another 10 hours. This resulted in a Zr-free NCA material coated with LFMP and LFP. The molar ratio of Mn:Fe in the LFMP was 7:3.

[0078] Example 3

[0079] 100g of the positive electrode active material NCA-1 from Preparation Example 1, 3.383g of ferrous oxalate, 1.659g of manganese oxide, and 5.399g of ammonium dihydrogen phosphate were ball-milled for 5 hours to uniformly mix. The mixture was then transferred to an atmospheric box furnace and sintered at 3°C / min to 650°C for 10 hours under a nitrogen atmosphere. The temperature was then raised to 730°C for another 10 hours. This resulted in LFMP- and LFP-coated NCA-1. The molar ratio of Mn:Fe in the LFMP was 7:3.

[0080] Example 4

[0081] 100g of the positive electrode active material NCA-1 from Preparation Example 1, 3.383g of ferrous oxalate, 1.659g of manganese oxide, and 5.399g of ammonium dihydrogen phosphate were ball-milled for 5 hours to uniformly mix. The mixture was then transferred to an atmospheric box furnace and sintered at 700°C for 10 hours at a temperature of 5°C / min under a nitrogen atmosphere. The temperature was then raised to 750°C for another 10 hours. This resulted in LFMP- and LFP-coated NCA-1. The molar ratio of Mn:Fe in the LFMP was 7:3.

[0082] Example 5

[0083] 100g of the positive electrode active material NCA-1 from Preparation Example 1, 3.383g of ferrous oxalate, 1.659g of manganese oxide, and 5.399g of ammonium dihydrogen phosphate were ball-milled for 5 hours to uniformly mix. The mixture was then transferred to an atmospheric box furnace and sintered at 2°C / min to 600°C for 10 hours under a nitrogen atmosphere. The temperature was then raised to 700°C for 10 hours. This yielded NCA-1 coated with LFMP and LFP. The molar ratio of Mn:Fe in the LFMP was 7:3.

[0084] Comparative Example 1

[0085] 100 g of the positive electrode active material NCA-1 from Preparation Example 1, 1.440 g of ferrous oxalate, 1.659 g of manganese oxide, and 3.843 g of ammonium dihydrogen phosphate were ball-milled for 5 hours to uniformly mix. The mixture was then transferred to an atmospheric box furnace and sintered at 650°C for 10 hours at a temperature of 3°C / min under a nitrogen atmosphere. This yielded LFMP-coated NCA-1.

[0086] Comparative Example 2

[0087] 100 g of the positive electrode active material NCA-1 from Preparation Example 1, 5.303 g of ferrous oxalate, and 5.399 g of ammonium dihydrogen phosphate were ball-milled for 5 h to uniformly mix. The mixture was then transferred to an atmospheric box furnace and sintered at 3°C / min to 730°C for 10 h under a nitrogen atmosphere to obtain LFP-coated NCA-1.

[0088] Comparative Example 3

[0089] 100g of the positive electrode active material NCA-2 from Preparation Example 2, 2.246g of ferrous oxalate, 1.244g of manganese oxide, and 3.816g of ammonium dihydrogen phosphate were ball-milled for 5 hours to uniformly mix. The mixture was then transferred to an atmospheric box furnace and sintered at 650°C at 3°C / min under a nitrogen atmosphere for 10 hours. The temperature was then raised to 730°C and sintered for another 10 hours. This resulted in LFMP- and LFP-coated NCA-2. The molar ratio of Mn:Fe in the LFMP was 7:3.

[0090] Comparative Example 4

[0091] LMFP and LFP were weighed according to the mass fraction of NCA-1, respectively, 0.8% and 0.5%, where the Mn / Fe molar ratio of LMFP was 7:3. The three were ball milled in a ball mill for 5 h for mechanical fusion. The mixture was then moved to an atmosphere box furnace and sintered at 600 °C at 3 °C / min under nitrogen atmosphere for 10 h.

[0092] The high nickel ternary positive electrode materials of Examples 1-5 and Comparative Examples 1-4 were used to prepare battery materials for performance testing.

[0093] The high-nickel ternary positive electrode materials obtained in Examples 1-5 and Comparative Examples 1-4 were assembled into button cells. The specific method was as follows: the active material (prepared high-nickel positive electrode material), conductive agent (acetylene black), and binder (PVDF) were dispersed in a dispersant (NMP) at a mass ratio of 95:2:3, and vacuum-stirred for 5 hours to mix them evenly. The mixed slurry was then coated on an aluminum foil current collector on a heated flat-plate coating machine, placed in a vacuum oven, and dried at 120°C for 6 hours. The dried electrode was then rolled 4-5 times with the roller gap adjusted to zero to a compaction density of 3.0-3.4 g / cm. 3 The positive electrode was cut into 14mm diameter discs using a manual slicer. A C2032 button cell was assembled in an Ar-filled glove box using a 16mm diameter pure lithium sheet as the negative electrode, a 1 mol / L LiPF6 + DEC / EC (1:1) mixed solution as the electrolyte, and a 25μm thick polyethylene porous membrane as the separator.

[0094] Table 1 shows the 0.2C discharge capacity and the 50-cycle retention rate of 0.2C charge / 2C discharge at high temperature (60°C) for the high nickel ternary positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-4.

[0095] Table 1 Battery performance data of ternary positive electrode materials of Examples and Comparative Examples

[0096]

[0097]

[0098] As can be seen from Table 1, the single LFP coating has an advantage in high temperature cycle retention, but its capacity is low; the single LFMP coating has a higher capacity, but its cycle performance is poor; compared with Example 3, Comparative Example 4 achieves the purpose of double coating by simply physically mixing LFMP, LFP and NCA and then sintering, but the alkali amount is not significantly reduced, and the corresponding capacity and cycle retention rate have no advantages. In addition, the present invention preferably controls the surface residual alkali amount within a reasonable range by adjusting the lithium ratio to achieve the composite coating of LFP and LFMP. For example, the battery performance of Comparative Example 3 is not ideal. In addition, from Figure 1 It can also be seen that the coating did not change the crystal structure of NCA.

[0099] Although the above embodiments have described the technical solutions of the present invention in detail, the technical solutions of the present invention are not limited to the above embodiments. Without departing from the idea and purpose of the present invention, any changes made to the technical solutions of the present invention will fall within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a high-nickel ternary positive electrode material for a lithium battery, characterized in that: The following steps are involved: (1) Weighing a precursor and a lithium source in a ratio of 1:Me of the total molar amount of nickel, cobalt, manganese or nickel, cobalt, aluminum in the precursor to the molar ratio of lithium in the lithium source, mixing the precursor, the lithium source and optional nano-zirconia powder in a ball mill for 3 to 5 hours to obtain a uniform mixture; wherein 1.01≤Me≤1.08; (2) sintering the mixed material of step (1) at a temperature of 1-5°C / min to T°C, maintaining the temperature for t hours, crushing and sieving the material after sintering to obtain a core of a high-nickel ternary positive electrode material, wherein the core is optionally Zr-doped lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, and the surface of the core contains LiOH with a mass fraction a of the core and Li2CO3 with a mass fraction b of the core; wherein 0.6%≤a≤1.2%; 0.3%≤b≤1.0%; (3) weighing the crushed and sieved material from step (2) and the iron source, phosphorus source, and manganese source in a certain proportion and mixing them in a ball mill for 3 to 5 hours to obtain a mixed material; (4) Sintering the mixture in step (3), raising the temperature to T1°C at 1-5°C / min, and keeping it warm for t1 hour to obtain a first coating layer; then continuing to raise the temperature to T2°C at 1-5°C / min, and keeping it warm for t2 hours to obtain a second coating layer; the sintered material is directly sieved to obtain the final high-nickel ternary positive electrode material for lithium batteries; wherein, 500°C≤T1≤800°C, 5h≤t1≤15h; 500°C≤T2≤800°C, 5h≤t2≤15h, and 50°C≤T2-T1≤150°C.

2. The preparation method according to claim 1, characterized in that In step (1), nano zirconium oxide is weighed so that the mass of zirconium in the nano zirconium oxide powder accounts for 0.3% of the total mass of nickel, cobalt, manganese or nickel, cobalt, and aluminum in the precursor.

3. The preparation method according to claim 1, characterized in that The molecular formula of the precursor in step (1) is [Ni x Co y M 1-x-y ](OH)2, wherein M=Mn and / or Al, 0.6≤x<1, 0<y<0.

4.

4. The preparation method according to claim 3, characterized in that The lithium source in step (1) is at least one of lithium carbonate, lithium hydroxide or lithium acetate.

5. The preparation method according to claim 1, characterized in that The value range of Me in step (1) is 1.03≤Me≤1.

06.

6. The preparation method according to claim 1, characterized in that The chemical formula of the core in step (2) is Li[Ni x Co y M 1-x-y ]O2, is an α-NaFeO2 phase crystal structure, wherein M=Mn and / or Al, 0.6≤x<1, 0<y<0.

4.

7. The preparation method according to claim 1, characterized in that In step (2), 0.8%≤a≤1.0%; 0.5%≤b≤0.8%.

8. The preparation method according to claim 1, characterized in that In step (2) or step (4): the range of temperature T is: 500°C ≤ T ≤ 1000°C; the range of holding time t is: 8h ≤ t ≤ 20h.

9. The preparation method according to claim 8, characterized in that In step (2) or step (4): the temperature T is in the range of 700°C ≤ T ≤ 900°C; The range of temperature T1 is: 600℃≤T1≤700℃; The range of temperature T2 is: 700℃≤T2≤800℃; The range of holding time t is: 10h≤t≤15h; The range of holding time t1 is: 8h≤t1≤12h; The range of the insulation time t2 is: 8h≤t2≤12h.

10. The preparation method according to claim 1, characterized in that The chemical formula of the first coating layer in step (4) is LiMn x Fe 1-x PO4, the chemical formula of the second coating layer is LiFePO4, both of which have an olivine structure, wherein: 0.3≤x≤0.

9.

11. The preparation method according to claim 10, characterized in that: 0.5≤x≤0.7。 12. The preparation method according to claim 1, characterized in that In step (3), the iron source is selected from at least any one of ferrous oxalate, ferrous acetate, ferric phosphate, and ferric oxide; the phosphorus source is selected from at least any one of ammonium hydrogen phosphate, diammonium dihydrogen phosphate, and ammonium phosphate; and the manganese source is selected from one or both of manganese oxide and manganese carbonate.

13. The preparation method according to claim 12, characterized in that In step (3), the iron source is ferrous oxalate; the phosphorus source is ammonium dihydrogen phosphate; and the manganese source is manganese oxide.

14. The preparation method according to claim 13, characterized in that The relationship between the mass of ferrous oxalate, diammonium dihydrogen phosphate and manganese oxide and the lithium hydroxide content a and lithium carbonate content b in step (2) is: m(FeC2O4)=[(0.8~5.6)*(0.3a)+8*(0.2b)] / 0.39; m(NH4H2PO4)=[4.5*(0.3a)+4.5*(0.2b)] / 0.27; m(MnO)=[(7.0~2.5)*(0.3a)] / 0.

77.

15. The preparation method according to claim 14, characterized in that m(FeC2O4)=[(2.5~4.0)*(0.3a)+8*(0.2b)] / 0.39; m(MnO)=[(5.5~4.0)*(0.3a)] / 0.

77.

16. The preparation method according to claim 1, characterized in that The sintering in step (2) is carried out in an oxygen atmosphere with an oxygen concentration of ≥90%; the sintering in step (4) is carried out in a nitrogen atmosphere with a nitrogen concentration of ≥90%.

17. A high-nickel ternary cathode material for lithium batteries prepared by the preparation method according to any one of claims 1 to 16, characterized in that: The high-nickel ternary positive electrode material is a core-shell structure, including an inner core and a first coating layer and a second coating layer sequentially coated on the surface of the inner core from the inside to the outside; the inner core is lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, the first coating layer is lithium manganese iron phosphate with an olivine structure, and the second coating layer is lithium iron phosphate with an olivine structure.

18. The high-nickel ternary cathode material for lithium batteries according to claim 17, characterized in that: The core is Zr-doped lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

19. A lithium battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the positive electrode comprises a positive electrode current collector and a positive electrode slurry coated on the surface of the positive electrode current collector, characterized in that: The positive electrode slurry comprises the high-nickel ternary positive electrode material prepared by the preparation method according to any one of claims 1 to 16 or the high-nickel ternary positive electrode material for lithium batteries according to claim 17 or 18.

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