Positive electrode material, preparation method thereof, and lithium ion battery

Abstract

The present application discloses a positive electrode material, including a positive electrode material matrix, the chemical formula of which is Li a Ni x Co y O2, wherein a>0.9, x≥0.95, y≤0.05, x+y=1; and a coating layer, the coating layer comprising a first coating layer present on the surface of the positive electrode material substrate, a second coating layer present on the surface of the first coating layer, and a third coating layer present on the surface of the second coating layer, the first coating layer comprising an amphoteric metal oxide, the second coating layer comprising a metal fluoride, and the third coating layer comprising lithium fluoride, aluminum oxide, and aluminum fluoride. The positive electrode material and preparation method of the present application can effectively improve the rate performance and cycle stability of lithium-ion batteries, have a simple process, low cost, and are suitable for mass production.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries, with their high operating voltage, energy density, long lifespan, and environmental friendliness, have become the power source for a new generation of electric vehicles, power tools, and electronic products. They are now widely used in diverse fields such as energy, transportation, and communications. Improving the rate performance, thermal stability, and cycling stability of lithium-ion batteries has long been a hot topic for researchers.

[0003] Existing lithium batteries generally use high-nickel ternary materials as positive electrode materials, but with the shortage of cobalt resources and the trend of rising raw material prices, high-nickel ternary materials are gradually moving towards ultra-high nickel (nickel content greater than 90%) to reduce the demand for cobalt on the material side. In related research, a method for preparing nickel-cobalt binary precursors has been mastered. By discarding manganese and aluminum, the nickel content is maximized to greatly increase the capacity of the positive electrode material. Due to the lack of manganese and aluminum, compared with traditional high-nickel ternary positive electrode materials, binary ultra-high nickel materials have lower cobalt content, resulting in poor cycle stability and rate performance. At the same time, due to the higher the nickel content, the lower the substrate sintering temperature, resulting in more lithium remaining on the surface of the material and poor processing performance.

[0004] Therefore, a positive electrode material and a preparation method thereof are needed to improve the rate performance and cycle stability of lithium batteries, improve processing performance, and reduce production costs. Summary of the Invention

[0005] In view of this, the present application provides a positive electrode material and a preparation method thereof and a lithium-ion battery to improve the rate performance and cycle stability of the lithium battery, while reducing the lithium residue on the surface of the positive electrode material to improve the processing performance.

[0006] The present invention provides a positive electrode material, which includes:

[0007] The positive electrode material matrix has the general chemical formula of Li a Ni x Co y O2, where a>0.9, x≥0.95, y≤0.05, x+y=1; and

[0008] The coating layer includes a first coating layer present on the surface of the positive electrode material substrate, a second coating layer present on the surface of the first coating layer, and a third coating layer present on the surface of the second coating layer, wherein the first coating layer contains an amphoteric metal oxide, the second coating layer contains a metal fluoride, and the third coating layer contains lithium fluoride, aluminum oxide, and aluminum fluoride.

[0009] In a feasible embodiment, the positive electrode material further includes a doping element, and the doping element is doped into the positive electrode material matrix.

[0010] In a feasible embodiment, the aluminum fluoride exists at the interface between the second coating layer and the third coating layer.

[0011] In a feasible embodiment, the mass of the metal element in the metal fluoride is 0.01 wt% to 1 wt% of the mass of the positive electrode material matrix.

[0012] In a feasible embodiment, the content of the lithium fluoride accounts for 0.001 wt% to 0.1 wt% of the positive electrode material.

[0013] In a feasible embodiment, the content of the aluminum oxide accounts for 0.01 wt% to 1 wt% of the positive electrode material.

[0014] In a feasible embodiment, the content of the aluminum fluoride accounts for 0.01 wt% to 1 wt% of the positive electrode material.

[0015] In a feasible embodiment, the doping element is selected from at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba.

[0016] In a feasible embodiment, the metal in the amphoteric metal oxide includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn.

[0017] In a feasible embodiment, the mass of the metal element in the amphoteric metal oxide is 0.01 wt% to 1 wt% of the mass of the positive electrode material matrix.

[0018] In a feasible embodiment, the metal in the metal fluoride includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn.

[0019] In a feasible embodiment, the doping elements are selected from at least two of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba.

[0020] The present invention also provides a method for preparing a positive electrode material, comprising the following steps:

[0021] After the precursor and the lithium source are mixed, the first sintering is performed to obtain the first sintered product. The chemical formula of the precursor is Ni x Co y (OH)2, where x≥0.95, y≤0.05, and x+y=1;

[0022] After mixing the first sintered product with an amphoteric metal oxide, performing a second sintering reaction to obtain a second sintered product; and

[0023] After the second sintered product is mixed with aluminum fluoride trihydrate, sintering is performed for the third time to obtain the positive electrode material.

[0024] In a feasible embodiment, the step of obtaining the first sintered product includes: mixing the precursor and the lithium source, adding a dopant, and performing a first sintering.

[0025] In a feasible embodiment, the dopant includes metal oxide and / or metal hydroxide, and the metal in the metal oxide and the metal hydroxide includes at least two of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba.

[0026] In a feasible embodiment, the mass of the metal element in the dopant is 0.01 wt% to 1 wt% of the mass of the precursor.

[0027] In a feasible embodiment, the molar ratio of lithium in the lithium source to the sum of nickel and cobalt in the precursor is 0.99 to 1.05.

[0028] In a feasible embodiment, the metal in the amphoteric metal oxide includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn.

[0029] In a feasible embodiment, the mass of the metal element in the amphoteric metal oxide is 0.01 wt% to 1 wt% of the mass of the positive electrode material matrix.

[0030] In a feasible embodiment, the mass of the aluminum fluoride trihydrate is 0.01 wt% to 1 wt% of the mass of the first sintered material.

[0031] In a feasible embodiment, the metal in the metal fluoride includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn.

[0032] In a feasible embodiment, the lithium source comprises at least one of lithium hydroxide and lithium carbonate.

[0033] In a feasible embodiment, the step of obtaining the first sintered material includes: mixing the precursor, lithium source and dopant evenly by ball milling, sintering at 400°C to 600°C in an oxygen-containing atmosphere for 3h to 10h, and then sintering at 650°C to 750°C in an oxygen-containing atmosphere for 3h to 10h.

[0034] In a feasible embodiment, the step of obtaining the second sintered product includes: mixing the first sintered product and the amphoteric metal oxide uniformly by ball milling, and then sintering at 400° C. to 700° C. for 3 h to 10 h in an oxygen-containing atmosphere.

[0035] In a feasible embodiment, the step of obtaining the positive electrode material includes: mixing the second sintered product with aluminum fluoride trihydrate by ball milling until uniformly mixed, and then sintering at 300° C. to 700° C. for 2 h to 10 h in an oxygen-containing atmosphere.

[0036] In a feasible embodiment, in the step of obtaining the positive electrode material, the second sintered material is mixed with aluminum fluoride trihydrate and mixed evenly by ball milling, and then sintered at 100°C to 400°C in an oxygen-containing atmosphere for 2h to 10h, and then sintered at 300°C to 700°C for 2h to 10h.

[0037] An embodiment of the present application further provides a lithium-ion battery, comprising the positive electrode material as described above or the positive electrode material obtained by the preparation method as described above.

[0038] The technical solution of this application has at least the following beneficial effects:

[0039] 1. The coating layer of the positive electrode material provided in the present application comprises a first coating layer of an amphoteric metal oxide, a second coating layer of a metal oxide, and a third coating layer comprising lithium fluoride, aluminum oxide, and aluminum fluoride. Compared with traditional metal oxide coating, the amphoteric metal oxide coating has a more uniform coating layer and eliminates the water washing step, thereby achieving the purpose of reducing residual alkali and improving processing performance, and avoiding the problems of lattice lithium loss, surface impedance increase, and significant decrease in capacity cycle caused by water washing; in addition, the fluoride coating can reduce material side reactions and improve the material's rate performance and cycle performance;

[0040] 2. The preparation method of the positive electrode material provided in the present application uses one or more two-metal oxides for coating during the second sintering of the material, which can not only form a coating layer to effectively improve the performance of the material, but also achieve the purpose of reducing the residual alkali on the surface; at the same time, during the third sintering of the material, the self-hydrolysis characteristics of aluminum fluoride trihydrate are utilized to coat the surface of the material with amphoteric metal oxide on the inner side, metal fluoride in the middle layer, and a mixed coating layer of lithium fluoride, aluminum oxide and aluminum fluoride on the outer side. While further reducing the residual alkali on the surface of the material, the fluoride coating layer as a protective film can effectively reduce the side reactions between the electrode and the electrolyte, thereby improving the rate performance and cycle stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only embodiments of the present application. Those skilled in the art can also derive other drawings based on the provided drawings without inventive effort.

[0042] Figure 1 Shown is a flow chart of the method for preparing the positive electrode material provided in this application;

[0043] Figure 2 Shown is a scanning electron microscope image of the positive electrode material obtained in Example 1;

[0044] Figure 3 Shown is a scanning electron microscope image of the cross-section EDS test of the positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0045] To facilitate understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate exemplary embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0047] Existing binary ultra-high nickel cathode materials suffer from poor cycling stability and rate performance due to their low cobalt content. Furthermore, higher nickel content leads to lower substrate sintering temperatures, resulting in more lithium residue on the material surface. To improve the rate performance and cycling stability of lithium-ion batteries, the present invention provides a cathode material.

[0048] The positive electrode material includes: a positive electrode material matrix, the chemical formula of the positive electrode material matrix is Li a Ni x Co y O2, wherein a>0.9, x≥0.95, y≤0.05, x+y=1; and a coating layer, the coating layer includes a first coating layer present on the surface of the positive electrode material substrate, a second coating layer present on the surface of the first coating layer and a third coating layer present on the surface of the second coating layer, the first coating layer comprises an amphoteric metal oxide, the second coating layer comprises a metal fluoride, and the third coating layer comprises lithium fluoride, aluminum oxide and aluminum fluoride.

[0049] Specifically, in one embodiment of the present application, the positive electrode material further includes a doping element, and the doping element is doped into the positive electrode material matrix.

[0050] Specifically, in one embodiment of the present application, the doping element is selected from at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba.

[0051] In the above embodiment, by doping metal elements into the positive electrode material matrix, the performance in multiple directions such as electrochemical performance, crystal structure, surface morphology and performance, nickel-lithium mixing degree, lithium ion diffusion coefficient, etc. can be adjusted to compensate for a series of problems caused by the lack of Mn / Al elements and the low Co element, improve the safety and stability of the material, and improve the cycle performance and rate performance of the material; through the first coating layer of amphoteric metal oxide, the second coating layer containing metal oxide and the third coating layer containing fluoride, compared with the traditional metal oxide calcination coating, the coating layer is more uniform, and it can also avoid the problems of lattice lithium loss caused by water washing, increased surface impedance, and a significant decrease in capacity cycle; in addition, the fluoride coating can also reduce material side reactions and improve the cycle performance of the material.

[0052] Specifically, in one embodiment of the present application, the doping elements are selected from at least two of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba.

[0053] In the above embodiment, by doping two or more metal elements into the positive electrode material matrix, the performance in multiple directions such as electrochemical performance, crystal structure, surface morphology and performance, nickel-lithium mixing degree, lithium ion diffusion coefficient, etc. can be adjusted to compensate for a series of problems caused by the lack of Mn / Al elements and the low Co element, improve the safety and stability of the material, and improve the cycle performance and rate performance of the material; through the first coating layer of amphoteric metal oxide, the second coating layer containing metal oxide and the third coating layer containing fluoride, compared with the traditional metal oxide calcination coating, the coating layer is more uniform, and it can also avoid the problems of lattice lithium loss caused by water washing, increased surface impedance, and a significant decrease in capacity cycle; in addition, the fluoride coating can also reduce the side reactions of the material and improve the cycle performance of the material.

[0054] In the above-mentioned embodiment, under the synergistic effect of multiple elements, the interlayer spacing of lithium is increased, the cation mixing is reduced, the efficiency of charge transfer and the lithium ion diffusion coefficient are improved, thereby effectively improving the surface performance and structural performance of the material in multiple directions; one or more amphoteric metal oxides are used to coat the positive electrode material matrix, which can not only form a first coating layer to effectively improve the performance of the material, but also achieve the purpose of reducing the surface residual alkali; the first coating layer is also coated with a second coating layer containing metal fluoride and a third coating layer containing lithium fluoride, aluminum oxide and aluminum fluoride, which can further reduce the surface residual alkali while effectively reducing the side reactions of the material and improving the rate performance and cycle stability of the material.

[0055] Specifically, in one embodiment of the present application, aluminum fluoride is present at the interface between the second coating layer and the third coating layer. Aluminum fluoride can prevent hydrogen fluoride from further reacting with the surface coating layer, thereby controlling the thickness of the coating layer. At the same time, aluminum fluoride can reduce side reactions between the electrode and the electrolyte, thereby improving the rate performance and cycle stability of the material.

[0056] Specifically, in one embodiment of the present application, the mass of the metal element in the metal fluoride is 0.01 wt % to 1 wt % of the mass of the positive electrode material matrix.

[0057] Specifically, in one embodiment of the present application, the content of lithium fluoride accounts for 0.001 wt% to 0.1 wt% of the positive electrode material.

[0058] Specifically, in one embodiment of the present application, the content of aluminum oxide accounts for 0.01 wt% to 1 wt% of the positive electrode material.

[0059] Specifically, in one embodiment of the present application, the content of aluminum fluoride accounts for 0.01 wt % to 1 wt % of the positive electrode material.

[0060] Specifically, in one embodiment of the present application, the metal in the amphoteric metal oxide includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn; the mass of the metal element in the amphoteric metal oxide is 0.01 wt% to 1 wt% of the mass of the positive electrode material matrix. By coating the positive electrode material matrix with the amphoteric metal oxide, the amphoteric metal oxide reacts with residual hydroxide on the surface, thereby reducing some of the residual alkali on the surface and forming a first coating layer to improve material performance.

[0061] Specifically, in one embodiment of the present application, the metal in the metal fluoride includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn. The material surface is coated with an amphoteric metal oxide on the inside, a metal fluoride in the middle, and a mixed coating of lithium fluoride, aluminum oxide, and aluminum fluoride on the outside. This further reduces residual alkali on the material surface. The fluoride coating acts as a protective film, effectively minimizing side reactions between the electrode and the electrolyte, thereby improving the material's rate capability and cycling stability.

[0062] This application provides a method for preparing a positive electrode material, such as Figure 1 As shown, the method includes the following steps S100-S300:

[0063] S100, after mixing the precursor and the lithium source, perform the first sintering to obtain the first sintered product. The chemical formula of the precursor is Ni x Co y (OH)2, wherein x≥0.95, y≤0.05, and x+y=1.

[0064] In a specific embodiment, the molar ratio of lithium in the lithium source to the sum of nickel and cobalt in the precursor is 0.99 to 1.05, for example, 1.02 or 1.03, but is not limited to the values listed, and other values not listed within the numerical range are also applicable.

[0065] Furthermore, in one embodiment of the present application, in step S100, after the precursor and the lithium source are mixed, a dopant is added and a first sintering is performed. The lithium source includes at least one of lithium hydroxide and lithium carbonate.

[0066] In a specific embodiment, the dopant includes a metal oxide and / or a metal hydroxide, wherein the metal in the metal oxide and the metal hydroxide includes at least two of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba. The mass of the metal in the dopant is 0.01 wt% to 1 wt% of the mass of the precursor. For example, typical but non-limiting examples include: 1000 g of a nickel-cobalt binary precursor with 1.4 g of ZrO2 and 1.6 g of Ba(OH)2, and 1000 g of a nickel-cobalt binary precursor with 0.7 g of ZrO2, 0.2 g of MgO, 2.1 g of Al2O3, and 1.6 g of Ba(OH)2. By doping with two or more metal elements and lithium sources, the performance in multiple directions such as electrochemical properties, crystal structure, surface morphology and performance, degree of nickel-lithium mixing, and lithium ion diffusion coefficient can be adjusted to compensate for a series of problems caused by the lack of Mn / Al elements and low Co elements, thereby improving the safety and stability of the material and improving the cycle performance and rate performance of the material.

[0067] Specifically, the precursor, lithium source, and dopant are mixed uniformly by ball milling, and then sintered at 400°C to 600°C for 3 to 10 hours in an oxygen-containing atmosphere, and then sintered at 650°C to 750°C for 3 to 10 hours in an oxygen-containing atmosphere. For example, the sintering temperature may be 500°C and 700°C or 550°C and 720°C, and the sintering time may be 4 hours, 5 hours, or 6 hours, but the values listed are not limited thereto, and other values not listed within the numerical range are also applicable.

[0068] This application first uses a precursor, a lithium source and a dopant as raw materials, mixes them at high speed and then sinters the matrix. Under the synergistic effect of multiple elements, the surface stability, crystal structure stability and electrochemical performance of the material are simultaneously improved.

[0069] S200, mixing the first sintered product with the amphoteric metal oxide, and then performing a second sintering reaction to obtain a second sintered product.

[0070] Specifically, the metal in the amphoteric metal oxide includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn. The mass of the metal element in the amphoteric metal oxide is 0.01 wt% to 1 wt% of the mass of the first sinter. For example, 2.8 g ZrO2 and 1000 g of the first sinter, or 2.8 g TiO2 and 1000 g of the first sinter, or 1.8 g TiO2, 3.8 g Al, and 1000 g of the first sinter. Preferably, the mass of the metal element in the amphoteric metal oxide is 0.1 wt% to 0.3 wt% of the mass of the first sinter. By coating the first sinter with the amphoteric metal oxide, the amphoteric metal oxide reacts with the residual alkali on the surface, thereby reducing some of the residual alkali on the surface and forming a first coating layer to improve material properties.

[0071] Specifically, the first sintered product and the amphoteric metal oxide are mixed uniformly by ball milling and then sintered at 400° C. to 700° C. for 3 to 10 hours in an oxygen-containing atmosphere. For example, the sintering temperature may be 600° C. or 630° C., and the sintering time may be 5 hours, 6.5 hours, or 8 hours. However, these values are not limited thereto, and other values not listed within this range are also applicable.

[0072] The first sintered material is mixed with one or more amphoteric metal oxides selected from the group consisting of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn. After mixing, a second sintering step is performed to coat the first sintered material with a uniform coating to stabilize the surface structure and enhance its electrochemical properties. Simultaneously, the amphoteric oxide reacts with residual alkali (lithium hydroxide or lithium carbonate) remaining on the surface of the material, effectively reducing the residual alkali on the surface.

[0073] S300, mixing the second sintered product with aluminum fluoride trihydrate, and then sintering for a third time to obtain a positive electrode material.

[0074] Specifically, the mass of aluminum fluoride trihydrate is 0.01 wt% to 1 wt% of the mass of the second sinter. For example, 4.8 g of AlF3·3H2O and 1000 g of the second sinter prepared in the previous step, or 5.7 g of AlF3·3H2O and 1000 g of the second sinter prepared in the previous step, are suitable. However, these values are not limited to the values listed above, and other values not listed within this range are also applicable. Preferably, the mass of aluminum fluoride trihydrate is 0.05 wt% to 0.2 wt% of the mass of the first sinter.

[0075] Specifically, the metal in the metal fluoride includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn.

[0076] Specifically, the second sintered material is mixed with aluminum fluoride trihydrate by ball milling and then sintered at 300°C to 700°C for 2h to 10h in an oxygen-containing atmosphere. Preferably, the second sintered material is mixed with aluminum fluoride trihydrate by ball milling and then sintered at 100°C to 400°C for 2h to 10h in an oxygen-containing atmosphere, and then sintered at 300°C to 700°C for 2h to 10h. The thermal decomposition of AlF3·3H2O consists of a two-step dehydration reaction and a hydrolysis reaction of the dehydrated product. Aluminum fluoride dehydrates rapidly in the temperature range of 122°C to 200°C, begins to hydrolyze at 300°C, and hydrolyzes violently above 500°C. During hydrolysis, a layer of aluminum oxide is formed on the surface, and HF gas is slowly generated. A portion of the HF gas reacts with the residual alkali on the surface to form lithium fluoride, and a portion reacts with the metal oxide of the first coating layer to form metal fluoride. Therefore, the sample, after the first coating, was uniformly mixed with aluminum fluoride trihydrate and sintered a third time. The result was a cathode material with multiple coating layers, low surface residual alkali, and excellent structural and electrochemical properties. Because aluminum fluoride trihydrate undergoes a staged autohydrolysis, staged calcination allows for more precise control of the hydrolysis rate and hydrogen fluoride generation rate, enabling better achievement of the desired results based on the experimental design.

[0077] By mixing the sample after the first coating with aluminum fluoride trihydrate again and then sintering, the hydrogen fluoride generated during the hydrolysis of aluminum fluoride trihydrate as the temperature rises reacts with the residual alkali on the surface of the first coating layer to produce lithium fluoride, and reacts with the metal oxide of the first coating layer to form a second coating layer including multiple metal fluorides (including Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn) and a third coating layer including lithium fluoride, aluminum oxide, and aluminum fluoride outside the first coating layer. In this way, while further reducing the residual alkali on the surface, the side reactions of the material can be effectively reduced, and the rate performance and cycle stability of the material can be improved.

[0078] The present application uses one or more amphoteric metal oxides to coat the positive electrode material during the second sintering, thereby forming a coating layer to effectively improve the performance of the material and reduce the residual alkali on the surface. At the same time, the third sintering of the material utilizes the self-hydrolysis characteristics of aluminum fluoride trihydrate to coat the material surface with an amphoteric metal oxide on the inner side, a metal fluoride in the middle layer, and a mixed coating layer of lithium fluoride, aluminum oxide and aluminum fluoride on the outer side. While further reducing the residual alkali on the surface of the material, the fluoride coating layer as a protective film can effectively reduce the side reaction between the electrode and the electrolyte, thereby improving the rate performance and cycle stability of the material. At the same time, this positive electrode material sintering process does not require the participation of water, eliminates steps such as water washing and drying, and has a simple process and low cost. Compared with the atomic layer deposition (ALD) coating aluminum trifluoride technology, it is low cost and has the conditions for mass production.

[0079] The present application also provides a lithium-ion battery comprising the above-mentioned positive electrode material or the positive electrode material obtained by the above-mentioned preparation method.

[0080] The following further illustrates the embodiments of the present application in multiple embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0081] Example 1

[0082] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 1.4gZrO2 and 1.6gBa(OH)2, ball-mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 500℃ in the first stage and 700℃ in the second stage; after crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0083] 2. Weigh 2.8 g ZrO2 and 1000 g of the matrix prepared in the previous step, mix them by ball milling, and then calcine them at 600°C. After sintering, crush them and sieve them through 325 mesh to obtain a calcined sample.

[0084] 3. Weigh 5.7 g of AlF3·3H20 and 1000 g of the second-sintered sample prepared in the previous step, mix by ball milling, and then perform third sintering at 500°C. After sintering, crush and sieve through 325 mesh to obtain the positive electrode material.

[0085] Figure 2 The following is a scanning electron microscope image of the positive electrode material obtained in Example 1. Figure 2As shown in FIG, the positive electrode material is a complete sphere, the primary particles grow well, there is a clear coating layer on the surface, and there is no obvious residual alkali on the surface. The cross-section EDS test of the positive electrode material of Example 1 is performed, and the results are as follows Figure 3 The outermost surface of the secondary sphere is enriched with fluorine and aluminum. Moving inward, through a thin layer containing fluorine and zirconium, the fluorine content gradually decreases, leading to the first coating layer, primarily composed of zirconium oxide. Qualitative analysis of the material using XPS testing revealed that the fluorine ions on the outermost surface are negatively charged, while the aluminum ions are positively charged. Therefore, it can be determined that the main compounds present are aluminum fluoride, aluminum oxide, and lithium fluoride.

[0086] The positive electrode material obtained in this embodiment includes a positive electrode material matrix and a coating layer. The chemical formula of the positive electrode material matrix is Li 1.02 Ni 0.98 Co 0.02 O2; the amphoteric metal oxide of the first coating layer is ZrO2; the second coating layer is mainly ZrF4 and LiF; the third coating layer is mainly AlF3, Al2O3 and LiF; the doping elements are Zr and Ba; the mass of the metal elements in the amphoteric metal oxide is 0.2% of the mass of the positive electrode material matrix.

[0087] The results of the performance test of the positive electrode material prepared in Example 1 are shown in Table 1.

[0088] Example 2

[0089] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 1.4gZrO2 and 1.6gBa(OH)2, ball-mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 500℃ in the first stage and 700℃ in the second stage. After crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0090] 2. Weigh 2.8 g of TiO2 and 1000 g of the matrix prepared in the previous step, mix by ball milling, and then calcine at 600°C. After sintering, crush and sieve through 325 mesh to obtain a calcined sample.

[0091] 3. Weigh 4.8 g of AlF3·3H20 and 1000 g of the second-sintered sample prepared in the previous step, ball-mill the mixture, and then perform third-sintering at 550°C. After sintering, crush and sieve through 325 mesh to obtain the positive electrode material.

[0092] The positive electrode material obtained in this embodiment includes a positive electrode material matrix and a coating layer. The chemical formula of the positive electrode material matrix is Li 1.02 Ni 0.98Co 0.02 O2; the amphoteric metal oxide of the first coating layer is TiO2; the second coating layer is mainly TiF4 and LiF; the third coating layer is mainly AlF3, Al2O3 and LiF; the doping elements are Zr and Ba; the mass of the metal elements in the amphoteric metal oxide is 0.16% of the mass of the positive electrode material matrix.

[0093] The results of the performance test of the positive electrode material prepared in Example 2 are shown in Table 1.

[0094] Example 3

[0095] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 0.7gZrO2, 0.2gMgO, 2.1gAl2O3 and 1.6gBa(OH)2, ball mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 500℃ in the first stage and 700℃ in the second stage. After crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0096] 2. Weigh 1.8g TiO2, 3.8g Al2O3, and 1000g of the matrix prepared in the previous step, ball-mill the mixture, and calcine at 600°C. After sintering, crush and sieve through 325 mesh to obtain a calcined sample.

[0097] 3. Weigh 4.8 g of AlF3·3H20 and 1000 g of the second-sintered sample prepared in the previous step, ball-mill the mixture, and then perform third-sintering at 550°C. After sintering, crush and sieve through 325 mesh to obtain the positive electrode material.

[0098] The positive electrode material obtained in this embodiment includes a positive electrode material matrix and a coating layer. The chemical formula of the positive electrode material matrix is Li 1.02 Ni 0.98 Co 0.02 O2; the amphoteric metal oxides of the first coating layer are Al2O3 and TiO2; the second coating layer is mainly AlF3, TiF4 and LiF; the third coating layer is mainly AlF3, Al2O3 and LiF; the doping elements are Zr, Mg, Al and Ba; the mass of the metal elements in the amphoteric metal oxides is 0.3% of the mass of the positive electrode material matrix.

[0099] The results of the performance test of the positive electrode material prepared in Example 3 are shown in Table 1.

[0100] Example 4

[0101] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 1.4gZrO2 and 1.6gBa(OH)2, ball-mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 530℃ in the first stage and 680℃ in the second stage. After crushing and 325 mesh sieving, the positive electrode material matrix can be obtained.

[0102] 2. Weigh 1.8 g TiO2, 3.8 g Al2O3, and 1000 g of the matrix prepared in the previous step, ball-mill the mixture, and calcine at 630°C. After sintering, crush and sieve through 325 mesh to obtain a calcined sample.

[0103] 3. Weigh 4.8g of AlF3·3H2O and 1000g of the second-sintered sample prepared in the previous step, ball-mill the mixture, and then perform a third sintering process at 250°C for the first stage and 580°C for the second stage. After sintering, crush and sieve through a 325-mesh sieve to obtain the positive electrode material.

[0104] The positive electrode material obtained in this embodiment includes a positive electrode material matrix and a coating layer. The chemical formula of the positive electrode material matrix is Li 1.02 Ni 0.98 Co 0.02 O2; the amphoteric metal oxides of the first coating layer are Al2O3 and TiO2; the second coating layer is mainly AlF3, TiF4 and LiF; the third coating layer is mainly AlF3, Al2O3 and LiF; the doping elements are Zr and Ba; the mass of the metal elements in the amphoteric metal oxides is 0.3% of the mass of the positive electrode material matrix.

[0105] The results of the performance test of the positive electrode material prepared in Example 4 are shown in Table 1.

[0106] Example 5

[0107] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, and then add 1.4gZrO2. After ball milling and mixing the raw materials evenly, calcinate them in an oxygen atmosphere. The calcination temperature is 530℃ in the first stage and 680℃ in the second stage. After crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0108] 2. Weigh 1.8 g TiO2, 3.8 g Al2O3, and 1000 g of the matrix prepared in the previous step, mix by ball milling, and then calcine at 630°C. After sintering, crush and sieve through 325 mesh to obtain a calcined sample.

[0109] 3. Weigh 4.8g of AlF3·3H2O and 1000g of the second-sintered sample prepared in the previous step, ball-mill the mixture, and then perform a third sintering process at 250°C for the first stage and 580°C for the second stage. After sintering, crush and sieve through a 325-mesh sieve to obtain the positive electrode material.

[0110] The positive electrode material obtained in this embodiment includes a positive electrode material matrix and a coating layer. The chemical formula of the positive electrode material matrix is Li 1.02 Ni 0.98 Co 0.02 O2; the amphoteric metal oxides of the first coating layer are Al2O3 and TiO2; the second coating layer is mainly AlF3, TiF4 and LiF; the third coating layer is mainly AlF3, Al2O3 and LiF; the doping element is Zr; the mass of the metal elements in the amphoteric metal oxides is 0.1% of the mass of the positive electrode material matrix.

[0111] The results of the performance test of the positive electrode material prepared in Example 5 are shown in Table 1.

[0112] Example 6

[0113] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh LiOH·H2O with a purity of 99% according to the ratio of Li / (Ni+Co)=1.02, ball-mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere at a calcination temperature of 500°C in the first stage and 700°C in the second stage; after crushing and 325-mesh sieving, the positive electrode material matrix can be obtained.

[0114] 2. Weigh 2.8 g ZrO2 and 1000 g of the matrix prepared in the previous step, mix them by ball milling, and then calcine them at 600°C. After sintering, crush them and sieve them through 325 mesh to obtain a calcined sample.

[0115] 3. Weigh 5.7 g of AlF3·3H20 and 1000 g of the second-sintered sample prepared in the previous step, mix by ball milling, and then perform third sintering at 500°C. After sintering, crush and sieve through 325 mesh to obtain the positive electrode material.

[0116] The positive electrode material obtained in this embodiment includes a positive electrode material matrix and a coating layer. The chemical formula of the positive electrode material matrix is Li 1.02 Ni 0.98 Co 0.02 O2; the amphoteric metal oxide of the first coating layer is ZrO2; the second coating layer is mainly ZrF4 and LiF; the third coating layer is mainly AlF3, Al2O3 and LiF; the mass of the metal elements in the amphoteric metal oxide is 0.2% of the mass of the positive electrode material matrix.

[0117] The results of the performance test of the positive electrode material prepared in Example 6 are shown in Table 1.

[0118] Comparative Example 1

[0119] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 1.4gZrO2 and 1.6gBa(OH)2, ball-mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 500℃ in the first stage and 700℃ in the second stage. After crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0120] 2. Weigh 2.8 g ZrO2 and 1000 g of the matrix prepared in the previous step, mix by ball milling, and then calcine at 600°C. After sintering, crush and sieve through 325 mesh to obtain a calcined sample.

[0121] 3. Weigh 2.85g H3BO3 and 1000g of the second-sintered sample, mix them by ball milling, and then perform third-sintering at 350°C. After sintering, crush and sieve through 325 mesh to obtain the positive electrode material.

[0122] The results of the performance test of the positive electrode material prepared in Comparative Example 1 are shown in Table 1.

[0123] Comparative Example 2

[0124] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 1.4gZrO2 and 1.6gBa(OH)2, ball-mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 500℃ in the first stage and 700℃ in the second stage. After crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0125] 2. Weigh 2.8g TiO2 and 1000g of the matrix prepared in the previous step, mix by ball milling, and calcine at 600°C. After sintering, crush and sieve through 325 mesh to obtain the positive electrode material.

[0126] The results of the performance test of the positive electrode material prepared in Comparative Example 2 are shown in Table 1.

[0127] Comparative Example 3

[0128] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02(OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 0.7gZrO2, 0.2gMgO, 2.1gAl2O3 and 1.6gBa(OH)2, ball mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 500℃ in the first stage and 700℃ in the second stage. After crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0129] 2. Weigh 3.1 g of Zr(HPO4)2 and 1000 g of the matrix prepared in the previous step, mix by ball milling, and then calcine at 600°C. After sintering, crush and sieve through 325 mesh to obtain a calcined sample.

[0130] 3. Weigh 4.8 g of AlF3·3H20 and 1000 g of the second-sintered sample prepared in the previous step, ball-mill the mixture, and then perform third-sintering at 550°C. After sintering, crush and sieve through 325 mesh to obtain the positive electrode material.

[0131] The results of the performance test of the positive electrode material prepared in Comparative Example 3 are shown in Table 1.

[0132] Comparative Example 4

[0133] 1. Weigh 1000g of nickel-cobalt binary precursor Ni 0.98 Co 0.02 (OH)2, weigh 99% pure LiOH·H2O according to the ratio of Li / (Ni+Co)=1.02, then add 1.4gZrO2 and 1.6gBa(OH)2, ball-mill the raw materials to mix evenly, and calcine them in an oxygen atmosphere. The calcination temperature is 500℃ in the first stage and 700℃ in the second stage. After crushing and 325 mesh screening, the positive electrode material matrix can be obtained.

[0134] 2. The substrate was washed with water, filtered, and dried. 1000 g of the washed sample was weighed and mixed with 5.7 g of AlF3·3H20 by ball milling. The mixture was then calcined at 350°C for three times. After sintering, the substrate was crushed and sieved through 325 mesh to obtain the positive electrode material.

[0135] The results of the performance test of the positive electrode material prepared in Comparative Example 4 are shown in Table 1.

[0136] Performance Testing

[0137] Both the comparative examples and the examples were tested using button-type batteries for the first discharge capacity. Charge and discharge conditions were set at 25°C, 3.0V to 4.3V, and 0.1C for the first charge and discharge. The resulting discharge capacity was the first discharge capacity, and the first charge and discharge efficiency was calculated as the first discharge capacity divided by the first charge capacity. The capacity retention rate was measured after 50 cycles of charge and discharge at a rate of 0.5C / 1C. The first discharge capacity during these 50 cycles was recorded as the 1C discharge capacity.

[0138] The comparative examples and examples all used titration to test the hydroxide and carbonate concentrations. A small amount of powder was mixed with deionized water and stirred for a period of time, then filtered. After adding an indicator, the material was titrated with a certain concentration of hydrochloric acid to measure the hydroxide and carbonate concentrations. The results of the above performance tests are as follows:

[0139] Table 1. Performance comparison results

[0140]

[0141]

[0142] As shown in Table 1, the positive electrode materials prepared in Examples 1 to 6 of the present application all have excellent electrochemical properties, good rate performance, outstanding long cycle performance, and low surface alkali content.

[0143] From the data comparison of Example 1 and Comparative Example 1 in Table 1, it can be seen that compared with the traditional process of coating the substrate with boric acid, the sample after the first layer of coating is uniformly mixed with aluminum fluoride trihydrate again and sintered for the third time by adjusting the sintering conditions, while further reducing the surface residual alkali, the rate performance and cyclic stability of the material can be improved. From the data comparison of Example 2 and Comparative Example 2 in Table 1, it can be seen that compared with the traditional process of coating the substrate once, the sample after the first layer of coating is uniformly mixed with aluminum fluoride trihydrate again and sintered for the third time by adjusting the sintering curve, while further reducing the surface residual alkali, the rate performance and cyclic stability of the material can be improved. From the data comparison of Example 3 and Comparative Example 3, it can be seen that compared with the traditional process of coating the substrate with phosphate, the sample after the first layer of coating is uniformly mixed with aluminum fluoride trihydrate again and sintered for the third time by adjusting the sintering curve, while further reducing the surface residual alkali, the rate performance and cyclic stability of the material can be improved. Comparison of the data in Example 1 and Comparative Example 4 shows that when amphoteric metal oxide coating is used instead of water washing, drying and other steps, the capacity and cycle performance are greatly improved, while also eliminating the sewage treatment step required for conventional water washing to remove residual alkali.

[0144] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are protected by this application.

Claims

1. A positive electrode material, characterized in that The positive electrode material includes: The positive electrode material matrix has the general chemical formula of Li a Ni x Co y O2, where a>0.9, x≥0.95, y≤0.05, x+y=1; and The coating layer includes a first coating layer present on the surface of the positive electrode material substrate, a second coating layer present on the surface of the first coating layer, and a third coating layer present on the surface of the second coating layer, wherein the first coating layer contains an amphoteric metal oxide, the second coating layer contains a metal fluoride, and the third coating layer contains lithium fluoride, aluminum oxide, and aluminum fluoride.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material includes at least one of the following features af: a. The positive electrode material further comprises a doping element, wherein the doping element is doped in the positive electrode material matrix; b. The aluminum fluoride is present at the interface between the second coating layer and the third coating layer; c. The mass of the metal element in the metal fluoride is 0.01wt% to 1wt% of the mass of the positive electrode material matrix; d. The content of the lithium fluoride accounts for 0.001wt% to 0.1wt% of the positive electrode material; e. The content of the aluminum oxide accounts for 0.01wt% to 1wt% of the positive electrode material; f. The content of the aluminum fluoride accounts for 0.01 wt% to 1 wt% of the positive electrode material.

3. The positive electrode material according to claim 2, characterized in that The doping element is selected from at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba.

4. The positive electrode material according to claim 1, characterized in that The positive electrode material includes at least one of the following features a to d: a. The metal in the amphoteric metal oxide includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn; b. The mass of the metal element in the amphoteric metal oxide is 0.01 wt% to 1 wt% of the mass of the positive electrode material matrix; c. The metal in the metal fluoride includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn; d. The positive electrode material further contains doping elements, which are doped in the positive electrode material matrix, and the doping elements are selected from at least two of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba.

5. A method for preparing the positive electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: After the precursor and the lithium source are mixed, the first sintering is performed to obtain the first sintered product. The chemical formula of the precursor is Ni x Co y (OH)2, where x≥0.95, y≤0.05, and x+y=1; After mixing the first sintered product with an amphoteric metal oxide, the product is sintered for a second time to obtain a second sintered product; and After the second sintered product is mixed with aluminum fluoride trihydrate, sintering is performed for the third time to obtain the positive electrode material.

6. The preparation method according to claim 5, characterized in that The step of obtaining the first sintered product includes: mixing the precursor and the lithium source, adding a dopant, and performing a first sintering.

7. The preparation method according to claim 6, characterized in that It satisfies at least one of the following conditions a to i: a. The dopant comprises metal oxide and / or metal hydroxide; b. The dopant comprises a metal oxide and / or a metal hydroxide, wherein the metal in the metal oxide and the metal hydroxide comprises at least two of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Ag, Sn, Au, Mn, Mg, Sr, Ga, Y, Al, and Ba; c. The mass of the metal element in the dopant is 0.01 wt% to 1 wt% of the mass of the precursor; d. The molar ratio of lithium in the lithium source to the sum of nickel and cobalt in the precursor is 0.99 to 1.05; e. The metal in the amphoteric metal oxide includes at least one of Be, Ti, V, Fe, Co, Zn, Ge, Zr, Al, Ag, Sn, Au, and Mn; f. The mass of the metal element in the amphoteric metal oxide is 0.01 wt% to 1 wt% of the mass of the first sintered product; g. The mass of the aluminum fluoride trihydrate is 0.01 wt% to 1 wt% of the mass of the second sintered material; h. The lithium source comprises at least one of lithium hydroxide and lithium carbonate.

8. The preparation method according to claim 6, characterized in that It satisfies at least one of the following conditions a to c: a. The step of obtaining the first sintered product comprises: mixing the precursor, the lithium source and the dopant uniformly by ball milling, sintering them at 400° C. to 600° C. for 3 h to 10 h in an oxygen-containing atmosphere, and then sintering them at 650° C. to 750° C. for 3 h to 10 h in an oxygen-containing atmosphere; b. The step of obtaining the second sintered product comprises: mixing the first sintered product and the amphoteric metal oxide uniformly by ball milling, and then sintering the mixture at 400° C. to 700° C. for 3 h to 10 h in an oxygen-containing atmosphere; c. The step of obtaining the positive electrode material comprises: mixing the second sintered product and the aluminum fluoride trihydrate by ball milling until uniformly mixed, and then sintering at 300° C. to 700° C. for 2 h to 10 h in an oxygen-containing atmosphere.

9. The preparation method according to claim 8, characterized in that In the step of obtaining the positive electrode material, the second sintered product and the aluminum fluoride trihydrate are mixed uniformly by ball milling, and then sintered at 100°C to 400°C in an oxygen-containing atmosphere for 2h to 10h, and then sintered at 300°C to 700°C for 2h to 10h.

10. A lithium ion battery, characterized in that: The invention comprises the positive electrode material according to any one of claims 1 to 4 or the positive electrode material obtained by the preparation method according to any one of claims 5 to 9.

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