Ternary polycrystal positive electrode material and preparation method therefor, lithium-ion battery and electric device

Abstract

The present application relates to a ternary polycrystal positive electrode material and a preparation method therefor, a lithium-ion battery and an electric device. The ternary polycrystal positive electrode material comprises a ternary positive electrode material matrix and a composite oxide coating layer coating the surface of the matrix, wherein the composite oxide coating layer is rich in Co, Nb and M3 elements, with the M3 element being selected from at least one of Si, W, Sn, La, Zr, Ce, Mg and Al. With regard to the composite oxide coating layer rich in Co, Nb and M3 elements on the surface of the ternary polycrystal positive electrode material in the present application, all the elements cooperate with one another, such that the positive electrode material having the composite oxide coating layer rich in Co, Nb and M3 elements has better electrochemical performance.

Description

A ternary polycrystalline cathode material and its preparation method, lithium-ion battery and power device thereof

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on May 28, 2024, application number 202410672263.0, entitled "A ternary polycrystalline cathode material and its preparation method, lithium-ion battery and power device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of lithium-ion battery technology, and particularly relates to a ternary polycrystalline cathode material and its preparation method, a lithium-ion battery, and an electrical device. Background Technology

[0004] High-nickel ternary layered transition metal oxide cathode materials possess high energy density and cost-effectiveness, making them one of the most competitive cathode materials for lithium-ion power batteries and attracting widespread attention from researchers. However, while increasing the nickel content (Ni≥80%) increases energy density, it also brings some urgent technical challenges to be addressed.

[0005] In high-nickel ternary materials, some failure occurs on the material surface, and Ni fails during cycling. 2+ The proportion of the interface has increased due to Ni 2+ With Li + The approximate ionic radii of the two molecules will lead to increased lithium-nickel mixing, further triggering phase transitions in the bulk and surface phases, accompanied by the release of lattice oxygen. During charging, the released oxygen undergoes side reactions with the electrolyte, producing gases such as CO2, which deteriorates the material interface and seriously affects the battery's safety performance.

[0006] To minimize the Ni content of the material 2+ The lithiation process requires the addition of an excess of lithium source and is carried out under pure oxygen conditions. However, the lithium remaining on the material surface after sintering readily reacts with moisture and CO2 in the air, existing as Li2CO3 and LiOH on the material surface. Therefore, the high alkalinity of the high-nickel material surface induces the degradation of polyvinylidene fluoride (PVDF), making the slurry jelly-like and deteriorating the homogenization process. On the other hand, residual lithium on the surface increases the material impedance, hindering lithium-ion diffusion during charging and discharging, thus increasing battery polarization and reducing cycle performance.

[0007] Common methods for reducing residual alkali include water washing and surface coating. While water washing can significantly reduce residual alkali, polar water molecules can also cause Li+ oxidation on the material surface. + / H +Exchange damages the material surface, increasing its impedance. In common coating methods, cobalt coating reacts with residual alkali on the surface to form a cobalt-rich structure, reducing the surface nickel content and mitigating reaction with the electrolyte. Patent document CN112750999B describes a gradient coating of Co onto the surface of a high-nickel single crystal, significantly improving energy density and cycle retention. However, the coating agent used in the dry mixing process is nanoparticles, which are prone to agglomeration during mixing, making it difficult to ensure coating uniformity. Non-uniform coating means uneven reaction between the coating agent and residual alkali on the surface, resulting in areas of excessively thick and thin coating layers on the surface of a single particle. During charge-discharge cycling, this causes different areas of Li in the single particle to... + Increased differences in the degree of embedding / extraction can lead to localized stress, which may eventually cause cracks in the material. Summary of the Invention

[0008] The technical problem to be solved by this application is to overcome the deficiencies and defects mentioned in the background art above, and to provide a ternary polycrystalline cathode material and its preparation method, a lithium-ion battery and an electrical device.

[0009] To solve the above-mentioned technical problems, the technical solution proposed in this application is as follows:

[0010] The first aspect of this application provides a ternary polycrystalline cathode material, comprising a ternary cathode material matrix and a composite oxide coating layer covering the surface of the matrix; wherein the composite oxide coating layer is rich in Co, Nb, and M3 elements, wherein the M3 element is selected from at least one of Si, W, Sn, La, Zr, Ce, Mg, and Al. In this application, "rich in" Co, Nb, and M3 elements in the coating layer means that the content of Co, Nb, and M3 elements in the coating layer is higher than that in the matrix.

[0011] In this application, regions on the material surface with significantly higher Co, Nb, and M3 content than those inside the particles, as observed on EPMA, are considered to be Co, Nb, and M3-rich regions.

[0012] In some embodiments, in the aforementioned ternary polycrystalline cathode material, the average thickness of the Co-rich region in the composite oxide coating layer is 0.70 μm-1.50 μm, and the average thickness of the Nb-rich region is 0.50 μm-1.80 μm.

[0013] In some embodiments, in the aforementioned ternary polycrystalline cathode material, the standard deviation of the thickness of the Co-rich region in the composite oxide coating layer is 0.10 μm-0.30 μm, and the standard deviation of the thickness of the Nb-rich region is 0.10 μm-0.30 μm.

[0014] In some embodiments, in the aforementioned ternary polycrystalline cathode material, the average Co atom content in the composite oxide coating layer is 1.300%-2.000%, and the average Nb atom content is 0.020%-0.080%.

[0015] In some embodiments, in the aforementioned ternary polycrystalline cathode material, the average standard deviation of the Co atom percentage in the composite oxide coating layer is 0.150%-0.200%, and the average standard deviation of the Nb atom percentage is 0.010%-0.020%.

[0016] If the average percentage of Co and Nb atoms exceeds this range, it indicates that the coating layer is too thick, and the effect of improving ionic conductivity is not significant. By controlling the enrichment thickness and regional content of each element on the surface within an appropriate range, the promoting effect of the three elements can be more fully utilized, further improving high-temperature cycling, high-temperature DCR growth, and thermal stability.

[0017] In some embodiments, the ternary polycrystalline cathode material further includes a boron compound layer, which coats the surface of the composite oxide coating layer.

[0018] In some embodiments, the chemical formula of the ternary polycrystalline cathode material matrix is ​​Li. a Ni b Co c M1 d M2 e O2, where M1 includes at least one of Mn and Al, M2 includes at least one of Zr, Sr, W, Al, Ti, Mo, Ce, Ca, Ta and Mg, 0.97≤a≤1.10, 0.300≤b≤0.990, 0.005≤c≤0.300, 0.005≤d≤0.300, and 0≤e≤0.030.

[0019] As a general inventive concept, this application also provides a method for preparing the above-mentioned ternary polycrystalline cathode material, comprising the following steps:

[0020] (1) The ternary precursor material, lithium source and compound containing M2 element are mixed and sintered to obtain a sintered material;

[0021] (2) The first sintered material is mixed with a cobalt source, a niobium source and a compound containing M3 element and then sintered to obtain a second sintered material, which is a ternary polycrystalline cathode material.

[0022] In some embodiments, in the above preparation method, in step (1), the sintering is segmented sintering, first heating to 400℃~600℃, holding for 2h~5h, then heating to 650℃~850℃, holding for 8h~14h.

[0023] In some embodiments, in the above preparation method, in step (2), the sintering is segmented sintering, first heating to 200℃~300℃, holding for 2h~4h, then heating to 550℃~720℃, holding for 8h~12h.

[0024] In the technical solution of step (2) of this application, a calcination temperature platform is set near the thermal decomposition temperature of the cobalt and niobium sources, allowing the coating agent sufficient time to decompose into fine oxides and uniformly disperse on the material surface. During the second stage of heat preservation, the reaction with residual alkali on the surface is more thorough and complete, achieving the purpose of uniform coating. This method of setting a platform to allow the coating agent to fully decompose and generate fine oxides and distribute them uniformly compensates for the defects of uneven dry mixing, making the reaction between the coating agent elements and residual lithium on the surface more complete, and uniformly constructing a Co / Nb-rich region on the surface. The nano-sizing of the coating agent during shell construction not only allows the coating agent to fully react with residual alkali on the surface, but also prevents the electrolyte from eroding the material surface, and reduces side reactions on the material surface. Therefore, the stability of the material is increased, thereby improving the discharge capacity and excellent cycle stability of the material. If the set temperature of the first stage is lower than the set temperature range, the effect is similar to not setting the temperature of the first stage, that is, the coating agent cannot reach the decomposition temperature and cannot make full use of the thermal decomposition process; if the set temperature of the second stage is higher than the set temperature range, it means that the coating agent is heated at a faster rate and cannot be nano-sized. The effect is similar to the platform without the first stage, and the coating reaction is not fully completed.

[0025] In some embodiments, the lithium source in the above preparation method includes at least one of lithium carbonate, lithium hydroxide, and lithium oxide.

[0026] In some embodiments, the cobalt source in the above preparation method includes at least one of cobalt oxide, cobalt hydroxide, cobalt hydroxyoxide, cobalt tetroxide, cobalt carbonate, cobalt sulfide, and cobalt acetate.

[0027] In some embodiments, the niobium source in the above preparation method includes at least one of elemental niobium powder, niobium pentoxide, lithium niobate, barium niobate, niobium oxalate, and niobium hydroxide.

[0028] In some embodiments, the M2-containing compound in the above preparation method includes at least one of zirconium oxide, strontium oxide, tungsten oxide, aluminum oxide, titanium oxide, molybdenum oxide, cerium oxide, calcium sulfate, tantalum oxide, and magnesium oxide.

[0029] In some embodiments, the M3-containing compound in the above preparation method includes at least one of silicon oxide, tungsten oxide, lanthanum oxide, cerium oxide, zirconium oxide, magnesium oxide, tin oxide, sodium aluminate, and aluminum oxide.

[0030] In some embodiments, in the above preparation method, in step (1), the molar ratio of the ternary precursor material, the lithium source, and the M2 element in the M2-containing compound is 1:(0.97-1.10):(0.0001-0.03).

[0031] In some embodiments, in the above preparation method, in step (2), the molar ratio of the calcined material, cobalt element in the cobalt source, niobium element in the niobium source, and M3 element in the M3-containing compound is 1:(0.001-0.03):(0.0001-0.015):(0.0001-0.015).

[0032] In some embodiments, in the above preparation method, the di-calcined material obtained in step (2) is mixed with the boron-containing compound according to a molar ratio of 1:(0.001-0.03) of the di-calcined material and the boron-containing compound, and then sintered to obtain a ternary polycrystalline cathode material; wherein the boron-containing compound includes at least one of boric acid and boron oxide; the sintering temperature is 240℃~440℃, and the sintering time is 3h~14h.

[0033] As a general inventive concept, this application also provides a lithium-ion battery, wherein the cathode material used is the above-mentioned ternary polycrystalline cathode material or the ternary polycrystalline cathode material prepared by the above-mentioned preparation method.

[0034] As a general inventive concept, this application also provides an electrical device including the aforementioned lithium-ion battery.

[0035] Compared with the prior art, the advantages of this application are:

[0036] (1) The surface of the ternary polycrystalline cathode material of this application is a composite oxide coating layer rich in Co, Nb and M3 elements. The rich Co has the advantage of significantly consuming residual alkali and reducing DCR growth. The rich Nb has the characteristics of further reducing residual alkali and improving cycle performance. The rich M3 element can further reduce DCR growth. The elements work together to ensure that the composite oxide coating layer can significantly improve the high-temperature cycle, high-temperature DCR growth and thermal stability of the cathode material.

[0037] (2) In the preparation method of this application, a thermal decomposition temperature calcination platform matching the coating agent is set, so that the coating agent is more uniformly attached to the material surface, reacts more fully with the surface residual alkali and is conducive to the formation of Co / Nb rich region; at the same time, the coating layer formed can also prevent the electrolyte from eroding the material surface, reduce the side reaction on the material surface, and thus increase the stability of the material, thereby improving the discharge capacity and excellent cycle stability of the material. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the disclosed drawings without creative effort.

[0039] Figure 1 is an FE-SEM image of the ternary polycrystalline cathode material of Embodiment 2 of this application;

[0040] Figure 2 is a diagram of the EPMA interface in the Co-rich region of the ternary polycrystalline cathode material of Embodiment 2 of this application;

[0041] Figure 3 is an EPMA interface diagram of the Nb-rich region of the ternary polycrystalline cathode material in Embodiment 2 of this application;

[0042] Figure 4 is a first cycle charge-discharge curve of the ternary polycrystalline cathode material of Examples 1-5 and Comparative Examples 1-4 of this application;

[0043] Figure 5 is a charge-discharge cycle diagram of the ternary polycrystalline cathode material in Examples 1-5 and Comparative Examples 1-4 of this application;

[0044] Figure 6 is a charge-discharge DCR growth graph of the ternary polycrystalline cathode materials of Examples 1-5 and Comparative Examples 1-4 of this application;

[0045] Figure 7 is a DSC result diagram of the ternary polycrystalline cathode material of Example 2 and Comparative Example 1 of this application. Detailed Implementation

[0046] To facilitate understanding of this application, a more comprehensive and detailed description of the application will be provided below in conjunction with the accompanying drawings and preferred embodiments. However, the scope of protection of this application is not limited to the specific embodiments described below. Clearly, the embodiments described below are merely some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0047] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.

[0048] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0049] Example 1:

[0050] A ternary polycrystalline cathode material with the chemical formula: Li 1.06 Ni 0.9095 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.001 Al 0.004 B 0.01 O2, including the ternary cathode material matrix Li 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2 and a composite oxide coating layer and a boron compound layer sequentially coated on the substrate surface, the composite oxide coating layer being rich in Co, Nb and Al elements.

[0051] The preparation method of the ternary polycrystalline cathode material in this embodiment includes the following steps:

[0052] (1) The ternary precursor Ni 0.95 Co 0.02 Mn 0.03 (OH)₂, lithium hydroxide, zirconium oxide, and strontium oxide were dry-mixed in a molar ratio of 1:1.06:0.004:0.0015. After uniform mixing, the mixture was sintered at 500°C for 4 hours in a pure oxygen atmosphere, followed by heating to 730°C and holding for 11 hours. After cooling and sieving, a sintered material with the chemical formula Li₂ was obtained. 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2;

[0053] (2) The calcined material obtained in step (1), cobalt oxide, niobium pentoxide, and aluminum oxide were dry-mixed in an elemental molar ratio of 1:0.02:0.001:0.004. After uniform mixing, the mixture was placed in a pure oxygen atmosphere, heated to 250℃ for 3 hours, and then heated to 680℃ for 8 hours. After cooling and sieving, the calcined material was obtained, with the chemical formula Li. 1.06 Ni 0.9195 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.001 Al 0.004 O2;

[0054] (3) The sintered material obtained in step (2) is dry-mixed with boric acid at an elemental molar ratio of 1:0.01. After uniform mixing, the mixture is sintered at 300℃ for 12 hours in a pure oxygen atmosphere. After cooling and sieving, the ternary polycrystalline cathode material is obtained, with the chemical formula Li. 1.06 Ni 0.9095 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.001 Al 0.004 B 0.01 O2.

[0055] Example 2:

[0056] A ternary polycrystalline cathode material with the chemical formula: Li 1.06 Ni 0.909 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.0015 Ce 0.004 B 0.01 O2, including the ternary cathode material matrix Li 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2 and a composite oxide coating layer and a boron compound layer sequentially coated on the substrate surface, the composite oxide coating layer being rich in Co, Nb and Ce elements.

[0057] The preparation method of the ternary polycrystalline cathode material in this embodiment includes the following steps:

[0058] (1) The ternary precursor Ni 0.95 Co 0.02 Mn 0.03(OH)₂, lithium hydroxide, zirconium carbonate, and strontium hydroxide were dry-mixed in an elemental molar ratio of 1:1.06:0.004:0.0015. After uniform mixing, the mixture was sintered at 500℃ for 4 hours in a pure oxygen atmosphere, followed by sintering at 730℃ for 11 hours. After cooling and sieving, a sintered material with the chemical formula Li₂ was obtained. 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2;

[0059] (2) The first-burned material obtained in step (1), cobalt hydroxide, niobium oxalate, and cerium oxide are dry-mixed in a metal element molar ratio of 1:0.02:0.0015:0.004. After uniform mixing, the mixture is placed in a pure oxygen atmosphere, heated to 250℃ for 4 hours, and then heated to 680℃ for 8 hours. After cooling and sieving, a second-burned material is obtained, the chemical formula of which is Li. 1.06 Ni 0.919 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.0015 Ce 0.004 O2;

[0060] (3) The sintered material obtained in step (2) is dry-mixed with boric acid at an elemental molar ratio of 1:0.01. After uniform mixing, the mixture is placed in a pure oxygen atmosphere and sintered at 300℃ for 12 hours. After cooling and sieving, a ternary polycrystalline cathode material is obtained, with the chemical formula Li. 1.06 Ni 0.909 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.0015 Ce 0.004 B 0.01 O2.

[0061] Example 3:

[0062] A ternary polycrystalline cathode material with the chemical formula: Li 1.06 Ni 0.9135 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.002 La 0.004 B 0.01 O2, including the ternary cathode material matrix Li 1.058 Ni 0.9445 Co 0.02 Mn0.03 Zr 0.004 Sr 0.0015 O2 and a composite oxide coating layer and a boron compound layer sequentially coated on the substrate surface, the composite oxide coating layer being rich in Co, Nb and La elements.

[0063] The preparation method of the ternary polycrystalline cathode material in this embodiment includes the following steps:

[0064] (1) The ternary precursor Ni 0.95 Co 0.02 Mn 0.03 (OH)₂, lithium hydroxide, zirconium carbonate, and strontium carbonate were dry-mixed in an elemental molar ratio of 1:1.058:0.004:0.0015. After uniform mixing, the mixture was sintered at 500°C for 4 hours in a pure oxygen atmosphere, followed by sintering at 730°C for 11 hours. After cooling and sieving, a sintered material with the chemical formula Li was obtained. 1.058 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2;

[0065] (2) The first-burned material obtained in step (1), cobalt tetroxide, lithium niobate, and lanthanum trioxide were dry-mixed at an elemental molar ratio of 1:0.02:0.002:0.004. After uniform mixing, the mixture was placed in a pure oxygen atmosphere, heated to 250℃ for 2 hours, and then heated to 680℃ for 8 hours. After cooling and sieving, the second-burned material was obtained, with the chemical formula Li. 1.06 Ni 0.9185 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.002 La 0.004 O2;

[0066] (3) The sintered material obtained in step (2) is dry-mixed with boric acid at an elemental molar ratio of 1:0.005. After uniform mixing, it is placed in a pure oxygen atmosphere and sintered at 300℃ for 12 hours. After cooling and sieving, a ternary polycrystalline cathode material is obtained, with the chemical formula Li. 1.06 Ni 0.9135 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.002 La 0.004 B 0.005 O2.

[0067] Example 4:

[0068] A ternary polycrystalline cathode material with the chemical formula: Li 1.06 Ni 0.9195 Co 0.04 Mn 0.03 Zr 0.008 Sr 0.0015 Nb 0.001 O, including the ternary cathode material matrix Li 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2 and a composite oxide coating layer on the surface of the substrate, the composite oxide coating layer being rich in Co, Nb and Zr elements.

[0069] The preparation method of the ternary polycrystalline cathode material in this embodiment includes the following steps:

[0070] (1) The ternary precursor Ni 0.95 Co 0.02 Mn 0.03 (OH)₂, lithium hydroxide, zirconium oxide, and strontium oxide were dry-mixed in an elemental molar ratio of 1:1.06:0.004:0.0015. After uniform mixing, the mixture was sintered at 500℃ for 4 hours in a pure oxygen atmosphere, followed by sintering at 730℃ for 11 hours. After cooling and sieving, a sintered material with the chemical formula Li₂ was obtained. 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2;

[0071] (2) The sintered material obtained in step (1), cobalt oxide, niobium pentoxide, and zirconium dioxide were dry-mixed in an elemental molar ratio of 1:0.02:0.001:0.004. After uniform mixing, the mixture was placed in a pure oxygen atmosphere, heated to 250℃ for 3 hours, and then heated to 680℃ for 8 hours. After cooling and sieving, the sintered material was obtained, with the chemical formula Li. 1.06 Ni 0.9195 Co 0.04 Mn 0.03 Zr 0.008 Sr 0.0015 Nb 0.001 O2.

[0072] Example 5:

[0073] The ternary polycrystalline cathode material of this embodiment differs from that of Example 1 only in the sintering procedure of step (2). In step (2) of this embodiment, the uniformly mixed material is placed in a pure oxygen atmosphere and directly heated to 680°C for sintering for 8 hours. After cooling and sieving, the second-burned material is obtained. Other processes and parameters are consistent with those of Example 1.

[0074] Comparative Example 1:

[0075] The ternary polycrystalline cathode material of this comparative example is prepared in the same way as that of Example 2, except that no niobium source is added in step (2). Other processes and parameters are the same as those of Example 1.

[0076] Comparative Example 2:

[0077] The ternary polycrystalline cathode material of this comparative example is prepared in the same way as that of Example 5, except that no niobium source is added in step (2). The other processes and parameters are the same as those of Example 5.

[0078] Comparative Example 3:

[0079] The ternary polycrystalline cathode material in this comparative example has the chemical formula Li. 1.06 Ni 0.923 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.0015 O2, including the ternary cathode material matrix Li 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2 and a composite oxide coating layer on the surface of the substrate, the composite oxide coating layer being rich in Co and Nb elements.

[0080] The preparation method of the ternary polycrystalline cathode material in this comparative example includes the following steps:

[0081] (1) The ternary precursor Ni 0.95 Co 0.02 Mn 0.03 (OH)₂, lithium hydroxide, zirconium carbonate, and strontium hydroxide were dry-mixed in an elemental molar ratio of 1:1.06:0.004:0.0015. After uniform mixing, the mixture was sintered in a pure oxygen atmosphere at 500°C for 4 hours, followed by sintering at 730°C for 11 hours. After cooling and sieving, a sintered material with the chemical formula Li₂ was obtained. 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2;

[0082] (2) The sintered material obtained in step (1), cobalt oxide, and niobium oxalate were dry-mixed at an elemental molar ratio of 1:0.02:0.0015. After uniform mixing, the mixture was placed in a pure oxygen atmosphere, heated to 250℃ for 3 hours, and then heated to 680℃ for 8 hours. After cooling and sieving, a ternary polycrystalline cathode material with the chemical formula Li was obtained. 1.06 Ni 0.923 Co 0.04 Mn 0.03 Zr 0.004 Sr 0.0015 Nb 0.0015 O2.

[0083] Comparative Example 4:

[0084] The ternary polycrystalline cathode material in this comparative example has the chemical formula: Li 1.06 Ni 0.9345 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 B 0.01 O2, including the ternary cathode material matrix Li 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2 and a B coating layer covering the substrate surface.

[0085] The preparation method of the ternary polycrystalline cathode material in this comparative example includes the following steps:

[0086] (1) The ternary precursor Ni 0.95 Co 0.02 Mn 0.03 (OH)₂, lithium hydroxide, zirconium carbonate, and strontium hydroxide were dry-mixed in an elemental molar ratio of 1:1.06:0.004:0.0015. After uniform mixing, the mixture was sintered at 500℃ for 4 hours in a pure oxygen atmosphere, followed by sintering at 730℃ for 11 hours. After cooling and sieving, a sintered material with the chemical formula Li₂ was obtained. 1.06 Ni 0.9445 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 O2;

[0087] (2) The sintered material obtained in step (1) is dry-mixed with boric acid at an elemental molar ratio of 1:0.01. After uniform mixing, the mixture is placed in a pure oxygen atmosphere and sintered at 300℃ for 12 hours. After cooling and sieving, a ternary polycrystalline cathode material is obtained, with the chemical formula Li.1.06 Ni 0.9345 Co 0.02 Mn 0.03 Zr 0.004 Sr 0.0015 B 0.01 O2.

[0088] The average thickness and atomic percentage of the Co / Nb-rich region were measured for the ternary polycrystalline cathode materials of each embodiment and comparative example. The testing method was as follows:

[0089] EPMA test average thickness: As shown in Figures 2 and 3, four straight lines passing through the center of the circle are used to divide the cross-section of the particle into 8 equal parts. The two ends of each straight line are visible as Co-rich or Nb-rich regions. The thickness of the Co-rich or Nb-rich regions is measured (a total of 8 data points). The arithmetic mean of each thickness data point is the average thickness, and the standard deviation of the thickness is calculated.

[0090] EPMA testing of atomic percentage: As shown in Figures 2 and 3, four straight lines passing through the center of the circle are used to divide the cross-section of the particle into eight equal parts, forming eight radii. Each radius is then divided into nine equal parts, resulting in ten test points. EPMA is used to measure the Co or Nb atomic percentage at the three closest points (0, 0.67 μm, and 1.34 μm in the figure) along each radius line. The arithmetic mean of these three points is taken as the Co or Nb atomic percentage for that radius. The arithmetic mean of the Co or Nb atomic percentages across the eight radii of the particle is then taken as the average atomic percentage. The standard deviation of the atomic percentage is then calculated.

[0091] The electrochemical performance and differential scanning calorimetry (DSC) of the ternary polycrystalline cathode materials prepared in each embodiment and comparative example were tested using the following methods:

[0092] The above-mentioned ternary polycrystalline positive electrode material, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were stirred and dispersed with solvent NMP at a mass ratio of 92.5:5:2.5, coated onto an aluminum foil substrate, and rolled to obtain a positive electrode sheet; lithium metal sheet was used as the negative electrode sheet; a 1 mol / L LiPF6 solution was used as the electrolyte, and the solvent was a mixed solvent of EC and DMC in a ratio of 1:2, with 1% VC added as an additive; the above components were assembled into a CR2032 coin cell for battery testing, with a charging cut-off voltage of 4.30V and a discharging cut-off voltage of 3.0V.

[0093] DSC test procedure: ① 2.5-4.25V, 0.2C / 0.2C cycle for 1 week, 0.2C charge to 4.25V full charge; ② Immerse the disassembled full electrode in DMC solution for 1 hour, dry, repeat once; ③ Transfer the positive electrode to an aluminum crucible, add a quantitative amount of electrolyte, and seal; ④ Conduct the test under the following conditions: N2 atmosphere, 10℃ / min.

[0094] The test results are shown in Table 1. The first cycle charge-discharge curves of Examples 1-5 and Comparative Examples 1-4 are shown in Figure 4. The charge-discharge cycle graph is shown in Figure 5. The charge-discharge DCR growth graph is shown in Figure 6.

[0095] Table 1. Performance test results of the ternary polycrystalline cathode materials in each embodiment and comparative example.

[0096] Figure 1 shows the FE-SEM image of the ternary polycrystalline cathode material prepared in Example 2, Figure 2 shows the EPMA interface image of the Co-rich region, and Figure 3 shows the EPMA interface image of the Nb-rich region. Figures 2 and 3 clearly show the Co-rich and Nb-rich regions on the surface of the ternary polycrystalline cathode material of Example 2. The thickness, average thickness, and standard deviation of these regions in different directions are shown in Table 2. The atomic percentage, average atomic percentage, and standard deviation are shown in Table 3. Similarly, Table 4 summarizes the thickness and atomic percentage results of the element-rich regions in each example and comparative example.

[0097] Table 2. Elemental depth and standard deviation in different directions of the Co / Nb-rich region in Example 2

[0098] Table 3. Atom percentages in different directions of the Co / Nb-rich region in Example 2.

[0099] Table 4. Thickness and atomic percentage of element-enriched regions in the ternary polycrystalline cathode materials of each embodiment and comparative example.

[0100] According to the test results, the Co and Nb in the ternary polycrystalline cathode material in the embodiment are within the range of this application, and the material has low residual lithium and excellent high-temperature cycling performance.

[0101] By comparing Example 2 with Comparative Examples 1-2, it can be concluded that the lack of Nb compounds in the coating layer cannot significantly improve the cycling performance of the material, and the residual alkali is higher. Furthermore, the lack of Nb and the segmented sintering further reduce the electrical performance. This indicates that the combination of segmented sintering and niobium can significantly improve the cycling performance of the material and effectively reduce the residual alkali, obtaining a uniform Co and Nb-rich region without sacrificing capacity.

[0102] In the examples, the thickness and standard deviation of the element-enriched region were lower than those of the comparative example, indicating that the examples had a more uniform protective layer. This demonstrates that the material reacts effectively with residual alkali, reducing surface side reactions and ultimately ensuring improved cycling performance. The DSC results of Example 2 and Comparative Example 1 are shown in Figure 7. Example 2 exhibits a lower peak intensity and a higher peak temperature compared to the uncoated Nb-rich Comparative Example 1, indicating that the thermal stability of the material containing the Nb-rich region is effectively improved.

[0103] A comparison of the data from Examples 1 and 5 reveals that the absence of a first-stage sintering in step (2) resulted in a limited reduction in residual alkali. Furthermore, Figure 5 shows a limited improvement in the cycle performance of Example 5, and Figure 6 shows an increase in the cycle impedance of Example 5, indicating an insufficient coating reaction. This suggests that the absence of a second-stage sintering low-temperature platform in Example 5 easily leads to a larger standard deviation in both the thickness and atomic percentage of the Co / Nb-rich region, which is detrimental to uniform element coating.

[0104] The above description is merely a preferred embodiment of this application, and the scope of protection of this application is not limited to the above embodiments. For those skilled in the art, any improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of this application.

[0105] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A ternary polycrystalline cathode material, said ternary polycrystalline cathode material comprising a ternary cathode material matrix and a composite oxide coating layer coated on the surface of the matrix; wherein, The composite oxide coating layer is rich in Co, Nb, and M3 elements, wherein the M3 element is selected from at least one of Si, W, Sn, La, Zr, Ce, Mg, and Al.

2. The ternary polycrystalline cathode material as described in claim 1, wherein, In the composite oxide coating layer, the average thickness of the Co-rich region is 0.70 μm-1.50 μm, and the average thickness of the Nb-rich region is 0.50 μm-1.80 μm.

3. The ternary polycrystalline cathode material according to any one of claims 1 to 2, wherein, In the composite oxide coating layer, the standard deviation of the thickness of the Co-rich region is 0.10 μm-0.30 μm, and the standard deviation of the thickness of the Nb-rich region is 0.10 μm-0.30 μm.

4. The ternary polycrystalline cathode material according to any one of claims 1 to 3, wherein, In the composite oxide coating layer, the average percentage of Co atoms is 1.300%-2.000%, and the average percentage of Nb atoms is 0.020%-0.080%.

5. The ternary polycrystalline cathode material according to claim 4, wherein, In the composite oxide coating layer, the average standard deviation of the Co atom percentage is 0.150%-0.200%, and the average standard deviation of the Nb atom percentage is 0.010%-0.020%.

6. The ternary polycrystalline cathode material according to any one of claims 1 to 5, wherein, The ternary polycrystalline cathode material also includes a boron compound layer, which is coated on the surface of the composite oxide coating layer.

7. The ternary polycrystalline cathode material according to any one of claims 1 to 6, wherein, The chemical formula of the ternary cathode material matrix is ​​Li. a Ni b Co c M1 d M2 e O2, where M1 includes at least one of Mn and Al, M2 includes at least one of Zr, Sr, W, Al, Ti, Mo, Ce, Ca, Ta and Mg, 0.97≤a≤1.10, 0.300≤b≤0.990, 0.005≤c≤0.300, 0.005≤d≤0.300, and 0≤e≤0.

030.

8. A method for preparing a ternary polycrystalline cathode material as described in any one of claims 1 to 7, wherein, Includes the following steps: (1) The ternary precursor material, lithium source and compound containing M2 element are mixed and sintered to obtain a sintered material; (2) The first sintered material is mixed with a cobalt source, a niobium source and a compound containing M3 element and then sintered to obtain a second sintered material, which is a ternary polycrystalline cathode material.

9. The preparation method according to claim 8, wherein, In step (1), the sintering is segmented sintering, first heating to 400℃~600℃ and holding for 2h~5h, then heating to 650~850℃ and holding for 8h~14h.

10. The preparation method according to any one of claims 8 to 9, wherein, In step (2), the sintering is segmented sintering, first heating to 200℃~300℃ and holding for 2h~4h, then heating to 550℃~720℃ and holding for 8h~12h.

11. The preparation method according to any one of claims 8 to 10, wherein, The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium oxide; The cobalt source includes at least one of cobalt oxide, cobalt hydroxide, cobalt hydroxyoxide, cobalt tetroxide, cobalt carbonate, cobalt sulfide, and cobalt acetate; The niobium source includes at least one of elemental niobium powder, niobium pentoxide, lithium niobate, barium niobate, niobium oxalate, and niobium hydroxide. The compounds containing the M2 element include at least one of zirconium oxide, strontium oxide, tungsten oxide, aluminum oxide, titanium oxide, molybdenum oxide, cerium oxide, calcium sulfate, tantalum oxide, and magnesium oxide; The compounds containing the M3 element include at least one of silicon oxide, tungsten oxide, lanthanum oxide, cerium oxide, zirconium oxide, magnesium oxide, tin oxide, sodium aluminate, and aluminum oxide.

12. The preparation method according to any one of claims 8 to 11, wherein, In step (1), the molar ratio of the ternary precursor material, the lithium source, and the M2-containing compound is 1:(0.97-1.10):(0.0001-0.03); In step (2), the molar ratio of the sintered material, the cobalt element in the cobalt source, the niobium element in the niobium source, and the M3 element in the M3-containing compound is 1:(0.001-0.030):(0.0001-0.015):(0.0001-0.015).

13. The preparation method according to any one of claims 8 to 12, wherein, According to the molar ratio of boron in the sintered material and the boron-containing compound being 1:(0.001-0.03), the sintered material obtained in step (2) is mixed with the boron-containing compound and sintered to obtain a ternary polycrystalline cathode material.

14. The preparation method according to claim 13, wherein, The boron-containing compound includes at least one of boric acid and boron oxide; the sintering temperature of the secondary sintering material and the boron-containing compound is 240℃~440℃, and the sintering time is 3h~14h.

15. A lithium-ion battery, wherein, The cathode material used is the ternary polycrystalline cathode material according to any one of claims 1 to 7 or the ternary polycrystalline cathode material prepared by the preparation method according to any one of claims 8 to 14.

16. An electrical appliance, wherein, Including the lithium-ion battery as described in claim 15.

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