Composite modified ternary positive electrode material and preparation method thereof

Abstract

The application discloses a composite modified ternary positive electrode material and a preparation method thereof. The ternary positive electrode material comprises a substrate and a coating layer on the surface of the substrate, the surface of the substrate is doped with W, the coating layer is a composite coating layer, the composite coating layer comprises a F-doped WO3 matrix, and the matrix is embedded with Li2WO4 and M1-F compounds, wherein M1 is an alkali metal or an alkaline earth element. The preparation method comprises the following steps: firstly, a ternary positive electrode material substrate is prepared; then, the ternary positive electrode material substrate and a coating additive containing W, F and M1 are uniformly mixed and sintered in an oxygen atmosphere, the sintering temperature is 450 DEG C to 700 DEG C, and the holding time is 4 to 8 hours, so as to obtain the composite modified ternary positive electrode material. The surface of the lithium ion battery positive electrode material is modified by the composite coating layer, multiple synergistic effects are realized, and the electrochemical performance of the material is significantly improved, especially the rate performance and the cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a ternary cathode material and its preparation method. Background Technology

[0002] Lithium-ion battery cathode materials such as layered LiNixCoyMnzO2 (NCM) or LiNixCoyAlzO2 (NCA) ternary materials have been widely used in power batteries and energy storage due to their high energy density and good cost-effectiveness. With the rapid development of high-power demand scenarios such as electric vehicles, start-stop systems, and power tools, the market has placed higher demands on the rate performance, fast charging and discharging capabilities, and cycle stability of lithium-ion batteries. However, traditional ternary materials often face problems such as insufficient lithium-ion diffusion kinetics and exacerbated interfacial side reactions under high current, resulting in room for improvement in their rate performance and cycle life. Summary of the Invention

[0003] In order to overcome the technical problems of insufficient cycle stability and rate performance of ternary cathode materials under high-rate charge-discharge conditions in the prior art, the present invention provides a composite modified ternary cathode material and its preparation method.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0005] This invention provides a composite modified ternary cathode material, comprising a substrate and a coating layer on the surface of the substrate, wherein the surface of the substrate is doped with W, and the coating layer is a composite coating layer comprising an F-doped WO3 matrix, wherein Li2WO4 and M1-F compounds are embedded in the matrix, wherein M1 is an alkali metal or alkaline earth element.

[0006] This invention constructs a composite coating layer on the surface of a ternary cathode material, using F-doped WO3 as a continuous matrix and embedding Li2WO4 and MI-F compounds. Li2WO4 itself possesses good lithium-ion conductivity, while F doping further broadens the diffusion channels of lithium ions on the cathode material surface. The doped MI-F compounds can introduce more defects or form a rapidly ion-conducting interface phase in the WO3 matrix, optimizing the Li2WO4 content. + The migration pathway involves M1, where alkali metals or alkaline earth elements have a stronger binding affinity to F compared to other metal ions, making the M1-F effect more pronounced. By modifying the surface of lithium-ion battery cathode materials with the aforementioned composite coating, multiple synergistic effects are achieved, significantly improving the electrochemical performance of the material, particularly its rate performance and cycle stability.

[0007] As an alternative embodiment, in the cathode material provided by the present invention, the mass ratio of the sum of the masses of W, F and M1 in the composite coating layer to the mass of the matrix is 0.001 to 0.01:1, and the mass percentage of W is greater than that of F.

[0008] In the present invention, controlling the mass ratio of W+F+M1 to the matrix is beneficial to improving the rate performance and cycle stability of the material, and controlling the mass percentage of W to be greater than that of F is beneficial to forming an F-doped WO₃ structure.

[0009] As an alternative embodiment, in the cathode material provided by the present invention, the molar ratio of W, F and M1 elements in the composite coating layer is W:F:M1= x:y:1, wherein 0<x≤5, n<y<9, and n is the absolute value of the valence state of M1.

[0010] As an alternative embodiment, in the cathode material provided by the present invention, n<y≤3.

[0011] As an alternative embodiment, in the cathode material provided by the present invention, M1 is selected from at least one of Ca, Mg, Na, K, Sr, Ba and Li.

[0012] As an alternative embodiment, in the cathode material provided by the present invention, the interior of the matrix is doped with X element, and X is selected from one or more of Zr, Al, W, Nb, Ti, Sr, Y, La and Ta.

[0013] Based on the same technical concept, the present invention also provides a preparation method of the above composite-modified ternary cathode material, comprising the following steps: S1, uniformly mixing a ternary precursor, a lithium source and a doping additive containing element X, and sintering to obtain a ternary cathode material matrix; S2, uniformly mixing the ternary cathode material matrix obtained in S1 with a coating additive containing W, F and M1, and sintering in an oxygen-containing atmosphere, wherein the sintering temperature is 450°C to 700°C, and the holding time is 4 to 8h, so as to obtain a composite-modified ternary cathode material.

[0014] In this invention, the sintering in S2 is a one-step sintering process, including holding at 450℃ to 700℃ for 4 to 8 hours, with the sintering atmosphere being air or oxygen. At this sintering temperature range, some W reacts with residual alkali on the substrate surface to form Li2WO4, and simultaneously reaches the temperature at which M1 reacts with F, generating an M1-F second phase distributed within the first phase WO3, forming a composite coating layer. The remaining F will dope into the WO3 lattice, introducing anion defects and increasing lithium-ion migration channels. Simultaneously, at this temperature, trace amounts of W diffuse and dope into the substrate surface lattice, forming a W-rich surface doped layer or defect structure, enhancing the strength of the transition metal-oxygen bond and stabilizing the lattice structure. By modifying the surface of the cathode material, the electrochemical performance of the material is significantly improved, especially its rate performance and cycle stability.

[0015] As an optional implementation, in the preparation method provided by the present invention, in step S1, the doping additive containing element X is selected from one or more of ZrO2, Al2O3, Al(OH)3, WO3, Li2WO4, Nb2O3, LiNbO3, TiO2, La2O3, Y2O3, SrCO3, SrO, and Ta2O5.

[0016] As an optional implementation, in the preparation method provided by the present invention, in S1, sintering is either one-step sintering or two-step sintering. One-step sintering involves directly heating to 600℃~1000℃ and sintering for 10~15h. Two-step sintering includes a first-stage sintering and a second-stage sintering. In the first-stage sintering, the temperature is raised to a pre-sintering platform of 450℃~800℃ and held for 3~6h. In the second-stage sintering, the temperature is raised to 600℃~1000℃ and held for 10~15h. The temperature difference between the second-stage sintering and the first-stage sintering is greater than 100℃.

[0017] As an optional implementation, in the preparation method provided by the present invention, in step S2, the coating additive containing W, F, and M1 is selected from one or more of WO3, Na2WO4, MgWO4, PVDF, NaF, LiF, CaF2, CaCO3, CaO, MgO, MgCO3, SrO, SrCO3, and K2CO3.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention utilizes the interaction of elements such as W, F, and M1. The M1 element acts as a "bridge" between Li2WO4 and the matrix material, and the W / F elements act as "bridges" between the three coating materials M1-F, WO3, and Li2WO4. The strong chemical bonds and tight interlocking between the components (including the matrix, W-doped layer, Li2WO4, and F-doped WO3 matrix) strengthen the bonding between the coating layer and the matrix, and between the coating materials, thereby preventing peeling during long-term cycling. This gradient transition region forms a unique interfacial chemical environment, which is beneficial to reducing the lithium-ion diffusion barrier, jointly alleviating the capacity and voltage decay during fast charging and discharging and cycling, and significantly improving the rate performance and cycle stability of the material.

[0019] (2) This invention effectively isolates the direct contact between the cathode material and the electrolyte by constructing a composite coating layer on the surface of the ternary cathode material, thereby reducing side reactions such as transition metal dissolution and electrolyte decomposition. Specifically, the F element, on the one hand, stabilizes the crystal structure in WO3, and on the other hand, forms the M1-F compound which preferentially reacts with HF in the electrolyte, forming a chemical barrier that significantly inhibits the erosion of the cathode material by HF, optimizes interface stability, reduces impedance growth during cycling, and extends battery life.

[0020] (3) This invention utilizes the high diffusivity of W ions to construct a W-rich surface doped layer on the substrate surface. The resulting defect-type structure can enhance the bond energy of TM-O, suppress phase transition and lattice oxygen evolution under high pressure, and improve the structural stability and power characteristics of the material under high current.

[0021] (4) The present invention utilizes secondary sintering to introduce a coating additive containing W, F and M1. By sintering in an oxygen atmosphere at 450℃~700℃, the multifunctional composite coating layer can be constructed in situ and in an orderly gradient on the surface of the cathode material that has been stabilized after the first sintering. This significantly improves the interface stability and ion transport dynamics, while avoiding the damage to the bulk structure caused by the secondary sintering at excessively high temperatures and the adverse diffusion of the coating components into the bulk phase. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1The figures show the XPS spectra of Examples 1, 1, 2 and 3 of the present invention. Figure (a) shows the F 1s spectrum of Example 1 and Comparative Example 1; Figure (b) shows the Ca 2p spectrum of Example 1 and Comparative Example 2; Figures (c) and (d) show the Li 1s and O 1s spectra of Example 1 and Comparative Example 3, respectively; and Figure (e) shows the W 4f spectrum of Example 1. Figure 2 The Nyquist curves for Embodiment 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention; Figure 3 The XRD patterns of Embodiment 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present invention; Figure 4 The XRD patterns are those of Embodiments 8 and 9 of the present invention. Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] 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 the invention.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0027] Example 1 A composite modified ternary cathode material includes a W-doped matrix and a composite coating layer on the surface of the matrix. The composite coating layer includes an F-doped WO3 matrix, and the matrix is ​​embedded with Li2WO4 and CaF2 compounds.

[0028] The preparation method of the positive electrode material is as follows: (1) Ni 0.5 Co 0.2 Mn 0.3 The (OH)2 precursor, Li2CO3, and ZrO2 were uniformly mixed in a molar ratio of 1:1.06:0.2. The mixture was heated to 910℃ in air at a rate of 3℃ / min and held for 12 hours. After cooling to room temperature, the mixture was crushed and sieved to obtain a calcined matrix.

[0029] (2) The sintered matrix obtained in step (1) is uniformly mixed with WO3, PVDF and CaCO3 in the following proportions: the molar ratio of WO3, PVDF and CaCO3 is W:F:Ca = 3:2.5:1, and the total mass ratio of W, F and Ca elements provided by the three to the mass ratio of the matrix is ​​0.005:1. The mixture is heated to 580°C in air atmosphere and held for 5 hours. After cooling to room temperature, it is crushed and sieved to obtain the composite modified ternary cathode material.

[0030] Example 2 A composite modified ternary cathode material includes a W-doped matrix and a composite coating layer on the surface of the matrix. The composite coating layer includes an F-doped WO3 matrix, and the matrix is ​​embedded with Li2WO4 and NaF compounds.

[0031] The preparation method of the positive electrode material is as follows: (1) Ni 0.6 Co 0.1 Mn 0.3 The (OH)2 precursor, Li2CO3, Al(OH)3 and Nb2O5 were uniformly mixed in a molar ratio of 1:1.07:0.1:0.1. The mixture was heated to 750℃ at a rate of 3℃ / min in an oxygen atmosphere and held for 5 hours. Then the temperature was raised to 940℃ and held for 13 hours. The mixture was then cooled to room temperature, crushed and sieved to obtain a calcined matrix.

[0032] (2) The sintered matrix obtained in step (1) is uniformly mixed with WO3, PVDF and Na2CO3 in the following proportions: the molar ratio of WO3, PVDF and Na2CO3 is W:F:Na = 2:1.3:1, and the total mass ratio of W, F and Na elements provided by the three to the mass ratio of the matrix is ​​0.004:1. The mixture is heated to 615℃ in air atmosphere and held for 5 hours. After cooling to room temperature, it is crushed and sieved to obtain the composite modified ternary cathode material.

[0033] Example 3 A ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes an F-doped WO3 matrix and Li2WO4 and NaF compounds embedded in the matrix. The preparation method differs from Example 2 in that the total mass ratio of W, F, and Na elements provided by WO3, PVDF, and Na2CO3 in step (2) to the mass ratio of the matrix is ​​0.002:1. Other preparation methods are consistent with Example 2.

[0034] Example 4 A ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes an F-doped WO3 matrix and Li2WO4 and NaF compounds embedded in the matrix. The preparation method differs from Example 2 in that the total mass ratio of W, F, and Na elements provided by WO3, PVDF, and Na2CO3 in step (2) to the mass ratio of the matrix is ​​0.009:1. Other preparation methods are consistent with Example 2.

[0035] Example 5 A composite-modified ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes an F-doped WO3 matrix, and Li2WO4 and NaF compounds are embedded in the matrix. The preparation method differs from Example 2 in that, in step (2), WO3, PVDF, and Na2CO3 are uniformly mixed in the following ratio: the molar ratio of WO3, PVDF, and Na2CO3 is W:F:Na = 5:4:1, and the total mass ratio of W, F, and Na elements provided by the three components to the mass ratio of the matrix is ​​0.004:1. Other preparation methods are the same as in Example 2.

[0036] Example 6 A composite modified ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes an F-doped WO3 matrix, and the matrix is ​​embedded with Li2WO4 and MgF2 compounds. The mass ratio of the coating agent WO3 is 0.735%, the mass ratio of PTFE is 0.046%, and the mass ratio of MgWO4 is 0.019%.

[0037] The preparation method of the positive electrode material is as follows: (1) Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor, LiOH, ZrO2, TiO2 and Al2O3 were uniformly mixed in a molar ratio of 1:1.07:0.5:0.4:0.5. The mixture was heated to 500℃ at a rate of 3℃ / min in an oxygen atmosphere and held for 4 hours. Then, the temperature was increased to 800℃ and held for 12 hours. The mixture was cooled to room temperature, crushed and sieved to obtain a calcined matrix.

[0038] (2) The sintered matrix obtained in step (1) is uniformly mixed with WO3, PTFE and MgWO4 in the following proportions: the molar ratio of WO3, PVDF and MgWO4 is W:F:Mg=5:6:1, and the total mass ratio of W, F and Mg elements provided by the three to the mass ratio of the matrix is ​​0.008:1. The mixture is heated to 460℃ at a rate of 3℃ / min under an oxygen atmosphere and held for 6h. After cooling to room temperature, it is crushed and sieved to obtain the composite modified ternary cathode material.

[0039] Example 7 A ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes an F-doped WO3 matrix, and Li2WO4 and MgF2 compounds are embedded in the matrix. The preparation method differs from that of Example 6 in that, in step (2), WO3, PTFE, and MgWO4 are uniformly mixed in the following ratio: the molar ratio of WO3, PTFE, and MgWO4 is W:F:Mg = 5:3:1, and the total mass ratio of W, F, and Mg elements provided by the three components to the mass ratio of the matrix is ​​0.015:1. Other preparation methods are the same as in Example 6.

[0040] Example 8 A ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes an F-doped WO3 matrix, and Li2WO4, SrF2, and NaF compounds are embedded in the matrix. The preparation method differs from Example 6 in that, in step (2), WO3, PVDF, NaF, and SrCO3 are uniformly mixed in the following ratio: the molar ratio of WO3, NaF, and SrCO3 is W:F:Na:Sr = 3:3:1:0.5, and the total mass ratio of W, F, Na, and Sr elements provided by the three components to the mass ratio of the matrix is ​​0.005:1. The mixture is heated to 680°C at a rate of 3°C / min under an oxygen atmosphere and held at that temperature for 8 hours. Other preparation methods are the same as in Example 6.

[0041] Example 9 A ternary cathode material includes a W-doped substrate and a composite coating layer on the substrate surface. The composite coating layer includes an F-doped WO3 matrix, and the matrix is ​​embedded with Li2WO4, SrF2, and NaF compounds. The preparation method differs from that of Example 8 in that the mixture described in step (2) is heated to 720°C at a rate of 3°C / min under an oxygen atmosphere and held at that temperature for 8 hours. Other preparation methods are the same as in Example 8.

[0042] Comparative Example 1 A ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes an F-doped WO3 matrix and Li2WO4 embedded in the matrix. The preparation method differs from that of Example 1 in that CaCO3 is not added in step (2), while the other preparation methods are the same as those in Example 1.

[0043] Comparative Example 2 A ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes a WO3 matrix and Li2WO4 and CaO embedded in the matrix. The preparation method differs from that of Example 1 in that PVDF is not added in step (2), while the other preparation methods are the same as those in Example 1.

[0044] Comparative Example 3 A ternary cathode material includes a substrate doped with F and a CaF2 coating layer on the surface of the substrate. The difference between its preparation method and that of Example 1 is that WO3 is not added in step (2), while the other preparation methods are the same as those of Example 1.

[0045] Comparative Example 4 A ternary cathode material includes a W-doped matrix and a composite coating layer on the matrix surface. The composite coating layer includes a WO3 matrix, and Li2WO4 and NaF compounds are embedded in the matrix. The preparation method differs from Example 2 in that, in step (2), WO3, PVDF, and Na2CO3 are uniformly mixed in the following ratio: the molar ratio of WO3, PVDF, and Na2CO3 is W:F:Na = 2:0.2:1, and the total mass ratio of W, F, and Na elements provided by the three components to the mass ratio of the matrix is ​​0.004:1. Other preparation methods are the same as in Example 2.

[0046] Performance testing The lithium-ion battery cathode materials prepared in all examples and comparative examples were used as cathodes, and lithium metal sheets were used as anodes to prepare coin cells. The coin cells prepared with the materials from the examples and comparative examples were subjected to two 0.1C constant current charge-discharge cycles within voltage ranges of 3.0–4.3V, 3.0–4.45V, and 3.0–4.3V at room temperature, followed by 0.2C charging and subsequent charge-discharge cycles at rates of 0.2C, 0.5C, 1C, 2C, 5C, and 0.2C, and then 50 cycles at 5C. The electrical performance results of the lithium-ion battery materials in all examples and comparative examples are shown in Tables 1, 2, and 3. Furthermore, the coin cells assembled with the materials prepared in Example 1 and Comparative Examples 1, 2, and 3 were subjected to EIS testing at a scan rate of 5 mV / s within the range of 100 kHz to 10 mHz. The Nyquist curves are shown below. Figure 2 As shown.

[0047] Table 1: Electrical performance of Example 1 and Comparative Examples 1, 2, and 3

[0048] Table 2: Electrical performance of Examples 2-5 and Comparative Example 4

[0049] Table 3: Electrical performance of Examples 6-9

[0050] Comparative Example 1 and Comparative Examples 1, 2, and 3, Figure 1The XPS spectra in Example 1 show that the F 1s peak shifts to a lower binding energy, indicating that the chemical state of F changes from the CF bond in PVDF to a state closer to ionicity. Simultaneously, the shape of the Ca 2p spectrum changes; the proportion of the Ca 2p3 / 2 peak decreases compared to Comparative Example 2, while the proportion of the Ca 2p1 / 2 peak at higher binding energies increases (31.2% → 33.8%), indicating that the chemical environment of Ca also changes. These two changes occur synergistically, both pointing to the reaction of F with Ca to form CaF2. Compared to Comparative Example 3, in Figure (c), the increased proportion of the Li-O peak, the shift of the peak corresponding to residual lithium towards lower binding energies, and the formation of a new peak at a higher binding energy indicate that W coating consumes some of the residual lithium and forms Li2WO4. Meanwhile, the O 1s spectrum in Figure (d) shows an increased proportion of the Li-O peak, and the original CO3... 2- The corresponding peak shifts towards lower energies, consistent with the formation of Li₂WO₄. Furthermore, correspondingly, in the W₄f spectrum of Figure (e), compared to standard WO₃ (W₂WO₄), the peak value shifts towards lower energies. 6+ (W 4f7 / 2~35.8eV), Example 1 due to WO4 2- The formation of tetrahedra leads to a decrease in the binding energy of W electrons, and under the influence of F doping with WO3, the overall energy shifts further towards lower binding energies, thus reducing W 4f7 / 2 to 33.9 eV. Figure 3 XRD analysis also confirmed that the materials were all layered oxide pure phases. However, Comparative Example 3, which did not contain W, showed a shift compared to Example 1 and other comparative examples, which is related to the W doping on the surface of the cathode particles. Combining the data in Table 1 and the Nyquist curves, the charge transfer resistance and diffusion resistance of Example 1 were both at low levels, indicating that this composite coating layer, with F-doped WO3 as a continuous matrix and embedded with Li2WO4 and M1-F compounds, is beneficial to improving the electrochemical performance of the material.

[0051] Comparing Examples 2, 3, and 4 with Comparative Example 4, it is evident that within the preferred total amount of coating layer, the material's performance is more effectively utilized. Excessive amounts can negatively impact the material's ionic conductivity, while insufficient amounts can affect its interfacial stability under high current. Furthermore, an incorrect coating layer ratio prevents the formation of F-doped WO3, thereby reducing ionic conductivity and leading to decreased rate performance or accelerated cycle decay under high current.

[0052] Comparing Example 2 and Example 5, Example 5 has slightly lower performance because the molar ratio of the coating material is not within the preferred range, resulting in less M1-F material and insufficient optimization of the lithium ion diffusion path.

[0053] Comparing Examples 6 and 7, an excessively high total amount of coating layer reduces the proportion of active material, which seriously affects the ionic and electronic conductivity of the material.

[0054] Comparing Examples 8 and 9, as follows Figure 4 The XRD pattern shows that the (003) peak and the (104) peak are shifted relative to Example 8, and the shifting pattern is similar to that of Example 1 relative to Comparative Example 3. The excessively high calcination temperature causes more W ions to be doped into the cathode particles in the coating layer, resulting in a slight decrease in performance.

[0055] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A composite-modified ternary cathode material, characterized in that, Comprises a substrate and a coating layer on the surface of the substrate, the surface of the substrate is doped with W, the coating layer is a composite coating layer, the composite coating layer comprises an F-doped WO3 matrix, and Li2WO4 and an M1-F compound are embedded in the matrix, wherein M1 is an alkali metal or alkaline earth metal element.

2. The composite-modified ternary cathode material according to claim 1, characterized in that, The mass ratio of the sum of the masses of W, F and M1 in the composite coating layer to the mass of the substrate is 0.001 to 0.01:1, and the mass percentage of W is greater than that of F.

3. The composite-modified ternary cathode material according to claim 1, characterized in that, The molar ratio of W, F and M1 elements in the composite coating layer is W:F:M1 = x:y:1, wherein 0 < x ≤ 5, n < y < 9, and n is the absolute value of the valence state of M1.

4. The composite-modified ternary cathode material according to claim 3, characterized in that, n < y ≤ 3.

5. The composite-modified ternary cathode material according to any one of claims 1 to 4, characterized in that, M1 is at least one selected from the group consisting of Ca, Mg, Na, K, Sr, Ba and Li.

6. The composite-modified ternary cathode material according to any one of claims 1 to 4, characterized in that, The interior of the substrate is doped with element X, and X is one or more selected from the group consisting of Zr, Al, W, Nb, Ti, Sr, Y, La and Ta.

7. A method for preparing a composite modified ternary cathode material as described in any one of claims 1 to 6, characterized in that, Comprises the following steps: S1, uniformly mixing a ternary precursor, a lithium source and a doping additive containing element X and sintering to obtain a ternary positive electrode material substrate, wherein X is one or more selected from the group consisting of Zr, Al, W, Nb, Ti, Sr, Y, La and Ta; S2, uniformly mixing the ternary positive electrode material substrate obtained in S1 with a coating additive containing W, F and M1 and sintering in an oxygen-containing atmosphere, wherein the sintering temperature is 450°C to 700°C, and the holding time is 4 to 8h, so as to obtain a composite modified ternary positive electrode material.

8. The method for preparing the ternary cathode material according to claim 7, characterized in that, In S1, the doping additive containing element X is one or more selected from the group consisting of ZrO2, Al2O3, Al(OH)3, WO3, Li2WO4, Nb2O3, LiNbO3, TiO2, La2O3, Y2O3, SrCO3, SrO and Ta2O5.

9. The method for preparing the ternary cathode material according to claim 7, characterized in that, In S1, the sintering is one-step sintering or two-step sintering, wherein the one-step sintering is directly heating to 600°C to 1000°C for sintering for 10 to 15h; the two-step sintering comprises a first-stage sintering and a second-stage sintering, the first-stage sintering is heating to a pre-sintering platform of 450°C to 800°C for holding for 3 to 6h, the second-stage sintering is heating to 600°C to 1000°C for holding for 10 to 15h, and the difference between the second-stage sintering temperature and the first-stage sintering temperature is greater than 100°C.

10. The method for preparing the ternary cathode material according to claim 7, characterized in that, In S2, the coating additive containing W, F or M1 is one or more selected from the group consisting of WO3, Na2WO4, MgWO4, PVDF, PTFE, NaF, LiF, CaF2, CaCO3, CaO, MgO, MgCO3, SrO, SrCO3 and K2CO3.

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