Ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention discloses a ternary positive electrode material, a preparation method thereof and a lithium ion battery. The general formula of the ternary positive electrode material is LiNixCoyMnzM1-x-y-zO2, x is larger than or equal to 0.6 and smaller than 1, y is larger than 0 and smaller than or equal to 0.2, z is larger than 0 and smaller than or equal to 0.2, M is a doping element, and M is selected from one or more of Nb, W, Ta, Ti, Hf, Mo, La, Ce and Zr; the ternary positive electrode material is tested through an X-ray energy disperse spectroscopy (EDS), the molar percentage content of M tested under the energy of 10 keV is recorded as P1, the molar percentage content of M tested under the energy of 20 keV is recorded as P2, and the ternary positive electrode material meets the condition that P2 / P1 is larger than 0.2 and smaller than 0.9. According to the method, deep transition metal ion doping of the surface layer of the ternary material is achieved, in the circulation process, the deep doped ions play a stronger rivet role in the structure, and long-term circulation structural stability can be achieved.

Description

Technical Field

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

[0002] Lithium-ion battery (LIB) technology is a key component of today's energy infrastructure. Its further development toward higher energy density, longer cycle life, better safety and lower cost is crucial for emerging applications such as utility-scale energy storage and drones. Ternary cathode materials (NCM) have stood out in the competition of cathode systems due to their comprehensive performance advantages and have become one of the mainstream technology routes.

[0003] In the fabrication process of NCM materials, to optimize the coulombic efficiency in the first cycle and alleviate lithium loss during cycling, traditional sintering methods generally adopt a high-lithium strategy—by setting a lithium ratio coefficient of 1.01-1.1, excess lithium is replenished during the high-temperature solid-state reaction. However, during the sintering process of high-lithium, lithium ions preferentially become ordered, leading to a significant increase in the energy barrier for subsequent dopant elements (such as Ti, Mg, Zr, etc.) to diffuse into the crystal lattice, forming a "shallow surface doping" phenomenon. This non-uniform doping can only produce limited positive effects within a few nanometers on the material surface and cannot penetrate deep into the crystal lattice to build long-term stable structural modifications, thus limiting the potential for improving the material's cycling stability. Summary of the Invention

[0004] The purpose of this invention is to provide a ternary cathode material, its preparation method, and a lithium-ion battery. The ternary cathode material prepared by this method has excellent rate performance and cycle stability, and the preparation process is simple.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a ternary cathode material with the general formula LiNi. x Co y Mn z M 1-x-y-z O2, 0.6≤x<1, 0<y≤0.2, 0<z≤0.2, M is a dopant element, selected from one or more of Nb, W, Ta, Ti, Hf, Mo, La, Ce, and Zr; the ternary cathode material is tested by X-ray energy dispersive spectroscopy (EDS), wherein the molar percentage of M tested at 10keV is denoted as P1, and the molar percentage of M tested at 20keV is denoted as P2, and the ternary cathode material satisfies 0.2<P2 / P1<0.9.

[0006] Furthermore, the value of P2 in the ternary cathode material ranges from 0.1% to 2%.

[0007] Secondly, the present invention provides a method for preparing the ternary cathode material, comprising the following steps: S1. The nickel-cobalt-manganese ternary precursor and lithium salt are mixed in a molar ratio of 1:(0.8 to 0.98) and sintered at 870 to 1000 °C in a pure oxygen atmosphere to obtain an ordered superlattice intermediate. S2. The ordered superlattice intermediate is mixed with the remaining lithium salt, a dopant containing the transition metal M, and a layer-expanding agent, and sintered in a pure oxygen atmosphere to obtain a ternary cathode material with deep M surface doping and an ordered superlattice structure. The molar ratio of the ordered superlattice intermediate to the remaining lithium salt is 1:(0.12 to 0.32).

[0008] In the above preparation method, the general structural formula of the nickel-cobalt-manganese ternary precursor is [Nix1Coy1Mnz1](OH)2, wherein 0.6≤x1<1, 0<y1≤0.2, and 0<z1≤0.2. The lithium salt is selected from one or more of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0009] In the above preparation method, the holding time for sintering in step S1 is 3 to 8 hours.

[0010] In the above preparation method, the transition metal M is selected from one or more of Nb, W, Ta, Ti, Hf, Mo, La, Ce, and Zr. Based on the center of the ordered superlattice, the mass percentage of the dopant is 0.1% to 1%.

[0011] In the above preparation method, the layer-expanding agent can provide an ionic radius greater than that of Li. + The metal ions, preferably Na+, are preferred. + More preferably, the layer-expanding agent is selected from one or more of Na2CO3, NaOH, CH3COONa, and Na2SO4. Based on the center of the ordered superlattice, the mass percentage of the layer-expanding agent is 0.3% to 1%.

[0012] In the above preparation method, the sintering temperature in step S2 is 650-820℃, and the holding time is 10-15h.

[0013] Secondly, the present invention provides a ternary cathode material prepared by the method described in any of the preceding claims.

[0014] Thirdly, the present invention provides a lithium-ion battery comprising the aforementioned ternary cathode material.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1. This invention employs a lithium-deficient pre-sintering method, which generates an ordered superlattice structure in which TM ions occupy Li sites during the pre-sintering process. This is beneficial for stabilizing lithium ion diffusion channels, increasing the lithium ion diffusion coefficient, and thus improving the electrochemical performance of the material.

[0016] 2. This invention uses a layer-expanding agent to achieve high-concentration transition metal ion doping in the deep surface layer of ternary materials. During cycling, the deeply doped ions play a stronger "rivet" role in the structure, which can achieve long-term cycling structural stability.

[0017] 3. The preparation process of this invention is simple, highly reproducible, and conducive to large-scale production. Attached Figure Description

[0018] Figure 1 The SEM image of M-NCM was prepared for Example 1 of this invention.

[0019] Figure 2 The XRD pattern of M-NCM prepared for Embodiment 1 of the present invention is shown.

[0020] Figure 3 shows the EDS surface distribution of the M-NCM prepared in Embodiment 1 of the present invention at 10 keV and 20 keV. Figure 3A-1 0keV, Figure 3B-2 0keV. Detailed Implementation

[0021] As described in the background section, in traditional high-lithium NCM preparation processes, lithium ions are preferentially ordered, resulting in subsequent doping elements only forming "shallow surface doping," which is detrimental to improving the material's cycle stability. To address these issues, this invention provides a ternary cathode material with deep surface doping.

[0022] The first part of this invention provides a ternary cathode material with the general formula LiNi. x Co y Mn z M 1-x-y-z O2, 0.6≤x<1, 0<y≤0.2, 0<z≤0.2, M is a dopant element selected from one or more of Nb, W, Ta, Ti, Hf, Mo, La, Ce, and Zr; the ternary cathode material is tested by X-ray energy dispersive spectroscopy (EDS), wherein the molar percentage of M tested at 10 keV is denoted as P1, and the molar percentage of M tested at 20 keV is denoted as P2, and the ternary cathode material satisfies 0.2<P2 / P1<0.9. In this invention, the term energy refers to X-ray energy.

[0023] Based on the above technical solution, the molar percentage of M tested at different energies represents the content of M at different depths of the material. Within the P2 / P1 range of this invention, unlike shallow surface doping, the molar percentage of M is relatively high in the deep surface layer. Therefore, the ternary cathode material of this invention can achieve deep surface doping of the doping element M. Optionally, P2 / P1 can specifically be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, such as 0.72.

[0024] Furthermore, the molar percentage of M, P2, of the ternary cathode material tested at 20keV energy is 0.1% to 2%, such as 0.1%, 0.2%, 0.34%, 0.5%, 1.0%, 1.5%, or 2.0%.

[0025] In one specific embodiment of the present invention, P2 / P1=0.72, and the molar percentage of each metal element is shown in Table 1.

[0026] The second part of this invention provides a method for preparing the ternary cathode material, comprising the following steps: S1. The nickel-cobalt-manganese ternary precursor and lithium salt are mixed in a molar ratio of 1:(0.8 to 0.98) and sintered at 870 to 1000 °C in a pure oxygen atmosphere to obtain an ordered superlattice intermediate. S2. The ordered superlattice intermediate is mixed with the remaining lithium salt, a dopant containing the transition metal M, and a layer-expanding agent, and sintered in a pure oxygen atmosphere to obtain a ternary cathode material with deep M surface doping and an ordered superlattice structure. The molar ratio of the ordered superlattice intermediate to the remaining lithium salt is 1:(0.12 to 0.32).

[0027] Based on the above technical solution, this invention first obtains partially TM (Ni, Co, Mn)-occupied Li by lithium-deficient pre-sintering (approximately 0.8-0.98 lithium content, sintering at 870-1000℃). + The ordered superlattice structure of the sites, in which partially ordered TM (Ni, Co, Mn) occupies Li + The structure of the site can stabilize ion diffusion channels and reduce Li + The diffusion barrier is lowered to improve the rate performance of the material. Then, the remaining lithium source, dopant, and a certain proportion of layer-expanding agent (Na) are added. + ) is added to the pre-sintered material for sintering, because Li + Incompletely ordered; during the sintering process, a small amount of Na... + It will enter the surface Li + By establishing sites, layer expansion is achieved, allowing dopants to penetrate deeper into the surface of NCM, resulting in longer-term cycle stability.

[0028] According to an embodiment of the present invention, the general structural formula of the nickel-cobalt-manganese ternary precursor is [Nix1Coy1Mnz1](OH)2, wherein 0.6≤x1<1, 0<y1≤0.2, 0<z1≤0.2 (x1+y1+z1=1); as an example, the structural formula of the nickel-cobalt-manganese ternary precursor is Ni 0.83 Co 0.10 Mn 0.07 (OH)₂, i.e., x₁=0.83, y₁=0.10, z₁=0.07. The lithium salt is selected from one or more of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0029] In step S1, the method of the present invention can obtain an ordered superlattice intermediate by precisely controlling the degree of lithium deficiency (i.e., 1:(0.8~0.98)) and the sintering temperature (870~1000℃) during the pre-sintering stage. As an example, the molar ratio of the nickel-cobalt-manganese ternary precursor to the lithium salt is 1:0.85 or 1:0.95. If the degree of lithium deficiency is too low, it will exacerbate uncontrolled migration of positive and negative ions, leading to defect proliferation, which is detrimental to long-term cycling stability. As an example, the sintering temperature includes, but is not limited to, 900~950℃, 900 or 950℃. The inventors have found that an ordered superlattice intermediate cannot be formed at a sintering temperature that is too low (e.g., 800℃).

[0030] According to an embodiment of the present invention, the holding time for sintering in step S1 is 3 to 8 hours, including but not limited to 5 hours. It is understood that the method further includes a step of removing and crushing the sample after sintering in step S1.

[0031] Accordingly, the remaining lithium salt is added in step S2. As an example, the molar ratio of the nickel-cobalt-manganese precursor to the remaining lithium salt is 1:0.2 or 1:0.12.

[0032] According to embodiments of the present invention, the transition metal M is selected from one or more of Nb, W, Ta, Ti, Hf, Mo, La, Ce, and Zr. The dopant is an oxide of the transition metal, such as Nb₂O₅ or WO₃. Based on the center of the ordered superlattice, the mass percentage of the dopant is 0.1% to 1%, including but not limited to 0.5%.

[0033] According to an embodiment of the present invention, the layer-expanding agent can provide an ionic radius greater than that of Li. + The metal ions, preferably Na+, are preferred. +More preferably, the layer-expanding agent is selected from one or more of Na₂CO₃, NaOH, CH₃COONa, and Na₂SO₄. Based on the center of the ordered superlattice, the mass percentage of the layer-expanding agent is 0.3% to 1%, including but not limited to 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1.0%. The inventors have found that when the mass percentage of the layer-expanding agent is too high, it excessively occupies Li₂. + The active sites are insufficient, which leads to the inability to fully utilize the capacity. When the mass percentage of the layer expander is too small, the layer expander cannot fully exert its layer expander effect, which in turn prevents the deeper incorporation of high-valence atoms and is not conducive to improving cycle stability. 0.5% is preferred.

[0034] According to an embodiment of the present invention, the sintering temperature in step S2 is 650–820°C, including but not limited to 750°C and 800°C, and the holding time is 10–15 hours, including but not limited to 12 hours. It is understood that the method further includes, after sintering in step S2, removing the sample and performing post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20°C.

[0035] In the second part, the present invention provides a ternary cathode material, which is prepared by any of the methods described above.

[0036] Thirdly, the present invention provides a lithium-ion battery comprising the aforementioned ternary cathode material.

[0037] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0038] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0039] In the following examples, the amount of lithium used refers to the molar ratio with the ternary precursor. For example, lithium hydroxide with a lithium content of 0.85 means that the molar ratio of Ni83 hydroxide precursor to lithium hydroxide is 1:0.85.

[0040] Example 1 First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07(OH)₂) and 0.85 wt% lithium hydroxide were added to a high-speed mixer and mixed thoroughly. The mixture was then placed in a kiln and held at 900℃ for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2 wt% lithium hydroxide, 0.5 wt% NaOH, and 0.5 wt% Nb₂O₅ were added and mixed thoroughly in a high-speed mixer. The mixture was then placed in a kiln and held at 750℃ for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating sieve. It is important to note that all processes must be carried out in a drying room with a dew point temperature of -20℃ to obtain Nb-doped ternary material with an ordered superlattice structure. The SEM and XRD images of the obtained Nb-doped ternary material with an ordered superlattice structure are shown below. Figure 1-2 As shown.

[0041] Example 2 First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 0.85% lithium carbonate were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 950°C for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2% lithium carbonate, 0.5 wt% NaOH, and 0.5 wt% Nb2O5 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 800°C for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20°C to obtain Nb-doped ternary material with an ordered superlattice structure.

[0042] Example 3 First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 0.93% lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 900℃ for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.12% lithium hydroxide, 0.5 wt% NaOH, and 0.5 wt% Nb2O5 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 750℃ for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20℃ to obtain Nb-doped ternary material with an ordered superlattice structure.

[0043] Example 4 The difference from Example 1 is that Nb2O5 is replaced with WO3.

[0044] First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 0.85% lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 900℃ for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2% lithium hydroxide, 0.5 wt% NaOH, and 0.5 wt% WO3 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 750℃ for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20℃ to obtain W-doped ternary material with an ordered superlattice structure.

[0045] Example 5 The difference from Example 1 is that NaOH is replaced with Na2CO3.

[0046] First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 0.85% lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 900℃ for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2% lithium hydroxide, 0.5 wt% Na2CO3, and 0.5 wt% Nb2O5 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 750℃ for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20℃ to obtain Nb-doped ternary material with an ordered superlattice structure.

[0047] Example 6 The difference from Example 1 is that the amount of NaOH is adjusted to 1%.

[0048] First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07(OH)2) and 0.85% lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 900℃ for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2% lithium hydroxide, 1 wt% NaOH, and 0.5 wt% Nb2O5 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 750℃ for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20℃ to obtain Nb-doped ternary material with an ordered superlattice structure.

[0049] Comparative Example 1 The difference from Example 1 is that lithium hydroxide and other raw materials are mixed together and sintered in one step.

[0050] Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 1.05% lithium hydroxide, 0.5wt% NaOH and 0.5wt% Nb2O5 are added to a high-speed mixer and mixed evenly. Then, the mixture is placed in a kiln and kept at 750℃ for 12 hours under a pure oxygen atmosphere. After cooling, it is taken out and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20℃ to obtain Nb-doped ternary material with an ordered superlattice structure.

[0051] Comparative Example 2 The difference from Example 1 is that the addition of the layer-expanding agent is omitted.

[0052] First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 0.85% lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 900°C for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2% lithium hydroxide and 0.5 wt% Nb2O5 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 750°C for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20°C to obtain Nb-doped ternary material with an ordered superlattice structure.

[0053] Comparative Example 3 The difference from Example 1 is that the amount of NaOH is adjusted to 0.1%.

[0054] First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 0.85% lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 900℃ for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2% lithium hydroxide, 0.1 wt% NaOH, and 0.5 wt% Nb2O5 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 750℃ for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20℃ to obtain Nb-doped ternary material with an ordered superlattice structure.

[0055] Comparative Example 4 The difference from Comparative Example 3 is that the temperature of the lithium-deficient pre-sintering process was adjusted to 800℃.

[0056] First, the Ni83 hydroxide precursor (Ni 0.83 Co 0.10 Mn 0.07 (OH)2) and 0.85% lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixture was then placed in a kiln and held at 800°C for 5 hours under a pure oxygen atmosphere. After removal, it was crushed to obtain an intermediate with an ordered superlattice structure. Subsequently, 0.2% lithium hydroxide, 0.1 wt% NaOH, and 0.5 wt% Nb2O5 were added and mixed evenly in a high-speed mixer. The mixture was then placed in a kiln and held at 750°C for 12 hours under a pure oxygen atmosphere. After cooling, it was removed and subjected to post-processing steps such as gas-powder crushing and demagnetization by vibrating screen. It should be noted that all processes must be carried out in a drying room with a dew point temperature of -20°C.

[0057] Material characterization The materials obtained in Example 1 and Comparative Examples 2 and 3 were subjected to EDS testing at different voltages. The testing method is as follows: the prepared materials were subjected to energy dispersive spectroscopy (EDS) measurements at 10 keV and 20 keV to characterize their elemental signals at different depths. The EDS surface distribution diagrams of the material prepared in Example 1 at 10 keV and 20 keV are shown below. Figure 3A and Figure 3B As shown in Table 1-2, the total number of distribution spectra at 10 keV and 20 keV are also shown.

[0058] Table 1. Distribution of 10keV: Total Spectrum

[0059] Table 2. Distribution map of 20keV, total spectrum.

[0060] Based on the EDS surface scan results at different keVs, the proportions of different metal elements can be obtained. For easy comparison, the following table replaces them with molar ratios and compares them with the results of comparative examples 2 and 3.

[0061] Table 3. Molar ratios of metal elements tested under different voltages in Examples 1, 2, and 3.

[0062] The test results above show that all three samples exhibited detectable Nb signals at 10 eV using EDS, indicating successful Nb doping on the surface. Example 1 still showed a detectable Nb signal of 0.34 mol% at 20 keV, while Comparative Example 3, with a small amount of layer-expanding agent, showed only 0.1 mol%. When the layer-expanding agent was removed, the Nb signal at 20 keV was only 0.02 mol%, indicating that the Nb doping was more thorough under the influence of the layer-expanding agent.

[0063] Performance testing The above-mentioned M-NCM, conductive agent (carbon black) and binder (PVDF) were mixed in a mass ratio of 95:3:2. After adding an appropriate amount of NMP slurry, the mixture was coated and dried to obtain the positive electrode. The negative electrode was a lithium sheet, and the electrolyte was 1 mol / L LiPF6-EC / DMC (volume ratio 1:1). The CR2032 button cell was assembled in an argon-filled glove box and subjected to different rate and cycle tests in a voltage range of 2.8-4.45 V.

[0064] The experimental results are shown in Table 4.

[0065] Table 4. Ratio and Cycling Performance

[0066] As can be seen from Examples 1-6 in Table 1, the ternary cathode material prepared by the method of the present invention has excellent rate performance and cycle stability.

[0067] The comparison results between Example 1 and Comparative Example 1 show that the ternary cathode material obtained by the present invention has better rate performance and cycle stability than the traditional one-step high-lithium NCM preparation process.

[0068] The comparison results between Example 1 and Comparative Example 2 show that the ternary cathode material prepared by adding the layer expander can significantly improve its cycle stability. Comparative Example 2 without the layer expander only retains 80% of its capacity after 213 cycles, while the number of cycles after adding the layer expander reaches a considerable 1256 cycles. This is because the addition of the layer expander in this invention allows the dopant to penetrate deeper into the surface layer of the NCM, and there is still 0.34 mol% elemental doping at an EDS depth of 20 keV, which is conducive to achieving longer cycle stability.

[0069] The comparison results between Example 1 and Comparative Example 3 show that when the amount of the layer expander is reduced to 0.1%, the cycling stability will decrease. This is because when the amount of the layer expander is too low, it cannot fully exert its layer expansion effect. The material prepared in Comparative Example 3 has only 0.1 mol% element doping at an EDS depth of 20 keV, which cannot effectively suppress the stress and structural damage generated during cycling for a long time, resulting in poor cycling stability.

[0070] The comparison results between Example 1 and Comparative Example 4 show that a sintering temperature that is too low during the lithium-deficient pre-burning process can also lead to a significant decrease in cycle stability. This is because the sintering temperature during the lithium-deficient pre-burning process in Comparative Example 4 is low (800°C), which makes it impossible to form an intermediate containing an ordered superlattice structure.

[0071] In summary, by precisely controlling the degree of lithium deficiency and temperature conditions during the pre-sintering stage, a thermodynamically stable locally ordered superlattice structure is induced. Combined with sodium ion-assisted deep-surface high-concentration doping technology, the high-valence dopant ions act as "rivets" during long-term cycling, suppressing side reactions and significantly improving the material's structural stability and cycle life.

[0072] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A ternary cathode material, characterized in that, Its general formula is LiNi x Co y Mn z M 1-x-y-z O2, 0.6≤x<1, 0<y≤0.2, 0<z≤0.2, M is a dopant element, selected from one or more of Nb, W, Ta, Ti, Hf, Mo, La, Ce, and Zr; the ternary cathode material is tested by X-ray energy dispersive spectroscopy (EDS), wherein the molar percentage of M tested at 10keV is denoted as P1, and the molar percentage of M tested at 20keV is denoted as P2, and the ternary cathode material satisfies 0.2<P2 / P1<0.

9.

2. The ternary cathode material according to claim 1, characterized in that: The value of P2 in the ternary cathode material ranges from 0.1% to 2%.

3. The method for preparing the ternary cathode material according to claim 1 or 2, characterized in that, Includes the following steps: S1. The nickel-cobalt-manganese ternary precursor and lithium salt are mixed in a molar ratio of 1:(0.8 to 0.98) and sintered at 870 to 1000 °C in a pure oxygen atmosphere to obtain an ordered superlattice intermediate. S2. The ordered superlattice intermediate is mixed with the remaining lithium salt, a dopant containing the transition metal M, and a layer-expanding agent, and sintered in a pure oxygen atmosphere to obtain a ternary cathode material with deep M surface doping and an ordered superlattice structure. The molar ratio of the ordered superlattice intermediate to the remaining lithium salt is 1:(0.12 to 0.32).

4. The method for preparing the ternary cathode material according to claim 3, characterized in that: The general structural formula of the nickel-cobalt-manganese ternary precursor is [Nix1Coy1Mnz1](OH)2, where 0.6≤x1<1, 0<y1≤0.2, and 0<z1≤0.

2. And / or, the lithium salt is selected from one or more of lithium hydroxide, lithium carbonate, and lithium nitrate; And / or, the holding time for sintering in step S1 is 3 to 8 hours.

5. The method for preparing the ternary cathode material according to claim 3, characterized in that: The dopant is an oxide of the transition metal M.

6. The method for preparing the ternary cathode material according to claim 5, characterized in that: Based on the ordered superlattice intermediate, the mass percentage of the dopant is 0.1% to 1%.

7. The method for preparing the ternary cathode material according to claim 3, characterized in that: The layer-expanding agent can provide an ionic radius greater than Li. + The metal ions, preferably Na+, are preferred. + More preferably, the layer-expanding agent is selected from one or more of Na2CO3, NaOH, CH3COONa, and Na2SO4.

8. The method for preparing the ternary cathode material according to claim 7, characterized in that: Based on the ordered superlattice intermediate, the mass percentage of the layer-expanding agent is 0.3% to 1%.

9. The method for preparing the ternary cathode material according to claim 3, characterized in that: The sintering temperature in step S2 is 650–820°C, and the holding time is 10–15 h.

10. A lithium-ion battery, characterized in that, The ternary cathode material includes the ternary cathode material as described in claim 1 or 2, or the ternary cathode material prepared by the method described in any one of claims 3-9.

Images