Ternary positive electrode material and preparation method and application thereof

Abstract

The invention discloses a ternary positive electrode material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The method comprises the following steps: modifying a ternary matrix material in a composite doping manner of rare earth elements and transition metals, and then coating the surface of the material with a layer of amorphous ferric fluoride in a manner of combining atomic layer deposition with fluorination reaction. The ternary positive electrode material provided by the invention has higher rate capability and better cycling stability, and can maintain better chemical performance under high current density, so that the problems of capacity loss and poor electrical performance of the ternary positive electrode material of the lithium battery in a high-voltage long-cycle process are greatly relieved.

Description

Technical Field

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

[0002] Nickel-cobalt-manganese (NCM) ternary cathode materials play a decisive role in the energy density, safety, and lifespan of lithium-ion batteries. Nickel-rich layered oxides, as a high-performance ternary material, have been extensively studied. However, research has shown that nickel-rich materials undergo a series of side reactions during charge and discharge, which accelerates the structural distortion of the cathode and causes a decline in electrochemical performance. This phenomenon is further amplified at high cutoff voltages.

[0003] At present, the research on the application of ternary materials under high voltage mainly focuses on two core issues: the bulk phase and the interface. (1) How to stabilize the layered structure of the material, suppress cation mixing, and improve lithium ion transport dynamics under high voltage application conditions; (2) How to reduce the side reactions on the material surface, suppress the oxidative decomposition of the electrolyte, the release of surface oxygen and the dissolution of transition metals, and further enhance thermal stability and safety.

[0004] In summary, developing a ternary cathode material that can be adapted to high-voltage systems, ensuring both the material's cycle performance and its capacity and rate performance, is of significant practical importance. Summary of the Invention

[0005] The purpose of this invention is to provide a ternary cathode material adapted to high-voltage systems, its preparation method, and its application. The ternary cathode material of this invention improves the high-voltage performance, cycle life, and safety of lithium-ion batteries.

[0006] This invention first provides a method for preparing a ternary cathode material, comprising the following steps:

[0007] S1. The ternary precursor material, lithium source, rare earth oxide and high-valence transition metal oxide are mixed and dispersed in a dispersion medium, and then sintered at high temperature in an oxygen-containing atmosphere to obtain the ternary matrix material.

[0008] S2. An amorphous FeOx layer is deposited on the surface of the ternary matrix material to obtain an amorphous FeOx-coated ternary material;

[0009] S3. The amorphous FeOx-coated ternary material is placed in a gaseous environment containing HF and NH3 and kept at a constant temperature to obtain the ternary cathode material.

[0010] The present invention modifies the ternary matrix material by means of composite doping of rare earth elements and transition metals, and then coats a layer of amorphous iron fluoride (α-FeF3) on the surface of the material by using atomic layer deposition (ALD) combined with fluorination reaction. The ternary cathode material provided by the present invention has higher rate performance and better cycle stability. At the same time, it can also maintain good chemical properties at high current density, greatly alleviating the problems of capacity loss and poor electrical performance of the ternary cathode material of lithium batteries during high-voltage long-term cycling.

[0011] In the preparation method of the ternary cathode material described above, in step S1, the chemical formula of the ternary precursor material is Ni , , , , ,

[0018] ,

[0017] ,

[0016] ,

[0015] ,

[0014] ,

[0019] Co y Mn z (OH)2, where 0.5 ≤ x ≤ 0.8, 0.05 < y ≤ 0.2, 0.1 ≤ z ≤ 0.3, and x + y + z = 1; specifically, it can be Ni 0.65 Co 0.08 Mn 0.27 (OH)2 or Ni 0.8 Co 0.1 Mn 0.1 (OH)2;

[0012] The lithium source is lithium hydroxide and / or lithium carbonate;

[0013] The rare earth oxide is at least one of cerium oxide, yttrium oxide, niobium oxide, lanthanum oxide, and gadolinium oxide;

[0014] The high-valent transition metal oxide is at least one of niobium oxide, zirconium oxide, tungsten oxide, and tantalum oxide;

[0015] The dispersion medium is anhydrous ethanol, ethanol solution, isopropanol, or water;

[0016] The molar ratio of the ternary precursor material, lithium source, rare earth oxide, and high-valent transition metal oxide is 1:(1 - 1.15):(0.001 - 0.01):(0.001 - 0.02); specifically, it can be 1:1.06:0.005:0.0075 or 1:1.06:0.005:0.01.

[0017] In the preparation method of the ternary cathode material described above, in step S1, the high-temperature sintering includes two stages: pre-sintering and sintering;

[0018] The temperature of the pre-sintering is 450 - 750 °C, specifically 650 °C; the pre-sintering time is 5 - 10 h, specifically 5 h;

[0019] The temperature of the sintering is 800 - 950 °C, specifically 900 °C; the sintering time is 10 - 15 h, specifically 13 h;

[0020] In the oxygen-containing atmosphere, the volume percentage of oxygen is greater than or equal to 21%.

[0021] The above-mentioned method for preparing ternary cathode materials further includes step S1, which involves mixing and dispersing the ternary precursor material, lithium source, rare earth oxide and high-valence transition metal oxide in a dispersion medium and then ball milling the mixture; followed by high-temperature sintering after ball milling.

[0022] Specifically, the ball milling time is 4-6 hours and the rotation speed is 300 rpm.

[0023] The ternary matrix material obtained in step S1 has a D50 of 3-8 μm and a specific surface area of ​​0.5-3.0 m². 2 / g.

[0024] In the above-mentioned method for preparing ternary cathode materials, in step S2, the precursor for depositing the amorphous FeOx layer is Fe(CO)5 (iron pentacarbonyl), and the oxidant is ozone and / or oxygen.

[0025] The deposition temperature is 150-200℃;

[0026] The deposition cycle is 50-200 times.

[0027] In step S2, the deposition thickness of the amorphous FeOx layer is 2-5 nm;

[0028] In step S2, an amorphous FeOx layer is deposited on the surface of the ternary substrate material using a fully automated atomic layer deposition system.

[0029] In the above-mentioned method for preparing ternary cathode materials, in step S3, the temperature for heat preservation is 200-300℃, specifically 300℃ or 250℃; and the heat preservation time is 2-3 hours.

[0030] The preparation method of the above-mentioned ternary cathode material, step S3 specifically includes the following: placing the amorphous FeOx-coated ternary material in a tube furnace, introducing NH4F at the front end of the tube furnace, first heating to 150-200℃ to release HF and NH3 gases, and then holding at 200-300℃ for 2-3 hours to obtain the ternary cathode material.

[0031] After the heat preservation, there are further steps of washing the material with water to remove residual NH4F and drying; specifically, the drying temperature is 60-80℃ and the time is 6-8h; the drying is vacuum drying.

[0032] The present invention further provides a ternary cathode material prepared by the above preparation method.

[0033] Specifically, the ternary cathode material is adapted to high-voltage systems.

[0034] Third, the present invention provides the application of the above-mentioned ternary cathode material in the preparation of lithium-ion battery cathodes.

[0035] Fourth, the present invention provides a lithium-ion battery cathode, wherein the active material is the ternary cathode material.

[0036] Finally, the present invention also provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery is the aforementioned positive electrode.

[0037] The present invention has the following beneficial effects:

[0038] (1) The present invention uses rare earth elements and transition metals to dop ternary cathode materials, which significantly improves the structural stability, electrochemical performance and safety of the materials under high voltage through synergistic effect.

[0039] (2) Rare earth elements have larger ionic radii, which can increase the interlayer spacing after doping and reduce the lattice stress during lithium ion insertion / extraction. Meanwhile, high-valence metals (such as Zr) can also be doped. 4+ This can induce local structural distortions, thereby enhancing lithium-ion transport kinetics. Furthermore, rare earth elements have oxygen affinity, which can reduce oxygen vacancy generation under high voltage and suppress lattice oxygen release. High-valence metal doping can also balance the low valence states of rare earth elements, reducing the amount of Li in the lattice. + / Ni 2+ Vacancies, inhibiting transition metals (Mn) 3+ Ni 3+ The dissolution of ).

[0040] (3) This invention uses α-FeF3 to coat ternary materials. The amorphous high toughness alleviates the volume expansion stress of NCM particles under high voltage and reduces the formation of microcracks. At the same time, a physical barrier is formed on the material surface to isolate direct contact with the electrolyte and inhibit the dissolution of transition metals (Mn / Ni) and HF corrosion. The amorphous structure provides a fast lithium-ion channel, while Fe... 3+ The electronic insulation properties suppress surface side reactions, which is more conducive to improving long-cycle performance under high voltage.

[0041] (4) This invention uses ALD combined with fluorination to achieve material surface coating, resulting in a uniform coating layer that avoids the agglomeration problem of traditional wet coating, while the composition is controllable. By adjusting the number of ALD cycles and fluorination time, the stoichiometric ratio of the coating layer can be precisely designed, which has certain advantages in the preparation process. Attached Figure Description

[0042] Figure 1 This is a SEM image of the ternary cathode material prepared in Example 1 of the present invention.

[0043] Figure 2 The image shows the XRD pattern of the ternary cathode material prepared in Example 1 of this invention. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0045] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0046] Unless otherwise specified, the quantitative experiments in the following examples are all repeated three times, and the results are averaged.

[0047] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0048] Example 1

[0049] S1, commercial ternary precursor Ni 0.65 Co 0.08 Mn 0.27 (OH)₂, lithium carbonate, La₂O₃, and Ta₂O₅ were dispersed in a 95% (v / v) ethanol solution at a molar ratio of 1:1.06:0.005:0.0075, using ethanol as the dispersant. The mixture was ball-milled for 4 hours at 300 rpm. The dried material was then subjected to high-temperature sintering in an oxygen atmosphere (oxygen content not less than 21% or pure oxygen; in this embodiment, air was used). The pre-sintering temperature was 650°C for 5 hours, followed by sintering at 900°C for 13 hours to obtain a ternary matrix material with a D50 of 3.5 μm and a BET of 0.85 μm. 2 / g;

[0050] S2. The ternary matrix material was dried in a vacuum oven at 80°C for 12 hours to remove adsorbed water from the surface. Then, a rotary reactor was used to ensure uniform powder dispersion during the ALD process. Finally, an ALD (Automated Atomic Layer Deposition) system was used, with the reaction chamber temperature controlled at 150°C. Fe(CO)5 was used as the precursor, O3 as the oxidant, and the cycle was 100 times to deposit an amorphous FeOx layer with a thickness of 3 nm on the surface of the ternary matrix material.

[0051] S3. The prepared amorphous FeOx-coated ternary material is placed in a tube furnace. NH4F is introduced into the front end of the tube furnace. The material is first heated to 150°C to release HF and NH3 gases, and then kept at 250°C for 3 hours. After the reaction is completed, the material is repeatedly washed with deionized water to remove residual NH4F. After vacuum drying at 80°C, the ternary cathode material is obtained.

[0052] SEM images of the ternary cathode material prepared in this embodiment are shown below. Figure 1 ,Depend on Figure 1 As can be seen, this material mainly maintains a normal single-crystal morphology. See the XRD pattern. Figure 2 ,Depend on Figure 2 It can be seen that due to the lattice expansion of materials doped with rare earth elements, the diffraction peaks shift to lower angles.

[0053] Example 2

[0054] Compared to Example 1, the difference is that Ni in S1 0.65 Co 0.08 Mn 0.27 The molar ratio of (OH)2, lithium carbonate, La2O3 and Ta2O5 is replaced with 1:1.06:0.005:0.01, while other steps, raw materials and parameters remain unchanged.

[0055] Example 3

[0056] Compared to Example 1, the difference in S2 is that the number of cycles is 200, while other steps, raw materials, and parameters remain unchanged. The deposition thickness of the amorphous FeOx layer is 5 nm.

[0057] Example 4

[0058] Compared with Example 1, the raw materials and parameters in S1 and S2 remain unchanged. In S3, the heat preservation temperature is replaced with 300°C.

[0059] Example 5

[0060] Compared to Example 1, the difference is that the commercial ternary precursor is replaced with Ni. 0.8 Co 0.1 Mn 0.1 (OH)2, with all other steps, raw materials and parameters remaining unchanged.

[0061] Example 6

[0062] Compared with Example 1, the difference is that the rare earth metal oxide is replaced with Y2O3 and the high-valence transition metal oxide is replaced with Nb2O5, while the other steps, raw materials and parameters remain unchanged.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that the doping step in S1 is omitted, and the commercial ternary precursor Ni is used instead. 0.65 Co 0.08 Mn 0.27(OH)2 and lithium carbonate are dispersed in an ethanol solution at a molar ratio of 1:1.06 and ball-milled for 4 hours at 300 rpm. The dried material is then subjected to high-temperature sintering in air at a pre-sintering temperature of 650°C for 5 hours, followed by sintering at 900°C for 13 hours to obtain the ternary matrix material. Steps S2 and S3 are the same as in Example 1.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that the ALD-bonded fluorinated material surface coating steps S2 and S3 are omitted.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 1 is that the doping and coating steps are omitted, and the commercial ternary precursor Ni is directly applied. 0.65 Co 0.08 Mn 0.27 (OH)2 and lithium carbonate were mixed in a molar ratio of 1:1.06 and then subjected to high-temperature sintering (air atmosphere). The pre-sintering temperature was 650℃ and the sintering time was 5h. The temperature was then raised to 900℃ and sintered for 13h to obtain ternary material.

[0069] Comparative Example 4

[0070] The ternary cathode material prepared in Example 1 was assembled into a CR2016 coin cell according to the method in Example 7 for electrical performance testing. The difference from Example 7 is that the cutoff voltage for electrical performance testing is 4.3V.

[0071] Example 7, Performance Testing

[0072] The electrical performance testing method is as follows: Using the ternary cathode material prepared in the above examples and comparative examples as the cathode active material, and mixing the ternary cathode material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 90:5:5 in an N-methylpyrrolidone solution, the mixture was then uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain a compacted density of 3.5 g / cm³. 3 The positive electrode is selected; 1.0 mol / L LiPF6 is dissolved in EC / DMC / DEC (the volume ratio of EC, DMC and DEC is 1:1:1) as the electrolyte. The positive electrode, separator (Celgard 24), electrolyte and lithium metal negative electrode are assembled into CR2016 coin cell in a glove box.

[0073] The assembled coin cells were subjected to electrochemical performance tests at 25°C, with an initial voltage of 2.8V and a cutoff voltage of 4.5V. First, the cells were charged and discharged sequentially at rates of 0.2C / 0.2C, 0.33C / 0.33C, 1C / 1C, 3C / 3C, and 0.2C / 0.2C for the first four weeks. Then, the cells were charged and discharged at a rate of 1C / 1C until 300 cycles were completed. The test results are shown in Table 1.

[0074] Table 1 Electrochemical performance of cathode materials in different embodiments and comparative examples

[0075]

[0076] Based on the data from Example 1 and Comparative Examples 1, 2, and 3, it can be seen that the modification method of using rare earth elements and transition metals for composite doping followed by ALD combined with fluorination to achieve surface coating of the material has a significant effect on improving the material's capacity, rate capability, and cycle performance.

[0077] Comparing the data from Examples 1 and 2, it can be seen that the rate performance of the material is optimal when the molar ratio of rare earth elements to high-valence transition metals is 0.005:1.

[0078] Meanwhile, the data from Comparative Examples 1 and 3 show that α-FeF3 coating greatly improves the cycling performance of the material. The combined effect of rare earth elements and transition metal doping on the overall performance of the material is even greater.

[0079] The cutoff voltage of Comparative Example 4 is 4.3V, while the application example of this invention is 4.5V, which is already in the high voltage range. In contrast, the battery assembled with the ternary cathode material prepared by this invention exhibits better cycle capacity retention and rate performance at a cutoff voltage of 4.5V. That is, increasing the voltage does not lead to a decrease in capacity retention, and the ternary cathode material prepared by this invention is suitable for high voltage systems.

[0080] In summary, the ternary cathode material prepared by the method of the present invention is more conducive to improving the rate performance of the material, especially the capacity performance at high voltage, and has an important impact on the cycle stability of the material.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a ternary cathode material, characterized in that: The preparation method includes the following steps: S1. The ternary precursor material, lithium source, rare earth oxide and high-valence transition metal oxide are mixed and dispersed in a dispersion medium, and then subjected to high-temperature sintering in an oxygen-containing atmosphere to obtain the ternary matrix material. S2. An amorphous FeOx layer is deposited on the surface of the ternary matrix material to obtain an amorphous FeOx-coated ternary material; S3. The amorphous FeOx-coated ternary material is placed in a gaseous environment containing HF and NH3 and kept at a constant temperature to obtain the ternary cathode material.

2. The method for preparing the ternary cathode material according to claim 1, characterized in that: In step S1, the chemical formula of the ternary precursor material is Ni. x Co y Mn z (OH)₂, where 0.5 ≤ x ≤ 0.8, 0.05 <y≤0.2、0.1≤z≤0.3、x+y+z=1; The lithium source is lithium hydroxide and / or lithium carbonate; The rare earth oxide is at least one of cerium oxide, yttrium oxide, niobium oxide, lanthanum oxide, and gadolinium oxide; The high-valence transition metal oxide is at least one of niobium oxide, zirconium oxide, tungsten oxide, and tantalum oxide; The dispersion medium is anhydrous ethanol, ethanol solution, isopropanol or water; The molar ratio of the ternary precursor material, lithium source, rare earth oxide, and high-valence transition metal oxide is 1:(1-1.15):(0.001-0.01):(0.001-0.02).

3. The method for preparing the ternary cathode material according to claim 1, characterized in that: In step S1, the high-temperature sintering includes two stages: pre-sintering and sintering. The pre-sintering temperature is 450-750℃; the pre-sintering time is 5-10h; The sintering temperature is 800-950℃; the sintering time is 10-15h; In the oxygen-containing atmosphere, the volume percentage of oxygen is greater than or equal to 21%.

4. The method for preparing the ternary cathode material according to claim 1, characterized in that: In step S2, the precursor for depositing the amorphous FeOx layer is Fe(CO)5, and the oxidant is ozone and / or oxygen. The deposition temperature is 150-200℃; The deposition cycle is 50-200 times.

5. The method for preparing the ternary cathode material according to claim 1, characterized in that: In step S3, the temperature for heat preservation is 200-300℃; the heat preservation time is 2-3 hours.

6. The method for preparing the ternary cathode material according to claim 1, characterized in that: Step S3 specifically includes the following: placing the amorphous FeOx-coated ternary material in a tube furnace, introducing NH4F at the front end of the tube furnace, first heating to 150-200℃ to release HF and NH2 gases, and then holding at 200-300℃ for 2-3 hours to obtain the ternary cathode material.

7. The ternary cathode material prepared by the preparation method according to any one of claims 1-7.

8. The application of the ternary cathode material according to claim 7 in the preparation of lithium-ion battery cathodes.

9. A lithium-ion battery positive electrode, characterized in that: The active material of the lithium-ion battery cathode is the ternary cathode material as described in claim 7.

10. A lithium-ion battery, characterized in that: The positive electrode of the lithium-ion battery is the positive electrode as described in claim 9.

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