Surface-modified single-crystal ternary positive electrode material, and preparation method and application thereof

Abstract

The application provides a surface-modified single-crystal ternary positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing a ternary positive electrode precursor with an acidic chelating etching solution to perform chelating etching treatment, so as to obtain a modified precursor; (2) mixing the modified precursor with a lithium source, and performing sintering treatment, so as to obtain the surface-modified single-crystal ternary positive electrode material; wherein the solute of the acidic chelating etching solution comprises a zirconium-containing chelate and an etchant. Through the surface zirconium citrate chelating etching process, a three-dimensional structure of zirconium-doped and zirconium-coated compounds is formed on the surface of the positive electrode material after sintering, and through the chelating dispersion effect of zirconium citrate, the gradient doping mechanism and the in-situ interface reconstruction, the problems of residual alkali control, lattice distortion and interface failure of the ultra-high nickel single-crystal material are solved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a surface-modified single-crystal ternary cathode material, its preparation method, and its application. Background Technology

[0002] The rapid development of new energy vehicles has placed higher demands on long driving ranges, leading to a continuous increase in the demand for high-energy-density lithium-ion batteries. Ultra-high nickel ternary cathode materials (Ni≥90%) have become a research hotspot due to their theoretical capacity of up to 280mAh / g. However, ultra-high nickel ternary cathode materials are prone to Ni degradation during cycling. 4+ Ion dissolution, structural phase transitions, and the tendency for cracks or breakage can exacerbate side reactions with the electrolyte, leading to capacity decay and safety hazards.

[0003] To address these issues, single-crystal structure design becomes crucial. Current methods for synthesizing ultra-high nickel single-crystal ternary cathode materials involve sintering pre-fabricated ultra-high nickel ternary precursors and lithium sources. However, existing ultra-high nickel single-crystal ternary cathode materials suffer from three major technical bottlenecks: 1) Residual alkali problem: Traditional processes result in residual alkali content as high as 2000-3000 ppm, leading to a rapid increase in interfacial impedance; 2) Lattice distortion: High nickel content easily induces lattice distortion, resulting in poor cycle stability; 3) Interfacial failure: The lack of a stable protective layer on the surface of single-crystal particles makes them prone to grain boundary slip and side reactions during cycling.

[0004] CN113644262A discloses a layered, large-particle-size, high-nickel single-crystal ternary cathode material and its preparation method. The preparation method includes the following steps: weighing nickel salt, cobalt salt, manganese salt, and strontium salt and dispersing them in pure water to obtain a precursor solution; atomizing the precursor solution and then heating it to decompose it, obtaining precursor powder; heat-treating the precursor powder, then thoroughly mixing the heat-treated precursor powder, a first lithium source, and zirconium oxide, and sequentially heating and melting, followed by a single-crystal sintering to obtain a single-crystal ternary material; subjecting the single-crystal ternary material to airflow milling, water washing, filtration, and drying, then adding a second lithium source, continuing to mix evenly, and performing a second sintering to obtain the layered, large-particle-size, high-nickel single-crystal ternary cathode material. While the use of a layered, large-particle-size precursor improves the tap density, it does not solve the problems of residual alkali and interface stability.

[0005] CN103359795A discloses a cobalt-coated composite multi-element lithium-ion battery cathode material precursor, its preparation method, and its application. The precursor consists of a core and a nano-cobalt tetroxide layer coating the core surface. While the cobalt coating improves rate performance, it does not achieve the synergistic effect of lattice doping and interface reconstruction.

[0006] The cathode material described in the above scheme has a high residual alkali content and suffers from problems such as lattice distortion and interface failure, resulting in poor overall performance of the material. Summary of the Invention

[0007] The purpose of this invention is to provide a surface-modified single-crystal ternary cathode material, its preparation method, and its application. This invention uses a zirconium citrate chelate etching process to form a three-dimensional structure of zirconium doping and zirconium-coated compounds on the surface of the cathode material. This invention changes the conventional etching conditions and solves the problems of residual alkali control, lattice distortion, and interface failure in ultra-high nickel single-crystal materials by sintering under suitable conditions, thereby significantly improving the cycle stability and rate performance of the material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a surface-modified single-crystal ternary cathode material, the method comprising the following steps:

[0010] (1) The ternary cathode precursor is mixed with an acidic chelating etching solution and subjected to chelating etching to obtain a modified precursor.

[0011] (2) The modified precursor is mixed with a lithium source and sintered to obtain a surface-modified single-crystal ternary cathode material;

[0012] The solute in the acidic chelating etching solution includes zirconium-containing chelates and acidic etching agents.

[0013] This invention utilizes an acidic chelating etching solution to chelate and etch a ternary precursor followed by sintering. The zirconium-containing chelate in the acidic chelating etching solution plays a multifunctional regulatory role, including chelation dispersion (during the chelation etching process, the zirconium-containing chelate in the acidic chelating etching solution complexes and coats the precursor surface), gradient doping (during the sintering process, the zirconium-containing chelate on the precursor surface penetrates into the precursor, forming a gradient doped structure, thereby regulating the lattice of the cathode material), and residual alkali capture (taking zirconium citrate as an example, zirconium citrate electrolysis generates citrate and zirconium ions, and the citrate ions generate citric acid under acidic conditions). By consuming residual alkali through neutralization reactions, a ternary cathode precursor coated with zirconium-containing chelates is formed during surface etching. After sintering, a three-dimensional structure of zirconium doping and zirconium-coated compounds is formed on the surface of the cathode material. This solves the problems of particle dispersion, lattice distortion, interface failure and residual alkali control in ultra-high nickel single crystal materials, and improves the cycle stability of the material. The zirconium-containing chelate is also thermally decomposed during sintering to form in-situ coated zirconium-containing compounds with high lithium-ion conductivity (such as Li2ZrO3), which significantly improves the cycle stability and rate performance of the cathode material.

[0014] Preferably, the median particle size D50 of the ternary cathode precursor in step (1) is 2μm to 5μm, for example: 2μm, 2.5μm, 3μm, 4μm or 5μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] The ternary cathode precursor described in this invention can be obtained directly by controlling the appropriate particle size through co-precipitation, or it can be obtained by crushing large-particle-size ternary cathode precursors. Small-particle-size ternary cathode precursors, with their advantages of high specific surface area and more active sites, can form a more stable zirconium-containing chelate coating layer on their surface.

[0016] Preferably, the general chemical formula of the ternary cathode precursor in step (1) is Ni x Co y Mn 1-x-y (OH)₂, where 0.9 ≤ x ≤ 0.98, 0 <y<0.1。

[0017] The ternary cathode precursor described in this invention is prepared by a conventional co-precipitation method.

[0018] Preferably, the acidic etchant includes HCl.

[0019] Preferably, the zirconium-containing chelate comprises zirconium citrate and / or zirconium tartrate.

[0020] Preferably, the mass concentration of zirconium chelate in the acidic chelating etching solution in step (1) is 0.1 wt.% to 3 wt.%, for example: 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2 wt.%, or 3 wt.%.

[0021] Preferably, the mass concentration of the etchant in the acidic chelating etching solution in step (1) is 0.5 wt.% to 5 wt.%, for example: 0.5 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, or 5 wt.%.

[0022] Preferably, the pH of the acidic chelating etching solution in step (1) is 3 to 5, for example: 3, 3.5, 4, 4.5 or 5, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] This invention controls the pH of the acidic chelating etching solution within the above-mentioned range by using HCl as an etchant and zirconium-containing chelates together. This ensures the etching effect while removing residual alkali and enriching and coating the zirconium-containing chelates on the surface of the ternary cathode precursor.

[0024] Preferably, the mass ratio of the zirconium-containing chelate to the ternary cathode precursor in the acidic chelating etching solution in step (1) is (0.001 to 0.01):1, for example: 0.001:1, 0.002:1, 0.005:1, 0.008:1 or 0.01:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, stirring is performed during the chelation etching process described in step (1).

[0026] Preferably, the temperature of the chelation etching process in step (1) is 20℃~30℃, for example: 20℃, 22℃, 25℃, 28℃ or 30℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] Preferably, the chelation etching process in step (1) takes 0.3h to 2h, for example: 0.3h, 0.8h, 1h, 1.2h or 2h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the lithium source in step (2) includes lithium hydroxide and / or lithium carbonate.

[0029] Preferably, the sintering process in step (2) includes pre-sintering and secondary sintering.

[0030] Preferably, the preheating temperature is 450℃~550℃, for example: 450℃, 480℃, 500℃, 520℃ or 550℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the pre-firing time is 2h to 6h, for example: 2h, 3h, 4h, 5h or 6h.

[0032] Preferably, the temperature of the second firing is 700℃~850℃, for example: 700℃, 720℃, 750℃, 800℃ or 850℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0033] Preferably, the second firing time is 8h to 20h, for example: 8h, 10h, 12h, 15h or 20h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] The modified precursor of the present invention forms a three-dimensional structure of zirconium doping and zirconium-coated compounds on the surface of the cathode material through sintering. The zirconium-containing chelate on the surface will also be thermally decomposed during the sintering process to form in-situ coated zirconium-containing compounds (such as Li2ZrO3) with high lithium-ion conductivity, which significantly improves the cycle stability and rate performance of the cathode material.

[0035] In a second aspect, the present invention provides a surface-modified single-crystal ternary cathode material, wherein the surface-modified single-crystal ternary cathode material is prepared by the preparation method described in the first aspect.

[0036] Thirdly, the present invention provides a positive electrode sheet comprising a surface-modified single-crystal ternary positive electrode material as described in the second aspect.

[0037] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the third aspect.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) This invention forms a three-dimensional structure of zirconium doped and zirconium-coated compounds on the surface of cathode material by controlling the surface zirconium citrate chelate etching and sintering process. By optimizing the etching conditions, sintering parameters, single crystal particle size and surface residual alkali content, the cycle stability and rate performance of the material can be significantly improved.

[0040] (2) The method described in this invention prepares surface-modified single-crystal ternary cathode materials with a yield of >95%, which is easy to industrialize.

[0041] (3) The battery made from the surface-modified single-crystal ternary cathode material described in this invention can achieve a 1C / 0.1C discharge capacity ratio of over 91.7% and a capacity retention rate of over 92.3% after 100 cycles at 1C. Attached Figure Description

[0042] Figure 1 This is a SEM image of the surface-modified single-crystal ternary cathode material prepared in Example 1.

[0043] Figure 2 This is a SEM image of the ultra-high nickel single-crystal ternary cathode material prepared in Comparative Example 1. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0045] Example 1

[0046] This embodiment provides a surface-modified single-crystal ternary cathode material, and the preparation method of the surface-modified single-crystal ternary cathode material is as follows:

[0047] (1) The chemical formula Ni 0.92 Co 0.04 Mn 0.04 The precursor of (OH)2 (D50 = 10 μm) was pulverized by air jet milling to obtain a small-particle ternary cathode precursor with D50 = 3.5 μm. 10 g of the small-particle ternary cathode precursor was placed in a hydrochloric acid solution containing 0.05 g of zirconium citrate (pH = 4, zirconium citrate mass concentration of 0.8 wt.%, HCl mass concentration of 2 wt.%) and stirred at 25 °C for 1 h. Then it was dried to obtain the modified precursor.

[0048] (2) The modified precursor and lithium hydroxide were mixed at Li:M = 1.02:1, pre-calcined at 500°C for 4 hours and then calcined at 780°C for 12 hours to obtain the surface-modified single-crystal ternary cathode material.

[0049] The SEM image of the surface-modified single-crystal ternary cathode material is shown below. Figure 1 As shown. By Figure 1 As can be seen, the present invention forms a three-dimensional structure of zirconium doping and zirconium-coated compounds on the surface of the cathode material through a surface zirconium citrate chelation-gradient sintering process, and finally obtains an ultra-high nickel single crystal ternary cathode material with good dispersibility and a particle size of about 2 to 3 μm.

[0050] Example 2

[0051] This embodiment provides a surface-modified single-crystal ternary cathode material, and the preparation method of the surface-modified single-crystal ternary cathode material is as follows:

[0052] (1) The chemical formula Ni 0.90 Co 0.05 Mn 0.05 The precursor of (OH)2 (D50 = 6 μm) was pulverized by air jet milling to obtain a ternary cathode precursor with small particles of D50 = 2 μm. 10 g of the small ternary cathode precursor was placed in a hydrochloric acid solution containing 0.01 g of zirconium citrate (pH = 3, zirconium citrate concentration of 0.1 wt.%, HCl concentration of 5 wt.%) and stirred at 30 °C for 0.3 h. Then it was dried to obtain the modified precursor.

[0053] (2) The modified precursor and lithium hydroxide were mixed at Li:M (M is Ni+Co+Mn)=1.02:1, pre-calcined at 450℃ for 2h and then calcined at 700℃ for 8h to obtain the surface-modified single-crystal ternary cathode material.

[0054] Example 3

[0055] This embodiment provides a surface-modified single-crystal ternary cathode material, and the preparation method of the surface-modified single-crystal ternary cathode material is as follows:

[0056] (1) The chemical formula Ni 0.90 Co 0.05 Mn 0.05 The precursor of (OH)2 (D50 = 15 μm) was pulverized by air jet milling to obtain a ternary cathode precursor with small particles of D50 = 5 μm. 10 g of the small ternary cathode precursor was placed in a hydrochloric acid solution containing 0.1 g of zirconium citrate (pH = 5, zirconium citrate mass concentration is 3 wt.%, HCl mass concentration is 0.5 wt.%) and stirred at 20 °C for 2 h. Then it was dried to obtain the modified precursor.

[0057] (2) The modified precursor and lithium hydroxide were mixed at Li:M = 1.02:1, pre-calcined at 550°C for 6 hours and then calcined at 850°C for 20 hours to obtain the surface-modified single-crystal ternary cathode material.

[0058] Example 4

[0059] The only difference between this embodiment and Embodiment 1 is that the mass concentration of zirconium citrate in the acidic chelating etching solution is 5 wt.%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0060] Example 5

[0061] The only difference between this embodiment and Embodiment 1 is that the mass concentration of zirconium citrate in the acidic chelating etching solution is 0.05 wt.%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0062] Example 6

[0063] The only difference between this embodiment and Embodiment 1 is that the hydrochloric acid content in the acidic chelating etching solution is changed, and the pH of the acidic chelating etching solution is adjusted to 2. All other conditions and parameters are exactly the same as in Embodiment 1.

[0064] Example 7

[0065] The only difference between this embodiment and Embodiment 1 is that the hydrochloric acid content in the acidic chelating etching solution is changed, and the pH of the acidic chelating etching solution is adjusted to 6. All other conditions and parameters are exactly the same as in Embodiment 1.

[0066] Example 8

[0067] The only difference between this embodiment and Embodiment 1 is that sintering is carried out at 780°C, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0068] Comparative Example 1

[0069] This comparative example directly uses Ni particles with a D50 of 5μm. 0.92 Co 0.04 Mn 0.04 Preparation of ultra-high nickel single-crystal ternary cathode material using (OH)2 precursor.

[0070] SEM images of the ultra-high nickel single-crystal ternary cathode material are shown below. Figure 2 As shown.

[0071] Comparative Example 2

[0072] The only difference between this comparative example and Example 1 is that a hydrochloric acid solution with pH=4 was used to treat Ni. 0.92 Co 0.04 Mn 0.04 The (OH)2 precursor was etched, and other conditions and parameters were exactly the same as in Example 1.

[0073] Comparative Example 3

[0074] The only difference between this comparative example and Example 1 is that a zirconium citrate solution containing 0.01g of zirconium citrate and without hydrochloric acid was used to treat Ni. 0.92 Co 0.04 Mn 0.04 The (OH)2 precursor was modified, and other conditions and parameters were exactly the same as in Example 1.

[0075] Performance testing:

[0076] The positive electrode materials obtained in the examples and comparative examples were used to prepare lithium-ion batteries: The obtained positive electrode material, conductive carbon black SP (TIMCAL) and polyvinylidene fluoride PVDF (HSV900) were mixed in a mass ratio of 90:5:5, with N-methylpyrrolidone as the solvent. The mixture was stirred into a slurry, and the slurry was uniformly coated onto aluminum foil using a doctor blade with a coating gap of 100 μm. After coating, the foil was first dried by blowing air, then rolled and cut into circular electrode sheets, and then vacuum dried at 120°C. The weight of the electrode sheets was then weighed to obtain the positive electrode sheet of a button half-cell. The negative electrode was a lithium metal sheet, the separator was a PP microporous membrane, and the electrolyte was a basic lithium battery electrolyte. The positive electrode sheet, lithium metal sheet, separator and electrolyte were assembled to obtain a button cell.

[0077] The batteries were tested using a battery testing system (Landian CT2001A, Wuhan, China). First, they were activated three times at 0.1C rate / 2.7–4.3V. Then, the activated coin cells were subjected to electrochemical performance testing at 2.7–4.3V@0.1C / 1C. The test results are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] As can be seen from Table 1, and from Examples 1-8, the battery made of the surface-modified single-crystal ternary cathode material of the present invention can achieve a 0.1C first discharge specific capacity of more than 214.5 mAh / g, a 1C / 0.1C discharge capacity ratio of more than 91.7%, and a capacity retention rate of more than 92.3% after 100 cycles at 1C.

[0082] A comparison of Examples 1 and 4-5 shows that the concentration of zirconium citrate in the acidic chelate etching solution affects the performance of the surface-modified single-crystal ternary cathode material described in this invention. Controlling the mass concentration of zirconium-containing chelates in the acidic chelate etching solution between 0.1 wt.% and 3 wt.% results in a surface-modified single-crystal ternary cathode material with better performance. If the mass concentration of zirconium-containing chelates in the acidic chelate etching solution is too high, the coating layer will be thicker and the doping amount will be higher, leading to a decrease in discharge capacity and rate performance, while the cycle stability will be less affected. Conversely, if the mass concentration of zirconium-containing chelates in the acidic chelate etching solution is too low, the coating layer will be thinner and the doping amount will be lower, resulting in a poorer effect on lattice regulation and surface protection, leading to a decrease in cycle stability and rate performance, while the discharge capacity will slightly increase.

[0083] A comparison of Examples 1 and 6-7 shows that the pH of the acidic chelating etching solution affects the performance of the surface-modified single-crystal ternary cathode material described in this invention. Controlling the pH of the acidic chelating etching solution between 3 and 5 results in a surface-modified single-crystal ternary cathode material with better performance. If the pH of the acidic chelating etching solution is too low (too acidic), it leads to an increase in defects on the material surface after acid etching, resulting in poorer morphology and crystallinity, thus deteriorating battery performance. If the pH of the acidic chelating etching solution is too high (too weak), the acid etching effect on the precursor surface is weakened, which is not conducive to the formation of more active sites and affects the chelation effect of zirconium citrate. It is also not conducive to reducing the residual alkali content on the surface in the subsequent process, thus deteriorating battery performance.

[0084] A comparison of Examples 1 and 8 shows that the present invention can effectively remove the residual substances after the decomposition of Zr-containing chelates on the surface through stepped segmented sintering, thereby improving the overall performance of the battery.

[0085] A comparison of Example 1 and Comparative Examples 1-3 shows that whether or not surface chelation coating is performed and whether or not hydrochloric acid solution is used for acid etching of the surface structure both affect the performance of lithium-ion batteries. Without the addition of zirconium citrate for surface chelation coating, the ultra-high nickel single-crystal cathode material lacks a zirconium doping layer and coating layer, resulting in lower cycle stability and rate performance. Furthermore, if hydrochloric acid is not used for acid etching during the surface chelation coating process to form active sites containing unsaturated bonds, the doping and coating effect of the zirconium surface will also be affected, thus impacting the improvement of battery performance.

[0086] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a surface-modified single-crystal ternary cathode material, characterized in that, The preparation method includes the following steps: (1) The ternary cathode precursor is mixed with an acidic chelating etching solution and subjected to chelating etching to obtain a modified precursor. (2) The modified precursor is mixed with a lithium source and sintered to obtain a surface-modified single-crystal ternary cathode material; The solute in the acidic chelating etching solution is a zirconium-containing chelate and an acidic etching agent, wherein the zirconium-containing chelate is zirconium citrate and / or zirconium tartrate. The median particle size D50 of the ternary cathode precursor in step (1) is 2μm~5μm, the mass concentration of zirconium chelate in the acidic chelate etching solution in step (1) is 0.1wt.%~3wt.%, the pH of the acidic chelate etching solution is 3~4, and the mass ratio of zirconium chelate to ternary cathode precursor in the acidic chelate etching solution is (0.001~0.01):1; The sintering process in step (2) includes pre-firing and secondary firing. The temperature of the pre-firing is 450℃~550℃, and the temperature of the secondary firing is 700℃~850℃.

2. The preparation method according to claim 1, characterized in that, The general chemical formula of the ternary cathode precursor in step (1) is Ni x Co y Mn 1-x-y (OH)₂, where 0.9 ≤ x ≤ 0.98, 0 <y<0.1。 3. The preparation method according to claim 1, characterized in that, The acidic etching agent includes HCl.

4. The preparation method according to claim 1, characterized in that, The mass concentration of the acidic etchant in the acidic chelating etching solution in step (1) is 0.5 wt.%~5 wt.%.

5. The preparation method according to claim 1, characterized in that, Stirring is performed during the chelation etching process described in step (1).

6. The preparation method according to claim 1, characterized in that, The temperature for the chelation etching process in step (1) is 20℃~30℃.

7. The preparation method according to claim 1, characterized in that, The chelation etching process in step (1) takes 0.3h to 2h.

8. The preparation method according to claim 1, characterized in that, The lithium source in step (2) includes lithium hydroxide and / or lithium carbonate.

9. The preparation method according to claim 1, characterized in that, The preheating time is 2h to 6h.

10. The preparation method according to claim 1, characterized in that, The second firing time is 8h to 20h.

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