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

Abstract

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

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to a surface-modified single-crystal ternary cathode material and a preparation method and application thereof. Background Art

[0002] The rapid development of new energy vehicles has put forward higher requirements for long driving range. The demand for high energy density lithium-ion batteries is growing. 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 the cycle. 4+ Ion dissolution, structural phase change, and the occurrence of cracks or breakage exacerbate side reactions with the electrolyte, leading to capacity decay and safety hazards.

[0003] To solve the above problems, single crystal structure design becomes the key. The existing synthesis method of ultra-high nickel single crystal ternary cathode materials is to sinter the prefabricated ultra-high nickel ternary precursor and lithium source. However, the existing ultra-high nickel single crystal ternary cathode materials have three major technical bottlenecks: 1) the residual alkali problem. The residual alkali content of the traditional process is as high as 2000-3000ppm, which leads to a rapid increase in interface impedance; 2) lattice distortion: high nickel content easily causes lattice distortion and poor cycle stability; 3) interface failure: the surface of the single crystal particles lacks a stable protective layer, and grain boundary slip and side reactions are prone to occur during the cycle.

[0004] CN113644262A discloses a layered, large-particle, high-nickel single-crystal ternary cathode material and its preparation method. The preparation method comprises 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 and decomposing it to obtain a precursor powder; heat-treating the precursor powder, then thoroughly mixing the heat-treated precursor powder, a first lithium source, and zirconium oxide, followed by heating and melting, and a primary sintering to obtain a single-crystal ternary material; air-flow milling the single-crystal ternary material, washing, filtering, and drying it, followed by adding a second lithium source, further mixing, and a secondary sintering to obtain a layered, large-particle, high-nickel single-crystal ternary cathode material. While the use of a layered, large-particle precursor improves tap density, it does not address the issues 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 oxide layer coated on the core surface. While the cobalt coating improves rate performance, it fails to achieve the synergistic effect of lattice doping and interface reconstruction.

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

[0007] The purpose of the present invention is to provide a surface-modified single-crystal ternary positive electrode material, a preparation method and application thereof. The present invention forms a three-dimensional structure of doped zirconium and coated zirconium compounds on the surface of the positive electrode material through a surface zirconium citrate chelate etching process. The present invention changes the conventional etching conditions and sintering under appropriate conditions solves the problems of residual alkali control, lattice distortion and interface failure of ultra-high nickel single crystal materials, thereby significantly improving the cycle stability and rate performance of the material.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

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

[0010] (1) mixing the ternary cathode precursor with an acidic chelating etching solution and performing chelating etching treatment to obtain a modified precursor;

[0011] (2) mixing the modified precursor with a lithium source and sintering the mixture to obtain a surface-modified single crystal ternary cathode material;

[0012] Wherein, the solute of the acidic chelate etching solution includes a zirconium-containing chelate and an acidic etchant.

[0013] The present invention uses an acidic chelating etching solution to chelate-etch the ternary precursor and then sinter it. 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 is complexed and coated on the surface of the precursor), gradient doping (during the sintering process, the zirconium-containing chelate on the surface of the precursor penetrates into the precursor to form a gradient doping structure, and the lattice of the positive electrode material is controlled) and residual alkali capture (the zirconium-containing chelate takes zirconium citrate as an example, and the zirconium citrate is electrolyzed to generate citrate and zirconium ions, and the citrate generates citric acid under acidic conditions). By neutralization reaction to consume residual alkali, etc., a ternary positive electrode precursor coated with a zirconium chelate is formed during the surface etching process, and a three-dimensional structure of zirconium-doped and coated zirconium compounds is formed on the surface of the positive electrode material after sintering treatment, which solves the problems of particle dispersion, lattice distortion, interface failure and residual alkali control of ultra-high nickel single crystal materials, and improves the cycle stability of the material; the zirconium-containing chelate will also decompose under heat during the sintering process to form an in-situ coated zirconium-containing compound with high lithium ion conductivity (such as Li2ZrO3), which significantly improves the cycle stability and rate performance of the positive electrode material.

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

[0015] The ternary positive electrode precursor described in the present invention can be obtained directly by co-precipitation to control the appropriate particle size, or it can be obtained by crushing the large-particle ternary positive electrode precursor. The small-particle ternary positive electrode precursor can form a more stable zirconium chelate coating layer on its surface due to its advantages of high specific surface area and more active sites.

[0016] Preferably, the 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 of the present invention is prepared by a conventional co-precipitation method.

[0018] Preferably, the acidic etchant comprises HCl.

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

[0020] Preferably, the mass concentration of the zirconium chelate in the acidic chelate 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., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0023] The present invention controls the pH of the acidic chelate etching solution within the above range by using the etchant HCl and the zirconium-containing chelate, thereby removing residual alkali and enriching and coating the zirconium-containing chelate on the surface of the ternary cathode precursor while ensuring the etching effect.

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

[0025] Preferably, stirring is performed during the chelate etching treatment in step (1).

[0026] Preferably, the temperature of the chelate etching treatment in step (1) is 20°C to 30°C, for example, 20°C, 22°C, 25°C, 28°C or 30°C, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0027] Preferably, the time of the chelate etching treatment in step (1) is 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 values not listed within the numerical range are also applicable.

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

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

[0030] Preferably, the pre-firing temperature is 450°C to 550°C, for example, 450°C, 480°C, 500°C, 520°C or 550°C, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

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

[0032] Preferably, the temperature of the secondary calcination is 700°C to 850°C, for example, 700°C, 720°C, 750°C, 800°C or 850°C, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

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

[0034] The modified precursor of the present invention forms a three-dimensional structure of zirconium-doped and coated zirconium compounds on the surface of the positive electrode material after sintering treatment. The zirconium-containing chelate on the surface will also be thermally decomposed during the sintering process to form an in-situ coated zirconium-containing compound (such as Li2ZrO3) with high lithium ion conductivity, which significantly improves the cycle stability and rate performance of the positive electrode 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] In a third aspect, the present invention provides a positive electrode plate, which comprises the surface-modified single crystal ternary positive electrode material as described in the second aspect.

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

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

[0039] (1) The present invention forms a three-dimensional structure of doped zirconium and coated zirconium compounds on the surface of the positive electrode material through surface zirconium citrate chelate etching control 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 surface-modified single-crystal ternary cathode material prepared by the method of the present invention has a yield rate of >95%, and is easy to industrialize.

[0041] (3) The 1C / 0.1C discharge capacity ratio of the battery made of the surface-modified single-crystal ternary cathode material of the present invention can reach more than 91.7%, and the capacity retention rate after 100 cycles at 1C can reach more than 92.3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is an SEM image of the surface-modified single-crystal ternary positive electrode material obtained in Example 1.

[0043] Figure 2 This is the SEM image of the ultra-high nickel single crystal ternary positive electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0045] Example 1

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

[0047] (1) The chemical formula is Ni 0.92 Co 0.04 Mn 0.04 The (OH)2 precursor (D50 = 10 μm) was pulverized by air flow 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, and then dried to obtain a modified precursor;

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

[0049] The SEM image of the surface modified single crystal ternary cathode material is as follows: Figure 1 As shown. Figure 1 It can be seen that the present invention forms a three-dimensional structure of doped zirconium and coated zirconium compounds on the surface of the positive electrode material through the surface zirconium citrate chelation regulation-gradient sintering process, and finally obtains an ultra-high nickel single crystal ternary positive electrode material with good dispersion 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. The preparation method of the surface-modified single-crystal ternary cathode material is as follows:

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

[0053] (2) The modified precursor is mixed with lithium hydroxide according to Li:M (M is Ni+Co+Mn) = 1.02:1, pre-fired at 450°C for 2 hours and then calcined at 700°C for 8 hours to obtain the surface-modified single crystal ternary positive electrode material.

[0054] Example 3

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

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

[0057] (2) The modified precursor was mixed with lithium hydroxide according to Li:M=1.02:1, pre-fired at 550°C for 6 hours and then calcined at 850°C for 20 hours to obtain the surface-modified single crystal ternary positive electrode 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.%, and the other conditions and parameters are exactly the same as those 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.%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0062] Example 6

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

[0064] Example 7

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

[0066] Example 8

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

[0068] Comparative Example 1

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

[0070] The SEM image of the obtained ultra-high nickel single crystal ternary cathode material is as follows Figure 2 shown.

[0071] Comparative Example 2

[0072] The only difference between this comparative example and Example 1 is that the Ni 0.92 Co 0.04 Mn 0.04 The (OH)2 precursor was used for etching, and the other conditions and parameters were exactly the same as those in Example 1.

[0073] Comparative Example 3

[0074] The difference between this comparative example and Example 1 is that the zirconium citrate solution containing 0.01g zirconium citrate and no hydrochloric acid is used to treat Ni 0.92 Co 0.04 Mn 0.04 The (OH)2 precursor was modified, and the 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, and N-methylpyrrolidone was used as the solvent. The mixture was stirred into a slurry, and the resulting slurry was evenly coated on an aluminum foil with a scraper with a coating gap of 100 μm; after coating, it was first blown dry, then rolled and cut into circular electrode sheets, and then vacuum dried at 120° C. and weighed to obtain a button half-cell positive electrode sheet; a metal lithium sheet was used as the negative electrode, a PP microporous membrane was used as the separator, and a lithium battery basic electrolyte was used as the electrolyte. The positive electrode sheet, the metal lithium sheet, the separator and the electrolyte were assembled to obtain a button battery;

[0077] The battery test was performed using a battery test system (Blue Power CT2001A, Wuhan, China). The battery was first activated three times at a rate of 0.1C / 2.7-4.3V. The activated button cells were then electrochemically tested at 2.7-4.3V at 0.1C / 1C. The test results are shown in Table 1.

[0078] Table 1

[0079]

[0080]

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

[0082] By comparing Example 1 with Examples 4-5, it can be seen that during the preparation process of the surface-modified single-crystal ternary positive electrode material of the present invention, the concentration of zirconium citrate in the acidic chelating etchant affects its performance. The mass concentration of the zirconium-containing chelate in the acidic chelating etchant is controlled at 0.1wt.% to 3wt.%, and the performance of the surface-modified single-crystal ternary positive electrode material is better. If the mass concentration of the zirconium-containing chelate in the acidic chelating etchant is too high, the coating thickness will be thicker and the doping amount will be higher, thereby resulting in a decrease in discharge capacity and rate performance, while the cycle stability is not significantly affected. If the mass concentration of the zirconium-containing chelate in the acidic chelating etchant is too low, the coating thickness will be thinner and the doping amount will be lower, and the effects of lattice adjustment and surface protection will be worse, thereby resulting in reduced cycle stability and rate performance, while the discharge capacity is slightly improved.

[0083] By comparing Example 1 with Examples 6-7, it can be seen that during the preparation process of the surface-modified single-crystal ternary cathode material of the present invention, the pH of the acidic chelating etchant affects its performance. When the pH of the acidic chelating etchant is controlled between 3 and 5, the performance of the surface-modified single-crystal ternary cathode material is better. If the pH of the acidic chelating etchant is too low (too strong acidity), the defects on the material surface after acid etching increase, the morphology and crystallinity deteriorate, and thus the battery performance deteriorates. If the pH of the acidic chelating etchant is too high (too weak acidity), 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, and is also not conducive to the subsequent reduction of the residual alkali content on the surface, thereby deteriorating the battery performance.

[0084] From the comparison between Example 1 and Example 8, it can be seen that the present invention can fully remove the residual substances after the Zr-containing chelate compound is decomposed on the surface through the stepped segmented sintering, thereby improving the overall performance of the battery.

[0085] 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 acidic etching of the surface structure in the present invention will affect the performance of the lithium-ion battery. If zirconium citrate is not added for surface chelation coating, the surface of the ultra-high nickel single crystal positive electrode material will lack a surface zirconium doping layer and coating layer, resulting in low cycle stability and rate performance of the battery. If hydrochloric acid is not used for acidic etching during the surface chelation coating process to form active sites containing unsaturated bonds, the doping and coating effects of the surface zirconium will also be affected, thereby affecting the improvement of battery performance.

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

Claims

1. A method for preparing a surface-modified single-crystal ternary cathode material, characterized in that: The preparation method comprises the following steps: (1) mixing the ternary cathode precursor with an acidic chelating etching solution and performing chelating etching treatment to obtain a modified precursor; (2) mixing the modified precursor with a lithium source and sintering the mixture to obtain a surface-modified single crystal ternary cathode material; Wherein, the solute of the acidic chelate etching solution includes a zirconium-containing chelate and an acidic etchant.

2. The preparation method according to claim 1, wherein The median particle size D50 of the ternary cathode precursor in step (1) is 2 μm to 5 μm; Preferably, the 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 or 2, wherein The acidic etchant includes HCl; Preferably, the zirconium-containing chelate comprises zirconium citrate and / or zirconium tartrate; Preferably, the mass concentration of the zirconium chelate in the acidic chelate etching solution in step (1) is 0.1 wt.% to 3 wt.%; Preferably, the mass concentration of the etchant in the acidic chelating etching solution in step (1) is 0.5 wt.% to 5 wt.%; Preferably, the pH of the acidic chelating etching solution in step (1) is 3-5.

4. The preparation method according to any one of claims 1 to 3, wherein The mass ratio of the zirconium-containing chelate to the ternary positive electrode precursor in the acidic chelate etching solution of step (1) is (0.001-0.01):

1.

5. The preparation method according to any one of claims 1 to 4, characterized in that Stirring during the chelate etching process in step (1); Preferably, the temperature of the chelate etching treatment in step (1) is 20° C. to 30° C.; Preferably, the chelate etching treatment in step (1) lasts for 0.3 h to 2 h.

6. The preparation method according to any one of claims 1 to 5, characterized in that The lithium source in step (2) includes lithium hydroxide and / or lithium carbonate.

7. The preparation method according to any one of claims 1 to 6, wherein The sintering process in step (2) includes pre-sintering and secondary sintering; Preferably, the pre-firing temperature is 450°C to 550°C; Preferably, the pre-burning time is 2h to 6h; Preferably, the temperature of the secondary calcination is 700°C to 850°C; Preferably, the second calcination time is 8h to 20h.

8. A surface-modified single crystal ternary cathode material, characterized in that: The surface-modified single-crystal ternary cathode material is prepared by the preparation method according to any one of claims 1 to 7.

9. A positive electrode plate, characterized in that: The positive electrode plate comprises the surface-modified single crystal ternary positive electrode material as claimed in claim 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 9.

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