High-voltage positive electrode and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a high-voltage positive electrode and a preparation method thereof. The high-voltage positive electrode provided by the invention comprises a substrate material and a coating layer coated on the surface layer of the substrate material, the coating layer comprises zirconium oxide doped with rare earth metal oxide, and the addition amount of the coating layer is 2000-3000 ppm based on the mass of the substrate material. By doping the rare earth metal into the zirconium oxide, on one hand, the rare earth metal is utilized to optimize the lattice structure of the zirconium oxide and improve the stability and conductivity of the positive electrode material, on the other hand, the doping of the rare earth metal is utilized to improve the electron transmission capability of the coating layer, and the electron transmission rate of the positive electrode material in the charge-discharge process is improved; and the power density and the energy density of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a high - voltage cathode and a preparation method thereof. Background Art

[0002] With the increasing prominence of energy shortage and resource tension problems, the development of sustainable and recyclable battery technologies has become crucial. Lithium - ion batteries, with their excellent energy density and outstanding output power, have become the research focus and application emphasis in the current energy storage field. The cathode materials of lithium - ion batteries include layered oxide cathode materials, spinel - type cathode materials, polyanion - type cathode materials, and lithium - rich manganese - based cathode materials, etc. Among them, the spinel - type cathode material can reach a voltage plateau of 4.7V and an energy density of 650Wh / kg, and has attracted much attention due to its three - dimensional lithium - ion transport channels. However, in the face of extreme environments, the spinel - type cathode material shows poor stability, prone to irreversible surface phase transformation, transition metal dissolution, electrolyte oxidation, and side reactions between the electrolyte and the electrode material, resulting in battery capacity attenuation.

[0003] Currently, most use surface coating technology to coat a stabilizing material on the surface of the spinel - type cathode material to avoid the destruction of the cathode material structure during charge - discharge due to side reactions. However, most of the existing coating agents have poor conductivity and impose a certain hindrance on the electron and ion transport of the cathode material. Summary of the Invention

[0004] Therefore, to solve the above problems, the present invention provides a high - voltage cathode and a preparation method thereof.

[0005] On the one hand, the present invention provides a high - voltage cathode, including a substrate material and a coating layer coated on the surface layer of the substrate material. The coating layer includes zirconia doped with rare - earth metal oxides. Based on the mass of the substrate material, the addition amount of the coating layer is 2000 - 3000ppm.

[0006] In some embodiments, the rare - earth metal includes at least one of yttrium or scandium.

[0007] In some embodiments, based on the mass of zirconia, the mass fraction of the rare - earth metal oxide is 0.2% - 0.4%.

[0008] In some embodiments, the chemical formula of the substrate material is Li a Ni x Mn 1-x O2, where 0.24 ≤ x ≤ 0.26 and 0.5 ≤ a ≤ 0.55.

[0009] In some embodiments, the rare - earth metal elements are yttrium and scandium.

[0010] On the other hand, the present invention provides a method for preparing the above high-voltage positive electrode, comprising the following steps: S1, forming a mixed solution of a zirconium source and a dopant, injecting an aging agent therein, and obtaining an intermediate through solid-liquid separation, drying, and sintering; S2, mixing a substrate material and the intermediate, and sintering to obtain a high-voltage positive electrode.

[0011] Preferably, the zirconium source includes at least one of zirconium oxychloride, zirconium nitrate, or zirconium sulfate.

[0012] Preferably, the dopant includes at least one of yttrium salts and scandium salts;

[0013] Preferably, the aging agent includes one of ammonia water and sodium hydroxide.

[0014] Preferably, the yttrium salt includes at least one of yttrium nitrate, yttrium chloride, or yttrium sulfate.

[0015] Preferably, the scandium salt includes at least one of scandium nitrate, scandium chloride, or scandium sulfate.

[0016] In some embodiments, the pH value of the system after injecting the aging agent is 9.5 - 11.

[0017] In some embodiments, the mass ratio of the zirconium source to the dopant is 80 - 130:0.2 - 0.7.

[0018] In some embodiments, the mass ratio of the zirconium source, yttrium salt, and scandium salt is 80 - 130:0.1 - 0.3:0.1 - 0.4.

[0019] In some embodiments, in step S1, the sintering temperature is 800 - 900 °C, the sintering time is 1 - 3 h, and the sintering atmosphere is an inert gas.

[0020] In some embodiments, the drying temperature is 80 - 120 °C, and the drying time is 3 - 5 h.

[0021] In some embodiments, the solid-liquid separation step in step S1 includes filtration.

[0022] In some embodiments, in step S2, the sintering temperature is 250 - 650 °C, the sintering time is 4 - 6 h, and the sintering atmosphere is an air atmosphere.

[0023] In some embodiments, the method for preparing the substrate material includes mixing a lithium source and a precursor and sintering, and the chemical formula of the precursor is Ni x Mn 1-x (OH)2, where 0.24 ≤ x ≤ 0.26, and the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0024] Meanwhile, the present invention also provides a lithium-ion battery, comprising the above high-voltage positive electrode or a high-voltage positive electrode prepared by the preparation method of the above high-voltage positive electrode.

[0025] The technical solution of the present invention has the following advantages:

[0026] A high-voltage positive electrode provided by the present invention comprises a substrate material and a coating layer coated on the surface layer of the substrate material. The coating layer comprises zirconia doped with rare earth metal oxide. Based on the mass of the substrate material, the addition amount of the coating layer is 2000-3000 ppm. By doping rare earth metals into zirconia, on the one hand, the lattice structure of zirconia is optimized by the rare earth metals to improve the stability and conductivity of the positive electrode material; on the other hand, the electron transport ability of the coating layer is improved by the doping of rare earth metals. By increasing the electron transfer rate of the positive electrode material during charge and discharge, the power density and energy density of the battery are improved. In addition, the coating layer provided by the present invention has a cubic crystal structure, which provides a channel for the migration of lithium ions, effectively slows down the capacity attenuation during charge and discharge, and prolongs the service life of the positive electrode material. At the same time, the present invention limits the addition amount of the coating layer to improve the capacity performance and avoid the coating layer being too thick, resulting in ion transport hindrance and affecting the capacity performance.

[0027] In the high-voltage positive electrode provided by the present invention, the rare earth metal elements are yttrium and scandium. Compared with only using a single rare earth metal element, the present invention uses a combination of two rare earth metal elements, which broadens the temperature range of the stable phase of the positive electrode material and further improves the stability of the positive electrode material. Detailed Embodiments

[0028] The following embodiments are provided to better further understand the present invention. They are not limited to the best embodiment, and do not limit the content and protection scope of the present invention. Any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features that is the same as or similar to the present invention falls within the protection scope of the present invention.

[0029] For those steps or conditions not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be used. For reagents or instruments not specified by the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0030] Example 1

[0031] This example provides a preparation method of a high-voltage positive electrode, and the specific steps and parameters are as follows:

[0032] (1) According to the molar ratio of the lithium source to the precursor being 0.5:1, lithium hydroxide and the precursor Ni 0.25Mn 0.75 (OH)2 were mixed, and the temperature was raised to 700 °C at a heating rate of 5 °C / min in a box furnace and pre-calcined for 6 h, then the temperature was raised to 960 °C at a heating rate of 5 °C / min and calcined for 12 h. After cooling to 650 °C and holding for 4 h, it was then cooled to room temperature. After pulverization, a first calcined material was obtained. During the sintering process, the sintering atmosphere was air, and the air flow rate was 3 m 3 / h;

[0033] (2) 100 g of zirconium oxychloride (ZrOCl2·8H2O) and 0.3 g of yttrium nitrate (Y(NO3)3·6H2O) were placed in 1 L of deionized water and stirred at 150 rpm for 20 min at 25 °C until dissolved to obtain a solution containing Zr ions and Y ions; ammonia water solution was slowly injected into the solution under stirring. A large number of crystal nuclei were formed instantaneously, the pH value was adjusted to 10, and it was left to age and filtered at 25 °C to obtain a Y-doped zirconium hydroxide precipitate.

[0034] (3) The precipitate obtained in step (2) was washed repeatedly with anhydrous ethanol 3 times to remove unreacted impurities. The washed precipitate was placed in an oven and dried at 100 °C for 3 h to obtain a dried precipitate;

[0035] The dried precipitate was calcined at 800 °C for 1 h in a nitrogen atmosphere to obtain nano-porous Y-doped zirconia powder.

[0036] (4) The first calcined product prepared in step (1) and the nano-porous Y-doped zirconia powder in step (3) were stirred at 3000 rpm for 20 min to be mixed evenly to obtain a mixture. Among them, based on the mass of the first calcined product, the doping amount of the nano-porous Y-doped zirconia powder was 2000 ppm. In an air atmosphere, the mixture was heated to 500 °C at a heating rate of 5 °C / min in a box furnace and calcined for 4 h, and then naturally cooled and sieved to obtain a high-voltage positive electrode.

[0037] Example 2

[0038] This example provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are the same as those in Example 1, except that scandium nitrate (Sc(NO3)3) was used to replace yttrium nitrate (Y(NO3)3·6H2O) in step (2), and the mass of scandium nitrate (Sc(NO3)3) was 0.34 g.

[0039] Example 3

[0040] This embodiment provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are the same as those in Embodiment 1, except that scandium nitrate (Sc(NO3)3) and yttrium nitrate (Y(NO3)3·6H2O) are used to replace yttrium nitrate (Y(NO3)3·6H2O) in step (2). Among them, the mass of scandium nitrate (Sc(NO3)3) is 0.17 g, and the mass of yttrium nitrate (Y(NO3)3·6H2O) is 0.15 g. That is, in step (2), 100 g of zirconium oxychloride (ZrOCl2·8H2O), 0.17 g of scandium nitrate (Sc(NO3)3), and 0.15 g of yttrium nitrate (Y(NO3)3·6H2O) are put into 1 L of deionized water.

[0041] Example 4

[0042] This embodiment provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are the same as those in Embodiment 1, except that scandium nitrate (Sc(NO3)3) and yttrium nitrate (Y(NO3)3·6H2O) are used to replace yttrium nitrate (Y(NO3)3·6H2O) in step (2). Among them, the mass of scandium nitrate (Sc(NO3)3) is 0.34 g, and the mass of yttrium nitrate (Y(NO3)3·6H2O) is 0.15 g. That is, in step (2), 100 g of zirconium oxychloride (ZrOCl2·8H2O), 0.34 g of scandium nitrate (Sc(NO3)3), and 0.15 g of yttrium nitrate (Y(NO3)3·6H2O) are put into 1 L of deionized water.

[0043] Example 5

[0044] This embodiment provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are the same as those in Embodiment 1, except that scandium nitrate (Sc(NO3)3) and yttrium nitrate (Y(NO3)3·6H2O) are used to replace yttrium nitrate (Y(NO3)3·6H2O) in step (2). Among them, the mass of scandium nitrate (Sc(NO3)3) is 0.17 g, and the mass of yttrium nitrate (Y(NO3)3·6H2O) is 0.30 g. That is, in step (2), 100 g of zirconium oxychloride (ZrOCl2·8H2O), 0.17 g of scandium nitrate (Sc(NO3)3), and 0.30 g of yttrium nitrate (Y(NO3)3·6H2O) are put into 1 L of deionized water.

[0045] Example 6

[0046] This embodiment provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are the same as those in Embodiment 1, except that scandium nitrate (Sc(NO3)3) and yttrium nitrate (Y(NO3)3·6H2O) are used to replace yttrium nitrate (Y(NO3)3·6H2O) in step (2). Among them, the mass of scandium nitrate (Sc(NO3)3) is 0.34 g, and the mass of yttrium nitrate (Y(NO3)3·6H2O) is 0.30 g. That is, in step (2), 100 g of zirconium oxychloride (ZrOCl2·8H2O), 0.34 g of scandium nitrate (Sc(NO3)3), and 0.30 g of yttrium nitrate (Y(NO3)3·6H2O) are put into 1 L of deionized water.

[0047] Embodiment 7

[0048] This embodiment provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are as follows:

[0049] (1) According to the molar ratio of lithium source to precursor being 0.55:1, lithium carbonate and the precursor Ni 0.24 Mn 0.76 (OH)2 are mixed. In a box furnace, the temperature is raised to 700 °C at a heating rate of 5 °C / min for pre-calcination for 6 h, then the temperature is raised to 960 °C at a heating rate of 5 °C / min for calcination for 12 h. After cooling to 650 °C and holding for 4 h, it is then cooled to room temperature and pulverized to obtain a first calcined material. During the sintering process, the sintering atmosphere is air, and the air flow rate is 3 m 3 / h;

[0050] (2) Take 80 g of zirconium nitrate, 0.3 g of yttrium chloride, and 0.17 g of scandium chloride and put them into 1 L of deionized water. Stir at a speed of 150 rpm at 25 °C for 20 min until dissolved to obtain a solution containing Zr ions, Y ions, and Sc ions; continue to slowly inject ammonia water into the solution under stirring. A large number of crystal nuclei are formed instantaneously, and the pH value is adjusted to 9.5. After standing and aging at 25 °C and filtering, a Y, Sc-doped zirconium hydroxide precipitate is obtained.

[0051] (3) The precipitate obtained in step (2) is repeatedly washed 4 times with absolute ethanol to remove unreacted impurities. The washed precipitate is placed in an oven and dried at 80 °C for 5 h to obtain a dried precipitate;

[0052] The dried precipitate is calcined at 900 °C for 1 hour in a nitrogen atmosphere to obtain nano-porous Y, Sc-doped zirconia powder.

[0053] (4) Take the first-fired product obtained in step (1) and the nano-porous Y, Sc-doped zirconia powder in step (3), stir and mix them evenly at a rotation speed of 3000 rpm for 20 min to obtain a mixture. Among them, based on the mass of the first-fired product, the doping amount of the nano-porous Y, Sc-doped zirconia powder is 3000 ppm. In an air atmosphere, heat the mixture in a box furnace to 250 °C at a heating rate of 5 °C / min, calcine for 6 h, and then naturally cool and screen to obtain a high-voltage positive electrode.

[0054] Example 8

[0055] This example provides a method for preparing a high-voltage positive electrode, and the specific steps and parameters are as follows:

[0056] (1) According to the molar ratio of lithium source to precursor being 0.5:1, mix lithium acetate and the precursor Ni 0.26 Mn 0.74 (OH)2, raise the temperature to 700 °C in a box furnace at a heating rate of 5 °C / min and pre-calcine for 6 h, then raise the temperature to 960 °C at a heating rate of 5 °C / min and calcine for 12 h. Cool down to 650 °C and keep it warm for 4 h, and then cool down to room temperature. After pulverization, a first-fired material is obtained. During the sintering process, the sintering atmosphere is air, and the air flow rate is 3 m 3 / h;

[0057] (2) Take 130 g of zirconium sulfate, 0.1 g of yttrium sulfate and 0.1 g of scandium sulfate and put them into 1 L of deionized water. Stir at a rotation speed of 150 rpm at 25 °C for 20 min until dissolved to obtain a solution containing Zr ions, Y ions and Sc ions; continue to slowly inject ammonia water solution into the solution under stirring, a large number of crystal nuclei are formed instantaneously, adjust the pH value to 11, stand and age at 25 °C, and filter to obtain a Y, Sc-doped zirconium hydroxide precipitate.

[0058] (3) Wash the precipitate obtained in step (2) with absolute ethanol repeatedly for 5 times to remove unreacted impurities. Place the washed precipitate in an oven and dry it at 120 °C for 3 h to obtain a dried precipitate;

[0059] Calcine the dried precipitate in a nitrogen atmosphere at 800 °C for 3 hours to obtain nano-porous Y, Sc-doped zirconia powder.

[0060] (4) Take the first-fired product obtained in step (1) and the nano-porous Y-doped zirconia powder in step (3), stir and mix them evenly at a rotation speed of 3000 rpm for 20 min to obtain a mixture. Among them, based on the mass of the first-fired product, the doping amount of the nano-porous Y, Sc-doped zirconia powder is 3000 ppm. In an air atmosphere, heat the mixture in a box furnace to 650 °C at a heating rate of 5 °C / min, calcine for 4 h, and then naturally cool and screen to obtain a high-voltage positive electrode.

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing a high-voltage positive electrode, and the specific steps and parameters are as follows:

[0063] Take the first-fired product obtained in step (1) of Example 1. In an air atmosphere, heat the first-fired product in a box furnace at a heating rate of 5 °C / min to 500 °C, calcine for 4 h, and then naturally cool and screen to obtain a high-voltage positive electrode.

[0064] Comparative Example 2

[0065] This comparative example provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are the same as those in Example 1, except that in step (2), there is only the first-fired product and no yttrium nitrate.

[0066] Comparative Example 3

[0067] This comparative example provides a method for preparing a high-voltage positive electrode, and the specific steps and parameters are as follows:

[0068] Take the first-fired product obtained in step (1) of Example 1 and mix it with nanoscale zirconia to form a mixture. In an air atmosphere, heat the mixture in a box furnace at a heating rate of 5 °C / min to 500 °C, calcine for 4 h, and then naturally cool and screen to obtain a high-voltage positive electrode. Among them, based on the mass of the first-fired product, the addition amount of nanoscale zirconia is 2000 ppm.

[0069] Comparative Example 4

[0070] This comparative example provides a method for preparing a high-voltage positive electrode, and the specific steps and parameters are as follows:

[0071] Use the first-fired product obtained in step (1) of Example 1 as the high-voltage positive electrode.

[0072] Comparative Example 5

[0073] This comparative example provides a method for preparing a high-voltage positive electrode. The specific steps and parameters are the same as those in Example 1, except that in step (4), the addition amount of the nano-porous Y-doped zirconia powder is 4000 ppm.

[0074] Experimental Example

[0075] Perform electrochemical performance tests on the high-voltage positive electrodes of Examples 1-6 and Comparative Examples 1-5. The specific steps are as follows:

[0076] Homogenize the above high-voltage positive electrode, polyvinylidene fluoride (PVDF), and Super P (conductive carbon black SP) in a mass ratio of 97.2:1.3:1.5, and then spread the aluminum foil on a coater for coating (surface density is 15 mg / cm 2-17 mg / cm 2 ), put it in a blast drying oven at 80 °C for 2 h, then punch holes, weigh it, and bake the electrode sheet to use as the positive electrode. The negative electrode uses metallic lithium to make a CR2032 button cell. Finally, put the cell into a blue electrochemical testing system for electrical performance testing;

[0077] Testing method: At 25 °C, first cycle 3 times at 0.33 C to activate the cell, then perform cyclic charge and discharge at 1 C, with the charge and discharge voltage range of 3.5 V - 4.95 V, and measure the cyclic performance of the button cell. The results are shown in Table 1.

[0078] At 45 °C, first cycle 3 times at 0.33 C to activate the cell, then perform cyclic charge and discharge at 1 C, with the charge and discharge voltage range of 3.5 V - 4.95 V, and measure the cyclic performance of the button cell. The results are shown in Table 2.

[0079] Table 1 Cyclic performance of button cell at 25 °C

[0080]

[0081] Table 2 Cyclic performance of button cell at 45 °C

[0082]

[0083]

[0084] According to the data in Table 1 and Table 2, it can be seen that using rare earth element-doped ZrO2 as the coating agent, both the discharge specific capacity at 25 °C or 45 °C and the capacity retention rate after 200 cycles at 1 C are higher than those of the comparative example. It shows that using rare earth element-doped ZrO2 as the coating agent can improve the electrochemical performance of spinel lithium nickel manganate at room temperature and high temperature of 45 °C to a certain extent. Comparative example 5 uses an excessive amount of coating agent. Although it improves the 1 C capacity retention rate to a certain extent, its 1 C discharge specific capacity decreases, and the two cannot be taken into account at the same time.

[0085] Obviously, the above-mentioned embodiments are only examples clearly described, rather than limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A high voltage positive electrode, characterized in that: The invention comprises a base material and a coating layer coated on the surface of the base material, wherein the coating layer comprises zirconium oxide doped with rare earth metal oxide, and the addition amount of the coating layer is 2000-3000 ppm based on the mass of the base material.

2. The high voltage positive electrode according to claim 1, characterized in that: The rare earth metal includes at least one of yttrium or scandium; and / or, Calculated based on the mass of zirconium oxide, the mass fraction of the rare earth metal oxide is 0.2%-0.4%.

3. The high voltage positive electrode according to claim 2, characterized in that: The chemical formula of the base material is Li a Ni x Mn 1-x O2, where 0.24≤x≤0.26, 0.5≤a≤0.55; and / or, The rare earth metals are yttrium and scandium.

4. A method for preparing a high voltage positive electrode according to any one of claims 1 to 3, characterized in that: The following steps are included: S1, forming a mixed solution of a zirconium source and a dopant, injecting an aging agent therein, and obtaining an intermediate through solid-liquid separation, drying and sintering; S2, mixing the base material and the intermediate, and sintering to obtain a high voltage positive electrode.

5. The preparation method according to claim 4, characterized in that: The zirconium source comprises at least one of zirconium oxychloride, zirconium nitrate or zirconium sulfate; and / or, The dopant includes at least one of yttrium salt and scandium salt; and / or, The aging agent includes one of ammonia water and sodium hydroxide.

6. The preparation method according to claim 5, characterized in that: The yttrium salt comprises at least one of yttrium nitrate, yttrium chloride or yttrium sulfate; and / or, The scandium salt includes at least one of scandium nitrate, scandium chloride or scandium sulfate.

7. The preparation method according to claim 4, characterized in that: The pH value of the system after the injection of the aging agent is 9.5-11; and / or, The mass ratio of the zirconium source to the dopant is 80-130:0.2-0.7; and / or, The mass ratio of the zirconium source, the yttrium salt and the scandium salt is 80-130:0.1-0.3:0.1-0.

4.

8. The preparation method according to claim 4, characterized in that: In step S1, the sintering temperature is 800-900°C, the sintering time is 1-3h, and the sintering atmosphere is an inert gas; and / or, The drying temperature is 80-120°C and the drying time is 3-5h; and / or, The solid-liquid separation step in step S1 includes filtration; and / or, In step S2, the sintering temperature is 250-650° C., the sintering time is 4-6 hours, and the sintering atmosphere is air atmosphere.

9. The preparation method according to claim 4, characterized in that: The preparation method of the base material comprises mixing a lithium source and a precursor, and sintering them. The chemical formula of the precursor is Ni x Mn 1-x (OH)2, where 0.24≤x≤0.26, The lithium source includes at least one of lithium carbonate, lithium hydroxide and lithium acetate.

10. A lithium ion battery, characterized in that: A high-voltage positive electrode comprising the high-voltage positive electrode described in any one of claims 1 to 3 or a high-voltage positive electrode prepared by the method for preparing a high-voltage positive electrode described in any one of claims 4 to 9.

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