A method for preparing and applying a modified high-nickel cobalt-free cathode.

Abstract

This application discloses a method for preparing and applying a modified high-nickel cobalt-free cathode. The preparation method includes: step S1, mixing an aqueous solution containing lithium salt, nickel salt, and manganese salt with an aqueous solution containing monolayer MXene material to obtain a dispersion; step S2, mixing the dispersion with a solution containing a complexing agent, adjusting the pH, and reacting to obtain a gel; step S3, calcining the gel in an air or oxygen atmosphere to obtain the modified high-nickel cobalt-free cathode. This invention incorporates the two-dimensional material MXene during the synthesis of ternary materials. It can provide one or more doping sources from high-valence Ti, Mo, and V. After calcination, the corresponding cations will be doped into the cathode material to improve the electronic structure of the high-nickel cobalt-free cathode and stabilize the layered structure.

Description

Technical Field

[0001] This application relates to a method for preparing and applying a modified high-nickel cobalt-free cathode, which belongs to the field of lithium-ion batteries. Background Technology

[0002] Lithium nickel manganese cobalt oxide (LNCM) cathode materials for lithium-ion batteries (theoretical capacity ~270 mAh / g) have attracted wider attention due to their significantly higher theoretical capacity than lithium iron phosphate cathodes (theoretical capacity 170 mAh / g). However, due to the global scarcity of cobalt resources, the price of cobalt raw materials has been rising exponentially, leading to a continuous increase in the cost of downstream LNCM cathodes. Therefore, developing cobalt-free materials has become an inevitable trend to effectively reduce cathode costs. However, cobalt plays a crucial role in LNCM cathodes by inhibiting cation mixing, stabilizing the layered structure of the material, and thus improving the cycle and rate performance of the material. Currently, no suitable element has been found to completely replace cobalt in this role.

[0003] Although cobalt cannot be completely replaced at present, research shows that ion doping of cobalt-free cathodes can adjust the electronic structure of the cathode, stabilize the material structure to a certain extent, suppress cation mixing, and improve cycle stability. Summary of the Invention

[0004] Based on this, the main objective of this invention is to provide a method for preparing modified high-nickel cobalt-free cathodes by using MXene two-dimensional materials as both anion and cation doping sources.

[0005] According to a first aspect of this application, a method for preparing a modified high-nickel cobalt-free cathode is provided, the method comprising:

[0006] Step S1: Mix the aqueous solution containing lithium salt, nickel salt and manganese salt with the aqueous solution containing monolayer MXene material to obtain a dispersion;

[0007] Step S2: Mix the dispersion with a solution containing a complexing agent, adjust the pH, and react to obtain a gel;

[0008] Step S3: Calcining the gel in an air or oxygen atmosphere to obtain the modified high-nickel cobalt-free cathode.

[0009] Optionally, the monolayer MXene material is selected from Ti3C2T. x Ti2C T x Mo2C2T x V2CT x Mo2CT x One or more of them.

[0010] Optionally, the ratio of the number of moles of lithium salt to the total number of moles of nickel salt and manganese salt is (1.01 to 1.2):1.

[0011] Optionally, the nickel salt has a molar content of 70% to 96% in the metal salt;

[0012] The metal salts include lithium salts, manganese salts, and nickel salts.

[0013] Optionally, the lithium salt is selected from one or more of acetate, sulfate, and nitrate;

[0014] The nickel salt is selected from one or more of acetate, sulfate, and nitrate;

[0015] The manganese salt is selected from one or more of acetate, sulfate, and nitrate.

[0016] Optionally, the amount of the monolayer MXene material added is 0.5%-10% of the total mass of the metal salt;

[0017] The metal salts include lithium salts, manganese salts, and nickel salts.

[0018] Optionally, the upper limit of the amount of the monolayer MXene material added is independently selected from 10%, 8%, 7%, 5%, 3%, and 1% of the total mass of the metal salt, and the lower limit is independently selected from 0.5%, 8%, 7%, 5%, 3%, and 1%.

[0019] Optionally, the complexing agent is selected from one or two of ethylenediaminetetraacetic acid and citric acid monohydrate;

[0020] Preferably, the molar ratio of the complexing agent to the metal salt is (1-3):(0.5-1.5);

[0021] The number of moles of the metal salt is expressed as the number of moles of metal ions contained therein.

[0022] Preferably, the molar ratio of the complexing agent to the metal salt is 2:1.

[0023] Optionally, obtaining the monolayer MXene material includes the following steps:

[0024] Monolayer MXene material was obtained by acid etching of the aluminum layer in the MAX phase material.

[0025] Optionally, the acid is selected from HF.

[0026] Optionally, the MAX phase material includes one or more of Ti3AlC2, Ti2AlC, Mo2TiAlC2, V2AlC, and Mo2AlC.

[0027] Optionally, in step S2, adjusting the pH includes: adjusting the pH of the mixed solution to 7-8 using a pH adjuster;

[0028] The pH adjuster is selected from ammonia and / or sodium hydroxide.

[0029] Optionally, in step S3, the calcination includes a first calcination stage and a second calcination stage;

[0030] The temperature of the first calcination stage is 300℃~500℃; the time is 4h~10h.

[0031] The temperature of the second calcination stage is 600℃~850℃, and the time is 8h~24h.

[0032] Optionally, the heating rate during the calcination process ranges from 0.5℃ / min to 5℃ / min.

[0033] Optionally, the upper limit of the heating rate during the calcination process is independently selected from 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, and 1℃ / min, and the lower limit is independently selected from 0.5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, and 1℃ / min.

[0034] Optionally, the reaction is carried out at 70℃~90℃ for 5-6 hours.

[0035] As a specific embodiment, the preparation method of the modified high-nickel cobalt-free cathode is as follows:

[0036] (1) The aluminum layer in the MAX phase material was etched by hydrofluoric acid, and a single layer of MXene material was obtained after multiple centrifugal cleaning and ultrasonic treatment, and then prepared into an aqueous solution of a certain concentration.

[0037] (2) Weigh lithium salt, nickel salt and manganese salt in a certain stoichiometric ratio, prepare a clear aqueous solution, and add a certain volume of MXene aqueous solution to prepare a uniform dispersion.

[0038] (3) Weigh out the corresponding complexing agent according to the ratio of 1:1 of the molar amount of complexing agent to the molar amount of metal ions, and prepare a clear solution of a certain volume.

[0039] (4) Add the solution from step (2) dropwise to the solution from step (3) while stirring continuously. Adjust the pH to 7-8 with ammonia or sodium hydroxide solution, and stir for 5-6 hours in a water bath to form a gel. After thoroughly vacuum drying the gel, calcine it in an air or oxygen atmosphere for 5 hours, grind and disperse it in a mortar, and finally sinter it at high temperature in an air or oxygen atmosphere to obtain modified LiNi. x Mn 1-x Cobalt-free cathode.

[0040] According to a second aspect of this application, a modified high-nickel cobalt-free cathode prepared according to the above method is provided.

[0041] According to a third aspect of this application, a lithium-ion battery is provided, the lithium-ion battery comprising the above-described modified high-nickel cobalt-free cathode.

[0042] The beneficial effects that this application can produce include:

[0043] This invention primarily proposes a novel doping method by incorporating two-dimensional MXene during the synthesis of ternary materials. On one hand, MXene can provide one or more doping sources from high-valence Ti, Mo, and V. After calcination, the corresponding cations will be incorporated into the cathode material to improve the electronic structure of the high-nickel, cobalt-free cathode and stabilize its layered structure. Simultaneously, the small amount of -F groups in MXene will form LiF on the material surface, further preventing direct contact between the cathode material and the electrolyte and reducing side reactions. On the other hand, the two-dimensional MXene carbides can effectively separate LiNi... x Mn 1-x The particles prevent the aggregation of positive electrode particles and improve conductivity. Furthermore, the pores formed by the carbon elements in MXene after oxygen sintering enhance the wetting effect of the electrolyte, thereby improving the battery's cycle performance. Attached Figure Description

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Figure 1 The Ti3C2T prepared in Example 1 x XRD pattern of the powder;

[0046] Figure 2 The Ti-LiNi prepared in Example 1 0.8 Mn 0.2 Powder SEM image, scale 10 micrometers;

[0047] Figure 3 The LiNi prepared in Comparative Example 1 0.8 Mn 0.2 Powder SEM image, scale 10 micrometers;

[0048] Figure 4 The image shows the cycle performance of batteries prepared from the samples prepared in Example 1 and Comparative Example 1.

[0049] Figure 5 The image shows the cycle performance of batteries prepared from the samples prepared in Example 2 and Comparative Example 2.

[0050] Figure 6The image shows the cycle performance of batteries prepared from the samples prepared in Example 3 and Comparative Example 3. Detailed Implementation

[0051] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0052] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0053] Example 1:

[0054] (1) Weigh 1g of LiF powder and dissolve it in 20ml of 9M HCl. After stirring for 10min, slowly add 1g of Ti3AlC2 powder and etch in a 35℃ water bath for 36h. After etching, wash the solution by centrifugation until the pH is greater than 6, then sonicate for 60min. The supernatant obtained by centrifugation is the monolayer Ti3C2T. x Configuring Ti3C2T to 10 mg / ml x The solution is ready for use.

[0055] (2) Weigh out lithium acetate dihydrate (2.04 g), nickel acetate tetrahydrate (3.79 g), and manganese acetate tetrahydrate (0.93 g) in a stoichiometric ratio of 1.05:0.8:0.2, add 10 ml of deionized water and 30 ml of Ti3C2T x The solution (4.4% of the total metal ions by mass) was stirred until evenly dispersed.

[0056] (3) Weigh 8.205g of citric acid monohydrate, dissolve it in 30ml of deionized water, and stir until transparent.

[0057] (4) The metal salt solution from step (2) was added dropwise to the citric acid solution and stirred for 10 min. The pH was adjusted to 7-8 with ammonia, and the mixture was heated in a water bath at 80°C for 5 h to form a gel. After vacuum drying at 120°C, the gel was transferred to a tube furnace. The temperature was increased to 450°C at a rate of 1°C / min under an oxygen atmosphere and calcined for 5 h. The gel was then removed, ground, and pressed into a tablet. Finally, the temperature was increased to 800°C and calcined for 12 h under the same conditions to obtain the final Ti-doped LiNi. 0.8 Mn 0.2 denoted as Ti-LiNi 0.8 Mn 0.2 .

[0058] Example 2:

[0059] (1) Weigh 1g of LiF powder and dissolve it in 20ml of 9M HCl. After stirring for 10min, slowly add 1g of Mo2AlC powder and etch in a 35℃ water bath for 36h. After etching, wash the solution by centrifugation until the pH is greater than 6, then sonicate for 60min. The supernatant obtained by centrifugation is the monolayer Mo2CT. x Mo2CT was prepared at a concentration of 10 mg / ml. x The solution is ready for use.

[0060] (2) Weigh out lithium acetate dihydrate (2.04 g), nickel acetate tetrahydrate (3.41 g), and manganese acetate tetrahydrate (1.30 g) in a stoichiometric ratio of 1.05:0.72:0.28, add 10 ml of deionized water and 9 ml of Mo2CT. x The solution (1.3% of the total metal ions by mass) was stirred until it was evenly dispersed.

[0061] (3) Weigh 8.205g of citric acid monohydrate, dissolve it in 30ml of deionized water, and stir until transparent.

[0062] (4) The metal salt solution from step (2) was added dropwise to the citric acid solution and stirred for 10 min. The pH was adjusted to 7-8 with ammonia, and the mixture was heated in a water bath at 80°C for 5 h to form a gel. After vacuum drying at 120°C, the gel was transferred to a tube furnace. The temperature was increased to 450°C at a rate of 1°C / min under an oxygen atmosphere and calcined for 5 h. The gel was then removed, ground, and pressed into a tablet. Finally, the temperature was increased to 750°C and calcined for 12 h under the same conditions to obtain the final Mo-doped LiNi. 0.72 Mn 0.28 denoted as Mo-LiNi 0.72 Mn 0.28 .

[0063] Example 3:

[0064] (1) Weigh 1g of LiF powder and dissolve it in 20ml of 9M HCl. After stirring for 10min, slowly add 1g of Mo2AlC powder and etch in a 35℃ water bath for 36h. After etching, wash the solution by centrifugation until the pH is greater than 6, then sonicate for 60min. The supernatant obtained by centrifugation is the monolayer Mo2CT. x Mo2CT was prepared at a concentration of 10 mg / ml. x The solution is ready for use.

[0065] (2) Weigh out lithium acetate dihydrate (2.04 g), nickel acetate tetrahydrate (4.36 g), and manganese acetate tetrahydrate (0.37 g) in a stoichiometric ratio of 1.05:0.92:0.08, add 10 ml of deionized water and 60 ml of Mo2CT. xThe solution (containing 8.9% of the total metal ions by mass) was stirred until evenly dispersed.

[0066] (3) Weigh 8.205g of citric acid monohydrate, dissolve it in 30ml of deionized water, and stir until transparent.

[0067] (4) The metal salt solution from step (2) was added dropwise to the citric acid solution and stirred for 10 min. The pH was adjusted to 7-8 with ammonia, and the mixture was heated in a water bath at 80°C for 5 h to form a gel. After vacuum drying at 120°C, the gel was transferred to a tube furnace. The temperature was increased to 450°C at a rate of 1°C / min under an oxygen atmosphere and calcined for 5 h. The gel was then removed, ground, and pressed into a tablet. Finally, the temperature was increased to 800°C and calcined for 12 h under the same conditions to obtain the final Mo-doped LiNi. 0.92 Mn 0.08 denoted as Mo-LiNi 0.92 Mn 0.08 .

[0068] Comparative Example 1:

[0069] (1) Weigh lithium acetate dihydrate (2.04 g), nickel acetate tetrahydrate (3.79 g) and manganese acetate tetrahydrate (0.93 g) in a stoichiometric ratio of 1.05:0.8:0.2, dissolve them in 40 ml of deionized water, and stir until clear.

[0070] (2) Weigh 8.205g of citric acid monohydrate, dissolve it in 30ml of deionized water, and stir until transparent.

[0071] (3) The metal salt solution from step (2) was added dropwise to the citric acid solution and stirred for 10 min. The pH was adjusted to 7-8 with ammonia, and the mixture was heated in a water bath at 80°C for 5 h to form a gel. After vacuum drying at 120°C, the gel was transferred to a tube furnace. The temperature was increased to 450°C at a rate of 1°C / min under an oxygen atmosphere and calcined for 5 h. The gel was then removed, ground, and pressed into tablets. Finally, the temperature was increased to 800°C and calcined for 12 h under the same conditions to obtain LiNi. 0.8 Mn 0.2 Comparison sample.

[0072] Comparative Example 2:

[0073] (1) Weigh lithium acetate dihydrate (2.04 g), nickel acetate tetrahydrate (3.41 g), and manganese acetate tetrahydrate (1.30 g) in a stoichiometric ratio of 1.05:0.72:0.28, dissolve them in 40 ml of deionized water, and stir until clear.

[0074] (2) Weigh 8.205g of citric acid monohydrate, dissolve it in 30ml of deionized water, and stir until transparent.

[0075] (3) The metal salt solution from step (2) was added dropwise to the citric acid solution and stirred for 10 min. The pH was adjusted to 7-8 with ammonia, and the mixture was heated in a water bath at 80°C for 5 h to form a gel. After vacuum drying at 120°C, the gel was transferred to a tube furnace. The temperature was increased to 450°C at a rate of 1°C / min under an oxygen atmosphere and calcined for 5 h. The gel was then removed, ground, and pressed into tablets. Finally, the temperature was increased to 750°C and calcined for 12 h under the same conditions to obtain LiNi. 0.72 Mn 0.28 Comparison sample.

[0076] Comparative Example 3:

[0077] (1) Weigh lithium acetate dihydrate (2.04 g), nickel acetate tetrahydrate (4.36 g), and manganese acetate tetrahydrate (0.37 g) in a stoichiometric ratio of 1.05:0.92:0.08, dissolve them in 40 ml of deionized water, and stir until clear.

[0078] (2) Weigh 8.205g of citric acid monohydrate, dissolve it in 30ml of deionized water, and stir until transparent.

[0079] (3) The metal salt solution from step (2) was added dropwise to the citric acid solution and stirred for 10 min. The pH was adjusted to 7-8 with ammonia, and the mixture was heated in a water bath at 80°C for 5 h to form a gel. After vacuum drying at 120°C, the gel was transferred to a tube furnace. The temperature was increased to 450°C at a rate of 1°C / min under an oxygen atmosphere and calcined for 5 h. The gel was then removed, ground, and pressed into tablets. Finally, the temperature was increased to 800°C and calcined for 12 h under the same conditions to obtain Mo-LiNi. 0.92 Mn 0.08 Comparison sample.

[0080] The LiNi prepared in the above examples and comparative examples 0.8 Mn 0.2 LiNi 0.72 Mn 0.28 LiNi 0.92 Mn 0.08 Ti-LiNi 0.8 Mn 0.2 Mo-LiNi 0.72 Mn 0.28 and Mo-LiNi 0.92 Mn 0.08 The PVDF and super P were dissolved in NMP at a mass ratio of 9:0.5:0.5, coated evenly onto aluminum foil, dried and cut to prepare electrode sheets with a diameter of 14 mm. Using lithium metal as the counter electrode, 2025 specification button batteries were assembled for battery cycle performance testing.

[0081] Figure 1 The Ti3C2T prepared in Example 1 xThe XRD pattern of the powder shows that Ti3C2T was successfully etched. x The main peak at approximately 6.3° is peak (002). (Comparison) Figure 2 and Figure 3 Electron micrographs, Figure 2 The particles in it are relatively dispersed, while Figure 3 The obvious aggregation in Comparative Example 1 indicates that the Ti3C2T added during the synthesis process... x It can indeed effectively separate LiNi 0.8 Mn 0.2 Particles, inhibiting aggregation. And as... Figure 4 As shown, within a voltage range of 2.8V-4.5V at a 2C rate, Ti3C2T is added. x The battery's capacity retention rate after 100 cycles increased from 64.6% to 83%, indicating that the doping of Ti ions and a small amount of F ions can effectively improve the electronic structure of the cobalt-free cathode, stabilize the layered structure, and suppress electrolyte side reactions, thereby significantly improving the cycle life of the cobalt-free cathode. Figure 5 and Figure 6 This is a comparison of the electrochemical performance of Examples 2 and 3 with Comparative Examples 2 and 3. Also under the test conditions of 2C rate and 2.8V-4.5V, Mo2CT was added. x Examples 2 and 3 show that the capacity retention rates are improved from 66% and 65.8% to 87.6% and 81.1%, respectively, compared to Comparative Examples 2 and 3. This demonstrates that the doping method and selected ions in the examples can effectively improve the cycle life of the cobalt-free cathode.

[0082] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a modified high-nickel cobalt-free cathode, characterized in that, The preparation method includes: Step S1: Mix the aqueous solution containing lithium salt, nickel salt and manganese salt with the aqueous solution containing monolayer MXene material to obtain a dispersion; Step S2: Mix the dispersion with a solution containing a complexing agent, adjust the pH, and react to obtain a gel; Step S3: Calcining the gel in an air or oxygen atmosphere to obtain the modified high-nickel cobalt-free cathode; The monolayer MXene material is selected from Ti3C2T. x Ti2C T x Mo2C2T x V2CT x Mo2CT x One or more of them; The amount of the monolayer MXene material added is 0.5%-10% of the total mass of the metal salt; The metal salts include lithium salts, manganese salts, and nickel salts.

2. The preparation method according to claim 1, characterized in that, The ratio of the number of moles of lithium salt to the total number of moles of nickel and manganese salt is (1.01~1.2):

1.

3. The preparation method according to claim 2, characterized in that, The nickel salt has a molar content of 70% to 96% in the metal salt; The metal salts include lithium salts, manganese salts, and nickel salts.

4. The preparation method according to claim 1, characterized in that, The lithium salt is selected from one or more of acetate, sulfate, and nitrate; The nickel salt is selected from one or more of acetate, sulfate, and nitrate; The manganese salt is selected from one or more of acetate, sulfate, and nitrate.

5. The preparation method according to claim 1, characterized in that, The complexing agent is selected from one or two of ethylenediaminetetraacetic acid and citric acid monohydrate.

6. The preparation method according to claim 1, characterized in that, The molar ratio of the complexing agent to the metal salt is (1-3):(0.5-1.5). The number of moles of the metal salt is expressed as the number of moles of metal ions contained therein.

7. The preparation method according to claim 1, characterized in that, The process of obtaining the monolayer MXene material includes the following steps: A single-layer MXene material was obtained by acid etching of the aluminum layer in the MAX phase material. The MAX phase material includes one or more of Ti3AlC2, Ti2AlC, Mo2TiAlC2, V2AlC, and Mo2AlC.

8. The preparation method according to claim 1, characterized in that, In step S2, adjusting the pH includes: adjusting the pH of the mixed solution to 7-8 using a pH adjuster; The pH adjuster is selected from ammonia and / or sodium hydroxide.

9. The preparation method according to claim 1, characterized in that, In step S3, the calcination includes a first calcination stage and a second calcination stage; The temperature of the first calcination stage is 300℃~500℃; the time is 4h~10h. The temperature of the second calcination stage is 600℃~850℃, and the time is 8h~24h; The heating rate during the calcination stage ranges from 0.5℃ / min to 5℃ / min. The reaction was carried out at 70℃~90℃ for 5-6 hours.

10. A modified high-nickel cobalt-free cathode prepared by the method according to any one of claims 1 to 9.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes the modified high-nickel cobalt-free cathode as described in claim 10.

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