Preparation method of ternary positive electrode material coated with silicon-based negative electrode material

Abstract

The invention discloses a ternary positive electrode material coated silicon-based negative electrode material, and its preparation method is as follows: aluminum silicon alloy is placed in a dilute hydrochloric acid solution, stirred and dried; the dried sample is taken and a chelating agent solution is added thereto; 2 mol / L nickel salt, 2 mol / L cobalt salt, 2 mol / L manganese salt are mixed, and 1 mol / L lithium salt is mixed; the mixture of citric acid and the etched aluminum silicon alloy is water-bathed, and then the mixed salt solution and 2 mol / L ammonia water are added to a beaker, the pH is adjusted between 6 10, and then the solution is stirred until a sol is formed; the sol is dried, then ground and crushed, placed in a muffle furnace for pretreatment, and then placed in a tubular furnace for sintering. The coated ternary positive electrode material can provide lithium ions for the silicon negative electrode, improve the conductivity of the material, protect the contact between silicon and the electrolyte, and improve the cycle performance of silicon.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery positive electrode materials, and in particular relates to a method for preparing a silicon-based negative electrode material coated with a lithium-containing compound. Background Art

[0002] Compared with existing graphite negative electrodes, silicon negative electrodes have a theoretical specific capacity ten times that of graphite and a suitable lithium deintercalation potential, making them expected to become the next generation of commercial negative electrode materials for lithium-ion batteries. However, the volume expansion rate of silicon during the cycle is as high as 300%, resulting in rapid decay of the cycle capacity, so silicon needs to be modified.

[0003] In the prior art, a silicon-carbon negative electrode material with a yolk-shell or a coated metal oxide is selected to modify the silicon-based negative electrode to improve the electrochemical performance. The first prior art is to prepare a silicon-carbon composite material with a yolk-shell structure, by first coating a layer of calcium carbonate or other coating agents on the silicon surface, and then using a sol-gel method to mix silicon with various carbon precursors, coating the carbon precursor on the silicon surface, etching away the coated calcium carbonate, and reserving space for the volume expansion of silicon. It is then carbonized at high temperature to prepare a silicon-carbon composite material with a yolk-shell structure. Although this structure can suppress volume expansion and improve the conductivity of silicon, the compaction density of silicon is very low due to the space between silicon and carbon. At the same time, the thickness of the carbon layer coated by the sol-gel method is mostly uncontrollable. If the thickness of the carbon layer is too thick, the first coulomb efficiency of silicon will drop significantly. If the carbon layer is too thin, the huge volume expansion of silicon during the cycle will break the carbon layer, resulting in poor cycle stability. Compared to carbon coating, the second existing technology is coating with metal oxides (aluminum oxide, titanium dioxide, etc.). This allows for controllable thickness, and the metal reinforcement is much stronger than carbon, thus effectively suppressing silicon volume expansion. However, most metal oxides have poor conductivity. If the coating is too dense, it will affect the transmission of lithium ions and the metal oxide will also reduce the material's capacity.

[0004] The present invention provides a novel ternary positive electrode material coated silicon-based negative electrode technology, aiming to improve the initial efficiency and cycle stability of the silicon-carbon negative electrode. Summary of the Invention

[0005] The present invention provides a novel ternary positive electrode material coated with a silicon-based negative electrode material and a preparation method thereof, aiming to improve the initial efficiency and cycle stability of the silicon-carbon negative electrode.

[0006] The preparation method of the ternary positive electrode material coated silicon-based negative electrode material is as follows: placing an aluminum-silicon alloy (silicon content 10-30%) in a dilute hydrochloric acid solution, stirring and then drying; taking the dried sample, adding 2-4 mol / L (for example, 10-100 mL) of a chelating agent solution thereto to obtain an etched aluminum-silicon alloy mixture; mixing 2-4 mol / L of a nickel salt, 2-4 mol / L of a cobalt salt, 2-4 mol / L of a manganese salt, and 1-4 mol / L of a lithium salt to obtain a salt solution; bathing the mixture of citric acid and the etched aluminum-silicon alloy, then adding the mixed salt solution and 2-4 mol / L of ammonia water to a beaker, adjusting the pH to between 6 and 10, and then stirring the solution in a three-necked flask until a sol is formed; drying the sol, then grinding and crushing it, placing it in a muffle furnace for pretreatment, and then placing it in a tubular furnace for sintering.

[0007] The silicon-aluminum alloy preferably has a silicon content of 10-20% and a particle size of 0.1-10 μm; the stirring parameter is 300-500 r / min at 1-30 min; the drying is performed by centrifuging and washing and then placing the sample in a 60-100°C oven to dry for 6-12 h; the chelating agent solution is preferably one of citric acid, ethylenediamine, and DETA; the nickel salt is preferably one of nickel sulfate, nickel nitrate, and nickel acetate; the cobalt salt is preferably one of cobalt sulfate, cobalt nitrate, and cobalt acetate; and the manganese salt is preferably one of manganese sulfate, manganese nitrate, and manganese acetate. The mixed molar ratio of nickel:cobalt:manganese is preferably 1-8:1-2:1-3; the lithium salt is preferably one of lithium carbonate, lithium hydroxide, and lithium acetate; the water bath temperature is 90-100°C; the sol drying conditions are: in a vacuum drying oven, the temperature is 80-160°C, and the holding time is 300-900min; the muffle furnace pretreatment conditions are: holding at 400-600°C for 30-300min; the sintering conditions in the tubular furnace are: sintering at 600-950°C and holding for 8-12h.

[0008] For example, the preparation method of the ternary positive electrode material coated silicon-based negative electrode material of the present invention can be as follows:

[0009] Place the aluminum-silicon alloy in a dilute hydrochloric acid solution and stir at 300-500 rpm for 1-30 minutes. Centrifuge, wash, and dry the sample. Place the dried sample in an 80°C oven and dry for 6-12 hours. Place a certain amount of the dried sample in a three-necked flask and add a certain amount of chelating agent solution (citric acid, ethylenediamine, or DETA). Mix 2-4 mol / L of a nickel salt (nickel sulfate, nickel nitrate, or nickel acetate), a cobalt salt (cobalt sulfate, cobalt nitrate, or cobalt acetate), and a manganese salt (manganese sulfate, manganese nitrate, or manganese acetate) in a certain molar ratio (nickel:cobalt:manganese can be 1:1:1, 5:2:3, 6:2:2, or 8:1:1). Add a certain amount of a lithium salt (lithium carbonate, lithium hydroxide, or lithium acetate) to the beaker. Place the citric acid and etched three-necked flask in a 90-100°C water bath. Add the mixed salt solution and 2-4 mol / L ammonia solution to a beaker, adjust the pH to 6-10, and stir the solution in the three-necked flask until a sol forms. Place the formed sol in a vacuum drying oven at 80-160°C for 300-900 minutes. Grind the dried material in a mortar and pestle, then pre-treat it in a muffle furnace at 400-600°C for 30-300 minutes. After treatment, sinter it in a tube furnace at 600-950°C for 8-12 hours.

[0010] The present invention also relates to a ternary positive electrode material coated silicon-based negative electrode material obtained by the above preparation method.

[0011] The present invention also relates to the application of the ternary positive electrode material coated silicon-based negative electrode material in button batteries.

[0012] As mentioned above, the application of the ternary positive electrode material coated silicon-based negative electrode material in the button battery is preferably to mix the ternary positive electrode material coated silicon-based negative electrode material with SP and sodium alginate in a mass ratio of 6-10:1-2:1-2 (more preferably 6-10:1:1) to make a button battery.

[0013] The ternary positive electrode material coated silicon-based negative electrode material is further preferably mixed with SP and sodium alginate in a mass ratio of 8:1:1. The button battery is a CR2036 button battery. When used, the charge and discharge voltage is 0.01-1.5V, the initial charge and discharge current is 0.5A, and the subsequent cycle current is 1A.

[0014] The present invention has the following technical effects:

[0015] (1) Compared with nano-silicon-based negative electrodes, porous silicon etched from aluminum-silicon alloy can bring higher first coulomb efficiency and alleviate the volume expansion of silicon. The coated ternary positive electrode material can provide lithium ions for the silicon negative electrode, improve the conductivity of the material and protect the contact between silicon and the electrolyte, thereby improving the cycle performance of silicon.

[0016] (2) The NCM of the present invention serves as both a coating agent and a lithium replenisher, achieving both coating and replenishment simultaneously. Unlike existing metal oxide or carbon coatings, NCM can provide excess lithium ions, improve the conductivity of the material, and enhance the cycling stability of the material. However, no other material has been found in the prior art that can replace NCM as both a coating agent and a lithium replenisher. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0018] Figure 1 EIS spectra of silicon-based anode and silicon-based anode coated with ternary cathode material;

[0019] Figure 2 This is a cycle comparison chart of two materials: silicon-based negative electrode and silicon-based negative electrode coated with ternary positive electrode material. DETAILED DESCRIPTION

[0020] To facilitate understanding of the present invention, various exemplary embodiments of the present invention are now described in detail. This description should not be considered as a specific limitation of the present invention, but should be understood as a more detailed description of certain aspects, features and embodiments of the present invention.

[0021] Example 1

[0022] A commercially available aluminum-silicon alloy (11% silicon content) with a particle size of 1-3 μm was placed in a 2 mol / L hydrochloric acid solution and magnetically stirred at 300 rpm for 30 minutes. The stirred sample was centrifuged, washed, and dried, and then dried in an 80°C vacuum oven for 8 hours. 100 g of the dried aluminum-silicon alloy was placed in a three-necked flask, and 50 mL of a 2 mol / L citric acid chelating agent was added. 25 mL of a 2 mol / L nickel acetate solution, 10 mL of a 2 mol / L cobalt acetate solution, 15 mL of a 2 mol / L nickel acetate solution, and 100 mL of a 2 mol / L lithium acetate solution were added to the beaker and stirred to mix. The three-necked flask was heated in a 100°C water bath, and the mixture in the beaker was slowly added to the flask. 2 mol / L hydrochloric acid was added to adjust the pH to 9. The mixture was added dropwise with stirring until a sol was formed, after which stirring was stopped. The resulting sol was placed in a vacuum drying oven at 120°C for 360 minutes. The dried material was then ground in a mortar and pestle and then placed in a muffle furnace at 500°C for 240 minutes. After removal, it was placed in a tube furnace at 920°C, vented with air, and held for 10 hours to complete sample preparation. The prepared sample was mixed with SP and sodium alginate in an 8:1:1 ratio to form a CR2036 button cell. The charge and discharge voltage ranged from 0.01 to 1.5V, with an initial charge and discharge current of 0.5A and subsequent cycling currents of 1A.

[0023] Comparative Example 1

[0024] Commercially available 30-50nm silicon powder was mixed with SP and sodium alginate in a ratio of 8:1:1 to produce a CR2036 button-type battery. The battery had a charge and discharge voltage of 0.01-1.5V, an initial charge and discharge current of 0.5A, and subsequent cycling currents of 1A.

[0025] Table 1 Comparison of the first coulombic efficiency of the two materials

[0026] Si@NCM obtained by the present invention Si First coulombic efficiency% 80.62 62.54

[0027] Figure 1 The EIS spectra of silicon-based negative electrode and silicon-based negative electrode coated with ternary positive electrode material are shown below. Figure 1 It can be seen that the silicon-based negative electrode coated with the ternary positive electrode material has a smaller semicircle radius and a smaller slope, indicating that the coating of the positive electrode material improves the conductivity of the silicon-based material, thereby reducing the charge transfer impedance and diffusion impedance; Figure 2 This is a cycle comparison chart of silicon-based negative electrode and silicon-based negative electrode coated with ternary positive electrode material. Figure 2It can be seen that the silicon-based negative electrode coated with NCM has a higher initial discharge capacity than the uncoated one. This is because the coated NCM can provide a portion of lithium ions to be embedded in the silicon during the initial discharge, thereby improving the initial discharge capacity. In subsequent cycles, since the NCM plays a role in stabilizing the structure and isolating the electrolyte, the cycle stability is also significantly better than that of the uncoated one. As can be seen in Table 1, the initial coulombic efficiency of the battery after coating with NCM is as high as 80.62%, while that of the uncoated silicon is only 62.54%. This is mainly because, on the one hand, the coated NCM can provide lithium ions, and on the other hand, the NCM can reduce the consumption of lithium ions in the electrolyte, thus significantly improving the initial coulombic efficiency.

[0028] It can be seen that the NCM described in the present invention serves as both a coating agent and a lithium replenishing agent, completing the coating and lithium replenishment at the same time. At the same time, unlike the existing metal oxide coating or carbon coating, NCM can not only provide excess lithium ions, but also improve the conductivity of the material and the cycle stability of the material; this is something that cannot be achieved by the existing technology.

[0029] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a ternary positive electrode material coated with a silicon-based negative electrode material, characterized in that: The method specifically includes the following steps: placing an aluminum-silicon alloy in a dilute hydrochloric acid solution, stirring and then drying; taking the dried sample, adding a chelating agent solution thereto to obtain an etched aluminum-silicon alloy mixture; mixing 2-4 mol / L of nickel salt, 2-4 mol / L of cobalt salt, 2-4 mol / L of manganese salt, and 1-4 mol / L of lithium salt to obtain a salt solution; placing the citric acid and the etched aluminum-silicon alloy mixture in a water bath, then adding the mixed salt solution and 2-4 mol / L of ammonia water into a beaker, adjusting the pH to between 6 and 10, and then stirring the solution until a sol is formed; drying the sol, then grinding and crushing it, placing it in a muffle furnace for pretreatment, and then placing it in a tubular furnace for sintering.

2. The method for preparing a ternary positive electrode material coated with a silicon-based negative electrode material according to claim 1, characterized in that: The silicon content in the silicon aluminum alloy is 10-30%, and the particle size is 0.1-10 μm.

3. The method for preparing a ternary positive electrode material coated with a silicon-based negative electrode material according to claim 1, characterized in that: The stirring condition is 300-500 r / min for 1-30 min; the drying condition is to put the sample into a 60-100° C. oven for drying for 6-12 h after centrifugal washing.

4. The method for preparing a ternary positive electrode material coated with a silicon-based negative electrode material according to claim 1, characterized in that: The chelating agent solution is one of citric acid, ethylenediamine and DETA; the lithium salt is one of lithium carbonate, lithium hydroxide and lithium acetate.

5. The method for preparing a ternary positive electrode material coated with a silicon-based negative electrode material according to claim 1, characterized in that: The nickel salt is one of nickel sulfate, nickel nitrate, and nickel acetate; the cobalt salt is one of cobalt sulfate, cobalt nitrate, and cobalt acetate; the manganese salt is one of manganese sulfate, manganese nitrate, and manganese acetate; and the mixed molar ratio of nickel:cobalt:manganese is 1-8:1-2:1-3.

6. The method for preparing a ternary positive electrode material coated with a silicon-based negative electrode material according to claim 1, characterized in that: The sol drying conditions are: in a vacuum drying oven, the temperature is 80-160°C, and the insulation time is 300-900 minutes.

7. The method for preparing a ternary positive electrode material coated with a silicon-based negative electrode material according to claim 1, characterized in that: The pretreatment conditions in the muffle furnace are: keeping warm at 400-600°C for 30-300 minutes; the sintering conditions in the tubular furnace are: sintering at 600-950°C and keeping warm for 8-12 hours.

8. A ternary positive electrode material coated with a silicon-based negative electrode material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the ternary positive electrode material coated silicon-based negative electrode material according to claim 8 or the ternary positive electrode material coated silicon-based negative electrode material obtained by the preparation method according to any one of claims 1 to 7 in button batteries.

10. Application of the ternary positive electrode material coated silicon-based negative electrode material in button batteries according to claim 9, characterized in that: The ternary positive electrode material-coated silicon-based negative electrode material is mixed with SP and sodium alginate in a mass ratio of 6-10:1-2:1-2 to prepare a button battery.

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