Chitosan-coated nano silicon negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery negative electrode materials, and discloses a chitosan-coated nano silicon negative electrode material as well as a preparation method and application thereof. According to the preparation method, a chitosan layer is constructed on the surface of nano silicon, and a surfactant is introduced, so that the surface tension of a chitosan solution is reduced, and the coating integrity of the chitosan layer is greatly improved. Firstly, polar groups of chitosan can form abundant hydrogen bonds with the aqueous binder, so that the peel strength of the electrode plate is improved; secondly, the chitosan layer can limit the volume expansion of the silicon particles; and finally, in the cycle process of the battery, the chitosan layer can enhance the adsorption of hexafluorophosphate radicals in the electrolyte to form more stable and thinner SEI rich in LiF, and the phenomenon that the SEI film on the silicon surface is continuously broken and reformed is also inhibited. The chitosan-coated nano silicon negative electrode material disclosed by the invention has excellent rate capability and cycling stability.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery negative electrode materials, and in particular to a chitosan-coated nano-silicon negative electrode material and a preparation method and application thereof. Background Art

[0002] Graphite material is the most commonly used negative electrode material for commercial lithium-ion batteries. As lithium-ion batteries develop towards high energy density and high power density, the low specific capacity and poor rate performance of graphite materials are becoming more and more obvious. The development of the next generation of high-capacity negative electrode materials is of great significance to the development of new energy vehicles and large-scale energy storage batteries. Silicon negative electrode materials have very high theoretical specific capacity (more than 10 times the theoretical specific capacity of graphite), moderate charge and discharge platform, and abundant resources. They are the most promising new negative electrode materials for the next generation of high-performance lithium-ion batteries and have broad market prospects.

[0003] Despite this, the industrial application of silicon negative electrode materials also faces very severe challenges. The first is the huge volume effect of this material (the volume expansion during lithium insertion exceeds 300%), which leads to the pulverization of silicon particles, thereby losing effective contact between silicon particles. At the same time, the solid electrolyte interface (SEI) film on the silicon surface cannot be stabilized, resulting in continuous lithium consumption.

[0004] Therefore, how to improve the performance of silicon negative electrode materials is an urgent problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to provide a chitosan-coated nano-silicon negative electrode material and a preparation method and application thereof, so as to solve the above-mentioned problems existing in the existing silicon negative electrode materials.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a chitosan-coated nano-silicon negative electrode material, comprising the following steps:

[0008] mixing chitosan and a solvent to obtain a chitosan solution;

[0009] Mixing chitosan solution, nano-silicon and water to obtain a mixed solution of chitosan and nano-silicon;

[0010] Adding a surfactant to a mixed solution of chitosan and nano-silicon, and then adding a precipitant to obtain a precipitate;

[0011] The precipitate is washed and dried to obtain chitosan-coated nano-silicon negative electrode material.

[0012] Preferably, in the above method for preparing chitosan-coated nano-silicon negative electrode material, the solvent is acrylic acid and / or glacial acetic acid; and the relative molecular mass of the chitosan is 1,000 to 1,000,000.

[0013] Preferably, in the above method for preparing chitosan-coated nano-silicon negative electrode material, the particle size of the nano-silicon is 50 to 200 nm.

[0014] Preferably, in the above method for preparing chitosan-coated nano-silicon negative electrode material, the mass of the chitosan is 0.5-10% of the mass of the nano-silicon.

[0015] Preferably, in the above method for preparing chitosan-coated nano-silicon negative electrode material, the surfactant is one or more of carboxymethyl cellulose, polyacrylic acid, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, Span 20-80, and Tween 20-80.

[0016] Preferably, in the above method for preparing a chitosan-coated nano-silicon negative electrode material, the mass fraction of the surfactant in the mixed solution of chitosan and nano-silicon is 0.1-10%.

[0017] Preferably, in the above method for preparing chitosan-coated nano-silicon negative electrode material, the precipitant is one or more of phosphate, polyphosphate and sulfate.

[0018] Preferably, in the above method for preparing a chitosan-coated nano-silicon negative electrode material, the concentration of the precipitant in the mixed solution of chitosan and nano-silicon is 0.05-5 mol / L.

[0019] The invention also provides a chitosan-coated nano-silicon negative electrode material prepared by a method for preparing a chitosan-coated nano-silicon negative electrode material.

[0020] The invention also provides an application of a chitosan-coated nano-silicon negative electrode material in a lithium-ion battery.

[0021] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention utilizes the excellent adsorption, film-forming and permeation properties of chitosan to construct a chitosan layer on the surface of nano-silicon, and by introducing a surfactant, the surface tension of the chitosan solution is reduced, thereby greatly improving the coating integrity of the chitosan layer. First, the polar groups of chitosan can form abundant hydrogen bonds with the aqueous binder, thereby improving the peeling strength of the electrode plate; second, the chitosan layer can limit the volume expansion of the silicon particles; finally, during the battery cycle, the chitosan layer can enhance the adsorption of hexafluorophosphate in the electrolyte, forming a more stable, thinner and LiF-rich SEI, and the phenomenon of continuous rupture and reformation of the SEI film on the silicon surface is also suppressed. The chitosan-coated nano-silicon negative electrode material of the present invention has excellent rate performance and cycle stability.

[0023] (2) The preparation process of the present invention is simple, the raw material cost is low, and it is non-toxic and harmless, which is conducive to large-scale production in the future and has important application value and prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

[0025] Figure 1 This is an electron microscope image of the negative electrode material of Comparative Example 1;

[0026] Figure 2 This is an electron microscope image of the negative electrode material of Example 1;

[0027] Figure 3 The first charge and discharge curves of the negative electrode materials of Example 1 and Comparative Example 1;

[0028] Figure 4 It is a long-term cycle performance diagram of the negative electrode materials of Example 1 and Comparative Example 1;

[0029] Figure 5 It is a rate performance diagram of the negative electrode materials of Example 1 and Comparative Example 1;

[0030] Figure 6 The first cycle-voltammogram of the negative electrode materials of Example 1 and Comparative Example 1;

[0031] Figure 7 It is a partial enlarged view of the first cycle-voltammetry curve of the negative electrode material of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing a chitosan-coated nano-silicon negative electrode material, comprising the following steps:

[0033] mixing chitosan and a solvent to obtain a chitosan solution;

[0034] Mixing chitosan solution, nano-silicon and water to obtain a mixed solution of chitosan and nano-silicon;

[0035] Adding a surfactant to a mixed solution of chitosan and nano-silicon, and then adding a precipitant to obtain a precipitate;

[0036] The precipitate is washed and dried to obtain chitosan-coated nano-silicon negative electrode material.

[0037] In the present invention, the solvent is preferably acrylic acid and / or glacial acetic acid, more preferably acrylic acid or glacial acetic acid, and more preferably acrylic acid.

[0038] In the present invention, the relative molecular mass of the chitosan is preferably 1,000 to 1,000,000, more preferably 10,000 to 500,000, and even more preferably 100,000.

[0039] In the present invention, the particle size of the nano-silicon is preferably 50 to 200 nm, more preferably 80 to 150 nm, and even more preferably 100 nm.

[0040] In the present invention, the mass of the chitosan is preferably 0.5-10% of the mass of the nano-silicon, more preferably 0.7-5%, and even more preferably 1%.

[0041] In the present invention, the surfactant is preferably one or more of carboxymethyl cellulose, polyacrylic acid, sodium dodecylbenzene sulfonate, cetyltrimethylammonium bromide, Span 20-80, and Tween 20-80, further preferably one or more of cetyltrimethylammonium bromide, Span 20-80, and Tween 20-80, and more preferably a mixture of Span 80 and Tween 80.

[0042] In the present invention, the mass fraction of the surfactant in the mixed solution of chitosan and nano-silicon is preferably 0.1-10%, more preferably 0.2-5%, and more preferably 0.5%.

[0043] In the present invention, the step of adding the surfactant further includes stirring for 2 hours.

[0044] In the present invention, the precipitant is preferably one or more of phosphate, polyphosphate, and sulfate, more preferably phosphate or sulfate, and more preferably sodium sulfate.

[0045] In the present invention, the concentration of the precipitant in the mixed solution of chitosan and nano-silicon is preferably 0.05-5 mol / L, more preferably 0.1-2 mol / L, and more preferably 0.2 mol / L.

[0046] The invention also provides a chitosan-coated nano-silicon negative electrode material prepared by a method for preparing a chitosan-coated nano-silicon negative electrode material.

[0047] The invention also provides an application of a chitosan-coated nano-silicon negative electrode material in a lithium-ion battery.

[0048] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] Example 1

[0050] This embodiment provides a chitosan-coated nano-silicon negative electrode material, and the preparation method thereof comprises the following steps:

[0051] (1) Dissolve 0.1 g of chitosan (molecular weight 100,000) in 2% acrylic acid solution and stir for 12 h to obtain a chitosan solution;

[0052] (2) 0.5 mL of chitosan solution and 0.5 g of nano-silicon (particle size of 100 nm) were added to 50 mL of deionized water and stirred for 2 h to obtain a mixed solution 1, wherein the mass of chitosan was 1% of the mass of nano-silicon;

[0053] (3) adding 0.1 g of Tween 80 and 0.05 g of Span 80 to the mixed solution 1, stirring for 2 h, to obtain a mixed solution 2; wherein the mass fraction of the surfactant in the mixed solution 1 is 0.3%;

[0054] (4) Add 1.42 g Na 2 SO 4 , centrifuge to obtain a precipitate; wash the precipitate three times with deionized water and ethanol respectively, and dry it in an oven at 80°C to constant weight to obtain a chitosan-coated nano-silicon negative electrode material.

[0055] Example 2

[0056] This embodiment provides a chitosan-coated nano-silicon negative electrode material, which is specifically referred to in Embodiment 1, except that the surfactant in step (3) is sodium dodecylbenzene sulfonate.

[0057] Example 3

[0058] This embodiment provides a chitosan-coated nano-silicon negative electrode material, which is specifically referred to in Embodiment 1, except that the surfactant in step (3) is hexadecyltrimethylammonium bromide.

[0059] Example 4

[0060] This embodiment provides a chitosan-coated nano-silicon negative electrode material, which is specifically referred to in Embodiment 1, except that the surfactant in step (3) is polyacrylic acid.

[0061] Comparative Example 1

[0062] This comparative example provides a nano-silicon negative electrode material, which is specifically referred to in Example 1, except that chitosan coating is not performed, and the nano-silicon with a particle size of 50 to 200 nm in step (2) is used as the negative electrode material.

[0063] Comparative Example 2

[0064] This comparative example provides a chitosan-coated nano-silicon negative electrode material, which is specifically referred to Example 1, except that step (3) does not contain surfactants Tween 80 and Span 80.

[0065] The chitosan-coated nano-silicon negative electrode material of Example 1 and the nano-silicon negative electrode material of Comparative Example 1 were characterized in terms of their morphology. Figure 1-2 As shown. Figure 1-2 It can be seen that the chitosan-coated nano-silicon particles are more uniform than the original nano-silicon particles. The nano-silicon particles in Comparative Example 1 are seriously agglomerated and have larger particles, which indicates that the chitosan modification layer is uniformly coated on the surface of the nano-silicon particles to form a continuous coating layer.

[0066] The electrochemical performance tests were conducted on the negative electrode materials of Examples 1 to 4 and Comparative Examples 1 to 2, respectively. The specific method is: the negative electrode material, conductive carbon black, and sodium hydroxycellulose / styrene-butadiene rubber composite commercial binder solution are fully and evenly dispersed in a mass ratio of 7:1:2, and then coated and dried to obtain a silicon negative electrode sheet. After slicing and vacuum drying at 140°C, the sheets were assembled into C2032 button cells in a glove box and subjected to electrochemical performance tests. All batteries were first charged with 0.05C current for 3 cycles, and then subjected to 0.5C cycle tests and rate tests (0.2C full charge, and discharge tests at 0.2C, 0.5C, 1C, 2C, 5C, and 10C, respectively, where the small rates of 0.05C and 0.1C were charged and discharged at the same rate). The results are shown in Tables 1 and Figure 3 to Figure 7 shown.

[0067] Table 1 Coating integrity and electrochemical performance test results

[0068]

[0069] As shown in Table 1, the coating completeness of chitosan is different depending on the type of surfactant, which indicates that the type of surfactant changes the distribution state of chitosan on the silicon surface.

[0070] from Figure 3 and Figure 4 It can be seen that the first charge and discharge capacity and long-term cycle performance of Example 1 are significantly improved compared with those of Comparative Example 1. The chitosan coating layer greatly improves the first reversible capacity and long-term cycle performance of the silicon negative electrode, confirming the excellent electrochemical performance of chitosan-modified silicon materials. Figure 5 It can be seen that the discharge capacity of the chitosan-modified silicon material at different rates is higher than that of the unmodified original silicon negative electrode, showing excellent rate performance. The first cycle-ampere curves of the negative electrode materials of Example 1 and Comparative Example 1 are shown in Figure 6 As shown, from Figure 6 It can be seen that the cyclic voltammetry curves before and after chitosan coating are similar, indicating that the lithium insertion and extraction mechanism and activity of the material are not affected. The partial enlarged diagram of the first cyclic voltammetry curve of the negative electrode material of Example 1 and Comparative Example 1 is shown in Figure 7 As shown, after local magnification and comparison, it can be seen that after chitosan coating, the intensity of the first irreversible reaction peak decreases, indicating that the surface modification layer inhibits the irreversible reduction decomposition reaction of the electrolyte on the silicon surface.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a chitosan-coated nano-silicon negative electrode material, characterized in that: The following steps are involved: mixing chitosan and a solvent to obtain a chitosan solution; Mixing chitosan solution, nano-silicon and water to obtain a mixed solution of chitosan and nano-silicon; Adding a surfactant to a mixed solution of chitosan and nano-silicon, and then adding a precipitant to obtain a precipitate; The precipitate is washed and dried to obtain chitosan-coated nano-silicon negative electrode material.

2. The method for preparing a chitosan-coated nano-silicon negative electrode material according to claim 1, characterized in that: The solvent is acrylic acid and / or glacial acetic acid; the relative molecular mass of the chitosan is 1000-1000000.

3. The method for preparing a chitosan-coated nano-silicon negative electrode material according to claim 2, characterized in that: The particle size of the nano silicon is 50-200 nm.

4. The method for preparing a chitosan-coated nano-silicon negative electrode material according to claim 1 or 3, characterized in that: The mass of the chitosan is 0.5-10% of the mass of the nano-silicon.

5. The method for preparing a chitosan-coated nano-silicon negative electrode material according to claim 4, characterized in that: The surfactant is one or more of carboxymethyl cellulose, polyacrylic acid, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, Span 20-80, and Tween 20-80.

6. The method for preparing a chitosan-coated nano-silicon negative electrode material according to claim 5, characterized in that: The mass fraction of the surfactant in the mixed solution of chitosan and nano-silicon is 0.1-10%.

7. The method for preparing a chitosan-coated nano-silicon negative electrode material according to claim 6, characterized in that: The precipitant is one or more of phosphate, polyphosphate and sulfate.

8. The method for preparing a chitosan-coated nano-silicon negative electrode material according to claim 1, 6 or 7, characterized in that: The concentration of the precipitant in the mixed solution of chitosan and nano-silicon is 0.05-5 mol / L.

9. A chitosan-coated nano-silicon negative electrode material obtained by the method for preparing a chitosan-coated nano-silicon negative electrode material according to any one of claims 1 to 8.

10. Use of the chitosan-coated nano-silicon negative electrode material according to claim 9 in lithium-ion batteries.

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