Two-dimensional silicon, its preparation method and application thereof in lithium battery

Abstract

The application belongs to the technical field of lithium batteries, and relates to preparation of a silicon negative electrode material, in particular to two-dimensional silicon, a preparation method thereof and application of the two-dimensional silicon in lithium batteries. Silicon-calcium alloy and copper halide are mixed and ground to obtain a mixed powder; potassium chloride and sodium chloride are added to the mixed powder, and grinding is performed to carry out etching reaction, so that calcium in the silicon-calcium alloy is etched off; the mixture after the etching reaction is added to an aqueous solution of ferric chloride to carry out oxidation reaction, so that copper in the mixture is oxidized into copper ions, and then the precipitate is separated, and the two-dimensional silicon is obtained. The preparation method provided by the application not only can prepare two-dimensional Si with good electrochemical performance, but also has the advantages of simple preparation method, high efficiency, green environmental protection and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and relates to preparation of a silicon negative electrode material, in particular to two-dimensional silicon, a preparation method thereof and application of the two-dimensional silicon in lithium batteries. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing an understanding of the general background of the application and does not necessarily constitute an admission or a recognition that the information forms part of the prior art that is already known in any country in the world.

[0003] The silicon negative electrode will produce huge volume expansion (~400%) during the cycle process, causing the pulverization and breakage of silicon and the falling off from the current collector, resulting in the rapid attenuation of battery performance, in addition, the poor conductivity of silicon leads to poor rate performance of the assembled battery when the silicon is used as a negative electrode. One of the methods to solve the above problems is to prepare two-dimensional Si material. Si has a high theoretical capacity, and the two-dimensional structure of Si can effectively inhibit the volume expansion of Si during the cycle process; in addition, the layered structure of two-dimensional silicon can provide a faster ion diffusion channel, so that it has better electrochemical performance. However, the inventors found that the existing preparation technology has defects such as complex preparation and high cost, so it is necessary to develop a simple method for preparing two-dimensional Si. SUMMARY

[0004] In order to solve the problems of the prior art, the application aims to provide two-dimensional silicon, a preparation method thereof and application of the two-dimensional silicon in lithium batteries, the preparation method provided by the application can not only prepare two-dimensional Si with good electrochemical performance, but also has advantages such as simple preparation method, high efficiency and green environmental protection.

[0005] The specific technical scheme is as follows:

[0006] The application provides a preparation method of two-dimensional silicon, comprising the following steps:

[0007] The silicon-calcium alloy and the copper halide are mixed and ground to obtain a mixed powder;

[0008] Potassium chloride and sodium chloride are added to the mixed powder, and grinding is performed to carry out etching reaction, so that the calcium in the silicon-calcium alloy is etched off;

[0009] The mixture after the etching reaction is added to an aqueous solution of ferric chloride to carry out oxidation reaction, so that the copper in the mixture is oxidized to copper ions, and then the precipitate is separated, and the two-dimensional silicon is obtained.

[0010] The application firstly grinds the silicon-calcium alloy and copper chloride to mix the silicon-calcium alloy and copper chloride uniformly, then adds potassium chloride and sodium chloride to grind, promotes the replacement reaction of calcium in the silicon-calcium alloy and copper ions in the copper chloride, and simultaneously inserts the potassium chloride and sodium chloride into the interlayer of silicon to help form two-dimensional silicon; and then adds to the aqueous solution of ferric chloride to oxidize copper by trivalent iron, dissolves the potassium chloride and sodium chloride in the silicon interlayer, and thus forms two-dimensional silicon.

[0011] During the grinding process of adding potassium chloride and sodium chloride, the added potassium chloride and sodium chloride can provide a molten salt environment, and at the same time, the particle sizes of the potassium chloride and sodium chloride are different, which can generate more heat during the grinding process, so that the reaction does not need additional heating and can be carried out at room temperature. In addition, compared with other salts (such as nitrate, sulfate), the use of potassium chloride and sodium chloride can reduce the cost and reduce the introduction of new impurities.

[0012] The application also provides two-dimensional silicon obtained by the above preparation method.

[0013] The application also provides application of the above two-dimensional silicon in a lithium battery.

[0014] The application also provides a battery negative electrode comprising the above two-dimensional silicon.

[0015] The application also provides a lithium battery comprising a battery positive electrode and the above battery negative electrode.

[0016] The application has the following beneficial effects:

[0017] (1) The application obtains two-dimensional Si powder by a mechanical grinding method, the obtained material has a uniform two-dimensional structure, reduces the process and cost, and can be prepared at normal temperature and pressure without high temperature and pressure and special environment, and the process is simple.

[0018] (2) The application is simple to operate, the precursors used are all selected from commercial materials, the preparation process is simple, easy to mass production, and is expected to realize commercialization.

[0019] (3) Research shows that: compared with the hydrochloric acid etching method and the vacuum stripping method, the two-dimensional Si powder prepared by the application not only maintains excellent electrochemical performance, but also has simpler preparation conditions and shorter time, and is green and environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings accompanying the specification of the application form a part of the application and serve to provide further understanding of the application, and the illustrative embodiments of the application and their descriptions serve to explain the application, and do not constitute an improper limitation on the application.

[0021] Figure 1The XRD pattern of the mixture after reaction and two-dimensional Si prepared in Example 1 of the present application.

[0022] Figure 2 The SEM pattern of the mixture after reaction prepared in Example 1 of the present application.

[0023] Figure 3 The SEM pattern of two-dimensional Si prepared in Example 1 of the present application.

[0024] Figure 4 The electrochemical test pattern of the battery prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0025] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0026] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0027] In view of the fact that the existing method for preparing two-dimensional Si is relatively complex, the present application provides two-dimensional silicon, a preparation method thereof and application thereof in lithium batteries.

[0028] In a typical embodiment of the present application, a preparation method of two-dimensional silicon is provided, comprising the following steps:

[0029] Mix and grind the silicon-calcium alloy and copper halide to obtain a mixed powder;

[0030] Add potassium chloride and sodium chloride to the mixed powder, and grind to perform etching reaction, so that the calcium in the silicon-calcium alloy is etched away;

[0031] Add the mixture after etching reaction to an aqueous solution of ferric chloride to perform oxidation reaction, so that the copper in the mixture is oxidized to copper ions, and then the precipitate is separated out.

[0032] The silicon-calcium alloy and copper halide are added together and ground in the present application, so as to make them mix more uniformly. In this way, potassium chloride and sodium chloride are added thereto. Grinding can initiate reaction, so that the silicon-calcium alloy is etched by copper halide as much as possible. If the raw materials are added together, some silicon-calcium alloy may not be in contact with copper halide, and thus cannot be etched.

[0033] The halogenated copper is a compound with copper ions as cations, such as copper chloride, cuprous bromide, cuprous iodide, etc., and the cost of copper chloride is lower than that of other halogenated copper.

[0034] In some embodiments, the molar ratio of the silicon-calcium alloy and the halogenated copper is 1:1-1.5. This can ensure complete conversion of the silicon-calcium alloy while avoiding waste caused by excessive addition of the halogenated copper.

[0035] In some embodiments, the mixing and grinding time is 5-10 min. Under this condition, the silicon-calcium alloy and the copper chloride can be fully mixed.

[0036] In some embodiments, the molar ratio of the potassium chloride and the sodium chloride is 1:1-1.5. This molar ratio can ensure that the reaction can proceed more uniformly.

[0037] In some embodiments, the grinding time for the etching reaction is 15-20 min.

[0038] In some embodiments, the concentration of the aqueous ferric chloride solution is 0.5-1 mol / L. -1 The concentration of the ferric chloride solution is relatively safe, and the copper removal efficiency is high.

[0039] In some embodiments, the reaction time for the oxidation reaction is 3-12 h. Under this condition, not only can the copper be completely removed, but also other soluble impurities can be completely removed.

[0040] The separation and precipitation method can be static separation by relying on its own gravity to settle and separate the solid and liquid, and then removing the solution; can be centrifugal separation, which separates the solid and liquid by centrifugation, and then removes the solution; or can be directly separated by filtration. In some embodiments, the separation and precipitation method after the oxidation reaction is filtration. The filtration includes normal pressure filtration and reduced pressure filtration, and the efficiency of the reduced pressure filtration is higher.

[0041] After the separation and precipitation, drying is performed, and in some embodiments, the drying includes vacuum drying and freeze drying. At room temperature, the two-dimensional silicon outer layer can be oxidized to silicon oxide. Vacuum drying and freeze drying are both reactions performed in the absence of oxygen. The vacuum drying temperature is 50-80 DEG C, and the freeze drying temperature is -50 to -30 DEG C.

[0042] Another embodiment of the present application provides a two-dimensional silicon obtained by the above preparation method.

[0043] A third embodiment of the present application provides an application of the above two-dimensional silicon in a lithium battery.

[0044] A fourth embodiment of the present application provides a battery negative electrode comprising the above two-dimensional silicon.

[0045] Specifically, the negative electrode is made into a slurry by the two-dimensional silicon, a binder and a conductive agent, and then coated on the surface of a current collector, and dried to obtain.

[0046] In a fifth embodiment of the present application, a lithium battery is provided, which comprises a battery positive electrode and the battery negative electrode described above.

[0047] Specifically, the battery is assembled by the battery positive electrode, the battery negative electrode, a separator and an electrolyte.

[0048] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples and comparative examples.

[0049] Example 1

[0050] A method for preparing two-dimensional Si by mechanical grinding, the steps are as follows:

[0051] (1) Put 1 g of silicon-calcium alloy and 1.67 g of copper chloride into a mortar and mix and grind for 10 min to make them uniformly mixed.

[0052] (2) Add 0.76 g of potassium chloride and 0.6 g of sodium chloride to the mixture and continue to grind until the mixture reacts and the color of the reactants begins to fade, and stop grinding (the total grinding time is 15 min) to make the reaction fully proceed.

[0053] (3) Put the reacted mixture into an aqueous solution of ferric chloride and stir for 6 h, the ferric chloride will react with the copper generated in the mechanical grinding to dissolve in the aqueous solution, then the remaining solid is suction filtered and dried to obtain two-dimensional Si powder.

[0054] Figure 1 The XRD pattern of the reacted mixture and two-dimensional Si proves that two-dimensional Si is successfully prepared, Figure 2 The SEM pattern of the reacted mixture shows that the silicon-calcium alloy is successfully etched into a two-dimensional structure after the reaction; Figure 3 The SEM pattern of two-dimensional Si proves the removal of impurities and the two-dimensional structure of the product.

[0055] Performance test: two-dimensional Si is used as the negative electrode active material, PAA is used as the binder, and Super P is used as the conductive agent. The proportion of active material, PAA and Super P is 8:1:1. Lithium sheet is used as the counter electrode and reference electrode, and LiPF6+EC / DEC / 10% FEC is used as the electrolyte. The voltage range is 0.01V-1.5V. Figure 4 The electrochemical test of the battery is carried out at 2000mA g -1The material has good electrochemical performance, as evidenced by the fact that the capacity retention rate is 95% after 1000 cycles at a current density of 0.5 A / g.

[0056] Example 2

[0057] A method for preparing two-dimensional Si by a mechanical grinding method, the steps being as follows:

[0058] (1) Put 1 g of a silicon-calcium alloy and 2 g of copper chloride into a mortar and mix and grind for 10 min, so that they are uniformly mixed.

[0059] (2) Add 0.76 g of potassium chloride and 0.6 g of sodium chloride to the mixture and continue to grind, so that the reaction proceeds fully.

[0060] (3) Put the reacted mixture into an aqueous solution of iron chloride and stir for 6 h, and then perform suction filtration on the remaining solid, and dry to obtain two-dimensional Si powder. Assemble a battery and test the electrochemical performance.

[0061] Example 3

[0062] A method for preparing two-dimensional Si by a mechanical grinding method, the steps being as follows:

[0063] (1) Put 1 g of a silicon-calcium alloy and 2 g of copper chloride into a mortar and mix and grind for 5 min, so that they are uniformly mixed.

[0064] (2) Add 0.76 g of potassium chloride and 0.6 g of sodium chloride to the mixture and continue to grind, so that the reaction proceeds fully.

[0065] (3) Put the reacted mixture into an aqueous solution of iron chloride and stir for 12 h, and then perform suction filtration on the remaining solid, and dry to obtain two-dimensional Si powder. Assemble a battery and test the electrochemical performance.

[0066] Example 4

[0067] A method for preparing two-dimensional Si by a mechanical grinding method, the steps being as follows:

[0068] (1) Put 1 g of a silicon-calcium alloy and 2 g of copper chloride into a mortar and mix and grind for 10 min.

[0069] (2) Add 0.76 g of potassium chloride and 0.6 g of sodium chloride to the mixture and continue to grind.

[0070] (3) Put the reacted mixture into an aqueous solution of iron chloride and stir for 8 h, and then perform suction filtration on the remaining solid, and dry to obtain two-dimensional Si powder. Assemble a battery and test the electrochemical performance.

[0071] Example 5

[0072] A method for preparing two-dimensional Si by a mechanical grinding method, the steps are as follows:

[0073] (1) Put 1 g of silicon-calcium alloy and 1.67 g of copper chloride into a mortar and mix and grind for 8 min.

[0074] (2) Add 0.76 g of potassium chloride and 0.6 g of sodium chloride to the mixture and continue to grind.

[0075] (3) Put the reacted mixture into an aqueous solution of ferric chloride and stir for 3 h, then perform suction filtration on the remaining solid, and dry to obtain two-dimensional Si powder. Assemble a battery to test the electrochemical performance.

[0076] Comparative Example 1

[0077] (1) Put 1 g of silicon-calcium alloy and 1.67 g of copper chloride into a mortar and mix and grind for 10 min,

[0078] (2) Add 1.52 g of potassium chloride to the mixture and continue to grind, and the mixture has no color change, so the reaction cannot be carried out.

[0079] Comparative Example 2

[0080] (1) Put 1 g of silicon-calcium alloy and 1.67 g of copper chloride into a mortar and mix and grind for 10 min.

[0081] (2) Add 1.2 g of sodium chloride to the mixture and continue to grind, and the mixture has no color change, so the reaction cannot be carried out.

[0082] Comparative Example 3

[0083] (1) Put 1 g of silicon-calcium alloy, 1.67 g of copper chloride, 0.76 g of potassium chloride and 0.6 g of sodium chloride into a mortar and mix and grind for 15 min.

[0084] (2) Put the reacted mixture into an aqueous solution of ferric chloride and stir for 6 h, then perform suction filtration on the remaining solid, and dry to obtain a two-dimensional silicon and silicon-calcium alloy mixed product.

[0085] At the same time, the addition of copper chloride will not be uniform in contact with the silicon-calcium alloy, resulting in residual unreacted silicon-calcium alloy in the reaction, which indicates that the silicon-calcium alloy and copper chloride should be mixed thoroughly before adding potassium chloride and sodium chloride.

[0086] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing two-dimensional silicon, characterized in that: The steps include: The calcium silicon alloy and the copper halide are mixed and ground to obtain a mixed powder; Potassium chloride and sodium chloride are added to the mixed powder, and the mixture is ground to cause an etching reaction, thereby etching away the calcium in the silicon-calcium alloy; The mixture after the etching reaction is added to an aqueous solution of ferric chloride to carry out an oxidation reaction, so that the copper element in the mixture is oxidized into copper ions, and then the precipitate is separated to obtain the product.

2. The method for preparing two-dimensional silicon according to claim 1, wherein: The molar ratio of silicon calcium alloy to copper halide is 1:1 to 1.5; Alternatively, the mixing and grinding time is 5 to 10 minutes.

3. The method for preparing two-dimensional silicon according to claim 1, wherein: The molar ratio of potassium chloride to sodium chloride is 1:1 to 1.

5.

4. The method for preparing two-dimensional silicon according to claim 1, wherein: The concentration of ferric chloride aqueous solution is 0.5~1mol L -1 ; Alternatively, the reaction time of the oxidation reaction is 3 to 12 hours.

5. The method for preparing two-dimensional silicon according to claim 1, wherein: The method of separating the precipitate after the oxidation reaction is filtration; Alternatively, the precipitate is separated and then dried, and the drying includes vacuum drying and freeze drying.

6. A two-dimensional silicon, characterized in that: The method is obtained by any one of claims 1 to 5.

7. Use of the two-dimensional silicon according to claim 6 in a lithium battery.

8. A battery negative electrode, characterized in that: Including the two-dimensional silicon as described in claim 6.

9. The battery negative electrode according to claim 8, wherein: The negative electrode is obtained by preparing a slurry from the two-dimensional silicon, a binder and a conductive agent, coating the slurry on the surface of a current collector, and drying the slurry.

10. A lithium battery, characterized in that: The invention comprises a battery positive electrode and the battery negative electrode according to claim 8 or 9.

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