Lithium-silicon alloy, preparation method and application thereof

Abstract

The application discloses a lithium-silicon alloy and a preparation method and application thereof, and comprises the following steps: S1: lithium pieces and silicon powder are mixed according to a mass ratio of 0.2-1.1 and are placed in a reaction vessel; under the protection of inert gas, the reaction is heated to obtain alloy powder; S2: the alloy powder is mixed with polytetrafluoroethylene according to a mass ratio of 10-20; under the protection of inert gas, ball milling reaction is carried out to obtain the lithium-silicon alloy. The preparation method of the lithium-silicon alloy of the application attaches lithium fluoride, carbon and carbon fluoride on the surface of lithium-silicon alloy powder, wherein the lithium fluoride has good mechanical strength, and can improve the mechanical properties of the lithium-silicon alloy as a whole; the carbon has good electrical conductivity, and can improve the electrical conductivity of the lithium-silicon alloy, improve the surface reaction kinetics of the silicon negative electrode, and improve the electrochemical performance of the battery; the organic phase of the carbon fluoride has good hydrophobicity, can prevent moisture in the air from contacting the lithium-silicon alloy, avoid side reactions of the lithium-silicon alloy, and improve the stability of the lithium-silicon alloy.

Description

Technical Field

[0001] This invention belongs to the field of lithium-silicon alloy material preparation technology, specifically relating to a lithium-silicon alloy, its preparation method, and its application. Background Technology

[0002] With the rapid development of electronic technology and the new energy industry, the performance improvement and optimization of lithium-ion batteries, as an important energy storage device, has become a focus of attention for many researchers. Among them, silicon anodes have great potential in improving the energy density of lithium-ion batteries due to their high specific capacity and abundant resources.

[0003] During the lithium-ion insertion and extraction process, silicon anode materials undergo tremendous volume expansion and contraction, leading to the rupture of silicon anode material particles, the shedding of active materials, and the rupture of the solid electrolyte interphase (SEI), which severely affects the cycle performance and lifespan of the battery.

[0004] To address this problem, existing solutions mainly include: using nano-silicon materials, preparing silicon-based composite materials, introducing conductive agents, or modifying the silicon surface. While these solutions can improve the cycle performance of silicon anodes to some extent, they still cannot completely solve the problems of silicon volume expansion and low initial coulombic efficiency. Summary of the Invention

[0005] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for preparing lithium-silicon alloy, which solves the problem that silicon anode materials obtained by existing preparation methods are prone to particle breakage, active material shedding and solid electrolyte interface breakage during the lithium ion insertion and extraction process.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a lithium-silicon alloy is provided, comprising the following steps:

[0007] S1: Alloy preparation;

[0008] Lithium flakes and silicon powder are mixed at a mass ratio of 0.2 to 1.1 and placed in a reactor vessel. The mixture is heated under an inert gas atmosphere to produce an alloy powder.

[0009] S2: Forms a protective layer on the alloy surface;

[0010] The alloy powder is mixed with polytetrafluoroethylene at a mass ratio of 10-20, and ball milling is carried out under inert gas protection to obtain lithium silicon alloy.

[0011] As a further improvement of the present invention, the heating reaction temperature in step S1 is 300±10℃ and the reaction time is 2±0.2h.

[0012] As a further improvement of the present invention, lithium-silicon alloy powder is prepared in step S1, wherein the lithium-silicon alloy has the chemical formula Li. x Si y , where x:y is 1:1 to 1:6.

[0013] As a further improvement of the present invention, the lithium-silicon alloy includes LiSi, Li3Si2, and Li 12 Si7, Li2Si, Li7Si3, Li5Si 12 Li3Si, Li 13 Si4, Li 21 Si5, Li 22 One or more of Si5, Li5Si, or Li6Si.

[0014] As a further improvement of the present invention, in step S2, the ball milling reaction is carried out in a ball milling jar, and zirconium dioxide grinding beads are added to the ball milling jar for grinding.

[0015] As a further improvement of the present invention, in step S2, the ball milling time is 2 hours and the ball milling speed is 1000~1200 r / min.

[0016] As a further improvement of the present invention, the inert gas in steps S1 and S2 is argon.

[0017] As a further improvement of the present invention, the protective layer formed on the alloy surface in step S2 includes lithium fluoride, carbon, and fluorinated carbon.

[0018] This application also includes a lithium-silicon alloy prepared by the method described above.

[0019] This application also includes the application of a lithium-silicon alloy as a negative electrode material for lithium-ion batteries.

[0020] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0021] (1) The method for preparing the lithium silicon alloy of the present invention adopts ball milling and reacts the lithium silicon alloy with polytetrafluoroethylene under conventional conditions to form lithium fluoride, carbon and fluorinated carbon on the surface of the lithium silicon alloy powder. Among them, lithium fluoride has good mechanical strength and can improve the mechanical properties of the lithium silicon alloy as a whole; carbon has good electrical conductivity and can improve the electrical conductivity of the lithium silicon alloy, enhance the surface reaction kinetics of silicon anode, and improve the electrochemical performance of battery; the organic phase of fluorinated carbon has good hydrophobic properties, which can prevent moisture in the air from contacting the lithium silicon alloy, avoid side reactions of lithium silicon alloy, and improve the stability of lithium silicon alloy.

[0022] (2) The preparation method of the lithium silicon alloy of the present invention has simple overall preparation process conditions, and only needs to be generated under a protective gas atmosphere, which greatly reduces the difficulty of preparing lithium silicon alloy and increases the possibility of practical application of lithium silicon alloy anode. Attached Figure Description

[0023] Figure 1 This is a TEM image from Embodiment 4 of the present invention;

[0024] Figure 2 This is the first charge-discharge curve diagram in Embodiment 4 of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] This invention provides a method for preparing lithium-silicon alloy, which specifically includes the following steps:

[0027] S1: Alloy preparation;

[0028] Lithium flakes and silicon powder are mixed at a mass ratio of 0.2 to 1.1 and placed in a reactor vessel. The mixture is heated under an inert gas atmosphere to produce an alloy powder.

[0029] S2: Forms a protective layer on the alloy surface;

[0030] The alloy powder is mixed with polytetrafluoroethylene at a mass ratio of 10-20, and ball milling is carried out under inert gas protection to obtain lithium silicon alloy.

[0031] Specifically, in the above steps, step S1 is mainly for the reaction to obtain lithium-silicon alloy powder. This application allows for the preparation of lithium-silicon alloy powder either in-house or by purchasing it. Step S2 is mainly for forming a protective layer on the surface of the lithium-silicon alloy to improve its mechanical properties, electrical conductivity, and stability under operating conditions.

[0032] In the preparation and selection of conventional silicon anode materials, lithium-silicon alloys can effectively solve the volume expansion problem caused by lithium intercalation into silicon and improve the initial coulombic efficiency of the battery. However, lithium-silicon alloys are highly reactive and readily react with moisture, oxygen, nitrogen, and other gases in the air, making the preparation of lithium-silicon alloy anodes more difficult.

[0033] Based on this, the preparation method of the lithium-silicon alloy in this application adopts ball milling to react the lithium-silicon alloy with polytetrafluoroethylene under conventional conditions to form lithium fluoride, carbon, and fluorinated carbon on the surface of the lithium-silicon alloy powder. It utilizes the good mechanical strength of lithium fluoride to give the lithium-silicon alloy good overall mechanical properties; utilizes the electrical conductivity of carbon to improve the overall electrical conductivity of the lithium-silicon alloy; and utilizes the hydrophobic properties of the fluorinated carbon organic phase to isolate the lithium-silicon alloy from moisture in the external air, avoid side reactions of the lithium-silicon alloy, and improve the stability of the lithium-silicon alloy.

[0034] Specifically, the reaction equation between the lithium silicon alloy and polytetrafluoroethylene in S2 of this application is as follows:

[0035] 2nLi+(CF2)n---2nLiF+nC (Formula 1)

[0036] The reaction produces lithium fluoride and carbon, which compensate for the mechanical and electrical properties of lithium-silicon alloys, respectively. The fluorinated carbon is the incompletely produced carbon fluoride (CF). x To form a hydrophobic layer on the surface of the lithium-silicon alloy. Therefore, in step S1 of this application, lithium needs to be in excess relative to silicon to ensure that it reacts with polytetrafluoroethylene to form lithium fluoride and carbon, while in step S2, polytetrafluoroethylene needs to be in excess to ensure that there is a residual CF. x A hydrophobic layer is formed on the surface of the lithium-silicon alloy.

[0037] Furthermore, as a preferred embodiment of the present invention, the heating reaction temperature in step S1 is 300±10℃, and the reaction time is 2±0.2h. A stainless steel crucible is selected as the reaction vessel to avoid reaction between lithium, silicon, etc., and the preparation vessel. The reaction temperature is set at 300℃, with temperature fluctuations within 10℃; the reaction time is 2h, with reaction completion time fluctuations within 0.2h.

[0038] More preferably, the lithium-silicon alloy powder prepared in step S1 of this application has the chemical formula Li x Si y Where x:y is 1:1 to 1:6, the above lithium-silicon alloys include LiSi, Li3Si2, and Li 12 Si7, Li2Si, Li7Si3, Li5Si 12 Li3Si, Li 13 Si4, Li 21 Si5, Li 22 One or more of Si5, Li5Si, or Li6Si.

[0039] In a preferred embodiment of the present invention, the ball milling reaction in step S2 is carried out in a ball mill jar, and the grinding beads in the ball mill jar are zirconium dioxide. Zirconia grinding beads have high hardness and do not react with polytetrafluoroethylene or lithium-silicon alloys.

[0040] More preferably, the ball milling time for the above-mentioned ball milling reaction is 2 hours, and the ball milling speed is 1000~1200 r / min.

[0041] More preferably, the inert gas in steps S1 and S2 is argon. Lithium and lithium-silicon alloys are both relatively reactive metals that can react with moisture and oxygen in the air under normal conditions. Therefore, an inert gas is needed for protection to avoid the introduction of external impurities. Optionally, in addition to argon as a protective gas, other inert gases that do not react with silicon, lithium, or lithium-silicon alloys can also be used.

[0042] The lithium-silicon alloy prepared in this application has good mechanical properties, electrical conductivity and stability. When applied to the anode of lithium-ion batteries, it has high initial coulombic efficiency and long cycle life, and has good practical value.

[0043] In some specific embodiments, a method for preparing a lithium-silicon alloy includes the following steps:

[0044] S1: Mix lithium foil and silicon powder in a mass ratio of 0.2~1.1 into a stainless steel crucible, and heat at 300℃ for 2 hours under an argon protective atmosphere;

[0045] S2: Mix the lithium silicon alloy powder obtained in step S1 with polytetrafluoroethylene (PTFE) at a mass ratio of 10~20, place it in a ball mill jar, add zirconium dioxide grinding beads, and ball mill in a ball mill for 2 hours under an argon protective atmosphere.

[0046] To better illustrate the preparation method, product, and application of the present invention, the following specific embodiments and comparative examples are provided:

[0047] Example 1

[0048] S1: Mix 100 mg of lithium flakes and 500 mg of silicon powder in a stainless steel crucible and heat at 300 °C for 2 h under an argon protective atmosphere.

[0049] S2: Mix 300 mg of the powder from step S1 with 15 mg of PTFE, place the mixture in a ball mill jar, add the ball milling beads, and ball mill on a ball mill for 2 h under an argon atmosphere. The ball mill speed is 1000 r / min.

[0050] Example 2

[0051] S1: Mix 300 mg of lithium flakes and 500 mg of silicon powder in a stainless steel crucible and heat at 300 °C for 2 h under an argon protective atmosphere.

[0052] S2: Mix 300 mg of the powder from step S1 with 20 mg of PTFE, place the mixture in a ball mill jar, add the ball milling beads, and ball mill on a ball mill for 2 h under an argon atmosphere. The ball mill speed is 1100 r / min.

[0053] Example 3

[0054] S1: Mix 400 mg of lithium flakes and 500 mg of silicon powder in a stainless steel crucible and heat at 300 °C for 2 h under an argon protective atmosphere.

[0055] S2: Mix 300 mg of the powder from step S1 with 25 mg of PTFE, place the mixture in a ball mill jar, add the ball milling beads, and ball mill on a ball mill for 2 h under an argon atmosphere. The ball mill speed is 1200 r / min.

[0056] Example 4

[0057] S1: Mix 550 mg of lithium flakes and 500 mg of silicon powder in a stainless steel crucible and heat at 300 °C for 2 h under an argon protective atmosphere.

[0058] S2: Mix 300 mg of the powder from step S1 with 30 mg of PTFE, place the mixture in a ball mill jar, add the ball milling beads, and ball mill on a ball mill for 2 h under an argon atmosphere. The ball mill speed is 1200 r / min.

[0059] Figure 1 The image shown is a TEM image from Example 4. As can be seen from the image, the surface of the lithium-silicon alloy is covered with a protective layer. This protective layer can prevent moisture in the air from contacting the lithium-silicon alloy, thereby improving the stability of the lithium-silicon alloy in the air.

[0060] Figure 2 The first charge-discharge curve of the electrode fabricated in air using a binder prepared from polyvinylidene fluoride dissolved in N-methylpyrrolidone in Example 4, based on lithium-silicon alloy powder, is shown. Figure 2 It can be seen that the lithium-silicon alloy has good stability in air, the prepared electrode can exert its capacity, and the coulombic efficiency exceeds 100% for the first time.

[0061] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a lithium-silicon alloy, characterized by, Comprising the following steps: S1: preparing an alloy powder; Mixing lithium pieces and silicon powder in a mass ratio of 0.2-1.1 in a reaction vessel, heating and reacting under inert gas protection to obtain an alloy powder; the heating and reacting temperature is 300±10℃, and the reaction time is 2±0.2h; S2: forming a protective layer on the surface of the alloy powder, the protective layer being lithium fluoride, carbon and carbon fluoride; Mixing the alloy powder and polytetrafluoroethylene in a mass ratio of 10-20, and performing a ball milling reaction under inert gas protection to obtain a lithium-silicon alloy; the ball milling time in the ball milling reaction is 2h, and the ball milling rotation speed is 1000-1200r / min.

2. The method of producing a lithium-silicon alloy according to claim 1, characterized by, The lithium-silicon alloy includes one or more of LiSi, Li3Si2, Li 12 Si7, Li2Si, Li7Si3, Li5Si 12 , Li3Si, Li 13 Si4, Li 21 Si5, Li 22 Si5, Li5Si, or Li6Si.

3. The method of producing a lithium-silicon alloy according to claim 1, characterized by, In step S2, the ball milling reaction is performed in a ball milling tank, and zirconium dioxide grinding beads are added to the ball milling tank for grinding.

4. The method of producing a lithium-silicon alloy according to claim 1, characterized by, The inert gas in step S1 and step S2 is argon.

5. A lithium-silicon alloy characterized by, Obtained by using the preparation method of the lithium-silicon alloy as described in any one of claims 1-4.

6. Use of the lithium-silicon alloy as described in claim 5 as a negative electrode material for a lithium ion battery.

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