Porous silicon negative electrode material and preparation method and application thereof

Abstract

The present application belongs to the technical field of new energy materials, and particularly relates to a porous silicon negative electrode material, a preparation method thereof and application thereof. The preparation method of the present application uses a molten salt method to prepare a porous silicon material in a high-temperature reaction kettle, reacts magnesium silicide with aluminum chloride in a high-temperature molten salt environment, removes magnesium salt by water washing and acid washing of the product, and obtains a pure porous silicon negative electrode material. This material can effectively alleviate the volume change of silicon during the charging and discharging cycle process, improve the cycle stability and the electrical conductivity of the material, and at the same time, the porous structure provides a large number of active sites for lithium ions, which helps to improve the electrochemical stability. The prepared porous silicon negative electrode material has a high specific surface area, can provide more active surface for the embedding and releasing of lithium ions, and thus realizes higher battery capacity and charging speed. The process is simple, environmentally friendly and low in cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials, and particularly relates to a porous silicon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid growth of the electric vehicle and consumer electronics markets, the research and application of power batteries are also booming. As one of the most popular power batteries at present, lithium ion batteries are widely concerned and extensively researched due to their high working voltage, large specific capacity, long cycle life, no memory effect, low self-discharge rate, environmental protection and safety and other advantages. With the increasing demand of the market for high-energy density and high-safety lithium ion batteries, the theoretical capacity of the existing commercial graphite negative electrode is only 372 mAh / g, which cannot meet the market demand. Therefore, seeking a lithium ion battery with higher energy density has become a hot research topic at present.

[0003] In recent years, porous silicon materials have attracted much attention in the field of lithium ion battery negative electrode materials. The theoretical capacity of silicon is as high as 4200 mAh / g, and it is an ideal lithium ion battery negative electrode active material. However, due to the severe volume change of silicon during charging and discharging, the expansion rate is as high as 300%, which easily causes the material to pulverize, thereby causing serious damage to the material structure, making the electrode active material and the current collector separate, the electrical contact is lost, and the cycle life is greatly reduced. In addition, due to the formation of lithium silicate, the initial irreversible capacity is high, and the material pulverization also causes the repeated growth and fragmentation of the SEI film, which limits its application as a lithium ion battery negative electrode material. Therefore, optimizing the performance of the silicon negative electrode material has become an important research direction, and has important value and significance.

[0004] At present, the preparation of pure silicon negative electrode materials can be divided into electrochemical deposition method, gas deposition method and mechanical ball milling method, each of which has its own advantages and disadvantages, and the cost is relatively high. In the present application, sodium chloride, aluminum chloride and magnesium silicide powder are put into a reaction kettle in a certain proportion, heated to 100-1000 DEG C at a certain heating rate, and a mixture of silicon and magnesium salt is generated by reaction. After water washing, acid washing, filtering and drying, pure silicon is obtained. This method has the advantages of simple preparation method, low preparation cost, high purity, good recyclability, strong controllability and environmental friendliness, and is a relatively excellent porous silicon negative electrode preparation method. SUMMARY

[0005] The technical problem solved by the present application is to provide a porous silicon negative electrode material and a preparation method and application thereof. The technical scheme adopted is as follows:

[0006] A kind of porous silicon negative material, by magnesium silicide and aluminium chloride, sodium chloride react in high-temperature molten salt environment, obtain pure porous silicon and magnesium salt, the particle size distribution of the porous silicon is between 5nm-500nm.

[0007] A kind of porous silicon negative material preparation method, comprising the following steps:

[0008] (a) magnesium silicide is mixed with aluminium chloride and sodium chloride in a certain proportion in high-temperature reaction kettle, inert gas is passed, with a certain heating rate to 100-800 DEG C, and keeps warm for a certain time;

[0009] (b) the mixture of silicon and magnesium salt prepared in the above step (a) is washed by stirring with deionized water, and the water is clear after sedimentation and pouring off, and the above steps are repeated until the water is clear;

[0010] (c) hydrochloric acid is added to the last solution in the above step (b), stirred for a period of time, then filtered, and the product is dried in a blast drying oven to obtain pure porous silicon negative material.

[0011] Preferably, in the step (a), the molar ratio of aluminium chloride and magnesium silicide is 0.1-10:1;The molar ratio of sodium chloride and magnesium silicide is 0.1-10:1.

[0012] Preferably, in the step (a), the inert gas is at least one of helium, nitrogen, argon and carbon dioxide.

[0013] Preferably, in the step (a), the heating rate is 0.1-10 DEG C / min, and the holding time is 1-10 h.

[0014] Preferably, in the step (c), the stirring time after adding hydrochloric acid is 1-10 h.

[0015] Preferably, in the step (c), the temperature of the blast drying oven is set to 50-100 DEG C, and the drying time is 1-24 h.

[0016] The porous silicon material prepared by the above method can be used to prepare lithium ion battery negative electrode.

[0017] The application also provides a use of the porous silicon negative material prepared by the above method, which is used in lithium ion battery negative electrode, the electrolyte of the lithium ion battery is any one of LiPF6 dissolved in ethylene carbonate (EC)+dimethyl carbonate (DMC), LiPF6 dissolved in ethylene carbonate (EC)+diethyl carbonate (DEC), LiPF6 dissolved in ethylene carbonate (EC)+diethyl carbonate (DEC)+dimethyl carbonate (DMC), the positive electrode material uses LiMn2O4, and the separator is polypropylene microporous membrane.

[0018] In the above use, the concentration of LiPF6 in the lithium ion battery electrolyte is 0.5-1.5 mol / L.

[0019] Compared with the prior art, the present application has the advantages of

[0020] The preparation method of the present application uses a molten salt method in a high-temperature reaction kettle to prepare porous silicon material. Magnesium silicide and aluminum chloride are reacted in a high-temperature molten salt environment, and the product is washed with water and acid to remove magnesium salt, obtaining pure porous silicon negative electrode material. This material can effectively alleviate the volume change of silicon during the charge and discharge cycle, improve the cycle stability and electrical conductivity of the material, and the porous structure provides a large number of active sites for lithium ions, which helps to improve the electrochemical stability.

[0021] The prepared porous silicon negative electrode material has a high specific surface area, which can provide more active surface for lithium ion intercalation and release, thereby achieving higher battery capacity and charging speed. The present application has made significant progress in improving the specific capacity, cycle performance and rate performance of lithium ion batteries, and more importantly, it proposes a new method for preparing porous silicon, which is simple, environmentally friendly and low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM photo of the porous silicon negative electrode material provided for Example 1 of the present application.

[0023] Figure 2 The first charge-discharge curve of the porous silicon negative electrode material provided for Example 1 of the present application.

[0024] Figure 3 The cycle curve of the porous silicon negative electrode material provided for Example 1 of the present application at a current density of 0.5 A / g. DETAILED DESCRIPTION

[0025] The accompanying drawings are for illustrative purposes only; in order to facilitate understanding of the technical solutions of the present application, the present application will be described in detail below in combination with the prior art, but the technical solutions of the present application are not limited to the embodiments.

[0026] It should be understood that certain prior art and common knowledge can be omitted for those skilled in the art.

[0027] Example 1

[0028] A preparation method of a porous silicon negative electrode material, comprising the following steps:

[0029] (a) 1g of magnesium silicide, 1g of sodium chloride and 4g of aluminum chloride are weighed on an electronic balance, and the weighed chemicals are poured into a clean reaction kettle.

[0030] (b) In the above reaction kettle, argon is introduced and the residual air in the reaction kettle is exhausted for a certain period of time.

[0031] (c) After the reaction kettle is sealed, it is heated to 300°C at a heating rate of 2°C / min in a high-temperature furnace, and kept for 5h.

[0032] (d) After high-temperature reaction, it is placed in a 500mL beaker, 300mL deionized water is added, and after settling, it is filtered, and the above steps are repeated several times until the water is clear.

[0033] (e) 10mL of hydrochloric acid is added to the solution obtained in step (d), stirred for 4h, and then filtered to obtain a solid.

[0034] (f) The solid obtained in step (e) is placed in a 60°C air-drying oven for 12h, and the pure porous silicon negative electrode material is finally obtained.

[0035] Example 2

[0036] A method for preparing a porous silicon negative electrode material, in step (c), the temperature is raised to 250°C at a rate of 2°C / min in a high-temperature furnace, and kept for 5h.

[0037] Other places not mentioned are the same as in Example 1.

[0038] Example 3

[0039] A method for preparing a porous silicon negative electrode material, in step (c), the temperature is raised to 350°C at a rate of 2°C / min in a high-temperature furnace, and kept for 5h.

[0040] Other places not mentioned are the same as in Example 1.

[0041] Example 4

[0042] A method for preparing a porous silicon negative electrode material, in step (c), the temperature is raised to 400°C at a rate of 2°C / min in a high-temperature furnace, and kept for 5h.

[0043] Other places not mentioned are the same as in Example 1.

[0044] Example 5

[0045] A method for preparing a porous silicon negative electrode material, in step (c), the temperature is raised to 450°C at a rate of 2°C / min in a high-temperature furnace, and kept for 5h.

[0046] Other places not mentioned are the same as in Example 1.

[0047] Example 6

[0048] A method for preparing a porous silicon negative electrode material, in step (a), 1 g of magnesium silicide, 1 g of sodium chloride and 5.6 g of aluminum chloride are weighed on an electronic balance, and the weighed medicines are poured into a clean reaction kettle.

[0049] The other unmentioned places are the same as example 1.

[0050] Example 7

[0051] A method for preparing a porous silicon negative electrode material, in step (a), 1 g of magnesium silicide, 1 g of sodium chloride and 3 g of aluminum chloride are weighed on an electronic balance, and the weighed medicines are poured into a clean reaction kettle.

[0052] The other unmentioned places are the same as example 1.

[0053] Example 8

[0054] A method for preparing a porous silicon negative electrode material, in step (a), 1 g of magnesium silicide, 1 g of sodium chloride and 2.3 g of aluminum chloride are weighed on an electronic balance, and the weighed medicines are poured into a clean reaction kettle.

[0055] The other unmentioned places are the same as example 1.

[0056] As Figure 1 shown in the scanning electron microscope (SEM) photograph of the porous silicon negative electrode material prepared in example 1, the particle size distribution of the porous silicon material is between 5 nm and 500 nm, and the particles of different sizes are beneficial to improve the tap density of the negative electrode material.

[0057] With the negative electrode material as the active material, PAA as the binder, and conductive acetylene black added, the proportion is: active material: PAA: acetylene black = 7:2:1. Add an appropriate amount of deionized water in a mortar, grind and disperse uniformly to form a slurry, then uniformly coat the slurry on a copper foil, put it into an oven to dry at 60℃ for 12h, roll and slice after drying, and prepare a circular electrode with a diameter of 12mm.

[0058] With lithium sheet as the counter electrode, polypropylene microporous membrane as the separator, and 1 mol / L LiPF6 in ethylene carbonate (EC) + dimethyl carbonate (DMC) (volume ratio 1:1) as the electrolyte, then in an argon atmosphere glove box, the metal lithium sheet as the counter electrode, Cegard2300 membrane as the separator, 1.0 mol / L LiPF6 as the solute, V(EC):V(DMC)=1:1 as the electrolyte, and the active material electrode as the working electrode, the battery components including the positive and negative electrode shells, gaskets, springs, etc. are assembled in a certain order to form a 2032 half battery.

[0059] The specific assembly process is as follows: firstly, the negative shell is placed on the workbench, 2-3 drops of electrolyte are added, then the working electrode with active material is placed on the electrolyte and soaked, then 2 drops of electrolyte are added on the working electrode to ensure complete soaking, then the separator is quickly placed on the working electrode, then 2 drops of electrolyte are added on the separator, then the lithium sheet, gasket and spring are sequentially placed, finally the positive shell is placed on top and manually compacted with tweezers, and finally the battery is sealed with a sealing machine. After the battery is prepared, it needs to be aged for more than 24 hours before electrochemical testing. The button cell is subjected to charge-discharge cycle test: the charge-discharge cut-off voltage is 0.01-1.50V, the charge-discharge current is 0.5A / g, and the charge-discharge cycle is 100 times. Figure 2 The initial capacity of the porous silicon material is 3046mAh / g, and the first coulombic efficiency is 87%.

[0060] From Figure 3 The cycle curve of the porous silicon material at a current density of 0.5A / g shows that the porous silicon material has excellent cycle performance.

[0061] The initial capacity and first coulombic efficiency of each porous silicon negative electrode material prepared in Examples 2-8 are compared, and the specific data are shown in Table 1.

[0062] Table 1 is a comparison of the performance of the porous silicon negative electrode materials prepared in each example

[0063] Initial capacity (mAh / g) First coulombic efficiency (%) Example 2 1180.95 75.05 Example 3 2258.81 78.57 Example 4 3458.67 91.02 Example 5 3548.52 89.55 Example 6 3629.31 86.34 Example 7 3274.7 88.61 Example 8 2764.69 88.17

[0064] As can be seen from Table 1, the porous silicon negative electrode material prepared by the method of the present application has excellent battery performance, with an initial capacity of at least 1000, a highest initial capacity of 3629.31mAh / g, a lowest first coulombic efficiency of 75.05%, and a highest first coulombic efficiency of 91.02%, indicating that the method has obvious advantages.

[0065] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A method for preparing a porous silicon anode material, characterized in that, Pure porous silicon and magnesium salts are obtained by reacting magnesium silicide with aluminum chloride and sodium chloride in a high-temperature molten salt environment. The particle size distribution of the porous silicon is between 5 nm and 500 nm. The preparation method includes the following steps: (a) Magnesium silicide, aluminum chloride, and sodium chloride are mixed in a certain proportion in a high-temperature reactor, an inert gas is introduced, and the temperature is raised to 250-400°C at a rate of 2°C / min, and the holding time is 5 h; wherein the mass ratio of aluminum chloride, magnesium silicide, and sodium chloride is 4:1:

1. (b) Add the mixture of silicon and magnesium salts prepared in step (a) above to deionized water, stir and wash, discard after sedimentation, and repeat the above steps until the water is clear; (c) Add hydrochloric acid to the solution at the end of step (b) above, stir for 4 h, then filter, and dry the product in a forced-air drying oven to obtain pure porous silicon anode material; wherein the volume ratio of hydrochloric acid used to the mass ratio of magnesium silicide used is 10 mL: 1 g.

2. The method for preparing a porous silicon anode material according to claim 1, characterized in that, In step (a), the inert gas is at least one of nitrogen, argon, and carbon dioxide.

3. The method for preparing a porous silicon anode material according to claim 1, characterized in that, In step (c), the temperature of the forced-air drying oven is set to 50–100°C, and the drying time is 1–24 h.

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