Preparation method and application of yttrium-doped porous silicon material

Abstract

The invention belongs to the technical field of lithium ion battery materials, and relates to a preparation method and application of an yttrium-doped porous silicon material, and the preparation method comprises the following steps: S1, preparing a silicon-yttrium alloy precursor; s2, mixing the silicon-yttrium alloy precursor with magnesium powder, and performing heat treatment; s3, nitridation reaction; and S4, carrying out acid etching. According to the YSi2 fine grain reinforced porous silicon-based material provided by the invention, a fine grain strengthening mechanism caused by grain boundary segregation in a structural material is introduced into a silicon negative electrode material, so that the intrinsic strength of the silicon material is improved, pulverization and crack propagation of the material are inhibited, and excellent cycle performance and outstanding rate capability are obtained; the invention provides a novel fine grain reinforced silicon negative electrode model, provides theoretical and experimental guidance for research and development of high-strength and high-specific-energy battery materials, solves the problems of low intrinsic strength, large volume expansion and poor conductivity of the silicon negative electrode material, and has the advantages of simple preparation process, short period, low energy consumption and no carbon, and can be produced on a large scale.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a preparation method and application of yttrium-doped porous silicon materials. Background Art

[0002] With the rapid development of industries such as portable electronic devices and electric vehicles, consumers have shown an increasing demand for the energy density of lithium-ion batteries. Silicon-based materials have an extremely high theoretical specific capacity (about 4200 mAh / g), which is much higher than the theoretical specific capacity of traditional graphite anodes (about 372 mAh / g). This means that under the same mass, silicon anodes can store more lithium ions, thereby providing a higher energy density for the battery, effectively increasing the battery's cruising range, and being of great significance for application scenarios with high requirements for cruising range such as electric vehicles. It is expected to occupy an important position in the future lithium battery market.

[0003] While pursuing high energy density, the safety and cycle stability of the battery are also crucial. Traditional silicon-based anodes will undergo severe volume expansion (up to 300%) during charge and discharge processes, which may lead to the destruction of the electrode structure, pulverization of active materials, and continuous rupture and regeneration of the solid electrolyte interface (SEI) film, thereby affecting the cycle life and safety of the battery. Therefore, it is necessary to modify silicon-based anodes to meet the requirements of practical applications.

[0004] Currently, there are mainly three ways to inhibit the expansion and pulverization of silicon anode materials: (1) nanosizing or porosifying to slow down relative volume expansion and pulverization; (2) binders to restrain expansion and repair pulverization; (3) constructing a stable "outer shell" to limit volume expansion and electrode pulverization. Although the above methods can reduce problems such as relative volume expansion / shrinkage and stress concentration during the lithium deintercalation / insertion process of silicon, and alleviate the cracking and pulverization of silicon, they cannot solve the problems of low intrinsic strength and poor conductivity of silicon anode materials. Summary of the Invention

[0005] In view of the above deficiencies in the prior art, the present invention provides a preparation method and application of yttrium-doped porous silicon materials, which solve the problems of low intrinsic strength, large volume expansion, and poor conductivity of silicon anode materials. The preparation process is simple, with a short cycle, low energy consumption, and no carbon, and can be mass-produced. The specific technical solutions are as follows:

[0006] The first object of the present invention is to provide a preparation method of yttrium-doped porous silicon materials, including the following steps:

[0007] S1: Heat-treat silicon powder and yttrium powder to obtain a silicon-yttrium alloy precursor;

[0008] S2: Mix the yttrium-silicon alloy precursor with magnesium powder and then perform heat treatment to obtain the first mixed powder; the first mixed powder is a gray-blue mixed powder of MgY and Mg2Si;

[0009] S3: Perform a nitridation reaction on the first mixed powder in a nitrogen atmosphere to obtain the second mixed powder; the first mixed powder is a mixed powder of Mg3N2, Si, and YSi2;

[0010] S4: Etch the second mixed powder in an acid to obtain a yttrium-doped porous silicon material, that is, a porous silicon material strengthened by YSi2 fine crystals.

[0011] The present invention uses silicon powder, yttrium powder, and magnesium powder as raw materials to obtain a yttrium-silicon-magnesium alloy through alloying annealing. Based on the different reaction activities of magnesium, silicon, and yttrium with nitrogen, magnesium powder will generate magnesium nitride in a nitrogen atmosphere and act as a pore-forming agent; after the magnesium nitride is etched by an acid, a porous silicon skeleton structure containing YSi2 is formed. Since the atomic radius of Y (about 180 pm) is much larger than that of Si (about 110 pm), the yttrium-silicon alloy treated by alloying annealing has a large lattice distortion energy and is prone to form YSi2 segregation at the silicon grain boundaries during the cooling process, thereby inhibiting the migration of silicon grain boundaries, playing a role in fine grain strengthening, improving the mechanical strength of the material, and alleviating the problem of expansion and pulverization of the silicon negative electrode during the lithium insertion and extraction process of the battery. At the same time, the incorporation of metallic yttrium improves the conductivity of the silicon matrix, which helps to develop the fast charging performance of the silicon negative electrode.

[0012] Silicon itself is a semiconductor material with poor conductivity. The present invention not only effectively improves the conductivity of the silicon negative electrode in terms of structural design, but also adds elements with high conductivity to silicon to improve the conductivity. The doping of metal elements can introduce extra electrons or change the electronic structure of silicon, improve the conductivity of the material, make the transmission of electrons in the electrode smoother, and is beneficial to improving the rate performance and charge-discharge efficiency of the battery; metal elements can also enhance the structural stability. They can form alloy phases with silicon, change the silicon grain size, and improve the mechanical properties of the silicon matrix, thereby inhibiting the volume expansion and pulverization of silicon during the charge-discharge process and improving the cycle life of the electrode.

[0013] Furthermore, the particle sizes of the silicon powder and the yttrium powder are 1 - 3 μm.

[0014] The present invention adopts a method of designing a micron-porous structure for the silicon matrix to make up for the shortcomings of the silicon negative electrode. The porous micron structure can provide an internal space for the expansion of silicon, improve the structural stability of the material, and the micron size ensures the tap density of the material, which can reduce the volume expansion and improve the initial efficiency to a certain extent.

[0015] Further, in the step S1, the mass ratio of the silicon powder to the yttrium powder is (70-99):(1-30); preferably, the mass ratio of the silicon powder to the yttrium powder is (75-97):(3-25); more preferably, the mass ratio of the silicon powder to the yttrium powder is (85-95):(5-15); most preferably, the mass ratio of the silicon powder to the yttrium powder is 95:5.

[0016] In the present invention, the selection of the mass ratio of the silicon powder to the yttrium powder is crucial. If the content of non-active yttrium increases, the comprehensive performance of the porous silicon anode material will decline. On the contrary, if the yttrium content is too low, it is difficult to effectively utilize the fine grain strengthening effect to improve the intrinsic strength of the silicon matrix, and the increase in conductivity is limited.

[0017] Further, the heat treatment in the step S1 is carried out in an inert atmosphere furnace, and the temperature is raised to 450-700 °C at a rate of 1-25 °C / min, held for 3-20 h, taken out after cooling, so that silicon and yttrium undergo an alloying reaction to form a silicon-yttrium alloy precursor of YSi2 and Si. Preferably, the heating rate is 1-10 °C / min, more preferably 3-5 °C / min; preferably, the holding temperature is 500-700 °C, more preferably 600-650 °C; preferably, the holding time is 5-10 h, more preferably 5-8 h.

[0018] Further, in the step S2, the mass ratio of the silicon-yttrium alloy precursor to the magnesium powder is 1:1.7-3; preferably 1:1.75-3; more preferably 1:1.75-2; most preferably 1:1.75.

[0019] Further, the heat treatment in the step S2 is carried out in an inert atmosphere tube furnace, and the temperature is raised to 450-700 °C at a rate of 1-20 °C / min, held for 3-20 h, taken out after cooling, to obtain MgY and Mg2Si blue-gray powders; preferably, the heating rate is 1-10 °C / min, more preferably 3-5 °C / min; preferably, the holding temperature is 500-700 °C, more preferably 550-600 °C; preferably, the holding time is 5-10 h, more preferably 5-8 h.

[0020] The selection of the temperature and time of the heat treatment in the step S2 of the present invention is crucial. If the temperature is too low or the holding time is insufficient, the alloying reaction cannot proceed or the reaction is incomplete, and uniform MgY and Mg2Si powders cannot be obtained, and thus a porous silicon anode material strengthened by YSi2 fine grains cannot be obtained. However, if the temperature is too high or the holding time is too long, magnesium is likely to evaporate, resulting in the unnecessary consumption of magnesium and the remaining silicon powder that cannot participate in the alloying reaction.

[0021] Further, in the steps S1 and S2, the inert atmosphere is preferably argon.

[0022] Furthermore, the nitridation reaction in step S3 is carried out in a tubular furnace into which ammonia gas is introduced. The nitrogen gas flow rate is 100 - 200 L / min. The tubular furnace is heated at a heating rate of 1 - 10 °C / min to 650 - 850 °C and held for 3 - 20 h. After the holding is completed, it is cooled with the furnace to obtain a mixed powder of Mg3N2, Si, and YSi2. Preferably, the heating rate is 5 - 10 °C; the holding temperature is 750 - 780 °C; the holding time is 6 - 8 h.

[0023] The present invention puts forward requirements for controlling the temperature and holding time of the nitridation reaction in step S3. If the holding temperature is too high, silicon nitride of the ceramic phase will be formed on the surface of the silicon material. If the holding temperature is too low, ammonia gas cannot be decomposed, making it difficult to carry out the nitridation reaction. If the reaction holding time is too short, the nitridation reaction is insufficient and Mg2Si cannot be converted into Mg3N2. If the reaction time is too long, it will cause unnecessary waste of ammonia gas.

[0024] Furthermore, in step S4, the acid is 1M hydrochloric acid and the etching time is 2 - 6 h. Further, after the etched product is washed with deionized water until neutral and then vacuum freeze-dried, a porous silicon negative electrode material with YSi2 fine grain strengthening can be obtained.

[0025] The second object of the present invention is to provide the application of the yttrium-doped porous silicon material prepared by the preparation method of the above yttrium-doped porous silicon material in the preparation of lithium-ion battery materials.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. The present invention provides a porous silicon-based material with YSi2 fine grain strengthening, introducing the fine grain strengthening mechanism caused by grain boundary segregation in structural materials into the silicon negative electrode material, improving the intrinsic strength of the silicon material, inhibiting material pulverization and crack propagation, and proposing a new model for fine grain strengthening of silicon negative electrodes, providing theoretical and experimental guidance for the research and development of high-strength and high specific energy battery materials.

[0028] 2. Different from the traditional method of modifying silicon-based negative electrode materials from the outside to the inside, in the present invention, due to the large lattice distortion energy caused by the atomic radius difference between Y and Si, YSi2 nanoparticles segregate at the grain boundaries of the porous silicon, inhibiting the growth of silicon grains, synergistically improving the intrinsic strength and bulk phase conductivity of silicon, effectively inhibiting the microcracks generated during the lithium deintercalation / insertion process of silicon, and obtaining excellent cycle performance and outstanding rate performance.

[0029] 3. The preparation process of the porous silicon-based negative electrode material with YSi2 fine grain strengthening provided by the present invention is simple, the raw material cost is low and environmentally friendly, effectively improving the structural stability of the porous silicon, bringing excellent comprehensive lithium storage performance, and having good industrialization prospects. Description of the Drawings

[0030] Figure 1 XRD pattern of the phase change during the preparation of Example 1 of the present invention;

[0031] Figure 2 Comparison chart of the full width at half maximum (FWHM) of the p-YSi2-Si material and the p-Si material prepared in Example 1 of the present invention;

[0032] Figure 3 Comparison chart of the grain size of the p-YSi2-Si material and the p-Si material prepared in Example 1 of the present invention;

[0033] Figure 4 SEM image of the p-YSi2-Si material prepared in Example 1 of the present invention;

[0034] Figure 5 First charge-discharge curve of the p-YSi2-Si material prepared in Example 1 of the present invention;

[0035] Figure 6 Electrochemical rate performance chart of the p-YSi2-Si material prepared in Example 1 of the present invention;

[0036] Figure 7 The p-YSi2-Si material prepared in Example 1 of the present invention at 1Ag -1 Electrochemical cycling performance chart at a current density of;

[0037] Figure 8 Specific capacity-voltage diagram of Comparative Example 7 of the present invention;

[0038] Figure 9 Diffusion coefficient diagram during discharge of Comparative Example 7 of the present invention. Specific embodiments

[0039] The principles and features of the present invention are described below in conjunction with examples. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0040] Example 1

[0041] A preparation method of a yttrium-doped porous silicon material, comprising the following steps:

[0042] (1) Put silicon powder and yttrium powder into a sand mill respectively, grind at a speed of 1500 r / min for 1 h to obtain fine powder, and then place the powder obtained by grinding in a centrifuge and centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle size. The particle size of the silicon powder and the yttrium powder is 1-3 μm;

[0043] (2) Take 47.5 g of silicon powder obtained by sanding in step (1) and 2.5 g of yttrium powder (the mass ratio of silicon particles to yttrium particles is 95:5). After mixing evenly, place them in an inert atmosphere tube furnace and heat them to 650 °C at a heating rate of 5 °C / min and hold for 6 h to obtain a silicon-yttrium alloy precursor. As shown by Figure 1 the XRD pattern of

[0044] (3) Mix the silicon-yttrium alloy precursor obtained in step (2) and magnesium powder in a mass ratio of 1:1.75, put them into an alloy can, and then place the alloy can in an inert atmosphere tube furnace. Heat it to 550 °C at a rate of 5 °C / min and hold for 6 h. After cooling, take it out. As can be seen from Figure 1 the XRD pattern of

[0045] (4) Place the product obtained in step (3) in a quartz crucible and carry out the nitridation reaction of MgY and Mg2Si in a tube furnace with ammonia gas introduced. The ammonia gas flow rate is 100 L / min. The tube furnace is heated to 750 °C at a heating rate of 5 °C / min and held for 6 h. After the holding is completed, it is cooled with the furnace. As can be seen from Figure 1 the XRD pattern of

[0046] (5) Put the product obtained in step (4) into 1 M hydrochloric acid and etch for 4 h. Then wash it with deionized water until neutral, and after vacuum freeze-drying, a porous silicon anode material strengthened by YSi2 fine grains (denoted as p-YSi2-Si) can be obtained, as shown in Figure 2 ;

[0047] Figure 3 is a comparison chart of the grain sizes of the p-YSi2-Si material and the p-Si material prepared in Example 1 of the present invention. It can be seen that the grain size of the p-YSi2-Si material is smaller than that of the p-Si material, indicating that the incorporation of yttrium metal effectively reduces the grain size of the porous silicon material, thereby achieving the effect of fine grain strengthening. Figure 4 is the SEM image of the p-YSi2-Si material prepared in Example 1 of the present invention. It can be seen that it has a porous morphology similar to an ant nest, indicating that it has a similar morphology to p-Si, can alleviate the volume expansion during charge and discharge, and improve the battery cycle life.

[0048] Perform performance tests on p-YSi2-Si. Figure 5 is the first charge-discharge curve of p-YSi2-Si. Its first discharge is 2783.3 mAh / g, and the first Coulomb efficiency reaches 82.41%; Figure 6 is for p-YSi2-Si at 0.1 - 5 A g -1The rate performance at a current density of, when the current density reaches 5 Ag -1 The specific capacity of 674.2 mAh / g can still be maintained; Figure 7 For p-YSi2-Si, the specific capacity of 1446.4 mAh / g can be maintained after cycling 200 times at a current density of 1 A / g; The above shows that the p-YSi2-Si material prepared in Example 1 has excellent cycling performance and outstanding rate performance.

[0049] Comparative Example 1

[0050] A preparation method of a yttrium-doped porous silicon material, comprising the following steps:

[0051] (1) Put silicon powder and yttrium powder into a sand mill respectively, sand mill at a speed of 1500 r / min for 1 h to obtain fine powder, and then put the powder obtained by sand milling into a centrifuge, centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle size, and the particle size of the silicon powder and yttrium powder is 1-3 μm;

[0052] (2) Take 47.5 g of silicon powder and 2.5 g of yttrium powder obtained in step (1) (the mass ratio of silicon particles to yttrium particles is 95:5), mix them evenly and place them in an inert atmosphere tube furnace, and heat them to 650 °C at a heating rate of 5 °C / min and keep them warm for 6 h to obtain a silicon-yttrium alloy precursor;

[0053] (3) Mix the silicon-yttrium alloy precursor obtained in step (2) with magnesium powder according to a mass ratio of 1:3, put it into an alloy can, and then place the alloy can in an inert atmosphere tube furnace, heat it to 550 °C at a rate of 5 °C / min and keep it warm for 6 h, take it out after cooling, and obtain MgY, Mg2Si and the remaining Mg powder through alloying reaction;

[0054] (4) Place the product obtained in step (3) in a quartz crucible, and carry out the nitridation reaction of MgY and Mg2Si in a tube furnace with ammonia gas introduced, the ammonia gas flow rate is 100 L / min, the tube furnace is heated to 750 °C at a heating rate of 5 °C / min and kept warm for 6 h, and after the heat preservation is completed, it is cooled with the furnace, and Mg3N2, Si and YSi2 are obtained through the nitridation reaction;

[0055] (5) Put the product obtained in step (4) into 1 M hydrochloric acid, etch for 4 h, then wash it with deionized water until neutral, and vacuum freeze-dry to obtain a porous silicon anode material strengthened by YSi2 fine crystals;

[0056] The electrochemical performance of the porous silicon material prepared in this example is similar to that of Example 1. Adding an excessive amount of magnesium powder in step (3) will cause unnecessary waste, but it has basically no effect on the final performance.

[0057] Comparative Example 2

[0058] A preparation method of yttrium-doped porous silicon material, comprising the following steps:

[0059] (1) Put silicon powder and yttrium powder into a sand mill respectively, grind at a speed of 1500 r / min for 1 h to obtain fine powder, and then place the powder obtained by grinding in a centrifuge, centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle size, and the particle size of the silicon powder and yttrium powder is 1-3 μm;

[0060] (2) Take 47.5 g of silicon powder and 2.5 g of yttrium powder obtained in step (1) (the mass ratio of silicon particles to yttrium particles is 95:5), mix them evenly and place them in an inert atmosphere tube furnace, and heat up to 450 °C at a heating rate of 5 °C / min and hold for 6 h;

[0061] (3) Mix the product obtained in step (2) with magnesium powder according to a mass ratio of 1:1.75, put it into an alloy can, and then place the alloy can in an inert atmosphere tube furnace, heat up to 550 °C at a rate of 5 °C / min and hold for 6 h, and take it out after cooling;

[0062] (4) Place the product obtained in step (3) in a quartz crucible, and carry out a nitriding reaction in a tube furnace with ammonia gas introduced, the ammonia gas flow rate is 100 L / min, and the tube furnace is heated up to 750 °C at a heating rate of 5 °C / min and held for 6 h, and after the holding is completed, it is cooled with the furnace;

[0063] (5) Put the product obtained in step (4) into 1 M hydrochloric acid, etch for 4 h, then wash with deionized water until neutral, and after vacuum freeze-drying, a porous silicon negative electrode material strengthened by YSi2 crystals cannot be obtained.

[0064] This is because the reaction temperature in step (2) is too low, Y and Si cannot be fully alloyed, and YSi2 cannot be effectively generated, resulting in no precipitation of YSi2 at the silicon grain boundaries.

[0065] Comparative Example 3

[0066] A preparation method of yttrium-doped porous silicon material, comprising the following steps:

[0067] (1) Put silicon powder and yttrium powder into a sand mill respectively, grind at a speed of 1500 r / min for 1 h to obtain fine powder, and then place the powder obtained by grinding in a centrifuge, centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle size, and the particle size of the silicon powder and yttrium powder is 1-3 μm;

[0068] (2) Take 47.5 g of the silicon powder obtained in step (1) and 2.5 g of yttrium powder (the mass ratio of silicon particles to yttrium particles is 95:5). After mixing evenly, place them in an inert atmosphere tube furnace and heat them to 650 °C at a heating rate of 5 °C / min and hold for 2 h.

[0069] (3) Mix the product obtained in step (2) with magnesium powder according to a mass ratio of 1:1.75, put it into an alloy can, then place the alloy can in an inert atmosphere tube furnace, heat it to 550 °C at a rate of 5 °C / min and hold for 6 h, and take it out after cooling.

[0070] (4) Place the product obtained in step (3) in a quartz crucible, and carry out the nitridation reaction of MgY and Mg2Si in a tube furnace with ammonia gas introduced. The ammonia gas flow rate is 100 L / min, and the tube furnace is heated to 750 °C at a heating rate of 5 °C / min and held for 6 h. After the holding is completed, it is cooled with the furnace.

[0071] (5) Put the product obtained in step (4) into 1 M hydrochloric acid and etch for 4 h, then wash it with deionized water until neutral, and after vacuum freeze-drying, the porous silicon anode material strengthened by YSi2 fine crystals cannot be obtained.

[0072] This is because the reaction time in step (2) is too short, and Y and Si cannot be fully alloyed, resulting in the failure of YSi2 to precipitate at the silicon grain boundaries.

[0073] Comparative Example 4

[0074] A preparation method of a yttrium-doped porous silicon material, comprising the following steps:

[0075] (1) Put the silicon powder and yttrium powder into a sand mill respectively, sand mill at a rotation speed of 1500 r / min for 1 h to obtain fine powders, and then place the powders obtained by sand milling in a centrifuge and centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle sizes. The particle sizes of the silicon powder and yttrium powder are 1-3 μm.

[0076] (2) Take 47.5 g of the silicon powder obtained in step (1) and 2.5 g of yttrium powder (the mass ratio of silicon particles to yttrium particles is 95:5). After mixing evenly, place them in an inert atmosphere tube furnace and heat them to 650 °C at a heating rate of 5 °C / min and hold for 6 h to obtain a silicon-yttrium alloy precursor.

[0077] (3) Mix the silicon-yttrium alloy precursor obtained in step (2) with magnesium powder according to a mass ratio of 1:1.75, put it into an alloy can, then place the alloy can in an inert atmosphere tube furnace, heat it to 450 °C at a rate of 5 °C / min and hold for 6 h, and take it out after cooling. The alloying reaction does not occur, and MgY and Mg2Si powders cannot be obtained.

[0078] (4) Place the product obtained in step (3) in a quartz crucible and carry out a nitridation reaction in a tubular furnace with ammonia gas introduced. The ammonia gas flow rate is 100 L / min. The tubular furnace is heated to 750 °C at a heating rate of 5 °C / min and held for 6 h, and then cooled with the furnace after the holding ends;

[0079] (5) Place the product obtained in step (4) in 1 M hydrochloric acid and etch for 4 h, then wash with deionized water until neutral, and after vacuum freeze-drying, a porous silicon anode material strengthened by YSi2 fine crystals cannot be obtained.

[0080] This is because the reaction temperature in step (3) is too low, and Mg2Si that fails to form leads to uneven structure and the formation of granular silicon.

[0081] Comparative Example 5

[0082] A preparation method of a yttrium-doped porous silicon material, comprising the following steps:

[0083] (1) Put silicon powder and yttrium powder into a sand mill respectively, grind at a rotation speed of 1500 r / min for 1 h to obtain fine powders, and then place the powders obtained by grinding in a centrifuge and centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle sizes. The particle sizes of the silicon powder and the yttrium powder are 1 - 3 μm;

[0084] (2) Take 47.5 g of the silicon powder and 2.5 g of the yttrium powder obtained in step (1) (the mass ratio of silicon particles to yttrium particles is 95:5), mix them evenly and place them in an inert atmosphere tubular furnace, heat to 650 °C at a heating rate of 5 °C / min and hold for 6 h to obtain a silicon-yttrium alloy precursor;

[0085] (3) Mix the silicon-yttrium alloy precursor obtained in step (2) and magnesium powder according to a mass ratio of 1:1.75, put them into an alloy can, and then place the alloy can in an inert atmosphere tubular furnace, heat to 550 °C at a rate of 5 °C / min and hold for 6 h, take it out after cooling to obtain MgY and Mg2Si powders;

[0086] (4) Place the product obtained in step (3) in a quartz crucible and carry out a nitridation reaction of MgY and Mg2Si in a tubular furnace with ammonia gas introduced. The ammonia gas flow rate is 100 L / min. The tubular furnace is heated to 650 °C at a heating rate of 5 °C / min and held for 6 h, and then cooled with the furnace after the holding ends. Due to the too low nitridation reaction temperature, incomplete nitridation of Mg element fails to generate Mg3N2;

[0087] (5) Place the product obtained in step (4) in 1 M hydrochloric acid and etch for 4 h, then wash with deionized water until neutral, and after vacuum freeze-drying, a porous silicon anode material strengthened by YSi2 fine crystals cannot be obtained.

[0088] This is because the reaction temperature in step (4) was too low to form Mg3N2, resulting in the failure to produce a continuous template and the formed silicon having no porous morphology.

[0089] Comparative Example 6

[0090] A preparation method of a yttrium-doped porous silicon material includes the following steps:

[0091] (1) Put silicon powder and yttrium powder into a sand mill respectively, grind at a speed of 1500 r / min for 1 h to obtain fine powder, and then place the powder obtained by grinding in a centrifuge and centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle size. The particle size of the silicon powder and yttrium powder is 1 - 3 μm;

[0092] (2) Take 47.5 g of silicon powder and 2.5 g of yttrium powder obtained in step (1) (the mass ratio of silicon particles to yttrium particles is 95:5), mix them evenly and place them in an inert atmosphere tube furnace, heat up to 650 °C at a heating rate of 5 °C / min and keep warm for 6 h to obtain a silicon-yttrium alloy precursor;

[0093] (3) Mix the silicon-yttrium alloy precursor obtained in step (2) and magnesium powder according to a mass ratio of 1:1.75, put them into an alloy can, and then place the alloy can in an inert atmosphere tube furnace, heat up to 550 °C at a rate of 5 °C / min and keep warm for 6 h, take it out after cooling to obtain MgY and Mg2Si powders;

[0094] (4) Place the product obtained in step (3) in a quartz crucible, carry out the nitridation reaction of MgY and Mg2Si in a tube furnace with ammonia gas introduced. The ammonia gas flow rate is 100 L / min, and the tube furnace is heated up to 750 °C at a heating rate of 5 °C / min and kept warm for 2 h. After the heat preservation is completed, it is cooled with the furnace. Due to the too short nitridation reaction time, the nitridation reaction is incomplete and the Mg element cannot be completely converted into Mg3N2;

[0095] (5) Put the product obtained in step (4) into 1 M hydrochloric acid, etch for 4 h, then wash it with deionized water until neutral, and a porous silicon negative electrode material strengthened by YSi2 fine crystals cannot be obtained after vacuum freeze-drying.

[0096] This is because the reaction time in step (4) was too short to completely form Mg3N2, resulting in the failure to produce a continuous template and the formed silicon having no porous morphology.

[0097] Comparative Example 7

[0098] A preparation method of a yttrium-doped porous silicon material includes the following steps:

[0099] (1) Put silicon powder and yttrium powder into a sand mill respectively, grind at a speed of 1500 r / min for 1 h to obtain fine powder, and then place the powder obtained by grinding into a centrifuge, centrifuge at a speed of 100 r / min for 5 min to obtain silicon powder and yttrium powder with uniform particle size. The particle size of the silicon powder and yttrium powder is 1 - 3 μm;

[0100] (2) Take 49 g of silicon powder and 1 g of yttrium powder (mass ratio of silicon particles to yttrium particles is 98:2) obtained in step (1), mix them evenly and place them in an inert atmosphere tube furnace, heat up to 650 °C at a heating rate of 5 °C / min and keep it warm for 6 h to obtain a silicon-yttrium alloy precursor;

[0101] (3) Mix the silicon-yttrium alloy precursor obtained in step (2) with magnesium powder according to a mass ratio of 1:1.75, put it into an alloy can, and then place the alloy can in an inert atmosphere tube furnace, heat up to 550 °C at a rate of 5 °C / min and keep it warm for 6 h, take it out after cooling, and obtain MgY and Mg2Si powders after alloying reaction;

[0102] (4) Place the product obtained in step (3) in a quartz crucible, and carry out the nitridation reaction of MgY and Mg2Si in a tube furnace with ammonia gas introduced. The ammonia gas flow rate is 100 L / min, and the tube furnace is heated up to 750 °C at a heating rate of 5 °C / min and kept warm for 6 h. After the heat preservation is over, it is cooled with the furnace. The nitridation reaction obtains Mg3N2, Si and YSi2;

[0103] (5) Put the product obtained in step (4) into 1 M hydrochloric acid, etch for 4 h, then wash it with deionized water until neutral, and after vacuum freeze-drying, a porous silicon anode material strengthened by YSi2 fine crystals can be obtained.

[0104] Due to the decrease in the addition amount of yttrium, the initial specific capacity of this material has increased to some extent, but the conductivity has decreased, as Figure 8 and Figure 9 and the precipitated YSi2 is less, and it is difficult to produce the effect of fine crystal strengthening on the silicon skeleton, thus inhibiting volume expansion and structural pulverization.

[0105] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of yttrium-doped porous silicon material, characterized in that, It includes the following steps: S1: Heat-treat silicon powder and yttrium powder to obtain a silicon-yttrium alloy precursor; S2: Mix the silicon-yttrium alloy precursor with magnesium powder and then conduct heat treatment to obtain a first mixed powder; S3: Conduct a nitridation reaction on the first mixed powder in a nitrogen atmosphere to obtain a second mixed powder; S4: Etch the second mixed powder in an acid to obtain a yttrium-doped porous silicon material.

2. The preparation method of the yttrium-doped porous silicon material according to claim 1, wherein The particle sizes of the silicon powder and the yttrium powder are 1 - 3 μm.

3. The preparation method of the yttrium-doped porous silicon material according to claim 1, wherein, In step S1, the mass ratio of the silicon powder to the yttrium powder is (70 - 99):(1 - 30).

4. The preparation method of the yttrium-doped porous silicon material according to claim 1, characterized in that, In step S1, the heat treatment is carried out in an inert atmosphere furnace, heating up to 450 - 700 °C at a rate of 1 - 25 °C / min and holding for 3 - 20 h.

5. The preparation method of the yttrium-doped porous silicon material according to claim 1, wherein, In step S2, the mass ratio of the silicon-yttrium alloy precursor to the magnesium powder is 1:1.7 - 3.

6. The preparation method of the yttrium-doped porous silicon material according to claim 1, characterized in that, In step S2, the heat treatment is carried out in an inert atmosphere tube furnace, heating up to 450 - 700 °C at a rate of 1 - 20 °C / min and holding for 3 - 20 h.

7. The preparation method of the yttrium-doped porous silicon material according to claim 1, characterized in that, In step S3, the nitridation reaction is carried out in a tube furnace with ammonia introduced, the nitrogen gas flow rate is 100 - 200 L / min, the tube furnace is heated up to 650 - 850 °C at a heating rate of 1 - 10 °C / min and held for 3 - 20 h, and after the holding is completed, it is cooled with the furnace.

8. The preparation method of the yttrium-doped porous silicon material according to claim 1, characterized in that, In step S4, the acid is 1M hydrochloric acid, and the etching time is 2 - 6 h.

9. The method for preparing the yttrium-doped porous silicon material according to claim 4 or 6, characterized in that, In steps S1 and S2, the inert atmosphere is argon.

10. Application of a yttrium-doped porous silicon material prepared by the preparation method of a yttrium-doped porous silicon material according to any one of claims 1 - 9 in the preparation of lithium-ion battery materials.

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