Lithium-silicon alloy powder based on regulating the direction of a thermal trigger reaction and electrode preparation method

Abstract

Based on the regulation of the direction of the heat triggered reaction, lithium-silicon alloy powder and electrode preparation method, 1) put the lithium source on the edge of the silicon powder on the hot plate, ensure physical contact; 2) by limiting the thickness of the silicon powder, the temperature distribution of the reaction field is regulated, and the direction of the heat triggered lithium-silicon spontaneous reaction is limited, Li 4.1 Si is synthesized; 3) DOL is used as a solvent, PEO is used as a binder, and SP is used as a conductive agent to prepare an electrode containing Li 4.1 Si. The hot plate method is suitable for nano-sized to micro-sized silicon powder, and the lithium-silicon chain reaction can be triggered above 180℃, and the production scale can be expanded with the expansion of the size of the hot plate. After the reaction is completed, there is no excess lithium in the product, and lithium-silicon alloy powder can be quickly obtained. DOL and PEO retain the electrochemical activity of Li 4.1 Si, suitable for preparing electrodes. The preparation process of the invention is simple and practical, low in cost, and easy to realize large-scale commercial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silicon-based negative electrode materials, in particular to lithium-silicon alloy powder based on regulating the direction of heat-triggered reaction and electrode preparation method. BACKGROUND

[0002] With the popularity and application of high-capacity and high-power electrical terminals, high-specific-energy electrodes have been widely researched and industrially attempted. Among them, silicon-based high-specific-energy electrodes are at the forefront of industrialization, but they still have limitations such as low initial efficiency and difficulty in matching with positive electrodes.

[0003] Therefore, pre-lithiation and lithium-rich research on silicon-based materials has become a highly competitive strategy. Through direct contact with lithium source or direct addition of lithium compound, researchers have made many breakthrough attempts. The preparation of lithium-silicon alloy usually adopts methods such as resistance heating and high-energy ball milling. For example, by heating the lithium source crucible, adding nano-silicon powder and stirring to mix, lithium-silicon alloy of kilograms is prepared; or by using n-hexane as a lubricant, lithium powder and silicon powder are added to a high-energy ball milling tank to prepare lithium-silicon alloy. Ideally, the thermal reaction of lithium source and silicon powder in a molar ratio will completely generate lithium-silicon alloy powder, and the reaction speed is extremely fast and only controlled by physical contact and reaction temperature. However, the direction of heat-triggered lithium-silicon reaction is disordered. In the mass production of lithium-silicon alloy, due to the poor thermal conductivity of silicon powder, the lithium source in a molar ratio has problems such as easy solidification in the low-temperature zone (<180℃) and excess in the high-temperature zone. They not only stick the generated lithium-silicon alloy to form super-large particle agglomerates, but also consume limited lithium sources, leading to excess silicon powder, hindering the rapid and batch production of lithium-silicon alloy powder. At the same time, the high reactivity of lithium-silicon alloy makes the traditional N-methyl pyrrolidone (NMP) solvent incompatible, greatly limiting the preparation of lithium-silicon alloy electrodes. Therefore, developing a method for rapid and batch production of lithium-silicon alloy powder and its electrode has important significance for the performance improvement and commercial application of silicon negative electrodes. SUMMARY

[0004] The purpose of the present application is to solve the above-mentioned problems in the prior art, to provide lithium-silicon alloy powder based on regulating the direction of heat-triggered reaction and electrode preparation method, to regulate the direction of heat-triggered reaction, and to rapidly and batch produce lithium-silicon alloy powder and synthesize high-initial-efficiency electrodes.

[0005] In the heating process of the hot plate method, the temperature gradient is negatively related to the thickness of the reaction silicon powder. By controlling the thickness of the laid silicon powder, a temperature field with a minimum local temperature >180℃ is constructed in the reaction field, the direction of the spontaneous reaction of lithium-silicon is controlled to trigger on the plane, and the molar ratio (Li 4.1The lithium source under the Si) appears low-temperature solidification and local excess problems, reaches the purpose of uniform lithiation, complete lithiation under the theoretical condition, and further rapidly and batch prepares the lithium silicon alloy powder. Meanwhile, mixed with the non-polar solvent DOL, the binder PEO and the like, after coating and drying, the Li 4.1 Si alloy is obtained.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0007] The preparation method of the lithium silicon alloy powder based on the regulation of the direction of the heat triggered reaction comprises the following steps:

[0008] 1) forming physical contact: in the glove box with the water oxygen content not higher than 0.1 ppm, the silicon powder is uniformly paved on the hot plate, the lithium source is placed at the edge of the silicon powder, and the physical contact is formed;

[0009] 2) reaction field temperature regulation: the temperature distribution of the reaction field is regulated by limiting the paving thickness of the silicon powder, after the hot plate is heated, the heat triggers the spontaneous reaction of lithium silicon, and the Li 4.1 Si alloy is obtained.

[0010] The hot plate is selected from an aluminum-based or iron-based heating platform.

[0011] In the present application, the temperature of the reaction field is 180-600 DEG C.

[0012] The particle size range of the silicon powder is 30 nm-100 microns.

[0013] The paving thickness of the silicon powder is h≤3.5 cm.

[0014] The lithium source is selected from commercial lithium sheet, lithium ribbon or lithium ingot, and the lithium source can be placed at one or several places at the edge of the silicon powder.

[0015] A preparation method of an electrode: in the glove box with the water oxygen content not higher than 0.1 ppm, using dioxolane (DOL) as a solvent, polyethylene oxide (PEO) as a binder, and high-conductivity material as a conductive agent, a electrode containing active substances is prepared by beating and coating; the active substances at least include the Li 4.1 Si alloy, which can be pure Li 4.1 Si powder, or the Li 4.1 Si powder and graphite / silicon powder.

[0016] The high-conductivity material includes at least one of SP and CNTs.

[0017] According to the mass ratio, the active substance: PEO: conductive agent = (0.6-0.95): (0.05-0.15): (0.05-0.25).

[0018] Calculated by mass, the solid-liquid ratio is 0.1 to 0.7.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] 1. In the present invention, the heat-triggered spontaneous reaction of lithium silicon is fast, and lithium silicon alloy powders at the gram level can be quickly prepared in batches, and the scale of preparation can be expanded as the size of the hot plate increases.

[0021] 2. In the present invention, thanks to the regulation of the reaction direction, the lithium source in the reaction product is fully utilized, there is no excess lithium, and no subsequent crushing treatment is required, and lithium-silicon alloy powder can be directly obtained.

[0022] 3. DOL is easily soluble in PEO and can maintain Li 4.1 The electrochemical activity of Si and the slurry are volatile at room temperature, which is beneficial for the rapid preparation of Li-containing 4.1 Si electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic top view of the hot plate method used in the present invention to prepare lithium silicon alloy;

[0024] Figure 2 This is a schematic diagram of the main view of the hot plate method used in the present invention to prepare lithium silicon alloy;

[0025] Figure 3 is the XRD pattern of the lithium-silicon alloy prepared in Example 1 of the present invention;

[0026] Figure 4 This is a SEM image of the lithium-silicon alloy prepared in Example 1 of the present invention;

[0027] Figure 5 This is a graph showing the first charge and discharge curve of the electrode prepared in Example 1 of the present invention;

[0028] Figure 6 TEM image of the lithium-silicon alloy prepared in Example 2 of the present invention;

[0029] Figure 7 This is an SEM image of the lithium-silicon alloy prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0031] Example 1

[0032] 1) Forming physical contact: In a glove box with water and oxygen content ≤0.1 ppm, 20 g of silicon powder (1 μm) was evenly laid in the middle of a hot plate of 10 x 10 cm, forming a silicon powder area of 7 x 7 cm, h = 2.1 cm. 20.30 g of lithium sheet was placed at the edge of the silicon powder and formed physical contact, as shown in Figures 1-2 .

[0033] 2) Reaction field temperature regulation: The front and side of the laid silicon powder were recorded by a handheld thermal imager. After the hot plate was heated to 350 °C, the thermal contact triggered the spontaneous reaction of lithium and silicon, and the reaction ended after 1 min. The reaction product area was 7.5 x 7.9 cm, h = 2.4 cm, and the uppermost layer of lithium-silicon alloy powder was 185.7 °C at this time.

[0034] Referring to Figure 3 , the product was Li 4.1 Si by XRD test. Referring to Figure 4 , the SEM images before and after the reaction showed that the lithium-silicon alloy appeared spheroidization phenomenon, and the particle size distribution after expansion was uniform.

[0035] 3) Electrode preparation: In a glove box with water and oxygen content ≤0.1 ppm, 0.5 g of Li 4.1 Si was taken as the active material, 50 mg of PEO was taken as the binder, 50 mg of SP was taken as the conductive agent, 5 mL of DOL was taken as the solvent, and the mixture was evenly mixed and then loaded into a transparent container and sealed., magnetic stirring for 12 h; then the slurry after stirring was scraped on a copper foil, and after 30 min, an electrode sheet was obtained.

[0036] The obtained electrode was assembled into a half-cell with lithium sheet, and a blue light tester was used to test the first charge and then discharge at a current density of 0.2 A / g, and the ICE was calculated. As shown in Figure 5 , the ICE of the battery was 99.78%. It showed that the electrode prepared by this method had excellent electrochemical activity.

[0037] Example 2

[0038] 1) Forming physical contact: In a glove box with water and oxygen content ≤0.1 ppm, 20 g of silicon powder (50 nm) was evenly laid in the middle of a hot plate of 10 x 10 cm, forming a silicon powder area of 7 x 7 cm, h = 2.9 cm. 20.30 g of lithium sheet was placed at the edge of the silicon powder and formed physical contact.

[0039] 2) Reaction field temperature regulation: The front and side of the silicon powder were recorded by a hand-held thermal imager. After the hot plate was heated to 500°C, the thermal contact triggered the spontaneous reaction of lithium and silicon, and the reaction ended after 53 s. The reaction product area was about 7.4 x 8.5 cm, h = 3.5 cm, and the uppermost temperature of the lithium-silicon alloy powder was 181.2°C at this time. The product was Li 4.1 Si by XRD test. Figure 6 The TEM image of the lithium-silicon alloy after the reaction is shown, and the particle size expands to about 100 nm.

[0040] 3) Electrode preparation: In the glove box with water and oxygen content less than 0.1 ppm, 0.15 g of Li 4.1 Si and 0.35 g of silicon powder (50 nm) were taken as active materials, 50 mg of PEO was taken as a binder, 100 mg of SP was taken as a conductive agent, 5 mL of DOL was taken as a solvent, and the mixture was mixed uniformly and then loaded into a transparent container and sealed. The slurry after stirring was scraped on a copper foil, and the electrode sheet was obtained after 30 min of static state.

[0041] The obtained electrode was assembled into a half-cell with lithium pieces, and a blue light tester was used to test the first discharge and then charge at a current density of 0.2 A / g. The first coulombic efficiency (ICE) of the battery was 96.3%.

[0042] Example 3

[0043] 1) Forming physical contact: In the glove box with water and oxygen content less than 0.1 ppm, 5 g of silicon powder (200 nm) was uniformly laid in the middle of a 5 x 5 cm hot plate, forming a silicon powder area of 3 x 3.4 cm, h = 0.9 cm. 5.10 g of lithium pieces were placed at the edge of the silicon powder and formed physical contact.

[0044] 2) Reaction field temperature regulation: The front and side of the silicon powder were recorded by a hand-held thermal imager. After the hot plate was heated to 250°C, the thermal contact triggered the spontaneous reaction of lithium and silicon, and the reaction ended after 1.5 min. The reaction product area was about 3.1 x 3.6 cm, h = 1.2 cm, and the uppermost temperature of the lithium-silicon alloy powder was 186°C at this time. The product was Li 4.1 Si by XRD test. Figure 7 The SEM image of the lithium-silicon alloy after the reaction is shown, and the expanded particle size is about 1 μm.

[0045] 3) Electrode preparation: In the glove box with water and oxygen content less than 0.1 ppm, 0.05 g of Li 4.1Si as active material, 50 mg of PEO as binder, 50 mg of SP as conductive agent, 5 mL of DOL as solvent, mix uniformly, then put into a transparent container and seal, magnetic stirring for 12 h; then the slurry after stirring is completed is scraped on a copper foil, and an electrode sheet is obtained after standing for 30 min.

[0046] The obtained electrode is assembled into a half battery with lithium sheet, and a first discharge and then charge test is carried out at a current density of 0.2 A / g by using a blue light tester, and the first coulombic efficiency (ICE) is calculated. The ICE of the battery is 86.6%.

[0047] Example 4

[0048] 1) Form physical contact: In a glove box with water and oxygen content ≤0.1 ppm, 10 g of silicon powder (3 μm) is uniformly laid in the middle of a 10×10 cm hot plate to form a silicon powder area of 8×9.2 cm, h=0.5 cm. 10.20 g of lithium sheet is placed at the edge of the silicon powder and forms physical contact.

[0049] 2) Reaction field temperature regulation: The front and side of the laid silicon powder are recorded by using a handheld thermal imager. After the hot plate is heated to 300℃, the thermal contact triggers the spontaneous reaction of lithium silicon, and the reaction ends after 47 s. The reaction product area is about 8×9.3 cm, h=0.6 cm, and the uppermost layer temperature of the lithium silicon alloy powder is about 206℃ at this time. The product is Li 4.1 Si by XRD test.

[0050] 3) Electrode preparation: In a glove box with water and oxygen content ≤0.1 ppm, 0.5 g of Li 4.1 Si as active material, 50 mg of PEO as binder, 50 mg of SP as conductive agent, 5 mL of DOL as solvent, mix uniformly, then put into a transparent container and seal, magnetic stirring for 12 h; then the slurry after stirring is completed is scraped on a copper foil, and an electrode sheet is obtained after standing for 30 min.

[0051] The obtained electrode is assembled into a half battery with lithium sheet, and a first discharge and then charge test is carried out at a current density of 0.13 A / g by using a blue light tester, and the first coulombic efficiency (ICE) is calculated. The ICE of the battery is 99.81%.

[0052] Example 5

[0053] 1) Form physical contact: In a glove box with water and oxygen content ≤0.1 ppm, 3 g of silicon powder (10 μm) is uniformly laid in the middle of a 10×10 cm hot plate to form a silicon powder area of 1.5×1.5 cm, h=1.2 cm. 3.05 g of lithium sheet is placed at the edge of the silicon powder and forms physical contact.

[0054] 2) Reaction field temperature regulation: The front and side of the silicon powder were recorded by a hand-held thermal imager. After the hot plate was heated to 450℃, the thermal contact triggered the spontaneous reaction of lithium and silicon, and the reaction ended after 55S. The reaction product area was about 1.6*1.8cm, h=1.3cm, and the uppermost temperature of the lithium-silicon alloy powder was about 256.4℃. The product was Li 4.1 Si by XRD test.

[0055] 3) Electrode preparation: In a glove box with water and oxygen contents less than 0.1ppm, 0.4g of Li 4.1 Si was taken as the active material, 20mg of PEO was taken as the binder, 40mg of SP was taken as the conductive agent, 3.6mL of DOL was taken as the solvent, and the mixture was uniformly mixed, then was loaded into a transparent container and sealed, and was magnetically stirred for 12h; then the slurry after stirring was scraped on a copper foil, and the electrode sheet was obtained after standing for 30min.

[0056] The obtained electrode was assembled into a half battery together with a lithium sheet, and a blue light tester was used to perform first charge and then discharge test at a current density of 0.1A / g, and the initial coulombic efficiency (ICE) was calculated, and the ICE of the battery was 101.2%.

[0057] The hot plate method of the application is suitable for nano-sized to micro-sized silicon powder, and the lithium-silicon chain reaction can be triggered above 180℃, and the preparation scale can be expanded with the expansion of the size of the hot plate. After the reaction is completed, there is no excess lithium in the product, and the lithium-silicon alloy powder consistent with the particle size distribution of the silicon powder can be quickly obtained. DOL and PEO retain the electrochemical activity of Li 4.1 Si, and are suitable for preparing electrodes. The preparation process of the application is simple and practical, low in cost, and easy to realize large-scale commercial production.

Claims

1. A method for preparing lithium-silicon alloy powder based on regulating the direction of thermally triggered reaction, characterized in that The following steps are involved: 1) Physical contact: In a glove box with a water and oxygen content no higher than 0.1 ppm, spread the silicon powder evenly on a hot plate. The hot plate temperature is provided by a heating platform and ranges from 180°C to 600°C. The lithium source is placed at the edge of the silicon powder to establish physical contact. 2) Reaction field temperature control: The temperature distribution of the reaction field is controlled by limiting the thickness of the silicon powder. The thickness of the silicon powder is h ≤ 3.5 cm. After the hot plate is heated, the heat triggers the spontaneous reaction of lithium silicon, and Li 4.1 Si alloy.

2. The method for preparing lithium-silicon alloy powder based on regulating the direction of thermally triggered reaction according to claim 1, characterized in that: The hot plate is an aluminum-based or iron-based heating platform.

3. The method for preparing lithium-silicon alloy powder by regulating the direction of a thermally triggered reaction according to claim 1, wherein: The particle size of the silicon powder ranges from 30 nm to 100 μm.

4. The method for preparing lithium-silicon alloy powder based on regulating the direction of thermally triggered reaction according to claim 1, characterized in that: The lithium source is selected from commercial lithium sheets, lithium strips or lithium ingots, and the lithium source is placed at one or several locations on the edge of the silicon powder.

5. A method for preparing an electrode, characterized in that: In a glove box with water and oxygen content not higher than 0.1 ppm, DOL is used as a solvent, PEO is used as a binder, and a highly conductive material is used as a conductive agent. The highly conductive material includes at least one of SP and CNTs. An electrode containing an active material is prepared by beating and coating. The active material includes at least Li 4.1 Si alloy, the Li 4.1 The Si alloy is the Li Si alloy prepared by the method for preparing lithium silicon alloy powder based on regulating the direction of thermally triggered reaction according to any one of claims 1 to 4. 4.1 Si alloy.

6. The method for preparing an electrode according to claim 5, wherein: The active material also includes one or more of graphite or silicon powder.

7. The method for preparing an electrode according to claim 5, wherein: Calculated by mass ratio, the active material: PEO: conductive agent = (0.6~0.95): (0.05~0.15): (0.05~0.25).

8. The method for preparing an electrode according to claim 5, wherein: Calculated by mass, the solid-liquid ratio is 0.1~0.7.

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