Method for realizing silicon size regulation and battery performance stability by taking high initial current as electrochemical initiator

Abstract

The invention belongs to the technical field of electrochemistry, and particularly relates to a method for realizing silicon size regulation and battery performance stability by taking high initial current as an electrochemical initiator. The preparation method comprises the following steps: mixing porphyrin COF coated nano silicon, a multi-walled carbon nanotube and sodium alginate, adding deionized water to prepare slurry, coating a copper foil with the slurry, drying, slicing to prepare a silicon negative pole piece, assembling a silicon / / LI battery, standing, and carrying out electrochemical cycle treatment to realize regulation and control of the silicon size in the silicon negative pole piece. On the premise of taking the porphyrin COF as a protection framework, the original high current is taken as an initiator, the volume expansion effect of silicon is utilized, in-situ regulation and control of the silicon size are realized, the stability of an electrode material is finally improved, and the high-performance silicon negative electrode is obtained.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a method for achieving silicon size control and stable battery performance by using high initial current as an electrochemical initiator. Background Technology

[0002] In the field of energy storage, nano-silicon possesses extremely high theoretical capacity, but its severe volume expansion and electrode collapse greatly limit its application. Current research largely relies on passively introducing conductive protective layers to mitigate expansion, failing to fundamentally solve the expansion problem. Furthermore, the issue of unstable solid electrolyte interphase (SEI) films forming on the silicon surface remains unresolved.

[0003] Therefore, it is necessary to start from the inside of silicon, turn the passive into the active, and take advantage of its expansion characteristics. High current can be used as its intrinsic initiator to achieve reasonable control of silicon size, fundamentally solve the problem of silicon volume expansion, and thus effectively improve the stability and cycle life of electrode materials. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a method for achieving silicon size control and stable battery performance using a high initial current as an electrochemical initiator. This invention utilizes the high initial current density applied during battery cycling to accelerate the volume expansion of silicon particles as a favorable intrinsic condition for in-situ silicon size control. In the presence of a porphyrin COF protective layer, in-situ silicon size control is achieved by changing the initial current density during cycling.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for achieving silicon size control and battery performance stability through electrochemical cycling, comprising the following steps: (1) Take porphyrin COF-coated nano-silicon, multi-walled carbon nanotubes and sodium alginate and mix them; (2) Add deionized water, ball mill, and obtain slurry; (3) The slurry is coated onto copper foil, dried, and sliced ​​to obtain a silicon negative electrode sheet; (4) The silicon negative electrode, polypropylene separator, electrolyte and lithium sheet are assembled in a glove box under argon atmosphere to obtain silicon / / Li battery; (5) After standing, the silicon / / Li cell is subjected to an initial current density of not less than 100 mA g. -1 Electrochemical cycling treatment was used to obtain silicon anode materials with controlled silicon size.

[0006] Further, in step (1), the mass ratio of the porphyrin COF-coated nano-silicon, multi-walled carbon nanotubes and sodium alginate is 7:2:1 to 7:1:2.

[0007] Further, in step (2), the ball milling rate is 400~600 r / min, and the ball milling time is 12~24 h.

[0008] Furthermore, in step (3), the drying temperature is 60~80 ℃ and the drying time is 12~24 h.

[0009] Furthermore, in step (3), the thickness of the copper foil is 12~20 μm.

[0010] Furthermore, in step (3), the slice refers to a round slice with a diameter of 14-16 mm.

[0011] Furthermore, in step (4), the electrolyte is composed of LiPF6, ethylene carbonate and diethyl carbonate.

[0012] Furthermore, the concentration of LiPF6 in the electrolyte is 1~1.2 mol / L.

[0013] Furthermore, in step (4), the size of the lithium sheet is 12.5~15.8 mm.

[0014] Furthermore, in step (4), the pressure of battery assembly is 100~200 MPa.

[0015] Furthermore, in step (5), the settling time is 12~24 h.

[0016] Further, in step (5), the initial current density is 100~1000 mA g. -1 .

[0017] Furthermore, in step (5), the number of electrochemical cycles is 5 to 40.

[0018] A second aspect of the present invention provides a silicon anode material with silicon size control prepared by the above-described method.

[0019] A third aspect of the present invention provides an application of the silicon anode material with controlled silicon size described above in a lithium-ion battery, wherein the silicon anode material with controlled silicon size is used as the anode material of the lithium-ion battery.

[0020] Compared with the prior art, the beneficial effects of the present invention are: Through the above method, the present invention successfully achieved in-situ size control of silicon particles. By changing the initial current density and utilizing its intrinsic expansion properties, silicon particles of different sizes after electrochemical cycling, as well as the phase transition of silicon and the phase transition of silicon-lithium alloy after electrochemical cycling, were obtained, and finally, long-cycle application of ultra-high current silicon anode was realized.

[0021] This invention explores the lithium storage mechanism of silicon under different initial currents, as well as the phase transitions of silicon and lithium silicide during this process. It also focuses on the size changes of silicon during electrochemical cycling, investigating the relationship between initial current, silicon-lithium alloy, and silicon size, and their combined impact on battery cycle performance. This technology has significant potential in the energy storage field and will contribute to the industrial application of silicon anodes.

[0022] Specifically, the present invention has the following advantages: (1) The present invention rationally transforms the harmful volume expansion of silicon under high current into an initiator that actively reduces the size, thereby achieving in-situ control of silicon size and eliminating the cumbersome steps and costs of external silicon design.

[0023] (2) This invention demonstrates different lithium storage mechanisms and phase transitions through electrodes controlled by different initial current densities. The dQ / dV curves and XRD patterns reveal different silicon phase distributions and lithiated silicon distributions in the cycled electrodes. The silicon size induced by different initial current densities was visualized and controlled. TEM images showed a significant reduction in silicon size after high initial current density control, and the electrode at ultra-high current density exhibited ultra-stable cycling performance (20000 mA g). -1 At current density, the capacity retention is 71.9%. Attached Figure Description

[0024] Figure 1 The diagram shows the lithium storage mechanism of a silicon anode after cycling at high and low initial current densities.

[0025] Figure 2 For silicon anodes that have undergone high / low initial current density cycling at 1000 mA g -1 Cyclic performance curves at current density.

[0026] Figure 3 The figures show the dQ / dV curves of the silicon anode at high and low initial current densities, respectively.

[0027] Figure 4 TEM images of the silicon anode before cycling, after 5 / 40 cycles at high initial current density, and after 5 / 40 cycles at low initial current density.

[0028] Figure 5 The images show the XRD patterns of the silicon anode before cycling, after 5 / 40 cycles at high initial current density, after 5 cycles at low initial current density, after 5 cycles at low initial current density, and after 35 cycles at subsequent high current density.

[0029] Figure 6The cycling performance curve of the silicon anode at ultra-high current density (20000 mA g) after high initial current density cycling. -1 (current density). Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0032] The preparation method of porphyrin COF-coated nano-silicon is as follows: A methanol solution of PEI is added to a methanol solution of nano-silicon, and then dried at high temperature to obtain PEI-modified nano-silicon Si-PEI; then, Si-PEI and PVP are dispersed in o-dichlorobenzene / n-butanol, and COF monomer and glacial acetic acid are added. After maintaining at 110-130 °C for 70-80 h, the mixture is washed, dried, and ground to obtain Si@COF; finally, Si@COF and cobalt acetate tetrahydrate are dispersed in methanol, reacted at room temperature, and then washed, dried, and ground to obtain Si@COF-Co, which is the porphyrin COF-coated nano-silicon used in this patent. (For specific synthesis examples, see patent: CN120109177B) Example 1: A method for achieving silicon size control and stable battery performance through electrochemical cycling (1000 mAg) -1 (Initial current density, 5 cycles) (1) Take porphyrin COF-coated nano-silicon, multi-walled carbon nanotubes and sodium alginate and mix them in a mass ratio of 7:2:1; (2) Take 100 mg of the above mixture, add deionized water, transfer it to a ball milling jar, and ball mill at a rate of 400 r / min for 12 h to obtain a slurry; (3) The above-obtained slurry is coated on a 12 μm thick copper foil and dried under vacuum at 60°C for 12 h. The dried copper foil is then cut into round pieces with a size of 14 mm to obtain a silicon negative electrode sheet. (4) The silicon negative electrode, polypropylene separator, 80 μL electrolyte (1 M LiPF6 ethylene carbonate and diethyl carbonate solution), and 15.8 mm lithium sheet were assembled in an argon atmosphere glove box at a pressure of 100 MPa to obtain a silicon / / Li battery. (5) After standing for 24 h, the silicon / / Li cell was subjected to an initial current density of 1000 mA g. -1 The silicon anode material with controlled silicon size was obtained by electrochemical cycling treatment with 5 cycles.

[0033] Example 2: A method for achieving silicon size control and battery performance stabilization through electrochemical cycling. The difference between this embodiment and embodiment 1 is that in step (1), porphyrin COF-coated nano-silicon, multi-walled carbon nanotubes and sodium alginate are mixed in a mass ratio of 7:1:2, while the rest is the same as in embodiment 1.

[0034] Example 3: A method for achieving silicon size control and battery performance stabilization through electrochemical cycling. The difference between this embodiment and embodiment 1 is that in step (4), the volume of the electrolyte is 100 uL, while the rest is the same as in embodiment 1.

[0035] Example 4: A method for achieving silicon size control and stable battery performance through electrochemical cycling (1000 mAg) -1 (Initial current density, 40 cycles) The difference between this embodiment and Embodiment 1 is that, in step (5), the silicon / / Li cell is subjected to an initial current density of 1000 mA g. -1 The electrochemical cycling treatment was performed, with 40 cycles, and all other aspects remained the same as in Example 1.

[0036] Example 5: A method for achieving silicon size control and battery performance stabilization through electrochemical cycling (100 mAg) -1 (Initial current density, 5 cycles) The difference between this embodiment and Embodiment 1 is that, in step (5), the silicon / / Li cell is subjected to an initial current density of 100 mA g. -1 The electrochemical cycle treatment was performed, with 5 cycles, and all other aspects remained the same as in Example 1.

[0037] Example 6: A method for achieving silicon size control and battery performance stabilization through electrochemical cycling (100 mAg) -1 (Initial current density, 40 cycles) The difference between this embodiment and Embodiment 1 is that, in step (5), the silicon / / Li cell is subjected to an initial current density of 100 mA g. -1 The electrochemical cycling treatment was performed, with 40 cycles, and all other aspects remained the same as in Example 1.

[0038] Example 7: A method for achieving silicon size control and stable battery performance through electrochemical cycling (100 mAg) -1Initial current density: 5 cycles + 1000 mA g -1 (Initial current density, 35 cycles) The difference between this embodiment and Embodiment 1 is that, in step (5), the silicon / / Li cell is subjected to an initial current density of 100 mA g. -1 The electrochemical cycle was performed for 5 cycles, followed by a current density of 1000 mA g. -1 The electrochemical cycle treatment was performed for 35 cycles, and other aspects remained the same as in Example 1.

[0039] Comparative Example 1: No electrochemical cycling treatment The difference between this comparative example and Example 1 is that the electrochemical cycling treatment in step (5) is not performed, while the rest is the same as Example 1.

[0040] Test case Figure 1 The diagrams show the lithium storage mechanism of the silicon anode after cycling at high initial current density in Example 1 and after cycling at low initial current density in Example 5, revealing the phase transition process of silicon / lithium silicon alloys under different initial current densities, as well as the change in silicon size.

[0041] The silicon / / Li cells that underwent high / low initial current density cycling treatments in Examples 1 and 5, respectively, were subjected to a current density of 1000 mA g. -1 Cyclic performance tests were conducted under the specified conditions, and the resulting cyclic performance curves are shown below. Figure 2 As shown, the silicon / / Li battery in Example 1, after undergoing high initial current density cycling treatment, exhibits better cycling stability, which preliminarily verifies... Figure 1 The mechanism in it.

[0042] The dQ / dV curves of the silicon anode in Examples 1 and 5 at high and low initial current densities are shown below. Figure 3 As shown; the XRD patterns of the silicon anode before cycling (Comparative Example 1), after 5 cycles at high initial current density (Example 1), after 40 cycles at high initial current density (Example 4), after 5 cycles at low initial current density (Example 5), and after 5 cycles at low initial current density followed by 35 cycles at high current density (Example 7) are as follows. Figure 5 As shown, through Figure 3 The dQ / dV curve and Figure 5 The XRD patterns revealed different silicon phase distributions and lithiated silicon distributions in the cycled electrodes. TEM images of the silicon anodes before cycling (Comparative Example 1), after 5 cycles at high initial current density (Example 1), after 40 cycles at high initial current density (Example 4), after 5 cycles at low initial current density (Example 5), and after 40 cycles at low initial current density (Example 6) are shown below. Figure 4As shown, it can be seen that the silicon size can be visualized and controlled after different initial current densities, and the silicon size was significantly reduced after high current density control.

[0043] The silicon / / Li battery that underwent high initial current density cycling treatment in Example 1 was subjected to a current density of 20000 mA g. -1 Cyclic performance tests were conducted under the specified conditions, and the cyclic performance curves were obtained as follows: Figure 6 As shown, the silicon / / Li battery exhibits ultra-stable cycling performance at ultra-high current densities after high initial current density cycling treatment. In the presence of the porphyrin COF protective layer, the high initial current density, acting as an initiator, significantly improves the silicon size and cycling performance at ultra-high current densities.

[0044] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for achieving silicon size control and stable battery performance through electrochemical cycling, characterized in that, Includes the following steps: (1) Take porphyrin COF-coated nano-silicon, multi-walled carbon nanotubes and sodium alginate and mix them; (2) Add deionized water, ball mill, and obtain slurry; (3) The slurry is coated onto copper foil, dried, and sliced ​​to obtain a silicon negative electrode sheet; (4) The silicon negative electrode, polypropylene separator, electrolyte and lithium sheet are assembled in a glove box under argon atmosphere to obtain silicon / / Li battery; (5) After standing, the silicon / / Li cell is subjected to an initial current density of not less than 100 mA g. -1 Electrochemical cycling treatment was used to obtain silicon anode materials with controlled silicon size.

2. The method for achieving silicon size control and battery performance stability through electrochemical cycling treatment according to claim 1, characterized in that, In step (1), the mass ratio of the porphyrin COF-coated nano-silicon, multi-walled carbon nanotubes and sodium alginate is 7:2:1 to 7:1:

2.

3. The method for achieving silicon size control and battery performance stability through electrochemical cycling treatment according to claim 1, characterized in that, In step (2), the ball milling rate is 400~600 r / min, and the ball milling time is 12~24h.

4. The method for achieving silicon size control and battery performance stability through electrochemical cycling according to claim 1, characterized in that, In step (3), the drying temperature is 60~80 ℃ and the drying time is 12~24 h.

5. The method for achieving silicon size control and battery performance stability through electrochemical cycling treatment according to claim 1, characterized in that, In step (4), the electrolyte is composed of LiPF6, ethylene carbonate and diethyl carbonate.

6. The method for achieving silicon size control and battery performance stability through electrochemical cycling according to claim 5, characterized in that, The concentration of LiPF6 in the electrolyte is 1~1.2 mol / L.

7. The method for achieving silicon size control and battery performance stability through electrochemical cycling according to claim 1, characterized in that, In step (5), the initial current density is 100~1000 mA g. -1 .

8. The method for achieving silicon size control and battery performance stability through electrochemical cycling according to claim 1, characterized in that, In step (5), the number of electrochemical cycles is 5 to 40.

9. A silicon anode material with controlled silicon size prepared by the method according to any one of claims 1-8.

10. The application of a silicon anode material with silicon size controlled as described in claim 9 in a lithium-ion battery, characterized in that, The silicon anode material with controlled silicon size is used as the anode material for lithium-ion batteries.

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