Modified silicon electrodes, their preparation, and applications in solid-state batteries

Abstract

The present invention belongs to the field of solid-state batteries and specifically relates to a method for preparing a modified silicon anode. Nano-silicon material is placed in a modifying liquid A for a first modification treatment to obtain modified silicon particles; the modifying liquid A is a solution containing polypropylene carbonate; the modified silicon particles and a binder are slurried and then composited onto a negative electrode current collector to form a silicon anode layer on the negative electrode current collector to obtain a silicon anode; the silicon anode layer of the silicon anode is composited with a modifying liquid B, and then a second modification treatment is performed under light irradiation to obtain the modified silicon anode; the modifying liquid B comprises Formula 1#imgabs0#, Formula 2#imgabs1#, Formula 3#imgabs2#, and a lithium salt. The present invention also includes a silicon anode obtained by the preparation method and its application. The silicon anode described in the present invention can effectively improve its performance in a solid-state battery system, and can improve its long cycle life and performance in a solid-state battery system.

Description

Technical Field

[0001] The present invention belongs to the field of solid electrode negative electrode preparation, and in particular relates to a new silicon electrode for long-life solid batteries. Background Art

[0002] Solid-state batteries use solid electrolytes and have the potential for high energy density, long life, fast charging capabilities, and safety. Compared to traditional lithium-ion batteries, solid-state batteries use solid electrolytes instead of liquid electrolytes, which can significantly reduce the risk of leakage and combustion, and improve battery stability and safety. In addition, solid-state batteries perform better in low-temperature environments and are more adaptable to temperature changes. These characteristics make solid-state batteries have broad application prospects in fields such as electric vehicles, wearable devices, portable electronics, and large-scale energy storage systems. With in-depth research and technological advancements, solid-state batteries are expected to become an important component of next-generation energy storage technology.

[0003] In order to realize the performance potential of solid-state batteries, new positive and negative electrode materials need to be matched. The graphite negative electrode material used in traditional lithium-ion batteries has approached its theoretical capacity limit, so finding new negative electrode materials has become the key to the advancement of battery technology. Silicon, as a negative electrode material, has received widespread attention because of its higher theoretical specific capacity than graphite (about 3579mAh / g, more than ten times that of graphite). The combination of silicon negative electrode and solid electrolyte is not only expected to solve the volume expansion problem of silicon negative electrode, but also may achieve a significant improvement in battery performance, opening up a new path for the development of next-generation battery technology. Therefore, the research on silicon negative electrode of solid-state batteries not only has important academic value, but also has huge application potential.

[0004] Current issues with silicon anodes in solid-state batteries primarily include volume expansion, short cycle life, and poor interfacial stability. Silicon undergoes significant volume changes during charge and discharge, which can damage the electrode structure and degrade battery performance. Furthermore, interfacial reactions between the silicon anode and the solid electrolyte can increase interfacial impedance, impacting battery cycling stability. These issues require innovations in materials engineering and battery design to address.

[0005] With technological advancements, the prior art has also disclosed some improved silicon anode solid-state battery technologies. For example, Chinese patent publication CN116417587A discloses a silicon anode material for an all-solid-state lithium-ion battery, its preparation method, and application. The all-solid-state silicon anode material for a lithium-ion battery comprises: a micron silicon material body, a nano-silicon material coated on the surface of the micron silicon material body, and a polymer binder bonded between the micron silicon material body and the nano-silicon material. Another example is Chinese patent publication CN117080390A, which discloses a method for preparing a silicon anode material coated with a solid electrolyte layer. The method comprises the following steps: placing lithium carbonate and an organic polymer monomer in an inert solvent for a solvothermal reaction, wherein the organic polymer monomer undergoes a ring-opening reaction to produce a mixture A containing an oligoether polymer; dissolving an organic solid electrolyte and a lithium salt in the organic solvent to obtain a solution B; and mixing the mixture A, solution B, and silicon anode particles until uniformly mixed and stirred, followed by spray drying to obtain a silicon anode material coated with a solid electrolyte layer.

[0006] Although existing technologies can improve the performance of silicon negative electrodes in solid-state electrolytes to a certain extent, it is still difficult to effectively solve their expansion problems in solid-state battery systems, and it is still difficult to adapt to the long-term stable cycle and structural stability requirements of solid-state batteries in a wide temperature range. Summary of the Invention

[0007] In order to solve the problem that the huge volume expansion of silicon negative electrode causes electrode structure destruction and separation from the electrolyte causing performance degradation when used in solid-state batteries, the present invention provides a preparation method of modified silicon electrode, aiming to improve its adaptability to solid-state batteries, and further improve the electrochemical properties of the assembled solid-state battery, such as long cycle and wide temperature range.

[0008] The second purpose of the present invention is to provide a modified silicon electrode obtained by the preparation method and its application in solid-state batteries.

[0009] The third object of the present invention is to provide a solid-state battery comprising the modified silicon negative electrode.

[0010] Due to its large expansion and pulverization and low conductivity, silicon anodes are difficult to adapt to the long cycle and ultra-wide temperature range application requirements of solid-state batteries. To address this problem, the present invention has conducted in-depth research and provides the following improvement solutions:

[0011] A method for preparing a modified silicon negative electrode comprises placing a nano-silicon material in a modification solution A for a first modification treatment to obtain modified silicon particles; the modification solution A is a solution containing polypropylene carbonate;

[0012] The modified silicon particles and the binder are slurried and then composited on the negative electrode current collector to form a silicon negative electrode layer on the negative electrode current collector to obtain a silicon negative electrode;

[0013] Compounding the modification solution B on the silicon negative electrode layer of the silicon negative electrode, and then performing a second modification treatment under light irradiation to obtain the modified silicon negative electrode;

[0014] The modified solution B comprises formula 1, formula 2, formula 3 and lithium salt;

[0015]

[0016] Said R1 and R2 are independently H or alkyl;

[0017] Said R3 is an alkyl group or a substituted alkyl group;

[0018] The R4 is a hydroxyalkyl group or a hydroxy-substituted aryl group;

[0019] Ar1 and Ar2 are independently aryl or substituted aryl, and R is alkyl, alkoxy or aryl;

[0020] The substituents in the substituted alkyl and substituted aryl groups include at least one of phenyl, ether, ester and hydroxyl groups.

[0021] The present invention innovatively uses modification liquid A to perform the first stage modification on nano-silicon in advance, and then uses modification liquid B to perform the second stage modification after it is formed into a silicon electrode. In this way, based on the chemical bridging and physicochemical modification characteristics between the first stage modification and the second stage modification, the adaptability of the modified silicon negative electrode to solid-state batteries can be improved, which helps to improve the structural stability of the prepared modified silicon negative electrode in the solid-state battery, improve the interface effect, and thus help to significantly improve the electrochemical performance of the solid-state battery, especially help to improve its long-range cycle and wide temperature range stability.

[0022] In the present invention, the D50 of the nano-silicon material is 50-200 nm.

[0023] In the present invention, the solvent in the modified liquid A is a solvent that can dissolve the polypropylene carbonate, such as acetone. There is no particular requirement for the content of the polypropylene carbonate in the modified liquid A.

[0024] Preferably, the weight ratio of the nano-silicon material to polypropylene carbonate is 100:0.5-2.

[0025] The present invention can prepare a silicon negative electrode from the modified silicon material based on conventional means.

[0026] For example, the modified silicon material can be dispersed into a slurry using a solvent, and then coated on a conventional negative electrode current collector (such as copper foil), and then dried to obtain the silicon negative electrode.

[0027] The binder includes at least one of PVDF, CMC, SBR and PAA.

[0028] Preferably, the weight ratio of the modified silicon particles to the binder is 80-98:1-5.

[0029] Preferably, a conductive agent is further added to the slurry, wherein the weight ratio of the modified silicon particles to the conductive agent is 80 to 98:1 to 10. The conductive agent can be a component well known in the industry, for example, a carbon-based conductive agent such as conductive carbon black.

[0030] In the present invention, on the basis of the first stage modification, a second stage modification is further carried out. In this way, based on the physicochemical reaction between the two stages modification, the adaptability of the prepared silicon negative electrode in the solid-state battery can be improved, and its long-term stability can be improved.

[0031] In the present invention, the formula 1 is formula 1a;

[0032]

[0033] Formula 2 is Formula 2a;

[0034]

[0035] In formula 3, the aryl group is a phenyl group or an alkyl-substituted phenyl group;

[0036] More preferably, the formula 3 is a compound of formula 3a;

[0037]

[0038] In formula 3a, R is ethoxy or phenyl;

[0039] Preferably, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), and lithium bis(fluorosulfonyl)imide.

[0040] In the present invention, in the modified solution B, the mass ratio of Formula 1, Formula 2, Formula 3 and lithium salt is 60-80:15-35:1-5:10-30; preferably 70-75:20-25:3-4:15-20.

[0041] In the present invention, the modified solution B is compounded on the silicon negative electrode layer of the silicon negative electrode by means of blade coating or spin coating;

[0042] Preferably, the wavelength of the light irradiation is 200-300 nm.

[0043] Preferably, the power of the light irradiation is 500-5000W, and further can be 900-1100W.

[0044] Preferably, the light irradiation time is 5 to 30 minutes, and further can be 10 to 20 minutes.

[0045] In the present invention, ultrasound assistance is performed simultaneously during the light irradiation process. Research in the present invention shows that light irradiation with the preferred ultrasound assistance helps to further optimize the surface structure and the bridging effect of the layers, which helps to further enhance the long-term cycling performance of the prepared silicon anode in the solid-state battery system.

[0046] Preferably, the frequency of ultrasound is 50-80 kHz, and the power is 3.5-8.5 w / cm2.

[0047] The present invention also provides a modified silicon negative electrode prepared by the preparation method.

[0048] The present invention also provides an application of the modified silicon negative electrode prepared by the preparation method in the preparation of a solid-state battery.

[0049] The present invention also provides a solid-state battery, which comprises a modified silicon negative electrode prepared by the preparation method of the present invention.

[0050] Beneficial effects

[0051] The present invention is innovatively based on the combined operation of the first-stage modification, the second-stage modification and the modified components, so that synergy can be achieved. Based on the physicochemical characteristics of the second-stage modification and the chemical reaction between the two-stage modification, the adaptability of the prepared silicon negative electrode in the solid-state battery can be enhanced, thereby improving its long-range cycle stability in the solid-state battery system, and achieving good operation of the battery in a wide temperature range of -35°C to 75°C. DETAILED DESCRIPTION

[0052] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited thereto.

[0053] In the present invention, the raw materials are all common commercial raw materials known in the battery field. For example, the molecular weight of the polypropylene carbonate can be 30,000 to 60,000.

[0054] Example 1

[0055] Step 1: Dissolve polypropylene carbonate in acetone solution, then stir with nano-silicon (D50 is 105±5nm), the mass ratio of polypropylene carbonate to nano-silicon is 1:100, and after stirring evenly, evaporate the acetone at 60°C to obtain a modified nano-silicon.

[0056] Step 2: A section of modified nano-silicon is used as an electrode active material, mixed with a binder (CMC) and a conductive agent to form a slurry, and then coated on a copper foil and dried to obtain a nano-silicon electrode, wherein the weight ratio of the section of modified nano-silicon: CMC: SBR: Super C is 90:3.5:3:3.5.

[0057] Step 3: Formula 1a, Formula 2a, Formula 3aa (Formula 3a where R is phenyl), and lithium bis(trifluoromethanesulfonyl)imide are mixed evenly in a mass ratio of 70:20:3:20 to form a modified liquid B. Then, using the nano-silicon electrode as the substrate, the precursor liquid is poured on the surface and flattened with a scraper. Then, it is irradiated with a 1000±50W ultraviolet lamp at a wavelength of 200-300nm for 10-15 minutes to obtain the desired long-life solid battery silicon electrode.

[0058] Example 2

[0059] Compared with Example 1, the only difference is that in step 1, the mass ratio of polypropylene carbonate to nano-silicon is 1.5:100; in step 2, the weight ratio of modified nano-silicon: CMC: SBR: Super C is 90:4:3:3. Other operations and parameters are the same as in Example 1.

[0060] Example 3

[0061] Compared with Example 1, the only difference is that the mass ratio of Formula 1a, Formula 2a, Formula 3aa (Formula 3a where R is phenyl) and lithium bis(trifluoromethanesulfonyl)imide is 75:25:4:15. Other operations and parameters are the same as those in Example 1.

[0062] Example 4

[0063] Compared with Example 1, the only difference is that the irradiation process in step 3 is carried out under an ultrasonic field, wherein the ultrasonic frequency is 60-70 kHz and the power is 5-5.5 W / cm2. Other operations and parameters are the same as those in Example 1.

[0064] Comparative Example 1

[0065] Compared with Example 1, the only difference is that step 1 is not performed, and the nano-silicon is directly subjected to step 2 and subsequent treatments. Other operations and parameters are the same as those in Example 1.

[0066] Comparative Example 2

[0067] Compared with Example 1, the only difference is that in step 1, polyacrylic acid is used to replace the polypropylene carbonate, and other operations and parameters are the same as those in Example 1.

[0068] Comparative Example 3

[0069] Compared with Example 1, the only difference is that in step 3, Formula 2a is not added, and other operations and parameters are the same as Example 1.

[0070] Comparative Example 4

[0071] Compared with Example 1, the only difference is that in step 3, the comparative compound ) replaces the formula 2a, and other operations and parameters are the same as those in Example 1.

[0072] Comparative Example 5

[0073] Compared with Example 1, the only difference is that the modifying liquid B of step 3 is added in step 1, and in step 3, the modifying liquid B is no longer added, that is, in step 1, the modifying liquid B of step 3 is added to the modifying liquid A, and the treatment of step 1 is performed, followed by the treatment of step 2, and then the light treatment of step 3. The other operations and parameters are the same as those in Example 1.

[0074] The prepared silicon anode electrode and lithium sheet were directly assembled into a solid-state half-cell (with the silicon layer of the silicon anode facing the lithium sheet anode). The half-cell was then subjected to charge and discharge tests at 25°C, -35°C, and 75°C, a test rate of 0.2C, and a voltage range of 0.05-1.5V.

[0075] Test results table 1:

[0076] Table 1

[0077]

[0078] As shown in Table 1, the combined effects of the first and second stage modifications and the modified components can achieve synergy. Based on the physicochemical characteristics of the second stage modification and the chemical interaction between the two stages, the adaptability of the prepared silicon anode in solid-state batteries can be enhanced, thereby improving its long-term cycling stability in solid-state battery systems and achieving good battery operation over a wide temperature range of -35°C to 75°C. Ultrasonic-assisted light irradiation, in particular, helps further optimize the interface structure and enhance the long-term cycling and ultra-low and ultra-high temperature adaptability of the prepared silicon anode.

Claims

1. A method for preparing a modified silicon negative electrode, characterized in that: The nano-silicon material is placed in a modification liquid A for a first modification treatment to obtain modified silicon particles; the modification liquid A is a solution containing polypropylene carbonate; The modified silicon particles and the binder are slurried and then composited on the negative electrode current collector to form a silicon negative electrode layer on the negative electrode current collector to obtain a silicon negative electrode; Compounding the modification solution B on the silicon negative electrode layer of the silicon negative electrode, and then performing a second modification treatment under light irradiation to obtain the modified silicon negative electrode; The modified solution B comprises formula 1, formula 2, formula 3 and lithium salt; Formula 1 Formula 2; Formula 3; In Formula 3, R is an ethoxy group or a phenyl group.

2. The method for preparing a modified silicon negative electrode according to claim 1, wherein The D50 of the nano-silicon material is 50-200 nm.

3. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The weight ratio of the nano-silicon material to the polypropylene carbonate is 100:0.5-2.

4. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The binder includes at least one of PVDF, CMC, SBR and PAA.

5. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The weight ratio of the modified silicon particles to the binder is 80-98:1-5.

6. The method for preparing a modified silicon negative electrode according to claim 1, wherein: A conductive agent is further added to the slurry, wherein the weight ratio of the modified silicon particles to the conductive agent is 80-98:1-10.

7. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), and lithium bis(fluorosulfonyl)imide.

8. The method for preparing a modified silicon negative electrode according to claim 1, wherein: In the modified solution B, the mass ratio of the formula 1, formula 2, formula 3 and lithium salt is 60-80:15-35:1-5:10-30.

9. The method for preparing a modified silicon negative electrode according to claim 8, wherein: In the modified solution B, the mass ratio of Formula 1, Formula 2, Formula 3 and lithium salt is 70-75:20-25:3-4:15-20.

10. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The modified liquid B is compounded on the silicon negative electrode layer of the silicon negative electrode by means of scraping or spin coating.

11. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The wavelength of light irradiation is 200~300nm.

12. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The power of light irradiation is 500~5000W.

13. The method for preparing a modified silicon negative electrode according to claim 1, wherein: The light irradiation time is 5 to 30 minutes.

14. The method for preparing a modified silicon negative electrode according to claim 1, wherein: Ultrasound assistance is carried out simultaneously during the light irradiation process.

15. The method for preparing a modified silicon negative electrode according to claim 14, wherein: Ultrasonic frequency 50~80kHz, power 3.5~8.5w / cm 2 .

16. A modified silicon negative electrode prepared by the preparation method according to any one of claims 1 to 15.

17. Use of a modified silicon negative electrode prepared by the preparation method according to any one of claims 1 to 15 in the preparation of a solid-state battery.

18. A solid-state battery, characterized in that: A modified silicon negative electrode prepared by the preparation method according to any one of claims 1 to 15.

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