Self-diagnosis silicon-based negative pole piece and preparation method, overvoltage judgment method and application thereof

Abstract

The invention provides a self-diagnosis silicon-based negative pole piece and a preparation method, an overvoltage judgment method and application thereof. The self-diagnosis silicon-based negative pole piece comprises a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer comprises a silicon-based composite material, a conductive agent, a binder and a microencapsulation color developing agent, and the microencapsulation color developing agent is used for diagnosing the occurrence of the fracture condition of the silicon-based composite material. According to the invention, the microencapsulated color developing agent is introduced into the pole piece, so that rapid, visual and lossless diagnosis of the overvoltage of the silicon-based negative electrode is realized, and the method has the advantages that: the non-blind area diagnosis of the bulk phase of the pole piece can be realized; accurate triggering can be realized, and the reliability is high; and online quick judgment can be realized by observing color change with naked eyes. Moreover, the microencapsulated color developing agent is compatible with the preparation process of the existing silicon-based pole piece, does not influence the performance of a final battery cell, and provides an effective online quality control means for large-scale high-quality manufacturing of a silicon-based negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of battery material technology, specifically relating to a self-diagnostic silicon-based negative electrode sheet, its preparation method, overvoltage determination method, and application. Background Technology

[0002] With the increasing demands for energy density in lithium-ion batteries, silicon-based materials (such as silicon-carbon composites) have become an ideal alternative to traditional graphite anodes due to their extremely high theoretical specific capacity (approximately 4200 mAh / g). However, silicon materials exhibit a significant volume effect (~300%) during charge and discharge, resulting in a marked difference in processing performance compared to graphite. A prominent issue lies in compaction density. The compaction density of traditional graphite anodes can reach 1.6~1.9 g / cm³. 3 Due to their material properties, silicon-carbon anodes typically have low compaction densities; for example, the compaction density of silicon-carbon composites is only 0.7~1 g / cm³. During the electrode rolling process, in pursuit of high energy density, operators may apply excessive rolling pressure. For silicon-carbon anodes, this excessive pressure can easily crush the brittle SiC particles, exposing the elemental silicon inside. This exposed elemental silicon is highly chemically reactive and reacts rapidly with moisture and oxygen in the air. ; These reactions generate an insulating silicon dioxide layer on the silicon surface, leading to the irreversible consumption of active lithium and causing the silicon material to lose its electrochemical activity. The direct consequences are: reduced initial coulombic efficiency of the cell, inability to effectively improve energy density, and the risk of gas generation, affecting the cycle life and safety performance of the battery.

[0003] Currently, the battery manufacturing industry lacks an effective means to quickly and non-destructively determine whether silicon-carbon electrodes have been crushed on the production line. Conventional detection methods, such as scanning electron microscopy (SEM) or transmission electron microscopy (TEM), while accurate, require complex sample preparation processes, expensive equipment, and specialized operators, and are extremely time-consuming, making them unsuitable for real-time monitoring on the production floor. Therefore, the risk of electrode damage and active material failure due to overpressure has long remained uncontrollable and unknowable, severely restricting the large-scale, high-quality application of silicon-carbon anodes.

[0004] Therefore, how to quickly, intuitively, and non-destructively determine whether silicon-carbon anode plates have experienced overvoltage on the production line without affecting the electrochemical performance of the final battery cell is a major technical challenge that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a self-diagnostic silicon-based anode electrode, its preparation method, overvoltage determination method, and applications. This invention achieves self-diagnosis of overvoltage conditions in silicon-based anode electrodes by introducing a microencapsulated colorimetric agent into the active material layer, offering multiple technical advantages: First, it enables bulk phase diagnosis: it can detect overvoltage conditions at any location along the electrode thickness direction without detection blind spots; second, it enables precise triggering: it can determine the cracking of the silicon-based composite material only when the rolling pressure of the silicon-based anode electrode exceeds the critical pressure, avoiding false triggering and ensuring high reliability; third, it enables rapid online diagnosis: the detection process requires no additional equipment, and the determination can be completed quickly by visually observing color changes, meeting the real-time monitoring needs of production lines. Furthermore, this microencapsulated colorimetric agent can be directly used as one of the raw materials for preparing the active material layer without changing the existing silicon-based anode electrode preparation process, and has no negative impact on the final cell performance. In summary, this microencapsulated colorimetric agent can quickly, intuitively, and non-destructively determine overvoltage during the rolling process of silicon-based anode sheets, while ensuring that the cell performance is not affected. This provides an efficient and reliable online quality control method for the large-scale, high-quality manufacturing of silicon-based anodes.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a self-diagnostic silicon-based negative electrode, the self-diagnostic silicon-based negative electrode comprising a current collector and an active material layer disposed on at least one surface of the current collector; the active material layer comprising a silicon-based composite material, a conductive agent, a binder, and a microencapsulated colorimetric agent, the microencapsulated colorimetric agent being used to diagnose the occurrence of cracking of the silicon-based composite material.

[0008] This invention achieves self-diagnosis of overvoltage conditions in silicon-based anode sheets by introducing a microencapsulated colorimetric agent into the active material layer. It offers several technical advantages: First, it enables bulk phase diagnosis, detecting overvoltage at any location along the thickness of the electrode sheet without blind spots. Second, it enables precise triggering, determining the rupture of the silicon-based composite material only when the rolling pressure of the silicon-based anode sheet exceeds the critical pressure, avoiding false triggering and ensuring high reliability. Third, it enables rapid online diagnosis, requiring no additional equipment; the determination can be completed quickly by visually observing color changes, meeting the real-time monitoring needs of the production line. Furthermore, this microencapsulated colorimetric agent can be directly used as a raw material in the preparation of the active material layer without altering the existing silicon-based anode sheet manufacturing process, and it has no negative impact on the final cell performance. In summary, this microencapsulated colorimetric agent enables rapid, intuitive, and non-destructive overvoltage determination during the rolling process of silicon-based anode sheets, while ensuring that cell performance remains unaffected. This provides an efficient and reliable online quality control method for the large-scale, high-quality manufacturing of silicon-based anodes.

[0009] Preferably, the microencapsulated colorimetric agent has a core-shell structure, with the core comprising a colorimetric reaction system and the shell comprising an electrochemically inert organic compound.

[0010] In this invention, both the electrochemical inert organic compound and the colorimetric reaction system can be dissolved and eluted by the electrolyte, and at specific addition amounts, they have no negative impact on the performance of the battery cell.

[0011] Preferably, the bursting pressure of the outer shell meets the following requirements: P1 < P2 < P3, where P1 is the rolling pressure required for the self-diagnostic silicon-based negative electrode sheet to achieve the target physical properties during the rolling process, P2 is the bursting pressure of the outer shell, and P3 is the crushing pressure of the silicon-based composite material. For example, when the silicon-based negative electrode sheet achieves the target physical properties (e.g., compaction density of 1.5-1.8 g / cm³) during the rolling process... 3 When the required rolling pressure is 30-50 MPa (i.e., P1), the crushing pressure of the silicon-based composite material is 100 MPa (i.e., P3). At this time, the crushing pressure P2 of the shell in the microencapsulated colorimetric agent is 60-90 MPa, such as 60 MPa, 70 MPa, 80 MPa or 90 MPa.

[0012] In this invention, by limiting the rupture pressure of the outer shell to meet the above requirements, the microencapsulated color developer will only rupture when the silicon-based negative electrode sheet exceeds the rolling pressure required to achieve the target physical indicators during the rolling process, exposing the internal color reaction system. This allows the system to come into contact with the fresh elemental silicon that has been broken and exposed due to pressure and quickly generate a color reaction, thereby accurately and reliably converting invisible microscopic mechanical damage into intuitive macroscopic color signals.

[0013] Preferably, P2 = 60-100MPa, for example, it can be 60MPa, 65MPa, 70MPa, 75MPa, 80MPa, 85MPa, 90MPa, 95MPa or 100MPa, etc.

[0014] Preferably, the average particle size of the microencapsulated colorimetric agent is 0.5-10 μm, for example, it can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.

[0015] Preferably, the thickness of the outer shell is 0.1-1μm, for example, it can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm or 1μm, etc.

[0016] In this invention, a suitable shell thickness helps to synergistically control the overall mechanical strength of the microcapsules, ensuring that they rupture precisely within a preset overpressure range, while maintaining good encapsulation stability and washability.

[0017] Preferably, the microencapsulated colorimetric agent has a mass percentage of 0.05-5 wt% in the active material layer, for example, it can be 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%, etc., and is preferably 0.15-3 wt%.

[0018] In this invention, an appropriate amount of microencapsulated colorimetric agent is used. On the one hand, this ensures that when the electrode is over-pressured, the ruptured microcapsules can release sufficient colorimetric agent, thereby generating a significant and easily identifiable color signal, ensuring the sensitivity and reliability of the detection results. On the other hand, the introduction of microcapsules does not significantly change the conductive network, pore structure, and active material ratio of the electrode. Therefore, it has almost no negative impact on the key performance characteristics of the electrode, such as electronic conductivity, ion transport capability, and overall energy density. Furthermore, the trace amount of microencapsulated colorimetric agent can be completely dissolved and washed away by the electrolyte after injection, leaving no harmful solid residues or chemical contamination inside the electrode. This fundamentally ensures the electrochemical performance and safety reliability of the final battery cell.

[0019] Preferably, the colorimetric reaction system includes an oil-soluble redox indicator.

[0020] In this invention, the color-changing principle of the oil-soluble redox indicator is as follows: the oil-soluble redox indicator reacts with the silicon exposed after the silicon-based composite material is broken. That is, the oxidized indicator acts as an electron acceptor and is reduced by the exposed elemental silicon with strong reducing properties. Its molecular structure changes and it is transformed into a reduced product, thereby producing a color change.

[0021] Preferably, the oil-soluble redox indicator comprises any one or a combination of at least two of tetrachlorobenzoquinone, a derivative of tetrachlorobenzoquinone, dichloroindophenol, a derivative of dichloroindophenol, methylene blue, or a derivative of methylene blue.

[0022] Alternatively, the colorimetric reaction system may include an oil-soluble acid-base indicator and an acid stabilizer.

[0023] In this invention, the color-changing principle of the oil-soluble acid-base indicator is as follows: the oil-soluble acid-base indicator reacts with the silicon exposed after the silicon-based composite material is broken, that is, the exposed elemental silicon (Si) reacts with trace amounts of moisture (H2O) in the environment or on the surface of the material to generate alkaline silicate or silanol species, which leads to a significant increase in the local microenvironment pH value at the damage point. As a result, the pH-sensitive oil-soluble acid-base indicator undergoes a protonation / deprotonation transition due to its molecular structure, thus producing a visible color change from "acid color" to "alkaline color".

[0024] Preferably, the oil-soluble acid-base indicator includes any one or a combination of at least two of Neutral Red, Bromothymol Blue, or Dimethyl Yellow.

[0025] Preferably, the acid stabilizer includes any one or a combination of at least two of triethyl citrate, diethyl oxalate, or potassium hydrogen phthalate.

[0026] Preferably, the mass ratio of the oil-soluble acid-base indicator to the acid stabilizer is 1:(5-50), for example, it can be 1:5, 1:10, 1:20, 1:30, 1:40 or 1:50, etc., preferably 1:(10-30).

[0027] In this invention, an oil-soluble acid-base indicator and an acid stabilizer in an appropriate mass ratio can be combined to synergistically construct a dynamically stable and responsive chemical signal switching system.

[0028] Preferably, the electrochemically inert organic compound includes any one or a combination of at least two of polyurethane, epoxy resin, polycarbonate, polymethyl methacrylate, polystyrene, ethyl cellulose, or silicate.

[0029] Preferably, the degree of crosslinking of the outer shell is 30-90%, for example, it can be 30%, 40%, 50%, 60%, 70%, 80% or 90%, etc.

[0030] In this invention, a suitable degree of crosslinking helps to form a dense and rigid network structure, thereby precisely controlling the mechanical properties of the microcapsule shell and ensuring that its rupture pressure falls stably within a preset sensitive range.

[0031] Preferably, the current collector is a copper foil.

[0032] Preferably, the silicon-based composite material is a mixture of silicon material and graphite; wherein the silicon material includes any one of nano-silicon material, silicon-carbon material or silicon-oxygen material.

[0033] In this invention, the silicon-oxygen material is not pure silicon dioxide. Its structure can be understood as follows: nanoscale silicon clusters (i.e., elemental Si) are dispersed within an amorphous silicon oxide (e.g., SiO2) matrix. Therefore, when this silicon-oxygen material is subjected to excessive rolling pressure: the particles break, and the brittle silicon-oxygen particles themselves fracture. On the fresh fracture surface, the nanoscale silicon clusters and highly reactive metastable silicon oxides that were originally encapsulated inside are directly exposed. These newly exposed interfaces have extremely high reactivity and will rapidly react with moisture in the air. Essentially, they remain exposed elemental silicon or reactive silicon species (such as Si). 0 Si +The silicon reacts with H2O to generate hydrogen gas and cause a local pH change (generating basic silicic acid species). Therefore, as long as the rolling process causes the silicon-oxygen particles to break, the reactive silicon components inside will be exposed, thereby triggering a colorimetric reaction.

[0034] Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, carbon nanotubes, or graphene.

[0035] Preferably, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride, sodium carboxymethyl cellulose, or styrene-butadiene rubber.

[0036] Preferably, the thickness of one side of the active material layer is 80-120 μm, for example, it can be 80 μm, 90 μm, 100 μm, 110 μm or 120 μm.

[0037] Preferably, in the active material layer, the mass ratio of the silicon-based composite material, the conductive agent, the binder, and the microencapsulated colorimetric agent is (93-97):(0.5-3):(1-3):(0.05-5). The silicon-based composite material is selected from the range "93-97", for example, 93, 94, 95, 96, or 97. The conductive agent is selected from the range "0.5-3", for example, 0.5, 1, 1.5, 2, 2.5, or 3. The binder is selected from the range "1-3", for example, 1, 2, or 3. The microencapsulated colorimetric agent is selected from the range "0.05-5", for example, 0.05, 0.1, 0.5, 1, 2, 3, 4, or 5.

[0038] In a second aspect, the present invention provides a method for preparing a self-diagnostic silicon-based negative electrode as described in the first aspect, the method comprising the following steps:

[0039] Silicon-based composite materials, conductive agents, binders, and microencapsulated color developers are mixed in a solvent to obtain a mixed slurry;

[0040] The mixed slurry is coated on at least one side of the current collector and dried to obtain the self-diagnostic silicon-based negative electrode.

[0041] Preferably, the preparation method of the microencapsulated colorimetric agent includes in-situ polymerization.

[0042] Preferably, the in-situ polymerization method includes the following steps:

[0043] (1) Prepare an oil phase containing a colorimetric reaction system, and then add the oil phase to an aqueous phase containing an emulsifier to form an oil-in-water emulsion.

[0044] (2) The oil-in-water emulsion and the shell precursor are mixed and subjected to in-situ polymerization to obtain a microencapsulated colorimetric agent.

[0045] Preferably, the temperature of the in-situ polymerization reaction is 50-70°C, for example, 50°C, 60°C or 70°C, and the time is 3-5 hours, for example, 3 hours, 4 hours or 5 hours.

[0046] Preferably, the emulsifier comprises gelatin.

[0047] Preferably, the outer shell is a polymer monomer, which includes any one or a combination of at least two of polyurethane monomers, epoxy resin monomers, polycarbonate monomers, polymethyl methacrylate monomers, or polystyrene monomers.

[0048] Thirdly, the present invention provides an overvoltage determination method for silicon-based negative electrode sheets, the overvoltage determination method comprising the following steps:

[0049] A self-diagnostic silicon-based negative electrode as described in the first aspect is provided as the electrode to be tested.

[0050] The electrode to be tested is rolled.

[0051] The color change on the surface of the electrode after rolling is observed to determine the overvoltage condition of the electrode under test. The specific determination method is as follows:

[0052] If there is no change in surface color, the rolling process is considered normal and recorded as a normal area; if a color change occurs on the surface, the silicon-based composite material in the area of ​​color change is considered to be cracked and recorded as an over-pressure area.

[0053] The overpressure determination method provided by this invention is intuitive to operate, quick to determine, and completely non-destructive to the electrode body. This method does not rely on complex instruments and can identify the crack area (i.e., the overpressure area) in real time and directly during the rolling process, thus providing a reliable basis for process optimization and online quality control of silicon-carbon anode electrodes.

[0054] Preferably, when the colorimetric reaction system of the microencapsulated colorimetric agent of the electrode to be tested includes an oil-soluble redox indicator, the color change characteristic of the overpressure region is: the color fades or changes to a reduced state color; or, when the colorimetric reaction system of the microencapsulated colorimetric agent of the electrode to be tested includes an oil-soluble acid-base indicator and an acid stabilizer, the color change characteristic of the overpressure region is: the color changes from acidic to alkaline.

[0055] It should be noted that the fading or reversion to a reduced state of color means that when the colorimetric system is an oil-soluble redox indicator, its color change originates from an irreversible redox reaction with exposed elemental silicon. The indicator molecule, acting as an oxidant (in an oxidized state, possessing color A), is reduced by elemental silicon, transforming into its reduced product (which may be color B or colorless). Therefore, the colorimetric characteristic of the overpressure region is the fading or reversion to color B of the original color A. This process is a permanent change in molecular structure caused by a chemical reaction.

[0056] It should be noted that the change from acidic to alkaline color refers to the reversible change in the molecular structure of oil-soluble acid-base indicators under different acidity and alkalinity (pH) environments, which leads to a change in their absorption spectrum and ultimately manifests as a visible color change. The acidic color is the stable color that the indicator exhibits when the pH value of the environment is low (acidic conditions), while the alkaline color is the different color that it transforms into when the pH value of the environment rises to a certain range (alkaline conditions). This transformation is not arbitrary; each oil-soluble acid-base indicator has its own specific "color change range" (pH range).

[0057] Fourthly, the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes a self-diagnostic silicon-based negative electrode as described in the first aspect.

[0058] Preferably, after the lithium-ion battery is filled with electrolyte, the microencapsulated colorimetric agent in the self-diagnostic silicon-based negative electrode is dissolved and dispersed in the electrolyte. For example, the electrolyte contains lithium salt and organic solvent. In this electrolyte system, the shell polymer material (such as polyurethane, PMMA, etc.) and the core oil phase component of the microcapsules can be effectively dissolved, swollen, and dispersed to form a uniform solution or colloid, thereby ensuring that they do not remain in the electrode pores or interfaces, and protecting the electrochemical performance of the battery.

[0059] It should be noted that if the self-diagnostic silicon-based negative electrode sheet provided by this invention does not change color after completing the overvoltage determination, then there is no need to adjust the process, and subsequent cell assembly and electrolyte cleaning can be carried out directly.

[0060] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] This invention achieves self-diagnosis of overvoltage conditions in silicon-based anode sheets by introducing a microencapsulated colorimetric agent into the active material layer. It offers several technical advantages: First, it enables bulk phase diagnosis, detecting overvoltage at any location along the thickness of the electrode sheet without blind spots. Second, it enables precise triggering, determining the rupture of the silicon-carbon composite material only when the rolling pressure of the silicon-based anode sheet exceeds the critical pressure, avoiding false triggering and ensuring high reliability. Third, it enables rapid online diagnosis, requiring no additional equipment; the determination can be completed quickly by visually observing color changes, meeting the real-time monitoring needs of the production line. Furthermore, this microencapsulated colorimetric agent can be directly used as a raw material in the preparation of the active material layer without altering the existing silicon-based anode sheet manufacturing process, and it has no negative impact on the final cell performance. In summary, this microencapsulated colorimetric agent enables rapid, intuitive, and non-destructive overvoltage determination during the rolling process of silicon-based anode sheets, while ensuring that cell performance remains unaffected. This provides an efficient and reliable online quality control method for the large-scale, high-quality manufacturing of silicon-based anodes. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the structure of the microencapsulated colorimetric agent provided in Example 1 of the present invention.

[0064] Figure 2 This is a flowchart of the overvoltage determination method for the self-diagnostic silicon-carbon negative electrode sheet provided in Embodiment 1 of the present invention.

[0065] Figure 3 This is a color comparison diagram of the normal area and the overvoltage area in the self-diagnostic silicon-carbon negative electrode plate overvoltage determination method provided in Example 1 of the present invention.

[0066] Figure 4 This is a comparison chart of the cycle curves of the silicon-carbon negative electrode sheets provided in Embodiment 1 and Comparative Example 1 of the present invention.

[0067] Wherein, 1-kernel; 2-shell. Detailed Implementation

[0068] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0069] Example 1

[0070] This embodiment provides a self-diagnostic silicon-carbon negative electrode sheet, which includes a current collector and an active material layer disposed on one side surface of the current collector; the active material layer includes a silicon-carbon composite material, a conductive agent, a binder, and a microencapsulated colorimetric agent, wherein the microencapsulated colorimetric agent is used to diagnose the occurrence of cracking of the silicon-carbon composite material.

[0071] The current collector is copper foil, and the silicon-carbon composite material is a mixture of silicon-oxygen materials and graphite; the conductive agent is conductive carbon black, and the binder is sodium carboxymethyl cellulose; the mass ratio of the silicon-carbon composite material, conductive agent, binder, and microencapsulated colorimetric agent is 95.5:1.5:2:1; the microencapsulated colorimetric agent has a core-shell structure, as shown in the schematic diagram below. Figure 1 As shown, the core 1 includes an oil-soluble redox indicator, which is tetrachloro-o-benzoquinone; the outer shell 2 includes polyurethane; the average particle size of the microencapsulated colorimetric agent is 3 μm; the thickness of the outer shell 2 is 0.4 μm; the mass percentage of the microencapsulated colorimetric agent in the active material layer is 1 wt%; the degree of crosslinking of the outer shell 2 is 70%; and the single-sided thickness of the active material layer is 120 μm.

[0072] The rupture pressure P2 of the outer shell 2 in the microencapsulated colorimetric agent is 60-100 MPa.

[0073] This embodiment also provides a method for preparing the above-mentioned self-diagnostic silicon-carbon negative electrode sheet, the preparation method including the following steps:

[0074] (1) The microencapsulated colorimetric agent was prepared by in-situ polymerization, and the specific steps included:

[0075] (a) Dissolve 1g of tetrachlorobenzoquinone in 10g of dibutyl phthalate to obtain the oil phase; mix 100g of deionized water with 2g of gelatin to obtain the aqueous phase.

[0076] The oil phase is added to the aqueous phase, and high-speed shear emulsification is performed to form an oil-in-water emulsion.

[0077] (b) Add 2g of toluene diisocyanate to the oil-in-water emulsion and mix. Then carry out an in-situ polymerization reaction at 60°C for 4 hours. After the reaction is completed, filter, wash and dry to obtain the microencapsulated color developer.

[0078] (2) The silicon-carbon composite material, conductive carbon black, sodium carboxymethyl cellulose and the microencapsulated color developer are mixed in N-methylpyrrolidone and stirred thoroughly by a planetary mixer to obtain a mixed slurry;

[0079] The mixed slurry is coated on one side of a copper foil and dried under vacuum at 120°C to obtain the self-diagnostic silicon-carbon negative electrode sheet.

[0080] This embodiment also provides an overvoltage determination method for the aforementioned self-diagnostic silicon-carbon negative electrode sheet, such as... Figure 2 As shown, the overvoltage determination method includes the following steps:

[0081] (I) Provide the self-diagnostic silicon-carbon negative electrode as described above as the electrode to be tested.

[0082] (II) The electrode to be tested is rolled at a pressure of 80 MPa.

[0083] (III) Observe the color change of the electrode surface after rolling to determine the overpressure condition of the electrode to be tested. The specific determination method is as follows: if there is no change in surface color, the rolling process is determined to be normal and recorded as normal area; if the surface color changes, the silicon-carbon composite material in the area of ​​color change is determined to be broken and recorded as overpressure area.

[0084] Figure 3 The diagram shows a color comparison between the normal area and the overvoltage area in the silicon-carbon negative electrode sheet overvoltage determination method provided in Example 1 of the present invention. The left image shows that the electrode sheet surface has a uniform color and maintains the original color of the electrode sheet, so it is determined to be a normal area. The right image shows that obvious white spots appear on the electrode sheet surface, so it is determined to be an overvoltage area (tetrachloro-o-benzoquinone is reduced by exposed silicon and faded).

[0085] Example 2

[0086] This embodiment provides a self-diagnostic silicon-carbon negative electrode sheet, which includes a current collector and an active material layer disposed on one side surface of the current collector; the active material layer includes a silicon-carbon composite material, a conductive agent, a binder, and a microencapsulated colorimetric agent, wherein the microencapsulated colorimetric agent is used to diagnose the occurrence of cracking of the silicon-carbon composite material.

[0087] The current collector is copper foil, the silicon-carbon composite material is a mixture of silicon-oxygen materials and graphite, the conductive agent is conductive carbon black, and the binder is sodium carboxymethyl cellulose; the mass ratio of the silicon-carbon composite material, conductive agent, binder, and microencapsulated colorimetric agent is 95.5:1.5:2.5:0.5; the microencapsulated colorimetric agent has a core-shell structure, the core of which includes an oil-soluble redox indicator, namely dichlorophenolindophenol, and the outer shell includes polymethyl methacrylate; the average particle size of the microencapsulated colorimetric agent is 1 μm, and the thickness of the outer shell is 0.5 μm; the mass percentage of the microencapsulated colorimetric agent in the active material layer is 0.5 wt%; the degree of crosslinking of the outer shell is 60%; and the single-sided thickness of the active material layer is 100 μm.

[0088] The rupture pressure P2 of the outer shell in the microencapsulated colorimetric agent is 70-90 MPa.

[0089] This embodiment also provides a method for preparing the above-mentioned self-diagnostic silicon-carbon negative electrode sheet, the preparation method including the following steps:

[0090] (1) The microencapsulated colorimetric agent was prepared by in-situ polymerization, and the specific steps included:

[0091] (a) Dissolve 1g of dichlorophenolindophenol in 10g of dibutyl phthalate to obtain the oil phase; mix 100g of deionized water with 2g of gelatin to obtain the aqueous phase.

[0092] The oil phase is added to the aqueous phase, and high-speed shear emulsification is performed to form an oil-in-water emulsion.

[0093] (b) Add 3g of polymethyl methacrylate monomer to the oil-in-water emulsion and mix. Then carry out an in-situ polymerization reaction at 70°C for 3 hours. After the reaction is completed, filter, wash and dry to obtain the microencapsulated color developer.

[0094] (2) The silicon-carbon composite material, conductive carbon black, sodium carboxymethyl cellulose and the microencapsulated color developer are mixed in N-methylpyrrolidone to obtain a mixed slurry;

[0095] The mixed slurry is coated on one side of a copper foil and dried to obtain the self-diagnostic silicon-carbon negative electrode sheet.

[0096] Example 3

[0097] This embodiment provides a self-diagnostic silicon-carbon negative electrode sheet, which includes a current collector and an active material layer disposed on one side surface of the current collector; the active material layer includes a silicon-carbon composite material, a conductive agent, a binder, and a microencapsulated colorimetric agent, wherein the microencapsulated colorimetric agent is used to diagnose the occurrence of cracking of the silicon-carbon composite material.

[0098] The current collector is copper foil, the silicon-carbon composite material is a mixture of silicon oxide and graphite; the conductive agent is conductive carbon black, and the binder is sodium carboxymethyl cellulose; the mass ratio of the silicon-carbon composite material, conductive agent, binder, and microencapsulated colorimetric agent is 93:1:1:5; the microencapsulated colorimetric agent has a core-shell structure, the core comprising an oil-soluble acid-base indicator and an acid stabilizer in a mass ratio of 1:30, the oil-soluble acid-base indicator being neutral red, and the acid stabilizer being triethyl citrate, and the outer shell comprising ethyl cellulose; the average particle size of the microencapsulated colorimetric agent is 10 μm, and the thickness of the outer shell is 1 μm; the mass percentage of the microencapsulated colorimetric agent in the active material layer is 5 wt%; the degree of crosslinking of the outer shell is 80%; and the single-sided thickness of the active material layer is 80 μm.

[0099] The rupture pressure P2 of the outer shell in the microencapsulated colorimetric agent is 60-80 MPa.

[0100] This embodiment also provides a method for preparing the above-mentioned self-diagnostic silicon-carbon negative electrode sheet, the preparation method including the following steps:

[0101] (1) Preparation of microencapsulated colorimetric reagent, the specific steps of which include:

[0102] (a) Dissolve 0.1g of oil-soluble acid-base indicator Neutral Red and 3g of acid stabilizer Triethyl Citrate in 20g of ethyl acetate, then add 2g of ethyl cellulose and 0.2g of crosslinking agent Toluene Diisocyanate, and stir until completely dissolved to obtain the oil phase.

[0103] (b) Mix 100g of deionized water with 1g of emulsifier polyvinyl alcohol, stir to dissolve, and obtain an aqueous phase.

[0104] (c) The oil phase is added to the aqueous phase and sheared at 10,000 rpm for 5 min to form an oil-in-water emulsion.

[0105] (d) The emulsion is transferred to a reaction vessel and stirred continuously at 60°C for 4 hours to allow the ethyl acetate solvent to evaporate slowly. At the same time, toluene diisocyanate reacts with the hydroxyl groups in the ethyl cellulose molecules to form an ethyl cellulose shell with a cross-linked network.

[0106] (e) After the reaction is complete, the solid product is collected by filtration, then washed three times with deionized water, and dried under vacuum at 40°C for 12 h to obtain the microencapsulated colorimetric agent.

[0107] (2) The silicon-carbon composite material, conductive carbon black, sodium carboxymethyl cellulose and the microencapsulated color developer are mixed in N-methylpyrrolidone to obtain a mixed slurry;

[0108] The mixed slurry is coated on one side of a copper foil and dried to obtain the self-diagnostic silicon-carbon negative electrode sheet.

[0109] Example 4

[0110] The difference between this embodiment and Embodiment 1 is that the thickness of the outer shell of the microencapsulated colorimetric agent is 0.05 μm.

[0111] The remaining preparation methods and parameters are consistent with those in Example 1.

[0112] Example 5

[0113] The difference between this embodiment and Embodiment 1 is that the thickness of the outer shell of the microencapsulated colorimetric agent is 1.5 μm.

[0114] The remaining preparation methods and parameters are consistent with those in Example 1.

[0115] Example 6

[0116] The difference between this embodiment and Embodiment 1 is that the mass percentage of the microencapsulated colorimetric agent in the active material layer is 0.01 wt%.

[0117] The remaining preparation methods and parameters are consistent with those in Example 1.

[0118] Example 7

[0119] The difference between this embodiment and Embodiment 1 is that the microencapsulated colorimetric agent accounts for 5.5 wt% of the mass of the active material layer.

[0120] The remaining preparation methods and parameters are consistent with those in Example 1.

[0121] Example 8

[0122] The difference between this embodiment and Embodiment 3 is that the core of the microencapsulated colorimetric agent does not contain an acidic stabilizer.

[0123] The remaining preparation methods and parameters are consistent with those in Example 3.

[0124] Example 9

[0125] The difference between this embodiment and Embodiment 1 is that the cross-linking degree of the outer shell in the microencapsulated colorimetric agent is 20%.

[0126] The remaining preparation methods and parameters are consistent with those in Example 1.

[0127] Example 10

[0128] The difference between this embodiment and Embodiment 1 is that the cross-linking degree of the outer shell in the microencapsulated colorimetric agent is 100%.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Example 11

[0131] The difference between this embodiment and Embodiment 1 is that the microencapsulated colorimetric agent does not contain a shell.

[0132] The remaining preparation methods and parameters are consistent with those in Example 1.

[0133] Comparative Example 1

[0134] The difference between this comparative example and Example 1 is that the active material layer does not contain microencapsulated colorimetric agents.

[0135] The remaining preparation methods and parameters are consistent with those in Example 1.

[0136] Figure 4 The cycling curves of the silicon-carbon anode sheets provided in Example 1 and Comparative Example 1 are shown in the figure. As can be seen from the figure, the addition of microencapsulated colorimetric agent in the silicon-carbon anode material prepared by the present invention has no negative impact on the electrochemical performance of the battery.

[0137] Performance testing

[0138] The electrode regions identified as normal areas in the silicon-carbon negative electrode sheets provided in the above embodiments and comparative examples were used to assemble CR2032 coin cells, with lithium metal as the counter electrode, Celgard 2400 polypropylene porous membrane as the separator, and a solution containing 1M LiPF6 in the electrolyte, wherein the solvent is a mixed solvent composed of EC:EMC:DEC in a volume ratio of 1:1:1, and contains 10% by mass of fluoroethylene carbonate additive.

[0139] The coin cell was subjected to its first coulombic efficiency test at 0.5C rate, and its cycle performance was tested at 25℃ and 0.5C charge / discharge rate, with a cutoff voltage of 0.005-1.5V. The capacity retention rate was recorded after 100 cycles.

[0140] The results are shown in Table 1.

[0141] Table 1

[0142]

[0143] analyze:

[0144] As shown in Table 1, this invention achieves self-diagnosis of overvoltage conditions in silicon-carbon anode sheets by introducing microencapsulated colorimetric agents into the active material layer, offering multiple technical advantages: First, it enables bulk phase diagnosis: it can detect overvoltage conditions at any location along the thickness direction of the electrode sheet without any blind spots; second, it enables precise triggering: it can determine the cracking condition of the silicon-carbon composite material only when the rolling pressure of the silicon-carbon anode sheet exceeds the critical pressure, avoiding false triggering and ensuring high reliability; third, it enables rapid online diagnosis: the detection process requires no additional equipment, and the determination can be completed in a short time by visually observing color changes, meeting the real-time monitoring needs of the production line. Furthermore, this microencapsulated colorimetric agent can be directly used as one of the raw materials for preparing the active material layer without changing the existing silicon-carbon anode sheet preparation process, and it has no negative impact on the final cell performance. In summary, this microencapsulated colorimetric agent can quickly, intuitively, and non-destructively determine overvoltage during the rolling process of silicon-carbon anode sheets, while ensuring that the cell performance is not affected. This provides an efficient and reliable online quality control method for the large-scale, high-quality manufacturing of silicon-carbon anodes.

[0145] As can be seen from the comparison between Example 1 and Examples 4-5, if the outer shell of the microencapsulated color developer is too thin, its mechanical strength is insufficient, and it is easy to break prematurely during normal rolling or slurry processing, resulting in false color development and loss of diagnostic significance; if the outer shell of the microencapsulated color developer is too thick, its rupture pressure is too high, and it may need to reach or exceed the crushing pressure of silicon-carbon active material to trigger, resulting in delayed color development or failure to develop color, and inability to reflect the overpressure state in a timely manner.

[0146] As can be seen from the comparison between Example 1 and Examples 6-7, if the mass ratio of the microencapsulated chromogenic agent in the active material layer is too small, the number of effective microcapsules per unit area will be insufficient. When overpressure occurs, the total amount of chromogenic agent released will be limited, which may result in weak, discontinuous, or visually difficult-to-identify colorimetric signals, reducing detection sensitivity and reliability. If the mass ratio of the microencapsulated chromogenic agent in the active material layer is too large, it may excessively occupy the space of the active material, slightly affecting the compaction density and electronic conductivity network of the electrode, and diluting the energy density of the electrode to a certain extent. At the same time, it increases the burden of subsequent cleaning and the risk of residue.

[0147] As can be seen from the comparison between Example 3 and Example 8, if the core of the microencapsulated colorimetric agent does not contain an acid stabilizer, the oil-soluble acid-base indicator cannot maintain a stable initial acid color state during storage and processing. It is easily affected by environmental factors and will undergo color drift or non-specific color change, resulting in unstable background signal and seriously interfering with the accurate interpretation of overvoltage trigger signal.

[0148] As can be seen from the comparison between Example 1 and Examples 9-10, if the cross-linking of the outer shell in the microencapsulated colorimetric agent is too low, the resulting three-dimensional network structure is loose, with poor mechanical strength and barrier properties. The microcapsules are prone to premature rupture, and the core material is prone to migration and leakage. If the cross-linking of the outer shell in the microencapsulated colorimetric agent is too high, the shell layer is too dense and rigid. Although the mechanical strength is high, it may be difficult to be effectively swollen and dissolved by the electrolyte after injection, resulting in incomplete cleaning. The residual solid particles may block the electrode pores and affect ion transport.

[0149] As can be seen from the comparison between Example 1 and Example 11, if the microencapsulated colorimetric agent does not contain a shell, the colorimetric agent is directly exposed to the slurry and electrode environment. It will react with the air or residual substances in the electrode after coating and drying, or it will be consumed and ineffective before rolling. It is impossible to achieve the accurate diagnostic function of "triggering only under overpressure", and it will directly contaminate the electrode, seriously affecting the electrochemical performance.

[0150] As can be seen from the comparison between Example 1 and Comparative Example 1, the microencapsulated colorimetric agent prepared by the present invention under the synergistic effect of multiple protection parameters has no negative impact on the electrochemical performance of the battery when added.

[0151] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A self-diagnosing silicon-based negative electrode sheet, characterized by, The self-diagnosis silicon-based negative electrode sheet comprises a current collector and an active material layer arranged on at least one side surface of the current collector; the active material layer comprises a silicon-based composite material, a conductive agent, a binder and a microencapsulated color developing agent for diagnosing the occurrence of the silicon-based composite material breakage.

2. The self-diagnosing silicon-based negative electrode sheet according to claim 1, characterized in that, The microencapsulated color developing agent has a core-shell structure, the inner core comprises a color developing reaction system, and the outer shell comprises an electrochemically inert organic compound. The breakage pressure of the outer shell satisfies the following requirements: P1 Preferably, P2=50-100 MPa.

3. The self-diagnosing silicon-based negative electrode sheet according to claim 2, characterized in that, The average particle size of the microencapsulated color developing agent is 0.5-10 μm. Preferably, the thickness of the outer shell is 0.1-1 μm. Preferably, the mass ratio of the microencapsulated color developing agent in the active material layer is 0.05-5 wt%, preferably 0.15-3 wt%. 4.The self-diagnosing silicon-based negative electrode sheet according to claim 2 or 3, characterized in that, The color developing reaction system comprises an oil-soluble oxidation-reduction indicator. Preferably, the oil-soluble oxidation-reduction indicator comprises any one or a combination of at least two of tetrachloro-o-benzoquinone, a derivative of tetrachloro-o-benzoquinone, dichloro-indophenol, a derivative of dichloro-indophenol, methylene blue or a derivative of methylene blue. Alternatively, the color developing reaction system comprises an oil-soluble acid-base indicator and an acidic stabilizer. Preferably, the oil-soluble acid-base indicator comprises any one or a combination of at least two of neutral red, bromothymol blue or dimethyl yellow. Preferably, the acidic stabilizer comprises any one or a combination of at least two of triethyl citrate, diethyl oxalate or potassium hydrogen phthalate. Preferably, the mass ratio of the oil-soluble acid-base indicator to the acidic stabilizer is 1:(5-50).

5. The self-diagnostic silicon-based negative electrode sheet according to any one of claims 2 to 4, characterized in that, The electrochemically inert organic compound comprises any one or a combination of at least two of polyurethane, epoxy resin, polycarbonate, polymethyl methacrylate, polystyrene, ethyl cellulose or silicate. Preferably, the cross-linking degree of the outer shell is 30-90%. Preferably, the silicon-based composite material is a mixture of a silicon material and graphite; the silicon material comprises any one of nano-silicon material, silicon-carbon material or silicon-oxygen material.

6. A method of manufacturing a self-diagnosing silicon-based negative electrode sheet according to any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: mixing the silicon-based composite material, the conductive agent, the binder and the microencapsulated color developing agent in a solvent to obtain a mixed slurry; coating the mixed slurry on at least one side surface of the current collector and drying to obtain the self-diagnosis silicon-based negative electrode sheet.

7. The production method according to claim 6, wherein The preparation method of the microencapsulated color developing agent comprises an in-situ polymerization method. Preferably, the in-situ polymerization method comprises the following steps: (1) preparing an oil phase containing a color developing reaction system, and then adding the oil phase into an aqueous phase containing an emulsifier to form an oil-in-water emulsion; (2) mixing the oil-in-water emulsion and a shell precursor to perform an in-situ polymerization reaction to obtain the microencapsulated color developing agent; Preferably, the in-situ polymerization reaction is performed at a temperature of 50-70 °C for 3-5 h.

8. A method for overdischarge determination of a silicon-based negative electrode sheet, characterized by, The overpressure determination method comprises the following steps: The self-diagnosis silicon-based negative electrode sheet according to any one of claims 1-5 is provided as a to-be-tested electrode sheet; The to-be-tested electrode sheet is rolled; The color change of the surface of the rolled electrode sheet is observed to determine the over-pressing condition of the to-be-tested electrode sheet, and the specific determination method is: If the surface color does not change, it is determined that the rolling process is normal, and it is recorded as a normal area; if the surface color changes, it is determined that the silicon-based composite material is broken in the area where the color changes, and it is recorded as an over-pressing area.

9. The overvoltage determination method according to claim 8, characterized by When the color developing reaction system of the microencapsulated color developing agent of the to-be-tested electrode sheet includes an oil-soluble oxidation-reduction indicator, the color change characteristic of the over-pressing area is that the color fades or changes to a reduced state color; Alternatively, when the color developing reaction system of the microencapsulated color developing agent of the to-be-tested electrode sheet includes an oil-soluble acid-base indicator and an acid stabilizer, the color change characteristic of the over-pressing area is that the color changes from an acid color to a base color.

10. A lithium-ion battery, characterized by, The lithium ion battery includes the self-diagnosis silicon-based negative electrode sheet according to any one of claims 1-5; After the lithium ion battery is injected with electrolyte, the microencapsulated color developing agent in the self-diagnosis silicon-based negative electrode sheet is dissolved by the electrolyte and dispersed in the electrolyte.

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