A silicon-based composite negative electrode material, a negative electrode sheet, an electrochemical device, and an electronic device

Abstract

This invention discloses a silicon-based composite anode material, anode sheet, electrochemical device, and electronic device. The silicon-based composite anode material includes a silicon-based active material and a composite layer coated on the surface of the silicon-based active material. The composite layer includes a rigid conductive polymer, a flexible polymer, and an ionic liquid. The rigid conductive polymer and the flexible polymer are bonded together through hydrogen bonding to form a "rigid-flexible" three-dimensional network framework, which effectively buffers the volume expansion of the silicon material. The ionic liquid is dispersed within the three-dimensional network framework, and the two interact electrostatically, thereby constructing continuous nanoscale ion-conducting channels and improving ion transport efficiency. The composite layer and the silicon-based active material are tightly connected through hydrogen bonding, greatly enhancing interfacial stability, effectively inhibiting the shedding of active material and promoting the formation of a stable SEI film, thereby improving battery cycle stability and extending battery cycle life.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to a silicon-based composite anode material, anode sheet, electrochemical device, and electronic device. Background Technology

[0002] With the rapid development of sustainable energy and electric transportation, higher demands are being placed on the energy density of electrochemical devices such as lithium-ion batteries. As a key component determining battery energy density, the innovation of anode materials is crucial. Silicon-based materials, with their theoretical specific capacity of up to 4200 mAh / g, are considered ideal candidates to replace traditional graphite anodes. However, silicon undergoes volume changes exceeding 300% during charge and discharge, leading to the breakage and pulverization of active material particles, as well as the continuous breakdown and reconstruction of the solid electrolyte interface film. These problems ultimately cause mechanical failure of the electrode structure and a sharp decline in capacity, severely hindering the commercial application of silicon-based anodes.

[0003] To address the aforementioned problems, existing technologies primarily employ the following strategies: One strategy involves using nanostructure design, specifically by constructing nanowires, nanoporous structures, or yolk-shell structures to buffer volume expansion. However, these methods typically involve complex synthesis processes and high costs, and the low tap density of nanomaterials limits the volumetric energy density of the battery.

[0004] Strategy two involves optimizing the surface coating and binder, specifically using polymer binders such as polyacrylic acid and sodium carboxymethyl cellulose, or flexible carbon layers to coat silicon particles. While this improves interfacial stability to some extent, the interfacial bonding of these materials is prone to failure under long-term, drastic volume deformation, leading to coating peeling and loss of active materials, thus failing to meet the requirements for long cycle life.

[0005] Therefore, there is an urgent need in this field to develop a novel silicon-based composite anode material that combines excellent mechanical stability, high efficiency in ion conduction, and strong interfacial bonding to simultaneously solve the core problems of volume expansion effect and interfacial instability. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a silicon-based composite anode material.

[0007] A second objective of this invention is to provide a negative electrode sheet.

[0008] A third objective of this invention is to provide an electrochemical device.

[0009] The fourth objective of this invention is to provide an electronic device.

[0010] In a first aspect, the present invention provides a silicon-based composite anode material, comprising a silicon-based active material and a composite layer coated on the surface of the silicon-based active material. The composite layer comprises a rigid conductive polymer, a flexible polymer, and an ionic liquid. The rigid conductive polymer and the flexible polymer are composited through hydrogen bonding to form a three-dimensional network framework. The ionic liquid is dispersed in the three-dimensional network framework, and there is an electrostatic interaction between the ionic liquid and the three-dimensional network framework. The composite layer is connected to the silicon-based active material through hydrogen bonding.

[0011] According to embodiments of the present invention, the silicon-based composite anode material has at least the following beneficial effects: The silicon-based composite anode material coats the surface of a silicon-based active material with a composite layer comprising a rigid conductive polymer, a flexible polymer, and an ionic liquid. The rigid conductive polymer and the flexible polymer in the composite layer are bonded together through hydrogen bonding to form a three-dimensional network framework. The rigid conductive polymer provides mechanical support to ensure the stability of the three-dimensional network framework, while the flexible polymer imparts good elasticity and deformability to the network framework and the composite layer, giving the composite layer fatigue resistance. The rigid conductive polymer and the flexible polymer combine through hydrogen bonding to form a "rigid-flexible" three-dimensional network framework, which can dynamically absorb the volume expansion stress of the silicon-based active material, preventing particle pulverization and structural damage to the composite layer. This improves structural durability and cycle stability, and extends the electrode's service life.

[0012] In the composite layer, the ionic liquid is dispersed in a three-dimensional network framework constructed from rigid conductive polymers and flexible polymers. The electrostatic interaction between the ionic liquid and the three-dimensional network framework allows the ionic liquid to be uniformly dispersed in the polymer three-dimensional network framework, forming a continuous nanoscale ionic conductive channel that runs through the composite layer. At the same time, the high ionic conductivity and wide electrochemical window of the ionic liquid itself can ensure the high efficiency and stability of the channel. This can reduce the transport impedance of metal ions (such as lithium ions) at the interface, enabling the electrochemical device to have excellent rate performance and release high capacity even at high charge / discharge rates.

[0013] Furthermore, the composite layer on the silicon-based composite anode material is connected to the silicon-based active material through hydrogen bonding. The composite layer and the silicon-based active material form a hydrogen bond network through hydrogen bonding to provide dynamic adaptability and energy dissipation capability. This strengthens the interfacial bonding between the composite layer and the silicon-based active material, improves interfacial stability, effectively inhibits the shedding of active material during long-term cycling, and ensures the integrity of the composite layer and the silicon-based active material during long-term cycling. Moreover, the robust interfacial bonding can reduce the continuous decomposition of the electrolyte caused by repeated exposure of the silicon-based active material surface, which helps to form a stable SEI film, thereby improving the cycle life of the electrochemical device.

[0014] According to some embodiments of the present invention, the rigid conductive polymer is a rigid conjugated polymer with an aromatic ring and / or aromatic heterocycle as the main chain.

[0015] According to some embodiments of the present invention, the rigid conductive polymer and the silicon-based active material are connected by hydrogen bonding.

[0016] According to some embodiments of the present invention, the flexible polymer is a polyester having flexible chain segments.

[0017] According to some embodiments of the present invention, the flexible polymer is an aliphatic linear polyester.

[0018] According to some embodiments of the present invention, the flexible polymer includes at least one of polycaprolactone (PCL), polyvalerol (PVL), and polytrimethylene carbonate (PTMC).

[0019] According to some embodiments of the present invention, the ionic liquid includes at least one of imidazole ionic liquids, quaternary ammonium salt ionic liquids, pyridine ionic liquids, piperidine ionic liquids, and pyrrole ionic liquids.

[0020] According to some embodiments of the present invention, the ionic liquid comprises at least one of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]TfO), and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine ([BMIM]NTf2).

[0021] According to some embodiments of the present invention, the mass percentages of the rigid conductive polymer, the flexible polymer, and the ionic liquid in the composite layer are 45%~65%, 30%~50%, and 1%~5%, respectively. For example, the mass percentage of the rigid conductive polymer in the composite layer may be, but is not limited to, 45%, 45.6%, 46%, 46.5%, 47%, 48%, 50%, 51.5%, 52%, 53%, 54.3%, 55%, 56%, 57.5%, 58%, 59%, 60%, 61%, 62.5%, 63%, or 65%, or fall within the range of any two of the above values; the mass percentage of the flexible polymer may be, but is not limited to, 30%, 31%, 32%, 32.5%, 33%, 34%, 35%, 36.5%, 37%, 38%, 39%, 40%, 42%, 43%, 45%, 46%, 47.5%, 48%, 48.2%, 49%, or 50%, or fall within the range of any two of the above values; the mass percentage of the ionic liquid may be, but is not limited to, 1%, 1.5%, 1.8%, 2%, 2.4%, 2.8%, 3%, 3.5%, 4%, 4.7%, or 5%, or fall within the range of any two of the above values.

[0022] According to some embodiments of the present invention, the particle size distribution of the silicon-based active material satisfies: 0.7 ≤ (D90-D10) / D50 ≤ 1.3. In some embodiments, (D90-D10) / D50 may be, but is not limited to, 0.7, 0.75, 0.8, 0.82, 0.85, 0.88, 0.9, 0.95, 0.97, 1.0, 1.05, 1.1, 1.12, 1.15, 1.18, 1.2, 1.23, 1.25, 1.26, 1.28, or 1.3, or fall within the range of any two of the above values. This ensures that the silicon-based active material has a narrow particle size distribution, thereby reducing the problem of interfacial stress concentration caused by excessive particle size differences. Furthermore, in some embodiments, the particle size distribution of the silicon-based active material satisfies: D10 = 80 nm ~ 250 nm, D50 = 300 nm ~ 800 nm, D90 = 250 nm ~ 1000 nm.

[0023] According to some embodiments of the present invention, the surface hydroxyl density of the silicon-based active material is OH mmol / g, and the mass percentage of the rigid conductive polymer in the composite layer is A, wherein OH and A satisfy: 2.4 ≤ OH / A ≤ 9.0. In some embodiments, OH / A may be, but is not limited to, 2.4, 2.7, 2.9, 3.0, 3.1, 3.3, 3.5, 3.6, 3.9, 4.0, 4.1, 4.3, 4.5, 5, 5.2, 5.5, 5.7, 5.9, 6, 6.5, 6.8, 7, 7.3, 7.5, 7.6, 8, 8.2, 8.5, 8.7, or 9.0, or fall within the range of any two of the above values.

[0024] According to some embodiments of the present invention, the surface hydroxyl density (OH) of the silicon-based active material satisfies the following condition: 1.2 ≤ OH ≤ 4.5 mmol / g. In some embodiments, OH may be, but is not limited to, 1.2, 1.25, 1.3, 1.45, 1.5, 1.65, 1.8, 2.0, 2.35, 2.5, 2.75, 3.0, 3.5, 3.8, 4.0, 4.2, or 4.5, or fall within the range of any two of the above values. A surface with a high hydroxyl density provides abundant sites for the coating of the composite layer. Hydrogen bonds are formed between the hydroxyl groups and the active groups on the composite layer to enhance the interfacial bonding strength, prevent the composite layer from detaching during charging and discharging, and improve the structural stability of the material.

[0025] According to some embodiments of the present invention, the mass percentage of the ionic liquid in the composite layer is B, the specific surface area of ​​the silicon-based active material is S m² / g, and B and S satisfy: 0.0075 ≤ B / S ≤ 0.030. In some embodiments, B / S may be, but is not limited to, 0.0075, 0.008, 0.009, 0.01, 0.012, 0.013, 0.015, 0.017, 0.021, 0.025, 0.027, or 0.030, or fall within the range of any two of the above values. By controlling B / S within the above range, it is beneficial to ensure that the ionic liquid is uniformly distributed on the surface of the silicon-based active material, forming an efficient ion conduction pathway.

[0026] According to some embodiments of the present invention, the specific surface area S m² / g of the silicon-based active material satisfies: 1.0 ≤ S ≤ 4. In some embodiments, S may be, but is not limited to, 1.0, 1.2, 1.5, 1.8, 1.9, 2.0, 2.3, 2.5, 2.6, 2.7, 3.0, 3.1, 3.4, 3.5, 3.7, 3.8 or 4, or fall within the range of any two of the above values.

[0027] According to some embodiments of the present invention, the silicon-based active material is selected from at least one of silicon, silicon carbide, silicon suboxide, and silicon dioxide.

[0028] In a second aspect, the present invention provides a negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer contains any of the aforementioned silicon-based composite negative electrode materials of the present invention.

[0029] The technical solution of the present invention regarding the negative electrode sheet has at least the following beneficial effects: In the negative electrode sheet of the embodiments of the present invention, the negative electrode active material layer contains any of the aforementioned silicon-based composite negative electrode materials of the present invention. Therefore, the negative electrode sheet has all the beneficial effects of silicon-based composite negative electrode materials, which will not be elaborated further.

[0030] According to some embodiments of the present invention, the negative electrode active material layer is disposed on both sides of the negative electrode current collector with the back facing away from it.

[0031] A third aspect of the present invention provides an electrochemical device comprising a negative electrode of any of the foregoing embodiments of the present invention.

[0032] In some embodiments of the present invention, the electrochemical device is a primary battery, a secondary battery, a fuel cell, a solar cell, or a capacitor.

[0033] In some embodiments of the present invention, the electrochemical device is a lithium secondary battery. For example, the lithium secondary battery may be a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0034] In some embodiments of the present invention, the electrochemical device further includes a positive electrode, a separator, and an electrolyte; the separator is sandwiched between the positive electrode and the negative electrode.

[0035] In some embodiments of the present invention, the electrolyte contains a lithium salt, the concentration of which is C mol / L. In the silicon-based composite negative electrode material contained in the negative electrode active material layer on the negative electrode sheet, the mass percentage of the flexible polymer in the composite layer is D, where C and D satisfy: 1.7 ≤ C / D ≤ 2.6. In some embodiments, C / D can be, but is not limited to, 1.7, 1.9, 2.1, 2.3, 2.4, 2.5, or 2.6, or fall within any two of the above values. In some embodiments, the lithium salt is LiPF6. By controlling C / D within the above range, the matching of the lithium affinity of the flexible polymer (such as PCL) with the lithium salt concentration is ensured, facilitating a dynamic balance between the lithium ion supply rate and the lithium ion reception and transport rate of the composite layer. This optimizes the lithium ion transport kinetics at the interface between the composite layer and the electrolyte, making lithium ion transport smoother, reducing interface impedance, and improving the charge / discharge efficiency and cycle performance of electrochemical devices (such as lithium-ion batteries).

[0036] In some embodiments of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector.

[0037] In a fourth aspect, the present invention provides an electronic device comprising any of the electrochemical devices described above.

[0038] In some embodiments of the present invention, electronic devices include, but are not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots. Detailed Implementation

[0039] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0040] Examples 1-17 Examples 1-17 present a silicon-based composite anode material comprising a silicon-based active material and a composite layer coated on the surface of the silicon-based active material. The silicon-based active material is silicon powder. The composite layer comprises a rigid conductive polymer polybenzodifurandione (PBFDO, molecular weight > 50 kDa), a flexible polymer polycaprolactone (PCL, molecular weight 20-80 kDa), and an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4). PBFDO and PCL are combined through hydrogen bonding to form a three-dimensional network framework that combines rigidity and flexibility. [BMIM]BF4 is uniformly dispersed in the three-dimensional network framework and has electrostatic interaction with the three-dimensional framework network. The composite layer is connected to the silicon particles through hydrogen bonding, which can strengthen the interfacial bonding between the composite layer and the silicon-based active material and improve the interfacial stability.

[0041] The above silicon-based composite anode materials are prepared by the following methods: S11. Pretreatment of silicon particles: Select silicon powder, control the particle size distribution and specific surface area of ​​silicon particles by air jet milling, and adjust the hydroxyl density on the surface of silicon particles by plasma treatment; specifically, control the particle size distribution, specific surface area and surface hydroxyl density of silicon particles in each embodiment according to the requirements in Table 1. S12. Preparation of composite layer: According to the amount of composite layer components in Table 1, PBFDO, PCL, and [BMIM]BF4 are dissolved in N-methylpyrrolidone, pretreated silicon powder is added, ultrasonically dispersed for 30 min, and then stirred at 80℃ for 5 h to make the composite layer coat the surface of silicon particles through hydrogen bonds. The mass ratio of silicon particles to composite layer is about 4:1, thus obtaining silicon-based composite anode material.

[0042] The above-mentioned silicon-based composite anode materials can be used to construct anode sheets. Furthermore, Examples 1 to 17 also propose anode sheets, including anode current collectors and anode active material layers disposed on both sides of thenode current collectors. Thenode current collector is a copper foil, and the anode active material layers include silicon-based composite anode materials in a mass ratio of 96:1:1.5:1.5, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC). The silicon-based composite anode materials on the anode active material layers of the anode sheets in Examples 1 to 17 respectively correspond to the silicon-based composite anode materials in Examples 1 to 17.

[0043] The above negative electrode sheet is specifically prepared by the following method: silicon-based composite negative electrode material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5 to obtain a negative electrode slurry. Then, the negative electrode slurry is coated on both sides of the copper foil of the negative electrode current collector. After baking, cold pressing and slitting, the negative electrode sheet is obtained.

[0044] The above negative electrode sheet can be further used to construct electrochemical devices such as lithium-ion batteries. Furthermore, Examples 1-17 each propose a lithium-ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheets in Examples 1-17 correspond to the negative electrode sheets used in Examples 1-17, respectively. The separator is a porous polyethylene film sandwiched between the positive and negative electrode sheets. The positive electrode sheet includes a positive current collector and positive active material layers disposed on both sides of the current collector. The current collector is made of aluminum foil. The positive active material layers include lithium cobalt oxide (positive active material), acetylene black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) in a mass ratio of 98:1.2:0.8. The electrolyte is a LiPF6 solution, with solvents consisting of ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) in a mass ratio of 25:25:15:31:4.

[0045] The above lithium-ion batteries are prepared by the following method: S21. The positive electrode active material lithium cobalt oxide, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 98:1.2:0.8 to obtain a positive electrode slurry. The positive electrode slurry is then coated on both sides of the positive electrode current collector Al foil. After drying, rolling and slitting, a positive electrode sheet is obtained. S22. Using a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and ethylene carbonate (VC) in a mass ratio of 25:25:15:31:4 as a solvent, lithium salt LiPF6 is mixed with the solvent to prepare an electrolyte. The electrolyte concentration is shown in Table 1. S23. Using a porous polyethylene (PE) film as a separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to provide a safety barrier. The electrode assembly is then wound up to obtain an electrode assembly, which is then placed in an aluminum-plastic film, injected with electrolyte, and encapsulated to obtain a lithium-ion battery.

[0046] Comparative Example 1 This comparative example presents a silicon-based composite anode material, which differs from the silicon-based anode material of Example 1 in that: the composite layer composition of this comparative example silicon-based composite anode material does not contain PBFDO, and the ratio of PCL to [BMIM]BF4 remains unchanged, while other aspects are the same as the anode sheet of Example 1.

[0047] This comparative example also proposes a negative electrode sheet, which differs from the negative electrode sheet of Example 1 in that: the negative electrode sheet of this comparative example uses the silicon-based composite negative electrode material of this comparative example instead of the silicon-based composite negative electrode material in Example 1, while the rest is the same as the negative electrode sheet of Example 1.

[0048] This comparative example also proposes a lithium-ion battery, which differs from the lithium-ion battery of Example 1 in that: the negative electrode sheet of this comparative example is used instead of the negative electrode sheet of Example 1 in the lithium-ion battery of this comparative example, and the rest is the same as the lithium-ion battery of Example 1.

[0049] Comparative Example 2 This comparative example presents a silicon-based composite anode material, which differs from the silicon-based anode material of Example 1 in that: the composite layer composition of this comparative example silicon-based composite anode material does not contain [BMIM]BF4, and the ratio of PBFDO to PCL remains basically unchanged, while the rest is the same as the anode sheet of Example 1.

[0050] This comparative example also proposes a negative electrode sheet, which differs from the negative electrode sheet of Example 1 in that: the negative electrode sheet of this comparative example uses the silicon-based composite negative electrode material of this comparative example instead of the silicon-based composite negative electrode material of Example 1, while the rest is the same as the negative electrode sheet of Example 1.

[0051] This comparative example also proposes a lithium-ion battery, which differs from the lithium-ion battery of Example 1 in that: the negative electrode sheet of this comparative example is used instead of the negative electrode sheet of Example 1 in the lithium-ion battery of this comparative example, and the rest is the same as the lithium-ion battery of Example 1.

[0052] Comparative Example 3 This comparative example presents a silicon-based composite anode material, which differs from the silicon-based anode material of Example 1 in that: the composite layer composition of this comparative example silicon-based composite anode material does not contain PCL, and the ratio of PBFDO to [BMIM]BF4 remains basically unchanged, while the rest is the same as the anode sheet of Example 1.

[0053] This comparative example also proposes a negative electrode sheet, which differs from the negative electrode sheet of Example 1 in that: the negative electrode sheet of this comparative example uses the silicon-based composite negative electrode material of this comparative example instead of the silicon-based composite negative electrode material in Example 1, while the rest is the same as the negative electrode sheet of Example 1.

[0054] This comparative example also proposes a lithium-ion battery, which differs from the lithium-ion battery of Example 1 in that: the negative electrode sheet of this comparative example is used instead of the negative electrode sheet in Example 1 in the lithium-ion battery of this comparative example, and the rest is the same as the lithium-ion battery of Example 1.

[0055] Comparative Example 4 This comparative example presents a silicon-based anode material, which differs from the silicon-based composite anode material of Example 1 in that: this comparative example directly uses the pretreated silicon particles from Example 1 as the silicon-based anode material, without coating its surface with a composite layer.

[0056] This comparative example also proposes a negative electrode sheet, which differs from the negative electrode sheet of Example 1 in that: the negative electrode sheet of this comparative example uses the silicon-based negative electrode material of this comparative example instead of the silicon-based composite negative electrode material of Example 1, while the rest is the same as the negative electrode sheet of Example 1.

[0057] This comparative example also proposes a lithium-ion battery, which differs from the lithium-ion battery of Example 1 in that: the negative electrode sheet of this comparative example is used instead of the negative electrode sheet of Example 1 in the lithium-ion battery of this comparative example, and the rest is the same as the lithium-ion battery of Example 1.

[0058] Performance testing Five lithium-ion batteries from each of the embodiments and comparative examples were taken, and the lithium-ion batteries were repeatedly charged and discharged through the following steps, and the cycle capacity retention rate and thickness expansion rate of the lithium-ion batteries were calculated.

[0059] First, the cell underwent its first charge and discharge cycle at 25°C. Constant current and constant voltage charging was performed at a charging current of 0.1C (the current required to completely discharge the theoretical capacity within 10 hours) until the upper limit voltage reached 4.3V. Then, constant current discharging was performed at a discharging current of 1C until the final voltage reached 3V. The discharge capacity and cell thickness of the first cycle were recorded. Next, 400 charge and discharge cycles were performed, and the discharge capacity and cell thickness of the 400th cycle were recorded. The cycle capacity retention rate and thickness expansion rate were then calculated using the following formulas: Cycle capacity retention = (Discharge capacity of the 400th cycle / Discharge capacity of the first cycle) × 100%; Thickness expansion rate = (Cell thickness in the 400th cycle / Cell thickness in the first cycle) × 100%.

[0060] The cycle capacity retention and thickness expansion rate of the lithium-ion batteries in each embodiment and comparative example were tested according to the above method, and the results are shown in Table 1.

[0061] Table 1

[0062] According to Table 1, a comparison of each embodiment (especially Embodiment 1) and Comparative Examples 1 to 4 shows that coating the surface of silicon particles with a composite layer including rigid conductive polymer PBFDO, flexible polymer PCL and ionic liquid [BMIM]BF4, the three work together to effectively solve the problem of huge volume expansion of silicon particles during charging and discharging, significantly improve the battery cycle capacity retention rate, and reduce the cell thickness expansion rate.

[0063] Specifically, the rigid conductive polymer PBFDO and the flexible polymer PCL in the composite layer can form a three-dimensional network framework that combines rigidity and flexibility through hydrogen bonding. This framework can dynamically absorb the volume expansion stress of the silicon-based active material, improving structural durability and cycle stability. The ionic liquid [BMIM]BF4 is uniformly dispersed and bonded to the three-dimensional network framework through electrostatic interactions, forming continuous nanoscale ionic conductive channels that penetrate the composite layer. The ionic liquid itself has high ionic conductivity and a wide electrochemical window, which can reduce the transport impedance of lithium ions at the interface, improve the battery rate performance, and enable it to release high capacity even at high charge / discharge rates. In addition, PBFDO, PCL and silicon particles can form a hydrogen bond network through hydrogen bonding to provide dynamic adaptability and energy dissipation capability. This strengthens the interfacial bonding between the composite layer and silicon particles, improves interfacial stability, ensures the long-term cycle stability of the composite layer and silicon particles, reduces the continuous decomposition of the electrolyte caused by repeated exposure of the silicon particle surface, and helps to form a stable SEI film, thereby providing the battery with cycle stability and cycle life.

[0064] Comparing Examples 1-5, it can be seen that in Examples 1-3, the particle size distribution of silicon particles in the silicon-based active material of the silicon-based composite anode material satisfies 0.7≤(D90-D10) / D50≤1.3, and the silicon particle size is in a narrow distribution state, which can reduce the problem of interface stress concentration caused by excessive particle size difference, reduce the battery cycle expansion rate, and improve the battery cycle capacity retention rate. However, in Example 4, the particle size distribution of silicon particles in the silicon-based composite anode material is (D90-D10) / D50=0.5 (<0.7), and in Example 5, the particle size distribution of silicon particles in the silicon-based composite anode material is (D90-D10) / D50=1.5 (>1.3). The cycle performance of the battery is lower than that of Examples 1-3, the cycle capacity retention rate is lower, and the cycle expansion rate is higher.

[0065] Comparing Examples 1 and 10-13, in Examples 1 and 10-11, the relationship between the surface hydroxyl density (OH mmol / g) of the silicon-based active material silicon particles and the mass percentage (A) of the rigid conductive polymer PBFDO in the composite layer satisfies the condition: 2.4 ≤ OH / A ≤ 9.0. This ensures that the hydroxyl groups react fully with the active sites on PBFDO to form a stable interfacial bonding layer, thereby improving battery cycle performance. However, compared to Examples 1 and 12-13, in Example 12, OH / A = 2.0 < 2.4, and in Example 13, OH / A = 9.6 > 9.0, resulting in relatively lower battery cycle performance, including a decrease in battery capacity retention and an increase in battery cycle expansion rate.

[0066] Compared with Examples 1 and 6-9, in Examples 1 and 6-7, the mass percentage B of the ionic liquid [BMIM]BF4 in the composite layer and the specific surface area S m² / g of the silicon-based active material silicon particles satisfy the following relationship: 0.0075≤B / S≤0.030. Compared with Example 8 (B / S=0.0429) and Example 9 (B / S=0.005), this is more conducive to ensuring that the ionic liquid is uniformly distributed on the surface of silicon particles to form an efficient ion conduction path and improve the battery cycle performance.

[0067] Compared with Examples 1 and 14-17, in Examples 1 and 14-15, the relationship between the concentration C mol / L of lithium salt LiPF6 in the electrolyte and the mass percentage D of flexible polymer PCL in the composite layer satisfies 1.7 ≤ C / D ≤ 2.6. Compared with Examples 16 (C / D = 3.0) and 17 (C / D = 1.3), this ensures the matching of the lithium affinity of PCL with the lithium salt concentration, which is beneficial to achieve a dynamic balance between the lithium ion supply rate and the lithium ion reception and transmission rate of the composite layer. This optimizes the lithium ion transmission kinetics at the interface between the composite layer and the electrolyte, reduces interface impedance, and improves the charge and discharge efficiency and cycle performance of the battery.

[0068] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A silicon-based composite anode material, characterized in that, The silicon-based composite anode material includes a silicon-based active material and a composite layer coated on the surface of the silicon-based active material. The composite layer includes a rigid conductive polymer, a flexible polymer, and an ionic liquid. The rigid conductive polymer and the flexible polymer are combined through hydrogen bonding to form a three-dimensional network framework. The ionic liquid is dispersed in the three-dimensional network framework, and there is an electrostatic interaction between the ionic liquid and the three-dimensional network framework. The composite layer is connected to the silicon-based active material through hydrogen bonding.

2. The silicon-based composite anode material according to claim 1, characterized in that, The composite layer satisfies at least one of the following conditions: Condition 11: The rigid conductive polymer is a rigid conjugated polymer with an aromatic ring and / or aromatic heterocyclic ring as its main chain; preferably, the rigid conductive polymer is connected to the silicon-based active material through hydrogen bonding. Condition 12: The flexible polymer is a polyester with flexible chain segments; preferably, the flexible polymer is an aliphatic linear polyester. Condition 13: The ionic liquid includes at least one of imidazole ionic liquids, quaternary ammonium salt ionic liquids, pyridine ionic liquids, piperidine ionic liquids, and pyrrole ionic liquids.

3. The silicon-based composite anode material according to claim 2, characterized in that, The rigid conductive polymer includes at least one of polybenzodifurandione, polypyrrole, polyaniline, and polythiophene; The flexible polymer includes at least one of polycaprolactone, polyvalerol, and polytrimethylene carbonate. The ionic liquid includes at least one of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

4. The silicon-based composite anode material according to claim 1, characterized in that, The mass percentages of the rigid conductive polymer, flexible polymer, and ionic liquid in the composite layer are 45%~65%, 30%~50%, and 1%~5%, respectively.

5. The silicon-based composite anode material according to any one of claims 1 to 4, characterized in that, The silicon-based composite anode material satisfies at least one of the following conditions: Condition 21: The particle size distribution of the silicon-based active material satisfies: 0.7≤(D90-D10) / D50≤1.3; preferably, D10=80 nm~250 nm, D50=300 nm~800 nm, D90=250 nm~1000 nm; Condition 22: The surface hydroxyl density of the silicon-based active material is OH mmol / g, and the mass percentage of the rigid conductive polymer in the composite layer is A, wherein OH and A satisfy: 2.4≤OH / A≤9.0; preferably, 1.2≤OH≤4.5; Condition 23: The mass percentage of ionic liquid in the composite layer is B, the specific surface area of ​​the silicon-based active material is S m² / g, and B and S satisfy: 0.0075≤B / S≤0.03; preferably, 1.0≤S≤4.

0.

6. The silicon-based composite anode material according to claim 5, characterized in that, The silicon-based active material is selected from at least one of silicon, silicon carbide, silicon suboxide, and silicon dioxide.

7. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer contains the silicon-based composite negative electrode material according to any one of claims 1 to 6.

8. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in claim 7.

9. The electrochemical device according to claim 8, characterized in that, It also includes a positive electrode, a separator, and an electrolyte, wherein the separator is sandwiched between the positive electrode and the negative electrode; preferably, the electrolyte contains a lithium salt, the concentration of the lithium salt in the electrolyte is C mol / L, and in the silicon-based composite negative electrode material contained in the negative electrode active material layer on the negative electrode, the mass percentage of the flexible polymer in the composite layer is D, and C and D satisfy: 1.7≤C / D≤2.

6.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 8 or 9.

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