Layered negative pole piece structure, electrode assembly, battery monomer, electrochemical device and electric equipment

Abstract

The utility model discloses a layered negative pole piece structure, an electrode assembly, a battery monomer, an electrochemical device and electric equipment, and the layered negative pole piece structure sequentially comprises an active graphite layer, a silicon-based negative pole layer, a porous PVDF-HFP layer and a graphene layer from at least one side of a current collector to the outside. Through the sequential design of the pole piece structure, the problems that the volume of a silicon-based negative pole material is seriously expanded and the negative pole piece is easy to fall off are solved, the safety performance of the battery is improved, and the energy density and the cycle performance of a system are effectively improved.

Description

Technical Field

[0001] This utility model relates to the field of battery structure design technology, specifically to a layered negative electrode structure, electrode assembly, battery cell, electrochemical device, and electrical equipment. Background Technology

[0002] With the widespread application of renewable energy and continuous innovation in energy storage technology, the market demand for high-performance batteries is increasing. Silicon-carbon anode materials, with their excellent theoretical capacity, good conductivity, and high cycle life, are gradually becoming key materials for improving the energy density of lithium-ion batteries.

[0003] However, the lithium insertion and extraction process may cause severe expansion of silicon-based materials, resulting in the pulverization or even peeling of the anode material during cell cycling, affecting the battery's cycle stability. At the same time, the expanding and ruptured particles will continuously consume electrolyte to form a new SEI film, resulting in an excessively thick SEI film, increased cell internal resistance, and a decrease in first-time efficiency. In addition, the high silicon content of high-silicon anodes will generate a large amount of heat when reacting with lithium, posing a safety risk. Directly adding lithium to the electrode may cause severe lithium dendrite growth.

[0004] Therefore, optimizing the structure of silicon-carbon anode materials to ensure their initial coulombic efficiency and cycle stability while suppressing silicon-carbon anode expansion and improving safety performance is a challenging problem that needs to be solved. Utility Model Content

[0005] This utility model addresses the problems in the prior art by disclosing a layered negative electrode structure. Through the sequential design of the electrode structure, it solves the problems of severe volume expansion of the negative electrode material and easy detachment of the negative electrode sheet, thereby improving battery safety performance and effectively enhancing the system's energy density and cycle performance.

[0006] This invention provides a layered negative electrode structure, which, from at least one side of the current collector outwards, sequentially includes an active graphite layer, a silicon-based negative electrode layer, a porous PVDF-HFP layer, and a graphene layer.

[0007] As a further option, the current collector is selected from any one of copper foil, composite copper foil, aluminum foil, titanium foil, and silver foil.

[0008] As a further option, the thickness of the current collector is selected from 5μm-15μm.

[0009] As a further option, the active graphite layer is selected from any one of natural graphite layers, artificial graphite layers, and composite graphite layers.

[0010] As a further option, the coating thickness of the active graphite layer is selected from 15-150 μm.

[0011] As some preferred embodiments, the coating thickness of the active graphite layer is selected from any one of 30μm-120μm, 40μm-90μm, and 50μm-70μm.

[0012] As some preferred embodiments, the coating thickness of the active graphite layer is selected from 40μm-70μm, for example, it can be any one of 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, and 70μm.

[0013] As a further option, the silicon-based anode layer is selected from any one of silicon particle layer, silicon-based alloy layer, silicon oxide layer, and silicon-carbon composite material layer.

[0014] As a further option, the coating thickness of the silicon-based anode layer is selected from 5μm to 150μm.

[0015] As some preferred embodiments, the coating thickness of the silicon-based anode layer is selected from any one of 10μm-120μm, 20μm-100μm, 30μm-80μm, and 40μm-60μm.

[0016] As some preferred embodiments, the coating thickness of the silicon-based anode layer is selected from 40μm-60μm, for example, it can be any one of 40μm, 45μm, 50μm, 55μm, and 60μm.

[0017] As a further option, the coating thickness of the porous PVDF-HFP layer is selected from 1μm to 50μm.

[0018] As some preferred options, the coating thickness of the porous PVDF-HFP layer is selected from any one of 5μm-40μm, 7μm-30μm, and 10μm-20μm.

[0019] As some preferred options, the coating thickness of the porous PVDF-HFP layer is selected from 10μm-20μm.

[0020] As a further option, the pore size of the porous PVDF-HFP layer is selected from 5μm-100μm.

[0021] As some preferred options, the pore size of the porous PVDF-HFP layer is selected from any one of 5μm-80μm, 5μm-60μm, 5μm-40μm, 5μm-30μm, 5μm-20μm, and 5μm-15μm.

[0022] As some preferred options, the pore size of the porous PVDF-HFP layer is selected from 5μm-15μm.

[0023] As a further option, the graphene layer is selected from any one of graphene layer, single-layer graphene layer, graphene oxide layer, reduced graphene oxide layer, nitrogen-doped graphene layer, and composite graphene layer.

[0024] As a further option, the graphene layer is selected from 5μm-20μm.

[0025] As a further option, the graphene layer is selected from 8μm-15μm.

[0026] As a further embodiment, the thickness of the layered negative electrode sheet after rolling is less than 300 μm.

[0027] As a further embodiment, the thickness of the layered negative electrode sheet after rolling is less than 200 μm.

[0028] As a further embodiment, the thickness of the layered negative electrode sheet after rolling is less than 100 μm.

[0029] This utility model also provides an electrode assembly, a battery cell, an electrochemical device, or an electrical device that includes a layered negative electrode structure.

[0030] Electrode components refer to the parts in an electrochemical device used for redox reactions, typically including positive and negative electrodes, and are one of the basic components of a battery cell.

[0031] A battery cell refers to a complete unit consisting of one or more electrode components, an electrolyte, and a separator; it is the basic unit of an electrochemical device.

[0032] An electrochemical device is a device that uses electrochemical reactions to convert energy. It typically consists of multiple battery cells, control circuits, cooling systems, and a casing.

[0033] Electrical equipment refers to equipment that relies on battery cells or electrochemical devices to provide electrical energy to perform certain specific functions.

[0034] The features and beneficial effects of this utility model are as follows:

[0035] (1) By separately coating the active graphite layer and the silicon-based anode layer, this invention avoids the damage to the battery structure caused by the volume expansion of the silicon anode during battery cycling, thereby improving the battery's cycle capability and safety performance.

[0036] (2) By setting a porous PVDF-HFP layer on the surface of the silicon-based anode layer, this utility model avoids the generation of lithium dendrites, regulates the lithium ion flux, and promotes the formation of LiF-rich SEI film. On the other hand, it also achieves the dispersion of graphene layer and provides space for the formation of conductive network between graphene layer and silicon-based anode layer. The setting of graphene layer 5 helps to combine with silicon-based anode layer to build a stable conductive path, improve battery specific capacity and cycle life, and at the same time, it can also help to use the high thermal conductivity and crystallinity of graphene layer to protect the internal structure and improve safety.

[0037] (3) In the negative electrode sheet of the battery of this utility model, optimizing the coating thickness design of each layer helps to improve the overall mechanical stability of the electrode and reduce material cracking and peeling caused by volume changes during charging and discharging. At the same time, this design ensures the overall stability of the structure, enabling each layer to effectively insert and extract ions, avoiding the risk of lithium plating due to uneven ion distribution, thereby improving the charging and discharging efficiency and power density of the battery. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A schematic diagram of the structure of the negative electrode sheet prepared in Example 1;

[0040] Figure 2 Disassembly diagram of the negative electrode sheet prepared in Example 1 after 100 cycles (lithium plating grade 0).

[0041] Figure 3 Disassembly diagram of the negative electrode sheet prepared in Comparative Example 1 after 100 cycles (lithium plating grade 1).

[0042] Figure 4 Disassembly diagram of the negative electrode sheet prepared in Comparative Example 3 after 100 cycles (lithium plating grade 2).

[0043] Figure 5 The image shows the disassembly of the negative electrode sheet prepared in Comparative Example 4 after 100 cycles (lithium plating grade 3).

[0044] Figure labeling: Current collector-1; Active graphite layer-2; Silicon-based anode layer-3; Porous PVDF-HFP layer-4; Graphene layer-5. Detailed Implementation

[0045] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this utility model can be combined with each other.

[0046] This invention provides a layered negative electrode structure, which, from at least one side of the current collector 1 outwards, sequentially includes an active graphite layer 2, a silicon-based negative electrode layer 3, a porous PVDF-HFP layer 4, and a graphene layer 5.

[0047] First, by coating the active graphite layer 2 and the silicon-based anode layer 3 separately, we can effectively reduce the risk of electrode breakage due to volume expansion during charging and discharging by avoiding direct contact between the silicon-based anode layer 3 and the current collector 1. Simultaneously, by allowing the active graphite layer 2 to directly contact the current collector 1, we can effectively avoid the overall pulverization and deactivation of active materials caused by silicon expansion in traditional silicon-carbon anode materials. Furthermore, direct contact between the active graphite layer 2 and the current collector results in better electronic conductivity and better compatibility with the current collector 1, ensuring structural stability. On the other hand, due to the higher platform of the silicon-based anode layer 3, when it is located on the surface of the active graphite layer 2, it can effectively prevent lithium intercalation and lithium plating during pre-lithiation. By separating the active graphite layer 2 and the silicon-based anode layer 3 from at least one side of the current collector 1 outwards, we effectively improve the stability of the layered anode sheet and enhance the electrochemical performance and cycle stability of the battery.

[0048] A porous PVDF-HFP layer 4 is disposed between the silicon-based anode layer 3 and the graphene layer 5. The porous PVDF-HFP layer 4, with its high mechanical and physical strength, helps the silicon-based anode layer 3 further suppress the formation of lithium dendrites. Simultaneously, the porous and highly polar structure and characteristics of the porous PVDF-HFP layer 4 also help the silicon-based anode layer 3 regulate the lithium-ion flux, avoiding the high heat generated by direct contact between a large number of lithium ions and the high-silicon content silicon-based anode layer 3, thus improving safety. Interestingly, the presence of the porous PVDF-HFP layer 4 also helps to promote the growth of the silicon-based anode layer 3. A LiF-rich SEI film is formed on the surface. On the one hand, the LiF-rich SEI film can effectively improve the diffusion efficiency of lithium ions and improve the lithium insertion and extraction behavior. On the other hand, the construction of the LiF-rich SEI film can also effectively support the silicon-based anode layer 3, slow down the consumption of the SEI film formed by the silicon-based anode layer 3, and thus extend the battery life. The setting of the porous PVDF-HFP layer 4 can effectively improve the thermal stability of the layered anode sheet, suppress lithium dendrite phenomenon, optimize lithium ion flux, and establish more charge transport channels, thereby effectively improving cell cycle and first efficiency, and improving safety.

[0049] On the other hand, although the active graphite layer 2 has good electrochemical stability and suitable lithium-ion storage capacity, its high specific surface area and low flatness between layers result in insufficient conductivity. Therefore, we constructed a silicon-based anode layer 3 and a porous PVDF-HFP layer 5 on top of the active graphite layer 2, and set a graphene layer 5 on the outermost layer. Compared with other conductive additives, we believe that graphene has better interfacial compatibility with silicon-based materials, thus enabling the construction of a more stable and dense conductive network. At the same time, the setting of the porous PVDF-HFP layer 5 provides sufficient space for the formation of the conductive network. With the combined action of the silicon-based anode layer 3, the porous PVDF-HFP layer 4, and the graphene layer 5, the conductivity of the active graphite layer 2 is effectively improved, thereby optimizing the specific capacity and cycle life of the layered anode sheet.

[0050] However, since graphene is composed of multiple carbon atoms arranged in sp² hybridization, graphene sheets are prone to agglomeration, resulting in an uneven interface between the electrode and electrolyte. This leads to uneven electrochemical reactions, affecting lithium-ion diffusion and the insertion and extraction of ions in the active graphite layer. Therefore, we placed a porous PVDF-HFP layer 4 between the graphene layer 5 and the silicon-based anode layer 3. The adhesion ability of the porous PVDF-HFP layer allows for better fixation of the graphene layer 5. In addition, due to the high crystallinity of graphene, the graphene layer 5, which is placed on the outermost layer of the layered anode structure, can act as a stable physical barrier, reducing the possibility of side reactions. At the same time, the excellent thermal conductivity of the graphene layer 5 can further optimize the conductivity and heat dissipation of the layered anode, improving the overall safety and electrochemical performance of the battery cell.

[0051] As a further option, the current collector 1 is selected from any one of copper foil, composite copper foil, aluminum foil, titanium foil, and silver foil.

[0052] As a further option, the thickness of the current collector 1 is selected from 5μm-15μm.

[0053] As a further option, the active graphite layer 2 is selected from any one of natural graphite layer, artificial graphite layer, and composite graphite layer.

[0054] As some specific examples, the natural graphite layer may consist of natural graphite material purchased from Qingdao Tianyuan Graphite Co., Ltd. and some necessary binders; the artificial graphite layer may consist of artificial graphite material SN-P2H purchased from Snow New Materials Co., Ltd. and some necessary binders; the composite graphite layer may consist of commercially available composite graphene material MAG-100 purchased from Snow New Materials Co., Ltd. and some necessary binders.

[0055] As a further option, the coating thickness of the active graphite layer 2 is selected from 15-150 μm. When the coating thickness of the active graphite layer 2 is greater than 150 μm, the excessively high coating thickness may lead to a longer lithium-ion conduction path and a decrease in conduction efficiency; while when the coating thickness of the active graphite layer 2 is less than 15 μm, the excessively low coating thickness may lead to a reduction in the usable active area, thereby reducing the energy density and specific capacity of the battery. Therefore, when the coating thickness of the active graphite layer 2 is selected from 15 μm to 150 μm, it helps to increase the active area while ensuring lithium-ion conduction efficiency, thereby improving the energy density and specific capacity of the battery.

[0056] As some preferred embodiments, the coating thickness of the active graphite layer is selected from 30μm-120μm, 40μm-90μm, and 50μm-70μm. The coating thickness of the active graphite layer 2 will affect the lithium-ion conduction path and active area of ​​the layered negative electrode sheet. When the coating thickness of the active graphite layer 2 is selected from 15-150μm, as the coating thickness of the active graphite layer 2 increases, the battery energy density and total capacity are optimized simultaneously, but the lithium-ion transport path may be affected. Therefore, the preferred coating thickness of the active graphite layer 2 is 30μm-120μm, 35μm-90μm, and 40μm-70μm.

[0057] As some preferred embodiments, the coating thickness of the active graphite layer 2 is selected from 40μm-70μm, for example, it can be any one of 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, and 70μm. When the coating thickness of the active graphite layer 2 is selected from 45μm-70μm, it helps to obtain better battery density and specific capacity. At the same time, the coating thickness of 40μm-70μm also helps to further reduce internal stress and improve the cycle stability of the battery.

[0058] As a further option, the silicon-based anode layer 3 is selected from any one of silicon particle layer, silicon-based alloy layer, silicon oxide layer, and silicon-carbon composite material layer.

[0059] As some specific examples, the silicon particle layer may consist of silicon particles Si13502 purchased from Zhongnuo New Materials Co., Ltd. and some necessary binders; the silicon-based alloy layer may consist of FeSi45 silicon-iron alloy powder purchased from Yuehan Metal Materials Co., Ltd. and some necessary binders; the silicon oxide layer may consist of silicon suboxide material YOB166 purchased from Tianmu Pioneer Battery Materials Co., Ltd. and some necessary binders; the silicon-carbon composite material layer may consist of either silicon-carbon composite material S0310 commercially available from Lanxi Zhide New Energy Materials Co., Ltd. or silicon-carbon composite material SH-01 commercially available from Shenghua New Energy Materials Co., Ltd., and some necessary binders.

[0060] As a further option, the coating thickness of the silicon-based anode layer 3 is selected from 5μm to 150μm. When the coating thickness of the silicon-based anode layer 3 is selected from 5μm to 150μm, it helps to improve the capacity density, optimize the conductive network, and alleviate the stress caused by the volume expansion during silicon charging and discharging to a certain extent, preventing the silicon anode material from cracking and falling off.

[0061] As some preferred embodiments, the silicon-based anode layer coating thickness 3 is selected from any one of 10μm-120μm, 20μm-100μm, 30μm-80μm, and 40μm-60μm. When the silicon-based anode layer coating thickness 3 is selected from 5-150μm, increasing the coating thickness of the silicon-based anode layer 3 will lead to optimized capacity density. However, further increasing the coating thickness of the silicon-based anode layer 3 may also lead to increased internal stress. Therefore, selecting the silicon-based anode layer coating thickness from 10μm-120μm, 20μm-100μm, 30μm-80μm, and 40μm-60μm helps to obtain better capacity density and lower internal stress, improve specific capacity and cycle capacity retention, and reduce anode expansion rate.

[0062] As some preferred embodiments, the thickness of the silicon-based anode three-layer coating is selected from 40μm-60μm, for example, it can be any one of 40μm, 45μm, 50μm, 55μm, and 60μm. When the thickness of the silicon-based anode three-layer coating is selected from 40μm-60μm, it helps to further leverage the advantages of the thickness of the silicon-based anode three-layer coating, obtain a layered anode sheet structure with good specific capacity performance, optimize the expansion rate of the layered anode sheet, and obtain a better cycle capacity retention rate.

[0063] As some specific examples, the porous PVDF-HFP layer 4 may be composed of either PVDF-HFP material purchased from Dongguan Taotao Plastic Raw Materials Co., Ltd. or PVDF-HFP material purchased from Suzhou Qinshang Plastic Chemical Co., Ltd., and some necessary binders.

[0064] As a further embodiment, the coating thickness of the porous PVDF-HFP layer 4 is selected from 1μm to 50μm. When the coating thickness of the porous PVDF-HFP layer 4 is selected from 1μm to 50μm, it helps to fully utilize its excellent mechanical and physical strength to suppress the formation of lithium dendrites. At the same time, controlling the coating thickness of the porous PVDF-HFP layer 4 to be selected from 1μm to 50μm can also alleviate the stress caused by the expansion of the silicon anode, further optimize the anode expansion rate, and improve the battery cycle capacity retention capability.

[0065] As some preferred embodiments, the coating thickness of the porous PVDF-HFP layer 4 is selected from any one of 5μm-40μm, 7μm-30μm, and 10μm-20μm. When the coating thickness of the porous PVDF-HFP layer 4 is selected from 1μm-50μm, the mechanical strength increases with the gradual increase of the coating thickness, thus better suppressing the formation of lithium dendrites and achieving the fixation of the graphene layer 5. However, at the same time, the internal stress is also affected. Therefore, it is necessary to find a range with higher mechanical strength and lower stress. Thus, the range of coating thickness of the porous PVDF-HFP layer 4 is further preferably 5μm-40μm, 7μm-30μm, and 10μm-20μm.

[0066] As some preferred embodiments, the coating thickness of the porous PVDF-HFP layer 4 is selected from 10μm-20μm, for example, it can be any one of 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, and 20μm.

[0067] As a further embodiment, the porous PVDF-HFP layer 4 has a pore size selected from 5μm to 100μm. The porous PVDF-HFP layer 4 can utilize its porous and highly polar structure to regulate lithium-ion flux and promote the formation of a "LiF-rich" SEI film. Therefore, by controlling the size of the pores in the porous PVDF-HFP layer 4, it is helpful to further regulate the lithium-ion flux and the formation of a LiF-containing SEI film. When the pore size on the porous PVDF-HFP layer 4 is selected from 5μm to 100μm, the lithium-ion flux can be regulated. At the same time, the pore size of 5μm-100μm also helps to enhance the local concentration of lithium ions and fluorine sources (such as fluorides in the electrolyte), thereby promoting the precipitation and formation of LiF.

[0068] As some preferred options, the pore size of the porous PVDF-HFP layer 4 is selected from any one of 5μm-80μm, 5μm-60μm, 5μm-40μm, 5μm-30μm, 5μm-20μm, and 5μm-15μm.

[0069] As some preferred embodiments, the pore size of the porous PVDF-HFP layer is selected from 5μm to 15μm, for example, it can be any one of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, and 15μm. When the pore size of the porous PVDF-HFP layer is selected from 5μm to 15μm, it helps to further control the lithium-ion flux, improve safety, suppress the expansion of the negative electrode, and improve the cycle capacity retention rate.

[0070] As a further option, the graphene layer 5 is selected from any one of graphene layer, single-layer graphene layer, graphene oxide layer, reduced graphene oxide layer, nitrogen-doped graphene layer, and composite graphene layer.

[0071] As specific examples, the graphene layer may consist of 97% pure graphene purchased from Shanghai McLean Biochemical Technology Co., Ltd., and some necessary binders; the monolayer graphene layer may consist of monolayer graphene purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., and some necessary binders; the graphene oxide layer may consist of graphene oxide purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and some necessary binders; the reduced graphene oxide layer may consist of Nanoinnova reduced graphene purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., and some necessary binders; the nitrogen-doped graphene layer may consist of nitrogen-doped graphene purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and some necessary binders; and the composite graphene layer may consist of MAG-100 composite graphene material purchased from Snow New Materials Co., Ltd., and some necessary binders.

[0072] As a further embodiment, the graphene layer 5 is selected from 5μm-20μm. A graphene layer with a thickness of 5μm-20μm can provide stronger conductivity and, combined with the silicon-based anode layer 3, construct a more stable conductive path. On the other hand, it can also work with the porous PVDF-HFP layer 4 to achieve more uniform dispersion and fixation. In addition, when the coating thickness of the graphene layer 5 is selected from 5μm-20μm, it can also fully exert the barrier effect, protect the inner structure, reduce the occurrence of side reactions, and generate a more stable SEI film. At the same time, when the coating thickness is selected from 5μm-20μm, it can also fully exert the thermal conductivity of graphene, improve the thermal conductivity of the layered anode sheet, and improve safety.

[0073] As a further option, the graphene layer is selected from 8μm-15μm, for example, it can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, or 15μm. When the graphene layer is selected from 8μm-15μm, it helps to further optimize the electrochemical performance of the layered negative electrode, reduce the negative electrode expansion rate, and improve the battery specific capacity, first-cycle coulombic efficiency, and cycle capacity retention rate.

[0074] As some preferred embodiments, the coating thickness of the active graphite layer 2 is 40μm-60μm; the coating thickness of the silicon-based anode layer 3 is 40μm-60μm; the coating thickness of the porous PVDF-HFP layer 4 is 10μm-20μm, with a pore size selected from 5μm-20μm; and the coating thickness of the graphene layer 5 is 10μm-15μm. Firstly, the active graphite layer 2 with a coating thickness of 40μm-60μm helps to further optimize the lithium-ion conduction path and improve conduction efficiency while ensuring energy density and specific capacity. The 40μm-60μm silicon-based anode layer 3 can further improve specific capacity, alleviate internal deformation stress, and optimize the conductive network constructed with the graphene layer 5 and the porous PVDF-HFP layer 4. When the coating thickness of the porous PVDF-HFP layer 4 is selected from 10μm-20μm, on the one hand, it helps to fully utilize the mechanical properties of the PVDF-HFP layer 4 and suppress the occurrence of dendrites; on the other hand, it also... This helps to achieve better dispersion of the graphene layer. When the pore size is selected from 5μm-20μm, the lithium-ion flux can be further adjusted and space for the formation of the conductive network can be provided. Finally, the 10μm-15μm coating thickness of the graphene layer 5 can provide better conductivity. Combined with the silicon-based anode layer 3, it can build a more stable conductive path and also help to achieve more uniform fixation with the porous PVDF-HFP layer 4. With the joint cooperation of the active graphite layer 2, silicon-based anode layer 3, porous PVDF-HFP layer 4, and graphene layer 5, it helps to obtain a layered anode electrode structure with higher safety and cycle stability.

[0075] As a further improvement, the layered negative electrode sheet has a thickness of less than 300 μm after rolling. When the thickness of the layered negative electrode sheet after rolling is less than 300 μm, it helps to shorten the ion diffusion path, thereby improving the charge and discharge rate of the battery.

[0076] As a further embodiment, the thickness of the layered negative electrode sheet after rolling is less than 200 μm.

[0077] As a further improvement, the layered negative electrode sheet has a thickness of less than 100 μm after rolling. When the thickness of the layered negative electrode sheet after rolling is less than 100 μm, it helps to further shorten the ion diffusion path and reduce the mechanical stress caused by volume changes during charging and discharging, thereby optimizing battery life.

[0078] This utility model also provides an electrode assembly, a battery cell, an electrochemical device, or an electrical device that includes a layered negative electrode structure.

[0079] Electrode components refer to the parts in an electrochemical device used for redox reactions, including positive and negative electrode plates, and are one of the basic components of a battery cell.

[0080] A battery cell refers to a complete unit consisting of one or more electrode components, an electrolyte, and a separator; it is the basic unit of an electrochemical device.

[0081] An electrochemical device is a device that uses electrochemical reactions to convert energy. It typically consists of multiple battery cells, control circuits, cooling systems, and a casing.

[0082] Electrical equipment refers to equipment that relies on battery cells or electrochemical devices to provide electrical energy to perform certain specific functions.

[0083] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0084] An exemplary structure of the layered negative electrode sheet structure provided by this utility model can be as follows: Figure 1 As shown, from both sides of the current collector 1 outwards, there are successively an active graphite layer 2, a silicon-based negative electrode layer 3, a porous PVDF-HFP layer 4, and a graphene layer 5.

[0085] As a specific example of the implementation of this utility model, detailed examples are provided below:

[0086] Example 1

[0087] From both sides of the current collector 1 outwards, the layers sequentially include an active graphite layer 2, a silicon-based anode layer 3, a porous PVDF-HFP layer 4, and a graphene layer 5. Specifically, the current collector 1 uses a 6μm thick copper foil coating; the active graphite layer 2 is a 50μm thick artificial graphite layer; the silicon-based anode layer 3 is a 50μm thick silicon oxide layer; the porous PVDF-HFP layer 4 is commercially available PVDF-HFP material from Dongguan Taotao Plastic Raw Materials Co., Ltd., with a coating thickness of 10μm and a pore size of 10μm; and the graphene layer 5 is commercially available 97% pure graphene from Shanghai Maclean Biochemical Technology Co., Ltd., with a coating thickness of 10μm. These layers are coated onto the current collector to obtain the desired effect. Figure 1 As shown.

[0088] Example 2

[0089] The preparation method and process are the same as in Example 1, except that the active graphite layer 2 is composed of MAG-100 composite graphene material purchased from Snow New Materials Co., Ltd. and some necessary binders.

[0090] Example 3

[0091] The preparation method and process are the same as in Example 1, except that the thickness of the active graphite layer 2 is 40 μm.

[0092] Example 4

[0093] The preparation method and process are the same as in Example 1, except that the silicon-based anode layer 3 is composed of silicon-carbon composite material SO310 commercially available from Lanxi Zhide New Energy Materials Co., Ltd., and some necessary binders.

[0094] Example 5

[0095] The preparation method and process are the same as in Example 1, except that the silicon-based anode layer 3 is composed of silicon-carbon composite material SH-01 commercially available from Shenghua New Energy Materials Co., Ltd., and some necessary binders.

[0096] Example 6

[0097] The preparation method and process are the same as in Example 1, except that the silicon-based anode layer 3 is a silicon oxide anode with a coating thickness of 40 μm.

[0098] Example 7

[0099] The preparation method and process are the same as in Example 1, except that the silicon-based anode layer 3 is a silicon oxide anode with a coating thickness of 60 μm.

[0100] Example 8

[0101] The preparation method and process are the same as in Example 1, except that the pore size of the porous PVDF-HFP layer 4 is 20 μm.

[0102] Comparative Example 1

[0103] The preparation method and process are the same as in Example 1, except that the active graphite layer 2 is not set.

[0104] Comparative Example 2

[0105] The preparation method and process are the same as in Example 1, except that the porous PVDF-HFP layer 4 is not provided.

[0106] Comparative Example 3

[0107] The preparation method and process are the same as in Example 1, except that the graphene layer 5 is not provided.

[0108] Comparative Example 4

[0109] The preparation method and process are the same as in Example 1, except that the positions of the silicon-based anode layer 3 and the active graphite layer 2 are swapped, that is, the silicon-based anode layer 3 is closer to the current collector 1.

[0110] Comparative Example 5

[0111] The preparation method and process are the same as in Example 1.1, except that the positions of the graphene layer 5 and the porous PVDF-HFP layer 4 are swapped, that is, the porous PVDF-HFP layer 4 is on the outermost side.

[0112] Comparative Example 6

[0113] The preparation method and process are the same as in Example 1, except that the active graphite layer 2 is replaced by a lithium metal layer.

[0114] Comparative Example 7

[0115] The preparation method and process are the same as in Example 1, except that the graphene layer 5 is replaced by a nitrogen-doped graphite layer.

[0116] After the prepared electrode sheets were thoroughly dried, they were assembled into coin cells. The electrical performance of the assembled coin cells was tested, and the test results are shown in Table 1.

[0117] Test process:

[0118] (1) Discharge at 0.1C to 0.005V;

[0119] (2) Charge to 2V at 0.1C.

[0120] Repeat the above steps 100 times.

[0121] Wherein, the negative electrode expansion rate = (thickness of the negative electrode sheet after rolling after cycling - thickness of the negative electrode sheet after rolling before cycling) / thickness of the negative electrode sheet after rolling before cycling × 100%

[0122] The test results of Examples 1-8 and Comparative Examples 1-7 are shown in Table 1.

[0123] Table 1

[0124]

[0125] Based on the severity of lithium plating, the situation is divided into 10 levels, with higher values ​​indicating more severe lithium plating. The criteria for distinguishing the 10 levels of lithium plating are shown in Table 3.

[0126] Table 2

[0127]

[0128] As observed in Examples 1-8 and Comparative Examples 1-7, Examples 1-8 exhibit higher specific capacity and first-cycle coulombic efficiency than Comparative Examples 1-7. After 100 cycles, the capacity retention of Examples 1-8 is generally better than that of Comparative Examples 1-7. Furthermore, after 100 cycles, the anode expansion rate of Examples 1-8 is generally better than that of Comparative Examples 1-7. Meanwhile, Examples 1-8 did not exhibit lithium plating, while Comparative Examples 1-7 all showed lithium plating. This indicates that the layered anode structure proposed in this scheme can effectively improve specific capacity and first-cycle coulombic efficiency, while optimizing cycle performance and avoiding the expansion phenomenon of silicon-containing anodes due to lithium dendrite formation.

[0129] From Example 1 ( Figure 1 As observed in Comparative Examples 1-3, the active graphite layer 2, silicon-based anode layer 3, porous PVDF-HFP layer 4, and graphene layer 5 are all essential components of the layered anode electrode structure. When the active graphite layer 2 is absent, the silicon-based anode layer 3 in Comparative Example 1 directly contacts the current collector 1, leading not only to first-order lithium plating but also potential damage to the silicon anode electrode due to volume expansion during charging and discharging. Therefore, Comparative Example 1 exhibits a higher anode expansion rate and a lower cycle capacity retention rate. Similarly, when the porous PVDF-HFP layer 4 is not present, lithium plating also occurs in Comparative Example 2. Furthermore, due to the lack of the porous PVDF-HFP layer 4 to regulate lithium-ion flux, the process of lithium-ion insertion and extraction from the silicon-based anode layer 3 becomes more disordered, making it difficult to form a LiF-rich SEI film, thus affecting battery cycling. Therefore, Comparative Example 2 exhibits a lower cycle capacity retention rate and a higher expansion rate than Example 1. Comparative Example 4 demonstrates the crucial role of the graphene layer 5 in the structure. The importance of constructing a layered negative electrode structure is highlighted. Without the graphene layer 5, Comparative Example 4 achieves a lithium plating grade of 2. However, its specific capacity, first-cycle coulombic efficiency, cycle capacity retention, and negative electrode expansion are all inferior to Example 1. This may be because the absence of the outermost graphene layer 5 allows the electrolyte to directly contact the active material, leading to frequent side reactions. Furthermore, the lack of the graphene layer 5 may hinder the dissipation of heat released during the reaction of lithium ions with the silicon-based negative electrode layer 3, thus affecting battery cycling. Additionally, the absence of graphene, with its good conductivity, may also negatively impact the battery's electrochemical performance. Therefore, Comparative Example 3 has a specific capacity of only 560.88 mAh / g, a first-cycle coulombic efficiency of only 87.36%, and a capacity retention of only 83.9% after 100 cycles, significantly lower than Example 1.

[0130] As observed in Example 1 and Comparative Example 4, when the silicon-based anode layer 3 is replaced with the active graphite layer 2, a severe lithium plating phenomenon (level 3) occurs in Comparative Example 4. At the same time, the cycle capacity retention rate and the anode expansion rate are significantly affected. This may be because after exchanging the silicon-based anode layer 3 with the active graphite layer 2, the barrier effect of the active graphite layer 2 on the silicon-based anode layer 3 cannot be utilized. In addition, the silicon-based anode layer 3 in direct contact with the current collector may lead to a severe lithium plating phenomenon. Therefore, in addition to coating the active graphite layer 2 and the silicon-based anode layer 3 separately, it is also necessary to ensure that the active graphite layer 2 is located between the current collector 1 and the silicon-based anode layer 3 in order to fully utilize the function of the separately coated active graphite layer 2.

[0131] Exchanging the graphene layer 5 with the porous PVDF-HFP layer 4 also affects the cycle performance and capacity retention of the battery. As observed in Example 1 and Comparative Example 5, the order in which the graphene layer 5 and the porous PVDF-HFP layer 4 are exchanged will not fully utilize the flux control capability and the suppression effect on lithium dendrites of the porous PVDF-HFP layer 4, resulting in lithium plating after 100 cycles. At the same time, the graphene layer 5 located inside the porous PVDF-HFP layer 4 will not be able to fully perform its barrier function, leading to frequent side reactions and an increase in the negative electrode expansion rate. The specific capacity and the first-cycle coulombic efficiency are also affected, resulting in a capacity retention of only 81.77% after 100 cycles, which is much lower than that in Example 1.

[0132] Therefore, as can be seen from Example 1 and Comparative Examples 4-5, in addition to ensuring the simultaneous presence of the active graphite layer 2, silicon-based anode layer 3, porous PVDF-HFP layer 4, and graphene layer 5, it is also necessary to further ensure that the active graphite layer 2, silicon-based anode layer 3, porous PVDF-HFP layer 4, and graphene layer 5 are sequentially arranged from at least one side outward from the current collector 1. Only in this way can the function of the layered anode electrode structure be fully utilized, the battery cycle stability and first-cycle coulombic efficiency be improved, lithium deposition be suppressed, and the anode expansion rate be reduced.

[0133] As can be seen from Example 1 and Comparative Example 6, when lithium sheets are used to replace the active graphite layer 2, the lithium plating level of Comparative Example 6 reaches level 2, the negative electrode expansion rate reaches 51.65%, and the capacity retention rate after 100 cycles is only 81.37%. This shows that the presence of the active graphite layer 2 can effectively improve the cycle capacity retention rate and avoid lithium plating and negative electrode expansion.

[0134] As observed in Example 1 and Comparative Example 7, when nitrogen-doped graphite layer is used to replace graphene layer 5, the specific capacity and first-cycle coulombic efficiency of Comparative Example 7 are significantly lower than those of Example 1. At the same time, the cycle capacity retention rate is also lower than that of Example 1, and lithium plating occurs. This may be because, compared with graphene, although nitrogen-doped graphite has good interfacial compatibility with silicon-based anode layer 3, its conductivity is inferior to that of graphene. Therefore, it is difficult to construct a stable conductive path through the porous PVDF-HFP layer, resulting in a decrease in the specific capacity and capacity retention rate of the layered anode sheet. Meanwhile, the graphene layer has higher crystallinity and thermal conductivity than the nitrogen-doped graphite layer, thus better protecting the internal layer structure and improving the safety of the battery.

[0135] Examples 1-2 demonstrate the preparation of active graphite layer 2 using different graphite materials. It can be observed that Examples 1-2 all exhibit good specific capacity and first-cycle coulombic efficiency. Furthermore, after 100 cycles, the capacity retention rate can reach over 92.2%, and no lithium plating phenomenon is observed. This indicates that the active graphite layer 2 prepared by different materials can effectively suppress the expansion of silicon-based anode layer 3.

[0136] Examples 1 and 3 demonstrate the effect of different coating thicknesses of the active graphite layer 2 on the performance of the layered anode sheet. When the active graphite layer 2 is 40 μm-70 μm thick, Examples 1 and 3 both exhibit excellent specific capacity and first-cycle coulombic efficiency. Furthermore, after 100 cycles, they still show good capacity retention and anode expansion rate, indicating that when the coating thickness of the active graphite layer 2 is selected from 40 μm to 70 μm, the electrochemical performance of the layered anode sheet can be effectively optimized, while effectively suppressing the expansion of the silicon-based anode layer 3 and preventing lithium deposition.

[0137] As can be observed from Examples 1, 4, and 5, after replacing the material used to prepare the silicon-based anode layer 3, Examples 1, 4, and 5 all exhibited good cycle capacity retention after 100 cycles. At the same time, no lithium plating occurred, indicating that the difference in silicon-based materials does not affect the expansion suppression effect of the layered anode sheet.

[0138] Different coating thicknesses of the silicon-based anode layer 3 may lead to different effects. As can be observed from Examples 1, 6, and 7, Example 7 exhibits better specific capacity than Examples 1 and 6. Meanwhile, Example 6 exhibits better first-cycle coulombic efficiency, cycle capacity retention, and suppression of anode expansion than Examples 1 and 7. Therefore, based on Examples 1, 6, and 7, the coating thickness of the silicon-based anode layer 3 can be further preferred to be 40 μm-60 μm.

[0139] As can be observed from Examples 1 and 8, when the pore size on the porous PVDF-HFP layer 4 is selected from 10μm to 20μm, Examples 1 and 8 both exhibit excellent first-cycle coulombic efficiency. At the same time, after 100 cycles, the cycle capacity retention rate is still higher than 92.5%. This may be because when the pore size on the porous PVDF-HFP layer 4 is selected from 10μm to 20μm, the regulating effect of the porous PVDF-HFP layer 4 on lithium-ion flux can be fully utilized, while promoting the construction of LiF-rich SEI film, thereby optimizing the first-cycle coulombic efficiency and cycle stability of Examples 1 and 8.

[0140] It should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A layered negative electrode structure, characterized in that, From at least one side outward from the current collector (1), it includes an active graphite layer (2), a silicon-based anode layer (3), a porous PVDF-HFP layer (4), and a graphene layer (5).

2. The layered negative electrode structure according to claim 1, characterized in that, The current collector (1) is selected from any one of copper foil, composite copper foil, aluminum foil, titanium foil, and silver foil; The thickness of the current collector (1) is selected from 5μm-15μm.

3. The layered negative electrode structure according to claim 1, characterized in that, The active graphite layer (2) is selected from any one of natural graphite layer, artificial graphite layer, and composite graphite layer; The coating thickness of the active graphite layer (2) is selected from 15-150 μm.

4. The layered negative electrode structure according to claim 1, characterized in that, The silicon-based anode layer (3) is selected from any one of silicon particle layer, silicon-based alloy layer, silicon oxide layer, and silicon-carbon composite material layer.

5. The layered negative electrode structure according to claim 1, characterized in that, The coating thickness of the silicon-based anode layer (3) is selected from 5μm to 150μm.

6. The layered negative electrode structure according to claim 1, characterized in that, The coating thickness of the porous PVDF-HFP layer (4) is selected from 1μm-50μm; The coating thickness of the porous PVDF-HFP layer (4) is selected from any one of 5μm-40μm, 7μm-30μm, and 10μm-20μm; The pore size of the porous PVDF-HFP layer (4) is selected from 5μm-100μm.

7. The layered negative electrode structure according to claim 1, characterized in that, The graphene layer (5) is selected from any one of the following: graphene layer, single-layer graphene layer, graphene oxide layer, reduced graphene oxide layer, nitrogen-doped graphene layer, and composite graphene layer.

8. The layered negative electrode structure according to claim 1, characterized in that, The thickness of the graphene layer (5) is selected from 5μm to 20μm.

9. The layered negative electrode structure according to claim 1, characterized in that, The thickness of the layered negative electrode sheet after rolling is less than 300 μm.

10. The layered negative electrode structure according to claim 3, characterized in that, The coating thickness of the active graphite layer (2) is selected from any one of 30μm-120μm, 40μm-90μm, and 50μm-70μm.

11. The layered negative electrode structure according to claim 3, characterized in that, The coating thickness of the active graphite layer (2) is selected from 40μm-70μm.

12. The layered negative electrode structure according to claim 5, characterized in that, The coating thickness of the silicon-based anode layer (3) is selected from any one of 10μm-120μm, 20μm-100μm, 30μm-80μm, and 40μm-60μm.

13. The layered negative electrode structure according to claim 6, characterized in that, The pore size of the porous PVDF-HFP layer (4) is selected from any one of 5μm-80μm, 5μm-60μm, 5μm-40μm, 5μm-30μm, 5μm-20μm, and 5μm-15μm.

14. The layered negative electrode structure according to claim 6, characterized in that, The pore size of the porous PVDF-HFP layer (4) is selected from 5μm-15μm.

15. The layered negative electrode structure according to claim 8, characterized in that, The thickness of the graphene layer (5) is selected from 8μm to 15μm.

16. The layered negative electrode structure according to claim 9, characterized in that, The thickness of the layered negative electrode sheet after rolling is less than 200 μm.

17. The layered negative electrode structure according to claim 9, characterized in that, The thickness of the layered negative electrode sheet after rolling is less than 100 μm.

18. An electrode assembly, characterized in that, Includes the layered negative electrode structure as described in any one of claims 1-17.

19. A single battery cell, characterized in that, Includes the layered negative electrode structure as described in any one of claims 1-17.

20. An electrochemical device, characterized in that, Includes the layered negative electrode structure as described in any one of claims 1-17.

21. An electrical appliance, characterized in that, Includes the layered negative electrode structure as described in any one of claims 1-17.

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