A negative electrode sheet for a secondary battery, a secondary battery, and an electronic device.

Abstract

This application relates to the field of battery technology, and particularly to a negative electrode sheet for a secondary battery, a secondary battery, and an electronic device. The negative electrode sheet includes a negative electrode current collector coated with a negative electrode composite material comprising porous graphene and a negative electrode substrate. The diameter distribution parameters, volatile matter content, and weight percentage of the porous graphene in the negative electrode sheet satisfy the following relationship: 0.02 ≤ A / (B*D) ≤ 0.80; the porous graphene is coated on the surface of the negative electrode substrate; where A represents the weight percentage of the porous graphene, B represents the volatile matter content of the porous graphene, and D represents the diameter distribution parameters of the porous graphene. By adding porous graphene to the conductive agent of the negative electrode sheet, and adjusting the diameter distribution parameters, volatile matter content, and weight percentage of the porous graphene in the negative electrode sheet to satisfy the above relationship, the battery performance of the secondary battery can be synergistically improved, especially its low-temperature charge-discharge performance, low-temperature polarization, and cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode sheet for a secondary battery, a secondary battery, and an electronic device. Background Technology

[0002] Rechargeable batteries are among the most promising clean energy sources. However, due to the increased charge migration impedance of functional ions at low temperatures, their diffusion rate in the electrodes decreases significantly, leading to common low-temperature performance limitations. For example, lithium iron phosphate (LFP) batteries may fail to charge and discharge at low temperatures. Furthermore, the increased viscosity of the electrolyte at low temperatures reduces the diffusion rate of functional ions in the solid phase, further decreasing ion transport rates. Existing technologies typically improve electrolyte formulations and reduce interfacial impedance to optimize low-temperature performance. However, the electrolyte and solid-phase compositions used in different battery systems vary greatly, resulting in complex compositions that require extensive research and optimization, leading to high R&D and manufacturing costs and hindering widespread application. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this application provides a negative electrode sheet for a secondary battery and a secondary battery itself, which can effectively improve the overall performance and low-temperature performance of the battery. It is also applicable to various battery systems, exhibiting good versatility and low cost. The specific technical solution is as follows:

[0004] On one hand, this application provides a negative electrode sheet for a secondary battery, including a negative electrode current collector, wherein the current collector is coated with a negative electrode composite material including porous graphene and a negative electrode main material, wherein the diameter distribution parameters, volatile matter and weight ratio of the porous graphene in the negative electrode sheet satisfy the following relationship: 0.02≤A / (B*D)≤0.80; the porous graphene is coated on the surface of the negative electrode main material;

[0005] Wherein, A represents the weight percentage of the porous graphene, B represents the volatile matter content of the porous graphene, and D represents the sheet size distribution parameter of the porous graphene.

[0006] Specifically, the porous graphene accounts for 0.5% ≤ A ≤ 1.5% of the weight of the negative electrode sheet.

[0007] Specifically, the volatile components of the porous graphene are 1% ≤ B ≤ 5%.

[0008] Specifically, the sheet diameter distribution parameter of the porous graphene is 2.0≤D≤5.5.

[0009] Specifically, the formula for calculating the sheet size distribution parameter of the porous graphene is: D = [(D1-D3) / D2]; D1 represents the sheet size corresponding to the cumulative volume percentage of the porous graphene in the aqueous solvent reaching the first preset percentage, D2 represents the sheet size corresponding to the cumulative volume percentage of the porous graphene in the aqueous solvent reaching the second preset percentage, and D3 represents the sheet size corresponding to the cumulative volume percentage of the porous graphene in the aqueous solvent reaching the third preset percentage, wherein the first preset percentage, the second preset percentage, and the third preset percentage decrease sequentially.

[0010] Specifically, the porous graphene in the negative electrode sheet satisfies at least one of the following characteristics:

[0011] The sheet diameter D1 of the porous graphene satisfies 10≤D1≤20μm;

[0012] The diameter D2 of the porous graphene sheet satisfies 3.5≤D2≤8μm;

[0013] The diameter D3 of the porous graphene sheet satisfies 0.5 ≤ D3 ≤ 2 μm.

[0014] Specifically, the first preset percentage is 80%-95%, the second preset percentage is 45%-60%, and the third preset percentage is 5%-15%.

[0015] Preferably, the sheet diameter distribution parameters, volatile matter content, and weight percentage of the porous graphene in the negative electrode sheet satisfy the following relationship: 0.02≤A / (B*D)≤0.60.

[0016] Specifically, the pore size of the porous graphene is 10–20 nm.

[0017] On the other hand, this application provides a secondary battery, which includes the negative electrode sheet as described above.

[0018] On the other hand, this application provides an electronic device that includes a secondary battery as described above.

[0019] Based on the above technical solution, this application has the following beneficial effects:

[0020] This application adds porous graphene to the conductive agent of the negative electrode sheet. By adjusting the sheet size distribution parameters, volatile matter, and weight ratio of the porous graphene in the negative electrode sheet to satisfy the above-mentioned relationship, the dispersion ability of porous graphene is significantly better than that of conventional graphene nanosheets. This effectively reduces the agglomeration of nanomaterials, lowers the internal resistance of the electrode sheet, and ensures that ions can freely shuttle through the porous structure of graphene. This avoids the need to bypass the micron-sized graphene sheets, shortens the ion transport path, optimizes the ion conduction ability, and improves the low-temperature lithium plating problem. Furthermore, porous graphene can be used as both a conductive agent and an ion conduction agent without the need to add other ion conduction agents, thus optimizing the material structure of the negative electrode system. Meanwhile, by coordinating and optimizing the constraints among characteristic parameters such as the weight ratio, volatile matter, and sheet size distribution of porous graphene, good dispersion of porous graphene is achieved. While ensuring its conductivity, the ion conduction path is shortened, the low-temperature performance of the battery is optimized, and the coating structure of the electrode host material (such as graphite) is constructed using porous graphene to alleviate the cycle decay problem caused by the volume expansion of the host material during charge and discharge. This synergistically improves the battery performance of the secondary battery, especially the low-temperature charge and discharge performance, low-temperature polarization, and cycle performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0022] Figure 1 This is a SEM image of the negative electrode sheet provided in the embodiments of this application;

[0023] Figure 2 This is a cyclic data graph provided in the embodiments of this application under the conditions of 25°C 1C / 1C. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] For the terms defined below, unless a different definition is given elsewhere in the claims or this specification, these definitions shall apply. All numerical values, whether explicitly indicated or not, are defined herein as being modified by the term "about." The term "about" generally refers to a range of numerical values ​​that a person skilled in the art would consider equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A range of numerical values ​​indicated by a low value and a high value is defined as including all numerical values ​​included within that range and all subranges included within that range.

[0026] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0027] The following describes a negative electrode sheet for a secondary battery provided by embodiments of this application, comprising a negative electrode current collector coated with a negative electrode composite material including porous graphene and a negative electrode main material. The diameter distribution parameters, volatile matter content, and weight percentage of the porous graphene in the negative electrode sheet satisfy the following relationship: 0.02≤A / (B*D)≤0.80; where A represents the weight percentage of the porous graphene, B represents the volatile matter content of the porous graphene, and D represents the diameter distribution parameters of the porous graphene. Specifically, at least one surface of the current collector is coated with the negative electrode composite material including the porous graphene and the negative electrode main material.

[0028] In this embodiment, the current collector is coated with a negative electrode composite material comprising porous graphene and a negative electrode substrate. The diameter distribution parameters, volatile matter content, and weight percentage of the porous graphene in the negative electrode sheet are preferably satisfied by the following relationship: 0.02 ≤ A / (B*D) ≤ 0.60; the porous graphene coats the surface of the negative electrode substrate. Specifically, the lower limit of A / (B*D) can include the following values: 0.02, 0.05, 0.1, 0.15, or 0.2; the upper limit of A / (B*D) can include the following values: 0.8, 0.7, 0.6, 0.55, or 0.5.

[0029] This application adds porous graphene to the conductive agent of the negative electrode sheet. Compared to graphene, porous graphene has weaker conductivity due to its higher degree of sp3 hybridization. However, in the water-based negative electrode system, by adjusting the sheet size distribution parameters, volatile matter, and weight ratio of porous graphene in the negative electrode sheet to satisfy the above-mentioned relationship, the dispersion ability of porous graphene is significantly better than that of conventional graphene nanosheets. This effectively reduces the aggregation of nanomaterials, thereby ensuring that, under the same addition amount and other negative electrode materials, the resistance of the negative electrode sheet containing porous graphene is similar to that containing graphene. For example, the resistance difference between the graphite / porous graphene electrode sheet and the graphite / conventional graphene electrode sheet is ±1%. Furthermore, in the negative electrode system of secondary batteries, the factor inhibiting battery performance is mainly the ion conduction ability, rather than the conductivity, especially under low-temperature conditions, where the influence of ion conduction ability is particularly prominent. Ion insertion and ion deposition reactions on battery electrodes (such as graphite electrodes) coexist and compete with each other. Under low-temperature conditions, ion diffusion in the electrode substrate (such as graphite) is suppressed, leading to a significant decrease in the ion insertion rate and making ion deposition reactions more likely to occur on the surface of the electrode substrate. By using porous graphene in the negative electrode system of the battery electrode, it is possible to ensure electron conduction while allowing ions to freely shuttle through the porous structure of graphene. This avoids the need to bypass micron-sized graphene sheets, shortens the ion transport path, optimizes ion conduction capability, and improves the low-temperature lithium plating problem. Furthermore, porous graphene can be used as both a conductive agent and an ion-conducting agent without the need to add other ion-conducting agents, thus optimizing the material structure of the negative electrode system. Meanwhile, by coordinating and optimizing the constraints among characteristic parameters such as the weight ratio, volatile matter, and sheet size distribution of porous graphene, good dispersion of porous graphene is achieved. While ensuring its conductivity, the ion conduction path is shortened, the low-temperature performance of the battery is optimized, and the coating structure of the electrode host material (such as graphite) is constructed using porous graphene to alleviate the cycle decay problem caused by the volume expansion of the host material during charge and discharge. This synergistically improves the battery performance of the secondary battery, especially the low-temperature charge and discharge performance, low-temperature polarization, and cycle performance.

[0030] Specifically, after 1500 cycles at 25℃ / 1C, the battery capacity still reaches over 94.4%. At 0℃ / 1C, no ion deposition reaction occurs, and the discharge energy efficiency reaches nearly 92%, with a constant current ratio exceeding 80%. Through further optimization of the aforementioned porous graphene parameters, after 1500 cycles at 25℃ / 1C / 1C, the battery capacity can reach nearly 95.5%, with a discharge energy efficiency exceeding nearly 94% and a constant current ratio exceeding 85%.

[0031] Specifically, the pore size of porous graphene is 10–20 nm. Thus, by controlling the pore size of porous graphene within this range, sufficient ion channels are ensured, while maintaining the expandability of porous graphene, thereby synergistically improving ion transport performance and reducing the cycling degradation problem caused by volume expansion.

[0032] Specifically, the weight percentages of other components in the negative electrode sheet are as follows: graphite 95.5%–97.5%; SBR 1%–2%; CMC 1%–2%.

[0033] Specifically, the weight percentage of porous graphene refers to the weight percentage of porous graphene in the negative electrode sheet. Specifically, it refers to the weight percentage of the total weight of the components in the negative electrode sheet excluding the negative electrode current collector. For example, if the negative electrode sheet is composed of the negative electrode current collector and porous graphene, graphite, SBR, and CMC coated on the negative electrode current collector, then the weight percentage of porous graphene is equal to the weight of porous graphene / (weight of porous graphene / weight of graphite + weight of SBR + weight of CMC).

[0034] In some embodiments, the areal density of the mixture coated on one side of the current collector is 90 ± 5 g / m³. 2 Preferably, the areal density is 90±1 g / m³. 2 .

[0035] In this embodiment of the application, the weight percentage of porous graphene in the negative electrode sheet is 0.5% ≤ A ≤ 1.5%. Specifically, the lower limit of the weight percentage of porous graphene in the negative electrode sheet may include the following values: 0.5%, 0.55%, 0.6%, 0.65%, or 0.7%, and the upper limit of the weight percentage of porous graphene in the negative electrode sheet may include the following values: 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, or 1.0%. When the weight percentage of porous graphene in the negative electrode is too small (e.g., less than 0.5%), the electrode exhibits poor conductivity, excessively high resistance, and low porosity, failing to meet the requirements for ion diffusion and conductivity. This leads to ion deposition and poor low-temperature performance of the battery. Conversely, when the weight percentage is too high (e.g., greater than 1.5%), the porosity of the negative electrode is too high, resulting in insufficient mechanical compressive strength to meet the compressive strength requirements of battery fabrication. The material structure is prone to damage, and the negative electrode exhibits severe rebound, reducing product yield and performance stability. By controlling the weight percentage of porous graphene in the negative electrode to the aforementioned values, the porosity of the negative electrode can be ensured, significantly improving the low-temperature performance of the battery while maintaining good mechanical strength to meet the requirements of battery fabrication.

[0036] In this embodiment of the application, the volatile matter content of the porous graphene is 1% ≤ B ≤ 5%. Specifically, the lower limit of the volatile matter content of the porous graphene may include the following values: 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2.0%, and the upper limit of the volatile matter content of the porous graphene may include the following values: 5%, 4.8%, 4.6%, 4.4%, 4.2%, or 4.0%. When the volatile content of porous graphene is too high (e.g., greater than 5%), the sp3 hybridization of porous graphene is too high and it cannot be effectively dispersed, failing to meet the conductivity requirements of the electrode and resulting in low conductivity. When the volatile content of porous graphene is too low (e.g., less than 1%), the porosity of porous graphene is too low, which is not conducive to the transport of functional ions and electrolyte wetting, and thus is detrimental to the low-temperature performance of the battery. By setting the volatile content of porous graphene to the above values, the dispersibility of porous graphene in the water-based negative electrode system is significantly improved, and the agglomeration of nanomaterials is significantly reduced. Thus, while ensuring the conductivity of the negative electrode material, the porosity of the material is also ensured, thereby significantly improving the ion-conducting ability of the negative electrode material and improving the transport efficiency of functional ions.

[0037] In this embodiment, the sheet size distribution parameter of the porous graphene is 2.0 ≤ D ≤ 5.5. Specifically, the lower limit of the sheet size distribution parameter of the porous graphene can include the following values: 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5; the sheet size distribution parameter of the volatiles of the porous graphene can include the following values: 5.5, 5.3, 5.1, 5.0, 4.9, or 4.8. D characterizes the secondary particle size distribution of the porous graphene and is determined based on the sheet size of the porous graphene at different cumulative volume percentages in an aqueous solvent. When the sheet size distribution parameter is too small (e.g., less than 2.0), the sheet size distribution of the porous graphene is too narrow, which cannot meet the coating requirements of the main material and cannot simultaneously achieve both long-range and short-range conductivity; when the sheet size distribution parameter is too wide (e.g., greater than 5.5), the porous graphene material is difficult to disperse and easily agglomerates. By setting the sheet diameter distribution parameter to the above values, porous graphene is interspersed in the negative electrode main material (such as graphite main material), and can effectively coat the main material particles, reduce the cycle decay caused by volume expansion, and form a rich porous conductive network structure, ensuring the porosity in the electrode sheet, which helps to accelerate the penetration rate of the electrode liquid in the electrode, and has more sufficient ion channels and electrolyte wetting under the same areal density and solid density conditions, thereby improving ion conductivity.

[0038] In this embodiment, the formula for calculating the sheet diameter distribution parameter of the porous graphene is: D = (D1 - D3) / D2; D1 represents the sheet diameter corresponding to the cumulative volume percentage of the porous graphene in the aqueous solvent reaching a first preset percentage, D2 represents the sheet diameter corresponding to the cumulative volume percentage of the porous graphene in the aqueous solvent reaching a second preset percentage, and D3 represents the sheet diameter corresponding to the cumulative volume percentage of the porous graphene in the aqueous solvent reaching a third preset percentage, wherein the first preset percentage, the second preset percentage, and the third preset percentage decrease sequentially.

[0039] In this embodiment, the porous graphene in the negative electrode sheet has the following sheet diameters: D1 = 10 ≤ D1 ≤ 20 μm; D2 = 3.5 ≤ D2 ≤ 8 μm; and D3 = 0.5 ≤ D2 ≤ 2 μm. Preferably, the porous graphene has the following sheet diameters: D1 = 12 ≤ D1 ≤ 16 μm; D2 = 3.5 ≤ D2 ≤ 7 μm; and D3 = 0.5 ≤ D2 ≤ 1.5 μm.

[0040] In this embodiment of the application, the first preset percentage is 80%-95%, preferably 90%, the second preset percentage is 45%-60%, preferably 50%, and the third preset percentage is 5%-15%, preferably 10%.

[0041] By setting D, D1, D2, and D3 to the values ​​mentioned above, a reasonable particle size distribution and sheet size of porous graphene in the electrode material are ensured, further optimizing the conductive network structure and material coating effect, thereby further improving battery performance, especially significantly improving the low-temperature performance of the battery.

[0042] In this embodiment of the application, the negative electrode current collector may include at least one of copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and composite current collector.

[0043] In this embodiment, the negative electrode sheet also includes graphite, which can be natural graphite or artificial graphite. Using graphite as the main material of the negative electrode can effectively control the specific capacity and conductivity of the negative electrode material layer, and the preparation process is mature and low in cost.

[0044] In this embodiment, the negative electrode sheet may further include a binder, which may include at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, polystyrene-butadiene copolymer, sodium carboxymethyl cellulose, polyimide, and polyamide-imide.

[0045] In this embodiment, the negative electrode sheet may further include a thickener, which may include at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, vinylene carbonate, chloroethylene carbonate, and vinyl sulfate.

[0046] In one embodiment, the binder in the negative electrode sheet is polystyrene-butadiene copolymer (SBR), and the thickener is carboxymethyl cellulose (CMC).

[0047] In summary, extensive experiments have shown that by adding porous graphene to the negative electrode sheet and limiting the sheet size distribution parameters, volatile matter, and weight percentage of the porous graphene in the negative electrode sheet to 0.5%≤A≤1.5%, 1%≤B≤5%, 2.0≤D≤5.5%, and ensuring that each parameter satisfies 0.02≤A / (B*D)≤0.80, good dispersion of porous graphene in the water-based negative electrode system can be achieved, ensuring conductive electron properties. Simultaneously, the migration path of functional ions is optimized, the migration distance is shortened, and the influence of the negative electrode material and solid-phase diffusion path on ion diffusion is reduced, accelerating ion diffusion rates at room temperature and low temperature, reducing electrode internal resistance, and accelerating electron conduction. Furthermore, the porous graphene can be used to construct a coating structure for the negative electrode material, mitigating the cycle degradation problem caused by the volume expansion of the negative electrode material during charge and discharge, and synergistically improving the room temperature performance, low temperature charge and discharge, low temperature polarization, and cycle performance of the secondary battery.

[0048] On the other hand, this application provides an electrode, which includes the negative electrode sheet as described above.

[0049] On the other hand, this application provides a secondary battery, including a positive electrode, a separator, an electrolyte, and the aforementioned negative electrode or electrode. The secondary battery may include, but is not limited to, lithium-ion secondary batteries and sodium-ion secondary batteries. In one embodiment, the active material in the negative electrode is nano-lithium iron phosphate, and the binder in the negative electrode is PVDF.

[0050] On the other hand, this application provides an electronic device, which includes the positive electrode or secondary battery as described above. Specifically, the electronic device may include, but is not limited to, computers, mobile phones, wearable electronic devices, in-vehicle terminal devices, VR devices, and other electronic terminal devices that require secondary batteries.

[0051] On the other hand, this application provides a method for preparing a secondary battery, comprising the following steps:

[0052] S1: Graphite, porous graphene, binder and thickener are mixed in a weight ratio of (95.5~96.5):(0.5~1.5):(1~1.5):(1.5~2.0), deionized water is added, and after mixing and stirring evenly, the mixture is coated on the negative electrode current collector. The negative electrode sheet is obtained through processes such as drying, cold pressing and die cutting.

[0053] S2: After uniformly mixing the positive electrode active material, PVDF and positive electrode conductive agent, the mixture is coated onto the positive electrode current collector, and then the positive electrode sheet is obtained through processes such as drying, cold pressing and die cutting.

[0054] S3: Stack the positive electrode, separator, and negative electrode in sequence. The separator is placed between the positive and negative electrode to isolate them. Then, the core is obtained by stacking or winding. The core is placed in a soft package and sealed. After drying, electrolyte is injected, vacuum sealed, and the battery is formed and tested to obtain a secondary battery.

[0055] Specifically, the binder used for the negative electrode sheet can be CMC, the thickener can be SBR, the negative electrode current collector can be copper foil, the positive electrode current collector can be carbon aluminum foil, and the positive electrode conductive agent can be conductive carbon black.

[0056] The following describes embodiments and comparative examples of this application in conjunction with the above technical solutions.

[0057] The secondary batteries in Examples 1-11 and Comparative Examples 1-2 were prepared by the following method:

[0058] S1: Graphite, porous graphene, CMC, and SBR are mixed in a weight ratio of (95.5–96.5):(0.5–1.5):1.3:1.7. Deionized water is added, and the mixture is stirred evenly before being coated onto the negative electrode current collector. The surface density of the coating on one side is 90 ± 1 g / m². 2 The negative electrode sheet is obtained through processes such as drying, cold pressing, and die cutting.

[0059] S2: Mix LFP, PVDF, and conductive carbon black in a weight ratio of 96.2:2.2:1.6, and then coat the mixture with PVDF after thorough mixing. The surface density of each side is 210±3 g / m². 2 The positive electrode sheet is obtained through processes such as drying, cold pressing, and die cutting.

[0060] S3: Stack the positive electrode, separator, and negative electrode in sequence. The separator is placed between the positive and negative electrode to isolate them. Then, the core is obtained by stacking or winding. The core is placed in a soft package and sealed. After drying, electrolyte is injected, vacuum sealed, and the battery is formed and tested to obtain a secondary battery.

[0061] The relevant parameters of porous graphene in the negative electrode sheets of Examples 1-11 and Comparative Examples 1-2 are shown in Table 1.

[0062] The positive electrode and battery assembly in Comparative Examples 3 and 4 were the same as in Examples 1-11, except for the materials and weight ratios added to the positive electrode. In Comparative Example 3, graphene was added, and the weight ratio of graphite, graphene, CMC and SBR was 96:1.0:1.3:1.7. In Comparative Example 4, SP-Li was added, and the weight ratio of graphite, SP-Li, CMC and SBR was 96:1.0:1.3:1.7.

[0063] The battery performance parameters of the secondary batteries in Examples 1-11 and Comparative Examples 1-4 are shown in Table 1.

[0064] The specific material parameter testing methods used in this embodiment are as follows:

[0065] 1) Volatile matter test of porous graphene: Weigh the porous graphene dried at 80℃ for 5 hours, the weight is m1, place it in a muffle furnace at 900℃ under nitrogen protection and heat for 15 minutes, then weigh it again at room temperature, the weight is m2; accordingly, B=(m1-m2) / m1*100%

[0066] 2) The sheet diameters D1, D2, and D3 of the porous graphene were measured using a Malvern 3000 laser particle size analyzer.

[0067] Table 1

[0068]

[0069]

[0070] Please refer to Figure 1 Porous graphene effectively coats the surface of the negative electrode material. Combining Examples 1 / 2 / 3 and Comparative Example 1 / 2, the order of A / B / [(D90-D10) / D50] was found to be: Comparative Example 1 < Example 1 < Example 2 < Example 3 < Comparative Example 2, with Example 2 showing the best low-temperature performance. Compared to Comparative Example 1, Example 1 showed better DCR at 0°C charging, higher energy efficiency at 0°C and 1C discharging, better constant current ratio at 0°C and 1C charging, and no lithium plating at 0°C and 1C charging. Example 3 showed the same pattern compared to Comparative Example 2. In Comparative Examples 3 / 4, when the amount of conductive agent (graphene or SP-Li) added was 1.0%, the low-temperature performance of Example 2 was significantly improved. (Combined with...) Figure 2 Example 2 showed the best cycling performance, which was significantly better than Comparative Examples 3 and 4, indicating that the coating of graphite with porous graphene is beneficial to long-term cycling performance.

[0071] In summary, this application has the following beneficial effects: This application adds porous graphene to the conductive agent of the negative electrode sheet, and adjusts the sheet size distribution parameters, volatile matter, and weight ratio of the porous graphene in the negative electrode sheet to satisfy the above-mentioned relationships. This makes the dispersion ability of porous graphene significantly better than that of conventional graphene nanosheets, effectively reducing the aggregation of nanomaterials, lowering the internal resistance of the electrode sheet, and ensuring that ions can freely shuttle through the porous structure of graphene. This avoids the need to bypass micron-sized graphene sheets, shortens the ion transport path, optimizes ion conduction ability, improves the low-temperature lithium plating problem, and allows porous graphene to be used simultaneously as a conductive agent and an ion conduction agent without the need to add other ion conduction agents, thus optimizing the material structure of the negative electrode system. Meanwhile, by coordinating and optimizing the constraints among characteristic parameters such as the weight ratio, volatile matter, and sheet size distribution of porous graphene, good dispersion of porous graphene is achieved. While ensuring its conductivity, the ion conduction path is shortened, the low-temperature performance of the battery is optimized, and the coating structure of the electrode host material (such as graphite) is constructed using porous graphene to alleviate the cycle decay problem caused by the volume expansion of the host material during charge and discharge. This synergistically improves the battery performance of the secondary battery, especially the low-temperature charge and discharge performance, low-temperature polarization, and cycle performance.

[0072] The foregoing description has fully disclosed the specific embodiments of this application. It should be noted that any modifications made to the specific embodiments of this application by those skilled in the art do not depart from the scope of the claims. Accordingly, the scope of the claims is not limited to the foregoing specific embodiments.

Claims

1. A negative electrode sheet for a secondary battery, comprising a negative electrode current collector, characterized by, The current collector is coated with a negative electrode composite material including porous graphene and a negative electrode main material, a flake diameter distribution parameter, volatile matter, and a weight percentage of the porous graphene in the negative electrode sheet satisfy the following relationship: 0.02≤A / (B*D)≤0.80; the porous graphene is coated on the surface of the negative electrode main material; wherein A represents the weight percentage of the porous graphene, B represents the volatile matter of the porous graphene, and D represents the flake diameter distribution parameter of the porous graphene; 0.5%≤A≤1.5%, 1%≤B≤5%, and 2.0≤D≤5.5; D = [(D1-D3) / D2]; D1 represents a flake diameter corresponding to a cumulative volume percentage of the porous graphene in an aqueous solvent reaching 80%-95%, D2 represents a flake diameter corresponding to a cumulative volume percentage of the porous graphene in the aqueous solvent reaching 45%-60%, and D3 represents a flake diameter corresponding to a cumulative volume percentage of the porous graphene in the aqueous solvent reaching 5%-15%, wherein 10≤D1≤20μm, 3.5≤D2≤8μm, and 0.5≤D3≤2μm.

2. The negative electrode sheet according to claim 1, characterized by, The flake diameter distribution parameter, volatile matter, and weight percentage of the porous graphene in the negative electrode sheet satisfy the following relationship: 0.02≤A / (B*D)≤0.

60.

3. The negative electrode sheet according to claim 1, wherein The porous graphene has a pore diameter of 10-20nm.

4. A secondary battery characterized by comprising: The secondary battery includes the negative electrode sheet according to any one of claims 1-3.

5. An electronic device, comprising: The electronic device includes the secondary battery according to claim 4.

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