Negative electrode sheet, battery, and electric device

Abstract

The application relates to a negative electrode sheet, a battery and an electric device. The negative electrode sheet has opposite first and second edges, when the first edge of the negative electrode sheet is immersed in an electrolyte, the electrolyte infiltrates the negative electrode sheet in a direction from the first edge to the second edge; at 1 standard atmosphere and 25 DEG C, the distance between the lowest point of a concave liquid surface formed after the electrolyte infiltrates the negative electrode sheet for 10 min and the first edge of the negative electrode sheet is H, the unit is cm, the compactness of the negative electrode sheet is P, the unit is g / cm 3 , H and P satisfy: 14.494<=H+7.48P<=18.994; the solvent of the electrolyte is one or more of vinyl carbonate, methyl ethyl carbonate, diethyl carbonate and polycarbonate, the electrolyte is lithium hexafluorophosphate, and the concentration of the electrolyte is 0.4-1.8 mol / L. The negative electrode sheet can be effectively infiltrated by the electrolyte, thereby being beneficial to the energy density and cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and particularly to negative electrode sheets, batteries, and electrical devices. Background Technology

[0002] With the rapid development of lithium-ion battery technology, consumer demand for lithium-ion batteries in various applications is gradually increasing, and higher requirements are being placed on the cycle performance and energy density of batteries in different application scenarios. However, from a technical perspective, it is difficult to achieve a perfect balance between high energy density and long cycle performance. Summary of the Invention

[0003] To address the challenge of balancing high energy density and long cycle performance in batteries, this invention provides a negative electrode, a battery, and an electrical device. The negative electrode can be effectively wetted by an electrolyte, thereby synergistically improving the battery's energy density and cycle performance.

[0004] The technical solution is as follows:

[0005] A negative electrode sheet having opposing first and second edges, wherein when the first edge of the negative electrode sheet is immersed in an electrolyte, the electrolyte wets the negative electrode sheet in a direction from the first edge to the second edge;

[0006] Let H (or wetting height) be the distance between the lowest point of the concave liquid surface formed after the electrolyte has wetted the negative electrode for 10 minutes at 1 standard atmosphere and 25°C, and the first edge of the electrode. The unit is cm. Let P be the compaction density of the negative electrode. The unit is g / cm³. 3 H and P satisfy:

[0007] 14.494≤H+7.48P≤18.994;

[0008] The solvent of the electrolyte is one or more of ethylene carbonate, methyl ethyl carbonate, diethyl carbonate and polycarbonate, and the electrolyte is lithium hexafluorophosphate, with a concentration of 0.4 mol / L to 1.80 mol / L.

[0009] If H+7.48P is lower than 14.494, it usually means that the electrode compaction is too low, resulting in a lower energy density of the battery. Alternatively, if the electrode compaction is too high, the wetting condition will be poor, and the battery will experience a drop in cycle performance due to insufficient electrolyte consumption. If H+7.48P is higher than 18.994, it means that the electrode compaction is low. Although the wetting condition is good, the energy density of the battery is low. Controlling H+7.48P to 18.994 ensures that the negative electrode can be effectively wetted by the electrolyte, which is beneficial for the synergistic effect of battery energy density and cycle performance.

[0010] In one embodiment, the ratio of the height of the first edge of the negative electrode immersed in the electrolyte to the height of the negative electrode is (0.1~0.15):1, and the wetting height of the negative electrode is obvious and unaffected by external air. If the immersion height in the electrolyte is too low, the contact area between the negative electrode and the electrolyte is small, making it more susceptible to environmental influences, and the electrolyte is prone to evaporation, resulting in large errors in the test results; if the immersion height is too high, the wetting height (or climbing height) is easily masked and difficult to determine.

[0011] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector;

[0012] The negative electrode active layer includes a negative electrode active material, additives, conductive agents, and binders;

[0013] The additive is lithium-rich sulfonated graphene.

[0014] Lithium-rich sulfonated graphene contains a large number of sulfonic acid groups and abundant lithium on its surface. The sulfonic acid groups are highly hydrophilic, improving the dispersibility and wetting properties of the negative electrode active material in the electrolyte, reducing ion diffusion resistance, enhancing the kinetic performance of the negative electrode, and increasing electron transport rate. The introduction of lithium increases ionic conductivity, synergistically improving the kinetic performance of the negative electrode, thus solving the problem of accelerated cycle life decay caused by uneven electrolyte distribution in the active material layer. The conductive agent collects microcurrents between active materials and between the active material and the current collector, reducing electrode contact resistance and accelerating electron movement. It also effectively increases the migration rate of lithium ions in the electrode material, thereby improving the charge-discharge efficiency of the electrode. The binder's main function is to provide strong adhesion to maintain the integrity of the electrode structure, ensuring the normal charge-discharge cycle of the lithium-ion battery.

[0015] In one embodiment, the mass content of sulfonic acid groups in the lithium-rich sulfonated graphene is 0.1% to 10%.

[0016] Ion transitions require energy, and the energy level of the ion determines the range of the transition. By using lithium-rich sulfonated graphene as an anode additive, the reaction environment of lithium ions becomes more suitable for ion transitions, meaning that the difficulty of ion transitions is reduced. This implies that the impedance caused by ion transitions is lower, which accelerates the reaction process and improves kinetic performance.

[0017] In one embodiment, the lithium-rich sulfonated graphene has a lithium to sulfur molar ratio of 1:(1-6).

[0018] Using such lithium-rich sulfonated graphene as a negative electrode additive increases the lithium-ion diffusion channels, while the polar agent of the sulfonate group is beneficial to improving the wetting effect of the electrode.

[0019] In one embodiment, the lithium-rich sulfonated graphene powder has a spherical morphology and a D50 particle size of 3 μm to 8 μm.

[0020] Lithium-rich sulfonated graphene with a D50 particle size of 3μm to 8μm and a spherical powder morphology was used as an anode additive. The spherical morphology increased the diffusion path of lithium ions, which helped to reduce diffusion resistance and improve kinetics.

[0021] In one embodiment, the negative electrode active layer comprises the following components by mass percentage:

[0022]

[0023] The negative electrode active layer includes a specific ratio of negative electrode active material, additives, conductive agents, and binders, giving the negative electrode sheet optimal processing performance, such as peel strength and electrode resistance. Furthermore, adding 0.05% to 5% by mass of negative electrode additives to the negative electrode active layer improves the electrode's wetting properties, reduces diffusion resistance, enhances kinetics, and also ensures optimal processing and dispersion performance of the slurry during the negative electrode sheet preparation process.

[0024] In one embodiment, the negative electrode active material is selected from one or a mixture of several of graphite, lithium metal, lithium alloy, carbon, petroleum coke, activated carbon, silicon compounds, tin compounds, titanium compounds, and tin-titanium alloys. These negative electrode active materials are widely available, abundant, and have relatively stable electrochemical performance. Furthermore, their actual specific capacity density can be close to the theoretical specific capacity, which is more conducive to improving the performance of the negative electrode while reducing costs.

[0025] In one embodiment, the D50 particle size of the negative electrode active material is 7 μm to 10 μm. The D50 particle size of the negative electrode active material (such as graphite) has a significant impact on kinetics; smaller particle sizes shorten the lithium-ion transport path, which is beneficial for improving kinetics. Researchers have found that when the D50 particle size of the negative electrode active material is 7 μm to 10 μm, the material exhibits the highest kinetics.

[0026] In one embodiment, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 ~1.65g / cm 3 Lower compaction results in lower battery energy density, while excessively high electrode compaction leads to poor wetting, causing insufficient electrolyte consumption and resulting in poor cycle performance. The optimal compaction density is 1.3 g / cm³. 3 ~1.65g / cm 3With 14.494≤H+7.48P≤18.994, the negative electrode can be effectively wetted by the electrolyte, which is beneficial to the synergistic effect of the battery's energy density and cycle performance.

[0027] In one embodiment, the conductive agent is selected from one or a mixture of several of acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black.

[0028] In one embodiment, the adhesive is selected from one or a mixture of several of the following: polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid.

[0029] This invention also provides the application of the negative electrode sheet as described above. The technical solution is as follows:

[0030] A battery comprising a negative electrode as described above.

[0031] An electrical device comprising a battery as described above. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the negative electrode sheet used in one embodiment of the present invention;

[0033] Figure 2 SEM and mapping of cross-sectional layers for the experimental and control groups. Figure 2 (a) No additives were introduced into the control group. Figure 2 (b)-(d) Cross-sectional SEM and mapping after the introduction of additives;

[0034] Figure 3 The ICP test results are for the negative electrode sheets prepared in Example 1 and Comparative Example 1.

[0035] Figure 4 The ICP test results are for the negative electrode sheets prepared in Example 2 and Comparative Example 2.

[0036] Figure 5 The electrochemical impedance performance test results of the batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 2 are as follows;

[0037] Figure 6 This is a three-dimensional schematic diagram of the immersion test device used in an embodiment of the present invention. Detailed Implementation

[0038] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0041] In this invention, the terms "preferredly," "more preferably," "better," and "even better" refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the invention. That is, in this invention, "preferredly," "more preferably," "better," and "even better" are merely descriptions of more effective implementations or examples, but do not constitute a limitation on the scope of protection of the invention.

[0042] In this invention, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0043] In this invention, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this invention, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0044] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0045] Unless otherwise specified, all steps of this invention may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise stated, a singular term may include a plural term and should not be understood as having a quantity of one.

[0047] In this invention, "above" or "below" both include the number itself. For example, "below 1" includes 1.

[0048] With the rapid development of lithium-ion battery technology, consumers' demand for lithium-ion batteries in different scenarios is gradually increasing, and they are placing higher demands on the cycle performance and energy density of batteries in different application scenarios.

[0049] However, from a technical standpoint, it is difficult to achieve a perfect balance between high energy density and long cycle performance. Traditional technologies often increase the compaction density of the electrode sheet to meet the demand for higher energy density, but at the same time, a high compaction density will seriously affect the effective wetting of the electrolyte inside the active material layer of the electrode sheet, thus leading to poor cycle performance.

[0050] To address the problem of the incompatibility between high energy density and long cycle performance in batteries, this invention provides a negative electrode, a battery, and an electrical device. The negative electrode can be effectively wetted by an electrolyte, thereby synergistically improving the energy density and cycle performance of the battery.

[0051] The technical solution is as follows:

[0052] See Figure 1The present invention provides a negative electrode 10 having a first edge 101 and a second edge 102 opposite to each other. When the first edge 101 of the negative electrode 10 is immersed in an electrolyte, the electrolyte wets the negative electrode in a direction from the first edge 101 to the second edge 102.

[0053] Let H be the distance between the lowest point of the concave liquid surface formed after the electrolyte has soaked the negative electrode for 10 minutes at 1 standard atmosphere and 25°C, and the first edge of the electrode. Let P be the compaction density of the negative electrode. 3 H and P satisfy:

[0054] 14.494≤H+7.48P≤18.994;

[0055] The solvent of the electrolyte is one or more of ethylene carbonate, methyl ethyl carbonate, diethyl carbonate and polycarbonate, and the electrolyte is lithium hexafluorophosphate, with a concentration of 0.4 mol / L to 1.80 mol / L.

[0056] If H+7.48P is lower than 14.494, it usually means that the electrode compaction is too low, resulting in a lower energy density of the battery. Alternatively, if the electrode compaction is too high, the wetting condition is poor, and the battery may experience a drop in cycle performance due to insufficient electrolyte consumption. If H+7.48P is higher than 18.994, it means that the electrode compaction is low. Although the wetting condition is good, the energy density of the battery is low. Controlling H+7.48P to 18.994 ensures that the negative electrode can be effectively wetted by the electrolyte, which is beneficial for synergistic effects on the battery's energy density and cycle performance.

[0057] In one specific embodiment, the solvent of the electrolyte is ethylene carbonate, the electrolyte is lithium hexafluorophosphate, and the concentration of the electrolyte is 1 mol / L.

[0058] In one embodiment, P is 1.3 g / cm³. 3 ~1.65g / cm 3 Including but not limited to 1.3g / cm 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 and 1.65g / cm 3Lower compaction results in lower battery energy density, while excessively high electrode compaction leads to poor wetting, causing insufficient electrolyte consumption and resulting in poor cycle performance. The optimal compaction density is 1.3 g / cm³. 3 ~1.65g / cm 3 The negative electrode can be effectively wetted by the electrolyte, which is beneficial for synergistically improving the battery's energy density and cycle performance. Furthermore, P is 1.4 g / cm³. 3 ~1.65g / cm 3 .

[0059] In one embodiment, the ratio of the height of the first edge of the negative electrode immersed in the electrolyte to the height of the negative electrode is (0.1~0.15):1. If the height of the first edge of the negative electrode immersed in the electrolyte is too low, the contact area between the negative electrode and the electrolyte is small, making it more susceptible to environmental influences, and the electrolyte is prone to evaporation, resulting in large errors in the test results; if the immersion height is too high, the wetting height (or climbing height) is easily masked and difficult to determine.

[0060] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector;

[0061] The negative electrode active layer includes a negative electrode active material, additives, conductive agents, and binders;

[0062] The additive is lithium-rich sulfonated graphene.

[0063] The inventors discovered that introducing hydroxyl, carboxyl, or sulfonic acid groups into organic compounds can improve hydrophilicity. In contrast, when sulfonic acid functional groups are introduced into organic compounds, they are more soluble in water and have better dispersibility in water or other polar solvents (such as N,N-dimethylformamide, DMF).

[0064] Specifically, given the high hydrophilicity of sulfonic acid groups, a covalent functionalization method was employed to sulfonate graphene materials to prepare sulfonated graphene (SG). Sulfonic acid groups were grafted onto the graphene surface to improve its polar dispersion properties. The sulfonic acid groups in graphene undergo a free radical addition reaction. The diazonium salt of aminobenzenesulfonic acid directly interacts with the carbon atoms on the benzene ring of graphene, breaking the carbon-carbon double bond and forming a covalent bond. This process removes a large number of oxygen-containing groups from the graphene surface. After free radical addition, a large number of sulfonate-containing free radicals are covalently bonded to the surface of the graphene sheets (synthetic route as follows), giving sulfonated graphene hydrophilicity. This improves the dispersion and wetting properties of the negative electrode active material in the electrolyte, reduces ion diffusion resistance, enhances the kinetic performance of the negative electrode sheet, increases the electron transport rate, and improves the distribution of the electrolyte in the active material layer. Conductive agents can collect microcurrents between active materials and between active materials and current collectors, thereby reducing electrode contact resistance and accelerating electron mobility. They also effectively increase the migration rate of lithium ions within the electrode material, thus improving the charge-discharge efficiency of the electrode. The main function of binders is to provide strong adhesion to maintain the integrity of the electrode structure, ensuring the normal operation of the lithium-ion battery during charge-discharge cycles.

[0065]

[0066] Furthermore, lithium-containing compounds, including lithium oxide and / or lithium hydroxide, are introduced into sulfonated graphene to increase the ionic conductivity by introducing a large number of lithium ions on the surface of the sulfonated graphene, thereby synergistically improving the dynamic performance of the negative electrode and solving the problem of accelerated cycle life decay caused by uneven distribution of electrolyte in the active material layer.

[0067] In one embodiment, the mass content of sulfonic acid groups in the lithium-rich sulfonated graphene is 0.1% to 10%, including but not limited to 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, and 10%. A decrease in the mass content of sulfonic acid groups results in a poorer wetting effect and reduced kinetic performance improvement on the negative electrode.

[0068] In one specific embodiment, the mass content of sulfonic acid groups in the lithium-rich sulfonated graphene is 1% to 10%.

[0069] In one embodiment, the molar ratio of lithium to sulfur in the lithium-rich sulfonated graphene is 1:(1-6). Using such lithium-rich sulfonated graphene as a negative electrode additive increases the lithium-ion diffusion channels, while the polarity of the sulfonate groups helps to improve the wetting effect of the electrode.

[0070] In one embodiment, the lithium-rich sulfonated graphene powder has a spherical morphology and a D50 particle size of 3 μm to 8 μm, including but not limited to 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, and 8 μm. Using lithium-rich sulfonated graphene with a D50 particle size of 3 μm to 8 μm and a spherical powder morphology as a negative electrode additive is beneficial for reducing diffusion resistance and improving kinetic performance.

[0071] In one embodiment, the negative electrode active layer comprises the following components by mass percentage:

[0072]

[0073]

[0074] The negative electrode active layer includes a specific ratio of negative electrode active material, additives, conductive agents, and binders, giving the negative electrode sheet optimal processing performance, such as peel strength and electrode resistance. In particular, the inventors have discovered that adding 0.05% to 5% (by mass) of negative electrode additives to the negative electrode active layer improves the wetting properties of the electrode sheet, reduces diffusion resistance, and enhances kinetics. Furthermore, it also optimizes the processing and dispersion properties of the slurry used in the negative electrode sheet preparation process. Lowering the additive content results in a lower proportion in the formulation system, leading to less noticeable improvements in wetting and kinetic performance; conversely, increasing the additive content increases costs.

[0075] Understandably, in the negative electrode active layer, the mass content of the negative electrode active material is 94% to 98%, including but not limited to 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, and 98%; the mass content of the additive is 0.05% to 5%, including but not limited to 0.05%, 0.1%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, and 0.5%; and the mass content of the conductive agent is 0.3% to 1%, including but not limited to 0.3%, 0.35%, and 0.5%. 4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, and 1% by mass; and the adhesive content is 0.5% to 2%, including but not limited to 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2%.

[0076] In one embodiment, the negative electrode active material is selected from one or a mixture of several of graphite, lithium metal, lithium alloy, carbon, petroleum coke, activated carbon, silicon compounds, tin compounds, titanium compounds, and tin-titanium alloys. These negative electrode active materials are widely available, abundant, and have relatively stable electrochemical performance. Furthermore, their actual specific capacity density can be close to the theoretical specific capacity, which is more conducive to improving the performance of the negative electrode while reducing costs.

[0077] In one embodiment, the conductive agent is selected from one or a mixture of several of acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black.

[0078] In one embodiment, the adhesive is selected from one or a mixture of several of the following: polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid.

[0079] This invention also provides a method for preparing a negative electrode, comprising the following steps:

[0080] A negative electrode active slurry is provided, the components of which include a negative electrode active material, additives, conductive agents and binders, wherein the additives are lithium-rich sulfonated graphene.

[0081] The negative electrode active slurry is coated on the surface of the negative electrode current collector to form a negative electrode active layer.

[0082] The above preparation method is simple to operate, controllable, requires little equipment, and is suitable for large-scale production.

[0083] In one embodiment, the method for preparing the negative electrode sheet includes the following steps:

[0084] The negative electrode active material, lithium-rich sulfonated graphene additive, conductive agent, and binder are thoroughly mixed in the above-mentioned mass ratio to obtain a negative electrode active slurry. Then, the negative electrode active slurry is coated on the surface of the current collector and pressed into a negative electrode film with a thickness of 200μm to 400μm. After being placed in an oven at 70℃ to 90℃ for 4h to 6h, the negative electrode film is rolled to complete the preparation of the negative electrode sheet.

[0085] This invention also provides the application of the negative electrode sheet as described above. The technical solution is as follows:

[0086] A battery comprising a negative electrode as described above.

[0087] In one embodiment, the battery is selected from one of button cells, pouch cells, prismatic cells, and cylindrical cells.

[0088] In one embodiment, the positive electrode of the battery includes a positive current collector and a positive active layer disposed on the surface of the positive current collector;

[0089] The positive electrode active layer includes positive electrode active material, polyvinylidene fluoride (PVDF), conductive carbon black (SP), and polyvinylpyrrolidone (PVP).

[0090] The present invention also provides a method for preparing a battery, comprising the following steps:

[0091] (1) Preparation of positive electrode: circular lithium sheet is used.

[0092] The positive electrode sheet for batteries is prepared according to conventional methods in the art. This invention does not limit the positive electrode active material used in the positive electrode sheet. Typically, a conductive agent (e.g., carbon materials such as carbon black) and a binder (e.g., PVDF) are added to the aforementioned positive electrode active material. These materials are usually mixed together and dispersed in a solvent (e.g., NMP), stirred evenly, and then uniformly coated onto a positive electrode current collector. After drying, the positive electrode sheet is obtained. Metal foil or porous metal plates can be used as the positive electrode current collector. Aluminum foil is preferred.

[0093] (2) Preparation of negative electrode sheet:

[0094] A negative electrode active slurry is provided, the components of which include a negative electrode active material, additives, conductive agents and binders, wherein the additives are lithium-rich sulfonated graphene.

[0095] The negative electrode active slurry is coated on the surface of the negative electrode current collector to form a negative electrode active layer.

[0096] An electrical device comprising a battery as described above.

[0097] The present invention will be illustrated by the following specific embodiments.

[0098] (1) Raw material description: The lithium-rich sulfonated graphene used in the examples was purchased from Suzhou Gaotong New Materials Technology Co., Ltd.

[0099] (2) ICP testing conditions: Thermo Fisher Scientific / ICP Inductively Coupled Ion Spectrometer / L-21-0398

[0100] (3) Button cell battery:

[0101] The coin cells of each embodiment and comparative example were prepared according to the following method:

[0102] 1) Preparation of positive electrode: Circular lithium sheet is used.

[0103] The positive electrode active material lithium iron phosphate, conductive agent carbon black, and binder PVDF are mixed together and dispersed in N-methylpyrrolidone (NMP). After stirring evenly, the mixture is uniformly coated onto the positive electrode current collector aluminum foil and dried to obtain the positive electrode sheet.

[0104] 2) Preparation of the negative electrode sheet:

[0105] A negative electrode active slurry is provided, the components of which include a negative electrode active material, additives, conductive agents and binders, wherein the additives are lithium-rich sulfonated graphene.

[0106] The negative electrode active slurry is coated on the surface of the negative electrode current collector to form a negative electrode active layer.

[0107] (4) Test method for examining the electrochemical impedance performance of the battery: After the prepared coin cell was discharged at 0.1C for 5h, an EIS test was performed.

[0108] Example 1

[0109] This embodiment provides a negative electrode sheet, its preparation method, and a battery, as detailed below:

[0110] (1) Composition of negative electrode sheet: negative electrode current collector and negative electrode active layer disposed on the surface of the negative electrode current collector;

[0111] The negative electrode active layer is composed of the following components by mass percentage:

[0112]

[0113] (2) Preparation of negative electrode sheet:

[0114] The negative electrode active material, graphite (D50 particle size of 9 μm), the additive lithium-rich sulfonated graphene (which is a secondary particle with a sulfonic acid group mass content of 1% to 10%, a lithium to sulfur molar ratio of 1:(1 to 6), and the powdered lithium-rich sulfonated graphene with a D50 particle size of 3 μm to 8 μm), the conductive agent, and the binder are thoroughly mixed in the above-mentioned mass ratios to obtain a negative electrode active slurry. The negative electrode active slurry is then coated onto one side of the current collector and pressed into a negative electrode film with a thickness of 200 μm. After drying in an oven at 80°C for 4 hours, the negative electrode film is rolled to complete the preparation of the negative electrode sheet, with a compaction density P of 1.45 g / cm³. 3 .

[0115] (3) Battery fabrication:

[0116] The negative electrode sheet obtained in (2) is made into a button cell.

[0117] Example 2

[0118] This embodiment provides a negative electrode sheet, its preparation method, and a battery, as detailed below:

[0119] (1) Composition of negative electrode sheet: negative electrode current collector and negative electrode active layer disposed on the surface of the negative electrode current collector;

[0120] The negative electrode active layer is composed of the following components by mass percentage:

[0121]

[0122] (2) Preparation of negative electrode sheet:

[0123] The negative electrode active material, graphite (D50 particle size of 7 μm), the additive lithium-rich sulfonated graphene (which is carbon-coated particles with a sulfonic acid group content of 1%–10%, a lithium to sulfur molar ratio of 1:(1–6), and a powdered lithium-rich sulfonated graphene with a D50 particle size of 3 μm–8 μm), the conductive agent, and the binder are thoroughly mixed in the above-mentioned mass ratios to obtain a negative electrode active slurry. The negative electrode active slurry is then coated onto one side of the current collector and pressed into a negative electrode film with a thickness of 200 μm. After drying in an oven at 80°C for 4 hours, the negative electrode film is rolled to complete the preparation of the negative electrode sheet, with a compaction density P of 1.45 g / cm³. 3 .

[0124] (3) Battery fabrication:

[0125] The negative electrode sheet obtained in (2) is made into a button cell.

[0126] Comparative Example 1

[0127] This comparative example provides a negative electrode sheet, its preparation method, and a battery, as detailed below:

[0128] (1) Composition of negative electrode sheet: negative electrode current collector and negative electrode active layer disposed on the surface of the negative electrode current collector;

[0129] The negative electrode active layer is composed of the following components by mass percentage:

[0130] The negative electrode active material is 98% graphite;

[0131] Conductive agent carbon 0.5%; and

[0132] Adhesive PVDF 1.5%.

[0133] (2) Preparation of negative electrode sheet:

[0134] The negative electrode active material, graphite (D50 particle size of 9 μm), conductive agent, and binder were thoroughly mixed in the above-mentioned mass ratio to obtain a negative electrode active slurry. This slurry was then coated onto one side of the current collector and pressed into a negative electrode film with a thickness of 200 μm. After drying in an oven at 80℃ for 4 hours, the negative electrode film was rolled to complete the preparation of the negative electrode sheet. The compaction density P was 1.45 g / cm³. 3 .

[0135] (3) Battery fabrication:

[0136] The negative electrode sheet obtained in (2) is made into a button cell.

[0137] Comparative Example 2

[0138] This comparative example provides a negative electrode sheet, its preparation method, and a battery, as detailed below:

[0139] (1) Composition of negative electrode sheet: negative electrode current collector and negative electrode active layer disposed on the surface of the negative electrode current collector;

[0140] The negative electrode active layer is composed of the following components by mass percentage:

[0141] The negative electrode active material is 98% graphite;

[0142] Conductive agent carbon 0.5%; and

[0143] Adhesive PVDF 1.5%.

[0144] (2) Preparation of negative electrode sheet:

[0145] The negative electrode active material, graphite (D50 particle size of 7 μm), conductive agent, and binder were thoroughly mixed in the above-mentioned mass ratio to obtain a negative electrode active slurry. This slurry was then coated onto one side of the current collector and pressed into a negative electrode film with a thickness of 200 μm. After drying in an oven at 80℃ for 4 hours, the negative electrode film was rolled to complete the preparation of the negative electrode sheet. The compaction density P was 1.45 g / cm³. 3 .

[0146] (3) Battery fabrication:

[0147] The negative electrode sheet obtained in (2) is made into a button cell.

[0148] 2. Test:

[0149] (1) The cross-sections of the negative electrode sheets prepared in Examples 1 and 2 were measured by SEM, and the results are shown in the figure. Figure 2 .

[0150] Depend on Figure 2 It can be seen that sulfur (S) exists in the lower layer of the cross-section of the electrode with lithium-rich sulfonated graphene additive.

[0151] (2) ICP tests were performed on the negative electrode sheets prepared in Examples 1 to 2 and Comparative Examples 1 to 2. The results are shown in the figure. Figure 3 and Figure 4 .

[0152] Depend on Figure 3 It can be seen that, compared to the electrode content of 4.62 ppm in Comparative Example 1, the electrode content after introducing lithium-rich sulfonated graphene additive in Example 1 is 24.45 ppm, an increase of 4.29 times. Figure 4 It can be seen that, compared with the electrode of Comparative Example 2 which has an S content of 4.14 ppm, the electrode of Example 2 with the introduction of lithium-rich sulfonated graphene additive has an S content of 28.01 ppm, which is 5.77 times higher; which fully confirms the presence of sulfonic acid groups in the material.

[0153] (3) The electrochemical impedance performance of the batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 2 was tested, and the results are shown in the figure. Figure 5 .

[0154] Depend on Figure 5 It can be seen that in the low-frequency region, the inclined straight portion of the electrode (Example Group) with lithium-rich sulfonated graphene additive is close to 90 degrees, indicating that it has a small ion diffusion resistance in its internal electrode structure; in the high-frequency region, the half-arc of the electrode with additive (Example Group) is significantly smaller than that of the control group without additive, indicating that this negative electrode additive is beneficial to improving the electron transport rate, and therefore has a lower charge transfer resistance, and the charge transfer impedance is significantly reduced under 50% SOC conditions.

[0155] (4) Immersion test:

[0156] (4.1) At normal pressure and 25℃, a negative electrode sample with a length of 22cm and a width of 2.5cm was fixed with double-sided tape. Figure 6 The sample needs to be straightened without bending during the fixing process in the grooves at the upper and lower ends of the partition shown. Then, the partition with the sample strip fixed is slowly placed into the shell, and the time and liquid level are recorded. Finally, the relationship between the wetting height and time of the electrolyte in a specific sample is obtained. The experimental environment needs to be controlled under a low humidity of 2%. Among them, (1) the compaction density P of each negative electrode is 1.45 g / cm³. 3 .

[0157] (2) The ratio of the height of the first edge of each negative electrode immersed in the electrolyte to the height of the negative electrode is 0.113:1;

[0158] (3) The composition of the electrolyte is as follows:

[0159] The solvent for the electrolyte is ethylene carbonate, the electrolyte is lithium hexafluorophosphate, and the electrolyte concentration is 1 mol / L.

[0160] The test results are shown in Table 1 below:

[0161] Table 1

[0162]

[0163] As shown in Table 1, adding 1% lithium-rich sulfonated graphene additive to the negative electrode can improve its wetting performance by approximately 17% to 39.3%.

[0164] (4.2) Referring to Example 1 and step (4.1), the wetting height and cycling effect under the same compaction density were examined, wherein the compaction density P of the negative electrode sheet was 1.55 g / cm³. 3 The test results after 10 minutes of soaking are shown in Table 2 below:

[0165] Table 2

[0166]

[0167]

[0168] As shown in Table 2, under the same compaction density, the electrolyte wetting height increases with the increase of the additive amount, and the capacity retention rate after 100 cls of cycling also increases accordingly. Reducing the compaction density can improve the electrode wetting performance, but at the expense of energy density.

[0169] (4.3) Referring to step (4.1), under room temperature conditions, 1% of lithium-rich sulfonated graphene was added to investigate the wetting height and circulation effect under different compaction densities. The test results are shown in Table 3 below:

[0170] Table 3

[0171]

[0172]

[0173] As shown in Table 3, with the same surface density, the wetting height of the electrolyte decreases with the increase of compaction density. This is mainly because the increased compaction density reduces the porosity of the electrode and worsens the electrolyte wetting. After adding 1% additive, the wetting height of the electrolyte under different compaction densities is greater than that of the blank group without additive, indicating that the additive can increase the wettability of the electrode to a certain extent.

[0174] Furthermore, as shown in Table 3, the relationship between the impregnation height (H) and compaction density (P) of the electrode with added additives satisfies: 14.494 ≤ H + 7.48P ≤ 18.994. The negative electrode has a length a of 20–22 cm, a width b of 2–2.5 cm, and a compaction density P of 1.3 g / cm³. 3 ~1.65g / cm 3 Where H is the sample wetting height in cm and P is the electrode compaction density in g / cm³. 3 .

[0175] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0176] The embodiments described above are merely illustrative 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 invention patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet has a first edge and a second edge. When the first edge of the negative electrode sheet is immersed in the electrolyte, the electrolyte wets the negative electrode sheet in a direction from the first edge to the second edge. Let H be the distance between the lowest point of the concave liquid surface formed after the electrolyte has soaked the negative electrode for 10 minutes at 1 standard atmosphere and 25°C, and the first edge of the electrode. Let P be the compaction density of the negative electrode. 3 H and P satisfy: 14.494 ≤ H + 7.48P ≤ 18.994; The solvent of the electrolyte is one or more of ethylene carbonate, methyl ethyl carbonate, diethyl carbonate and polycarbonate, and the electrolyte is lithium hexafluorophosphate, with a concentration of 0.4 mol / L to 1.8 mol / L.

2. The negative electrode sheet according to claim 1, characterized in that, The ratio of the height of the first edge of the negative electrode immersed in the electrolyte to the height of the negative electrode is (0.1~0.15):

1.

3. The negative electrode sheet according to claim 1, characterized in that, It includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector; The negative electrode active layer includes a negative electrode active material, additives, conductive agents, and binders; The additive is lithium-rich sulfonated graphene.

4. The negative electrode sheet according to claim 3, characterized in that, In the lithium-rich sulfonated graphene, the mass content of sulfonic acid groups is 0.1% to 10%.

5. The negative electrode sheet according to claim 3, characterized in that, In the lithium-rich sulfonated graphene, the molar ratio of lithium to sulfur is 1:(1-6).

6. The negative electrode sheet according to claim 3, characterized in that, The lithium-rich sulfonated graphene powder has a spherical morphology and a D50 particle size of 3μm to 8μm.

7. The negative electrode sheet according to any one of claims 3 to 6, characterized in that, The negative electrode active layer comprises the following components by mass percentage: The negative electrode active material is 94%–98%. Additives 0.05%–5%, Conductive agent 0.3%–1%, and Adhesive: 0.5%–2%.

8. The negative electrode sheet according to any one of claims 3 to 6, characterized in that, The negative electrode active material is selected from one or a mixture of several of lithium metal, lithium alloy, carbon, petroleum coke, silicon compounds, tin compounds, titanium compounds, and tin-titanium alloys.

9. The negative electrode sheet according to claim 8, characterized in that, The D50 particle size of the negative electrode active material is 7μm to 10μm.

10. The negative electrode sheet according to any one of claims 3 to 6, characterized in that, The compaction density of the negative electrode sheet is 1.3 g / cm³. 3 ~1.65g / cm 3 .

11. The negative electrode sheet according to any one of claims 3 to 6, characterized in that, The conductive agent is selected from one or a mixture of several of acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black.

12. The negative electrode sheet according to any one of claims 3 to 6, characterized in that, The adhesive is selected from one or a mixture of several of the following: polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, fluororubber, and polyacrylic acid.

13. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 12.

14. An electrical appliance, characterized in that, Includes the battery as described in claim 13.

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