Negative electrode sheet and preparation method therefor, battery cell and electric device

Abstract

A negative electrode sheet and a preparation method therefor, a battery cell and an electric device. The negative electrode sheet comprises: a negative electrode current collector and a negative electrode active material film layer arranged on at least one side of the negative electrode current collector. The negative electrode active material film layer comprises: an electrically conductive agent comprising carbon and an organic polymeric dispersant having a hydrophilic group and a hydrophobic group, and the organic polymeric dispersant has a weight-average molecular weight of 100 to 5,000. The negative electrode sheet and the preparation method therefor can make substances in the negative electrode active material film layer be uniformly dispersed, thereby prolonging the storage life of the battery and improving the cycle capacity retention rate thereof. Further provided are a battery cell and an electric device comprising the negative electrode sheet, such that improved cycle performance and storage life of the battery cell can be obtained.

Description

Negative electrode sheet and preparation method thereof, battery cell and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410172748.3 filed on February 7, 2024, entitled “Negative electrode sheet and preparation method thereof, battery cell and electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the field of battery technology, and specifically relates to a negative electrode plate and a preparation method thereof, a battery cell and an electrical device. Background Art

[0004] Battery cells, also known as rechargeable batteries, are batteries that can be repeatedly discharged and recharged for multiple uses. In recent years, as battery cells, particularly lithium-ion batteries, have become increasingly widely used, higher demands have been placed on their performance, particularly their cycle performance.

[0005] The battery body includes the negative electrode sheet. During the preparation of the negative electrode sheet, gelation often occurs, which increases the difficulty of coating and other processing, thus affecting the performance of the negative electrode sheet and the battery.

[0006] Therefore, how to prepare a negative electrode sheet with uniform distribution of components is a technical problem that needs to be solved urgently.

[0007] Summary of the Invention

[0008] The present application aims to provide a negative electrode plate and a method for preparing the same, which can achieve uniform distribution of materials within the negative electrode active material film layer of the negative electrode plate, thereby reducing uneven expansion of the negative electrode plate and improving the storage life of the battery. The present application also aims to provide a battery cell and an electrical device incorporating the negative electrode plate, thereby achieving improved battery cell cycle performance and storage life.

[0009] In a first aspect, an embodiment of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material film layer arranged on at least one side of the negative electrode current collector, the negative electrode active material film layer comprising: a conductive agent having carbon elements, an organic polymer dispersant having a hydrophilic group and a hydrophobic group, and the weight average molecular weight of the organic polymer dispersant is 100 to 5000.

[0010] The technical solution of the embodiment of the present application comprises a conductive agent having carbon elements and an organic polymer dispersant having hydrophilic groups and hydrophobic groups in the negative electrode plate. The organic polymer dispersant has a suitable weight-average molecular weight and a molecular chain with a suitable length, which reduces the overlap or even entanglement of the molecular chains in the negative electrode plate. The hydrophobic groups of the organic polymer dispersant are adsorbed on the surface of the conductive agent, so that the organic polymer dispersant forms a steric hindrance between the conductive agents, which promotes a more uniform dispersion of the conductive agent and improves the uniformity of the components of the negative active material film layer of the negative electrode plate, thereby facilitating the improvement of the cycle performance and storage life of the battery containing the negative electrode plate.

[0011] In some optional embodiments, the conductive agent includes a first conductive agent, and the first conductive agent includes one or more of carbon nanotubes, graphene, and nano-carbon fibers.

[0012] According to embodiments of the present application, the first conductive agent can be of the type described above, which can reduce the resistance of the negative electrode sheet. The combined effect of the first conductive agent and the organic polymer dispersant allows the hydrophobic groups of the organic polymer dispersant to adsorb on the surface of the conductive agent, creating steric hindrance between the organic polymer dispersant and the conductive agent, promoting more uniform dispersion of the conductive agent. This improves the uniformity of the components of the negative electrode active material film layer of the negative electrode sheet, helps limit or reduce uneven expansion of the negative electrode sheet, and thus increases the storage life of the negative electrode sheet and the battery.

[0013] In some optional embodiments, the weight average molecular weight of the organic polymer dispersant is 200 to 3500.

[0014] According to the embodiments of the present application, the organic polymer dispersant has the above-mentioned suitable weight-average molecular weight, and thus the organic polymer dispersant has a suitable molecular chain length, and its hydrophobic groups are adsorbed on the surface of the first conductive agent through intermolecular forces or van der Waals forces, thereby reducing the molecular chains that are too long and will overlap or even entangle with each other, causing the organic polymer dispersant to form steric hindrance between the first conductive agent, thereby promoting the first conductive agent to be dispersed more evenly, improving the uniformity of the components in the negative electrode active material film layer, and thus facilitating the improvement of the electrochemical performance of the battery containing the negative electrode plate.

[0015] In some optional embodiments, at a temperature of 25° C., the viscosity a of the organic polymer dispersant when its mass fraction in water is 10% is in a range of 10 mPa·S to 1000 mPa·S.

[0016] According to the embodiment of the present application, by detecting the viscosity of a certain mass fraction of an organic polymer dispersant in water, an organic polymer dispersant with a suitable viscosity can be selected to disperse the first conductive agent and other components in the slurry, thereby reducing the agglomeration and gelation phenomenon during the static state of the slurry, improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet, and improving the uniformity of the components in the negative electrode active material film layer, which is beneficial to improving the electrochemical performance of the battery containing the negative electrode sheet.

[0017] In addition, the viscosity of the organic polymer dispersant can reflect the type and molecular weight of the organic polymer dispersant, as well as the dispersion effect it brings, to a certain extent.

[0018] In the embodiments of the present application, the type of hydrophilic group is not significantly limited, and any hydrophilic functional group that can have hydrophilic properties and disperse in water can be used in the embodiments of the present application. In some optional embodiments, the hydrophilic group includes one or more of a hydroxyl group, a carboxyl group, an amide group, an amino group, an ether group, and a carbonyl group. In some embodiments, the hydrophilic group includes a carbon-nitrogen double bond.

[0019] According to the embodiment of the present application, the organic polymer dispersant in the negative electrode plate has the above-mentioned type of hydrophilic groups, so that the organic polymer dispersant forms a certain steric hindrance, reduces the probability of agglomeration and gelation of the first conductive agent between the negative electrode active material film layers, and achieves the effect of dispersing the first conductive agent and other components.

[0020] In the embodiments of the present application, there is no explicit limitation on the type of hydrophobic group; any hydrophobic functional group that can be adsorbed on the surface of the first conductive agent can be used in the embodiments of the present application. In some optional embodiments, the hydrophobic group includes one or more of an ester group, an alkyl group containing C8 to C18, an alkylene group containing C8 to C18, and an aryl group containing C6 to C12.

[0021] A hydrophobic group refers to a functional group with low hydrophilicity, typically containing a hydrophobic structure with carbon-hydrogen bonds. The first conductive agent comprising carbon elements includes a surface structure formed by carbon atoms. In the embodiments of the present application, the hydrophobic groups described above are generally more likely to adsorb on the surface of the first conductive agent, thereby dispersing the first conductive agent and improving the uniformity of the dispersion of the individual substances in the negative electrode active material film.

[0022] In some optional embodiments, the organic polymeric dispersant comprises R1-O-(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0023] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the dispersion uniformity of each component in the negative electrode active material film layer, and is beneficial to the electrochemical performance of the negative electrode sheet.

[0024] In some optional embodiments, the organic polymeric dispersant comprises) R1COO(CH2CH2O) n H or a modified product thereof, R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0025] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group and a carbonyl group (C=O bond) on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, and prevents the slurry from agglomerating and producing a gel phenomenon during the static process, thereby improving the uniformity of the components in the negative electrode active material film layer, thereby helping to improve the electrochemical performance of the battery containing the negative electrode plate.

[0026] In some optional embodiments, the organic polymeric dispersant comprises R1R2N-(CH2CH2O) n H or its modified form, R1 and R2 each represent an alkyl group containing C8 to C18, and 1≤n≤45.

[0027] According to the embodiment of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as a C8-C18 alkyl group, and an ether group, C=N on the other side, and has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the uniformity of the components in the negative electrode active material film layer, and is conducive to improving the electrochemical performance of the battery containing the negative electrode plate. In some optional embodiments, the organic polymer dispersant includes R1-CONH(CH2CH2O) n H or a modified product thereof, R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0028] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group and a carbonyl group (C=O bond) on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the uniformity of the components in the negative electrode active material film layer, and is beneficial to improving the electrochemical performance of the battery containing the negative electrode plate.

[0029] In some optional embodiments, the organic polymer dispersant includes one or more of polyoxyethylene sorbitan laurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan monooleate, lauryl alcohol polyoxyethylene ether, lauric acid diethanolamide, polyoxyethylene laurate, octadecylamine polyoxyethylene ether, and nonylphenol polyoxyethylene ether.

[0030] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic group and a hydrophilic group, and has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the dispersion uniformity of each component in the negative electrode active material film layer in the negative electrode plate, and reduces the uneven expansion of the negative electrode plate during the battery charging and discharging process.

[0031] In some optional embodiments, the organic polymeric dispersant comprises R1-(C6H4)-O(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤15.

[0032] According to the embodiments of the present application, -(C6H4)- represents a phenyl group. The aforementioned organic polymeric dispersant has a hydrophobic functional group such as a C8-C18 alkyl group on one side, and a hydrophilic group such as an ether group on the other side. Furthermore, the organic polymeric dispersant has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the aforementioned organic polymeric dispersant forms a steric hindrance between the first conductive agent, promoting a more uniform dispersion of the first conductive agent and improving the uniformity of the components in the negative electrode active material film layer, thereby facilitating improved electrochemical performance of the battery containing the negative electrode plate.

[0033] In some optional embodiments, the negative electrode active material layer includes 0.05% to 1% of the organic polymer dispersant based on the total mass of the negative electrode active material layer.

[0034] According to the embodiment of the present application, the organic polymer dispersant with the above-mentioned mass content in the negative electrode plate is conducive to the adsorption of one side of the organic polymer dispersant on the surface of the first conductive agent, so that the organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, thereby improving the uniformity of the various components of the negative electrode active material film layer of the negative electrode plate, thereby helping to improve the cycle performance of the battery containing the negative electrode plate.

[0035] In some optional embodiments, the first conductive agent is carbon nanotubes, the average diameter of the carbon nanotubes is 1 to 20 nm, and the average length of the carbon nanotubes is 1 to 50 μm.

[0036] According to an embodiment of the present application, the first conductive agent is carbon nanotubes, which can play a role in long-range conductivity and restrain the expansion of the negative electrode plate, which is beneficial to improving the stability of the negative electrode plate, thereby increasing the storage life of the battery.

[0037] According to the embodiment of the present application, the above-mentioned single-walled carbon nanotubes have the above-mentioned size characteristics, which represent that this type of high aspect ratio material in the slurry is very easy to cause slurry agglomeration and gelation due to its nanometer size effect and intermolecular force. In addition, due to the high aspect ratio, single-walled carbon nanotubes can interact with the conventional additive carboxymethyl cellulose (CMC) to form a three-dimensional network structure in the slurry, which aggravates the gelation phenomenon to a certain extent. By adding the above-mentioned organic polymer dispersant to the slurry, the gelation phenomenon caused by the single-walled carbon nanotubes can be improved, which is beneficial to the preparation of the negative electrode sheet. Therefore, the uniformity of the components in the negative electrode active material film layer is improved, which is beneficial to improving the electrochemical performance of the battery containing the negative electrode sheet.

[0038] In some optional embodiments, the first conductive agent is carbon nanofiber, the average tube diameter of the carbon nanofiber is 1 to 150 nm, and the average length of the carbon nanofiber is 1 to 50 μm.

[0039] According to the embodiment of the present application, the above-mentioned nano-carbon fibers can play a role in long-range conductivity and restraining the expansion of the negative electrode plate, which is beneficial to improving the stability of the negative electrode plate, thereby increasing the storage life of the battery.

[0040] In some optional embodiments, the first conductive agent is graphene; the average thickness of the graphene is 1 to 50 nm, and the length of the major axis of the graphene is 1 to 50 μm.

[0041] According to the embodiments of the present application, the above-mentioned graphene and organic polymer dispersant work together to improve the uniformity of the components in the negative electrode active material film layer, thereby facilitating the improvement of the electrochemical performance of the battery containing the negative electrode plate; it is also beneficial to improve the stability of the negative electrode plate, thereby increasing the storage life of the battery. In some optional embodiments, the slurry includes a negative electrode active material. In some embodiments, the negative electrode active material is a material containing silicon. In some optional embodiments, the negative electrode active material includes one or more of a silicon elemental material, a silicon-carbon material, and a silicon-oxygen material.

[0042] According to an embodiment of the present application, when the negative electrode active material is a material containing silicon element, that is, the above-mentioned type of material, the first conductive agent works together with the above-mentioned type of negative electrode active material. The first conductive agent plays a role of long-range conductivity and restraining the expansion of the silicon negative electrode, and also improves the life of the silicon-containing battery.

[0043] In some optional embodiments, the silicon-carbon material comprises 40% to 99.5% silicon, based on the total mass of the silicon-carbon material. According to embodiments of the present application, the silicon content within the above range is beneficial for controlling the expansion range of the negative electrode sheet produced from the slurry, thereby improving the storage life of the negative electrode sheet and the cycle performance of the battery.

[0044] In some optional embodiments, the negative electrode active material further includes a carbon-based material, wherein the carbon-based material includes one or more of artificial graphite and natural graphite, and the mass content of silicon in the negative electrode active material is 4% to 99.5%.

[0045] According to the embodiment of the present application, the mass content of the silicon-carbon material in the negative electrode active material is within the above-mentioned range, which is beneficial to controlling the expansion range of the negative electrode sheet prepared from the slurry, thereby being beneficial to the storage life of the negative electrode sheet and the cycle performance of the battery.

[0046] In the embodiments of the present application, the type of the second conductive agent is not specifically limited; any conductive agent that can be used in the slurry of the negative electrode sheet and has a good conductive effect can be used in the embodiments of the present application. To further improve the conductivity of the negative electrode sheet and reduce the internal resistance of the negative electrode sheet, in some optional embodiments, the slurry includes a second conductive agent, and the second conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, and carbon dots.

[0047] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising:

[0048] A slurry is provided, comprising water, a conductive agent having carbon elements, and an organic polymer dispersant having hydrophilic groups and hydrophobic groups, wherein the first conductive agent comprises one or more of carbon nanotubes, graphene, and nanocarbon fibers, and the weight-average molecular weight of the organic polymer dispersant is 100 to 5000.

[0049] The slurry is coated on the negative electrode current collector to form a negative electrode active material film layer, thereby preparing the negative electrode sheet of the second aspect.

[0050] According to the embodiments of the present application, the conductive agent present in the water-containing slurry causes the slurry to exhibit a certain gelation phenomenon, which is not conducive to the uniform dispersion of the various components in the slurry, thereby affecting the subsequent coating process of the slurry to prepare the negative electrode sheet, affecting the uniformity of the negative electrode sheet, and reducing the uneven expansion of the negative electrode sheet during the battery charging and discharging process. Furthermore, during the slurry rest process, after being left to stand, the conductive agent contained in the slurry can cause the slurry to exhibit a physical gelation phenomenon, causing the slurry to lose fluidity, thereby affecting the processing of the negative electrode sheet (scratches, pits, and large fluctuations in coating quality), causing production difficulties.

[0051] Surprisingly, when the slurry used for the negative electrode sheet in the embodiment of the present application includes an organic polymer dispersant with an appropriate weight-average molecular weight, resulting in molecular chains of appropriate length, the overlap or even entanglement of the molecular chains in the slurry is reduced. The hydrophobic groups of the organic polymer dispersant are adsorbed on the surface of the conductive agent, while the hydrophilic groups are hydrophilic groups. When in contact with the solvent water, the organic polymer dispersant forms a steric hindrance between the conductive agents, promoting a more uniform dispersion of the conductive agent, reducing the probability of agglomeration and gelation during the slurry standing process, and improving the uniformity of the dispersion of the various components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet. The uniformity of the resulting negative electrode sheet is also improved. The presence of the first conductive agent helps to limit the expansion of the negative electrode sheet, which is beneficial to the stability of the negative electrode sheet, and comprehensively improves the cycle performance and storage life of the battery containing the negative electrode sheet.

[0052] In some optional embodiments, the conductive agent includes a first conductive agent, and the first conductive agent includes one or more of carbon nanotubes, graphene, and nano-carbon fibers.

[0053] According to the method of the embodiment of the present application, a slurry containing water, a first conductive agent, and an organic polymer dispersant having a hydrophilic group and a hydrophobic group is prepared to form a negative electrode sheet. Since the first conductive agent includes carbon nanotubes, graphene, and nanocarbon fibers, it is easy to cause the slurry to gel. Therefore, an organic polymer dispersant having a hydrophilic group and a hydrophobic group is added thereto. The weight-average molecular weight of the organic polymer dispersant is 100 to 5000, so that it has a molecular chain of suitable length, which reduces the overlap or even entanglement of the molecular chains in the slurry. The hydrophobic groups of the organic polymer dispersant are adsorbed on the first conductive agent. On the surface of the conductive agent, the hydrophilic group is a hydrophilic group. When in contact with the solvent water, the organic polymer dispersant forms a steric hindrance between the first conductive agent, which makes the first conductive agent disperse more evenly and prevents the slurry from agglomerating and producing gelation during the static process, thereby improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet, and also improving the uniformity of the prepared negative electrode sheet. The presence of the first conductive agent is beneficial to limiting the expansion of the negative electrode sheet, which is beneficial to the stability of the negative electrode sheet, and comprehensively improves the cycle performance and storage life of the battery containing the negative electrode sheet.

[0054] In some optional embodiments, at a temperature of 25° C., the viscosity of the slurry is 1000 mPa·S to 20000 mPa·S.

[0055] According to the embodiment of the present application, the viscosity of the slurry is within the above range, and the organic polymer dispersant and the first conductive agent interact with each other to promote a more uniform dispersion of the first conductive agent and prevent the slurry from agglomerating and producing a gel phenomenon during the static process, thereby improving the dispersion uniformity of the components in the slurry and facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0056] In some optional embodiments, the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant is 100:(0.05-1):(0.05-1). In some optional embodiments, the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant is 100:(0.05-0.5):(0.05-0.5).

[0057] According to the embodiments of the present application, controlling the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant within the above-mentioned range is beneficial to improving the uniformity of the negative electrode sheet while taking into account the battery capacity and the internal resistance of the battery, limiting the expansion of the negative electrode sheet, and improving the stability of the negative electrode sheet, thereby increasing the storage life of the battery.

[0058] In some optional embodiments, the mass ratio of the first conductive agent to the organic polymer dispersant is 1:(0.1-3).

[0059] According to the embodiment of the present application, there is a correlation between the quality of the first conductive agent and the organic polymer dispersant. When the amount of carbon nanotubes added is large, the gelation of the slurry will become more serious. In this case, the amount of dispersant needed is larger, which is helpful in solving the problem of gelation of the slurry when it is left to stand. Therefore, the embodiment of the present application further reduces the gelation phenomenon that occurs when the slurry is left to stand by controlling the mass ratio of the first conductive agent and the organic polymer dispersant within the above range, improves the slurry dispersion effect, facilitates the subsequent preparation of the negative electrode sheet, and further improves the uniformity of the negative electrode sheet.

[0060] In a third aspect, embodiments of the present application provide a battery cell comprising the negative electrode sheet of the first aspect or the negative electrode sheet produced by the preparation method of the second aspect. The battery cell of the present application comprises the negative electrode sheet of the first aspect or the negative electrode sheet produced by the preparation method of the second aspect, and thus has at least the advantages of using the negative electrode sheet.

[0061] In a fourth aspect, an embodiment of the present application provides an electrical device comprising the battery cell of the fourth aspect. The electrical device of the present application comprises the battery cell of the third aspect of the present application, and thus has at least the advantage of being applied to a negative electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0063] FIG1 shows a schematic diagram of a battery cell according to an embodiment of the present application.

[0064] FIG. 2 shows an exploded schematic diagram of the battery cell shown in FIG. 1 .

[0065] FIG3 is a schematic diagram showing an embodiment of an electric device including the battery cell of the present application as a power source.

[0066] FIG4 shows a viscosity change curve of the slurry of Example 1 of the present application and the slurry of Comparative Example 1 after standing for 0 to 48 hours.

[0067] In the accompanying drawings, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0068] Below, with appropriate reference to the accompanying drawings, detailed descriptions are provided of the negative electrode sheet and its preparation method, electrode assembly battery cell, battery module, battery pack and electric device of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0069] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0071] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0072] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0073] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0074] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0075] Unless otherwise specified, the terms "connected" and "connection" in this application should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection, indirect connection through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0076] If not otherwise specified, in this application, the term "attach" refers to connection by adhesion, coating, etc.

[0077] Unless otherwise specified, in this application, the terms "first", "second", "third", "fourth", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0078] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be intercalated and extracted between the positive and negative electrodes of a battery cell, including but not limited to lithium ions, sodium ions, etc.

[0079] The term "several" or "multiple" used in this application refers to two or more items (including two items). The term "several" or "multiple items" used in this application refers to two or more items (including two items).

[0080] The battery cells mentioned in the embodiments of the present application may be lithium-ion batteries, sodium-ion batteries, lithium metal batteries, sodium metal batteries, etc., and the embodiments of the present application are not limited to this.

[0081] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The electrode sheet will undergo volume expansion during the static and formation process after the electrolyte is injected, which will increase the overall thickness of the battery, thereby affecting the battery performance. During the formation process of the battery cell, the electrode sheet expands. The reasons include volume expansion and stress relaxation expansion caused by the combination of active ions with electrode material particles (such as adsorption, embedding or combination). Studies have found that during the subsequent charging process after the battery is formed, the negative electrode sheet will also expand in volume. The main reason is that the active ions migrate from the positive electrode sheet to the negative electrode sheet and combine with the negative electrode active material (such as adsorption, embedding or combination), which increases the volume of the negative electrode active material, thereby causing the volume expansion of the negative electrode sheet.

[0082] In order to improve the life of the battery, the negative electrode active material film layer in the negative electrode sheet generally needs to be relatively homogeneous. The acquisition of a homogeneous negative electrode active material film layer depends on the negative electrode sheet homogenization system.

[0083] Taking the common battery cell negative electrode slurry system as an example, when the negative electrode active material film mainly includes the negative electrode active material, a binder, a conductive agent, and sometimes a dispersant, while dispersants such as carboxymethyl cellulose can provide a certain dispersion effect, when the conductive agent contains one or more of carbon nanotubes, graphene, and nanocarbon fibers, the slurry is more likely to gel when left standing.

[0084] Furthermore, when the negative electrode active material uses a negative electrode active material containing silicon elements, the content of conductive agents such as carbon nanotubes, graphene, and nanocarbon fibers added therein is higher, so the gelation phenomenon occurring during the homogenization process is more serious, affecting the performance of the negative electrode sheet.

[0085] The gelation phenomenon that occurs during the homogenization process of the slurry used to prepare the negative electrode sheets is unfavorable. This gelation phenomenon makes it impossible to stir the slurry evenly and causes a large number of particles to agglomerate. At the same time, the slurry in the gel state cannot be coated normally, which brings many inconveniences to the production of negative electrode sheets and battery cells.

[0086] In addition, the gelation phenomenon that occurs during the homogenization process brings a series of side effects, such as unbalanced expansion of the negative electrode plate, deterioration of the battery's cycle performance and storage life, etc.

[0087] In view of this, the technical solution of the embodiment of the present application provides a negative electrode plate and a preparation method thereof, which can at least reduce the gel phenomenon of the slurry used for the negative electrode plate, improve the quality of the negative electrode plate, and improve the cycle performance and storage life of the battery containing the negative electrode plate.

[0088] Negative electrode

[0089] In a first aspect, an embodiment of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material film layer arranged on at least one side of the negative electrode current collector, the negative electrode active material film layer comprising: a conductive agent having carbon elements, an organic polymer dispersant having a hydrophilic group and a hydrophobic group, and the weight average molecular weight of the organic polymer dispersant is 100 to 5000.

[0090] An organic polymeric dispersant is an organic compound. In a wet state, an organic polymeric dispersant can disperse aggregated solid particles, such as conductive agents. According to embodiments of the present application, an organic polymeric dispersant is a chemical substance used to disperse solid particles in a slurry and prevent their aggregation. This helps reduce agglomeration caused by attraction and cohesion between particles, thereby maintaining the uniformity and stability of the slurry and improving the uniformity of the dispersion of substances in the negative electrode active material film layer, particularly the uniform dispersion of the conductive agent.

[0091] A hydrophilic group refers to a chemical group that can interact with and attract water molecules, such as a carboxyl group or a hydroxyl group. A hydrophobic group refers to a chemical group that does not interact with and repels water molecules, such as a methyl group in an alkyl group. In the present application, a hydrophobic group can be understood as a lipophilic group.

[0092] According to the technical solution of the embodiment of the present application, the negative active material film layer of the negative electrode plate has a conductive agent of carbon elements and an organic polymer dispersant having a hydrophilic group and a hydrophobic group, and the organic polymer dispersant has a suitable weight-average molecular weight, so that it has a molecular chain of suitable length, which reduces the overlap or even entanglement of the molecular chains in the negative electrode plate. The hydrophobic groups of the organic polymer dispersant are adsorbed on the surface of the conductive agent, so that the organic polymer dispersant forms a steric hindrance between the conductive agents, which promotes the conductive agent to be dispersed more evenly, thereby improving the uniformity of the various components of the negative active material film layer of the negative electrode plate, thereby facilitating the improvement of the cycle performance of the battery containing the negative electrode plate.

[0093] The type of organic polymer dispersant can be detected by using technical means known in the art, such as nuclear magnetic resonance, pyrolysis-gas chromatography / mass spectrometry, gas chromatography-mass spectrometry, mass spectrometry, infrared spectroscopy, or one or more other methods to determine whether the slurry includes an organic polymer dispersant and to determine the type of the organic polymer dispersant. As an example, the method for detecting the type of organic polymer dispersant in the slurry is as follows: nuclear magnetic resonance and mass spectrometry can be used to determine whether the slurry includes an organic polymer dispersant and to determine the type of the organic polymer dispersant. In addition, the type of the organic polymer dispersant can be obtained by the type of organic polymer dispersant added during the preparation process.

[0094] The weight average molecular weight of an organic polymeric dispersant is well known in the art and can be measured using instruments and methods known in the art. For example, high temperature gel permeation chromatography (GPC) can be used. For example, a PolymerChar GPC-IR high temperature gel permeation chromatography (GPC) instrument can be used. The test can refer to the international standard ISO 16014-1-2019.

[0095] In some optional embodiments, the conductive agent includes a first conductive agent, and the first conductive agent includes one or more of carbon nanotubes, graphene, and nano-carbon fibers.

[0096] According to embodiments of the present application, the first conductive agent can be of the type described above, which can reduce the resistance of the negative electrode sheet. The combined effect of the first conductive agent and the organic polymer dispersant allows the hydrophobic groups of the organic polymer dispersant to adsorb on the surface of the conductive agent, creating steric hindrance between the organic polymer dispersant and the conductive agent, promoting more uniform dispersion of the conductive agent. This improves the uniformity of the components of the negative electrode active material film layer of the negative electrode sheet, helps limit or reduce uneven expansion of the negative electrode sheet, and thus increases the storage life of the negative electrode sheet and the battery.

[0097] In some optional embodiments, the weight average molecular weight of the organic polymer dispersant is 200 to 3500.

[0098] Alternatively, the weight average molecular weight of the organic polymeric dispersant may be 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, Any value among 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, 5000 or a range consisting of the above.

[0099] According to the embodiments of the present application, the organic polymer dispersant has the above-mentioned suitable weight-average molecular weight, and thus the organic polymer dispersant has a suitable molecular chain length, and its hydrophobic groups are adsorbed on the surface of the conductive agent through intermolecular forces or van der Waals forces, thereby reducing the overlap or even entanglement of the molecular chains that are too long, causing the organic polymer dispersant to form steric hindrance between the conductive agents, promoting a more uniform dispersion of the conductive agent, and improving the uniformity of the components in the negative electrode active material film layer, which is beneficial to improving the electrochemical performance of the battery containing the negative electrode plate.

[0100] In some optional embodiments, at a temperature of 25° C., the viscosity a of the organic polymer dispersant when its mass fraction in water is 10% is in a range of 10 mPa·S to 1000 mPa·S.

[0101] Optionally, the viscosity of the organic polymer dispersant in water can be any value among 10mPa·S, 20mPa·S, 30mPa·S, 40mPa·S, 50mPa·S, 60mPa·S, 70mPa·S, 80mPa·S, 90mPa·S, 100mPa·S, 200mPa·S, 300mPa·S, 400mPa·S, 500mPa·S, 600mPa·S, 700mPa·S, 800mPa·S, 900mPa·S, 1000mPa·S or a range of their combinations.

[0102] According to the embodiments of the present application, by detecting the viscosity of a certain mass fraction of an organic polymer dispersant in water, an organic polymer dispersant with a suitable viscosity can be selected to disperse other components in the slurry, such as the first conductive agent, thereby reducing the agglomeration and gelation phenomenon during the standing process of the slurry, improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet; and improving the uniformity of the components in the negative electrode active material film layer, which is beneficial to improving the electrochemical performance of the battery containing the negative electrode sheet.

[0103] In addition, the viscosity of the organic polymer dispersant can reflect the type and molecular weight of the organic polymer dispersant and the dispersion effect it brings to a certain extent.

[0104] The viscosity of an organic polymeric dispersant in water is well known in the art and can be measured using instruments and methods known in the art. For example, a Brookfield viscometer is used for testing at a speed of 12 rpm, in a 25°C water bath, for 10 minutes, with the average of the data from the sixth minute taken.

[0105] In the embodiments of the present application, the type of hydrophilic group is not significantly limited, and any hydrophilic functional group that can have hydrophilic properties and disperse in water can be used in the embodiments of the present application. In some optional embodiments, the hydrophilic group includes one or more of a hydroxyl group, a carboxyl group, an amide group, an amino group, an ether group, and a carbonyl group. In some embodiments, the hydrophilic group includes a carbon-nitrogen double bond.

[0106] According to the embodiments of the present application, the organic polymer dispersant has the above-mentioned type of hydrophilic groups, which is conducive to its dispersion in water, so that the organic polymer dispersant forms a certain steric hindrance, reduces the agglomeration and gelation between the first conductive agent, and achieves the effect of dispersing the first conductive agent and other components.

[0107] In the embodiments of the present application, there is no explicit limitation on the type of hydrophobic group; any hydrophobic functional group that can be adsorbed on the surface of the first conductive agent can be used in the embodiments of the present application. In some optional embodiments, the hydrophobic group includes one or more of an ester group, an alkyl group containing C8 to C18, and an alkylene group containing C8 to C18.

[0108] A hydrophobic group refers to a functional group with low hydrophilicity, usually a hydrophobic structure containing a carbon-hydrogen bond. The first conductive agent having carbon elements comprises a structural surface formed by carbon atoms. The embodiments of the present application having the above-mentioned types of hydrophobic groups are generally more inclined to adsorb on the surface of the conductive agent, thereby achieving the effect of dispersing the conductive agent, reducing its agglomeration and gelation; improving the uniformity of the components in the negative electrode active material film layer, thereby facilitating improving the electrochemical performance of the battery containing the negative electrode plate.

[0109] In some optional embodiments, the organic polymeric dispersant comprises R1-O-(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0110] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the uniformity of the components in the negative electrode active material film layer, and is beneficial to improving the electrochemical performance of the battery containing the negative electrode plate.

[0111] In some optional embodiments, the organic polymeric dispersant comprises) R1COO(CH2CH2O) n H or a modified product thereof, R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0112] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group and a carbonyl group (C=O bond) on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly; improves the uniformity of the components in the negative electrode active material film layer, which is beneficial to improve the electrochemical performance of the battery containing the negative electrode plate.

[0113] In some optional embodiments, the organic polymeric dispersant comprises R1R2N-(CH2CH2O) n H or its modified form, R1 and R2 each represent an alkyl group containing C8 to C18, and 1≤n≤45.

[0114] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group, C=N, on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the uniformity of the components in the negative electrode active material film layer, and is beneficial to improving the electrochemical performance of the battery containing the negative electrode plate.

[0115] In some optional embodiments, the organic polymeric dispersant comprises R1-CONH(CH2CH2O) n H or a modified product thereof, R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0116] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group and a carbonyl group (C=O bond) on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the uniformity of the components in the negative electrode active material film layer, and is beneficial to improving the electrochemical performance of the battery containing the negative electrode plate.

[0117] In some optional embodiments, the organic polymer dispersant includes a polyol-type alkane dispersant or a modified product thereof; optionally, the organic polymer dispersant includes one or more of polyoxyethylene sorbitan laurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan stearate, and polyoxyethylene sorbitan monooleate.

[0118] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group, and on the other side has any one or more hydrophilic groups of hydroxyl, carboxyl, and carbonyl (C=O bond), and has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the uniformity of the components in the negative electrode active material film layer, and is beneficial to improving the electrochemical performance of the battery containing the negative electrode plate.

[0119] In some optional embodiments, the organic polymeric dispersant comprises R1-(C6H4)-O(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤15.

[0120] According to the embodiments of the present application, -(C6H4)- represents a phenyl group. The aforementioned organic polymeric dispersant has a hydrophobic functional group such as a C8-C18 alkyl group on one side, and a hydrophilic group such as an ether group on the other side. Furthermore, the organic polymeric dispersant has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the aforementioned organic polymeric dispersant forms a steric hindrance between the first conductive agent, promoting a more uniform dispersion of the first conductive agent and improving the uniformity of the components in the negative electrode active material film layer, thereby facilitating improved electrochemical performance of the battery containing the negative electrode plate.

[0121] In some optional embodiments, the organic polymer dispersant includes one or more of polyoxyethylene sorbitan laurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan monooleate, lauryl alcohol polyoxyethylene ether, lauric acid diethanolamide, polyoxyethylene laurate, octadecylamine polyoxyethylene ether, and nonylphenol polyoxyethylene ether.

[0122] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic group and a hydrophilic group, and has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, improves the dispersion uniformity of each component in the negative electrode active material film layer in the negative electrode plate, and reduces the uneven expansion of the negative electrode plate during the battery charging and discharging process.

[0123] In some optional embodiments, the negative electrode active material layer includes 0.05% to 1% of the organic polymer dispersant based on the total mass of the negative electrode active material layer.

[0124] Optionally, the negative electrode active material film layer includes an organic polymer dispersant whose mass content can be any value among 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1% or a range of their compositions.

[0125] According to the embodiment of the present application, the organic polymer dispersant with the above-mentioned mass content in the negative electrode plate is conducive to the adsorption of one side of the organic polymer dispersant on the surface of the first conductive agent, so that the organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, thereby improving the uniformity of the various components of the negative electrode active material film layer of the negative electrode plate, thereby helping to improve the cycle performance of the battery containing the negative electrode plate.

[0126] The mass content of the organic polymeric dispersant can be determined using techniques known in the art, such as high-performance liquid chromatography (HPLC). For example, the mass content of the organic polymeric dispersant can be determined using GB / T 31414-2015. Furthermore, the mass of each organic polymeric dispersant can be determined by determining the type of organic polymeric dispersant added during the preparation process.

[0127] In some optional embodiments, the first conductive agent is carbon nanotubes, the average diameter of the carbon nanotubes is 1 to 20 nm, and the average length of the carbon nanotubes is 1 to 50 μm.

[0128] Optionally, the average diameter of the carbon nanotubes may be any value among 1 nm, 5 nm, 6 nm, 10 nm, 11 nm, 16 nm, 20 nm, or a range thereof.

[0129] Optionally, the average length of the carbon nanotubes may be any value among 1 μm, 6 μm, 11 μm, 16 μm, 21 μm, 26 μm, 31 μm, 36 μm, 41 μm, 46 μm, 50 μm, or a range thereof.

[0130] According to an embodiment of the present application, the first conductive agent is carbon nanotubes, which can play a role in long-range conductivity and restrain the expansion of the negative electrode plate, which is beneficial to improving the stability of the negative electrode plate, thereby increasing the storage life of the battery.

[0131] According to the embodiments of the present application, the above-mentioned single-walled carbon nanotubes have the above-mentioned size characteristics, which represent that this type of high aspect ratio material in the slurry is very easy to cause slurry agglomeration and gelation due to its nano-size effect and intermolecular force. In addition, due to its high aspect ratio, single-walled carbon nanotubes can interact with the conventional additive carboxymethyl cellulose (CMC) to form a three-dimensional network structure in the slurry, which to a certain extent aggravates the gelation phenomenon. By adding the above-mentioned organic polymer dispersant to the slurry, the gelation phenomenon caused by the single-walled carbon nanotubes can be improved, which is beneficial to the preparation of the negative electrode sheet; the uniformity of the components in the negative electrode active material film layer is improved, which is beneficial to improving the electrochemical performance of the battery containing the negative electrode sheet.

[0132] In some optional embodiments, the first conductive agent is carbon nanofiber, the average tube diameter of the carbon nanofiber is 1 to 150 nm, and the average length of the carbon nanofiber is 1 to 50 μm.

[0133] Optionally, the average tube diameter of the nano-carbon fiber can be any value among 1nm, 6nm, 11nm, 16nm, 21nm, 26nm, 31nm, 36nm, 41nm, 46nm, 51nm, 56nm, 61nm, 66nm, 71nm, 76nm, 81nm, 86nm, 91nm, 96nm, 101nm, 106nm, 111nm, 116nm, 121nm, 126nm, 131nm, 136nm, 141nm, 146nm, 150nm or any range of their combinations.

[0134] Optionally, the average length of the carbon nanofibers can be any value among 1 μm, 6 μm, 11 μm, 16 μm, 21 μm, 26 μm, 31 μm, 36 μm, 41 μm, 46 μm, 50 μm, or a range thereof.

[0135] According to the embodiment of the present application, the first conductive agent is nano-carbon fiber, which can play the role of long-range conductivity and restrain the expansion of the negative electrode plate, which is beneficial to improving the stability of the negative electrode plate, thereby increasing the storage life of the battery.

[0136] According to the embodiment of the present application, the above-mentioned nano-carbon fibers have the above-mentioned size characteristics, which represent that this type of high aspect ratio material in the slurry is very easy to cause slurry agglomeration and gelation due to its nano-size effect and intermolecular force. In addition, due to its high aspect ratio, the nano-carbon fibers can interact with the conventional additive carboxymethyl cellulose (CMC) to form a three-dimensional network structure in the slurry, which aggravates the gelation phenomenon to a certain extent. By adding the above-mentioned organic polymer dispersant to the slurry, the gelation phenomenon caused by the nano-carbon fibers can be improved, which is beneficial to the preparation of the negative electrode sheet. The uniformity of the components in the negative electrode active material film layer is improved, which is beneficial to improving the electrochemical performance of the battery containing the negative electrode sheet.

[0137] In some optional embodiments, the first conductive agent is graphene; the average thickness of the graphene is 1 to 50 nm, and the length of the major axis of the graphene is 1 to 50 μm.

[0138] Optionally, the average thickness of the graphene can be any value among 1 nm, 6 nm, 11 nm, 16 nm, 21 nm, 26 nm, 31 nm, 36 nm, 41 nm, 46 nm, 50 nm or a range thereof.

[0139] Optionally, the length of the long axis of the graphene may be any value among 1 μm, 6 μm, 11 μm, 16 μm, 21 μm, 26 μm, 31 μm, 36 μm, 41 μm, 46 μm, 50 μm, or a range thereof.

[0140] "Long diameter" usually refers to the longest line between a point on the edge and another point in an irregular figure, such as graphene in the projection plane, which is called the long diameter.

[0141] According to the embodiment of the present application, the first conductive agent is graphene, which can play a role in long-range conductivity and restrain the expansion of the negative electrode plate, which is beneficial to improving the stability of the negative electrode plate, thereby increasing the storage life of the battery.

[0142] According to the embodiment of the present application, the above-mentioned graphene has the above-mentioned size characteristics. The nano-size effect and intermolecular force of graphene easily lead to slurry agglomeration and gelation. In addition, graphene can interact with the conventional additive carboxymethyl cellulose (CMC) to form a three-dimensional network structure in the slurry, which aggravates the gelation phenomenon to a certain extent. By adding the above-mentioned organic polymer dispersant to the slurry, the gelation phenomenon caused by graphene can be improved, which is beneficial to the preparation of the negative electrode sheet. The uniformity of the components in the negative electrode active material film layer is improved, which is beneficial to improving the electrochemical performance of the battery containing the negative electrode sheet.

[0143] In some optional embodiments, the negative electrode plate includes a negative electrode active material. In some embodiments, the negative electrode active material is a material containing silicon. In some optional embodiments, the negative electrode active material includes one or more of a silicon elemental material, a silicon-carbon material, and a silicon-oxygen material. According to an embodiment of the present application, the organic polymer dispersant and the first conductive agent, to which a negative electrode active material containing silicon is further added, are beneficial for reducing or restraining the expansion of the negative electrode plate, extending the life of the negative electrode plate, and thus benefiting the cycle performance and storage life of the battery.

[0144] According to embodiments of the present application, when the negative electrode active material is a material containing silicon, i.e., the aforementioned types of materials, the first conductive agent works together with the aforementioned types of negative electrode active material to provide long-range conductivity and constrain the expansion of the silicon negative electrode, thereby extending the lifespan of the silicon-containing battery. This can increase the capacity of a battery cell containing this negative electrode plate and enable rapid ion diffusion.

[0145] In some optional embodiments, the negative electrode active material includes 40% to 99.5% of silicon based on the total mass of the negative electrode active material.

[0146] Optionally, the negative electrode active material includes silicon element in an amount of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 99%, 99.5% or any range thereof.

[0147] According to the embodiments of the present application, adding the aforementioned silicon content can increase the capacity of the negative electrode active material, thereby improving the battery's energy density. Silicon has high electrical conductivity, and adding an appropriate amount of silicon can enhance the electronic conductivity of the negative electrode active material film. Silicon-based materials have high ion diffusion coefficients, and the introduction of an appropriate amount of silicon can promote the rapid transport of active ions in the negative electrode active material, improving the battery's kinetic performance, including charge and discharge rates.

[0148] According to the embodiment of the present application, the silicon content is within the above range, which is beneficial to controlling the expansion range of the negative electrode sheet made from the slurry, thereby being beneficial to the storage life of the negative electrode sheet and the cycle performance of the battery.

[0149] In the embodiments of the present application, there is no obvious limitation on the type of binder, and any binder that can be applied to the slurry of the negative electrode sheet and has a certain bonding effect can be applied to the embodiments of the present application. In some optional embodiments, the slurry includes a binder, and optionally, the binder includes one or more of carboxymethyl cellulose, polyacrylic acid and its modifications, polyacrylamide and its modifications, polyvinyl alcohol and its modifications, polyacrylonitrile and its modifications, polyethyleneimine and its modifications, styrene-butadiene rubber and its modifications, styrene-acrylic emulsion and its modifications, polyacrylate and its modifications, polyurethane and its modifications, sodium alginate and its modifications, guar gum and its modifications, xanthan gum and its modifications, gum arabic and its modifications, β-cyclodextrin polymer, and carrageenan and its modifications. In some optional embodiments, the slurry includes a thickener. The thickener can be carboxymethyl cellulose and its salts.

[0150] In the embodiments of the present application, the type of the second conductive agent is not specifically limited; any conductive agent that can be used in the slurry of the negative electrode sheet and has a good conductive effect can be used in the embodiments of the present application. To further improve the conductivity of the negative electrode sheet and reduce the internal resistance of the negative electrode sheet, in some optional embodiments, the negative electrode active material film layer includes a second conductive agent, and the second conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, and carbon dots.

[0151] In some optional embodiments, the ratio of the thickness of the negative electrode active material film layer to the current collector is (5-50):1, optionally, (5-30):1. Controlling the ratio of the thickness of the negative electrode active material film layer to the current collector within the above range is beneficial for increasing the gram capacity of the negative electrode electrode sheet and the energy density of the battery while taking into account the stability of the negative electrode electrode sheet. The ratio of the thickness of the negative electrode active material film layer to the current collector can be the ratio of a single layer of the negative electrode active material film layer to the current collector, or it can be the ratio of the sum of the thickness of the first negative electrode active material film layer and the second negative electrode active material film layer on both sides of the current collector to the current collector.

[0152] In some optional embodiments, the thickness of the negative electrode active material film layer is 50 to 250 μm; alternatively, 50 to 150 μm. Controlling the thickness of the negative electrode active material film layer within the above range is beneficial for increasing the gram capacity of the negative electrode sheet while also ensuring the stability of the negative electrode sheet, thereby increasing the energy density of the battery.

[0153] The specific composition and structure of the negative electrode plate can be selected according to the type of battery cell, and the embodiments of the present application are not limited thereto.

[0154] For example, when the battery cell is a lithium-ion battery cell or a sodium-ion battery cell, the negative electrode plate includes a negative electrode current collector and a negative electrode active material film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces that are opposed in its thickness direction, and the negative electrode active material film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0155] The negative electrode active material is a material that can extract and insert active ions (such as lithium ions, sodium ions, etc.). The negative electrode active material can be a material known in the art. As an example, the negative electrode active material includes but is not limited to one or more of soft carbon, hard carbon, tin-based materials and lithium titanate. Tin-based materials may include one or more of elemental tin, tin oxide and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0156] In some embodiments, the negative electrode active material film layer may optionally include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like.

[0157] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0158] The negative electrode active material film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0159] The negative electrode plate does not exclude other additional layers besides the negative electrode active material film layer and the functional coating of the present application. For example, in some embodiments, the negative electrode plate of the present application may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate of the present application may further include a protective layer covering the surface of the negative electrode active material film layer.

[0160] When the battery cell is a lithium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a lithium plate or a lithium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam-like three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0161] When the battery cell is a sodium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a sodium plate or a sodium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), aluminum foam (or aluminum alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, aluminum (or aluminum alloy) mesh, etc.

[0162] Preparation method of negative electrode sheet

[0163] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising:

[0164] A slurry is provided, which includes water, a conductive agent having carbon elements, and an organic polymer dispersant having a hydrophilic group and a hydrophobic group, wherein the weight average molecular weight of the organic polymer dispersant is 100 to 5000.

[0165] The slurry is coated on the negative electrode current collector to form a negative electrode active material film layer to obtain the second negative electrode plate.

[0166] According to the method of the embodiment of the present application, a negative electrode sheet is prepared from a slurry containing water, a conductive agent containing carbon elements, and an organic polymer dispersant having hydrophilic groups and hydrophobic groups. Since the conductive agent containing carbon elements easily causes the slurry to gel, an organic polymer dispersant having hydrophilic groups and hydrophobic groups is added thereto. The weight-average molecular weight of the organic polymer dispersant is 100 to 5000, so that it has a molecular chain of suitable length, which reduces the overlap or even entanglement of the molecular chains in the slurry. The hydrophobic group of the organic polymer dispersant is adsorbed on the surface of the conductive agent, and the hydrophilic group is a hydrophilic group. When in contact with the solvent water, the organic polymer dispersant forms a steric hindrance between the conductive agent, which promotes a more uniform dispersion of the conductive agent and prevents the slurry from agglomerating and producing a gel during the static process. The uniformity of the dispersion of the components in the slurry is improved, which facilitates the subsequent use of the slurry and the processing of the negative electrode sheet, and also improves the uniformity of the prepared negative electrode sheet, thereby comprehensively improving the cycle performance and storage life of the battery containing the negative electrode sheet.

[0167] Slurry generally refers to a mixture of solid particles suspended in a liquid medium. An organic polymeric dispersant is an organic compound. It is a chemical substance used to disperse the solid particles in the slurry and prevent them from agglomerating. This helps reduce agglomeration caused by attractive forces and cohesive forces between particles, thereby maintaining the uniformity and stability of the slurry.

[0168] A hydrophilic group refers to a chemical group that can interact with and attract water molecules, such as a carboxyl group or a hydroxyl group. A hydrophobic group refers to a chemical group that does not interact with and repels water molecules, such as a methyl group in an alkyl group. In the present application, a hydrophobic group can be understood as a lipophilic group.

[0169] In some optional embodiments, the conductive agent includes a first conductive agent, and the first conductive agent includes one or more of carbon nanotubes, graphene, and nano-carbon fibers.

[0170] According to the method of the embodiment of the present application, a negative electrode sheet is prepared from a slurry containing water, a first conductive agent, and an organic polymer dispersant having a hydrophilic group and a hydrophobic group. Since the first conductive agent includes carbon nanotubes, graphene, and nano-carbon fibers, it is easy for the slurry to gel. Therefore, an organic polymer dispersant having a hydrophilic group and a hydrophobic group is added thereto. The weight-average molecular weight of the organic polymer dispersant is 100 to 5000, so that it has a molecular chain of suitable length, which reduces the overlap or even entanglement of the molecular chains in the slurry. The hydrophobic group of the organic polymer dispersant is adsorbed on the surface of the first conductive agent, and the hydrophilic group is a hydrophilic group. When in contact with the solvent water, the organic polymer dispersant forms a steric hindrance between the first conductive agent, thereby promoting a more uniform dispersion of the first conductive agent and preventing the slurry from agglomerating and producing a gel during the standing process. This improves the dispersion uniformity of the components in the slurry, facilitates the subsequent use of the slurry and the processing of the negative electrode sheet, and also improves the uniformity of the prepared negative electrode sheet.

[0171] In addition, the presence of the first conductive agent is beneficial to limiting the expansion of the negative electrode sheet and is beneficial to the stability of the negative electrode sheet.

[0172] In some optional embodiments, the weight average molecular weight of the organic polymer dispersant is 200 to 3500.

[0173] Alternatively, the weight average molecular weight of the organic polymer dispersant may be 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, Any value among 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, 5000 or a range consisting of the above.

[0174] According to the embodiments of the present application, the organic polymer dispersant has the above-mentioned suitable weight-average molecular weight, and thus the organic polymer dispersant has a suitable molecular chain length. Its hydrophobic group is adsorbed on the surface of the first conductive agent through intermolecular forces or van der Waals forces, which reduces the overlap or even entanglement of molecular chains that are too long. The hydrophilic group is a hydrophilic group that comes into contact with the solvent water. The organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly and reduces the probability of agglomeration and gelation during the static process of the slurry.

[0175] In some optional embodiments, at a temperature of 25° C., the viscosity a of the organic polymer dispersant when its mass fraction in water is 10% is in a range of 10 mPa·S to 1000 mPa·S.

[0176] Optionally, the viscosity of the organic polymer dispersant in water can be any value among 10mPa·S, 20mPa·S, 30mPa·S, 40mPa·S, 50mPa·S, 60mPa·S, 70mPa·S, 80mPa·S, 90mPa·S, 100mPa·S, 200mPa·S, 300mPa·S, 400mPa·S, 500mPa·S, 600mPa·S, 700mPa·S, 800mPa·S, 900mPa·S, 1000mPa·S or a range of their combinations.

[0177] According to the embodiments of the present application, by detecting the viscosity of a certain mass fraction of an organic polymer dispersant in water, an organic polymer dispersant with a suitable viscosity can be selected to disperse other components in the slurry, such as the first conductive agent, thereby reducing the agglomeration and gelation phenomenon during the standing process of the slurry, improving the dispersion uniformity of the components in the slurry, and facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0178] In addition, the viscosity of the organic polymer dispersant can reflect the type and molecular weight of the organic polymer dispersant, as well as the dispersion effect it brings, to a certain extent.

[0179] The viscosity of an organic polymeric dispersant in water is well known in the art and can be measured using instruments and methods known in the art. For example, a Brookfield viscometer is used. The viscometer is set to 12 rpm and tested in a 25°C water bath for 10 minutes. The average of the test data at the 6th minute is taken.

[0180] In the embodiments of the present application, the type of hydrophilic group is not significantly limited, and any hydrophilic functional group that can have hydrophilic properties and disperse in water can be used in the embodiments of the present application. In some optional embodiments, the hydrophilic group includes one or more of a hydroxyl group, a carboxyl group, an amide group, an amino group, an ether group, and a carbonyl group. In some embodiments, the hydrophilic group includes a carbon-nitrogen double bond.

[0181] According to the embodiments of the present application, the organic polymer dispersant in the slurry has the above-mentioned type of hydrophilic groups, which is conducive to its dispersion in water, so that the organic polymer dispersant forms a certain steric hindrance, reduces the agglomeration and gelation between the first conductive agent, and achieves the effect of dispersing the first conductive agent and other components.

[0182] In the embodiments of the present application, there is no explicit limitation on the type of hydrophobic group; any hydrophobic functional group that can be adsorbed on the surface of the first conductive agent can be used in the embodiments of the present application. In some optional embodiments, the hydrophobic group includes one or more of an ester group, an alkyl group containing C8 to C18, an alkylene group containing C8 to C18, and an aryl group containing C6 to C12.

[0183] A hydrophobic group refers to a functional group with low hydrophilicity, typically containing a hydrophobic structure with carbon-hydrogen bonds. The first conductive agent comprising carbon elements includes a surface structure formed by carbon atoms. In the embodiments of the present application, the hydrophobic groups described above are generally more likely to adsorb on the surface of the first conductive agent, thereby dispersing the first conductive agent and reducing its aggregation and gelation.

[0184] In some optional embodiments, the organic polymeric dispersant comprises R1-O-(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0185] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, and prevents the slurry from agglomerating and producing gelation during the static process, thereby improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0186] In some optional embodiments, the organic polymeric dispersant comprises) R1COO(CH2CH2O) n H or a modified product thereof, R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0187] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group and a carbonyl group (C=O bond) on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, and prevents the slurry from agglomerating and producing gelation during the static process, thereby improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0188] In some optional embodiments, the organic polymeric dispersant comprises R1R2N-(CH2CH2O) nH or its modified form, R1 and R2 each represent an alkyl group containing C8 to C18, and 1≤n≤45.

[0189] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group, C=N, on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlapping or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, and prevents the slurry from agglomerating and producing gelation during the static process, thereby improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0190] In some optional embodiments, the organic polymeric dispersant comprises R1-CONH(CH2CH2O) n H or a modified product thereof, R1 represents an alkyl group containing C8 to C18, and 1≤n≤45.

[0191] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group such as an alkyl group of C8 to C18, and an ether group and a carbonyl group (C=O bond) on the other side, and has a suitable weight-average molecular weight and viscosity, and a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, and prevents the slurry from agglomerating and producing gelation during the static process, thereby improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0192] In some optional embodiments, the organic polymer dispersant includes a polyol-type alkane dispersant or a modified product thereof. According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic functional group of the alkyl group, and the other side has any one or more hydrophilic groups of hydroxyl, carboxyl, and carbonyl (C=O bond), and it has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, promotes the first conductive agent to be dispersed more evenly, and prevents the slurry from agglomerating and producing a gel phenomenon during the static process, thereby improving the dispersion uniformity of the components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0193] In some optional embodiments, the organic polymeric dispersant comprises R1-(C6H4)-O(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤15.

[0194] According to the embodiments of the present application, -(C6H4)- represents a phenyl group. The aforementioned organic polymer dispersant has a hydrophobic functional group such as a C8-C18 alkyl group on one side, and a hydrophilic group such as an ether group on the other side. Furthermore, the organic polymer dispersant has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of the molecular chains in the slurry. Therefore, the aforementioned organic polymer dispersant forms a steric hindrance between the first conductive agent, promoting a more uniform dispersion of the first conductive agent and preventing agglomeration and gelation during the slurry standing process. This improves the uniformity of the dispersion of the various components in the slurry, facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0195] In some optional embodiments, the organic polymer dispersant includes one or more of polyoxyethylene sorbitan laurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan monooleate, lauryl alcohol polyoxyethylene ether, lauric acid diethanolamide, polyoxyethylene laurate, octadecylamine polyoxyethylene ether, and nonylphenol polyoxyethylene ether.

[0196] According to the embodiments of the present application, the above-mentioned type of organic polymer dispersant has a hydrophobic group and a hydrophilic group, and has a suitable weight-average molecular weight and viscosity, and has a suitable molecular chain length, which can reduce the overlap or even entanglement of molecular chains in the slurry. Therefore, the above-mentioned type of organic polymer dispersant forms a steric hindrance between the first conductive agent, which promotes the first conductive agent to be dispersed more evenly, and prevents the slurry from agglomerating and producing gelation during the static process, thereby improving the dispersion uniformity of the components in the slurry and facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0197] In some embodiments, the mass fraction of the organic polymeric dispersant in the dry weight of the slurry is

[0198] 0.05%-1%.

[0199] Optionally, the mass fraction of the organic polymer dispersant in the dry weight of the slurry can be any value among 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1% or any range of their compositions.

[0200] According to the embodiments of the present application, by adding an appropriate amount of organic polymer dispersant to the slurry, the dispersion of the conductive agent and other components in the slurry is improved. When the mass content of the organic polymer dispersant exceeds the above range, it may occupy a certain amount of space volume, thereby affecting the energy density of the battery prepared using the slurry.

[0201] According to the embodiments of the present application, the dry weight of the slurry refers to the mass when constant weight is reached after water is removed from the slurry. A certain amount of slurry is dried at a specific temperature (generally around 90-105 degrees) until the difference in the mass of the sample in two consecutive weighings does not exceed 0.1% of the mass of the sample before drying, i.e., constant weight is reached. The dry weight of the slurry is the weight M of the slurry when it reaches constant weight. The organic polymer dispersant in the separated slurry is M1, and the mass fraction of the organic polymer dispersant in the dry weight of the slurry is M1 / M. It can also be calculated by the mass of the raw materials added when preparing the slurry.

[0202] The mass content of the organic polymeric dispersant can be determined using techniques known in the art, such as high-performance liquid chromatography (HPLC). For example, the mass content of the organic polymeric dispersant can be determined using GB / T 31414-2015. Furthermore, the mass of each organic polymeric dispersant can be determined by determining the type of organic polymeric dispersant added during the preparation process.

[0203] In some optional embodiments, at a temperature of 25° C., the viscosity of the slurry is 1000 mPa·S to 20000 mPa·S, and optionally 5000 mPa·S to 15000 mPa·S.

[0204] At a temperature of 25°C, the viscosity of the slurry can be 1000mPa·S, 2000mPa·S, 3000mPa·S, 4000mPa·S, 5000mPa·S, 5500mPa·S, 6000mPa·S, 6500mPa·S, 7000mPa·S, 7500mPa·S, 8000mPa·S, 8500mPa·S, 9000mPa·S, 9500mPa·S, 10000mPa·S, 10500mPa·S, 11000mPa·S, 11500mPa·S, 120 Any numerical value among 1000mPa·S, 12500mPa·S, 13000mPa·S, 13500mPa·S, 14000mPa·S, 14500mPa·S, 15000mPa·S, 16000mPa·S, 17000mPa·S, 18000mPa·S, 19000mPa·S, and 20000mPa·S, or a range composed of the above.

[0205] According to the embodiment of the present application, the viscosity of the slurry is within the above range, and the organic polymer dispersant and the first conductive agent interact with each other to promote a more uniform dispersion of the first conductive agent and prevent the slurry from agglomerating and producing a gel phenomenon during the static process, thereby improving the dispersion uniformity of the components in the slurry and facilitating the subsequent use of the slurry and the processing of the negative electrode sheet.

[0206] In some optional embodiments, the first conductive agent is carbon nanotubes, the average diameter of the carbon nanotubes is 1 to 20 nm, and the average length of the carbon nanotubes is 1 to 50 μm.

[0207] According to the embodiments of the present application, the above-mentioned single-walled carbon nanotubes have the above-mentioned size characteristics, which represent that this type of high aspect ratio material in the slurry is very easy to cause slurry agglomeration and gelation due to its nanometer size effect and intermolecular force. In addition, due to its high aspect ratio, single-walled carbon nanotubes can interact with the conventional additive carboxymethyl cellulose (CMC) to form a three-dimensional network structure in the slurry, which to a certain extent exacerbates the gelation phenomenon. By adding the above-mentioned organic polymer dispersant to the slurry, the gelation phenomenon caused by single-walled carbon nanotubes can be improved, which is beneficial to the preparation of negative electrode sheets.

[0208] In some optional embodiments, the first conductive agent is carbon nanofiber, the average tube diameter of the carbon nanofiber is 1 to 150 nm, and the average length of the carbon nanofiber is 1 to 50 μm.

[0209] Optionally, the average tube diameter of the nano-carbon fiber can be any value among 1nm, 6nm, 11nm, 16nm, 21nm, 26nm, 31nm, 36nm, 41nm, 46nm, 51nm, 56nm, 61nm, 66nm, 71nm, 76nm, 81nm, 86nm, 91nm, 96nm, 101nm, 106nm, 111nm, 116nm, 121nm, 126nm, 131nm, 136nm, 141nm, 146nm, 150nm or any range of their combinations.

[0210] Optionally, the average length of the carbon nanofibers can be any value among 1 μm, 6 μm, 11 μm, 16 μm, 21 μm, 26 μm, 31 μm, 36 μm, 41 μm, 46 μm, 50 μm, or a range thereof.

[0211] According to the embodiments of the present application, the above-mentioned nano-carbon fibers have the above-mentioned size characteristics, which represent that this type of high aspect ratio material in the slurry is very easy to cause slurry agglomeration and gelation due to its nano-size effect and intermolecular force. In addition, due to its high aspect ratio, the nano-carbon fibers can interact with the conventional additive carboxymethyl cellulose (CMC) to form a three-dimensional network structure in the slurry, which aggravates the gelation phenomenon to a certain extent. By adding the above-mentioned organic polymer dispersant to the slurry, the gelation phenomenon caused by the nano-carbon fibers can be improved, which is beneficial to the preparation of the negative electrode sheet.

[0212] In some optional embodiments, the first conductive agent is graphene; the average thickness of the graphene is 1 to 50 nm, and the length of the major axis of the graphene is 1 to 50 μm.

[0213] Optionally, the average thickness of the graphene can be any value among 1 nm, 6 nm, 11 nm, 16 nm, 21 nm, 26 nm, 31 nm, 36 nm, 41 nm, 46 nm, 50 nm or a range thereof.

[0214] Optionally, the length of the long axis of the graphene may be any value among 1 μm, 6 μm, 11 μm, 16 μm, 21 μm, 26 μm, 31 μm, 36 μm, 41 μm, 46 μm, 50 μm, or a range thereof.

[0215] "Long diameter" usually refers to the longest line between a point on the edge and another point in an irregular figure, such as graphene in the projection plane, which is called the long diameter.

[0216] According to the embodiments of the present application, the graphene has the above-mentioned size characteristics, which means that this type of high aspect ratio material in the slurry is very likely to cause slurry agglomeration and gelation due to its nano-size effect and intermolecular forces. In addition, due to its high aspect ratio, graphene can interact with the conventional additive carboxymethyl cellulose (CMC) to form a three-dimensional network structure in the slurry, which to a certain extent exacerbates the gelation phenomenon. By adding the above-mentioned organic polymer dispersant to the slurry, the gelation phenomenon caused by graphene can be improved, which is beneficial to the preparation of the negative electrode sheet.

[0217] The diameter of a carbon nanotube can be the diameter of a cross section perpendicular to the length of the carbon nanotube, and can be measured using methods commonly used in the art. For example, the diameters of multiple groups of carbon nanotubes can be observed and measured using a microscope such as a transmission electron microscope (TEM) or a scanning electron microscope (SEM), and the average value is taken. The length of carbon nanotubes (CNTs), the diameter and length of carbon nanofibers, and the average thickness and major diameter of graphene can also be measured using the above methods.

[0218] In some optional embodiments, the mass ratio of the first conductive agent to the organic polymer dispersant is 1:(0.1-3).

[0219] Optionally, the mass ratio of the first conductive agent to the organic polymer dispersant is any value among 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3.0 or any range thereof.

[0220] According to the embodiment of the present application, there is a correlation between the quality of the first conductive agent and the organic polymer dispersant. When the amount of carbon nanotubes added is large, the gelation of the slurry will become more serious. In this case, the amount of dispersant needed is larger, which is helpful in solving the problem of gelation of the slurry when it is left to stand. Therefore, the embodiment of the present application further reduces the gelation phenomenon that occurs when the slurry is left to stand by controlling the mass ratio of the first conductive agent and the organic polymer dispersant within the above range, improves the slurry dispersion effect, facilitates the subsequent preparation of the negative electrode sheet, and further improves the uniformity of the negative electrode sheet.

[0221] The quality of the organic polymeric dispersant can be tested using techniques known in the art. In addition, the quality of each organic polymeric dispersant can be determined by the type and quality of the organic polymeric dispersant added during the preparation process.

[0222] In some optional embodiments, the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant is 100:(0.05-1):(0.05-1), and can be optionally 100:(0.05-0.5):(0.05-0.5).

[0223] Optionally, the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant can be 100:0.05:0.05, 100:0.1:0.1, 100:0.15:0.15, 100:0.2:0.2, 100:0.25:0.25, 100:0.3:0.3, 100:0.35:0.35, 100:0.4:0.4, 100:0.45:0.45, 1 Any ratio or range of their compositions among 00:0.5:0.5,100:0.55:0.55,100:0.6:0.6,100:0.65:0.65,100:0.7:0.7,100:0.75:0.75,100:0.8:0.8,100:0.85:0.85,100:0.9:0.9,100:0.95:0.95,100:1:1.

[0224] According to the embodiments of the present application, controlling the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant within the above-mentioned range is beneficial to improving the uniformity of the negative electrode sheet while taking into account the battery capacity and the internal resistance of the battery, limiting the expansion of the negative electrode sheet, and improving the stability of the negative electrode sheet, thereby increasing the storage life of the battery.

[0225] In some optional embodiments, the mass ratio of the negative electrode active material to the binder is 100:(1-10), and optionally 100:(2-6.5). Controlling the mass ratio of the negative electrode active material to the binder within the above range is beneficial to improving the stability of the negative electrode active material film layer, improving the peel strength between the negative electrode active material film layer and the negative electrode current collector, and is beneficial to the performance of the negative electrode sheet.

[0226] In some alternative embodiments, the slurry includes 0.05% to 1% of the first conductive agent based on the dry weight of the slurry.

[0227] Optionally, the dry weight of the slurry includes the first conductive agent in an amount by mass of any value within the range of 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, or 1%, or a combination thereof.

[0228] According to the embodiment of the present application, the first conductive agent in the above content can reduce the resistance of the negative electrode plate. The first conductive agent in the above content is conducive to limiting or reducing the expansion of the negative electrode plate, thereby improving the storage life of the negative electrode plate and the battery.

[0229] In some alternative embodiments, the slurry comprises 0.05% to 1% carbon nanotubes based on the dry weight of the slurry.

[0230] Optionally, the dry weight of the slurry includes carbon nanotubes in an amount by mass of any value within the range of 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, or a combination thereof.

[0231] According to the embodiments of the present application, the carbon nanotubes in the above content can reduce the resistance of the negative electrode sheet and help limit or reduce the expansion of the negative electrode sheet, thereby increasing the storage life of the negative electrode sheet and the battery.

[0232] In some optional embodiments, the slurry includes a negative electrode active material. In some embodiments, the negative electrode active material is a material containing silicon. In some optional embodiments, the negative electrode active material includes one or more of a silicon elemental material, a silicon-carbon material, and a silicon-oxygen material.

[0233] According to an embodiment of the present application, the negative electrode active material is a material containing silicon elements. When it is the above-mentioned type of material, the first conductive agent works together with the above-mentioned type of negative electrode active material. The first conductive agent plays a role in long-range conduction and restraining the expansion of the silicon negative electrode, and also improves the life of the silicon-containing battery.

[0234] In some optional embodiments, the silicon-carbon material includes silicon in an amount of 40% to 99.5% by mass, optionally 40% to 60% by mass, based on the total mass of the silicon-carbon material.

[0235] According to the embodiment of the present application, the silicon content is within the above range, which is beneficial to controlling the expansion range of the negative electrode sheet made from the slurry, thereby being beneficial to the storage life of the negative electrode sheet and the cycle performance of the battery.

[0236] In some optional embodiments, the negative electrode active material further includes a carbon-based material, which includes one or more of artificial graphite and natural graphite, and the mass content of the silicon element in the negative electrode active material is 4 to 99.5%, and can be optionally 10% to 60%.

[0237] According to the embodiment of the present application, the mass content of the silicon-carbon material in the negative electrode active material is within the above-mentioned range, which is beneficial to controlling the expansion range of the negative electrode sheet prepared from the slurry, thereby being beneficial to the storage life of the negative electrode sheet and the cycle performance of the battery.

[0238] In some optional embodiments, the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant is 100:(0.05-1):(0.05-1), and can be optionally 100:(0.05-0.5):(0.05-0.5).

[0239] Optionally, the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant can be 100:0.05:0.05, 100:0.1:0.1, 100:0.15:0.15, 100:0.2:0.2, 100:0.25:0.25, 100:0.3:0.3, 100:0.35:0.35, 100:0.4:0.4, 100:0.45:0.45, 1 Any ratio or range of their compositions among 00:0.5:0.5,100:0.55:0.55,100:0.6:0.6,100:0.65:0.65,100:0.7:0.7,100:0.75:0.75,100:0.8:0.8,100:0.85:0.85,100:0.9:0.9,100:0.95:0.95,100:1:1.

[0240] According to the embodiment of the present application, controlling the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant within the above-mentioned range is beneficial to improving the preparation process of the slurry for the negative electrode plate while taking into account the battery capacity and the battery internal resistance, and reducing the probability of the slurry gel phenomenon.

[0241] In the embodiments of the present application, there is no obvious limitation on the type of binder, and any binder that can be used in the slurry of the negative electrode sheet and has a certain bonding effect can be used in the embodiments of the present application. In some optional embodiments, the slurry includes a binder, and optionally, the binder includes one or more of carboxymethyl cellulose, polyacrylic acid and its modifications, polyacrylamide and its modifications, polyvinyl alcohol and its modifications, polyacrylonitrile and its modifications, polyethyleneimine and its modifications, styrene-butadiene rubber and its modifications, styrene-acrylic emulsion and its modifications, polyacrylate and its modifications, polyurethane and its modifications, sodium alginate and its modifications, guar gum and its modifications, xanthan gum and its modifications, gum arabic and its modifications, β-cyclodextrin polymer, and carrageenan and its modifications.

[0242] In the embodiments of the present application, the type of the second conductive agent is not specifically limited; any conductive agent that can be used in the slurry of the negative electrode sheet and has a good conductive effect can be used in the embodiments of the present application. To further improve the conductivity of the negative electrode sheet and reduce the internal resistance of the negative electrode sheet, in some optional embodiments, the slurry includes a second conductive agent, and the second conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, and carbon dots.

[0243] battery cells

[0244] In a third aspect, an embodiment of the present application provides a battery cell comprising the negative electrode sheet of the first aspect or the negative electrode sheet prepared by the preparation method of the second aspect. The battery cell comprising the negative electrode sheet at least has the advantages of the negative electrode sheet.

[0245] The present application has no particular limitation on the type of battery cells. For example, the battery cells may be lithium-ion batteries, sodium-ion batteries, etc. Sodium-ion batteries may be selected as the battery cells.

[0246] In some optional embodiments, a battery cell includes a positive electrode sheet, a separator, and an electrolyte.

[0247] [Positive electrode]

[0248] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode active material film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0249] The positive electrode active material film layer includes a positive electrode active material. The positive electrode active material can be a positive electrode active material commonly known in the art for use in battery cells.

[0250] For example, when the battery cell is a lithium-ion battery cell or a lithium metal battery cell, the positive electrode active material may include one or more of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium phosphates containing an olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used.

[0251] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e A fOne or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.

[0252] As an example, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0253] When the battery cell is a sodium ion battery cell or a sodium metal battery cell, the positive electrode active material may include but is not limited to one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0254] As an example, the positive electrode active material may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials and general formula X p M' q (PO4) r O x Y 3-x One or more materials. pM' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X includes H + 、Li + 、Na + , K + and NH4 + One or more of, M' is a transition metal cation, which can be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, which can be selected from one or more of F, Cl and Br.

[0255] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0256] In some embodiments, the positive electrode active material film layer may further optionally include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0257] In some embodiments, the positive electrode active material film layer may further optionally include a positive electrode binder. This application does not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0258] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0259] The positive electrode active material film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0260] [Isolation film]

[0261] The separator is placed between the positive electrode and the negative electrode to prevent short circuits between the positive and negative electrodes. This application does not limit the type of separator, and any known porous separator with good chemical and mechanical stability can be used.

[0262] In some embodiments, the material of the isolation membrane can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0263] [Electrolytes]

[0264] In some embodiments, the battery cell includes an electrolyte. The electrolyte conducts active ions between the positive and negative electrode plates. This application does not specifically limit the type of electrolyte, and the electrolyte may be selected based on needs. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution).

[0265] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0266] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, the electrolyte salt includes one or more selected from lithium salts for lithium ion batteries and sodium salts for sodium ion batteries. As an example, the lithium salt includes one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluorooxalatophosphate (LiTFOP). As an example, the sodium salt includes one or more selected from NaPF6, NaClO4, NaBCl4, NaSO3CF3, Na(CH3)C6H4SO3.

[0267] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0268] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0269] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0270] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0271] The present application has no particular limitation on the shape of the battery cell, which can be a flat body, a rectangular parallelepiped, or other shapes. FIG1 shows a battery cell 5 of a rectangular parallelepiped structure as an example.

[0272] In some embodiments, as shown in Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate together form a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 of the first aspect of the embodiment of the present application or the electrode assembly 52 prepared by the method according to the second aspect of the embodiment of the present application is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be adjusted according to demand.

[0273] The embodiment of the present application provides a battery, including the battery cell of the third aspect. The battery can be understood as a battery module or a battery pack.

[0274] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0275] Optionally, the battery module may further include a housing having an accommodation space, wherein the plurality of battery cells are accommodated in the accommodation space.

[0276] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0277] [Preparation method]

[0278] The method for preparing the battery cell of the present application is well known, and the method at least includes the step of preparing the electrode assembly according to the second aspect of the embodiment of the present application.

[0279] In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a secondary battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After packaging, standing, forming, shaping and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel, or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel, or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0280] In some embodiments, the electrode assembly can be placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, shaping and other processes, a battery cell is obtained.

[0281] Electrical devices

[0282] In a fourth aspect, an embodiment of the present application provides an electrical device comprising the battery cell of the third aspect, thereby having at least the advantages corresponding to the battery cell.

[0283] Battery cells can be used as power sources or energy storage units for electrical devices. Electrical devices include, but are not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0284] Figure 3 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0285] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0286] Example

[0287] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0288] Example 1

[0289] Preparation of the negative electrode: A mixture of artificial graphite (the first active material) and silicon-carbon (the second active material), acetylene black (the conductive agent), carbon nanotubes (CNTs) (the conductive agent), styrene acrylic rubber (SAR) (the SAR is added in the form of a styrene acrylic emulsion) as a binder, CMC-Na (the thickener), and lauryl alcohol polyoxyethylene ether (the dispersant) are thoroughly stirred and mixed in a suitable amount of deionized water solvent system in a mass ratio of 86.265:9.585:1:0.1:2:1:0.05 to obtain a slurry with a solid content of 53%. The mass content of silicon in the silicon-carbon material is 40%. The slurry is coated on a 6μm thick copper foil, then dried, cold pressed, and slit to obtain a negative electrode. The thickness of the negative electrode active material film is 110μm.

[0290] Preparation of lithium batteries

[0291] Negative electrode sheet: the negative electrode sheet prepared above

[0292] Preparation of positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.2 Mn 0.2O2), conductive agent carbon nanotubes (CNT), conductive carbon black (SP), and binder polyvinylidene fluoride (PVDF) are dissolved in a solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.9:0.1:1:2, and the mixture is fully stirred and mixed to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 70%. The positive electrode slurry is coated on an Al foil with a thickness of 13 μm, and then dried, cold pressed, and cut to obtain a positive electrode sheet, wherein the thickness of the positive electrode active material film layer is 120 μm.

[0293] Preparation of separator: A polyethylene (PE) porous polymer film with a thickness of 12 μm was used as the separator.

[0294] Electrolyte: Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a volume ratio of 1:1:1, LiPF6 was added with a molar concentration of 1 mol / L, and stirred evenly.

[0295] Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide separation. The electrodes are then wound to form an electrode assembly, and electrolyte is added. The battery is then hot-pressed at 100°C and 250 MPa for 2 minutes to complete.

[0296] Example 2-1 to Example 2-3

[0297] The preparation method is similar to that of Example 1, except that the average diameter of the first conductive agent in Example 2-1 is different, the average length of the first conductive agent in Example 2-2 is different, and the average diameter and average length of the first conductive agent in Example 2-3 are different. See Table 1.

[0298] Example 3-1 to Example 3-2

[0299] The preparation method is similar to that of Example 1, except that the average tube diameter, average length and content of the first conductive agent of Example 3-1 and Example 3-2 are different, and the content of the organic polymer dispersant is different, see Table 1.

[0300] Example 4-1 to Example 4-5

[0301] The preparation method is similar to that of Example 1, except that the type of organic polymer dispersant is different, see Table 1.

[0302] Example 5-1 to Example 5-2

[0303] The preparation method is similar to that of Example 1, except that the type and size of the first conductive agent are different, see Table 1.

[0304] Comparative Example 1

[0305] Preparation of negative electrode sheets: The first active material artificial graphite and the second active material silicon-carbon material, the conductive agent acetylene black, the conductive agent carbon nanotube CNT, the binder styrene acrylic rubber (SAR), and the thickener CMC-Na are fully stirred and mixed in an appropriate amount of deionized water solvent system in a mass ratio of 86.265:9.585:1:0.1:2:1:0.05 to obtain a negative electrode slurry, and the negative electrode slurry is coated on Cu foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0306] Test section

[0307] 1) Organic polymer dispersant viscosity test method: The organic polymer dispersant was dissolved in water at a mass fraction of 10%. The viscosity was measured using a Brookfield rotor viscometer at 12 rpm in a 25°C water bath for 10 minutes. The average of the data from the 6th minute was taken.

[0308] 2) Method for testing slurry viscosity: a Brookfield rotor viscometer was used with the rotor viscometer set at 12 rpm for testing in a 25°C water bath for 10 minutes, and the average of the data at the 6th minute was taken.

[0309] The viscosity of the slurries of Example 1 and Comparative Example 1 was tested using a Brookfield rotor viscometer. The viscosity changes of Example 1 and Comparative Example 1 are shown in FIG4 , which illustrates that the viscosity of Example 1 is relatively stable, which is beneficial to the preparation of the negative electrode sheet and is beneficial to the performance of the negative electrode sheet.

[0310] 3) Judgment criteria for slurry gel and determination of 48h slurry viscosity rebound rate:

[0311] After the slurry is stirred by a double planetary mixer for 180 minutes, it is tested using a Brookfield rotor viscometer with the rotor viscometer set to a speed of 12 rpm. The test time is 10 minutes in a 25°C water bath. The average of the viscosity data at the 6th minute is taken and recorded as the initial viscosity value. After standing for 48 hours, the viscosity after standing is measured using a Brookfield rotor viscometer (the test conditions are consistent with the determination conditions of the initial viscosity value). The viscosity after standing is greater than the initial viscosity value, and the slurry is scooped with a spoon, the amount scooped is level with the spoon opening, about 98%-110% of the spoon capacity, and the spoon is lifted. The slurry does not flow downward or drips in blocks or agglomerates (i.e., a gel state that cannot flow appears), and there is no continuous linear flow, which indicates that a gel phenomenon has occurred.

[0312] 48h slurry viscosity rebound rate = (viscosity after standing - initial viscosity value) / initial viscosity value × 100 / 100.

[0313] After testing, the slurry in Example 1 was allowed to stand for 48 hours. The amount of slurry scooped with a spoon was equal to the opening of the spoon, which was approximately 98%-110% of the capacity of the spoon. When the spoon was lifted, the slurry flowed down in a continuous linear manner, indicating that it had gelled. The slurry in Comparative Example 1 did not flow downward in a linear manner or dripped in lumps or agglomerates (i.e., a gel state that could not flow) after standing for 48 hours. It did not flow downward in a continuous linear manner, indicating that it had gelled.

[0314] No gelation occurred in Example 1, but gelation occurred in Comparative Example 1, indicating that the method of the embodiment of the present application can avoid the occurrence of gelation in the slurry used for the negative electrode sheet, which is beneficial to the preparation of the negative electrode sheet and the performance of the negative electrode sheet.

[0315] 4) The capacity retention rate test method is as follows: At 25°C, the lithium-ion battery is charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V until the current is less than 0.05C, and then discharged at a constant current of 0.33C to 3.0V. This charge and discharge cycle is considered one charge and discharge cycle. Repeat this charge and discharge cycle, and calculate the capacity retention rate of the lithium-ion battery after 300 cycles.

[0316] Capacity retention rate (%) of the lithium ion battery after 300 cycles at 25° C. = (discharge capacity at the 300th cycle / discharge capacity at the first cycle)×100%.

[0317] 4) Battery storage life: Capacity retention rate (%) of lithium-ion battery after 150 days storage at 60°C = (discharge capacity at 150 days / discharge capacity at first cycle) × 100%

[0318] The test results are shown in Table 2.

[0319] Table 1

[0320] Table 2

[0321] Comprehensive test results from the examples also indicate that the inclusion of an organic polymer dispersant in the negative electrode slurry, in contact with the first conductive agent solvent, water, results in a more uniform dispersion of the conductive agent. After the slurry was left to stand for 48 hours, no gelation occurred, improving the uniformity of the dispersion of the various components in the slurry and facilitating subsequent use of the slurry and processing of the negative electrode. Furthermore, batteries prepared with this slurry exhibited excellent storage life and capacity retention. This may be due to the absence of gelation, which improves the uniformity of the dispersion of the various components in the slurry and the negative electrode active material film layer of the negative electrode. This allows for more uniform expansion and contraction of the thickness of the negative electrode during charge and discharge, thereby improving the battery's storage life and capacity retention.

[0322] Comparing Example 1 with Comparative Example 1, it can be seen that no organic polymer dispersant is added to the negative electrode plate and the slurry. Therefore, the battery storage life and capacity retention rate of Comparative Example 1 are worse than those of Example 1. The reason may be that no organic polymer dispersant is added to Comparative Example 1, and the slurry gels. Therefore, during the battery charge and discharge process, the thickness of the negative electrode plate expands and contracts unevenly, thereby reducing the battery performance.

[0323] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material film layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material film layer comprises: The invention provides a carbon element conductive agent and an organic polymer dispersant having a hydrophilic group and a hydrophobic group, wherein the weight average molecular weight of the organic polymer dispersant is 100 to 5000.

2. The negative electrode sheet according to claim 1, wherein: The weight average molecular weight of the organic polymer dispersant is 200 to 3500.

3. The negative electrode sheet according to claim 1 or 2, wherein: The conductive agent includes a first conductive agent, and the first conductive agent includes one or more of carbon nanotubes, graphene, and nano-carbon fibers.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The hydrophilic group includes one or more of a hydroxyl group, a carboxyl group, an amide group, an amino group, an ether group, and a carbonyl group; and / or, The hydrophobic group includes one or more of an ester group, an alkyl group containing C8 to C18, an alkylene group containing C8 to C18, and an aryl group containing C6 to C12.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein: The organic polymer dispersant includes any one or more of 1) to 6): 1)R1-O-(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤45; 2)R1COO(CH2CH2O) n H or its modified form, R1 represents an alkyl group containing C8 to C18, 1≤n≤45; 3)R1R2N-(CH2CH2O) n H or its modified form, R1 and R2 each represent an alkyl group containing C8 to C18, 1≤n≤45; 4)R1-CONH(CH2CH2O) n H or its modified form, R1 represents an alkyl group containing C8 to C18, 1≤n≤45; 5) Polyol type alkane dispersants or modified products thereof; 6)R1-(C6H4)-O(CH2CH2O) n H) or a modified product thereof, wherein R1 represents an alkyl group containing C8 to C18, and 1≤n≤15.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The organic polymer dispersant includes one or more of polyoxyethylene sorbitan laurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan monooleate, lauryl alcohol polyoxyethylene ether, lauric acid diethanolamide, polyoxyethylene laurate, octadecylamine polyoxyethylene ether, and nonylphenol polyoxyethylene ether.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: At a temperature of 25° C., the viscosity a of the organic polymer dispersant when its mass fraction in water is 10% is in a range of 10 mPa·S to 1000 mPa·S.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein: The negative electrode active material layer includes 0.05% to 1% of an organic polymer dispersant based on the total mass of the negative electrode active material layer.

9. The negative electrode sheet according to any one of claims 3 to 8, wherein: The first conductive agent satisfies one or more of the following conditions: 1) The first conductive agent is a carbon nanotube, the average diameter of the carbon nanotube is 1 nm to 20 nm, and the average length of the carbon nanotube is 1 μm to 50 μm; 2) The first conductive agent is the carbon nanofiber, the average tube diameter of the carbon nanofiber is 1 nm to 150 nm, and the average length of the carbon nanofiber is 1 μm to 50 μm; 3) The first conductive agent is the graphene; the average thickness of the graphene is 1 nm to 50 nm, and the length of the major axis of the graphene is 1 μm to 50 μm.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein: The negative electrode active material film layer includes a negative electrode active material, and the negative electrode active material includes one or more of silicon single substance material, silicon-carbon material, and silicon-oxygen material.

11. The negative electrode sheet according to claim 10, wherein: The negative electrode active material is a silicon-carbon material, and based on the total mass of the silicon-carbon material, the silicon-carbon material includes 40% to 99.5% of silicon element.

12. The negative electrode sheet according to claim 10 or 11, wherein: The negative electrode active material further comprises a carbon-based material, which comprises one or more of artificial graphite and natural graphite. The mass content of silicon in the negative electrode active material is 4% to 99.5%.

13. The negative electrode sheet according to any one of claims 1 to 12, wherein: The negative electrode active material film layer includes a second conductive agent, which includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, and carbon dots.

14. A method for preparing a negative electrode sheet, wherein: include: Providing a slurry comprising water, a conductive agent having carbon elements, and an organic polymer dispersant having a hydrophilic group and a hydrophobic group, wherein the organic polymer dispersant has a weight average molecular weight of 100 to 5000; The slurry is coated on the negative electrode current collector to form a negative electrode active material film layer, thereby preparing the negative electrode sheet according to any one of claims 1 to 13.

15. The preparation method according to claim 14, wherein At a temperature of 25° C., the viscosity of the slurry is 1000 mPa·S to 20000 mPa·S.

16. The preparation method according to claim 14 or 15, wherein The conductive agent includes a first conductive agent, and the first conductive agent includes one or more of carbon nanotubes, graphene, and nano-carbon fibers.

17. The preparation method according to claim 16, wherein The mass ratio of the first conductive agent to the organic polymer dispersant is 1:(0.1-3).

18. The preparation method according to claim 16 or 17, wherein The slurry includes a negative electrode active material, and the mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant is 100:(0.05-1):(0.05-1).

19. The preparation method according to claim 18, wherein The mass ratio of the negative electrode active material, the first conductive agent, and the organic polymer dispersant is 100:(0.1-0.5):(0.1-0.5).

20. A battery cell, wherein: The invention comprises the negative electrode sheet according to any one of claims 1 to 13 or the negative electrode sheet prepared by the preparation method according to claims 14 to 19.

21. An electrical device, wherein: Comprising the battery cell according to claim 20.

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