Negative plate, preparation method thereof and battery

Abstract

The invention discloses a negative plate, a preparation method thereof and a battery, and belongs to the technical field of batteries, the negative plate comprises a negative current collector and a negative active layer, and the negative active layer is arranged on at least one side of the negative current collector; the passivation layer is arranged on the side, away from the negative electrode current collector, of the negative electrode active layer, and the passivation layer comprises a composite lithium-containing compound and a composite conductive binder; the composite conductive binder comprises a conductive core layer and a coating layer, the conductive core layer comprises a conductive carbon base material, the coating layer comprises a conductive polymer layer and a binder layer, the surface of the conductive core layer is coated with the conductive polymer layer, and the binder layer is grafted to the side, away from the conductive core layer, of the conductive polymer layer. According to the composite conductive adhesive with integrated design of conductivity and cohesiveness, the ion transmission efficiency and the electron transmission efficiency of a passivation layer can be improved, so that the internal resistance of a battery is effectively reduced; the composite conductive binder can enable the passivation layer and the negative active material layer to be combined more tightly, reduce the interface impedance and improve the performance of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a negative electrode sheet and its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles and electronic products. The negative electrode of a lithium-ion battery is a key factor affecting its performance. During the first charge, a SEI film forms on the surface of the negative electrode. This SEI film prevents the negative electrode from directly contacting the electrolyte, thereby reducing side reactions and improving battery performance. However, when the negative electrode material is graphite, as a typical intercalation-type negative electrode material, the graphite particles repeatedly expand and contract during the continuous charge and discharge process, causing the SEI film to rupture and reducing the cycle stability of the lithium-ion battery.

[0003] In related technologies, an interface protective layer is formed on the surface of the negative electrode active material layer to improve the cycle stability of the battery. However, the conductivity and stability of this interface protective layer are poor, thus affecting the performance of the negative electrode and the battery. Summary of the Invention

[0004] This application provides a negative electrode sheet and its preparation method, as well as a battery, aiming to solve the problem of poor battery performance caused by the poor conductivity and stability of existing interface protective layers.

[0005] In a first aspect, this application provides a negative electrode sheet, comprising: Negative electrode current collector, A negative electrode active layer is disposed on at least one side of the negative electrode current collector; and A passivation layer is disposed on the surface of the negative electrode active layer away from the negative electrode current collector. The passivation layer includes a composite lithium-containing compound and a composite conductive binder. The composite conductive adhesive includes a conductive core layer and a coating layer; the conductive core layer includes a conductive carbon substrate, and the coating layer includes a conductive polymer layer and an adhesive layer. The conductive polymer layer coats the surface of the conductive core layer, and the adhesive layer is grafted onto the side of the conductive polymer layer facing away from the conductive core layer.

[0006] This application involves setting a passivation layer on the surface of the negative electrode active layer. The passivation layer comprises a composite lithium-containing compound and a composite conductive binder. This composite conductive binder, with its integrated conductivity and adhesion design, ensures that the composite lithium-containing compound and the composite conductive binder in the passivation layer are highly dispersed and more uniformly dispersed. This creates uniform and dense ion and electron transport channels within the passivation layer, improving ion and electron transport efficiency. Consequently, the battery exhibits lower interfacial impedance, effectively reducing internal resistance and improving rate performance and cycle performance. Simultaneously, the composite conductive binder enables a tighter bond between the passivation layer and the negative electrode active material layer, further reducing interfacial impedance and enhancing rate performance. By configuring the composite conductive adhesive to include a conductive core layer and a coating layer, the conductive core layer includes a conductive carbon substrate, which provides electronic conductivity to the composite conductive adhesive. The coating layer includes a conductive polymer layer and an adhesive layer grafted onto the surface of the conductive polymer layer. The conductive polymer layer can form a tightly connected electronic transport network with the conductive carbon substrate, and the conductive polymer layer can be strongly connected with the adhesive layer, thus providing stable conductivity and adhesion performance to the composite conductive adhesive.

[0007] Optionally, the composite lithium-containing compound includes a first lithium-containing compound and a second lithium-containing compound, wherein the first lithium-containing compound includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalateborate, and the second lithium-containing compound includes at least one of lithium carbonate, lithium nitrate, and lithium hydroxide.

[0008] The first lithium-containing compound of this application can be hydrolyzed or dissociated to form lithium fluoride, thereby making the SEI film induced during the first formation of the battery contain lithium fluoride, thus making the SEI film more robust and improving its mechanical strength; the second lithium-containing compound can be reduced to inorganic phases with high ionic conductivity such as lithium oxide and lithium nitride during the first formation of the battery, thereby making the SEI film contain inorganic phases with high ionic conductivity such as lithium oxide and lithium nitride, thus improving the ionic conductivity of the SEI film.

[0009] Optionally, the mass percentage of the composite conductive binder and the composite lithium-containing compound is 80%~90%:10%~20%.

[0010] This application improves the rate performance of the battery by ensuring that the mass percentages of the composite conductive binder and the composite lithium-containing compound are within a suitable range. The composite conductive binder can ensure the continuity of electron transport inside the passivation layer, while also firmly and uniformly anchoring the composite lithium-containing compound in the passivation layer. The composite lithium-containing compound can supplement an appropriate number of lithium ions, so that the ionic conductivity of the passivation layer is within a suitable range.

[0011] Optionally, the mass ratio of the first lithium-containing compound and the second lithium-containing compound is 1~2:1~2.

[0012] This application achieves better control of the ionic conductivity of the passivation layer and balances the ionic conductivity and mechanical strength of the SEI film by maintaining an appropriate mass ratio of the first lithium-containing compound and the second lithium-containing compound, thereby improving the rate performance and cycle stability of the battery.

[0013] Optionally, in the composite conductive adhesive, the mass ratio of the conductive core layer, the conductive polymer layer, and the adhesive layer is 0.5~1.5:2.5~3.5:4.5~5.5.

[0014] This application achieves a better balance between the electronic conductivity and adhesion of the composite conductive adhesive by setting the mass ratio of the conductive core layer, conductive polymer layer, and adhesive layer within a suitable range, thereby maximizing the effectiveness of the composite conductive adhesive.

[0015] Optionally, the thickness of the passivation layer is 2μm to 3μm.

[0016] The passivation layer of appropriate thickness in this application not only improves its puncture resistance and avoids direct contact between the positive and negative electrode plates, thus improving the cycle stability of the battery, but also minimizes the impact of the passivation layer on the rate performance and energy density of the battery.

[0017] Optionally, the conductive carbon substrate includes at least one of carbon black, graphene, and carbon nanotubes; and / or, the conductive polymer layer is made of at least one of polyaniline, polyacetylene, polypyrrole, and polythiophene; and / or, the passivation layer adhesive layer is made of at least one of polyacrylic acid, polyacrylonitrile, styrene-butadiene, sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, rubidium polyacrylate, cesium polyacrylate, francium polyacrylate, barium polyacrylate, strontium polyacrylate, lithium carboxymethyl cellulose, beryllium carboxymethyl cellulose, and sodium carboxymethyl cellulose.

[0018] This application improves the conductivity of the composite conductive adhesive by using a highly conductive carbon substrate as the conductive core layer. By appropriately selecting the material types of the conductive polymer layer, the conjugated structure of the conductive polymer provides conditions for the delocalization of free electrons, thereby ensuring the high conductivity of the conductive polymer layer. Furthermore, by appropriately selecting the material types of the adhesive layer, it enables successful grafting onto the surface of the conductive polymer layer while providing adhesive properties.

[0019] Secondly, embodiments of this application provide a method for preparing the negative electrode sheet provided in the first aspect of this application, comprising: Provide negative electrode current collector; A negative electrode slurry is provided, coated onto the negative electrode current collector, and dried to form a negative electrode active layer. A passivation layer slurry containing a composite lithium compound and a composite conductive binder is prepared. The passivation layer slurry is coated on the side of the negative electrode active layer away from the negative electrode current collector and dried to form a passivation layer on the surface of the negative electrode active layer.

[0020] This application uses a wet coating process to form a uniform negative electrode active material layer on the negative electrode current collector. Then, a passivation layer slurry containing a composite lithium compound and a composite conductive binder is prepared. The composite lithium compound and the composite conductive binder provide ionic conductivity, electronic conductivity and adhesion to the passivation layer slurry. The wet coating process forms a high-performance passivation layer on the side of the negative electrode active layer away from the negative electrode current collector, providing conditions for the formation of a highly stable SEI film, thereby improving the cycle stability and rate performance of the battery.

[0021] Optionally, the method for preparing the composite conductive adhesive includes: The conductive core layer is dispersed in an acid solution, and conductive polymer monomers and a first solvent are added to obtain a first solution after dispersion. An oxidant is added to the first solution to react and polymerize the conductive polymer monomers, forming a conductive polymer layer on the surface of the conductive core layer, thus obtaining an intermediate. The intermediate and passivation layer binder are dispersed in a second solvent to form a second solution; The free radical initiator is dispersed in a third solvent to form a third solution; A third solution is added to the second solution to react, thereby grafting an adhesive layer onto the surface of the conductive polymer layer, resulting in a slurry containing a composite conductive adhesive.

[0022] This application first disperses the conductive core layer in an acid solution, which provides the preconditions for the polymerization of conductive polymer monomers. Then, an oxidant is added to the first solution, causing the conductive polymer monomers to polymerize in situ on the surface of the conductive core layer to form a conductive polymer layer, yielding an intermediate. Next, the intermediate and a passivation layer binder are dispersed in a second solvent to form a second solution. Then, a free radical initiator is dispersed in a third solvent. The presence of the free radical initiator provides favorable conditions for the grafting of the passivation layer binder onto the surface of the conductive polymer layer. The third solution is added to the second solution, and the free radical initiator initiates a grafting reaction between the passivation layer binder and the conductive polymer layer, allowing the binder layer to graft onto the surface of the conductive polymer layer. Simultaneously, moderate cross-linking between the passivation layer binders is initiated, improving the adhesion and mechanical properties of the binder layer.

[0023] Optionally, the solid content of the passivation layer slurry is 20% to 25%.

[0024] This application achieves a uniform and relatively dense passivation layer by reasonably setting the solid content of the passivation layer slurry.

[0025] Thirdly, embodiments of this application provide a battery, including a negative electrode sheet prepared by the method for preparing a negative electrode sheet provided in the first aspect of this application or the method for preparing a negative electrode sheet provided in the second aspect of this application; the battery also includes a positive electrode sheet and a separator. The separator is disposed between the negative electrode sheet and the positive electrode sheet, and a passivation layer is disposed on the side of the negative electrode sheet near the separator.

[0026] By applying the negative electrode sheet provided in the first aspect of this application or the negative electrode sheet prepared in the second aspect to the battery, the battery can have excellent rate performance and cycle stability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the negative electrode sheet provided in the embodiments of this application.

[0029] Explanation of reference numerals in the attached figures: 100. Negative electrode sheet; 10. Negative electrode current collector; 20. Negative electrode active layer; 30. Passivation layer. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] This application provides a negative electrode 100, its preparation method, and a battery. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0032] SEI film (Solid Electrolyte Interphase) refers to a thin film that is uniformly covered and has ionic conductivity and electronic insulation properties, which is spontaneously formed during the initial formation of a lithium-ion battery when the components of the electrolyte undergo reduction and decomposition on the surface of the negative electrode.

[0033] The technical solution of this application is as follows: Firstly, please refer to Figure 1 An embodiment of this application provides a negative electrode sheet 100, including a negative electrode current collector 10, a negative electrode active layer 20 and a passivation layer 30. The negative electrode active layer 20 is disposed on at least one side of the negative electrode current collector 10, and the passivation layer 30 is disposed on the side surface of the negative electrode active layer 20 opposite to the negative electrode current collector 10. The passivation layer 30 includes a composite lithium-containing compound and a composite conductive binder.

[0034] The composite conductive adhesive includes a conductive core layer and a coating layer; the conductive core layer includes a conductive carbon substrate, and the coating layer includes a conductive polymer layer and an adhesive layer. The conductive polymer layer coats the surface of the conductive core layer, and the adhesive layer is grafted onto the side of the conductive polymer layer facing away from the conductive core layer.

[0035] In this application, a passivation layer 30 is formed on the surface of the negative electrode active layer 20. The passivation layer 30 comprises a composite lithium-containing compound and a composite conductive binder. The composite conductive binder possesses both conductivity and adhesion properties. This integrated design of conductivity and adhesion in the composite conductive binder results in a highly dispersed and more uniform dispersion of the composite lithium-containing compound and the composite conductive binder in the passivation layer 30. The uniformly dispersed composite lithium-containing compound not only constructs uniform and dense ion transport channels in the passivation layer 30, giving the passivation layer 30 stronger ion conductivity, but also… The composite lithium-containing compound can replenish lithium ions to the surface of the negative electrode active layer 20 during battery discharge, alleviating the concentration polarization internal resistance between the negative electrode active layer 20 and the electrolyte, further improving the lithium ion conduction efficiency during battery discharge, and reducing the impact of the passivation layer 30 on the battery rate performance. The highly dispersed composite conductive binder forms a continuous, dense, and uniform conductive network in the passivation layer 30, constructing an efficient electron transport channel, resulting in a lower interface impedance, thereby effectively reducing the battery's internal resistance and improving its rate performance and cycle performance. In other words, the passivation layer 30 of this application has both efficient electron transport and ion transport capabilities. When the negative electrode sheet 100 is applied to a battery, it can significantly improve the battery's rate performance, cycle performance, and high-temperature storage performance.

[0036] Understandably, by configuring the composite conductive binder to include a conductive core layer and a coating layer, the conductive core layer comprises a conductive carbon substrate with excellent electronic conductivity, thus providing electronic conductivity to the composite conductive binder. The coating layer comprises a conductive polymer layer and an adhesive layer grafted onto the surface of the conductive polymer layer, with the conductive polymer layer coating the surface of the conductive core layer. On the one hand, the conductive polymer layer acts as a conductive bridge, forming a tightly connected electronic transport network with the conductive carbon substrate; on the other hand, the conductive polymer layer strongly bonds with the adhesive layer, thereby providing stable conductivity and adhesion performance to the composite conductive binder. This application requires no additional conductive agent; the composite conductive binder can achieve superior conductivity at the interface, thus having almost no impact on the battery's rate performance.

[0037] Understandably, the composite conductive binder with integrated conductivity and adhesion design can increase the bonding force between the composite lithium-containing compound and the composite conductive binder in the passivation layer 30, improve the stability and mechanical strength of the passivation layer 30, reduce its puncture resistance, reduce the risk of short circuit due to direct contact between the negative and positive electrodes, and thus improve the cycle stability of the battery. Simultaneously, the composite conductive binder enables the passivation layer 30 to bond more tightly to the negative electrode active material layer, further reducing interfacial impedance, improving the battery's rate performance, and maintaining the stability of the SEI film. This reduces the risk of SEI film rupture caused by repeated expansion and contraction of the negative electrode active material layer during battery charging and discharging, thereby improving the battery's cycle performance. Furthermore, the passivation layer 30 of this application can also improve the stability of the negative electrode active material layer and reduce the risk of the negative electrode active material layer peeling off from the negative electrode current collector 10.

[0038] Understandably, the presence of the passivation layer 30 not only reduces the direct contact between the negative electrode active layer 20 and the electrolyte, lowering the probability of side reactions, improving the cycle stability of the battery, and reducing the self-discharge rate, but also reduces the powder shedding problem of the negative electrode sheet 100, further improving the cycle performance of the battery and reducing the self-discharge rate.

[0039] In some embodiments, the composite lithium-containing compound includes a first lithium-containing compound and a second lithium-containing compound, wherein the first lithium-containing compound includes at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium difluorooxalate borate (LiDFOB), and the second lithium-containing compound includes at least one of lithium carbonate, lithium nitrate, and lithium hydroxide.

[0040] In this application, the first lithium-containing compound is configured as the aforementioned fluorinated lithium salt, which can be hydrolyzed or dissociated to form lithium fluoride. This results in the SEI film induced during the initial battery formation process containing lithium fluoride, thereby making the SEI film more robust and improving its mechanical strength. The second lithium-containing compound, during the initial battery formation, can be reduced to inorganic phases with high ionic conductivity, such as lithium oxide and lithium nitride. This also results in the SEI film containing these inorganic phases, further improving its ionic conductivity. In other words, the combination of the first and second lithium-containing compounds in this application enables the SEI film to possess both high mechanical strength and high ionic conductivity.

[0041] For example, the purity of both the first lithium-containing compound and the second lithium-containing compound is greater than 99%.

[0042] In some embodiments, the mass percentage of the composite conductive binder and the composite lithium-containing compound is 80%~90%:10%~20%, for example, it can be 80%:20%, 83%:17%, 85%:15%, 88%:12%, 90%:10%, etc.

[0043] In this application, by maintaining the mass percentages of the composite conductive binder and the composite lithium-containing compound within a suitable range, a higher proportion of the composite conductive binder not only provides stable adhesion and film-forming ability for the passivation layer 30, but also ensures the continuity of electron transport within the passivation layer 30. Simultaneously, it firmly and uniformly anchors the composite lithium-containing compound within the passivation layer 30. A suitable proportion of the composite lithium-containing compound replenishes an appropriate number of lithium ions, ensuring the ionic conductivity of the passivation layer 30 remains within a suitable range. The appropriate ratio of the composite conductive binder to the composite lithium-containing compound allows for better synergy between the ionic and electronic conductivity of the passivation layer 30, thereby improving the rate performance of the battery. Furthermore, the appropriate proportion of the composite lithium-containing compound can better regulate the microstructure of the SEI film, improving its stability and ionic conductivity.

[0044] In some embodiments, the mass ratio of the first lithium-containing compound and the second lithium-containing compound is 1~2:1~2, for example, it can be 1:1, 1:1.5, 1:2, 1.5:1, 2:1, etc.

[0045] In this application, by maintaining a mass ratio of the first lithium-containing compound and the second lithium-containing compound of 1~2:1~2, the appropriate ratio of the first and second lithium-containing compounds can better control the ionic conductivity of the passivation layer 30 and balance the ionic conductivity and mechanical strength of the SEI film, thereby improving the rate performance and cycle stability of the battery. This application, through the synergistic effect of the mass percentages of the composite conductive binder and the composite lithium-containing compound, as well as the mass ratio of the first and second lithium-containing compounds, forms a high-performance and stable passivation layer 30 and SEI film, thereby improving battery performance.

[0046] In some embodiments, the mass ratio of the conductive core layer, the conductive polymer layer, and the adhesive layer in the composite conductive adhesive is 0.5~1.5:2.5~3.5:4.5~5.5, for example, it can be 0.5:2.5:4.5, 0.5:3.5:4.5, 0.5:2.5:5.5, 1.5:2.5:4.5, 1.5:3.5:4.5, 1.5:2.5:5.5, 1:3:5, 0.8:3.5:5.3, 0.5:3.5:5.5, etc.

[0047] In this application, by setting the mass ratio of the conductive core layer, the conductive polymer layer and the adhesive layer in the composite conductive adhesive within a suitable range, the electronic conductivity and adhesion of the composite conductive adhesive are better balanced, thereby giving fuller play to the role of the composite conductive adhesive.

[0048] In some embodiments, the thickness of the passivation layer 30 is 2μm to 3μm, for example, it can be 2μm, 2.3μm, 2.5μm, 2.8μm, 3μm, etc.

[0049] In this application, by setting the thickness of the passivation layer 30 to 2μm~3μm, the passivation layer 30 of suitable thickness can not only improve its puncture resistance and avoid direct contact between the positive electrode and the negative electrode 100, thus improving the cycle stability of the battery, but also minimize the impact of the passivation layer 30 on the rate performance and energy density of the battery.

[0050] In some embodiments, the conductive carbon substrate includes at least one of carbon black, graphene, and carbon nanotubes.

[0051] This application improves the conductivity of the composite conductive binder by using at least one of carbon black, graphene, and carbon nanotubes as the conductive carbon substrate and by selecting a highly conductive conductive carbon substrate as the conductive core layer.

[0052] For example, carbon black includes at least one of acetylene black, Ketjen black, etc.

[0053] For example, carbon black includes Super P (SP).

[0054] In some embodiments, the material of the conductive polymer layer includes at least one of conductive polymers such as polyaniline (PANI), polyacetylene (PA), polypyrrole (PPy), and polythiophene (PTh).

[0055] It is understandable that by rationally setting the types of materials for the conductive polymer layer, on the one hand, the conjugated structure of the polymer provides conditions for the delocalization of free electrons, thereby ensuring the high conductivity of the conductive polymer layer and forming a complete conductive channel with the conductive core layer; on the other hand, the polymer can be uniformly coated on the surface of the conductive core layer through in-situ polymerization of monomers, making the preparation of the conductive polymer layer easier.

[0056] In some embodiments, the adhesive layer material includes at least one selected from polyacrylic acid (PAA), polyacrylonitrile (PAN), styrene-butadiene (SBR), sodium polyacrylate (PAANa), lithium polyacrylate (PAALi), potassium polyacrylate (PAAK), calcium polyacrylate (PAACa), magnesium polyacrylate (PAAMg), rubidium polyacrylate (PAARb), cesium polyacrylate (PAACs), francium polyacrylate (PAAF), barium polyacrylate (PAABa), strontium polyacrylate (PAASr), lithium carboxymethyl cellulose (CMCLi), beryllium carboxymethyl cellulose (CMCB), and sodium carboxymethyl cellulose (CMCNa).

[0057] It is understandable that by properly setting the type of material in the adhesive layer, it is possible to achieve successful grafting onto the surface of the conductive polymer layer while providing adhesive performance.

[0058] In some embodiments, the negative electrode active layer 20 includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, wherein the mass percentages of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder are 96%~97%:0.4%~0.6%:1.5%~2%.

[0059] In this application, the negative electrode active layer 20 includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. During battery charging and discharging, the negative electrode active material reversibly inserts and extracts lithium ions, providing conditions for the battery's charging and discharging process. The negative electrode conductive agent forms a conductive network in the negative electrode active layer 20, reducing the contact resistance between particles in the negative electrode active layer 20 and ensuring rapid electron transport. The negative electrode binder bonds the negative electrode active material and the negative electrode conductive agent to form a stable negative electrode active layer 20. By rationally setting the mass percentages of the negative electrode active material, negative electrode conductive agent, and negative electrode binder, an appropriate proportion of negative electrode active material provides sufficient insertion and extraction sites for lithium ion transport, enabling efficient lithium ion transport during battery charging and discharging. An appropriate proportion of negative electrode conductive agent can form a sufficient conductive network in the negative electrode active layer 20, achieving rapid electron conduction. An appropriate amount of binder ensures a firm bond between the negative electrode active material and the negative electrode conductive agent while avoiding reduction in battery energy density.

[0060] For example, the negative electrode active material includes at least one of graphite and silicon-oxygen composite materials. This application selects a negative electrode active material with high theoretical capacity, which can improve the energy density of the battery.

[0061] For example, the negative electrode conductive agent includes at least one of carbon black, graphene, and carbon nanotubes.

[0062] For example, the negative electrode binder includes styrene-butadiene rubber (SBR).

[0063] For example, the negative electrode active layer 20 also includes a dispersant, which includes sodium carboxymethyl cellulose (CMCNa), and the mass percentages of the negative electrode active material, negative electrode conductive agent, negative electrode binder and dispersant are 96%~97%:0.4%~0.6%:1.5%~2%:1.0%~1.5%.

[0064] Secondly, embodiments of this application provide a method for preparing the negative electrode 100 provided in the first aspect of this application, comprising: Provide negative electrode current collector 10; A negative electrode slurry is provided, and the negative electrode slurry is coated onto the negative electrode current collector 10 and dried to form a negative electrode active layer 20. A passivation layer slurry containing a composite lithium compound and a composite conductive binder is prepared. The passivation layer slurry is coated on the side of the negative electrode active layer 20 away from the negative electrode current collector 10 and dried to form a passivation layer 30 on the surface of the negative electrode active layer 20.

[0065] In this application, a negative electrode slurry is first coated onto the negative electrode current collector 10, forming a uniform negative electrode active material layer on the negative electrode current collector 10 through a simple wet coating process. Next, a passivation layer slurry containing a composite lithium-containing compound and a composite conductive binder is prepared. The composite lithium-containing compound and the composite conductive binder provide ionic conductivity, electronic conductivity, and adhesion to the passivation layer slurry. The passivation layer slurry is then coated onto the side of the negative electrode active layer 20 facing away from the negative electrode current collector 10 through a wet coating process, forming a high-performance passivation layer 30. This provides conditions for the formation of a highly stable SEI film, thereby improving the cycle stability and rate performance of the battery. The preparation method of the negative electrode sheet 100 in this application can be used without changing existing battery manufacturing processes, perfectly compatible with existing technologies.

[0066] In some embodiments, the method for preparing the composite conductive adhesive includes: The conductive core layer is dispersed in an acid solution, and conductive polymer monomers and a first solvent are added to obtain a first solution after dispersion. An oxidant is added to the first solution to react and polymerize the conductive polymer monomers, forming a conductive polymer layer on the surface of the conductive core layer, thus obtaining an intermediate. The intermediate and passivation layer binder are dispersed in a second solvent to form a second solution; The free radical initiator is dispersed in a third solvent to form a third solution; A third solution is added to the second solution to react, thereby grafting an adhesive layer onto the surface of the conductive polymer layer, resulting in a slurry containing a composite conductive adhesive.

[0067] In this application, the conductive core layer is first dispersed in an acid solution. The acid solution protonates the conductive polymer monomers, forming cations of the conductive polymer monomers, providing a prerequisite for the polymerization of the conductive polymer monomers. Next, an oxidant is added to a first solution to oxidize the cations of the conductive polymer monomers into free radical cations of the conductive polymer monomers. These free radical cations undergo addition and dehydrogenation reactions, and through in-situ crosslinking, polymerize on the surface of the conductive core layer to form a conductive polymer layer, yielding an intermediate. Then, the intermediate and a passivation layer binder are dispersed in a second solvent, ensuring uniform dispersion and forming a second solution. Next, a free radical initiator is dispersed in a third solvent. The presence of the free radical initiator provides a favorable condition for the grafting of the passivation layer binder onto the surface of the conductive polymer layer. The third solution is added to the second solution, causing the free radical initiator to decompose and generate free radicals, initiating a grafting reaction between the passivation layer binder and the conductive polymer layer. This allows the binder layer to be grafted onto the surface of the conductive polymer layer, while simultaneously initiating appropriate crosslinking between the passivation layer binders, improving the adhesion and mechanical properties of the binder layer.

[0068] For example, the first solvent includes at least one of deionized water, alcohols (methanol, ethanol, n-propanol, etc.), and oil-based solvents (acetonitrile, chloroform, acetone, etc.).

[0069] For example, the second solvent includes at least one of deionized water, alcohols (methanol, ethanol, n-propanol, etc.), and oil-based solvents (acetonitrile, chloroform, acetone, etc.).

[0070] For example, the third solvent includes at least one of deionized water, alcohols (methanol, ethanol, n-propanol, etc.), and oil-based solvents (acetonitrile, chloroform, acetone, etc.).

[0071] For example, the third solution also includes a dispersing agent, including N,N-dimethylacetamide.

[0072] For example, preparing a passivation layer slurry containing a composite lithium compound and a composite conductive binder includes: adding the composite lithium compound to a slurry containing the composite conductive binder, dispersing it, and then forming the passivation layer slurry. This application simplifies the preparation process by adding the composite lithium compound to a slurry containing the composite conductive binder, dispersing it, and then forming the passivation layer slurry, thus reducing the need for separating, drying, and redispersing the composite conductive binder.

[0073] In some embodiments, the solid content of the passivation layer slurry is 20% to 25%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, etc.

[0074] In this application, by reasonably setting the solid content of the passivation layer slurry, the appropriate solid content enables the passivation layer slurry to be coated on the surface of the negative electrode active layer 20 in a relatively dense and uniform manner, thereby forming a uniform and relatively dense passivation layer 30.

[0075] Thirdly, embodiments of this application provide a battery, including a negative electrode 100 prepared by the method of preparing the negative electrode 100 provided in the first aspect of this application or the method of preparing the negative electrode 100 provided in the second aspect of this application; the battery also includes a positive electrode and a separator. The separator is disposed between the negative electrode 100 and the positive electrode, and a passivation layer 30 is disposed on the side of the negative electrode 100 near the separator.

[0076] In this application, the negative electrode 100 provided in the first aspect or the negative electrode 100 prepared in the second aspect of this application is applied to a battery, thereby enabling the battery to have excellent rate performance and cycle stability. During safety tests such as nail penetration, the passivation layer 30 can prevent direct contact and short circuit between the negative electrode 100 and the positive electrode, improving the battery's safety performance.

[0077] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer, wherein the positive active layer is disposed on at least one side of the positive current collector.

[0078] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, wherein the mass percentages of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder are 94%~96%:2%~3%:2%~3%.

[0079] For example, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate.

[0080] For example, the positive electrode conductive agent includes at least one of carbon black, graphene, and carbon nanotubes.

[0081] For example, the negative electrode binder includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0082] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0083] Example 1 This embodiment provides a negative electrode sheet 100, including a negative electrode current collector 10, a negative electrode active layer 20, and a passivation layer 30. The negative electrode active layer 20 is disposed on both sides of the negative electrode current collector 10, and the passivation layer 30 is disposed on the side surface of the negative electrode active layer 20 facing away from the negative electrode current collector 10. The passivation layer 30 includes a composite lithium-containing compound and a composite conductive binder. The composite conductive binder includes a conductive core layer and a coating layer; the conductive core layer includes a conductive carbon substrate, and the coating layer includes a conductive polymer layer and an binder layer. The conductive polymer layer coats the surface of the conductive core layer, and the binder layer is grafted onto the side surface of the conductive polymer layer facing away from the conductive core layer. The conductive carbon substrate is SP, the conductive polymer layer is made of PANI, and the binder layer is made of PAA.

[0084] The passivation layer 30 has a thickness of 2.5 μm.

[0085] The mass percentage of the composite conductive binder and the composite lithium-containing compound is 85%:15%.

[0086] The composite lithium-containing compound includes a first lithium-containing compound and a second lithium-containing compound. The first lithium-containing compound is LiPF6, and the second lithium-containing compound is Li2CO3. The mass ratio of LiPF6 to Li2CO3 is 1:1.

[0087] The preparation method of the negative electrode 100 includes: (1) Provide copper foil; (2) Weigh the graphite material, carbon black, CMC and SBR in a mass percentage of 96.5%:0.5%:1.2%:1.8%, disperse the graphite material, carbon black and CMC in deionized water, and then add SBR to prepare a negative electrode slurry with a solid content of 50%.

[0088] The negative electrode slurry was coated onto both sides of the copper foil using a transfer coating method, baked at 120°C for 15 minutes, and dried to form a negative electrode active layer 20 on the copper foil.

[0089] (3) In a stirred flask, add 20 parts by weight of 0.1 mol / L HCl and 1 part by weight of SP in sequence, stir for 20 min, then add 3.5 parts by weight of aniline monomer and 30 parts by weight of deionized water, and mix well to form the first solution. Then slowly add 2.1 parts by weight of ammonium persulfate to the first solution, and stir continuously for 6 h at 0℃~15℃. After washing with deionized water, dry at 70℃ to obtain PANI-coated SP powder, i.e., the intermediate. Mix 0.8 parts by weight of the intermediate and 5.3 parts by weight of PAA, and then add to 50 parts by weight of deionized water and mix well to form the second solution. Then add 1.3 parts by weight of ammonium persulfate and 0.1 parts by weight of N,N-dimethylacetamide to 30 parts by weight of deionized water to form the third solution. The third solution is slowly added to the second solution, and the mixture is stirred continuously at 60°C for 4 hours to finally form a slurry containing a certain mass fraction of composite conductive binder, wherein the mass ratio of the conductive core layer, the conductive polymer layer and the binder layer in the composite conductive binder is 0.8:2.8:5.3.

[0090] Li2CO3 and LiPF6 were added to a slurry containing a composite conductive binder and dispersed and stirred for 2-3 hours under the action of a mixer to obtain a passivation layer slurry with a solid content of 23%.

[0091] (4) The passivation layer slurry is coated onto the negative electrode active layer 20 using a gravure coating machine and dried at 110°C for 15 minutes to form a passivation layer 30 on the surface of the negative electrode active layer 20, thus obtaining the negative electrode sheet 100 of Example 1.

[0092] Example 2 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass percentage of the composite conductive binder and the composite lithium-containing compound is 80%:20%. The other aspects are the same as in Embodiment 1 and will not be repeated here.

[0093] Example 3 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass percentage of the composite conductive binder and the composite lithium-containing compound is 90%:10%. The other aspects are the same as in Embodiment 1 and will not be repeated here.

[0094] Example 4 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass percentage of the composite conductive binder and the composite lithium-containing compound is 95%:15%. The other aspects are the same as in Embodiment 1 and will not be repeated here.

[0095] Example 5 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass percentage of the composite conductive binder and the composite lithium-containing compound is 75%:25%. The other aspects are the same as in Embodiment 1 and will not be repeated here.

[0096] Example 6 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass ratio of LiPF6 to Li2CO3 is 1:2. All other aspects are the same as in Embodiment 1 and will not be repeated here.

[0097] Example 7 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass ratio of LiPF6 to Li2CO3 is 2:1. All other aspects are the same as in Embodiment 1 and will not be repeated here.

[0098] Example 8 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass ratio of LiPF6 to Li2CO3 is 3:1. All other aspects are the same as in Embodiment 1 and will not be repeated here.

[0099] Example 9 This embodiment provides a negative electrode 100, which differs from Embodiment 1 only in that the mass ratio of LiPF6 to Li2CO3 is 1:3. All other aspects remain the same as in Embodiment 1 and will not be repeated here.

[0100] Example 10 This embodiment provides a negative electrode 100. Compared with embodiment 1, the only difference is that the mass ratio of the conductive core layer, the conductive polymer layer, and the binder layer in the composite conductive binder is 0.5:3.5:5.5. Step (3) is as follows: 20 parts by weight of 0.1 mol / L HCl and 0.63 parts by weight of SP are added sequentially to a stirred flask and stirred for 20 min. Then, 4.4 parts by weight of aniline monomer and 30 parts by weight of deionized water are added and mixed evenly to form a first solution. Then, 2.1 parts by weight of ammonium persulfate are slowly added to the first solution and stirred continuously for 6 h at 0℃~15℃. After washing with deionized water, the solution is dried at 70℃ to obtain PANI-coated SP powder, i.e., the intermediate. 0.8 parts by weight of the intermediate and 5.5 parts by weight of PAA are mixed and then added to 50 parts by weight of deionized water and mixed evenly to form a second solution. Next, 1.3 parts by weight of ammonium persulfate and 0.1 parts by weight of N,N-dimethylacetamide were added to 30 parts by weight of deionized water to form a third solution. The third solution was slowly added to the second solution, and the mixture was stirred continuously at 60°C for 4 hours to finally form a slurry containing a certain mass fraction of composite conductive binder. The rest was consistent with Example 1 and will not be repeated here.

[0101] Example 11 This embodiment provides a negative electrode 100. Compared with embodiment 1, the only difference is that the mass ratio of the conductive core layer, the conductive polymer layer, and the binder layer in the composite conductive binder is 1.5:2.5:4.5. Step (3) is as follows: 20 parts by weight of 0.1 mol / L HCl and 1.9 parts by weight of SP are added sequentially to a stirred flask and stirred for 20 min. Then, 3.1 parts by weight of aniline monomer and 30 parts by weight of deionized water are added and mixed evenly to form a first solution. Then, 2.1 parts by weight of ammonium persulfate are slowly added to the first solution and stirred continuously for 6 h at 0℃~15℃. After washing with deionized water, the solution is dried at 70℃ to obtain PANI-coated SP powder, i.e., the intermediate. 0.8 parts by weight of the intermediate and 4.5 parts by weight of PAA are mixed and then added to 50 parts by weight of deionized water and mixed evenly to form a second solution. Next, 1.3 parts by weight of ammonium persulfate and 0.1 parts by weight of N,N-dimethylacetamide were added to 30 parts by weight of deionized water to form a third solution. The third solution was slowly added to the second solution, and the mixture was stirred continuously at 60°C for 4 hours to finally form a slurry containing a certain mass fraction of composite conductive binder. The rest was consistent with Example 1 and will not be repeated here.

[0102] Example 12 This embodiment provides a negative electrode 100. Compared with embodiment 1, the only difference is that the mass ratio of the conductive core layer, the conductive polymer layer, and the binder layer in the composite conductive binder is 0.3:3.7:5.8. Step (3) is as follows: 20 parts by weight of 0.1 mol / L HCl and 0.4 parts by weight of SP are added sequentially to a stirred flask and stirred for 20 min. Then, 4.6 parts by weight of aniline monomer and 30 parts by weight of deionized water are added and mixed evenly to form a first solution. Then, 2.1 parts by weight of ammonium persulfate are slowly added to the first solution and stirred continuously for 6 h at 0℃~15℃. After washing with deionized water, the solution is dried at 70℃ to obtain PANI-coated SP powder, i.e., the intermediate. 0.8 parts by weight of the intermediate and 5.8 parts by weight of PAA are mixed and then added to 50 parts by weight of deionized water and mixed evenly to form a second solution. Next, 1.3 parts by weight of ammonium persulfate and 0.1 parts by weight of N,N-dimethylacetamide were added to 30 parts by weight of deionized water to form a third solution. The third solution was slowly added to the second solution, and the mixture was stirred continuously at 60°C for 4 hours to finally form a slurry containing a certain mass fraction of composite conductive binder. The rest was consistent with Example 1 and will not be repeated here.

[0103] Example 13 This embodiment provides a negative electrode 100. Compared with embodiment 1, the only difference is that the mass ratio of the conductive core layer, the conductive polymer layer, and the binder layer in the composite conductive binder is 1.8:2.2:4.3. Step (3) is as follows: 20 parts by weight of 0.1 mol / L HCl and 2.3 parts by weight of SP are added sequentially to a stirred flask and stirred for 20 min. Then, 2.8 parts by weight of aniline monomer and 30 parts by weight of deionized water are added and mixed evenly to form a first solution. Then, 2.1 parts by weight of ammonium persulfate are slowly added to the first solution and stirred continuously for 6 h at 0℃~15℃. After washing with deionized water, the solution is dried at 70℃ to obtain PANI-coated SP powder, i.e., the intermediate. 0.8 parts by weight of the intermediate and 4.3 parts by weight of PAA are mixed and then added to 50 parts by weight of deionized water and mixed evenly to form a second solution. Next, 1.3 parts by weight of ammonium persulfate and 0.1 parts by weight of N,N-dimethylacetamide were added to 30 parts by weight of deionized water to form a third solution. The third solution was slowly added to the second solution, and the mixture was stirred continuously at 60°C for 4 hours to finally form a slurry containing a certain mass fraction of composite conductive binder. The rest was consistent with Example 1 and will not be repeated here.

[0104] Comparative Example 1 This comparative example provides a negative electrode 100, which differs from Example 1 only in that the passivation layer 30 is not provided. That is, the negative electrode 100 of Comparative Example 1 includes a negative electrode current collector 10 and a negative electrode active layer 20. The negative electrode active layer 20 is disposed on both sides of the negative electrode current collector 10. The rest is consistent with Example 1 and will not be described again here.

[0105] Comparative Example 2 This comparative example provides a negative electrode 100. Compared with Example 1, the only difference is that the passivation layer 30 of Comparative Example 2 includes a composite lithium-containing compound, a conductive carbon substrate SP, and a binder PAA. The mass percentage of the conductive binder (including the conductive carbon substrate SP and the binder PAA) to the composite lithium-containing compound is 85%:15%. Step (3) is as follows: Li2CO3, LiPF6, the conductive carbon substrate SP, and the binder PAA are added to deionized water. The mass ratio of the conductive carbon substrate SP and the binder PAA is 0.8:5.3. The mixture is dispersed and stirred for 2-3 hours under the action of a stirrer to obtain a passivation layer slurry with a solid content of 23%. That is, the conductive carbon substrate SP and the binder PAA are not composited. The rest is consistent with Example 1 and will not be repeated here.

[0106] Comparative Example 3 This comparative example provides a negative electrode 100. Compared with Example 1, the only difference is that the passivation layer 30 of Comparative Example 2 includes a composite lithium-containing compound, a conductive carbon substrate SP, a binder PAA, and polyaniline. The mass percentage of the conductive binder (including the conductive carbon substrate SP, the binder PAA, and polyaniline) to the composite lithium-containing compound is 85%:15%. Step (3) is as follows: Li2CO3, LiPF6, the conductive carbon substrate SP, the binder PAA, and polyaniline are added to deionized water. The mass ratio of the conductive carbon substrate SP, the binder PAA, and polyaniline is 0.8:3.5:5.3. Under the action of a stirrer, the mixture is dispersed and stirred for 2h~3h to obtain a passivation layer slurry with a solid content of 23%. That is, the conductive carbon substrate SP and the binder PAA are not composited. The rest is consistent with Example 1 and will not be repeated here.

[0107] Comparative Example 4 This comparative example provides a negative electrode 100. Compared with Example 1, the only difference is that the composite conductive binder includes a conductive core layer and a coating layer. The conductive core layer includes a conductive carbon substrate SP, and the coating layer includes a binder layer. The material of the binder layer is PAA. Step (3) is as follows: 20 parts by weight of 0.1 mol / L HCl and 0.8 parts by weight of SP are added sequentially to a stirred flask and stirred for 20 min. Then, 5.3 parts by weight of PAA and 30 parts by weight of deionized water are added and mixed evenly to form a first solution. Then, 2.1 parts by weight of ammonium persulfate and 0.1 parts by weight of N,N-dimethylacetamide were slowly added to the first solution, and the mixture was stirred continuously at 60°C for 4 hours to obtain PAA-coated SP powder. Li2CO3, LiPF6 and PAA-coated SP powder were added to deionized water, and the mass ratio of conductive carbon substrate SP to binder PAA was 0.8:5.3. The mixture was dispersed and stirred for 2-3 hours under the action of a stirrer to obtain a passivation layer slurry with a solid content of 23%. Other aspects were the same as in Example 1, and will not be repeated here.

[0108] Comparative Example 5 This comparative example provides a negative electrode 100. Compared with Example 1, the only difference is that the composite conductive binder does not include a conductive core layer. Step (3) is as follows: 20 parts by weight of 0.1 mol / L HCl are added to a stirred flask and stirred for 20 min. Then, 3.5 parts by weight of aniline monomer and 30 parts by weight of deionized water are added and mixed evenly to form a first solution. Then, 2.1 parts by weight of ammonium persulfate are slowly added to the first solution and stirred continuously for 6 h at 0℃~15℃. After washing with deionized water, the solution is dried at 70℃ to obtain PANI. 0.8 parts by weight of PANI and 5.3 parts by weight of PAA are mixed and added to 50 parts by weight of deionized water and mixed evenly to form a second solution. Then, 1.3 parts by weight of ammonium persulfate and 0.1 parts by weight of N,N-dimethylacetamide are added to 30 parts by weight of deionized water to form a third solution. The third solution was slowly added to the second solution, and the mixture was stirred continuously at 60°C for 4 hours to form a slurry containing a certain mass fraction of conductive binder. Li2CO3 and LiPF6 were added to the slurry containing conductive binder and dispersed and stirred for 2-3 hours under the action of a stirrer to obtain a passivation layer slurry with a solid content of 23%. Other aspects were the same as in Example 1 and will not be repeated here.

[0109] Comparative Example 6 This comparative example provides a negative electrode 100, which differs from Example 1 only in that the composite lithium-containing compound is replaced with LiPF6. All other aspects are the same as in Example 1 and will not be described again here.

[0110] Comparative Example 7 This comparative example provides a negative electrode sheet 100. Compared with Example 1, the only difference is that the composite lithium-containing compound is replaced with Li2CO3, and the others are the same as those in Example 1, which will not be elaborated here.

[0111] The negative electrode sheets 100 of Examples 1 to 13 and Comparative Examples 1 to 7 were assembled into batteries, and the battery performance was tested. The results are shown in Table 1.

[0112] The battery assembly process is as follows: Lithium cobaltate, positive electrode conductive agent, and PVDF were weighed according to the mass percentages of 95.2%:2.5%:2.3%. The positive electrode conductive agent includes carbon black and carbon nanotubes, and the mass ratio of carbon black to carbon nanotubes is 1:1. After adding carbon black and carbon nanotubes to the PVDF colloidal solution and stirring evenly, lithium cobaltate was added and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry was coated on both opposite sides of the aluminum foil, and after baking and rolling, a positive electrode sheet was obtained. The positive electrode sheet, separator, and the negative electrode sheets 100 of Examples 1 to 9 and Comparative Examples 1 to 7 were stacked, and after slitting and sheet making, a battery core was obtained using a winding process. The battery core was baked, injected with electrolyte, encapsulated, formed, second-sealed, and subjected to capacity aging to obtain a soft-pack battery. Among them, the electrolyte is a commercially available conventional electrolyte, and the lithium salt therein is lithium hexafluorophosphate (LiFP6).

[0113] Puncture pass rate test: The battery was charged to full charge, placed in an environment at 45°C for 30 min, and then immediately taken out for testing. Using a battery core puncture testing machine, a steel nail with a diameter of 3 mm was used to pass through the battery core from the middle of the front side at a rate of 150 mm / s and maintained for 6 h. If the battery does not catch fire or explode, it is qualified. 8 / 10Ok means that in the puncture tests of 10 batteries, 8 batteries passed the test and are qualified products.

[0114] High-temperature storage test: The battery was discharged once at a current of 0.2C, then recharged to 4.4V, with a cut-off current of 0.02C, and then discharged to 3.0V. The discharge capacity C1 was recorded. Then the battery was fully charged, and then stored at a high temperature for 30 days. After taking it out and discharging it to 3.0V, the capacity C2 was recorded. The capacity retention rate = C2 / C1 * 100%.

[0115] Internal resistance test of 5Ah battery: The battery was charged to full charge, and the internal resistance of the battery was tested and recorded using a voltage internal resistance meter.

[0116] 800-cycle capacity retention rate test: The battery was cycled in a way of charging at 0.5C and discharging at 0.5C, with a voltage range of 4.4V to 3.0V and a cut-off current of 0.02C.

[0117] Table 1

[0118] As shown in Table 1, Examples 1-3, the battery performance is superior when the mass percentage of the composite conductive binder and the composite lithium compound is 80%-90%:10%-20%. This is mainly because the ionic conductivity and electronic conductivity of the passivation layer 30 formed within this ratio range can better synergize. Simultaneously, the appropriate amount of composite conductive binder makes the passivation layer 30 denser and stronger, and the adhesion between the passivation layer 30 and the negative electrode active layer 20 is stronger, resulting in superior battery performance. Data from Examples 4-5 shows that when the proportion of composite conductive binder is too small, the composite lithium compound cannot be firmly bonded, resulting in poor mechanical properties of the passivation layer 30 and a relatively low puncture pass rate. When the proportion of composite conductive binder is too large, although the battery puncture pass rate is high, the electron transport efficiency of the passivation layer 30 is low, and the synergy between ionic conductivity and electronic conductivity cannot be well achieved, resulting in a higher internal resistance and a relatively lower capacity retention rate.

[0119] Data from Examples 1 and 6-7 show that the mass ratio of LiPF6 to Li2CO3 has a significant impact on battery performance. When the mass ratio of LiPF6 to Li2CO3 is in the range of 1-2:1-2, the appropriate ratio of LiPF6 and Li2CO3 can better regulate the ionic conductivity of the passivation layer 30 and balance the ionic conductivity and mechanical strength of the SEI film, thereby resulting in better rate performance, cycle stability, and high-temperature storage performance of the battery. Data from Examples 8-9 show that when the proportion of LiPF6 or Li2CO3 is too high, the synergistic effect of LiPF6 and Li2CO3 will be disrupted, affecting the structure and performance of the passivation layer 30 and the SEI film, and thus affecting the battery performance.

[0120] Data from Examples 1 and 10-13 show that changes in the mass ratio of the conductive core layer, conductive polymer layer, and binder layer in the composite conductive binder affect the battery performance. Only when the three components are within a suitable ratio range do the battery exhibit superior puncture resistance, high-temperature performance, internal resistance, and capacity retention. This may be because when the three components are within a suitable ratio range, the conductive core layer, conductive polymer layer, and binder layer in the resulting composite conductive binder are arranged in a specific manner, resulting in better synergistic effects and thus superior battery performance.

[0121] As shown in Comparative Example 1, when the passivation layer 30 is not provided, the battery's puncture pass rate, high-temperature storage performance, and cycle stability decrease significantly, while the internal resistance increases. This is mainly because without the passivation layer 30, the surface of the negative electrode active layer 20 is essentially unprotected, and the mechanical properties of the SEI film are poor. This results in a sharp decrease in the battery's puncture pass rate and an inability to effectively isolate the electrolyte from eroding the negative electrode active layer 20, thus affecting the battery's high-temperature storage performance and cycle stability. This further demonstrates that the presence of the passivation layer 30 enables the battery to have better cycle performance, rate performance, and high-temperature stability, effectively mitigating the battery's self-discharge.

[0122] As shown in Comparative Example 2, when the conductive carbon substrate SP and binder PAA are simply mixed, the battery's puncture resistance and internal resistance increase significantly, while the capacity retention rate during high-temperature storage and the capacity retention rate after 800 cycles decrease significantly. This may be because the electron transport network and ion transport network formed in the passivation layer 30 of Comparative Example 2 are relatively dispersed and uneven, thus affecting the ionic conductivity and electronic conductivity of the passivation layer 30. At the same time, the binder cannot tightly and firmly bond the conductive carbon substrate SP, and the adhesion between the passivation layer 30 and the negative electrode active layer 20 is weak, resulting in a large interfacial impedance, which further affects the battery's performance.

[0123] As can be seen from the data in Comparative Example 3, the performance of the battery obtained by simply mixing the conductive carbon substrate SP, the binder PAA and polyaniline is still poor, which further illustrates that the composite conductive binder with a specific structure formed by the conductive carbon substrate SP, the binder PAA and polyaniline of this application can significantly improve the performance of the battery.

[0124] As can be seen from the data of Comparative Examples 4 and 5, when either the conductive carbon substrate SP or the polyaniline conductive polymer is missing from the composite conductive binder, the overall performance of the battery decreases significantly. This further illustrates that the composite conductive binder with a specific structure formed by the conductive carbon substrate SP, binder PAA, and polyaniline of this application can significantly improve the performance of the battery.

[0125] As can be seen from the data of Comparative Examples 6 and 7, when the composite lithium-containing compound is replaced with a single lithium salt, the mechanical properties and ionic conductivity of the passivation layer 30 and the SEI film cannot be well balanced, resulting in poor battery performance.

[0126] In summary, this application improves battery performance by including a composite lithium-containing compound and a composite conductive binder in the passivation layer 30, and by the synergistic effect of the mass percentage of the composite conductive binder and the composite lithium-containing compound, the mass ratio of the first lithium-containing compound and the second lithium-containing compound, and the composite conductive binder with a specific structure.

[0127] The above provides a detailed description of a negative electrode 100, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A negative electrode (100), characterized in that, include: Negative electrode current collector (10). A negative electrode active layer (20) is disposed on at least one side of the negative electrode current collector (10); and A passivation layer (30) is disposed on the side surface of the negative electrode active layer (20) facing away from the negative electrode current collector (10). The passivation layer (30) comprises a composite lithium-containing compound and a composite conductive binder. The composite conductive adhesive comprises a conductive core layer and a coating layer; the conductive core layer comprises a conductive carbon substrate, the coating layer comprises a conductive polymer layer and an adhesive layer, the conductive polymer layer coats the surface of the conductive core layer, and the adhesive layer is grafted onto the side surface of the conductive polymer layer opposite to the conductive core layer.

2. The negative electrode (100) according to claim 1, characterized in that, The composite lithium-containing compound includes a first lithium-containing compound and a second lithium-containing compound. The first lithium-containing compound includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalate borate. The second lithium-containing compound includes at least one of lithium carbonate, lithium nitrate, and lithium hydroxide.

3. The negative electrode (100) according to claim 1 or 2, characterized in that, The mass percentage of the composite conductive binder and the composite lithium-containing compound is 80%~90%:10%~20%.

4. The negative electrode (100) according to claim 2, characterized in that, The mass ratio of the first lithium-containing compound to the second lithium-containing compound is 1~2:1~2.

5. The negative electrode sheet (100) according to any one of claims 1 to 4, characterized in that, In the composite conductive adhesive, the mass ratio of the conductive core layer, the conductive polymer layer, and the adhesive layer is 0.5~1.5:2.5~3.5:4.5~5.

5.

6. The negative electrode sheet (100) according to any one of claims 1 to 5, characterized in that, The passivation layer (30) has a thickness of 2μm to 3μm.

7. The negative electrode sheet (100) according to any one of claims 1 to 6, characterized in that, The conductive carbon substrate includes at least one of carbon black, graphene, and carbon nanotubes; and / or, The conductive polymer layer is made of at least one of polyaniline, polyacetylene, polypyrrole, and polythiophene; and / or, The adhesive layer is made of at least one of the following: polyacrylic acid, polyacrylonitrile, styrene-butadiene, sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, calcium polyacrylate, magnesium polyacrylate, rubidium polyacrylate, cesium polyacrylate, francium polyacrylate, barium polyacrylate, strontium polyacrylate, lithium carboxymethyl cellulose, beryllium carboxymethyl cellulose, and sodium carboxymethyl cellulose.

8. A method for preparing the negative electrode sheet (100) according to any one of claims 1 to 7, characterized in that, include: Provide negative electrode current collector (10); A negative electrode slurry is provided, and the negative electrode slurry is coated onto the negative electrode current collector (10) and dried to form a negative electrode active layer (20). A passivation layer slurry containing a composite lithium compound and a composite conductive binder is prepared. The passivation layer slurry is coated on the side of the negative electrode active layer (20) away from the negative electrode current collector (10) and dried to form a passivation layer (30) on the surface of the negative electrode active layer (20).

9. The method for preparing the negative electrode sheet (100) according to claim 8, characterized in that, The method for preparing the composite conductive adhesive includes: The conductive core layer is dispersed in an acid solution, and conductive polymer monomers and a first solvent are added to obtain a first solution after dispersion. An oxidant is added to the first solution to react and polymerize the conductive polymer monomers, forming a conductive polymer layer on the surface of the conductive core layer, thus obtaining an intermediate. The intermediate and the passivation layer binder are dispersed in a second solvent to form a second solution; The free radical initiator is dispersed in a third solvent to form a third solution; The third solution is added to the second solution to react, so that an adhesive layer is grafted onto the surface of the conductive polymer layer, resulting in a slurry containing the composite conductive adhesive.

10. The method for preparing the negative electrode sheet (100) according to claim 8 or 9, characterized in that, The solid content of the passivation layer slurry is 20%~25%.

11. A battery, characterized in that, The negative electrode (100) includes the negative electrode (100) prepared by the preparation method of the negative electrode (100) according to any one of claims 1 to 7 or the negative electrode (100) according to any one of claims 8 to 10. The battery also includes a positive electrode and a separator; The separator is disposed between the negative electrode (100) and the positive electrode, and the passivation layer (30) is disposed on the side of the negative electrode (100) near the separator.

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